Recovering oil from emulsion by stirring, heating, and settling

Claim 1

A process for treating sludge containing oil, water and particulate solid, said sludge having, in parts by weight, a free-water content in the range of from about 4 to 50 parts per part of said solid, comprising: (1) forming a first upper layer comprising oil or oil and water and a first lower layer comprising an aqueous suspension of said solid and residual oil by stirring said sludge while maintaining the resulting mixture at a mixing temperature in the range above about 95° F. and below the boiling point thereof, and thereafter maintaining said mixture under sludge settling conditions including a settling temperature in the range above 95° F. and below the boiling point thereof for a period in the range of from about 0.5 to 24 hours and sufficient for said first layers to form, said stirring expending for each 1000 gallons of said sludge an amount of mechanical energy in the range of from about 0.1 to 5 horsepower; (2) withdrawing at least a portion of said first upper layer from the resulting settled mixture; (3) withdrawing at least a portion of said first lower layer from said resulting settled mixture; (4) separating at least a portion of said withdrawn portion of said first lower layer into (i) a second upper layer comprising at least a portion of said residual oil, or said portion and water; and (ii) a second lower layer, said second lower layer having an upper zone comprising water substantially free of said solid and a lower zone comprising settled solid, the remainder of said residual oil, and water by maintaining said withdrawn portion of said first lower layer under sludge settling conditions for a period in the range from about 0.5 to 48 hours; (5) withdrawing at least a portion of said second upper layer from the resulting settled withdrawn portion of said first lower layer; (6) withdrawing at least a portion of said upper zone from said settled withdrawn lower portion and returning at least a portion of it to said first lower layer, and (7) withdrawing at least a portion of said lower zone from said settled withdrawn lower portion, said portion of said lower zone containing, based upon said settled solid, less than 30 weight percent of oil.