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Effect of CO₂ and H₂O on Char Properties. Part 1: Pyrolysis Char Structure and Reactivity

Ouyang, Juncheng, Hong, Dikun, Jiang, Liangkui, Li, Zehua, Liu, Huan, Luo, Guangqian, Yao, Hong
Energy & fuels 2020 v.34 no.4 pp. 4243-4250
Raman spectroscopy, carbon dioxide, coal, combustion, furnaces, gas chromatography, models, oxygen, pyrolysis, scanning electron microscopy, thermogravimetry
CO₂ and H₂O have great influence on pyrolysis char structure and its reactivity. Particularly, the effect of CO₂ and H₂O on pyrolysis char kinetic parameters are unrevealed. Char structure and the corresponding combustion kinetic parameters play a very important role for designing and modeling oxy-fuel combustion. This work focuses on the effects of CO₂ and H₂O on pyrolysis gas, coal burnout degree, char structure, and corresponding combustion kinetic parameters. The volatile compositions were measured by gas chromatography. Coal burnout degree, char structure, and reactivity were measured by a drop tube furnace, Raman spectroscopy, scanning electron microscopy and thermogravimetric anaylsis, respectively. Our results indicate that a H₂O-containing atmosphere results in decreasing char yield, developed and disordered char structure, and high reaction rate constant. All of these features are more obvious in a H₂O-containing atmosphere than in a CO₂-containing atmosphere. Moreover, a H₂O-containing atmosphere reduces char–O₂ reaction rate, as well as coal burnout degree in a low oxygen atmosphere at early and middle combustion stages (i.e., burnout degree <80%), but increases at the end stage of combustion (i.e., burnout degree >80%). Our investigation will give basic kinetic parameters and features of char properties obtained in CO₂ and H₂O atmospheres.