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Computer-Aided Evaluation of Steam Power Plants Performance Based on Energy and Exergy Analysis

Master's Thesis 2017 130 Pages

Engineering - Mechanical Engineering

Excerpt

Contents

Acknowledgement

Abstract

Contents

List of Tables

List of Figures

Nomenclature

1 Introduction
1.1 Introduction

2 Literature review
2.1 Introduction
2.2 Scope of work

3 Energy and Exergy Analyses of the Power Plant
3.1 Introduction
3.2 Power plant description
3.2.1 Boiler
3.2.2 Turbine
3.2.3 Condenser
3.2.4 c ondensate pumps
3.2.5 Feed-water pumps
3.2.6 Feed-water heating system
3.3 Energy
3.4 Energy efficiency
3.5 Exergy
3.5.1 Reference environment
3.5.2 Dead state
3.5.3 Exergy destruction
3.6 Exergetic efficiency
3.7 Energy and exergy analyses of the power plant
3.7.1 Boiler
3.7.2 Turbine
3.7.3 Pumps
3.7.4 F eed-water heaters
3.7.5 Condenser
3.7.6 Power plant

4 Exergy Analyses of the Boiler and Auxiliaries
4.1 Introduction
4.2 Standard reference state
4.3 Fuel properties
4.3.1 Fuel model
4.3.2 Heating value
4.3.3 Adiabatic flame temperature
4.4 Thermodynamics properties
4.5 Exergy
4.5.1 Total exergy o f mixture
4.5.2 Exergy of product gases
4.5.3 Exergy of combustion air
4.6 Boiler exergetic analyses
4.6.1 Combustion process
4.6.2 Heat transfer process
4.6.3 Air preheater
4.6.4 Steam coil air preheater
4.6.5 Stack

5 Energy and Exergy Analyses Software Program
5.1 Introduction
5.2 EEA data entry
5.3 EEA results

6 Application and Results of Energy and Exergy Analyses Program for Steam Power Plant
6.1 Introduction
6.2 Studying a single case in detail
6.3 Comparison between loads
6.4 Exergetic destruction over years

7 Conclusions and Recommendations
7.1 Introduction
7.2 Conclusions
7.3 Recoimnendations

References

Appendix A

Appendix в

Appendixe

List of Tables

Table 3.1: Boiler specifications

Table 3.2: Turbines specifications

Table 3.3: Condenser specifications

Table 3.4: Condensate pump specifications

Table 3.5: Feed-water booster pump specifications

Table 3.6: Feed-water main pump specifications

Table 3.7: LPH 1 and 2 specifications

Table 3.8: Heaters 3, 5, 6, 7 and 8 specifications

Table 3.9: Deaerator specifications

Table 3.10: Overall turbine system thermodynamics model

Table 3.11: Turbines thermodynamics model

Table 3.12: Pumps thermodynamics model

Table 3.13: Feed-water heaters thermodynamics model

Table 5.1: Streams thermodynamics properties

Table 5.2: Equipment’s power

Table 5.3: Power loss and exergy destruction

Table 5.4: Exergy analyses

Table 5.5: Exergy analyses of main systems

Table 5.6: Boiler streams’ thermodynamics properties

Table 5.7: Boiler exergy analyses

List of Figures

Fig. 1.1: Evolution from 1990 to 2040 of world energy consumption

Fig. 3.1: Power plant layout

Fig. 3.2: Outline of boiler construction

Fig. 3.3: Boiler main streams

Fig. 3.4: Condenser main streams

Fig. 4.1: Schematic diagram of air preheater

Fig. 4.2: Schematic diagram of steam coil air preheater

Fig. 5.1: EE A main form

Fig. 5.2: Fuel operating parameters form

Fig. 5.3: Air and product gases operating parameters fonn

Fig. 5.4: Water and steam operating parameters fonn

Fig. 5.5: Boiler input power fonn

Fig. 5.6: Hydrocarbon fuels

Fig. 5.7: Turbine system form

Fig. 5.8: Condenser shell side form

Fig. 5.9: Condensate pump form

Fig. 5.10: Condenser cooling water side fonn

Fig. 5.11: Closed feed-water heaters form

Fig. 5.12: Open feed-wat er heater

Fig. 5.13: Electrical feed-water pump

Fig. 5.14: Mechanical feed-water pump

Fig. 5.15: Energy and exergy summary of the power plant

Fig. 5.16: Power loss and exergy destruction

Fig. 5.17: Exergetic efficiency of all components

Fig. 5.18: Exergetic destruction pie chart of all components

Fig. 5.19: Exergetic efficiency of main systems

Fig. 5.20: Exergetic destruction pie chart of main systems

Fig. 5.21: Boiler efficiencies

Fig. 5.22: Fuel model thermochemical properties

Fig. 5.23: Combustion process details

Fig. 5.24: Boiler exergetic efficiency

Fig. 5.25: Boiler exergetic destruction pie chart

Fig. 6.1: Different boiler efficiencies comparison

Fig. 6.2: Power plant efficiency comparison

Fig. 6.3: Exergetic destruction in boiler processes

Fig. 6.4: Boiler efficiencies

Fig. 6.5: Power plant efficiency in different years

Fig. C. 1 : Bumer impeller and gas spuds corrosion

Fig. C.2: Bumer impeller and gas spuds corrosion

Fig. C.3: Deposits accumulation on heating surfaces

Fig. C.4: Deposits accumulation on heating surfaces

Fig. C.5: Clogged spaces between tubes

Fig. C.6: Tubes displacement

Fig. C.7: Tubes displacement

Fig. C.8: Burner impeller and gas spuds after replacement

Fig. C.9: Heating surfaces after chemical cleaning

Fig. C.10: Tubes relocation

Nomenclature

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Abbreviations

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Acknowledgement

I owe to Allah for his giving and assistance to finish this research and enabling me to complete it successfully. I would like to thank all who supported me to complete this thesis. First of all, I am extremely grateful to my research supervisor, Prof. Dr. Eed Abdel-Hadi, who gives me advice and encouragement throughout this thesis. I thank him for his effort and guidance. Also, I would like to thank Prof. Dr. Sherif Hady and Dr. Islam Helaly, for their encouragement, insightful comments and criticism which incited me to enrich my research work. I am thankful to my colleagues in Cairo West Thermal Power Plant for their help, support, encouragement and technical advice. Finally, I want to express my sincere gratitude to my beloved parents, wife, my family and my friends for their love and continuous spiritually and materially support.

Abstract

Energy is the cornerstone of the economic development, so it is bound to reexamine the energy policies and take drastic steps to cope with the growing energy consumption. One way used to overcome the power consumption problem is to seek for minimizing losses, which is made by studying the management of power production in steam power plants from the first and second laws of thermodynamics point of view. Some researchers adopt a new approach using a computer software in their studies. A computer program called Energy and Exergy Analyses (EEA) was proposed and built to cover the shortage and overcome the problems of the previous programs. EEA has an interactive fonn containing many systems which have not been studied in the earlier programs. The proposed program is applicable to any steam power plant. The reversible, isentropic and the actual power of each equipment in the plant are calculated. EEA calculates the thennophysical properties of all supplied streams. It calculates the thermal efficiency, the exergetic efficiency and the exergetic destruction of the power plant. Also, the energy loss and the exergy destruction in the power plant’s systems are listed. It presents the exergetic efficiency and destruction of each component and make a comparison between them. As the boiler is a major and important system in the power plant, EEA presents its results in detail. The program gives the energy and exergy efficiencies of the boiler. Generated fuel model and its specifications is presented and it is used in the combustion process fonnula. Air fuel ratio and adiabatic flame temperature in the stoichiometric and actual combustion are shown. EEA produces the results in reports which contain tables and charts to facilitate the analyses of these results. The recorded parameters of Cairo West Thermal Power Plant (Units 7 & 8) are used to test and show the capabilities of the proposed program. It is found that the condenser is the main source of energy loss in the power plant. In the opposite, the boiler is the main source of exergy destruction in the power plant due to combustion and heat transfer processes. As a result of using Mazout as a main fuel for a long time, many problems occur in the boiler causing increase in the exergetic destruction in the combustion and heat transfer processes. This destruction led to a gigantic exergetic destruction in the boiler which decreased the overall power plant exergetic efficiency. In order to overcome these problems, it is recoimnended to increase the burners’ impeller spaces and supply air pipe to burners’ gas spud to cool it down. Also, we recommend to operate the upper row of burners with natural gas in mixed fire combustion and retest the fuel oil additive dosing substance chemically.

