Studying on char combustion characteristics in fly-ash for circulating fluidized bed boilers

A mathematical model of single char particle combustion in circulating fluidized bed (CFB) boiler is developed in this paper. Its numerical solution in operating conditions of CFB boiler verifies the nature of a phenomenon that the distribution of carbon content of char particles in fly-ash has a peak value versus their diameters. The results show that the temperature of the fine char particle is close to the bed temperature, and there also exists a peak value for the burn-out time of char particles versus their diameters. The countermeasures are presented to improve combustion of char particles, such as uses of the fly-ash recirculation and the hot cyclone.