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

Most existing models do not deal with the change in intrinsic reactivity during the evolution of the pore structure. The objective of the present paper is to model the reactivity of the porous medium and to show the mutual influence of reactivity and pore structure. Based on a parallel study, a model for the change of the concentration of the active sites is developed. Coalescence of the microcrystals of the porous network is considered as the cause for this change. After every coalescence 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 of the active sites located near the edges of microrods and at their circumferential surface are considered independently. The model calculations show a monotonic increase of the intrinsic reaction rate during conversion. The model successfully reconstructs the available experimental data on the consumption rates of highly porous chars.