Modeling of the Pore Structure Evolution in Porous Char Particles During Combustion

摘要

The pore structure in char particles changes greatly during combustion, which significantly affects the char combustion characteristics. This article describes a model for the evolution of the char pore structure. A fractal pore model is used to generate the porous char particles to simulate the char combustion for various porosities, theta, specific surface areas, S-g, fractal dimensions, D-f, and particle diameters, d(p). Then, expressions are given to associate these pore structure parameters with the char conversion, X, and the operating conditions, using a modulus, chi, indicating the pore diffusion resistance. As X increases, theta increases, D-f and d(p) decrease, and S-g increases to a maximum first and then decreases. In some cases, S-g only decreases with increasing X when the reaction rates are too high or the conditions are such that the O-2 cannot diffuse into the particle. The results compare well with the pore structure parameters of three Chinese chars combusted in a drop tube furnace at different conversions measured by a mercury porosimeter.