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Improvement of the Performance of Thermal Power Systems Through Energy and Exergy Analysis

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Improvement of the Performance of Thermal Power Systems Through Energy and Exergy Analysis.

ABSTRACT

This research work is aimed at using energy and exergy analysis with thermodynamic data to suggest improvements in the performance of steam and gas turbine power plants.

In this regard, specific data from Egbin steam power plant and Geregu I gas turbine power plant were used for the analysis.

In the analysis, scientific tools such as Engineering Equation Solver (EES) programme with built-in functions for most thermodynamic and transport properties was used to calculate the enthalpy and entropy at various nodal points.

While EXCEL spreadsheet and SCILAB software code were used to analyze both the energetic and exergetic efficiencies of the individual components, thermal efficiencies, gross station heat rate etc.

This software was also used to calculate the exegetic performance coefficient and exegetic sustainability indicators of the power plants.

The results of the analysis at both design and operating conditions show that exergy destruction occur more in the boiler/steam generator of Egbin steam power plant and combustion chamber of Geregu I gas turbine power plant than in other major components of each plant.

The normal operating conditions of the steam boiler exit pressure and temperature are 125.70/540.72 and condenser pressure and temperature are 0.0872bar and 42.950Crespectively for Egbin steam power plant in the year 2009.

From the study, the maximum exergy loss was found in the boiler/steam generator with a value of 55.32% in the year. Changing the boiler exit pressure and temperature from the normal operating conditions to 165.70/560.72 (ie, in steps of 10 bar and 50C), the exergy loss reduced to 53.99%.

The cycle thermal energy and exergy efficiencies at the normal operating conditions were 41.03% and 39.94 % respectively.

Improvement in the cycle thermal energy and exergy efficiencies with the same steps from normal operating conditions to 165.70/560.72 was 41.23% and 40.12% respectively.

The improvement increased the power output from 197593.8KW to 199358.57kW showing a power increase of 1764.77kW or 1.765MW. The gross station heat rate decreased from 8775kJ/kWh to 8732kJ/kWh which is good for the life of the plant.

Also, the improvement increased the energetic performance coefficient from 0.6133 to 0.6188.

The exergy sustainability indicators such as the environmental effect factor decreased from the value 1.0412 to 1.0230 showing about a 1.75% reduction in hazardous gaseous emissions to the environment.

Another exergy indicator, the sustainability index factor increased from the value 0.9604 to 0.9775 indicating 1.78% resource utilization and sustainability.

For Geregu I gas turbine plant, the operating condition of the combustion chamber is the pressure of 11 bar and 10600C Turbine Inlet Temperature (TIT).

The study showed that maximum exergy loss was found in the combustion chamber at a value of 26.30%. It is higher than any other major component at the operating conditions in the year 2009.

Adjusting the normal operating pressure and temperature to 15 bar and 10800C reduced the exergy destruction ratio to 26.06%. The gas turbine cycle energy and exergy efficiencies increased from 32.77% to 34.85% and30.44% to 32.34% respectively.

The power output in the year was increased from 133456.01kW to 145013.13kW showing a power increase of 11557.12kW or 11.56 MW due to the improvement.

For energetic sustainability indicators, the environmental effect factor decreased from the value 0.7132 to 0.6522 indicating an 8.55% reduction in greenhouse gas emission to the environment and ecology.

The sustainability index factor was increased from the value of 1.4022 to1.5332 showing 9.34% energy resource utilization for societal development.

In conclusion, any increase in exergy efficiency has an effect on the environmental effect factor and sustainability index factor for both power plants. Therefore, an increase in exergy efficiency improves the energetic sustainability index.

However, any increase in the environmental effect factor decreases the sustainability index factor. These parameters are expected to quantify how thermal power plants become more environmentally benign and sustainable.

TABLE OF CONTENTS

Title page i
Approval Page ii
Certification iii
Dedication iv
Acknowledgements v
Nomenclature vii
Table of Contents xi
List of Tables xiv
List of Figures xix
Abstract xxiii

CHAPTER ONE: INTRODUCTION

1.0 Background 1
1.1 Energy Sources in Nigeria 3
1.2 Electricity Generation in Nigeria 4
1.3 Statement of Problem 7
1.4 Aims and Objectives of Study 8
1.5 Scope of Study 9
1.6 Significance of Study 9
1.7 Study Area 10

