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SYNOPSIS
SOME STUDIES ON PERFORMANCE IMPROVEMENTS
OF COMBINED CYCLE POWER PLANTS
1. Introduction
The broad vision behind the Indian energy policy is “To consistently meet the demand for
energy services of all sectors including the lifeline energy needs of vulnerable
households, in all parts of the country, with safe and convenient energy at the least cost in
a technically efficient, economically viable and sustainable manner” [India energy book
2012]. Data of installed electricity generation capacity and capacity utilization stresses
the need to improve efficiency of the technology used in electricity generation. In recent
years Compound Annual Growth Rate (CAGR) of production of Energy in India by
primary sources is largest for the natural gas viz. 9.13% [Energy statistics 2012].
India’s energy-mix comprises both non-renewable and renewable energy sources.
Information on reserves of non-renewable sources of energy like coal, lignite, petroleum,
natural gas and the potential for generation of renewable energy sources is a pre- requisite
for assessing the country’s potential for meeting its future energy needs. As on 31.03.11
the estimated reserves of coal was around 286 billion tonnes, crude oil and natural gas
757 million tonnes (MT) and 1241 billion cubic meters (BCM), respectively. The total
potential for renewable power generation in the country as on 31.03.11 is estimated at
89760 MW. This includes an estimated potential of wind power of 49132 MW (55%),
small-hydro power (SHP) 15,385 MW (17%), biomass power 17,538 MW(20%) and
5000 MW (6%) from bagasse-based cogeneration. Capital costs of generation plants vary
according to the fuel type typically Coal-based plant: Rs. 3.8 to 4 crore, Gas-based plant:
Rs. 3.5 crore, Hydro: Rs. 5 crore, Wind: Rs. 5-6 crore and Nuclear: Rs. 6 crore per MW
in year 2007.
The combined-cycle power plant is a promising mode of energy recovery and
conservation, and is an economically interesting proposition. The combined-cycle
generation system features high thermal efficiency, low installed cost, fuel flexibility
with a wide range of gas and liquid fuels, low operation and maintenance costs, operating
1
flexibility, high reliability and availability, short installation times and high efficiency in
small capacity increments.
It may be concluded that according to the availability of fuel and technology, at present
India can rely on the combined cycle power plants. Incorporation of new methods and
technology for performance improvement in terms of efficiency, reliability and more of
environmental friendly electricity generation need to be explored.
2. Literature Review
Due to the inexorable rise of electricity demand, researchers in the power plant area are
hankering for best utilization of energy resources. Literature review of combined cycle
power plant is divided in to three parts. First part is dealing with the recent developments
in CCPP thermodynamic cycles and second part includes methods for the improvement
of CCPP. Third part is dealing with use of graph theoretic approach for prediction of
effect of two or more parameters on other performance parameters.
2.1. Recent Developments in Combined Cycle Power Plant (CCPP) Thermodynamic
Cycles
CCPP and its performance review can be had from Najjar & Akyurt (1994), Horlock
(1995), Heppenstall (1998), Pilavachi (2000) and Wu & Wang (2006).
Morosuk & Tsatsaronis (2012) presented a way for combining exergoeconomic and the
exergoenvironmental analysis and for formulating common conclusions for further
improvement of an energy conversion system by taking into account simultaneously the
minimization of cost and of environmental impact.
Vallianou & Frangopoulos (2012) studied a trigeneration system consisting of a gas
engine with heat recovery, an absorption chiller driven by thermal energy, electrically
driven compression chillers and two thermal storage tanks (one with hot and one with
cold water). The objective of the work reported was operation optimization of
trigeneration system under load-varying conditions taking into consideration the transient
behavior of the three aforementioned components.
2
Gaggioli (2012) provided guidance for the selection of the dead state for exergy analysis,
especially important in applications to energy-conversion and materials processing plant
engineering, and to ecology.
Bassily (2012) found steam-air cooling of the gas turbine (GT) and optimization as
important methods for enhancing the efficiency and power of the combined cycle power
plants. It was analyzed that a steam-air cooled GT uses less air for GT cooling; thus,
allows more air to be available for the combustion process and increases output power
significantly.
