Kinetic and thermodynamic investigations of CO2 gasification of coal chars prepared via conventional and microwave pyrolysis

Abstract

This study examined an isothermal CO2 gasification of four chars prepared via two different methods, i.e., conventional and microwave-assisted pyrolysis, by the approach of thermogravimetric analysis. Physical, chemical, and structural behaviours of chars were examined using ultimate analysis, X-ray diffraction, and scanning electronic microscopy. Kinetic parameters were calculated by applying the shrinking unreacted core (SCM) and random pore (RPM) models. Moreover, char-CO2 gasification was further simulated by using Aspen Plus to investigate thermodynamic performances in terms of syngas composition and cold gas efficiency (CGE). The microwave-induced char has the largest C/H mass ratio and most ordered carbon structure, but the smallest gasification reactivity. Kinetic analysis indicates that the RPM is better for describing both gasification conversion and reaction rates of the studied chars, and the activation energies and pre-exponential factors varied in the range of 78.45–194.72 kJ/mol and 3.15–102,231.99 s−1, respectively. In addition, a compensation effect was noted during gasification. Finally, the microwave-derived char exhibits better thermodynamic performances than the conventional chars, with the highest CGE and CO molar concentration of 1.30% and 86.18%, respectively. Increasing the pyrolysis temperature, gasification temperature, and CO2-to-carbon molar ratio improved the CGE.

Recent Progress on Hydrogen-Rich Syngas Production from Coal Gasification

“…Therefore, the RPM cannot be used to predict the variations in the char structures during the gasification process, especially in the post-reaction stage. Jiang et al [168] proved by a kinetic analysis that the RPM is better to describe both CO 2 gasification conversion and reaction rates of the studied chars than the SCM, and the calculated pre-exponential factors and activation energies fall within the range of 3.15-102,231.99 s −1 and 78.45-194.72 kJ/mol, respectively. Dai et al [169] employed the RPM to estimate the kinetic parameters containing the pre-exponential factor and pore structure parameter by the experimental data from CO 2 gasification of biochar and anthracite.…”