DESIGN, CONSTRUCTION AND PERFORMANCE EVALUATION OF A BIOMASS FIRED OVEN

Project Abstract

<p>&nbsp;                 <b>ABSTRACT</b>&nbsp;</p><p>Baking and roasting are important cooking operations domestically and commercially carried out in bakeries, eateries and homes. It involves cooking with hot air as a result of heat and mass transfer processes. Baking and roasting of food items could be done using an oven. Therefore, this work is aimed at harnessing agricultural waste materials as heat sources in oven cooking and baking operations. The design, construction and performance evaluation of a biomass fired oven was undertaken. The oven consists of a baking chamber and a detachable combustion unit. The baking chamber and combustion unit were constructed using mild steel sheet of 4mm thickness with internal dimensions 50×50×35cm and 25×25×10cm respectively and with a total external dimensions measuring 56×55×61cm. The oven is insulated with fibre-glass material in order to prevent heat loss to the environment. The oven was evaluated using biomass- charcoal, rice husk and sawdust briquettes as heating materials in order to determine the efficiency of the oven. Other tests include determination of baking time, specific fuel consumption, temperature profile and impact assessment of the baking system on the environment. The result of the performance evaluation showed that the time taken for baking was lowest using charcoal at 75 minutes for cake and 30 minutes for bread, while rice husk and sawdust briquettes took 92 and 85 minutes, and 32 and 31 minutes for cake and bread respectively. The specific fuel consumption and thermal efficiency of the oven were also lowest with charcoal and highest with rice husk briquettes. The particulate matter (PM2.5), carbon monoxide (CO) and carbon dioxide (CO2) emissions were highest for rice husk briquettes and lowest for charcoal. It is recommended that the oven be made available for cooking and baking operations in bakeries, eateries and homes. Its availability will minimize dependence on electricity and environmental pollution caused by other cooking systems.<br></p>

