A Feasibility Study into the Use of Marine Gas Engines for Cogeneration

A Feasibility Study into the Use of Marine Gas Engines for Cogeneration
A feasibility study into
the use of
marine gas engines for
cogeneration.
A Thesis presented in partial fulfilment of the
Degree of Master of Science
in
Energy Systems and the Environment.
By Andrew Miller (BENG, MIIE).
Department of Mechanical Engineering,
University of Strathclyde,
Glasgow.
September 2004.
1
DECLARATION OF AUTHOR’S RIGHTS.
The copyright of this thesis belongs to the author under the terms of the United Kingdom
Copyright Acts as qualified by the University of Strathclyde Regulation 3.49.
Due acknowledgement must always be made of the use of any material contained in, or
derived from, this thesis.
2
COPYRIGHT ON DRAWINGS.
The engineering drawings that are contained within this thesis are subject to copyright and
must not be placed at the disposal of any unauthorised third party, otherwise the Author and
the University of Strathclyde maybe subject to legal action.
3
ACKNOWLEDGEMENTS.
I would like to thank the following people for their assistance in the writing of this thesis:
•
Dr. Paul Strachan, Senior Lecturer, Department of Mechanical Engineering, University
of Strathclyde, for acting in his professional capacity as my Project Supervisor.
•
Mr Sean Daniels, Sales Manager, Senior Thermal Engineering, for providing technical
information on waste heat recovery boilers.
•
Ms Ann Gardiner, Future Energy Solutions, for technical assistance with Combined
Heat and Power Quality Assurance Scheme rules and regulations.
4
ABSTRACT.
The aim of this thesis is to perform a feasibility study into the construction of a
cogeneration plant, to provide 9.5MWe of electricity and 8 tonnes per hour of process
steam, to meet the heat and power requirements of a large manufacturing company
that is based in the West Midlands, England, UK.
The plant currently imports its electricity from the national grid system and produces
its own steam, for process and heating requirements, from onsite oil fired package boilers.
However, the boiler plant is outdated and as part of the companys ongoing capital
investment programme, in order to comply with the Integrated Pollution Prevention
and Control Directive 1996, combined heat and power was identified as an alternative
to installing a new package boiler plant. A cogeneration plant would also offer the benefit
of independent power production for the site.
Through literature review, the cogeneration technologies that are currently available have
been studied and marine gas engines were identified as the best available technology to
meet the manufacturing plants needs.
A detailed study was then undertaken into the development of the cogeneration plant,
including a technical assessment of marine gas engines, a thermodynamic assessment
of the engines exhaust gas system and the waste heat recovery boiler, an assessment to
determine the plants eligibility to be considered as good quality combined heat and power
and a financial assessment, based on several natural gas fuel price and bank interest rate
scenarios.
Finally, an analysis was carried out to determine the carbon emissions savings that
could be achieved by the proposed plant and an environmental impact assessment
was undertaken, to ensure that the development would comply with the Local Planning
Authority guidelines.
5
TABLE OF CONTENTS.
Front Cover...........................................................................................................................1
Declaration of author‘s rights................................................................................................2
Copyright on drawings………………………………...............................................................3
Acknowledgements...............................................................................................................4
Abstract.................................................................................................................................5
Table of contents...................................................................................................................6
Introduction to thesis.............................................................................................................9
Methodology……………………………….............................................................................13
Chapter 1 - What is cogeneration?…………….………………………………........................14
1.1 - Types of cogeneration plant………………………………...................................15
1.2 - Power plant efficiencies……….……………..………………………………..........19
1.3 - Power plant carbon emissions…..………………………….................................21
1.4 - Advantages of using cogeneration……………………………….........................23
Chapter 2 - European Union installed cogeneration plant capacity………………………….25
2.1 - EU strategy on cogeneration.............................................................................28
2.2 - UK installed cogeneration plant capacity……....................................................31
2.3 - UK energy policy towards cogeneration…………………………………………...35
2.4 - UK emissions trading scheme………………………………................................39
2.5 - Power plant planning and consents procedures……………………………….....40
Chapter 3 - Cogeneration plant selection…....…………………............................................42
3.1 - Plant mains gas pressure reducing station……………………...........................45
3.2 - Gas engine design and development………………………..…..........................47
3.3 - Rigid and resilient engine mounting……………………………….......................53
3.4 - Turbochargers and air systems………………………………..............................54
6
3.5 - Fuel gas system……………………………….....................................................56
3.6 - Lubricating oil and cooling water systems………………………………..............57
3.7 - Exhaust gas system………………………………...............................................58
3.8 - Engine fire protection system……………………………….................................60
3.9 - Condensate return system and steam raising plant………………………………61
Chapter 4 - Technical evaluation overview………………………………...............................64
4.1 - Proposed site for the cogeneration plant………................................................65
4.2 - Gas engine manufacturers……………………………….....................................68
4.3 - Calculation of the exhaust pipe size and heat transfer coefficients...................71
4.4 - Calculations for the exhaust pipe heat loss………………………………............77
4.5 - Calculations for the steam production rate…………………………….................85
4.6 - Evaluation of the cogeneration plant operating conditions………………………90
4.7 - CHPQA Scheme technical calculations………………………………..................92
Chapter 5 - Financial appraisal for the proposed plant………………………………...........100
5.1 - Calculations for the plants carbon emissions savings………………………….110
Chapter 6 - Environmental impact assessment for the proposed plant…………………….115
6.1 - Environmental impact assessment continued………………………………......117
Chapter 7 - Discussion…………….....................................................................................121
7.1 - Conclusions………………………....................................................................123
7.2 - Direction of future work…………….................................................................124
References……………………………….............................................................................125
Bibliography………………………………............................................................................127
Appendix A - Industrial gas turbine technical data sheet……………………………...........128
Appendix B - Marine gas engine engineering drawing………………………………...........129
7
Appendix C - Marine gas engine technical data sheet………………………………...........130
Appendix D - Marine gas engine fuel consumption chart………………………………........131
Appendix E - ANSI pipe schedule chart………………………………..................................132
Appendices F1 to F4 - Planning permission application form.………………………………133
Appendices G1 to G4 - Environmental impact assessment form.…………………………..137
Appendices H1 to H2 - Cogeneration plant design stages…………………………….141-142
8
INTRODUCTION.
The overall aim of this thesis is to perform a feasibility study into the use of marine engines to
supply combined heat and power to a manufacturing site that is based in an industrial area of
the West Midlands, England, United Kingdom.
The cogeneration plant must be capable of continuous operation at a base-load of 9.5MWe
and should be able to produce up to 8 tonnes per hour of saturated steam at 7 bar pressure,
for the adjacent manufacturing sites process steam and heating requirements.
The cogeneration plant is to be designed for 25 years of operation and any surplus power
produced by the plant, will be sold to the national grid system.
During the winter period, the plant is expected to operate at 9.5MWe and to produce 8 tonnes
per hour of steam, 24 hours per day and during the spring period the plant shall operate at
9.5MWe and produce 8 tonnes per hour of steam, from 6am to 10pm in the evening.
During the summer period, the manufacturing plant will only require 9.5MWe of power and
8 tonnes per hour of steam, between 6am and 10am in the morning, as the plant shall be
undertaking its summer maintenance overhaul.
Finally, during the autumn period, the plant is expected to operate at 9.5MWe and 8 tonnes per
hour of steam, between 6am and 10pm in the evening.
The actual dates for which the seasonal electricity and heat profiles are based upon are detailed
in table 1.
The electricity and steam production profiles for the cogeneration plant on a seasonal basis are
outlined in figures 1 to 8.
Winter period
Spring period
Summer period
Autumn period
Ist Nov - 31st Jan
1st Feb - 30th April
1st May - 31st July
1st Aug - 31st Oct
Table 1 - Plant seasonal operation dates.
9
Power - MWe.
10
8
6
4
2
0
00:00
06:00
12:00
18:00
24:00
Time of day.
Steam T/Hr.
Figure 1 - Winter electricity generation profile.
10
8
6
4
2
0
00:00
06:00
12:00
18:00
24:00
Time of day.
Figure 2 - Winter steam production profile.
Power - MWe.
10
8
6
4
2
0
00:00
06:00
12:00
18:00
22:00
24:00
Time of day.
Figure 3 - Spring electricity generation profile.
10
Steam T/Hr.
10
8
6
4
2
0
00:00
06:00
12:00
18:00
22:00
24:00
Time of day.
Figure 4 - Spring steam production profile.
Power - MWe.
10
8
6
4
2
0
00:00
06:00
10:00
18:00
24:00
Time of day.
Figure 5 - Summer electricity generation profile.
Steam T/Hr.
10
8
6
4
2
0
00:00
06:00
10:00
18:00
24:00
Time of day.
Figure 6 - Summer steam production profile.
11
Power - MWe.
10
8
6
4
2
0
00:00
06:00
12:00
18:00
22:00
24:00
Time of day.
Figure 7 - Autumn electricity generation profile.
Steam T/Hr.
10
8
6
4
2
0
00:00
06:00
12:00
18:00
22:00
24:00
Time of day.
Figure 8 - Autumn steam production profile.
The steam that has been utilized in the manufacturing plants site will be returned to the
cogeneration plants feed-water storage vessel as hot water at 8 tonnes per hour, 60ºC
and 4 bar pressure.
12
METHODOLOGY.
In order to undertake a coherent feasibility study, the following objectives were set:
•
To research the engineering and scientific principles behind combined heat and power
production and to gain an overview of the types of commercially available cogeneration
plant.
•
To quantify the current installed cogeneration plant capacity in Europe and the
United Kingdom and to evaluate the current European Union and the British
Government’s policies towards cogeneration.
•
To develop an understanding of the Local Authority Planning and Consents procedures
for the construction of a 9.5MWe cogeneration plant.
•
Based, on the above literature review, to determine the best practicable means of
generating combined heat and power for the proposed site, including a technical
evaluation of the reciprocating engines that were selected for the plant.
•
To undertake a thermodynamic assessment into the design of a heat recovery steam
generator (waste heat boiler), in order to ensure that the plant can generate sufficient
steam to meet the manufacturing plants process requirements.
•
To assess the economic and financial risks associated with the proposed development
and to calculate the carbon emissions savings from the proposed plant.
•
To carry out an environmental impact assessment for the proposed development.
•
Finally, to present the overall conclusions from the research conducted, as to whether
the project is financially viable.
13
CHAPTER 1 - WHAT IS COGENERATION ?
Combined heat and power (CHP) or co-generation is a process that involves the
simultaneous generation of usable heat and power. The most widely used designs of
cogeneration plant are based upon reciprocating diesel or gas engines, gas turbines
and steam turbine plant [1].
The heat energy that is contained within the gas turbine and reciprocating engines flue
gases and from the steam turbine extractions (bled steam) can be recovered by passing
the exhaust gases or steam through a heat exchanger, to produce hot water or steam for
use in central heating systems, district heating systems, laundry plants and process plants.
The mechanical or shaft power that is produced by the reciprocating engine, gas turbine
or steam turbine is normally used to drive an alternator to produce electricity. However,
the power generated by the engine or turbine could also be used to drive a compressor,
reduction gearbox, ships propeller or other motive device instead.
The main advantages of using cogeneration plants to produce on-site heat and power are
that the process makes more efficient use of the fuel energy input and therefore increases
the power plant efficiency.
Furthermore, the cogeneration process produces significantly less carbon dioxide emissions
than would otherwise be produced from the separate production of heat using a package
boiler and from the generation of electricity using a large decentralised fossil fired power
station.
14
1.1 - TYPES OF COGENERATION PLANT.
There are five principle designs of cogeneration plant that are widely used around the world.
These are:
1. Reciprocating engine based cogeneration plant.
2. Gas turbine based cogeneration plant.
3. Combined cycle gas turbine based cogeneration plant.
4. Pass out, condensing steam turbine based cogeneration plant (POCO).
5. Back pressure steam turbine based cogeneration plant.
1.1.1 - RECIPROCATING ENGINE BASED PLANT.
The two designs of reciprocating engine that are used in this type of cogeneration plant
are the compression ignition diesel engine and the spark ignition gas engine [2,3].
The leading manufacturers of reciprocating engines for cogeneration are Man
(Burmeister & Wain), Rolls Royce (Allen and Bergen diesels), Perkins diesels and
Wartsila (Sulzer diesels).
These manufacturers produce a range of engines from 0.2MWe up to 20MWe, which
can run on coal bed methane, diesel oil, heavy fuel oils, landfill gas and natural gas.
The reciprocating engine is usually coupled to an alternator in order to generate electricity
and the engines exhaust gases are diverted through a heat exchanger to produce hot water
or small quantities of steam.
It is also possible to recover the low grade heat energy from the reciprocating engines
charge air, jacket water and lubricating oil cooling systems, in order to further increase
the cycle efficiency of the cogeneration plant. However, it is standard for most plants to
reject this heat energy to the atmosphere using a radiator type cooling system.
A typical reciprocating engine cogeneration plant would operate at an electrical efficiency
of 25% and would have the potential to recover up to 39% of the fuel input as useful heat
energy, based upon the gross calorific value of the fuel.
15
1.1.2 - INDUSTRIAL GAS TURBINE BASED PLANT.
The main type of gas turbines that are used in cogeneration plants are aero-derivative gas
turbines. These plants would normally run on natural gas or diesel oil, although other fuels
including naphtha can also be used.
The leading manufacturers of aero-derivative gas turbine plant are Caterpillar (Solar),
General Electric, Rolls Royce and Ruston (Siemens) gas turbines, whose turbines range
in power output from 3MWe to 50MWe [3,4].
These types of gas turbine are normally coupled to an alternator in order to generate
electricity and their exhaust gases are passed through a heat recovery steam generator
in order to produce large quantities of hot water or steam for heating or process requirements.
A standard industrial gas turbine cogeneration plant would normally operate at an electrical
efficiency of around 22% and would have the potential to recover up to 47% of the fuel input
as useful heat energy.
1.1.3 - COMBINED CYCLE GAS TURBINE BASED PLANT.
The two designs of combined cycle power plant are the single shaft and the multi-shaft
combined cycle plant. These plants would normally run on natural gas or diesel oil fuels.
The leading manufacturers of combined cycle power plants are Alstom (ABB), General
Electric and Siemens Westinghouse, whose gas turbines range in power output from
70MWe to 300MWe [5,6].
The single shaft design of power plant is more compact than a conventional combined cycle
power plant and offers additional cost benefits as only one alternator is required in order to
generate electricity.
With a multi-shaft combined cycle gas turbine power plant, there are normally one or more
gas turbines, each producing electricity and steam from their own separate alternator and
heat recovery steam generator. The steam is then fed to one large steam turbine in order
to generate additional electricity.
16
A standard combined cycle gas turbine power plant would have an electrical efficiency of
around 25%, with the potential to recover up to 49% of the fuel input as useful heat energy.
1.1.4 - PASS OUT, CONDENSING STEAM TURBINE BASED PLANT.
Steam would normally be produced in a coal, gas or oil fired boiler and would then be
expanded in a pass out condensing steam turbine (POCO).
During the expansion process, some of the steam is extracted from the turbine cylinder
at an intermediate pressure (bled steam) and then passed through a heat exchanger to
produce hot water or steam, for process or district heating requirements, before being
returned to the water / steam cycle as hot water [4].
The remainder of the steam would be fully expanded down to the condenser pressure,
before exiting the turbine casing (Hence the name - condensing steam turbine).
1.1.5 - BACK PRESSURE STEAM TURBINE BASED PLANT.
Steam would again be produced in a coal, gas or oil fired boiler, before entering the back
pressure steam turbine. The steam would then be either partly or wholly expanded in the
steam turbine, before being exhausted from the turbine casing at the required pressure for
the sites process steam requirements.
Pass out condensing steam turbine and back pressure cogeneration plant normally have
electrical efficiencies of between 10% and 13%, with 61% of the fuel input being available
as useful heat energy.
Table 2 illustrates the average electrical and thermal efficiencies for various types of
cogeneration plant [7].
17
CHP prime mover
Back pressure steam turbine
Pass out steam turbine
Gas turbine chp
Combined cycle gas turbine
Reciprocating engine
Average
Electrical
efficiency
(% GCV)
10
13
22
25
25
21
Heat
efficiency
(% GCV)
61
61
47
49
39
52
Overall
efficiency
(% GCV)
71
74
69
74
65
72
Table 2 - Cogeneration plant electrical and thermal efficiencies.
18
1.2 - POWER PLANT EFFICIENCIES.
As previously stated, one of the main advantages that cogeneration plants offer over
conventional power plants are that they are designed to able to recover the heat energy
from the reciprocating engine or gas turbines flue gases that would normally be rejected to
the power stations chimney or stack.
The additional heat energy that can be recovered by using a cogeneration system leads to
an overall increase in the thermodynamic cycle efficiency of the plant. Figure 9 shows a
sankey or energy balance diagram for a marine gas engine.
Figure 9 - Reciprocating gas engine sankey diagram.
1.2.1 - CONVENTIONAL POWER PLANT CYCLE EFFICIENCY.
