Modeling char combustion: The influence of parent coal petrography and pyrolysis pressure on the structure and intrinsic reactivity of its char

Abstract

Chars were made from four Australian coals of varying vitrinite content at pressures of 5, 10, and 15 atm. The morphology of the chars was correlated with the petrography of the parent coal. The intrinsic reaction rates of the chars at high pressures were measured, and no systematic effect of pyrolysis pressure or maceral concentration was found. It is concluded that observed variations in conversion rates under process conditions are likely to be due to char structural properties and not a result of variation in the intrinsic reactivity of the carbon in the chars. Consequently, this paper presents a char structural submodel that is integrated into an existing char combustion model to account for the combustion behavior of char particles of different morphologies. The char morphology used in the model was predicted using the developed correlation with parent coal petrography, so that a petrographic analysis as well as the proximate and ultimate analyses is required for model input. Validation of the model shows that chars produced at high pressure with a high percentage of cenospherical types burn more rapidly under process conditions than those at low pressure, with model predictions matching measurements. It is suggested that incorporating the char structural submodel into the existing char combustion model improves its predictability.