# SIMULATION OF 1610 HELIUM LIQUEFIER Department of Mechanical Engineering

```SIMULATION OF 1610 HELIUM LIQUEFIER
A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE
REQUIREMENTS FOR THE DEGREE OF
Master of Technology
in
Mechanical Engineering
By
AARIF B
(Roll No: 211ME3184)
Department of Mechanical Engineering
National Institute of Technology
Rourkela
2013
SIMULATION OF 1610 HELIUM LIQUEFIER
A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE
REQUIREMENTS FOR THE DEGREE OF
Master of Technology
in
Mechanical Engineering
By
AARIF B
(Roll No: 211ME3184)
Under the guidance of
Prof. Ranjit Kumar Sahoo
Department of Mechanical Engineering
National Institute of Technology
Rourkela
2013
National Institute of Technology
Rourkela
This is to certify that the thesis entitled, “SIMULATION OF 1610 HELIUM
LIQUEFIER” submitted by Mr. AARIF B in partial fulfillment of the requirements for
the award of Master of Technology Degree in Mechanical Engineering with
specialization in Thermal Engineering at the National Institute of Technology,
Rourkela (Deemed University) is an authentic work carried out by him under my
supervision and guidance.
To the best of my knowledge, the matter embodied in the thesis has not
been submitted to any other University/ Institute for the award of any degree or
diploma.
Date:
Prof. RANJIT KUMAR SAHOO
Department of Mechanical
Engineering National Institute of
Technology Rourkela – 769008
i
CONTENTS
CERTIFICATE
i
CONTENTS
ii
ACKNOWLEDGEMENT
iv
ABSTRACT
v
LIST OF FIGURES
vi
LIST OF TABLES
vii
NOMENCLATURE
viii
CHAPTER 1
1
1. INTRODUCTION
1
1.1 Principle of liquefaction
2
1.2 System performance parameters
3
1.3 The Thermodynamically ideal system
4
1.4 Production of low temperature
6
1.4.1 Joule-Thomson effect
6
1.4.2 Adiabatic expansion
7
1.5 Objective
7
CHAPTER 2
8
2. LITERATURE REVIEW
8
2.1 Literature review
9
2.2 Development of Liquefaction system
10
2.2.1 Claude System
10
2.2.2 Cascade System
12
2.2.3 Collins Helium Liquefaction System
14
2.2.4 Stirling Cycle
15
ii
CHAPTER 3
17
3. PROCESS DESIGN
17
3.1 Process design of helium liquefier
18
3.2 Simplification of process flow-sheet
18
3.3 Component and parameter analysis
19
3.4 T-S Diagram
21
3.5 Aspen One
22
3.6 The components or blocks or equipment
26
3.7 Procedure of process design using Aspen Hysys
28
3.8 Fluid package
30
3.9 Input value
31
3.10 Process flow in Aspen Hysys
33
CHAPTER 4
36
4. RESULTS AND DISCUSSION
36
4.1 Performance analysis
37
4.1.1 Mass flow ratio diverted through Expanders, X1, and X2
37
4.1.2 Mass flow ratio diverted for precooling, X0
39
4.1.3 Effectiveness of heat exchangers, ɛ
40
4.1.4 Effect of variation of Expanders (Expansion Engine) Efficiency, ɳ
43
CHAPTER 5
45
5. CONCLUSIONS
46
REFERENCES
47
iii
ACKNOWLEDGEMENT
I am extremely fortunate to be involved in an exciting and challenging research project like
“Simulation of 1610 Helium Liquefier”. It has enriched my life, giving me an opportunity
to work in a new environment of Aspen Hysys. This project increased my thinking and
understanding capability as I started the project from scratch.
I would like to express my greatest gratitude and respect to my supervisor Prof. Ranjit
Kumar Sahoo, for his excellent guidance, valuable suggestions and endless support. He has
not only been a wonderful supervisor but also a genuine person. I consider myself extremely
lucky to be able to work under guidance of such a dynamic personality. Actually he is one of
such genuine person for whom my words will not be enough to express.
I would like to express my sincere thanks to Prof. Sunil Kumar Sarangi for his precious
suggestions and encouragement to perform the project work. He was very patient to hear my
problems that I am facing during the project work and finding the solutions. I am very much
thankful to him for giving his valuable time for me.
I would like to express my sincere thanks to Mr. Balaji, Mr. Sachindra Kumar Rout for
their precious suggestions and encouragement to perform the project work. He was very
patient to hear my problems that I am facing during the project work and finding the
solutions. I am very much thankful to him for giving his valuable time for me.
I would like to express my thanks to all my classmates, all staffs and faculty members of
mechanical engineering department for making my stay in N.I.T. Rourkela a pleasant and
memorable experience and also giving me absolute working environment where I unlashed,
my potential.
Date:
AARIF B
Roll. No. 211ME3184
M.Tech. (Thermal)
iv
ABSTRACT
Cryogenics is generally described as the science and technology of producing low
temperature environment. The various cryogenic cycles such as Collins cycle, Linde cycle
etc. govern the liquefaction of various industrial gases, namely, helium, nitrogen etc.
In this project work, helium liquefier has been simulated with the help of the simulation tool
Aspen hysys and simulation work is carried out at steady state using MBWR (Modified
Benedict–Webb–Rubin) equation of state in order to get the desired output.
The present analysis is carried out to assess the role of different component efficiencies in
predicting overall system efficiency at the design and off design conditions. In this analysis,
the temperature is assumed to evaluate the expander efficiency and heat exchanger
effectiveness in order to optimize the plant efficiency. The evaluated thermodynamic
parameters are obtained and the optimum mass fraction through expander for maximum
liquid yield is calculated.
Key words: Cryogenics, helium liquefier, Aspen Hysys, MBWR, yield
v
LIST OF FIGURES
Figure No.
Title
Page No.
CHAPTER 1
1.1
(a) T-S plane of thermodynamic cycle
1.2
Isenthalpic expansion of a real gas
(b) Experimental set-up
5
6
CHAPTER 2
2.1
Claude liquefaction systems
11
2.2
T-S diagram for Claude system
12
2.3
Hybrid cascade liquefaction system for liquefaction of helium.
