Evolution of coal char porosity from CO2-pyrolysis experiments

Abstract

Pyrolysis experiments on a high volatile bituminous Columbian coal were performed in a laminar drop tube reactor at T = 1300 K and 1475 K. Measurements in CO2 were carried out at different residence times up to 150 ms, and the data were complemented by end-point measurements in N2 at approximately 165 ms. These low residence times are typical for the duration of pyrolysis in pulverized coal flames. Mass loss has been determined by solid sampling based on the ash tracer method, and the evolution of porosity was evaluated. Pyrolysis mass loss kinetics were determined based on a single first order reaction and a competing two-step reaction model with distributed activation energies. The particle temperature and residence time needed for the determination of the kinetics were derived by CFD simulations. Results indicate that, despite the low residence time selected, the influence of the Boudouard reaction on mass loss and, hence, evolution of porosity cannot be neglected. In general, porosity increases with increasing residence time and progressing mass loss and porosity is influenced by the both, the release of volatiles and the contribution of gasification.