Chapter 1 Introduction

1.1 Introduction

Major cities around the world have been reduced to rubble after the second world war. So, many countries focus on the reconstruction and the economic development. Since the energy is the cornerstone of the economic development, it is bound to reexamine the energy policies and take drastic steps in order to cope with the growing energy consumption. As a result of researches on this topic, it appears that there is a massive increment in the energy consumption as it shown in Fig. 1.1. It presents the growing energy consumption of the world from 1990 to 2012. Moreover, it presents that the consumption increment in the next two decades led by The Non-OECD (Non Organisation for Economic Co-operation and Development) countries [1].

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Fig. 1.1: Evolution from 1990 to 2040 of world energy consumption.

Many scientists embarked on studies to overcome the energy consumption problem. Many solutions are considered for this problem which include:

1. The management of energy in tenns of conservation and efficiency in:
- Production
- Transmission
- Usage

2. Developing alternative energies:
- Solar energy
- Wind energy
- Geothennal energy
- Biofuel and ethanol
- Hydrogen

One way used to overcome the energy consumption problem is to study the management of the power production in steam power plants. By focusing on these plants, it is found that a significant part of power is lost without any benefit from it which means that companies pay a lot of money for less power.

Earlier studies analyzed the power plants from the first law of thermodynamics point of view which concerns with the quantity of energy. Also, many of these studies adopt the second law of thermodynamics in the analyses because it concerns with the quality of energy. By focusing on these studies, it is found that the researchers adopted two different methods.

1. Traditional method

Researchers gather the power plant operating parameters and do the calculations manually, then analyze the results such as; Rashad and El Maihy [2], Erdem et al. [3] and Aljundi [4]. It is found that the traditional method is very long and consumes much time, especially in analyzing the results when using many conditions such as; increasing or decreasing pressure, temperature or flow rates.

2. Computer application method

Many researchers have tried to overcome the traditional method which consumes much time by adopting a new approach using a computer aided programs. The researchers wrote codes for computer programs like Engineering Equation Solver (EES) or design a program to do the energy and exergy calculations instantaneously, then they get the results and analyze it. Other researchers use computer programs such as Stat-Ease Design-Expert software to analyze the results. By focusing on the earlier studies, It is found that Ahmadi and Toghraie [5], Singh et al. [6], Altayib [7] and Ahmadi and Dineer [8] used this method.

Chapter 2

Literature review

2.1 Introduction

In this study the computer application method is adopted and applied to all different designs of the steam power plants to cover the shortage in the earlier programs and to overcome the problems of these programs such as:

- Some mechanical systems and components are not mentioned in these studies, like De- Superheating System.
- The specificities of the studied power plants, cannot be applied to other power plants.
- The original source code of the program should be edited and reconfigured to be suitable for the new power plant, which is not easy for the normal user to do.
- Some of these programs are not interactive (work line by line), so they cannot give the user the ability to edit the current or previous projects.

Several authors wrote many books to introduce the energy and exergy analyses. Also, many researchers presented a lot of studies performed on different power plants in order to increase the energy and exergy efficiencies of these plants.

The thermodynamics laws and the aspects of energy, entropy, and exergy were covered in detail by Dineer and Rosen [9]. The energy balance was explained and how it cannot be used as a criterion for the usefulness or quality of the various energies in the system. Also, it does not give any information on the energy losses. Moreover, they discussed the energy and exergy analyses and how these can be used to locate the system which is responsible for losses in a process. Furthermore, examples, practical applications, and case studies are discussed in the book covering a wide range of the exergy applications showing how exergy can be used in design, analysis and optimization. Finally, Moran [10] presented the thennal system design from the second law point of view.

An introduction to the chemical thermodynamics for engineers is presented by Sato [11]. Additionally, he discussed exergy balance diagram and exergy vector diagram. Furthermore, the total exergy of substances which composed of a physical part and a chemical part was presented. Finally, he shows that the physical part of exergy is depending on the changes in temperature, pressure and concentration (mixing) of the substances while the chemical part of exergy is depending on the chemical fonnation of the substances in the standard state.

Ahmadi and Toghraie [5] performed energy and exergy analyses of 200 MW of Shahid Montazeri Power Plant of Isfahan, Iran using EES (Engineering Equation Solver) software. They found that the condenser is the main source of the energy loss. On the other hand, the boiler is the main source of exergy destruction. Likewise, Singh et al. [6] perfonned energy and exergy analyses on 250MW thennal unit in Bhilai, India. They calculated and presented the energy loss, exergy loss, efficiencies of each component and the overall plant. Finally, they developed a c++ code to use it for iterative calculations.

Energy, exergy, exergoeconomic and exegoenvironmental analyses were perfonned for fifteen gas turbine units in the Makkah Power Plant in Saudi Arabia by Altayib [7] in 2011.He perfonned a parametric study to improve the turbine system by changing the operating parameters such as; fuel flow rate, combustion air flow rate and temperature. He found that “the overall plant energetic and exergetic efficiencies increased by 20% and 12%, respectively, with cooling down the compressor inlet temperature to 10°C”. Also, he found that the major exergy loss was found in the combustion chamber. Furthermore, he showed that the increment of the exergetic efficiency and the decrement of the fuel injection rate reduce C02 emissions. Finally, he used the Stat-Ease Design-Expert software to analyze the results.

Ahmadi and Dineer [8] performed a study depending on energy, exergy, exergoeconomic and exegoenvironmental analyses. They developed a simulation program using Matlab software in order to find the best design parameters (optimum solution) for a Gas Turbine (GT) power plant model. They investigated the results and compared them with the operating parameters of Shahid Salimi gas turbine power plant in Neka, Iran. They presented multiple optimum solutions to increase the exergy efficiency, decrease the total cost rate of the product and decrease the environmental impact. Accordingly, the decision maker had to compromise, according to his preferences and criteria, in order to choose the optimum solution.

In a study perfonned in Egypt, the main systems of Shobra El-Khima Power Plant except the boiler are analyzed from the thermodynamics point of view by Rashad and El Maihy [2]. They calculated the energy loss and exergy destruction at different loads. Furthermore, they found that, despite the condenser is the main reason for energy loss in the plant, it is thermodynamically insignificant due to its low quality. On the other hand, they showed that the major exergy loss is due to the turbine system.

Erdem et al. [3] investigated the thermodynamics performance of nine different coal-fired thermal power plants in Turkey. They performed an energy and exergy analyses of these plants at design conditions in order to determine the thermal efficiency, exergy efficiency and exergy destruction for each system in these power plants. They presented and compared the results in order to be helpful for future improvements for these power plants. Moreover, these results will be a valuable reference for designers for their future works.

In Jordan, Al-Hussein Power Plant was studied by Aljundi [4] from the first and second laws of thermodynamics viewpoint. As expected, it is found that the main system responsible for energy loss is the condenser and boiler is the main system responsible for the exergy destruction. Also, the effect on the exergy destruction and exergy efficiency of each system were calculated when the environment temperature changed slightly without any change of the main conclusion that the boiler is the main system responsible for the exergy destruction.

The energy, exergy and exergoeconomic analyses of Hamedan steam power plant which located in the western part of Iran are studied. Ameri et al. [12] found that the largest amount of energy loss of the power plant occurs in the condenser. Moreover, they found that the boiler comes in the second place. In the opposite, the exergy analyses show that the boiler is the main source of exergy destruction. Finally, the exergoeconomic analyses of the power plant showed that the cost of exergy destruction of the boiler is the highest compared to other systems.

In Turkey, energetic and exergetic analyses for diesel engine powered cogeneration plant was investigated by Abusoglu and Kanoglu [13]. The results showed that the diesel engine is responsible for the major loss in the plant. Furthermore, they emphasize that the plant performance will be better by making some small improvements to the engine design and operation.

Energy and exergy analyses of Neka Combined cycle power plant in Iran were performed by Ameri et al. [14]. They found that the combustion process is the reason for the major exergy loss. Moreover, losses in the heat recovery steam generator (HRSG) come in the second place. Furthermore, they demonstrated that despite the output power increased by adding a duct burner to HRSG, the energy and exergy efficiencies decreased.

