In this study, effect of particle c

In this study, effect of particle concentration distribution on radiative heat transfer in circulating fluidizedbed combustors (CFBCs) is investigated. The aim is to identify how important it is to include axial and radialvariations of particle concentration along the splash and dilute zones in radiative heat transfer calculationsand to determine the predictive accuracy of simple 0D and 1D approximations for particle concentrationdistribution in the riser by benchmarking their predictions against a semi-empiric 2D axisymmetric modeldeveloped for a wide range of operating conditions and systems. Input data required for the radiationmodel are provided from measurements carried out in a 150 kWt cylindrical Circulating Fluidized BedCombustor (CFBC) test rig burning low calorific value Turkish lignite with high volatile matter/fixed carbon(VM/FC) ratio in its own ash. Radiative transfer equation (RTE) is solved for 2-D axisymmetric cylindricalenclosure which contains gray, absorbing, emitting gas mixture with gray, absorbing, emitting, anisotropically scattering particles bounded by diffuse, gray/black walls. Incident heat fluxes and source terms alongthe riser are predicted by the Method of Lines (MOL) solution of Discrete Ordinates Method (DOM) withLeckner’s correlations for combustion gases, geometric optics approximation for particles and normalizedHenyey-Greenstein for the phase function. Comparisons reveal that 0D and 1D representations of particleconcentration distribution lead to overprediction of incident heat fluxes in both splash and dilute zones,where discrepancy of 0D model is larger. Similarly, errors in source term predictions introduced by simplifying the particle concentration distribution via deploying 0D and 1D models are found to be significantlylarge. These findings indicate that rigorous evaluation of particle concentration distribution is essential foraccurate prediction of radiative heat transfer in CFBCs despite its high CPU requirements.
2017 Published by Elsevier Ltd.