Patent GB-719872-A (GB)
Title: Improvements in or relating to the conversion of heavy petroleum feed stocks into lighter products
IPC: C10G9/00
Filed: 1952-03-05
Abstract: <PICT:0719872/III/1> <PICT:0719872/III/2> Heavy hydrocarbon oils, such as reduced crudes and pitch, are converted into lighter products by heating the oil at 750 DEG -1150 DEG F. for a period not in excess of 5 seconds so as to partially vaporise the oil, separating the vapours from the non-vaporized residue, introducing the vapours (or the condensate thereof) immediately (i.e. without intervening storage and/or fractionation), into a catalytic cracking zone, and introducing the non-vaporized residue into a coking zone containing a dense fluidized bed of hot inert solid particles (e.g. of petroleum coke), wherein thermally-cracked vapours and coke are produced. The thermally-cracked vapours withdrawn from the coking zone may be introduced into the catalytic cracking zone, or they may be passed to a separate recovery system.  The initial vaporization step, which may be accompanied by mild thermal cracking, may be carried out by contacting the oil, preferably preheated to 600 DEG -800 DEG F., with hot inert solid particles and/or an inert gas. Heating in a vacuum may also be employed to effect the rapid partial vaporization.  A pitch or reduced crude (Conradson carbon value-10 to 30 weight per cent.) is supplied at 650 DEG -750 DEG F. through line 1, Fig. 1, into vaporizer-line 2.  Finely divided petroleum coke (100-300 microns), heated between 1100 DEG  and 1500 DEG F., is also introduced into line 2, from line 3, the weight ratio of solids to oil being 5 : 1 to 50 : 1; whereupon the mixture attains a temperature of 1050 DEG  to 1100 DEG F., and a substantial portion of the pitch is vaporized, the unvaporized portion being deposited on the solid particles.  The mixture is allowed to remain in line 2 for 0.5 to 1 second, the contact time being controlled by the admission of steam through line 9.  The mixture is discharged from line 2 into cyclone 4.  The separated vapours are passed through line 5 and introduced, together with finely divided silica-alumina catalyst injected through line 8, into catalytic cracking unit 6, which is maintained at a temperature between 800 DEG  and 1000 DEG F.  The effluent from unit 6 is passed to fractionating column 7 in order to separate gasoline. The solid particles, containing residual pitch amounting to 2 to 20 weight per cent. of the feed, are passed from cyclone 4 through line 10 into vessel 11, where they are maintained at a temperature of 1050 DEG -1100 DEG F., steam being introduced through line 13 to keep the particles in the form of a dense fluidized bed.  The bottoms withdrawn from column 7 may be passed to vessel 11 through line 16.  The vapours liberated in vessel 11 are withdrawn through line 14, and are either combined with the vapours flashed off in vaporizer 2, or passed through cyclone 17 to a separate recovery system.  The average residence time of the particles in vessel 11 may range from 1 to 10 minutes.  Some of the relatively dry particles are withdrawn from vessel 11 through well 30, stripped of residual volatiles by steam introduced through line 31, and returned to line 2 via line 3.  Particles are also withdrawn from vessel 11 through well 19 and standpipe 20, and are passed to line 23 wherein the temperature of the particles is raised to between 1100 DEG  and 1500 DEG F. by combustion of some of the coke with air introduced through line 26.  Alternatively, or in addition to supplying heat by combustion, heat may be produced in auxiliary fuel burner 24, the hot flue gases being then introduced into line 23. The heated particles are separated from gases in cyclone 27, and returned through dip leg 28 to vessel 11, at a rate sufficient to maintain the desired temperature therein.  When it is desired to maintain a higher temperature in line 2 than in vessel 11, some of the hot particles withdrawn from cyclone 27 are introduced directly through line 29 and steam-line 9 into line 2.  Excess coke produced in the process may be removed through line 32 or any other convenient point.  In a modification vaporizing-line 2 is mounted directly above vessel 11; and the thermally-cracked vapours, inert gas and entrained inert particles, leaving the top of vessel 11, enter line 2 and partially vaporize the feed thereto.  In another embodiment, Fig. 4 a hot extraneous gas is utilized to partially vaporize the feed.  A vacuum residuum, from line 1, is mixed in line 2 with flue gases at 1500 DEG -2000 DEG F., withdrawn from cyclone 27, in an amount sufficient to vaporize about 20 to 75 per cent. of the residuum.  The resulting mixture of flue gas and vaporized feed is separated from non-vaporized feed in cyclone 4; and the separated vapours are promptly cooled to 400 DEG F. in heat-exchanger 8.  The hydrocarbon condensate is separated from the flue gas in drum 41, and is introduced into catalytic cracking zone 6.  The non-vaporized feed is withdrawn from cyclone 4 and introduced through line 10 into thermal-cracking vessel 11.  Coke particles withdrawn from vessel 11 through well 19 and line 20, are mixed in line 23 with flue gases from burner 24 which may be at a temperature between 2500 DEG  and 3500 DEG F. or higher.  The resulting direct heat exchange between the gases and the coke particles produces a mixture at 1500 DEG -2000 DEG F.  The mixture may be passed to cyclone 27 via line 37; and the separated coke returned to vessel 11 via leg 28, while the gas is introduced through line 36 into line 2.  Alternatively the mixture of coke and flue gas is discharged directly from line 23 into line 2; the coke then being separated in cyclone 4 together with non-vaporized feed.  In a simpler modification, coke circulation is omitted, and hot flue gas is passed directly from burner 24 into line 2.  Other inert materials which may be used in the process instead of coke are sand, spent clay, and pumice.  The viscosity of the feed may be reduced by dilution with naphtha. Catalysts mentioned are activated clay, activated alumina, and synthetic composites of silica with a minor proportion of alumina, magnesia or boria. Specifications 700,309 and 710,144 are referred to.