Effect of air flow rate and fuel moisture on the burning behaviours of biomass and simulated municipal solid wastes in packed beds

Combustion of biomass and municipal solid wastes is one of the key areas in the global cleaner energy strategy. But there is still a lack of detailed and systematically theoretical study on the packed bed burning of biomass and municipal solid wastes. The advantage of theoretical study lies in its ability to reveal features of the detailed structure of the burning process inside a solid bed, such as reaction zone thickness, combustion staging, rates of individual sub-processes, gas emission and char burning characteristics. These characteristics are hard to measure by conventional experimental techniques. In this paper, mathematical simulations as well as experiments have been carried out for the combustion of wood chips and the incineration of simulated municipal solid wastes in a bench-top stationary bed and the effects of primary air flow rate and moisture level in the fuel have been assessed over wide ranges. It is found that volatile release as well as char burning intensifies with an increase in the primary air flow until a critical point is reached where a further increase in the primary air results in slowing down of the combustion process; a higher primary airflow also reduces the char fraction burned in the final char-burning-only stage, shifts combustion in the bed to a more fuel-lean environment and reduces CO emission at the bed top; an increase in the moisture level in the fuel produces a higher flame front temperature in the bed at low primary air flow rates. (C) 2004 Elsevier Ltd. All rights reserved.