Radiative Properties of Residual Char and Its Effects on Radiative Heat Transfer in Pulverized Coal Fired Furnaces

Abstract

AbstractThis paper gives a comprehensive modelling analysis of the radiative properties of residual char and its effect on radiative heat transfer in pulverised coal furnaces. Firstly, the effective optical constant is introduced into the model of the radiative properties of unburned char. Three structure models of unburned char are considered, i.e. constant diameter model, shrinking core model, and a transient model. The result shows that regardless of the structure of residual char, the absorption in the initial stage of combustion of large char particles (D>10μm) does not decrease, while a sharp decrease occurs near the burnout (B>0.9). Then radiative property models of particles were incorporated into a CFD code to investigate its effect on overall radiative heat transfer in pulverized coal furnaces. The numerical results of a 300 MW tangentially fired furnace show that residual char shields radiative heat transfer along the radial direction in the upper zone of the furnace, and thus the temperature at the exit of the furnace is higher. By ignoring the additional absorption of residual char, it will lead to a lower predicted radiant heat flux to the area of platen superheater