Drying kinetics characteristics of lignite using thermogravimetric analysis

This study investigated the chemical functional groups' changes and drying kinetics characteristics of lignite during the non-isothermal drying process. Compared with the chemical functional groups' changes of raw lignite, chemical functional groups of lower bonding energy such as -OH, -COOH, C-O-C, and C-O, which was decreased in the dried lignite. Two periods of the non-isothermal drying in lignite were observed: the fast heating period and the falling rate period. With increasing heating rate of drying, the needed drying time of lignite decreased, but the drying rate of lignite increased during the non-isothermal drying process. With increasing heating rate, the effective diffusion coefficient values of lignite ranged from 1.08 x 10(-11) to 2.47 x 10(-11) m(2)/s. Two different kinetics models, iso-conversional Kissinger-Akahira-Sunose and Ozawa-Flynn-Wall models, were applied to calculate the drying kinetics parameters of lignite. The average activation energy of two models for non-isothermal drying process was 72.43 and 75.13 kJ/mol, respectively. The study can obtain the information on heat and mass transfer of lignite during the non-isothermal drying process.