Research On Vacuum Membrane Distillation For Recirculating Cooling Sewage

In this thesis, PVDF hollow fiber membrane module was adopted, vacuummembrane distillation（VMD） technology was used to deal with recirculating coolingsewage. and got the best process parameters by the test,then provide technical supportfor engineering application.Under the test conditions,membrane flux increases as the hot side temperatureincreases and the cold side vacuum degree grows, the increase of the flow rate alsohas a little influence to membrane flux. When changes the operation parameters, thequality of production water are not effected too much.Under the conditions that thevacuum degree is0.087MPa,the hot side raw material liquid’s temperature is70℃and the circulation flow is15.18L/h, the membrane flux can reach11.23L·m^-2·h^-1,theconductivity is2μS/cm⁴μS/cm,total hardness is always less than1mg/L, turbidity is inNTU0.1fluctuates up and down, the content of UV254in between0.02and0.04, TOCis between0.1⁰.2mg/L.The raw water was softened preliminarily,and then treated by membranedistillation,the results shows that the membrane flux rise and the quality of theproduction water is better when do the test under the same condition;membranedistillation process goes better when the raw water is acidic than it is alkalinity; Withthe increase of the concentration ratio the membrane flux decreases,whenconcentration ratio reaches20，membrane flux drops to2.89L·m^-2·h^-1,but the qualityof production water are not effected too much.To improve the membrane flux,the test also done that when the feed liquidcirculating in membrane component,bubbling air at the same time, the results showthat the membrane flux has improved obviously, when the drum volume increasesfrom0to60L/h, membrane flux increases from6.86L·m^-2·h^-1to11.23L·m^-2·h^-1, andthen kept on increasing the air the membrane flux change little, therefore,when theflow rate of feed liquid circulation is15.18L/h, the best drum volume would be60L/h.On account of the membrane fouling,different cleaning methods were adopted inthis paper,and the results showed that the best cleaning solution is to clean themembrane with1%citric acid soak1h, and then flush it with distilled water for20minto make sure it’s clean on the surface,after that with0.1%sodium hydroxide soak1h, flush it with distilled water again.The membrane flux can be recovered to around96%in this way.Analyze the vacuum membrane distillation technology for technical andeconomic aspects and comparing with reverse osmosis technology, under thecondition of condition that make full use of the waste heat from power plant, vacuummembrane distillation’s operation cost is lower than reverse osmosis desalinationtechnology, membrane distillation technology has great development space and wideapplication prospects.