Abstract: A flexible steam cracking process for hydrocarbon feeds comprises injection of particles with an average size of between 0.02 mm and 4 mm, at a circulation rate in indirect transfer line exchangers (4) of 20 to 180 m/s, and in a sufficient quantity to limit the increase in temperature at the outlet to the exchangers (4) to a value of less than 100.degree. C. per month, into at least one point upstream of an indirect transfer line exchanger (4), cracking zone (2) remaining in communication with downstream means (6) for the treatment of cooled effluents. At least 70% by weight of the quantity of injected particles is introduced between the outlet to the cracking zone (2) and the tubes of the indirect transfer line exchanger (4). Chemical decoking is carried out in the tubes of the cracking zone at time intervals of less than 4 months by establishing accelerated coke gasification conditions, for example by injecting compounds which catalyse gasification by steam, or by decoking in air and/or steam.

Abstract: A steam cracking process and facility is described which comprises injection of erosive powder to effect at least partial decoking of transfer line exchangers without interrupting the steam cracking stream. The powder, preferably injected just upstream of the transfer line exchangers (TLE) (4), is separated from the cracked gases in primary gas/solid separators (5), temporarily stored in receiving drums at a controlled temperature and evacuated to a common powder storage and/or treatment module by pneumatic transfer by means of a relatively low flow of uncondensable gas. The process and facility can be used to collect solid fragments generated by injection of chemical compounds which are catalysts for the gasification of coke by steam.

Abstract: A method of decoking the inside walls of a hydrocarbon steam-cracking installation by means of solid particles of very small size, which particles are injected into the hydrocarbon feedstock flowing through tubes (12) of the steam-cracking furnace (10) and through indirect quench means (16). A cyclone (28) at the outlet from said indirect-quench means serving to separate the solid particles from the gaseous products and enabling the solid particles to be recycled through the installation after being mixed with a liquid or a gas and after their pressure has been raised. The invention also relates to a steam-cracking installation enabling the method to be performed.

Abstract: An installation for steam cracking hydrocarbons comprises at least one hydrocarbon cracking furnace, an indirect quench heat exchanger for the effluents leaving the furnace, direct quench means for said effluent, and means (36, 38) for injecting erosive solid particles into the installation for decoking purposes. The installation also includes a cyclone (10) placed at the outlet from the indirect quench heat exchanger to separate the solid particles from the gaseous effluent, with the solid particle outlet (14) from said cyclone being connected to storage tanks (20, 30) connected in series with isolating valves (16, 28, 34), a source (38) of gas under pressure being provided to raise the pressure in one of the tanks and to inject the solid particles into the installation.

Abstract: A method of steam cracking hydrocarbons in a steam cracking furnace (10) having tubes (12) connected to indirect quench menas (16) for the gaseous effluent leaving the furnace, the method consisting in allowing a layer of hard coke to form on the inside walls of the furnace tubes (12) and then in injecting a small quantity of solid erosive particles into the steam and hydrocarbon feedstock to be cracked, with the particles being separated from the gaseous effluent in a cyclone (28) provided at the outlet from the indirect quench means. The invention serves in particular to enable a steam cracking installation to operate continuously.

Abstract: A method and apparatus for steam cracking hydrocarbons in a furnace (10) having rectilinear single-pass tubes (12) which are interconnected at their outlet ends by a manifold (18) within which the steam cracking effluents are subjected to limited pre-quenching by injection of a cooler gaseous medium, with the effluents then being conveyed to quenching means (22). The invention serves in particular to increase the yield of hydrocarbon steam cracking installations.