The overall cycle efficiency of a conventional reciprocating engine power plant, based
on the above diagram (See figure 9) would be defined as:
Overall cycle efficiency = Power plant electrical output
Power plant fuel input
Overall cycle efficiency = Power plant electrical output
Mass of fuel * Calorific value
[J/s]
.
[kg/s] * [J/kg]
19
1.2.2 - COGENERATION PLANT CYCLE EFFICENCY.
Whereas, the overall cycle efficiency for a cogeneration plant, would be defined as:
Overall cycle efficiency = Power plant electrical output + heat output
Power plant fuel input
[kg/s] * [J/kgK] * [K]
Overall cycle efficiency = Power output + m * Cp * (T2 - T1)
Mass of fuel * Calorific value of fuel
[kg/s] * [J/kg]
Overall cycle efficiency = Power plant electrical output + m * Cp * (T2 - T1)
[--]
Mass flow-rate of fuel * Calorific value of fuel
Where m = Mass flow-rate of the engine exhaust gases - [kg / s].
T1 = Exhaust gas inlet temperature to boiler -
[K].
T2 = Exhaust gas outlet temperature from boiler -
[K].
Cp = Specific heat capacity of the exhaust gas -
[J / kgK].
1.2.3 - HEAT ENERGY RECOVERED.
From the above equations, it can be seen that the following amount of heat energy could
be recovered by the use of a heat exchanger or heat recovery steam generator, as part of
a cogeneration plant:
Heat energy recovered = m * Cp * (T2 - T1)
[W]
1.2.4 - INCREASE IN CYCLE EFFICENCY.
From the above equations, it can also be seen that the increase in overall cycle efficiency
from using a heat exchanger or heat recovery steam generator as part of a cogeneration
plant would be:
Increase in cycle efficiency = m * Cp * (T2 - T1) * 100
[%]
Mass of fuel * Calorific value of fuel
20
1.3 - POWER PLANT CARBON EMISSIONS.
The second major advantage of generating electricity and hot water or steam from
cogeneration plants is that the carbon emissions produced by the plant are less than
the total carbon emissions that would be produced from electricity only production using
large fossil fired power stations and from heat only production using conventional package
boilers [7].
A standard cogeneration plant burning natural gas fuel would produce carbon emissions
of around 50gC per kWh of natural gas consumed. Table 3 details the actual carbon
emissions for various cogeneration fuels.
Whilst, a conventional coal fired power station burning coal to produce electricity only,
would emit 263gC per kWh of electricity generated and an oil fired package boiler producing
hot water or steam would emit 98gC per kWh of heat energy produced. Tables 4 and 5 outline
the carbon emissions from various types of fossil fired power station and heat only boiler plant.
CHP fuel
Coal
Fuel oil
Gas oil
Natural gas
Carbon emissions
in gC/kWh
89
73
68
50
Table 3 - Cogeneration plant carbon emissions.
Fuel used
Coal
Oil
Gas
Efficiency
range %
32 - 37
25 - 37
32 - 52
Average
efficiency %
36.4
27.1
45.1
Delivered
Carbon emissions
efficiency %
in gC/kWh
34
263
25
268
42
119
Table 4 - Fossil fired power station efficiencies and carbon emissions.
21
Fuel used
Coal
Oil
Gas
Average
Efficiency
range %
Average
efficiency %
51 - 81
58 - 87
61 - 82
70
74
76
75
Carbon emissons
in gC/kW h heat
output
127
98
66
81
% of total
fuel mix
8
31
61
100
Table 5 - Heat only boiler plant efficiencies and carbon emissions.
1.3.1 - CARBON EMISSION SAVINGS.
The actual amount of carbon emissions that maybe saved every year by installing a
cogeneration plant, depends on the type of fossil fired generating capacity and heat
only boiler plant that is being displaced by the cogeneration plant.
In general, the type of fossil fired generating plant that is being displaced is not known,
as the electricity that is transmitted in the national grid system comes from various different
types of generating plant.
It is therefore standard practice to use an average carbon emissions value of 183gC per
kWh of electricity generated from conventional fossil fired power stations, when calculating
the actual carbon emissions savings.
However, the fuel used in heat only boiler plant is normally known and it is therefore
possible to calculate the emissions reduction from displacing it with a cogeneration plant.
1.3.2 - CARBON EMISSIONS.
It should be noted that where carbon emissions have been stated in this Chapter, then:
12 grams of carbon emissions = 44 grams of carbon dioxide gas emissions.
22
1.4 - ADVANTAGES OF USING COGENERATION.
The main advantages for factories, hospitals and other businesses installing their own
cogeneration plants are that they can produce their own heat and power requirements,
independently of external suppliers.
In the near future, this may be the overriding reason for the increased use of cogeneration
in the United Kingdom, as many large coal fired power stations will be forced to close due to
stricter carbon emissions regulations and because they are at the end of their useful working
lives.
The possible impact of these closures may well be that there is an increased demand for
electricity across the country, leading to rising electricity costs and power blackouts.
1.4.1 - PLANT AVAILABILITY.
The most modern cogeneration plants are able to operate at high availabilities of between
90% and 96% per annum, with minimal annual down-time for maintenance and service
purposes.
1.4.2 - BLACKSTART CAPABILITY.
In the unlikely event of a total black-out or failure of the national grid system, then
medium sized cogeneration plants that are based on diesel engines, gas engines and
gas turbines would have an important role to play in restarting the national grid system,
as they are able to start-up unassisted, without mains power being available.
The electricity generated by these cogeneration plants would then be used to restart the
major items of auxiliary plant that are contained within large power stations across the
United Kingdom, including the main boiler feed, condensate extraction and cooling water
pumps, which are rated at around 2.0MWe each.
23
1.4.3 - ISLAND MODE CAPABILITY.
The vast majority of cogeneration plants can also operate in island mode operation,
which means that they can generate electricity even when unconnected to the national
grid system.
This is particularly beneficial for airports, hospitals, manufacturing plants and other
industries who require uninterrupted power supplies 24 hours per day.
1.4.4 - PLANT CONSTRUCTION TIMES.
Most industrial gas turbine and reciprocating engine cogeneration plants are based on
skid mounted units which are easy to install and connect to the local electricity distribution
system.
These types of plant can also be constructed in several months, when required.
24
CHAPTER 2 - EU INSTALLED COGENERATION PLANT CAPACITY.
In 1998, the total installed capacity of cogeneration plants in the European Union [8]
was 72,000MWe.
The countrys with the largest installed base of cogeneration plants were Germany
(22,000MWe), Italy (9,500MWe), the Netherlands (8,500MWe), Denmark (7,000MWe)
and Finland (5,000MWe).
25000
22000
20000
15000
10000
7000
5000
0
Denmark
9500
8500
Italy
Netherlands
5000
Finland
Germany
CHP capacity in MWe
Figure 10 - European Union cogeneration plant installed capacity in 1998.
2.0.1 - EU ENERGY PRODUCTION FROM COGENERATION PLANTS.
When we compare the actual amounts of energy that were generated from cogeneration
plants in 1998, then we find that the Netherlands produced the largest amount of energy
from cogeneration (47,835 GWh per year).
They were closely followed by Italy who produced 44,856 GWh and then Germany who
generated 41,770 GWh of energy per year.
The amounts of energy produced from cogeneration, by all European Countries, between
1994 and 1998 is shown in figure 11.
25
50000
40000
30000
20000
10000
0
Be
De Ger Gree Sp
Fr
Ir
Italy Lux NL Aus Por Fin Swe UK
CHP in GWh - 1994
CHP in GWh - 1998
Figure 11 - Energy production from cogeneration plants in the European Union.
2.0.2 - EU COGENERATION MARKET SHARE.
Of all the countries in the European Union, Denmark, the Netherlands and Finland
have the highest overall percentages of their total electricity requirements generated
from cogeneration plants.
Denmark produced 62.3%, the Netherlands produced 52.6% and Finland generated
35.8% of their total electricity from cogeneration plants, whilst France, Greece and
Ireland in contrast, only generated 2% of their total electricity requirements from
cogeneration plants.
The changes in European Union cogeneration plant market share between 1994 and
1998 are illustrated in figure 12.
26
70
60
50
40
30
20
10
0
Be
De
Ger Gree Sp
Fr
Ir
Italy Lux
CHP % share - 1994
NL Aus Por Fin Swe UK
CHP % share - 1998
Figure 12 - European Union cogeneration plant market share.
27
2.1 – EU STRATEGY ON COGENERATION.
The European Union set out in its Cogeneration Strategy published in 1997, that it has
an overall target of doubling the share of electricity production from cogeneration, from
8% in 1997, to 18%, by 2010 [9].
The scientific studies that were then carried out by the European Union suggested that
if this target was met, then over 65 million tonnes of carbon dioxide emissions could be
avoided every year.
2.1.1 - EU GREEN PAPER, A STRATEGY FOR THE SECURITY OF ENERGY SUPPLY.
The European Commission stated in its Green Paper titled “Towards a European Strategy
for the Security of Energy Supply”, published on the 29th November 2000, that Europe is
currently dependent on external energy supplies for 50% of its total energy requirements
[10].
The Green Paper predicts that external energy supplies will account for around 70% of
all European Union energy requirements by 2030 and concludes that in order for the EU
to reduce its dependence on foreign imports and to limit its emissions of greenhouse gases,
then it would need to implement measures to reduce energy demand.
2.1.2 - EU POLICY ON SUSTAINABLE DEVELOPMENT.
The European Commission published its strategy “A Sustainable Europe for a Better World,
A European Union Strategy for Sustainable Development” on the 15th May 2001 [11].
The main conclusions of the EU Sustainable Development Strategy were that there is a
need for increased use of clean energy and clear action to reduce energy demand within
all of the European Union countries.
28
2.1.3 - EU DIRECTIVE ON PROMOTION OF COGENERATION (2004/8/EEC).
In order to promote the use of high-efficiency cogeneration plant more effectively across
all European Union countries and to comply with the recommendations of the EU Green
Paper and the Sustainable Development Policy, the EU introduced a new Directive on the
11th February 2004, on the “Promotion of Cogeneration based on useful heat demand in
the internal energy market” [12].
The aims of the Directive are to further the European Union’s goals of reducing primary
energy demand, improving energy security of supply, avoiding electricity network losses
and reducing greenhouse gas emissions.
The Directive also aims to provide a framework within which cogeneration plants can
overcome existing market barriers and advance the market share for cogeneration in
all European Union countries.
The Directive stresses the need for Member Countries to implement support schemes
(investment aid, tax exemptions, etc) with a minimum duration of at least four years, in
order to give companies financial incentives to invest in cogeneration plant.
All Member States also need to ensure that any support for existing and future cogeneration
plants is based upon the useful heat demand and the primary energy savings that can be
achieved by using a cogeneration plant, in light of the possibility that other forms of
renewable energy production maybe more efficient.
2.1.4 - INTEGRATED POLLUTION PREVENTION AND CONTROL DIRECTIVE (IPPC).
The European Union Integrated Pollution Prevention and Control Directive (1996) came
into force in the United Kingdom on the 1st August 2000.
The Directive will be phased in to cover all sectors of British industry by the beginning of
October 2007 [13].
The introduction of the Directive means that all large companies must provide documentary
evidence of the condition of their plant with regards to pollution and emissions levels and to
29
show that any processes that they use comply with the Best Available Techniques and
Technologies, before they will be granted an IPPC Permit to continue operating.
It is widely anticipated that the IPPC Directive will force companies with old heat and power
generation equipment to invest in new cogeneration plant, in order to fully comply with the
Directive.
2.1.5 - LARGE COMBUSTION PLANTS DIRECTIVE.
The introduction of the revised Large Combustion Plants Directive (LCPD) also encourages
all European Union Member states to move towards more efficient and cleaner means of
generating electricity.
The Directive requires cogeneration plants to be developed where they are technically or
economically feasible, bearing in mind the market and distribution situation [13].
30
2.2 - UK INSTALLED COGENERATION PLANT CAPACITY.
At the end of December 2002, there were a total of 1,539 cogeneration plants generating
electricity in the United Kingdom. The total installed capacity of these plants was 4,742
MWe, which is equivalent to 6.1% of the United Kingdoms total installed generating
capacity [14,15].
The number of cogeneration plants that have been built in the United Kingdom has also
risen by 15% from 1,357 plants in 1998 to 1,561 plants at the end of 2001.
However, during 2002, the number of cogeneration plants that were actually generating
electricity into the national grid system fell slightly, from 1,561 plants at the beginning of
the year to 1,539 plants at the end of the year. This led to a reduction in total generating
capacity of only 11MWe.
The main reasons for the small reduction in cogeneration capacity were because several
owners mothballed their plants, due to the low wholesale electricity prices and the high
cost of gas, which meant it was uneconomical for them to generate.
Figure 13 illustrates the number of operational cogeneration plants and their total installed
capacity between 1998 and 2002.
4753
4730
5000
3680
4000
4742
3912
3000
2000
1357
1383
1522
1561
1539
1000
0
1998
1999
No. of chp plants
2000
2001
2002
Capacity, in MWe
Figure 13 - UK cogeneration plant installed capacity.
31
2.2.1 - COGENERATION PLANT SIZE.
The majority of UK cogeneration plants, based on figures for 2002, were less than
1MWe in size, with plants with an electrical output of less than 100kWe accounting
for 43.1% and plants with an output of up to 999kWe accounting for 40.6% of the
total number installed.
Figure 14 shows the percentage of cogeneration plants that fall into each power output
category.
100 - 999 kWe (40.6%)
1 - 9.9 MWe (11.8%)
< 100 kWe (43.1%)
> 10 MWe (4.4%)
Figure 14 - Cogeneration plants installed by size.
2.2.2 - COGENERATION PLANT POWER OUTPUT.
The vast majority of the energy that is produced from cogeneration plants comes from
plants that have an output of greater than 1MWe.
Cogeneration plants that have an output of between 1MWe and 9.9MWe currently account
for 16% and plants with an output of greater than 10MWe account for a further 79.9% of the
total energy that is produced from cogeneration.
Figure 15 shows the percentages of the total energy produced from cogeneration plants,
depending on the size of plant.
32
100 - 999 kWe (3.2%)
1 - 9.9 MWe (16.0%)
< 100 kWe (0.9%)
> 10 MWe (79.9%)
Figure 15 - Energy production depending on the cogeneration plant size.
2.2.3 - COGENERATION PLANT FUELS.
The principle fuel that is used in UK cogeneration plants is natural gas, which currently
accounts for 64% of the fuel mix.
The breakdown of natural gas usage is as follows, 38% is used in combined cycle gas
turbine plants, 11% in simple cycle gas turbine plants, 7% in gas engines and 5% in
steam turbine plant.
The “other fuels” that are used in cogeneration plants are coke oven gas, gas oil and
manufacturing process by-products which account for a further 15% of the fuel mix.
Other fuels (15.0%)
Refinery gas (7.0%)
Renewables (2.0%)
Coal (6.0%)
Furnace gas (1.0%)
Fuel oil (5.0%)
Natural gas (64.0%)
Figure 16 - Cogeneration plant fuel mix.
33
2.2.4 - INDUSTRIES USING COGENERATION.
There are four main industrial sectors in the United Kingdom which account for over three
quarters of the demand for electricity that is produced from cogeneration plant.
These sectors are the chemical industry (32%), oil refineries (20%), the electricity supply
industry (13%) and the paper and publishing industries (12.5%), respectively.
Figure 17 shows the principle industries that have installed cogeneration plants.
Paper industry (12.5%)
Electricity industry (13.0%)
Minerals industry (4.5%)
Oil refineries (20.0%)
Commerce industry (6.0%)
Other sectors (3.5%)
Food industry (8.5%)
Chemical industry (32.0%)
Figure 17 - Industries using cogeneration.
34
2.3 - UK ENERGY POLICY TOWARDS COGENERATION.
The Government has stated in the Energy White Paper 2003 that it has set a target for
10,000MWe of good quality cogeneration plants, as defined by CHPQA scheme, to be
built in the United Kingdom by 2010. This would lead to a reduction in carbon emissions
of 1.25 million tonnes every Year [16].
The Government has also stated that it will review the power station consents process to
ensure that all new applications for permission to build power stations, will have submitted
substantial documentation to prove that they have considered all economically viable options
for cogeneration and community heating plants first, before being granted planning permission.
Furthermore, during the consultation process for the White Paper, many small cogeneration
companies complained that they could not obtain quick and easy connection to the local
electricity distribution network, as their was no financial incentive for the Distributed Network
Operators (DNO) to connect them to the system.
Therefore, OFGEM has been tasked with looking into the possibility of implementing a
financial incentive scheme to begin operation in April 2005, in order to counter the
difficulties that were experienced by these companies.
2.3.1 - ENERGY EFFICIENCY OBLIGATION.
The Government introduced an Energy Efficiency Commitment (EEC) in April 2002. The
commitment places legal obligations on all electricity and gas suppliers to achieve targets
on the promotion of energy efficiency between 2002 and 2005 [17].
Cogeneration is therefore one of a number of measures that electricity and gas suppliers
may use in order to meet their commitments under the Energy Efficiency Obligation.
2.3.2 - GOVERNMENT ESTATE.
