ABSTRACT

The design and thermal analysis of a small-scale municipal solid waste-fired steam boiler has been presented in this work. The analysis was based on the selected design parameters: operating steam pressure of 10 bar, with fuel consumption rate of 500 Kg/h and combustion chamber which utilizes mass burn incineration using waterwall furnace. The plant is designed as a possible option for thermal utilization of rural and urban wastes in Nigeria. The average daily generation of MSW was considered in order to assess the availability of the material. The data were collected from Enugu State Waste Management Authority (ENSWAMA).This was calculated based on the state population, urbanization and industrialization strengths. Calculation of calorific value of the waste to determine the heat contents was carried out using two methods: Bomb calorimeter and Dulong’s formula. Some samples of the garbage was analysed with bomb calorimeter in the National Centre For Energy Research & Development Laboratory, University Of Nigeria Nsukka. This is important because it a direct measure of the temperature requirements that the specific waste will place on the system. The calorific values obtained from this analysis were 12572.308 KJ/kg, 14012.05 KJ/kg, 21833.26 KJ/kg and 20551.01 KJ/kg for paper products, woods, plastics and textiles waste respectively, while the energy content obtained from the elemental composition of waste using Dulong’s formula was 15,101 KJ/kg .The maximum temperature of the furnace attained from the energy balance based on this value around the combustion chamber was 833.7 K and the amount of air required per kg of MSW was 8.66. Flue gas analysis was also carried out to determine the mass of dry flue gas used in the furnace. To reduce the moisture content of the waste, waste conditioner, connected to flue gas outlet was considered in this work. As this will increase the boiler efficiency by reducing fuel consumption rate in the furnace after preheating the waste. Draught analysis was also considered in order to force adequate air through the combustion chamber; to draw out the resulting hot flue gas from the combustion chamber and to vent the products of combustion to atmosphere after necessary heat recovery in the refuge conditioner through chimney. This was done by expressing the draught pressure in terms of mm of the water and determination of Chimney height and diameter. Finally, the control of atmospheric emission was also considered with the use of Scrubber and bag filter.

 

 

TABLE OF CONTENTS

TITLE PAGE…………………………………………………………………….……..…i

CERTIFICATION………………………………………………………………………..ii

DEDICATION……………………………………………………………………………iii

ACKNOWLEDGEMENT……………………………………..………………….………iv

ABSTRACT………………………………………………………………………..…….v

TABLE OF CONTENTS………………………………………………………….…….vi

LIST OF TABLES…………………………………………………………………..…..ix

LIST OF FIGURES………………………………………………………………..……xi

LIST OF SYMBOLS……………………………………………………………………xiii

CHAPTER ONE: INTRODUCTION…………………………………………………..1

• The need of the project………………………………………………….……………1

1.1 Discussion of the project plan………………………………………………………..3

• Application of the project…………………………………………………………….4
• Significance of the project plan………………………………………………………4
• Objectives of the present study………………………………………………………5

