Patent ID: 7670573

Claim:
An apparatus for cracking a hydrocarbon feedstock containing resid and coke precursors, comprising: (a) a heating zone for heating said hydrocarbon feedstock to provide heated hydrocarbon feedstock; (b) a mixing zone for mixing a primary dilution steam stream with said heated hydrocarbon feedstock to provide a mixture stream containing coke precursors; (c) a flash/separation vessel for flashing said mixture stream to form a coke precursor depleted vapor phase and a coke precursor rich liquid phase, said vessel comprising (i) a bottom outlet in the flash/separation vessel which comprises internal surfaces and associated outlet piping, which surfaces and piping during operation become coated with said liquid phase and thereafter at least partially coked; (ii) an overhead outlet for removing the vapor phase and a trace of condensed vapor phase, which overhead outlet comprises internal surfaces and associated outlet piping, which surfaces and piping during operation become coated with condensed vapor phase and thereafter at least partially coked; (iii) an inlet for introducing sufficient purging steam to said flash/separation vessel to remove said vapor phase from said vessel and said liquid phase from said internal surfaces and/or outlet piping; and (iv) an inlet providing an air/steam mixture stream characterized by an air/steam weight ratio ranging from about 0.01 to about 0.5 for introducing said air/steam mixture through said flash/separation vessel under conditions sufficient to at least partially combust coke on said internal surfaces and/or outlet piping; (d) a pyrolysis furnace comprising a convection section, and a radiant section for thermally cracking the vapor phase to produce an effluent comprising light olefins; (e) a means for quenching the effluent comprising light olefins; (f) a recovery train for recovering cracked product comprising light olefins from the quenched effluent; (g) a means for determining the level of coking in said flash/separation vessel and/or in said associated outlet piping; and (h) a control valve for interrupting the flow of said hydrocarbon feedstock with resid and coke precursors to said flash/separation vessel when a predetermined level of coking in the flash/separation vessel is reached.