Abstract: A method for recovering sensible heat from a thermally decomposed high temperature hydrocarbon gas product in the form of high pressure steam of from 40 to 100 kg/cm.sup.2 has been discovered. This method comprises pre-cooling at first the thermally decomposed gas product of high temperature by mixing said gas product with sprayed low temperature hydrocarbon oil as a quenching oil to a temperature of about 300.degree. to 400.degree. C.; and then passing the mixture through the tubes of a shell-and-tube type heat exchanger so as to transfer the heat of said resulting mixture into a high pressure water flowing through the space of the shell side thereof to recover a high pressure steam, followed by separating the condensed hydrocarbon oil from the mixture to reuse said oil by recirculation.

Abstract: A decoking apparatus suitable for use on a reaction vessel for the thermal cracking of heavy petroleum oils the apparatus essentially including a rotatable main injection pipe to be disposed in the reaction vessel and having a multitude of jet nozzles along its length, and a second or auxiliary injection pipe positioned in the proximity of the main injection pipe to inject a scrubbing liquid over the outer peripheral walls of the main injection pipe to prevent deposition of coke. The main and auxiliary injection pipes are both supplied with heavy petroleum oil to remove the coke deposition from the reactor wall by the heavy petroleum oil jets from the main injection pipe while wetting the exterior of the main pipe with the heavy petroleum oil injected by the auxiliary injection pipe.

Abstract: Disclosed herein is a method of thermally cracking a heavy petroleum oil by introducing the heavy petroleum oil into a reactor and contacting the heavy petroleum oil thus introduced with a gas, which does not react with the heavy petroleum oil, at a temperature of 400.degree.-2000.degree. C. thereby thermally cracking the heavy petroleum oil. The method uses plural reactors and introduces the heavy petroleum oil into the reactors in a specified manner, and charges the reactor in advance with a specified amount of heavy petroleum oil of a specified temperature.

Abstract: A method for recovering sensible heat from a thermally decomposed high temperature hydrocarbon gas product in the form of high pressure steam of from 40 to 100 kg/cm.sup.2 has been discovered. This method comprises pre-cooling at first the thermally decomposed gas product of high temperature by mixing said gas product with sprayed low temperature hydrocarbon oil as a quenching oil to a temperature of about 300.degree. to 400.degree. C.; and then passing the resulting mixture through the tubes of a shell-and-tube type heat exchanger so as to transfer the heat of said mixture into a high pressure water flowing through the space of the shell side thereof to recover a high pressure steam, followed by separating the condensed hydrocarbon oil from the mixture to reuse said oil by recirculation.