1.5 Scope of the work………………………………………………………………….…5

CHAPTER TWO: LITERATURE REVIEW……………………………………….……6

2.0 Historical background………………………………………………………………….6

2.1 Waste Generation, Disposal and Management in Nigeria………………………..….9

2.2 Waste classifications………………………………………………………………….11

2.3 Municipal solid waste (MSW)……………………………………………………….12

2.4 Incinerations……………………………………………………..…………………..13

2.4.1 Basic Types of incineration plants…………………………………….………….15

2.5 Air Pollution Control System…………………………………….………………..28

2.5.1 Dry scrubber………………………………………………….………………….28

2.5.2 Bag filterhouse…………………………………………………….…………….30

CHAPTER THREE: RESEARCH METHODOLGY…………………………………32

3.1 Estimation of the amount of waste generated in each state of the federation

to assess it availability…………………………………………………………….32

3.2 Combustion Analysis of municipal solid waste (MSW)……………………….…33

3.2.1 Calculation of Combustion air supply…………………………………………..36

3.2.2 Flue gas analysis…………………………………………………………………38

3.2.3 Calculation of flue gas specific heat capacity…………………………………..39

3.2.4. Flue gas specific exergy value……………………………………………….…42

3.2.5 Calculation of Calorific value of MSW…………………………………………43

3.3 Design of a mass burn incinerator with energy recovery,

making use of waterwall furnace…………………………..……………………..45

3.4 Waste Reception and Sorting……………………………………………………..46

3.5 Operation of the MSW Steam boiler………………………………………………47

3.6 Sizing Of An Incinerator………………………………………………………….59

3.6.1 Critical thickness of insulation for the boiler…………………..………………51

3.7 Selections Of Materials and operating pressure……….………..………………..52

3.8 Boiler Calculations……………………………………………………………….53

3.8.1 Maximum temperature of the furnace……………………………………..……53

3.8.2 Boiler Efficiency………………………………………………………….……..55

3.8.3 Equivalent Evaporation Of Boiler………………………….…………………… 55

3.8.4 Boiler Horse Power (BHP)…………………………………………….…………55

3.8.5 Furnace calculations………………………………………………….………….56

3.9 Heat Transfer Rate Equations………………………………………….………….56

3.10 Sizing of height and diameter of chimney………………………….…………….62

CHAPTRER FOUR: RESULTS AND DISCUSSION…………………………………..67

4.1 parameters for solution of the municipal solid waste-boiler design equations……67

4.2 Influence of various factors on combustion process………………………………69

4.2.1 Influence of moisture content……………………………………………………69

4.2.2 Influence of excess air…………………………………………………………..70

4.2.3 Influence of excess air on the moisture content of the waste……….…………..70

4.2.4 Analysis of elements responsible for energy losses……………………………..71

4.2.5 Influence of height of chimney above the fire grate in metres………………….71

4.2.6 Influence of specific heat capacity and specific exergy value

of flue gas on combustion……………………………………………………….72

CHAPTER FIVE: CONCLUSIONS AND RECOMMENDATIONS………………81

REFERENCES………………………………………………………………..……….85

APPENDICES………………………………………………………………..………89

APPENDIX A: EES FORMULATION OF THE MSW STEAM BOILER

DESIGN EQUATIONS……………………………….……….……89

APPENDIX B: MSW BOILER SPECIAL FEATURES……………………..…….91

 

 

CHAPTER ONE

INTRODUCTION

1.0 The need of the project    

A significant challenge confronting engineers and scientists in developing countries is the search for appropriate solution for the collection, treatment, and disposal or reuse of  domestic waste to produce energy. Although the energy needs have been met by the discovery of fossil fuel deposits, these deposits are limited in quantity; exploration and production costs to make them commercially available are high. Our energy needs have also grown exponentially, corresponding with human population growth and technological advancement.

        The global energy crisis in the 1970s driven by crude oil politics and global warming is an example reminding us of the need for resources conversation and the need to develop environmentally-friendly, cheaper and easily decentralisable sources of energy through Municipal Solid Waste.

Waste-to-energy facilities are part of the solution of the worldwide solid waste disposal problem. These facilities, when combined with recycling of critical material, composting, and landfilling, will be a long-term economic solution as long as they are designed and operated in an environmentally acceptable manner.

As a result of high carbon dioxide, emission from thermal energy conversion of fossil fuels which is one of the major causes of the greenhouse effect, boiler technologies based on biomass conversion represent a great potential to reduce emission since they are base on the utilization of renewal energy source.

Furthermore, since conventional energy sources are finite and fast depleting, and energy demands is in the increase, it is necessary for scientists and engineers to explore alternative energy sources, such as municipal solid waste (MSW). Biomass is abundantly available on the earth in the form of agricultural residues, city garbage, cattle dung, and normally, it is under utilized. For an efficient utilization of these resources, adequate design of municipal solid waste- fired steam boiler as shown in this work in order to extract heat produced in the combustion of waste is necessary, considering the high calorific value of MSW calculated and the availability of this material around us. The environmental benefits of biomass technologies are among its greatest assets. Global warming is gaining greater acceptance in the scientific community. There appears now to be a consensus among the world’s leading environmental scientists and informed individuals in the energy and environmental communities that there is a discernable human influence on the climate; and that there is a link between the concentration of carbon dioxide (one of the greenhouse gases) and the increase in global temperatures. Municipal Solid Waste when used can play an essential role in reducing greenhouse gases, thus reducing the impact on the atmosphere.

In addition, some of the fine particles emitted from MSW are beneficial. Bottom and fly ash are being mixed with sludge from brewery’s wastewater effluent treatment in a composting process, thus resulting in the production of a solid fertilizer. The possibility of selling the bottom and fly ash to the ceramics industry is also being considered, which increases the potentials of MSW fired steam boiler.

 

Indeed, this project if successful carried out, would meet all the millennium development Goal (MDGs) agenda and catalyses the affordable power supply in Nigeria.

 

 

1.1 Discussion of the project plan

Energy can be recovered from the organic fraction of waste (biodegradable as well as non-biodegradable) basically through two methods as follows (Energy recovery, 2008):

• Thermo-chemical conversion: This process entails thermal de-composition of organic matter to produce heat energy.
• Bio-chemical conversion: This process is based on enzymatic decomposition of organic matter by microbial action to produce methane gas or alcohol.