Ahmadi & Dincer (2011) used a modified version of evolutionary algorithm (non-
dominated sorting genetic algorithm) for multi objective optimization of a Gas Turbine
power plant. The design parameters considered were air compressor pressure ratio,
compressor isentropic efficiency, gas turbine isentropic efficiency, combustion chamber
inlet temperature and gas turbine inlet temperature. Results showed that by selecting
proposed sets of design parameters 33.56% increment in the total exergy efficiency and
decrease in the environmental impacts by 50.50%.
Poma et al. (2010) improved the initial design of a waste-to-energy plant integrated with
a combined cycle through a thermoeconomic procedure, and accomplished a reduction in
the unit cost of electricity and an increment on the power production.
Woudstra et al. (2010) explored the potential for improvement of a power cycle by using
the so-called internal exergy efficiency, which intends to measure the difference between
the actual exergy losses with the ones of the corresponding ideal reversible case.
Regulagadda et al. (2010) conducted energy and exergy parametric studies of a coal-fired
power plant. It was observed that the optimum cycle pressure ratio was higher for
efficiency than for power.
Ertesvag et al. (2005) have shown the exergy analysis of a gas-turbine combined-cycle
power plant with pre-combustion CO2 capture. A concept for natural-gas (NG) fired
power plants with CO2 capture was investigated using exergy analysis. This research
explores the effects of the changed NG composition and environmental temperature.
Sengupta et al. (2007) have studied the exergy analysis of a coal-based 210 MW thermal
power plant. The exergy efficiency was calculated using the operating data from the plant
3
at different conditions, viz. at different loads, different condenser pressures, with and
without regenerative heaters and with different settings of the turbine governing.
Butcher and Reddy (2007) have studied Second law analysis of a waste heat recovery
based power generation system for various operating conditions. The temperature profiles
across the heat recovery steam generator (HRSG), network output, second law efficiency
and entropy generation number were simulated for various operating conditions. The
variation in specific heat with exhaust gas composition, pinch point and temperature were
accounted in the analysis and results.
Ameri et al. (2008) studied the exergy analysis of a 420MW combined cycle power plant.
The results showed that the combustion chamber, gas turbine, duct burner and heat
recovery steam generator (HRSG) are the main sources of irreversibility representing
more than 83% of the overall exergy losses.
Som and Datta (2008) studied thermodynamic irreversibilities and exergy balance in
combustion processes. The present paper makes a comprehensive review pertaining to
fundamental studies on thermodynamic irreversibility and exergy analysis in the
processes of combustion of gaseous, liquid and solid fuels. The major source of
irreversibilities was the internal thermal energy exchange associated with high
temperature gradients caused by heat release in combustion reactions.
Khaliq and Kaushik (2004a) carried an improved second-law analysis of the combined
power-cycle with reheat and showed the importance of the parameters examined. The
analysis has included the exergy destruction in the components of the cycle and an
assessment of the effects of pressure ratio; temperature ratio and number of reheat stages
on the cycle performance.
Khaliq and Kaushik (2004b) presented simplified and systematic methodology based on
first and second law for the thermodynamic performance evaluation, of combustion gas
turbine cogeneration system with reheat.
2.2. Methods of Improving Combined-Cycle Performance
The main categories of combined-cycles may be classified by (a) the rate of excess air
utilized, (b) the number of steam pressure levels used in heat recovery, (c) the availability
4
of supplemental firing and (d) the use of steam reheat (e) Inlet air cooling (IAC) (f)
Steam Injected Gas Turbine (STIG) (g) Alternate working fluids.
Bolland (1991) studied alternative arrangements for improving the efficiency of the
combined-cycle. These were the dual pressure reheat cycle, the triple-pressure cycle, the
triple-pressure reheat cycle, the dual pressure supercritical reheat cycle and the triple
pressure supercritical reheat cycle.
Allen and Triassi (1989) investigated the performance of heavy-duty and aircraft-
derivative gas turbines for utility and industrial applications, comparing single and two-
shaft arrangements as combined cycles.
Gerri and Colage (1985) scrutinized the influence of steam cycle regeneration on
combined plant performance and demonstrated a positive influence on combined-cycle
efficiency for small degrees of regeneration.
