Gas Fired Fluidized Beds

Abstract

Investigations, both experimental and theoretical, have been made of gas combustion in fluidized beds. A mathematical model has been developed which gives a qualitative estimation of the bed temperature profiles in the axial direction. The concept of Effective Thermal Conductivity is discussed, and bed conductivities are re-defined bearing in mind the contribution of particle recirculation. Experiments have been performed with particle sizes ranging from 0.6 mm to 1.4 mm diameter. Results are presented for the effect of particle size, bed height and throughput on the bed behaviour. Two distributor plates have been used: mild steel and refractory. Comparisons are made between the two. Stability of combustion has been studied, and two mechanisms have been observed by means of which a bed becomes unstable. Chemical analysis of the combustion products has shown that even with shallow beds (5 cm deep), CO emissions are very small with excess air levels of not less than five percent.