Because mill scale is denser than water, it settles to the bottom of the scale pit and the longitudinal clarifier. An excavator removes the scale collected in the pit. In the clarifier, a scraper pushes settled scale to the deepest point, where it is dredged periodically.
Oil and grease phases that are lighter than water collect on the surface of the longitudinal clarifier.
The flow through the clarifier carries floating oil towards the pump chamber.
A baffle holds back the floating oil-and-grease mixture.
Water passes beneath the baffle into the pump chamber and is then pumped back into the circuit through a gravel filter. Bearing grease, lubricating oil, hydraulic oil and other hydrocarbons—mixed with mill scale and solid particles—float on the cooling water. This floating oil layer must be removed continuously so that as little hydrocarbon contamination as possible reaches the gravel filter. One simple and reliable method is a height-adjustable skimming channel.
The inlet edge of the skimming channel is adjusted precisely to the liquid surface. Water and oil therefore flow continuously from the surface into the channel and leave the cooling-water circuit. The disadvantage of this simple, reliable method is the large amount of water removed with the oil and grease. A typical channel discharge contains only 1–2% oil and 98–99% water, so the discharged mixture still requires a separate and comparatively laborious separation step.
For easier and more efficient removal of the floating oil phase, a FRIESS S100 oil skimmer can be combined with an oil-attracting hose and a pumped collection tank.
