COAL DESULFURIZATION BY MILD PYROLYSIS IN A DUAL-AUGER COAL FEEDER

A dual-screw coal feeder reactor was constructed and tested for desulf urization of coal. The reactor consists of two concentric screw tubes, the inner tube acting as a coal pyrolyzer and the outer tube acting a s a desulfurizer with hot calcined lime (CaO) pellets or other renewab le sorbent pellets. The experimental results showed that under mild py rolysis conditions, the devolatilization and the desulfurization proce sses of Ohio #8 coal could be represented by a pseudo first-order reac tion model. Up to 33.2% of the total sulfur, which includes almost all the organic sulfur, was removed at a temperature of 475 degrees C and a residence time of 6 min using a coal particle size of 4-35 mesh. Th e activation energies for the devolatilization and the desulfurization processes were estimated to be 170,021 kJ/kg mol and 78,732 kJ/kg mel , respectively. The H2S concentration in the pyrolyzed gas was reduced from 4% to an undetectable level in the outer tube desulfurizer indic ating a high sulfur removal efficiency of CaO pellets in the dual-scre w feeder reactor. (C) 1997 Elsevier Science B.V.