Effect of the Pressure and Temperature of Devolatilization on the Morphology and Steam Gasification Reactivity of Coal Chars

The effect of operating conditions (pressure and temperature) on char morphology and structure during coal devolatilization was studied. For this purpose, five different rank coals were selected: a lignite, three bituminous coals, and a semi-anthracite. The coal chars were prepared by devolatilization in a novel pressurized fixed-bed reactor. The pyrolysis experiments were carried out isothermally at temperatures of 800, 900, and 1000 degrees C and pressures of 1, 5, 10, and 20 atm. The chars obtained from the bituminous coals at elevated pressure experienced a high degree of swelling, whereas those from the lignite and semi-anthracite were hardly affected at all by pressure. The devolatilization temperature did not appear to have any significant effect on char morphology below 1000 degrees C. The reactivity of the char samples prepared under different pyrolysis conditions was studied by isothermal thermogravimetric analysis at 1000 degrees C under a steam atmosphere. The chars obtained at elevated pressure were found to be more reactive than those produced at atmospheric pressure. An increase in the pyrolysis temperature led to a decrease in char reactivity.