Textos de Apoio

O

PERAÇÃO DE

I

NSTALAÇÕES

M

ARÍTIMAS

Engenharia de Máquinas Marítimas

J

ORGE

T

RINDADE

ENIDH

2012

Este texto destina-se a dar apoio ao funcionamento da unidade curricular “Operação de Instalações Marítimas”, do 3 o ano da Licenciatura em Engenharia de Máquinas Marítimas. Tem por base os manuais de operação das instalações propulsoras simuladas, com motor

diesel a dois tempos [1], e com turbinas a vapor [2]. No entanto, estes

dois tipos de instalações propulsoras são apenas uma pequena amostra da vasta variedade de equipamentos que o engenheiro de máquinas marítimas encontrará durante a sua carreira profissional. Assim, sempre que possível, procura-se dar um enquadramento mais generalizado para cada tipo de equipamento considerado, mesmo que depois o seu funcionamento não possa ser demonstrado em simulador. Estas

descrições são adaptadas das referências [3, 4] e de vários manuais

de equipamentos. Para a elaboração dos tópicos relacionados com

a operação de caldeiras foi utilizada a referência [5] que, não sendo

particularmente vocacionada para instalações marítimas, apresenta o assunto de uma forma muito abrangente.

Optou-se, para já, por não traduzir estes textos para português. Esta opção deve-se à falta de disponibilidade para realizar este trabalho no curto prazo mas tem também em consideração o actual contexto em que o engenheiro de máquinas marítimas exerce a sua actividade, num ambiente em que prevalece a língua inglesa.

i

ii

Contents

1 Introduction

1.1

1.1

Propulsion plants . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

1.1

1.1.1

Simulated diesel engine propulsion plant

. . . . . . . . . . . . . . . . . . .

1.2

1.1.2

Simulated steam turbines propulsion plant . . . . . . . . . . . . . . . . . . .

1.7

2 Ship Operation

2.1

2.1

Watch-keeping and equipment operation . . . . . . . . . . . . . . . . . . . . . . . .

2.1

2.1.1

The Engineering Department . . . . . . . . . . . . . . . . . . . . . . . . . .

2.1

2.1.2

The watch-keeping system . . . . . . . . . . . . . . . . . . . . . . . . . . .

2.2

2.1.3

Operating the watch

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

2.2

2.1.4

UMS operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

2.4

2.1.5

Periodic safety routines . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

2.5

2.2

Safe working practices . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

2.5

2.2.1

Electrical hazards . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

2.7

2.2.2

Unattended machinery spaces . . . . . . . . . . . . . . . . . . . . . . . . .

2.7

2.3

Engine room and oil log books . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

2.8

2.4

Engine readiness

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.11

2.4.1

Stand-By . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.11

2.4.2

At Sea . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.12

2.4.3

Finished With Engine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.13

3 Electric Generators and Switchboards

3.1

3.1

Shore supply

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

3.1

3.2

Emergency generator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

3.2

3.2.1

Emergency generator operation

. . . . . . . . . . . . . . . . . . . . . . . .

3.3

3.2.2

Emergency generator tests . . . . . . . . . . . . . . . . . . . . . . . . . . .

3.4

3.3

Diesel generators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

3.4

3.3.1

Diesel generator start procedure . . . . . . . . . . . . . . . . . . . . . . . .

3.6

3.3.2

Diesel generator stopping

. . . . . . . . . . . . . . . . . . . . . . . . . . .

3.6

iii

iv CONTENTS

3.3.3

Synchronising procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . .

3.7

3.3.4

Generator control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

3.8

3.4

Shaft-generator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

3.9

3.4.1

Shaft generator operating procedures

. . . . . . . . . . . . . . . . . . . . . 3.11

3.4.2

Shaft generator control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.12

3.5

Turbo-generator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.13

3.6

Switchboards . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.17

3.6.1

Main switchboard . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.17

3.6.2

Emergency switchboard . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.19

3.6.3

Non-essentials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.19

3.6.4

Earth leakage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.20

4 Auxiliary Equipment

4.1

4.1

Stern tube system . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

4.1

4.2

Ventilation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

4.3

4.3

Cooling systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

4.5

4.3.1

Sea water system . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

4.5

4.3.2

Fresh water system . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

4.8

4.4

Compressed air systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

4.9

4.4.1

Start air system . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

4.9

4.4.2

Service and control air system . . . . . . . . . . . . . . . . . . . . . . . . . 4.10

4.5

Fresh water distribution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.11

4.6

Fresh water generator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.12

4.6.1

VLCC fresh water generator . . . . . . . . . . . . . . . . . . . . . . . . . . 4.13

4.6.2

Steam plant fresh water generators . . . . . . . . . . . . . . . . . . . . . . . 4.15

4.7

Refrigeration system . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.18

4.8

Bilge system . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.21

4.8.1

Bilge regulations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.21

4.8.2

Bilge system description . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.22

4.8.3

Bilge separator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.22

4.8.4

Bilge operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.24

4.8.5

Incinerator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.25

4.9

Sewage system . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.27

4.9.1

Chemical sewage treatment

. . . . . . . . . . . . . . . . . . . . . . . . . . 4.27

4.9.2

Biological sewage treatment . . . . . . . . . . . . . . . . . . . . . . . . . . 4.27

4.10 Deck machinery . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.29

4.10.1 Steam machinery . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.29

4.10.2 Hydraulic systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.29

4.10.3 Electrical operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.30

CONTENTS v

4.11 Ship governing and manouvering equipment . . . . . . . . . . . . . . . . . . . . . . 4.30

4.11.1 Steering gear . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.30

4.11.2 Bow thruster . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.35

4.12 Propeller servo . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.36

4.12.1 Propeller servo oil system description . . . . . . . . . . . . . . . . . . . . . 4.37

4.12.2 Propeller servo oil operation . . . . . . . . . . . . . . . . . . . . . . . . . . 4.37

5 Boilers and Steam Generators

5.1

5.1

Modes of operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

5.1

5.2

Thermal oil boilers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

5.1

5.3

Steam boilers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

5.2

5.3.1

Dead plant start-up . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

5.2

5.3.2

Normal operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

5.4

5.4

VLCC steam plant description . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

5.5

5.4.1

Operating modes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

5.5

5.4.2

Oil fired boiler . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

5.6

5.4.3

Exhaust gas boiler . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.10

5.5

Boiler for LPG steam propulsion plant . . . . . . . . . . . . . . . . . . . . . . . . . 5.11

5.5.1

Fuel supply system . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.12

5.5.2

Boiler burners . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.16

5.5.3

Air and flue gas systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.18

5.5.4

Remote control panel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.19

5.5.5

Feed water and steam systems . . . . . . . . . . . . . . . . . . . . . . . . . 5.20

5.6

Steam/Steam generators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.21

6 Fuel Oil Treatment

6.1

6.1

Bunkering . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

6.1

6.2

Fuel oil transfer system . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

6.2

6.3

Settling tanks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

6.2

6.4

Service tanks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

6.3

6.5

Separators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

6.4

6.5.1

DO separator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

6.4

6.5.2

HFO separators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

6.6

7 Diesel Engines

7.1

7.1

Engine operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

7.1

7.1.1

Preparations for stand-by . . . . . . . . . . . . . . . . . . . . . . . . . . . .

7.1

7.1.2

Engine starting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

7.2

7.1.3

Engine reversing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

7.2

7.1.4

Shut-down procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

7.2

7.2

Safety issues . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

7.3

7.2.1

Crankcase oil mist detector . . . . . . . . . . . . . . . . . . . . . . . . . . .

7.3

7.2.2

Scavenging fire . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

7.4

7.2.3

Economizer fire . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

7.5

7.3

VLCC propulsion machinery . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

7.5

7.3.1

ME cylinders . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

7.6

7.3.2

Fresh water cooling system . . . . . . . . . . . . . . . . . . . . . . . . . . .

7.8

7.3.3

Lubricating oil system . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

7.9

7.3.4

Fuel oil system . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.12

7.3.5

Fuel oil high pressure system . . . . . . . . . . . . . . . . . . . . . . . . . . 7.16

7.3.6

Turbocharger system . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.17

7.3.7

Selective catalytic reduction unit . . . . . . . . . . . . . . . . . . . . . . . . 7.19

7.3.8

Manoeuvring pneumatic system . . . . . . . . . . . . . . . . . . . . . . . . 7.21

7.3.9

AutoChief control system

. . . . . . . . . . . . . . . . . . . . . . . . . . . 7.25

7.3.10 Remote control panel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.34

7.3.11 Local control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.42

7.3.12 Load diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.44

7.3.13 Cylinder diagram indicators . . . . . . . . . . . . . . . . . . . . . . . . . . 7.46

8 Steam Plants

8.1

8.1

Steam plant operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

8.1

8.1.1

Steam valves maneuvering . . . . . . . . . . . . . . . . . . . . . . . . . . .

8.1

8.1.2

Plant start-up . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

8.3

8.1.3

Boiler water treatment . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

8.3

8.2

Auxilliary systems

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

8.4

8.2.1

Condensers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

8.4

8.2.2

Feedwater system . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

8.7

8.2.3

General service steam system . . . . . . . . . . . . . . . . . . . . . . . . . 8.12

8.3

Steam systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.14

8.3.1

Superheated lines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.14

8.3.2

Desuperheated line . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.15

8.3.3

Back pressure line . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.15

8.3.4

Steam dump

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.16

8.4

Operation of steam turbines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.17

8.4.1

Main engine description . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.17

8.4.2

Warming-through a steam turbine . . . . . . . . . . . . . . . . . . . . . . . 8.23

8.4.3

Manoeuvring . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.23

8.4.4

Emergency astern operation . . . . . . . . . . . . . . . . . . . . . . . . . . 8.23

8.4.5

Full away . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.24

CONTENTS vii

8.4.6

Port arrival . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.24

viii CONTENTS

1

Introduction

1.1

Propulsion plants

The propulsion of the vast majority of merchant ships utilizes marine diesel engines as prime movers.

A typical propulsion plant of a merchant ship include a single, slow speed, turbocharged, two-stroke marine diesel engine directly coupled, via the shafting system, to a single, fixed pitch propeller.

Medium speed engines are favored for smaller cargo ships, ferries, cruise liners, RoRo freight carriers and diverse specialist tonnage such as icebreakers, offshore support and research vessels. The most common form of indirect drive of a propeller features one or more medium speed four-stroke engines connected through clutches and couplings to a reduction gearbox to drive either a fixed or controllable pitch propeller. The controllable pitch propeller eliminates the need for a direct-reversing engine, while the gearing allows to select a suitable propeller speed.

Compared to direct diesel drives, diesel electric propulsion systems are technically and operationally superior in virtually all applications. This superiority has been a major reason for the steadily growing demand for diesel-electric drives in marine engineering applications. Electrical propulsion system offers numerous advantages for ships that are subject to specific requirements. They are rated as particularly economical, environmentally friendly and reliable, offer considerable comfort in terms of operation and control, have optimal maneuvering and positioning properties, low vibration and noise levels, and additionally enable the best possible utilization of space owing to their reduced noise levels. The choice of diesel electrical system as the power source for the propulsion system of a vessel has nothing to do with hydrodynamic efficiency.

The propulsion system of a vessel provides thrust to move the vessel and is still chosen by the designer based on merits for the vessel’s application. Conventional propellers, controllable pitch propellers, azimuthing drives, transverse tunnel thrusters, and low speed water jet systems can be driven with equal effectiveness by a diesel-electrical system.

Most of the LNG carriers now in service adopt the steam turbine propulsion system with duel fuel boiler. Since the oil crisis, conversion of the propulsion system has been made in almost all merchant

1.1

1.2

CHAPTER 1. INTRODUCTION ships, by the application of low-speed diesel engine directly coupled with propeller. In the case of

LNG carriers, however, the current system is adopted in all such carriers because it is the best method of treating BOG safely and efficiently.

In LNG carriers that transport LNG in the refrigerated condition, BOG is inevitably produced as a result of heat coming from outside the tanks. In order to control the tank pressure rise, BOG is utilized as boiler fuel to get propulsive force by the steam turbine. In cases where the combustion heat of BOG is in excess of the required propulsive force, surplus heat is disposed of in the sea water. In cases where the combustion heat of BOG is less than the required propulsive force, the required heat is made up by additional burning of heavy fuel oil (bunker oil) or forcing vaporization of LNG. The current system is capable of using both LNG and heavy fuel oil as fuel, and thus of selecting the most economical fuel mixture.

Gas turbines have dominated warship propulsion for many years but their potential remains to be fully realized in the commercial shipping sector. In recent years, however, gas turbine suppliers with suitable designs have secured propulsion plant contracts from operators of large cruise ships and high speed ferries, reflecting the demand for compact, high output machinery in those tonnage sectors, rises in cycle efficiency and tightening controls on exhaust emissions. The main candidates for gas turbine propulsion in commercial shipping are the cruise ships, large ferries LNG carriers and fast container ships. The combination of low power maneuvering and high-power operation is accomplished in many naval applications by using a combined diesel or gas turbine propulsion system.

1.1.1

Simulated diesel engine propulsion plant

The ship simulated, schematically represented in Fig. 1.1, is a VLCC with block coefficient 0.801 and

following main particulars:

- Dead weight 187997 tons;

- Length overall 305m;

- Length between perpendiculars 295m;

- Breadth moulded 47m;

- Depth moulded 30.40 m;

- Summer draught 19.07 m;

- Speed 14 knots.

The main engine for ship propulsion is a MAN B&W 5L90MC, with Continuous Service Rating

(CSR) of 17.4 MW at the corresponding speed of 74 rpm. The propeller system includes both fixed and controllable pitch propeller options, selectable from the Main Engine Control Console (AUTOCHIEF)

The electrical power plant includes:

- two 850 kW/440V/60Hz diesel engine driven synchronous generators;

1.1. PROPULSION PLANTS 1.3

Figure 1.1: Main particulars of the VLCC simulated.

- one 1200 kW/440V/60Hz synchronous shaft driven generators;

- one 850 kW/440V/60Hz steam turbine driven generator;

- one 180 kW/440V/60Hz emergency generator;

One 750 kW controllable pitch bow thruster improves the maneuverability of the ship. The steering gear plant is double acting, rotary vane type, IMO model.

The following main tanks are included in the simulation:

- 2 HFO settling tanks;

- 1 HFO service tank;

- 1 DO service tank;

- 4 Fuel oil bunker tanks;

- 1 Spill oil tank;

- 1 Sludge tank;

- 1 Clean bilge tank;

- 1 DO storage tank;

- 1 Cylinder lubricating oil storage tank;

- 2 Ballast wing tanks;

- 1 Fore peak tank.

Flowcharts of the activities required to acquire own electric supply, harbor and maneuvering con-

ditions are represented in Fig. 1.2, 1.3 and 1.4, respectively.

1.4

CHAPTER 1. INTRODUCTION

1.1. PROPULSION PLANTS 1.5

1.6

CHAPTER 1. INTRODUCTION

1.1. PROPULSION PLANTS 1.7

1.1.2

Simulated steam turbines propulsion plant

The second propulsion plant considered here is related to a LNG carrier. Two boilers produce steam at 60.5 bar and 515

C for the superheated system, and 278

C on the desuperheated system, burning

HFO and/or LNG boil-off gas.

High and low pressure ahead turbines and the astern turbine are coupled to a fixed pitch propeller.

Main and auxiliary sea water pumps and a scoop provide cooling for main and auxiliary machinery.

Electric power plant includes two diesel-generators and two turbo-generators. A feed-water and steam

flow diagram is represented in Fig. 1.5.

Figure 1.5: Feed water and steam flow overview.

Figure 1.6 includes a flowchart representing main steps preparing the steam propulsion plant to

port condition. One should note that some details of the plant are here very simplified or even neglected. Details related to the emergency generator or the shore power supply, stern tube, bilge, steering gear, etc. are here omitted. However, the ship will obviously include those systems and the correct procedures will be necessary for ship operation.

Figures 1.7 and 1.8 include the port condition to stand-by condition procedure and the preparation

for boil-off gas burning departing from the stand-by condition, respectively.

1.8

CHAPTER 1. INTRODUCTION

1.1. PROPULSION PLANTS 1.9

Figure 1.7: Flowchart from port condition to stand-by condition.

Figure 1.8: Flowchart for

BOG burning preparation.

1.10

CHAPTER 1. INTRODUCTION

2

Ship Operation

2.1

Watch-keeping and equipment operation

The responsibilities of the marine engineer are rarely confined to the machinery space. Different companies have different practices, but usually all shipboard machinery, with the exception of radio equipment, is maintained by the marine engineer. Electrical engineers may be carried on very large ships, but if not, the electrical equipment is also maintained by the engineer. A broad-based theoretical and practical training is therefore required for a marine engineer. He must be a mechanical, electrical, air conditioning, ventilation and refrigeration engineer. He must also deal with the specialized requirements of a floating platform in a most corrosive environment. Furthermore, he must be self-sufficient and capable of getting the job done with the facilities at his disposal.

The modern ship provides the facilities to support a small community for a long period of time.

The equipment is a complete system comprising small items or individual larger items. In the latter case, especially, the choices are often considerable. A knowledge of machinery and equipment operation provides the basis for effective maintenance.

The around the clock’ operation of a ship at sea requires a rotative system of attendance in the machinery space, the watch-keeping system, that has endured until recently. The arrival of “Unattended

Machinery Spaces” (UMS) has begun to change this traditional practice of watch-keeping.

2.1.1

The Engineering Department

The Chief Engineer is directly responsible to the Master for the satisfactory operation of all machinery and equipment. Apart from assuming all responsibility, his role is mainly that of consultant and adviser. It is not usual for the Chief Engineer to keep a watch.

The Second Engineer is the executive officer. He is responsible for the practical upkeep of machinery and the manning of the engine room. On some ships the Second Engineer may keep a watch.

Other Engineers are usually in charge of a watch. Each one may have particular areas of responsibility, such as generators or boilers. Electrical Engineers may be carried on large ships or where company

2.1

2.2

CHAPTER 2. SHIP OPERATION practice dictates. Where no specialist Electrical Engineer is carried, the duty will fall on one of the engineers.

Various engine room ratings will usually form part of the engine room complement. Donkey-men are usually senior ratings who may attend the auxiliary boiler while the ship is in port. Otherwise, they will direct the ratings in the maintenance and upkeep of the machinery space. A storekeeper may also be carried and on tankers, a pump man is employed to maintain and operate the cargo pumps.

The engine room ratings, e.g. firemen, greasers, etc., are usually employed on watches to assist the engineer in charge.

2.1.2

The watch-keeping system

The system of watches adopted on board a ship is usually a four hour period of working with eight hours rest for the members of each watch. The three watches in any 12 hour period are usually 12-04,

04-08 and 08-12. The word ’watch’ is taken as meaning the time period and also the personnel at work during that period.

Type of ship, the type of machinery and degree of automation, the qualifications and experience of the watch members, any special conditions such as weather, ship location, international and local regulations, etc. will be taken into account to the watch-keeping arrangements and the make up of the watch, decided by the Chief Engineer. The engineer officer in charge of the watch is the Chief

Engineer’s representative and is responsible for the safe and efficient operation and upkeep of all machinery affecting the safety of the ship.

2.1.3

Operating the watch

An engineer officer in charge, with perhaps one or more ratings, will form the watch. Each member of the watch should be familiar with his duties and the safety and survival equipment in the machinery space. This would include a knowledge of the fire fighting equipment with respect to location and operation, being able to distinguish the different alarms and the action required, an understanding of the communications systems and how to summon help and also being aware of the escape routes from the machinery space.

At the beginning of the watch the current operational parameters and the condition of all machinery should be verified and also the log readings should correspond with those observed. The engineer officer in charge should note if there are any special orders or instructions relating to the operation of the main machinery or auxiliaries. He should determine what work is in progress and any hazards or limitations this presents. The levels of tanks containing fuel, water, slops, ballast, etc., should be noted and also the level of the various bilges. The operating mode of equipment and available standby equipment should also be noted.

At appropriate intervals, the main propulsion plant, auxiliary machinery and steering gear spaces should be inspected. Any routine adjustments may then be made and malfunctions or breakdowns can be noted, reported and corrected. During these tours of inspection bilge levels should be noted, piping

2.1. WATCH-KEEPING AND EQUIPMENT OPERATION 2.3

and systems observed for leaks, and local indicating instruments can also be observed.

Where bilge levels are high, or the well is full, it must be pumped dry. Particular attention must be taken to the relevant oil pollution regulations both of a national and international nature, depending upon the location of the ship. The discharging of oil from a ship usually results in the engineer responsible and the master being arrested.

Bridge orders must be promptly carried out and a record of any required changes in speed and direction should be kept. When under stand-by or maneuvering conditions, with the machinery being manually operated, the control unit or console should be continuously manned.

Certain watch-keeping duties will be necessary for the continuous operation of equipment or plant, the transferring of fuel for instance. In addition to these regular tasks, other repair or maintenance tasks may be required of the watch-keeping personnel. However, no tasks should be set or undertaken which will interfere with the supervisory duties relating to the main machinery and associated equipment.

During the watch, a log will be taken recording various parameters of main and auxiliary equipment. This may be a manual operation or provided automatically on modern vessels by a data logger.

Fuel consumption figures are used to determine the efficiency of operation, in addition to providing a check on the available bunker quantities. Lubricating oil tank levels and consumption to some extent indicate engine oil consumption. The sump level is recorded and checked that it does not rise or fall, but a gradual fall is acceptable as the engine uses some oil during operation. If the sump level were to rise this would indicate water leakage into the oil and an investigation into the cause must be made.

The engine exhaust temperatures should all read about the same to indicate an equal power production from each cylinder. The various temperature and pressure values for the cooling water and lubricating oil should be at, or near to, the manufacturer’s designed values for the particular speed or fuel lever settings. Any high outlet temperature for cooling water would indicate a lack of supply to that point.

Various parameters for the main engine turbo-blowers are also logged. The air cooler is used to increase the charge air density to enable a large quantity of air to enter the engine cylinder. If cooling were inadequate a lesser mass of air would be supplied to the engine, resulting in a reduced power output, inefficient combustion and black smoke.

Various miscellaneous level and temperature readings are taken of heavy oil tanks, both settling and service, stern tube bearing temperature, sea water temperature, etc. The operating diesel generators will have their exhaust temperatures, cooling water and lubricating oil temperatures and pressures logged in much the same way as for the main engine. A more complete list of operating variables to

be logged is included in Sec. 2.3.

Other auxiliary machinery and equipment, such as heat exchangers, fresh water generator (evaporator), boiler, air conditioning plant and refrigeration plant will also have appropriate readings taken.

There will usually be summaries or daily account tables for heavy oil, diesel oil, lubricating oil and fresh water, which will be compiled at noon. Provision is also made for remarks or important events to be noted in the log for each watch.

For a steam turbine driven vessel the main log readings will be for the boiler and the turbine.

2.4

CHAPTER 2. SHIP OPERATION

Boiler steam pressure, combustion air pressure, fuel oil temperatures, etc., will all be recorded. For the turbine the main bearing temperatures, steam pressures and temperatures, condenser vacuum, etc., must be noted. All logged values should correspond fairly closely with the design values for the equipment.

The completed log is used to compile a summary sheet or abstract of information which is returned to the company head office for record purposes. The log of running hours will be of particular importance since this will be the basis for overhauling the machinery.

Where situations occur in the machinery space which may affect the speed, maneuverability, power supply or other essentials for the safe operation of the ship, the bridge should be informed as soon as possible. This notification should preferably be given before any changes are made to enable the bridge to take appropriate action.

The engineer in charge should notify the Chief Engineer in the event of any serious occurrence or a situation where he is unsure of the action to take. Examples might be, if any machinery suffers severe damage, or a malfunction occurs which may lead to serious damage. However, where immediate action is necessary to ensure the safety of the ship, its machinery and crew, it must be taken by the engineer in charge.

At the completion of the watch each member should hand over to his relief, ensuring that he is competent to take over and carry out his duties effectively.

2.1.4

UMS operation

The machinery spaces will usually be manned at least eight hours per day. During this time the engineers will be undertaking various maintenance tasks, the duty engineer having particular responsibility for the watch-keeping duties and dealing with any alarms which may occur. When operating unmanned anyone entering the machinery space must inform the deck officer on watch. When working, or making a tour of inspection alone, the deck officer on watch should be telephoned at agreed intervals of around 15 or 30 minutes.

When the machinery space is unattended, a duty engineer will be responsible for supervision. He will normally be one of three watch-keeping engineers and will work on a 24 hour on, 48 hours off rota. During his rota period he will make tours of inspection about every four hours beginning at 7 or

8 o’clock in the morning. The tour of inspection will be similar to that for a conventional watch with due consideration being given to the unattended mode of machinery operation. Trends in parameter readings must be observed, and any instability in operating conditions must be rectified, etc. A set list or mini-log of readings may have to be taken during the various tours. Between tours of inspection, the duty engineer will be on call and should be ready to investigate any alarms relayed to his cabin or the various public rooms. The duty engineer should not be out of range of these public rooms alarms without appointing a relief and informing the bridge.

The main log book readings will be taken as required while on a tour of inspection. The various regular duties, such as fuel transfer, pumping of bilges, and so on, should be carried out during the

2.2. SAFE WORKING PRACTICES 2.5

day-work period, but it remains the responsibility of the duty engineer to ensure that they are done.

2.1.5

Periodic safety routines

In addition to watch-keeping and maintenance duties, various safety and emergency equipment must be periodically checked. As an example, it is good practice to perform the following inspections at least weekly:

- Emergency generator should be started and run for a reasonable period while fuel oil, lubricating oil and cooling water supplies and tank levels are checked;

- Emergency fire pump should be run and the deck fire main operated for a reasonable period and the operating parameters should be checked;

- Carbon dioxide cylinder storage room should be visually examined and the release box door should be opened to test the alarm and check that the machinery-space fans stop;

- One smoke detector in each circuit should be tested to ensure operation and correct indication on the alarm panel (aerosol test sprays are available to safely check some types of detector);

- Fire push-button alarms should be tested, by operating a different one during each test;

- Any machinery space ventilators or skylights should be operated and greased, if necessary, to ensure smooth, rapid closing should this be necessary.

- Fire extinguishers should be observed in their correct location and checked to ensure they are operational.

- Fire hoses and nozzles should likewise be observed in their correct places. The nozzles should be tried on the hose coupling. Any defective hose should be replaced;

- Any emergency batteries, e.g. for lighting or emergency generator starting, should be examined, have the acid specific gravity checked, and be topped up, as required;

- All lifeboat engines should be run for a reasonable period and fuel oil and lubricating oil levels should be checked;

- All valves and equipment operated from the fire control point should be checked for operation, where this is possible;

- Any watertight doors should be opened and closed by hand and power and the guides should be checked to ensure that they are clear and unobstructed.

2.2

Safe working practices

Accidents, often result in injury, are usually the consequence of carelessness, mistakes or lack of thought. Avoiding accidents is largely achieved by the adoption of safe working practices. Working clothes should be chosen with the job and its hazards in mind. They should fit fairly closely with no

2.6

CHAPTER 2. SHIP OPERATION loose flaps, straps or ragged pockets. Clothing should cover as much of the body as possible and a stout pair of shoes should be worn. Neck chains, finger rings and wristwatches should not be worn, particularly in the vicinity of rotating machinery. Where particular hazards are present appropriate protection, such as goggles or ear muffs, should be worn.

When lifting equipment during overhaul, screw-in eye bolts should be used where possible. These should be fully entered up to the collar and the threads on the eye-bolt and in the equipment should be in good condition. Any lifting wires should be in good condition without broken strands or sharp edges. When overhauling machinery or equipment it must be effectively isolated from all sources of power. This may involve unplugging from an electrical circuit, the removal of fuses or the securing open of circuit breakers. Suction and discharge valves of pumps should be securely closed and the pump casing relieved of pressure. Special care should be taken with steam-operated or steam-using equipment to ensure no pressure build-up can occur.

Before any work is done on the main engine, the turning gear should be engaged and a warning posted at the control position. The turning gear should be made inoperative if not required during the overhaul. Where it is used, care must be taken to ensure ail personnel are clear before it is used.

Lubricating oil in the working area should be cleaned up and where necessary suitable staging erected.

Where overhead work is necessary, suitable staging should be provided and adequately lashed down.

Staging planks should be examined before use and where suspect discarded. Where ladders are used for access they must be secured at either end.

Boiler blow-backs can cause serious injury that can usually be avoided. The furnace floor should be free of oil and burners regularly checked to ensure that they do not drip when not in use. The manufacturer’s instructions should be followed with regard to lighting up procedures. Generally this should involve blowing through the furnace (purging) with air prior to lighting up. The fuel oil must be at the correct temperature and lit with a spark plug or a torch. If ignition does not immediately occur the oil should be turned off and purging repeated before the next attempt is made. The burner should be withdrawn and examined before it is lit.

Scavenge fires are dangerous. Cylinder oil can collect in the scavenge space of an engine. Unburned fuel and carbon may also be blown into the scavenge space as a result of defective piston rings, faulty timing, a defective injector, etc. A build-up of this flammable mixture presents a danger as a blow past of hot gases from the cylinder may ignite the mixture, and cause a scavenge fire. A loss of engine power will result, with high exhaust temperatures at the affected cylinders. The affected turbochargers may surge and sparks will be seen at the scavenge drains. Once a fire is detected the engine should be slowed down, fuel shut off from the affected cylinders and cylinder lubrication increased.

All the scavenge drains should be closed. A small fire will quickly burn out, but where the fire persists the engine must be stopped. A fire extinguishing medium should then be injected through the fittings provided in the scavenge trunking. On no account should the trunking be opened up.

To avoid scavenge fires occurring the engine timing and equipment maintenance should be correctly carried out. The scavenge trunking should be regularly inspected and cleaned if necessary.

Where carbon or oil build up is found in the scavenge, its source should be detected and the fault

2.2. SAFE WORKING PRACTICES 2.7

remedied. Scavenge drains should be regularly blown and any oil discharges investigated at the first opportunity.

Particular attention should be paid to the crankcase oil mist detector. The presence of an oil mist in the crankcase is the result of oil vaporisation caused by a hot spot. Explosive conditions can result if a build up of oil mist is allowed. The oil mist detector uses photoelectric cells to measure small increases in oil mist density. A motor driven fan continuously draws samples of crankcase oil mist through a measuring tube. An increased meter reading and alarm will result if any crankcase sample contains excessive mist when compared to either clean air or the other crankcase compartments. The rotary valve which draws the sample then stops to indicate the suspect crankcase. The comparator model tests one crankcase mist sample against all the others and once a cycle against clean air. The level model tests each crankcase in turn against a reference tube sealed with clean air. The comparator model is used for crosshead type engines and the level model for trunk piston engines.

Entry into an enclosed space should only take place under certain specified conditions. An enclosed space, such as a duct keel, a double bottom tank, a cofferdam, a furnace or drum boiler, etc.

cannot be assumed to contain oxygen. Anyone requiring to enter such a space should only do so with the permission of a responsible officer. The space should be well ventilated before entry takes place and breathing apparatus taken along; it should be used if any discomfort or drowsiness is felt. Another person should remain at the entrance to assist, if necessary. Means of communication should be arranged between the person within the space and the attendant. Lifelines and harness should be available at the entrance to the space. The attendant should first raise the alarm, even when the occupant appears in danger, and should not enter the space unless equipped with breathing apparatus. Training in the use of safety equipment and the conduct of rescues is essential for all personnel involved.

2.2.1

Electrical hazards

The danger of electric shock is much greater for persons working in a hot, humid atmosphere since this leads to wetness from body perspiration. Fatal shocks have occurred at as low as 60V and all circuits must be considered dangerous. All electrical equipment should be isolated before any work is done on it. The circuit should then be tested to ensure that it is dead. Working near to live equipment should always be avoided, if possible. Tools with insulated handles should be used to minimize risks.

The treatment of anyone suffering from severe electric shock must be rapid to be effective. First they must be removed from contact with the circuit by isolating it or using a non-conducting material to drag them away. Electric shock results in a stopping of the heart and every effort must be made to get it going again. Apply any accepted means of artificial respiration to bring about revival.

2.2.2

Unattended machinery spaces

The sophistication of modern control systems and the reliability of the equipment used have resulted in machinery spaces remaining unattended for long periods. Certain essential requirements must be met to ensure the safety of the ship and its equipment during UMS operation. These requirements are

2.8

described in the following paragraphs.

CHAPTER 2. SHIP OPERATION

Bridge control

A control system to operate the main machinery must be provided on the bridge. Instrumentation providing certain basic information must be provided.

Machinery control room

A centralized control room must be provided with the equipment to operate all main and auxiliary machinery easily accessible.

Alarm and fire protection

An alarm system is required which must be comprehensive in coverage of the equipment and able to provide warnings in the control room, the machinery space, the accommodation and on the bridge.

A fire detection and alarm system which operates rapidly must also be provided throughout the machinery space, and a fire control point must be provided outside the machinery space with facilities for control of emergency equipment.

Emergency power

Automatic provision of electrical power to meet the varying load requirements. Emergency electrical power and essential lighting must be provided. This is usually met by the automatic start-up of a stand-by generator.

2.3

Engine room and oil log books

Record keeping is an important aspect of the life of a marine engineer. There are various types of records which need to be maintained. From the perspective of the ship’s engine room, the engineers need to keep a clear record of machinery parameters, running hours and several other things. This has been done traditionally using paper daily log books, although with the increasing use of computers on ships, these daily log books might be replaced by electronic log books, but currently these paper books are in popular use. Moreover, whatever be the media for recording, the prime importance is of noting down the relevant information for future reference and retrieval as and when required.

The engine room log book is also an important document in case of accident and this gives the clear picture of the engine room working condition and the situation existed in the engine room.

