| Efficient sewage purification is an important prerequisite for iron and steel enterprises to improve water-saving efficiency and ensure safe and stable operation.At present,sand filter is widely used in iron and steel enterprises to purify sewage,which has poor filtering effect and filter material is easy to fail.Therefore,it is very urgent to develop a new purification process with good purification effect and long service life.Due to the advantages of high efficiency,environmental protection and no chemical additives,membrane separation technology has become an important means in the field of gas purification and sewage treatment.However,membrane separation technology has not been applied to the filtration process of continuous casting cooling water.In this project,continuous casting cooling water is taken as the research target,and the polyvinyl chloride membrane and ultra high molecular weight polyethylene membrane are used to purify it.The effects of flow conditions such as the type,concentration and size of inorganic particles on membrane fouling were studied.On this basis,the influence of flow conditions such as particle size,electrical property and pH value of emulsified oil on membrane fouling was studied,and the interaction between emulsified oil and inorganic particles was clarified.The main membrane pollutants were identified,which was beneficial to control membrane fouling and provided feasible scheme and theoretical basis for membrane fouling prevention and control.Physical-chemistry properties of the porous polyvinyl chloride composite materials,including surface microstructure,wettability(for water and oil)and permeability coefficient,were investigated,and the antifouling performance of polyvinyl chloride membrane in composite membrane filter was analyzed.The results shows that the structure of exine and intine of the porous polyvinyl chloride membrane is similar,which is formed by the aggregation of particles with the same size.Pores are in the range of 20-60 ?m.The pore size distribution is uniform.The permeability coefficient of membrane is small and it belongs to weak permeable material.Combined with the industrial experimental of continuous casting turbid circulating water in steel plant,the removal rate of turbidity is up to 45.8%,the removal rate of suspended solids are up to 31%,and the water quality can be improved.However,after usage for 3 years,the structure of membrane is damaged,and it could not meet the requirements of water purification.Ultra high molecular weight polyethylene(UHMWPE)was selected as organic membrane.The effects of inorganic particle concentration and particle size on membrane fouling in turbid circulating water were systematically studied.It was found that the large size and high concentration of inorganic particles contribute to slow down membrane fouling.The microstructure of ultra high molecular weight polyethylene membrane was analysized,it consists of agglomerated particles and macropores with different sizes of 40-152 ?m in diameter.The most available pore diameter of the membrane is 52 ?m.The pore distribution is narrow.The separation performance of membrane was mainly investigated.When the concentration of inorganic particles was 0.4 g/L,the irreversible fouling resistance was the lowest,and the flux recovery rate was the highest,reaching 91.41%.The membrane fouling caused by the large size inorganic particles(70?m)is the least.The flux decline rate slows down with the increase of inorganic particle size,and the flux recovery rate increases with the increase of inorganic particle size.Based on the influence of inorganic particles on membrane fouling,the effect of mixed filtration of inorganic particles and emulsion oil on membrane fouling was investigated.It was found that the severity of membrane fouling is determined by interaction between inorganic particles and emulsion oil,the concentration of emulsified oil,particle size of oil droplets,charged emulsion oil and pH value of water.The decreasing trend of membrane specific flux slowed down with the decrease of gear oil/CTAB emulsified oil concentration,thus reducing membrane fouling.When the oil droplet size is 67.69 ?m,the irreversible pollution caused by gear oil/CTAB emulsified oil is the lowest,and the antifouling performance of membrane is the best.The membrane sufferes the lightest fouling for treating negatively charged gear oil/CTAB emulsion oil at pH=11,which is attributed to that electrostatic repulsion promotes adhesion resistance of emulsion oil.The flux recovery led by the three surfactants followed this order:SDS<Tween-80<CTAB.membrane for treating oppositely charged gear oil/CTAB emulsion oil has most membrane fouling,and the main mechanism of membrane fouling is middle blockage.When the filtration volume exceeds 70 L,the membrane fouling mechanism changes to cake blockage.However,the membrane for treating similarly charged gear oil/SDS emulsion oil has less membrane fouling.And the main mechanism of membrane fouling is cake clogging at the later stage of filtration.Ultra high molecular weight polyethylene membrane is used to purify the turbid circulating water with inorganic particles and emulsified oil.The water purification effect is good.Under the same filtration conditions,the service life of ultra high molecular weight polyethylene membrane is longer than that of polyvinyl chloride membrane.A sewage purification device with ultra high molecular weight polyethylene pipe membrane as filter element in iron and steel enterprises was constructed.Content of suspended matter and oil in the inlet and outlet of continuous casting turbid circulating water were systematically studied.The removal rate of suspended is up to 32%,the oil content in the outlet water was reduced to 3.5 mg/L,and the removal rate of oil is up to 67%.Filtration effect is significantly improved compared with these of the traditional filtration equipment.At that point,the industrial test of clean circulation water was carried out.By comparing turbidity and the amount of make-up water in inlet and outlet,it was found that the amount of make-up water of clean circulating water for oxygen generation machine was reduced by 54%after being filtered by composite membrane filter.Turbidity was reduced to 16 NTU in the outlet,and the turbidity removal rate was about 37%,so that the water quality was significantly improved. |
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