Design and Performance Evaluation of a Biomass Gasifier: Case Study of Coffee and Rice Husks
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About 36.1% of Kenya’s population lives below the poverty line. Low income has forced most of the Kenyans to opt for the cheapest available sources of energy. Biomass fuels are the most important source of energy in Kenya with wood-fuel (firewood and charcoal) accounting for over 68% of the total primary energy consumption. In spite of past efforts to promote substitutes for wood-fuel, the number of people relying on them is not decreasing. Consequently, it is projected that biomass will continue to be the main source of energy for the majority of the rural population and urban poor. Each year, over 2.8 million people in the world die prematurely from diseases caused by inhaling smoke from indoor fires due to incomplete combustion of biomass fuels in open fires and inefficient stoves. As a result of deforestation, biomass resources (fire wood and charcoal) are getting scarce. Waste products from agro-processing industries such as coffee husks, rice husks have been a major challenge in disposal. Biomass gasification is one of the few technologies that can potentially turn these wastes into energy for both industrial and domestic use. Although gasification has been around for more than 200 years, the technology is still new in Kenya. This study involved designing and developing a household-size biomass gasifier for the production of syngas using locally available biomass fuels namely; rice husks and coffee husks. Characterization of test fuels was based on their calorific value, percentage moisture content, volatile matter, ash content, fixed carbon, bulk density and porosity. Calorific value of rice husks and coffee husks was 15.9±0.8kJ/g and 18.1±0.8 kJ/g respectively. Bulk density of sampled rice husks and coffee husks was 127.4±1.2 kg/m3 and 218.0±1.6 kg/m3 respectively. Porosity of sampled rice husks and coffee husks was 87.4±0.9% and 71.9±0.6% respectively. Moisture content of sampled rice husks and coffee husks was 8.0±0.0% and 8.8±0.3% respectively. The percentage volatile matter of sampled rice husks and coffee husks was 62.8±0.3% and 78.4±0.0% respectively. The percentage ash content of sampled rice husks and coffee husks was 20.2±0.4% and 3.9±0.1 respectively. The percentage fixed carbon of sampled rice husks and coffee husks was 17.0±0.7% and 17.7±0.1% respectively. The maximum temperature obtained inside the gasifier reactor was mainly in the range 800°C to 1100°C. 1.5 liters of water at an average temperature of 24°C boiled in the stove within 4.7 to 8.5 minutes. Economic analysis of the gasifier found out that if a family shifts from LPG to using the constructed gasifier the payback period is 1.09 years, net benefit is Ksh45,000 (450USD) and rate of return on investment is 214.29%.