The Thermo-chemical conversion processes are useful for wastes containing high percentage of organic non-biodegradable matter and low moisture content. The main technological options under this category include Incineration and Pyrolysis/ Gasification.

         The bio-chemical conversion processes, on the other hand, are preferred for wastes having high percentage of organic bio-degradable (putrescible) matter and high level of moisture/ water content, which aids microbial activity. The main technological options under this category are Anaerobic Digestion, also referred to as Biomethanation.

This work is based on the first approach- thermal conversion of municipal solid waste using incineration Technology from which energy is released for generation of dry saturated steam; operating at pressure of 10 bar. The dry saturated steam is at the temperature that corresponds to the boiler pressure. The steam is not superheated, and does not contain moisture. The period of incineration is about 4 hours. Combustion inside the furnace is continuous. The waste is dried inside the waste conditioner (hopper) to remove the moisture content before it is transferred in the furnace. The mass-burn energy recovery system is used in order to avoid the need of pre-processing e.g. shredder, pre-trommel screen, secondary trommel screen, one stage of size reduction, and a magnetic separator as the key unit operations in refused derived fuel (RDF). Water wall/tubes arrangement is used to raise the required steam.

Finally, atmospheric emissions resulting primarily from the by-products of the combustion process (acidic gas, and particulates) are removed with scrubber and filter house before it exits into the atmosphere through chimney.

It is assumed that the municipal solid waste have not been left too long in the open place to avoid decay or being exposed to much rain.

1.2 Application of the project

The heat generated in the burning of this waste is used

• Directly for heating purposes;
• To produce steam for industrial purposes like driving equipment such as pumps and compressors.

1.3 Significance of the project

Economic factor: This project will directly contribute towards increasing job opportunities. Waste can now be sold by individuals to the boiler operators who make use of heat formed from it for steam generation.

Environmental: It will contributes significantly towards the mitigation of global climate change, local environmental sustainability, cost effectiveness and the sustainable use of natural resources (social issues).

Health:  In the reduction of total quantity of waste produced, thereby improving in the standard of living by reducing health hazards and environmental pollution.

 

 

1.4 Objectives of the present study

This project is based specifically on the design and thermal analysis of municipal solid waste steam boiler that will generate saturated steam for heating and industrial purposes using mass burn incineration technology incorporated with waterwall furnace.

1.5 Scope of the work

In this work, Type 1 waste classification has been used which consists of 25 percent of moisture content and 10 percent of incombustible solids, and has a heating value of 15119 kJ/kg as fired (N.T.Engineering, 2009).

The work covers the following:

(1) Assessment of quantity of waste available in the country;

(2) Determination of Physical and chemical characteristics (quality) of the waste used;

(3) Thermal analysis of MSW boiler;

(4) Designing a mass burn incinerator with energy recovery, making use of waterwall furnace; and

(5) Determination of the height and diameter of the chimney for adequate discharge of flue gases in the atmosphere.

ABSTRACT

The design and thermal analysis of a small-scale municipal solid waste-fired steam boiler has been presented in this work. The analysis was based on the selected design parameters: operating steam pressure of 10 bar, with fuel consumption rate of 500 Kg/h and combustion chamber which utilizes mass burn incineration using waterwall furnace. The plant is designed as a possible option for thermal utilization of rural and urban wastes in Nigeria. The average daily generation of MSW was considered in order to assess the availability of the material. The data were collected from Enugu State Waste Management Authority (ENSWAMA).This was calculated based on the state population, urbanization and industrialization strengths. Calculation of calorific value of the waste to determine the heat contents was carried out using two methods: Bomb calorimeter and Dulong’s formula. Some samples of the garbage was analysed with bomb calorimeter in the National Centre For Energy Research & Development Laboratory, University Of Nigeria Nsukka. This is important because it a direct measure of the temperature requirements that the specific waste will place on the system. The calorific values obtained from this analysis were 12572.308 KJ/kg, 14012.05 KJ/kg, 21833.26 KJ/kg and 20551.01 KJ/kg for paper products, woods, plastics and textiles waste respectively, while the energy content obtained from the elemental composition of waste using Dulong’s formula was 15,101 KJ/kg .The maximum temperature of the furnace attained from the energy balance based on this value around the combustion chamber was 833.7 K and the amount of air required per kg of MSW was 8.66. Flue gas analysis was also carried out to determine the mass of dry flue gas used in the furnace. To reduce the moisture content of the waste, waste conditioner, connected to flue gas outlet was considered in this work. As this will increase the boiler efficiency by reducing fuel consumption rate in the furnace after preheating the waste. Draught analysis was also considered in order to force adequate air through the combustion chamber; to draw out the resulting hot flue gas from the combustion chamber and to vent the products of combustion to atmosphere after necessary heat recovery in the refuge conditioner through chimney. This was done by expressing the draught pressure in terms of mm of the water and determination of Chimney height and diameter. Finally, the control of atmospheric emission was also considered with the use of Scrubber and bag filter.

