Experimental Study On Processing Cl-in WFGD Wastewater By Electrolysis-electrodialysis Method

Limestone-gypsum wet desulfurization process produces a certain amount of desulfurization wastewater in order to discharge chloride ions that are accumulated in the system and avoid equipment to be corroded.The concentration of Cl-in desulfurization wastewater is 8000-20000mg/L,it will pollute the environment if it is discharged directly.However,conventional desulfurization wastewater treatment methods are difficult to remove chloride ions in desulfurization wastewater,which makes desulfurization wastewater difficult to discharge directly and recycle.In view of this problem,our group proposed a novel strategy of using electrolysis-electrodialysis to dispose chloride ions existing in the wet FGD system and had a good effect.This paper continued to study the electrolytic characters and influence factors exist in the electrolysis-electrodialysis process.First,to explore the effect of every parameter on the electrolysis-electrodialysis process under the condition of non-continuity,experiments were conducted on a small electrolysis setup with three compartments and a pair of membranes,which using CaCl2 solution to simulate the desulfurization wastewater.The experiment results show that enhancing the concentration of Cl-can enhance the current efficiency and reduce the energy consumption,but when the concentration of Cl-got to a certain value,the reduction of energy consumption was no longer obvious;the smaller the plate distance,the lower cell voltage and energy consumption,the higher current efficiency;when the NaCl solution exist in the anode chamber,the cell voltage and energy consumption do not decrease obviously;When Mg2+ exists in the cathode chamber and the middle chamber,it will form a precipitation and adhere to the cation membrane and the cathode plate,then impede the migration and discharge on the cathode plate of the ions,which can increase the cell voltage and energy consumption;if the concentration of Mg2+ is more than 0.179 mol/L,the sediment that adhered to the cathode plate and the cation membrane is more;if the concentration of Mg2+ in the desulfurization wastewater is less than 0.179 mol/L,the sediment is not obvious.Second,to study the effect of every parameter on the electrolysis-electrodialysis process under the condition of continued electrolysis,experiments were conducted on a small electrolysis setup with three compartments and a pair of membranes,which using CaCl2 solution to simulate the desulfurization wastewater.The experiment results show that enhancing the current can help enchance the migration rate of ions and accelerate the reaction rate.However,the increase of current will make the cell voltage and energy consumption also increase;enhancing the concentration of electrolyte can help reduce the cell voltage and energy consumption.When the concentration of the electrolyte exists in the cathode chamber and anode chamber increase,it will impede the migration of ions and make the energy consumption increase;keep the current stable,when the concentration of the electrolyte exists in the middle chamber increase,it has little effect to the reduction of Cl-.Besides,if the concentration of the electrolyte is too high,the energy consumption will no longer reduce obviously;when the flow of electrolyte increases to a certain value,the ions exist in the electrolyte will be affected by convective diffusion.When the flow velocity increases,the disturbance in the chamber will be more violent,and affect the migration and discharge on the cathode plate of the ions.This study shows that the electrolysis-electrodialysis process can remove the chloride ions exist in the desulfurization system,and it is possible to realize resource utilization.This paper provides a novel methods for advanced treatment of the desulfurization wastewater,and lays a solid foundation for further study.