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

Artikel i vetenskaplig tidskrift, 2015

Heat transfer to wall panels in the furnace of a circulating fluidized bed (CFB) is investigated by means of a 1.5-dimensional mathematical model together with measurements from a 4-MWth CFB unit under air and oxy-fuel conditions. The conditions at the wall panels correspond to solids concentration between 0.35 and 18 kg/m3 and temperatures between 1054 and 1168 K. The heat transfer coefficient to the wall panels is similar in oxy-fuel and air-firing due to that the solids flow, which plays the main role in CFB furnace heat transfer, was kept similar in air and oxyfuel conditions. The modeled furnace heat extraction and in-furnace vertical profiles of temperature and solids concentration show generally good agreement with the corresponding measured values. Modeling results show that for all cases studied, the share of radiation in the total furnace heat extraction exceeds 70% and increases with the increase in furnace temperature. Modeling results also show that gas radiation has a small influence on furnace heat extraction.