The operator team of a big coolant separation system recognized after a longer period of operation that because of the higher content of oil in the delivered waste coolant, the oil content in the clean water is higher than desired. The operator team checked different technical possibilities in order to reduce the oil content of the clean water. They decided to install an oil skimmer on each buffer tank in order to remove the floating oil. Without the free oil there is less load on the coolant separation system. This is why the operator team expects that the oil content in the clean water gets reduced and that the separation result will be improved.

Each buffer tank is built as a round tank and has a volume of 500 m³. The water level in both tanks is able to fluctuate up to 9.5 m by normal operation. The removal of oil needs to be guaranteed at every liquid level. In addition they asked for an extremely robust and fail savesystem which works fully automatic 24 h/day, 7 days/week.


Due to their experiences with Friess oil skimmers on different other water treatment systems the operator team decided to ask, next to other suppliers, Friess GmbH. The team of Friess GmbH suggested, due to the guidelines, to use an oil skimmer model S 100 in a special edition. The challenge was the requirement to remove the oil at every liquid level. The solution elaborated by Friess: an oil skimmer model S 100 with housing on each tank. Both tanks are covered with a sheet metal roof. Friess cut a rectangular hole for the oil skimmer in each roof. Then a rectangular flange was welded in the cutout. The oil skimmer S 100 with housing was mounted on the top of the flange.

Mounting of oil skimmer S 100 with housing

The oil collector tube was guided through the cutout of the roof on to the liquid surface. Up to 18 m of the oil collector tube may float on the liquid surface at the highest liquid level. Under bad circumstances the oil collector tube may form knots. In order to avoid the forming of knots Friess designed a floating tube guide.

The oil collector tube will be guided by a floating pontoon. The floating pontoon on the other hand will be guided along a stainless steel rope. At maximum water level the oil collector tube will be pulled as far away as possible from the oil skimmer. At low water level a short loop of oil collector tube floats on the water directly underneath the oil skimmer. At minimum surface there is still around 0.5 m of the oil collector tube on the surface in order to collect floating oil. With this construction the oil collector tube will be able to float on the surface without forming knots.

Floating tube guide at lowest level

The oil collected by the oil skimmers flows through a pipeline DN 100 by gravity into a small collecting tank. The collected oil is pumped by an excentric screw pump into the waste oil collecting tank 80 m away. The whole construction including pipeline, pump, switchbox, wiring and the coordination between the carnage and staging was realized by the team of Friess GmbH.

Switch box with controls for oil skimmer, heating system and pump