Performance analysis of a fixed-bed biomass gasifier using high-temperature air

Gasification of biomass using high-temperature agents (air/steam) has been proven to have many features superior to those of conventional gasification using low-temperature agents. In this work, an experimental fixed-bed gasifier is utilized to investigate the gasification of biomass using high-temperature air up to 1473 K. A mathematical model has been formulated for the prediction of the main chemical and physical processes and is used to study the influence of temperature, oxygen concentration and flow rate of the feed gas. Predicted gas species concentration profiles and their maximum values are in reasonable agreements with the measurements. The results show that: (a) When the temperature of feed gas is increased, a higher gasification rate, a higher ignition front rate, and higher molar fractions of fuel gases (CO, H2 and CmHn), thus a higher LHV are obtained. (b) Increased oxygen concentration leads to higher peak values of the fuel gas concentrations, a higher gasification rate, and a larger ignition front rate. (c) Based on the air temperature, two distinct ignition modes are identified: the reaction-controlled and convective-controlled modes. (d) A critical air temperature exists, above which further preheating is no longer efficient if the purpose is to maximise the yield of gaseous products.