REACTIVITIES OF IN-SITU AND EX-SITU COAL CHARS DURING GASIFICATION INSTEAM AT 1000-1400-DEGREES-C

A unique feature of this study is the gasification of chars (in situ c hars) in steam, starting from coals and proceeding uninterrupted, as o pposed to a large number of previous studies, in which coals are first devolatilized in inert atmosphere, and the resulting chars (ex situ c hars) are then gasified under conditions different from that of devola tilization. A large number of conversion and reactivity data were dete rmined for both in situ and ex situ chars gasified in steam at 1000-14 00 degrees C. The results obtained for bituminous coal, subbituminous coal and lignite indicate that the reactivities of the resulting in si tu chars are up to six times higher than that of the corresponding ex situ chars. Further, the reactivities of all the in situ chars decreas e monotonically as gasification proceeds, whereas maximum reactivities exist for ex situ chars at carbon conversions between 0.05 and O.15,. For all the in situ or the ex situ chars investigated in this work, t he conversions at different gasification temperatures, when plotted ag ainst a dimensionless gasification time tau,'unified' into a single ch aracteristic curve with distinctly different shape for each type of ch ar. The activation energies of the in situ chars obtained are in the r ange of 56-85 kJ/mol, while that of the ex situ chars are between 63 a nd 99 kJ/mol. In addition, the dependence of initial reactivity of the in situ char on steam partial pressure during gasification may be des cribed by a Langmuir-type expression.