Steel-mill cooling water becomes contaminated with oil, grease and sludge. In the settling basin, most of the sludge sinks to the bottom, while oil, grease and a small amount of sludge remain floating on the surface.
Scrapers move the sludge at the bottom of the basin into a sludge collection container, where it is removed by excavator. Floating oil accumulates in front of a baffle, while the water passes underneath into the next chamber. Three pumps then return the cleaned water to the cooling circuit.
Oil, grease, lubricating oil and hydraulic oil—mixed with dust, dirt and sludge—float on the surface upstream of the baffle. To minimize operating costs, the separated waste oil must contain less than 5% water. Because the entire separation system is installed outdoors, it also has to operate reliably throughout the year.
To remove oil from the entire basin surface, the customer chose a tube oil skimmer. Tube guides were installed so that the oil-collecting tube could sweep across the full surface. The skimmer operates continuously, 24/7, to keep the water as clean as possible. The collected oil and a small amount of water flow into a decanter, where the water settles to the bottom and the oil rises to the top.
The oil flows over a weir into the waste-oil tank, while the water is returned to the cooling-water basin. Electronic speed control allows the skimmer output to be adjusted to the quantity of oil on the surface. An additional protective contact prevents the motor from overheating at low speed. For winter operation, the skimmer, oil collection area and decanter are heated.
The heater switches on when the temperature falls below 3°C. The level in the waste-oil tank is monitored continuously. When the tank reaches its maximum level, the skimmer shuts down and an alarm is displayed in the system’s central control cabinet.
Continuous skimmer operation keeps the cooling water free of floating oil and maintains the water quality required by the system. Electronic controls allow the oil-skimming system to operate around the clock without manual supervision.