13
2.4
Collins helium liquefaction system
15
2.5
Stirling cycle refrigerator
16
CHAPTER 3
3.1
Schematic of helium liquefier
18
3.2
T-S Diagram of helium liquefier
21
3.3
Business areas of aspen one
22
3.4
aspen one engineering classification
23
3.5
Variation of temperature with Enthalpy
30
3.6
Variation of temperature with Entropy
31
3.7
Process Flow Diagram of Helium Liquefier in Aspen Hysys
33
CHAPTER 4
4.1
Variation of yield with mass flow ratio diverted through the expanders
38
4.2
Effect of yield with mass flow X0
39
4.3
Variation of yield with Effectiveness of heat exchangers (
=
=0.75)
41
4.4
Variation of yield with Effectiveness of heat exchangers ( =
=0.74)
42
4.5
Variation of yield with Efficiency of Expanders ( = = = = =0.97)
43
4.6
Variation of yield with Efficiency of Expanders ( = = = = =0.96)
44
vi
List of Tables
Table No.
Title
Page No.
CHAPTER 3
3.1
Material stream properties from Aspen Hysys
35
CHAPTER 4
4.1
Effect of yield with mass flow X0
39
4.2
Variation of yield with Effectiveness of heat exchangers ( =
=0.75)
40
4.3
Variation of yield with Effectiveness of heat exchangers ( =
=0.74)
41
4.4
Variation of yield with Efficiency of Expander ( = = = = =0.97)
43
4.5
Variation of yield with Efficiency of Expander ( = = = = =0.96)
44
vii
NOMENCLATURE
T = Temperature
P = Pressure
̇ = Work transfer
̇ = mass flow rate
y = yield ( ̇
̇
)
h = specific enthalpy
s = specific entropy
ɛ = Effectiveness of heat exchangers
ɳ = Efficiency of expanders (Expansion Engine)
X0 = Mass flow ratio diverted for precooling
X1 = Mass flow ratio diverted through Expander1
X2 = Mass flow ratio diverted through Expander 2
E30 = Heat Exchanger 1
E31 = Heat Exchanger 2
E32 = Heat Exchanger 3
E33 = Heat Exchanger 4
E34 = Heat Exchanger 5
E37 = Expander 1(Expansion Engine 1)
E39 = Expander 2(Expansion Engine 2)
C = Capacity rate
= Smaller quantity of
̇
and
= mass of helium delivered from compressor
LN2 = Liquid nitrogen
̇ = liquid production
viii
Chapter 1
Introduction
1
1.1 Principle of Liquefaction :
The process in which gas is physically converted into liquid state is called
liquefaction. Many gases like carbon dioxide can be converted into gaseous state by simple
cooling at normal atmospheric pressure and some others require pressurisation. Liquefaction
process is mainly used for analyse the fundamental properties of gas molecules, for storage of
gases in air conditioning and refrigeration.
Liquefaction of gases is accomplished by refrigerating and cooling the gas below its
critical temperature so that liquid can be formed at some suitable pressure below the critical
pressure. Thus gas liquefaction process is a special case of gas refrigeration. In both cases,
the gas is first compressed using compressor to an elevated pressure in an ambient
temperature. This high-pressure gas is passed through heat exchanger to a throttling valve and
expansion engine. When the gas is expanding to the lower pressure from the J-T Valve,
cooling may take place, and some liquid may be formed. The remaining low-pressure gas
returns to the compressor inlet to repeat the cycle. Both refrigerators and liquefiers operate on
this basic principle.
In a liquefying system, the total mass of gas that is warmed in the heat exchanger is
less than that of the gas to be cooled by the amount liquefied because of liquid accumulation,
this will creating an imbalance mass flow in the heat exchanger. In a refrigerator the cool and
warm gas flows are equal in the heat exchanger because there is no accumulation of
refrigerant in any part of the system. This result shows as a "balanced flow condition" in a
refrigerator heat exchanger. The refrigeration and liquefaction both, has identical
thermodynamic principles. However the design and analysis of the two systems are quite
2
different because of the condition of balanced flow in the refrigerator and unbalanced flow in
liquefier systems.
Liquefaction of helium (Helium-4) with the Hampson-Linde cycle led to a Nobel
Prize for Heike Kamerlingh Onnes in 1913. At ambient pressure the boiling point of liquefied
helium is 4.22 K (-268.93°C). Below 2.17 K liquid helium-4 has many amazing properties,
such as exhibiting super fluidity (under certain conditions it acts as if it had zero viscosity)
and climbing the walls of the vessel. Liquid helium (Helium-4) is used as a cryogenic
refrigerant; it is commercially used in superconducting magnets such as those used in MRI or
NMR.
The liquefaction of gases is a complicated process that uses various compressions and
expansions to achieve high pressures and very low temperatures; using for example turbo
expanders. The liquefaction of air is used to obtain nitrogen, oxygen and argon by separating
the air components by distillation.
This chapter discusses several of the systems used to liquefy the cryogenic fluids. We
shall be concerned with the performance of the various systems, where performance is
specified by the system performance parameters or payoff functions.
1.2 System performance parameters:
There are three payoff functions are used to indicate the performance of a liquefaction
systems:
̇
1. Work required per unit mass of gas compressed(
2. Work required per unit mass of gas liquefied(
̇
̇)
̇ )
3. Fraction of the total flow of gas that is liquefied(y= ̇
̇)
The last two functions are related to the first one by
(
̇
̇)=(
̇
̇ )y
(1.1)
3
In liquefaction system, we should maximize the fraction of gas that is liquefied and minimize
the work requirements. These payoff functions are different for different gases; therefore we
should also need another performance parameter that would allow the comparison of the
same system using different fluids. That parameter is called figure of merit (FOM) for a
liquefaction system. It is defined as the theoretical minimum work requirement divided by the
actual work requirement for the system:
FOM= ̇
̇=(
̇
̇
̇ )/ (
̇ )
(1.2)
The figure of merit is a number between 0 and 1. It gives the actual system how approaches
closely the ideal system performance.
There are various performance parameters that apply to the components of systems. These are
1. Compressor and expander adiabatic efficiencies.
2. Compressor and expander mechanical efficiencies.
3. Heat exchanger effectiveness.
4. Pressure drops through piping, heat exchanger. And so on.
5. Heat transfer to the system from ambient surroundings.
1.3 The Thermodynamically ideal system:
This system is thermodynamically ideal, but it is not ideal for practical system. The Carnot
cycle is perfect cycle of thermodynamics. Liquefaction is an open system process, therefore
for an ideal liquefaction we choose the first two processes in the Carnot cycle; a reversible
isothermal compression followed by a reversible isentropic expansion. The gas is compressed
reversibly and isothermally from ambient conditions to some high pressure. If this high
pressure is selected so that gas will become saturated liquid upon reversible isentropic
expansion through the expander. The final pressure and the initial pressure are equal. The
pressure attained at the end of isothermal compression is extremely high in the order of 70
4
GPa or 80GPa for nitrogen. It is not possible to attain this pressure in a liquefaction system,
which is the reason it is not an ideal process for a practical system.
