Counter-current preheated air and steam gasification of wood char

Gasification converts biomass to H₂ and CO rich product gas using air, oxygen and/or steam as reaction agents. In this work, the gasification of char was investigated in a laboratory scale counter-current fixed bed gasifier with preheated air and steam as the gasifying agent. Lump wood charcoal was used as the fuel and the reactor bed was maintained at temperatures of 750-960°C 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 spatial temperature, gas composition and mass conversion were measured for various steam and air flow rates and 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 high gasifier operating temperature was observed to have a positive effect on the tar cracking. The product yield was found to be sensitive to the steam/air ratio, feed flow rates, reactor temperature and 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.