Process and apparatus for cracking hydrocarbon oils. [action of heated surfaces at elevated temperatures]

A method of cracking oils comprises subjecting a body of oil in a still to the action of heated surfaces and thereby heating the oil to a cracking temperature under pressure and introducing a current or currents of gas, acting on the ''air-lift'' principle, in upwardly directed jets in an upwardly directed passage within the body of oil. The gaseous current or currents are made up of gases produced during the cracking operations. The apparatus for carrying out this process includes a still provided with heating means for heating the oil to a cracking temperature under pressure, means for withdrawing gases from the still, and means for reintroducing a gaseous current or currents comprising a portion of the same into the still in upwardly directed jets near the lower end of an upwardly directed circulation pipe arranged in the still and adapted for coating with the gaseous current or currents for effecting circulation of the oil over the heating surfaces of the still.