Investigation of particle radiation and its effect on NO prediction in a pilot-scale facility for both air and oxy-coal combustion

Radiation heat transfer plays an important role in pulverised coal combustion, influencing the overall combustion efficiency, pollutant formation and flame ignition and propagation. In this paper, the radiation properties of the particles as well as gas property models on the overall influence of the prediction of the formation of NOx pollutants in a pulverised coal combustion have been investigated. The non-grey weighted sum of grey gases (WSGG) model has been employed to calculate the radiation of the gas phase coupled with the radiation interaction from the particulate phase. The Mie theory, as well as constant or linear models, have been employed to describe the particle radiative properties. The prediction results, calculated from the data from a 250 kW pilot scale combustion test facility (CTF), are compared against experimental measurements under air-fired condition and a range of oxyfuel conditions. The results show that the choice of radiation solution can have a considerable impact on the radiative heat transfer results, in which the Mie theory shows a significant improvement in the incident wall heat flux compared to the constant or linear models. Also, the more accurate solution employed for radiation of gases and particles considerably improves the NOx prediction in the flame region.