Instead of filtering the oil I built a prototype rig to re-refine it. Lister says to use only distillate fuel, which this is. This process removes the soot, dirt, water, and other impurities. It gives a return of approximately 50% useable fuel oil. The process is basically the same as used by the original refinery. I use an old propane tank for the dirty supply oil, which is equipped with heating elemints to heat the oil to approximately 300 F. I pull a slight vacuum to eliminate the air and combustion hazzard. Another tank is beside it and this tank has a high vacuum. As you know, water will boil at room temperature if the vacuum is low enough. The same goes for the oil. The hot dirty oil is let into the vacuum tank with a small valve, and the oil is allowed to vaporize. I use pound cake pans to collect the distilled oil. These pans have a central hole for the vapor to pass through and I cut a small hole in the bottom of one side for the condensed oil to drain into a pipe fitting connected to the outside and then to a collection tank. Both the distillation column and the collecting tank are under vacuum. The temperature used determines the weight of the oil collected. Successively higher temperatures collect heavier oil. Once all of the useable fuel oil is collected the bottom oil is drawn off and taken to a used oil collection point or given to a local asphalt plant.
The lighter fractions can be burned as is while the heavier constituents make a very good diesel fuel extender.
Mike