【課題】 排煙脱硫排水を蒸発濃縮する蒸発濃縮装置に 付着した石膏スケールを効率的に除去する方法を提供す る。
【解決手段】 排煙脱硫排水を蒸発濃縮する際に生ずる 蒸発濃縮装置に付着した石膏スケールを石膏溶解剤で洗 浄して除去する方法において、該石膏スケールの結晶形 態を２水和物から１／２水和物へ変化させて石膏溶解剤 で洗浄することを特徴とする石膏スケールの除去方法。
PROBLEM TO BE SOLVED: To efficiently remove gypsum scale by changing the crystalline form of the gypsum scale from dihydrate to hemihydrate and cleaning it with a gypsum dissolving agent in the case of cleaning and removing the gypsum scale generated at the time of evaporating and concentrating stack gas desulfurization waste water and stuck to an evaporation concentration device with the gypsum dissolving agent. SOLUTION: Stack gas desulfurization waste water is supplied from a line (aa) to a pH adjusting vessel 1 and adjusted its pH by injecting a pH adjusting chemical from a chemical vessel 5 through a pump 6. The pH adjusted waste water is supplied to an evaporation concentrator 2 through a pump 7. The evaporation concentrator 2 is evacuated by a vacuum pump 8 through a condenser 3 and steam supplied from the line (aa) is used as a heating source. The waste water in the evaporation concentrator 2 is evaporated and concentrated while being circulated by a pump 9. In the case that the gypsum scale is stuck to the evaporation concentrator 2, the gypsum scale is removed by circulating the circulating concentrated liquid at >=90 deg.C and, after the gypsum scale is kept at >=90 deg.C, circulating the pH adjusting chemical in the evaporation concentrator 2 through a pump 13.