Characteristics and reactivities of Ca(OH)2/silica fume sorbents for low-temperature flue gas desulfurization

Ca(OH)(2)/silica fume sorbents were prepared with various Ca(OH)(2)/silica fume weight ratios and slurrying times at 65degreesC and a water/solid ratio of 10/1. Dry sorbents prepared were characterized, and their reactivities toward SO2 were measured in a differential fixed-bed reactor at the conditions similar to those in the bag filters in the dry and semidry flue gas desulfurization (FGD) processes. The reaction between Ca(OH)(2) and silica fume in the slurry was very fast. The formation of calcium silicate hydrates, which were mainly C-S-H(I), resulted in sorbent particles with a highly porous structure that seemed compressible under high pressures. The sorbents were mesoporous, and their specific surface areas and pore volumes were much larger than those of Ca(OH)(2) alone. The utilization of Ca of sorbent increased with increasing silica fume content mainly due to the increase in the specific surface area of sorbent. The sorbent with 70 wt% Ca(OH)(2) had the maximum 1 h SO2 capture. Sorbents with Ca(OH)(2) contents less than 100 wt% and greater than 21 wt% would have a SO2 capture greater than that of Ca(OH)(2) alone. Both the 1 h utilization of Ca and SO2 capture per unit specific surface area of sorbent decreased in general with increasing specific surface area. At the same Ca(OH)(2) content, the 1 h utilization of Ca or SO2 capture of the Ca(OH)(2)/silica fume sorbent was greater than that of the Ca(OH)(2)/fly ash sorbent; however, the amount Of SO2 captured per unit surface area of the former sorbent was smaller than that of the latter sorbent. The results of this study are useful to the preparation of silica-enhanced sorbents for use in the dry and semidry FGD processes. (C) 2003 Elsevier Ltd. All rights reserved.