G. Liu et al., The porous structure of bituminous coal chars and its influence on combustion and gasification under chemically controlled conditions, FUEL, 79(6), 2000, pp. 617-626
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.