Gasification kinetics of coal chars in carbon dioxide

Abstract

Five chars were prepared at 1273 K from coals of different rank. The chars were gasified in a thermobalance to total conversion in carbon dioxide in the temperature range 1143–1559 K and flow rate of 50 cm3 min−1. Using the shrinking spherical ashless particle model of gasification, activation energies and frequency factors were evaluated. Optical microscopy indicated that the three chars of lowest rank were isotropic, one char was anisotropic and the fifth had the basic anisotropy of the parent anthracite. Although at 1273 K values of the first-order rate constant for the surface reaction, ks, decreased from 0.13 to 0.0090 cm s−1 with increasing rank of parent coal, activation energies only varied between 175 and 195 kJ mol−1. Frequency factors, kso, decreased with decreasing rate from 3.0 × 106 to 2.5 × 105 cm s−1.