Coal desulfurization by mild pyrolysis in a dual-auger coal feeder

A dual-screw coal feeder reactor was constructed and tested for desulfurization of coal. The reactor consists of two concentric screw tubes, the inner tube acting as a coal pyrolyzer and the outer tube acting as a desulfurizer with hot calcined lime (CaO) pellets or other renewable sorbent pellets. The experimental results showed that under mild pyrolysis conditions, the devolatilization and the desulfurization processes of Ohio #8 coal could be represented by a pseudo first-order reaction 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. The 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 indicating a high sulfur removal efficiency of CaO pellets in the dual-screw feeder reactor. (C) 1997 Elsevier Science B.V.