CHAPTER TWO: LITERATURE REVIEW

2.0 Energy Demand and Supply 11
2.1 Overview of Thermal Power Plants 12
2.2 Theoretical Review of Similar Works 15

CHAPTER THREE: METHODOLOGY

3.0 Conceptual Framework 19
3.1 General Approach 19
3.2 Sources of Data 20
3.3 System Description 21
3.3.1 Case I- Egbin Steam Power Plant 21
3.3.2 Case II- Geregu I Gas Turbine Power Plant 24
3.4 Assumptions for Power Plants Analysis 27
3.5 Combustion Equation 28
3.6 Air-Fuel Ratio 29
3.7 Adiabatic Flame or Combustion Temperature 29
3.8 Specific gravity, Volumetric and Mass Flow rate of Fuel 30
3.9 Mass Balance 30
3.10 Energy Balance Equation 31
3.10.1 Boiler/Steam Generator 31
3.10.2 Turbine Sub-system 32
3.10.3 Condenser Sub-system 33
3.10.4 Pump Subsystem 34
3.10.5 Feedwater Heater Sub-system 34
3.10.6 Deaerator 36
3.10.7 Drain Cooler 37
3.10.8 Cooling Water 37
3.10.9 Energy Analysis of the Plant 37
3.11 Exergy Analysis 37
3.11.1 Exergy Balance Equation 38
3.11.2 Exergy destruction factor or efficiency defect 40
3.11.3Fuel Depletion Ratio 40
3.11.4Irreversibility Factor of Component 40
3.11.5 Boiler/Steam Generator 40
3.11.6 Turbine Sub-system 41
3.11.7 Condenser Sub-system 42
3.11.8 Pump Sub-system 43
3.11.9Feedwater Heater Sub-system 44
3.11.10Deaerator 46
3.11.11 Cooling Water 46
3.11.12Drain Cooler 46
3.11.13Exergy Efficiency of the Plant 48
3.11.14Exergetic Performance Coefficient of the Plant 48
3.11.15Exergetic Sustainability Indicators 48
3.12 Air-standard Cycle for Geregu I Power plant 49
3.12.1 Energy Analysis of Compressor Sub-system 51
3.12.2 Energy Analysis of Combustion Chamber Sub-system 51
3.12.3 Energy Analysis of Turbine Sub-system 52
3.12.4 Thermal Efficiency of Gas Turbine Plant 53
3.13 Exergy Analysis of Gas Turbine Plant 53
3.13.1 Exergy Analysis of Compressor Subsystem 53
3.13.2 Exergy Analysis of Combustion Chamber Sub-system 55
3.13.3 Exergy Analysis of Turbine Sub-system 56
3.13.4 Exergy Loss of Exhaust Sub-system 57
3.13.5 Gas Turbine Cycle Exergy Efficiency 57

CHAPTER FOUR: DATA PRESENTATION AND ANALYSIS

4.0Combustion Equation of Fuel used for Egbin Steam Power Plant 58
4.1 Energy Analysis of Boiler/Steam generator 61
4.1.1 Exergy or Second Law Analysis of Boiler/Steam Generator 62
4.2 Calculating ThermomechanicalExergy of Egbin Steam Power Plant 62
4.2.1Standard Chemical Exergy of the Hydrocarbons used in Egbin Steam 66
4.2.2 Calculating Chemical Exergy of Fuel used in Egbin Steam Power Plant 67
4.2.3Calculating Total Fuel Exergy of Egbin Steam Power Plant 68
4.2.4 Adiabatic Combustion Temperature for Egbin Steam Power Plant 68
4.3Energy and Exergy Analysis of Turbine Sub-system 71
4.3.1 Energy Analysis of High-Pressure Turbine (HPT) 72
4.3.2Exergy Analysis of High-Pressure Turbine (HPT) 74
4.3.3 Energy Analysis of Intermediate Pressure Turbine (IPT) 74
4.3.4 Exergy Analysis of Intermediate Pressure Turbine (IPT) 77
4.3.5 Energy Analysis of the Low-Pressure Turbine(LPT) 78
4.3.6 Exergy Analysis of Low-Pressure Turbine (LPT) 81
4.4 Energy Analysis of the Condenser Sub-system 82
4.4.1 Exergy Analysis of the Condenser Sub-system 83
4.5 Energy Analysis of the Condenser Effective Pump (CEP) 83
4.5.1 Exergy Analysis of the Condenser Effective Pump(CEP) 85
4.5.2 Energy Analysis of the Boiler Feed Pump (BFP) 86
4.5.3 Exergy Analysis of the Boiler Feed Pump (BFP) 87
4.6 Energy Analysis of High-Pressure Feedwater Heater 6 88
4.6.1 Exergy Analysis of the High-Pressure Feedwater Heater 6 89
4.6.2 Energy Analysis of High-Pressure Feedwater Heater 5(HPH5) 90
4.6.3 Exergy Analysis of High-Pressure Feedwater Heater 5(HPH5) 91
4.6.4 Energy Analysis of Low-Pressure Feedwater Heater 3(LPH3) 92
4.6.5 Exergy Analysis of Low-pressure Feedwater Heater 3(LPH3) 93
4.6.6 Energy Analysis of Low-pressure Feedwater Heater 2(LPH2) 94
4.6.7 ExergyAnalysis of Low-Pressure Feedwater Heater 2(LPH2) 95
4.6.8 Energy Analysis of Low-pressure Feedwater Heater 1(LPH1) 96
4.6.9 Exergy Analysis of Low-Pressure Feedwater Heater 1(LPH1) 97
4.6.10 Energy Analysis of the Deaerator 99
4.6.11 Exergy Analysis of the Deaerator 99
4.6.12 Energy Analysis of the Drain cooler 100
4.6.13 Exergy analysis of the Drain Cooler 101
4.6.14Energy and Exergy Analysis of the Cooling Water 101
4.6.15Energy and Exergy Analysis of the Power Plant 102
4.7 Analysis of Air-Standard Cycle of Geregu I Power Plant 103
4.8 Energy Analysis of Compressor Sub-system 104
4.8.1 Exergy Analysis of the Compressor Sub-system 106
4.8.2 Combustion Equation of Fuel used in Geregu I Gas Turbine Plant 108
4.8.3 Energy Analysis of Combustion Chamber Sub-system 111
4.8.4 Specific Heat of Combustion Products 112
4.8.5 Calculating the thermomechanicalExergy of fuel used in Geregu I gas power plant 114
4.8.6 Standard Chemical Exergyof Hydrocarbons used in GereguI gas power plant 117
4.8.7 Calculating Chemical Exergy of fuel used in Geregu I power plant 118
4.8.8Calculating Exergy destruction at the Combustion Chamber119
4.8.9 Calculating Fuel Exergy of Geregu I gas Turbine Power Plant 120
4.8.10Exergy Analysis of the Combustion Chamber Sub-system 120
4.8.11Adiabatic Flame or Combustion Temperature of Geregu I Power Plant 121
4.8.12 Energy Analysis of Turbine Sub-system 123
4.8.13 Exergy Analysis of Turbine Subsystem 132
4.8.14 Exergy Loss in the Exhaust Sub-system 134
4.8.15Thermal Efficiency of the Gas Turbine Cycle 134
4.8.16 Exergy Analysis of the Gas Turbine Cycle 135

