This application concerns the recovery of large amounts of oil from rolling fluid in a steel mill. In the production of sheet steel, large amounts of oil are used, in combination with a emulsion that is meant for cooling and lubrication. Both the emulsion and the oil are collected in a holding tank, from where the emulsion is pumped up again. The oil must be recovered from the holding tank so that it can be re-used.
The dimensions of the holding tank are L x W x H = 25 x 5 x 4 meter. Per hour approximately 500 - 650 liters of oil are added, which has to be removed by the Suparator® separation system. The temperature of the fluid can run up to 80 °C and the pH value is around 7.
For the production process it is essential that a certain fraction of the oil is kept in emulsion, for the rolling fluid to have lubricating properties as well as cooling properties. Therefore a certain amount of emulsifier is added to the cooling water.
The oil that is used has a significant amount of edible fats (mainly animal fats) added to it. This is to make the oil adhere better to the surface of the sheet steel that is produced, and to the rolls, that way providing for a better lubrication. These edible fats however will cause the oil to absorb more water and to readily built water-in-oil emulsions.
The installation is based on the Skim & Treat® method, developed by Suparator. Floating Suparskim® skimmers in the holding tank skim off the top layer; cooling water with oil. The fluid, skimmed off by the skimmers, is transferred to the Suparator® separation system where the oil is separated from the cooling water. The cooling water flows back into the holding tank under gravity; the oil is pumped away.
The sketch on the right shows the layout of the installation. Move your mouse over the image and click on the different components of the installation to view the photos.
Each of the three Skim & Forward units has a capacity of 1.500 liters/hour, bringing the total flow to the separation system at 4.500 liters/hour.
The holding tank could not be cleaned prior to the start-up of the installation. This resulted in excessive amounts of oil in the initial phase. During this phase the Suparator® separation system separated up to 2000 liters of oil per hour. Large amounts of debris and solidified dirt from the holding tank caused the strainers on the Skim & Forward units to require frequent cleaning. The lumps of "solidified" dirt broke up fairly well but the debris in it was retained in the strainers. As old dirt was removed from the tank more and more, the interval for cleaning the strainers increased from 4 hours to over 1 week.
Oil separation stabilized at approximately 1.200 liters/hour which was explained from the water that was absorbed by the oil in the process.