The Minister for Sustainable Energy, Lord Whitty stated on the 26th February 2004, that
all Government Departments are required to source at least 15% of their electricity
35
requirements from good quality combined heat and power plants by 2010.
The Government has estimated that by 2010 that there is the potential for around 30
to 35MWe of installed cogeneration capacity on the Government Estate [18,19].
2.3.3 - CHP QUALITY ASSURANCE PROGRAMME (CHPQA).
The Government has recently set-up a new initiative called the Combined Heat and
Power Quality Assurance (CHPQA) programme, in order to monitor the countrys
progress towards meeting its target of 10,000MWe of installed cogeneration plant
capacity by 2010.
The CHPQA programme provides a practical, robust and determinate methodology
for assessing and defining good quality combined heat and power for all or part of a
cogeneration plants fuel inputs and electricity outputs [20].
The programme also allows for responsible persons to apply for certification and registration
of their cogeneration plant in accordance with the criteria for good quality combined heat
and power and hence allows them to qualify for financial benefits including climate change
levy exemption and enhanced capital allowances.
2.3.4 - CLIMATE CHANGE LEVY.
The climate change levy is an environmental tax, which came into force on the 1st April
2001. It is payable by all non-domestic users of energy including industry, commerce and
the public sector, with exemptions from the levy for good quality combined heat and power.
The amount of Climate Change Levy that is applicable depends on the quantity of fossil
fuel that is consumed. The Levy is charged at the rates specified in table 6 and is aimed
at reducing fossil fuel energy consumption [21,22,23].
36
Electricity
Natural gas
Coal and Lignite
Liquified Petroleum Gas
0.43 pence /
0.15 pence /
0.15 pence /
0.07 pence /
kWh
kWh
kWh
kWh
Table 6 - Climate change levy charges.
2.3.5 - ENHANCED CAPITAL ALLOWANCES.
The Government introduced an enhanced capital allowances scheme in April 2001 as
part of the wider climate change levy programme and all good quality cogeneration
plants as defined under CHPQA rules are eligible for enhanced capital allowances [24].
Enhanced capital allowances are 100% first year capital allowances for businesses to
invest in certain energy saving equipment.
The introduction of enhanced capital allowances gives businesses and energy service
companies the opportunity to write off some of the cost of their investment in energy
saving equipment, against the taxable profits of their business (tax relief), during the
period in which they make the investment.
The types of energy saving equipment that are eligible for enhanced capital allowances
include:
•
Fuel storage and handling equipment.
•
Gas and steam turbines, reciprocating engines, alternators and associated equipment.
•
Heat recovery boilers, absorption chillers, heat rejection equipment.
•
Silencers, exhaust stacks and related ancillary equipment.
However, the cost of the cogeneration plant buildings cannot be written off against a
companies taxable profits.
37
2.3.6 - EXEMPTION FROM BUSINESS RATES.
It is possible for companies who generate electricity from cogeneration plants to be
exempt from business rates.
For a company to gain exemption from payment of business rates, the sole or primary
purpose of its property must be for the generation of electricity and the actual plant
capacity must be at least 500kWe [17,21]
The cogeneration plant and machinery in the building will be exempt from business
rates, if it is deemed as good quality cogeneration plant under CHPQA rules. However
the actual building or structure that is used to house the cogeneration plant will still be
subject to business rates.
It should be noted that companies who operate cogeneration plants on their site, but
the primary function of the site is not for the production of electricity are not eligible for
exemption of payment of business rates on their plant and equipment.
2.3.7 - ELECTRICITY GENERATION LICENCE EXEMPTION SCHEME.
On the 1st October 2001, the Government brought into force legislation relaxing the licence
exemption criteria for all categories of local power generation and electricity supply [17].
The new licence criteria increases the limit of electricity that can be generated and supplied
without a licence to:
•
Supplies of no more than 5MWe, of which no more than 2.5MWe would be supplied
to domestic customers.
•
Furthermore, electricity supplies to a single customer or group of customers, provided
these customers are based on the site where the electricity is generated or take the
power directly over private wires, are also exempt.
The purpose of the license exemption scheme was to reduce the administrative burden
that would be placed on many small generators becoming licensed electricity suppliers.
38
2.4 - UNITED KINGDOM EMISSIONS TRADING SCHEME.
The Emissions Trading Scheme [25] commenced in March 2002 and gives participating
UK companies specific yearly emissions allowances (in carbon dioxide equivalent).
If a company exceeds its yearly emission’s allowance, then they must purchase additional
allowances from the market in order to make up the deficit. Conversely, if a company emits
less than its allowance, then it can then sell its surplus credits to the market and therefore
obtain some financial gain.
The aim of the Emissions Trading Scheme is to give financial incentives to companies who
have high carbon dioxide emissions, in order that they reduce their emissions by investing
in new plant and technology.
Cogeneration plant is therefore one of a range of options that maybe suitable for companies
who wish to reduce their emissions from old or outdated boiler plant.
However, depending on the capital cost of investing in new plant and technology, it may be
more cost effective for a company to purchase emissions credits from the market.
2.4.1 - EUROPEAN UNION EMISSIONS TRADING SCHEME.
The European Union has recently introduced new legislation to allow for a European
Emissions Trading Scheme to commence operation on the 1st January 2005 [26].
The scheme will initially cover Europe wide emissions of carbon dioxide gas only, which
is emitted from large mineral oil refineries, coke ovens, cement and glass manufacturing
plants, metal ore extraction plants and steel production plants.
The scheme is similar to the UK Emissions Trading Scheme, however if a company exceeds
its annual emissions limit and has not purchased sufficient credits from the market, then the
European Union has the power to impose a financial penalty of 40 Euros for every tonne of
carbon dioxide gas that exceeds the installation’s limit.
39
2.5 - POWER PLANT PLANNING AND CONSENTS PROCEDURES.
Before any combined heat and power plant can be built in the United Kingdom it is subject
to approval from either the Secretary of State for Trade and Industry or the Local Planning
Authority [27,28,29].
The proposed development of a 9.5MWe Combined Heat and Power Plant that is being
used as the basis for this thesis is subject only to the consent of the Local Planning
Authority, under the Town and Country Planning Act 1990 (See Appendix F).
However, any proposal to build a new gas or oil fired power station, including cogeneration
plants, above 10MWe in power output, is subject to Energy Policy Clearance from the
Department of Trade and Industry, under Section 14(1) of the Energy Act 1976.
2.5.1 - THE LOCAL PLANNING AUTHORITY.
Once the plant developer has submitted proposals for the cogeneration plant, the Local
Authority will study the details to ensure that any new buildings, structures or alterations
to existing buildings are carried out in such a manner that the development is in keeping
with the surrounding area.
The planning system is specifically designed to ensure that the countryside, historic
buildings and sites of special scientific interest are not adversely affected by any
proposed development.
In granting a consent, the Local Planning Authority will normally give “Deemed Planning
Permission” with a number of planning conditions attached, in order to mitigate the impact
of the development in terms of noise, access and landscaping on the surrounding area.
2.5.2 - ENVIRONMENTAL IMPACT ASSESSMENTS.
The application for planning permission should include a detailed environmental impact
assessment, in order to allow the Local Authority to assess any potential environmental
impact of the proposed development [30].
40
2.5.3 - PLANNING POLICY GUIDANCE NOTES.
The Government has recently set out its policies on planning issues at a national level in
the Planning Policy Guidance Notes (PPG).
These notes provide comprehensive guidance to all Local Authorities and others, on the
Governments planning policies, in order for them to comply with new European Union
Directives [30].
For cogeneration plants that are proposed to be built in existing industrial areas or on
waste or derelict ground, Planning Policy Guidance Note 4 states that these types of
development are to be encouraged, wherever practicable, as they can help to regenerate
the surrounding local area.
41
CHAPTER 3 - COGENERATION PLANT SELECTION.
From the literature review that was carried out in Chapters 1 and 2, diesel engines, gas
engines and industrial gas turbines were identified as being the most suitable prime movers
for the proposed cogeneration plant.
Table 7 below, details the principle characteristics of each prime mover [1].
Dies el
engines
Power output range 0.2 - 20MWe.
Operate at 750 - 1500 rpm .
Run on m arine dies el oils and heavy fuel oils .
Requirem ent for fuel s torage tanks and fuel heating equipm ent.
Heat to power ratios of between 0.5 - 3.1 : 1
Overall efficiencies of around 65%.
Produce low pres s ure s team and m edium tem perature hot water.
Suitable for cyclical operation.
Requires jacket water and charge air cooling s ys tem s .
Typical engine availability of between 85 - 90%.
High nois e levels at low frequency.
Unit can be m aintained by engine fitters , us ually s hort overhaul periods .
Exhaus t gas em is s ions of 73 gC / kWh of oil cons um ed.
Three off, 3.35MWe, KVGB-16 dies el engines = £2,580,000
Gas
engines
Power output range 0.2 - 15MWe.
Operate at 750 - 1500 rpm .
Run on natural gas , landfill gas and naphtha.
No requirem ent for fuel s torage tanks .
Heat to power ratios of between 1 - 3 : 1
Overall efficiencies of around 65%.
Produce low pres s ure s team and m edium tem perature hot water.
Suitable for continuous and cyclical operation
Requires jacket water and charge air cooling s ys tem s .
Typical engine availability of between 90 - 96%.
High nois e levels at low frequency.
Unit can be m aintained by engine fitters , us ually s hort overhaul periods .
Exhaus t gas em is s ions of 50 gC / kWh of gas cons um ed.
Three off, 3.16MWe, KVGB-18 gas engines = £2,733,000.
Gas
turbines
Power output range 0.25 - 50MWe.
Operate at 16,000 - 18,000 rpm and geared down to 1500rpm .
Run on natural gas , light fuel oils and naphtha.
No requirem ent for fuel s torage tanks .
Heat to power ratios of between 1.5 - 5 : 1
Overall efficiencies of around 69%.
Produce high grade s team and high tem perature hot water.
Suitable for long term continuous operation.
No requirem ent for water cooling s ys tem s .
Typical turbine availability of between 90 - 96%.
High nois e levels at high frequency.
Unit requires factory trained technicians for m aintenance.
Exhaus t gas em is s ions of 50 gC / kWh of gas cons um ed.
Two off, 4.7MWe, Typhoon indus trial gas turbines = £2,700,000.
Table 7 - Characteristics of prime movers.
42
It was concluded that marine derivative gas engines would offer the best practicable
means of producing 9.5MWe of electricity and 8 tonnes per hour of process steam for
the manufacturing plant. The decision to opt for a cogeneration plant that is based on
marine gas engines was made for the following reasons:
Firstly, although industrial gas turbines can offer high plant availability, low emissions, and
are slightly cheaper than marine gas engines, they operate at extremely high speeds and
are geared down to 1500rpm, in order to produce electricity. They are also more suited to
applications where high grade steam and high temperature hot water are required.
Based on a cogeneration plant operating two 4.7MWe Typhoon industrial gas turbines, it
would be possible to generate considerably more steam than is actually required by the
manufacturing plant, as the gas turbines exhaust gas mass flow-rate and temperature
are approximately 40.6 kg / s and 536ºC (See Appendix A).
This design of cogeneration plant would not make the best possible use of the heat energy
that is contained within the gas turbines exhaust gases and it is also extremely likely that
the plant would not meet the Combined Heat and Power Quality Assurance Scheme criteria
for good quality cogeneration, as all of the heat energy that is contained within the exhaust
gases would not be fully utilised. This would mean that the plant would not be eligible for
climate change levy exemption and the plants financial viability would be reduced.
The main reasons for choosing not to opt for a diesel engine based cogeneration plant
were that although the plant would be around £150,000 less than a gas engine plant, diesel
engines would produce higher exhaust gas emissions than gas turbines and gas engines,
the plant would also require large fuel oil storage tanks, oil purification equipment and all
of the fuel oil pipe-work would need to be fitted with trace heating equipment, in order to
prevent the heavy fuel oil from solidifying. The diesel engines would require more
maintenance than gas turbines and gas engines, also.
Therefore, it was concluded that marine gas engines would be the best practicable option
for generating combined heat and power, as they would be able to produce small amounts
of low pressure steam. They also offer the benefit of low exhaust gas emissions and the
natural gas for the plant could be supplied directly from the Transco mains gas network.
43
The gas engine cogeneration plant would also make more efficient use of the engines
exhaust gases and it is therefore foreseen that the plant would meet the CHPQA criteria
and would be exempt from climate change levy on all its fuel inputs and electricity outputs.
The following sections of this Chapter give a brief description of the lean burn gas engine
and the other major items of plant and equipment that would be installed in a typical
cogeneration plant.
44
3.1 - PLANT MAINS GAS PRESSURE REDUCING STATION.
The Transco mains gas transmission pipeline supplies natural gas at a pressure of 7 bar.
The mains gas that enters the pressure reducing station is then throttled via control valves
to give the desired gas pressure that is required by a particular company or site.
The gas is normally metered at inlet to the reducing station and at outlet to each individual
customer, using an analogue and a digital type gas flow-meter.
A standard pressure reducing station would have a corrugated iron roof, with several vents
located in it, in order to prevent the build up of natural gas, from leaks that may occur in the
pipe system. The roof also helps to protect all the equipment inside the station from becoming
corroded by the elements.
The reducing station should be enclosed on all four sides by an eight foot high barbed security
fence, in order to protect the equipment from vandals and animals. Access to the reducing
station, for authorised persons, would be through a padlocked gate.
Figures 18 and 19 show a typical mains gas pressure reducing station, including the gas
outlet pipe.
Figure 18 - Photograph of a mains gas pressure reducing station.
45
Figure 19 - Photograph of a mains gas outlet pipe.
46
3.2 - GAS ENGINE DESIGN AND DEVELOPMENT.
In 1984, due to a downturn in the marine industry, Bergen diesels (now Rolls Royce
diesels), started to develop a large, medium speed marine engine that could run on
either natural gas, landfill gas or coke oven gas.
In order for them to reduce the costs of developing the new engine, they decided to
convert several existing 4 stroke, turbocharged and inter-cooled, V twin, 250mm bore
and 300mm stroke marine diesel engines to run specifically on these fuels [31,32].
The gas engines that they developed were based on the spark ignition lean burn otto
cycle principle of engine operation.
A photograph of a 3MWe spark ignition gas engine and an engineering drawing detailing
the engines overall dimensions, are shown in figures 20 and 21, below, for reference.
Figure 20 - Photograph of a 3MWe gas engine.
Note: The above gas engine is an 18 cylinder V design, with twin turbochargers and two stage
charge air cooling. The yellow pipe indicates the main fuel gas inlet to each cylinder and the preignition gas pipes are the small bore yellow pipes at the cylinder head level.
47
The dome shaped items that are connected to the engines crankcase doors are ventilators,
which are fitted in order to prevent any of the lubricating oil vapour and the engines exhaust
gases from building up inside the engines crankcase and causing an explosion.
Figure 21 - Gas engine elevation drawing.
3.2.1 - LEAN BURN PRINCIPLE.
The lean burn principle of engine operation is a unique process, which can increase the
power output and efficiency of a spark ignition engine, whilst also reducing the emissions
of nitrous oxides, carbon monoxide and un-burnt hydrocarbons.
A conventional spark ignition engine would normally run rich with an excess air ratio of
approximately 0.9 for best power output and for best fuel efficiency, the engine would
normally run slightly lean with an excess air ratio of 1.25.
However, the performance and emissions that were produced by these engines was
severely limited as the engines approached their knock limit at an excess air ratio of 1.3.
This led manufacturers to develop the lean burn engine, which was designed to extend
the misfire and knock limits of the engine to cope with excess air ratios of 1.8 and above.
Figure 22 shows the increase in gas engine efficiency and the reduction in exhaust gas
emissions that can be achieved by using lean burn technology.
48
Figure 22 - Lean burn gas engine performance.
3.2.2 - IGNITION GAS PRE-CHAMBER.
In order for the manufacturers to design engines that were capable of running on very lean
mixtures, it was necessary for them to redesign the engines combustion system, in such a
manner that the ignition energy of the lean mixture would be increased sufficiently to allow
the mixture to fire reliably.
This was achieved by designing a small ignition gas pre-chamber, which was incorporated
into the engines cylinder head.
The central pre-chamber is fed with a very small, but controlled amount of pure fuel gas,
by the engine control system, each time, just before the piston reaches top dead centre.
The gas is then ignited by a spark plug that is located inside the pre-chamber and the gas
flame that is produced is then forced through a 6 hole pepper pot nozzle into the main
combustion chamber at the bottom of the cylinder head.
The gas flame then acts as an external ignition source, by raising the ignition energy
of the already highly compressed lean fuel gas and air mixture and causes it ignite
just before the engines pistons reach top dead centre.
49
Figure 23 - Photograph of a gas engine cylinder head.
Figure 24 - Photograph of a gas engine cylinder head.
Note: The swage-lock connection at the top left of the cylinder head is used to supply fuel
gas to the gas pre-ignition chamber. The top bore is connected to the main fuel gas inlet
supply pipe and the bottom bore is connected to the turbocharger manifold.
50
3.2.3 - ENGINE CONTROL SYSTEM.
In order to run-up, run-down, increase or decrease the load on the engine, then an electrical
signal must be sent to the engines governor system.
