Waste Oil Purification. Waste oil treatment uses a combination of approaches based on different methods (force field and porous membrane).
Centrifuges use a combination of electric and centrifugal fields. The electric field is generated by the outside power source or the triboelectric effect, creating a non-uniform field that improves the efficiency of cleaning.
The cleaning efficiency of waste oil can be increased with ferromagnetic particles in magnetic and centrifugal fields. For this purpose the centrifuge rotor is equipped with permanent magnets. Also, purification is improved by combining force fields and porous filters.
Waste Oil Purification. There are also hydrodynamic filters which combine the inertial forces and filtration. The filter cleans itself in the process, when the oil flows along the filter membrane or the membrane is moved against the oil flow. The character of the movement may vary: recurrent, rotary or reciprocating.
The main advantage of the hydrodynamic filters with a fixed filter element is their simple design and minimal maintenance. But their drawback is losing some of the cleaned oil along with waste. In general, we have the following pattern: the higher the degree of purification, the greater the losses. The solution would be to move a filter against the oil stream, but this complicates the design of the cleaner and the use of mechanical, pneumatic or hydraulic gear system. The cleaning efficiency of the hydrodynamic filters can be improved with electric precipitation devices.
Filtering centrifuges combine centrifugal force and filtration. The wall of the rotor is made of porous material. The pressure difference across the filter is created by the centrifugal force, and the impurities get trapped in the filter material.
Magnetic filters combine filter elements for non-magnetic particles with a permanent magnet for ferromagnetic contaminants. The filter elements, beside the main function, also protect the magnets from oil aging products. Such devices can clean waste oil with a lot of metal particles.