ABSTRACT

This research work is aimed at using the 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. These software were 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 step 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 were 41.23% and 40.12% respectively. The improvement increased the
power output from 197593.8KW to 199358.57kW showing 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 exergetic performance
coefficient from 0.6133 to 0.6188. The exergy sustainability indicators such as
environmental effect factor decreased from the value 1.0412 to 1.0230 showing about 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

 

 

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 the Study 8
1.5 Scope of the Study 9
1.6 Significance of the 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
x
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 Sub – system 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 a 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
xi
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 Sub –system 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
Power Plant
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
xii
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
xiii
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 Sub- system 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 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 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 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

 

 

CHAPTER ONE

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 numerous 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, [1]. In recent years, global warming has been a
major issue due to 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 which 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, [2] 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 consideration. 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.
The most commonly used method for analysis of an energy conversion system is the first law
of thermodynamics. Engineers and scientist have been traditionally applying the first law of
thermodynamics to calculate the enthalpy balances for more than a century to quantify the
loss of efficiency in a process due to loss of energy. However, the first law of
thermodynamics deals with the quantity of energy and asserts that energy cannot be created or
destroyed, [3]. This law serves as a necessary tool for accounting for energy during a process
and offers no challenges to the engineer. However, in recent years the second law analysis,
2
also known as exergy analysis of energy systems has more and more drawn the interest of
energy engineers and scientific community. Exergy analysis provides an effective technique
for measuring and optimizing performance of a thermal system by accounting for energy
quality. It can also be used to assess the sustainability level of energy systems. Sustainability
means a supply of energy resources that is sustainably available at reasonable cost and causes
no minimal negative effects. Sustainability is necessary to overcome current ecological,
economic, and developmental problems. The exergy sustainability indicators include exergy
efficiency, waste exergy ratio, recoverable exergy rate, exergy destruction factor,
environmental effect factor and exergetic sustainability index, [4].
For power plants, exergy analysis allows one to determine the maximum potential for
electricity production associated with the incoming fuel or any flow in the plant. This
maximum is achieved if the fuel or flow is utilized in processes that ultimately bring it to
complete thermodynamic equilibrium with the environment, while generating electricity
reversibly. Thus, exergy analysis provides the theoretical efficiency limitations upon any
power plant. Losses in the potential for electricity generation occur due to irreversibilities and
determined directly with exergy analysis. The exergy concept has gained considerable interest
in the thermodynamic analysis of thermal processes and plant systems since it has been seen
that the first law analysis has been insufficient from an energy performance point of view.
Based on the second law of thermodynamics, the exergy analysis represents the third step in
the plant system analysis, following the mass and the energy balances. The aim of the exergy
analysis is to identify the magnitudes and the locations of exergy losses, in order to improve
the existing systems, processes or components, or to develop new processes or systems, [5].
The method of exergy analysis is particularly suited for furthering the goal of more efficient
resource utilization, since it enables the location, and time magnitudes of wastes and losses to
be determined. Improved resource utilization can be realized by reducing exergy destruction
within a system. The objective in exergy analysis is to identify sites where exergy destructions
and losses occur and rank them for significance. Exergy losses include the exergy flowing to
the surroundings, whereas exergy destruction indicates the loss of exergy within the system
boundary due to irreversibility. This allows attention to be centered on the aspects of system
operation thatoffer the greatest opportunities for improvement, [6]. Exergy analysis which is
