Pressure and particle property impacts on radiation in oxy-coal combustion

Abstract A numerical study evaluating the significance of scattering phase function, particle size, particle distribution and pressure in an oxy-coal combustor was conducted. Particle absorption and scattering coefficients were calculated from particle properties and Mie theory. Mie theory was also used to identify appropriate scattering phase functions as a function of particle size. A strongly forward scattering function represented by a Henyey-Greenstein function was found to match scattering behavior for particle diameters greater than approximately 10 μm. A comparison of highly forward scattering based on two mono-sized particle distributions (15 µm and 119 µm) and a polydisperse size distribution (27.9 µm SMD) showed small particles produced peak incident wall heat fluxes 30–40% greater than large particles due to the increased number density with the smaller particles. The polydisperse distribution produced flux profiles similar but slightly higher than the 15 µm mono-sized particles. Although strongly forward scattering was found to best represent particle scattering for this system, data did suggest that phase function/scattering coefficient influence becomes more important with increasingly small particle size. Two particle distribution profiles (narrow and wide) were used to represent different coal flame profiles. A wide particle distribution across the combustor diameter produced higher incident wall heat fluxes than a narrow distribution limited to the center region of the combustor. Increased particle size decreased the effect of distribution. Incident wall heat flux was found to increase with increasing combustor pressure up to approximately 5 atm and 10 atm, respectively, for wide and narrow particle distributions. This was primarily due to increased particle absorption and scattering coefficients. Additional pressure increases beyond this up to 20 atm had minimal impact on wall fluxes due to saturated values of the particle absorption coefficient.