 

 

TABLE OF CONTENTS

TITLE PAGE…………………………………………………………………….……..…i

CERTIFICATION………………………………………………………………………..ii

DEDICATION……………………………………………………………………………iii

ACKNOWLEDGEMENT……………………………………..………………….………iv

ABSTRACT………………………………………………………………………..…….v

TABLE OF CONTENTS………………………………………………………….…….vi

LIST OF TABLES…………………………………………………………………..…..ix

LIST OF FIGURES………………………………………………………………..……xi

LIST OF SYMBOLS……………………………………………………………………xiii

CHAPTER ONE: INTRODUCTION…………………………………………………..1

• The need of the project………………………………………………….……………1

1.1 Discussion of the project plan………………………………………………………..3

• Application of the project…………………………………………………………….4
• Significance of the project plan………………………………………………………4
• Objectives of the present study………………………………………………………5

1.5 Scope of the work………………………………………………………………….…5

CHAPTER TWO: LITERATURE REVIEW……………………………………….……6

2.0 Historical background………………………………………………………………….6

2.1 Waste Generation, Disposal and Management in Nigeria………………………..….9

2.2 Waste classifications………………………………………………………………….11

2.3 Municipal solid waste (MSW)……………………………………………………….12

2.4 Incinerations……………………………………………………..…………………..13

2.4.1 Basic Types of incineration plants…………………………………….………….15

2.5 Air Pollution Control System…………………………………….………………..28

2.5.1 Dry scrubber………………………………………………….………………….28

2.5.2 Bag filterhouse…………………………………………………….…………….30

CHAPTER THREE: RESEARCH METHODOLGY…………………………………32

3.1 Estimation of the amount of waste generated in each state of the federation

to assess it availability…………………………………………………………….32

3.2 Combustion Analysis of municipal solid waste (MSW)……………………….…33

3.2.1 Calculation of Combustion air supply…………………………………………..36

3.2.2 Flue gas analysis…………………………………………………………………38

3.2.3 Calculation of flue gas specific heat capacity…………………………………..39

3.2.4. Flue gas specific exergy value……………………………………………….…42

3.2.5 Calculation of Calorific value of MSW…………………………………………43

3.3 Design of a mass burn incinerator with energy recovery,

making use of waterwall furnace…………………………..……………………..45

3.4 Waste Reception and Sorting……………………………………………………..46

3.5 Operation of the MSW Steam boiler………………………………………………47

3.6 Sizing Of An Incinerator………………………………………………………….59

3.6.1 Critical thickness of insulation for the boiler…………………..………………51

3.7 Selections Of Materials and operating pressure……….………..………………..52

3.8 Boiler Calculations……………………………………………………………….53

3.8.1 Maximum temperature of the furnace……………………………………..……53

3.8.2 Boiler Efficiency………………………………………………………….……..55

3.8.3 Equivalent Evaporation Of Boiler………………………….…………………… 55

3.8.4 Boiler Horse Power (BHP)…………………………………………….…………55

3.8.5 Furnace calculations………………………………………………….………….56

3.9 Heat Transfer Rate Equations………………………………………….………….56

3.10 Sizing of height and diameter of chimney………………………….…………….62

CHAPTRER FOUR: RESULTS AND DISCUSSION…………………………………..67

4.1 parameters for solution of the municipal solid waste-boiler design equations……67

4.2 Influence of various factors on combustion process………………………………69

4.2.1 Influence of moisture content……………………………………………………69

4.2.2 Influence of excess air…………………………………………………………..70

4.2.3 Influence of excess air on the moisture content of the waste……….…………..70

4.2.4 Analysis of elements responsible for energy losses……………………………..71

4.2.5 Influence of height of chimney above the fire grate in metres………………….71

4.2.6 Influence of specific heat capacity and specific exergy value

of flue gas on combustion……………………………………………………….72

CHAPTER FIVE: CONCLUSIONS AND RECOMMENDATIONS………………81

REFERENCES………………………………………………………………..……….85

APPENDICES………………………………………………………………..………89

APPENDIX A: EES FORMULATION OF THE MSW STEAM BOILER

DESIGN EQUATIONS……………………………….……….……89

APPENDIX B: MSW BOILER SPECIAL FEATURES……………………..…….91

 

 

CHAPTER ONE

INTRODUCTION

1.0 The need of the project    

A significant challenge confronting engineers and scientists in developing countries is the search for appropriate solution for the collection, treatment, and disposal or reuse of  domestic waste to produce energy. Although the energy needs have been met by the discovery of fossil fuel deposits, these deposits are limited in quantity; exploration and production costs to make them commercially available are high. Our energy needs have also grown exponentially, corresponding with human population growth and technological advancement.

