Patent ID: 7244871

Claim:
A process for removing coke formed during cracking of a hydrocarbon feedstock containing resid and coke precursors, said process comprising: (a) heating said hydrocarbon feedstock; (b) mixing the heated hydrocarbon feedstock with a primary dilution steam stream to form a mixture stream containing coke precursors; (c) flashing the mixture stream in a flash/separation vessel to form a coke precursor depleted vapor phase and a coke precursor rich liquid phase; (d) removing the liquid phase through a bottom outlet and vapor phase with a trace of condensed vapor phase through an overhead outlet in the flash/separation vessel which vessel comprises internal surfaces and associated outlet piping, which surfaces and piping become coated during operation with said liquid phase and/or said condensed vapor phase and thereafter at least partially coked; (e) cracking the vapor phase in a radiant section of a pyrolysis furnace to produce an effluent comprising olefins, said pyrolysis furnace comprising a radiant section and a convection section; (f) quenching the effluent and recovering cracked product therefrom; and (g) determining the level of coking in said flash/separation vessel or in piping immediately downstream of said flash/separation vessel, and when a predetermined upper coke level is reached; (i) interrupting flow of said hydrocarbon feedstock containing resid and coke precursors to said flash/separation vessel; (ii) purging said flash/separation vessel with steam under conditions sufficient to substantially remove said vapor phase from said vessel and said liquid phase from said internal surfaces and/or outlet piping; (iii) introducing an air/steam mixture through said flash/separation vessel under conditions sufficient to at least partially combust coke on said internal surfaces and outlet piping; and (iv) restarting the flow of said hydrocarbon feedstock to said flash/separation vessel when a predetermined lower coke level on said internal surfaces and/or outlet piping is reached.