Study On Precipitation Of Inorganic Salt And Migration And Transformation Of Chlorine In Spray Drying Of Desulfurization Wastewater

With the increasing demand for desulfurization wastewater from the Ministry of Environmental Protection,zero-emission technology for desulfurization wastewater has gradually begun to be applied.The flue evaporation technology is widely concerned by its simple process,low operating cost and no secondary pollutants,the rotary atomization spray drying zero-discharge technology has great technical feasibility.The precipitation of inorganic salts,the migration of Cl in the process and its impact on subsequent equipment and comprehensive utilization of fly ash are related to the application prospect of this technology;therefore,the study of inorganic salt emission characteristics and the rule of Cl migration in the rotary atomization spray drying zero discharge technology can provide an important theoretical basis for the engineering application of spray drying zero emission technology.Based on the established desulfurization wastewater evaporation simulation test system,the ion chromatograph,plasma emission spectrometer,field emission scanning electron microscope,X-ray diffractometer and other analytical test instruments were used to investigate the composition and morphology of gas and solid product during the evaporation process of desulfurization wastewater,and explore the effects of different evaporation temperatures,different metal ions,TDS concentration and pH values of different desulfurization wastewaters on the volatilization characteristics of HCl during the evaporation process of desulfurization wastewater.The results showed that two products are produced during the evaporation process of the desulfurization wastewater,such as HCl,MgSO₄,NaCl,CaSO₄.Changing the evaporation temperature and the pH value of the wastewater will affect the volatilization of HCl,while Cl^-concentration and the metal ion species will not affect.For the rotary atomization spray drying process,the emission characteristics of gas and solid products,inorganic salts transformission and Cl migration in the process of atomization evaporation of desulfurization wastewater were further studied.The results showed that the products of the desulfurization wastewater after evaporation contain fly ash with inorganic salts and gas with HCl.The products have mainly C,O,Si,Al,S,Ca,Mg,K and other elements,the main components are mullite,SiO₂,Al₂O_3,KCl,MgSO₄,CaSO₄?0.5H₂O.The surface of the product is rough with irregular crystals.Changing the evaporation of desulfurization wastewater and TDS will affect the discharge concentration of the drying tower.The evaporation temperature and pH of the desulfurization wastewater will affect the proportion of chlorine in the gas and solid phase.Finally,using the spray-drying zero-emission project of desulfurization wastewater of 330MW coal-fired power plant,combined with the actual situation on site,the effects of rotary atomization drying process on desulfurization wastewater under on-site conditions and the effects on flue gas properties,dry products and fly ash utilization were investigated.The results are:evaporation of desulfurization wastewater will cause the gas temperature drop,the humidity of inorganic salts rise and the outlet dust concentration and SO₂ reduce to some extent.The salt in the desulfurization wastewater is basically transferred into the ash hopper at the bottom of the drying tower and the flue gas in the outlet flue gas,which will not affect the resource utilization of the subsequent fly ash.It is a zero-discharge technology for desulfurization wastewater with a wide application prospect.