Design And Construction Of An Improved Wood Stove

ABSTRACT

The design and construction of an improved wood stove is undertaken in this work. The design improvement of the stove focused on the following areas: provision of insulation around the combustion chamber to reduce conduction heat loss across the walls of the chamber, incorporation of smoke rings at the top of the stove, provision of sizable and adjustable air inlet to ensure the availability of sufficient air for the complete combustion of the fuel wood, and the incorporation of chimney to convey flue gases away from the place of use. Performance test results show that the wood stove has a maximum thermal efficiency of 64.4% and power delivery of 2.52kW, but a minimum specific fuel consumption of 0.447. This indicates a better performance when compared to the average thermal efficiency value of 17.9% for traditional mud stove as reported by George (1997), or the Kilakala stove which has a fuel saving capacity of 30% (Crewe 1990, Otiti 1991). The performance is also better when compared to the Improved Vented Mud stove (IVM) which has the average thermal efficiency values across fuels that vary from 10% to 23% which is comparable with the range of 10.8% to 19.6% reported by Pal and Joshi (1989). On smokiness, it was observed that virtually all the flue gases were conveyed out of the test area through the chimney.

TABLE OF CONTENT

COVER PAGE

APPROVAL PAGE

DEDICATION

ACKNOWLEDGEMENT

TABLE OF CONTENT

• INTRODUCTION
• STATEMENT OF THE PROBLEM
• AIM OF THE STUDY
• ADVANTAGES OF THE STUDY
• SCOPE OF THE STUDY
• DEFINITION OF TERMS

CHAPTER TWO

2.0     LITERATURE REVIW

2.1     OVERVIEW OF WOOD-BURNING STOVE

2.2     OPERATION OF WOOD-BURNING STOVE

2.3       FIREWOOD : HARDWOOD OR SOFTWOOD

2.4     REVIEW OF STOVE MODELS

2.5     SAFETY AND POLLUTION CONSIDERATIONS

2.6     DESCRIPTION OF THE COOKSTOVES

CHAPTER THREE

3.0     DESIGN DESCRIPTION, ANALYSIS AND CALCULATION
3.1     DESIGN DESCRIPTION
3.2     DESIGN ANALYSIS AND CALCULATIONS

CHAPTER FOUR

4.0     RESULT

4.1     PERFORMANCE TESTING OF THE BIOMASS STOVE

4.2     TEST RESULTS FOR BOILING AND SIMMERING OF WATER

4.3     ANALYSIS OF TEST RESULTS

4.4     DISCUSSION OF RESULTS

CHAPTER FIVE

5.1     CONCLUSION

5.2     REFERENCES

CHAPTER ONE

1.0                                          INTRODUCTION

1.1                            BACKGROUND OF THE STUDY

Several sources indicate that wood is the most widely used domestic fuel. Hall et al. (1982) reported that about half of the world’s population cooks with biomass fuel for all or some of their meals. The dependence on fuel wood by the rural dwellers of most developing countries including Nigeria is estimated at about 100%, while the annual consumption of fuel wood in Nigerian is estimated at about 70 million cubic meters. FAO has estimated that about two million people around the world use wood stove for their domestic cooking and for keeping their surroundings warm. The large preference for wood as fuel is predicated upon the fact that apart from wood and coal the other primary non-renewable sources of energy such as petroleum, natural gas and liquefied natural gas are no longer easy to come-by in terms of cost and availability. The lifetime for these other alternatives is estimated to range from 15 years for natural gas to nearly 300 years for coal (Yawas 2003). The demand for fuel wood will, therefore, continue to increase in response to the cost and availability factors stated above. This will in turn also continue to elicit innovations and improvements in the design of wood-burning stoves.

The development of wood-burning stove is not a recent development, several improvement works have been done on the stove design. Apart from the economic and environmental considerations, the other main issue which motivates the various developmental efforts of the wood stove is the health factor (Joseph et al. 1990, Karekezi 1992). The Kilakala stove, a mud stove built using locally available materials and developed at the Sokoine University, Tanzania, has a fuel saving capacity of 30% (Crewe 1990, Otiti 1991). One of the major disadvantages of the stove was that it did not provide sufficient illumination (Otiti 1991). The Kenya Ceramic Jiko (KCJ), one of the most successful urban stove projects in the Eastern African region, which is disseminated throughout Kenya (Kammen and Fayemi Kammen 1992) is reported to have a useful heat of about 25-40 % of the heat generated, which represents a significant increase from an open fire that directs only about 5-10% of the heat generated from the fire to the cooking pot. The Improved Vented Mud stove (IVM), a two-pot stove with chimney, also called the Nada Chula, developed in India has the average thermal efficiency values across fuels that varies from 10 to 23.5% which is comparable with the range of 10 to 19.6% reported by Pal and Joshi (1989). The version of (IVM), made of ceramic lining with mud coating and called the Improved Vented Ceramic (IVC), has higher efficiencies for all fuels except crop residues. George (1997) found the thermal efficiency of the traditional mud (TM) stove, which is a simple U-shaped heavy stove for a single pot made with locally available clay and coated with cow-dung clay mixture, to average 17.9%. The Angethi stove used for charcoal and char briquettes and fabricated with galvanized iron bucket, mud/concrete, and grate has a thermal efficiency of 17.5%, which is comparable with that (15.3%) quoted by Wazir (1981). However, in these various developmental efforts, the level of achievement of some of the objectives still leaves a lot of room for improvement.

