API SEPARATOR ( American petroleum institute)
An API separator tank consists of two basic sections -
a. Inlet section
b. Oil-Water separation channel
Oil water separation theory is based on the rise rate of the oil globules (vertical velocity) and its relationship to the surface loading rate of the separator. The rise rate is the velocity at which oil particles move towards the separator surface as a result of the differential density of the oil and the aqueous phase of the wastewater. The surface loading rate is the flow rate to the separator divided by the surface area of the separator. In an ideal separator, any oil globule with a rise rate greater than or equal to the surface loading rate will reach the separator surface and be removed. An ideal separator is assumed to have no short circuiting, turbulence, or eddies. The required surface loading rate for removal of a specified size of oil droplet can be determined from the equation for rise rate.
The equipment works on the principle of Stokes Law that defines the rise velocity of a particle of oil based on its size and density. Generally, the specific gravity difference between the oil to be separated and water is much closer than the specific gravity of water and suspended solids. Therefore, the design of the API separator is based on the specific gravity difference between the oil to be separated and wastewater. With this design criterion, a majority of suspended solids will settle in the unit. The equipment is designed to treat oil globule size of 150 microns and above. Once the suspended solids and oil are removed from the wastewater in the API separator, the middle phase, water, is then directed on for the advanced treatment in various wastewater treatment plants.
Usually, the oil layer is skimmed-off and afterwards re-processed or disposed of, and the bottom sediment layer is removed by a flight and chain scraper (or a similar device) and a sludge pump. The layer of water is sent for further treatment that usually consists of a dissolved air flotation unit for the further removal of any residual oil. After this, it is also sent to some type of biological treatment unit for the removal of undesirable dissolved chemical compounds.
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6 июн 2018