In a study was perfonned by Rivero and Garfias [15], the Szargut model calculations of the standard chemical exergy of elements, organic and inorganic substances are reviewed and checked. Moreover, they presented updated values of the standard chemical exergy of elements. Finally, they studied the comparison between the new values and the old values of Szargut.

Çolpan [16] studied the energy, exergy and thermo-economic analyses of Bilkent Combined Cycle Cogeneration Plant in Turkey. He focused on the main causes of the thermodynamics imperfection in the system. Moreover, he identified the potential modifications and improvements for the system.

Afifi [17] performed energy and exergy analyses on co-generation plant which produce electric power and heat energy to the Egyptian Minerals and salts Company, El-Fayoum, Egypt. He found that the exergy loss in the combustion process is the main cause of exergy destruction of the boiler which becomes the main source of exergy destruction of the co-generation plant. Furthermore, he proved that using the fuel oil as the main fuel, achieving the greatest exergy efficiency of the combustion process. Finally, he showed that the exergy loss in the deaerator increases with the boiler pressure increasing.

Full energy and exergy analyses were carried out to figure the potential modifications and improvements for the Ghazlan Thermal Power Plant in the Kingdom of Saudi Arabia. The calculations required in the analyses are perfonned using a computer program, written in Fortran, by Al-Bagawi [18].

A computer program, written in Turbo Pascal, is presented by Fungtammsan et al. [19]. They used it to perform the energy and exergy analyses of Mae Moh Power Plant Unit 1 in Thailand. The results showed that the major energy loss in the boiler is due to the energy carried out with flue gases. Moreover, it emphasizes that the combustion process is the main reason for the exergy destruction.

2.2 Scope of work

This study aims to help in solving the energy consumption problem by increasing the energy and exergy efficiencies of steam power plants by:

- Indicating the major places of energy losses and exergy destructions.
- Showing the amount of energy and exergy losses in major components of the power plant.
- Depicting the effect of the pressure, temperature, flow rate and load variations on the power plant efficiency.
- Indicating the possible ways shall be adopted to reduce the energy and exergy losses.
Because of the problems and disadvantages of earlier studies, this study will propose a methodology which can be applied to evaluate the performance of power plants. It will depend not only on the first law of thermodynamics, but also the second law of thermodynamics. A new software called Energy and Exergy Analyses (EEA), only built by the researcher, will be proposed.

EEA will allow the users to determine the energy and exergy of the power plants by supplying data into the program. Also, it will highlight the system which causes the most energy and exergy losses, allowing researchers to focus their efforts on improving their designs. Additionally, it will calculate the energy and exergy saved under a variety of conditions such as; increasing or decreasing pressure, temperature or flow rate. Moreover, it will calculate the energy and exergy efficiencies of the different systems in the power plant. Finally, it will present the overall energy and overall exergy efficiencies of the power plant.

The results from the program will be introduced in tables and charts in order to facilitate the analyses. Furthermore, recorded data of the Cairo West Thennal Power Plant will be used to evaluate and show the capabilities of the present program. Moreover, the system will be analyzed depending on the EEA results. Finally, some suggestions will be made to cut the losses and increase the power plant efficiency.

Chapter 3

Energy and Exergy Analyses of the Power Plant

3.1 Introduction

The present study has been performed on the Cairo West Thermal Power Plant (Units 7 & 8). It is a reheat and regenerative steam power plant which located in Egypt. It consists of two units. Each unit used to generate 350 MW of electricity and supply it to the Egyptian National Grid of Electricity. The operating parameters of the power plant will be analyzed from the first law of thermodynamics point of view which concerns with the quantitative energy analysis. Additionally, the second law of thermodynamics will be adopted to consider the qualitative energy analysis.

3.2 Power plant description

The flow diagram of the Cairo West Thermal Power Plant is illustrated in Fig. 3.1. It shows the condensate extracted from the condenser and pumped to the deaerator through the low-pressure heaters (LPH 1 and 2 and LPH 3). Booster pumps raise the pressure of the feed-water and supply it to the main pumps through heater 5 and heater 6. Then main pumps increase the feed-water pressure and supply it to the boiler through heater 7 and heater 8. Boiler generates the superheated steam and deliver it to the high-pressure turbine. The steam is used to operate the steam turbine which drives the generator to produce 350 MW electrical power. The condensed steam is collected and stored at the bottom of the condenser in the hot well to start the feed-water cycle again.

3.2.1 Boiler

The outline of the boiler construction is shown in Fig. 3.2. The feed­water, which leaves heater 8, goes to the drum through the economizer tubes. The drum cyclone separates water and its attendant solids. Steam free water

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Fig. 3.1 ะ Power plant layout.

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Fig. 3.2: Outline of the boiler construction, circulates naturally through down comers and water walls. Saturated steam leaves the drum through the saturated steam tubes then flows to the primary, secondary and tertiary superheaters.

A spray system is used to control the steam temperature. The first stage water spray system located between the primary and secondary superheaters sections. The second stage water spray system located between the secondary and tertiary superheaters sections. Additionally, the boiler outlet steam (main steam) goes to the high-pressure turbine. Table 3.1 shows the boiler specifications as given by Babcock-Hitachi K.K., 2010 [20]. The table lists the type of the boiler, the draught system and the combustion fuels. Also, the boiler design parameters are given.

Table 3.1: Boiler specifications

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3.2.2 Turbine

“The steam turbine is a two-cylinder tandem compound double exhaust, condensing reheat turbine”. Only the first blade of the high pressure-intermediate pressure turbine (HP-IP) is impulse and the rest is a reaction turbine. A group of main stop valve and two plug type governing valves which control the steam flow is located on the high-pressure turbine side and another group is located on the other side. The steam passes through the HP turbine and exits through two openings in the outer casing base toward the boiler’s re-heat tubes. Reheated steam enters the intermediate pressure turbine through two groups of reheat stop and interceptor valves located on each side of the turbine. The exhausted steam from the intermediate pressure turbine goes to the low-pressure turbine through the crossover pipe without any valves. The low-pressure turbine is a double flow turbine. The steam enters the low-pressure turbine at the center and goes to each end then to the condenser. Steam is extracted from the turbines to the feed-water heating system through openings at the lower casing of the turbines. Table 3.2 shows the turbine specifications according to (Mitsubishi Heavy Industries Ltd. 2010) [21]. It presents the type of the systems. Moreover, it lists the design parameters. Finally, it presents the number of extractions.

3.2.3 Condenser

Circulating water pumps are pumping raw water from the Nile in the condenser through tubes. The water condenses the low-pressure turbine outlet steam by absorbing heat. Due to the steam condensation, the volume is reduced establishing a vacuum. The condenser system has a vacuum to remove air and non-condensable gases from the condenser keeping the condenser pressure vacuum. The condensed steam is collected and stored at the bottom of the condenser in the hot well. Table 3.3 lists the condenser specifications according to (Mitsubishi Heavy Industries Ltd. 2010) [21]. Moreover, it shows the type of the condenser and the design parameters. Finally, it mentions the number of tubes.

Table 3.2: Turbines specifications

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Table 3.3: Condenser specifications

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3.2.4 Condensate pumps

The condensate extraction pump is provided to extract water from the condenser hot well and deliver it to the deaerator storage tank through low pressure feed-water heaters (LPH 1 and 2 and LPH 3). Table 3.4 shows the condensate pump specifications as shown by Termomeccanica Pompe 2010a [22]. Moreover, it shows the type of the pump and the number of stages. Finally, the table lists the design parameters.

Table 3.4: Condensate pump specifications

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3.2.5 Feed-water pumps

The feed-water pressure increased on 2 stages. At the beginning, booster pumps raise the pressure of the feed-water and supply it to the main pumps through heater 5 and heater 6. Then the main pumps increase the feed­water pressure and supply it to the boiler through heater 7 and heater 8. Table 3.5 and Table 3.6 show the feed-water pumps specifications as presented by Termomeccanica Pompe 2010b [23]. Moreover, the type of the pumps and the design parameters are indicated.

Table 3.5: Feed-water booster pump specifications

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Table 3.6: Feed-water main pump specifications

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3.2.6 Feed-water heating system

Each unit of Cairo West Thermal Power Plant (U 7 & 8) has seven closed feed-water heaters and one deaerator (open feed-water heater) to increase the feed water temperature, improving the power plant efficiency.

