Effect of Additives to Improve Calcium-Based Sorbents in Semi-Dry Flue Gas Desulphurization

Semi-dry flue gas desulfurization (FGD) technology is used by some coal-based power plants to remove sulfur dioxide from flue gas. In semi-dry FGD systems, SO2 is removed by calcium-based sorbents in a reactive spray dryer, but the level of desulfurization is lower than in wet FGD systems. This work evaluates the effects of seven additives in the desulfurization of the flue gas: magnesium hydroxide, ammonium nitrate, ammonium acetate, ammonium phosphate, sodium hydroxide, citric acid, and urea. Slurries with calcium hydroxide concentrations of 10 and 20 wt% containing 2 and 4 wt% of an additive were applied in the removal of SO2. Additives containing ammonium intensified the removal of SO2 and increased the yield of the reaction. The SO2 content in the flue gas reduced by 73.8% when applying a slurry containing 4 wt% of ammonium nitrate and 10 wt% of Ca(OH)2. The use of this slurry increased the removal of SO2 by 13.5% when compared to the best result obtained using calcium hydroxide slurry without any additive.