Fig 1.1: (a) T-S plane of thermodynamic cycle
(b) Experimental set-up
The First law of thermodynamic for steady flow:
̇
̇
̇
∑
∑
̇
(1.3)
Applying the First law to the system shown in figure:
̇
̇
̇(
)
̇
(1.4)
The heat transfer process is reversible and isothermal in the Carnot cycle. Thus, from the
second law of Thermodynamics:
̇
̇
̇
(1.5)
Because the process from point 2 to point f is isentropic, S 2 = S3, where S is the entropy of the
fluid. Substituting QR, we may determine the work requirement for the ideal system.
̇
( ̇)
(
)
(
)
5
̇
̇
(1.6)
1.4 Production of low temperature:
1.4.1 Joule-Thomson effect:
The joule-Thomson valve or an expansion valve used in many practical liquefaction systems
to produce low temperature. If we apply the first law for steady flow to the expansion valve,
with the assumption of zero heat transfer and zero work transfer and for negligible kinetic
and potential changes, we find h1= h2. So the flow within the valve is irreversible and is not
an isenthalpic process, the inlet and the outlet lie on the same enthalpy curve. We note that
there is a region in which an expansion through the valve produces an increase in
temperature, while in another region the expansion results in a decrease in temperature. So
we should operate the expansion valve in a liquefaction system in the region where there is a
net decrease in temperature results. The curve separates two regions is called the inversion
curve. The effect of change in temperature for an isenthalpic change in pressure is
represented by the Joule-Thompson coefficient.
Fig 1.2: Isenthalpic expansion of a real gas
6
1.4.2 Adiabatic expansion:
The adiabatic expansion is the second method for producing low temperatures. This will
accomplished by the gas is passing through a work producing device (expansion engine). In
the ideal case, the expansion would be adiabatic and reversible therefore isentropic. In this
case we can define the isentropic coefficient which expresses the temperature change due to a
pressure change at constant entropy.
(1.7)
1.5 Objective:
The present research work has following objectives
1. Simulate the liquefiers for helium and investigate the effects of different operating
parameter on the output of liquefaction process efficiency using ASPEN HYSYS
simulator.
2. Process design means, determination of the type of thermodynamic processes
included in the fixing the points (pressure and temperature) and thermodynamic cycle.
3. While designing the process, constraints, equipment availability and cost should be
kept in mind. Process design also includes the setting the parameters up to the
optimum condition that maximum amount of liquid will be obtained.
7
Chapter 2
Literature review
8
2.1 Literature review:
Hubbell and Toscano [1] presented an entropy generation concept for carrying out
thermodynamic optimisation of the helium liquefaction cycle. Minta and Smith [2] used a
similar method of minimisation of the generated entropy in a cycle model with continuous
precooling. Khalil and McIntosh [3] carried out an exhaustive study to optimise inlet
pressure, temperature of first expander and number of expanders. Also, Hilal [4] analysed the
effect of the number of expansion engines in cascade form or in the independent form and
pressure on the COP of the refrigerator and liquefier. He showed that there is a significant
increase in coefficient of performance (COP) value in case of independent expansion engines
over the one obtained in case of cascaded form. The required optimum pressure is also lower.
In the recent past, this topic of cycle simulation is again gaining importance due to the
increasing need of the efficient helium liquefiers for cooling of superconducting magnets.
Nobutoki et al. [5] and Malaaen et al. [6] have presented simulation programs for the Large
Helical Device (LHD) and the Large Hadron Collider (LHC) projects, respectively, for
helium liquefaction/refrigeration plants in order to estimate, understand and analyse the
performance of cryogenic processes before investing in the actual manufacturing of these
plants. Helium liquefier based on the Collins cycle consisting of six heat exchangers and two
reciprocating expanders, Atrey [7] has evaluated the relative importance of the effectiveness
of each heat exchanger and efficiency of expanders on the performance of the liquefier. For
the simulation of helium systems, a 32-parameter modified Benedict–Webb–Rubin (MBWR)
EOS, which has been developed by McCarty and Arp [8] is widely accepted and considered
as the most accurate one. Rijo Jacob Thomas et al.[9] evaluated that Substituting MBWR
EOS by simpler equations of state (EOS(s)) at selected thermodynamic planes, where the
simpler EOS(s) have the similar accuracy as that of MBWR EOS may enhance ease of
computation. Some studies have investigated the importance of heat exchangers on a helium
9
liquefaction/refrigeration cycles. Daus et al. [10] have shown the power consumption, heat
transfer surface and the relative plant costs as functions of the temperature difference of heat
exchanger. Toscano et al. [11] have evaluated the thermodynamic performance of the central
helium liquefier of Fermi National Accelerator Laboratory (FNAL) for different sets of
temperature approach of heat exchangers. Khalil et al. [12] have given the practical
temperature approaches of heat exchangers for different multi-expander Claude based helium
refrigeration cycles having up to five expanders. Research on helium liquefiers has gained
momentum due to the demand for more efficient large-scale helium liquefiers for cooling the
superconducting magnets used in applications like particle accelerators, tokomaks, etc.
Aronson [13] has discussed the factors affecting the expansion efficiency and the
considerations to be made while using multi-expanders in a cycle. Khalil and McIntosh [14]
has determined the optimum inlet temperature to expander for Claude-based refrigeration
cycles up to six expanders. Hilal [15] has optimized both refrigeration and liquefaction cycles
in terms of number of expanders, their arrangements and inlet temperature to expanders. For
a 1.8K refrigerator with two expanders, Hilal and Eyssa [16] determined the optimum inlet
temperature to expander and the flow fraction through expander.
2.2 Various Liquefaction systems:
2.2.1 Claude System:
The system consists of a compressor, three heat exchangers, expansion engine and a joulethomson valve. The expansion engine is diverts a fraction of the incoming high-pressure gas
stream performing work as the gas expands into low-pressure side. Modern liquefier is more
complex than the Claude system but use similar combinations of expansion processes. The
Claude system provides following advantages over the simple Joule-Thomson refrigeration
scheme.
10
1. It has more efficient because part of the process is isentropic with inherently higher
thermodynamic efficiency.
2. The efficiency can be improved by taking advantage of the work produced by the
expansion circuit, an option that makes sense particularly for large systems/
3. There are two or more coupled flow circuits, the main cooling circuit and that through
expander, it is possible to vary the fraction of the flow to achieve higher performance
characteristics.
