Influence of forward scattering on prediction of temperature and radiation fields inside the pulverized coal furnace

Abstract

Radiation is dominant mode of heat transfer in all types of combustion systems. Radiative heat transfer is described by radiative transfer equation, which indicates the importance of radiative properties of medium. Increase of radiation intensity due to emission of radiation is directly proportional to absorption coefficient of medium, and to scattering coefficient due to inscattering. In-scattering of radiation depends also on scattering phase function. Radiative properties of dispersed phase of pulverized coal flame are mainly determined by flyash particles, particle diameter of which is in the range from 0,1 to 50,0 μm. For particles of that size and for near infrared spectral interval, scattering phase function of single particle changes its form from almost isotropic to almost forward. Sensitivity of numerical simulations of pulverized coal furnaces to type of radiation scattering is the main objective of investigation. Tangentially fired dry bottom pulverized coal furnace of 210 MWe boiler has been chosen for numerical simulations. Numerical simulations have solved chemically reacting two phase particle gas flow with radiative heat transfer. Radiative heat transfer has been modelled using six-flux model. Radiative properties have been determined for absorbing, emitting and scattering medium. Scattering coefficients of the six-flux model have been determined for forward and isotropic scattering phase function. Grid indipendent results of numerical simulations have been obtained. Numerical simulations have been verified by comparison with results of measurements. Sensitivity of numerical simulations to type of radiation scattering has been investigated through comparison of temperature field, total radiation fluxes field, field of incident wall fluxes and absorbed heat by furnace walls. Although it has been shown that absorbed heat by furnace walls is bigger in case of isotropic scattering, result of investigation has shown that numerical simulations are almost insensitive to type of radiation scattering.