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

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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.

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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

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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

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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

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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

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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

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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.

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(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

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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

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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.

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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.

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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

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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.

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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).

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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.

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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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