The combustion of simulated waste particles in a fixed bed

Stable combustion of waste in an incinerator is necessary for optimal operation. However, complicated reactions, as well as heat and mass transfer, make understanding the process difficult. An experimental bed reactor is utilized to investigate the combustion of simulated waste particles, and a computational model is introduced to predict the phenomena. When the bed is brought into a radiating environment, an apparent flame zone is formed at the bed's top surface after a certain time delay. Subsequently, the flame front moves downwards into the bed of fuel. The flame propagation speed, i.e., the rate of progress of the apparent flame zone, is dependent on the air supply rate, the calorific value of the solid fuel, and the particle size. Based on the availability of oxygen, two distinct reaction modes are identified: the oxygen-limited mode and the reaction-limited mode. An increase in the flow rate of air eventually leads to flame extinction, as a result of excessive cooling by convection. The numerical results show good agreement with the experimental observations. The transient behavior of the local temperature and the rate of oxygen consumption are adequately reproduced. The effect of the combustion parameters on combustion in the bed is also discussed further. (C) 2000 by The Combustion Institute.