The plant manufacturer needed a system that would regularly and reliably remove a floating layer of lubricating oil, hydraulic oil, graphite and scale—fully automatically and without manual cleaning.
A well-known German manufacturer of crankshafts for petrol and diesel engines installed a new drop-forging press supplied by a leading Japanese equipment manufacturer. The press foundations and installation area were completely redesigned and rebuilt. A graphite-containing emulsion cools and lubricates the forging dies. When sprayed onto the hot dies, most of the water evaporates while the graphite provides lubrication. The remaining water drains into a collection sump in the basement, where excess lubricating oil also accumulates. Submersible pumps transfer the oily emulsion into two wastewater collection tanks on the ground floor, each with a capacity of approximately 30 m³. During the retention period, oil separates from the water and rises to the surface. A scraper conveyor removes settled solids from each tank into a container.
The operator reported a lubricating-oil consumption of approximately 1,000 litres every 20 days. The skimming system in each wastewater collection tank had to remove this volume of oil and transfer it to a mobile waste-oil collection container. All system tanks were required to use environmentally compatible materials.
For protection, the tanks had to be double-walled and equipped with leak and level monitoring. The limited available space also placed very high demands on the construction and design of every component.
Because the operator had already achieved positive results with FRIESS oil-skimmer systems at other locations, it recommended that the system manufacturer contact FRIESS.
Because the wastewater collection tanks had to fit within the existing production building, space was severely limited. To accommodate the initially required wastewater volume of approximately 40 m³, two differently sized tanks were designed. The final capacity was reduced from 40 m³ to 30 m³ per tank. Each tank was equipped with a FRIESS W40 oil skimmer and a guided floating oil-collection hose to remove the floating phase over a large surface area.
The floating collection hose continuously picks up the oil phase from the wastewater surface. Ceramic scraper blades inside the W40 remove the oil from the hose, and the separated oil flows through a funnel into a sealed, double-walled waste-oil container with a capacity of 1 m³.
When the waste-oil container reaches its maximum level, a level sensor stops the skimmer and issues a notification. The collected oil is then pumped from the container for disposal.
The water level in each wastewater tank is monitored by sensors. When the maximum level is reached, the basement feed pumps are shut down. The interstitial space between the double walls is also monitored for leaks. The de-oiled wastewater is periodically removed by a vacuum tanker through a suction connection on each tank; any leak triggers an alarm.
A standalone PLC controller operates the complete skimmer system and is linked to the higher-level control room, allowing operation either from the system PLC or from the central control system.
The complete system was planned by the FRIESS GmbH team in close coordination with the Japanese system manufacturer and in accordance with the end customer’s extensive delivery specifications.
Following a full-day inspection and acceptance test by Japanese engineers at FRIESS in Monheim am Rhein, the system was delivered to the customer’s construction site. Each wastewater collection tank weighed more than four tonnes and was over 8.0 m long, yet had to be installed between two columns with only a few centimetres of clearance. After assembly by FRIESS GmbH personnel, the system passed acceptance and the TÜV leak test before successful commissioning.
After the oil-skimmer system was successfully commissioned, full-system testing began. Wastewater treatment with the installed skimming system ran smoothly, and the treated wastewater was virtually oil-free.
