In the steel plant, in order to eliminate the deformation heat generated during cold rolling of the strip, the emulsion is often used as a lubricant and a coolant. The emulsion is heated by evaporation of water to increase the salt content, reduce the stability, and also deteriorate due to oxidation or bacterial action. Therefore, a part of the old emulsion is continuously discharged and a new emulsion is added. The general emulsion is used for 2-3 months. It is necessary to update all. A certain amount of treatment is required before discharge to remove oily substances from the wastewater. The general treatment methods are chemical method and membrane separation method, and membrane separation method can be further divided into organic membrane method and inorganic membrane method.
At present, the main method for treating emulsified oil wastewater abroad is membrane filtration. The film used was mainly an organic film of 0.01 μm and an inorganic film of 0.05 to 0.2 μm. There are three main methods of treatment in China: chemical methods, organic membrane methods, and inorganic membrane methods.
The chemical method
The chemical method for treating emulsified oil wastewater is relatively simple, and the one-time investment is relatively small. However, this method requires a large amount of chemical agents, a large area, and it is difficult to achieve the desired demulsification effect. The treated water quality is very poor and difficult to control, which is too different from the membrane treatment effect. In addition, the use of this method is poor in operability, and at the same time new oil-containing sludge is produced, so this method has been gradually replaced by membrane separation.
The membrane separation method mainly achieves the purpose of oil-water separation by effective interception of oil droplets and suspended particles by the membrane. It has the advantages of good effluent quality, convenient operation, small floor space and no new sludge.
Organic membrane separation
Polymer organic membranes have been studied and applied in this respect. However, due to the limitations of the materials themselves, there are certain restrictions on the control methods of membrane fouling and membrane cleaning methods, mainly because the flux is low and the oil content of the effluent is difficult to stabilize. Due to the limitation of the material of the organic film, the film is easily deformed, resulting in a change in the pore size of the membrane, which eventually leads to instability of the water quality of the permeate. There are several sets of organic membrane processing equipment imported from abroad, and the main problems in the imported organic membrane processing technology are:
1. One-time investment in imported organic membrane equipment;
2. The membrane tube is easy to age and needs to be replaced once in about 2~3 years;
3. The operation energy consumption is large, and the normal operation and maintenance costs are high;
4. The treatment effect and membrane flux are unstable due to the change of the concentration of the cold-rolled emulsion wastewater, which is prone to cause problems such as excessive flux drop and low rejection rate.
Inorganic membrane separation
At present, inorganic membranes are used in the treatment of emulsified oil wastewater by inorganic membranes at home and abroad. The ceramic membrane oily wastewater treatment equipment produced by Jiuwu Hi-tech has outstanding advantages such as corrosion resistance, high mechanical strength, small floor space, narrow pore size distribution and long service life. And it is stable in operation, high in flux, good in effluent quality, and oil content is less than 5ppm. The normal operation does not consume chemicals and does not produce new sludge, and the quality of the recovered oil is good. The ceramic membrane permeable water can be processed by the membrane bioreactor (MBR) to meet the national industry emission standards; it can be further processed by reverse osmosis membrane (RO) to meet the requirements of the production process, and the water resources can be recycled.
The treatment effect of ceramic membrane treated emulsified oil wastewater equipment and domestic imported organic membrane processing equipment is basically the same. The price of imported organic membrane equipment is about 3 times that of domestic ceramic membrane equipment. The energy consumption of imported organic membrane processing equipment is more than 10 times that of ceramic membranes. Normal equipment maintenance and pharmaceutical costs are also much higher than domestic ceramic membrane equipment. In addition to considering the service life of the equipment, the comprehensive cost of treating each ton of emulsified oil wastewater is about 6 times that of the domestic ceramic membrane. Therefore, the use of ceramic membrane to treat emulsified oil wastewater has great technical and economic advantages in China.