A flow scheme of the Claude liquefaction system is shown in fig 2.1
Fig 2.1: Claude liquefaction systems
11
Fig 2.2: T-S diagram for Claude system
The Claude cycle is displayed on a T-S diagram in fig 2.2. The points as indicated on the fig
1 are also shown in fig 2. The point (3) is indicates the position where the two circuit
separate. The isentropic expansion reduces the temperature as shown in point (e). The higherpressure stream continues until point (5) where the J-T valve produces an isenthalpic
expansion into the two-phase region. Thus, in the Claude system there are two free
parameters to select, the higher pressure valve, p2, and the fraction of gas through the
expansion engine circuit,
̇
̇
. To see how the parameters enter the calculations of yield
and net work, it is necessary to consider the thermodynamics of both processes.
2.2.2 Cascade System:
The intermediate-temperature fluids are used in the liquefaction of low-temperature liquids
and this technique has been established since the beginning of cryogenics. In fact this concept
12
is first used by Pictet for liquefaction of
. The Cascade liquefaction system is special case
of this concept, consist of a series of closed-cycle systems each using the change of state
from liquid to gas to achieve cooling. Thus the true cascade system has working fluids with
overlapping two-phase coexistence regions. Helium liquefiers based on the Claude systems or
a modification of it have considerably higher liquefaction yield when liquid nitrogen
precooling is included in the system.
The application of such a hybrid cascade system is shown in fig 3. The system consists of
many circuits each containing a different working fluid. All circuits(except helium liquefier)
operate in a closed-cycle mode, Where the liquids provides the cooling to next lower stage.
So the system uses the Joule-Thomson effect for the working fluid to be below its inversion
temperature before cooling occur. The working fluid has inversion temperatures above the
boiling point of the next higher working fluid in the system. The helium is precooled by a
closed cycle hydrogen liquefier as shown in fig 2.3. The inversion temperature of hydrogen is
202K. it can be precooled by liquid nitrogen or a similar fluid with T<202K.
Fig 2.3: Hybrid cascade liquefaction system for liquefaction of helium.
13
2.2.3 Collins Helium Liquefaction System:
In 1940s the Collins helium liquefier worked out of an effort to produce a commercial system
using expansion engines to precool several heat exchangers. The Collins system actually
similar to the Claude system except uses between two and five expansion engines rather than
just one. A schematic diagram of a two-engine Collins system is shown in fig 2.4. Depending
on the number of expansion circuits, i, there are equal number of expansion circuit mass
flows to select,
̇
The temperature at the inlet to each expansion engine determined to
compute the yield. Once these quantities are known a straightforward computation to
determine the yield for the Collins system,
(2.1)
The first Collins liquefiers were developed with two expansion engines. During steady state
operation the approximate values for the expander mass flow fractions are
=0.30 and
=0.55 at 15 bars. Insertion of these numerical values into (1) leads to yield of only 3.6%.
However, it has been demonstrated the liquid yield could be improved by a factor of 2-3 by
liquid nitrogen precooling.
14
Fig 2.4: Collins helium liquefaction system
2.2.4 Stirling Cycle:
An alternative concept for the production of helium has worked out of the application of a
heat engine cycle invented by stirling in 1827. The stirling cycle produces cooling by
operating inverse. The Phillips Company was the first to produce liquefier that operated on
this principle. The cycle consists of two isothermal and two isochoric processes. Cooling is
achieved by adiabatic expansion of the working fluid, but instead of heat exchangers, the
stirling cycle use the regenerator. The regenerator is a porous material used for storing the
thermal inertia of the system. A schematic diagram of the stirling system is shown in fig 2.5.
There are three main components: compressor, regenerator (R) and displacer (D). The
displacer works in consort with the compressor to provide low-temperature compression and
expansion processes.
15
Fig 2.5: Stirling cycle refrigerator
At (1) - The helium is compressed
(2) - The displacer is moved to its upper position forcing the fluid through the regenerator
into the expansion chamber. This process takes place at constant volume.
(3) - An expansion of the fluid in the lower chamber achieved by moving the displacer
upward with the compressor.
(4) - The displacer is returned to its lowest position, forcing the fluid back through the
regenerator to the compression chamber.
16
Chapter 3
Process design
17
3.1 Process design of helium liquefier:
Fig 3.1: Schematic of helium-1610 liquefier
The helium liquefier consist of seven heat exchanger (includes 2 heat exchanger for liquid
nitrogen precooling), two reciprocating expanders which is connected in parallel. When the
design data in terms of nodal temperatures across expanders and heat exchanger, efficiencies
of expanders and effectiveness of heat exchangers, mass flow rate through expanders,
compressor and J-T valve, etc. are available then the helium liquefier is possible.
The design is critical at low temperature due to changes in thermophysical properties of
helium gas the parameters like heat exchanger effectiveness, expander efficiencies, total mass
flow rate, mass flow fraction through expanders, and temperature of gas before expansion,
etc., and affects the performance of helium liquefier.
18
3.2 Simplification of process flow-sheet:
The computational complexity has been reduced simplification of process flow diagram. In
order to reduce computational complexities following assumptions have been made without
affecting the accuracy of the simulation results.
1. The pressure drops in the piping and adsorbers have been added to the valves or heat
exchangers placed nearby.
2. Pressure, temperature, mass flow rate have been kept constant.
3. Compressor station and gas management system ignored
4. The by-pass lines and manual valves ignored. So that the straight forward cool-down
sequence adopted.
This led to the simplification of the original PFDs, shown in fig.3.1.
3.3 Component and parameter analysis:
A. Effectiveness of heat exchangers, ɛ:
The effectiveness of heat exchangers, ɛ, is defined as
ɛ = actual heat transfer/ maximum possible heat transfer
ɛ=
(3.1)
=
(3.2)
Where,
C – Capacity rate (product of mass flow rate and specific heat capacity of gas)
Suffix c and h – cold and hot fluid respectively
Suffix o and i - outlet and inlet respectively
– Smaller quantity of
and
19
B. Efficiency of expansion engine, ɳ:
The efficiency of expansion engine, ɳ, is defined as
ɳ = actual enthalpy drop/ maximum possible
Enthalpy drop =
(3.3)
Where,
- The enthalpy at the point where expansion takes place
- The enthalpy at the actual point after expansion
- The enthalpy at the point if the expansion is isentropic in nature.
C. Throttle valve (J-T Valve):
Throttling is an isenthalpic process. Equating the enthalpies before and after throttling
(3.4)
Where,
- Enthalpy before throttling
- Enthalpy after throttling
D. Yield:
The rate of liquid production ( ̇ ) is nondimensionalized as the fraction of the total
compressor flow ( ̇
.