the combined first and second law analysis gives much more meaningful evaluation indicating
the association of irreversibilities or exergy destruction with combustion and heat transfer
3
processes. This allows thermodynamic evaluation of energy conservation option in power
and refrigeration cycles, thereby provides an indicator that points the direction in which
engineers should concentrate their efforts to improve the performance of thermal systems. The
second law of thermodynamics has proved to be a very powerful tool in the optimization of
complex thermodynamic systems, [7],[8],[9].
1.1 EnergySources in Nigeria
The country is endowed with both the conventional and the non-conventional energy
resources. The conventional comprises mostly of the non-renewable resources such as crude
petroleum oil, natural gas, coal, tar sand and uranium, [10]. The country has the tenth largest
oil and gas reserves in the world. The various non-conventional energy resources available in
the country that can be harnessed for power generation are nuclear, solar, wind power,
biomass energy, wave and tidal energy and geothermal energy. Nigeria’s near equatorial
location, extensive and diverge vegetation, prevailing trade winds and many rivers endow her
with large quantities and quality of renewable energy sources,[11].These include solar
radiation, hydro power, wind and biomass energy. Nigeria’s coal reserves are large and
estimated at 2.7 billion metric tonnes of which 650 million tonnes are proven reserves. About
95% of the Nigerian coal production in late 1950s and early 1960s was consumed locally,
mainly for railway transportation, electricity production and industrial heating in cement
production. Nigeria has abundant reserves of natural gas. The quantity of natural gas is at
least twice as much as the oil, and the horizon for the availability of natural gas is definitely
longer than that of oil. In energy terms, the quantity of natural gas used for electricity
generation is very significant. The known reserves of natural gas have been estimated at about
187.44 trillion standard cubic feet or 5.30 x 1012 standard cubic meters as at the year
2007,[12].
The third major source of energy, oil, is Nigeria’s major source of revenue used for
development. As at January 2005, Nigeria’s proven crude reserve stood at 35.2 billion barrels.
The majority of the reserves are found along the country’s coastal Niger Delta. As at 2007,
Nigeria’s energy resource availability expressed in barrels (bbls) and standard cubic feet (scf)
and other units showed that crude oil availability in Nigeria stood at 36.5 billion barrels. Other
energy resources include natural gas whose availability is 187.44 trillion standard cubic feet,
coal and lignite estimated at 2.7 billion tonnes as shown in Table 1.1
4
Table 1.1: Energy Resource Availability in Nigeria
RESOURCES AVAILABILITY
Crude oil 36.5 billion bbl
Natural gas 187.44 trillion scf
Coal and lignite 2.7 billion tones
Tar sands 31 billion bbl oil equivalent
Hydropower (large scale) 11,250mw
Hydropower (small scale) 3,500mw (estimate)
Solar radiation 3.5 – 7.0kwh/m2-day
Wind 2 – 4m/s annual average
Fuel wood 13.1 million ha of forest/wood land
Animal waste
Very significant
Quantity not available
Crop residue
Tidal energy
Uranium
Source: Energy Commission of Nigeria, 2007
Solar radiation intensity varies in a quasi-predictable way. It varies with day and night,
location, weather and climate. It increases with altitude and solar altitude angle. For instance,
at an altitude of 3,000m and solar altitude angle of 900 (i.e. overhead) it gets as high as
1.18KW/m2, while at sea levels it is < 1.0 KW/m2. It is reduced by cloudiness, atmospheric
gases, atmospheric particles (aerosols) and obstructions.
1.2 Electricity Generation in Nigeria
Generation of electricity is a very complex process involving many sub-processes and has
multiple critical parameters. A decline in thermal efficiency leads to a higher cost of
electricity generation due to more fuel usage and also will result in much higher carbon
deposits. Therefore, it is very important to stress on the performance of power plants.
Electricity generation is the conversion of other kinds of energy, mainly primary energy into
electrical energy. Generally, the process of generating electricity goes through several
5
transformations from primary energy directly into electricity. For instance, in a thermal power
station, the primary energy is converted to a high temperature steam, as an intermediate heat
source, then into mechanical energy in the turbine physically connected with the generators
where the electrical energy is produced.
Power generation in Nigeria is mainly from three technologies only which include hydroelectric
power stations, steam and gas thermal stations. Most of these facilities are being
managed by the Power Holding Company of Nigeria (PHCN); a government owned utility
company that coordinates all activities of the power sector such as generation, transmission,
distribution and marketing before they were privatized. Since inception of PHCN, the
authority expands annually in order to meet the ever increasing demand. Unfortunately, the
majority of Nigerians have no access to electricity and the supply to those provided is not