Rice (1980) carried out a critical analysis of the reheat gas turbine cycle combined with
the steam turbine Rankine cycle, which arrangement promises to increase power plant
thermal efficiency appreciably. He established the cycle pressure ratio, firing
temperature, and output as operating parameters. The results of this analysis were applied
to the reheat LM5000 and the reheat steam cycle. Rice (1986) also suggested a method
for choosing optimal values of combined-cycle parameters such as pinch point, gas
pressure drop, single or dual pressure and reheat, based on the economical internal rate of
return.
Lugand and Parietti (1991) showed that a three-pressure level steam reheat cycle,
featuring a 200 MW gas turbine engine with a firing temperature of 1260°C, yields plant
efficiencies in excess of 53%.
A parametric analysis was conducted by Cerri and Sciubba (1987) for a plant equipped
with a gas generator and with steam injection into an after-burner placed upstream of the
power turbine. The steam was to be produced by a waste-heat recovery section made up
of a boiler and distillation plant fed by the gas turbine exhaust. The results showed a 13%
improvement in plant efficiency and a doubling of the specific work output when
compared with a standard gas turbine cycle with full reheat and optimal steam injection.
De Lucia et al. (1994) studied gas turbines with inlet air cooling and reported that
evaporative cooling could enhance the power produced by 2–4% per year, with rather
5
low investment. Absorption cooling can enhance power production by 5-10% on yearly
basis, depending on site climate, and upto 18% in the warmest month.
Kakaras et al. (2004, 2006) described three cooling methods a) evaporative cooling b)
refrigeration cooling c) evaporative cooling of precompressed air to improve gas turbine
based power plant performance.
Srinivas et al. (2008) carried out thermodynamic evaluation for a combined cycle with
Steam Injected Gas Turbine (STIG) having dual pressure heat recovery steam generator
(HRSG).
Jericha et al. (2008) proposed Graz Cycle which is an oxy-fuel power cycle with the
capability of retaining all the combustion generated CO2 for further use.
2.3. Graph Theory Analysis
Combined cycle power plant (CCPP) is a very large and complex system. Performance of
its components and systems are closely intertwined and insuperable without taking the
effect of others. Such as the performance of steam turbine not only depends upon steam
turbine efficiency but it is also affected by other systems such as heat recovery steam
generator (HRSG) and water system. So design of combined cycle power plant,
improvement in existing plant and comparison of two real life operating power plants
requisite a multi attribute decision making (MADM) technique to analyze the effect of
one system/design parameter on the other systems/design parameters.
Mohan et. al. (2008) proposed a graph model in conjunction with the matrix method to
obtain real time reliability index (RTRI) for a steam power plant (SPP). This model
enables incorporation of any number of systems and subsystems of the SPP as also the
interaction among them in the study of performance of a SPP. Further it was pointed out
that the methodology developed can be applied for obtaining other RAMS (Reliability,
Availability, Maintainability, Serviceability) indices: availability and maintainability;
including optimum selection, bench marking, and sensitivity analysis of a SPP.
Tang (2001) proposed a new method based on graph theory and Boolean function for
assessing reliability of mechanical systems. The proposed methodology incorporates the
graph theory for system level reliability and Boolean analysis for interactions. The
6
combination of graph theory and Boolean function provides an effective way to evaluate
the reliability of a large and complex mechanical system.
Mohan et al. (2003) developed a mathematical model using graph theory and matrix
method to evaluate the performance of a steam power plant.
Mohan et al. (2006) applied Graph Theoretic Approach (GTA) to calculate real-time
efficiency index (RTEI) for a steam power plant which is the ratio of the values of
variable permanent system structure function (VPF) in real-time (RT) situation to its
achievable design value.
Garg et al. (2006) developed a deterministic quantitative model based on graph
theoretical methodology to compare various technical and economical features of wind,
hydro and thermal power plants.
Simple model, easy to implement, lesser computational cost and flexible with changing
environment is required to evaluate the combined cycle power plant efficiency on design
basis or analysis basis. From the literature, it is clear that graph theory and matrix
approach as a decision making method offers a generic, simple, easy, convenient and
ingenious way of decision making that involves less computational efforts.
2.4. Conclusion and Gaps from Literature Review
The review shows that a number of alternative designs of these sub-systems are available
and there is continual upgrading in their design. From the economical, environmental and
practical point of view, the combination of a simple gas turbine cycle coupled to a
Rankine steam bottoming cycle (which may be with dual/triple pressure and reheat)
without supplementary firing is the most common type of power plants.