Yield = ̇
̇
(3.5)
20
3.4 T-S Diagram:
300
HP
250
13
TEMPERATURE(K)
200
150
2
12B
100
EXP-1
50
3A1
VAPOUR
11
EXP-2
J.T
4
5A1
6
0
0
7
2
8
10B
9
8B
4
6
8
ENTROPY (KJ/gmol-K)
Fig 3.2: T-S Diagram of helium liquefier
21
10
12
14
3.5 Aspen One:
A. Introduction:
Aspen one is software and it is AspenTech’s comprehensive set of software solutions and
professional services designed to help process companies achieve their operational excellence
objectives. It gives the value of simulation models to help process companies increase
operational efficiency and profitability across their global enterprise. Aspen-one cover four
major fields Chemical, Energy, Polymer, Pharmaceuticals.
Fig 3.3: Business areas of aspen one
22
B. Aspen one engineering classification:
Fig 3.4: aspen one engineering classification
23
Aspen Hysys is a process simulation environment used in many processing industries like
Gas &Oil and Refining. With Aspen Hysys can create rigorous steady state and dynamic
models for plant design, troubleshooting, performance monitoring, business planning,
operational improvement, and asset management. Through Aspen Hysys interface, can easily
manipulate process variables and unit operation topology as well as fully customize your
simulation using its customization and extensibility capabilities. The process simulation of
Aspen Hysys enables to predict the behaviour of a process using basic engineering
relationships such as mass and energy balances, phase and chemical equilibrium and reaction
kinetics. With reliable thermodynamic data, realistic operating conditions and the rigorous
Aspen Hysys equipment models, they can simulate actual plant behaviours. Some of the
important Aspen Hysys features are listed below:

Windows Interoperability: Hysys interface contains a process flow sheet view for
graphical layout, data browser view for entering data the patented Next expert
guidance system to guide the user through a complete and consistent definition of the
process flow sheet.

Plot Wizard: Hysys can enable the user to easily create plots of simulation results.

Flow sheet Hierarchy and Templates: Collaborative engineering is supported through
hierarchy blocks that allow sub-flow sheets of greater detail to be encapsulated in a
single high-level block. These hierarchy blocks can be saved as flow sheet templates
in libraries.

Equation-Oriented Modelling: Advanced specification management for equation
oriented model configuration and sensitivity analysis of the whole simulation or
specific parts of it. The combination of Sequential Modular and Equation Oriented
solution technology allows the user to simulate highly nested processes typically in
the chemical industry.
24

Thermo physical Properties: Physical property models and various data are keys to
generating accurate simulation results that can be used with confidence. Aspen Hysys
uses the extensive and proven physical property models, data, estimation methods
available in Aspen Properties™, which covers a wide range of processes from simple
ideal behaviour to strongly electrolytes and non-ideal mixtures. The built-in database
contains parameters for more than 8500 components, covering organic and inorganic,
aqueous, and salt species and more than 37000 sets of binary interaction parameters
for 4000 binary mixtures.

Convergence Analysis: to automatically analyse and suggest optimal tear streams,
flow sheet convergence method and solution sequence for even the largest flow sheets
with multiple stream and information recycles.

Sensitivity Analysis: to easily generate tables and plots showing how process
performance varies with changes to selected equipment specifications and operating
conditions.

Design Specification: Hysys has capabilities to automatically calculate operating
conditions or equipment parameters to meet specified performance targets.

Data-Fit: to fit process model with actual plant data and ensure an accurate validated
representation of the actual plant.

Determine Plant Operating Conditions that will maximize any objective function
specified, including process yields, stream purities, energy usage, and process
economics.

Simulation Basic Manager: This feature available in Aspen Hysys for using different
fluids like air, acetylene, nitrogen, helium as per requirement. Also several fluid
packages like ASME, BWRS, and MBWR are provided to calculate properties at
different states.
25
3.6 The components or blocks or equipment:
The description of the various components and the conditions at which they operate are
described as below.
1. Aspen Hysys Object:
A. Mixer:
The Mixer operation combines two or more inlet streams to produce a single outlet
stream. A complete balance of heat and material is performed with the Mixer. That is, the one
unknown temperature among the inlet and outlet streams is always calculated rigorously. If
the properties of all the inlet streams to the Mixer are known (temperature, pressure, and
composition), the properties of the outlet stream is calculated automatically since the
composition, pressure, and enthalpy is known for that stream.
B. Heat Exchanger/LNG:
The LNG (Liquefied Natural Gas) exchanger model solves heat and material balances
for multi-stream heat exchangers. The solution method can handle a wide variety of specified
and unknown variables. For the overall exchanger, we can specify various parameters,
including heat leak or heat loss, UA and temperature approaches. Two solution approaches
are employed; in case of a single unknown, the solution is directly calculated from an energy
balance. In case of multiple unknowns, an iterative approach is used that attempts to
determine the solution that satisfies not only the energy balance, also any constraints, such as
temperature approach or UA.
26
C. Separator:
Multiple feeds, one vapour and one liquid product stream. In Steady State mode, the
Separator divides the vessel contents into its constituent vapour and liquid phases
2. Logical units:
A. Spreadsheet:
The Spreadsheet applies the functionality of Spreadsheet programs to flowsheet
modelling. With essentially complete access to all process variables, the Spreadsheet is
powerful and has many applications in HYSYS. The HYSYS Spreadsheet has standard row
and column functionality. You can import/export a variable, or enter a number or formula
anywhere in the Spreadsheet.
The Spreadsheet can be used to manipulate or perform custom calculations on flowsheet
variables. Because it is an operation calculations are performed automatically; Spreadsheet
cells are updated when flowsheet variables change.
One application of the Spreadsheet is the calculation of pressure drop during dynamic
operation of a Heat Exchanger. In the HYSYS Heat Exchanger has constant pressure drop on
both sides regardless of flow. However, using the Spreadsheet, the actual pressure drop on
one or both sides of the exchanger could be calculated as a function of flow. Complex
mathematical formulas can be created, by using syntax which is similar to conventional
Spreadsheet. Arithmetic, trigonometric, and logarithmic functions are examples of the
mathematical functionality available in the Spreadsheet. The Spreadsheet also provides
logical programming in addition to its comprehensive mathematical capabilities.
27
B. Recycle:
The streams are recycled by using this logical operation. The logical block connects
the two streams around the tear (remember the tear does not have to be the official "recycle",
but instead should be the best place in the loop to make the break for convergence purposes).