The governor system then automatically changes the position of the gas inlet throttle valves,
which are mechanically linked to the air inlet flap admission valves, in order to ensure that
the correct amounts of air and gas are admitted to each cylinder head, regardless of the
speed or load that the engine is operating at.
The gas and air is then thoroughly mixed as it passes through the engine inlet valves
and admitted into the respective engine cylinder, where it is then compressed to a high
pressure.
The engine ignition central processing unit uses the signals from electrical pickups that
are mounted on the engines flywheel and camshaft, to indicate when each cylinders
respective piston is nearly at top dead centre and sends a 24 volt signal to an electrical
coil that is mounted on each cylinder head (See figure 25).
The coil then steps up the 24 volt signal to a voltage of 40,000 volts and distributes the
signal via short high tension lead to a single spark plug that is fitted inside each cylinders
gas pre-ignition chamber.
The plug then sparks across its gap and ignites the pre-chamber ignition gas and as already
stated above, the pre-chamber gas helps to raise the ignition energy of the lean mixture and
helps it to combust more easily.
51
Figure 25 - Gas engine control system.
52
3.3 - RIGID AND RESILIENT ENGINE MOUNTING.
The floor foundations on which the gas engine shall be mounted are specifically designed
to support both the weight of the engine and generator set, which can be up to 60 tonnes
for a 3MWe engine package and to minimise any propagation of the engines vibration into
the surrounding buildings and structures.
The engine and generator set are normally mounted on a skid arrangement, which is
rigidly mounted on to the concrete floor foundations with anchor bolts.
As an alternative, a chock-fast “orange” material maybe used as the foundation material.
Chock-fast is a compression load bearing material, it has a low viscosity and low surface
tension and in liquid form it is easy to apply.
The depth of the foundations when using chock fast should be between 10 and 40mm, with
the area of individual chock-fast slaps being no less than 130 cm².
As another alternative, the engine and generator set could also be resiliently mounted to the
floor foundation, in order to isolate the engine from shock loading, including earthquakes.
The two main types of resilient mounting system are based on either steel springs with a
rubber damper element fitted in-between or a rubber element bonded to a steel plate type
design.
53
3.4 - TURBOCHARGERS AND AIR SYSTEMS.
All large marine gas engines are fitted with either a single or twin type turbochargers,
depending on whether the engine is an in line or v type design.
The purpose of the turbocharger is to increase the engines efficiency and power output
by passing the engines exhaust gases through an impulse turbine which is connected via
a shaft to an air compressor, which consequently rotates faster and draws in additional
quantities of combustion air to the engine.
The compressor then increases the combustion air pressure slightly, before it actually
enters the engines cylinders.
3.4.1 - CHARGE AIR COOLING.
All marine engine turbochargers are also fitted with intercoolers, which can be of either a
single stage or twin stage charge air cooling design.
The high temperature charge air cooler is cooled with water from the engines jacket water
system and the low temperature charge air cooler is cooled by water from the raw water
cooling system.
The purpose of the intercoolers is to cool the compressed air in the turbocharger, in order
to reduce its volume, so that more air can then be drawn into the turbocharger.
The intercoolers also increase the area under the Temperature - Entropy diagram and thus
they improve the engines power output and overall efficiency.
3.4.2 - ENGINE COMBUSTION AIR SYSTEM.
Each gas engine enclosure is normally supplied individually with combustion air, which is
drawn in through louver type air filters, by a single forced draught fan which is located in
the engines combustion air duct.
54
The combustion air filter is typically about 6 metres by 3 metres in size and is installed
at roof level on one of the cogeneration plants exterior walls. These filters are designed
to remove 95% of all airborne particles, that are greater than five microns in size.
The amount of air that is discharged by the forced draught fan into the engine room enclosure
can be controlled by manually adjusting the guide vane position on the exhaust dampers.
Furthermore, the turbocharger air inlets are also fitted with fine blanket type air filters, in
order to further purify the engine combustion air.
3.4.3 - ENGINE ROOM VENTILATION SYSTEM.
Each gas engine enclosure is also fitted with a ventilation system, in order to cool the gas
engine and to maintain the engine enclosure temperature below 30 ºC.
The ventilation system also helps to remove any fuel gas that may have leaked into the
engine enclosure from the gas supply pipes and to disperse any exhaust gases and lube
oil vapour that may have leaked out of the exhaust gas manifold and the crankcase ventilators.
3.4.4 - STARTING AND CONTROL AIR SYSTEMS.
All cogeneration plants are equipped with compressed air systems, which provide each gas
engine with starting air at a pressure of between 18 bar and 30 bar. The compressed air is also
reduced in pressure to 7 bar, for use as control air for the pneumatic actuators that are installed
in the plant.
It is standard practice for most cogeneration plants to be fitted with two full duty electrically
driven and one full duty diesel driven air compressor, in order to ensure that the plant has
sufficient starting and control air, at all times.
The starting air is admitted into each cylinder head by a solenoid type air release valve and the
engine then run on starting air for about five seconds, before the fuel gas is admitted, in order to
ensure that there is no fuel gas left in the exhaust system, as this could lead to an explosion or
scavenge fire occurring.
55
3.5 - FUEL GAS SYSTEM.
The purpose of the engines fuel gas module is to regulate the pressure, flow-rate and purity
of fuel gas that is supplied to the engine from the mains gas pressure reducing station.
The main component of the fuel gas module is the gas regulating line, which comprises of
several gas filters, gas control valves and isolating valves, which remove any impurities in
the fuel gas and regulate the pressure of the gas to a maximum of 2.3 bar at inlet to the
engine. In the event of an engine trip, any fuel gas that remains in the system can be vented
to atmosphere, via a vent line, also.
It should be noted that all gas engine manufacturers require detailed information on the
composition of the fuel gas that will be burnt in their engines, as there is a risk that there
can be a chemical interaction between the natural gas and certain types of engine
lubricating oil.
SUBJECT TO COPYRIGHT – SEE HARD COPY.
Figure 26 - Engine fuel gas regulating system.
56
3.6 - LUBRICATING OIL SYSTEM.
The purpose of the lubricating oil system is to supply a sufficient flow of oil at a pressure
of between 4 and 5 bar and a temperature of 60ºC, in order to lubricate and cool the
engines main crankshaft bearings and the piston big end and small end bearings. The
system also supplies oil at a reduced pressure of 0.5 bar to lubricate the rocker arms.
Each gas engine is fitted with a main shaft driven lube oil pump for normal operation and
an electrical auxiliary pump for when the engine is off load.
3.6.1 - RAW WATER COOLING SYSTEM.
The purpose of the raw water cooling system is to supply a sufficient flow of water at an
inlet temperature of 45ºC to cool the lubricating oil system and at an inlet temperature of
55ºC to cool the low temperature charge air cooler. The raw water is then cooled by passing
it through an outdoor radiator system.
The raw water should also be mixed with antifreeze and an inhibitor, in order to prevent
the system from freezing in Winter-time and to minimise the risk of corrosion, sediments
and surface growths forming inside the pipe-system.
3.6.2 - JACKET WATER COOLING SYSTEM.
The purpose of the jacket water cooling system is to supply a sufficient flow of water at
an inlet temperature of 45ºC to cool the high temperature charge air cooler.
The jacket water then passes into the engine block at a minimum temperature of 70ºC
and cools the block, wet liners and the cylinder heads, before exiting the engine at 90ºC.
The jacket water is then cooled by passing it through an outdoor radiator system, also.
Each gas engine is normally fitted with a shaft driven jacket water pump for normal
operation and an auxiliary electrical driven jacket water pump, which will circulate the
jacket water round the engine for fifteen minutes after the engine comes off load, in
order to prevent the jacket water from boiling.
57
3.7 - EXHAUST GAS SYSTEM.
The engine exhaust system comprises of a lagged exhaust gas pipe, which leads the gases,
firstly through a bellows arrangement, in order to minimise any thermal stresses in pipe. The
gases are then led through a substantial length of pipe to the waste heat recovery boiler.
It is standard practice for the heat recovery boiler to be fitted with a bypass system, so
that when steam or hot water is not required, then the engines hot exhaust gases can be
diverted directly to the plants stack or chimney. This also allows for the water and steam
systems to be isolated for routine maintenance purposes (See figure 27).
The exhaust gas manifold for each engine is also connected to an extractor fan, which
discharges to the outside of the cogeneration plants building, in order that the exhaust
system maybe purged of any fuel gas that may have accumulated in it, due to a failure
of a gas engine to start.
3.7.1 - EXHAUST STACK.
The plants chimney or stack should be designed to have a positive height, above the roof
levels of nearby buildings, in order to allow for a good dispersal of the engines exhaust
gases.
The standard size of exhaust stack for a 9.5MWe cogeneration plant is around 35
metres in height.
58
Figure 27 - Engine exhaust gas system.
59
3.8 - ENGINE FIRE PROTECTION SYSTEM.
All cogeneration plants are required to ensure that they have installed suitable flammable
gas detection, smoke detection, fire alarms, fire exits and fire protection equipment on their
site before they will be issued with a Fire Certificate by the Fire Brigade and covered for
loss by their insurance company.
A single gas engine enclosure would normally be fitted with at least two smoke and two
gas detectors, that should be located at roof height at diagonally opposite ends of the
engine enclosure.
Each engine should be also be protected by a carbon dioxide fire protection system.
The protection system normally consists of a bank of eight 35 kg carbon dioxide cylinders,
that are connected to a series of spray nozzles that surround the engine on two sides and
which are specifically set to give the best coverage of the engine.
When a fire is detected in the enclosure, then an electrical signal is sent to the outlet valve
on the bank of carbon dioxide bottles, which releases the liquid carbon dioxide and causes it
to expand into a gas as it exits the spray nozzles.
The nozzles allow the carbon dioxide gas to blanket the whole engine compartment and this
reduces the oxygen levels in the vicinity of the burning material and causes the fire to go out
naturally.
60
3.9 - CONDENSATE RETURN SYSTEM AND STEAM RAISING PLANT.
The condensate from the manufacturing company will be pumped to the new cogeneration
plant and stored in a de-aerator tank, which will be located at a vertical height of 10 metres
above the plants ground level.
The de-aerator tank acts as a high level feed water storage vessel and supplies a net
positive suction head to the main boiler feed water pumps in order to prevent them from
cavitating.
The boiler feed pumps will then pump the hot water directly into the heat recovery boiler,
via two control valves, which control the flow of water to the boiler, depending on the engine
load (See figure 28).
The feed water that is stored inside the de-aerator tank is normally dosed with sodium
hydroxide (caustic soda) and tri-sodium phosphate, in order to control the feed-water
alkalinity to an optimum pH of between 8.8 and 9.2 and to prevent the build up of scale
on the boiler tubes, by converting the calcium and magnesium salts that are present in
the feed-water into calcium and magnesium phosphates.
The feed water is also dosed with hydrazine, which acts as an oxygen scavenger and
removes any dissolved oxygen that maybe present in the feed-water, as the dissolved
oxygen can accelerate corrosion in the heat recovery boiler.
The feed water is dosed at outlet from the de-aerator and dosing is continued until
the dissolved oxygen content falls below 0.007 parts per million. The hydrazine also
acts as a weak alkali and any hydrazine not consumed in oxygen scavenging process,
assists with raising the alkalinity of the feed-water.
3.9.1 - HEAT RECOVERY BOILER (HRSG).
The most common type of heat recovery boiler that is used in small-scale cogeneration plants
is the single pass, counter flow, shell and tube design of heat exchanger.
In the counter flow design of heat exchanger, the engines exhaust gases are passed through
61
the tubes of the heat recovery steam generator, whilst the hot water or condensate is
circulated over the tubes in the opposite direction, by means of a small, single stage,
centrifugal boiler feed-water pump.
The steam that is produced, is then led out of the top of the heat recovery boiler and through
the steam pipe-work to the main steam leg, where it will then be routed into the manufacturing
plants process steam system (See figure 28).
A portion of the steam produced by the heat recovery boiler is normally returned to the
de-aerator tank, in order to maintain a high feed water temperature inside the tank, during
all operating conditions, also.
For cogeneration plants using natural gas fuelled reciprocating engines, the minimum exhaust
gas outlet temperature from the heat recovery boiler is around 120ºC to 130 ºC, due to heat
exchanger design reasons and to ensure that the exhaust gases have sufficient buoyancy to
rise up the stack.
For diesel engines the minimum exhaust gas outlet temperature from the boiler is around 170ºC,
as below this temperature it is possible for the sulphur in the exhaust gases to condense and
form sulphuric acid on the boiler tubes.
It should also be noted that for gas engine cogeneration plants, it is possible to install an
economiser, which can extract the useful heat energy contained within the engines exhaust
gases, down to an exhaust gas outlet temperature of 60ºC. However, this would increase the
cost and complexity of building the plant.
3.9.2 - BOILER BLOWDOWN SYSTEM.
The purpose of the boiler blow-down system is to remove any concentrations of soluble
substances, including calcium, magnesium and silica, that are present in the boiler feed water.
The heat recovery boiler is normally fitted with an automatic blow-down system, which
automatically opens the blow-down valves at regular intervals for several minutes, in
order to divert some of the steam to the blow-down vessel, where any total dissolved
solids are removed and the steam vented off to the atmosphere.
62
Figure 28 - Cogeneration plant water / steam cycle.
63
CHAPTER 4 - TECHNICAL EVALUATION OVERVIEW.
The technical evaluation process firstly aimed to evaluate the Local Authority Planning
and Consents procedures for the construction of the proposed cogeneration plant, in
order to ascertain whether or not the project was likely to be granted “Deemed Planning
Permission”.
The second stage was then to identify engine manufacturers who would be in a position to
supply large gas engines that are capable of producing a total power output of 9.5MWe.
The third stage of the process was to calculate the size of the engines exhaust gas pipes and
to determine if there would be sufficient heat energy available from the selected engines exhaust
gases to produce 8 tonnes per hour of saturated steam, at 7 bar pressure, in a waste heat
recovery boiler.
Finally, the last stage of the process was to calculate whether or not the plant would qualify as
good quality combined heat and power, under CHPQA rules, by completing the relevant
CHPQA forms.
64
4.1 - PROPOSED SITE FOR THE COGENERATION PLANT.
The proposed site for the cogeneration plant is in an industrial area local to a large
manufacturing plant in the West Midlands, England, UK.
There is a large amount of waste ground local to the manufacturing plant that could be
used to site the cogeneration plant and because the proposed site is in an industrial area,
it is anticipated that there will be little opposition from the local community.
It is also foreseen that the Local Planning Authority will have no objections to the proposed
site for the plant as the land is currently lying vacant and the surrounding area would be
regenerated as part of the construction process, thus complying with Planning Policy
Guidance Note 4 on Urban Regeneration.
The cogeneration plant building would be sound-proofed to minimise any noise pollution
and the area adjacent to the plant would be landscaped to minimise any visual impact.
A typical layout drawing and schematic drawing for the proposed plant are shown in figures
29 and 30.
Furthermore, an environmental impact assessment for the proposed plant is given
in Chapter 6, also.
65
Figure 29 - Cogeneration plant engineering drawing.
SUBJECT TO COPYRIGHT – SEE HARD COPY
66
Figure 30 - Cogeneration plant layout drawing.
67
4.2 - GAS ENGINE MANUFACTURERS.
The engine manufacturers listed in table 8, were identified from trade publications and the
worldwide web as being in a position to supply gas engines for the proposed cogeneration plant
[2,3,6].
The technical specifications for the various gas engines and the number of engines that would
be required for the plant are also shown in the table.
Jenbacher gas engine
Jenbacher gas engine
Rolls Royce gas engine
Rolls Royce gas engine
Wartsila gas engine
Wartsila gas engine
Type J616GS
Type J620GS
Type KVGB16
Type KVGB18
Type 12V34SG
Type 18V34SG
2.19MW
3.2MW
2.81MW
3.16MW
4.04MW
6.06MW
1500 rpm
1500 rpm
1000 rpm
1000 rpm
750 rpm
750 rpm
50Hz
50Hz
50Hz
50Hz
50Hz
50Hz
5 reqd.
3 reqd.
4 reqd.
3 reqd.
3 reqd.
2 reqd.
Table 8 - Gas engine manufacturers and product range.
4.2.1 - SELECTION OF GAS ENGINE MANUFACTURER.
The Rolls Royce Bergen KVGB-18 and the Jenbacher J620GS gas engines were then
identified as being the most suitable engines to meet the plants requirements for 9.5MWe
of power.
The final decision as to which manufacturer to select to build the plant would then rest
with the client and would be based upon the relative costs of each engine type and on
the clients preference for a particular engine manufacturer.
The decision would also be influenced by the delivery date for the engines to site and on
the earliest guaranteed plant start-up date.
The main reason for not choosing the Wartsila range of gas engines was that the 12V34SG and
the 18V34SG engines produced 2.5MWe more power output than was actually required by the
cogeneration plant.
68
4.2.2 - GAS ENGINE TECHNICAL INFORMATION.
The Jenbacher Engine Company and Rolls Royce Bergen Diesels were then contacted for
technical information on their range of gas engines.
From the information received, it was possible to base the technical calculations used in
this thesis on the Bergen KVGB-18 gas engine (See Appendix C).
