(476b) Updraft Counter-Current Fixed Bed Gasification of Wood Char

Gasification converts biomass into H₂ and CO rich product gas by using air, oxygen and/or steam as reaction agent. The gasification of char was investigated using a laboratory scale counter-current fixed bed gasifier with preheated air and steam. Lump wood charcoal was used as the fuel and the reactor bed was maintained at temperatures of 750-960ºC by external heaters. The design of this gasifier is part of a two stage integrated unit that aims ultimately at utilizing biomass fuel such as wood chips or biomass pellets. The high operating temperature of the gasifier was seen to have a positive effect on the thermal tar cracking. The spatial temperature, gas composition and mass conversion were measured for various steam and air flow rates and the key results on the equivalence ratio, heating value of product gases and carbon conversion rates were evaluated. H₂ (17-28 vol%), CO (5-11 vol%) and CO₂ (18-21 vol%) formed a major portion of the product gas. The hydrogen yield was found to be sensitive to the steam/air ratio, feed flow rates, reactor temperature and particle size. The production of synthesis gas was influenced by the air to steam ratio and the total reactant flow rate. By supplying more air in the oxidation zone, the production of hydrogen and carbon monoxide decreased as combustion occurred in the bed. The addition of excess steam led to a lower bed temperature and resulted in a decrease of synthesis gas production. The minimum bed height to which the gasification showed a decrease in yield was 2.5-3.5 times the fuel particle size. The experimental work was coupled with the chemical equilibrium calculation and detailed mathematical modelling to further understand the equilibrium composition, conversion rates and temperature profile.