Thermal Behavior and Characteristics of Functional Groups on Lignite Secondary Oxidation. Issue 4 (12th March 2022) - Huang, Zhian
ABSTRACT: At present, the thermal behavior of lignite and the reaction process of functional groups during secondary oxidation have not been accurately explained. Therefore, the macro thermal behavior and micro characteristics of spontaneous combustion of lignite during secondary oxidation were studied. Coal samples were pre-oxidized to 80 °C, 120 °C, 160 °C, and 200 °C (labeled as raw coal, C-80, C-120, C-160, and C-200, respectively). A thermogravimetric (TG) analyzer and Fourier-Transform Infrared (FTIR) spectrometer were used. The results showed that the high adsorption temperature T1 and critical temperature T2 of C-80 were higher than those of raw coal by 4.41 °C and 11.07 °C, respectively. They indicated that pre-oxidation inhibited the low-temperature oxidation process. The active temperature T4 gradually decreased from C-80 to lower than that of raw coal. The T4 of C-200 was about 20 °C lower than that of raw coal, proving that pre-oxidation accelerated oxygen absorption and the weight-gaining process. The activation energy of pre-oxidized coal samples was significantly lower than that of raw coal samples. The C-80 and C-120 samples had the lowest activation energies: 114.542 kJ/mol and 114.539 kJ/mol, respectively. The content of free hydroxyl groups in pre-oxidized coal samples decreased in general. At C-120, the aliphatic hydrocarbon generation rate significantly increased, and the percentage of peak area continued to increase. During secondary oxidation of C-120 coal samples, various absorption peaks gradually enhanced. Consequently, C-120 was more prone to spontaneous combustion during secondary oxidation.