Oil–water separator

An oil water separator (OWS) is a piece of equipment used to separate oil and water mixtures into their separate components. There are many different types of oil-water separator. Each has different oil separation capability and are used in different industries. Oil water separators are designed and selected after consideration of oil separation performance parameters and life cycle cost considerations. "Oil" can be taken to mean mineral, vegetable and animal oils, and the many different hydrocarbons.

Oil water separators can be designed to treat a variety of contaminants in water including free floating oil, emulsified oil, dissolved oil and suspended solids. Not all oil separator types are capable of separating all contaminants. The most common performance parameters considered are:

An API oil–water separator is a device designed to separate gross amounts of oil and suspended solids from the wastewater effluents of oil refineries, petrochemical plants, chemical plants, natural gas processing plants and other industrial sources. The name is derived from the fact that such separators are designed according to API Publication 421, February 1990, published by the American Petroleum Institute. These separators can be used to separate large oil droplets, typically greater than 150 micron.

The purpose of shipboard oily water separator (OWS) is to separate oil and other contaminants that could be harmful for the oceans. They are most commonly found on board ships where they are used to separate oil from oily waste water such as bilge water before the waste water is discharged into the environment. These discharges of waste water must comply with the requirements laid out in Marpol 73/78.

Bilge water is a near-unavoidable product of shipboard operations. Oil leaks from running machinery, such as diesel generators, air compressors, and the main propulsion engine. Modern OWSs have alarms and automatic closure devices which are activated when the oil storage capacity of the oil water separator has been reached.

A gravity plate separator contains a series of plates through which the contaminated water flows. The objective of the design is to allow oil droplets in the water to coalesce on the underside of the plate eventually forming larger oil droplets which floats off the plates and accumulates at the top of the chamber. The oil accumulating at the top is then transferred with some en-trained water to a waste oil tank. This type of oily water separator is very common for many industrial applications as well as in ships but it has some flaws that decrease efficiency. Oil particles that are sixty micrometers in size or smaller do not get separated. Also the presence of chemicals and surfactants in the water greatly reduce oil droplet coalescence, impeding the separation effect The variety of oily wastes in bilge water can limit removal efficiency especially when very dense and highly viscous oils such as bunker oil are present. Plates must be replaced when fouled, which increases the costs of operation.

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