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

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-O-2 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.