Fluidised bed gasification and pyrolysis of woodchips.

The work presented in this thesis includes experimental investigation using a basic fluidised bed to gasify woodchips and cold modelling studies to improve the fluid bed reactor dynamics incorporating bed internals, such as draft tubes and jets. Low grade fuel gas was produced from woodchips as feedstock, in a 154 mm i/d fluidised bed as the main experimental part of the project using air as the gasifying medium. The influence of a number of process variables on the gasification process were studied including fuel feedrates, temperatures and bed heights, with respect to their effects on quality and quantity of the fuel gas produced. It was found that fuel gas of about 6 MJ/Nm3 can be obtained with temperatures in excess of 700 °c and with fuel feedrates in excess of 3.5 times stoichiometric. The process also benefitted from increasing the static bed heights of the fluidised bed, which was due to the better separation of the combustion and gasification zones. The cold modelling studies coducted using a 2-D glass model employing a draft tube a nd jet system, and using a novel photographic technique produced more realistic data. This showed that both the systems in question produced induced recirculation rates which can be controlled by the process variables such as bed height, bed and jet velocities. Further studies employing these systems for biomass conversion should prove that a better fuel gas quality and quantity can be achieved. In addition a variety of feedstocks can be utilised using the same reactor configuration.