Modelling of a pressurised entrained flow coal gasifier: the effect of reaction kinetics and char structure

Abstract

A model for a pressurised entrained flow coal gasifier is presented, with the effect of pressure, reaction kinetics and char structure on the gasification reactions being outlined. A sensitivity analysis to reaction kinetics and char structure was performed, and model predictions are compared with published atmospheric and high-pressure gasification data. It was found that both reaction kinetics and char structure are important in predicting coal gasification. The initial surface area may be more significant than intrinsic reactivity for bituminous coal chars. Low-pressure gasification kinetics (i.e. pressure order) cannot be extrapolated to high-pressure conditions. A significant difference in predicted carbon conversion was observed between various char structural models. It is suggested that the random pore model gives a reasonable prediction. Volatile matter has significant effect on carbon conversion due to the formation of high-surface area char particles. Increasing vitrinite content in coal correlates with increased carbon conversion. The model predictions show reasonable agreement with published experimental data on both atmospheric and high-pressure gasifiers in terms of carbon conversion and gaseous product composition. Comparisons with previous models and sensitivity analyses suggest that it is necessary to include the effect of char structure, and more sophisticated reaction kinetics than single order rates are required when modelling coal gasification.