3.2.6.1 Closed feed-water heaters

The low-pressure heaters (LPH 1 and 2) are combined in one shell and placed in the condenser shell under LP turbine exhaust, so they can be considered one heater. Table 3.7 presents LPH 1 and 2 specifications according to Mitsubishi Heavy Industries Ltd. 2010 [21]. The table lists the heater type and design parameters.

Table 3.7: LPH 1 and 2 specifications

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Table 3.8 shows the specifications of the closed feed-water heaters 3,5,6,7 and 8 as presented by SPC Ltd. 2010 [24]. The heaters’ type and design parameters are indicated in the table. Moreover, it lists the number of shells and the surface area of each shell.

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3.2.6.2 Deaerator

In steam cycle, it is important to remove the non-condensable gases from the system. The non-condensable gases are mostly air that leaks into the condenser, also they include other gases caused by decomposition of water into oxygen and hydrogen and chemical reaction between water and materials of construction. Deaerator is an open feed-water heater. It removes the non-condensable gases from the feed-water cycle. Moreover, it generates a static head on the boiler feed booster pump suction. Table 3.9 shows the deaerator’s specifications and the design parameters as presented by SPC Ltd. 2010 [24].

Table 3.9: Deaerator specifications

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3.3 Energy

Any system has energy can move objects or do work. In nature, work converts easily into heat, but a thennal device is needed to convert heat into work and make it useful. The first law of thermodynamics states that energy cannot be created nor destroyed, but it can be changed from one fonn to another. It focuses on the quantity of the energy and energy transfonnation [9]. Neglecting the kinetic and potential energies, the first law of thermodynamics fonnula for control volume is:

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3.4 Energy efficiency

Different sources of ineversibility such as; mechanical friction, expansion, compression, mixing, chemical reaction and heat transfer cause losses in any thennodynamics system. Therefore, no system can be reversed without absorbing more energy. Energy (thennal) efficiency of thennodynamics system is the ratio between the useful energy output to the energy input.

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Where,

η!: Efficiency according to first law of thermodynamics (Energy efficiency)

3.5 Exergy

The second law of thermodynamics does not focus on the quantity of energy only like the first law of thermodynamics, but it focuses on the quality of energy also. Exergy is an expression appeared depending on the second law of thermodynamics. It is used to analyze the thermodynamics systems. Exergy is defined as “the maximum shaft work that can be done by composite of the system and a specified reference environment” [9]

3.5.1 Reference environment

Reference enviromnent is the surroundings of the system or components. Moreover, it is not affected by any thermodynamics process. Finally, its properties remain unchanged.

3.5.2 Dead state

Dead state is the state at which exergy cannot be extracted from the system. In other words, the system and its environment are in a thennal equilibrium.

3.5.3 Exergy destruction

Different sources of irreversibility in any thermodynamics system such as; mechanical friction, expansion, compression, mixing, chemical reaction and heat transfer cause losses in exergy which called exergy destruction.

Exergy is transferred in three forms: 1. Exergy transfer by heat

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Where,

Exq: Exergy transfer associated with heat transfer, kJ

T0: Temperature at environment, к T : System temperature, к Q: Heat transfer, kJ

2. Exergy transfer by work

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Where,

Exw: Exergy transfer associated with work, kJ

w: Work, kJ

3. Exergy transfer by mass

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Where,

Exm : Exergy transfer associated with mass transfer, kJ m: Mass, kg

ex: Specific exergy, kJ/kg

h0 : Specific enthalpy at environment, kJ/kg

s : Specific entropy, kJ/kg.K

s0: Specific entropy at environment, kJ/kg.K

V: Velocity, m/s

g: Gravitational acceleration, m/s[2] z: Elevation, m

The exergy balance of control volumes:

Exq Ex^y + Exmi Exme ΕΧ(165 ÂExçy (3.7)

Rate form:

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For Steady flow:

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For adiabatic steady flow:

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Where,

Exdes : Exergy destruction (Irreversibility), kJ

I : Exergy destruction rate (Irreversibility rate), kW

P0 : Pressure at environment, kPa

v: Specific volume, m[3]/kg

cv: Control volume

Ex: Exergy rate, kW

3.6 Exergetic efficiency

The exergetic efficiency, which also can be called as second law efficiency is a major factor used to analyze any system from a thermodynamics perspective. It is defined as the ratio between the product exergy and the fuel exergy. The product exergy is the required outcome of this system such as; electrical power, mechanical power, superheated steam. The fuel exergy is the input used to get the product such as; actual fuel, electric power to rotating device, high temperature stream used for heating. [10]

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Where,

ไๅ แ : Efficiency according to second law of thermodynamics (Exergy efficiency)

3.7 Energy and exergy analyses of the power plant

The energy and exergy analyses will be discussed for the main components of the plant and the overall plant in the next section. Before the analyses, some assumptions have been made and taken into consideration:

- Steady operating conditions.
- All calculations use mass flow rate instead of mass.
- Air is treated as ideal gas.
- Combustion gases are treated as ideal gas mixtures.
- Kinetic and potential energies are neglected.
- Heat losses to the surrounding are neglected.
- Pressure change in the boiler is neglected.
- Product gases mixtures are considered a gaseous phase (no condensation).

3.7.1 Boiler

Boiler is a main component in the steam power plant. It is used to convert the chemical energy of the fuel into thennal energy (heat). This energy is used to generate the super-heated steam. This steam drives the turbine, which drives the generator to produce the electric power. Part of energy is lost in the boiler due to many factors such as [25]:

- Heat loss due to moisture in product gases due to hydrogen combustion.
- Heat loss due to radiation and convection from the external surfaces of the boiler.
- Heat loss due to excess air.
- Heat loss due to stack flue gases.

The energy losses in the boiler are calculated according to Eq. (3.15) as follows:

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Where,

Q! B : Heat rate loss in boiler, kW

The main streams of the Cairo West Thennal Power Plant’s boiler are shown in Fig. 3.3.

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Fig. 3.3: Boiler main streams.

Boiler efficiency is the ratio between energy output to the energy input. Different types of efficiencies appeared due to the different explanations of the energy input.

Types of efficiencies

1. According to energy input:

- Boiler fuel efficiency

The chemical energy of the fuel is considered the energy input, as shown in Eq. (3.16) [25].

- Boiler gross efficiency

The sensible heat of the fuel, electrical equipment’s energy and the energy of the combustion air are considered energy input as shown in Eq. (3.18) [25].

2. According to the calorific value:

- Gross calorific value (Higher Heating Value)

The gross calorific value is used to calculate the chemical energy of the fuel. American ASME adopted this method in its standard. Additionally, it will be used in this study.

- Net calorific value (Lower Heating Value)

The net calorific value is used to calculate the chemical energy of the fuel. Gennan DIN 1942 adopted this method in its standard.

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CV: Calorific value, kJ/kg

HV : Fuel higher heating value, kJ/kg

IFV : Fuel lower heating value, kJ/kg

WBД : Power input to the boiler for fans and other devices, kW

The exergetic efficiency of the boiler will effect on the overall power plant efficiency. The exergy destruction due to combustion process is the major factor effects on the boiler efficiency. Also, exergy destruction due heat transfers between the water, steam and product gases effects on the boiler efficiency. The air preheater and steam coil system effect slightly on the exergy efficiency of the boiler. Eq. (3.23) shows the exergy destruction rate of the boiler. Moreover, the boiler exergetic efficiency can be calculated according to Eq. (3.24).

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3.7.2 Turbine

The turbine is a mechanical device which expands steam passing through it to produce work. It delivers the work to the generator to produce electricity. According to the first law of thermodynamics, the theoretical power output, the isentropic power output and the isentropic efficiency of the turbine are calculated as presented in the next equations:

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Where,

Wisen: Mechanical isentropic power, kW

Wcale: Mechanical calculated power without coupling and electrical losses in the generator, kW

Energy losses occur in the turbine system due to many factors such as:

- Friction loss in the regulating valves, blades and nozzles.
- Mechanical friction between the rotor and bearings.
- Residual velocity at the last stage exit.
- Moisture content at low pressure stages.
- Heat loss from the turbine casing, even it is insulated.
- The mechanical losses from the coupling between turbine and generator.
- The mechanical and electrical losses in the generator.