        The global energy crisis in the 1970s driven by crude oil politics and global warming is an example reminding us of the need for resources conversation and the need to develop environmentally-friendly, cheaper and easily decentralisable sources of energy through Municipal Solid Waste.

Waste-to-energy facilities are part of the solution of the worldwide solid waste disposal problem. These facilities, when combined with recycling of critical material, composting, and landfilling, will be a long-term economic solution as long as they are designed and operated in an environmentally acceptable manner.

As a result of high carbon dioxide, emission from thermal energy conversion of fossil fuels which is one of the major causes of the greenhouse effect, boiler technologies based on biomass conversion represent a great potential to reduce emission since they are base on the utilization of renewal energy source.

Furthermore, since conventional energy sources are finite and fast depleting, and energy demands is in the increase, it is necessary for scientists and engineers to explore alternative energy sources, such as municipal solid waste (MSW). Biomass is abundantly available on the earth in the form of agricultural residues, city garbage, cattle dung, and normally, it is under utilized. For an efficient utilization of these resources, adequate design of municipal solid waste- fired steam boiler as shown in this work in order to extract heat produced in the combustion of waste is necessary, considering the high calorific value of MSW calculated and the availability of this material around us. The environmental benefits of biomass technologies are among its greatest assets. Global warming is gaining greater acceptance in the scientific community. There appears now to be a consensus among the world’s leading environmental scientists and informed individuals in the energy and environmental communities that there is a discernable human influence on the climate; and that there is a link between the concentration of carbon dioxide (one of the greenhouse gases) and the increase in global temperatures. Municipal Solid Waste when used can play an essential role in reducing greenhouse gases, thus reducing the impact on the atmosphere.

In addition, some of the fine particles emitted from MSW are beneficial. Bottom and fly ash are being mixed with sludge from brewery’s wastewater effluent treatment in a composting process, thus resulting in the production of a solid fertilizer. The possibility of selling the bottom and fly ash to the ceramics industry is also being considered, which increases the potentials of MSW fired steam boiler.

 

Indeed, this project if successful carried out, would meet all the millennium development Goal (MDGs) agenda and catalyses the affordable power supply in Nigeria.

 

 

1.1 Discussion of the project plan

Energy can be recovered from the organic fraction of waste (biodegradable as well as non-biodegradable) basically through two methods as follows (Energy recovery, 2008):

• Thermo-chemical conversion: This process entails thermal de-composition of organic matter to produce heat energy.
• Bio-chemical conversion: This process is based on enzymatic decomposition of organic matter by microbial action to produce methane gas or alcohol.

The Thermo-chemical conversion processes are useful for wastes containing high percentage of organic non-biodegradable matter and low moisture content. The main technological options under this category include Incineration and Pyrolysis/ Gasification.

         The bio-chemical conversion processes, on the other hand, are preferred for wastes having high percentage of organic bio-degradable (putrescible) matter and high level of moisture/ water content, which aids microbial activity. The main technological options under this category are Anaerobic Digestion, also referred to as Biomethanation.

This work is based on the first approach- thermal conversion of municipal solid waste using incineration Technology from which energy is released for generation of dry saturated steam; operating at pressure of 10 bar. The dry saturated steam is at the temperature that corresponds to the boiler pressure. The steam is not superheated, and does not contain moisture. The period of incineration is about 4 hours. Combustion inside the furnace is continuous. The waste is dried inside the waste conditioner (hopper) to remove the moisture content before it is transferred in the furnace. The mass-burn energy recovery system is used in order to avoid the need of pre-processing e.g. shredder, pre-trommel screen, secondary trommel screen, one stage of size reduction, and a magnetic separator as the key unit operations in refused derived fuel (RDF). Water wall/tubes arrangement is used to raise the required steam.

Finally, atmospheric emissions resulting primarily from the by-products of the combustion process (acidic gas, and particulates) are removed with scrubber and filter house before it exits into the atmosphere through chimney.

