Study On The Membrane Purification Process Of Desulfurization Wastewater Form Coal-fired Power Plant

The coal-fired power plant waste water still contains a large amount of soluble ions after desulfurization,which has some harm to the environment and ecology.Among them,Cl^-as the most difficult ions to remove,also has a corrosive effect on the equipment.At present,industrial desulfurization wastewater is mainly treated by evaporation,precipitation,and membrane separation treatment technologies.This article adopts"pretreatment+advanced treatment"membrane separation treatment process for the experimental study of desulfurization wastewater treatment.This article combines microfiltration membranes and ultrafiltration membranes into a"pretreatment unit."Experiments show that the pretreatment unit has a significant removal effect on the turbidity and suspended solids of the desulfurization wastewater.Secondly,through the experimental scheme,using the effluent from the pretreatment unit as the raw material,experiments were performed on the factors such as the membrane pressure,inlet temperature,rinsing ratio,membrane type,and membrane combination of the nanofiltration membrane advanced treatment unit to explore its effect on the rejection of nanofiltration membrane treatment.The results show that the main factors affecting the rejection of membrane separation are membrane pore size,membrane concentration difference,and the nature of fluid solute.In other words,when the temperature rises,the retention rate of the nanofiltration membrane will rise first and then decrease;the membrane pressure increases,the retention rate increases and tends to be stable;the ratio of clear water to concentration of the effluent increases,the rejection rate decreases;membrane elements with larger membrane pore diameters,the rejection rate is smaller.The change of these conditions will cause certain concentration polarization or membrane blockage during the membrane separation process,which will also have certain risks for the operation and maintenance of the membrane system.Through nanofiltration membrane experiments on the above conditions,the best conditions for the separation of nanofiltration membranes were found:using US Dow NF90 nanofiltration membrane was used for advanced treatment of desulfurization wastewater at a membrane pressure of 0.65 MPa,inlet water temperature of 20°C,and rinsing ratio of effluent of 1:1.Based on the best conditions,the treatment effect of the nanofiltration membrane advanced treatment process on the desulfurization wastewater has reached:TDS decreased from16780ppm to 622ppm,with a total retention rate of 96.29%;Cl^-from 1717.25ppm to177.5ppm,the total retention rate of 94.41%;SO₄^2.reduced from 3274.85ppm to106.8ppm,with a total retention rate of 96.74%;Ca²⁺decreased from 681.12ppm to6.88ppm,and the total retention rate was 98.99%;Mg²⁺decreased from 1704.35 ppm to16.51 ppm with a total rejection rate of 99.03%;The COD dropped from 792 ppm to104.9 ppm and the total retention rate was 86.76%.At the end of this article,it also explored the conceptual assumptions for the separation of conventional nanofiltration membranes.Through the establishment of three experimental programs,whether the desulfurization wastewater needs to pass the"two-stage nanofiltration"problem has been studied experimentally.The final result shows that the nanofiltration membrane advanced treatment technology is necessary to undergo the“two-stage nanofiltration”for the water treatment process.