These losses reduce the power gain from the turbine system as shown in Eq. (3.30):

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Wact : Actual electrical power produced by the generator, kW

From the second law of thermodynamics viewpoint, the exergy drop of the steam, passing through the turbine, (Reversible Power) can be considered the turbine’s fuel exergy. Moreover, the power drop of the steam, passing through the turbine, (theoretical calculated Power) can be considered the turbine’s product exergy. Furthermore, the theoretical calculated power output, the reversible power output, the exergy destruction rate and the exergetic efficiency of the turbine can be calculated according to equations from Eq. (3.31) through Eq. (3.35). Finally, Table 3.10 and Table 3.11 present the thermodynamics model for the Cairo West Thermal Power

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Table 3.10: Overall turbine system thermodynamics model

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3.7.3 Pumps

The pump is a mechanical device. It pressurizes the water using shaft work delivered by external sources. According to the first law of thermodynamics, the theoretical power input, the isentropic power input and the isentropic efficiency of the pump can be calculated as:

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From the second law of thermodynamics viewpoint, the exergy gained by the water, passing through the pump, (reversible power) can be considered the pump ’ s product. Additionally, the energy gained by the water, passing through the pump, (theoretical calculated power) can be considered the pump’s fuel. Furthermore, the reversible power input, the exergy destruction rate and the exergetic efficiency of the pumps can be calculated as shown in equations fromEq. (3.41) through Eq. (3.44). Finally, Table 3.12 presents the thermodynamics model of pumps used in the Cairo West Thennal Power Plant.

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3.7.4 Feed-water heaters

Feed-water heater is a heat exchanger used to heat the condensate water and feed-water using steam extracted from the turbines. Cairo West Thennal Power Plant has the two types of feed-water heaters.

1. Closed feed-water heater

Extracted steam from the turbines is used to heat the condensate water and the feed-water without any mixing in the heaters.

2. Deaerator

Extracted steam from the LP turbine, mixes directly with the feed-water in the open feed-water heater.

The heat losses can be calculated by making energy balance for the heaters as follows:

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Where,

Q1htr : Heat rate loss in heater, kW

From the second law of thermodynamics viewpoint, the exergy drop of hot stream can be considered the heater fuel. Moreover, the exergy gain of the condensate water or feed-water can be considered the heater product. Furthermore, Eq. (3.47) and Eq. (3.48) present the exergy destruction rate and the exerg etic efficiency of the heaters. Moreover, Table 3.13 presents the thermodynamics model of the closed feed-water heaters existed in the Cairo West Thermal Power Plant. Finally, it shows the thermodynamics model of the deaerator.

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Table 3.13: Feed-water heaters exergy analyses (continued).

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3.7.5 Condenser

The condenser is a heat exchanger. It extracts heat and condenses the exhausted steam from the low-pressure turbine. Moreover, it removes air and non-condensable gases from the cycle. Finally, the main streams of the Cairo West Thennal Power Plant’s condenser are shown in Fig. 3.4.

The rejected heat in the condenser is calculated as follows:

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Where,

Ql.Cond: Heat rate loss (rejected) in the condenser, kW hcw: Specific enthalpy of condensate water, kJ/kg

According to the second law of thermodynamics, the exergy destruction of the condenser can be calculated as follows:

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3.7.6 Power plant

Power plant thermal efficiency is the ratio between the generated energy to the input energy.

Chapter 4

Exergy Analyses of the Boiler and Auxiliaries

4.1 Introduction

The boiler is a main component in the steam power plant at which steam generated by high pressure and temperature by burning fuel. Natural Gas is the main fuel of the Cairo West Thermal Power Plant boiler. Moreover, Mazout (No. 6 oil) is a backup fuel. Therefore, all calculations have been made based on natural gas.

4.2 Standard reference state

There are many tables for chemical properties with different zeros. Therefore, a reference point is needed to be used in calculations. This reference point called Standard Reference State (SRS). International Union of Pure and Applied Chemistry (IUPAC) and National Institute of Standards and Technology (NIST) chose the Standard Reference State at 1 bar and 298.15 °K (25 °C).

4.3 Fuel properties

The fuel used in the power plants has been always a mixture of hydrocarbons, which differs from each single fuel in properties. So, a fuel model will be generated and its properties will be calculated. Finally, EEA uses the fuel properties listed in NIST-JANAF thermochemical tables [26].

4.3.1 Fuel model

An equivalent hydrocarbon model (CwHxOyNz) will be used to facilitate the combustion formula balancing and the combustion calculations which is calculated as follows [27]:

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4.3.2 Heating value

Heating value is the maximum amount of heat released due to a complete combustion process of unit mole (or mass) of fuel in the standard reference state. The Lower Heating Value (LHV) is used when the product gases contain water vapor state. While the Higher Heating Value (HHV) is used when the water condensed into a liquid state in products. Equations from Eq. (4.8) through Eq. (4.12) show the heating value calculations [28].

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Where,

HR: Heat of reactant, kJ/kmol fuel Нрд : Heat of products in liquid state, kJ/kmol fuel Hp v: Heat of products in vapor state, kJ/kmol fuel h° : Enthalpy of formation, kJ/kmol fuel

4.3.3 Adiabatic flame temperature

When a fuel is burned with the theoretical amount of air in an insulated control volume (adiabatic system) the product temperature will be maximum at the adiabatic flame temperature (AFT). As a result of supplying excess air to achieve a complete combustion process, the flame temperature reduced. The adiabatic flame temperature is calculated according to the next steps [28].

Step 1: Calculate the heat of reactants

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Step 2: Assume that all products’ compositions are nitrogen

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Step 3: As the combustion process is adiabatic, then Hp = HR

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Use Eq. (4.16) to get the molar enthalpy of the products (hp).

Step 4: Use the previous value of the specific enthalpy of the products and get the corresponding temperature from the Nitrogen properties table.

Step 5: Get products’ properties at this temperature and check if it satisfies Eq. (4.17).

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Step 6: If the left-hand side of Eq. (4.17) is not equal to the right-hand side, choose a lower temperature and repeat the previous steps until both sides are equal.

Where,

h: Molar enthalpy, kJ/kmol h: Change in molar enthalpy, kJ/kmol h of fuel can be neglected h°: Molar enthalpy at environment, kJ/kmol

4.4 Thermodynamics properties

In this section, the enthalpy and entropy of the product gases at furnace, air heater inlet, air heater outlet and stack outlet will be calculated.

The enthalpy of the product gases per kinol of fuel can be calculated as shown in Eq. (4.18):

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Also, the enthalpy of the product gases per kg of fuel can be determined according to Eq. (4.19):

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Moreover, the enthalpy of the product gases’ stream in kW can be calculated as presented in Eq. (4.20):

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Furthermore, the calculated specific enthalpy (enthalpy per kg) of the product gases is given by Eq. (4.21) and Eq. (4.22):

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Finally, the entropy of the product gases can be calculated by the same manner as used to calculate the specific enthalpy.

4.5 Exergy

The exergetic efficiency of the boiler effects on the overall power plant efficiency. The exergy destruction, due to combustion process, is the major factor effects on the boiler efficiency. Also, exergy destruction, due heat transfers between the water, steam and product gases, effects on the boiler efficiency. The air preheater and steam coil system effect slightly on the exergy efficiency of the boiler.

4.5.1 Total exergy of mixture

Total Exergy of a mixture depends on the physical, chemical and mixing exergies of the substances [10], [11].

The physical exergy per kmol of fuel is calculated according to Eq. (4.23):

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Also, the chemical exergy per kmol of fuel is calculated as shown in Eq. (4.24):

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Moreover, the mixing exergy per kmol of fuel is presented in Eq. (4.25):

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Moreover, the exergy of the mixture per kmol of fuel is calculated according to Eq. (4.26) and Eq. (4.27):

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Furthermore, the exergy of the mixture per kg of fuel is shown in Eq. (4.28):

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Furthermore, the total exergy of the mixture in kW is calculated as presented in Eq. (4.29):

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Additionally, the specific exergy per kg of the product gases is given in Eq. (4.30):

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Finally, the fuel model exergy can be calculated using equations from Eq. (4.23) through Eq. (4.30) with neglecting the physical exergy.

