The porous structure of bituminous coal chars and its influence on combustion and gasification under chemically controlled conditions

Bituminous chars with a strongly non-uniform porous structure have not been accounted for in existing pore models used to predict reactivity. A new ap proach has been developed to predict a particle structure parameter used in the random pore model. The reaction rate has been correlated with the carb on burn-off. Six bituminous coal chars were produced by pyrolysis in a pres surised drop tube furnace and their reaction rates were measured under vari ous conditions using a pressurised thermogravimetric analyser. The char mor phology and the porous structure of the char particles were obtained using image analysis. The porous structure of char particles was also characteris ed using mercury porosimetry. It is shown that after high-pressure pyrolysi s, most of the char panicles are of a high porosity, low: surface area and a non-uniform porous structure with a large central void surrounded by a th in shell which will influence apparent char reactivity and ash formation. i mage analysis also confirmed that the maceral composition of the coals and the pyrolysis pressure influence char morphology. A maximum reaction rate f or each char was observed at a carbon conversion of 10-20 wt% during both c har combustion and gasification. The particle structure parameters were pre dicted based on the measured porosity and surface area of macropores and mi cropores in the particle, and show reasonable agreement with those derived from experimental measurements, The predicted reaction rate agrees well wit h experimental measurements obtained under various conditions. (C) 2000 Els evier Science Ltd. All rights reserved.