Coupling Pyrolysis and Gasification Processes for Methane-Rich Syngas Production: Fundamental Studies on Pyrolysis Behavior and Kinetics of a Calcium-Rich High-Volatile Bituminous Coal

The coupling pyrolysis and gasification (CPG) process in the fluidized bed reactor to produce methane-rich syngas is an attractive technology in efficient and clean utilization of coals. Pyrolysis plays a leading role in this technology and other relevant processes. Pyrolysis behavior, gaseous product evolution, and kinetics of a calcium-rich high-volatile bituminous coal were deeply investigated using thermogravimetry coupled with online Fourier transform infrared spectroscopy. The results showed that inherent minerals in the coal were mainly gypsum, calcite, and quartz. Except for SiO₂, CaO is the most abundant species in the coal ash. The first-stage mass loss of coal before 654 °C was attributed to functional group cleavage and aromatic ring condensation reactions, during which the relative content of CH₄ was the largest among the hydrocarbon gases. The second-stage mass loss was mainly caused by mineral (calcite and gypsum) decomposition. It has demonstrated that the major source of CH₄ formation was from cracking of aryl methyl rather than the long alkyl side chains on aromatics in the coal. Furthermore, pyrolysis of the coal could be divided into three kinetic stages based on the activation energy variation. The first and last stages for chemical bond cleavage and mineral decomposition in coal were both controlled by an internal diffusion mechanism. However, the second stage involving a condensation reaction followed a second-order reaction mechanism