Where,

ēXph : Molar physical exergy, kJ/kmol ēxch: Molar chemical exergy, kJ/kmol ēxmix: Molar mixing exergy, kJ/kmol ēch: Standard Molar Chemical Exergy, kJ/kmol R: Universal gas constant, kJ/kmol.K

4.5.2 Exergy of product gases

The chemical reaction between the oxygen and the fuel produces gases in the furnace. The product gases exergy at the furnace, air heater inlet, air heater outlet and the stack outlet points can be obtained by using equations fromEq. (4.23) through Eq. (4.30).

4.5.3 Exergy of combustion air

It is easy to get the combustion air properties from the air properties table in [29] and use them to calculate the combustion air exergy according to Eq. (4.31).

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4.6 Boiler exergetic analyses

The boiler is one of the main systems in the steam power plant. Moreover, it has a significant effect on the power plant exergetic efficiency. Therefore, it is important to study each boiler’s component in detail and processes occurs in it.

4.6.1 Combustion process

The exergy destruction, due to combustion process, is one of the major factor effect on the boiler efficiency. Moreover, it can be reduced by increasing the combustion air temperature, mixing the fuel and air very well and reducing the excess air. Finally, the combustion process’s exergetic destruction and efficiency can be calculated according to Eq. (4.36) and Eq. (4.37) respectively [10].

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Where,

ExProd: Combustion product gases, kW

4.6.2 Heat transfer process

The product gases, due to combustion process, heat the feed-water passes through the water walls to the drum. Moreover, these gases superheat the steam temperature, which passes through the super heater and re-heater tubes as shown in Fig. 3.2. Due to this process, the exergy destruction of the boiler increases. Finally, the exergy destruction and exergetic efficiency of this process can be calculated as shown in Eq. (4.40) and Eq. (4.41) respectively.

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4.6.3 Air preheater

The air preheater is a heat exchanger, which recovers the waste heat from the boiler outlet product gases to the cold combustion air. Moreover, it saves the fuel and increases the adiabatic flame temperature. Furthermore, Fig. 4.1 illustrates the air preheater streams. Finally, the exergetic destruction and efficiency of the air preheater can be obtained as shown in Eq. (4.44) and Eq. (4.45) respectively.

4.6.4 Steam coil air preheater

It is a heat exchanger used to heat the combustion air using steam passes through coils. It is used when the fuel is switched from the natural gas into fuel oil (Mazout). Moreover, it is used to ensure that the product gas temperature is more than the dew point to prevent the fonuation of sulfuric acid. Furthermore, Fig. 4.2 shows the steam coil air preheater streams. Finally, the exerg etic destruction and efficiency of the steam coil air preheater can be obtained according to Eq. (4.48) and Eq. (4.49) respectively.

4.6.5 Stack

Stack is a channel used to collect flue gases exit from the boiler to pass through it. Furthermore, it improves the efficiency of the boiler by increasing the draught effect of the combustion air entering into the furnace. Finally, Eq. (4.50) is used to calculate the stack exergetic destruction.

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Chapter 5

Energy and Exergy Analyses Software Program

5.1 Introduction

Energy and Exergy Analyses (EEA) is a computer program was proposed and built by the author only to calculate the energy and exergy analyses of the steam power plants. It is written using an Object Oriented Programming language (Microsoft Visual c#) with the aid of Microsoft Excel and SAP Crystal Reports. Moreover, the visual basic code of X-Steam Tables is converted into visual c# code and used to get the thermodynamics properties of the water and steam streams. Finally, a new code is added to get the specific entropy of the points in the wet region.

Users will supply the operating parameters to the program to get the energy and exergy of the power plants. The program can determine which system causes the most energy and exergy losses, allowing researchers to focus their efforts on improving their designs. Additionally, it calculates the energy and exergy saved under a variety of conditions such as; increasing or decreasing pressure, temperature or flow rate. Moreover, it calculates the energy and exergy efficiencies of the different systems in the steam power plants. Furthermore, EEA calculates the overall energy and overall exergy efficiencies of the power plant. It introduces the results in tables and charts in order to facilitate the results analyses. Finally, recorded data of Cairo West Thennal Power Plant is used to evaluate and show the capabilities of the present program.

5.2 EEA data entry

In this section, a single case is supplied to the EEA. Moreover, EEA forms and capabilities will be presented and discussed in detail.

The main fonn of the EEA is shown in Fig. 5.E It contains the main systems may be existed at any steam power plant. Furthennore, it contains the generated reports to show the results. Finally, it contains the sunounding properties.

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Fig. 5.1: EEA main form.

Steam generated from the boiler is due to the combustion process of the fuel and air mixture. The operating parameters of air, fuel, product gases, water and steam are entered in the boiler form as shown in Fig. 5.2, Fig. 5.3, Fig. 5.4 and Fig. 5.5.

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Fig. 5.2: Fuel operating parameters form.

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Fig. 5.3: Air and product gases operating parameters form,

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Fig. 5.4: Water and steam operating parameters form.

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Fig. 5.5: Boiler input power form,

Power plants are always using a mixture of hydrocarbon fuels in the combustion process, that differs from each single fuel in properties as shown in Fig. 5.2. To overcome this issue, EEA covers a wide range of fuels as shown in Fig. 5.6, then uses them to generate the fuel model. Moreover, EEA calculates the chemical properties of the fuel model which includes:

- Molar mass
- Gross (Higher) heating value (HHV)
- Net (Lower) heating value (LHV)
- Specific exergy
- Exergy

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Fig. 5.6 ะ Hydrocarbon fuels.

The turbine expands the steam passing through it to produce the mechanical power used to roll the electrical generator. Operating parameters of the turbine system are supplied to the turbine fonn as shown in Fig. 5.7. EEA calculates the thermal efficiency of the power plant based on the theoretical power produced from the turbines. Moreover, it calculates the thennal efficiency of the power plant based on the actual power produced by the generator which is supplied in the fonn by the user.

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The condenser form shown in Fig. 5.8 is used to insert the operating parameters of the steam and water streams in the shell side. Moreover, the

condensate pump can be assumed as a part of the condenser as is shown in the figure or as a separate system as shown in 6.9. Finally, this form is used to insert the operating parameters of the circulating cooling water as presented in Fig. 5.10.

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Fig. 5.8: Condenser shell side form.

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Fig. 5.9: Condensate pump form,

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Fig. 5.10: Condenser cooling water side form.

In Cairo West Power Thermal Plant, a multiple of feed-water heaters increase the water temperature improving the power plant efficiency. EEA covers both open and closed feed-water heaters. The closed feed-water heaters operating parameters can be supplied in the closed feed-water heater fonn as shown in Fig. 5.11. Furthermore, EEA facilitates entering data for one up to 10 heaters to be valid for different designs of steam power plants. Finally, the open feed-water heater operating parameters are entered in the open feed-water heater fonn as shown in Fig. 5.12.

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Fig. 5.11 ะ Closed feed-water heaters form.

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Fig. 5.12: Open feed-water heater,

Feed-water pumping system increases the water pressure and supply it to the boiler. Some designs of steam power plants have booster pumps in the feed-water system. Other systems do not have booster pumps in the feed­water system. Therefore, EEA covers both designs as shown in Fig. 5.13. Moreover, it supplies the designs which use steam turbine to drive the pump as shown in Fig. 5.14.

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Fig. 5.13: Electrical feed-water pump.

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Fig. 5.14: Mechanical feed-water pump.

5.3 EEA results

EEA makes the calculations and produce the results in reports which contain tables and charts. In this section, the results of case (B) will be presented in detail in order to present the EEA capabilities.

EEA summarizes the power plant energy and exergy results presenting them in Fig. 5.15. It shows the exergy efficiency and destruction of the power plant. Moreover, it presents the theoretical and actual generated power, consumed power and net generated power of the power plant. Finally, it shows the thermal efficiency of the power plant based on the lower and higher heating values.

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Fig. 5.15: Energy and exergy summary of the power plant.

EEA presents the thennal properties of all streams which used in many calculations such as; power, thermal efficiency, exergy destmction, exergy efficiency. Table 5.1 shows the thermal properties of some of these streams.

Power plants consist of many systems. Some of these systems consume power, such as feed-water pump. In the opposite, the turbine is the main system generating the power. Table 5.2 shows the isentropic, actual and reversible generated and consumed power in all systems. Furthermore, Table 5.3 lists the power loss and exergy destruction in many systems in the power plant. Finally, EEA presents and compares these losses in the bar chart shown in Fig. 5.16.

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Table 5.4: Exergy analyses

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Fig. 5.17: Exergetic efficiency of all components.