The technical specification and operating conditions for the KVGB-18 gas engine at full
and at part loads of 50% and 80% are shown in the tables 9 and 10.
Number of cylinders
Cylinder bore
Piston stroke
Engine M.C.R
Engine rated speed
Exhaust mass flow-rate
Exhaust volume flow-rate
Exhaust temperature
Temperature after turbocharger
18
250 mm
300 mm
3.16 MWe
1000 rpm
21,000 kg / hour
42,600 m³ / hour
520 ºC
420 ºC
Table 9 - KVGB18 gas engine technical data (M.C.R).
Exhaust mass flow-rate at 80% load
Temperature after turbocharger
Exhaust mass flow-rate at 50% load
Temperature after turbocharger
17,550 kg / hour
420 ºC
12,400 kg / hour
400 ºC
Table 10 - KVGB18 gas engine technical data (50% & 80% M.C.R).
From the technical data sheet on the KVGB-18 gas engine, it was ascertained that
the exhaust gas temperature at exit from the turbocharger would be approximately
420ºC.
69
Then, using basic heat transfer and fluid dynamics equations it was possible to calculate
the ideal size of exhaust gas pipe and the heat loss in the exhaust gas pipe between the
turbocharger outlet and the inlet to the waste heat recovery boiler, in order to calculate the
exhaust gas inlet temperature to the boiler.
The actual thermodynamic calculations that were undertaken for the proposed plant are detailed
in the following sections (See sections 4.3 to 4.6).
70
4.3 - CALCULATION OF THE EXHAUST PIPE SIZE AND HEAT TRANSFER COEFFICIENTS.
The exhaust gas volume flow-rate, for one engine operating at its maximum continuous rating
is calculated as follows:
M.C.R exhaust gas flow-rate = MCR exhaust gas volume flow-rate
3,600
[m³ / h]
[s / h]
M.C.R exhaust gas flow-rate = 42,600 / 3,600
[m³ / s]
M.C.R exhaust gas flow-rate = 11.833 m³ / s.
4.3.1 - EXHAUST GAS VELOCITY.
When designing an exhaust gas system it is standard engineering practice to ensure that
the exhaust gas velocity does not exceed 46 metres per second, due to noise and vibration
constraints.
Therefore, the exhaust gas velocity was calculated first for a 24” exhaust pipe and then for
a 36” pipe, in order to ascertain the ideal pipe diameter to minimise noise and vibration levels.
The exhaust pipe wall thickness, which the gas velocity calculations were based upon, was
0.375” (9.525mm), in order to minimise the overall weight of the pipe-work system (See ANSI
Pipe Schedule - Appendix E).
4.3.2 - 24” PIPE GAS VELOCITY.
The exhaust gas velocity in the 24” exhaust pipe was calculated as follows:
Pipe outside diameter = 24”
= 0.6096 metres.
Pipe wall thickness
= 0.375“ = 0.00953 metres.
Pipe inside diameter
= 0.6096 - (2 * 0.00953) = 0.5905 metres.
71
Pipe inside area = 3.14 * (inside diameter)²
[m²]
4
Pipe inside area = 3.14 * (0.5905 * 0.5905)
[m²]
4
Pipe inside area = 0.2739 m².
Exhaust gas velocity = Exhaust gas volume flow-rate
Pipe inside area
[m³ / s]
[m²]
[m / s]
Exhaust gas velocity = 11.833
0.2739
Exhaust gas velocity = 43.2 m / s.
4.3.3 - 36” PIPE GAS VELOCITY.
The 36” exhaust gas pipe dimensions and the gas velocity were calculated in the same way
as for the 24” pipe.
The actual pipe dimensions and the gas velocity are given below:
Pipe outside diameter = 36”
= 0.9144 metres.
Pipe wall thickness
= 0.375” = 0.00953 metres.
Pipe inside diameter
= 35.25” = 0.9144 - (2 * 0.00953) = 0.89535 metres.
Pipe inside area
= 0.6296 m².
Exhaust gas velocity
= 18.8 m / s.
The exhaust gas velocity in the 36” pipe was calculated as 18.8 m / s and by using this
size of pipe we should be able to reduce the noise emanating from the exhaust gas system
considerably.
72
4.3.4 - EXHAUST PIPE HEAT LOSS VARIABLES.
The heat loss from the exhaust gas pipe is dependent on a number of factors including the
exhaust gas inlet temperature, the ambient outside air temperature, the length, inside and
outside diameters and the thermal conductivity of the exhaust gas pipe and on the thickness
and thermal conductivity of pipe insulation material.
The ambient air temperature inside the cogeneration plant building, will vary depending
on the time of day and on the time of year and the heat loss from the exhaust pipes will
be larger during colder ambient conditions.
The seasonal ambient air temperatures [33] for Central England are shown in table 11.
The thermal conductivities [34] for the steel exhaust gas pipe at various temperatures
and for rock-wool insulation material at 100ºC are shown in the table 12.
Finally, the heat loss through the pipe is also dependent on the heat transfer coefficients
for the exhaust gas and for the air surrounding the pipe insulation material.
Spring
Summer
Autumn
Winter
15.3ºC
19.6ºC
12ºC
9.3ºC
Table 11 - Seasonal ambient air temperatures.
Steel pipe at 27ºC
Steel pipe at 127ºC
Steel pipe at 227ºC
Steel pipe at 327ºC
Steel pipe at 427ºC
Steel pipe at 527ºC
Rockwool insulation at 100ºC
55 W / mK
52 W / mK
48 W / mk
45 W / mK
42 W / mK
38 W / mK
0.045 W / mK
Table 12 - Thermal conductivity values.
73
4.3.5 - EXHAUST GAS PROPERTIES.
The exhaust gas heat transfer coefficient can be calculated by using empirical heat transfer
equations that relate to forced convection, as the exhaust gases can be thought of as being
forced through the exhaust gas pipe by the upwards motion of the engines pistons in their
respective cylinders during the exhaust stroke.
Unfortunately, there is very little thermodynamic data given in Rogers and Mayhew steam tables
that relates to exhaust gases.
Therefore, in order to calculate the heat transfer coefficient of the exhaust gases, it has been
necessary to use the thermodynamic data relating to carbon dioxide gas as an approximation
[35].
Specific heat capacity
Density
Dynamic viscosity
Thermal conductivity
1122 J / kgK
0.782 kg / m³
0.0000305 kg / ms
0.04752 W / mK
Table 13 - Properties of carbon dioxide gas.
4.3.6 - EXHAUST GAS HEAT TRANSFER COEFFICIENT.
The Reynolds number of the exhaust gas flow must first be calculated in order to ascertain
whether the gas flow is laminar or turbulent flow [34,36].
The Reynolds number is calculated as follows:
Reynolds number =
Gas density * Gas velocity * Pipe diameter
[--]
Dynamic viscosity
Reynolds number = 0.782 * 18.8 * 0.89525
[--]
0.0000305
Reynolds number = 430,659.
74
Since the Reynolds number is greater than 3,800, then the gas flow can be termed as turbulent
flow.
4.3.7 - PRANDTL NUMBER.
The Prandtl number and the Nusselt number for forced convection and turbulent flow were then
calculated in order to determine the value of the exhaust gas heat transfer coefficient.
Prandtl number = Dynamic viscosity * Specific heat capacity
[--]
Thermal conductivity
Prandt number =
[--]
0.0000305 * 1122
0.04752
Prandtl number = 0.722.
4.3.8 - NUSSELT NUMBER AND HEAT TRANSFER COEFFICIENT.
Nusselt number = 0.0225 * (Reynolds number) 0.8 * (Prandtl number) 0.33
[--]
Nusselt number = 0.0225 * (430,659) 0.8 * (0.722) 0.33
[--]
Nusselt number = 0.0225 * 32,159 * 0.9
[--]
Nusselt number = 650.
Nusselt number = Heat transfer coefficient * Pipe diameter
[--]
Thermal conductivity
Heat transfer coefficient = Nusselt number * Thermal conductivity
[W / m²K]
Pipe diameter
Heat transfer coefficient = 650 * 0.04752
[W / m²K]
0.89535
Heat transfer coefficient = 34.5 W / m²K.
75
4.3.9 - HEAT TRANSFER COEFFICIENT FOR AIR.
The heat transfer coefficient for air, based on a natural convection process, has been calculated
assuming that the temperature difference between the outside of the pipe lagging material and
the ambient air is a maximum of 15 ºC [34,36].
Heat transfer coefficient = 1.34 * ((Pipe lagging temperature - ambient air temperature)) 0.25
((Pipe diameter))
Heat transfer coefficient = 1.34 * (15 / 0.9155)
0.25
Heat transfer coefficient = 2.7 W / m²K.
76
4.4 - CALCULATIONS FOR THE EXHAUST PIPE HEAT LOSS.
The heat loss from the exhaust gas pipe, which has a layer of insulation surrounding it,
can then be calculated by using the following equation:
Heat loss through pipe = Q =
2 * 3.14 * L * (Tb - Ta)
.
((1/r1ha + 1/r3hb + ln(r2/r1)/k1 + ln(r3/r2)/k2))
Where
Q = Pipe heat loss
[W]
ha = Heat transfer coefficient of the exhaust gas
[W / m²K]
hb = Heat transfer coefficient of air
[W / m²K]
k1 = Thermal conductivity of the exhaust pipe at 427ºC
[W / mK]
k2 = Thermal conductivity of the pipe lagging material at 100ºC
[W / mK]
L = Length of the exhaust gas pipe
[m]
r1 = Inside pipe diameter / 2
[m]
r2 = Outside pipe diameter / 2
[m]
r3 = Outside radius of pipe + thickness of lagging
[m]
Ta = Exhaust gas temperature at inlet to the exhaust pipe
[K]
Tb = Ambient air temperature
[K]
Note: The heat loss value that is obtained by using the above equation will be a negative value,
as Ta>Tb.
77
4.4.1 - EXHAUST GAS OUTLET TEMPERATURE.
The heat loss from the exhaust gas pipe can also be calculated by using the steady flow energy
equation.
The heat loss value that would be obtained would be identical to that calculated by using
equation 4.4, above.
Q - W = ma (h2 - h1) + ma (C2² - C1²) / 2 + ma * g * ( Z2 - Z1) - Steady Flow Eq.
Where Q = Pipe heat loss
[W]
C1 = Exhaust gas velocity at inlet to exhaust pipe
[m / s]
C2 = Exhaust gas velocity at outlet to exhaust pipe
[m / s]
Cp = Specific heat capacity at constant pressure of the exhaust gas
[J / kgK]
g = 9.81
[m / s²]
h1 = Exhaust gas enthalpy at exhaust pipe inlet
[J / kg]
h2 = Exhaust gas enthalpy at exhaust pipe outlet
[J / kg]
ma = Exhaust gas mass flowrate
[kg / s]
T2 = Exhaust gas temperature at exit from exhaust pipe
[K]
T1 = Exhaust gas temperature at inlet to exhaust pipe
[K]
W = Work done on the exhaust gas
[W]
Z1 = Exhaust gas pipe inlet vertical height above reference point
[m]
Z2 = Exhaust gas pipe outlet vertical height above reference point
[m]
Assuming that:
•
No work is done on the exhaust gas between the inlet and outlet pipes.
•
The pipe inlet and outlet heights are at the same level above a known reference point.
•
The pipe area is the identical at inlet and outlet.
78
Then the steady flow energy equation can be reduced to:
Heat loss through pipe = Q = ma * (h2 - h1) = ma * Cp * (T2 - T1)
The above equation can then be rearranged, in order to determine the exhaust gas temperature
at inlet temperature to the heat recovery boiler:
Exhaust gas temperature at inlet to heat recovery boiler = T2 = T1 + (Q / (ma * Cp)).
The above equations were then used to calculate the heat loss through the exhaust gas pipe
and the exhaust gas temperature at inlet to the heat recovery boiler, depending on the length
of the pipe, the lagging material thickness and on the seasonal ambient air temperature.
The results are shown in the tables 14 to 18, for KVGB-18 gas engines operating independently
and in parallel with one another.
The heat savings that can be achieved from using 6” and 9” lagging, instead of 4” lagging
have also been calculated and are shown in table 19, for one engine operating at maximum
continuous rating.
79
Lagging
Thickness
(")
Pipe
Length
(m)
Spring
Heat Loss
(kW)
Summer
Heat Loss
(kW)
Autumn
Heat Loss
(kW)
Winter
Heat Loss
(kW)
4"
4"
4"
30m
50m
70m
14.88
24.8
34.71
14.7
24.5
34.28
14.99
24.99
34.96
15.07
25.1
35.14
6"
6"
6"
30m
50m
70m
10.94
18.24
25.54
10.8
18.02
25.22
11.02
18.38
25.72
11.07
18.47
25.85
9"
9"
9"
30m
50m
70m
8.03
13.37
18.73
7.93
13.2
18.5
8.09
13.46
18.87
8.13
13.53
18.96
Table 14 - Seasonal pipe heat loss for one engine at 100% M.C.R.
Lagging
Thickness
(")
Pipe
Length
(m)
Average
Heat Loss
(kW)
Two Pipes
Heat Loss
(kW)
Three Pipes
Heat Loss
(kW)
Exhaust
Temperature
(ºC)
4"
4"
4"
30m
50m
70m
14.91
24.85
34.77
29.82
49.7
69.54
44.73
74.55
104.31
417.7
416.1
414.6
6"
6"
6"
30m
50m
70m
10.96
18.28
25.58
21.92
36.56
51.16
32.88
54.84
76.74
418.3
417.2
416
9"
9"
9"
30m
50m
70m
8.05
13.39
18.77
16.1
26.78
37.54
24.15
40.17
56.3
418.7
417.9
417.1
Table 15 - Average annual pipe heat losses for 1, 2 and 3 engines at 100% M.C.R.
80
Lagging
Thickness
(")
Pipe
Length
(m)
Average
Heat Loss
(kW)
Two Pipes
Heat Loss
(kW)
Three Pipes
Heat Loss
(kW)
Exhaust
Temperature
(ºC)
4"
4"
4"
30m
50m
70m
14.91
24.85
34.77
29.82
49.7
69.54
44.73
74.55
104.31
417.2
415.4
413.5
6"
6"
6"
30m
50m
70m
10.96
18.28
25.58
21.92
36.56
51.16
32.88
54.84
76.74
418
416.6
415.2
9"
9"
9"
30m
50m
70m
8.05
13.39
18.77
16.1
26.78
37.54
24.15
40.17
56.3
418.5
417.5
416.5
Table 16 - Average annual pipe heat losses for 1, 2 and 3 engines at 80% M.C.R.
Lagging
Thickness
(")
Pipe
Length
(m)
Spring
Heat Loss
(kW)
Summer
Heat Loss
(kW)
Autumn
Heat Loss
(kW)
Winter
Heat Loss
(kW)
4"
4"
4"
30m
50m
70m
14.15
23.58
32.99
13.97
23.27
32.57
14.26
23.76
33.25
14.33
23.88
33.42
6"
6"
6"
30m
50m
70m
10.39
17.34
24.27
10.26
17.11
23.96
10.48
17.48
24.46
10.53
17.57
24.59
9"
9"
9"
30m
50m
70m
7.63
12.71
17.81
7.53
12.54
17.58
7.69
12.8
17.95
7.73
12.87
18.04
Table 17 - Seasonal pipe heat loss for one engine at 50% M.C.R.
81
Lagging
Thickness
(")
Pipe
Length
(m)
Average
Heat Loss
(kW)
Two Pipes
Heat Loss
(kW)
Three Pipes
Heat Loss
(kW)
Exhaust
Temperature
(ºC)
4"
4"
4"
30m
50m
70m
14.17
23.62
33.06
28.34
47.24
66.12
42.51
70.86
99.18
396
393.8
391.3
6"
6"
6"
30m
50m
70m
10.41
17.38
24.32
20.82
34.76
48.64
31.23
52.14
72.96
397.2
395.4
393.6
9"
9"
9"
30m
50m
70m
7.65
12.73
17.85
15.3
25.46
35.7
22.95
38.19
53.55
398
396.6
395.3
Table 18 - Average annual pipe heat loss for 1, 2 and 3 engines at 50% M.C.R.
Lagging
Thickness
(")
Pipe
Length
(m)
Spring Heat Summer Heat Autumn Heat Winter Heat
Savings
Savings
Savings
Savings
(kW)
(kW)
(kW)
(kW)
6"
9"
30m
30m
26.48%
46.03%
26.53%
46.05%
26.48%
46.03%
26.54%
46.05%
6"
9"
50m
50m
26.45%
46.08%
26.44%
46.12%
26.45%
46.13%
26.41%
46.10%
6"
9"
70m
70m
26.42%
46.03%
26.43%
46.03%
26.43%
46.02%
26.43%
45.98%
Table 19 - Energy savings from 6” and 8” lagging material.
4.4.2 - DISCUSSION OF PIPE HEAT LOSS RESULTS.
The heat loss from the exhaust gas pipes reduces considerably and the exhaust gas
temperatures at inlet to the waste heat boiler correspondingly increase, for all pipe
lengths and for engines operating at 50%, 80% and 100% M.C.R, as we increase the
thickness of the pipe lagging material.
