Method of heat recovering from high temperature thermally cracked hydrocarbons

A method of recovering heat from a high temperature gas product obtained by thermal decomposition of hydrocarbons in the form of high pressure steam which comprises

• (a) precooling, in a vessel comprising a precooling zone, a heat exchange zone and a separating zone, the high temperature gas product in the precooling zone by mixing said gas product with a sprayed low temperature hydrocarbon oil of a by-product obtained from said thermal decomposition of hydrocarbons, which contains from 30 to 80 percent by weight of a pitch based on the weight of said sprayed low temperature hydrocarbon oil, as a quench to a temperature of from 300.degree. C. to 400.degree. C.;
• (b) passing the resulting mixture downwardly from the precooling zone through the tubes of a substantially vertical shell-and-tube type heat exchange means, at a linear gas velocity of 15 to 50 meters per second in said tubes to form a thin liquid film layer of the sprayed oil on the inside walls thereof, and transferring the heat contained in said resulting mixture into a high pressure water flowing through the shell side of the heat exchange means and recovering therefrom a high pressure steam of from 40 to 100 kg/cm.sup.2 ;
• (c) separating the said hydrocarbon oil in the separating zone from said resulting mixture passed through the tubes of said heat exchange means downwardly to the separating zone;
• and
• (d) recirculating the separated hydrocarbon oil as a quench to the precooling zone.