Most of the thermodynamically analysis and parametric studies are based on step by step
calculation of cycle processes of different combined cycle configurations. The basis of
comparison has mostly been the energy analysis (efficiency). Some author also present
comparison on the basis of availability/exergy analysis of cycle processes.
The effect of various operating parameter such as exhaust gas composition, the variation
of specific heat with gas composition and gas inlet temperature, TIT, bottoming cycle
pressures, pinch point (PP), approach point (AP), gas side pressure drop, steam injection
7
mass ratio, deaerator temperature ratio, steam reheat pressure ratio, HP steam pressure,
compressor pressure ratio and combustion chamber temperature etc.
Although there has been mention of simulation program in different papers, and a
generalized procedure for simulation strategy is not available in open literature. Hence,
there is a need of studying of power plant response to change in outside conditions
(ambient conditions and part load) both for economy and safe operation.
During literature survey it is found that Graph Theoretic Approach has not been used for
performance analysis of combined cycle power plant.
3. Objective of research work
In view of the finding reported in the previous sections the following objectives for
research work have been framed:
(a) To study the effect of various design parameters on first law and second law
efficiency of cogeneration and combined cycle.
(b) To study the effect of more than one parameter on thermodynamic efficiency of
different cycles.
(c) To develop methodology for Multi Attribute Decision Making (MADM) technique
capable of studying interdependency of design parameters along with incorporation
of tangible and intangible parameters.
4. Research Methodology
The proposed research work is carried out in the following way:
(i) An exhaustive literature survey had been carried out in the area of combined cycle
power plant.
(ii) Development of mathematical modeling for topping and bottoming cycles using
software Engineering Equation Solver (EES). EES is selected because fluid
properties are inbuilt function of the software.
8
(iii) Simulation studies of gas turbine – combined cycle power plant for wide range of
input conditions and operating parameters, design parameters and different
configurations.
(iv) GTA is found to be suitable for studying interdependency of design parameters
along with incorporation of tangible and intangible parameters.
(v) With the help of GTA system modelling for CCPP is carried out to study the
performance of plant under different operating parameters.
5. Modeling of Systems
In the present work analysis of cogeneration cycle and combined cycle is carried out.
Mathematical modeling for exergy and energy analysis of cogeneration cycle is carried
out for different design parameters. Mathematical modeling based on mass, energy and
exergy, balance across each component is followed by execution of computer program in
software Engineering Equation Solver (EES) for different cycle operating parameters.
For the combined cycle power plant first law analysis is carried out for single pressure,
dual pressure and triple pressure Heat Recovery Steam Generator (HRSG) and for single
steam extraction and double steam extraction. Second law analysis for CCPP with single
drum HRSG is done. Reliability and efficiency analysis of combined cycle power plant is
carried out with Graph Theoretic Approach also.
5.1. Cogeneration Cycle Power Plant
Ambient air enters the compressor and after compression its temperature and pressure is
increased. Compressed air is passed through a regenerator where high temperature
combustion gases coming out of gas turbine transfer their heat to the compressed air.
After gaining heat, compressed air comes to combustion chamber and fuel is added. After
burning with air, chemical energy of fuel is converted into thermal energy. Combustion
products temperature depends upon turbine inlet temperature (TIT) which is fixed by
thermal stress limit of gas turbine blade material. Combustion product temperature is
controlled by making A/F mixture a lean mixture. Gases coming out from gas turbine
9
have large amount of thermal energy. Major part of this thermal energy is transferred to
compressed air in regenerator and high pressure water in process heater. Flue gas
temperature at process heater outlet depends upon the dew point temperature of flue
gases. Temperature below dew point causes the corrosion of stack by flue gases.
Figure 1. Schematic diagram of Cogeneration cycle with regenerator
In present work, mathematical modeling based on mass, energy and exergy, balance
across each component is followed by execution of computer program in software
Engineering Equation Solver (EES) for different cycle operating parameters.