Entries depend on the plant details. Common entries for a diesel engine propulsion plant are:

- Timing of watch (00:00-04:00; 04:00-08:00; 08:00-12:00; 12:00-16:00; ...);

- Main Engine;

- Fuel lever setting;

- Engine load;

2.3. ENGINE ROOM AND OIL LOG BOOKS

- Engine revolution counter;

- Average speed (rpm);

- Fuel flow meter reading;

- Main engine fuel oil inlet temperature;

- Main engine fuel consumption for 4 hours;

- Main engine cylinder exhaust gas temperature;

- Main engine piston and jacket cooling fluid temperature;

- Sea water inlet and outlet temperature on air, lube oil, piston and jacket coolers;

- Main engine sump level;

- Pressures:

- Sea water pressure;

- Jacket cooling water pressure;

- Piston cooling water pressure;

- Lube oil pressure (bearing, crosshead, camshaft);

- Fuel oil pressure;

- Air reservoirs pressure;

- Turbochargers:

- Turbocharger speed (rpm);

- Cooling water inlet and outlet temperature;

- Air cooler inlet and outlet temperature;

- Pressure drop across turbocharger air cooler filter;

- Air temperature inlet and outlet of the turbocharger;

- Exhaust gas temperature inlet and outlet;

- Other temperatures and levels;

- Heavy oil service and settling tank temperature;

- Thrust bearing temperature and pressure;

- Stern tube temperature and pressure;

- Sea water temperature;

- Engine room temperature;

- Refrigerating and air conditioning units:

- Suction and discharge pressure of refrigerant;

- Lube oil pressure;

2.9

2.10

CHAPTER 2. SHIP OPERATION

- Lube oil suction and discharge pressure;

- Air inlet and outlet temperature;

- Refrigerated compartment temperatures:

- Meat room;

- Fish room;

- Vegetable room;

- Dairy room;

- Handling room;

- Fresh water generator:

- Jacket cooling water inlet and outlet temperature;

- Condenser sea water inlet and outlet temperature;

- Shell temperature;

- Vacuum pressure;

- Ejector pump pressure;

- Distillate pump pressure;

- Feed line pressure;

- Flow meter reading for fresh water;

- Auxiliary machinery:

- Exhaust temperatures of all units;

- Cooling water temperatures of all units;

- Alternator forward and aft bearing temperatures;

- Scavenge air pressure and temperature;

- Air cooler inlet and outlet temperatures;

- Lube oil inlet and outlet temperatures;

- Sea water inlet and outlet temperatures;

- Turbocharger of auxiliary engine exhaust temperature;

- Tank Levels:

- Heavy oil service and settling tank readings;

- Diesel oil service and settling tank readings;

- Cylinder lube oil storage and daily tank reading;

- Main engine crank case lube oil storage tank reading;

- Auxiliary engine crank case lube oil storage tank reading;

2.4. ENGINE READINESS 2.11

- Stern tube gravity tank (high/low) tank readings;

- Stern tube aft and fwd seal tank level.

Most of the readings and records shown above can also be taken from the ship’s control room, although it is advisable to take local readings, when possible, and compare to those of the remote indications. This will also give an idea about the variation in the two so that in case of any large deviations, necessary checks can be performed. Also in case of rush hours such as maneuvering, the engineers would know the actual readings if they are familiar with the deviations in control room and actual readings.

The oil record book is one of the most important documents on-board with a written record for compliance of annex I of MARPOL. When operating oily water separator, 15 ppm equipment for discharging treated bilge water overboard, the operation is recorded with time, position of ship, quantity discharged and retention. Maintenance operation of MARPOL equipments should be recorded with the type of maintenance, date and time.

Bunkering operation should be recorded including date, time, bunkering grade, quantity bunkered, port of bunkering. Any internal bilge or sludge transfer should also be recorded with date and time and quantity transferred.

The oil record book should always be accompanied with required certificates and all the receipts of bunker and sludge or bilge disposal operation.

All the operation and records are acknowledged by officer carrying the job along with chief engineer signature. At the end of every page, master will sign the oil record book.

2.4

Engine readiness

The status lights are used as a communication between the Bridge and ECR as the request for engine readiness. The actual engine readiness would be discussed by verbal communications, but the status lights are used to convey a request by the Bridge and an acceptance by the ECR. Readiness status are:

- Stand-by;

- At Sea;

- Finished With Engine.

The meaning of each one of these readiness conditions is briefly described in the following paragraphs.

2.4.1

Stand-By

When the engine room is put in stand-by condition, the officer in charge of the engineering watch shall ensure that all machinery and equipment which may be used during maneuvering is in a state of immediate readiness and that an adequate reserve of power is available for steering gear and other requirements.

2.12

CHAPTER 2. SHIP OPERATION

The ECR should only accept Stand-By when the engine and its associated system are ready to provide full maneuvering capabilities. The following sub-systems should be ready:

- Two diesel generators connected to the 440V main switchboard;

- Oil fired boiler operating and on-line;

- Auxiliary blowers operating in automatic;

- Two steering gear motors operating;

- Engage the shaft-generator, if to be used during sea passage.

Check that indicator cocks are closed and turning gear disengaged. Reset any slow down or shut down alarms (the speed lever must be set to stop position to be able to reset any shut downs). Check that no safety overrides are present.

All bridge orders shall be promptly executed. Changes in direction or speed of the main propulsion units shall be recorded, except where the government of a state party to the International Convention on Standards of Training, Certification and Watch-keeping for Seafarers, 1978 has determined that the size or characteristics of a particular ship make such recording impracticable. The officer in charge of the engineering watch shall ensure that the main propulsion unit controls, when in the manual mode of operation, are continuously attended under stand-by or maneuvering conditions.

2.4.2

At Sea

The “At Sea” status communicates that the Bridge no longer requires full maneuvering of the propulsion engine, as the vessel is in open water. This will allow the engineering staff to operate the engine room systems in a more economical mode. Therefore, one or more of the diesel engine for electric energy production would be replaced by the turbo and/or the shaft alternator and then shut down. One of the two operating steering gear motors should be stopped.

The speed and power of the engine would be increased up to the required sea speed. The main engine fuel consumption should be changed to HFO. The distiller must be operated to start fresh water production.

The officer in charge of the engineering watch shall bear in mind that changes in speed, resulting from machinery malfunction, or any loss of steering, may imperil the safety of the ship and life at sea. The bridge shall be immediately notified, in the event of fire, and of any impending action in machinery spaces that may cause reduction in the ship’s speed, imminent steering failure, stoppage of the ship’s propulsion system or any alteration in the generation of electric power or similar threat to safety. This notification, where possible, shall be accomplished before changes are made, in order to afford the bridge the maximum available time to take whatever action is possible to avoid a potential marine casualty.

The officer in charge of the engineering watch shall notify the chief engineer without delay:

- when engine damage or a malfunction occurs which may be such as to endanger the safe operation of the ship;

2.4. ENGINE READINESS 2.13

- when any malfunction occurs which, it is believed, may cause damage or breakdown of propulsion machinery, auxiliary machinery or monitoring and governing systems;

- in any emergency or if in any doubt as to what decision or measures to take.

Despite the requirement to notify the chief engineer in the referred circumstances, the officer in charge of the engineering watch shall not hesitate to take immediate action for the safety of the ship, its machinery and crew where circumstances so require.

2.4.3

Finished With Engine

When the main engine is no longer required because ship is in port, or at a secure anchorage. The main engine and auxiliary systems would be partly shut down, and possible heating introduced. When

FWE order is received, the following procedure could be instigated:

- Close the main engine start air isolation valve;

- Place the start air valve in the block position;

- Engage the turning gear;

- Open the indicator cocks;

- Open valves to the fresh water pre-heater, close the by-pass valve and open the steam inlet valve.

2.14

CHAPTER 2. SHIP OPERATION

3

Electric Generators and

Switchboards

3.1

Shore supply

Ships generate emissions while docked in port by running their auxiliary engines to create on-board electric power. In ports with heavy ship traffic, this practice creates emissions and negative health and environmental impact to the local surrounding communities. NO x and SO x emissions from ships are a major global pollution problem and several regulatory parties including IMO/MARPOL and EU have issued legislation which sets absolute limits on sulphur content in fuel and sulphur oxide and nitrogen oxide emissions from ships. Meeting these new standards will require cleaner and much more costly marine fuels with low sulphur content, which will stimulate interest in shore power.

Shore power is especially applicable to ships operating on dedicated routes and vessels that consume large amounts of power and emit high levels of air pollutants when berthed. Typical vessel types include ferries, cruise ships, LNG carriers, tankers and container ships. Also, many ships when in port use shore power to carry out maintenance work.

To connect shore supply, the following procedure should be performed. Ensure all generators are disconnected and emergency bus bar and bus tie are also disconnected. Connect incoming cable on

shore and check phase rotation, Fig. 3.1 or Fig. 3.2. If required, twist phase. Close shore circuit

breaker to supply main bus. Close emergency bus, if required or when starting from cold condition, and continue start sequence.

Shore circuit breaker must be tripped before connecting main generator to bus.

3.1

3.2

CHAPTER 3. ELECTRIC GENERATORS AND SWITCHBOARDS

Figure 3.1: VLCC electric power plant.

Figure 3.2: Main switchboard synchronizing panel.

3.2

Emergency generator

Emergency generator is provided on board merchant ships as one of the emergency source of electrical power. When the main source of power fails, the emergency source of electrical power should automatically start and supply the main bus bar, via the emergency bus bar, within 45 seconds, as

3.2. EMERGENCY GENERATOR 3.3

required by SOLAS regulations. The primary automatic starting arrangement is usually an electric motor cranking the flywheel of the prime mover. The electric motor draws its power from the battery which is charged from emergency switchboard.

3.2.1

Emergency generator operation

The VLCC model includes a detailed sub-model for the emergency generator operation, Fig. 3.3.

Starting procedure is as follows:

- Ensure battery voltage is correct;

- Generator in manual operation press start;

- Turn on voltage control and adjust to proper value (440V in this case);

- Use governor control to give proper frequency (60Hz in this case);

- Connect emergency generator breaker;

- Trip main bus breaker connection to emergency bus.

Figure 3.3: Emergency generator diagram.

The stopping procedure is:

- Ensure that main bus bar has supply;

- Connect main bus bar breaker connection to emergency bus;

- Open emergency generator breaker;

- Stop generator.

3.4

CHAPTER 3. ELECTRIC GENERATORS AND SWITCHBOARDS

The generator is normally in AUTO (Fig. 3.3), voltage control ON and circuit breaker OPEN

(Fig. 3.1). If supply to the emergency switchboard is lost, the generator will automatically start and

close the circuit breaker supplying the emergency bus. The main bus will be isolated due to the connection circuit breaker opening on low voltage. When the emergency bus is again supplied from the main bus, connection circuit breaker closed, the emergency generator will automatically stop and

open the circuit breaker, Fig. 3.4 .

Figure 3.4: Emergency generator and switchboard diagram.

3.2.2

Emergency generator tests

As any other emergency equipment, the generator should be tested regularly to ensure that it will

function when required, see Fig. 3.1 or 3.3. With the generator in AUTO, TEST 1 will simulate low

voltage on the emergency bus causing the generator to start. The generator will attempt a maximum of three starts. Releasing TEST 1 the generator stops.

Before using TEST 2 the bridge must be informed and check that the elevator is not in use because

TEST 2 will temporarily interrupt the emergency supply. TEST 2 disconnects the emergency bus from the main bus simulating total supply failure, the generator starts and supplies the emergency bus.

Releasing TEST 2 reconnects the emergency bus to the main bus and the generator stops.

3.3

Diesel generators

Most propulsion plants include diesel-generators. Operating procedures for these diesel engines are similar to those relative to other diesel engines. The simulated VLCC propulsion plant includes two

3.3. DIESEL GENERATORS 3.5

diesel-generators. The control of the diesel engines may be LOCAL, Fig. 3.5, or REMOTE, Fig. 3.6

or 3.7, from the engine control room.

Figure 3.5: Diesel generator schematics including local control.

Figure 3.6: Generator control on POWER CHIEF panel.

3.6

CHAPTER 3. ELECTRIC GENERATORS AND SWITCHBOARDS

3.3.1

Diesel generator start procedure

The preparation of a diesel generator include the following tasks:

- Check level in the fresh cooling water expansion tank and refill if necessary.

- Check that the fresh water temperature controller is working and in AUTO. Normal set point is

65 − 75

C.

- Ensure sea water flow;

- Check level in lubricating oil sump tank (min 40%) and refill from storage tank if necessary;

- Line-up lubrication oil system (normally one filter is in operation and one filter is cleaned and on stand-by);

- Ensure that lubrication oil valve to the sludge tank is closed.

- Start the electrically driven pre-lubrication oil pump and check that the oil pressure is increasing;

- Set the electrical lubricating oil pump in AUTO;

- Check water level in the fuel oil service tanks and drain if necessary;

- Ensure fuel oil supply from diesel oil service tank and fuel oil system to generator engine are open;

- Open fuel oil inlet valve to fuel oil pump;

- Open fuel oil valve before fuel oil filters (normally one filter is in operation and one filter is cleaned and on stand-by);

- Check the position of the fuel oil supply 3-way valve;

- Open start air valves (Start air must be at least 15 bar);

- If any of the alarm lamps (red) at the local panel are lit, press the RESET button;

To start locally select LOCAL on the Engine Control Panel. Start the engine from the LOCAL panel by pressing the START button. When the engine control panel is in REMOTE, the engine can only be started from the POWER CHIEF panel or Electric Power Plant.

The generator can now be connected to the main bus using the synchroscope panel or Electric

Power Plant panel. To use the POWER CHIEF panel the generator must be switched to REMOTE.

3.3.2

Diesel generator stopping

The generator can be stopped when in REMOTE from the POWER CHIEF panel or the Electric Power

Plant panel. To stop locally, firstly ensure that generator breaker is open. With the engine control in

LOCAL, press STOP. If the generator is to be stopped for maintenance leave control in LOCAL and close starting air valve. Placing the electric lubricating oil pump in manual prevents start from remote positions.

3.3. DIESEL GENERATORS 3.7

Figure 3.7: Diesel generator control panel.

3.3.3

Synchronising procedure

To connect a generator to the main switchboard, already fed by another generator, the synchronising procedure must be followed. Manual and automatic options are available. Main steps on a manual synchronising procedure are:

- The incoming generator must be running and not in AUTO;

- Select incoming generator, voltage and frequency can be compared with bus;

- Adjust excitation if necessary to give equal voltages;

- Adjust governor control so that incoming generator is slightly faster than bus frequency;

- Synchroscope indicator should be turning slowly in a clockwise direction;

- Connect breaker when the top synschroscope indicator is lit;

- The breaker connected light will show that the generator is now connected to the bus.

- Increase the governor speed to give the incoming generator some load.

- To manually share the load equally use the governor controls for each generator.

To disconnect a generator from the main switchboard, the procedure is as follows:

- Ensure generator to be disconnected is not in AUTO;

- Use governor controls on each generator to reduce the load on outgoing generator to near zero

(be carefull to do not reverse power);

3.8

CHAPTER 3. ELECTRIC GENERATORS AND SWITCHBOARDS

- Select outgoing generator;

- Disconnect, breaker connected light goes out.

3.3.4

Generator control

The shaft and diesel generators may be operated in four different control modes, selected by pressing the dedicated push buttons at the POWER CHIEF Generator Control panel:

- Equal load;

- Optimal load;

- Cyclic load;

- Alert Mode.

Providing the generators are in AUTO, EQUAL LOAD balances load evenly between generators, when two or more are running in parallel. This mode is normally selected when safety is the most important issue (during manoeuvring, loading, discharging, etc.). OPTIMAL LOAD provides maximum fuel economy and is usually selected during sea voyages. First priority takes maximum load while second priority takes the rest of the load. Cyclic load is selected by pressing the CYCLIC LOAD push-button. This mode is similar to the OPTIMAL LOAD mode, but after a certain period of time generator 1 and 2 will change in taking the highest load. This mode will cycle the load between the engines in such way that one of the diesels is running at max. load while the other diesel handles the remaining load and thereby prevents carbonising of the cylinders, valves, etc. The cyclic load mode is selected when it is necessary to run more than one diesel on low power. Alert mode is selected when the automatic stopping of a generator is undesirable. Alert mode can be used with equal load, optimum load and cyclic mode. When ALERT MODE is selected the automatic disconnection and stopping of generators is inhibited. This mode is used when a large excess capacity is required, i.e.

manoeuvring, or when sudden large power surges may occur, i.e. when using the bow thruster.

Push-button AUTO puts the diesel-generator into auto mode provided that:

- READY lamp is lit;

- In this mode the Power Chief will take care of starting and stopping, connecting and disconnecting and load sharing of the generators;

- If the lamp is flashing, the Auto mode is cancelled because of the READY conditions is no longer met;

Conditions related to the READY lamp are:

- Engine Control in REMOTE;

- LO Priming Pump in AUTO;

- All trip RESET;

3.4. SHAFT-GENERATOR 3.9

- Voltage Control ON.

On the priority selection, one should consider:

- PRIOR 1 Push-button to select highest priority, that is first in and last out.

- PRIOR 2 Push-button to select medium priority, that is later in and earlier out than number 1.

Diesel-generator operation procedure

Preparations before operating POWER CHIEF generator control panel should be performed as defined

in Sec. 3.3.1. Diesel generators to be ready and in alarm free condition. In MANUAL mode:

- Push START button for the respective generator engine;

- When running light appears, generator is ready for connection to main bus bar;

- Push CONNECT to connect generator to main bus bar;

- After connection of generator(s), voltage and frequency must be checked.

If emergency generator is running it will automatically disconnect and stop. Shore power must be manually disconnected.

For automatic power management, connect first generator manually as described. Then execute the following procedure:

- Press buttons AUTO and PRIORITY 1 for this generator set.

- After preparing of second generator, READY signal will be lit on POWER CHIEF panel.

- Press buttons AUTO and PRIORITY 2 for this generator.

- Select required control mode.

Second generator will automatically start, take load, and stop according to the electrical consumption and the selected control mode.

3.4

Shaft-generator

Shaft generators driven by the main propulsion engine(s) to provide electrical power are in widespread use, reducing the need to run auxiliary generator sets. But there have been limitations. The ship’s electrical system normally requires a fixed frequency and this means that engine speed has to be kept constant, which often leads to inefficient engine operation.

The gear constant ratio is the simplest shaft generator, as no speed control or frequency control systems are incorporated. In the vast majority of cases, is used to produce electric power with a constant electrical frequency during the voyage. Since the frequency produced by the alternator is proportional to the speed of the engine, the engine must be operated at constant speed. This is only possible if a controllable pitch propeller is installed. When a fixed pitch propeller is used, the speed

3.10

CHAPTER 3. ELECTRIC GENERATORS AND SWITCHBOARDS of the propeller, and thus of the engine, varies with the required speed of the ship and the resistance acting on the ship. The operation of the engine at constant speed means reduced propeller efficiency at reduced propulsion load compared with a controllable pitch propeller running in combinator mode

(reduced speed at reduced propulsion load) or a fixed pitch propeller. The thermal efficiency of the main engine is also slightly lower in constant speed mode than in combinator mode.

The Renk constant frequency drive includes an epicyclic gear with a hydrostatic superposition

drive, Fig 3.8. The superposition drive comprises a hydrostatic motor controlled by an electronic

control unit and driven by a built-on pump. The hydrostatic system drives the annulus of the epicyclic gear in either direction of rotation, based on the detected output speed, and thus continuously varies the gear ratio over an engine speed variation of 30%. In the standard layout the constant output speed range of the gearbox is set between 100% and 70% of the engine speed at specified MCR.

Figure 3.8: Renk constant frequency drive.

The introduction of advanced power electric system, see Fig. 3.9, for conditioning the power

coming from a shaft generator so that the switchboards see a constant voltage and frequency at any engine speed opens the way for much more flexible use of engine and propeller speed variations to maximise both propeller and engine efficiencies by running them at their design points. A more efficient system also helps reduce CO

2 and NO x emissions.

The shaft generator can also act as a motor, feeding in power to drive the propeller, attractive where a vessel may spend extended periods cruising very slowly, or loitering for example waiting for a place at the quay. The main engine can be shut off and power from one or more generators used for propulsion.

3.4. SHAFT-GENERATOR 3.11

Figure 3.9: Shaft generator advanced power electric system.

3.4.1

Shaft generator operating procedures

The simulated VLCC propulsion plant includes a shaft generator with an advanced electric power control system. Generator and Power Take-In modes are available. The shaft generator/motor main components are:

- Control system;

- Static converter;

- Shaft generator/motor;

- Synchronous condenser.

The power from the shaft of the main engine drives the shaft generator via a gear and a clutch, see

Fig. 3.10. The clutch is driven by control air and will not operate if the control air is missing or the

inlet shaft speed is above 300 rpm. The load is limited to half between 200 and 400 rpm and maximum power is available above 400 rpm. The synchronous condenser controls voltage and frequency.

The shaft-generator starting procedure is:

- Ensure auxiliary power on and cooling fan is running;

- Open air valve to clutch.

- Ensure input shaft speed below 300 rpm and connect clutch in local control.

- When clutch has engaged change to remote control.

- Check that enough reserve power is available to start the synchronous condenser, about 150 kW;

- Start synchronous condenser;

- The generator can be connected manually or automatically from the Power Chief panel in the normal manner.

To use PTI the generator breaker must first be connected in the normal manner. PTI can be selected locally or from the Power Chief panel. In PTI mode select either AVAILABLE MODE to use

3.12

CHAPTER 3. ELECTRIC GENERATORS AND SWITCHBOARDS

Figure 3.10: Shaft-generator system plant.

all available power (300kW will be in reserve) or select SETTING MODE where the engine power can be set up to a maximum of 300kW in reserve.

When stopping shaft-generator it is normal to leave the clutch engaged when main engine is running otherwise, in order to engage clutch, the engine would have to be slowed down. If the generator is not required, disconnect circuit breaker in the normal manner. The synchronous generator may now be stopped.

If maintenance is to be carried out it will be necessary to turn off the auxiliary power, disengage the clutch and close the air valve to the clutch.

3.4.2

Shaft generator control

A prerequisite for shaft generator operation is that the main engine remote control is in the SHAFT

GENERATOR mode. The functions AUTO and PRIORITY are not available for shaft generators.

The shaft generators must always be managed manually.

Remote control functions for shaft-generator are as follows:

- Push-button START starts the synchronous condenser;

- Push-button STOP stops the synchronous condenser;

- Light READY indicates that the shaft generator clutch is engaged;

- Push-button CONN for remote manual connection of the generator breaker;

- Push-button DISC for remote manual disconnection of the generator breaker;

- RUN lamp indicates that the synchronous condenser is running;

3.5. TURBO-GENERATOR 3.13

Figure 3.11: Shaft-generator control panel

- IN lamp indicates that the generator breaker is connected.

To manually connect an engaged shaft generator via the power management system, switch off the

AUTO and activate the CONN button. The power management system will automatically synchronise and connect the shaft generator to the bus bar. To manually disconnect the shaft generator via the power management system switch off the AUTO and activate the DISCONNECT button. The system will automatically reduce the load and disconnect.

Push-button AUTO puts the generator into auto mode provided that READY and RUN lamps are lit. In this mode, the Power Chief will take care of connecting, disconnecting and load sharing of the generator. If the lamp is flashing, the AUTO mode is cancelled because of the READY conditions is no longer met.

3.5

Turbo-generator

Like any other machinery, the turbo-generator needs to start under a sequential starting procedure to achive trouble-free operation. The correct procedure ensures that no part of the machinery goes through any kind of stress, thermal or mechanical.

The simulated VLCC plant includes one 7 bar pressure superheated steam turbo-generator. The preparation of this turbo-generator should start checking if superheated steam is available at 7 bar pressure. The condenser should already be prepared. Then, open the following valves:

- steam line drain;

- sealing steam outlet;

3.14

CHAPTER 3. ELECTRIC GENERATORS AND SWITCHBOARDS

Figure 3.12: Turbo-generator system.

- turbo generator outlet to main condenser;

- lube oil filter inlet;

- lube oil cooling water shut-off valve;

- Sealing steam valve.

Check the level and water content of the turbo generator oil sump tank. Place lube oil pump in AUTO.

Engage and start the turning gear for about 30 minutes.

Before start the turbo-generator disengage turning gear and reset the turbine trip. Open the turbo generator emergency stop valve to 15%. The turbo-generator should start to rotate slowly. Let the turbine rotate for 2 minutes at low speed. Continue to open the valve very slowly, up to 40% over 15 minutes. Once the machine is up to speed (6400 rpm) the emergency stop valve should be opened to

100% and steam line drain closed. Monitor all temperatures and pressures to ensure no alarms are

active. The turbo generator can now begin electrical supply to main switchboard, see Fig. 3.6.

On the LNG carrier propulsion plant, the two turbine generators are supplied with superheated steam at boiler conditions (60 bar, 510

C) and normally exhaust to the main condenser. In emergency conditions the exhaust can be led to the atmospheric condenser.

The turbine generators are supplied with superheated steam from both boilers. The steam to both turbines passes through a line stop valve, emergency stop valve and control valve, and then over the turbine stages driving the unit. Gland steam is supplied to both ends of the turbines, ensuring no air passage at the glands.

The turbines drive the generators through a single helical reduction single gearbox with forced lubrication. The turbine speed is maintained at a constant 8000 rpm, corresponding to a generator

3.5. TURBO-GENERATOR 3.15

speed of 1800 rpm, by a mechanical hydraulic governor. The turbine and gearing bearings are force lubricated by a shaft driven pump when the unit is at full speed, which takes suction from the built-in sump and discharges to the bearings, gears and control oil circuits.

The steam valve is maintained in the open position by the control oil and is tripped by venting the control oil to the sump, closing the steam supply valve. Prior to starting, and during the turbine stopping period, an electrically driven lube oil pump operates to supply oil to the systems. When

Figure 3.13: LNG carrier turbo-generator system.

starting, the oil supplied to the control system opens the steam supply valve as well as supplying the bearings. When stopping, oil is supplied to the turbine and generator bearings as the turbine runs down. The electrically driven lube oil pump can be operated in the manual or automatic modes according to circumstances and requirements. Drains from the steam supply piping and turbine wheel housing keep the turbine free of water.

The axial position of the rotor is constantly monitored, with excess axial movement (from thrust bearing failure) tripping the turbine. Failure of this trip could allow the turbine blades and nozzles to come into contact. Also fitted is an excessive vibration monitor, which again will trip the unit preventing major mechanical damage.

The generator is supported on two plain bearings. It is cooled through a closed lube oil circuit, with the temperature being maintained through a fresh water supplied cooler. The lube oil pumps take suction from the lube oil sump, built into the base of the turbine generator. The main oil pump is shaft driven, and supplies all the oil requirements when the turbine is running. The electric driven oil pump has an electrically driven motor and supplies control and lubricating oil before and after the shaft driven pump is delivering full pressure, and also if the shaft driven pump should fail in service. Both pumps deliver into a common line, which provides pressure for the control oil and for the bearing

3.16

CHAPTER 3. ELECTRIC GENERATORS AND SWITCHBOARDS and reduction gear lubrication. The main lube oil cooler is the surface cooling shell and tube type with cooling water supplied from the central cooling system. The oil temperature is maintained by a control valve, which allows oil to pass through the cooler, circulating the sump.

When the turbine is started the auxiliary, electrically driven, lube oil pump should be running.

The pump builds-up the oil pressure to allow the opening of the main stop valve steam regulating mechanism and, provided all other services and valves have been set, the turbine will run up to speed.

As the turbine speed rises and the shaft driven lube oil pump takes over the oil supply to the systems, the auxiliary pump will stop. This electrically driven pump should be placed in automatic mode, and will start automatically if the main line oil pressure drops either as the turbine is slowing down or if there is a fault in main lube oil pump. After the turbine has stopped and has been allowed to cool down, the auxiliary lube oil pump can be switched off.

The turbo-generator is tripped by any of the following conditions:

- turbine over-speed;

- axial displacement of rotor;

- high vibration;

- low lube oil pressure;

- high lube oil temperature;

- high back pressure.

The main stop quick closing valve trip oil cylinder, the speed governor, power cylinder and the overspeed trip have a continuous supply of oil to maintain their running positions. Should any of these trips be activated, the oil in the system is allowed to drain to the sump, so closing the main steam stop valve. After tripping on overspeed, the trip must be manually reset, but only when the turbine speed has reduced below 75% of normal, to prevent damage to cut out pawl. The constant turbine speed is maintained by controlling the amount of steam admitted to the turbine nozzles, so meeting the varying load demands imposed by the electric generator. The steam regulating valve is controlled through a lever arm by the power cylinder, which amplifies a signal from the governor.

The operating procedure for these turbo-generators are described in the following check-lists. The starting procedure is:

- Confirm that the steam and power supply sources are available;

- Check that the oil level in the sump tank is a normal as required;

- Confirm that the main stop valve, exhaust valve, and the packing steam supply valves are closed;

- Start the electrically driven auxiliary lube oil pump and confirm the oil supply to the bearings and gearing;

- Ensure the line and casing drain valves are open to the bilge;

- Open the gland steam shut off and extraction valves;

3.6. SWITCHBOARDS 3.17

- Open the discharge line valve to the correct condenser ensuring the main turbine condenser vacuum is not affected;

- When ready to start slowly open the main stop valve and allow the unit to turn;

- Increase the speed slowly and allow the turbine to warm through as the superheated steam passes through it;

- As revolutions increase, inspect the entire unit for lube oil and steam leakage. Also monitor vibration levels;

- If any unusual vibrations occur, always stop the turbine and inspect the fault before restarting;

- When up to full speed, the stop valve should be fully open;

- Shut all drains, ensure that the main lube oil pump is taking the lubrication supply and that the auxiliary pump has cut-out;

- Place the auxiliary lube oil pump in AUTO mode for starting if the lube oil supply pressure drops;

- Adjust the voltage and frequency if necessary, synchronise with the on line unit and connect to main switchboard;

- Allow the units to take similar loads and monitor them until steady loads are maintained.

The stopping procedure is:

- Remove the load from the generator to be stopped to near zero and, when reduced, open the circuit breaker;

- Close the emergency stop valve and allow the turbine to slow down;

- As the revolutions fall, and the lube oil discharge pressure from the shaft driven lube oil pump drops, ensure the auxiliary lube oil pump starts to maintain the lube oil flow;

- When the turbine has stopped, close the discharge valve and the main steam line stop valve;

- Close the gland steam shut off and extraction valves;

- Ensure that LO supply is maintained until generator has stopped and cooled down.

Actually, the above enumerated electrical operations should be executed on main switchboard

control panel. On this simplified simulation they are performed on the panel included in Fig. 3.14.

3.6

Switchboards

3.6.1

Main switchboard

The starters are grouped into four main sections. Deck machinery and bow thruster are supplied via a bus tie. Each starter group has indication for current, active power, reactive power and power factor.

3.18

CHAPTER 3. ELECTRIC GENERATORS AND SWITCHBOARDS

Figure 3.14: LNG carrier electrical power plant.

Figure 3.15: Main switchboard starters panel.

Starters indicated with an asterisk are supplied from elsewhere and are not included in the calculations for the starter group.

The breakers are operated by pressing the IN button. Pressing IN again will open the breaker. The green indicator shows if the machinery is running. The display value of the breakers may be changed from active power to current.

3.6. SWITCHBOARDS 3.19

Figure 3.16: Electrical distribution diagram.

The feeders are grouped into four main sections. The 220V sections are fed from the main bus via a circuit breaker and transformer. Each feeder group has indication for current, active power, reactive power and power factor. Feeders indicated with an asterisk are supplied from elsewhere and are not included in the calculations for the feeder group.

The breakers are operated by pressing the IN button. Pressing IN again will open the breaker. The display value of the breakers may be changed from active power to current.

In case of overload of available supply the breakers can be grouped for non-essentials to automatically disconnect. Non-essentials must be circuits not required for the safe operation of the vessel.

3.6.2

Emergency switchboard

The emergency switchboard, Fig. 3.4, supplies circuits necessary for the safety of the vessel: com-

munications, navigation lights, fire alarm, fire fighting, emergency air compressors, etc. The feeders are grouped into four main sections. Two 440V sections and two 220V sections are supplied via a circuit breaker and transformer. The display value of the breakers may be changed from active power to current.

The emergency batteries are supplied by battery chargers via the 440V emergency bus. There are two sets of batteries, one for starting the emergency generator and one for the main 24V supply.

3.6.3

Non-essentials

The breakers can be grouped for non-essentials to automatically disconnect in case of overload of available supply. Non-essentials must be circuits not required for the safe operation of the vessel.

3.20

CHAPTER 3. ELECTRIC GENERATORS AND SWITCHBOARDS

3.6.4

Earth leakage

Total earth leakage current is constantly monitored. Earth fault finding is available by selecting 440V,

220V or 24V distribution system and switching between phases.

4

Auxiliary Equipment

4.1

Stern tube system

The stern tube is a hollow tube passing at the lower stern part of the ship carrying tail shaft and connecting it to the propeller out at sea. The stern tube includes the bearing for the tail shaft, lubrication arrangement and, most importantly, the sealing arrangements. The stern tube bearing serves two important purposes:

- It supports the tail-shaft and a considerable proportion of the propeller weight;

- It also acts as a gland to prevent the entry of sea water to the machinery space.

Early arrangements used bearing materials such as lignum vitae, a very dense form of wood, which were lubricated by sea water. Most modern designs use an oil lubrication arrangement for a white metal lined stern tube bearing. Different sealing arrangements are used to prevent water ingress and oil leakage. They are as follows:

- stuffing boxes consisting of packing material;

- lip seals in contact with shaft to prevent passage of oil or water along the shaft;

- radial face seals supported with springs fitted radially around the shaft, aft bulkheads and after end of the stern tube.

Out of these, the lip seal arrangement, see Fig. 4.1, is most popularly used.

