Insights into the effect of particle size on coal char particle gasification by thermogravimetric analyzer and high temperature stage microscope

The comparison of gasification characteristics obtained by different methods can provide an in-depth understanding for intrinsic reactivity which is a crucial basis for predicting gasification behavior and optimizing gasifier. Comparative study on the effects of particle size on the reactivity and kinetics was conducted by thermogravimetric analyzer (TGA) and high temperature stage microscope (HTSM). Then the influence of diffusion on gasification characteristics by different methods was analyzed. Results showed that the shrinkage ratio of coal char increased with increasing gasification temperature, and the shrinkage ratio of small particle was higher than that of large particle. The reason was that the shrinkage ratio was determined by sintering when the ash content in char was less different. Also, the observed reactivity in TGA was far less than that in HTSM and the reactivity difference between small particle and large particle in HTSM was much larger than that in TGA, which was determined by the fact that the significant external and bed diffusion effects could not really be eliminated in TGA. Whereas those diffusions were completely eliminated due to sparse dispersion of particles in HTSM. Meanwhile, the modified volume model (MVM) was the best model to describe the char gasification process. The validity of MVM was verified by using the model-free method. Additionally, the internal diffusion effectiveness factor revealed that the internal diffusion of large particle measured in HTSM was more significant than that in TGA, indicating that the result of smaller particle measured in HTSM was closer to the intrinsic reactivity.