The operators of a large coolant separation system found after extended operation that the high oil load in the incoming waste coolant was leaving more residual oil in the clean water than expected.
The operating team evaluated a range of technologies to reduce the oil content in the clean water. It decided to install an oil skimmer in each buffer tank to remove floating free oil. With the free oil removed, the coolant separation system would operate under less load, improving separation performance and reducing residual oil in the clean water.
Each buffer tank was a cylindrical vessel with a capacity of 500 m³. During normal operation, the liquid level in both tanks could fluctuate by as much as 9.5 m. Oil therefore had to be removed reliably at every liquid level. The installation also required an extremely robust, fail-safe solution capable of fully automatic operation 24 hours a day, seven days a week.
Drawing on its experience with FRIESS oil skimmers in various water treatment systems, the operating team contacted FRIESS GmbH and other suppliers. The FRIESS engineering team proposed a special version of the S100 oil skimmer to meet the specification.
The key challenge was to remove oil at every liquid level. FRIESS developed a solution using one housed S100 oil skimmer on each tank. Both tanks had sheet-metal roofs. A rectangular opening was cut into each roof, and a matching flange was welded into place. The S100 oil skimmer and its housing were then mounted directly on the flange.
The oil-collecting tube passes through the roof opening to the liquid surface. At the maximum liquid level, up to 18 m of tube can float on the water. Under unfavorable conditions, such a long tube could form knots. To prevent this, FRIESS developed a floating guide: the tube is routed through a floating bridge, which is itself guided along a stainless-steel cable.
At the highest liquid level, the oil-collecting tube extends as far away from the skimmer as possible. At lower levels, a small loop of tube floats on the liquid surface beneath the skimmer. Even at the minimum level, approximately 0.5 m of tube remains on the surface to collect floating oil. This arrangement allows the tube to follow the changing liquid level without forming knots.
Oil recovered by the skimmer flows by gravity through a DN 100 pipeline into a small collection vessel. An eccentric screw pump then transfers the recovered oil to a waste-oil storage tank located 80 m away.
The FRIESS GmbH team coordinated the complete installation, including the piping, pump, control cabinet, electrical wiring and mounting components.
