An enhanced model of particle radiation properties in high ash gas-particle dispersion flow through industrial gas-to-steam heat exchangers

Abstract

Ash particle radiation typically contributes considerably to the total heat absorbed by steam heat exchangers found in pulverized fuel-fired energy systems. As particle concentrations increase due to higher ash content in the parent fuel, radiation scattering should be considered. Furthermore, the relative size of the particles compared to thermal radiation wavelengths also affects the emission, absorption and scattering characteristics. This study presents a refined particle diameter-dependent emissivity and scattering factor model for computational fluid dynamics modelling of heat exchangers located in boilers firing high ash fuels. To demonstrate the impact of the newly proposed model a case study reheater located in an actual boiler, firing high-ash fuel, was studied. The results of the particle radiation property model were also compared to models typically found in the relevant literature. The results show that the new model predicts lower radiation emission when compared to the models reported in literature. This was shown not to be due to increased radiation losses (absorption and scattering) but rather due to reduced particle emission, which in turn is due to the particle diameter-emissivity dependence. The results were also compared to real plant measurements at three different boiler load cases and showed good agreement between calculated and measured steam temperatures.