The stern tube lubricating and sealing system for the VLCC ship is represented in Fig. 4.2. Oil

is pumped to the bush through external axial grooves and passes through holes on each side into internal axial passages. The oil leaves from the ends of the bush and circulates back to the pump and the cooler. The stern tube bearings are lubricated by two separate gravity lube oil tanks, one highand one low-gravity, chosen according to vessel draft. One of two header tanks will provide a back pressure in the system and a period of oil supply, in the event of pump failure. A low-level alarm will

4.1

4.2

CHAPTER 4. AUXILIARY EQUIPMENT

Figure 4.1: Stern tube lip seals.

be fitted to each header tank. Oil pressure in the lubrication system is higher than the static sea water head to ensure that sea water cannot enter the stern tube in the event of seal failure.

Figure 4.2: Stern tube system diagram.

The oil is pumped from the stern tube sump tank to the selected gravity tank, from where it flows to the stern tube bearings by gravity. The gravity tank is automatically filled by one of the lubricating oil pumps and surplus oil is continuously drained to the sump tank through an overflow pipe. The oil is cooled as it is pumped to the gravity tank (low temperature fresh water cooled). If the running pump fails to maintain the level in the gravity tank, the stand-by pump will start at low level in the gravity tank, provided that the pump is in AUTO mode.

4.2. VENTILATION 4.3

Refilling of the lubricating oil sump tank is carried out by starting the make-up pump. The oil can be transferred to the spill oil tank in case of contamination. The stern tube has a forward seal oil system that can be topped-up from the gravity feed line.

The main steps to start the stern tube system are:

- ensure cooling water to stern tube oil cooler;

- refill lubricating oil sump tank if necessary;

- select required gravity tank using 3-way valve in filling line;

- select correct gravity feed to stern tube;

- start the lubricating oil pump in MANUAL;

- when one pump is started and tank levels are normal, set the other pump in AUTO.

If the running pump is unable to maintain the level in the gravity tank, the stand-by pump starts automatically. Periodically, check level of oil in sealing tank, fill from make-up valve and drain water, if required. Stop of pumps should be carried out manually.

4.2

Ventilation

Ventilation is the provision of a supply of fresh untreated air through a space. Natural ventilation occurs when changes in temperature and consequent air density cause circulation in the space. Mechanical or forced ventilation uses fans for a positive movement of large quantities of air. Natural ventilation is used for some small workshops and stores but is impractical for working areas where machinery is present or a number of people are employed. Forced ventilation may be used in cargo spaces where the movement of air removes moisture or avoids condensation, removes odors or gases, etc.

The machinery space requires ventilation. As a result of its large size and the fact that large volumes of air are consumed, a treatment plant would be extremely costly to run. Ventilation is therefore provided in sufficient quantities for machinery air consumption and also to achieve a cooling effect. A portion of fuel consumed by the engines is lost to the environment in the form of heat radiated to the surrounding air. In addition, heat from generator inefficiencies and exhaust piping can easily equal engine-radiated heat. Any resulting elevated temperatures in the engine room may adversely affect maintenance, personnel, switchgear, and engine or generator set performance. Engine room ventilation air (cooling air) has two basic purposes:

- To provide an environment that permits the machinery and equipment to function properly:

- To provide an environment in which personnel can work comfortably and effectively.

The use of insulation on exhaust pipes, silencers, and jacket water pipes will reduce the amount of heat radiated by auxiliary sources. Radiated heat from the engines and other machinery in the engine

4.4

CHAPTER 4. AUXILIARY EQUIPMENT room is absorbed by engine room surfaces. Some of the heat is transferred to the sea through the ship’s hull. The remaining radiated heat must be carried away by the ventilation system. A system for exhausting ventilation air from the engine room must be included in the ventilation system design.

In many installations, combustion air is drawn from outside the engine room via ductwork that is designed to move a large amount of air with very little restriction. These installations have very little impact on engine room ventilation design. Other installations, however, require that combustion air be drawn directly from the engine room. In these installations, combustion air requirements become a significant ventilation system design parameter. Approximate consumption of combustion air for a diesel engine is 0.1 m

3 of air/min/brake kW produced.

Required ventilation airflow depends on the desired engine room air temperature as well as the cooling air and combustion air requirements outlined above. While it is understood that total engine room ventilation airflow must take all equipment and machinery into account.

The primary reason for maintaining engine room at an appropriate temperature is to protect various components from excessive temperatures. Items that require cool air are:

- Electrical and electronic components;

- Cool air to the air cleaner inlet;

- Cool air to the torsional vibration damper;

- Habitable temperatures for the engine operator or service personnel;

- Cooling air for the generator or other driven equipment.

Operation in extreme cold weather may require reducing ventilation airflow to avoid uncomfortably cold working conditions in the engine room. This can be easily done by providing ventilation fans with two speed (100% and 50% or 67% speeds) motors.

Ventilation air exhaust systems should be designed to maintain a slight positive or negative pressure in the engine room, depending on the specific application. Positive pressure should normally not exceed 0.05 kPa. This positive pressure provides the following advantages:

- It prevents the ingress of dust and dirt, which is especially beneficial for those applications involving engines that draw their combustion air from the engine room.

- It creates an out draft to expel heat and odor from the engine room.

Some applications, such as a marine application where the engine room is adjacent to living quarters, require that a slight negative pressure be maintained in the engine room. This negative pressure should not normally exceed 0.15 kPa. The excess exhaust ventilation provides the following advantages.

- It compensates for the thermal expansion of incoming air.

- It creates an in draft to confine heat and odor to the engine room.

The ventilation system of the VLCC consists of four supply fans and four extractor fans for the

main engine room, as indicated in Fig. 4.3. The axial-flow fans provide air through ducting to the

4.3. COOLING SYSTEMS 4.5

various working platforms. The hot air rises in the center and leaves through louvers or openings, usually in the funnel. The air pressure in the engine room space will vary depending on which fans are running and also on whether the main engine and diesel generators are running. Insufficient air supply will lead to the engine room temperature rising. Indication is also given of fire detection in the engine room and deck areas. The engine room supply and exhaust fans will be stopped when the

Emergency Shut Off is actuated or the CO

2 cabinet door is open.

The engine control room and cargo control room have supply fans. The machinery control room, as a separate space, may well be arranged for air conditioning, with an individual unit which draws air through trunking from the outside and exhausts back to the atmosphere. The purifier room and sewage room have exhaust fans. Accommodation fans are also started from this panel. The panel gives indication of the engine room and ambient temperatures, as well as the air pressure within the engine room.

Figure 4.3: Ventilation control panel.

4.3

Cooling systems

4.3.1

Sea water system

The ultimate cooling system on a ship is naturally the sea water cooling system. The temperature control is usually achieved by adjusting the cooling liquid outlet valve. The inlet valve is left open and this ensures a constant pressure within the cooler. This is particularly important with sea water cooling, where reducing pressure could lead to aeration or the collecting of air within the cooler.

Air remaining in a cooler will reduce the cooling effect. Vents are provided in the highest points of

4.6

CHAPTER 4. AUXILIARY EQUIPMENT coolers which should be opened on first filling, and occasionally afterwards. Vertical mounting of single pass coolers will ensure automatic venting. Positioning the inlet cooling water branch facing downwards and the outlet branch upwards will achieve automatic venting with horizontally mounted coolers. Drain plugs are also fitted at the lowest point in coolers.

Clean heat transfer surfaces are the main requirements for satisfactory operation. With sea water cooling, the main problem is fouling of the surfaces, i.e. the presence of marine plant and animal growth. On shell and tube coolers, the end covers are removed to give access to the tubes for cleaning.

Special tools are usually provided by the cooler manufacturer for cleaning the tubes. The end covers can also be cleaned.

Tube leakage can be checked, or identified, by having the shell side of the cooler circulated, while the cooling water is shut-off and the end covers removed. Any seepage into the tubes will indicate the leak. It is also possible to introduce fluorescent dyes into the shell-side liquid. Any seepage will show under an ultraviolet light as a bright green glow. Leaking tubes can be temporarily plugged at each end or removed and replaced with a new tube.

Plate-type coolers which develop leaks present a more difficult problem. The plates must be visually examined to detect the faulty point. The joints between the plates can present problems in service, or on assembly of the cooler after maintenance.

Where coolers are out of use for a long period, such as during surveys or major overhauls, they should be drained on the sea water side, flushed through or washed with fresh water, and left to dry until required for service.

The VLCC ship sea water cooling system is included in Fig. 4.4. Sea water is pumped by two

electrically driven pumps from sea chests through the sea water filter. The sea water flows from the pumps to six coolers, connected in parallel:

- Fresh water cooler No 1 and No 2;

- Steam condenser;

- Diesel-generators No 1 and No 2 fresh water coolers;

- Air conditioning condenser.

Sea water is taken from either a high suction sea chest via a strainer when the vessel is loaded or a low suction sea chest when the vessel is in ballast condition. In order to avoid too low sea water temperatures at the cooler inlets, a controllable recirculation valve is used to circulate water from the overboard line back to the common sea water suction line. During cargo operations, there will be an increasing load on the steam condenser. To meet the additional need for cooling water, the system is equipped with an auxiliary pump, larger than the main pumps. Two fire and general service pumps are provided which can service the fire and the ballast systems. Main sea water pump No 2 can be used as an emergency bilge pump. The emergency fire pump has a separate suction from its own sea chest.

The sea water system on a steam turbines driven ship is similar. The LPG carrier sea system

diagram is included in Fig. 4.5. Cooling sea water supply to the main condenser is guaranteed by

4.3. COOLING SYSTEMS

Figure 4.4: VLCC sea water system diagram.

4.7

Figure 4.5: LNG carrier sea water system diagram.

electrically driven centrifugal pumps. There are two main sea water pumps, which also supply cooling flow for the atmospheric condenser. The main sea water circulating pumps take suction from the high or low sea chests, placed in the lower flat of the engine room. The draft of the vessel will indicate which sea chest to use. When the ship speed is higher then a critical value, main condenser sea water circulation can also be achieved from the scoop.

4.8

CHAPTER 4. AUXILIARY EQUIPMENT

Sea chests, sea water lines and all sea water cooled condensers are protected from environmental hazards by an anti-fouling system. Marine Growth Protection System (MGPS) units inject treatment product into all sea chests and is then circulated through out the sea water system.

Two auxiliary sea water pumps supply cooling for the central fresh water cooling system and the main condenser vacuum pumps. The central fresh water cooling system provides cooling for:

- Main turbine lubricating oil;

- Feed pumps lubricating oil;

- Drains cooler;

- Turbo-generator lubricating oil.

4.3.2

Fresh water system

The VLCC plant includes a fresh water cooling system, see Fig. 4.6, split in two sub-systems:

- the low temperature sub-system (LTFW), that cools all the auxiliary equipment and the main engine scavenging air;

- the high temperature sub-system (HTFW), dedicated to cool the cylinder liners of the main engine.

Figure 4.6: Fresh water system diagram.

This division is common for propulsion plants including two- and four-stroke diesel engines. In this plant, the HTFW temperature is controlled by a mixing valve. In other plants, independent fresh water coolers may exist for high and low temperature loops. Usually, the steam turbines propulsion

4.4. COMPRESSED AIR SYSTEMS 4.9

plants only include a low temperature fresh water system, mainly dedicated to provide circulating flow for oil coolers.

LTFW system

Normally, only one LTFW pump is in operation. The auxiliary LTFW pump is mainly used when in harbor or after blackout. The fresh water system is cooled by the sea water. The fresh water temperature in the LTFW system is controlled by a PID controller, which actuates a three-way mixing valve, placed after the two fresh water coolers. This controller can be operated in manual or automatic mode. The controller input signal is given by the temperature before the LTFW pumps. From the

LT/HT junction, some of the LTFW is led directly to the fresh water coolers, while some is led to the

HTFW loop.

HTFW system

The fresh water through the main engine is driven by two main or one auxiliary HTFW pumps, of which only one of the main pumps is normally in operation. The auxiliary pump is provided for use in port. If the main engine has been stopped for a long period of time, it is required to heat the HTFW with the pre-heater, which is heated with steam.

The venting valve after cylinders should always be open, to keep a small amount of water flowing from the cylinders to the expansion tank in order to release entrapped air. The HTFW system is controlled by a PID controller, which operates a three-way mixing valve, mixing hot water from main engine outlet with cold water from the LT/HT junction. The expansion tank must be filled periodically.

Some of the heat may be used for the production of distilled water by the fresh water generator.

4.4

Compressed air systems

Compressed air systems are the high pressure for diesel engines starting and the lower pressure one for control and general service air.

4.4.1

Start air system

The purpose of this system is to provide starting air for diesel engines and ensure that first start is available, if all power is lost. The compressed air system includes two main starting air compressors,

one emergency air compressor, two start air receivers and one emergency start air receiver, see Fig. 4.7.

Compressors start and stop are set on pressure-switches. All compressors start and stop automatically, according to receivers pressure, by the POWER CHIEF system, if the compressor is in AUTO position.

The emergency compressor is supplied from the emergency switchboard.

Each starting air compressor is cooled by LTFW and monitored by an independent local safety system. The start air compressors will trip, indicated by a red light, if:

4.10

CHAPTER 4. AUXILIARY EQUIPMENT

Figure 4.7: Starting air system diagram.

- discharge air temperature > 110

C;

- lube oil pressure < 0.75 bar.

The starting air compressors are normally operated with one compressor selected as MASTER.

The start air receivers can be operated in parallel, or one of the receivers can be pressurized and shut off as a stand-by receiver. The main and the auxiliary diesel engines are supplied by separate air lines and stop valves from one or both of the air receivers.

There is a non-return valve in the connection from the main start air to the auxiliary start air to ensure that the emergency start air receiver only supplies the auxiliary engines. The safety valves for the start air receivers open at approximately 32 bar.

The air receivers and the air coolers will gradually fill with water, depending on compressed air production and air humidity. The receivers and coolers must be manually drained regularly. Much water in the start air receivers will reduce starting capacity.

If the service air compressor fails, make-up air can be taken from the start air receiver No 1. The air make-up valve is usually left open for safety reasons. If the service air compressor trips, service and control air pressure is not lost, but supplied through the starting air receivers. This may prevent a serious situation like a shut down of the main engine in narrow waters. Carefully consider if, or when, to close the service air make-up valve.

4.4.2

Service and control air system

The purpose of the service air compressor system is to provide air to the control equipment and control valves in the engine room, and for general consumption purposes in engine room and at deck.

4.5. FRESH WATER DISTRIBUTION 4.11

The service air system consists of one service air compressor, one service air receiver and a filter drier/reducer assembly for maneuvering system air and for control air. The compressor starts and stops automatically, according to the receiver pressure, by the POWER CHIEF system, if the compressor is set in AUTO mode.

Figure 4.8: Service air system diagram.

The service air compressor is also cooled by LT fresh water and monitored by an independent, local, safety system. The air compressor will trip at:

- discharge air temperature > 100

C;

- lube oil pressure < 0.75 bar.

As in the starting air system, the air receiver and the air coolers will gradually fill with water, depending on compressed air production and air humidity and must be manually drained regularly.

Much water in the service air receiver will reduce the operating capacity. The air to the maneuvering system and control equipment is filtered and dried, and pressure reduced by a pressure reduction valve, as part of the filter/drier assembly. The maneuvering air and the main control air are delivered at different pressures.

4.5

Fresh water distribution

The fresh water distribution system consists of:

- a pressurized hydrophore tank with necessary pumps and valves;

- a drinking water tank;

4.12

- and a fresh water heater.

CHAPTER 4. AUXILIARY EQUIPMENT

The capacity of the system is approx. 10 t/h of cold water, hot water and drinking water; The hydrophore tank volume is 3 m

3 and pressure should be kept between 3 and 4 bar.

Figure 4.9: Fresh water distribution system.

4.6

Fresh water generator

Old cargo ships were required to carry large supplies of fresh water to sustain the crew on a long voyage. A ship that had run out of fresh water would be in trouble. Today, most commercial ships are equipped with a fresh water generator, a type of evaporator that converts sea water into fresh water.

The concept of a fresh water generator is simple; sea water is evaporated using a heat source, separating pure water from salt, sediment and other elements. Fresh water generators often use the diesel engine jacket as a heat source, although steam can also be used as a heat source. Because fresh water generators often use existing heat to run, the cost of operation is low.

There are two main elements in a fresh water generator. One heat exchanger evaporates the sea water and another condenses the vapor into fresh water. In the condenser element, the vapor is condensed through cooling, often simply using cold sea water to cool the outside of the unit.

The fresh water generator should include a feature to monitor the salinity of the processed water.

If the salinity exceeds a specified level, usually between one and ten parts per million (ppm), the fresh water generator will automatically return the water to the feed line and put it through the cycle again.

4.6. FRESH WATER GENERATOR 4.13

Figure 4.10: Fresh water generators and salinometer.

4.6.1

VLCC fresh water generator

The evaporator heating is supplied from the main engine HTFW circuit by controlling a bypass valve.

The ejector pump is supplied from the main sea water system. The vacuum allows the utilisation of low temperature heating sources. The vapours generated pass through a fine mesh, to prevent salt water carryover, to the condenser.

The maximum evaporator capacity is 30 ton/day at sea water temperature 32

C. The condition of the fresh water is monitored by a salinometer. If the salinity is high, the condensate is recirculated to the evaporator. The distillate water is led to the distilled fresh water tank.

Operation

The sequence to start the fresh water production is as follows, see Fig. 4.11:

- Set salinity controller to MANUAL;

- Close evaporator drain and vacuum breaker valves;

- Open valve for sea water supply to ejector pump;

- Open sea water valve for condenser;

4.14

CHAPTER 4. AUXILIARY EQUIPMENT

Figure 4.11: VLCC fresh water generator.

- Open sea water overboard valve from ejectors;

- Start ejector pump and check pressure and flow;

- Open sea water feed valve to evaporator;

- Wait for the total pressure in the generator to drop to approximately 0.10 bar;

- Open evaporator heating shut off valves;

- Close evaporator heating by-pass valve gradually while checking that the generator pressure does not exceed 0.1 bar;

- When fresh water is visible in sight glass, open recirculation valve and start the distillate pump;

- When salinity control is below alarm limit, activate salinity control by pressing AUTO at salinity control panel.

The stopping sequence is:

- Set salinity controller to MANUAL;

- Open distillate recirculation valve;

- Stop destilate pump;

- Open evaporator heating by-pass valve gradually;

- Open the vacuum breaker valve;

- Close evaporator heating shut-off valves;

- Wait for the pressure raise in the generator to near the atmospheric pressure;

4.6. FRESH WATER GENERATOR

- Stop ejector pump and close related sea water valves;

- Close sea water valve for condenser;

- Close sea water feed valve to evaporator;

- Open evaporator drain valve.

4.15

4.6.2

Steam plant fresh water generators

The steam turbines plant for the propulsion of the LNG carrier includes two fresh water generators.

One is called as sea water cooled distiller and the other as condensate cooled distiller.

The distilled water tank is filled with fresh water from the sea water cooled or the condensate cooled distiller. Make-up of primary water to the boiler system is fed to the main condenser recirculation line or to the atmospheric drain tank. Make-up of fresh water to the low pressure steam generator is fed to the secondary feed water tank.

Sea water cooled distiller

This distiller is a single stage, tube and shell type fresh water generator. It has a sea water cooled condenser. The cooling water flow is driven by a combined condenser and ejector sea water pump.

The feed water is taken from the condenser outlet sea water flow. Chemicals can be added to the feed water from a chemical feed tank, for scaling and corrosion control.

The distiller has two ejectors, one for brine and one for air, supplied with operating water from the condenser outlet flow.

Steam for heating the feed is taken from the back pressure steam system. Condensate is circulated in the heating section by means of a steam injector. Net condensed steam flows to the atmospheric drain tank.

A distillate pump transfers the fresh water to the distilled water tank or, if the measured salinity is too high, to the brine section for overboard discharge.

To start the fresh water production, the following procedure must be executed to prepare the distiller:

- Open the suction and discharge valves of the ejector pump;

- Open condenser inlet and outlet valves;

- Open the overboard valve for combined brine/air ejector;

- Close the vacuum breaker valve;

- Open feed water inlet valve and close brine drain valve;

- Start the ejector pump to create vacuum;

- Open brine and air ejector suction valves.

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CHAPTER 4. AUXILIARY EQUIPMENT

Figure 4.12: Steam plant sea water cooled distiller.

The pressure at combined brine/air ejector inlet should be greater than 3.5 bar and the back pressure at combined brine/air ejector should not exceed 0.6 bar.

To start evaporation, when a minimum vacuum of 0.85 bar exists inside the distiller:

- Open valve for feed water treatment;

- Open injector water drain to atmospheric tank;

- Open steam shut off valve from back pressure steam system, adjust steam flow to maintain a brine temperature of less than 48

C.

When condensation starts and a fresh water level is seen in the condenser:

- Open the inlet valve to distilled water tank and distillate pump;

- Select AUTO operation for salinity control;

- Start distillate pump.

The procedure to stop the plant is:

- Close the back pressure steam shut off valve and injector drain to atmospheric tank;

- Close the valve for feedwater treatment;

- Stop the condensate pump, close the discharge valve and distilled water tank filling valve;

- Turn off the salinity control;

- Stop the ejector pump and close feed water valve, suction and overboard valves;

4.6. FRESH WATER GENERATOR

- Close the ejector suction valves;

- Open the vacuum breaker valve and the brine drain valve.

4.17

Condensate cooled distiller

This distiller is a two-stage distillation plant, for high performance fresh water production during main turbine operation.

In the first distillation stage, steam from the LP bleed is used to heat the sea water feed. The steam is condensed in the sea water heater and the drain pumped to the atmospheric drain tank. The steam produced by the evaporating sea water is used as heating steam in the second distillation stage during which it is condensed and pumped to the distilled water tank. The evaporated sea water of the second stage is condensed in the main condensate cooled condenser. The heat of condensation is recovered in the form of temperature increase of the main condensate flow leaving the distiller to the dearator.

The produced fresh water of the second stage is transferred by a distillate pump to the distilled water tank. Water not satisfying the salinity requirement is led to the brine section of the second stage and rejected. A sea water pump is used to supply feed water and for driving the two combined brine/air ejectors. A chemical feed tank is provided for feed water treatment to prevent scaling and corrosion in both stages.

Figure 4.13: Steam plant condensate cooled distiller.

The procedure to start this distiller is:

- Open ejector pump sea chest, discharge and overboard valves and start the pump;

- Close vacuum breaker and brine drain valves for both stages;

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CHAPTER 4. AUXILIARY EQUIPMENT

- Open both ejector suction valves;

- Open sea water feed valves to both stages;

When the vacuum has reached 0.8 bar in both stages:

- Open the chemical dosage valves to both feeds;

- Open condenser inlet and outlet valves and close the by-pass;

- Open steam supply valve from the LP bleeder;

- Adjust steam flow to maintain maximum temperature of 48

C in the first stage heater;

- Open discharge valve and start drain pump when level is seen in 1st stage heater;

- Open distilled water filling valve and distillate pumps discharge valves;

- Select AUTO for salinity control and start distillate pumps when levels are seen in 2nd stage heater and condenser.

To stop the plant, the following procedure should be followed:

- Close LP bleeder steam supply valve;

- When 1st stage heater is empty, stop drain pump and close discharge valve;

- Stop distillate pumps when 2nd stage heater and condenser are empty, close discharge valves and distilled water tank filling valve;

- Turn off salinity control;

- Open main condensate line by-pass valve, close condenser inlet and outlet valves;

- Close feed water chemical dosage;

- Stop ejector pump and close feed valves, ejector suction valves, discharge valve and sea water inlet and overboard valves;

- Open vacuum breaker valves and drain the heaters of both stages.

4.7

Refrigeration system

The refrigeration plant consists of the following main components:

- One electrically driven 50 kW screw compressor;

- One compressor lubricating oil recovery system;

- One sea water cooled condenser;

- One refrigerant liquid receiver;

- Two refrigerated compartments.

4.7. REFRIGERATION SYSTEM

The plant comprises the following two compartments:

- The meat/fish store (−18

C), including:

- one 4 kW air fan for cooling down;

- one 1.5 kW air fan for normal operation;

- one evaporator with dry expansion;

- evaporator electrical defrost device;

- The provision store for perishable goods (+5

C), including:

- one air fan;

- one evaporator with dry expansion;

- one evaporator pressure controller.

4.19

Figure 4.14: Refrigeration system diagram.

Refrigeration system description

The compressor is lubricated and cooled by oil. The lubricating oil is separated from the compressed refrigerant gas in the oil separator. The bottom part of the separator serves as an oil reservoir.

If the oil level is less than 20% of full, new oil must be added. A substantial part of the compressor heat is transferred to the cooling oil in the compressor screw, and the oil must be cooled. This is done by sea water in the lubricating oil cooler.

The compressor electric motor load varies according to the compressor condition, namely the suction pressure, the discharge pressure and gas flow. Electric overload will occur if the load is

4.20

CHAPTER 4. AUXILIARY EQUIPMENT higher than a preset adjustable limit. The effective compression ratio, and thus the capacity of the screw compressor, is adjusted by means of a suction slide valve. It is positioned by a PID controller, controlled by the meat/fish store temperature.

Two pumps are available to supply the sea water flow to the condenser. Normally, just one is in operation, while the other is standby. The sea water flow can be adjusted by a throttle valve at the condenser outlet (only the inlet valve is adjustable in the simulator but the correct valve to throttle is the outlet one). The liquid refrigerant flows by gravity to the receiver. The valve called “vapour valve” is for pressure equalizing between the condenser and the liquid receiver vessel. If it is closed, draining of the condenser will be obstructed. The temperature of the meat/fish store is regulated by the compressor load while the provision store temperature is set by the position of the evaporator pressure regulator valve.

Refrigeration system operation

The main steps to prepare the refrigeration system for cooling-down the compartments are:

- line-up valves in the lubrication oil system and start the pump;

- check the lubrication oil, and if necessary refill by means of the make-up pump;

- open vapour and liquid valves between condenser and receiver;

- open sea water cooling valves to lubrication oil cooler and condenser and start sea water pump;

- condenser cooling water control valve must be set to a suitable opening to maintain appropriate condensation pressure.

Lubricating oil heating should be performed for at least one hour before starting the compressors.

To start the system:

- open the liquid valves from receiver to evaporators;

- start air fans in compartments;

- reset the trip functions, if any present, and start the compressor;

- set temperature control into MAN and adjust capacity control slide valve to 10%, otherwise compressor will trip on overload.

Gradually increase compressor capacity manually, checking the compressor electric power consumption during cooling down. Set temperature controller into AUTO when temperature in meat/fish store is below −10

C. Normal temperature in meat/fish store is −18

C. When meat/fish store temperature approaches −18

C change to 1.5 kW fan. Adjust provision store evaporator capacity regulator to maintain provision store temperature at 5

C.

4.8. BILGE SYSTEM 4.21

4.8

Bilge system

4.8.1

Bilge regulations

To reduce pollution of the world’s coasts and waters by the shipping industry, a great number of laws, regulations and penalties have been established and are being enforced. These include regulations set by:

- International Convention for the Prevention of Pollution from Ships, 1973, as modified by the

Protocol of 1978 (MARPOL 73/78 Annex I);

- Federal Water Pollution Control Act of 1970 (FWPCA);

- Oil Pollution Act of 1990 (OPA 90).

An Oily Water Separator (OWS) is a piece of shipboard equipment that allows to separate oil from bilge water, before the bilge water is discharged overboard. Bilge water is an almost unavoidable product in ship operations. Bilge water that is generated in proximity to shipboard equipment, such as in the engine room, often contains oil and its direct discharge would result in undesirable transfer of waste oil to the marine environment. By international agreement under the MARPOL convention, most commercial vessels need to be fitted with an oily water separator to remove oil contaminants before bilge water is pumped overboard.

Figure 4.15: Bilge separators.

The regulations concerning the pumping of machinery space bilge are of greatest interest. Bilge general regulation, as established by MARPOL 73/78 rule 9, is as follows:

- ... any discharge into the sea of oil or oily mixtures from ships to which this Annex applies shall be prohibited except where all the following conditions are satisfied:

- ...

- from a ship of 400 gross tonnage and above:

4.22

CHAPTER 4. AUXILIARY EQUIPMENT

- the ship is not within a special area;

- the ship is proceeding en route;

- the oil content of the effluent does not exceed 15 parts per million (ppm);

- the ship has in operating equipment required by Regulation 16 (an oil content monitor, oil separating or filtering device which will automatically stop discharging when the oil content of the effluent exceeds 15 ppm).

Oil record book

The following operations must be recorded in the oil record book:

- Ballasting or cleaning of oil fuel tanks;

- Discharge of dirty ballast or cleaning water from oil fuel tanks;

- Collection and disposal of oil residues (sludge);

- Automatic and non-automatic discharge overboard or disposal otherwise of bilge water which has accumulated in machinery spaces;

- Condition of oil discharge monitoring and control system (failures and repairs);

- Accidental or other exceptional discharge of oil;

- Bunkering of fuel or bulk lubricating oil;

4.8.2

Bilge system description

The following bilge wells are included on the VLCC engine room:

- Aft;

- Port;

- Starboard;

- Forward.

A sludge tank and an incinerator are also included.

4.8.3

Bilge separator

Oily water separator equipment has been a shipboard requirement since the 1970’s but recently it has become evident that oily water separators have not been as effective as had been assumed, and alleged improper operation of this equipment by crew members (sometimes called the magic pipe) has resulted in criminal prosecutions in the United States and, to a lesser extent, in Europe. The Chief

Engineer shall ensure that the certificate for the equipment and the required signboards are present and readable at all times. All engineers who are authorized by the Chief Engineer to operate the equipment shall be totally familiar with normal operations, the piping system to and from the separator, and the testing procedures.

4.8. BILGE SYSTEM 4.23

Figure 4.16: Bilge Wells/Incinerator

The equipment shall be operated in full compliance with MARPOL Annex I, and absolutely NO

BY-PASSING of the equipment shall be done no matter what. If there is the slightest doubt that the equipment is operating satisfactorily, it shall not be used until a proper investigation and tests have been carried out, under supervision of the Chief Engineer. The bilge water overboard discharge valve shall be kept closed and padlocked. It shall only be opened after permission from the Chief Engineer.

Figure 4.17: Bilge separator.

4.24

CHAPTER 4. AUXILIARY EQUIPMENT

Preparation

To start the operation of the bilge separator, it is necessary to pre-heat the vessel. In our case, the heating is provided by an electric resistance. Thus, main steps are:

- Start electric heating and set separator operation in MANUAL;

- Set the separator into AUTO mode when sufficient temperature is achieved (50

C);

- Check the setting of the ppm detector.

Operation

The separator operation should be in AUTO mode. In this mode, sludge, recirculation and overboard intermediate valves are automatically controlled, as follows:

- The overboard intermediate valve is closed and the recirculation valve opened if the ppm limit in the overboard water is above a preset limit;

- When the oil/water interface sensor detects low level (much oil), the sludge valve is opened;

- The bilge separator pump may be started/stopped automatically according to the bilge well level

(dependent on suction from the engine room bilge well).

- If the bilge pump is ON for more than 20% (adjustable) of the OFF time an alarm is activated.

As stated before, the AUTO pump operation is only related to the start/stop, based the the engine room well level.

4.8.4

Bilge operation

Several operations can be performed on the bilge system. The procedures for the most common are given in the following paragraphs.

Daily bilge services

The procedure to drain the engine room wells is:

- Check level and oil content in bilge well;

- Open suction valve from bilge well;

- Open valves through separator;

- Check that over board valve is closed;

- Open discharge valve to “Clean Bilge Tank”;

- Check that bilge separator is in AUTO;

- Start bilge pump in manual.

If bilge has high oil content:

- Open 3-way valve before bilge separator and discharge directly to sludge tank;

- Let the oily water mixture separate in sludge tank before emptying water to clean bilge tank.

4.8. BILGE SYSTEM

Emptying “clean bilge tank”

To empty the “clean bilge tank” overboard:

- Check and record tank level, time and ship’s position;

- Check that bilge separator is ready;

- Open suction valve from clean bilge tank;

- Open discharge over board;

- Check that bilge separator is in AUTO;

- Start bilge pump;

- Observe PPM-meter to avoid pumping oil overboard;

- Check and note tank level, time and ship’s position when finished.

4.25

Stopping bilge separator

The collected oil must be removed and the separator cleaned before stopping the bilge pump. So, when stopping the bilge separator:

- Ensure operation in MANUAL mode;

- Close bilge suction valve and open sea suction to flush separator;

- Manually open “sludge valve” to remove recovered oil;

- Stop pump and close sea suction and overboard valves.

4.8.5

Incinerator

Pollution at sea is a matter of great importance which has compelled concerned authorities to make legislation stricter by banning disposal at sea at many sensitive areas. Stricter legislation with regard to pollution of the sea, limits and, in some instances, completely bans the discharge of untreated waste water, sewage, waste oil and sludge. According to Annex V of MARPOL 1973/78 convention of

IMO, guidelines regarding the waste material storage and disposal of waste at sea need to be strictly followed.

Incineration of various materials such as galley waste, food scraps, accommodation waste, linen, card boards, oil sludge from lubricating oil, fuel oil, bilge and purifier, and sewage sludge, is one of the most effective ways of disposal and saving storage capacity of the tanks and waste storage containments on ships. Moreover, the residue left from the incineration can be easily disposed off as it mainly consists of ash. When used in conjunction with a sewage plant and with facilities for burning oil sludges, the incinerator forms a complete waste disposal package. The ultimate situation of no discharge can be achieved by the use of a suitable incinerator. Incinerators for shipboard use are

shown in Fig. 4.18.

4.26

CHAPTER 4. AUXILIARY EQUIPMENT

Figure 4.18: Incinerators.