The flow sheet must have completed before you can install the RECYCLE. That means there
need to be values for both the calculated stream and the assumed stream. Once the Recycle is
attached and starts to run, HYSYS compares the two values between two streams, adjusts the
assumed stream, and runs the flow sheet again. HYSYS repeats this process until the two
streams match within specified tolerances.
Those tolerances are set on the Parameters Page. There are tolerances for temperature,
pressure, Vapour Fraction, Flow, Enthalpy, and Composition. The tolerances you enter are
not absolute. They are multipliers for HYSYS internal convergence tolerances. For example,
the internal value for Temperature is .01 degrees (note that is in Kelvin, because HYSYS
does all of its calculations in an internal unit set), above explanation defines multiplier often
means the two streams must be within a tenth of a degree of each other.
On the Numerical Page, among other things, you may set the RECYCLE to either Nested (the
Op is called whenever it is encountered in the flow sheet) or Simultaneous (all of the
RECYCLEs are invoked).
3.7 Procedure of process design using Aspen Hysys:
To create a new case, from the File menu, select New. In the sub-menu, click Case. Then the
Simulation Basis Manager window will appear.
The Simulation Basis Manager is the important property view of the Simulation environment.
One of the important concepts that HYSYS is based upon is Environments. The Simulation
28
Basis environment allows to input or access information within the Simulation Basis manager
while the other areas of HYSYS are put on holds avoiding unnecessary Flowsheet
calculations. Once enter the Simulation environment, all changes that were made in the
Simulation environment will take effect at the same time. Conversely, all thermodynamic
data is fixed and will not be changed as manipulations to the Flowsheet take place in the
Simulation environment. The minimum information required before leaving the Simulation
Basis manager is atleast one installed Fluid Package with an attached Property Package and
At least one component in the Fluid Package. The Components Manager is available on the
Components tab of the Simulation Basis Manager. This tab provides a location where sets of
chemical components being modelled may be retrieved and controlled. These component sets
are stored in the form of Component Lists that may be a collection of library pure
components. The Components Manager always contains a Master Component List that
cannot be deleted. This master list contains every component available from "all" component
lists. If add components to any other component list, they automatically added to the Master
Component List. Also, if delete a component from the master component, it also gets deleted
from any other component list that is using that component.
The Fluid Package Manager is available on the Fluid Pkgs tab of the Simulation Basis
Manager. This tab provides a location where multiple fluid packages can be created and
controlled. Each fluid package available to simulation is listed in the Current Fluid packages
group with the following information: name, number of components attached to the fluid
package, and property package attached with the fluid package. From the Fluid Pkgs tab of
the Simulation Basis Manager click either the View or Add button to open the Fluid Package
property view. Make sure select the proper fluid package when using the view option. Click
on the Set Up tab. From the Component List Selection drop-down list, select the components
you want to use in your fluid package.
29
3.8 Fluid package:
The applicability of Equation of state in modelling helium system has been explained by Rijo
Jacob Thomas [9]. For modelling helium system proper equation of state is used. The
application of proper EOS increase the accuracy of the simulation result because the accuracy
is depends upon the property data. For computation of thermodynamics properties of helium
32-parameter MBWR equation of state is used and it eliminates the difficulties in
computation process.
The thermodynamics properties are generated from the
software, by giving the
input values in terms of temperature and pressure. This generated thermodynamics properties
are compared with Apen Hysys simulation result. From this comparison gives small
percentage of divergence so using 32-parameter MBWR EOS gives accurate solution when
compared with other equation of state. The comparison of MBWR EOS with
are shown in fig.
1800
1600
ENTHALPY (KJ/Kg)
1400
1200
1000
ALL PROPS
800
HYSYS
600
400
200
0
0
50
100
150
200
250
300
TEMPEATURE (K)
Fig 3.5: Variation of temperature with Enthalpy
30
350
0.12
ENTROPY (J/Mol-K)
0.1
0.08
0.06
ALL PROPS
HYSYS
0.04
0.02
0
0
50
100
150
200
250
300
350
TEMPERATURE (K)
Fig 3.6: Variation of temperature with Entropy
3.9 Input value:
From simulation basis manager in the component pure helium is taken as material stream and
MBWR as fluid packages. There all unit operations are arranged in order and linked by
material streams. For each unit operations following input values are entered.
1. HP (inlet stream)
Mass flow rate =300 kg/hr
Inlet temperature = 300 K
Inlet pressure = 15 bar
31
2. LN2 (Liquid nitrogen inlet streams)
Mass flow rate =300 kg/hr
Inlet temperature = 77.35 K
Inlet pressure = 1.013 bar
3. Separator-1
Flow ratio through liquid nitrogen precooling = 0.40
4. Separator-2, 3
Flow ratio through expansion engine = 0.40
5. Expansion Engine (E37)
Efficiency = 75%
Outlet pressure = 1.548 bar
6. Expansion Engine (E39)
Efficiency = 75%
Outlet pressure = 2.732 bar
7. Heat Exchanger (E30, E31, E32, E33, E34)
Pressure drops in all Hx = 0.1 bar
LMTD
E30 = 26.73 C
E31 = 3.94 C
E32 = 2.48 C
E33 = 0.93 C
E34 = 1.10 C
8. J-T Valve
Outlet pressure = 1.150 bar
32
3.10 Process flow in Aspen Hysys:
Amount of liquid yield can be seen from the tank. It comes 18.98 kg/hr.
Fig 3.7: Process Flow Diagram of Helium Liquefier in Aspen Hysys
Fig 3.7 shows the process flow diagram that drawn in Hysys. Table 3.1 shows the state and
properties of all the streams in the process flow diagram mass flow at LHE , gives the liquid
helium that produced.
