Gasification behavior and kinetics of chars derived from coal pyrolysis in a CO-containing atmosphere

Abstract

Char gasification enables clean and efficient utilization of low-rank coal resources. The CO2 gasification behavior and kinetics of char samples produced via low-rank coal pyrolysis under the N2 and CO-containing atmospheres (char-N2 and char-CO) were investigated based on a series of thermogravimetric experiments, and the physicochemical structure of chars were characterized via Raman diffraction, X-ray diffraction, and CO2 adsorption methods, respectively. The apparent activation energies (Ea) of char-N2 and char-CO were obtained using the Flynn–Wall–Ozawa method and the reaction mechanism was determined via the Malek method. The results indicate that the graphitization and order degrees of the carbon chemical structure of char-CO are higher than those of char-N2 below gasification temperature (approximately 850 °C), whereas the specific surface area of char-CO is higher than that of char-N2 before gasification. Char-CO gasifies faster than char-N2 owing to its developed pore structure, and the gasification activation energy is lower than that of char-N2 (from 450 °C to 650 °C, the activation energy of char-N2 is 186.3 kJ mol−1, 192.4 kJ mol−1, and 203.6 kJ mol−1, and that of char-CO is 175.8 kJ mol−1, 187.5 kJ mol−1, and 199.1 kJ mol−1, respectively). The CO2 gasification reaction process of char-N2 and char-CO can be explained using a three-dimensional diffusion model. Moreover, the ash content in coal char affects the diffusion of reaction carrier gas and gas products during the gasification process, indicating that diffusion is the primary limiting factor in coal char CO2 gasification.