When a mixture of oil, dirt and water stands undisturbed, gravity tends to separate the liquid into an upper layer of oil, an intermediate layer of water and a lower layer of dirt or solid material. When the mixture is placed in a rapidly revolving bowl, centrifugal force accelerates the separation. Solids collect upon the bowl, water forms an intermediate layer and clean oil, being the lightest constituent, moves to the center of the bowl. The discharge holes of the bowl may be arranged so that water can be drawn off and discharged. The solids are cleaned from the walls as required.
The speed of rotation, viscosity of the oil and the speed of the oil flow through the centrifuge affect the quality of separation. Practical experience dictates the speed of oil flow through the centrifuge for proper cleaning. More material is removed by lower flow rates. If the feed is too rapid, only partial clarification will result. Heating the oil to reduce the viscosity is one of the most effective methods of improving purification. For best results, viscosity of the oil should be less than 100 sus.
A centrifuge may be operated as a purifier or a clarifier. If the oil contains water, then a purifier is used. The purifier has two sets of discharge holes. Water is discharged from one set and oil is discharged from another. If the oil contains only solid matter, then the centrifuge is set up as a clarifier by covering the water discharge holes leaving with only the oil discharge holes open. |