It is assumed that the municipal solid waste have not been left too long in the open place to avoid decay or being exposed to much rain.

1.2 Application of the project

The heat generated in the burning of this waste is used

• Directly for heating purposes;
• To produce steam for industrial purposes like driving equipment such as pumps and compressors.

1.3 Significance of the project

Economic factor: This project will directly contribute towards increasing job opportunities. Waste can now be sold by individuals to the boiler operators who make use of heat formed from it for steam generation.

Environmental: It will contributes significantly towards the mitigation of global climate change, local environmental sustainability, cost effectiveness and the sustainable use of natural resources (social issues).

Health:  In the reduction of total quantity of waste produced, thereby improving in the standard of living by reducing health hazards and environmental pollution.

 

 

1.4 Objectives of the present study

This project is based specifically on the design and thermal analysis of municipal solid waste steam boiler that will generate saturated steam for heating and industrial purposes using mass burn incineration technology incorporated with waterwall furnace.

1.5 Scope of the work

In this work, Type 1 waste classification has been used which consists of 25 percent of moisture content and 10 percent of incombustible solids, and has a heating value of 15119 kJ/kg as fired (N.T.Engineering, 2009).

The work covers the following:

(1) Assessment of quantity of waste available in the country;

(2) Determination of Physical and chemical characteristics (quality) of the waste used;

(3) Thermal analysis of MSW boiler;

(4) Designing a mass burn incinerator with energy recovery, making use of waterwall furnace; and

(5) Determination of the height and diameter of the chimney for adequate discharge of flue gases in the atmosphere.

ABSTRACT

The design and thermal analysis of a small-scale municipal solid waste-fired steam boiler has been presented in this work. The analysis was based on the selected design parameters: operating steam pressure of 10 bar, with fuel consumption rate of 500 Kg/h and combustion chamber which utilizes mass burn incineration using waterwall furnace. The plant is designed as a possible option for thermal utilization of rural and urban wastes in Nigeria. The average daily generation of MSW was considered in order to assess the availability of the material. The data were collected from Enugu State Waste Management Authority (ENSWAMA).This was calculated based on the state population, urbanization and industrialization strengths. Calculation of calorific value of the waste to determine the heat contents was carried out using two methods: Bomb calorimeter and Dulong’s formula. Some samples of the garbage was analysed with bomb calorimeter in the National Centre For Energy Research & Development Laboratory, University Of Nigeria Nsukka. This is important because it a direct measure of the temperature requirements that the specific waste will place on the system. The calorific values obtained from this analysis were 12572.308 KJ/kg, 14012.05 KJ/kg, 21833.26 KJ/kg and 20551.01 KJ/kg for paper products, woods, plastics and textiles waste respectively, while the energy content obtained from the elemental composition of waste using Dulong’s formula was 15,101 KJ/kg .The maximum temperature of the furnace attained from the energy balance based on this value around the combustion chamber was 833.7 K and the amount of air required per kg of MSW was 8.66. Flue gas analysis was also carried out to determine the mass of dry flue gas used in the furnace. To reduce the moisture content of the waste, waste conditioner, connected to flue gas outlet was considered in this work. As this will increase the boiler efficiency by reducing fuel consumption rate in the furnace after preheating the waste. Draught analysis was also considered in order to force adequate air through the combustion chamber; to draw out the resulting hot flue gas from the combustion chamber and to vent the products of combustion to atmosphere after necessary heat recovery in the refuge conditioner through chimney. This was done by expressing the draught pressure in terms of mm of the water and determination of Chimney height and diameter. Finally, the control of atmospheric emission was also considered with the use of Scrubber and bag filter.

 

 

TABLE OF CONTENTS

TITLE PAGE…………………………………………………………………….……..…i

CERTIFICATION………………………………………………………………………..ii

DEDICATION……………………………………………………………………………iii

ACKNOWLEDGEMENT……………………………………..………………….………iv

ABSTRACT………………………………………………………………………..…….v

TABLE OF CONTENTS………………………………………………………….…….vi

LIST OF TABLES…………………………………………………………………..…..ix

LIST OF FIGURES………………………………………………………………..……xi

LIST OF SYMBOLS……………………………………………………………………xiii

CHAPTER ONE: INTRODUCTION…………………………………………………..1

• The need of the project………………………………………………….……………1

1.1 Discussion of the project plan………………………………………………………..3

• Application of the project…………………………………………………………….4
• Significance of the project plan………………………………………………………4
• Objectives of the present study………………………………………………………5