33
Name
HP
1
2A
1A
2B
Vapour Fraction
1.0000
1.0000
1.0000
1.0000
1.0000
Temperature(K)
300.0
300.0
300.0
111.2
140.0
Pressure(bar)
15.00
15.00
15.00
14.90
14.90
Molar Flow (kgmole/s)
2.082e-002
1.249e-002
8.327e-003
1.249e-002
8.327e-003
Mass Flow(kg/s)
8.333e-002
5.000e-002
3.333e-002
5.000e-002
3.333e-002
Liquid Volume Flow(m3/s) 6.717e-004
4.030e-004
2.687e-004
4.030e-004
2.687e-004
Heat Flow(kW )
130.2
78.13
52.09
29.09
24.39
2C
2
3D
3A1
3A
Name
Vapour Fraction
1.0000
1.0000
1.0000
1.0000
1.0000
Temperature(K)
122.7
107.5
44.70
44.70
44.70
Pressure(bar)
14.90
14.80
14.70
14.70
14.70
Molar Flow (kgmole/s)
2.082e-002
2.082e-002
2.082e-002
1.249e-002
8.327e-003
Mass Flow(kg/s)
8.333e-002
8.333e-002
8.333e-002
5.000e-002
3.333e-002
Liquid Volume Flow(m3/s) 6.717e-004
6.717e-004
6.717e-004
4.030e-004
2.687e-004
Heat Flow(kW )
53.48
46.86
19.44
11.66
7.775
4
3B
5D
5A1
5A
Name
Vapour Fraction
1.0000
1.0000
1.0000
1.0000
1.0000
Temperature(K)
25.73
24.80
17.72
17.72
17.72
Pressure(bar)
14.60
1.548
14.50
14.50
14.50
Molar Flow(kgmole/s)
1.249e-002
8.327e-003
1.249e-002
7.494e-003
4.996e-003
Mass Flow(kg/s)
5.000e-002
3.333e-002
5.000e-002
3.000e-002
2.000e-002
Liquid Volume Flow(m3/s) 4.030e-004
2.687e-004
4.030e-004
2.418e-004
1.612e-004
Heat Flow(kW )
6.502
4.275
4.167
2.500
1.667
6
5B
7
Name
LHE
8
Vapour Fraction
1.0000
1.0000
0.8242
0.0000
1.0000
Temperature(K)
7.070
10.79
4.359
4.359
4.359
Pressure(bar)
14.40
2.732
1.150
1.150
1.150
Molar Flow(kgmole/s)
7.494e-003
4.996e-003
7.494e-003
1.317e-003
6.177e-003
Mass Flow(kg/s)
3.000e-002
2.000e-002
3.000e-002
5.273e-003
2.473e-002
Liquid Volume Flow(m3/s) 2.418e-004
1.612e-004
2.418e-004
4.250e-005
1.993e-004
34
Heat Flow(kW )
Name
0.3567
1.037
0.3567
-2.367e-002 0.3804
8B
9
10
10A
11
Vapour Fraction
1.0000
1.0000
1.0000
1.0000
1.0000
Temperature(K)
6.739
15.50
25.42
25.14
37.81
Pressure(bar)
1.150
1.050
0.9500
0.9500
0.8500
Molar Flow(kgmole/s)
1.117e-002
1.117e-002
1.117e-002
1.950e-002
1.952e-002
Mass Flow(kg/s)
4.473e-002
4.473e-002
4.473e-002
7.806e-002
7.813e-002
Liquid Volume Flow(m3/s) 3.605e-004
3.605e-004
3.605e-004
6.292e-004
6.298e-004
Heat Flow(kW )
3.559
5.892
10.17
15.34
1.416
Name
12A
13
LN2
14
15
Vapour Fraction
1.0000
1.0000
0.0000
0.4066
1.0000
Temperature(K)
105.4
226.2
77.35
76.49
280.0
Pressure(bar)
0.7500
0.6500
1.013
0.9130
0.8130
Molar Flow(kgmole/s)
1.952e-002
1.952e-002
2.975e-003
2.975e-003
2.975e-003
Mass Flow(kg/s)
7.813e-002
7.813e-002
8.333e-002
8.333e-002
8.333e-002
Liquid Volume Flow(m3/s) 6.298e-004
6.298e-004
1.033e-004
1.033e-004
1.033e-004
Heat Flow(kW )
91.81
-10.12
-3.499
24.20
12B
3C
5C
8A
10B
Vapour Fraction
1.0000
1.0000
1.0000
1.0000
1.0000
Temperature(K)
105.4
44.69
17.73
6.743
25.15
Pressure(bar)
0.7500
14.70
14.50
1.150
0.9500
Molar Flow(kgmole/s)
1.952e-002
2.082e-002
1.249e-002
1.117e-002
1.952e-002
Mass Flow(kg/s)
7.813e-002
8.333e-002
5.000e-002
4.473e-002
7.813e-002
Liquid Volume Flow(m3/s) 6.298e-004
6.717e-004
4.030e-004
3.605e-004
6.298e-004
Heat Flow(kW )
19.43
4.169
1.417
10.18
42.77
Name
42.77
Table 3.1: Material stream properties from Aspen Hysys
35
Chapter 4
Results and Discussion
36
4.1 Performance analysis:
The parametric variation on the liquefaction system gives the optimum performance. This
analysis also describe the off design performance analysis. The parameters are
 Effectiveness of heat exchangers, ɛ

Efficiency of expanders(Expansion Engine), ɳ

Mass flow ratio diverted for precooling, X0
 Mass flow ratio diverted through Expanders, X1, and X2
4.1.1 Mass flow ratio diverted through Expanders, X1, and X2:
The cold produced in expanders and in the J-T expansion valve is responsible for bringing
down the temperature of helium gas from 300K to below 7.5K. The mass flow rate diverted
through the expander is directly proportional to the refrigeration effect produced in the
expander. Temperature level of expanders decides if machine would function as a liquefier or
as refrigerator.
When increasing expander flow the cooling produced by the expander is increased so the high
pressure stream gets more cooling. The temperature before J-T valve is decreases it also
increases the yield. At the same time vapour returning to the compressor is reduces so the
mass flow through the expander is reduces consequently the yield is reduced.
To identify the optimum mass flow requirement of each expander, the distribution of the total
expander flow between the two expander (E37, E39) is varied. When varying the expander
flow other parameters affect the cycle performance such as isentropic efficiency of expanders,
heat exchanger effectiveness, etc. are kept constant.
37
1. Mass flow ratio diverted through the expanders ( = = = = =0.97,
= =0.75)
0.0645
0.064
0.0635
Yield
0.063
X2=0.35
X2=0.4
0.0625
X2=0.45
0.062
0.0615
0.061
0.3
0.35
0.4
0.45
0.5
0.55
X1
Fig 4.1: Variation of yield with mass flow ratio diverted through the expanders
Observations:
It is noticed from the Fig.4.1 that the combination of X1=0.43 and X2=0.35 shows the
maximum value as compared to any other combinations of X1 and X2. This is the optimum
value for the given ɛ and ɳ indicated. It states that, for this combination of X1 and X2, the
output in terms of liquefaction quantity is maximum. The optimum value lies at a
combination where X1 and X2 together constitute about 78-79% of the total mass flow rate
while the remaining 21-22% of the total mass flow rate goes through the J-T valve. Below the
77% there is no liquefaction indicated by the divergence of the program. This is due to the
point of the isenthalpic line after J-T expansion translates into the gaseous region, i.e. outside
dome.