The combustion chamber is usually a cylinder lined with refractory material. An auxiliary oilfired burner is used to ignite the waste and oil sludge and is thermostatically controlled to minimize fuel consumption.

A sludge burner is used to dispose of oily sludge and works in conjunction with the auxiliary burner. Combustion air is provided by a forced draught fan and swirls upwards from tangential ports in the base. A rotating-arm device accelerates combustion and also clears ash and non-combustible matter into an ash hopper. The loading door is interlocked to stop the fan and burner when opened.

Solid material, usually in sacks, is burnt by an automatic cycle of operation. Liquid waste is stored in a tank, heated and then pumped to the sludge burner where it is burnt in an automatic cycle. After use, the ash box can be emptied overboard.

Incinerator operation

The procedure for burning collected oil in the sludge tank is as follows:

- Note amount of oil in sludge tank;

- Open valve from sludge tank to burner pump;

- Open valve to incinerator;

- Start incinerator by pushing "Flame ON" button;

- Incinerator will automatically stop at low level in sludge tank;

- Note and record amount of sludge incinerated;

- Stop pump and close valves.

4.9. SEWAGE SYSTEM 4.27

4.9

Sewage system

The discharge of untreated sewage in controlled or territorial waters is usually banned by legislation.

International legislation is in force to cover any sewage discharges within specified distances from land. As a result, and in order to meet certain standards, all new ships have sewage treatment plants installed.

Untreated sewage as a suspended solid is unsightly. In order to break down naturally, raw sewage must absorb oxygen. In excessive amounts it could reduce the oxygen content of the water to the point where fish and plant life would die. Pungent smells are also associated with sewage as a result of bacteria which produce hydrogen sulphide gas. Particular bacteria present in the human intestine known as E. coli are also to be found in sewage. The E. coli count in a measured sample of water indicates the amount of sewage present.

Two particular types of sewage treatment plant are in use, employing either chemical or biological methods. The chemical method is basically a storage tank which collects solid material for disposal in permitted areas or to a shore collection facility. The biological method treats the sewage so that it is acceptable for discharge inshore.

4.9.1

Chemical sewage treatment

This system minimizes the collected sewage, treats it and retains it until it can be discharged in a decontrolled area, usually well out to sea. Shore receiving facilities may be available in some ports to take this retained sewage. This system must therefore collect and store sewage produced while the ship is in a controlled area. The liquid content of the system is reduced, where legislation permits, by discharging wash basins, bath and shower drains straight overboard. Any liquid from water closets is treated and used as flushing water for toilets. The liquid must be treated such that it is acceptable

in terms of smell and appearance. A treatment plant is shown diagrammatically in Fig. 4.19. Various

chemicals are added at different points for odor and color removal and also to assist breakdown and sterilization. A comminutor is used to physically break up the sewage and assist the chemical breakdown process. Solid material settles out in the tank and is stored prior to discharge into the sullage tank: the liquid is recycled for flushing use. Tests must be performed daily to check the chemical dosage rates. This is to prevent odors developing and also to avoid corrosion as a result of high levels of alkalinity.

4.9.2

Biological sewage treatment

The biological system uses bacteria to completely break down the sewage into an acceptable substance for discharge into any waters. The extended aeration process provides a climate in which oxygenloving bacteria multiply and digest the sewage, converting it into a sludge. These oxygen-loving bacteria are known as aerobic.

The treatment plant uses a tank which is divided into three watertight compartments: an aeration

4.28

CHAPTER 4. AUXILIARY EQUIPMENT

Figure 4.19: Chemical sewage plant.

compartment, settling compartment and a chlorine contact compartment (Fig. 4.20). The sewage

enters the aeration compartment where it is digested by aerobic bacteria and micro-organisms, whose existence is aided by atmospheric oxygen which is pumped in. The sewage then flows into the settling compartment where the activated sludge is settled out. The clear liquid flows to the chlorinator and after treatment to kill any remaining bacteria it is discharged. Tablets are placed in the chlorinator and require replacement as they are used up. The activated sludge in the settling tank is continuously recycled and builds up, so that every two to three months it must be partially removed. This sludge must be discharged only in a decontrolled area.

Figure 4.20: Biological sewage treatment plant.

4.10. DECK MACHINERY 4.29

4.10

Deck machinery

The various items of machinery and equipment found outside the machinery space will now be described. In general, these include deck machinery such as mooring equipment, anchor handling equipment, cargo handling equipment and hatch covers. Other items include lifeboats and life-rafts, emergency equipment, watertight doors, stabilizers and bow thrusters.

The operations of mooring, cargo handling and anchor handling all involve controlled pulls or lifts using chain cables, wire or hemp ropes. The drive force and control arrangements adopted will influence the operations and the associated equipment. Three forms of power are currently in use: steam, hydraulic and electric. Each one will be briefly described in turn, together with its advantages and disadvantages.

4.10.1

Steam machinery

With a steam powering and control system, the steam pipelines are run along the deck to the various machines. Steam is admitted first to a directional valve and then to the steam admission valve. Doubleacting steam engines, usually with two cylinders, are used to drive the machinery. Additional back pressure valves are used with mooring winches to control tension, when the machine is stalled or brought to a stop by the load. Arrangements must also be made, often associated with the back pressure valve, to counteract the fluctuations in main steam line pressure as a result of other users of steam.

The steam-powered system was widely used on tankers since it presented no fire or explosion risk, but the lengths of deck pipework, and the steam engines themselves, presented considerable maintenance tasks which have generally resulted in their replacement by hydraulically powered equipment.

4.10.2

Hydraulic systems

The open-loop circuit takes oil from the tank and pumps it into the hydraulic motor. A control valve is positioned in parallel with the motor. When it is open the motor is stationary; when it is throttled or closed the motor will operate. The exhaust oil returns to the tank. This method provides smooth changes in motor speed.

The live-line circuit, on the contrary, maintains a high pressure from which the control valve draws pressurized oil to the hydraulic motor, in series with it, as and when required.

In the closed-loop circuit, the exhaust oil is returned direct to the pump suction. Since the oil does not enter an open tank, the system is considered closed.

Low-pressure systems use the open-loop circuit and are simple in design as well as reliable. The equipment is, however, large, inefficient in operation and overheats after prolonged use. Mediumpressure systems are favored for marine applications, using either the open or closed circuit. Smaller installations are of the open-loop type. Where considerable amounts of hydraulic machinery are fitted the live-circuit, supplied by a centralized hydraulic power system, would be most economical.

4.30

CHAPTER 4. AUXILIARY EQUIPMENT

4.10.3

Electrical operation

Early installations used d.c. supply with resistances in series to provide speed control. This inefficient power-wasting method was one possibility with d.c., but a better method was the use of Ward-Leonard control. The high cost of all the equipment involved in Ward-Leonard control and its maintenance is, however, a considerable disadvantage.

Machines operated on an a.c. supply require a means of speed control with either pole-changing or slip-ring motors being used. Slip-ring motors require low starting currents but waste power at less than full speed and require regular maintenance. Pole-changing motors are of squirrel cage construction, providing for perhaps three different speeds. They require large starting currents, although maintenance is negligible.

Apart from the advantages and disadvantages for each of the drive and control methods, all electric drives have difficulty with heavy continuous overloads. Each system has its advocates and careful design and choice of associated equipment can provide a satisfactory installation.

4.11

Ship governing and manouvering equipment

4.11.1

Steering gear

The steering gear provides a movement of the rudder in response to a signal from the bridge. The total system may be considered made up of three parts, control equipment, a power unit and a transmission to the rudder stock. The control equipment conveys a signal of desired rudder angle from the bridge and activates the power unit and transmission system until the desired angle is reached. The power unit provides the force, when required and with immediate effect, to move the rudder to the desired angle. The transmission system, the steering gear, is the means by which the movement of the rudder is accomplished.

Certain requirements must currently be met by a ship’s steering system. There must be two independent means of steering, although where two identical power units are provided an auxiliary unit is not required. The power and torque capability must be such that the rudder can be swung from 35

◦ one side to 35

◦ the other side with the ship at maximum speed, and also the time to swing from 35

◦ one side to 30

◦ the other side must not exceed 28 seconds. The system must be protected from shock loading and have pipework which is exclusive to it as well as be constructed from approved materials.

Control of the rudder must be provided in the steering gear room.

Tankers of 10000 ton gross tonnage and upwards must have two independent steering gear control

systems which are operated from the bridge, see Fig. 4.21. Where one fails, change-over to the other

must be immediate and achieved from the bridge position. The steering gear itself must comprise two independent systems where a failure of one results in an automatic changeover to the other within 45 seconds. Any of these failures should result in audible and visual alarms on the bridge.

Steering gears can be arranged with hydraulic control equipment known as a “telemotor”, or with electrical control equipment. The power unit may in turn be hydraulic or electrically operated. Each

4.11. SHIP GOVERNING AND MANOUVERING EQUIPMENT 4.31

Figure 4.21: Bridge steering gear and rudder control panel.

Figure 4.22: ECR steering gear pumps control.

of these units will be considered in turn, with the hydraulic unit pump being considered first. A pump is required in the hydraulic system which can immediately pump fluid in order to provide a hydraulic force that will move the rudder. Instant response does not allow time for the pump to be switched on and therefore a constantly running pump is required which pumps fluid only when required. A variable delivery pump provides this facility.

4.32

CHAPTER 4. AUXILIARY EQUIPMENT

Power units

Two types of hydraulically powered steering gears are in common use, the ram and the rotary vane types.

Ram type

Two particular variations, depending upon torque requirements, are possible the two-ram and the

four-ram. A two-ram steering gear is shown in Fig. 4.23. The rams acting in hydraulic cylinders

operate the tiller by means of a swivel crosshead carried in a fork of the rams. A variable delivery pump is mounted on each cylinder and the slipper ring is linked by rods to the control spindle of the telemotor receiver. The variable delivery pump is piped to each cylinder to enable suction or discharge from either. A replenishing tank is mounted nearby and arranged with non-return suction valves which automatically provide make-up fluid to the pumps.

Figure 4.23: Two-ram steering.

A by-pass valve is combined with spring-loaded shock valves which open in the event of a very heavy sea forcing the rudder. Once the heavy sea has passed, the pump is actuated and the steering gear will return the rudder to its original position.

During normal operation one pump will be running. If a faster response is required, for instance in confined waters, both pumps may be in use. The pumps will be in the no-delivery state until a rudder movement is required by a signal from the bridge telemotor transmitter. The telemotor receiver cylinder will then move, causing a pumping action. Fluid will be drawn from one cylinder and pumped

4.11. SHIP GOVERNING AND MANOUVERING EQUIPMENT 4.33

to the other, thus turning the tiller and the rudder. A return linkage mounted on the tiller will reposition the floating lever on the telemotor receiver so that no pumping occurs when the required rudder angle is reached.

A four-ram steering gear is shown in Fig. 4.24. The basic principles of operation are similar to the

two-ram gear, except that the pump will draw from two diagonally opposite cylinders and discharge to the other two. The four-ram arrangement provides greater torque.

Figure 4.24: Four-ram steering gear.

Rotary vane type

With this type of steering gear a vaned rotor is securely fastened onto the rudder stock, Fig. 4.25.

The rotor is able to move in a housing which is solidly attached to the ship’s structure. Chambers are formed between the vanes on the rotor and the vanes in the housing. These chambers will vary in size as the rotor moves and can be pressurised since sealing strips are fitted on the moving faces. The chambers either side of the moving vane are connected to separate pipe systems or manifolds. Thus, by supplying hydraulic fluid to all the chambers to the left of the moving vane and drawing fluid from all the chambers on the right, the rudder stock can be made to turn anti-clockwise. Clockwise movement will occur if pressure and suction supplies are reversed.

Figure 4.25: Rotary vane type steering gear.

Three vanes are usual and permit an angular movement of 70

. The vanes also act as stops limiting

4.34

CHAPTER 4. AUXILIARY EQUIPMENT rudder movement. The hydraulic fluid is supplied by a variable delivery pump and a relief valve is fitted in the system to prevent over-pressure and allow for shock loading of the rudder.

VLCC steering gear description

The VLCC rotary vane type steering gear comprises two identical hydraulic systems. Each system includes:

- One steering gear pump unit comprising;

- One control valve block assembly;

- Measuring, indicating and alarm facilities for pressure, temperature, level and flow;

- Control and safety equipment.

One expansion tank is common to both hydraulic systems. The system also includes an emergency steering control equipment and a rudder angle indication.

The steering gear pump unit comprises:

- oil tank with a bottom drain valve;

- steering gear pump of the fixed displacement type;

- return line oil filter;

- level indication;

- monitoring equipment;

Figure 4.26: Steering Gear System

4.11. SHIP GOVERNING AND MANOUVERING EQUIPMENT 4.35

Safematic system

The oil tank is connected to the bottom of the expansion tank, common to both hydraulic systems and normally the oil tank is full. According to international regulations, the steering gear system of larger ships must be provided with automatic separation of the two hydraulic systems, in case of a large oil leakage at one of the systems. Both steering gear are connected to the expansion tank.

A major oil leak at one of the systems will lead to a decrease of the oil level in the expansion tank and a LOW LEVEL ALARM - EXPANSION TANK. If the oil level continues to decrease, stand-by steering gear pump receives a START command. If the expansion tank oil level is still decreasing, it will reach the level where the expansion tank is split up into two chambers by an internal partition plate. Each steering gear system is now supplied from its own expansion tank chamber and the decrease in oil level will only take place in the chamber connected to the defective system. A low level switch in the chamber in question stops the respective steering gear pump and shifts the safematic control valve block into a position where:

- the two system are separated;

- the steering gear chambers connected to the defective system are by-passed.

After the separation, the defective system will be shut down. The pump stops and the control valveblock will close.

Steering gear tests

Prior to a ship’s departure from any port the steering gear should be tested to ensure satisfactory operation. These tests should include:

- Operation of the main steering gear;

- Operation of the auxiliary steering gear or use of the second pump which acts as the auxiliary;

- Operation of the remote control (telemotor) system or systems from the main bridge steering positions;

- Operation of the steering gear using the emergency power supply;

- The rudder angle indicator reading;

- The alarms fitted to the remote control system and the steering gear power units.

During these tests the rudder should be moved through its full travel in both directions and the various equipments visually inspected for damage or wear. The communication system between the bridge and the steering gear compartment should also be operated.

4.11.2

Bow thruster

The bow thruster is a propulsion device fitted to certain types of ships to improve maneuverability.

The thrust unit consists of a propeller mounted in an athwartships tunnel and provided with some

4.36

CHAPTER 4. AUXILIARY EQUIPMENT auxiliary drive such as an electric or hydraulic motor. During operation, water is forced through the tunnel to push the ship sideways, either to port or starboard, as required. The unit is normally bridge controlled and is most effective when the vessel is stationary.

A controllable-pitch type thruster unit is shown in Fig. 4.27. A servo motor located in the gear

housing enables the propeller blade pitch to be altered, to provide water flow in either direction. With this arrangement any non-reversing prime mover, like a single-speed electric motor, may be used. The prime mover need not be stopped during manoeuvring operations since the blades can be placed at zero pitch when no thrust is desired. The drive is obtained through a flexible drive shaft, couplings and bevel gears. Special seals prevent any sea water leakage into the unit. The complete assembly includes part of the athwartships tunnel through which water is directed to provide the thrust.

Figure 4.27: Bow thruster.

4.12

Propeller servo

A controllable pitch propeller is a type of propeller with blades that can be rotated around their axis to change the pitch. When the pitch is set to negative values, a reverse thrust is created for braking or going backwards, without the need of changing the direction of shaft rotation.

Ships with controllable pitch propellers have improved propulsive efficiency over a broad range of speeds and load conditions. The controllable pitch propeller also improves maneuverability of the ship. The improved maneuverability, and the use of the bow thruster, can eliminate the need for tugs while berthing. Large vessels that make long trips at a constant speed, like crude oil tankers or the largest container ships, do not utilize controllable pitch propellers. A controllable pitch propeller is usually found on ferries, cruise ships, small cargo vessels, tugs and dredgers.

4.12. PROPELLER SERVO 4.37

4.12.1

Propeller servo oil system description

A controllable pitch propeller requires a hydraulic system to control the position of the blades. The propeller pitch servo is operated by high-pressure hydraulic oil supplied by two electrically driven pumps. Usually only one pump is used while the other in stand-by mode. The pitch control is dependent on hydraulic pressure. At low oil pressure, the maximum rate of pitch change is reduced correspondingly. The pressure is controlled by by-passing oil through the pressure control valve.

Default pressure is 45 bar.

The return oil is cooled by LTFW, the temperatured is controlled to 45

C and drains to the servo oil tank.

Figure 4.28: Propeller Servo Oil System

4.12.2

Propeller servo oil operation

The starting procedure requires that main sea water system and LTFW system must be in service.

Then:

- Open fresh water inlet valve to servo lubricating oil cooler;

- Open selected filter inlet valve;

- Check level in servo oil tank;

- Select LOCAL or REMOTE for pitch control;

- Start the lubricating oil pump locally or from the PowerChief control panel;

- Put the lubricating oil pumps into AUTO mode.

4.38

CHAPTER 4. AUXILIARY EQUIPMENT

5

Boilers and Steam Generators

5.1

Modes of operation

There are different modes of boiler plant operation. The one normally dealt with is “normal operation”, when the plant is generating steam and all the operator need do is monitor it in the event something goes wrong. The other modes of operation require some act to change the condition of the plant. We may consider four types of start-up:

- first start-up;

- dead plant start-up;

- normal boiler start-up;

- emergency boiler start-up.

Other mode to include in certain cases is the stand-by operation.

It is not possible to provide a specific set of instructions to perform those activities because every steam plant is different. The following should be considered as general guidelines. Later, more precise procedures are given for the operation of the VLCC and LPG carrier boilers. One should note that the start-up operations mentioned here are assumed to occur after a plant was laid-up according to the correct procedures.

5.2

Thermal oil boilers

Careful attention is to be paid to the selection of the proper type of heating for various machines in the shipping industry. In this regard, specific knowledge concerning the two heating media, steam and thermal oil, and the function of the heated machine is of vital importance. In thermal fluid systems, the produced heat is transferred to the ship’s heat consumers by means of a transfer fluid. The working temperature depends on the kind of ship and the cargo and are between 160

C and 300

C. The fluid

5.1

5.2

CHAPTER 5. BOILERS AND STEAM GENERATORS remains in liquid-phase during the whole process. The heat carriers are mineral or synthetic oils, so that no corrosion can occur in pipes and parts of plant, and freezing will not be possible. An expansion vessel serves to collect volume increase of expanding heat carrier oil, when heating up. The nitrogen in the expansion vessel guarantees the necessary pressure balance and protects the thermal oil from the oxygen in the air. This is the reason why the thermal oil doesn’t oxidize even when we have high temperatures.

The fluid circulates through the closed system, passing fuel-oil fired heaters and economizers. For circulation of thermal oil, supply of heat consumers and boilers an electric driven operating pump is necessary. A second pumps serves as stand-by pump which switches on automatically in case of breakdown of operating pump. Each of these pumps may be used as operating pump alternatively.

The drainage and storage tank will be installed at the lowest point of the whole system. It follows, therefore, that different double bottom sections of the ship should be used.

Thermal fluid systems on ships are used for heating of:

- Engine room heat consumers like fuel tanks, separators, fuel heaters;

- All types of cargoes;

- Tank washing systems;

- Steam generators for the production of steam for cleaning purposes;

- Air-conditioning and central heating systems.

The main advantages of a thermal oil plant lie with an easy temperature control of the heat consumer, the possibility of heating different heat consumers by a mixed-temperature control circuit at different thermal oil temperature, the comparatively low working pressure, the natural protection against corrosion, the running without danger of freezing, the high service life of the heat carrier oil, the low running costs, as well as nearly maintenance and service-free operation.

For thermal oil installations dead plant start-up, the system should be flooded, the expansion tank level confirmed, and circulating pumps started to generate at least minimum flow in the system. This may require a walk-through of all equipment rooms to ensure the systems are ready to circulate. Any equipment still receiving maintenance should be adequately isolated using proper lock-out and tag-out procedures.

5.3

Steam boilers

5.3.1

Dead plant start-up

Normally, when we say a plant is dead we mean dead cold. There is no heat in a boiler or any auxiliary equipment associated with normal operation. Broadly speaking, the term is used to describe a plant that has a warm boiler but is not maintaining normal operating pressure. A dead plant start-up is returning a dead plant that had been operating to operating condition.

5.3. STEAM BOILERS 5.3

A cold boiler should be returned to operating conditions slowly. When starting a boiler in a dead plant it is advisable to bring the served facility up with the boiler. That increases the time it takes to raise pressure on the boiler and the facility to allow for gradual heating. Open all valves that lead to consumers only after confirming all drains and vents have been closed or are manned by trained operators. In steam plants this process normally creates a flood of returned condensate as pressure builds so provisions for handling it should be prepared. Lower the operating level of the boiler feed tank or deaerator and condensate tank in advance, if possible. If that is not possible, close isolating valves to feed those tanks and manually maintain the lowest reasonable level until pressure in the boiler is near normal.

The procedure adopted for raising steam will vary from boiler to boiler and the manufacturers’ instructions should always be followed. A number of aspects are common to all boilers and a general procedure might be as follows.

Preparations

The up-takes should be checked to ensure a clear path for the exhaust gases through the boiler. Any dampers should be operated and then correctly positioned. All vents, alarm, water and pressure gauge connections should be opened. The superheater circulating valves or drains should be opened to ensure a flow of steam through the superheater. All the other boiler drains and blow-down valves should be checked to ensure that they are closed. The boiler should then be filled to slightly below the working level with hot, if possible, deaerated water. The various header vents should be closed as water is seen to flow from them. The economiser should be checked to ensure that it is full of water and all air vented off.

The operation of the forced draught fan should be checked and where exhaust gas air heaters are fitted, they should be by-passed. The fuel oil system should be checked for the correct positioning of valves, etc. The fuel oil should then be circulated and heated.

Raising steam

The forced draught fan should be started and air passed through the furnace for several minutes to

“purge” it of any exhaust gas or oil vapours. The air slides (checks) at every register, except the

“lighting up” burner, should then be closed. The operating burner can now be lit and adjusted to provide a low firing rate with good combustion. The fuel oil pressure and forced draught pressure should be matched to ensure good combustion with a full steady flame.

Lock controls in manual at low fire. Starting a dead boiler should provide a very slow increase in temperature until the boiler’s contents are above 100

C. That minimizes damage to the refractory from pockets of absorbed moisture. A sudden increase in volume as liquid changes to steam will build up pressure inside the refractory and rupture it. It is sometimes necessary to repeat an initial dry-out because the refractory got wet or refractory repairs were performed while the plant was down.

The superheater header vents may be closed once steam issues from them. When a drum pressure

5.4

CHAPTER 5. BOILERS AND STEAM GENERATORS of about 210 kPa (2.1 bar) has been reached the drum air vent may be closed. Allowing a loss of steam until those pressures are reached helps ensure all the air is removed from the boiler.

The boiler must be brought slowly up to working pressure in order to ensure gradual expansion and to avoid overheating the superheater elements and damaging any refractory material. Boiler manufacturers usually provide a steam raising diagram in the form of a graph of drum pressure against hours after flashing up. As soon as possible compare initial operating data with current operating conditions to ensure there have been no significant changes in the boiler’s performance.

The main and auxiliary steam lines should now be warmed through and then the drains closed. In addition, the water level gauges should be blown through and checked for correct reading. When the steam pressure is about 300 kPa (3 bar) below the normal operating value the safety valves should be lifted and released using the easing gear.

Test the low water cutoff before reaching normal operating pressure and after the pressure is high enough for the boiler to return to firing. Lift test the safety valves when the pressure is above 75% of the safety valve set pressure. They could have corroded shut during the shutdown period.

Once at operating pressure, the boiler may be put on load and the superheater circulating valves closed. All other vents, drains and by-passes should then be closed. The water level in the boiler should be carefully checked and the automatic water regulating arrangements observed for correct operation.

At some point low fire will not be adequate for pressure to continue to rise. Increase the firing rate manually in small increments (less than 10%) and allow the combustion to stabilize before increasing it again. Initially, all the condensate will stay in the steam system because the pressure will be below atmospheric wherever automatic vents are not operating properly or do not exist. Condensate will not return until there is enough pressure differential to push it back to the boiler plant. At several points during the start-up, the pressure differential will accelerate condensate returning. Wait until the pressure is at, or slightly above, normal operating pressure to switch control to automatic.

With steam generation stabilized, draw water analysis and determine setup of chemical feed and blow-down controls.

5.3.2

Normal operation

The first duty when taking over a boiler-room shift is to make certain the pipe, fittings and valves between the water glass and boiler are free and open by blowing down the water column and water glass and noting the promptness of the return of water to the glass. The most important rule for the safe operation of boilers is to maintain the proper water-level at all times, and as constant a level as conditions will permit. If water is not visible in the water glass, shut the boiler off immediately until a safe water-level has been determined.

The low-water cutoff is the most important electrical/mechanical device on your boiler for maintaining a safe water level. If a low-water condition develops, it could very well result in an overheating and explosion of your boiler. The low-water cutoff should be tested at least weekly.

5.4. VLCC STEAM PLANT DESCRIPTION 5.5

Aside from the standpoint of economy, maintain the fire uniform as possible to avoid an excessive rate of combustion, undesirable variations in temperature and possible explosions. The destructive force in a boiler explosion is caused by the instant release of energy stored in the water as heat.

The safety valve is the most important valve on the boiler. Safety valves prevent dangerous over pressurization of the boiler. Safety valves are installed in case there is failure of pressure controls or other devices designed to control the firing rate. All safety valves should be kept free of debris by testing the safety valve regularly.

The concentration of solids in the boiler should be measured and the boiler blown-down at such intervals as necessary to maintain established limits. Blow-down is designed to remove solids that settled out of the boiler water. The sources include solids from make-up water, rust and other solid particles returned with condensate, and the intentional production of sludge by chemical water treatment. It contributes to the reduction of dissolved solids but at a considerable expense in water and energy. Skimming or surface blow-down arrangements are dedicated for oil and silica removal. The presence of oil in the boiler water is a common cause of surging, fluctuation of water level in the steam boiler. Water foaming, usually due to high ph, may cause similar symthoms. Blow-down valves should be maintained in good working order and are to be opened and closed carefully when used.

5.4

VLCC steam plant description

There are an oil fired water-tube boiler, for port and cargo/ballast pumping duties, and an exhaust gas boiler, for energy recovery at sea. Feedwater for the oil fired boiler is supplied by the main feedwater pump via the economiser section of the exhaust gas boiler. When the water is supplied through the auxiliary line there will be no pre-heating of the water. Water from the oil fired boiler drum is circulated through the exhaust gas boiler evaporator section, before being returned to the oil fired boiler drum.

Saturated steam is passed through the superheater section of the oil fired boiler to supply the cargo and ballast turbines during port operation. Saturated steam is passed through the superheater section of the exhaust gas boiler to supply the alternator turbine at sea.

5.4.1

Operating modes

The system is designed to operate in three distinctive modes:

- Port use without pumping operation;

- Cargo pumping;

- Turbo generator operation, at sea use.

When operating in port, without cargo operations, the oil fired boiler operates at a steam pressure of 7 bar (low setting) and steam is only required for heatings. When cargo pumping, the oil fired

5.6

CHAPTER 5. BOILERS AND STEAM GENERATORS boiler operates at a steam pressure of 16 (high setting). Superheated steam can be supplied to the four cargo pump turbines, and the ballast pump turbine, with a total output capacity of 40 tonne/hour.

Last operating mode considered is for turbo-generator operation during voyage. When main engine is running, the waste heat recovery is used to generate steam, between 7 and 12 bar. The minimum pressure of 7 bar can be maintained by automatic operation of the oil fired boiler, whilst the exhaust damper control will limit the maximum pressure to 12 bar.

Figure 5.1: VLCC steam generation and feedwater plant.

5.4.2

Oil fired boiler

Main particulars

The furnace is of membrane wall construction, except where the single bank of inverted U-tubes forms

the superheater, see Fig. 5.2. The superheater is protected from the main flames by a screen row of

tubes from the water drum to a header leading to the steam drum. After the superheater is a bank of generating tubes running between the two drums. Connecting the steam and water drums are unheated downcomers to promote circulation.

An internal de-superheater is fitted within the steam drum to provide saturated steam flow for heating purposes. This will ensure that steam flows through the superheater at all times, and should prevent excessive superheater metal temperatures, that could lead to superheater failure.

A steam driven sootblower system, within the generating tube bank, ensures that the heating surfaces are kept clean.

The saturated steam from the boiler drum is used for heating services in port and heating services and exhaust boiler superheater at sea. Boiler superheater supplies steam for the cargo and ballast

5.4. VLCC STEAM PLANT DESCRIPTION 5.7

Figure 5.2: Oil Fired Boiler pumps, turbo-alternator and deck machinery.

A vent valve is provided on the steam drum to vent air from the boiler during start-up, and to ensure that the steam drum does form vacuum during shut-down periods.

To provide a lower heat source to the separators and purifiers oil heaters, a pressure reducing valve is fitted. This valve should ensure that the steam temperature is moderate, below 160

C.

A steam dumping facility is provided. When it is activated, the steam is dumped directly to the condenser, thus avoiding loss of feed water that would occur if the boiler safety valves lift. A flashing light and alarm indicates that dumping is activated. Steam dumping starts at approximately 17 bar.

Combustion system

The boiler has two burners fitted in the furnace roof. One forced draft fan supplies the air required for combustion. Each fuel system, DO and HFO, has it’s own supply pump and the HFO system is fitted with a steam heater and steam tracing to assist oil flowing. Atomising steam, or air, is provided to improve the combustion of the fuel. A diesel oil pilot burner is provided to ensure main burner lighting-off.

The objectives of the combustion control system are:

- To control the oil flow to the boiler, to keep the steam pressure as close to the pressure set-point as possible;

- To supply correct amount of air relative to oil at any time, to ensure efficient and safe combustion;

5.8

CHAPTER 5. BOILERS AND STEAM GENERATORS

Figure 5.3: Oil fired boiler combustion control.

- To supply the correct amount of air to allow the inert gas system to operate at low oxygen concentration.

The master controller generates a signal to a “high/low” select logic box. The function of the “high/low” select logic is to ensure that air command increases before oil command when load increases, and that oil command is reduced before air command at load reduction. The set-points for the desired oil and air flow for the slave controllers, preventing excess smoke during load changes. The master controller is a PID acting controller with feed from steam flow out of the drum and from the steam pressure. The slave controllers are also PID controllers. They must be set in MANUAL mode during start-up.

Before start-up of the boiler the furnace must be air purged. In accordance with classification societies safety requirements, the purging period is set long enough to change about 4 times the air volume in the furnace.

After the boiler purge, the automatic sequence for burner light-off is as follows:

- air register is opened;

- the pilot oil pump is started;

- electric spark ignitor turned on;

- the pilot oil valve is opened and the pilot flame should ignite;

- main oil shut-off valve opened;

- atomising air/steam valve is opened, when in HFO operation.

If the flame detector does not see flame within approximately 6 seconds, the oil shut-off valve and the air register are closed. The boiler will trip and will need to be manually reset. When the burner

5.4. VLCC STEAM PLANT DESCRIPTION 5.9

is in operation, the flame will be “blown out” if there is too much air compared to oil and it will be difficult to ignite if there is too much oil for the available air.

Burner management

The provided burner management system operates the boiler at 8 bar on the low setting and 16 bar on the high setting. It starts and stops burner No 2 (slave burner) according to the boiler pressure.

The slave burner is started if the steam pressure is under low limit and is stopped if the pressure is over high limit. To avoid frequent start and stop of burners, caused by the mutual influence between combustion control and burner management, there is a time delay between start and stop.

are:

There are criteria to be fulfilled before AUTO mode burner management is ready for use. These

- HFO selected;

- HFO pump running;

- HFO temperature higher than 80

C;

- Draft air fan running;

- Atomising steam valve open;

- Burner trip reset (no trip present);

- All combustion controllers (4) in AUTO mode.

If a burner fault occurs, the burner is shut down and the “BURNER ON” light is flashing. Possible causes for a burner fault are (inspect the trip code):

- too much oil;

- too much air;

- flame detector failure.

A safety system cuts-off the fuel oil supply to the boiler by closing the trip valve at the following conditions:

- stopped combustion air fan;

- abnormal (low or high) drum water level;

- low atomising steam pressure;

- no flame indication, both burners;

- no purge operation;

- incorrect nozzle fitted.

5.10

CHAPTER 5. BOILERS AND STEAM GENERATORS

The boiler fan and HFO pump are automatically started at reduced main engine power i.e. the exhaust boiler is not sufficient to maintain the steam pressure. When the exhaust boiler is maintaining the steam pressure at increased main engine power, the oil fired boiler is stopped, the fan and HFO pump must be stopped manually.

Water level control

The performance of the water control loop is largely dependent on whether the main or the auxiliary feed water pump and control valve is in operation. When the water is supplied through the auxiliary line there will be no pre-heating of the water and a drop in steam pressure will occur if the cold feed water flow increases rapidly. A reduction in steam pressure tends to increase the feed water flow even more, due to the increased differential pressure across the feed valve. Therefore, there is a mutual disturbing interaction between the combustion control and the water level control system. The water flow influences the steam pressure and the steam pressure the water flow. It is of vital importance to keep steam pressure steady when the level controller is adjusted. It is therefore recommended that the master combustion controller is set to MANUAL during level control trimming.

5.4.3

Exhaust gas boiler

The VLCC exhaust gas boiler, schematically represented in Fig. 5.4, consists of two ducts through

which the exhaust gases from the main engine passes. One duct contains four banks of heat exchanger tubes:

- One economizer section;

- Two evaporator sections;

- One superheater section.

The other duct is plain to by-pass the heat exchangers. Dampers control the exhaust gas flow path, and the damper position is regulated by a PID controller from a steam pressure input.

