Influence of Pyrolysis Gas on Volatile Yield and CO2 Reaction Kinetics of the Char Samples Generated in a High-Pressure, High-Temperature Flow Reactor

Abstract

The influence of pyrolysis atmosphere on volatile yield, structural characteristics, and CO2 reaction kinetics have been examined on chars generated from Pittsburgh No. 8 coal at 6.2 bar pressure and 1100 °C in a high-pressure, high-temperature flow reactor (HPHTFR) in Ar, N2, 50 (vol. %) CO2 and N2 (i.e., CO2/ N2) atmospheres. The chars were characterized for volatile yield, thermal swelling ratio, surface area, pore size distribution, crystallite structure, defects to graphitic intensity ratio, and char-CO2 reactivity. Coal pyrolyzed in CO2/N2 showed higher volatile yield (27%) compared to coal pyrolyzed in argon (~16%) and nitrogen (~19%). Except for volatile yield, there was no significant difference in structural properties for chars generated in different pyrolysis atmospheres. The difference in volatile yield was found to be due to presence of unconverted tetrahydrofuran (THF) soluble tar/soot. The results also showed that the intrinsic reactivity was highest for char generated in N2 atmosphere and lowest for char generated in CO2/N2 atmosphere. The kinetic parameters (activation energy and pre-exponential factor) for the char-CO2 reaction were ascertained using nth order model. The activation energies did not differ significantly among the chars generated in different pyrolysis atmospheres. The order of reaction was found to follow: CO2/N2 char > N2 char ≈ Ar char.

Keywords

• gasification
• pyrolysis atmosphere
• kinetics
• high pressure
• high heating rate