The correlation between coal char structure and reactivity at rapid heating condition in TGA and heating stage microscope

Abstract

The coal pyrolysis and char gasification process have been widely studied in TGA at a low heating rate, which is far lower than the heating rate when coal particle enters into the boiler and gasifier. In this work, the isothermal CO2 gasification reactivity of in-situ coal chars was performed in rapid heating TGA and a heating stage microscope. The char structure parameters determined by XRD and Raman were combined to describe the char reactivity at the same temperature. Results showed that maximum weight loss rate (DTGmax) of raw coal evidently increased and the corresponding maximum rate temperature raised with the increasing of heating rate during pyrolysis. Nonetheless, the heating rate had slightly effect on gasification reactivity of in-situ char samples when it exceeded 50 K/min. Considering the physical meaning and universality of the coal char structure and gasification reactivity fitting, the XRD and Raman structural parameters were combined to describe the gasification reactivity. The new method for coal char reactivity under rapid heating rate is established, Rs=0.174+43.14d002,aLc,a+3.58ID3×ID4IG2. Furthermore, a visually heating stage microscope was also applied for determining the in-situ char reactivity through image analyzing. The gasification process of in-situ coal char particles fits the shrinking particle pattern at the original and midterm stages. However, the shrinking particle pattern changed into the shrinking core pattern at high carbon conversion. Moreover, the CO inhibition effect and inter-particle interaction account for the difference of gasification reactivity by rapid heating TGA and heating stage microscope.