Energy and Exergy Analysis of a Combined Cycle Power Plant

18 Figure 4.2 Schematic diagram of the description of the SPECO 78 method 19 Figure 5.1 The effect of gas turbine output power with the change of inlet air. 24 Figure 5.6.

LIST OF TABLES

Introduction

Introduction
Power Sector Scenario in Bangladesh

Present Power Generation Scenario in Bangladesh
Fuel based Power Plant Scenario of Bangladesh
Technology based Power Plant Scenario of Bangladesh

Background and the present state of Energy and Exergy Analysis
Definitions
Motivation for the Study
Objectives & Possible Outcomes
Organization of the thesis

In Chapter 3, a brief description of the background of a combined cycle power plant and the configuration of all major equipment is given here. In Chapter 5, discuss the energy analysis of Fenchuganj combined cycle power plant in detail and its application to case studies.

Table 1.2: Fuel based Energy Generation Capacity (On February 2020)

LITERATURE REVIEW

Conventional Energy Analysis
Conventional Exergy Analysis
Advanced Exergy Analysis
Exergy Economics
Conclusion

The results confirmed that 60.9% of the total exergy destruction occurs in the combustion chamber, which constitutes the primary source of irreversibilities in a system with high exergy destruction attributable to three causes: (i.) combined diffusion/fuel oxidation; (ii.) internal energy exchange – heat transfer; and (iii.) the mixing process. Here, exergy analysis of the considered combined cycle estimates the exergy efficiency and exergy destruction of essential components.

BACKGROUND

Combined Cycle Power Plant
Working Principle of Combined Cycle Power Plant
Description of the Fenchuganj Combined Cycle Power Plant

Gas Turbine
Heat Recovery Steam Generator
Steam turbine (ST)
Cooling Tower
Closed Cycle Circulating Water Pump
Water Treatment Tanks
Service Air Unit (Screw type air Compressor)
Condenser
Gas Supply Unit
Substation & National Grid

Flow Diagram of the Fenchuganj Combined Cycle Power Plant

The steam-water mixture in the tubes enters the steam drum, where steam is separated from the hot water using moisture separators and cyclones; the separated water is recirculated to the evaporator tubes. This power plant is one of the oldest combined cycle power plants in the public sector. The steam is produced in the HRSG and fed to the primary steam system of the HP.

Provides feed water to the HP drum during startup, shutdown and power operation of the combined cycle unit. The HP Steam Generation system is located downstream of the exhaust gas inlet of the HRSG. The steam is produced in the HRSG and fed to the LP main steam system.

Provides feed water to the LP drum during startup, shutdown and power operation of the combined cycle unit.

Figure 3.1: Flow diagram of a combined cycle power plant.

METHODOLOGY

Energy Analysis

Qualitative Assessment

HRSG, 2. Steam turbine

Quantitative Assessment
Exergy Analysis
Exergoeconomic Analysis

This assessment identifies best and more deficient practices in the power plant and recommends solutions to help adopt some of the best practices in the industry. Knowing the exergy addition and the corresponding cost at each previous step can be used to improve the costing process. When exergy is supplied to the stream, the cost of adding each exergy unit to the stream is calculated using the cost per exergy unit of product for the processing device in which the exergy addition occurs.

This closer look mainly includes the simultaneous consideration of the exergy and the corresponding monetary values added or removed from a material stream in each process step. In general, the analysis becomes more complicated when the new approach is used instead of the previous exergoeconomic methods. The above equation states that the outgoing exergy streams' total cost is equal to the total expense of obtaining them: the cost of the incoming exergy streams plus the capital and other costs.

Consequently, the unknown variables that must be calculated using the cost balance for the kth component are the costs per unit exergy of the exiting streams.

Figure 4.1: Flow Diagram of Energy Audit Methodology.

Energy Analysis

Energy Analysis
Result and Discussion

Effect of Power Output of Gas Turbine with change in Inlet Air Temperature
Effect of thermal efficiency of Gas turbine with change in Inlet Air Temperature
Effect of thermal efficiency of Gas turbine with Specific fuel consumption
Effect of Heat Rate (HR) in simple cycle with Inlet Air Temperature
Effect of Overall efficiency in simple cycle with Inlet Air Temperature
Effect of steam turbine net-work output with varying load
Effect of steam flow rate with steam turbine work output
Effect of Steam consumption/rating with steam flow rate
Effect of steam consumption/rating with varying load
Effect of combined cycle efficiency with varying load
Effect of Heat rate with Total work output
Heat balance of Heat Recovery Steam Generator (HRSG)
Service Air Unit (Screw type air Compressor)
Condenser
Cooling Tower

Comparing with other research works

This section describes the basic methodology for the energy analysis of the main components of the combined power plant Fenčuganj. Increasing the duty ratio and mass flow rate of the working fluid increases the power output. The heat rate of the device in simple cyclic operation increases with increasing inlet air (ambient) temperature.

The overall efficiency of the plant in a simple cycle decreased as the inlet air (ambient temperature) increased. In Figure 5.11 above, the steam consumption/power of the steam cycle increases as the mass flow rate of the steam decreases. The following table 5.22 shows the total costs of the chemical dosing of the installation in a year.

Therefore, energy losses decrease as the temperature of the mass flow rate of hot gases decreases.

Table 5.1: Energy Performance Parameter Equations.

Exergy Analysis

Exergy Analysis
Exergy Components and Exergy Balances
Exergetic efficiency
Comparing with other research works

Each state of the power plant and the following equations are written below with respect to Figure 5.1. Therefore, the definition of the product must be consistent with the purpose of purchasing and using the system. The overall exergetic efficiency of the system can be defined in terms of exergy destruction ratios.

