99/00792 The effects of unburned carbon on radiative heat transfer in a pilot pulverized coal furnace-numerical investigation

Abstract

This paper investigates the possible effect of residue char on the radiative heat transfer in a pilot furnace. Firstly, a program is constructed to incorporate radiative properties of particles in solving the radiative heat transfer, based on a computer code for predicting turbulent gas-solid flow and combustion. The radiative properties of single unburnt char are modeled by coated sphere model of Mie theory, while the local Planck average radiative properties of particle could be obtained by a scheme based on Lagrangian approach with particle turbulent dispersion, and the radiative heat transfer is solved by Discrete Transfer method. Then, comparisons are made among predicted results for a pilot-scale pulverized coal furnace by several particulate radiative properties models. It shows even for the pilot-scale furnace, the effect of particle concentration is more important than that of distinguishing between particles of char and ash. The residue carbon in ash has a tendency to enhance the radiative heat transfer for this case. The optimized burn-off rate to separate ash from char is near 0.65.