Sulfation and Carbonation of Basic Oxygen Furnace Slag/Ca(OH)2 Sorbents at High Temperatures.

The effects of compoments of flue gas generated from coal combustion on the sulfation and carbonation reactions of Ca(OH)2(HL), basic oxygen furnace slag(BOFS), and HL/BOFS(9/1) sorbents at high temperatures were studied using a differential fixed-bed reactor.
The sulfation rate for each sorbent increased with increasing reaction temperature(750-950℃) and SO2 concentration(1000-3000ppm). The conversions for Ca(OH)2 and HL/BOFS(9/1) were about the same and higher than that for BOFS.For Ca(OH)2, compared to the case of reaction under SO2/O2/N2 mixture, adding H2O alone, or adding H2O and NOx simultaneously, or increasing the O2 concentration(from 5% to 20%) when NOx was added enhanced the sulfation reaction, while the other gas compositions had little effect. For BOFS, adding NOx alone, or increasing H2O concentration(from 10% to 20%) when both H2O and CO2 were added inhibited the sulfation reaction, while the other gas compositions had enhancing effects.
The optimum carbonation temperature was 600℃for Ca(OH)2. The carbonation conversion increased as CO2 concentration (13%-80%) increased. Conversions of 0.88 and 0.93 were achieved when Ca(OH)2 reacted at 600℃,13% CO2, 5% O2 for 1min and 1h, respectively. An 1h conversion of 0.24 was achieved when BOFS was carbonated at same conditions. The presence of NOx slightly inhibited the carbonation of Ca(OH)2, while the precence of H2O or H2O/NOx had little effect. For the carbonation of BOFS, the presence of NOx had little effect and the presence of H2O had a slight enhancement effect. When both SO2 and CO2 were present, the carbonation conversion increased and the sulfation conversion decreased significantly with decreasing reaction temperature (600-750℃) or SO2 concentration (1000-5000ppm) and with increasing the CO2 concentration. The carbonation and sulfation conversions achieved for a sorbent reacted at 600℃,13% CO2, 5% O2 and 1000ppm SO2 for 10min were 0.91 and 0.07 for Ca(OH)2, 0.24 and 0.07 for BOFS, and 0.78 and 0.03 for HL/BOFS, respectively.