Simulation of the evolution of pressure in a lignite particle during pyrolysis

Evolution of pressure in a lignite particle during pyrolysis was simulated based on the gas motion equation in porous media and considering the Klinkenberg effect. The CPD model was used to describe pyrolysis. The pore diameter in the particle is close to the average free path of volatile gas molecules, so the solid phase restrains the movement of gas. Since flow out of the particle is restricted, the internal pressure rises. The internal pressure first increases and then decreases during pyrolysis, and the evolution is influenced by heating conditions. The pressure rise is larger at a higher heating rate, but the duration of the pressure peak is shorter. The total pressure in the particle is larger at a higher ambient pressure, but the pressure difference between the inside and the surrounding decreases with the increasing ambient pressure. Growing internal pressure can restrain tar gasification, which can lead to the increase of the metaplast content and the decline of tar yield.