An Adaptive Random Pore Model for Multimodal Pore Structure Evolution with Application to Char Gasification

An extension of the random pore model has been developed that allows different pore sizes to grow at different rates, depending on the instantaneous pore-scale reactant penetration at a given location within a reacting porous particle. This is accomplished by incorporating pore scale effectiveness factors, consistent with the random pore geometry, into equations for the growth of each individual pore size. This framework allows the evolution of the char structure with local conversion to adapt to changes in boundary conditions (reactants, temperature) and the development of intraparticle gradients, rather than being, predetermined by the initial pore structure (i.e., by the value of the random pore model structural parameter, psi). This framework also facilitates the calculation of intrinsic kinetic parameters from experimental measurements by providing an estimation of the fraction of the total surface area participating in a given reaction. Without using any fitting parameters, the model has been found to satisfactorily reproduce some coal char oxidation experiments from the literature. The model has also been applied to two cases of practical interest for char particle gasification: zone II reaction conditions and reactants that change over the course of conversion. In these casts, the results of the adaptive random pore model differ from those predicted by the original random pore model.