The primary function of an API Oil Water Separator is to separate free oil from the wastewaters mainly refinery wastewaters. The free oil is generally defined as oil globules having size of over 150 microns. The ability of a separator to remove free oil depends on a number of factors. This includes the type and state of the oil in the waste flow, the characteristics of the carrier stream and the design and size of the unit. The principle governing the separation of free oil from the wastewater is based on gravity separation wherein the oil, being lighter than water, floats to the surface on providing quiescent conditions.

The API separator tank consists of two basic sections - the inlet section and the oil water separator channel - each of which performs particular functions.

Inlet Section
The inlet section consists of the pre-separator flume and the forebay sections.

• Pre-separator Flume
  It serves two main functions: reduction of flow velocity and collection of floating oil. The effluent end of the pre-separator section contains three pieces of equipment: a bar screen or trash rack, an oil skimmer and an oil retention baffle in that order. Triveni supplies each of these equipment. For the various types of oil skimmers, refer to the oil skimmer section.
• Separator Forebay
  The pre-separator flume discharges into the separator forebay. This part of the separator acts as a header which distributes the influent to the separator channels. An oil skimmer may also be provided in this section for removal of any oil trapped in this section. Refer to the oil skimmer section for various types of oil skimmers supplied by Triveni.

Separator Section
The separator section generally employs the following equipment in the order.

• Velocity head diffusion devices
  These serve to reduce flow turbulence and to distribute the flow equally over the channel cross-sectional area. These can be either vertical slot baffle type or reaction jet baffle type. Triveni supplies each of these equipment.
• Oil & Sludge moving device
  Triveni supplies chain & scraper type mechanism for the purpose. The equipment comprises of two parallel strands of chain, one along each longitudinal wall, moving over motor driven sprockets and spanning the entire length of the tank. The chains are provided with flights at regular spacing and extending across the width of the channel. As the flights travel downstream, separated oil is moved towards an oil skimmer located at the downstream end of the tank. On the return trip, the flights move along the channel floor pushing sludge towards the sludge collecting hoppers or trough at the influent end.

The chains & sprockets can be provided in cast steel / stainless steel / non-metallic construction depending on requirement. The flights can be provided in wood / FRP construction. The tank internals viz. shafts, track angles, support brackets etc. can be in either steel / stainless steel construction.