regular. In a bid to make the power sector more functional, the PHCN was unbundled into 18
successor companies (1 Transmission, 11 Distribution and 6 Generation companies). This was
done due to current privatization in the sector [13].
Prior to 1960s, energy supply and consumption consisted predominantly of non-commercial
energy, viz-fuel wood, charcoal, solar radiation, agricultural waste and residues. Major
commercial fuel was coal used in railway engines and for power generation. Contributions to
commercial energy came frompetroleum products (petrol and diesel) for road vehicles and
from electricity (from coal and diesel generators). Up till 2005, the grid electricity supply
industry was predominantly the vertically integrated public utility-National Electric Power
Authority (NEPA), which owned about 98% generating capacity and 100% of transmission
and distribution capacity. In consequence and in particular through former President
OlusegunObasanjo’s power project and President Goodluck Jonathan’s power road map for
power sector reform of August 2010, actual maximum peak generation has now more than
doubled (4300MW) since the start of the reform in 2000 and installed generation is now
above 10109.5MW, [13].
At present, the installed capacities in power stations in Nigeria are shown in Tables 1.2, 1.3
and 1.4 for pre-1999 power stations and other power stations as contained in a document
prepared by Energy Commission of Nigeriain 2007.
6
Table 1 .2: Pre- 1999 Power Stations
Station Capacity (MW)
Kainji Hydro 760
JebbaHydro 578
Shiroro Hydro 600
Egbin Thermal 1320
Sapale Thermal 1020
Ijora Thermal 60
Delta Thermal 912
Afam Thermal 711
Orji River Thermal 30
NESCO 30
Total 6,021MW
Source: Energy Commission of Nigeia,2007
Other power generating stations include eight National Integrated Power Project (NIPP)
which were built in some states of the country. These are Gbarain Integrated Power Project in
Bayelsa State, Egbema Integrated Power Project located in Imo State, Ibom Integrated Power
Project in AkwaIbom State.
Table1.3: National Integrated Power Project (NIPP)
Station Capacity(MW)
Gbarain, Bayelsa 225
Ihubor, Edo 451
Omoku, Rivers 230
Sapela,Delta 451
Egbema, Imo 338
Calabar, Cross Rivers 561
IkotAbasi, AkwaIbom 300
Ibom Power, AkwaIbom 188
Total 2,744MW
Source: Energy Commission of Nigeria, 2007
7
Another milestone in the power sector for electricity generation is the establishment of
Independent Power Producer (IPP) in different parts of the country. These include the AES
power station in Lagos State, Alaoji power station in Abia State, Papalanto power station in
Ogun State and others.
Table 1.4: Independent Power Producers (IPP)
Station Capacity(MW)
Geregu, Kogi 414
Omotosho, Ondo 335
Papalanto,Ogun 335
Alaoji, Abia 346
AES, Lagos 270
Geometric, Aba 140
Agip JV, Okpai/Kwale, Delta 480
Chevron JV, Agura,Igbin, Lagos 750
Total Fina, Obite, Rivers 500
Exxon Mobil Bonny, Rivers 500
Total 4070MW
Source: Energy Commission of Nigeria,2007
These National Integrated Power Projects (NIPPs) and Independent Power Producers (IPPs)
will augment the power generated by these power generating stations to meet the electricity
demand of the country.
1.3 Statement ofProblem
The global power sector is facing a number of issues, but the most fundamental challenge is
meeting the rapidly growing demand for energy services in a sustainable way. This challenge
is further compounded by the today’s volatile market-rising fuel costs, increased
environmental regulations etc. Thermal power plants are one of the most important elements
of energy sector and they are masterworks that enable production of electrical energy which
can be thought as one of the basic needs after food and water. Preference of the thermal power
8
plant type in electricity production is a big dilemma and prior discussion subject to related
parties in recent years. For instance, environmentalist act against fossil-fuelled thermal power
plants or nuclear power plants and they try to warn decision makers about environmental
pollution, global warming, carbon emission etc. The primary energy source possibilities of
countries are one of the basic factors that determine the preferences of a thermal power plant.
Namely, USA, Germany, India and China produce more than 50% of their electrical energy
by coal-fired thermal power plant, while most of the thermal power plants, in countries that
have abundance of natural gas such as Qatar, are gas fired. The choice is directly related to the
reserve capabilities of the primary energy sources which are one of the main issues for
government policies and preferences.
Today, many generating utilities are striving to improve the efficiency of their existing power
generating stations. The problem of low power generation output from these plants is as a
result of defective plant components and improper fuel utilization in the systems.
1.4 Aims and Objectives of the Study
The aim of this research is to
(i) Carry out energetic and exergetic performance analysis, at the design and actual
operating conditions for the existing unit 5 (220MW) of the 1320MW Egbin steam
power plant and unit 11(138MW) of the 414MW Geregu I gas turbine power plant in
order to identify the components that needs improvement.
The objectives of the study are to determine:
(i) the quantity of energy and exergy flows and location of losses.
