OPERATION OF PACKED BED DOWNDRAFT BIOMASS GASIFIER WITH DIFFERENT AIR SUPPLY ARRANGEMENTS
Biomass is one of the renewable energy resources and it can be utilized through different routes for deriving energy. One such method is called thermo-chemical gasification, in which the solid biomass is converted to a gaseous fuel called producer gas in a reactor known as gasifier. In the present work, certain process parameters associated with the operation of a packed bed downdraft biomass gasifier fed with wood pieces were experimentally investigated for two cases of air supply arrangements. In the first case, the substoichiometric air required for gasification of biomass was supplied from top of the bed. In the second case, the air was supplied directly into the bed at mid height. During experiments on the first case, it was observed that the upper boundary of high temperature oxidation zone always had a tendency to propagate upwards from lower level to upper level through the biomass bed. The rate of propagation or propagation velocity was determined. It was found to depend on several factors like (a) air flow rate, (b) biomass bed height, (c) heat loss and (d) proximate analysis of biomass. During experiments on the second case, the temperature
distribution in the biomass bed remained steady; the gasifier
surface temperatures were lesser and the calorific value of
producer gas was also higher.