Thermal decomposition mechanisms of coal and coal chars under CO2 atmosphere using a distributed activation energy model

Highlights: • Char CO₂ gasification occurs during thermal decomposition under CO₂ atmosphere. • Kinetic compensation under non-isothermal conditions was studied. • Reaction kinetics modeled by the simplified distributed activation energy model. • This model is suitable for char generated at high temperature. • Different kinetic compensation effects occur during thermal decomposition. - Abstract: The thermal decomposition characteristics of Sanxing (SX) coal and coal chars (C500 and C850, produced at 500 and 850 °C, respectively) were tested by nonisothermal thermogravimetric analysis and a distributed activation energy model used to determine the kinetic parameters. The effects of char-making temperature were investigated. A sharp peak was seen in the relationship between X and activation energy (E) of the SX and C500 samples; no evident peak, but a ladder-shaped decline, was shown by C850. The temperatures at which E was maximized were relatively close for SX coal and C500, while the minimum value of activation energy was almost the same for the three samples. This showed the char-making process had less influence on the gasification reaction under high-temperature conditions. The results of the kinetic compensation effect between E and the pre-exponential factor (k₀) showed that different kinetic compensation mechanisms occurred for the pyrolysis- and gasification-dominated stages.