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.