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Fig. 5.18: Exergetic destruction pie chart of all components.

EEA lists the exergy analyses of the main systems in the power plant in Table 5.5. It presents the exerg etic efficiency and destruction of the main systems. Moreover, it provides each system destruction as a percentage of the total power plant destruction. Furthermore, it shows each system destruction as a percentage of the fuel exergy. In order to compare the exergetic efficiencies of the main systems, EEA illustrates a bar chart as shown in Fig. 5.19. Finally, it generates a pie chart shown in Fig. 5.20 to show the exergetic destruction of these systems and highlight the system responsible for the maximum exergetic destruction in the plant.

Table 5.5: Exergy analyses of main systems

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Fig. 5.20: Exergetic destruction pie chart of main systems.

The boiler is one of the major and important systems in the power plant, so EEA presents the boiler results in detail. Fig. 5.21 shows the gross and fuel energy efficiencies of the boiler. Moreover, it presents the exergetic efficiency of the boiler. Furthermore, the generated fuel model and its thermochemical properties are listed in Fig. 5.22. Additionally, Fig. 5.23 presents the combustion process fonnula of the fuel in the stoichiometric and actual cases. Finally, it lists the air fuel ratio and the adiabatic flame temperature.

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Fig. 5.22: Fuel model thermochemical properties.

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Fig. 5.23: Combustion process details.

EEA presents the thermal properties of all streams in the boiler which used in many calculations such as; power, thermal efficiency, exergy destruction, exergy efficiency. It lists these properties in Table 5.6.

EEA supplies the exergy analyses of the boiler in detail in Table 5.7. It presents the exergetic efficiency and destruction of the processes occur in the boiler. Moreover, it shows the exergetic efficiency and destruction of the boiler subsystems such as air preheater. Furthermore, it lists the destruction as a percentage of the total boiler destruction. Finally, it presents each system destruction as a percentage of the fuel exergy.

In order to compare the exergetic efficiencies of the boiler’s processes and subsystems, EEA generates a bar chart as shown in Fig. 5.24. Also, it provides a pie chart shown in Fig. 5.25 to illustrate the exergetic destruction of these systems.

Table 5.6: Boiler streams’ thermodynamics properties

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Table 5.7: Boiler exergy analyses

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Fig. 5.24 ะ Boiler exergetic efficiency.

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Fig. 5.25: Boiler exergetic destruction pie chart.

Chapter 6

Application and Results of Energy and Exergy Analyses Program for steam Power Plant

6.1 Introduction

The present work is designed to study the energy and exergy analyses of the Cairo West Thermal Power Plant of different cases. Furthermore, these cases were recorded on various dates and loads as listed in Appendix (A). Finally, the results of these cases will be presented in Appendix (B).

6.2 Studying a single case in detail

In this section, a single case will be discussed in detail· Case (B) lists the operating parameters of the power plant at 50% load (175 MW). These parameters are supplied to the EEA then it makes the calculations and produce the results in reports which contain tables and charts. Now, it is appropriate to show the results of this case.

Fig. 5.16 shows that 191.7 MW of heat rate rejected in the condenser which makes the condenser the main system responsible for power (energy) loss in the power plant. Moreover, a significant amount of power loss (39.1 MW) occurs in the boiler. Finally, the heat transfer process in the feed-water heaters is assumed to be perfect to get the extracted steam flow rate. Therefore, the losses in the feed-water heating system can be neglected.

Also, Fig. 5.16 reveals that despite the condenser is the main reason for energy loss in the power plant, its exergy destruction is insignificant. In the opposite, more than 193 MW of exergy is destructed in the boiler making it the main source of exergy destruction despite its low energy loss. Finally, the turbine system comes in the second place with a 17.9 MW exergy destruction.

As it can be seen from the pie chart shown in Fig. 5.18, more than 108 MW of exergy was destructed due to the combustion process. Furthermore, 82.2 MW of exergy was destructed due to heat transfer process.

The turbine system has the highest exergetic efficiency of the power plant with 90.8% as it is illustrated in Fig. 5.19. Also, it reveals that the boiler system has the lowest exergetic efficiency of the power plant with 51%. Furthermore, the pie chart shown in Fig. 5.20 reveals that 193.6 MW of exergy was destructed in the boiler making it the major system responsible for exergetic destruction in the power plant. Finally, it shows that the exergetic destruction of the turbine system is significant compared to other systems in spite of its high efficiency.

The previous results present a strong evidence that the boiler is the major system responsible for exergetic destruction in the power plant. Therefore, EEA presents the boiler results in detail. Fig. 5.24 shows that the air preheater has the highest exergetic efficiency in the boiler with 80.3%. Moreover, it reveals that the heat transfer process has the lowest exergetic efficiency in the boiler with 71.1%. Furthermore, the pie chart, presented in Fig. 5.25, shows that 56% of the boiler exergetic destmction is due to the combustion process. Moreover, it shows that more than 42% of the boiler exergy destruction is due to the heat transfer process. Finally, it shows that the exergetic destruction occurs in the air preheater is insignificant.

6.3 Comparison between loads

A comparison was made between the power plant’s loads at design data (Case A and Case E). Fig. 6.1 shows the gross energy efficiency, the fuel energy efficiency and the exergetic efficiency of the boiler in both cases. It reveals that the boiler exergetic efficiency is higher at the full load (Case E). Furthermore, Fig. 6.2 presents the power plant thermal and exergetic efficiencies in both cases. It shows that the power plant thermal and exergetic efficiencies are higher at full load (Case E). According to these results, it can be inferred that operating the power plant at full load is more efficient than operating it at half load.

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Fig. 6.2: Power plant efficiency comparison.

6.4 Exergetic destruction over years

A comparison among the power plant operating parameters at half load was made. Fig. 6.3 illustrates the results. It shows that, in 2013, there was a dramatic increment in the fuel flow rate and the heat transfer’s exergetic destruction.

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Fig. 6.3: Exergy destruction in boiler processes.

As a result of using the fuel oil number 6 (Mazout) as the main fuel for a long time, many problems occur in the boiler such as:

- Corrosion occurs in the burner impeller and gas spuds. Some burners are totally damaged as shown in Fig. c. 1. Other burners are partially damaged as presented in Fig. C.2.
- Ashes and deposits from the fuel oil combustion process fouled the heating surface of the boiler tubes as shown in Fig. C.3 and Fig. C.4.
- Ashes and deposits clogged the spaces between the tubes as presented in Fig. C.5.
- Some tubes displaced from its original locations clogging the product gases path as shown in Fig. C.6 and Fig. C.7.

Due to these problems, the fuel consumption increased to overcome the decrement of the heat absorption through the tubes which increased the combustion process destruction. Moreover, the heat transfer’s exergetic destruction increased dramatically which led to a gigantic destruction in the boiler system. As a result of the destruction increment, the thennal and exergetic efficiencies of the boiler decreased as shown in Fig. 6.4. Finally, the overall power plant thermal and exergetic efficiencies decreased as shown in Fig. 6.5.

Fig. 6.4: Boiler efficiencies.

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Fig. 6.5: Power plant efficiency in different years.

In 2015, the unit is shut down for a major overhaul. Damaged parts in the burners are replaced as shown in Fig. C.8. Furthermore, chemical cleaning of the tubes has been done removing much of the deposits as shown in Fig. c.9. Finally, some tubes are displaced close to its original positions as shown in Fig. C.10.

Due to these procedures, the exergetic destruction of the combustion process and the heat transfer process decreased in 2015 as shown in Fig. 6.3. This decrement led to a significant decrement in the boiler exergy destruction which increased the thermal and exergetic efficiencies of the boiler as shown in Fig. 6.4. Finally, the overall power plant thermal and exergetic efficiencies increased as shown in Fig. 6.5.

Chapter 7

Conclusions and Recommendations

7.1 Introduction

In this thesis, a computer program, EEA, was proposed to get the energy and exergy analyses of the steam power plants. It makes the calculations and summarizes the power plant energy and exergy results in reports containing tables and charts.