5.2. Combined Cycle Power Plant
In this part, system modeling of combined cycle power plant is described. Combined
cycle power plant considered for the present analysis is shown in figure 1. The air at the
ambient temperature and pressure enters the air compressor after being filtered by air
filter. Mechanical energy of compressor is used to compress the air so that higher
quantity of fuel may be added in air at lesser volume in combustion chamber. After
compression air comes to combustion chamber and mixes with the natural gas from the
fuel supply system. Activation energy for the reaction between air and fuel is being
provided by spark between two electrodes and reaction of air and fuel is at constant
pressure. After this, hot combustion gases enter the gas turbine where thermal energy of
10
flue gases is converted into mechanical power of gas turbines. HRSG is the link between
the gas turbine and the steam turbine process, whose function is to transfer heat energy
from exhaust gases to pressurized water and produces superheated steam. The steam is
separated in the boiler drum and supplied to the super heater section and boiler condenser
section. The super heated steam produced in the super heater then enters into the steam
turbine through the turbine stop valve. After expansion in steam turbine the exhaust
steam is condensed in the condenser. In the cooling water system, heat recovered from
the steam turbine exhaust is carried by the circulating water to the cooling tower, which
rejects the heat to the atmosphere. Because of this direct path to the atmosphere,
surrounding water bodies typically do not suffer adverse thermal effects. The power
Figure 2. Schematic flow diagram of Combined Cycle Power Plant
plant is a series system except for the cooling tower that is modeled as K out of N
systems, meaning that it is necessary a given number of cooling towers units working (K)
out of N to allow the plant to achieve nominal output. HRSG with double pressure and
steam turbine with single steam extraction and double steam extraction is studied.
5.3. Equations for Mathematical Modelling
Equations for the exergy analysis of cogeneration cycle are given by the following table.
11
Table 1. The exergy destruction rate and exergy efficiency equations for plant
components
Components Exergy Destruction Rate Exergy Efficiency
Air Compressor
Combustion
Chamber
Gas Turbine
Regenerator
HRSG
Steam Turbine
Steam Condenser
5.4. Methodology developed for Graph Theoretic Analysis
A methodology based on Graph Theory and matrix method is developed for evaluating
performance based on efficiency and reliability for combined cycle and cogeneration
cycle power plant. Digraph representation, Matrix representation and Permanent function
representation are the three steps of this methodology. The main steps of methodology
developed for the evaluation of CCPP performance index are as follows:
1. Identify the various system categories affecting the CCPP performance.
2. Develop the CCPP system digraph. This is the digraph at the system level.
3. Identify the various design parameters for each system category of CCPP system.
4. For each system category, develop a digraph among the design parameters based on
the interactions among them. This is the digraph at each sub-system level.
12
5. Based on the above-mentioned digraphs among sub-system design parameters,
develop the Variable Permanent Matrix (VPM) for each system category.
6. Calculate the permanent function at each sub-system level. For avoiding the
complexity, the numerical values of inheritance and interactions are used. A
computer program was developed using C++ language for calculating the value of
permanent function.
7. Develop the CCPP system matrix for the CCPP system digraph. This will be M x M
matrix with diagonal elements of Si (inheritance) and off-diagonal elements of cij
(interdependency). The value of the permanent function at each sub-system level
provides inheritance (diagonal elements of Si) for each system category. The values
of interaction among these system categories (off-diagonal elements) are to be
decided by the experts on the basis of scale of 1-5.
8. Calculate the permanent function of CCPP system matrix at the system level. This is
the value of CCPP performance which mathematically characterizes the
performance of any power plant based on the different design parameters and their
interdependence.
9. Compare different power plants in terms of CCPP performance index and list them
in descending order of their VPMCCPP values. The power plant having the lowest
value of VPMCCPP has the best chance of performance improvement.
10. Record the results of this study and document them for future analysis (Table 2).
6. Results and Discussion
Results from the mathematical modeling are obtained for different design parameters
with the help of computer programming executed in the software EES. Results obtained
from the analysis of cogeneration cycle are as following.
6.1. Effect of cycle pressure ratio on Cogeneration Cycle
It is found that with increase in cycle pressure ratio, exergy destruction in
cogeneration cycle is increased (figure 3).
It is found that with increase in cycle pressure ratio exergy destruction in compressor
is increased due to increase in compressor work. As CR is increased from 5 to 26
13
work consumed in the compressor is increased by 160.82%. But exergy destruction is
increased by 36.06% (figure 4).
