A kinetic study of coal reject-derived char activation with CO2, H2O, and air

Abstract

Activation reactions of coal reject-derived char (CRC) with CO2, H2O, and air are experimentally studied using a TGA technique. The experimental kinetic data are treated via kinetic data unification based on the half-time, and the intrinsic rate constants are extracted by the modified Arrhenius plot method. The effect of structural evolution on the overall rate changes is modelled with a modified random pore model and percolation model taking into account the ash content of the coal reject char. It is found that the relative reaction rates for the reaction pairs CO2-CRC, H2O-CRC and air-CRC are at an increasing order of sequence at a given temperature. The effect of gaseous pressure on the reaction rate is shown to be significant for CO2-CRC and H2O-CRC reactions. It has shown that both models can predict well the maximum rate and the conversion at which the maximum rate occurs. The agreement between the data and model predictions are generally good for H2O-CRC and CO2-CRC reactions, but not satisfactory for air oxidation. The model fitting also showed that the percolation model, taking into account the closed pore evolution, predicts the initial rate better than the modified random pore model. © 1991.