The economiser section will be put into operation once the oil fired boiler main feed system is in use. The evaporator section is started-up:

- Opening boiler circulating pump valves;

- Starting one of the two circulating pumps;

- Placing the circulating pumps on AUTO to provide stand-by operation.

When main engine has important load at sea, the superheater section can be put into operation starting the turbo-alternator.

5.5. BOILER FOR LPG STEAM PROPULSION PLANT 5.11

Figure 5.4: VLCC exhaust boiler for energy recovery.

5.5

Boiler for LPG steam propulsion plant

The furnace is roof fired with membrane walls, see Fig. 5.5. The mean combustion temperature in the

furnace will depend on:

- Fuel consumption and air temperature;

- Removed energy by heat radiation to water panel walls, screen tubes and superheater sections;

- Gas cooling due to heat convection to wall and screen tubes.

The superheater has two sections. After the steam is heated in the first section, some of the steam flow is directed to the control de-superheater in the steam drum, and cooled before heated in the second superheating section to final steam temperature. The heat transfer on the steam side decreases strongly by reduced steam flow or low steam pressure. This may cause unacceptable high metal temperatures and possibly superheater damage.

Heat transfer in the bank of steam generating tubes following the superheater sections depends on gas flow and temperature, and heat transfer coefficients. Fouled tubes will be reflected in reduced heat transfer, leading to decreased steam generation and increased gas temperature leaving the generating bank and increased superheated steam temperature. In addition, the flow resistance will increase.

The superheater, steam generating tube bank and economizer are all equipped with retractable soot blowers. After completion the soot blown, heat surfaces are clean.

5.12

CHAPTER 5. BOILERS AND STEAM GENERATORS

Figure 5.5: High pressure boiler.

5.5.1

Fuel supply system

Fuel oil is normally supplied to the three burners of each boiler from the HFO settling tank, by one of the two fuel oil service pumps. All fuel oil lines have steam tracing. Diesel oil may be used for flushing lines or for flashing the boilers from cold condition when no heating steam is available. All tank outlet valves are quick closing, remote operated, type.

Figure 5.6: Fuel oil system.

5.5. BOILER FOR LPG STEAM PROPULSION PLANT 5.13

The fuel oil service pump takes suction from the HFO settling tank, through a manually cleaned strainer. The strainer has a differential pressure alarm fitted and care should be paid to maintain a positive suction pressure at all times. The pumps can be operated either manually or automatically in stand-by mode. One pump will be running with the other on automatic start stand-by, in case the discharge pressure of the in-use pump falls. The system pressure is controlled by a recirculation valve, which allows oil to recirculate to the pumps suction maintaining a constant set pressure.

The oil then passes through the fuel oil heaters, normally one of which is in use, and the other clean and ready for use. The fuel oil is heated by general service saturated steam. To control the viscosity of heavy fuel oil, a viscosity sensor and steam control valves are provided. The steam control valve is regulated by the viscosity controller, maintaining the viscosity of fuel oil at the set-point value. Then, the fuel passes through a second, finer set of manually cleaned filters.

The heated and filtered fuel oil is supplied to both boilers burners and recirculates via the gas separator or returns to the settling tank.

Operating procedures to prepare light-off from cold are:

- Ensure HFO settling tank outlet and returns are closed;

- Open MDO outlet and supply valves to boilers;

- Line-up fuel oil supply system with pressure control valve in AUTO, set point 30 bar;

To supply heavy fuel oil to boiler, it is assumed that steam has been raised using diesel oil, with all inlet and outlet valves to pumps and heaters open. When sufficient steam pressure is raised on a boiler to supply the general service steam system, commence supplying steam to the heating coil of the settling tank. As the temperature rises, check the tank for water. The temperature would normally need to be around 50

C for good pumping conditions. Commence to supply steam to the in-use fuel oil heater. As diesel oil will be in the system, with the fuel oil pump taking suction from the diesel oil service tank, ensure that the temperature in the heater does not rise above 50

C. When the line temperature rises to approximately 50

C, open the settling tank outlet valve, and close the supply valve from the diesel oil system. As the heavier fuel oil purges the system of diesel oil, the system pressure will rise. Care should be taken to manually control the pump back pressure, and maintain it at a suitable value. Select AUTO mode for viscosity control and open the steam tracing valve for the fuel lines.

Prior to plant shut down, the system must be purged, changing to diesel oil. It is assumed both boilers are firing. The procedure is as follows:

- Shut off steam lines and steam tracing line to the fuel oil tanks and fuel oil heaters;

- Maintain a close surveillance over the fuel oil temperature, and when has dropped to approximately 85

C open the diesel oil service tank outlet to fuel oil pump suction line valve;

- Open diesel oil supply valves and close all fuel oil valves to pump suction from settling tank;

- Open HFO return line and close the fuel oil gas separator return valve;

5.14

CHAPTER 5. BOILERS AND STEAM GENERATORS

- Change over from atomizing steam supply to the boiler burners, closing the steam valves, and replace with atomizing air supply;

- After a few minutes, shut down one boiler. The action of stopping the burner opens each burner rail recirculation valve. Allow fuel to recirculate for a short time. After a few moments close the main fuel oil shut off valve to the fuel oil rail;

- When steam supply is no longer required, shut down the second boiler;

- Stop the pumps and close all fuel oil valves on the system.

Do not leave the diesel oil recirculating to the boiler for longer than necessary, as the diesel oil will be recirculating to the fuel oil settling tank. During this procedure, change to the spare unit of both the fuel oil pump suction and discharge filters, to ensure both units are flushed through. Also, change fuel flow to the second fuel oil heater to ensure that this is also flushed through and stop the in-use pump, allowing the stand-by unit to be in use, and flushed through.

The supply of heavy fuel oil (HFO) and boil-off gas (BOG) to the main boiler is shown and information on the boiler trip state. The burners are arranged in the roof of the furnace space. In automatic combustion control mode, HFO, BOG, or a combination of both can be used. Depending on boiler load one, two or three burners will normally be in operation at a time.

The HFO flow is controlled by a fuel oil control valve. The flow is measured by a fuel oil meter, which can be by-passed allowing for repair and cleaning of the meter. If the flow meter, is out of operation the combustion control system must be operated manually. Three valves are under control of the boiler safety system, the trip valve, the by-pass valve and the recirculation valve.

At boiler trip, the trip valve is closed, the by-pass valve opened and the recirculation valve opened.

When the trip is reset, the by-pass valve is closed. The fuel oil will then circulate in the burner line and return to the HFO service tank. This allows for pre-heating of the fuel line. When the first burner is lighted, the recirculation valve is closed. The boiler safety system trips the boiler on the following conditions:

- Flame out;

- Forced draft fan stopped;

- Drum water level very low;

- Drum water level very high;

- Deaerator level very low;

- Steam temperature very high;

- Black-out;

- Manual trip activation.

A boiler trip results in closing of the fuel oil trip valve and the fuel oil shut-off valves on the burners. The manual trip can be activated from the engine control room. The boiler gas line has

5.5. BOILER FOR LPG STEAM PROPULSION PLANT 5.15

individual trip valves for each boiler and a master trip valve in the main supply. The trip valves can be operated from the remote control panel.

The boiler gas trip will operate if the boiler trips, the gas pressure is too high or too low and if the master trip valve operates.

The master trip is activated by:

- ESDS system activation;

- Boiler gas extraction fan failure;

- Gas leakage detected;

- Engine room ventilation fan failure;

- Engine room extraction fan failure;

- BOG temperature too high or low;

- Fire alarm;

- Boiler FG trip;

- Boiler trip.

Nitrogen is supplied for purging of FG supply lines and to the burners on each boiler. For the system to operate, all trips must be reset and controls set in remote.

Figure 5.7: Fuel supply system.

5.16

CHAPTER 5. BOILERS AND STEAM GENERATORS

5.5.2

Boiler burners

The boiler’s three burners can be locally operated at the burner control panels. Each burner is equipped with the following main components:

- Burner lance;

- Electric igniter;

- Primary air damper;

- Secondary air damper;

- Fuel oil shut-off valves;

- Gas shut-off valves;

- Atomizing steam supply valve;

- HFO flow adjust valve;

- Nitrogen purging;

- Steam purging;

- Flame detector.

Figure 5.8: Boiler burners.

The HFO burner requires atomizing steam. Atomising air is available for initial warming-up.

Control can be transferred from REMOTE to LOCAL or vice-versa at the burner control panel. To light-off a burner, press the START button and the following sequence will be executed:

5.5. BOILER FOR LPG STEAM PROPULSION PLANT 5.17

- Primary air damper opens;

- Igniter is inserted and excitation turns on;

- Fuel oil valves 1 and 2 open;

- Igniter de-energized and retracted when flame detector is activated;

- Secondary air damper released.

If flame is not detected within the prescribed time, the burner is shut down.

The only inhibiting signal for local operation of the burner is boiler trip. It is the operator’s responsibility to purge the boiler properly before light-off and to have the combustion air fan damper and the fuel oil control valve in the correct positions. To shut down a burner, press the STOP button and the fuel oil valves and the air dampers will close. The firing rate can be adjusted by the manually operated fuel oil adjust valves. During automatic control on HFO, the HFO adjust valve should be left fully open.

The flame detector signal will reflect the stability and quality of the fuel combustion. Sealing air is required to avoid fouling of the flame detectors lens system.

Figure 5.9: Burners remote control panel.

Normally, burners light-off or shut-down will be done from the remote panel (Fig. 5.9). A burner

light-off initiated from the remote panel, requires that all preset conditions must be satisfied, before light-off is allowed. Preset conditions are related to:

- Fuel oil pressure;

- Fuel oil temperature;

5.18

CHAPTER 5. BOILERS AND STEAM GENERATORS

- Atomizing steam/air pressure;

- Control air pressure;

- Sealing air pressure.

In addition, any boiler trip must be reset if activated. This has to be done at the boiler local safety panel. For safety reasons, before light-off of the first burner the boiler furnace has to be air purged. A separate purge logic system is available for that purpose. The purge system automatically opens all air dampers on the boiler and sets the forced draft fan damper signal to a proper (high) purge value. It also sets the fuel control valve signal to a proper light-off value. When the purge time is elapsed and sufficient air flow registered, the air dampers are closed and the forced draft fan damper signal set to light-off value. The burner management system has two modes of operation, manual or automatic. In manual mode, each burner light-off or shutdown has to be initiated by pressing the

START or STOP push button of the burner in question.

In automatic control mode, the boiler is operated with up to three burners in service, according to load. Controlling signals are steam pressure, oil flow and master demand signal. If a burner in operation looses its flame signal, it will be shut down and flame failure indicated. The failure indication has to be acknowledged at the panel before the burner can be remotely started.

5.5.3

Air and flue gas systems

The drawing included in Fig. 5.10 shows the flow of air and flue gas, from the forced draft fan inlet

to tube stack uptake duct. Air is entering the forced draft fans, heated in the air pre-heater and finally mixed with fuel and burned in the furnace space. Flue gas is radiating heat to the furnace walls and superheater, cooled by convection heat transfer in the steam generating tube bank and the superheater and further cooled in the feed water economizer.

The air flow is controlled by air dampers on the suction side of each forced draft fan. The damper is normally controlled by a signal from the combustion control system. When the damper control selector is set to LOCAL, manual position control is available. The forced draft fans represent very heavy consumers on the electric power system. The discharge shut-off damper is automatically opened/closed according to whether motor is running or not.

The air pre-heater is of the steam heated type. The steam is supplied by the back pressure line.

The burner management system releases the secondary air dampers control. The actual damper position is controlled by the differential pressure between the air box and the furnace. A common differential pressure controller controls all secondary air dampers. The secondary air dampers will open slowly at wind box differential pressure above a set limit.

The sealing air system comprises a sealing air fan and sealing air supply lines to boiler casing and burners. Correct sealing air pressure is required for automatic burner control (is part of the “pre-set condition” requirement). Lack of sealing air will make the flame detectors unreliable.

All gas piping and associated valves to the engine room are contained in the gas piping duct.

When operating on gas the leakage gas extraction fan must be running to vent the gas piping ducting.

5.5. BOILER FOR LPG STEAM PROPULSION PLANT 5.19

Figure 5.10: Air and flue gas systems.

A gas detector automatically trips the master FG valve should leakage occur.

To prepare boiler light-off:

- Check drum water level;

- Open drain valves and vent valve;

- Line up sealing air line and start sealing air fan;

- Start forced draft fan;

- Set forced draft fan control in REMOTE;

- Burners in REMOTE;

- Start boiler air purge.

To light-off the boiler:

- Boiler safety trips must be clear;

- Atomising air open for DO operation, steam for HFO operation;

- After PURGE is complete;

- START burner.

5.5.4

Remote control panel

Each boiler is normally remotely controlled from the panel shown in Fig. 5.11. The controllers are

grouped according to the area of control they are related to:

5.20

CHAPTER 5. BOILERS AND STEAM GENERATORS

- Combustion control (superheated steam outlet pressure);

- Feed water control (water drum level);

- Steam temperature control (superheated steam outlet temperature).

Each controller can be set in manual or automatic control mode. The output of the controller is displayed in the window after the AUTO/MANUAL selector. In manual mode, controller output signal is simply entered in the display window. The set-point of each controller is displayed and can be changed.

All controlled variables and important auxiliary variables are shown on analogue instruments.

The ability to dump excess steam is available. This may be required when operating on BOG. In order to maintain the cargo tank pressure the BOG can be burnt off in the boiler, if the rate of gas production is excessive the steam dump will control the boiler pressure enabling the excess gas to be burnt. Even burning HFO, the steam dump valve operation is very usefull in case of sudden turbine trips, avoiding the operation of boiler safety valves.

Figure 5.11: Boiler remote control panel.

5.5.5

Feed water and steam systems

The feed water flow from the deaerator is controlled by the feed water control valve. Its valve position can be set directly in LOCAL control. REMOTE control is from the boiler control panel.

The feed water is pre-heated in the economizer. This unit can be by-passed if necessary. A tank for adding chemicals to the boiler water, and a separate chemical feed line to the water drum, is included.

The steam drum is equipped with two separate safety valves, as required by safety regulations. It contains necessary water/steam separating cyclones and a control de-superheater for control of final

5.6. STEAM/STEAM GENERATORS 5.21

Figure 5.12: Feed water and steam systems.

steam temperature. From the water/steam separators in the steam drum, saturated steam enters the first superheater section. The steam flow is then divided, some goes to the control de-superheater for cooling, and the remaining flows through the flow control orifice plate directly to the second superheater section. The automatic steam temperature control valve adjusts the flow to the steam de-superheater so the steam temperature at the second superheater section outlet is correct. Both superheater sections can be drained.

The water drum contains the internal de-superheater. From this de-superheater, steam is supplied to the LP steam generator, to the back pressure system and to boiler sootblowers.

When warming through, a vent is available from the superheater outlet to ensure steam flow at all times. Valves for bottom blow-down or surface skimming are included.

5.6

Steam/Steam generators

The high pressure steam plants often include a steam generator for a secondary steam system, preventing oil contamination on primary system. A low pressure steam generator is provided here, where the low pressure steam of 8 bar is generated for supplying the auxiliary services.

The general service steam system is completely disconnected from the main steam system to prevent the boiler and steam high pressure system from contaminated drains.

On the LPG steam propulsion plant, the steam generator produces secondary, low pressure steam to be used for the following purposes:

- Heating of heavy fuel oil to boilers;

5.22

CHAPTER 5. BOILERS AND STEAM GENERATORS

Figure 5.13: General service low pressure steam system.

- Heating of bunker and cargo tanks;

- Steam for accommodations heating;

- BOG heater;

- Vaporizer;

- Glycol heating system;

- Lubricating oil heater for compressors.

During voyage, the primary steam to the LP steam generator is normally supplied from the HP bleed. If the main turbine bleed pressure is too low, steam is provided from the internal de-superheater through a pressure reduction valve. The flow of steam to the heat exchanger in the steam generator’s steam drum is automatically controlled to keep the secondary steam pressure constant.

Condensates from the heat exchanger are cooled in a separate drain cooler before discharged to the deaerator. The primary condensate discharge rate is controlled, maintaining the drain cooler always filled with water.

Secondary condensate drain from miscellaneous heaters is cooled and collected in the inspection tank. The inspection tank is designed for easy observation and removal of possible oil contamination.

The drain cooler leads to the LP steam generator feed water tank. The tank level is automatically maintained from the distilled water tank to compensate for any losses. The secondary condensate is transferred from the feed water tank to the LP steam generator by the secondary feed water pumps.

The water from the pumps passes through the primary drain cooler for pre-heating, before it is fed to the steam drum. The water level in the steam drum is controlled by the secondary feed water control.

5.6. STEAM/STEAM GENERATORS 5.23

The procedure for the operation of the secondary LP steam generator is:

- Open the distilled tank outlet and set the feed water level control to AUTO to replenish feed water automatically;

- Line up the LP feed water pumps and fill the steam generator to the normal level;

- Set the level control to AUTO before supplying heating steam to LP steam generator.

- Open the heating steam valves;

- Slightly open the primary steam heating control valve manually;

- Gradually open the primary steam heating steam control valve until the down stream pressure reaches up to 10 bar;

- After confirming secondary steam generating, switch the primary steam heating steam flow control valve to AUTO.

5.24

CHAPTER 5. BOILERS AND STEAM GENERATORS

6

Fuel Oil Treatment

6.1

Bunkering

The loading of fuel oil into a ship’s tanks from a shoreside installation or bunker barge takes place about once a trip. The penalties for oil spills are large, the damage to the environment is considerable, and the ship may well be delayed or even arrested if this job is not properly carried out.

Figure 6.1: Barge bunkering.

Most ships will have a procedure which is to be followed, or some form of general instructions, which might include:

- All scuppers are to be sealed off, i.e. plugged, to prevent any minor oil spill on deck going overboard;

- All tank air vent containments or drip trays are to be sealed or plugged;

- Sawdust should be available at the bunkering station and various positions around the deck;

- All fuel tank valves should be carefully checked before bunkering commences. The personnel involved should be quite familiar with the piping systems, tank valves, spill tanks and all tanksounding equipment;

6.1

6.2

CHAPTER 6. FUEL OIL TREATMENT

- All valves on tanks which are not to be used should be closed or switched to the ’off position and effectively safeguarded against opening or operation;

- Any manual valves in the filling lines should be proved to be open for the flow of liquid;

- Proven, reliable tank-sounding equipment must be used to regularly check the contents of each tank. It may even be necessary to “dip” or manually sound tanks to be certain of their contents;

- A complete set of all tank soundings must be obtained before bunkering commences.

- A suitable means of communication must be set up between the ship and the bunkering installation before bunkering commences.

- On-board communication between involved personnel should be by hand radio sets or some other satisfactory means.

- Any tank that is filling should be identified in some way on the level indicator, possibly by a sign or marker reading “FILLING”.

- In the event of a spill, the Port Authorities should be informed as soon as possible to enable appropriate cleaning measures to be taken.

6.2

Fuel oil transfer system

The heavy fuel oil transfer system includes four bunker tanks, one spill oil tank, a transfer pump and necessary piping. The transfer pump can suck oil from any of the bunker tanks or the spill oil tank and discharge it to the settling tanks or back to the bunker tanks. The bunker tanks are heated by steam, set by manually controlled throttle valves.

To prepare an HFO transfer operation, heat properly the fuel oil to be transferred. Co-ordinate with the deck department before attempting to transfer fuel oil. To start the transfer:

- Open inlet to selected tank from HFO transfer pump;

- Ensure that valves to other tanks are closed;

- Open outlet from selected bunker tank;

- Start transfer pump;

Control tanks level carefully, preventing overflows.

6.3

Settling tanks

The system comprises two HFO Settling tanks. The purposes of the HFO settling tanks are:

- Settle bulk water and sludges;

- Act as buffer tank for the HFO separator system;

6.4. SERVICE TANKS 6.3

Figure 6.2: Fuel oil transfer system.

- Supply the HFO separators with fuel oil of an almost constant temperature.

Bulk water settled in the settling tanks can be drained from the bottom of the tank to the sludge tank via a drain valve. The temperature is controlled by simple thermostatic P-controllers, positioning the steam control valves according to tank temperature and temperature set.

Each tank has a return line with shut-off valve for excess oil from the HFO separator feed pumps.

Overflow from the settling tanks is led to the spill oil tank.

6.4

Service tanks

Fuel oil service tanks comprise the fuel oil service tank and the diesel oil storage tank. The fuel oil service tanks store and, when necessary, pre-heat the cleaned fuel oil. The HFO service tank supplies fuel oil to:

- Fuel oil service system for main engine and generators;

- Boiler burner system.

The diesel oil service tank supplies diesel oil to:

- Fuel oil service system;

- Diesel generators;

- Boiler burner system.

6.4

CHAPTER 6. FUEL OIL TREATMENT

Figure 6.3: Fuel oil settling tanks.

Figure 6.4: Fuel oil service tanks.

6.5

Separators

6.5.1

DO separator

System description

The diesel oil separator takes suction from the diesel oil storage tank and discharge to the diesel oil service tank. The separator is provided with a separate electrical driven displacement feed pump

6.5. SEPARATORS 6.5

with adjustable speed. By means of a 3-way valve, located before the preheater, the feed pump may discharge directly to the service tank, by-passing the separator.

The separator is provided with an operation water gravity tank. During operation, there is a constant consumption of operating water and the operating water gravity tank must be manually refilled on low alarm. The oily water sludge and the drain from the shooting are collected in the sludge tank.

Figure 6.5: DO purifier system.

Operating procedures

DO separator starting procedure:

- Open outlet valve from diesel oil storage tank and inlet valve to diesel oil service tank;

- Fill operating water tank, if necessary;

- Start purifiers feed pump and adjust flow (less than 20% when starting);

- Set temperature controller in auto and adjust set point to 60

C;

- Start purifier;

- Adjust purifier discharge valve;

- Open make-up water valve (hot water for bowl content displacement), and:

- For AUTO procedure:

- After purifier has reached full speed, switch purifier controller to AUTO.

- For MANUAL procedure:

6.6

CHAPTER 6. FUEL OIL TREATMENT

- After purifier has reached full speed open make-up valve and wait until mimic reads

BOWL CLOSED AND EMPTY;

- Open seal/flush valve for 15 seconds to ensure proper water seal in bowl;

- When mimic reads BOWL CLOSED AND SEALED, open oil flow to purifier by clicking open on three way recirculation valve towards purifier.

The DO separator sludge ejection cycle comprises the following operatios:

- Close recirculation valve;

- After LOST SEAL appears, open seal/flush valve for 5 seconds to empty bowl;

- Close make-up valve;

- Open operating valve for 5 seconds, mimic reads BOWL OPEN DESLUDGING and BOWL

OPEN, EMPTY;

- Close operating valve;

- Wait 15 seconds;

- Open make-up valve;

- When indicator reads BOWL CLOSED & EMPTY, open seal/flush valve until mimic reads

BOWL CLOSED AND SEALED;

- When BOWL CLOSED AND SEALED appears, open recirculation valve towards purifier.

6.5.2

HFO separators

System description

There are two HFO separators of the ALCAP type. ALCAP means Alfa-Laval Clarifier And Purifier control system. Others manufacturers present similar systems, as:

- Westfalia: Unitrol

- Mitsubishi: E-Hidens II for automatic control of the fuel oil treatment.

Untreated oil, heated to the correct temperature, is fed continuously to the separator for the cleaning of impurities. After centrifugal separation, cleaned oil is continuously pumped away and separated sludge and water accumulate at the bowl periphery.

The system operates on the ALCAP principle. A water transducer in the clean oil outlet measures the capacitive resistance and signals changes to the control unit. Depending on the water content, the control unit either opens the drain valve or expels the water through the bowl discharge ports during sludge discharge. The total losses of sludge, oil and water during the discharge process are considerably less than other separator models due to bowl design, size, longer discharge intervals and accurate controls.

6.5. SEPARATORS 6.7

Figure 6.6: ALCAP separators bowl.

The separator is driven by an electric motor via a friction clutch and belt. The separator bowl is fixed at the top of a spindle, which is supported by bearings and special composite springs. A patented paring tube adapts itself to remove the water from the bowl and a paring disc pumps away the cleaned oil. No adjustments are necessary in the bowl, and no gravity discs are fitted.

The two HFO separators take suction from the settling or service tanks and discharge to the same tanks. Main operation modes are:

- Service tank filling, i.e., one separator taking suction from the selected HFO settling tank and discharge to the HFO service tank;

- Recirculating service tank, i.e., one separator takes suction from the HFO service tank and discharge to the HFO service tank.

Operation procedures

Preparation

Preparation includes the following:

- Open outlet valve from selected HFO settling or service tank;

- Open HFO separator oil inlet valve;

- Open HFO separator oil outlet valve to HFO settling or service tank;

- Open valve for displacement water;

- Drain settling tank.

6.8

CHAPTER 6. FUEL OIL TREATMENT

Figure 6.7: HFO Separators

Starting

Concluded the preparation and verified the tank temperatures, the procedure to start the operation of a HFO purifier is:

- Start HFO separator feed pump;

- Adjust desired flow (start with less than 25%);

- Open HFO separator heater steam shut off valve;

- Adjust temperature set point to 98

C and set to AUTO;

- Check that the purifier brake is not engaged;

- Start electric motor of the purifier;

- Wait for purifier speed to stabilise (observe the amp-meter and “WAITING FOR SPEED” indication on ALCAP control panel);

- Put the ALCAP control into operation by pressing the START button on the control panel.

When correct oil temperature is achieved (observe indication on the ALCAP control panel), the three-way valve will open for delivery to the separator. Observe and adjust flow after separator.

Stopping procedure

Before stop the purifier perform a manual discharge. When discharge sequence has finished:

- Push the STOP button on the ALCAP control panel;

- Stop the purifier;

6.5. SEPARATORS

- Stop the feed pump;

- Close valves;

- If high vibration occurs engage brake to stop the purifier immediately.

6.9

6.10

CHAPTER 6. FUEL OIL TREATMENT

7

Diesel Engines

7.1

Engine operation

Medium- and slow-speed diesel engines will follow a fairly similar procedure for starting and manoeuvring. When reversing gearboxes or controllable-pitch propellers are used the engine reversing is not necessary. A general procedure is now given for engine operation which details the main points in their correct sequence. When a manufacturer’s operating manual is available, it should be consulted and used.

7.1.1

Preparations for stand-by

Before a large diesel is started must be warmed through by circulating hot water through the cylinder liners, heads, etc. This will enable the various engine parts to expand in relation to one another. The various supply tanks, filters, valves and drains are all to be checked. The lubricating oil pumps and circulating water pumps are started and all the visible flow returns should be observed.

All control equipment and alarms should be examined for correct operation.

The indicator cocks are open, the turning gear engaged and the engine turned through several complete revolutions. In this way, any water which may have collected in the cylinders will be forced out.

The fuel oil system is checked and circulated with DO or hot HFO, depending on the engine fuel system. Auxiliary scavenge blowers, if manually operated, should be started.

The turning gear is then stopped and disengaged. If possible, the engine should be turned over on air before closing the indicator cocks.

Insufficient pre-heating of the main engine before starting may cause misalignment of the main bearings and fresh water leaking. Line-up the pre-heating loop, and start the pre-heating or auxilliary circulation pump. Open steam to the water heater. When steam pressure is present, switch on the steam heater controller, if available. The controller will ensure that the cylinder liner water will maintain correct temperature. Correct pre-heating temperature is normally about 55 − 60

C.

7.1

7.2

CHAPTER 7. DIESEL ENGINES

The engine is now available for stand-by. The time involved in these preparations will depend upon the size of the engine.

7.1.2

Engine starting

The direction handle is positioned ahead or astern. This handle may be built into the telegraph reply lever. The camshaft is thus positioned relative to the crankshaft to operate the various cams for fuel injection, valve operation, etc.

The manoeuvring handle is moved to “start”. This will admit compressed air into the cylinders in the correct sequence to turn the engine in the desired direction. A separate air start button may be used.

When the engine reaches its firing speed the manoeuvring handle is moved to the running position.

Fuel is admitted and the combustion process will accelerate the engine and starting air admission will cease.

7.1.3

Engine reversing

When running at manoeuvring speeds, where manually operated auxiliary blowers are fitted they should be started. The fuel supply is shut-off and the engine will quickly slow-down.

The direction handle is positioned astern. Compressed air is admitted to the engine to turn it in the astern direction. When turning astern under the action of compressed air, fuel will be admitted.

The combustion process will take over and air admission cease.

When running at full speed, the auxiliary blowers, where manually operated, should be started and fuel shut off from the engine. Blasts of compressed air may be used to slow the engine down. When the engine is stopped, the direction handle should be positioned astern. Compressed air is admitted to turn the engine astern and fuel is admitted to accelerate the engine. The compressed air supply will then cease.

7.1.4

Shut-down procedure

Prior to stopping the engine, the fresh water generator must be secured and the jacket cooling water by-pass opened to prevent under cooling of the jackets during manoeuvring. During short stops the main HTFW pump may be left running and the jacket pre-heater put in use. For longer stops use the auxiliary HTFW pump and the jacket pre-heater. If securing the engine for maintenance shut off steam to preheater until temperature has cooled to about 40

C or ambient engine temperature and stop all pumps.

To secure the LTFW system all plant must be shut down and then all LTFW pumps may be stopped.

7.2. SAFETY ISSUES 7.3

7.2

Safety issues

7.2.1

Crankcase oil mist detector

This device is fitted to monitor the presence of an oil mist in the crankcase. In this monitoring process samples of the air and vapours mixture taken continually from the crankcase of a diesel engine. This device will detect the level of oil mist concentration which must remain below level. In case of coming to this level a warning is given to the engineer and prevent serious damages and explosion. Modern oil mist detectors also measures crank case pressure in the event of large pressure build-up by piston seal leakage, giving an alarm and an auto shut-down. The detection points are sensed simultaneously, not one by one using microprocessors.

The presence of an oil mist in the crankcase is the result of oil vaporization caused by a “hot spot”.

Oil mist builds up when the equilibrium is lost: generation of oil mist versus condensation on colder surfaces and drainage back into crankcase and sump. This hotspot is produced by other heating of any engine bearing or overheating of any other moving parts of the engine time-chain or gear drives.

Explosive condition can result if build up of oil mist is allowed. Hence continuous monitoring of vapours intensity is required. The detector should be checked daily and the sensitivity tested.

Action to be taken in the event of a oil mist detector alarm are:

1. Inform Chief engineer;

2. Inform bridge and find out traffic condition or possibility of running aground.

3. Change over controls to ECR and reduce engine speed at once and prepare for stoppage. Reduction of rpm will minimize further creation of oil mist. However the ships forward momentum will cause propeller will turn the crank shaft;

4. Increase the cooling of bearings by increasing ME oil circulation.

5. Stop the engine and engage the turning gear.

6. Open sky-light, ventilate engine room and maintain crew away from ME crankcase doors and, more important, crankcase relief valves/flame arrestor.

7. Continue with lubrication for at least 30 minutes. Do not open crankcase doors for at least 30 minutes after stopping, to avoid closing the fire triangle with oxygen.

8. Stop the lub oil pump. Open all lower most doors , and try to locate hot spot. Look for discolouration at the surface, squeezed out white babitt metal. Find out the hot spot by looking for excessive flow of lub oil, high temperature at sliding surfaces.

9. After repairing defect, start lube oil pump and check oil flow through each bearing, while turning the engine on turning gear.

10. Clean the detector and check the “ZERO” setting and sensitivity test of the mist detector.

11. Start the engine and gradually increase the speed.

7.4

CHAPTER 7. DIESEL ENGINES

12. Stop the engine again after about 15 minutes of running.

When a crankcase explosion occurs usually there is another secondary explosion due to sudden inrush of fresh air into the vaccumised crank case. Crankcase explosions and pressure piling usually cause loss of life. Engine room fires are caused by mist being sucked towards air inlet of turbocharger.

Spurious piston rod stuffing box parts like springs have also caused crankcase explosions.

Flame arrester quenches the slower propagating flame front preventing a major engine room fire.

7.2.2

Scavenging fire

For any fire to begin there must be present a combustible material, oxygen or air to support combustion and a source of heat of a temperature high enough to start combustion.

Scavenging air fires, on larger two stroke, slow speed engines, can occur where an excess of combustible, such a coke, builds up in the scavenging air manifold. This can be aggravated by oil collection at the bottom of the manifold. Coke can be a result of blow back, this could be as a result of poor exhaust valve operation, injector performance, or poor fuel quality which delays burn until scavenge ports are exposed. The oxygen necessary for combustion comes from the scavenge air which is plentiful supply for the operation of the engines. The heat in the scavenge space, around the cylinder, brings the oil to a condition where it is easily ignited. The high temperature required to start combustion may arise from piston-ring blow past.

The first indication of a scavenge fire may be a slight reduction in the engine speed due to the reduction in power which comes about when a fire starts. Other indications are a higher exhaust temperature at the cylinders where the scavenge fire has started and irregular speed of turbo-blowers

(possible surging). External indications will be given by a smoky exhaust and the discharge of sooty smuts or carbon particles. Discharging of spark, flame or smokes through drain cocks from scavenge air boxes. Other possible indications are the rise of pressure and temperature of air in the air box below the piston, a visible evidence of fire if a transparent window, is fitted, and an increased cooling water outlet temperature of the affected unit.

If the scavenge trunk is oily the fire may spread back from the space around or adjacent to the cylinders where fire started and will show itself as very hot spots on areas of the scavenge trunk surfaces. In ships where the engine room is periodically unmanned, temperature sensors are fitted at critical points within the scavenge spaces. On uniflow-scavenged engines the sensors are fitted round the cylinder liner just above the scavenge ports. A temperature higher than reference or normal then activates the alarm system.

If a scavenge fire starts, two immediate objectives arise:

- Contain the fire within the scavenge space of the engine;

- Prevent or minimize damage to the engine.

