Process analysis and gasification of rice husk by using downdraft fixed bed gasifier

The use of fossil fuels has great impact on environment and energy security problems. Besides, the rising cost of fuel oil compelled the industry to search for alternative fuels, and biomass in general and rice husks in particular are considered a suitable candidate. Bio energy has significant potential contribution for sustainable energy systems, especially when converted to modern energy carriers such as electricity, gaseous or liquid fuels. Rice is cultivated in more than 75 countries in the world. The rice husk is the outer cover of the rice and on average it accounts for 20% of the paddy produced, on weight basis. The worldwide annual husk is about 80 million tons with an annual energy potential of 1.2∼10⁹ GJ corresponding to a heating value of 15 MJ/kg. Maximum rice husk produced by milling process of rice mills in Bangladesh usually burned in the mill boilers to produce process heat for parboiling of paddy rice and excess husk are sold to the market as fuel for cooking purposes and a considerable portion is misused. Therefore, syngas from rice husk can be produced as an auspicious source of energy. It can be used to generate heat and power like natural gas, synthesize other chemicals and liquid fuels, or produce H₂. One of the promising approaches for syngas production from biomass is downdraft fixed bed gasification among the several approaches till developed. Optimization of operating conditions (combustion zone temperature, reaction zone temperature, intake air temperature, humidity of intake air and air flow rate) can give a satisfactory result for the quality syngas production. In this paper rice husk was used as potential biomass feed stocks. The moisture content of the feed material is less than 10% on weight basis and consumption rate of rice husk is 3.62 kg/h. Temperature inside the reaction zone (970∼994) K, primary air flow rate 2.7 m³/h, humidity of outside air (45∼50%) and exit temperature of the producer gas (140∼160)°C were measured. This paper gives an optimistic operating condition for quality syngas production.