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 facility and a process for steam cracking include controlled injection of solid particles into a transfer line exchanger (3). The particles are injected via injection lines, numbering between 1 and 8, just upstream of an impact-diffuser (6) comprising solid surfaces disposed on either side of the line for transfer of the cracked gases to the exchanger; this impact-diffuser is located in the inlet cone (2) of the exchanger, is permeable to the gases via a plurality of passages and at least 70% opaque viewed from the transfer line.

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.