Patent GB-700309-A (GB)
Title: Improvements in or relating to coking and cracking of heavy hydrocarbon feeds
IPC: C10B55/10
Filed: 1951-12-05
Abstract: <PICT:0700309/III/1> In a process for obtaining coke and liquid products such as naphtha and gas oil from heavy oil residues or the like, the feed material is sprayed on to a bed or introduced into a stream of inert solid particles, preferably coke particles, in a coking zone at a temperature of between 800-1200 DEG  F. thereby depositing coke on the particles and liberating hydrocarbon vapours which are contacted with a fluidized catalyst in a cracking zone at a temperature of between 800-1000 DEG  F., the fluidized catalyst having a substantially different particle size range to the inert solid particles so that the catalyst and inert solid particles may readily be separated from a mixture of both.  Spent catalyst particles are withdrawn from the cracking zone and regenerated by burning off the carbonaceous deposits on them in a fluidized regeneration zone, the heated catalysts being then used to supply the heat required for both the coking and cracking operations. The inert solid particles preferably have the larger particle size and the heat of the regenerated catalyst may be supplied to the coking zone by mixing the heated catalyst with coke withdrawn from the coking zone, separating the thus cooled catalyst and heated coke and returning separated catalyst and coke to the cracking and coking zones.  In one embodiment employing a two-stage coking step and having coking zones 2 and 16 with fluidized beds 3 and 17 of coke particles having a size in the range of 100-500 microns, the heavy oil residues preferably preheated to about 700 DEG  F. are sprayed into the upper bed 3 which is maintained at a temperature of about 850-950 DEG  F.  The resulting hydrocarbon vapours pass upwardly into a cracking zone 6 containing a bed of catalyst 7, for example a synthetic silica-alumina, or-magnesia or -boria composite, having a particle size in the range of 50-150 microns and maintained at about 900-1000 DEG  F., vaporous products from the cracking zone 6 pass to a conventional recovery system.  Spent catalyst is withdrawn through a line 10 and conveyed to a fluidized regeneration zone 13, air for combustion being admitted through line 12.  The regeneration zone is operated at about 1100-1250 DEG  F., a heat exchanger coil 14 being provided to absorb any heat surplus to the requirements of the cracking and coking zones and may be used to preheat the feed material.  Coke is withdrawn from the bed 3 through a well 15 passing to the lower bed 17 maintained at about 1000 DEG  F. where any oily residue on the particles is coked.  From the bed 17 coke is withdrawn through line 18 as a product and through line 19 for reheating in a mixing and elutriation zone 20 to which heated catalyst is supplied by line 21 from the regeneration zone 13.  Steam or other inert gas is admitted to the zone 20 through line 22 at a velocity such that the catalyst particles are entrained and carried off overhead while the larger coke particles are fluidized and pass downwardly out of the zone through line 23, being returned in suitable proportions to beds 3 and 17 through lines 32 and 31.  Entrained catalyst particles pass back to the cracking zone 6 although a proportion may be returned to the regeneration zone 13.  If desired more than two coking zones may be used and the coke particles may be replaced by particles of sand, spent clay or pumice if a coke of low ash content is not required.  In a modification the oil residue is mixed and entrained in an inert gas such as steam with heated coke particles withdrawn from the mixing and elutriation zone and transferred to a fluidized coking zone, partial coking of the feed being effected during the transfer.  The mixing and elutriation zone is arranged in the same vessel as the coking and cracking zones and adjacent to the coking zone.  In a further modification the feed is mixed with and coked by heated coke particles while entrained in an inert gas such as steam in a line leading into a fluidized cracking zone, heated catalyst from the regeneration zone being returned directly to the cracking zone.  The mixture of coke and catalyst in the cracking zone is continuously withdrawn and elutriated, entrained spent catalyst passing to the regeneration zone and coke is withdrawn as a product or admixed with a fresh quantity of feed and returned to the cracking zone.  The elutriation zone may be filled with a non-fluidized packing such as Raschig rings and the elutriation gas may be steam or a light hydrocarbon gas.  If necessary the viscosity of the feed material may be reduced by mixing with naphtha and clay or alumina may be used as the cracking catalyst.