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.
Highlights
Integrated gasification combined cycle (IGCC) is one of the advanced technologies that has potential to reduce coal’s carbon footprint
Pyrolysis of a bituminous coal was studied in N2 and CO2 and 50% N2 or (CO2 /N2) and Ar-based atmospheres in a high pressure, high temperature flow reactor
The volatile yield was highest for the char generated in the CO2 /N2 atmosphere compared to inert atmospheres, while there was no noticeable difference in volatile yield observed between N2 - and Ar-based environments
Summary
Integrated gasification combined cycle (IGCC) is one of the advanced technologies that has potential to reduce coal’s carbon footprint. The heart of the IGCC plant is the gasifier where the organic portion of the coal is converted into syngas (i.e., primarily CO+H2 ), while the inorganic portion of the coal is removed as slag. The syngas produced can be used for power generation and as input to fuel cells or as a base to chemicals and liquid fuel synthesis [1]. Despite many commercial operations for various applications, gasification rates at high pressures and temperatures, crucial to the design and troubleshooting of the gasifiers, are relatively unknown [1]. When coal is exposed to high temperatures, it releases volatiles quickly to form char. The char particles generated get converted to syngas through heterogeneous reactions with CO2 and H2 O
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