After cycle pressure ration of 26, regenerator is not beneficial in the cycle.
6.2. Effect of Inlet Air Temperature on Cogeneration Cycle
With increase in IAT exergy destruction in cycle is increased due to increase in
compressor work. As IAT is increased from 5 to 50°C work consumed in the
compressor is increased by 15.82% and exergy destruction by 35.65%.
6.3. Effect of Gas Turbine and Air Compressor efficiency on Cogeneration Cycle
From the results it is found that increase in the efficiency of gas turbine has more
effect on the exergy destruction in the cycle than gas turbine efficiency.
With increase in gas turbine efficiency from 70% to 95%, exergy destruction in
combustion chamber, compressor, heat recovery steam generator, regenerator and gas
turbine is decreased by 47.84%, 47.84%, 84.06%, 68.73% and 6.12% respectively.
While for air compressor with increase in efficiency from 70% to 95% exergy
destruction in compressor, heat recovery steam generator and gas turbine is decreased
by 29.22%, 90.60%, 51.83%, and 29.24% respectively.
Irrespective of results obtained for gas turbine, exergy destruction in regenerator is
increased by 9.09% due to increase in air compressor efficiency.
With increase in gas turbine efficiency from 70% to 95% exergy destruction in cycle
is decreased by 61.18%.
For air compressor increment in efficiency 70% to 95% exergy destruction in cycle is
decreased by 38.96%.
6.4. Effect of Regenerator effectiveness and specific heat ratio on Cogeneration
Cycle
Increase in regenerator effectiveness from 60% to 85% decreases exergy destruction
in cycle by 22.55%. Increase in specific heat ratio from 1.1 to 1.4 decreases exergy
destruction by 1.33% (figure 5).
For the combined cycle power plant energy and exergy analysis is carried out to study the
effect of different operating parameters. It is found that efficiency of the combined cycle
varies in a complex manner with variation of operating parameters.
14
6.5. Effect of Inlet Air Temperature on CCPP
In case of CCPP with change in IAT from 5 °C to 50°C first law and second law
efficiency are decreased from 34.65% to 33.24% and 34.97% to 33.7% respectively.
With change in IAT from 5 °C to 50°C, exergy destruction in cycle is increased by
7.73%.
6.6. Effect of Gas Turbine and Air Compressor efficiency on CCPP
With change in compressor efficiency from 80% to 95%, first law and second law
efficiency is increased from 32.6 % to 35.78% and 33.04% to 36.14% respectively
and exergy destruction is decreased by 13.98% in CCPP.
If gas turbine efficiency is increased from 80% to 95% then first law and second law
efficiency is increased from 31.03% to 38.04% and 31.59% to 37.235 respectively.
Exergy destruction in CCPP is decreased by 32.61% with increase in gas turbine
efficiency 80% to 95%.
6.7. Effect of cycle pressure ratio on CCPP
Increase in cycle pressure ratio from 4 to20 decreases exergy destruction in CCPP by
42.36% (figure 6).
Further first law and second law efficiency is increased from 30.47% to 33.1% and
31.32% to 33.21% respectively with increase in cycle pressure ratio from 4 to 20.
6.8. Effect of Turbine Inlet Temperature (TIT) on CCPP
Changing TIT from 1100°C to 1400°C increases first law and second law efficiency
from 33.69% to 37.77% and 33.97% to 38.34% respectively.
Exergy destruction in CCPP is decreased by 19.52% with increase in TIT from
1100°C to 1400°C.
6.9. Effect of Steam Extraction on CCPP
Work obtained from the steam turbine in a simple combined cycle is 23649 KJ while
from that of single steam extraction is 28627 kJ being other conditions same. Air
consumption comes down from 105.7 Kg/s to 83.74 Kg/s. Work obtained due to
double steam extraction is 16.99% more in comparison to single steam extraction
from steam turbine.
It is also found that design parameters are inter-related to each other and performance
of cycle is varied if more than one parameter is changed (figure 7).
15
6.10. Graph Theoretic Analysis for CCPP Performance
From Graph Theoretic Analysis it came out that combustion chamber system is the most
important system of combined cycle power plant as index value is changed maximum for
it (table 2). After that gas turbine system, steam turbine system, HRSG system,
compressor system and water system are important in the decreasing order. Same pattern
is observed to be followed in literature. So it may be concluded that GTA can be used for
CCPP performance analysis on efficiency and reliability basis.
