On gas and particle radiation in pulverized fuel combustion furnaces

Abstract

Radiation is the principal mode of heat transfer in a combustor. This paper presents a refined weighted sum of gray gases model for computational fluid dynamics modelling of conventional air–fuel combustion, which has greater accuracy and completeness than the existing gaseous radiative property models. This paper also presents new conversion-dependent models for particle emissivity and scattering factor, instead of various constant values in literature. The impacts of the refined or new models are demonstrated via computational fluid dynamics simulation of a pulverized coal-fired utility boiler. Although the refined gaseous radiative property model shows great advantages in gaseous fuel combustion modelling, its impacts are largely compromised in pulverized solid fuel combustion, in which particle-radiation interaction plays the dominant role in radiation heat transfer due to high particle loading. Use of conversion-dependent particle emissivity and scattering factor will not only change the particle heating and reaction history, but also alter the radiation intensity and thus temperature profiles in the furnace. For radiation modelling in pulverized fuel combustion, the priority needs to be placed on particle radiation and a proper description of particle emissivity and scattering factor is required. The refined gaseous radiative property model is still recommended for use in generic combustion modelling because of its inherent potential in improving the results, even though its advantages may be compromised by particle radiation in some cases. The gas and particle radiation modelling method and the conclusions presented in this paper are also applied to oxy-fuel combustion of pulverized fuels.