The engine must be put to dead slow ahead and the fuel must be taken off the cylinders affected by fire. The lubrication to these cylinders must be increased to prevent seizure and all scavenge drains

7.3. VLCC PROPULSION MACHINERY 7.5

must be shut to prevent the discharge of sparks and burning oil from the drains into engine rooms.

If necessary, release the smothering gases (steam or CO

2

) to extinguish fire. Once the fire is out and navigational circumstances allow it, the engine should be stopped and the whole of the scavenging port examined and any oil residues found round other cylinders removed. Before opening scavenge door ventilate the space thoroughly if CO

2 is released.

The actual cause of initiation of the fire should be investigated. If the scavenging fire is more major nature. It sometimes become necessary to stop the engine and use the steam or extinguishing arrangement fitted to the scavenging trunk. The fire is then extinguished before it can be spread to surfaces of the scavenging trunk. Where it may cause the paint to start burning if special nonflammable paint has not been used.

Intense fire can cause distortion and may upset piston alignment. Check by turning the engine and watch movement of piston in the liner, check for any occurrence of binding at part of stroke (binding indicates misalignment of piston). Check spring on scavenge space relief device, if the device was near the set of fire. Piston rod packing spring also should be checked, which may have become weakened by overheating. Check piston rings and liner for any distortion or reddish burning mark.

Check diaphragm and frame near affected part as well as guides and guide shoes. Check tension of tie bolts.

One of the first things that must receive attention is maintaining the scavenge space in as clean a condition as possible. This can be done by keeping scavenge drain pipes clear and using them regularly to drain off any oil which comes down into scavenge space drain pockets. The scavenge space and drain pockets should also be cleaned regularly to remove the thicker carbonized oil sludge which don’t drain down so easily and which are a common cause of choke drain pipes. The piston rings must be properly maintained and lubricated adequately so that ring blow-by (blow-past) is prevented. At the same time one must guard against exceed cylinder oil usage. With timed cylinder oil injection the timing should be periodically checked. Scavenge ports must be kept clear.

7.2.3

Economizer fire

Regarding fires in the economizer you should reduce engine speed or stop and try to extinguish them by the soot blowers. Do not stop the circulating water pumps or you might melt the whole economizer.

There are many schools of thought, to stop the engine or not. All agree to sootblow though, and keep the circulating water flowing.

7.3

VLCC propulsion machinery

The propulsion machinery is based on one MAN B&W 5L90MC,low speed, 5 cylinder configuration,

2-stroke, turbocharged, reversible diesel engine. The main engine is coupled to a propeller shaft with both fixed pitch propeller and controllable pitch propeller. Also, a shaft generator is attached to the main engine.

7.6

CHAPTER 7. DIESEL ENGINES

Cylinder Bore

Piston Stroke

Number of Cylinders

Number of Air Coolers

Number of Turbo Chargers

Continuous Service Rating

Corresponding Engine Speed

Mean Indicated Pressure

900 mm

2900 mm

5

2

2

17.4 MW

74 rpm

13.0 bar

Scavenge Air Pressure

Turbine Speed

2.1 bar

8000 rpm

Specific Fuel Oil Consumption 168 g/kWh

Table 7.1: VLCC main engine data.

Main engine data is included in Table 7.1. The propeller has 5 blades and the pitch/diameter ratio

is 0.9.

7.3.1

ME cylinders

For each cylinder, there is a screen (Fig. 7.1) to present the following parameters:

- Cylinder exhaust temperature, and deviation from the average exhaust temperature.

- Cylinder water temperature and deviation from the average water temperature.

- Cylinder piston oil temperature and deviation from the average piston oil temperature.

- Exhaust receiver pressure and temperature gauges;

- Cylinder exhaust temperature ball chart illustrating each cylinder;

- Scavenge receiver pressure and temperature gauges;

- Piston oil cooling temperature and flow indications;

- Main engine speed and power gauges;

- Cylinder oil flow;

- Fuel pump rack and VIT setting.

A blow down valve to drain the contents of the scavenge receiver is provided on each cylinder screen. This valve should opened twice daily.

The piston ring monitor screen (Fig. 7.2) provides an indication of the piston ring condition within

each cylinder. Two bar charts are provided for each cylinder. The cylinder can be selected, providing the display for each piston ring sealing and movement condition.

Under normal circumstances the ring sealing and movement will be high. Should the ring wear increase then ring sealing will reduce, whereas should the cylinder lubrication be reduced, then the ring movement will reduce. When the ring sealing and movement reduces below an acceptable level, then an alarm will be activated.

7.3. VLCC PROPULSION MACHINERY 7.7

Figure 7.1: Cylinder monitoring screen.

Figure 7.2: ME piston ring monitoring.

7.8

CHAPTER 7. DIESEL ENGINES

7.3.2

Fresh water cooling system

System description

As described in Sec. 4.3.2, the fresh water cooling system is separated in two subsystems:

- Low temperature system;

- High temperature system.

The Low Temperature Fresh Water (LTFW) system cools all auxiliary equipment, such as:

- start and service air compressors;

- lub.oil system for turbo-generator and cargo pump turbines;

- stern tube and propeller servo oil system;

- main engine air cooling system;

- oil coolers in the camshaft and main engine lub.oil system.

The High Temperature Fresh Water (HTFW) cools the cylinder liners of the main engine. Some of the excessive heat is used for heating the fresh water generator.

Operation procedure

Pre-heating

During out of service periods or if stopped for a prolonged period during manoeuvre the main engine must always be preheated. Insufficient pre-heating of the main engine before starting may cause misalignment of the main bearings and fresh water leaking.

Line-up the pre-heating loop, and start the pre-heating circulation pump. When steam pressure is present, switch on the steam heater controller. The controller will ensure that the jacket water will maintain correct temperature 55 − 60

C.

Normal operation

Check the position of all valves in suction and discharge line and start the electrical auxiliary jacking cooling water pump locally. Check sea cooling water system and the temperature controller. Normal temperature controller set point is 80

C. Put the auxiliary jacket cooling water pump into AUTO from the PowerChief Pump Control panel. The main jacket cooling water pump will then take control as soon as the main engine has reached normal speed and the auxiliary pump is automatically stopped.

During normal operation, with engine running the pre-heater would be shut off. The expansion tank level should be checked periodically.

7.3. VLCC PROPULSION MACHINERY 7.9

Shut down procedure

Prior to stopping the engine the fresh water generator must be secured and the jacket cooling water bye-pass opened to prevent under cooling of the jackets during manoeuvring. During short stops the main HTFW pump may be left running and the jacket pre-heater put in use. For longer stops use the auxiliary HTFW pump and the jacket pre-heater. If securing the engine for maintenance shut off steam to pre-heater until temperature has cooled to about 40

C or ambient engine temperature and stop all pumps. To secure the LTFW system all plant must be shut down and then all LTFW pumps may be stopped.

7.3.3

Lubricating oil system

System description

The lubrication oil from the main engine sump is collected in a sump tank below the engine. The

LO pumps are protected by a pressure relief valve which opens when the pressure rises over a preset value. The service tank oil can also be cleaned in a LO purifier. New oil is supplied by a make-up pump with flow directly to the sump tank.

The lubricating oil is cooled in two LT fresh water cooled LO coolers and is then passed through an automatic back-flush filter or a stand-by conventional filter before it enters the main engine. The

LO temperature is controlled by a PI controller, which regulates a by-pass valve for the LO coolers.

The LO filters must be checked regularly to avoid pressure and flow reduction.

The sump tank oil level will gradually decrease due to oil consumption and possible drain/sludge discharge from the purifier. The level is unstable in poor weather and if the level is low, there may be

“false” alarms or shut-downs.

If the purifier is operated with “broken” water seal, oil is continuously discharged to the sludge tank and there is a risk of emptying the LO well completely. The oil pressure after the pumps will be reduced towards zero as the LO sump well runs dry.

The oil temperature in the sump tank is affected by the return oil flow/temperature from the main engine, the oil flow/temperature from the purifier and the heat loss to the surroundings. If all inlet flows stop, the temperature will gradually approach ambient air temperature. Low oil temperature gives reduced flow at main engine.

A simple cylinder lubrication model is included. There will be a steady consumption of cylinder oil, dependent on main engine speed. The cylinder LO tank must be refilled periodically. At low cylinder LO tank level there will be ME slow down/shut down.

The lubrication oil from the main engine cam shaft is collected in a cam shaft LO tank. The LO pressure is controlled after the two cam LO pumps by a pressure control valve with return flow to the cam LO tank. Cam LO tank make-up is taken from the LO inlet main engine line. Discharge of the tank is directly to the spill oil tank. The cam lubrication oil is cooled by a LT fresh water cooled

LO cooler and is then passing a double filter before it enters the main engine. The LO temperature is controlled by a P controller, which regulates a by-pass valve for the cam LO cooler. The LO filters

7.10

CHAPTER 7. DIESEL ENGINES must be cleaned regularly to avoid pressure/flow reduction.

Operation procedures

Start-up for main engine

Ensure that main engine sump has sufficient oil. Set temperature controller to to AUTO and 45

C.

Ensure suction and delivery valves on both main lube oil pumps are open. Ensure one cooler has inlet and outlet valves open. Ensure inlet and outlet valves to back flush filter are open. Ensure main bearing supply valve is open.

Start one of the main lube oil pumps in manual wait until the lube oil pressure has risen to about

3 bar. Then, in pump/compressor Autochief panel, set pump control to AUTO. It should only be necessary for one pump to be running with the other in stand-by. Ensure oil is flowing to piston cooling and main bearings at correct temperature.

Start up of cam shaft system

Set temperature control to 50

C and AUTO. Camshaft lube oil tank has about 1.5m

3 capacity, topped-up from main system. Set cam lube oil pressure to 4 bar. Check one filter in use and suction and delivery valves on both pumps open. One pump started manually then switched to AUTO when pressure reaches about 3.7 bar.

Start up for cylinder LO system

Fill cylinder oil daily tank to near 80% of its capacity. Check all relevant valves are open. The cylinder oil flow will vary with engine speed.

System shut down

When engine has stopped at Finished With Engines, wait for approx. 30 minutes to ensure engine has cooled down and stop all lube oil pumps. Sump temperature in port is normally maintained by continually running the lube oil purifier.

ME bearings

The screen provides a clear display of all bearing temperatures, as well as the main parameters that affect bearing load, such as main engine speed, engine power, and the lubricating oil supply. The bearing temperature depends on the cylinder power, the lubricating oil flow and temperature, and ambient temperature. The shaft friction includes static friction as well as speed dependent friction.

Comparisons between the various bearings can be easily made, and should a bearing temperature increase above 80

C, then the indicating bar will change to red to aid identification. At the same time the bearing concerned will also change colour to red.

The screen will also display the presence of oil mist within the crankcase, as well as which units are affected. Should oil mist be detected, then the engine protection system will activate, and an engine slow down will occur.

7.3. VLCC PROPULSION MACHINERY 7.11

The MAN B&W procedures for reaction to an oil mist alarm, or other alarms that could lead to the oil mist situation are:

1. Reduce engine power/pitch down to slow-down level, if this is not an automatic function. This will drastically reduce the load on the engine bearings, and hence the production of oil mist.

2. Contact bridge, and ask to STOP engine. If the vessel is in a confined area, it may not be possible to stop the vessel. Hence the engine would continue on minimal power.

3. When stop order is received, stop the engine and close the fuel supply to the engine by stopping the booster pumps. This is will reduce the oil mist in the crankcase as the engine cools.

4. Switch off the auxiliary blowers.

5. Open engine room casing. This will reduce the pressure rise in the engine room, should the crankcase relief devices operate

6. Personnel to vacate engine room. This is for the personnel safety of the engine room staff should flames issue from the relief valves. It may be prudent to have a minimal staff in the control room to monitor the situation, and to maintain the main services, but under no circumstances should personnel operate on the exhaust of the engine.

7. Prepare fire fighting equipment. A safety precaution against outbreaks of fire in the engine room, from any flames issuing from the crankcase relief doors.

8. Do not open the crankcase until after at least 20 minutes. You must allow time for the oil mist to cool and fully condense. It is also recommended that the oil mist detector alarm level should reset, which indicates that the oil mist levels are well below the Lower Explosive Limit.

Obviously, no naked flames should be used on the initial entry.

9. Stop all lube oil pumps. To allow personnel entry into the crankcase.

10. Isolate the starting air, and engage the turning gear.

11. Open the crankcase doors, and inspect the following areas for overheating:

- Main and bottom end bearings;

- Thrust bearing;

- Crosshead bearings;

- Piston rods;

- Stuffing boxes;

- Chains;

- Vibration dampers;

- Moment compensators;

- Telescopic pipes;

- Cracked piston crown, allowing oil mist to enter crankcase via cooling oil return;

7.12

- Overheated diaphragm, from a scavenge fire;

12. Overheating can be identified by:

- Melted or squeezed white metal from the bearings;

- Discolouration of the crankcase paint in the vicinity;

- Burnt or carbonised oil deposits;

- Excessive bearing clearances;

- Excessive oil flow from a bearing.

CHAPTER 7. DIESEL ENGINES

7.3.4

Fuel oil system

General description

The purpose of the fuel oil service system is to pre-heat the fuel oil to correct injection viscosity, to fine-filter the fuel oil and to supply the main engines and the diesel generators with a continuous flow of fuel oil at a correct pressure.

Figure 7.3: Fuel oil supply and circulating systems.

The diesel engines are usually stopped and started with HFO in fuel lines. Diesel oil is used if engines are to be stopped for a prolonged period (dry-docking) or when conducting major overhauls to fuel system. If ambient temperature is extremely low, or if steam system is out of commission, change to diesel oil before stopping or empty lines by changing to diesel oil and re-circulating oil

7.3. VLCC PROPULSION MACHINERY 7.13

back to HFO service tank. Quicker change-over can be obtained with return to service tank open.

This, however, may cause needle valves to seize in fuel injectors.

All engines are running at the same viscosity and intended to operate on heavy fuel oil at all times, full power, manoeuvring and in port. Operation on diesel oil is only recommended during abnormal conditions and during major overhaul of the fuel oil system. The system is capable of preparing heavy fuel oil with a viscosity of 700 cSt. at 50

C and arranged as a pressurised fuel oil system in order to prevent foaming and high-pressure fuel oil pump cavitation.

Two supply pumps take suction from the heavy fuel oil service tanks or from the diesel oil service tank through an adjustable 3-way mixing valve. The supply line from each service tank is equipped with none-return valves in order to prevent confluence. The supply pumps discharge to the venting tank at a pressure of approx. 4 bar. The total amount of fuel oil supplied to the venting tank is measured by a flow meter. A by-pass valve is also provided. The capacity of each supply pump exceeds the maximum consumption of the main engines and the diesel engines.

If the plant is shut down with no heating, the oil in the venting tank will cool down because of heat loss to surroundings. The oil viscosity in the venting tank is dependent on temperature and possible dilution by diesel oil.

If a water leakage in the service tank heater has occurred it will collect in the vent tank and disturb the running of the diesel engines. The venting tank can be drained or emptied to the spill oil tank.

If the viscosity at the booster pump inlet is high, the fuel oil booster pump discharge pressure will decrease.

The venting box can be drained to the spill oil tank through a drain valve. Situated after the fuel oil meter, there is a Fuel-Water Emulsion Control Unit, designed for fuel emulsification to reduce the

NO x content in the engine exhaust gas. One very important thing to remember when adding water to the fuel is that to maintain the same engine power, the fuel link must increase. Therefore, all the parameters or limits depending on the fuel link position must be adjusted, with the same relative values as the actual water fraction.

Two fuel oil circulation pumps take suction from the venting box and/or the fuel oil supply pumps and discharge to the fuel oil circulating line, supplying fuel oil to the injection system of the main engines and of the diesel generators. The circulating line is equipped with two steam heated fuel oil heaters, one back-flush fuel oil filter and one bypass filter. The capacity of each heater is sufficient for the max consumption for the main engines and the diesel engines.

The oil viscosity in the circulating line depends on temperature and possible dilution by diesel oil.

The flow resistance in fuel oil heaters and filters is dependent on viscosity. A pressure drop in fuel oil filters and fuel oil heater results in a correspondingly drop of fuel oil pressure at the DG’s and ME’s high-pressure pumps. Above a viscosity of approximately 600 cSt the oil is beyond the pumping limit.

If the rate of temperature reduction/rise when changing from HFO to diesel oil is too high, some of the high pressure injection plungers might stick due to plunger liner contraction/reduced lubrication.

The oil delivery from the booster pumps is reduced if the suction pressure drops below a certain limit.

If the fuel oil temperature after the fuel oil heaters rises higher than the fuels boiling temperature

7.14

CHAPTER 7. DIESEL ENGINES

“gassing” of the oil occurs. Normally HFO gassing develops above 135

C and for DO above 80

C.

Fuel oil gassing causes:

- disturbed running of the main engine;

- very noisy signal from the viscosity meter.

There is a facility to run the diesel generators on diesel oil with the main engine on heavy fuel oil. The capacity of each circulating pump exceeds the max consumption of the main engines and the diesel engines. Excess fuel is normally returned to the venting box. Provision is also made to return the fuel oil to the service tanks through a 3-way change-over valve.

An adjustable (5 − 10 bar) back-pressure valve maintains a constant pressure in the circulation line. The fuel oil line to the main engines is equipped with an emergency shut off valve for remote control (outside engine room).

Steam for heating of the venting box and all fuel oil lines (steam tracing) is supplied through an adjustable (0 − 10 bar) steam reduction valve. Steam for fuel oil heaters and steam tracing can be shut-off by stop valves.

Fuel oil viscosity control

The viscosity controller positions the steam valve of the fuel oil heater directly (single PID loop), or indirectly by adjusting the set point of a separate slave controller (cascade control). The feedback signal to the slave controller is the mean tube metal temperature of the fuel oil heaters (High Selected).

At low load, it may prove to be necessary to stabilise the controller by reducing the steam supply to the fuel oil heaters. This controller can be configured in cascade. A controller connected this way will be more stable and less sensitive to supply steam pressure than with a direct connected PID control.

With main engine running, best result in viscosity control is obtained with controllers in CAS-

CADE mode and viscosity controller in AUTO.

Operation procedure

Preparation and starting at diesel oil

On the supply system:

- Set 3-way valve into diesel oil position (100% for pure diesel oil);

- Ensure sufficient level in diesel oil service tank and drain the tank;

- Line-up system from diesel oil service tank to venting tank, by-pass valve for fuel oil flow meter normally to be closed;

- Close venting box drain valve;

- Start one of the supply pumps manually and check the discharge pressure and flow.

7.3. VLCC PROPULSION MACHINERY 7.15

If there is no fuel oil consumption from the fuel oil supply system the supply pumps must be stopped in order to avoid damage of the pump due to high temperature.

On the circulation system:

- Open valves to one of the fuel oil heaters and the back flush filter;

- Check that the main engine fuel oil emergency shut off valve is open;

- Open fuel oil shut off valves for both main engines and the supply valve for the diesel generators;

- Return line valve pressure controller must be set to 7-8 barg;

- Check that the 3-way valve in the return line is set to return to venting tank;

- Set fuel oil viscosity controller into MANUAL;

- Check that the valves for steam supply to fuel oil heaters and steam tracing is closed;

- Start one fuel oil booster pump manually and check discharge pressure and flow;

- Select auto stand-by for supply pumps and for booster pumps at the PowerChief control panel.

If steam system is not effectively shut-off, closing the stop and control valves of the steam system, there is a risk when heating the diesel oil. Too high temperature of the diesel oil may cause poor lubrication of high-pressure pump’s plunger and of fuel oil nozzle needle valve due to low viscosity.

This again may cause piston or needle valve to seize.

Changing from diesel oil to heavy fuel oil

The procedure to change fuel oil comsumption from diesel oil to heavy fuel oil is:

- Ensure sufficient level in the HFO service tank and proper temperature in order to get a suitable oil viscosity;

- Drain water in the tank;

- Line-up the system from HFO service tank to 3-way mixing valve;

- Open steam valves to selected FO heater;

- Open steam valve for tracing;

- Set steam line pressure controller to desired setting. (5-8 bar) and check steam pressure;

- Set viscosity controller into Auto and set point at 11-15 cSt;

- Gradually change value of 3-way mixing valve to pure HFO while checking that the controller keeps the viscosity within appropriate limits.

Quicker change-over can be obtained with return to service tank open. This, however, may cause needle valves to seize in fuel injectors.

7.16

CHAPTER 7. DIESEL ENGINES

Changing from heavy fuel to diesel oil

The procedure to change fuel oil consumption from heavy fuel to diesel oil is:

- Slowly reduce the temperature on HFO by adjusting the viscosity controller manually;

- When temperature drops, gradually mix in diesel oil by adjusting the 3-way mixing valve;

- Observe the rate of temperature reduction. Too quick temperature drop can cause fuel oil highpressure pump’s plungers to seize due to plunger-liner contraction and reduced lubrication.

If for some reason venting box must be drained, the three-way valve can return the fuel oil to settling tanks.

7.3.5

Fuel oil high pressure system

Figure indicates the Variable Injection Timing (VIT) system. The VIT system will advance the fuel timing to raise the combustion pressure at engine loads below 100%, and hence improve the fuel efficiency. The start and finish of the fuel advancement can be adjusted over the load range of the engine, by means of the starting and ending point.

Figure 7.4: Fuel oil high pressure system.

To adjust the timing of the fuel pumps, three options are available:

1. The individual adjustment at the upper control lever to compensate for the wear within the fuel pump the timing would be advanced. Reduction of 1 mm mm in the fuel pump setting is approximately 0.8

◦ advancement.

7.3. VLCC PROPULSION MACHINERY 7.17

2. The collective adjustment input to compensate for the quality of the supplied fuel. Reducing the collective setting by 10% would advance all fuel pumps by 0.8

.

3. The variable adjustment due to fuel rack position to increase the fuel efficiency of the engine.

Dependant upon the start, break and end points, with default settings of 40, 52 and 61% to achieve actual engine characteristics.

Figure 7.5: VIT default setting.

The actual VIT advancement applied to each fuel pump is displayed beside the upper fuel pump control lever, and is the summation of the above three options. Hence each individual fuel pump can be adjusted to provide the optimum fuel timing with regard to fuel type and quality, and engine load. Excess fuel timing advancement should be avoided as this will increase the maximum combustion pressure, and hence the cylinder and bearing loading and affect the ability of the engine to start effectively.

Following adjustments on the VIT system, the engineer should monitor the combustion pressure over the engine load range, especially from 50 − 100% load using the cylinder diagram indicator.

7.3.6

Turbocharger system

General description

The main engine is supercharged by two constant pressure turbochargers. The turbo-charged air is cooled in a fresh water-cooled air cooler before entering the main engine.

To improve part load operation of the turbocharger system, slide valves are fitted at the outlet of the exhaust gas receiver. If automatic control of the auxiliary blowers are selected, then during part load operation of the engine only one slide valve (into No 1 turbocharger) will be open, but as the engine power increases this will cause the other slide valve (into No2 turbocharger) will open. This will allow full engine power to be produced.

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CHAPTER 7. DIESEL ENGINES

Figure 7.6: Turbocharger system.

The air cooler must be kept clean to enable it to provide a sufficient amount of cool air to the engine. Hot air will lead to high exhaust temperatures, greater heat losses and increased specific fuel oil consumption.

After the air leaves the air coolers, it enters the demister units that are fitted to reduce the water content of the air. Water is drained off the demister units via the water trap, where the level and flow of the drained water can be noted from the screen display.

Dirty turbo-charger air filters throttle the scavenging air flow and will result in reduced engine performance.

The exhaust gas from the main engine cylinders enters the common exhaust gas receiver. From this receiver the exhaust gas can either flow direct into waste heat exhaust gas boiler or via the Selective

Catalytic Reduction (SCR) Receiver before entering the exhaust gas boiler.

The exhaust boiler must be kept clean. High back pressure reduces scavenging air flow and engine efficiency, especially at high power.

The turbo-charger model is composed of two separate units, a centrifugal air compressor and a single stage gas turbine. Major variables influencing the compressor torque are:

- discharge pressure (air receiver)

- suction pressure (air filter differential pressure)

- air inlet temperature (density)

- compressor speed

7.3. VLCC PROPULSION MACHINERY 7.19

Major turbine torque variables are:

- exhaust receiver pressure

- exhaust receiver temperature

- back pressure (exhaust boiler differential pressure)

- turbine speed

The turbo-charger speed depends on the torque balance considering the turbine and the compressor units.

Operation procedure

Line-up the system by opening the fresh water cooling throttle valves to air coolers No1 and No2.

Ensure the scavenge air receiver drain is closed and check that the SCR Reactor is isolated at engine start-up. Differential pressure across cooler and air inlet filter should be checked regularly.

Check that the auxiliary blowers 1 and 2 are running in AUTO mode. Preset values for start/stop of aux. blower is respectively 0.2 bar and 0.4 bar.

7.3.7

Selective catalytic reduction unit

General description

The selective catalytic reduction unit (SCR) is provided to reduce the environmental impact of the diesel engine by minimising the nitrogen oxides (NO x

) emitted from the main engine exhaust stream.

The SCR unit is used to treat the exhaust gases before it enters the turbocharger. Ammonia is added to the gas stream, and the mixture then passes through a special catalyst at a temperature between 300 and 400

C. Within the SCR reactor, the hot exhaust gases that contain NO x gases are mixed with the ammonia stream. This reduces the NO x to N

2 and H

2

O. If the temperature of reaction is too high (above 490

C), the ammonia burns and does not react, and at low temperatures (below 250

C) the reaction rate is low and the catalyst can be damaged. Note that during the shut-down period (15 second default setting) both the by-pass and direct flow paths are open, to prevent a sudden change in the turbocharger operation parameters, and to allow the reactor to gradually cool-down. During the starting period (default 30 seconds) the SCR by-pass and inlet/outlet valves are also open to allow a gradual heating up of the reactor, and prevent a possible turbocharger surge caused by a rapid change on the turbocharger turbine speed.

The quantity of ammonia added is pre-programmed into the controlling processor. This provides the base control, with a feed back link provided by the NO x measurement taken from the exhaust stream. Using the feedback link alone would produce inaccurate control due to the sluggish nature of the reaction process and, hence, a feed forward signal from the main engine actual power is used to modify the controller output.

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CHAPTER 7. DIESEL ENGINES

Figure 7.7: Selective catalytic reduction unit.

The slip controller will adjust the NO x controller set-point down with the specified rate when the slip is below the slip set point (default 3 ppm), and up when the slip is above. This “optimal” mode will be turned off if the NO x controller is not in AUTO, or if the control state is not “active”, and it has to be manually switched on again. The SCR slip controller controls the rate at which the ammonia flow is changed. Within the pop-up window, these settings can be adjusted, with the default setting of increase 0.02 g/kWh/sec, and decrease 0.01 g/kWh/sec. The quantity of ammonia which can be added is limited, as excess amounts produce “ammonia slip”, by which free ammonia leaves with the exhaust stream. Thus, both ammonia and NO x levels are recorded in the exhaust stream, and levels of 10 ppm and 5 g/kWh expected values. These values are reduced from the engine cylinder exhaust

NO x concentration in the region of 20 g/kWh.

The ammonia is supplied as pressurised water free ammonia feed. The process units are contained within a safety area, as ammonia is combustible. Thus lines are double walled, and leak detection and appropriate venting of the storage and process areas must take place.

Operation procedure to start the SCR operation is:

- Line-up the system by opening the scavenge air valve to the air / ammonia static mixer;

- Open the outlet valve from the ammonia tank so that the ammonia vapour pressure rises;

- Input 5 g/kWh as the set-point for the NO x controller, and select the AUTO mode.

When the SCR control ready indication is lit, the SCR control can be selected. This will allow the automatic valves to change the exhaust gas flow into the SCR reactor.

7.3. VLCC PROPULSION MACHINERY 7.21

The SCR control panel indicates the status of the system, with the following indications:

- Stopped - When the system is non-operational;

- Active - The system is operational, hence the SCR reactor by-pass exhaust valves are closed and all the exhaust gas flow is directed through the reactor, and the ammonia inlet to the static mixer is open;

- Shutting Down - The system is changing from active to stopped, by changing the exhaust gas flow path from the exhaust receiver direct to the turbochargers;

- Starting - The system is changing from stopped to active, by directing the exhaust gas flow from the exhaust receiver to the SCR reactor;

- Stand-by (exh gas temp) - When the control system is selected ON, the exhaust temperature must be within pre-set temperatures to enable the system to start. These temperatures are adjustable (default settings are low limit 250

C and high limit 490

C).

The system will cease to operate if a trip is active. This will happen if any of the following occurs:

- Ammonia supply - When the ammonia supply is insufficient due to a low level in the ammonia tank, then the system will trip.

- Ammonia pressure - When the ammonia pressure is above 2.5 bar, then the system will trip.

- Mixing air supply - When the scavenge air flow into the static is low, then the system will trip.

- Excessive ammonia slip - When the quantity of ammonia input to the reactor is excessive, then the level of ammonia within the exhaust stream rises. This slip of the ammonia is measured, and when this reaches 60ppm for over 30 seconds then the system will trip.

- Ammonia leakage - As ammonia can produce a flammable and/or explosive mixture with air, any leakage in the deck housing containing the ammonia system is monitored and will cause the system to trip.

7.3.8

Manoeuvring pneumatic system

Figure 7.8 illustrates the components required to start, stop and reverse the main engine. The process

diagram shows the main inputs from the local control and engine control room that starts the engine.

Before the engine can be started in any selected control position the following valve position should be set:

1. The safety air block valve 16 should be open. This valve supplies the air to the fuel pump puncture valves should an engine safety trip be activated.

2. The starting air distributor block valve 127 should be open. This valve supplies the pilot air to open the individual cylinder starting valves.

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CHAPTER 7. DIESEL ENGINES

Figure 7.8: Main engine control and manoeuvring system.

3. The starting air block valve 1 should be open. This valve supplies the control air to the manoeuvring system.

4. The turning gear should be disengaged. Valve 115 supplies the control air to valve 33 and hence would block the start sequence if engaged.

5. The pressure of the service air supply should be checked to be above 6.5 bar

6. The pressure of the starting air supply should be checked to be above 25 bar.

Engine START operation in local control

1. To control the engine system at the engine side control, the local control is selected at the ME

Local Control station. This will cause valve 100 to pressurise valves 101 and 102.

2. Once in local control, the engine can be started, stopped and reversed at the local control panel.

3. To start the engine the start button is pressed which will activate valve 101. This action will activate valves 33, 25 and 117.

4. When 33 is activated, both valves 26 and 27 will operate. Valve 26 will supply the starting air distributor with pilot or starting air valve operating air. Valve 27 will cause valve Main starting valve to open pressurising the starting air manifold with high pressure 30 bar starting air.

7.3. VLCC PROPULSION MACHINERY 7.23

5. When 25 is activated, the fuel pump puncture valves are pressurised to ensure that fuel is not admitted during the air start admission period.

6. When 117 is activated, control air is admitted to valves 14 and 15. The selection of which valve

14 or 15 then admits air to activate the starting air distributor to the ahead or astern position is determined by the selection of ahead or astern at the ME Local Control station. Once the starting air distributor is in the end position or ahead or astern that the starting air distributor will allow the control air admitted via valve 26 to the correct cylinder starting valve that will cause the engine to rotate in the desired direction.

7. The engine speed will now increase due to the admission of the starting air. Once sufficient engine rotational speed has been reached (above 20 rpm), then the start button is pressed once again to release the start command. Releasing the start command will vent the valves 33, 25 and 117.

8. The speed of the engine would now be regulated by the position of the fuel control lever.

Engine STOP operation in local control

1. To control the engine system at the engine side control, the local control is selected at the ME

Local Control station. This will cause valve 100 to pressurise valves 101 and 102.

2. Once in local control, the engine can be started, stopped and reversed at the local control panel.

3. To stop the engine the stop button is pressed which will activate valve 102. This action will activate valves 25 and 117.

4. When 25 is activated, the fuel pump puncture valves are pressurised to stop the fuel pump admitting any more fuel and hence the engine will stop.

5. When 117 is pressurised, the starting air distributor is pushed to the ahead or astern position (as dictated by valve 105), but the engine will not start as valves 26 and 27 are not energised.

Engine AHEAD operation in local control

1. To control the engine system at the engine side control, the local control is selected at the ME

Local Control station. This will cause valve 100 to pressurise valves 101 and 102.

2. Once in local control, the engine can be started, stopped and reversed at the local control panel.

3. To start the engine in the ahead direction, then the AHEAD button is pressed which will cause valve 105 to pressurise the AHEAD signal line. This will in turn activate valves 14 and 10.

4. When 14 is activated, the starting distributor will be moved to the ahead position when the start signal is activated.

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CHAPTER 7. DIESEL ENGINES

5. When 10 is activated, the fuel pump reversing mechanism on all five fuel pumps will be moved to the ahead position, once the engine starts to move in the ahead position.

6. The selection of the ahead position is maintained whilst the engine is running. If the engine is to be operated in the astern direction, then the engine should be stopped first.

Engine ASTERN operation in local control

1. To control the engine system at the engine side control, the local control is selected at the ME local control station. This will cause valve 100 to pressurise valves 101 and 102.

2. Once in local control, the engine can be started, stopped and reversed at the local control panel.

3. To start the engine in the astern direction, then the ASTERN button is pressed which will cause valve 105 to pressurise the ASTERN signal line. This will in turn activate valves 15 and 11.

4. When 15 is activated, the starting distributor will be moved to the astern position when the start signal is activated.

5. When 11 is activated, the fuel pump reversing mechanism on all five fuel pumps will be moved to the astern position, once the engine starts to move in the astern position.

6. The selection of the astern position should be maintained whilst the engine is running. If the engine is to be operated in the ahead direction, then the engine should be stopped first.

