Structure changes of coal reject char during pyrolysis at low heating rates

Abstract

Pyrolysis of coal reject in an inert atmosphere is the first step of preparing a sorbent from this material. In this paper, studies on the physical structural changes and pore surface area and volume distribution of coal reject char during pyrolysis are presented. The effects of acid treatment, heating rate and temperature on the pore structural evolution are experimentally investigated. A thermogravimetric analyzer is used for the pyrolysis of coal reject in nitrogen to prepare the pyrolyzed char. Characterization of pore structure of the resulted chars is carried out using an accelerated surface area and porosimetry (ASAP 2000) system. The results showed that the generation, enlargement and coalescence of pores in the carbonaceous matrix of the coal reject are closely related to the physical structural changes such as softening, swelling and shrinking of the particle during pyrolysis. The heating rate of the particle during pyrolysis is an important factor influencing both micropore and mesopore structure. The effect of heating rate is mainly due to the effect of heating rate on softening and swelling. HCl treatment of the raw coal reject was found to modify the thermoplasticity of the particle, which results in a substantial increase of micropore surface area of the pyrolyzed char.