(ii) the energy efficiency of the plant and its components.
(iii) plant performance parameters such as heat rate, specific fuel consumption and
thermal discharge index.
(iv) theexergy efficiency of the plant and its components.
(v) theexergy destructionswithin the system components.
(vi) exergetic performance coefficient.
(vii) exergetic sustainability indicators- exergy destruction ratio, waste exergy ratio,
environmental effect factor and exergetic sustainability index and
(viii) systems that have potential for significant performance improvement.
9
To achieve these objectives, we summarize thermodynamic models for the considered power
plants on mass, energy and exergy balance equations.
1.5 Scope of the Study
The scope of this work involves
Ø analysis of thermal power systems.
Ø determining the irreversibility rates in the plant components.
Ø comparative performance of the power plants at both design and operating
conditions,and
Ø performing sensitivity analysis on the variation of thermodynamic intensive properties
like temperature and pressure in improving the plants performance.
1.6 Significance of the Study
The growth, prosperity and national security of any country are critically dependent upon the
adequacy of its electricity supply industry. Over the past two decades, the stalled expansion
of Nigeria’s grid capacity, combined with the high cost of diesel and petrol has crippled the
growth of the country’s productive and commercial industries. It has stifled the creation of
jobs which are urgently needed in a country with a large and rapidly growing population; and
the erratic and unpredictable nature of electricity supply has engendered a deep and bitter
sense of frustration that is felt across the country as a whole and in its urban centers in
particular. Electricity consumers and the citizenry as a whole demand a fundamental reversal
of the long and debilitating malaise which has blighted the industry and, in doing so, bridled
the tremendous energy and creativity of this great and populous nation. More particularly they
demand real and immediate improvements in service levels, [14].
Nigeria needs over 10,000 MW of electricity for her domestic and industrial demands of
which about 4000MW is currently being generated from power plant locations across the
country. The quantity generated are transmitted and distributed through the national grid to
primary energy consumers. As a result of inefficient operation of some of these plants owing
to long age in service, the need to identify the location of the inefficiency in the plant becomes
imperative. Generally, the performance of thermal power plants is evaluated through energetic
performance criteria based on first law of thermodynamics, including electrical power and
thermal efficiency. In recent decades, the exergetic performance based on the second law of
10
thermodynamics has been found to be a useful method in the design, evaluation, optimization
and improvement of thermal power plants. The exergetic performance analysis can not only
determine magnitudes, location and causes of irreversibilities in the plants, but also provides
more meaningful assessment of plant individual components efficiency, [15]. The use of
exergy analysis becomes the answer as a tool for pin-pointing inefficiencies. The features of
this technique make it valuable in the thermodynamic analysis aiming at the improvement of
the efficiency of existing thermal plants through an adjustment of their operating parameters
or in the design of efficient new thermal plants.
1.7 Study Area
Nigeria is the most populous African country with the total population estimate of over 152
million people. She has over ten power generating stations (both thermal and hydro power
stations) established before the year 1999.
Besides having these power stations, there are eight National Integrated Power Projects
(NIPPs) established after the year 1999 and many Independent Power Producers (IPPs). For
the purpose of this study, the Egbinpower station and the Geregu power station will be
considered because the former uses steam and water as working fluid and the later uses air
and combustion products as working fluid where the boiler/steam generator and combustion
chamber are fired by natural gas. These power plants contribute good percentages of over 15.9
million MW of electricity consumed for both domestic and industrial use by the populace
annually.
Egbin thermal plant is located atIjede area of Ikorodu, a suburb of Lagos State. The plant was
commissioned in 1985 and consists of 6 units of 220 (6X220) MW (Reheat – Regenerative).
They are dual fired (gas and heavy oil) system with modern control equipment, single reheat;
six stages of regenerative feed heating. Natural gas is supplied to the plant directly from the
Nigerian Gas Company (NGC) Lagos operations department, which is annexed to the thermal
plant. Since Egbin thermal plant is located on the shores of the lagoon, cooling water for the
plant’s condensers is pumped from the lagoon into the water treatment plant en route to the
condensers.
The Geregu I gas thermal power station located in Ajaokuta, Kogi State of Nigeria was
commissionedin 2006 and it consists of three independent units, each being rated

 

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