Oil Water Separator
An 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 design of the separator is based on the specific gravity difference between the oil and the wastewater because that difference is much smaller than the specific gravity difference between the suspended solids and water An Oil-Water Separator is a gravity separation device designed by using Stokes Law to define the rise of velocity of oil droplets based on their density and size. The design of the separator is based on the specific gravity difference between the oil and the wastewater because that difference is much smaller than the specific gravity difference between the suspended solids and water. Based on that design criterion, most of the suspended solids will settle to he bottom of the separator as a sediment layer, the oil will rise to top of the separator, and the wastewater will be the middle layer between the oil on top and the solids on the bottom.
Typically, the oil layer is skimmed off and subsequently re-processed or disposed of, and the bottom sediment layer is removed by a chain and flight scraper (or similar device) and a sludge pump. The water layer is sent to further treatment consisting usually of a dissolved air flotation (DAF) unit for further removal of any residual oil and then to some type of biological treatment unit for removal of undesirable dissolved chemical compounds.
Figure 1. Conceptual Diagram of a Simple Gravity Oil/Water Separator.
In a gravity operated O/WS, the oily wastewater is introduced through the system inlet. Water turbulence is calmed in the inlet chamber behind the first baffle, where solids settle out and form sludge on the bottom of the chamber. As the wastewater flows over the first baffle to the middle, or separation, chamber, oil droplets rise to the surface and are trapped behind a second, higher baffle, which has an opening along its bottom edge. The remaining water passes under the second baffle into the outlet chamber, where it is diverted to a discharge point. Consequently, solid sludge can be collected from the bottom of the inlet chamber and oil droplets that accumulate at the water's surface in the separation chamber can be skimmed off or otherwise routed to a separate holding tank.