The treatment of produced water from oil and gas extraction is typically done in stages. These stages involve primary treatment, secondary treatment and polishing. Each of these stages has specialized equipment in order to separate oil and solids from water. As far as primary treatment is concerned, there are three technologies used for purifying produced water namely, skimming tanks and vessels, hydrocyclones and separator. When produced water is taken to the primary treatment, it contains nearly 500 to 2000 ppm of oil. Water from bulk separators, treaters and compression scrubbers are cleaned in the primary treatment process.
The primary objective of primary treatment of produced water is to remove approximately 90 percent of the dispersed oil. This is done with the aid of a skim tank or hydrocyclones. After primary treatment, produced water should typically contain 50 to 200 ppm of oil and should provide a steady supply to the downstream secondary treatment equipment.
Skimming tanks are gravity separators that are designed to continuously separate oil droplets from the produced water. Skimming tanks are most often used for surge protection and for the removal for large quantities of sludge. Oil droplets rise to the surface and are thus skimmed off the surface of the water. The larger the size of the oil droplet, the more likely it is to rise above the surface of the produced water. Skimmers are of two types, horizontal skimmers and vertical skimmers. Vertical skimmers have an inherent disadvantage that oil droplets must flow upwards against the flow of water. Due to this, horizontal skimmers are mostly preferred due to their excellent efficiency.
In the case of a hydrocyclone, it uses pressure to force water in a spiral path. Due to the centrifugal forces that are generated in this process in a cylindrical chamber, the oil droplets are forced to the centre of the chamber, where they are collected and form a surface and flow in the reverse direction of the water. These oil droplets are then directed to an opening where they are removed from the produced water.
n this manner, oil is separated from the produced water in the primary treatment process. To know more about produced water treatment market.