Method of decoking a cracking plant

A method of operating a hydrocarbon cracking installation in which a cracking furnace is followed by a cracking gas cooler, said method comprising the steps of:

• (a) subjecting a hydrocarbon feedstock to a cracking temperature in said furnace by heating cracking tubes in said furnace and passing said feedstock therethrough, thereby producing cracking gases;
• (b) passing said cracking gases through said cooler while supplying said cooler with a coolant to reduce the temperature of said cracking gases, surfaces of said cracking tubes and said cooler developing carbonaceous deposits;
• (c) while further heating said furnace and cooling said surfaces of said cooler with said coolant, interrupting the passage of said feedstock through said cracking installation, feeding a gas mixture of oxygen and steam through said cracking tubes and at least a portion of the flow cross section of said cooler, thereby effecting substantial reduction of said carbonaceous deposits in said cracking tubes;
• (d) thereafter, while continuing to heat said furnace and cool said surfaces of said cooler, increasing the mass rate of flow of said gas mixture until the temperature in said cooler increases so far that carbonaceous deposits in said cooler are subjected to a watergas reaction;
• and
• (e) continuing step (d) until said carbonaceous deposits are removed from said cracking installation.