Coal pyrolysis at high temperatures and pressures. [800 to 1600/sup 0/C; 1 to 15 atmospheres]

In coal conversion processes, such as combustion or high-temperature gasification, the extent of pyrolysis is an important parameter which is affected by temperature. Increasing amounts of coal converted directly to gaseous species would reduce the remaining material which must be converted by the relatively slow char-gas reactions. Studies on this aspect, particularly at pressure and high temperatures, are scarce. To help fill in the data gaps, the present work has therefore been focused on the examination of pyrolysis at high temperatures (800 to 1600/sup 0/C), pressures (1 to 15 atm) and in various reacting and nonreacting gases. Devolatization generally increases with temperature in a manner consistent with the proposed three-stage mechanism for the evolution of volatiles. Results here show a plateau at 1200 to 1400/sup 0/C and a maximum devolatilization above 1500/sup 0/C. Reactive gases can interact with the freshly formed volatiles and affect the secondary char-forming reactions which can cause changes in the apparent percent pyrolysis. This was evident from the effects of moisture content, particle size, pressure and gaseous environment on the extent of pyrolysis. Reactivity of char formed in-situ and immediately reacted was found to be higher than reactivity of chars formed separately and then brought intomore » the reactive environment. It is suggested that morphological rearrangements may be important in pyrolysis and subsequent char reactions.« less