Numerical modelling of a fixed bed updraft long stick wood gasifier

Abstract

A computational model to evaluate the anticipated performance characteristics of an updraft fixed bed gasifier utilizing long stick wood as the source of fuel is presented. This type of gasifier obtains high-energy release rates due to the lower inlet air velocity and extended reaction zone. The numerical model couples the performance of the individual particles and the external gas phase reactions to describe the gasifier performance. By calculating the performance of individual particles, the computational model is able to determine the interaction between the combustion of charcoal particles in the lower portion of the bed and the pyrolysis of wood sticks in the upper region. Most importantly, the model can describe the effect on overall system performance when conditions within the gasifier are changed, such as changes in the wood or char particle size, moisture content, gasifier height, inlet velocity, etc. The results of the model are compared with the gasifier performance for a gasifier using sticks with a 6 cm diameter, a length of 68 cm and a dry density of 600 kg m−3. The model results are used to investigate the performance of the gasifier under a variety of load conditions, fuel sizes, and moisture conditions.