Study on the pyrolysis kinetics of low-medium rank coals with distributed activation energy model

A deep understanding of coal pyrolysis behaviors is essential for the clean and efficient coal utilization. Detailed structural characterization and kinetic analysis could provide valuable information about coal pyrolysis. This work deals with structural analysis and pyrolysis kinetics of four low-medium rank coals with the distributed activation energy model (DAEM). The carbon structures, pyrolysis characteristic and kinetic parameters were correlated to gain some updated insights into coal pyrolysis. The results show that aliphatic carbons gradually convert into aromatic ones, and the aromatic clusters grow in both size and weight with the rise of coal rank. The side-chains of aromatic clusters are shortened and eliminated thus aromaticity is increased. Characteristic temperatures of pyrolysis are closely related to coal properties and carbon types. Both initial and peak temperatures increase with FCar and Cd-af while decrease with VMar and H/C. Meanwhile, the initial temperature is related to the aliphatic carbon (f(al)) and aliphatic carbon bonded oxygen (f(al)(o)) due to their low bonding energies, while the peak temperature is linked to the aromatic carbon (f(a)) and aromatic bridgehead carbon (f(a)(B)) because of their higher bonding energy. DAEM model is reliable for analyzing pyrolysis kinetics of bituminous coals. The range of activation energy gradually narrows down with the increase of coal rank, corresponding to the concentrating distribution of different carbon types. Moreover, DAEM could accurately predict the pyrolysis behavior of bituminous coals at very high heating rates, but the effectiveness of DAEM in modeling and predicting pyrolysis of lignite is less satisfying.