Thermal radiation at high-temperature and high-pressure conditions: Comparison of models for design and scale-up of entrained flow gasification processes

Thermal radiation is an important sub-process in high-pressure entrained flow gasification. However, it was seldom investigated in previous CFD studies and was usually accounted for by common radiation and simplified gas radiation property models. Therefore, this study performed comparative one-dimensional radiation and two-dimensional CFD simulations with respect to the bioliq Entrained Flow Gasifier (bioliq EFG). The one-dimensional radiation simulations were applied to compare the effects of advanced and simplified gas radiation property models for atmospheric and high-pressure entrained flow gasification conditions, while the CFD simulations were carried out to investigate the performance of simplified gas radiation property models incorporated within the CFD model of the bioliq EFG. The segmental heat removal from the cooling screen of the bioliq EFG was applied as experimental basis for comparison with the numerical predictions. Based on the comparisons, this study provides recommendations for the selection of gas radiation property models for CFD simulations with the discrete ordinates model and with focus on entrained flow gasification. In case of largely isothermal and homogeneous conditions with exemption of the flame zone, weighted-sum-of-grey-gas models can be used with the discrete ordinates model if user-defined weighted-sum-of-grey-gas models (i) are obtained from accurate line-by-line calculations, (ii) are based on conditions prevailing in the reactor and (iii) are incorporated using the band approach. In absence of such weighted-sum-of-grey-gas models, full-spectrum correlated-k distribution models based on the latest tabulations can be used instead for CFD simulations of entrained flow gasification processes. In addition to that, sensitivity analyses showed that a coarse discretisation of the radiative transfer equation within the boundary layer, inaccurate gas species concentrations in the boundary layer (within a ±5% margin) and the P-1 approximation can be accepted for high-pressure conditions while soot radiation becomes important at soot volume fractions above 10−6 and should be accounted for if such conditions are expected.