7. Conclusions
1. Exergy destruction in regenerator and process heater is associated with heat transfer
and temperature difference.
2. Exergy destruction in gas turbine is more than air compressor.
3. Combustion chamber is the largest source of exergy destruction followed by
regenerator, HRSG, gas turbine and air compressor.
4. With change in cycle pressure ratio, exergy destruction in regenerator is decreased
highly than other components.
5. Graph theoretic model is flexible enough that enables incorporation of different
systems and subsystems of the CCPP as also the interaction among them in the study
of reliability and efficiency of a CCPP.
6. GTA model can be used for benchmarking also.
7. Organisation of thesis
The dissertation consists of seven chapters. In the chapter 1, the topic is introduced, and
in the chapter 2, a review of literature is presented. The methodology for graph theoretic
analysis is discussed in chapter 3, followed by mathematical modeling for energy and
exergy analysis in chapter 4. Results are presented in chapter 5, followed by discussions
in chapter 6. In chapter 7, conclusions and scope for further work are given. References
are placed after chapter 7.
16
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Appendix I
32000
34000
36000
38000
40000
42000
44000
46000
5 10 15 20 25 26
Cycle Pressure ratio
Exer
gy d
estru
ctio
n in
cyc
le
Figure 3. Exergy destruction in cogeneration cycle with increase in cycle pressure ratio.
35
45
55
65
75
85
95
5 10 15 20 25
Cycle pressure ratio
Effic
ienc
y (%
)
Air compressorexergetic efficiency
Gas turbine exergeticefficiency
Regeneratorexergetic efficiency
HRSG exergeticefficiency
Combustion chamberexergetic efficiency
Cogeneration cycleexergetic efficiency
Figure 4. Effect of cycle pressure ratio on exergetic efficiency of different components of the cycle
38700
38800
38900
39000
39100
39200
39300
39400
39500
39600
1.1 1.2 1.3 1.4
Specific Heat Ratio
Exer
gy d
estru
ctio
n in
cyc
le
(kJ/
Kg)
Figure 5. Effect of specific heat ratio on exergy destruction in cogeneration cycle.Combined Cycle Power Plant
20
28
29
30
31
32
33
34
35
4 8 12 16 20
Cycle Pressure Ratio
CC
PP E
ffic
ienc
y %
First Law Eff iciency
Second LawEfficiency
Figure 6. Effect of cycle pressure ratio on first law and second law efficiency of combined cycle power plant
40
45
50
55
60
65
4 8 12 16 20 24 28 32 36 40
Cycle Pressure Ratio
CCPP
Effi
cien
cy (%
)
1100 °C
1200 °C
1300°C
1400°C
Figure 8. Change in Combined Cycle efficiency with cycle pressure ratio with change in TIT at 25 °C
Table 2. Change in CCPP index with change in the assigned values of factorsSystem Assigned value of factors Index Value Change in Index
ValueS1 1 219033 617832S1 9 836865S2 1 182385 654480S2 9 836865S3 1 187833 649032S3 9 836865S4 1 199665 637200S4 9 836865S5 1 194985 641880S5 9 836865S6 1 237465 599400S6 9 836865
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Appendix-II
Nomenclature
= Exergy rate (kJ/s)
W = Work (kJ/kg (dry air))
eP = Specific exergy associated with process heat (kJ/kg (dry air))
m = Mass (kg)
n = Number of moles
p = Pressure (bar)
re = Expansion ratio
rp = Pressure ratio
s = Entropy (kJ/kg K)
t = Temperature (°C)
v = Specific volume (m3/kg)
Greek Symbols
η = Efficiency (%)
Subscripts
C = Compressor
CC = Combustion chamber
D = Destruction
HRSG = Heat recovery steam generator
P = Product
ST = Steam Turbine
W = Work
av = Average
f = Fuel
g = Gas
i = Inlet
o = Outlet
R = Regenerator
1,2,3…9 = State points in the cycle
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Papers published/ accepted /communicated Out of Research work
A) Paper Accepted and Published in International Journal:
1. Nikhil Dev, Samsher, S. S. Kachhwaha, “System Modeling and Analysis of a Combined Cycle Power Plant” International journal of system assurance and management (Springer), DOI 10.1007/s13198-012-0112-y.
