Modeling char surface area evolution during coal pyrolysis: Effect of swelling and gasification at high pressures

A previous model for char surface area change during atmospheric coal pyrolysis was modified to include the effect of particle swelling and gasification to predict the N₂ adsorption specific surface area of high-volatile bituminous char generated at high pressures with or without gasification. A correlation between the change of char surface area and the ratio of the expansion work for particle swelling to the mass of metaplast cross-linked with coal matrix was developed and analyzed. The number of the defect regions generated by gasification was considered in calculating adsorption sites quantitatively. Particle swelling opened and then compressed the space between metaplast clusters, making the N₂ adsorption specific surface area of char increased first and then decreased. After the gaps between metaplast clusters were filled, the specific surface area changes were minimal. Gasification generated new defect regions in clusters and reduced the clusters in char, making the specific surface area of char first increased and then decreased.