Effect of SO2 on the Reaction of Calcium Hydroxide with CO2 at Low Temperatures

The flue gas generated from a coal-fired power plant contains CO2 and SO2. The effect of SO2 concentration (<= 1000 ppm) on the reaction of CO2 with Ca(OH)(2) was studied using a differential fixed-bed reactor under the low-temperature and humid conditions similar to those in the bag filters of a dry or semidry flue gas desulfurization (FGD) system. When both CO2 and SO2 were present, they reacted with Ca(OH)(2) simultaneously to form calcium carbonate and sulfite, but part of the carbonate formed reacted further with SO2 to form sulfite. Ca(OH)(2) ceased to react due to the formation of an impervious product layer. The fraction of carbonate increased significantly with decreasing SO2 concentration in the range below 500 ppm SO2. but the fraction of sulfite decreased little except in the range below 100 ppm SO2 or at a relative humidity (RH) above 70%. Both fractions of carbonate and sulfite increased markedly with increasing relative humidity and slightly with increasing temperature, but they were little affected by the CO2 concentration and the presence of O-2. At SO2 concentrations <= 100 ppm, conversions of Ca(OH)(2) to carbonate in the range comparable to or higher than the typical conversions of Ca(OH)(2) for SO2 removal in a dry or semidry FGD process could be achieved. The results of this work are useful for evaluating, the feasibility of using solid wastes containing, CaO and/or Ca(OH)(2) to capture CO2 from flue gas at low temperatures.