Optimisation Of A Thermal Power Plant Using Heat Recovery

ABSTRACT

Thermal power plants present a problem of significant water consumption, carbon dioxide emissions, and environmental pollution. Several techniques have been developed to utilize flue gas, which can help solve these problems. Among these, the ones focusing on energy extraction beyond the dew point of the moisture present within the flue gas are quite attractive. In this study, a novel waste heat recovery system (WHRS) composed of an organic Rankine cycle (ORC) and cooling cycles using singular working fluid accompanied by phase change was proposed and optimized for maximum power output. Furthermore, WHRS configurations were analyzed for fixed water yield and fixed ambient temperature, covering possible trade-off scenarios between power loss and the number of stages as per desired yields of water recovery at ambient temperatures in a practical range. For a 600 MW power plant with 16% water vapor volume in flue gas at 150 ◦C, the WHRS can produce 4–6 MWe while recovering 50% water by cooling the flue gas to 40 ◦C at an ambient temperature of 20 ◦C. Pragmatic results and design flexibility, while utilizing single working fluid, makes this proposed system a desirable candidate for practical application.

Keywords: waste heat recovery; thermal power plant; flue gas; optimization of power plant

TABLE OF CONTENTS

TITLE PAGE

APPROVAL PAGE

DEDICATION

ACKNOWLEDGEMENT

ABSTRACT

TABLE OF CONTENT

CHAPTER ONE

1.0      INTRODUCTION

1.1      BACKGROUND OF THE PROJECT

1.2      PROBLEM STATEMENT

1.3      AIM AND OBJECTIVES OF THE PROJECT

1.4      SIGNIFICANCE OF THE PROJECT

CHAPTER TWO

2.0      LITERATURE REVIEW

2.1      REVIEW OF THE STUDY

2.2      DISCOVERY OF THERMAL POWER PLANT

2.3      REVIEW OF RELATED STUDIES

CHAPTER THREE

• METHOD

3.1            THERMAL DESIGN DEMAND
3.2            HRSG TEMPERATURE PROFILE, PINCH POINT AND APPROACH POINT
3.3            NECESSITY OF USING FINNED TUBES
3.4            THERMAL DESIGN SIMULATION OF THE HRSG SECTIONS

3.5            CONSTRAINTS IN THE THERMAL DESIGN OF HRSGS

3.6            CONSTRAINTS

CHAPTER FOUR

4.0      RESULT

4.1      INPUT DATA

4.2      HRSG OPTIMIZATION

CHAPTER FIVE

5.0      CONCLUSION AND RECOMMENDATION

5.1      CONCLUSION

5.2      RECOMMENDATION

REFERENCES

CHAPTER ONE

1.0                                                             INTRODUCTION

1.1                                               BACKGROUND OF THE STUDY

Power plants that utilize fossil fuels, such as coal, pose fuel consumption problems, ultimately resulting in higher CO₂ emissions, significant water consumption and hazardous gas emissions. Utilization of waste heat recovery from the flue gas of power plants leads to its condensation and can be a simultaneous solution for the problems mentioned above.

Many studies are being conducted to find ways to utilize flue gas to reduce carbon footprints; these include employing it in the synthesis of methane and ammonia (Castellani et al., 2018), as well as investigations focusing on waste heat recovery and utilization. Some studies focus on the reuse of exhaust gases for co-generation (García et al., 2019) and the use of this energy for pre-drying in coal power plants, which increases the thermal efficiency of the system by approximately 2% (Liu et al., 2016).

Currently, fossil-fuel-based power plants consume vast quantities of water for heat rejection, fuel preparation, power augmentation, emission control, and cycle makeup purposes. At the same time, global water resources are becoming more difficult to procure as water consumption exceeds renewal (Liu et al., 2016). Cooling systems are the most water-intensive portion of the thermoelectric generation process, presenting significant opportunities to reduce withdrawal and consumptive use of fresh water. Reuse of impaired water for cooling can reduce freshwater withdrawal and decrease water contamination as well as withdrawal-related impacts on aquatic life and the environment (Zhang et al., 2017). With the increasing trend of waste heat recovery technologies for fossil-fueled power plants, the need for water recovery from flue gas is also being seriously considered. There is a need to reduce the amount of fresh water needed for cooling purposes to enable power plant operation in more arid regions (Zhang et al., 2017).

The objective of this study is to optimize a waste heat recovery system, comprised of an organic Rankine cycle (ORC), for power generation, with the integration of pumped heat pipe cooling and vapor compression cycle cooling, utilizing a single working fluid to perform heat extraction for power output and water recovery. Also, the characteristics of the proposed system for different yields of water and ambient temperature conditions were investigated. Condensed water and flue gas should be further treated for proper utilization as previously mentioned but are not covered in the context of this study.

1.2                                                     PROBLEM STATEMENT

Coal is a very important fossil fuel. It is abundant and widely distributed in geography, but the coal utilization is related to environmental issues. In Gambia, coal-fired power is one of the means of power production sources. As a result of this, it is important therefore, better energy efficiency in coal-fired power plant is demanded. Due to the more and more stringent requirements of energy conservation and emissions reduction, there is a growing concern over the efficiency increase of coal-fired power plants. The largest heat loss in a boiler is in the exhaust flue gas, which greatly affects the thermal efficiency. It is widely accepted that 1% of the coal can be saved if the flue gas temperature is reduced by 12~15℃ [2]. One of the methods of achieving this is by heat recovery method.

1.3                                                    AIM AND OBJECTIVES OF THE STUDY

The main aim of this work is to carry out a study on a thermal power plant optimization using heat recovery in national water and electricity company, Gambia. The objectives of the study are:

1. To improve efficiency of the thermal power plant.
2. To provide a means of solving environmental issues of thermal power plant.

• To develop a model for the system analysis.

1.4                                                    SIGNIFICANCE OF THE STUDY

Thermal power plant optimization therefore is important for power plants to improve its power generation capacity drastically by reducing the failure rate. This study will help the system by decreasing the shutdown period of the plant and an increase in the system availability as well as the power of the system.