Project Overview

<p> <b>1.0 INTRODUCTION</b></p><p><b>1.1 BACKGROUND OF THE STUDY&nbsp;&nbsp;</b></p><p>Up to 2.4 billion people (approximately 40% of the earth's population) depend on biomass (including wood, charcoal, crop residues, and animal dung) as their main source of energy (Saldiva and Miraglia, 2004). Biomass represents between 50% and 90% of primary energy consumption in developing countries, and 12% and 15% of global primary energy consumption (Wereko-Brobby and Hagen, 1996). According to Bhattacharya and Salam (2006), biomass is the fourth largest source of energy worldwide and provides basic energy requirements for cooking and heating of rural households in developing countries. Use of biomass fuels is also well established in certain commercial establishments and industries. In developed countries, biomass energy use is mainly for space heating and power generation. The biomass fuels could potentially provide a much more extensive energy service than at present if these were used efficiently. Besides efficiency improvements of existing energy systems, putting huge quantities of biomass, mostly in the form of agricultural residues and wastes, which are currently disposed by burning or dumping, could potentially increase the energy supply from biomass substantially. Significant additional increase in biomass energy supplies should be possible through energy plantation. <br></p><p> Many of the developing countries produce huge quantities of agro residues but they are used inefficiently causing extensive pollution to the environment. The major residues are rice husk, coffee husk, coir pith, jute sticks, bagasse, groundnut shells, mustard stalks and cotton stalks. Sawdust, a milling residue is also available in huge quantity (Grover and Mishra, 1996). <br></p><p> 1.1 <b>THE OVEN</b></p><p>An Oven is equipment used in carrying out baking or roasting processes. It involves the use of dry heat to cook food. In an oven, heat is supplied to the surface of the food by a combination of infrared radiation from the oven walls, by convection from circulating air and by conduction through the pan or tray on which the food is placed (Fellows, 2000). Baking and roasting are essentially the same unit operation in food preparation. They both involve the use of heated air in the process to achieve the desired result. Baking and roasting as terminologies however differs in common usage. While baking is usually applied to flour-based foods such as cakes, bread, biscuits, roasting is attributed to raw foods such as meats, yam, fish, corn etc. Both processes alter the eating qualities of the food products and also can be used as a preservation process, by destruction of microorganisms and reduction of the water activity at the surface of the food. <br></p><p> Ovens are classified according to the mode of heating as direct and indirect heating. In directly heated ovens, air and the products of combustion are re-circulated by natural convection or by assisted convection (fans). The temperature in the oven is controlled automatically, by adjustment of air and fuel flow rates to the burners. Natural gas is commonly used in directly heated ovens, but propane, butane, fuel oil or solid fuels could also be used. In indirectly heated ovens, Steam tubes are either heated directly by burning fuel or supplied with steam from a remote boiler. The steam tubes then heat air in the baking chamber. Heated air is commonly re-circulated through the baking chamber and through a separate heat exchanger. Alternatively, combustion gases are passed through banks of radiator tubes in the baking chamber, or fuel is burned between a double wall and the combustion products are exhausted from the top of the oven. Electric ovens are heated by induction heating radiator plates or bars. In batch ovens, the walls and base are heated whereas in continuous ovens, heaters are located above, alongside and below a conveyor.<br></p><p> <b>1.2 PROBLEM STATEMENT&nbsp;</b></p><p>Conventional ovens which are usually powered by natural gas or electricity can be very expensive. This in turn discourages baking and roasting for domestic purposes because it becomes more economical to buy already baked foods such as bread and roasted foods like fish. Commercially, this high cost of fuels could also result to increased cost of production which eventually leads to baked foods being more expensive than it should be. In Nigeria where shortage of power supply is a big challenge, this also poses a problem to those that bake with electricity because if power should go off during the time of baking, this affects the quality of the baked foods. Ability to gauge the quantity of gas in a cylinder has also been identified as a problem during baking. This is because the quantity of gas in a cylinder cannot be known unless one has experience with it. This is a problem because one might be baking only for the gas to run out midway of the baking process and thereby causing disruption.&nbsp;</p><p>As regards roasting, in Nigeria, roasting is usually done in the open fires. Foods such as yam, plantain, corn, fish, meat, etc. are usually exposed to open fire during roasting process. This process exposes the food items to a lot of contaminants in the ambient environment. Additionally, roasting process does not utilize energy efficiently. A lot of heat energy is lost to the surroundings because there is no form of insulation and the top is usually open to the atmosphere. Environmentally, deforestation has been a global challenge. The rate at which wood is used is very alarming especially for combustion purposes.&nbsp;</p><p>Also, agricultural wastes constitute a nuisance in the environment. The likes of rice husks, corn cobs, palm kernel shells etc are becoming more difficult to dispose off. The wastes when utilized as fuels in oven could solve the problems of heating fuel in oven and environmental cleanliness at the same time. .&nbsp;</p><p>1.3 <b>OBJECTIVE&nbsp;</b></p><p>The major objective of this study is to harness biomass waste materials for use as a source of heat energy in oven baking and roasting operations. The specific objectives of the study includes:&nbsp;</p><p>· To design and construct a Biomass Fired Oven&nbsp;</p><p>· To evaluate the performance of the oven using biomass wastes as heating fuels. ·</p><p>&nbsp;To compare the performance of the oven using different solid fuels.&nbsp;</p><p>1.4&nbsp;<b>JUSTIFICATION&nbsp;</b></p><p>Baking and roasting are very important unit operation in food processing. It is an operation that takes place everyday especially by commercial vendors. It is important that the process is as affordable as possible. This work is aimed at cutting down the cost of fuels required in baking and roasting operations and also to reduce the dependence on electricity as much as possible. The study is considered to be environmentally friendly in that it is focused majorly at utilizing agricultural wastes such as rice husks and saw dust thereby reducing the amount of wastes littering the environment and at the same time using them to produce energy. In terms of acceptable hygiene, roasting is a process that lacks a lot of hygiene in Nigeria today. The food product being roasted is exposed to a lot of contaminants from the surroundings. The study is aimed at curbing the amount of contaminants roasted foods are exposed to, so as to prevent any form of diseases associated with it. In the same light, the study addressed the energy efficient issue because a lot of energy is known to be lost to the surroundings when roasting is conducted under open fire.<br></p><p> 1.5 <b>SCOPE OF STUDY</b>.</p><p>&nbsp;The study is limited to the design, construction and performance evaluation of a biomass heated oven. Three fuels were used to test the oven which includes charcoal, rice husk briquette and sawdust briquette. The performance evaluation of the oven was by baking. The foods that are baked were cake and bread. <br></p>