Experimental investigation on the changes in bed properties of a downdraft biomass gasifier

Abstract

Biomass gasifiers of fixed bed, downdraft type are generally used for driving internal combustion engines. As part of research work, a versatile, throat type, biomass gasifier was developed. The gasifier had facilities for bed temperature measurements, pressure measurements, physical observation, sampling of bed particles, bed agitation, etc. The generated producer gas was cleaned and cooled in downstream components namely, cyclone separator, dust filter and gas cooler such that water had no direct contact with producer gas. The dry cleaned producer gas was flared directly at the exit pipe. Bed temperatures and bed char properties viz., weight, volume, density and volatile matter content along the gasifier axis, wood feeding rate, gasification air and producer gas flow rates, etc. were observed and analyzed during the gasification of wood pieces. Temperature stratification was found to depend on biomass bed height, phase of operation, location of reaction zones and reactor pressure. Specific gasification rate for wood pieces was found to be 75 kg h-1 m-2 which was lesser than that for loose bioresidues. Mass balance was also done for the gasification system. The producer gas to wood ratio was determined to be 2.39 at an optimum equivalence ratio of 0.3. The volume of wood piece or char decreased by as high as 86% even before it enters the reduction zone of the gasifier.

International Journal of Engineering, Science and Technology, Vol. 2, No. 6, 2010, pp. 98-106