PROCESSES IN HIGHLY POROUS CHARS UNDER KINETICALLY CONTROLLED CONDITIONS .2. PORE REACTIVITY

Most existing models do not deal with the change in intrinsic reactivi ty during the evolution of the pore structure. The objective of the pr esent paper is to model the reactivity of the porous medium and to sho w the mutual influence of reactivity and pore structure. Based on a pa rallel study, a model for the change of the concentration of the activ e sites is developed. Coalescence of the microcrystals of the porous n etwork is considered as the cause for this change. After every coalesc ence event, the number of active sites is assumed to increase stepwise . The influence of the history of the microcrystals on the generation factor of active sites is taken into account. The changes of density o f the active sites located near the edges of microrods and at their ci rcumferential surface are considered independently. The model calculat ions show a monotonic increase of the intrinsic reaction rate during c onversion. The model successfully reconstructs the available experimen tal data on the consumption rates of highly porous chars.