Heat transfer in a 4-MWth circulating fluidized bed furnace operated under oxy-fired and air-fired conditions: Modeling and measurements

Heat transfer to wall panels in the furnace of a circulating fluidized bed (CFB) was investigated by means of a mathematical model in combination with measurements obtained from a 4-MWth CFB unit operated under air and oxy-fuel firing conditions. The conditions at the wall panels corresponded to a concentration of solids in the range of 0.35-18 kg/m3 and temperatures of 1054-1168 K. The coefficient of heat transfer to the wall panels was similar for the oxy-fuel-fired and air-fired systems, since the solids flow, which plays a major role in heat transfer in CFB furnaces, was maintained at similar levels in the air- and oxy-fuel-fired cases. The modeled heat extraction of the furnace and the in-furnace vertical profiles of temperature and solids concentrations were found to be in good agreement with the corresponding experimentally measured values. The modeling results show that: (1) for all the cases studied, the share of radiation in the total heat extraction of the furnace exceeds 70% and increases with increases in furnace temperature; and (2) that gas radiation has little influence on furnace heat extraction.