Engine AHEAD START operation in remote control (bridge or engine control room)

1. To control the engine system at one of the remote positions i.e. bridge or engine control room, the remote control is selected at the ME local control station. The new control station position will then be determined by the selection of either bridge or engine control room. This will cause valve 100 to block the air supply to valves 101 and 102.

2. Once in remote control, the engine can be started, stopped and reversed by operation of the single control lever.

3. To start the engine, the fuel lever is moved away from the stop position in the ahead direction, which will activate valves 86 and 90.

4. When 86 is activated, both valves 14 and 10 will operate. Both valves will ensure that the starting air distributor and fuel pump reversing mechanism are in the required ahead direction.

5. When 90 is activated, then valve 33 is activated. This will allow valves 26 and 27 to be activated.

Valve 26 will supply the starting air distributor with pilot or starting air valve operating air.

Valve 27 will cause valve main starting valve to open, pressurising the starting air manifold with high pressure 30 bar starting air.

7.3. VLCC PROPULSION MACHINERY 7.25

6. Note the fuel pump puncture valves are still pressurised via valves 84, 38 and 25. This signal is only reached when the start level RPM is reached, about 20 rev/min.

7. The engine speed will now increase due to the admission of the starting air. Once sufficient engine rotational speed has been reached (start level RPM), then valves 84 and 90 are released, and following a small time delay valve 86. This will vent valves 14, 10, 33, 26, 27, 33, 38, 25 and 117.

8. The speed of the engine would now be regulated by the position of the fuel control lever.

Engine STOP operation in remote control

1. To control the engine in remote control, the regulating lever is placed at zero. This will cause valve 84 to pressurise valve 38, which in turn will activate valve 25.

2. When 25 is activated, the fuel pump puncture valves are pressurised to stop the fuel pump admitting any more fuel and hence the engine will stop.

3. Valve 117 is also pressurised, so that upon starting the starting air distributor will quickly move to the desired position.

4. The stop signal on valve 84 is only released when the regulating lever is moved above the start position and the engine has started.

Slow turn operation

This engine is fitted with a slow turn arrangement that will slowly turn the engine when started.

This arrangement would be manually selected when the engine has been stopped for over 30 minutes to prevent any possible cylinder damage from water leaking into the cylinder.

1. When the SLOW TURN button is pressed then the valve 28 is activated. Any subsequent start sequence will only allow the small slow turning valve to open and block the opening of the man starting valve.

2. When the engine has rotated by at least one complete revolution, then the slow turn button is pressed once again to release valve 28, and hence allow the main starting air valve to open, and the engine speed should now increase to reach the start level RPM.

7.3.9

AutoChief control system

The main engine remote system is based on the Kongsberg Maritime AutoChief control system, which is installed onboard several hundred ships. AutoChief is designed for remote control of both reversible and non-reversible (CPP) engines.

The ME control system has a mimic diagram that displays the following information on the diode panel:

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CHAPTER 7. DIESEL ENGINES

Figure 7.9: AutoChief main engine control system.

- The command position (either bridge or engine control room)

- Stop command, when the fuel regulating lever is set to stop position

- Ahead, if the ahead direction is selected on the control panel

- Astern, if the astern direction is selected on the control panel

- Start blocked, if one or more of the following is activated:

- Start failure: After 3 start attempts and the engine is still not running

- Start air pressure too low (default setting = 12 bar)

- Control air pressure too low (default setting = 2 bar)

- Safety air pressure too low (default setting = 2.5 bar)

- Reversing failure

- Start air admission period too long

- Failure of the engine to reverse when the emergency brake command has been activated

- Turning Gear engaged

- Engine tripped CHECK

- Above reversing speed: When a running ahead or astern command is given, any braking air will not be supplied before the rpm is below the reversing level which is set to 33 rpm. When in

Emergency Run, the reversing level is raised to 40 rpm.

7.3. VLCC PROPULSION MACHINERY 7.27

- If the engine is not stopped within the Brake Air Time Limit (set to 8 seconds) the “Brake Air

Failure” alarm will be activated. A braking failure could occur when an astern command is given whilst the engine is at full sea speed. The inertial effects of the vessel will cause the propeller to continue to rotate even those there is no fuel admission.

- Indication that the fuel pump reversing mechanism is in either the ahead or astern position.

- Indication that the slow turning operation has been selected. This will delay the normal start of the engine, but ensures that cylinder damage is prevented from possible water ingress.

- Indication that the start command is active. This will activate the pneumatic valves within the manoeuvring system and should result in a successful engine start.

- Indication that a repeat start command has been initiated by the ME control system. A repeat start will be automatically activated if the main engine speed does not reach the start level RPM within a preset time. After three attempts the system will trip, producing a start failure alarm.

Further start attempts can only be made when the start block trip is manually reset.

- Indication of fuel off. Fuel injection is prevented, when the puncture valves fitted at the top of each fuel pump are opened by the stop air signal. This signal is present when the active manoeuvring lever is placed in the stop position, or there is an engine trip active.

- Indication of direction of propeller rotation.

In addition to the main mimic diagram, there are also a number of “pop-up” menus that provide additional information.

The AutoChief control state panel will provide the operator with additional information, and the ability to adjust system parameters that are not present within the main mimic diagram. Front panel indications (green lights):

- Engine stopped;

- Indication of running;

- Starting (command active, starting air should be supplied);

- Waiting for Ignition;

- Waiting for Reversing Speed (the engine speed must fall below 27 rpm, before starting air can be admitted to brake or stall the engine);

- Reversing Cam (camshaft is changing position);

- Braking Air On (Indicates that the engine rpm is below 27 rpm and that starting air is being admitted. When the limits override button is pressed, or the repeated start is active, this limit speed is raised to 40 rpm);

- Start/Reverse/Brake failure.

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CHAPTER 7. DIESEL ENGINES

Main engine shut-down

The shut-down panel provides the operator with the settings for the various main engine shut-down trips. Indications of shut-down are provided at the bridge and engine control room stations.

Front panel indications (red lights):

- Main LO Pressure (setting - 1.0 bar)

- Cam LO Pressure (setting - 1.5 bar)

- Thrust Bearing Temperature (setting - 85

C)

- Overspeed

Thermal monitor

The thermal monitor is provided to limit the heat load placed on the engine. The thermal monitor controls the speed at which the engine speeds-up and slows-down to minimise the thermal loading.

The rate of speed change is time-dependent, but is also influenced by the temperature of the engine.

Figure 7.10: Cold engine speed limit.

When the engine is cold, the maximum speed set point is reduced by the setting within the pop-up window (default value is 33 rpm). When running the main engine at any heat index below 100%, there

is also a max speed setpoint reduction, see Fig. 7.10. The actual max speed reduction is illustrated on

the front panel, and can be compared with the active speed set-point.

As illustrated in Fig. 7.11, the heat index is decreasing when the load is below “Low Load”, which

is set to 5.4 MW, and when the load is above “High Load”, the heat index is increasing. The thermal heat up constant is set to 15% per minute, while the thermal cool down constant is set to 5% per minute. As shown in the figure, the rate of the heat index is decreased when the load of the engine is above “High Load” which is set to 12.6 MW.

Front panel indications (yellow light and numeric values):

- Thermal limiter (indication by lit diode when active).

- Active speed set-point (indication of speed command from active control station)

7.3. VLCC PROPULSION MACHINERY 7.29

Figure 7.11: Thermal heat up.

- Thermal rpm limit (indication will vary according to heat index)

- Thermal heat index (indication will vary according to load)

Load limitation

The load monitor is provided to limit the load placed on the engine usually during speed increases.

The thermal monitor provides the basic heat up control function on a time basis, but the load monitor will prevent thermal overloading of the engine caused by external factors, such as hull fouling, prevailing weather, etc.

There are two limiters provided. The scavenge air limiter monitors the scavenge air pressure and prevents admission of fuel that could result in exhaust smoke due to insufficient scavenge air being

present. Fig. 7.12 shows the relationship of fuel index with scavenge air. When the scavenge pressure

is below 0.2 bar, the max fuel link position is 50%. When exceeding 0.2 bar, the max fuel link position limit is allowed to increase until the scavenge pressure exceeds 1.0 bar.

The torque limiter monitors the engine speed and position of the fuel rack to prevent excess torque being developed by the engine, which would thermally overload the engine and hence increase com-

7.30

CHAPTER 7. DIESEL ENGINES

Figure 7.12: Scavenge air limiter.

bustion chamber stresses. This is achieved by limiting the max fuel link position dependant upon the engine speed.

From the relationship:

Power

= Engine Speed × Engine Torque the speed is monitored and compared to the fuel rack, which is proportional to the power output of the engine. Hence to maintain or limit a constant torque the relationship of fuel rack vs. engine speed is maintained.

Thus there are three limitations to control engine load-up:

- The thermal limiter, which reduces the max fuel setting dependant upon heat index/engine power;

- The scavenge air limiter, which is dependant upon the scavenge air pressure;

- The torque limiter, which is dependant upon the engine speed itself.

Front panel indications (indication by lit yellow diode when active):

- Scavenge air limitation;

- Torque limitation.

Main engine slow-down

The slow-down system is provided to limit damage on the main engine when the operating parameters are outside normal limits. The engine power is reduced, which should reduce the effects of the defect, whilst maintaining a level of main engine power for propulsion and electrical supply (via the shaft alternator). This slow down panel provides the operator with the settings for the various main

7.3. VLCC PROPULSION MACHINERY 7.31

Figure 7.13: Torque air limiter.

engine slow downs. Indications of slow down are provided at the bridge and engine control room stations.

Front panel indications (red lights):

- Low main LO pressure (1.2 bar);

- High thrust bearing temperature (75

C);

- Low piston oil flow (16.9 kg/sec);

- High scavenge air temperature (75

C);

- High main LO temperature (60

C);

- High cam LO temperature (70

C);

- High piston cooling oil outlet temperature (70

C);

- High oil mist;

- High main bearing temperature (80

C);

- Low flow on cylinder lubricator;

- High exhaust temperature (460

C);

- High cylinder cooling water temperature (96

C);

- Low piston cooling oil pressure (0.5 bar);

- Low cylinder cooling water pressure (0.5 bar);

- High exhaust temperature deviation (45

C).

Main engine fail

Main engine fail is caused by the inability to carry out a operator command. Front panel indications

(red lights):

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CHAPTER 7. DIESEL ENGINES

- Start blocking, due to a valve closed within the ME manoeuvring system;

- Start air pressure too low;

- Control air pressure too low;

- Safety air pressure too low;

- Slow turn time-out (excess time on slow turn command);

- Start too long (excess time between start command and speed increase);

- Repeated start;

- External start block when turning gear is engaged.

The limits for the fail functions are:

- Min Start Air Pressure (12 bar - required for engine starting operation);

- Min Control Air Pressure (2 bar - required for manoeuvring system operation);

- Min Safety Air Pressure (2.5 bar - required for operation of the fuel pump puncture valves that will stop fuel injection);

- Max slow-turn time (no turn - 60 seconds, this will activate the fail as the engine only needs to operate on slow turn until one full revolution has been undertaken);

- Max start air time (no turn - 6 seconds, this will indicate that the engine is not attaining the normal speed on air admission, or that the signal to admit fuel has failed to activate).

Safety override

Various overrides are provided at the engine control room or bridge panel. Indication that a shutdown and/or slow-down is imminent is provided at these control panels. Hence the operator can pre-empt the engine load change by pressing the relevant override button. Indication of an override is provided within the front panel.

The front panel will also indicate that either the thermalload programme and/or the other load limits (scavenge air or torque limitation) is active. Both of these limits may be overridden by pressing the relevant button on the active ECR or Bridge manoeuvring panel.

Main engine governor

For educational purposes, the propeller can be configured as a fixed or variable pitch. The propeller type is selected at the active manoeuvring panel. In the fixed pitch mode, the propeller pitch is fixed to a ratio of 0.9 Pitch/Diameter and the engine load is controlled by adjusting the engine RPM from the lever on the active manoeuvring panel.

In the variable pitch mode, the pitch can be adjusted either remotely at the active manoeuvring panel, or locally at the pitch control input on this panel.

The speed control of the main engine is effected by the main engine governor. The governor control system compares the desired value from the active manoeuvring panel, with the actual or

7.3. VLCC PROPULSION MACHINERY 7.33

measured value of the engine speed. The governor is a three term PID controller, and the output is directly sent to the fuel linkage.

The governor control operation is similar to all controllers, in that the PID settings can be adjusted via the pop-up window. The governor can also be placed in local control, when the active manoeuvring panel is changed to LOCAL.

The available modes for the operation of control system are:

- Fixed Pitch Propeller in ECR control:

- Select governor operation in REMOTE;

- Select pitch control in REMOTE;

- Check that no shut-down, slow-down or safety override is present.

- Fixed Pitch Propeller in Local control:

- Select governor operation in LOCAL;

- Select pitch control in REMOTE;

- Check that no shut-down, slow-down or safety override is present.

- Variable Pitch Propeller in ECR control:

- Select governor operation in REMOTE;

- Select pitch control in REMOTE;

- Check that no shut-down, slow-down or safety override is present.

The critical speed for this engine is between 40 and 42 rpm. The engine should not be allowed to run within this rpm range. The AutoChief solves this by ignoring speed commands within the critical speed range. The AutoChief “waits” for a speed command outside the critical range before carrying out the new speed setting.

Figure 7.14: Critical speed barrier.

7.34

CHAPTER 7. DIESEL ENGINES

7.3.10

Remote control panel

The indicator panel provides the operator with an overview of the main parameters that influence the main engine. Each of the gauges readings can be located on their individual operating or control screens.

Figure 7.15: Main engine indication panel.

The AutoChief - Indicator Panel includes the following readings:

• Main gauges:

- Fuel Economy

- Propeller Speed

- Pitch Indicator

- Shaft Power

- Ship Speed

• Panel gauges:

- Start Air Pressure

- Main engine air flow

- Main engine fuel flow

- Main Engine Fuel Oil Pressure

7.3. VLCC PROPULSION MACHINERY

- FO Temperature HFO Service Tank

- Fuel Oil Temperature inlet of the Heaters

- Main Engine inlet fuel oil temperature

- Main Engine Fuel Oil Viscosity

- Service Air Pressure

- Main Engine Lubricating Oil inlet Pressure

- Main Engine Lubricating Oil inlet Temperature

- Main Engine Cam Shaft Lubricating Oil Pressure

- Main Engine Scavenging Air Pressure

- Main Engine Scavenging Air Temperature

- Main Engine Exhaust Gas Temperature

- Main Engine Turbocharger 1 Speed

- Main Engine Turbocharger 2 Speed

- Main Engine NO x indicator

- Main Engine Smoke Indicator

- Main Engine LTFW Temperature

- Main Engine LTFW Water Pressure

- Main Engine HTFW Inlet Temperature

- Main Engine HTFW Outlet Temperature

- Main Engine HTFW Water Pressure

- Ship Course

- Rudder Position

- Oil fired boiler drum level

- Oil fired boiler steam pressure

7.35

Control panel

The following controls are present at the AutoChief - ME Control Panel:

• Controls:

– Fuel control lever (also the combined RPM/Pitch lever when in combinator control)

– Emergency Stop

– Responsibility Transfer between Local/Engine Control Room/Bridge

– Status communication between Bridge and Engine Control Room for Finished with Engines/ECR Stand By/At Sea

– Control Mode between Fixed Pitch/Combinator/Economy/Fixed Speed/Direct Fuel Link/Locked

Fuel Link

7.36

CHAPTER 7. DIESEL ENGINES

– Combinator mode START/STOP button

– SLOW TURN request button

• Status indication:

– Fuel lever command request

– Control Mode Combi/Fixed Speed/Economy/Fixed Pitch/Direct fuel link/Locked fuel link

– Bridge Telegraph

– Main Engine Shut-Down

– Main Engine Slow-Down

– Main Engine Fail Status

– Override indicators for Shut-Down/Slow-Down/Thermal Load-Up programme/load

• Limits:

– Running hour

– Revolution counter

– ME RPM actual (digital and graphical display)

– ME RPM command (graphical display)

– ME RPM limit (graphical display)

– Bridge/ECR lever mismatch

– Fuel link command actual (graphical display)

– Fuel link command limit (graphical display)

– Fixed speed indication and set-point input

Various control modes can be selected:

- Combinator;

- Fixed speed;

- Economy;

- Fixed pitch;

- Direct fuel link;

- Locked fuel link.

Combinator

Combinator mode is used when a Controllable Pitch Propeller (CPP) function is required. The button beneath the fuel control lever controls stop and start of the engine.

At zero pitch the engine speed is reduced to improve manoeuvrability, and as the fuel control lever is increased, then the pitch and engine speed increases until the engine is operating at full speed. The

relationship between speed and pitch is fixed, as shown in Fig. 7.18.

7.3. VLCC PROPULSION MACHINERY 7.37

Figure 7.16: Main engine remote control panel.

Economy mode

This mode makes the most efficient use of the combinator control, where the pitch/RPM settings are optimised by the computer. The acceleration of the engine is slower than with normal combinator control, with the vessel draft influencing the engine set-point speed.

Fixed speed

In this mode the engine speed is set to a fixed value, and the pitch adjusted by the fuel control lever. This operating mode can be used for certain shaft alternator set-ups, but is not required with the converter unit model fitted.

Fixed Pitch

In this mode the propeller pitch is fixed at the optimum setting, close to the full power output of the engine. The speed of the engine is varied by the fuel control lever, with the speed signal being adjusted by the various limiters and filters.

Direct fuel link

In this mode the governor speed is set directly from the fuel control lever, and could be used to eliminate defects within the limiter controls. This would be activated when fault occurs in main engine governor unit. The system acts as if engine control handle and fuel linkage are directly related to each others position. i.e. when ECR handle is 50%, fuel link responds with 50% output.

7.38

CHAPTER 7. DIESEL ENGINES

Figure 7.17: Engine control modes.

Figure 7.18: Combinator mode engine speed and propeller pitch relationship.

7.3. VLCC PROPULSION MACHINERY 7.39

Figure 7.19: Economy propulsion mode.

Figure 7.20: Fixed speed mode.

Fixed fuel link The fixed fuel link eliminates the small fuel lever movements that are common within the PID governor, and improves fuel efficiency. The dead-band around the desired set-speed is increased. Should the engine speed deviate significantly, then the governor will provide a corrective action to retain the required engine speed.

Emergency stop

When this switch is activated, the engine is stopped as the fuel pump puncture valves are opened, spilling the high-pressure fuel generated by the fuel pump.

Transfer of responsibility

The responsibility buttons are provided to select the appropriate control station for the main engine.

The options are:

• Local

- This control station would be selected when a problem or defect was present within the main engine control system, such as governor or control station hardware defect. Local control will not overcome a starting system malfunction, as the starting system is common to all control stations.

7.40

CHAPTER 7. DIESEL ENGINES

• Engine Control Room

- This control station would be selected for engine manoeuvring from the engine control room, such as engine testing, or in situations when specific engine control is required (such as when a shut down or slow down is overridden)

• Bridge

- This control station is normally the default control station and would be used under most operating conditions.

Transfer from the ECR to bridge:

1. Check that the bridge and ECR levers are matched by observing the indicators on the left of the fuel control lever, and the lever mismatch light is unlit;

2. Press the push-button BRIDGE on AutoChief panel;

3. The BRIDGE button then starts to flash;

4. When the bridge accepts the transfer then the BRIDGE button turns to steady light.

Note the bridge personnel may be engineers manning the main engine bridge panel. The ship is now controlled from the bridge.

Transfer from the bridge to ECR:

1. Check that the Bridge and ECR levers are matched by observing the indicators on the left of the fuel control lever, and the lever mismatch light is unlit;

2. Press the push-button ECR on bridge panel;

3. The ECR button then starts to flash.

4. The operator now accepts the transfer to engine control room by pressing the ECR button

5. The ECR button turns to steady light.

The ECR now has control of the engine, and should utilise the telegraph system to convey engine movement requests from the bridge. This is carried out by:

1. Bridge presses the button of the required movement;

2. The selected button on the telegraph on the bridge and ECR starts to flash;

3. The ECR personnel confirms the engine request by pressing the flashing button on their panel;

4. The engine direction and speed should be adjusted to comply with the bridge request.

Move handle to relevant engine speed by point and click on the interactive field (default settings are dead slow/slow/half and full positions) or by typing in desired command in the numeric window. The engineer on duty can visually see the operation of the engine controls, with regard to ahead and astern command and actual camshaft position. The activation of both the stop and start signals can also be

7.3. VLCC PROPULSION MACHINERY 7.41

seen on this panel. If WRONG WAY alarm is activated, the camshaft direction does not correspond with command from bridge.

Transfer from ECR to local control:

1. Press the push-button LOCAL on AutoChief panel;

2. The LOCAL button then starts to flash;

3. On local control panel, the engineer accepts the transfer then the LOCAL button turns to steady light.

The ship is now controlled from the local control station. The local control station personnel should utilise the telegraph system to convey engine movement requests from the bridge. This is carried out by:

1. Bridge presses the button of the required movement;

2. The selected button on the telegraph on the Bridge and Local Control panel starts to flash;

3. The local control personnel confirms the engine request by pressing the flashing button on their panel;

4. The engine direction and speed should be adjusted to comply with the bridge request.

Transfer from the local control to ECR:

1. Press the push-button ECR on the local control panel;

2. The ECR button starts to flash;

3. Now, the engineer accepts the transfer to engine control room by pressing the ECR button;

4. The ECR button turns to steady light.

Engine safety panel

To operate the main engine safely, all critical parameters must be monitored in order to activate alarm and, if required, initiate automatic slow-down and/or shut-down of the engine.

The engine safety indicator panel will inform the operator that an engine failure has occurred and the parameters or channel that have triggered this failure.

Classification rules dictate that an engine failure requires a dedicated alarm, and that the failure should be manually reset. Adjustments of the actual failure set-points can be adjusted within the ME

Control System.

The various slow-down and shut-downs are monitored by the DataChief system, and transferred to AutoChief for initiation of the slow-down and or shut-down. Each of the slow-down and shut-down parameters is grouped and represented by an indicator light on the AutoChief panel.

When the indicator light starts flashing, slow-down/shut-down procedures are initiated. The safety system gives the operator the possibility to override shut-downs and slow-downs by pressing the

7.42

CHAPTER 7. DIESEL ENGINES relevant override buttons. Depending on set-up, the system will give the operator a warning on slowdown and shut-down. The default time delay for slow-down to be activated is 120 seconds. Within this period the operator may cancel the slow down. The actual diode will flash as long as the trigger or cause for slow down is present.

The default time delay for shut-down to be activated is 30 seconds. Within this period the engineer may cancel the shut-down, except for the overspeed, turning gear in and lube oil pressure. The actual diode will flash as long as the cause for shut-down is present. Note that slow turning should be performed if the main engine has stood still for more than 30 minutes. ME slow turning is carried out by manually pressing the SLOW-TURN button.

7.3.11

Local control

Local control of the main engine is provided to enable operation and control of the main engine should a defect or malfunction of the main control or manoeuvring system occur. In local control the automatic thermal load programme, main governor functions, and slow-down protection is overridden.

The local control panel contains the following operating functions:

- Local fuel control lever.

This is directly connected to the fuel linkage. The fuel control lever can be moved by either a direct input, or by selecting a fixed step on the right of the fuel control lever.

- Emergency telegraph.

This is automatically linked with the bridge telegraph when the local control is selected by both the bridge and local control stations.

- Indicator cocks.

These can be opened or closed. The cocks would be opened during engine shut down, and closed when the engine is started.

- Auxiliary Blowers.

These can be stopped or started in manual control, as well as being placed in automatic control for blower stop and start via the pressure switch on the scavenge air manifold.

- Turning gear engage and disengage.

Once the turning gear is engaged, it can be started to turn the engine before the engine is started.

This will ensure that no water has collected within the main engine cylinders (the indicator cocks should be opened whilst the turning gear is operating).

There are status indicators for:

- Fuel puncture valve.

The stop command for the engine will open the puncture valves. When the engine is running normally the puncture valves will be closed.

7.3. VLCC PROPULSION MACHINERY 7.43

Figure 7.21: AutoChief main engine control system.

- Camshaft position.

This indicates whether the camshaft is in the ahead or astern position.

- ME failure status.

This indicates locally whether there is a shut-down, slow-down or failure present.

All three main engine protection system can be reset at this local panel.

Starting procedure of the main engine at the local panel:

1. The local control is selected at either the Engine Control Room or Bridge. This will cause the local station indicator to flash.

2. The command is accepted at the local control panel. This will cause the local station indicator to remain lit.

3. The bridge should select ECR stand-By to indicate that engine operations are required.

4. The turning gear should be disengaged;

5. The indicators cocks should be closed;

6. The manoeuvring system should be prepared;

7. The ME Failure status should be checked, and any failure reset (f the failure can not be reset then the ECR panel should be consulted);

8. The auxiliary blowers should be placed on automatic, and the auxiliary blowers should start;

7.44

CHAPTER 7. DIESEL ENGINES

9. The emergency telegraph should be observed, and any command from the bridge acknowledged;

10. The fuel lever should be moved away from the stop position to fulfil the bridge request (the puncture valve will automatically close).

Before starting the engine after prolonged stop, always “blow through” engine with starting air with the indicator cocks open.

7.3.12

Load diagram

The load diagram is used to provide a graphical representation of the engine power and speed at any given time of the engine operation. Logarithmic scales are used for both power and speed, so that the relationship N e

= n

3 between them for a fixed pitch propeller installation can be shown as a straight line. The load diagram also provides valuable information about the limitations of engine operation.

Normally, the engine would be expected to operate within the limits of line 1-7 and 100% speed, but during shallow water operations, heavy weather, and during load-up periods, operation within lines

4-5-7-3 are permissible.

Figure 7.22: Main engine load diagram.

These specific lines are:

• Line 4 represents the limit of thermal loading that should be placed on the engine. Should the engine operate to the left of this line, then there is insufficient air for combustion, and hence this will impose a limitation of the torque the engine can produce at a given speed.

7.3. VLCC PROPULSION MACHINERY 7.45

• Line 5 represents the maximum mean effective pressure the engine can produce under continuous operation.

• Line 7 represents the maximum power the engine can produce under continuous conditions

(100% of Maximum Continuous Rating (MCR))

• Line 3 represents the maximum acceptable speed under continuous operation (105% of the given speed for that engine)

• Line 8 represents an overload condition of the engine.

The engine is designed to be able to operate for 1 hour in 12 between the lines 4 and 8, but in moderately heavy weather engine overload would easily occur when operating close to line 4 due the varying load imposed on the engine.

Within this normal operating range, the lines of 1, 2 and 6 represent the relationship of N e

= n

3

, thus reflect the expected operation of the engine for various conditions.

Line 1 represents the expected operation of the engine with the shaft alternator operating. This line passes through the optimisation point of the propeller / engine set-up, where the maximum fuel efficiency of the engine will occur.

Line 2 represents the operation of the engine when the shaft-alternator is not operating. This will reduce the power output of the engine, whilst it still delivers the expected speed.

Line 6 represents the light running operations of the engine. It is at this condition that the engine

/ propeller would be expected to operate at sea trails. However once delivered the expected fouling of the hull, propeller and engine, combined with the weather and wind condition will dictate that for a given speed output a higher power output is required.

By illustrating the original clean set-up of the engine, then the engineer can quickly see how much deterioration has occurred, and hence decide when cleaning of the hull, propeller and engine is required. Note that operation with increasing hull fouling will cause the engine to operate in an overload condition, i.e. to the left of line 8.

The other points to note on this diagram are:

- Point A - this represents the intersection between the expected operation line 6 and the maximum power line 7;

- Point M - this represents the maximum continuous rating (MCR) of the engine as specified by the engine manufacturer, thus for this engine this will be 16MW at 74 rev/min.

The load diagram can be used to determine when the engine is overloaded due to environmental conditions. Note this does not need to occur when the engine is developing excess power, as most damage occurs when operating to the left of line 8. The load diagram can also be used to the assess the effectiveness of the load limiters. They should prevent operation to the left of line 4. If the engine was initially loaded on line 2 then when the engine is loaded up, the speed power relationship will leave this line and move closer to line 4, especially if the shaft alternator is operating. The load limiter parameters must be adjusted if the engine load diagram indicates operation to the left of line 4 during

7.46

CHAPTER 7. DIESEL ENGINES load-up conditions. This will extend the time taken for the engine and vessel to speed up, but should prevent premature damage to the cylinder combustion components.

7.3.13

Cylinder diagram indicators

The cylinder indicator is used to enable regular monitoring of the engine cylinders. Faults within the combustion system can be located. There are four different displays that can be selected to indicate the cylinder pressure conditions, namely pressure/angle (also called a draw card or out of phase diagram), pressure/volume (also called a power card, or in-phase diagram), the weak spring diagram, and the delta pressure/angle diagram. Each diagram can be used to illustrate differing combustion traits.

Pressure/Angle

The pressure/angle diagram would be used for:

- Display the compression pressure curve, for comparisons with the other cylinders, to indicate cylinder sealing efficiency;

- Display the approximate timing of the fuel ignition;

- Display the fuel pressure trace, using the alternate pressure measurements of 0-3000bar.

Figure 7.23: Diagram pressure vs. angle indicator panel.

To enable the cylinder indicator to measure the combustion pressure, the following actions are required:

7.3. VLCC PROPULSION MACHINERY 7.47

1. Select one of the field button (I1 to I5) in the INDICATE column

2. Type in your identifying comments in the INDICATE field to aid future fault identification.

3. Select the same field button (I1 to I5) in the SELECT CURVE column. Either the blue, magenta, or brown curve can be selected.

4. Select the cylinder 1 to 5 that you wish to be measured.

Using cylinder 2 as an example, to measure and compare the same cylinder after a period of operation, or when a malfunction is present:

1. Carry out the tasks 1 to 3 above using the blue curve column and I2.

2. Select cylinder 2 to measure.

3. Select another field button (not chosen in point 1 such as I3) in the Indicate column.

4. Type in your identifying comments in the Indicate field.

5. Select I3 in Select Curve of the magenta column.

6. Select cylinder 2 to measure the combustion parameters of cylinder 2 again.

The following parameters are displayed in the numeric data display, at the instant when the cylinder indicator is taken, once a cylinder is selected together with the two indicate (I) buttons:

Speed

This is the engine speed (rpm).

Index

This is a measure of the fuel index

MIP

This is the Mean Indicated Pressure (MIP) measured in bar. This pressure is the equivalent pressure that acts on the piston throughout its vertical power stroke.

IkW

This is the indicated power of the cylinder.

TIGN

This is the timing of the ignition. The time between the TINJO and TIGN indicates the ignition delay present for that cycle. Increasing ignition delays will cause increased PMAX and large delta pressure/angle.

PMAX

This is the maximum pressure present during the working cycle. This will be affected by the quantity and timing of the fuel admission.

TMAX

This is the position of the maximum temperature during the working cycle.

7.48

CHAPTER 7. DIESEL ENGINES

PCOMPR

This is the pressure due to compression alone after the compression stroke. It provides valuable information to the efficiency of the compression stroke, and the sealing efficiency of the piston rings, liner, and cylinder cover valves.

PINJO

This is the fuel pressure when the fuel injector opens. It provides useful information that the fuel injector is correctly adjusted.

PINJM

This is the maximum fuel pressure generated by the fuel pump. This indicates the internal sealing properties of the pump, and whether internal wear is present.

TINJO

This is the timing of the fuel injection. The fuel pump timing will change when the VIT operation is selected, but it should be similar for all fuel pumps.

LINJ

This is the length of the fuel injection period, and is dependant on the setting of the fuel control lever.

On the lower part of the diagram, the button ZOOM can be used to zoom the diagram in horizontal direction to 300%. The button SPREAD is used to move overlaying curves apart vertically.

Figure 7.24: Diagram pressure vs. volume indicator panel.

7.3. VLCC PROPULSION MACHINERY 7.49

Press/Volume

The pressure/volume diagram displays the classical p-V diagram used in thermodynamic calculations to measure the power produced within a cylinder. The x axis displays the swept volume of the piston.

The pressure/volume diagram would be used for:

- Display the classical power diagram, where the area within the diagram equates to the power developed by that power stroke.

- Display the maximum pressure

- Display the expansion curve and thus indicating whether there is slow burning fuel or afterburning of the cylinder combustion products present.

To enable the pressure indicator to measure the same procedure is required as for any of the cylinder indication screens. Once one screen has been activated, then ALL screens will indicate the same numerical information on the left side of the screen display, although the graphical information will change.

Figure 7.25: Weak spring diagram.

Weak spring diagram

The weak spring diagram displays the scavenging process of the cylinder. The graphical display identifies the position of the opening of the exhaust valve, the opening and closing of the scavenge ports (same point before and after bottom dead centre), and the closing of the exhaust valve.

7.50

CHAPTER 7. DIESEL ENGINES

The weak spring diagram would be used for:

- Display the effects of fouled scavenge ports;

- Display the effects of a leaking exhaust valve.

To improve the display two ZOOM buttons are present at the base of the screen. Button ZOOM 1 enlarges the pressure scale from 0-15 bar to 0-6 bar. Button ZOOM 2 enlarges the scale to 1.0 to 3.5

bar, and displays the actual pressure within the exhaust and scavenge manifolds as dotted horizontal lines.

Figure 7.26: Delta-press/angle diagram.

Delta-Press/Angle

The delta pressure/angle or pressure derivative graph is used to provide additional information about the combustion process by displaying the rate at which the pressure changes within the combustion chamber.

The delta pressure/angle diagram would be used for:

- Display the point when fuel ignition occurs;

- Measure the maximum rate of pressure rise within the cylinder, to prevent shock loading damage to the piston rings and crosshead bearings.