38
4.1.2 Mass flow ratio diverted for precooling, X0 :
Mass flow ratio diverted for liquid nitrogen precooling gives some effect in the production of
yield. The yield is reduced because the liquefaction produced in the cycle is directly
proportional to the mass flow rate directed to expand through the J-T Valve. The variation of
yield with mass flow ratio as shown in Fig.4.2
1. Mass flow ratio diverted for precooling ( = = = = =0.97,
=
=0.75)
MASS FLOW, X0 YIELD
0.36
0.07321
0.38
0.06726
0.4
0.06327
0.42
0.05895
0.44
0.05606
0.46
0.05327
Table 4.1: variation of yield with precooling flow ratio
0.075
0.07
YIELD
0.065
0.06
0.055
0.05
0.35
0.37
0.39
0.41
X0
Fig 4.2: Effect of yield with mass flow X0
39
0.43
0.45
0.47
4.1.3 Effectiveness of heat exchangers, ɛ:
The T-S shows that the temperature before J-T expansion is important to determine
the amount of helium liquefied. The main purpose of heat exchanger is to reduce the
temperature from 300K to a reasonable value of T7 in order to get the liquefaction after the
J-T expansion.
The ɛ of the heat exchanger increases the performance of the liquefier is increases because
decrease in final value of T7 for a given mass flow rate. The temperature of all points is not
decreased by the same amount. The temperature of T7 decreases by various means i.e. by
increasing the ɛ of any heat exchangers or any two or all heat exchangers, and also be to an
increase in the ɳ of any or all the expanders.
1. Heat exchangers, ( =
=0.75, X1=X2=0.4)
EFFECTIVENESS
YIELD
E30
E31
E32
E33
E34
95
0.06149 0.06158 0.06172 0.06268 0.06281
96
0.06244 0.06232 0.0625
97
0.06327 0.06327 0.06327 0.06327 0.06327
98
0.06416 0.06435 0.06406 0.06355 0.06354
99
0.065
0.06298 0.063035
0.06524 0.06488 0.06382 0.06385
Table 4.2: variation of yield with heat exchanger effectiveness
40
0.07
0.068
0.066
0.064
Yield
0.062
E30
0.06
E31
E32
0.058
E33
0.056
E34
0.054
0.052
0.05
94.5
95
95.5
96
96.5
97
97.5
98
98.5
99
99.5
Effectiveness of Heat Exchangers, ɛ(%)
Fig 4.3: Variation of yield with Effectiveness of heat exchangers (
2. Heat exchangers, ( =
= =0.75)
=0.74, X1=X2=0.4)
EFFECTIVENESS
YIELD
E30
E31
E32
E33
E34
95
0.05958
0.0554
0.05981
0.06061
0.0598
96
0.06051
0.05843
0.06049
0.06102
0.06061
97
0.06142
0.06142
0.06142
0.06142
0.06142
98
0.06247
0.06443
0.06241
0.06182
0.06223
99
0.06387
0.06748
0.06282
0.06235
0.06305
Table 4.3: variation of yield with heat exchanger effectiveness
41
0.07
0.068
0.066
0.064
Yield
0.062
E30
0.06
E31
E32
0.058
E33
0.056
E34
0.054
0.052
0.05
94.5
95
95.5
96
96.5
97
97.5
98
98.5
99
99.5
Effectiveness of Heat Exchanger, ɛ (%)
Fig 4.4: Variation of yield with Effectiveness of heat exchangers (
= =0.74)
Observations:
The heat exchanger effectiveness is increased one by one to identify the individual
influence in liquid production. When varying the effectiveness of heat exchanger, the other
heat exchanger effectiveness kept constant (0.97, 0.96). The above figures(4.3,4.4) shows
that heat exchanger effectiveness has linear relationship with liquid production and each heat
exchanger has different gradient in the curve it shows that the effect of heat exchanger in
liquid production are not same.
42
4.1.4 Effect of variation of Expanders (Expansion Engine) Efficiency, ɳ:
The value of mass ratio through expander, effectiveness of heat exchangers is kept constant.
The effect of yield with the variation of expander efficiency is studied as shown in figure.
Yield increases with the increase in the efficiency of expander.
1. Expander , ( = = = = =0.97, X1=X2=0.4)
EFFICIENCY
YIELD
E37
E39
71
0.06135
0.05868
73
0.06201
0.06078
75
0.0629
0.0629
77
0.06397
0.0647
79
0.06506
0.06695
81
0.0665
0.06921
Table 4.4: Variation of yield with expander efficiency ( = = = = =0.97)
0.07
0.068
Yield
0.066
0.064
E37
E39
0.062
0.06
0.058
70
72
74
76
78
80
82
Expansion Engine efficiency, ɳ (%)
Fig 4.5: Variation of yield with Efficiency of Expander ( = = = = =0.97)
43
2. Expander, ( = = = = =0.96, X1=X2=0.4)
EFFECTIVENSS YIELD
E37
E39
71
0.05458 0.05293
73
0.05568 0.05501
75
0.05701 0.05701
77
0.05805 0.05895
79
0.05905 0.06062
81
0.06
0.06275
Table 4.5: variation of yield with expander efficiency ( = = = = =0.96)
0.064
0.062
Yield
0.06
0.058
E37
E39
0.056
0.054
0.052
70
72
74
76
78
80
82
Expansion Engine efficiency, ɳ (%)
Fig 4.6: Variation of yield with Efficiency of Expander ( = = = = =0.96)
44
Chapter 5
Conclusion
45
Conclusion:
The above project work gives a cycle simulation for the helium liquefaction with heat
exchanger, expander (expansion engine), JT valve. The simulation is carried out by using
process simulation software, Aspen Hysys. The preliminary data required in terms of pressure
and temperature, mass flow rate across heat exchanger, expander and other components of
the helium liquefier are found out. The parametric study is carried out to study the role of
different component efficiencies in deciding overall system efficiency. It is found that liquid
yield is directly proportional to heat exchanger effectiveness, expander efficiency, mass flow
rate diverted through the J-T Valve. When the effectiveness of heat exchanger and expander
efficiency decreases production of liquid also decreases. So increasing the heat exchanger
effectiveness increases the liquid production but increasing the efficiency of expander is
increase only the small amount of liquid production. This simulation done and analysis
carried out can serve as guide lines for the development of the helium liquefier in our nation
for the future mission.
46
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47
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