Continuous pyrolysis and decoking process for use in the production of acetylene

A continuous pyrolysis and decoking process for producing an acetylenic compound comprising conducting the process in a reaction zone (40) of refractory material, said reaction zone being elongate in one direction (one axis), and comprising a heating zone and a cooling zone following the heating zone, the heating zone comprising at least two rows (1, 2) defining flow paths substantially parallel to the axis and separated by an outside wall (70) of refractory material located between two successive flow paths, said process comprising passing through at least one of said rows a gaseous mixture supply (10, 60) containing a hydrocarbon containing at least one carbon atom and steam, and passing through at least one other of said rows a supply (60) of a non hydrocarbon fluid comprising steam, said rows comprising heating means (8) surrounded by sleeves (7) located internally of said flow paths and substantially perpendicular to the reactor axis, wherein coke is deposited in the reaction zone, the process being characterized in that the gaseous mixture is circulated in at least one row of the heating zone to pyrolyze said mixture to form an acetylenic compound and to produce a temperature at the outlet to said zone of at least 850.degree. C., and said non-hydrocarbon fluid comprising steam is passed into at least one other row of the heating zone in a sufficient quantity and at a sufficient temperature to decoke the reaction zone at least in part to form carbon monoxide and hydrogen endothermally and to produce a temperature at the outlet of said zone of at least 850.degree. C., and a temperature in the zone sufficient for a later pyrolysis step and recovering hydrocarbons and a decoking effluent from said reaction zone, measuring the extent of decoking and when the reaction zone is sufficiently decoked, placing the reaction zone onstream as a heating zone for pyrolysis said process being conducted so that during the decoking, at least one pyrolysis zone is onstream so as to permit the gaseous mixture to be pyrolyzed continuously said mixture in the pyrolysis zone having a weight ratio of H.sub.2 O to hydrocarbon of 0.55:1 to 20:1.