Effects of Pressure on Coal Pyrolysis at High Heating Rates and Char Combustion Effects of Pressure on Coal Pyrolysis at High Heating Rates and Char Combustion

by Zeng, Dong 1974-

Clean coal technologies are now becoming popular because of their high efficiencies and minimal environmental impact. Higher operating pressures have been applied to clean coal technologies. The effect of pressure on coal pyrolysis and char combustion has been extensively studied but still remains to be further explored. The objective of this project was to characterize high pressure, high heating rate coal pyrolysis and char combustion, with emphasis on improving coal/char high pressure combustion models.

A flat-flame burner was used in a high pressure laminar flow facility to conduct high temperature, high heating rate pyrolysis and combustion experiments for four coals. The high-heating-rate (10000 K/s), high-temperature atmosphere can better simulate industrial conditions than the conventional drop tube facility. Pressure and heating rate have a significant impact on the total volatiles, char physical structure including morphology, and char internal surface areas. The high heating rate decreases the swelling ratios of chars at pressures from 2.5 to 15 atm. TGA char oxidation reactivities were measured at the same total pressure as the char preparation pressure. The general trend was that the TGA reactivity on a gram per gram available basis decreased with increasing char formation pressure. When the reactivity was normalized by either the N2 or CO2 surface area, the normalized reactivity was found to be relatively constant with increasing pressure.

Char burnout was measured at different pressures and O2 concentrations at high temperature in the pressurized flat flame burner facility. For a given pressure, the particle diameter ratio based on coal (d/dcoal,0) decreased with increasing O2 concentration. Two char kinetic models (CBK 8 and CBK/E) were used to fit the char burnout data, and the modeling results showed that the intrinsic char oxidation rate increased with increasing total pressure at constant oxygen partial pressure.