1.2                                   PROBLEM STATEMENT

Although charcoal is believed to be an affordable, available, and the most convenient fuel source for households, its use in inefficient stoves would produce significant amounts of indoor air pollution and make it unsustainable. Therefore, continual technology development will suppress charcoal’s detriments and enhance its efficient utilisation while reducing significantly environmental impact.

1.3                                       AIM OF THE STUDY

This work therefore aims at developing a more efficient and safe charcoal burning stove that can reduce fuel consumption rates and indoor air pollution.

1.4                             ADVANTAGES OF THE STUDY

This work seeks improvement on the existing designs by making the following design considerations: enhancing the combustion process by providing for means of introducing sufficient air for combustion, further reducing the amount of heat loss from the combustion chamber by insulating with fiber glass, reducing the amount of heat loss by radiation by a careful design of the pot seat, and reducing the level of pollution of the kitchen environment with smoke emissions by the design of the pot seat and by incorporating a chimney.

1.5                                  SCOPE OF THE PROJECT

This paper deals with the development of a charcoal stove prototype from locally available materials including granite rock, stainless steel, and the glass wool. It describes the design features, thermodynamic performance, and thermophysical properties of the granite rock used in thermal-energy storage (TES) system fabrication. According to previous studies on thermophysical properties of granite rock, a suitable TES system should have high values of thermal conductivity, specific heat capacity, material density, and low values of porosity. High thermal storage efficiencies are as a result of high values of thermal conductivity, specific heat capacity, and density. High density and specific heat capacity values lead to a large volumetric heat capacity hence permitting compact storage in the systems, whereas low values of porosity indicate large bulk density and uniaxial compressive strength.

1.6                                   DEFINITION OF TERMS

Boundary layer—The very thin layer of slow moving air immediately adjacent to a pot surface; insulates the pot from hot flue gases and diminishes the amount of heat that enters the pot.

Charcoal—The black, porous material that contains mostly carbon that is produced by burning of wood or other biomass.

Convection—The heat transfer in a gas or liquid by movement of the air or water.

Combustion chamber—The region of the stove where the fuel is burned.

Combustion efficiency—The percentage of the fuel’s heat energy that is released during combustion. Combustion efficiency refers to the amount of the energy from the biomass that is turned into heat energy.

Draft—The movement of air through a stove and up a chimney.

Emissions—The byproducts from the combustion process that are discharged into the air.

Excess air—The amount of air used in excess of the amount for complete combustion.

Firepower—The rate of fuel consumption, usually in kg-fuel per hour.

Flue Gas—The hot gases that flow from the combustion chamber and out the chimney (if a chimney is present).

Fuel efficiency—The percentage of the fuel’s heat energy that is utilized to heat food or water.

Grate—A framework of bars or mesh used to hold fuel or food in a stove, furnace, or fireplace.

Haybox—A relatively airtight insulated enclosure that maintains the temperature of the pot enabling food to be cooked to completion after the pot is removed from the stove.

Heat transfer efficiency—The percentage of heat released from combustion that enters a pot.

High mass stove—A stove made of uninsulated earth, clay, cast iron, or other heavy material that requires significant energy to be warmed during stove operation.

High power—A mode of stove operation where the objective is to boil water as quickly as possible; the highest power at which a stove can operate.

Low power—A mode of stove operation where the objective is to simmer the water or food product; the lowest power at which a stove can operate and still maintain a flame and simmer food.

Pot skirt—A tube, usually made of sheet steel, that surrounds a pot creating a narrow space so that more of the heat in the flue gases enter the pot.

Retained heat—Heat energy that warms the enclosures around the fire that does not escape to the surroundings; can be used for space heating.

Water Boiling Test (WBT)—A test used to measure the overall performance of a cookstove. There are several versions of the water boiling test. In general the test consists of three phases. These are: (1) bringing water to a boil from a cold start; (2) bringing water to a boil when the stove is hot; and, (3) maintaining the water at simmering temperatures.

1.7                                   PROJECT ORGANISATION

The work is organized as follows: chapter one discuses the introductory part of the work, chapter two presents the literature review of the study, chapter three describes the methods applied, chapter four discusses the results of the work, chapter five summarizes the research outcomes and the recommendations.