The oxidative reactivity of coal chars in relation to their structure

During the oxidation of porous coal chars the internal surface area can increase as a function of the degree of conversion due to pore growth and the opening up of sealed internal pores or cavities. Consequently, rate expressions for their oxidation are more accurately described in terms of the intrinsic reactivity, where differences in surface area and porosity can be taken into account. The oxidative reactivity of coal chars is complicated by a number of different factors, which are explored in this paper. These include (i) the development of the pore structure during devolatilisation of the coal, (ii) the ash content, its distribution in the carbon matrix and effect on reactivity, (iii) the extent of the H and N functional groups present in the solid matrix, and their interrelation with residual volatile species which are present, (iv) the extent of the graphitic nature of the carbon surface and (v) the active surface area available for reaction. (C) 1999 Elsevier Science Ltd. All rights reserved.