Non-isothermal kinetics of coal char oxyfuel combustion by isothermal model-fitting method

Abstract

Non-isothermal kinetics of coal/char conversion obtained by model-fitting and model-free methods are always very different, and the effect of heating rate β on the kinetics is unclear. In this study, the oxyfuel combustion kinetics of two coal chars (NCP anthracite, DT bituminous) at βs of 2.5–40 K/min are investigated through thermogravimetric analysis. The direct model-fitting methods (DMFMs), the isothermal model-fitting method (IMFM) and the model-free methods (MFRMs) were used to obtain the non-isothermal kinetics. The results show that all the above models can fit experimental data well, due to the coefficients of determination values of these models are all above 0.99. However, the activation energies, Es, at different βs obtained by the DMFMs differ greatly from the isothermal kinetic parameters, the maximum differences in Es are 43–57 and 22–35 kJ/mol for the NCP and DT chars, respectively; while the Es obtained by the IMFM are almost same for each char, and more consistent with the isothermal experimental results, indicating β has little influence on the E. Moreover, the MFRMs are difficult to distinguish the influence of coal rank, due to the obtained mean (E¯) values of both chars conversion are practically equal, and much lower than the isothermal experimental results. Therefore, the IMFM is more suitable than DMFMs and MFRMs, for determining the non-isothermal kinetics of char oxyfuel conversion.