OPTIMAZATION OF EQUIVALENCE RATIO FOR DIFFERENT BIOMASS MIXTURE IN THE OPEN TOP DOWN DRAFT GASIFIER

Abstract

The aim of this study is to find out the Optimize Equivalence Ratio of biomass mixture with an open top down draft gasifier in order to improve the gasification processes & to make it commercially viable on different type of available biomass not just only woody biomass but also agro residues like rice husk briquette. A single reactor design handles all the bio-residues. While most gasifier designs are intended to operate with wood chips, the current design is aimed at handling agro-residues that are light, fine sized and with varying ash content. The reactor design replaces the grate by a screw for extracting ash and residual carbon. The problems of handling fine biomass and low melting ash created by the presence of alkalis in the biomass are overcome by briquetting the fine Bioresidue to solid pieces of high density and low moisture content. An open downdraft gasifier of 35kg/hr was consider to find the effect of equivalent ratio (Actual air fuel ratio to Stoichimetric air fuel ratio: ER) on the specific gas production, the heating value of gas produced and the cold gas efficiency using four combination of biomass viz 100% woody biomass, 100% rice husk briquettes, mixes of 70% wood & 30% rice husk briquettes & 50% wood & 50% rice husk briquettes. Six trials were carried out for each mixture by varying the supply air flow to change the ER. The gas samples were tested for their compositions under steady state operating conditions. Using mass balances for C and N, the cold gas efficiencies, calorific values and the specific gas production rates were determined. The results showed that with all types of biomass mixes the calorific value of gas reduced with the increase of ER. The cold gas efficiency reduced with ER in a similar trend for all the mixes. The specific gas production increased with ER. Only with 100% rice husk because of its high ash content Low heat value observed & the Equivalence ratio observed is more than 0.5 which showed the process approached towards Combustion instead gasification & the formation of clinker takes place result in poor gas quality because of the high ash fusion temperature of ash. Though if the rice husk blend with other biomass in such a way that the effective bulk density & the corresponding ash content should not exceed more than 750kg/cu.m & 10-12%, then the equivalence ratio close to 0.36 is observed but with the very frequent removal of ash based on the percentage of mixture from the char extraction system.