2. Nikhil Dev, Samsher, S.S. Kachhwaha “Computational Analysis of Dual Pressure Non-reheat Combined-Cycle Power Plant with Change in Drum Pressures” International Journal of Applied Engineering Research, vol 5, No.8 (2010), p. 1307-1313.
3. Nikhil Dev, Samsher, S.S. Kachhwaha “Graph Theoretic Assessment of Critical Component in Combined-Cycle Power Plant” International Journal of Engineering Studies, vol 4, No.1 (2012), p. 1-13.
4. Nikhil Dev, Samsher, S. S. Kachhwaha, Rajesh Attri, “Exergy analysis and simulation of a 30MW cogeneration cycle” Frontiers of Mechanical Engineering (Springer) (Accepted for publication).
5. Nikhil Dev, Samsher, S. S. Kachhwaha, Rajesh Attri, “GTA-based framework for evaluating the role of design parameters in cogeneration cycle power plant efficiency” Ain Shams Engineering Journal (Elsevier) (Accepted for publication).
B) Paper Presented in Conferences:
6. Nikhil Dev, Samsher, S.S. Kachhwaha “Modeling and Analysis of Dual Pressure Non-reheat Combined-Cycle with Change in Drum Pressures” Proceeding of international conference on advances in mechanical engineering held at SVNIT Surat, 04-06 January, 2010, p-114-118.
7. Nikhil Dev, Samsher, S.S. Kachhwaha, Sandeep Grover “Energy and Exergy Analysis of Cogeneration Cycle With Change in Gas Turbine Operating Parameters” Proceeding of international conference on emerging technologies for sustainable environment held at AMU Aligarh, 29-30 October, 2010, p- 412-414.
8. Nikhil Dev, Samsher, S.S. Kachhwaha, Sandeep Grover “A Comparison of Single and Dual Pressure Steam Extraction from Steam Turbine of Combined Cycle Power Plant” Proceeding of international conference on emerging trends in Mechanical Engineering held at Thapar University Patiala, 24-26 February, 2011, p-88.
9. Nikhil Dev, Samsher, S.S. Kachhwaha, Sandeep Grover “Mathematical modeling and exergetic analysis of cogeneration cycle with change in gas turbine parameters ” Proceeding of international conference on emerging trends in
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Mechanical Engineering held at Thapar University Patiala, 24-26 February, 2011, p-81.
10. Nikhil Dev, Samsher, S.S. Kachhwaha, “A Study of Combustion Product Concentration on Gas Turbine Performance” Proceeding of international conference CONIAPS-2011, held at UPES, Dehradun from 14-16 June, 2011, P084, pp-172.
11. Nikhil Dev, Samsher & S.S. Kachhwaha, “Simulation of gas turbine combustion chamber for CO2 emission minimization” SOCPROS-2011, Advances in Intelligent and Soft Computing (AISC, Springer), 2011, Vol 131, p 235-246.
12. Nikhil Dev, Samsher, S.S. Kachhwaha, Mohit “Mathematical Modelling and Computer Simulation of a Combined Cycle Power Plant” SOCPROS-2011, Advances in Intelligent and Soft Computing (AISC, Springer), 2011, Vol 131, p 341-350.
13. Nikhil Dev, Samsher, S. S. Kachhwaha, Rajesh Attri, “A review of combined cycle power plant thermodynamic cycles” Proceedings of national conference TAME-2012, from 19-20 October , 2012, p. 78-89.
C) Papers Communicated
14. Nikhil Dev, Samsher, S. S. Kachhwaha, Rajesh Attri, “Digraph and matrix method for assessing the role of design parameters in Gas Turbine Power Plant efficiency” Alexandria Engineering Journal (Elsevier).
15. Nikhil Dev, Samsher, S. S. Kachhwaha, Rajesh Attri, “Development of reliability index for combined cycle power plant using Graph Theoretic Approach” Ain Shams Engineering Journal (Elsevier).
16. Nikhil Dev, Samsher, S. S. Kachhwaha, Rajesh Attri, “System modeling and analysis of a cogeneration cycle power plant using Graph Theoretic Approach” Sadhana (Springer).
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