Unification of gasification kinetics of char in CO2 at elevated temperatures with a modified random pore model

The gasification of a char has, so far, been mainly studied at low temperatures and low heating rates, using thermogravimetric analysis. Studies on the gasification of a char in CO2 at elevated temperatures and high heating rates are necessary to develop integrated coal gasification combined-cycle (IGCC) technology. Coal gasification is a very complicated phenomenon, which makes a generalized understanding and description of gasification reactivity of a char very important. Using a unique fluidized bed, the reactivity of a char pyrolyzed at elevated temperatures and high heating rates was investigated. A generalized expression of the gasification reactivity of a char under various conditions was approached with a modified random pore model proposed in this work. It was clarified that a shrinking core model was not appropriate to describe char gasification in CO2, On the basis of our results and those in the literature, it was identified that the char reactivity could be unified with a master curve not only for chars pyrolyzed at low temperatures and low heating rates, but also for chars pyrolyzed at high temperatures and high heating rates. This master curve was independent of coal type, temperature, and the pyrolysis conditions under which a char was derived, despite the fact that these factors had complicated influences on the reaction rates. Our model can also predict the data in the literature very well. The model proposed in this work gave better predictions than the random pore model, up to high carbon conversions. It was recommended as a submodel for the comprehensive simulation of coal gasifiers.