82
The average heat energy savings that can be obtained from using 6” and 9” lagging,
instead of 4” lagging, are 26.5% and 46.05%, respectively.
The heat loss from the exhaust gas pipes is also greater in the autumn and winter seasons,
because of the lower ambient outside air temperatures.
The exhaust gas temperature at exit from the gas engine remains constant at 420ºC, when the
engine is operating at 80% and 100% M.C.R. However, the exhaust gas mass flow-rate is about
15% less at 80% load and this consequently has the effect of reducing the exhaust gas inlet
temperature to the waste heat boiler.
Furthermore, when the engines are operating at 50% load, the exhaust gas temperature
decreases to 400ºC and the exhaust gas mass flow-rate decreases to 12,400 kg / hour.
This decrease in the exhaust gas temperature causes the heat loss through the exhaust gas
pipe to decrease, but because the exhaust gas mass flow-rate also decreases, this results in a
lower overall temperature at inlet to the waste heat recovery boiler.
4.4.3 - EXHAUST PIPE DIMENSIONS.
Based on previous engineering experience, it was concluded that it would be necessary to
have a separate exhaust gas pipe, for each of the three gas engines that would be installed
at the proposed cogeneration plant.
From studying the layout drawings from a similar sized cogeneration plant, it was estimated
that each exhaust gas pipe would be approximately 50 metres in length, inclusive of vertical
sections of pipe-work and pipe bends.
Each exhaust pipe would be lagged with rock-wool insulation to a thickness of 9”, to keep
the heat loss in the system to a minimum and to give the highest possible exhaust gas inlet
temperature to the waste heat boiler.
Table 20 gives details of the heat losses that would be incurred in an exhaust gas system,
which is based on three gas engines operating at 100% load, with a total length of 150 metres
of 36” pipe, with 9” of lagging material surrounding it.
83
Lagging
Thickness
(")
Pipe
Length
(m)
Gas Engine
Power Output
(% M.C.R)
Three Exhaust
Pipes Heat Loss
(kW)
Exhaust Gas
Temp to HRSG
(ºC)
9"
9"
9"
50m
50m
50m
100%
80%
50%
40.17
40.17
38.19
417.9
417.5
396.6
Table 20 - Overall heat loss for three engines at 100% M.C.R.
84
4.5 - CALCULATIONS FOR THE STEAM PRODUCTION RATE.
The first step in the process was to draw a table containing the relevant enthalpies, heat rates,
pressures and temperatures for the water, steam and exhaust gases that will be present in the
heat exchanger [37], as shown in the table 21.
The second step was then to draw a Temperature (ºC) v Heat (kJ/kg) graph in order to ascertain
the exhaust gas outlet temperature from the waste heat recovery boiler, depending on whether a
10ºC or 15 ºC heat exchanger pinch point was used, as shown in figure 31.
State
1
2
3
A
B
C
Fluid
Water
Water / Steam
Steam
Exh. gas
Exh. gas
Exh. gas
Pressure
Temperature
Enthalpy
Heat
(bar)
(ºC)
(kJ / kg)
(kJ / kg)
7
7
7
/
/
/
60
165
165
417.9
175 / 180
To calculate
251.1
697
2764
/
/
/
0
445.9
2512.9
2512.9
445.9
0
Table 21 - Properties of water, steam and engine exhaust gases.
85
Figure 31 - Graph of Temperature (ºC) versus Heat (kJ/kg).
86
4.5.1 - CALCULATION OF THE EXHAUST GAS TEMPERATURE AT BOILER OUTLET.
The linear equation that is used to describe the exhaust gas cooling line can then be calculated
from:
Y = mX + C
Where m = Gradient of exhaust gas cooling line.
C = Y intercept for exhaust gas cooling line.
Gradient, m = (Y2 - Y1) / (X2 - X1)
[--]
Gradient, m = (417.9 - 175) / (2512.9 - 445.9)
[--]
Gradient, m = 0.1175.
Y intercept, C = Y - mX
[ºC]
Y intercept, C = 175 - (0.1175 * 445.9)
[ºC]
Y intercept, C = 122.6 ºC.
Exhaust gas temperature at boiler outlet = 122.6 ºC.
4.5.2 - STEAM PRODUCTION RATE THEORY.
The heat energy that is contained within the engines exhaust gases between 417.9ºC
and 122.6ºC is transferred to the hot water at 4 bar, 60 ºC, to produce saturated steam
in the waste heat recovery boiler.
The amount of steam that can be produced by the waste heat boiler was calculated as follows:
Flux of heat energy into boiler = flux of heat energy out of boiler
[W]
(Mw * h1) + (Mg * ha) = (Mw * h3) + (Mg * hc)
[W]
Mw * (h3 - h1) = Mg * (ha - hc)
[W]
Mw * (h3 - h1)
[W]
= Mg * Cp * (Ta - Tc)
87
Where ha = Enthalpy of exhaust gas at inlet to waste heat boiler
[J / kg]
hc = Enthalpy of exhaust gas at outlet from the waste heat boiler
[J / kg]
h1 = Enthalpy of water at inlet to waste heat boiler
[J / kg]
h3 = Enthalpy of water at outlet from the waste heat boiler
[J / kg]
Mg = Mass flow-rate of exhaust gas in / out of waste heat boiler
[kg / s]
Mw = Mass flow-rate of water and steam in / out of the waste heat boiler
[kg / s]
Cp = Specific heat capacity of exhaust gas
[J / kgK]
Ta
= Temperature of exhaust gas at inlet to waste heat boiler
[K]
Tc
= Temperature of exhaust gas at outlet from waste heat boiler
[K]
4.5.3 - STEAM PRODUCTION RATE.
Mw * (h3 - h1) = Mg * Cp * (Ta - Tc)
Mw * (2764 - 251) * 1000 = 17.499 * 1100 * (417.9 - 122.6)
Mw * 2,513,000 = 5,684,200
Mw = 2.26 kg / s.
Mw = (2.26 * 3600) / 1000 tonnes per hour.
Mw = 8.136 tonnes per hour of steam.
From the above equations it was calculated that 8.136 tonnes per hour of steam could be
produced from three KVGB-18 gas engines operating at 100% load, based on an exhaust
gas inlet temperature of 417.9 ºC and a heat exchanger pinch point of 10 ºC.
The above calculations were repeated for one, two and three gas engines operating
independently and in parallel with one another at 50%, 80% and 100% load and for heat
exchangers with either a 10 ºC or 15 ºC pinch point.
The results from these calculations are shown in table 22.
88
Engine load
(% M.C.R)
Exhaust gas Exhaust gas
inlet flow-rate inlet temp.
to HRSG
to HRSG
(kg / s)
(ºC)
Steam production
at 10 ºC
pinch point
(tonnes / hour)
Steam production
at 15 ºC
pinch point
(tonnes / hour)
1 Engine - 50%
1 Engine - 80%
1 Engine - 100%
3.44
4.875
5.833
396.6
417.5
417.9
1.46
2.26
2.71
1.43
2.22
2.66
2 Engines - 150%
2 Engines - 180%
2 Engines - 200%
9.273
10.708
11.667
410
417.7
417.9
4.17
4.97
5.42
4.09
4.88
5.32
3 Engines - 250%
3 Engines - 280%
3 Engines - 300%
15.1
16.541
17.499
413
417.8
417.9
6.88
7.68
8.13
6.75
7.54
7.98
Table 22 - Steam production rates.
4.5.4 - DISCUSSION OF RESULTS.
From table 22, it is evident that with three KVGB-18 gas engines operating at full load, it
is possible to generate 8.13 tonnes and 7.98 tonnes per hour of steam, assuming a heat
exchanger pinch point of either 10 ºC or 15 ºC.
Therefore, it should be practicable to generate sufficient steam for the manufacturing plants
process requirements.
If one gas engine is off-load for maintenance purposes, then the cogeneration plant will still
be able to supply the manufacturing company with 6.31MWe of electricity and either 5.32 or
5.42 tonnes per hour of process steam, respectively, depending on the pinch point temperature.
It should also be noted, however, that the KVGB-18 engine is an old design and that the latest
version, the KVGB-18G4 can produce up to 3.6MWe of power and a slightly higher exhaust gas
temperature, than the engine used for this case study.
It would therefore be anticipated that more than 5.42 tonnes per hour of steam could be
produced from only two engines operating and this would assist to make up the shortfall
in steam production to the manufacturing plant.
89
4.6 - EVALUATION OF THE COGENERATION PLANT OPERATING CONDITIONS.
The next phase of the feasibility study was to calculate the amount of electricity that would
be produced and the amount of natural gas and lubricating oil that would be consumed by the
three gas engines, under annual operation.
4.6.1 - DEFINITION OF PLANT AVAILABILITY.
The availability of the plant is defined as follows:
Availability = Number of MWh generated during period
Total number of MWh at 100% availability
4.6.2 - CALCULATION OF NATURAL GAS ENERGY CONSUMPTION.
From the engine manufacturers operating data, the KVGB-18 gas engines specific energy
consumption in MWh of natural gas, can be calculated, based on a net calorific value of
36.0 MJ / m³.
Natural gas burnt =
765 * 3 engines
[m³ / h]
Energy consumed = 2,295 * 36 = 82,620
[MJ / h]
Energy consumed = 82,620 * 1,000,000 * 5488
[J / yr]
Energy consumed = 125,949.6 MWh per year, based on the N.C.V.
4.6.3 - CALCULATION OF SPECIFIC LUBRICATING OIL CONSUMPTION.
The lubricating oil consumption for one KVGB-18 gas engine operating at full load is 1.8
litres of oil per hour. Therefore, the lubricating oil consumption for three gas engines operating
at full load would be 5.4 litres of oil per hour.
90
Table 23 gives details of the number of MWhours of electricity that would be generated
and the natural gas and lubricating oil consumption, depending on the annual availability of
the plant.
Plant
load
(MW)
Plant
availability
Total number
of hours
generated
Electricity
generated
(MWh)
Fuel gas
energy usage
NCV - (MWh)
Lube oil
consumption
(litres)
9.471
9.471
9.471
9.471
9.471
9.471
9.471
9.471
9.471
9.471
9.471
9.471
9.471
9.471
9.471
9.471
1
0.99
0.98
0.97
0.96
0.95
0.94
0.93
0.92
0.91
0.9
0.89
0.88
0.87
0.86
0.85
5,488.0
5,433.1
5,378.2
5,323.4
5,268.5
5,213.6
5,158.7
5,103.8
5,049.0
4,994.1
4,939.2
4,884.3
4,829.4
4,774.6
4,719.7
4,664.8
51,976.8
51,456.9
50,936.9
50,417.9
49,898.0
49,378.0
48,858.0
48,338.1
47,819.1
47,299.1
46,779.2
46,259.2
45,739.2
45,220.2
44,700.3
44,180.3
125,949.6
124,689.7
123,429.7
122,172.0
120,912.1
119,652.1
118,392.2
117,132.2
115,874.6
114,614.6
113,354.6
112,094.7
110,834.7
109,577.1
108,317.1
107,057.2
29,635.2
29,338.7
29,042.3
28,746.4
28,449.9
28,153.4
27,857.0
27,560.5
27,264.6
26,968.1
26,671.7
26,375.2
26,078.8
25,782.8
25,486.4
25,189.9
Table 23 - Annual electricity generation and fuel consumption.
91
4.7 - CHPQA SCHEME TECHNICAL CALCULATIONS.
In order for the cogeneration plant to be eligible for enhanced capital allowances and for
exemption of payment of business rates and climate change levy on its fuel input and on
any electricity output to the grid, then the plant must meet certain criteria that is specified
in the United Kingdom Combined Heat and Power Quality Assurance Scheme.
The overall objective of the Combined Heat and Power Quality Assurance Scheme is
to provide a standard criteria for determining the fuel energy input and heat and power
outputs from any cogeneration plant, against certain base-line levels.
For any new cogeneration plant to be certified as good quality under the CHPQA
Scheme, then the plant must have a quality index of greater than 105 and a power
efficiency of greater than 20%, under long term annual operation [20].
The quality index is based upon the useful heat output and power output efficiencies
for the specific type of plant under consideration and is a measure of the overall efficiency
of the plant.
4.7.1 - CALCULATION OF QUALITY INDEX AND POWER EFFICENCY.
The manufacturing plants heat output is based upon the amount of heat energy supplied from
the cogeneration plant, against a reference value for the feed-water inlet temperature to the
waste heat recovery boiler of 10ºC.
The fuel energy input to the cogeneration plant is based upon the plants annual gas
consumption on a gross calorific value basis, as opposed to the net calorific value basis
that is used by gas engine manufacturers when quoting their engines energy consumption.
It should be noted that for engines whose technical data is based on the net calorific value,
then the engines efficiency is higher and its fuel energy consumption is lower, than that of
an engine whose technical data is quoted on a gross calorific value basis.
The most relevant sections of the CHPQA Application Form F3, which were completed for
the proposed cogeneration plant, are shown in figures 32 to 36.
92
4.7.2 - FUEL ENERGY CONSUMPTION BASED ON GROSS CALORIFIC VALUE.
The conversion from natural gas energy consumption based on net calorific value basis to a
gross calorific value basis is shown below, using gas with a gross calorific value of 39 MJ / m3.
Energy consumed = 2295 * 39,000,000
[J / h]
Energy consumed = 8.9505 * 10 10
[J / h]
Energy consumed = 8.9505 * 10 10 * 5488
[J / yr]
Energy consumed = 4.912 * 10 14 / 3.6 * 10 9
[MWh]
Energy consumed = 136,445.4 MWh per Year, based on G.C.V.
Table 23 above, was then adjusted to take into account the natural gas consumption on a
gross calorific value basis and the new table, table 24, is shown below.
The values of heat and electricity production at 100% and 96% availability were then used as
the basis for calculating whether the plant could be determined as good quality combined heat
and power, under CHPQA rules.
Plant
load
(MW)
Plant
availability
Total num ber
of hours
generated
Electricity
generated
(MWh)
Fuel gas
cons um ption
GCV - (MWh)
Heat / s team
production
(MWh)
9.471
9.471
9.471
9.471
9.471
9.471
9.471
9.471
9.471
9.471
9.471
9.471
9.471
1
0.99
0.98
0.97
0.96
0.95
0.94
0.93
0.92
0.91
0.9
0.89
0.88
5,488.0
5,433.1
5,378.2
5,323.4
5,268.5
5,213.6
5,158.7
5,103.8
5,049.0
4,994.1
4,939.2
4,884.3
4,829.4
51,976.8
51,456.9
50,936.9
50,417.9
49,898.0
49,378.0
48,858.0
48,338.1
47,819.1
47,299.1
46,779.2
46,259.2
45,739.2
136,445.0
135,080.1
133,715.1
132,352.6
130,987.7
129,622.7
128,257.8
126,892.8
125,530.4
124,165.4
122,800.4
121,435.6
120,070.6
33,193.0
32,861.0
32,529.0
32,197.5
31,865.5
31,533.4
31,201.4
30,869.3
30,537.9
30,205.8
29,873.8
29,541.7
29,209.7
Table 24 - Electricity production and natural gas consumption (GCV).
93
Figure 32 - CHPQA Form F3, Part 1, Site Information.
94
Figure 33 - CHPQA Form F3, Part 1, Site Energy Demands.
95
Figure 34 - CHPQA Form F3, Projected Scheme Performance Details.
96
Figure 35 - CHPQA Form F3, Part 3, Projected Annual and Max Heat Operation.
97
Figure 36 - CHPQA Form F3, Part 4, Criteria For Good Quality CHP.
98
4.7.3 - ASSESSMENT OF COGENERATION PLANT AS GOOD QUALITY CHP.
The quality index and power efficiency for the proposed cogeneration plant were calculated to be
106.6 and 38.1%, respectively.
As the quality index and power efficiency are greater than the CHPQA threshold criteria of
a quality index of 105 and a power efficiency of 20%, then the proposed plant would be eligible
to register as good quality combined heat and power.
The plant would be entitled to exemption from the payment of climate change levy on its fuel
input and electricity output to the grid and for enhanced capital allowances and exemption on
business rates, also.
4.7.4 - OVERALL PLANT EFFICIENCY BASED ON GCV.
The overall efficiency of the proposed cogeneration plant when operating at 96% availability
and based on the gross calorific value of the fuel energy input and on the CHPQA definition of
heat energy output was calculated as follows:
Plant efficiency (GCV) = Heat output + Power output
Fuel Energy Input
Plant efficiency (GCV) = 31,865.5 + 48,898
[MWh]
[MWh]
[--]
130,987.7
Plant efficiency (GCV) = 0.624 = 62.4%.
99
CHAPTER 5 - FINANCIAL APPRAISAL FOR THE PROPOSED PLANT.
In order to ascertain whether it would be economically viable for the manufacturing company
to invest in a new cogeneration plant, a financial appraisal was undertaken to determine the
break-even cost of generating heat and power from the plant.
The break-even cost was then compared to the average price paid by UK industry in 2003 to
purchase a MWh of electricity from the National Grid, to determine the plants profitability.
5.0.1 - ANNUAL BANK REPAYMENT.