The following operating parameters are shown at each stage of the power plant schematic diagram shown in Figure 3.14. The exergetic rate of the gas cycle and steam cycle is used to calculate the exergy destruction, exergetic efficiency, exergetic destruction efficiency of air compressor, combustion chamber, gas turbine, steam turbine, HRSG, condenser, condensate pump and associated junction, boiler feed water Pump which is shown in Table 6.3. From the above Table 6.4, the following figures are shown here to graphically represent the exergetic performance of the various components under various conditions.

In which the maximum exergy destruction is 51.93% in the combustion chamber over the entire device system.

Table 6.1: Exergy equations of major component of the plant.

Percentage (%) of exergy destruction

Exergoeconomic Analysis

Exergoeconomic Analysis

Non-exergy cost parameter
Exergy cost parameter and cost balance equation

Monthly economic analysis

Capacity and Energy Payments

Monthly performance indicator parameter
Exergoeconomic parameter

The reference energy price consists of two components: i) the reference variable operation and maintenance component consisting of the reference foreign variable operation and maintenance component (the. PI(US)q = the value of the United States Consumer Price Index as published in the publication of the International Monetary Fund entitled. PI (US)b = the value of the United States Consumer Price Index, as published in the publication of the International Monetary Fund entitled "International Financial Statistics", for the month in which the Reference Date falls.

PI(Tk)q = the value of the Consumer Price Index of Bangladesh as published in the International Monetary Fund publication titled. International Financial Statistics" for the first month of the quarter "q" (ie January, April, July and October) in which the month "m" appears;. PI(Tk)b = the value of the Consumer Price Index of Bangladesh as published in the International Monetary Fund publication titled.

Fenchuganj combined cycle power plant data from January 2019 to June 2019 is used to calculate the power plant performance indicator parameter during that period.

Table 7.1: The equations of the non-exergy cost parameters.

A) The non-exergoeconomic parameter

B) Exergy cost parameter and cost balance equation

Average cost per unit fuel for exergy (CF), average price of the product (CP), cost rate of exergy destruction (CD) and exergoeconomic factor (fk) for each of the components to be calculated for exergoeconomic evaluation. The following figures and 7.3 show the graphical representation of exergy destruction costs, capital investment costs and exergoeconomic factor (fk) for each plant component.

Table 7.12: Cost formation of different component of the plant.

Exergy destruction Cost

The exergoeconomic factor shown in Figure 7.3 varies depending on the capital investment cost and the cost rate of exergy destruction. The lower cost rate of exergy destruction in the part is the higher exergoeconomic factor. This shows that if the destruction cost of the part is low, the exergo-economic factor of the part is higher.

Exergoeconomic factor (f k )

Comparing with other research works

Furthermore, exergoeconomic analysis aims to predict the cost of exergy flows at different points in the plant, determine the cost of destroyed exergy and predict the cost of the final product. The total cost of exergy destruction of the selected gas turbine plants varies between $1178/hour to $6870/hour. FCCP unit has the lowest total cost of exergy destruction and DEL3 unit has the highest total cost of exergy destruction.

The lowest cost of exergy destruction in the combustion chamber occurs in the FCCP unit and the highest is the DEL3 unit. The lowest cost of energy destruction in the gas turbine occurs in the AES1 unit and the highest in the DEL3 unit. Exergy destruction cost is maximum found at Guddu 747 MW power plant located in Pakistan and exergy destruction cost minimum is found at FCCP.

The maximum exergoeconomic factor found in the gas turbine and the lowest exergoeconomic factor found in the combustion chamber.

Table 7.14 Cost of Exergy Destruction Rate in different power plants in simple cycle operation

Economic dispatch order according to economic evaluation

For the smooth operation of the national grid system, dispatch instruction is one of the important factors. The Directorate makes the economic dispatch list of System Industry of Bangladesh Power Development Board and the concerned authorities of GOB. In 2019, the fuel consumption was 1.61 Tk/kWh, and the position in the economic dispatch list is 31st throughout the year.

In that sense, the economic dispatch order list should be in a higher position, but due to deterioration in efficiency of gas turbine and the exergy destruction rate, the fuel consumption and the variable operation and maintenance costs are higher than the other power plants. However, if any fault occurs in any machine, it is quickly removed, and the machine is online in time: scheduled outage and Maintenance Outage took for the regular maintenance of the plant. There will be a major renovation will be carried out on 17 contract year of the plant.

During the significant overhaul period of 17 years of the life cycle, it is possible to overcome the leakage problem in the HRSG and the plant's other equipment.

Conclusion

Conclusions
Recommendations for Future Works

For the combined cycle, the highest exergy destruction occurs in the combustion chamber and the second highest component is the HRSG. By reducing the air-fuel ratio and further preheating the combustion air, the exergy destruction could be reduced in the combustion chamber. Comparison of Fenchuganj Combined Cycle Power Plant with other plants also represents that the combustion chamber is the highest exergy destruction component of the plant.

The heat energy loss in the combustion chamber decreases with an increase in air mass flow rate. This high improvement potential in the combustion chamber is due to the irreversibility of combustion and the large temperature difference between the air entering the combustion chamber and the flame temperature. Installing an additional air compressor before the gas turbine air compressor will increase the air flow to the combustion chamber and reduce the air compressor work in the gas turbine.

A preheater could be introduced before the combustion chamber to reduce the rate of exergy destruction in the combustion chamber.

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Nomenclature