Evolution of pore structure during gas-solid reactions: Discrete models

Abstract Discrete numerical models were developed to describe pore structure transformations in gas-solid reacting systems. Computational grids with up to 16 million cells are employed to simulate random phenomena. Regions of various phases are defined and allowed to grow or interact according to rules modeling gas-solid reactions. This approach accurately tracks the loss of surface area due to pore overlap and transient profiles of porosities and surface areas can be obtained as functions of conversion. These models were used to simulate the noncatalytic gasification of coal chars containing ash and having unimodal, bimodal and trimodal pore size distributions. Simulation results of diffusional limitations in the micropores were used to interpret experimentally observed behavior of microporous chars under different reactive atmospheres. Model predictions for combustion with strong diffusional limitations indicate the macropore structure of some chars can lead to particle fragmentation at low conversions and enhancement of the gasification rate.