Evaluation of char reaction rate in a fluidised bed gasifier: from reactivity determination to reactor simulation

Paper in proceeding, 2009

This work analyses how to use char reactivities determined in the laboratory to predict carbon conversion in large-scale fluidised-bed gasifiers (FBG). It is shown how the char reactivity is determined in the laboratory to obtain kinetic expressions for FBG simulation, i.e. at high temperature and heating rates. A simple model is used to predict the char gasification rate in an FBG. It is shown that in most practical situations the average reactivity of char in the bed differs substantially from the reactivity calculated with the average conversion, leading to inaccuracies in predicting the carbon conversion in an FBG. Therefore, the distribution of conversion has to be addressed for proper prediction. The importance of accounting for the distribution of conversion is demonstrated in an example, where the char conversion in an industrial FBG is predicted.