Sv. Makarytchev et al., HIGH-TEMPERATURE SULFUR REMOVAL UNDER FLUIDIZED-BED COMBUSTION CONDITIONS - A CHEMICAL INTERPRETATION, Chemical Engineering Science, 50(9), 1995, pp. 1401-1407
Theoretical and experimental studies were conducted on coal sulphur re
moval under chaotically changing oxidizing and reducing conditions, wh
ich occur in the dense zone of bubbling fluidized beds. Experimental d
esulphurization trends were analyzed by comparison with multi-species
(50 gas-phase, 7 solid-phase species) equilibrium calculations for coa
l/steam/sorbent/air system. It was shown, that under fluctuating reduc
ing/oxidizing conditions, sulphur capture as CaS in locally reducing z
ones increased the sulphur retention level of the sorbent. In experime
nts, performed in a 8 cm i.d. bench-scale FBC boiler, effective sulphu
r retentions were obtained in the 800-1000 degrees C temperature range
. As a chemical interpretation, a time history of sorbent particle cal
cination-sulphation is proposed, which leads to the formation of a par
ticle structure with a sulphided (CaS) core and a sulphated (CaSO4) sh
ell. Full-scale applications are discussed and measures for improving
limestone utilization and high-temperature sulphur removal in fluidize
d beds are recommended.