8

Steam Plants

8.1

Steam plant operation

8.1.1

Steam valves maneuvering

Although the fact that piping systems are built with generous safety factors, we should consider the operation of valves one of the most critical skills for boiler operation. At some time, you will be torn between standing there and doing your job and running away because all the piping in the plant is shaking and making banging sounds. Most of the time those banging and shaking incidents are due to improper operation of a valve. Sometimes, the problem is not involved in operating the valve, it is because it did not work or was left in the wrong position.

A concept that should be kept in mind is that we can not control pressure, temperature or level.

The only thing we can control is flow. We maintain the pressure in a boiler by controlling the flow of fuel and air. The level is maintained by controlling the feed water flow. Pressure, temperature, level, and other measures will increase or decrease only with a change in flow.

When manipulating valves on steam piping, it is important to remember that a cold line is either full of air or water. When shutting down a steam system, the space occupied by the steam has to be filled with something when the steam condenses, either air or water. In any piping system, water will descend to the lowest level if allowed. Every time we fill or drain a system we should follow a prescribed procedure that is proved successful for our plant. If it is a new plant, we will have to develop the procedures so we should think about how we have done others and apply our experience in producing a prescribed procedure for each piping system in the new plant.

The first step in filling a system is opening vents and drains. Keep in mind that they are never empty, usually they are filled with air and it is necessary to get it out. When shutting down a system we have to open the vents and drains so the liquid can drain out and the air can fill the space left by condensing steam. It is always important to open some vents first, a little steam escaping proves that the valve is open. Once you have closed a main steam valve to a piping system, the pressure

8.1

8.2

CHAPTER 8. STEAM PLANTS will drop quickly and a vacuum could be generated before you get a vent or drain valve open. Open the vents first and let a little steam escape because it is safer. On large systems, it may take several vents and drains to admit air fast enough to prevent pulling a vacuum. Any system containing large pieces of equipment (deaerators, tanks, heat exchangers, etc.) should be monitored closely as you shut them down to ensure a vacuum does not happen because the equipment is not necessarily designed for a vacuum and atmospheric pressure can crush them. Simply draining water, without venting a system can also create damaging vacuums. Draining a water system without venting tanks can result in all those tanks being crushed by atmospheric pressure because the water draining out left a vacuum.

Filling any large system, whether with water or steam, should be done with a valve installed for that purpose. Normally, it is a small valve mounted on the side of the shut-off valve but it can also be piped as a by-pass. Take the required time to fill the system properly.

Always open and close valves slowly and do not spin valves. Make some valve wrenches, Fig. 8.1,

all you need is different sizes of round stock, a vise to bend it, and, for larger sizes, a torch to heat the metal so you can bend it. Valve wrenches are not for closing valves, only for opening them. The standard construction includes drilling a hole for a hook for hanging the wrench near the valve for use when you need it.

Figure 8.1: Valve wrench.

We should always crack any valve as the first stage of opening it. To crack a valve means to open it until the disc lifts off the seat, creating a small opening for the fluid to flow through. When the valve is large, wait a moment to see what happens while preparing to spin it shut again, if systems start hammering and banging. In this case, the most important thing to remember is that it will do the same thing the next time so change the operating mode to eliminate that action thereafter.

One last comment on operating valves. When you open a valve you should always close the handle back one half, then back one quarter, turn. That way, anyone coming along behind you will be able to tell immediately if the valve is open because they will try to close it and it will make at least a quarter turn toward closed. If you leave the valve jammed open, someone can think it is closed because it does not spin that quarter turn. The important valves have a stem position indicator so we can see their position.

8.1. STEAM PLANT OPERATION 8.3

8.1.2

Plant start-up

As soon as steam appears at the boiler vent, open vents to remove air from the steam distribution system. If the boiler feed tank is fitted with a steam heating sparge line, it should be placed in operation after the boiler vent valve is closed. If it is a coil heater, it may be allowed to come up with the plant.

Open the vent valves on the deaerator wide before admitting steam. Open gradually the steam supply to the deaerator only after there is a constant flow of water to the boiler. Any sudden surges in water flow could rapidly produce a vacuum in the deaerator. Also avoid any rapid changes in facility steam consumption that could cause a drop in steam pressure. If a vacuum is formed the deaerator and its storage tank could be damaged. Once the deaerator pressure is up to normal, open the isolating valves wide so the steam pressure regulator can function and close the vent valve to its normal throttling position.

After automatic boiler operation, the normal operating levels of the condensate tank and deaerator may be restored if they were lowered for the start-up. Increase the level gradually to avoid any damage associated with a rush of cold inlet water. Open cooling water valves to any quench system. Open valves to put the continuous blow-down heat recovery system into operation.

Record the start-up activity in the log and begin monitoring the plant as required for normal operation. It is very important to note all problems that came up, changes in operating procedures that were required to accomplish the start-up or correct problems, and the conditions at various times during the process with the times noted.

8.1.3

Boiler water treatment

Oxygen is the main cause of corrosion in hotwell tanks, feedlines, feedpumps and boilers. If carbon dioxide is also present then the pH will be low, the water will tend to be acidic, and the rate of corrosion will be increased. Typically the corrosion is of the pitting type where, although the metal loss may not be great, deep penetration and perforation can occur in a short period. Elimination of the dissolved oxygen may be achieved by chemical or physical methods, but more usually by a combination of both.

Steam at pressures less than 1 bar is lighter than air and steam at 1 bar and above is heavier than air. It is one reason why we keep a high pressure boiler vent valve open until the pressure is above 1.7

bar and vent low pressure boilers until we are carrying a load, counting on the flow of steam to sweep the heavier air out of the boiler. The essential requirements to reduce corrosion are to maintain the feedwater at a pH of not less than 8.5 to 9, the lowest level at which carbon dioxide is absent, and to remove all traces of oxygen.

Water exposed to air can become saturated with oxygen, and the concentration will vary with temperature: the higher the temperature, the lower the oxygen content. The first step in feedwater treatment is to heat the water to remove the oxygen. Typically, a boiler feed water tank should be operated at 85

C to 90

C. This leaves an oxygen content of around 2 mg/litre. Operation at higher temperatures than this at atmospheric pressure is difficult due to the close proximity of saturation temperature and the probability of cavitation in the condensate pump. The addition of an oxygen

8.4

CHAPTER 8. STEAM PLANTS scavenging chemical, sodium sulphite or hydrazine, will remove the remaining oxygen and prevent corrosion.

8.2

Auxilliary systems

8.2.1

Condensers

The condenser sea water boxes are protected by sacrificial mild steel plates which must be renewed regularly. The tube plates should be examined at the same time, to ensure no erosion has taken place as a result of too high circulating water speed. Any leaking tubes will cause feed-water contamination, and where this is suspected the condenser must be tested.

Air ejectors will operate inefficiently if the nozzles are coated or eroded. Regularly, they should be inspected and cleaned or replaced if required. The vacuum retaining valve should be checked for air tightness and also the ejector casing.

VLCC plant

In the VLCC steam plant, the condensate from heating and miscellaneous services returns to a condensate filter and inspection tank and then flows to the feed water tank.

The condenser receives steam from:

- the dump valve;

- the turbo-generator;

- cargo and ballast pump turbines.

To improve plant performance, the condenser is operated in a vacuum condition, created and maintained by vacuum pumps. The condensate is pumped directly to the feed water tank.

Steam propulsion plant

Exhaust steam from the main turbines, turbine generators, dump valves and other auxiliaries is condensed under vacuum in the sea water cooled main condenser. The condensate produced is extracted by the main condensate water pumps and circulated through various heat exchangers before entering the deaerator which is located at a high point in the engine room.

From the main condenser to the main feed pump inlet, the condensate temperature is raised from approximately 30

C to 130

C. This temperature increase results from the use of otherwise waste heat in the gland condenser, condensate cooled fresh water generator and LP feed heater.

The vacuum of the main condenser is maintained by two mechanical vacuum pumps of the water ring type. Normally, only one is in operation at a time.

The steam inlet to the main condenser comes from the LP turbine or the astern turbine, the steam dump line, the back pressure system and the turbo-generators. The condensate is collected in the

8.2. AUXILLIARY SYSTEMS 8.5

Figure 8.2: Steam condenser on VLCC propulsion plant.

hotwell, below the condenser shell. Condensate pumps, designed to be self-cavitating, are provided for main and stand-by operation. The main condenser and deaerator levels are controlled by automatic valves for recirculation, dump and make-up. These valves are fitted after the gland steam condenser, ensuring a condensate flow through it at all times.

The condenser level is alarm monitored. The high level alarm will initiate the automatic start of the stand-by condensate pump. This pump will also automatically stop when the normal level is regained.

The condensate pump discharge pressure is alarm monitored, with low-low pressure initiating the change-over of the pumps.

During the operation of a LNG carrier, dump steam is produced while burning excess of boil-off gas. The steam is desuperheated and dumped to the main condenser. A water curtain is arranged in way of this exhaust to the main condenser, with the spray water for the curtain supplied from the condensate line.

Sea water cooling to the main and atmospheric condensers is supplied by electrically driven centrifugal pumps or by the scoop, when the ship speed is greater than 10 knts. The main sea water circulating pumps take suction from the high or low sea chests. The draft of the vessel will indicate which sea chest to use. Sea chests, sea water lines and all sea water cooled condensers are protected from environmental hazards by an anti-fouling system. MGPS units inject anti-fouling products into all sea chests and then circulated through out the sea water system.

Two auxiliary sea water pumps supply cooling for the central cooling system and the main condenser vacuum pumps. The central cooling system provides cooling for:

- Main turbine lub oil system;

8.6

- Feed pumps lub oil systems;

- Drains;

- Turbo generator lub oil systems.

CHAPTER 8. STEAM PLANTS

Figure 8.3: Main condenser system.

The procedure to start the main condenser system is as follows:

- Line-up the main condenser and start main sea water circulation pump;

- Initial filling of the main condenser is made by direct drop from the distilled water tanks through filling valve;

- Ensure the condensate recirculation valve is operational, inlet and outlet valves open, gland condenser by-passed;

- Line-up and start a condensate pump;

- Line-up and start one main vacuum pump, bringing it into operation and raise the condenser vacuum;

- Ensure the condenser level control valve is operating correctly in AUTO;

- Line-up the feed inlet to the gland condenser, vent-off the unit, open the outlet valve and close the by-pass and vent valves;

- Open all valves on the second condensate pump, place it in stand-by mode and, when opportune, check that the auto cut-in operation is working;

- Continue to raise the main condenser vacuum, bringing into service the gland steam system.

8.2. AUXILLIARY SYSTEMS 8.7

8.2.2

Feedwater system

Condensate system

The condensate from the main condenser can be heated in the distiller condenser before it is used for cooling the gland condenser and finally, to be pre-heated in the LP feed water heater. The gland condenser receives steam from the following sources:

- Main turbine gland sealing;

- Feed water pumps gland sealing;

- Turbo generator gland sealing;

- Deaerator air extraction.

An electric fan keeps a small sub-atmospheric pressure in the gland steam condenser. The water level in this condenser is maintained by gravity driven discharge of condensate to the atmospheric drain tank.

The LP feed water heater receives steam from the LP bleed. The condensate level in the LP feed heater is controlled by automatic drain valves to the atmospheric drain tank or, in emergency, returned to the main condenser. The emergency drain valve is controlled by the same controller that controls the atmospheric drain valve. The feed water heater is vented to the main condenser.

Condensate from the distillers and atmospheric condenser are also returned to the atmospheric drain tank for recirculation by the drain pumps.

This system operates together with the main condensate system, where condensate from both systems join before entering the deaerator. The deaerator level control operates with the combination of both systems. Water enters the system, from the distilled water tank, in the atmospheric drain tank via the make-up valve. A direct line, from the distilled water tank to the main condenser, permits the initial filling of the condenser.

The feed water drain tank has two normal duty pumps fitted. The feed water is pumped by the in-use pump, through the feed water drain tank control valve, which maintains the feed water drain tank level. The pumps have a recirculation line back to the feed water drains tank, via an orifice plate, which ensures the pumps do not run dry. If the tank level becomes high, the stand-by drain pump will automatically start, and stop again when the tank level returns to normal. The atmospheric drain tank also has a larger capacity dump/drains pump fitted. This pump starts automatically on high-high level of the drain tank. These pumps can also supply spray water to the desuperheaters.

To start-up, line-up the valves on the pumps of the atmospheric drain tank system, ensuring that the pump and recirculation valves to return water to the tank are open. Ensure that the inlet and outlet valves to the distilled tank are open, as well as the valve on the distilled tank. Allow the drains tank to fill to normal level. When the normal level is reached, start-up a pump to discharge water to the deaerator. When the correct deaerator level is achieved, the control valve should open to maintain this level. Extraction pumps should be checked regularly to ensure that the sealing arrangements are

8.8

CHAPTER 8. STEAM PLANTS

Figure 8.4: Condensate system.

preventing air from entering the system. It is usual with most types of glands to permit a slight leakage of water to ensure lubrication of the shaft and the gland.

High pressure system

During normal operation, the feed water system must maintain a mass balance between feed water inlet and steam outlet, together with a normal water level in the boiler.

Deaerator

The deaerator is a contact feed water heater, feed water deaerator and feed system header tank, providing a positive inlet head for the main feed pumps. The main functions of the deaerator are:

- Remove dissolved oxygen from the condensate;

- Act as a regenerative feed water pre-heater;

- Serve as a water reservoir for the boilers;

- Serve as a feed water pumps suction pressure stabiliser to avoid cavitation.

The oxygen is removed by direct contact steam heating. Feed water from the condensate systems enters the deaerator and mixes with the steam supplied from the back pressure line. As the two mediums are mixed, as well as raising the water temperature, the nozzles break the water into very small droplets, releasing air and any other non-condensable gases. These, together with any associated water vapour, are drawn off to the gland condenser, where the water vapour is condensed and returned to the feed system and the non-condensable gases are extracted to atmosphere by the gland exhaust

8.2. AUXILLIARY SYSTEMS 8.9

Figure 8.5: High pressure feedwater system.

Figure 8.6: Dearator schematics.

fan and vented to atmosphere. A safety valve is included to protect from over-pressure. Water outlet from the deaerator is connected to main and electric feed water pumps and to the auxiliary boiler feed pump.

The steam cycle is a dynamic system and variations in flow require condensate make-up or spill.

The heated feed water is collected in the deaerator, which acts as a system header tank. The level is maintained in the deaerator by the automatic operation of the make-up and spill control valves in the condensate system.

8.10

CHAPTER 8. STEAM PLANTS

The deaerator level is controlled by the spilling of excess condensate back to the distilled water tanks at deaerator high level signal, and by accepting make-up to the system from the distilled water tanks at low level signal. The unit is also fitted with a low-low level alarm. The combination of feed spill/make-up and feed water drain tank control valves, are critical to ensure that the deaerator water level remains at a satisfactory level. The location of the deaerator high up in the engine room, provides the main feed pumps with a positive suction head of water.

Feed water treatment chemicals are injected into the drop line to the main feed pumps to remove any remaining traces of oxygen in the feed water.

Feed water pumps

There are three boiler feed water pumps, Fig. 8.7. One is driven by an electric motor and the

two other pumps are steam turbine driven. Just one pump is normally in operation at a time. The electrically driven feed pump is normally only used for cold start operations.

Steam to the feed water pump turbines is supplied from the auxiliary steam line. To protect the pumps from cavitation at low flow, a recirculation line, controlled by a signal of the measured total feed water flow, is included. An automatic control valve opens to allow the feed pumps to recirculate water back to the deaerator, when the boilers are operating at low load.

Figure 8.7: Feed water pumps.

Automatic start is provided for the stand-by turbine pump. For initial start, each pump is fitted with an electrical lubricating oil pump but, once running, a shaft driven pump provides the lubrication oil circulating pressure. The electrical lube oil pump will stop automatically when the shaft driven pump delivers the correct pressure. The electrical lubricating oil pump only provides oil pressure to lift the steam governor valve, and not as a back-up to the shaft driven pump.

8.2. AUXILLIARY SYSTEMS 8.11

Each turbine driven pump has a lubricating system, consisting of:

- Lube oil sump;

- Shaft driven lube oil pump;

- Electric lube oil pump for start;

- Lube oil filters;

- Lube oil cooler.

Draining valves for the turbine casing and for the steam supply line are provided, and also a gland sealing leak-off valve. The exhaust steam from the pump turbines goes to the back pressure system.

The pump speed is controlled by a speed governor. The speed setting can be local or remote.

In remote control mode, the speed set-point is given by a PID controller which maintains constant pressure before the feed water valve.

A safety system will cause the turbine to trip at:

- Overspeed;

- Low lube oil pressure;

- High lube oil temperature;

- High steam back pressure;

- High boiler drum level.

Before start a feed water pump, line-up boiler feed water valves and check if deaerator outlet valve is open. To turbine driven pumps, the starting procedure is as follows:

- Set feed water pump speed governor in LOCAL and set-point to 6000 rpm;

- Line-up lube oil system, including cooling;

- Open feed water pump suction valve;

- Open feed water pump recirculation/stop valve;

- Drain turbine casing;

- Drain steam line;

- Open gland bleeder valve;

- Open steam exhaust stop valve;

- Check and reset trip;

- Open steam supply stop valve;

- Start feed water pump, observing:

- Auto start of lube oil starting pump;

8.12

CHAPTER 8. STEAM PLANTS

- Turbine running;

- Feed water pump discharge pressure;

- Open feed water pump discharge valve and observe that pressure is increasing;

- Check deaerator inlet valve is open and set recirculation control to AUTO;

- Set feed water pump speed governor in AUTO;

- Set feed water pump speed governor in REMOTE;

- Set second feed water pump in stand-by.

Turbo-feed pumps are started with the discharge valve closed in order to build-up pressure rapidly and bring the hydraulic balance into operation. The turbine driving the pump will require warming through with the drains open before running up to speed and then closing the drains. The turbine overspeed trip should be checked regularly for correct operation and axial clearances should be measured with a special gauge.

8.2.3

General service steam system

A low pressure steam generator is provided, where low pressure steam of 8 bar is generated for auxiliary services. This general service steam system is completely disconnected from the main steam system to prevent the boiler and steam system from contaminated drains.

The steam generator produces low pressure steam to be used for the following purposes:

- Heating of heavy fuel oil to boilers;

- Bunker and cargo tanks heating;

- Accommodation heating;

- Boil-off gas heater;

- Forcing vaporizer;

- Glycol heating system;

- LO heater for compressors.

The primary steam to the LP steam generator is normally supplied from the HP bleeder. If the main turbine bleeder pressure is too low, steam is provided from the internal desuperheater through a pressure reduction valve.

The flow of primary steam to the steam generator drum is automatically controlled to keep the secondary steam pressure constant. The condensate from the heat exchanger is sub-cooled in a separate drain cooler before it is discharged to the deaerator. The primary condensate discharge rate is controlled so that the drain cooler is always filled with water. Secondary condensate drain from miscellaneous heaters is cooled and collected in the inspection tank. This is designed for easy observation and removal of possible oil contamination. The drain leads to the LP steam generator fresh water tank.

8.2. AUXILLIARY SYSTEMS 8.13

The tank level is automatically maintained from the distilled water tank to compensate any losses. The feed water is transferred from the FW tank to the LP steam generator by the LP feed water pumps.

The water from the pumps passes through the primary drain cooler for pre-heating, before it is fed to the steam drum. The water level in the steam drum is controlled by the secondary feed water control.

The procedure for the operation of the general service steam generator is as follows:

- Open the distilled tank outlet and set the feed water level control to AUTO to replenish feed water automatically;

- Line-up the LP feed water pumps and fill the steam generator to the normal level;

- Set the level control to AUTO before supplying heating steam to LP steam generator;

- Open the heating steam valves;

- Slightly open the primary steam heating control valve manually;

- Close vent valve when pressure reaches 1 bar;

- Gradually open the primary steam heating steam control valve until the downstream pressure reaches up to 10 bar;

- After confirming secondary steam generating, switch the primary steam heating steam flow control valve to AUTO.

Figure 8.8: General service steam system.

8.14

CHAPTER 8. STEAM PLANTS

8.3

Steam systems

All the steam requirements for the vessel are generated by the two main boilers. Steam from the steam drum is led to the primary superheater section through an orifice where the pressure drop is measured and converted to a signal for steam flow. The steam then flows through the primary section of the superheater and to the secondary superheater section. Taking some steam from the primary superheater and leading it through the temperature control desuperheater, situated in the water drum, regulates the outlet temperature of the steam. The control valve regulates the outlet from the desuperheater to the secondary superheater, depending on the temperature on the superheated steam leaving the boiler.

To ensure that there is always a flow through the secondary superheater a line, fitted with an orifice, by-passes the temperature control desuperheater and the control valve.

The piping from the main boiler superheater outlet is branched into three separate steam lines:

- Main superheated steam line;

- Auxiliary superheated steam line;

- Desuperheated steam line.

Figure 8.9: Steam systems.

8.3.1

Superheated lines

The main steam line supplies main turbines. The auxiliary steam line supplies the turbo-generators and the feed water pumps turbines. Special care must be taken when manoeuvring drain valves for warming and preparing steam lines before use.

8.3. STEAM SYSTEMS 8.15

8.3.2

Desuperheated line

The desuperheated steam line uses an internal desuperheater, located in the boiler steam drum, to desuperheat the steam for:

- sootblowing of main boilers;

- heating steam to the LP steam generator;

- make-up steam to the back pressure system.

Desuperheated steam is also released to one of the condensers by the steam dump system, when necessary, to prevent boiler overpressure.

8.3.3

Back pressure line

The steam supply to the back pressure system is the exhaust from the feed water pump turbines. The pressure is controlled by make-up steam from the IP bleeder or desuperheated steam line if main turbine is not in use. During manoeuvring, the IP bleeder line is also closed.

Figure 8.10: Back pressure steam system.

A drain valve is provided for preparation of the system before start. High pressure in this line is controlled by steam dumping to the main or atmospheric condenser. The back pressure line is protected by a safety valve. The back pressure steam system supplies steam to:

- Deaerator heating;

- Sea water cooled distiller;

8.16

CHAPTER 8. STEAM PLANTS

- Boiler combustion air heating.

Desuperheated steam also supplies the 16 bar HP service steam via a reducing valve. The HP service steam supplies:

- Boiler atomizing steam;

- Emergency supply to HFO heating;

- Heating steam to main turbines;

- Gland steam to turbo-generators.

8.3.4

Steam dump

The main boilers burn excess boil-off gas produced from the cargo. If the boil-off gas produced exceeds the requirements for normal steam production then the steam production is increased and the excess steam produced is dumped to the main condenser or atmospheric condenser via the steam dump system.

The dump system operates by venting the desuperheated steam to the condensers via silencers and external desuperheaters. The spray water for the desuperheater sprays is supplied from the discharge of main condensate and the drain pump.

Desuperheaters can discharge to the atmospheric condenser whenever the main condenser is unavailable. The temperature at the outlet from the desuperheater is measured and a corresponding signal is transmitted to the spray control valve, which alters the water supply accordingly.

Steam to the desuperheaters is supplied via an automatically controlled valve. Each desuperheater has its own control valve. The valve closes if any of the following conditions are detected:

- Main condenser pressure high;

- Main condenser sea water temperature high;

- Manual dump trip;

- Atmospheric condenser pressure high;

- Both inlet valves to condensers closed.

The operating procedure for this system is as follows:

- Make sure that the spray control valves are in AUTO mode;

- Line-up spray water line from the main condensate pump or drain pump;

- Open the desuperheater discharge valve to the main condenser or atmospheric condenser;

- Open the main supply valve to the desuperheaters;

- Make sure that the dump steam flow control valves are in AUTO mode.

8.4. OPERATION OF STEAM TURBINES 8.17

High boiler pressure

The main dump external desuperheaters are automatically controlled. The control valve to the desuperheater will open when the boiler pressure exceeds its normal set point providing stability during periods of fluctuation where the burners are reduced to minimum flow; when big load changing such as during manoeuvring, crash astern/ahead and emergency stop of the main turbine. The dump will control any excess steam pressure generated during these periods.

High tank pressure

In LNG carriers, if demand for steam is insufficient to consume all the boil-off gas from the cargo tanks, the firing rate of the gas burners will be increased accordingly and any excess steam dumped to the main condenser.

The amount of steam dumped depends on the steam consumption for the plant and the recommended excess boil-off gas amount signal from cargo part. The dump signal from the cargo tank part is inhibited when burning fuel oil only.

Figure 8.11: Steam dump systems.

8.4

Operation of steam turbines

8.4.1

Main engine description

The ahead and astern throttle valves are normally controlled from the turbine remote control panel.

When in LOCAL control, the engineer has direct control of the ahead and astern valve positions by

8.18

CHAPTER 8. STEAM PLANTS decrease/increase commands. The starboard and port nozzle group of the HP turbine can be opened or closed manually.

Isolating valves shut-off the main and emergency steam supply. There are steam bleeders on both the HP and the LP turbine and from the cross over pipe. The control of the bleeder valves is automatic or manual, selected from the remote panel. The HP bleeder supplies steam to the LP steam generator.

The intermediate bleeder supplies steam to the back pressure system. The LP bleeder supplies steam to the LP feed water heater and to the condensate cooled distiller.

Figure 8.12: Main turbines and reduction gears.

The drawing in Fig. 8.12 shows how the HP and LP turbines are coupled to the propeller shaft via

the epicyclical main reduction gear. The speed reduction from the HP turbine is performed in three stages, and the speed reduction from the LP turbine in two stages.

The thrust from the propeller is transmitted to the ship’s hull by the thrust bearing. The thrust bearing is lubricated from the main gear lubricatiing oil system. The turning gear, driven by an electric motor, can be engaged to the LP reduction gear end. The turning gear is operated during short stand still periods for lubrication of the gears and temperature distribution on the turbines.

Figure 8.13 shows details of the governing valve assembly, nozzle ring groups and valves to be

used for heating and draining before start of the turbine. Drain valves are provided for main and emergency steam lines and for the governing valve assembly casing. The leak control valve is for venting of possible steam between the astern control valve and the guardian valve. A pressure buildup in the space between these valves indicates a leaking astern valve. High pressure signal inhibits the opening of the ahead valve. Before the automatic cycling program for preheating of the turbines is started, the nozzle groups should be preheated by using the by-pass heating valve shown.

Gland sealing steam is supplied by the HP service line. The pressure is controlled by a supply

8.4. OPERATION OF STEAM TURBINES 8.19

Figure 8.13: Heat and drain system.

valve and bypass direct to the gland steam condenser. Before start-up, the gland exhaust shut-off valves must be opened, one at each bearing. Valves for draining the LP and HP turbines casing must be open during turbine warm-up.

Figure 8.14: Gland sealing system.

The lubricating oil system comprises:

- Sump tank;

8.20

CHAPTER 8. STEAM PLANTS

- Oil pumps;

- Oil coolers;

- Filters;

- Gravity tank;

- Lubricating points on turbines and gear;

- Oil supply to the thrust bearing.

Valves for oil filling or discharging are provided. A purifier for cleaning and pre-heating the lubricating oil is indicated. Normally, one electric LO pump operates in parallel with the shaft driven pump. The discharge pressure after the pumps is controlled by a pressure relief valve.

Figure 8.15: Lubricating system.

Two fresh water cooled lube oil coolers are provided. The oil temperature is controlled by a thermostatic valve, placed after the lube oil coolers. Before the oil enters the distribution pipe on the turbine casing it passes through a duplex oil filter. From the distribution pipe, lubricating oil is supplied to LP and HP turbine bearings, to reduction gear and to the thrust bearing. The lubricating

points and spray nozzles are indicated on Fig. 8.15. There is an emergency LO gravity tank, which is

capable of lubricating the turbine and gear bearings in case of failure of the normal oil supply, during the stopping period.

The safety system and the operation of ahead and astern manoeuvring valves require governing oil with adequate pressure. The governing oil is supplied by a pair of oil pumps. The pumps are electrically driven and have suction from the common oil sump tank. The governing oil pressure is set by a pressure relief valve.

8.4. OPERATION OF STEAM TURBINES 8.21

Figure 8.16: Safety system.

The guardian valve is automatically opened when the astern valve servo is opening. A simultaneous opening of the ahead and astern valve is inhibited. The servo oil pressure is reduced to zero if the trip system is activated, causing the steam throttle valves to close.

The trip system includes three basic parts:

- The overspeed relay, set by an emergency overspeed governor;

- An automatic trip valve;

- A manually operated trip valve.

The cause of a main turbine trip will be indicated on the turbine safety panel. The same information is indicated on the remote control panel of the main turbine. Any turbine trip has to be reset locally. All major measured variables are displayed, on analogue instruments, or on digital indicators.

Push-buttons for control responsibility transfer are included.

When the turbine plant is operated from the engine control room, any order will be given from the bridge telegraph. The desired shaft rotation speed will also be indicated at the local manoeuvring stand. The main turbine remote control system has three modes of operation:

- Warm-up;

- Manoeuvring;

- Normal power.

In warm-up mode, the main turbine is heated by automatic “rocking” of the turbine in ahead and astern direction. In manoeuvre mode, the maximum speed available for 100% lever position is

8.22

CHAPTER 8. STEAM PLANTS

Figure 8.17: Remote control panel.

reduced. In the normal power mode, the ahead and astern throttle valves are controlled according to speed lever signal and measured turbine revolution. A manual mode is available, in addition to the automatic ones, when the astern and ahead throttle valve positions can be controlled by direct increase or decrease commands.

The main turbine’s safety system works independently of the remote control system. A turbine trip signal causes the throttle valves to close immediately. The cause of a turbine trip is indicated on the control panel. It has to be reset on a corresponding trip indication panel at the local manoeuvring stand. Turbine trip is caused by:

- HP/LP turbine overspeed;

- HP/LP turbine rotor axial displacement;

- HP/LP turbine high vibration;

- Low lube oil pressure;

- High condenser water level;

- Low condenser vacuum;

- High speed during idling.

The opening and closing of the turbine steam bleeder valves can be automatically controlled. The opening/closing logic is connected to the HP turbine governing stage pressure.

8.4. OPERATION OF STEAM TURBINES 8.23

8.4.2

Warming-through a steam turbine

The steam turbine requires a considerable period for warming-through prior to any manoeuvring taking place. The operation of the turbine requires great care during manoeuvring.

Firstly, open all the turbine-casing and main steam line drain valves and ensure that all the steam control valves at the manoeuvring station and around the turbine are closed. All bled steam-line drain valves should be opened. Start the lubricating oil pump and see if the oil is flowing freely to each bearing and gear sprayer, venting off air if necessary and check that the gravity tank is overflowing.

Obtain clearance from the bridge to turn the propeller shaft. Engage the turning gear and rotate the turbines in each direction. Start the sea water circulating pump for the main condenser. Then start the condensate extraction pump with the air ejector recirculation valve wide open. Open the manoeuvring valve by-pass or “warming through” valve, if fitted. This allows a small quantity of steam to pass through the turbine and heat it. Raising a small vacuum in the condenser will assist this warming through. The turbines should be continuously turned with the turning gear until a temperature of about 75

C is reached at the LP turbine inlet. The expansion arrangements on the turbine, to allow freedom of movement, should be checked.

Gland sealing steam should now be partially opened up and the vacuum increased. The turning gear should now be disengaged. Short blasts of steam are now admitted to the turbine through the main valve to spin the propeller about one revolution. This should be repeated about every three to five minutes for a period of 15 to 30 minutes. The vacuum can now be raised to its operational value and also the gland steam pressure. The turbines are now ready for use.

While waiting for the first movements from the bridge, and between movements, the turbine must be turned ahead once every five minutes by steam blasts. If there is any delay gland steam and the vacuum should be reduced.

8.4.3

Manoeuvring

Once warmed through, the turbine rotor must not remain stationary more than a few minutes at a time because the rotor could sag or distort, which would lead to failure, if not regularly rotated.

Astern operation involves admitting steam to the astern turbines. Where any considerable period of astern running occurs turbine temperatures, noise levels, bearings, etc., must be closely observed. The turbine manufacturer may set a time limit of about 30 minutes on continuous running astern.

8.4.4

Emergency astern operation

If, when travelling at full speed ahead, an order for an emergency stop or astern movement is required then safe operating procedures must be ignored. Ahead steam is shut off, probably by the use of an emergency trip, and the astern steam valve is partly opened to admit a gradually increasing amount of steam. The turbine can thus be brought quickly to a stopped condition and if required can then be operated astern.

8.24

CHAPTER 8. STEAM PLANTS

The stopping of the turbine or its astern operation will occur about 10 to 15 minutes before a similar state will occur for the ship. The use of emergency procedures can lead to serious damage in the turbine, gearbox or boilers.

8.4.5

Full away

Manoeuvring revolutions are usually about 80% of the full away or full speed condition. Once the full away order is received, the turbine can gradually be brought up to full power operation, a process taking one to two hours. This will also involve bringing into use turbo-alternators which use steam removed or “bled” at some stage from the main turbines.

Checks should be made on expansion arrangements, drains should be checked to be closed, the condensate recirculation valve after the air ejector should be closed, and the astern steam valves tightly closed,

8.4.6

Port arrival

Prior to arriving at a port the bridge should provide one to two hours notice to enable the turbines to be brought down to manoeuvring revolutions. The full away procedure should now be done in reverse order. Another turbo-alternator or a diesel alternator will have to be started.

Bibliography

[1] Arild Hermansen. ERS MAN B&W 5L90MC-L11 Machinery & Operation MC90-IV. Kongsberg

Maritime, 2006.

[2] Harald Kluken. ERS SP Dual Fuel Machinery & Operation. Kongsberg Maritime, 2007.

[3] H. McGeorge. Marine Auxiliary Machinery. Butterworth, 2002.

[4] D. A. Taylor. Introduction to Marine Engineering. Elsevier, 2003.

[5] Kenneth E. Heselton. Boiler Operator’s Handbook. The Fairmont Press, Inc., 2005.

9.1

9.2

BIBLIOGRAPHY

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