1.5 Scope of the work………………………………………………………………….…5

CHAPTER TWO: LITERATURE REVIEW……………………………………….……6

2.0 Historical background………………………………………………………………….6

2.1 Waste Generation, Disposal and Management in Nigeria………………………..….9

2.2 Waste classifications………………………………………………………………….11

2.3 Municipal solid waste (MSW)……………………………………………………….12

2.4 Incinerations……………………………………………………..…………………..13

2.4.1 Basic Types of incineration plants…………………………………….………….15

2.5 Air Pollution Control System…………………………………….………………..28

2.5.1 Dry scrubber………………………………………………….………………….28

2.5.2 Bag filterhouse…………………………………………………….…………….30

CHAPTER THREE: RESEARCH METHODOLGY…………………………………32

3.1 Estimation of the amount of waste generated in each state of the federation

to assess it availability…………………………………………………………….32

3.2 Combustion Analysis of municipal solid waste (MSW)……………………….…33

3.2.1 Calculation of Combustion air supply…………………………………………..36

3.2.2 Flue gas analysis…………………………………………………………………38

3.2.3 Calculation of flue gas specific heat capacity…………………………………..39

3.2.4. Flue gas specific exergy value……………………………………………….…42

3.2.5 Calculation of Calorific value of MSW…………………………………………43

3.3 Design of a mass burn incinerator with energy recovery,

making use of waterwall furnace…………………………..……………………..45

3.4 Waste Reception and Sorting……………………………………………………..46

3.5 Operation of the MSW Steam boiler………………………………………………47

3.6 Sizing Of An Incinerator………………………………………………………….59

3.6.1 Critical thickness of insulation for the boiler…………………..………………51

3.7 Selections Of Materials and operating pressure……….………..………………..52

3.8 Boiler Calculations……………………………………………………………….53

3.8.1 Maximum temperature of the furnace……………………………………..……53

3.8.2 Boiler Efficiency………………………………………………………….……..55

3.8.3 Equivalent Evaporation Of Boiler………………………….…………………… 55

3.8.4 Boiler Horse Power (BHP)…………………………………………….…………55

3.8.5 Furnace calculations………………………………………………….………….56

3.9 Heat Transfer Rate Equations………………………………………….………….56

3.10 Sizing of height and diameter of chimney………………………….…………….62

CHAPTRER FOUR: RESULTS AND DISCUSSION…………………………………..67

4.1 parameters for solution of the municipal solid waste-boiler design equations……67

4.2 Influence of various factors on combustion process………………………………69

4.2.1 Influence of moisture content……………………………………………………69

4.2.2 Influence of excess air…………………………………………………………..70

4.2.3 Influence of excess air on the moisture content of the waste……….…………..70

4.2.4 Analysis of elements responsible for energy losses……………………………..71

4.2.5 Influence of height of chimney above the fire grate in metres………………….71

4.2.6 Influence of specific heat capacity and specific exergy value

of flue gas on combustion……………………………………………………….72

CHAPTER FIVE: CONCLUSIONS AND RECOMMENDATIONS………………81

REFERENCES………………………………………………………………..……….85

APPENDICES………………………………………………………………..………89

APPENDIX A: EES FORMULATION OF THE MSW STEAM BOILER

DESIGN EQUATIONS……………………………….……….……89

APPENDIX B: MSW BOILER SPECIAL FEATURES……………………..…….91

 

 

CHAPTER ONE

INTRODUCTION

1.0 The need of the project    

A significant challenge confronting engineers and scientists in developing countries is the search for appropriate solution for the collection, treatment, and disposal or reuse of  domestic waste to produce energy. Although the energy needs have been met by the discovery of fossil fuel deposits, these deposits are limited in quantity; exploration and production costs to make them commercially available are high. Our energy needs have also grown exponentially, corresponding with human population growth and technological advancement.

        The global energy crisis in the 1970s driven by crude oil politics and global warming is an example reminding us of the need for resources conversation and the need to develop environmentally-friendly, cheaper and easily decentralisable sources of energy through Municipal Solid Waste.

Waste-to-energy facilities are part of the solution of the worldwide solid waste disposal problem. These facilities, when combined with recycling of critical material, composting, and landfilling, will be a long-term economic solution as long as they are designed and operated in an environmentally acceptable manner.

As a result of high carbon dioxide, emission from thermal energy conversion of fossil fuels which is one of the major causes of the greenhouse effect, boiler technologies based on biomass conversion represent a great potential to reduce emission since they are base on the utilization of renewal energy source.