7.2 Conclusions

The recorded and design parameters of the Cairo West Thermal Power Plant (Units 7 & 8) were used to test and show the capabilities of EEA and the following conclusions are drawn:

1- EEA perfonns the energy calculations of the power plants in detail. It shows that the condenser is the main system responsible for power (energy) loss in the Cairo West Thermal Power Plant (Units 7 & 8) where 191.7 MW is rejected to the circulating cooling water. Meanwhile, the boiler comes in the second place where 39.1 MW is lost.
2- EEA calculates the exerg etic efficiency of each system. It reveals that, the turbine has the highest exergetic efficiency of the power plant where the efficiency is 90.8%, meanwhile, the boiler has the lowest exergetic efficiency of the power plant where the efficiency is 51%.
3- EEA calculates the exergetic destruction of the power plant systems. It proved that, the boiler is the main source of exergy destmction where the destruction is 193 MW despite its low energy loss. Moreover, the turbine system comes in the second place where 17.9 MW is destructed.
4- EEA covers a wide range of fuels and uses them to generate the fuel model. Moreover, it calculates the chemical properties of the fuel model. Generated fuel model and its specifications is presented and it is used in the combustion process fonnula. Finally, air fuel ratio and adiabatic flame temperature in the stoichiometric and actual combustion have been presented for each case.
5- Due to the significant impact of the exergy destruction in the boiler, EEA studied the boiler system in detail. The results reveal that, the exergy destruction in the boiler is due to the combustion and the heat transfer processes where the destruction is 108 MW and 82.2 MW respectively.
6- EEA results showed that the power plant thennal and exergetic efficiencies are higher at full load (Case E) where the efficiencies are 38.5% and 48% respectively, so operating the power plant at full load is more efficient than operating it at half load.

7.3 Recommendations

EEA shall be upgraded to cover more systems such as; Gas Turbine system, Combined Power Plants and non-conventional power plants as Geo Thermal Power Plants and Solar Power Plants. Furthermore, it is important to create a power plant designer, which allows users to supply the target electric load generation required and it will generate a power plant design and present the plant components with their technical specifications.

As a result of using Mazout as the main fuel for a long time in the Cairo West Thermal Power Plant (Units 7 & 8), many problems occur to the boiler. So, it is recoimnended to:

1. Replace the burners’ impellers with new ones with greater spaces to prevent ashes and deposits from clogging these spaces.
2. Supply air pipe to the gas spuds to cool it down, when using fuel oil in the combustion process.
3. Operate the upper row of burners with natural gas in the case of mixed fire operation. Therefore, higher flame temperature of the natural gas burners will achieve a complete combustion for the unbumed fuel oil products.
4. Make a chemical test for the fuel oil additives dosing substance to ensure that it is suitable for the fuel oil chemical composition.

In addition to these recommendations, further thermodynamics analyses of the Cairo West Thermal Power Plant should be performed in these cases:

i- Using fuel oil as the main fuel
ii- Using mixed firing

References

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[2] Rashad, A., and A. El Maihy, “Energy and Exergy Analysis of a Steam Power Plant in Egypt,” in AEROSPACE SCIENCES & AVIATION TECHNOLOGY (ASAT- 13), May 2009.

[3] Erdem, H. EL, A. V. Akkaya, B. Cetin, A. Dagdas, s. H. Sevilgen, B. Sahin, I. Teke, c. Gungor, and s. Atas, “Comparative Energetic and Exergetic Performance Analyses for Coal-Fired Thennal Power Plants in Turkey” Internationa1 Journal of Thermal Sciences, Voi. 48, No. 11, pp. 2179-2186, Nov. 2009.

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[7] Altayib, K., “Energy , Exergy and Exergoeconomic Analyses of Gas­Turbine Based Systems” M.Sc. Thesis, University of Ontario Institute of Technology, Canada, 2011.

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[10] Moran, M. J., “Fundamentals of Exergy Analysis and Exergy-Aided Thennal Systems Design” in Thermodynamic Optimization of Complex Energy Systems, A. Bejan and E. Mamut, Eds. Dordrecht: Springer Netherlands, pp. 73-92, 1999.

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[14] Ameri, M., p. Ahmadi, and s. Khamnohaimnadi, “Exergy Analysis of a 420 MW Combined Cycle Power Plant” InternationaI Journal of Energy Research, Voi. 32, No. 2, pp. 175-183, Feb. 2008.

[15] Rivero, R. and M. Garfias, “Standard Chemical Exergy of Elements Updated” Energy, Voi. 31, No. 15, pp. 3310-3326, Dec. 2006.

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[17] Afifi, I. EL, “Theoretical Analysis and Practical Application of Exergy for a Co-Generation Plant at Different Operating Conditions” M.Sc. Thesis, Cairo University, 2002.

[18] Al-bagawi, J. J. A., “Energy and Exergy Analysis of Ghazlan Power Plant” M.Sc. Thesis, KING FAHD UNIVERSITY OF PETROLEUM & MINERALS, 1994.

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New York, NY: The American Society of Mechanical Engineers, 1999.

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Appendix A

The present work is designed to study the energy and exergy analyses of the Cairo West Thennal Power Plant of different cases. These cases are taken in various dates and loads and listed in next tables.

Table A.1: Cairo West Thermal Power Plant’s operating parameters

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Table A.2: Cairo West Thermal Power Plant’s operating parameters

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The design data parameters used in boiler analyses are different than the parameters used for other systems analyses because the boiler contract considered other needs such as auxiliary steam supplied to the unit 5 and 6 steam transformer.

Table A.3: Boiler’s design parameters

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Table A.4: Cairo West Thermal Power Plant’s design parameters

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Appendix в

Case A results

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Fig. B.l: Energy and exergy summary of the power plant.

Table B.l: Power loss and exergy destruction

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Fig. B.2: Power loss and exergy destruction. Table B.2: Equipment’s power

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Fig. B.3: Exergetic efficiency of all components.

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Fig. B.4: Exergetic destruction pie chart of all components.

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Fig. B.5: Exergetic efficiency of main systems.

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Fig. B.6: Exergetic destruction pie chart of main systems

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Fig. В. 7 ะ Boiler efficiency.

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Fig. B.8: Fuel model thermochemical properties.

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Fig. B.9: Combustion process details

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Fig. B.IO: Boiler exergetic efficiency.

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Fig. B.ll: Boiler exergetic destruction pie chart

Case c results

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Fig. B.12: Energy and exergy summary of the power plant.

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Table B.6: Power loss and exergy destruction

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Fig. B.13: Power loss and exergy destruction.

Table B.7: Equipment’s power

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Fig. B.14: Exergetic efficiency of all components.

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Fig. B.15: Exergetic destruction pie chart of all components.

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Fig. B.16: Exergetic efficiency of main systems.

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Fig. B.17: Exergetic destruction pie chart of main systems

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Fig. B.18: Boiler efficiency.

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Fig. B.19: Fuel model thermochemical properties.

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Fig. B.20: Combustion process details

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Fig. B.21: Boiler exergetic efficiency.

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Fig. B.22: Boiler exergetic destruction pie chart

Case D results

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Fig. B.23: Energy and exergy summary of the power plant.

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Table B.ll: Power loss and exergy destruction

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Fig. B.24: Power loss and exergy destruction.

Table B.12: Equipment’s power

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Fig. B.25: Exergetic efficiency of all components.

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Fig. B.26: Exergetic destruction pie chart of all components.

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Fig. B.27: Exergetic efficiency of main systems.

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Fig. B.28: Exergetic destruction pie chart of main systems

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Fig. B.29: Boiler efficiency.

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Fig. B.30: Fuel model thermochemical properties.

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Fig. B.31: Combustion process details

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Fig. B.32: Boiler exergetic efficiency.

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Fig. B.33: Boiler exergetic destruction pie chart

Case E results

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Fig. B.34: Energy and exergy summary of the power plant.

Table B.16: Power loss and exergy destruction

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Fig. B.35: Power loss and exergy destruction. Table B.17: Equipment’s power

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Fig. B.36: Exergetic efficiency of all components.

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Fig. B.38: Exergetic efficiency of main systems.

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Fig. B.40: Boiler efficiency.

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Fig. B.41: Fuel model thermochemical properties.

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Fig. B.42: Combustion process details

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Fig. B.43: Boiler exergetic efficiency.

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Details

Pages
130
Year
2017
ISBN (Book)
9783668676114
File size
8 MB
Language
English
Catalog Number
v418177
Grade
90
Tags
EEA Efficiency Energy Exergy Steam Power Plant Entropy

Author

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Title: Computer-Aided Evaluation of Steam Power Plants Performance Based on Energy and Exergy Analysis