High voltage electric field method
The attraction or repulsion effect of electric field on the emulsion particles makes the fine oil particles collide with each other in motion, thereby destroying the hydration film and the double layer structure, so that the tiny oil particles can form larger oil particles floating on the water surface, so as to achieve the purpose of oil-water stratification. High voltage electric power can be AC, DC or pulse power supply.
The chemical demulsification method is to add demulsifier to the wastewater, destroy the hydration membrane of oil droplets, compress the electric double layer, and make the oil droplets aggregate and separate from water. The demulsification can be divided into salting out method, coagulation method, salting out coagulation mixing method and acidification method.
1. Salting out method: salt out method is to add salt electrolyte to destroy the hydration film of oil droplets and compress the thickness of electric double layer at the interface between oil particles and water, so as to make oil particles unstable. The simple salting out method has the advantages of large dosage, slow coalescence rate, large area of equipment, and poor treatment effect for emulsion with surfactant. However, because of its simple operation, low cost and more use, it is often used as a primary treatment. Common electrolytes are calcium chloride, magnesium chloride, sodium chloride, calcium sulfate, magnesium sulfate, etc.
2. Coacervation method: coagulating method is to add flocculant to the wastewater, and make use of the bridging effect of the flocculant to combine the oil particles into polymer. The commonly used flocculants are alum, polyaluminum chloride, activated silicic acid, polyacrylamide, ferrous sulfate, ferric chloride, magnesium bauxite, etc.
3. Acidification method: acidification method is to add sulfuric acid, hydrochloric acid, acetic acid or naphthenic acid to the wastewater to destroy the boundary membrane of oil droplets in the emulsion, so as to change the fatty acid soap into fatty acid and separate it. Since the pH value of waste water is reduced by this method, it is necessary to adjust the pH value with alkali agent after oil-water separation to meet the discharge standard.
4. Salting out coacervation mixing method: salting out coagulation mixing method is to add salt electrolyte into wastewater to make emulsion preliminarily demulsified, and then add coagulant to coagulate and separate oil particles.
This method refers to the separation of oil and water with the help of centrifugal force generated by centrifugal machinery. There are horizontal and vertical centrifuges. Under the action of centrifugal force, the water phase is discharged from the outer layer of the centrifuge and the oil phase is discharged from the middle part of the centrifuge.
Over consideration method
The emulsified oil wastewater is made to pass through the ultrafiltration membrane filter. Because the pore diameter of the ultrafiltration membrane is smaller than that of the oil bead, only water is allowed to pass through, and the oil particles larger than the membrane aperture are blocked, so as to achieve the purpose of emulsified oil-water separation.
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