A metal working plant had two rectangular settling tanks with a common wall between them in operation. Every hour, 10 to 20 liters of oil become mixed with the constantly circulating cooling water. Because of the lower specific weight of the oil it floated on the tank’s water surface. Since the accumulated oil was only removed periodically, the circulating pumps occasionally pumped cooling water mixed with oil through the cooling system. Even though the pump intake was about 2 meters below the surface, the suction side of the pump was strong enough to pull oil down from the surface into the submerged pump intake.

Oil circulating in the cooling water system led to frequent break-downs of the cooling water system and also to contamination of important cooling system components.

  1. The cooling water passing through filters located behind the settling tanks became contaminated with the oil resulting in filter system failures. This led to costly system repairs.
  2. Oil mixed with grease and dirt particles would coat the inside of the piping, resulting in a reduced cooling water flow in the system.  Small nozzles were particularly vulnerable to clogging, which meant that they had to be removed / cleaned / or replaced frequently.
  3. Because of the large volume of oil in the cooling water system, the cooling system no longer functioned properly.  The oil and grease also contaminated the product surfaces.

In order to optimize the cooling water system, to prevent interruptions and expensive cleaning repairs the Maintenance Department was looking for a system that would continuously remove oil from the settling tank water surface. They had the following requirements:

  1. No production flow stoppage.
  2. The oil flowing into the settling tanks has to be removed as rapidly as possible from the cooling water.
  3. Investment and system operating costs should be as low as possible.

After studying various solutions, the Maintenance Department chose two FRIESS Model S 100 Oil Skimmers for the following reasons.

  1. The floating oil was removed from the total water surface area of the tanks.
  2. The FRIESS Oil Skimmers operated continuously.
  3. The robust stainless steel construction and the ceramic scrapers offered long operating life with very low maintenance costs.
  4. They had positive references from other users of the FRIESS Oil Skimmer system.
  5. FRIESS could also meet the client’s specifications for additional equipment: a storage tank with pump, as well as a system installation design.

The available space around the settling tanks was very limited, therefore the normal Oil Skimmer installation location – at the sides of the tanks – was not possible. In addition to this lack of space to place the oil skimmer; there was also no space available where the oil collecting tank could be installed.

The FRIESS team therefore suggested mounting both oil skimmers on the oil collecting tank which was attached to the common wall of both settling tanks. The oil storage tank and its pump were mounted on the joint settling tank wall which now also allowed the Model S 100 Oil Skimmers for each settling tank to be mounted there.

The oil collector tube of the Model S 100 Oil Skimmer covers the whole width of the settling tank’s water surface area, and is perpendicular to the water flow in the tank. Any oil floating on the surface is therefore forced into contact with the oil collector tube, and the Model 100 Oil Skimmer captures and removes the oil. The oil collected by the Model 100 Oil Skimmer is scraped from the hose and falls straight down into the collection tank with the tank pump. To keep the cooling water as free from hydrocarbons as possible, the system operator decided to keep the system running 24/7. If the surface oil film is very thin the oil collector tube will pick up the oil but it is possible that some water droplets will be picked up as well. To reduce the water content of the removed oil, and reduce waste disposal costs as much as possible, the storage tank pump is in the main container, while a second, settling container is installed to further separate oil from the water. As the settling tank fills with water, residual oil floating on top of the water goes over the tank wall into the main oil collecting tank. A pipe that runs to the bottom of the settling tank drains off the cleaned water.

The oil level in the main collection tank is controlled. When a maximum limit is reached, the removed oil is pumped into a large holding tank for disposal.

Through the use of the FRIESS S 100 Oil Skimmer the oil content of the cooling water was reduced by over 90 %. After a basic cleaning, the cooling water filter system has operated without a failure. Production stoppages caused by clogged nozzles were eliminated.

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