Thermal cracking of heavy hydrocarbon oils

Abstract

A heavy hydrocarbon feed stock is, after being heat-treated in a first cracking zone, introduced into a second thermal cracking zone for obtaining a thermally cracked product and a pitch product. The second cracking zone has a plurality of cracking reactors which are connected in series, through which is successively passed the treated feed stock and to each of which is supplied a gaseous heat transfer medium to maintain the liquid phase therein at a temperature sufficient for effecting the thermal cracking and to strip the resulting distillable, cracked components from the liquid phase. The thermal cracking temperature in one reactor is so controlled as to become higher than that in its adjacent upstream-side reactor. The distillable, cracked components in respective reactors are removed overhead therefrom and separated into a heavy fraction and a light fraction, while the liquid phase in the downstream-end reactor is discharged therefrom for recovery as the pitch product. The light fraction is recovered as a light product oil, while the heavy fraction is fed to a third thermal cracking zone for obtaining a tar-containing product which is recycled to at least one of the reactors of the second thermal cracking zone.