For the manufacturing company to be in a position to place an order for the construction of the
cogeneration plant, then it would be necessary for them to obtain a bank loan, to cover the initial
investment costs [38].
The amount of annual repayment on the bank loan could then be calculated by using the
following equation:
Annual repayment on bank loan = Initial investment *
Capital recovery factor.
Annual repayment on bank loan = Initial investment *
i (1 + i) n
.
((1 + i) n - 1)
Where initial investment = Amount of money borrowed from the bank - [£].
i = Bank interest rate per annum - [As a decimal].
n = Repayment period - [years].
5.0.2 - SPECIFIC COSTS METHOD.
The break-even or specific cost (£ / MWh) of generating electricity from the cogeneration plant
could then also be calculated, as follows:
C = Annual repayment + Fuel costs + O & M costs + Taxes & Insurance
Number of MWh produced per Year
[£]
[MWh]
100
5.0.3 - INITIAL INVESTMENT.
The construction costs and prices for the capital plant and equipment to be installed in the
cogeneration plant were obtained by contacting the relevant engineering manufacturers and
suppliers.
The budget price for the overall construction and commissioning of the plant was estimated
to be £3,965,652, neglecting the fees for the projects architects and consultants and a reserve
that should be set aside to cover any cost over-runs, as shown in table 25.
The plants operation and maintenance costs were estimated at £108,035 per annum, as shown
in table 26 and the lubricating oil costs are shown in table 27.
The plants fuel costs were calculated for six natural gas price scenarios, as the price of natural
gas fluctuates significantly depending on the time of day and on the time of year and it also
varies relative to the cost of crude oil, as shown in table 28.
Description of plant and
equipment.
Delivery date
on order.
Budget price.
(£).
6 - 8 months
£2,732,652
One off Senior Thermal heat recovery boiler.
6 months
£150,000
One off 35 metre, triple flue exhaust gas stack.
2 months
£50,000
150 metres of 36" standard schedule tube.
6 weeks
£33,000
3 - 5 months
£1,000,000
1 year
£3,965,652
Three off Bergen KVGB - 18 gas engines.
All civil works, mechanical erection works
and plant commissioning.
Total budget price to build and commission a
9.5MW gas engine cogeneration plant.
Table 25 - Cogeneration plant budget price.
101
Description of operation and maintenance costs.
Estimated cost
per annum (£).
Operational Labour - two off plant fitters / technicians.
£46,000
Lubricating and hydraulic oil consumption.
£32,035
Tax and insurance on plant building and equipment.
£30,000
Total operational and maintenance costs per annum.
£108,035
Table 26 - Cogeneration plant operation and maintenance costs.
Plant
load
(MW)
Plant
availability
Total number
of hours
generated
Electricity
generated
(MWh)
Lube oil
consumption
(Litres)
Annual lube
oil costs
9.471
9.471
9.471
9.471
9.471
9.471
9.471
9.471
9.471
9.471
9.471
9.471
9.471
9.471
9.471
9.471
1
0.99
0.98
0.97
0.96
0.95
0.94
0.93
0.92
0.91
0.9
0.89
0.88
0.87
0.86
0.85
5,488.0
5,433.1
5,378.2
5,323.4
5,268.5
5,213.6
5,158.7
5,103.8
5,049.0
4,994.1
4,939.2
4,884.3
4,829.4
4,774.6
4,719.7
4,664.8
51,976.8
51,456.9
50,936.9
50,417.9
49,898.0
49,378.0
48,858.0
48,338.1
47,819.1
47,299.1
46,779.2
46,259.2
45,739.2
45,220.2
44,700.3
44,180.3
29,635.2
29,338.7
29,042.3
28,746.4
28,449.9
28,153.4
27,857.0
27,560.5
27,264.6
26,968.1
26,671.7
26,375.2
26,078.8
25,782.8
25,486.4
25,189.9
£33,429
£33,094
£32,760
£32,426
£32,035
£31,757
£31,423
£31,088
£30,755
£30,420
£30,086
£29,751
£29,417
£29,083
£28,749
£28,414
Table 27 - Annual lubricating oil consumption and costs.
102
Table 28 - Annual fuel gas costs.
103
5.0.4 - CAPITAL RECOVERY FACTOR.
The capital recovery factor was calculated for bank interest rates of 4%, 6% and 8% and was
based on a repayment period of 25 years.
Capital recovery factor =
i (1 + i) n
.
((1 + i) n - 1)
Capital recovery factor =
0.04 * (1 + 0.04)
25
((1 + 0.04) 25 - 1)
Capital recovery factor =
0.064.
Table 29, below, gives the values of the capital recovery factor, depending on the bank interest
rate.
Bank interest
rates
Payback period
Capital recovery
factor
4%
25 Years
0.064
6%
25 Years
0.0782
8%
25 Years
0.0937
Table 29 - Capital recovery factors.
5.0.5 - ANNUAL REPAYMENT.
The annual repayment on the initial investment of £3,965,652 - with 4% interest rates and a
25 year payback period was calculated, as below:
Annual repayment on bank loan = Initial investment * Capital recovery factor
Annual repayment on bank loan = £3,965,652 * 0.064
Annual repayment on bank loan = £253,802 per annum.
104
Total initial
investment in plant
and equipment
Annual repayment
based upon 4%
interest rate
Annual repayment
based upon 6%
interest rate
Annual repayment
based upon 8%
interest rate
£3,965,652
£253,802
£310,114
£371,582
Table 30 - Annual bank repayments.
5.0.6 - CALCULATION OF SPECIFIC COSTS.
The specific costs for the cogeneration plant to generate electricity, were calculated as follows:
C = Annual repayment + Fuel costs + O & M Costs + Taxes & Insurance
Number of MWh produced per Year
C = Annual repayment + Fuel costs + 108,035
.
49,898MWh per Year
[£]
[MWh]
[£]
[MWh]
Based on an annual bank repayment and fuel cost of £253,802 and £392,963 (96% availability),
the specific cost to generate one MWh of electricity would be:
C = £253,802 + £392,963 + £108,035
49,898 MWh
C = £15.12 / MWh of electricity generated to break-even.
The specific costs (£ / MWh) for the plant were then calculated based on an annual plant
availability of 96% and for six natural gas price scenarios and three bank interest rate
scenarios, as shown in Table 31.
105
Table 31 - Cogeneration plant balance sheet.
106
5.0.7 - BREAK EVEN ANNUAL FUEL COSTS.
From the cogeneration plants balance sheet, it can be seen that above a certain natural gas
price, then the plant starts to make a loss.
The actual natural gas price required for the cogeneration plant to break-even for the year can
be calculated by setting the profit on 49,898MWh of electricity equal to £56,169.2, as below:
Profit versus £27.02 / MWh base-line = Profit on 49,898MWh / Year
49,898MWh / Year
Profit versus £27.02 / MWh base-line = £56,169.2
49,898
Profit versus £27.02 / MWh base-line = £1.1257 per MWh.
The break-even generating cost can then be calculated relative to the £27.02 per MWh
base-line, as follows:
Breakeven generating cost = £27.02 / MWh - £1.1257 / MWh = £25.8943 per MWh.
The break-even generating cost is then entered into the specific costs calculation, for the
particular annual repayment, in order to determine the annual fuel cost, which can then be
divided by the number of MWh of gas consumed in one year, to give the overall breakeven
price of gas.
C = Annual repayment + Fuel costs + 108,035
49,898MWh per Year
.
[£]
.
[MWh]
£25.8943 = £253,802 + £108,035 + Annual fuel cost
49,898MWh per Year
Annual fuel cost = £930,236.8
107
Annual fuel cost per MWh = £930,236.8
.
130,987.7MWh
Annual fuel cost per MWh = £7.1017.
Therefore, based on an annual natural gas price of £7.1017 per MWh and 4% interest rates,
then the plant would break-even for the year.
The natural gas prices for the plant to break-even for the year, based on 6% and 8% interest
rates are shown in the table 32.
Bank
interest
rate
Annual
bank
repayment
Break-even
fuel gas
price
4%
£253,802
£7.1017 / MWh
6%
£310,114
£6.6718 / MWh
8%
£371,582
£6.2025 / MWh
Table 32 - Breakeven natural gas prices.
5.0.8 - DISCUSSION OF PLANT FINANCIAL APPRAISAL.
Based on 4%, 6% and 8% annual bank interest rates and an average yearly industrial electricity
price of £27.02 per MWh, then the proposed cogeneration plant would remain financially viable,
so long as the wholesale natural gas price remained below £7.10, £6.63 and £6.20 per MWh of
gas, respectively.
The actual price of purchasing natural gas from the energy market depends on the quantity of
gas that you wish to buy and the price obtained would be subject to negotiation as part of a long
term gas supply contract.
108
It is probable that considerable savings in natural gas prices could be achieved through
negotiation, but, due to the competitive energy market in the United Kingdom, it was not
possible to verify the actual wholesale gas price that could be obtained for the proposed
plant.
The simple payback period for the plant, if a natural gas price in the region of £5 per MWh
could be negotiated, would be between 14.4 years and 25 years, depending on the bank
interest rate.
The capital cost of investing in the plant would be around £4 million pounds and depending
on the value of the enhanced capital allowances that can be obtained for the plants machinery
and equipment, it maybe possible to reduce the overall initial cost of the investment quite
substantially.
This would have a “knock-on effect” of reducing the specific cost to produce one MWh
of electricity, also.
The technical calculations that have been undertaken show that the plant is eligible to be defined
as good quality combined heat and power, under CHPQA rules and would therefore be exempt
from the payment of the climate change levy of £1.50 per MWh of natural gas that is burnt and
£4.30 per MWh, on any electricity exports to the national grid system.
The plant would be able to further reduce its break-even costs to generate electricity, if it
exported its surplus power to the National Grid system, when the manufacturing company
does not require power, also.
109
5.1 - CALCULATIONS FOR THE PLANTS CARBON EMISSIONS SAVINGS.
The Department of Trade and Industry in collaboration with the Atomic Energy Authority
Technology plc have produced a technical paper which details the actual calculations
that should be undertaken in order to determine the amount of carbon emissions savings
that can be made from generating electricity and heat in a cogeneration plant [39].
The technical calculations are based on the cogeneration plant offsetting carbon emissions
that would otherwise be produced by the separate production of electricity in fossil fired power
stations and steam production from heat only package boilers.
The paper gives specific emissions factors in gC / kWh of heat or electricity that is produced
from various fossil fuel sources and the following sections (Sections 5.1.1 to 5.1.8) outline the
various steps required, in order to calculate the carbon emissions savings for the proposed
cogeneration plant.
5.1.1 - FOSSIL FIRED POWER STATION EMISSIONS.
The average emissions factor from a fossil fired power station in the United Kingdom is 183g
of carbon per kWh of electricity that is generated.
Based on the proposed plant operating at 96% availability, the amount of carbon emissions that
would be produced by an equivalent fossil fired power station generating the same amount of
electricity would be:
Fossil fired power station carbon emissions = 183 gC / kWh of electricity generated.
Fossil fired power station carbon emissions = 0.183 tC / MWh of electricity generated.
Fossil fired power station carbon emissions = 0.183 * 49,898 = 9,131 tonnes Carbon / year.
5.1.2 - OIL FIRED PACKAGE BOILER EMISSIONS.
The emissions factor for a standard oil fired package boiler producing hot water or steam only is
98g of carbon emissions per kWh of heat energy output.
110
Based on the proposed plant operating at 96% availability, then the amount of carbon emissions
that would be produced by the oil fired heat only boiler would be:
Oil fired package boiler carbon emissions = 98 gC / kWh of heat energy generated.
Oil fired package boiler carbon emissions = 0.098 tC / MWh of heat energy generated.
Oil fired package boiler carbon emissions = 0.098 * 31,865.5 = 3,123 tonnes Carbon / year.
5.1.3 - EQUIVALENT COGENERATION PLANT EMISSIONS.
The emissions factor for an equivalent cogeneration plant generating the same amount
of heat and electricity is 50g of carbon emissions per kWh of natural gas that is burnt on
a gross calorific value basis.
Cogeneration plant carbon emissions = 50 gC / kWh of gas that is burnt.
Cogeneration plant carbon emissions = 0.05 tC / MWh of gas that is burnt.
Cogeneration plant carbon emissions = 0.05 * 130,987.7 = 6,549 tonnes Carbon / year.
5.1.4 - ANNUAL CARBON EMISSIONS SAVING.
The amount of carbon emissions that can be reduced by using a cogeneration plant operating
at 96% availability, is calculated as follows:
Carbon savings = (CE fossil electricity + CE oil boiler) - (CE cogeneration plant).
Carbon savings = (9,131 + 3,123) - (6,549) = 5,705 tonnes Carbon / year.
5.1.5 - ANNUAL CARBON DIOXIDE GAS EMISSION SAVING.
The annual carbon dioxide gas emissions savings could then be calculated as follows:
1 Tonne of carbon emissions = 3.667 tonnes of carbon dioxide gas emissions.
5,705 Tonnes of carbon emissions = 20,919 tonnes of carbon dioxide gas emissions / year.
Annual carbon dioxide gas emissions savings = 20,919 tonnes of carbon dioxide / year.
111
5.1.6 - EMISSIONS SAVINGS, INCLUDING FOR 4% UNAVAILABILITY.
The carbon emissions that would be produced from using imported fossil fired electricity and
a standby oil fired boiler, to make-up for the shortfall in heat and power output, due to the 4%
unavailability of the cogeneration plant, are then calculated as below:
Carbon emissions from 4% imported power = (51,976.8 - 49,898) * 0.183
[tC / MWh]
Carbon emissions from 4% imported power = 380 tonnes Carbon / year.
Carbon emissions from 4% oil fired boiler heat = (33,193 - 31,865.5) * 0.098 [tC / MWh]
Carbon emissions from 4% oil fired boiler heat = 130 tonnes Carbon / year.
Total carbon emissions from oil fired boiler & imported power = 510 tonnes Carbon / year.
The overall carbon emissions savings from the cogeneration plant operating at 96% availability
would therefore be:
Overall carbon emissions savings = 5,705 - 510 = 5,195 tonnes Carbon / year.
Overall carbon dioxide gas savings = 5,195 * 3.667 = 19,050 tonnes CO2 / year.
5.1.7 - ANNUAL CARBON EMISSIONS SAVINGS.
Table 33 gives details of the carbon emissions savings that could be achieved for the proposed
cogeneration plant operating at various availabilities.
It should be noted, however, that the table does not include for the carbon emissions which
would be produced by the additional power and heat that that would need to be imported from
the National Grid and from the manufacturing plants own standby oil fired package boilers, to
make up for the unavailability of the cogeneration plant.
112
Table 33 - Cogeneration plant carbon emissions savings.
113
5.1.8 - DISCUSSION OF EMISSIONS SAVINGS.
The emissions savings that could be achieved by building the proposed cogeneration plant,
based on an operational availability of 96%, were calculated as 5,705 tonnes of carbon or
20,919 tonnes of carbon dioxide gas per year. This would account for an annual carbon
emissions reduction of 46.5%.
Whilst, the emissions savings that would be achieved if the manufacturing plant needed
to import the 4% of its annual electricity and heat requirements from the National Grid and
from a oil fired package boiler, due to the plants unavailability, would be 5,195 tonnes of
carbon or 19,050 tonnes of carbon dioxide gas per year. This would account for an annual
carbon emissions reduction of 42.4%.
114
CHAPTER 6 - ENVIRONMENTAL IMPACT ASSESSMENT FOR THE PROPOSED PLANT.
The following sections give a brief description of the factors that would need to be considered
when submitting an environmental impact assessment to the Local Planning Authority in support
of an application for “Deemed Planning Permission” to build a cogeneration plant.
6.0.1 - SITE GEOLOGY AND LANDSCAPING.
A ground analysis of the proposed site area should be carried out, to ensure that the site is
geologically sound and surface scans of the area should also be done to identify any cables
or drainage facilities running through the site area.
Soil samples should be taken from around the site area and should be sent to an independent
laboratory for analysis for heavy metals and other ground level contaminants.
A survey of the surrounding landscape, local to the site should be carried out, to identify any key
features of the proposed cogeneration plant that would require landscaping or screening.
6.0.2 - CONSTRUCTION SITE LAYOUT.
The construction site should be designed to accommodate all of the site staff and contractors
offices (porto-cabins), mess rooms, changing facilities, covered workshop areas, canteen, first
aid and male / female toilet and wash-room facilities.
Provision should also be made for all site services to be connected into the local clean water and
sewerage systems.
6.0.3 - SITE SECURITY.
The site should have a secure fenced lay-down area for the storage of raw materials, equipment
and containers for each contractor that is involved in the project. The site will also have 24 hour
security staff, to cover security, goods incoming and other issues.
115
The site should also be fenced on all sides to prevent unauthorised access.
6.0.4 - LOCAL ROAD NETWORK.
All major “A class” roads leading to the proposed site should be checked as to their
suitability (load bearing capacity and for width, height and length restrictions), in order
for the transportation of all of the construction materials, capital plant and equipment that
are required by the site.
The current traffic conditions, future traffic levels and all road junctions local to the proposed site
should also be examined to ensure that the proposed site traffic levels do not have any adverse
affect on the local population.
