Study On Treatment Of Desulfurization Wastewater By Bipolar Membrane Electrodialysis

More than 90%of coal-fired power plants in my country have adopted limestone-gypsum wet flue gas desulfurization technology.In the wet flue gas desulfurization process,in order to maintain the stable operation of the system and ensure the quality of gypsum,it is necessary to control the Cl^-concentration in the slurry,and a certain amount of desulfurization wastewater will be generated during the operation.Desulfurization wastewater has the characteristics of high suspended solids,high salt content,many types of heavy metals and high chemical oxygen demand（COD）,which is one of the most difficult wastewater treatment at the end of the power plant system,which seriously restricts the goal of coal-fired power plants to achieve zero discharge of wastewater.Based on the research on the recycling of desulfurization wastewater by bipolar membrane electrodialysis（BMED）technology,this paper explores the membrane stack structure of bipolar membrane electrodialysis and the treatment of the pretreated desulfurization wastewater by membrane materials,optimizes the treatment process,explores the optimal process parameters,and then explores the fouling of Ca²⁺and Mg²⁺on the membrane surface.The main work is as follows:（1）The BMED membrane stack test mainly investigates the effects of two compartment,three compartment,and four compartment structures on the treatment efficiency of simulated desulfurization wastewater,with a focus on the effects of current density,flow rate,and salt concentration on voltage,alkali yield,current density,and energy consumption.The experimental results show that the optimal compartment is three compartments,with a controlled current density of 30m A/cm²,a flow rate of 70m L/min,a salt concentration of0.91mol/L,a preparable acid concentration of 0.69mol/L,a alkali yield of 98.3%,an energy consumption of 6.97k Wh/kg,a current efficiency of 95.17%,and a conductivity of5.18m S/cm.（2）The BMED membrane material experiment mainly investigates the effects of conventional ion exchange membranes（CJMA-4）,acid blocking membranes（ATD）,and selective ion exchange membranes（ACS）on the treatment efficiency of membrane stacks.The experimental results show that the selective ion exchange membrane is more favorable for BMED treatment of simulated desulfurization wastewater.The optimal conditions are:current density of 30m A/cm²,flow rate of 70m L/min,and salt concentration of 1.04mol/L.At this point,the acid concentration can reach 0.68mol/L,the alkali yield is 84.7%,the energy consumption is 6.65k Wh/kg,the current efficiency is 78.9%,and the transmittance of SO₄^2-can be reduced to 49.1%.（3）The BMED membrane fouling test mainly studies the fouling and blockage of selective ion exchange membranes in Ca²⁺and hardness selectivity tests,and characterizes membrane surface sediments through SEM,EDS,and XRD.The test results indicate that after Ca²⁺and hardness selectivity tests,sediment will form on the surface of the selective cation exchange membrane,and the sediment in hardness selectivity tests is mainly Ca CO₃,Ca（OH）₂,Mg（OH）₂.There will also be differences on both sides of the positive membrane,with Mg（OH）₂precipitation mainly reflected on the salt chamber side of the positive membrane,and Ca CO₃precipitation mainly reflected on the alkali chamber side of the positive membrane.