A metalworking plant needed a cooling water oil skimmer system for two rectangular settling tanks separated by a common wall. Every hour, 10 to 20 litres of oil entered the continuously circulating cooling water. Because of its lower density, the oil floated on the tank surface. Since the accumulated oil was removed only occasionally, it could be drawn into the circulation pump and cause failures—even though the pump inlet was about two metres below the surface.
Oil circulating through the cooling-water system caused frequent failures and contamination of critical components:
To optimize the cooling-water system and avoid costly cleaning, the maintenance team looked for a system that would continuously remove oil from the surface of the settling tanks. The requirements were:
After evaluating several options, the maintenance team selected two FRIESS S100 oil skimmers for the following reasons:
Space around the settling tanks was extremely limited, so the skimmers could not be mounted at the tank sides and there was no room for a separate oil collection tank. The FRIESS team therefore proposed mounting both skimmers on a collection tank fixed to the common wall between the two settling tanks. The tank pump was also installed on this wall, allowing both S100 units to sit directly above the tank.
The collection tubes of the S100 oil skimmers cover the full surface of the settling tanks and run perpendicular to the water flow. Floating oil contacts the tubes, adheres to them and is removed by scrapers before being pumped into the collection tank. The system operates continuously, 24/7, to keep hydrocarbons in the cooling water as low as possible.
When the oil layer is very thin, the collection tube may also pick up small amounts of water. To reduce water in the recovered oil and minimize disposal costs, the tank pump is installed in the primary tank, while a second separate tank provides further oil-water separation. As the vessel fills, the oil remaining on the surface flows over the tank wall into the main collection tank, while a pipe at the bottom drains the clarified water.