6.0.5 - SITE WORKING HOURS.
The site day-shift working hours should be scheduled in order to minimise any possible
congestion on the roads and at road junctions local to the site and car sharing should be
encouraged by the Contractor, wherever practicable.
6.0.6 - SITE CAR PARKING.
The Contractor should ensure that there is adequate provision for staff and contractors car
parking on the site. The car park, access roads and paths on the site should be laid-out in a
heavy gravel material, in order to ensure that any rainfall that occurs, has a minimal affect on
the environment and the site working conditions.
6.0.7 - SITE SPEED LIMIT.
The speed limit on the proposed site should be set at 15 miles per hour maximum, for all
vehicles, including cars, cranes, forklifts and lorries.
116
6.0.8 - ABNORMAL SITE LOADS.
All large, heavy or wide loads that are required by the site should be scheduled to be delivered
during off peak hours, at night and at weekends in co-operation with the local police force, in
order to ensure minimal disruption to the local traffic and the local population.
6.0.9 - STATUTORY NOISE REQUIREMENTS.
The plant should be constructed to the latest United Kingdom and European Union
design standards and should comply with the statutory noise limits that are set down by
the Environment Agency.
The size of the combustion and ventilation air duct openings should be limited, the plants
engine enclosures should be sound proofed and the air cooled radiator systems should be
located to the rear of the plant, to minimise noise levels.
All diesel generators, except those that are required for security lighting, should be shut-down
after 8pm and during the hot commissioning phase, no boiler steam blow (steam purge) of the
main steam legs should be permitted after 8pm, also.
6.1 - SITE REFUSE COLLECTION.
The Contractor should provide suitable refuse collection facilities for cardboard, paper and waste
rubbish.
Special arrangements should also be made to dispose of antifreeze and inhibitor, cable drums,
oil drums, damaged lagging, packing cases and wooden crates, waste lubricating and hydraulic
oils, oily rags, scrap metal and civil works debris.
All storage and refuse skips should be provided with haps or metal covers, to prevent access by
vermin and the burning of waste materials on site should be prohibited, also.
Furthermore, all refuse facilities, collection and disposal should be done by licensed companies,
in accordance with ISO14001 Environmental Management System.
117
6.1.1 - STORAGE OF GAS CYLINDERS.
All gas cylinders, including acetylene, argon, oxygen and propane cylinders, that will be used
on the site for burning, heating and welding operations, should be stored without hoses and
regulators, in vented, outdoor, lockable-fenced compounds, when not in use.
This should minimise any risk of a gas explosion or fire occurring on the site. Furthermore,
portable fire fighting equipment including carbon dioxide, dry powder and foam fire extinguishers
shall be located at strategic points around the site.
6.1.2 - WELDING OPERATIONS.
During welding operations, it should be a site requirement that “welding screens” are positioned
strategically to prevent any bystanders or observers from contracting “arc eye”.
Adequate ventilation and fume extraction equipment should also be used when burning or
welding in confined spaces, also.
6.1.3 - RADIOGRAPHY.
The use of ionising radiation for non destructive testing (NDT) purposes should be carried out in
accordance with the clients engineering, safety and permit for work procedures.
In all circumstances, radiography should be carried out at night, with only authorised personnel
being allowed on site and all areas local to the procedure should be cordoned off, with warning
notices posted.
It is also a statutory requirement for every company in the United Kingdom to inform the Health
and Safety Executive when they intend to bring an ionising radiation source on to any type of
site.
118
6.1.4 - CONTROL OF SUBSTANCES HAZARDOUS TO HEALTH.
All chemicals and other liquids shall be used and stored in accordance with the Control of
Substances Hazardous to Health Regulations (COSHH).
The following chemicals, amongst others, shall be regularly used on site:
Caustic soda or sodium hydroxide - used to maintain boiler feed water pH.
Hydrazine - used as a boiler feed-water oxygen scavenger.
Hydrochloric acid - used to acid clean and treat (form magnetite) in boilers.
Tri-sodium phosphate - used to control sulphates and nitrates in boiler feed-water.
Ethylene glycol - used as an anti-freeze in raw and jacket water cooling systems.
Nalfleet inhibitor - used as a rust and fouling inhibitor in raw and jacket water systems.
Boiler feed water - disposed of in accordance with the relevant company procedures.
All types of oils - incl. engine lubricating oils, governor and turbocharger hydraulic oils.
Glues and adhesives - including evostick and hylomar gasket glues.
Paints - including zinc galvanising paint.
6.1.5 - EMERGENCY EYE WASH STATIONS.
The client should also provide emergency eye wash and emergency shower type installations at
strategic points around the site, in order to deal with any chemical incidents that may occur.
6.1.6 - STANDARDS ON SITE.
The standards on the site should be monitored by the Site Manager (daily) and audited
once per month by the clients Health and Safety Department to ensure that all Health,
Safety, Environmental and Compliance matters are being carried out satisfactorily, as per
the Construction, Design and Management Regulations and other related legislation.
All construction and commissioning work on the site should be carried out in accordance with the
relevant standards including ISO9001 and the Health and Safety at Work Act 1973.
119
6.1.7 - ADDITIONAL INFORMATION ON ENVIRONMENTAL IMPACT ASSESSMENTS.
The Office of the Deputy Prime Minister has published a checklist of issues that that should also
be considered for inclusion in an environmental impact assessment, as part of the planning
process (See Appendix G).
120
CHAPTER 7 - DISCUSSION.
From the research that has been carried out in this feasibility study into the proposed
development of a cogeneration plant in the West Midlands, England, it was found that
marine gas engines would offer a reliable means of producing sufficient heat and power
to meet the manufacturing plants requirements.
The technical and thermodynamic evaluation process concluded that three off Bergen
KVGB-18 marine gas engines operating in parallel with one another, would be sufficient to
produce enough power and heat to meet the plants requirements for 9.5MWe of electricity
and 8 tonnes per hour of process steam.
If one gas engine is off-load for maintenance purposes, then 6.3MWe of electricity and either
5.32 or 5.42 tonnes per hour of process steam could still be produced from the plant, depending
on the pinch point temperature of the waste heat recovery boiler.
The technical evaluation process calculated that the cogeneration plant would have a quality
index of 106.6 and a power efficiency of 38.1% and would therefore meet the CHPQA Scheme
criteria to qualify for registration as good quality combined heat and power.
As the plant can be considered as good quality combined heat and power, it shall be eligible
to apply for climate change levy exemption on all of its fuel inputs and electricity outputs to the
National Grid system.
Furthermore, without climate change levy exemption, the plant would not be financially viable, as
natural gas would be charged with a levy of £1.50 per MWh of gas consumed and any electricity
that was exported to the grid would also be levied at £4.30 per MWh.
Since the proposed cogeneration plant development will be less than 10MWe in power output,
then the application for Planning Permission only needs to be submitted to the Local Planning
Authority for approval.
This should save considerable time and expense as the application does not need to gain
Energy Policy Clearance from the Department of Trade and Industry, under Section 14(1)
of the Energy Act 1976.
121
The proposed site for the cogeneration plant is in an industrial area and it is therefore anticipated
that the Local Planning Authority will have no objections to the development, as it will comply
with Planning Policy Guidance Note 4 and help to regenerate the local area.
The overall cost to construct the plant was estimated at around £3,965,652, excluding architects
and consultants fees and the operation and maintenance costs for the plant were estimated to
be £108,035 per annum.
From the financial appraisal that was carried out for the plant, it was calculated that based on
an average industrial price for natural gas and electricity in 2003 of £8 per MWh and £27.02 per
MWh, respectively, then the plant would make a loss of £117,543.70, assuming 4% bank
interest rates. However, if the lowest bank interest rate that could be obtained was 8%, then the
plant would make an annual loss of £235,303.
The financial appraisal has shown that the plant is only viable if the wholesale cost of natural gas
can be negotiated through a long term energy supply contract to a price of around £5 per MWh.
If this can be achieved, then the plant would be able to make a profit of between £157,394.2 and
£275,153.5, based on 8% and 4% interest rates, respectively.
The best option for the construction and subsequent operation of the plant would probably be
for the manufacturing company to enter into a long term energy supply contract with a regional
electricity and gas supply company, as the company would be able to supply or purchase natural
gas at considerably reduced rates, than those which are available to industrial customers.
Furthermore, if the plant was owned by the electricity company and the sole purpose of the
property was for the generation of power, then the plant would be eligible for exemption from
business rates on all the plant and equipment that is contained within the cogeneration plants
building.
Finally, the overall carbon emissions savings from the plant are estimated to be 5,195 tonnes of
carbon or 19,050 tonnes of carbon dioxide gas per annum, compared to generating electricity in
a conventional fossil fired power station and producing heat from an oil fired package boiler.
An overview of the actual steps that should be undertaken when carrying out a feasibility study
into the use of combined heat and power is given in Appendix H.
122
7.1 - CONCLUSIONS.
The financial viability of the proposed cogeneration plant depends on the annual interest
rate that can be agreed with the bank and on the actual wholesale electricity and natural
gas prices that can be negotiated from the energy market.
If the lowest negotiable natural gas price that could be obtained, was to rise above a £6.50
per MWh and current industrial electricity prices remain low, at around £27.02 per MWh, then
it would not be financially viable for the manufacturing company to invest in a new plant, as the
payback period would be around 30 to 40 years.
In the near future, however, due to the closure of many of the countrys large coal fired power
stations, it is anticipated that the cost of electricity will increase significantly and once the
wholesale natural gas price levels out, then it is likely that the proposed development of the
cogeneration plant would be financially viable for the manufacturing company.
123
7.2 - DIRECTION OF FUTURE WORK.
It is recommended that a detailed investigation is carried out into the financial benefits that
can be obtained from enhanced capital allowances on cogeneration plant and machinery, as
this may help to make the cogeneration plant more financially viable, as the initial capital
investment in plant and machinery could be offset against the taxable profits of the business.
It is also recommended that a sensitivity analysis is carried to determine the consequences
of changes in wholesale electricity prices on the financial viability of the proposed plant.
124
REFERENCES.
[1] - www.cogen.org
[2] - www.wartsila.com
[3] - www.rolls-royce.com/energy
[4] - www.esolar.cat.com
[5] - www.alstom.com
[6] - www.gepower.com
[7] - www.dti.gov.uk/energy/inform/energy_trends/articles/6oct200.pdf
[8] - www.europa.eu.int/comm/energy/library/chpdraftdirectiveen.pdf
[9] - www.europa.eu.int/comm/energy/demand/legislation/heat_power_en.htm
[10] - www.europa.eu.int/comm/off/green/index_en.htm
[11] - www.europa.eu.int/eur-lex/en/com/cnc/2001/com2001_264en01.pdf
[12] - www.europa.eu.int/comm/energy/library/chpdraftdirectiveen.pdf
[13] - www.ippc-uk.co.uk/impactofippc.html
[14] - www.dti.gov.uk/energy/inform/dukes/dukes2003/06main.pdf
[15] - www.dti.gov.uk/energy/inform/energy_facts/chp/index.shtml
[16] - www.dti.gov.uk/energy/whitepaper/index.shtml
[17] - www.defra.gov.uk/environment/consult/chpstrat/pdf/chpstrat.pdf
[18] - www.sustainable-development.gov.uk/sdig/improving/targetse.htm
[19] - www.sustainable-development.gov.uk/sdig/improving/targetsa.htm
[20] - www.chpqa.com
[21] - www.defra.gov.uk/environment/ccl
[22] - www.hmce.gov.uk/forms/notices/ccl1-2.htm
[23] - www.defra.gov.uk/Environment/ccl
[24] - www.eca.gov.uk
[25] - www.defra.gov.uk/environment/climatechange/trading/index.htm
125
REFERENCES.
[26] - www.defra.gov.uk/environment/climatechange/trading/eu
[27] - www.scotland.gov.uk/about/planning/
[28] - www.ofgas.co.uk
[29] - www.dti.gov.uk/energy/leg_and_reg/consents/index.shtml
[30] - www.odpm.gov.uk
[31] - “Design and Development of Ulstein Bergen’s new lean burn spark ignition gas
engine“, by Lars M. Nerheim, Engine Technology and Development Manager,
Ulstein Bergen AS, September 1997.
[32] - Ulstein Bergen gas engine product literature - June 1998.
[33] - www.meto.gov.uk
[34] - Engineering Thermodynamics, Rogers and Mayhew, Fourth edition.
[35] - Rogers and Mayhew steam tables, Fourth Edition.
[36] - Applied Thermodynamics notes, R.C Maclean, University of Strathclyde.
[37] - Applied Thermodynamics notes, Dr P. Kew, Heriot Watt University.
[38] - Electrical Power Systems notes, Dr S. Jovanovic, University of Strathclyde.
[39] - www.dti.gov.uk/energy/inform/energy_trends
126
BIBLIOGRAPHY.
[1] – www.defra.gov.uk/environment/climatechange/cm4913/4913html/12.htm
[2] – www.nationalgrid.com/uk
[3] – www.electricity.org.uk
[4] – www.energynetworks.org
[5] – www.electricity.org.uk
[6] – www.elecpool.com
[7] – www.ofgas.gov.uk/elarch/reta_contents.htm
[8] – www.elexon.co.uk
[9] – www.electricity.org.uk
[10] - www.dti.gov.uk/energy/inform/dukes/dukes2003/05longterm.pdf
[11] - www.defra.gov.uk/environment/energy/chp/index.htm
127
APPENDIX A - INDUSTRIAL GAS TURBINE TECHNICAL DATA SHEET.
128
APPENDIX B - MARINE GAS ENGINE ENGINEERING DRAWING.
SUBJECT TO COPYRIGHT – SEE HARD COPY.
129
APPENDIX C - MARINE GAS ENGINE TECHNICAL DATA SHEET.
SUBJECT TO COPYRIGHT – SEE HARD COPY.
130
APPENDIX D - MARINE GAS ENGINE FUEL CONSUMPTION CHART.
SUBJECT TO COPYRIGHT - SEE HARD COPY.
131
APPENDIX E - ANSI PIPE SCHEDULE CHART.
132
APPENDIX F1 - PLANNING PERMISSION APPLICATION FORM.
133
APPENDIX F2 - PLANNING PERMISSION APPLICATION FORM.
134
APPENDIX F3 - PLANNING PERMISSION APPLICATION FORM.
135
APPENDIX F4 - PLANNING PERMISSION APPLICATION FORM.
136
APPENDIX G1 - ENVIRONMENTAL IMPACT ASSESSMENT FORM.
137
APPENDIX G2 - ENVIRONMENTAL IMPACT ASSESSMENT FORM.
138
APPENDIX G3 - ENVIRONMENTAL IMPACT ASSESSMENT FORM.
139
APPENDIX G4 - ENVIRONMENTAL IMPACT ASSESSMENT FORM.
140
APPENDIX H1 - COGENERATION PLANT DESIGN STAGES.
I.
II.
III.
IV.
ELECTRICITY AND HEAT DEMAND PROFILES.
A.
Determine the plant heat profiles on a seasonal basis.
B.
Determine the plant electricity profiles on a seasonal basis.
C.
Produce seasonal heat and electricity profile graphs.
COGENERATION PLANT SELECTION.
A.
Undertake a technical evaluation of the available cogeneration plant
technologies.
B.
Select the most practicable technology for your plant or site.
PLANNING AND CONSENTS PROCESS.
A.
If the proposed cogeneration plant is to be gas or oil fired and is greater than
10MWe in output, then Energy Policy Clearance is required from the
Department of Trade and Industry, under Section 14(1) Energy Act 1976.
B.
If the plant is less than 50MWe in output and is not gas or oil fired, then the
development is subject to approval from the Local Planning Authority only,
under the Town and Country Planning Act 1990.
THERMAL ASSESSMENT.
A.
Calculate the annual fuel input, heat output and electricity output for the plant in
MWh, in accordance with the Combined Heat and Power Quality Assurance
Scheme rules.
B.
Calculate the quality index and power efficiency for the plant, under annual
operation.
C.
Determine if the plant is eligible to be classed as good quality combined heat
and power, for its fuel inputs and electricity outputs.
141
APPENDIX H2 - COGENERATION PLANT DESIGN STAGES.
V.
VI.
FINANCIAL ASSESSMENT.
A.
Determine the bank interest rate which would be available for the proposed
plant, depending on the repayment period.
B.
Determine the initial capital investment costs for the plant and then calculate the
annual bank repayment charges.
C.
Determine the operation and maintenance costs, tax and insurance charges and
wholesale fuel costs for the plant.
D.
Calculate the plants overall specific costs (£ / MWh) and compare to the current
energy costs of operating your plant or site.
E.
Calculate the cost savings from investing in the new plant.
F.
Determine the payback period for the plant.
CARBON EMISSIONS.
A.
VII.
Calculate the carbon emissions savings from the proposed plant.
ENVIRONMENTAL IMPACT ASSESSMENT.
A.
Carry out an Environmental Impact Assessment for the development.
142
Was this manual useful for you? yes no
Thank you for your participation!

* Your assessment is very important for improving the work of artificial intelligence, which forms the content of this project

Related manuals

Download PDF

advertisement