Experimental Study On Advanced Treatment Of Desulfurization Wastewater By Vacuum Membrane Distillation

Thermal power plant desulfurization wastewater is generated from the limestone-gypsum wet desulfurization of flue gas and mainly includes pollutants such as suspended solids,heavy metals,and salts.From the current situation of desulfurization wastewater treatment,the traditional physical and chemical treatment can not meet the needs of wastewater reuse,and requires advanced treatment of desulfurization wastewater.Therefore,the introduction of vacuum membrane distillation for advanced desulfurization wastewater treatment,and achieved good results.details as follows:In the pretreatment of desulphurization wastewater,the optimization of pharmacy addition and matching in the traditional physicochemical method is mainly used to determine the best pharmacy collocation and addition amount.After adjustment of pH and sedimentation of heavy metals,flocculation experiments were conducted using polyaluminum chloride,polyaluminum sulfate,polyaluminum ferric chloride,polyferric sulfate and flocculant PAM(non-ionic)to perform experiments.The experiment shows that the treatment effect of waste water after the addition of any flocculant or coagulant alone is not up to the standard,and the coagulant aid and flocculant are used together.The combined use of flocculant and coagulant aid experiments showed that the amount of polyaluminum chloride added was 1.80-2.10 g/L+non-ionic polyacrylamide(PAM)2.0 g/L.The turbidity decreased from 21000 to about 5NTU,the TDS value decreased from 57000 to about 42300 mg/L,and the removal rate of calcium,magnesium,aluminum,chlorine,and sulfate ions in the wastewater was as high as 25%and 23%.%,30%,19%,18%.In the experimental study of vacuum membrane distillation,using pure water and mixed salt solution as the feed liquid,the mass transfer and heat transfer equations were determined through the influence of various operating parameters(temperature,vacuum,flow rate)and concentration on the vacuum membrane distillation process.The mathematical model established is a mixed model of Knudsen diffusion and viscous flow diffusion.The experimental results are in good agreement with the model results.It is verified that the model is suitable for the mixed salt solution of chloride salt and sulfate,and the desulfurization wastewater treated with the physicochemical method is used as the feed liquid to study the effect of operating conditions on the device flux,and the experimental results are as follows:The model is close.Through the study of the operating conditions and long-term operation of the vacuum membrane distillation process,the suitable parameters for the long-term operation of the experimental apparatus were determined as the feed temperature of 72.5?,the flow rate of 0.064 m/s,and the cold side vacuum of 0.085 MPa.Studying the continuous operation cycle shows that the operating efficiency of the vacuum membrane distillation unit is 30 mim,and the device's high throughput(14 L/m2·h or more)and high retention rate(99%or more)are maintained for more than 15 hours.In the vacuum membrane distillation continuous operation wastewater concentration experiment,the concentration of 741 mL of total wastewater from the device rose from 3.6%to 24.6%,and the rejection rate was higher than 99.1%After 15 hours of long-term operation of the vacuum membrane distillation unit,the rate of decline in flux increases,and membrane fouling requires severe membrane cleaning.Membrane fouling and different membrane cleaning methods are investigated.The alkali cleaning and ultrasonic cleaning methods are selected through coMParative experiments.The membrane flux recovered to 95.9%of the new membrane,and the retention rate was only 99%of the original membraneThe whole set of desulfurization wastewater advanced treatment process can recover 62%of the clean water in the desulfurization wastewater,and the process water quality is close to distilled water.The research results will provide a theoretical basis and scientific basis for the industrial application of advanced desulfurization wastewater treatment by vacuum membrane distillation technology,which is of great significance for the application of membrane distillation.