CHAPTER FIVE: RESULTS AND DISCUSSIONS

5.0 Presentation of the result of Egbin Steam Power Plant 136
5.1 Improvements on Boiler/Steam Generator Performance of Egbin Power Plant 147
5.2 Plant Performance indicators of Egbin steam power plant 167
5.3 Presentation of the result of Geregu I Gas Turbine Power Plant 173
5.4Improvement of the performance of the combustion chamber of Geregu I gas turbine power plant 180
5.5Plant performance indicators of Geregu gas turbine plant 204
5.6Presentation of the result of Air standard cycle analysis of GereguI gas turbine plant 209
5.7 Improvement on Power Output from Egbin and Geregu I Power Plants 210
5.8Comparison of the Efficienciesof Egbin and Geregu I Power Plants 212
Recommendation 215
Conclusion 215
REFERENCES
APPENDICES

INTRODUCTION

1.0 Background

Thermal power plants are widely utilized throughout the world for electricity generation. They include steam power plants, gas turbine power plants, nuclear power plants, internal combustion engines.

There are numerously aged and new thermal power plants that are in service throughout the world today, for example, about 1,300 steam power plants have been in service for more than 30 years in the USA.

In recent years, global warming has been a major issue due to the continuous growth of greenhouse gas emissions from different sources. The contributors to greenhouse effects are carbon dioxide (CO2), nitrogen dioxide (NO2) and sulphur dioxide (SO2).

Carbon dioxide is a major greenhouse gas that is mainly blamed for global warming. Different industrial processes such as power plants, oil refineries, fertilizer plants, cement and steel plants are the main contributors of CO2 emission.

Fossil fuels such as coal, oil and natural gas are the main energy sources for power generation and will continue to generate power due to large reserves and affordability. Demirbas reported that about 98% of CO2 emission results from fossil fuel combustion.

Many power companies have investigated and undertaken measures to improve the efficiencies of such power plants in order to minimize their environmental impacts(e.g. by reducing emissions of CO2, NO2 and SO2), and to make them more competitive, as deregulation of the power industry proceeds.

Such investigations have been based on energy considerations. It has also sparked interest in the scientific community to take a closer look at the energy conversion devices and to develop new techniques to better utilize the existing transfer and energy change.

REFERENCES

Valenti, M(1996) ‘ Upgrading aging steam turbines’ Mechanical Engineering, Vol. 118. No. 1. 76-80
Demirbas A (2008) Carbondioxide Emissions and Carbonations sensors Turkey, Energy Sources part A, 30 70- 78
Cengel, Y A and Boles, M A(2006) Thermodynamics. An Engineering Approach 5th Edition McGraw Hill New Delhi
Aydin H (2013) Exergetic sustainability analysis of LM6000 gas turbine power plant with steam cycle. Elsevier Journal Energy 57, 766-774.
Tekin, T and Bayramoglu, M(1998); Exergy Analysis of Sugar Production process from sugar Beets, Int. J Of Energy Research,22,591-601
Moran, M J and Shapiro, H. N(2006) Fundamentals of Engineering Thermodynamics, Fifth Edition, John Wiley and sons Inc.

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