Modeling Thermal Radiation With Focus on Particle Radiation in Grate Fired Furnaces Combusting MSW or Biomass: A Parametric Study

This parametric study shows that thermal radiation from particles, fly ash and char, can be highly relevant for estimating the radiative heat flux to surfaces in grate fired furnaces, especially to the hot bed. The large effects of particle radiative heat transfer come from cases with municipal solid waste (MSW) as fuel whereas biomass cases have moderate effect on the overall:radiative heat transfer. The parameters investigated in the study were the fuel parameters, representing a variety of particle loads and size distributions, emissivities of walls and bed, and the size of furnace. The investigations were conducted in a 3-D rectangular environment with a fixed temperature field, and homogeneous distribution of gases and particles. The choice of boundary emissivity was found to be much more or equally important as the particle radiation effects, dependent if biomass or MSW, respectively, was used as the fuel. The effect of particle radiation increased with increasing furnace size, mostly evident in the change of the radiative source term and the heat flux to the bed. Compared to previous studies of particle radiation in grate fired combustion, this study used realistic particle mass size distributions for fly ash. Estimates of char mass size distributions inside the furnace were conducted and used.