Method and apparatus for treatment of oil contaminated sludge

A process for treating an oil-containing sludge for recovery of oil-free solids therefrom, said sludge comprising an emulsion having a continuous liquid phase and a dispersed liquid phase, of mutually immiscible liquids, one of said liquids being an aqueous liquid freely miscible with water and the other of said liquids being a hydrocarbon oil, either or both of said liquids containing dispersed inorganic solids, said process comprising the steps of:

• (a) in a first, sludge-conditioning stage, preparing a conditioned sludge ready for centrifugation, said conditioned sludge being characterized by a solids content of less than 50% by weight, of wataer content of less than 90% by weight, an oil phase with an API gravity of less than 12.degree., a continuous aqueous phase, and the solids in the sludge being primarily water-wetted, said preparation being accomplished by addition of the appropriate amount of water, hydrocarbon diluent and conditioning agent to attain said characterization based on the results of predetermination of the characteristics of said oil-containing sludge prior to conditioning, and adjusting the temperature of the conditioned sludge to a temperature slightly below the boiling point of the lowest boiling constituent thereof;
• (b) in a second sludge treatment stage, subjecting the conditioned sludge to centrifugation, to separate therefrom a solids-rich material of low hydrocarbon content and an aqueous supernatant liquid of higher hydrocarbon content;
• and
• (c) in a liquid/liquid separation stage, causing the supernatant liquid to separate into an aqueous phase and a hydrocarbon phase.