Assessment of weighted-sum-of-gray-gases models for gas-ash particle mixture in ash deposition

The deposition layer formed by combustion products on the heat exchange surface reduces the operation efficiency. It is an urgent problem that needs to be solved to reduce unnecessary energy consumption. The comprehensive gas-ash particle dynamic deposition model developed by different radiation models is evaluated, and the radiation characteristics of gas and particles and the effects on deposition are revealed. The radiation transfer equation is solved by the discrete ordinate model, and the coupling of sub-models in the deposition model CFD framework is realized by user defined functions. Different forms of the weighted-sum-of-gray-gases model are integrated into the verified deposition model. In addition, the influence of operation conditions including absorbing gas content, pressure, temperature, and wall emissivity on the non-gray radiation characteristics of the gas is analyzed, and the contribution of particle radiation to the overall radiation at different volume fractions is considered. The results show that under oxy-fuel conditions, the growth amplitude of radiation source term gradually decreases with the increase of gas concentration because the sensitivity of radiation capacity to concentration is weakened at high concentrations. Pressure and temperature affect the radiation characteristics and spectral radiation intensity of the gas respectively, and the latter is more drastic than the former. In addition, with the increase of particle volume fraction, particle radiation dominates the overall radiation. Among the radiation models considered in the dynamic deposition model, the gas mixture model/particle gray model and gray gas model/particle non-gray model perform well. The results can provide practical guidance for the optimization of thermal equipment operation and soot-blowing schemes.