Improvement of SO2 removal by the solubility change of Ca(OH)2 in the spray dryer system

Experiments were carried out to verify the effect of the solubility change of the Ca(OH)(2) sorbent on the removal of SO2 in a lab-scale spray dryer system. First, to identify the solubility effect, HNO3 was added into Ca(OH)(2) slurry to increase the solubility of Ca(OH)(2) by neutralization. The improvement of SO2 removal by 5-10% occurred under the condition of both 50% relative solubility and constant pH of slurry. But SO2 removal efficiency decreased steeply when the relative solubility approached 100% and the pH of the slurry decreased rapidly. For the practical application of the solubility effect, NH4Cl and NH4OH were selected as additives. Ammonium chloride (NH4Cl) which could improved Ca(OH)(2) solubility removed more SO2 by 5-10% than NH4OH which showed no change in solubility. The optimal result was obtained when the slurry was fed at the ratio of 0.25mol NH4Cl/mol Ca(OH)(2). The Ca(OH)(2)/NH4Cl sorbent could remove more SO2 and improve Ca(OH)(2) utilization than Ca(OH)(2) sorbent in the Ca/S stoichiometric range of 1.0-1.4. It was concluded that the increase of sorbent solubility made the improvement in SO2 removal efficiency and Ca(OH)(2) utilization.