The combustion characteristics and kinetic analysis of low-rank coals with different vitrinite/inertinite ratio

To explain the effect of maceral composition on the combustion characteristics of coal, a series of low-rank coals with different vitrinite/inertinite ratio were collected as the research object, and the combustion characteristics, heat change process and gas escape behavior of the samples under air atmosphere were investigated using thermoanalytical methods (TG-MS-DTA). The results show that the maceral content has little effect on the temperature of the maximum reaction rate. However, it has an effect on the value of the maximum reaction rate, and the maximum reaction rate of the inertinite-rich coal is larger. Meanwhile, higher minerals in coal allow the reaction to reach its maximum rate at a higher temperature. The combustion process shows two obvious stages. The first stage (before 400 ℃) is exothermic slowly, corresponding to the devolatilization process, and the second stage (after 400 ℃) is exothermic rapidly, corresponding to the fixed-carbon combustion process. The exothermic characteristics of coal combustion show a slow to fast exothermic transition. Coal with different vitrinite/inertinite ratio mainly release CO₂, CO, H₂O during the combustion process, however, the relative content of the released gas is different. In the devolatilization stage, there is less CO₂ and CO released, while more H₂O release. In the fixed-carbon combustion stage, a large amount of CO₂ is released, the amount of CO released is slightly lower, and H₂O is the lowest. Among them, the inertinite-rich coal releases relatively more CO₂ during the combustion process and burns more completely under the same conditions. In addition, the kinetic calculation of the coal combustion process is carried out with the Coats-Redfern method, and the trend of reaction activation energy increases as the vitrinite/inertinite ratio decreases. However, it does not affect the inertinite-rich coal in the fixed-carbon combustion stage. The ability to burn rapidly may be due to the cell lumen structure formed by a large number of fusinites, which enlarges the contact area between the surface of coal particles and O₂, and the combustion reaction is sufficient.