Furthermore, since conventional energy sources are finite and fast depleting, and energy demands is in the increase, it is necessary for scientists and engineers to explore alternative energy sources, such as municipal solid waste (MSW). Biomass is abundantly available on the earth in the form of agricultural residues, city garbage, cattle dung, and normally, it is under utilized. For an efficient utilization of these resources, adequate design of municipal solid waste- fired steam boiler as shown in this work in order to extract heat produced in the combustion of waste is necessary, considering the high calorific value of MSW calculated and the availability of this material around us. The environmental benefits of biomass technologies are among its greatest assets. Global warming is gaining greater acceptance in the scientific community. There appears now to be a consensus among the world’s leading environmental scientists and informed individuals in the energy and environmental communities that there is a discernable human influence on the climate; and that there is a link between the concentration of carbon dioxide (one of the greenhouse gases) and the increase in global temperatures. Municipal Solid Waste when used can play an essential role in reducing greenhouse gases, thus reducing the impact on the atmosphere.

In addition, some of the fine particles emitted from MSW are beneficial. Bottom and fly ash are being mixed with sludge from brewery’s wastewater effluent treatment in a composting process, thus resulting in the production of a solid fertilizer. The possibility of selling the bottom and fly ash to the ceramics industry is also being considered, which increases the potentials of MSW fired steam boiler.

 

Indeed, this project if successful carried out, would meet all the millennium development Goal (MDGs) agenda and catalyses the affordable power supply in Nigeria.

 

 

1.1 Discussion of the project plan

Energy can be recovered from the organic fraction of waste (biodegradable as well as non-biodegradable) basically through two methods as follows (Energy recovery, 2008):

• Thermo-chemical conversion: This process entails thermal de-composition of organic matter to produce heat energy.
• Bio-chemical conversion: This process is based on enzymatic decomposition of organic matter by microbial action to produce methane gas or alcohol.

The Thermo-chemical conversion processes are useful for wastes containing high percentage of organic non-biodegradable matter and low moisture content. The main technological options under this category include Incineration and Pyrolysis/ Gasification.

         The bio-chemical conversion processes, on the other hand, are preferred for wastes having high percentage of organic bio-degradable (putrescible) matter and high level of moisture/ water content, which aids microbial activity. The main technological options under this category are Anaerobic Digestion, also referred to as Biomethanation.

This work is based on the first approach- thermal conversion of municipal solid waste using incineration Technology from which energy is released for generation of dry saturated steam; operating at pressure of 10 bar. The dry saturated steam is at the temperature that corresponds to the boiler pressure. The steam is not superheated, and does not contain moisture. The period of incineration is about 4 hours. Combustion inside the furnace is continuous. The waste is dried inside the waste conditioner (hopper) to remove the moisture content before it is transferred in the furnace. The mass-burn energy recovery system is used in order to avoid the need of pre-processing e.g. shredder, pre-trommel screen, secondary trommel screen, one stage of size reduction, and a magnetic separator as the key unit operations in refused derived fuel (RDF). Water wall/tubes arrangement is used to raise the required steam.

Finally, atmospheric emissions resulting primarily from the by-products of the combustion process (acidic gas, and particulates) are removed with scrubber and filter house before it exits into the atmosphere through chimney.

It is assumed that the municipal solid waste have not been left too long in the open place to avoid decay or being exposed to much rain.

1.2 Application of the project

The heat generated in the burning of this waste is used

• Directly for heating purposes;
• To produce steam for industrial purposes like driving equipment such as pumps and compressors.

1.3 Significance of the project

Economic factor: This project will directly contribute towards increasing job opportunities. Waste can now be sold by individuals to the boiler operators who make use of heat formed from it for steam generation.

Environmental: It will contributes significantly towards the mitigation of global climate change, local environmental sustainability, cost effectiveness and the sustainable use of natural resources (social issues).

Health:  In the reduction of total quantity of waste produced, thereby improving in the standard of living by reducing health hazards and environmental pollution.

 

 

1.4 Objectives of the present study

This project is based specifically on the design and thermal analysis of municipal solid waste steam boiler that will generate saturated steam for heating and industrial purposes using mass burn incineration technology incorporated with waterwall furnace.

1.5 Scope of the work

In this work, Type 1 waste classification has been used which consists of 25 percent of moisture content and 10 percent of incombustible solids, and has a heating value of 15119 kJ/kg as fired (N.T.Engineering, 2009).

The work covers the following:

(1) Assessment of quantity of waste available in the country;

(2) Determination of Physical and chemical characteristics (quality) of the waste used;

(3) Thermal analysis of MSW boiler;

(4) Designing a mass burn incinerator with energy recovery, making use of waterwall furnace; and

(5) Determination of the height and diameter of the chimney for adequate discharge of flue gases in the atmosphere.

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