Process for converting waste motor oil to diesel fuel

A continuous process for cracking unprocessed waste motor oil into a plurality of fuel oils comprising:

• thermally cracking the unprocessed waste motor oil in a cracking vessel at a cracking temperature ranging from about 625.degree. F. to 700.degree. F. to yield a vaporized fraction of cracked hydrocarbons and a liquid fraction of a fuel oil other than diesel;
• distilling the vaporized fraction of cracked hydrocarbons to separate out light ends, thereby yielding a remaining portion of the vaporized fraction of cracked hydrocarbons comprising a diesel fuel;
• withdrawing a portion of the liquid fraction from the cracking vessel, combining the withdrawn portion of the liquid fraction with additional waste motor oil to obtain a combined stream of additional waste motor oil, supplying the combined stream to a heat recovery device with a circulation pump, and subsequently introducing the combined stream, preheated to at least the cracking temperature, into the cracking vessel;
• continuously withdrawing the fuel oil other than diesel from the cracking vessel while continuously introducing the combined stream of additional waste motor oil preheated to the cracking temperature into the cracking vessel with the circulation pump to maintain a volume in the cracking vessel, wherein a cracking temperature in the cracking vessel is maintained by the preheated combined stream of additional waste motor oil;
• wherein the heat recovery device heats the combined stream of additional waste motor oil to at least the cracking temperature with heat generated by oxidation of vapors of the separated light ends in a thermal oxidizer.

A process of converting used motor oil into a No. 5 fuel oil and No. 2 diesel fuel without fouling of the process equipment, comprising:

• heating a quantity of unfiltered used motor oil, carrying a suspension of metal particles, at ambient pressure to a cracking temperature in a cracking vessel;
• withdrawing a first cracked oil from said cracking vessel, said first cracked oil comprising a non-diesel fuel oil carrying a suspension of metal particles upon which solid production products have formed;
• withdrawing a portion of liquid from the cracking vessel;
• combining the withdrawn portion of the liquid with additional used motor oil containing suspended metal particles to obtain a combined stream of additional used motor oil containing suspended metal particles:
• supplying the combined stream of additional used motor oil containing suspended metal particles to a heat recover device with a circulation pump;
• preheating the combined stream of additional used motor oil containing suspended metal particles to at least the cracking temperature with a heat recovery device;
• maintaining a fixed volume of used motor oil inside the cracking vessel by continuously introducing the combined stream of preheated additional used motor oil containing suspended metal particles into the cracking vessel such that the cracking temperature is maintained in the cracking vessel through such continuous introduction of the combined stream of preheated additional used motor oil;
• separating a vaporized fraction of cracked hydrocarbons in a distillation column, wherein the vaporized fraction of hydrocarbons enters the distillation column directly upon exiting the cracking vessel;
• separating light ends from the vaporized fraction, a remaining portion of the vaporized fraction comprising the No. 2 diesel fuel;
• supplying the light ends to a thermal oxidizer which supplies heat to the heat recovery device by oxidizing vapors of the light ends;
• blending the first cracked oil withdrawn from the cracking vessel with a No. 6 bunker oil to obtain the No. 5 fuel oil;
• and
• filtering the No. 5 fuel oil to remove the solid production products.