Patent GB-767312-A (GB)
Title: Improvements in or relating to cracking of hydrocarbons
IPC: C10G11/18
Filed: 1954-03-26
Abstract: Hydrocarbon oils are cracked by forming a suspension of particles of cracking catalyst having a specific gravity of 1.6 to 2.7 in the vaporized oil, passing the suspension at a temperature between 800 DEG  <PICT:0767312/III/1> and 1100 DEG F. and at a vapour velocity of 8 to 50 feet per second through a vertical elongated reaction zone having a length to diameter ratio in the range from 4:1 to 20:1, maintaining the ratio weight of feed passing through the reaction zone in an hour/weight of catalyst in the reaction zone at any particular instant in the range from about 20:1 to about 300:1, and separating the cracked product vapours from the suspension discharged from the reaction zone.  The method may be used for cracking gas oil, heavy naphtha, and kerosene.  Silica-alumina, silica-magnesia, and silica-zirconia catalysts may be used.  Gas oil, introduced through line 11, is heated to 450 DEG F. in heat exchanger 12, and is then passed through line 13 which divides into two streams.  One stream is introduced via line 17 into the lower part of vaporizer 18.  The other stream is raised to 840 DEG F. in furnace 15 and is then introduced into vaporizer 18, which is maintained at a temperature of 825 DEG F. and a pressure of 40 psig. Vapours from vaporizer 18 travel through line 20 to the base of conduit 22 where hot silica-alumina catalyst (particle diameters of 20 to 80 microns) is added, and forms a suspension in the vapour stream.  Liquid hydrocarbon recycle material is added through line 25 to the suspension while it is flowing through line 10, and liquid from vaporizer 18 is added via line 21.  Both these liquid streams become vaporized in line 10.  The suspension then enters reaction zone 24, which is maintained at a temperature of 930 DEG F. and a pressure of 30 psig.  The reaction zone has an overall length of 55 feet; its internal diameter is 8 feet for the upper 35 feet of its length, which tapers for its lower 20 feet of length to 6 feet internal diameter.  The suspension passes through zone 24 at a superficial gas velocity of 11 feet per second.  The catalyst to oil ratio in the suspension is about 4.6; and the weight ratio of feed passing through the reactor per hour to the weight of catalyst in the reactor is about 77.  The suspension discharged from zone 24 is introduced into distributer box 30, which is disposed in the middle section of separating vessel 27.  Part of the suspenion flows into the upper section of vessel 27, which is provided with cyclones 32; and the remainder descends into the lower section, which is provided with baffle plates 34 and is supplied with stripping steam via manifold 36. The cracked products leave vessel 27 through conduit 42, and are introduced into the lower section of fractionation tower 43. Tower 43 is operated at a top temperature of 275 DEG F. and a bottom temperature of 700 DEG F., the pressure therein being 22 psig.  Light hydrocarbons and gasoline are withdrawn from the head of the tower. Heating oil is withdrawn from the tower via line 47, light gas oil is withdrawn via line 48, and heavy gas oil is withdrawn via line 49.  A heavier fraction is withdrawn from tower 43 by a line 50 which connects into line 25, and is recycled to the reaction zone 24. Stripped catalyst flows out of the base of vessel 27 through conduit 38, and is then carried by air through conduit 40 into regenerator 411.  Additional air is introduced into the regenerator through line 53; and the regenerator is maintained at a temperature of 1100 DEG F. and a pressure of 11 psig, whereby the carbonaceous deposits are removed from the contaminated catalyst by combustion.  The regenerated catalyst is carried via line 54 and distribution box 56 into vessel 55, which is provided with cyclones 57.  The regenerated catalyst is separated from the flue gas in vessel 55; some of the regenerated catalyst is withdrawn through conduit 22 and mixed with fresh feed, while the remainder is recycled to the regenerator via conduits 60 and 62.  Flue gas at about 1000 DEG F. is withdrawn from vessel 55 via conduit 64, and passes through waste heat boiler 65. The cooled flue gas is then passed through cyclone 66 where the majority of the catalyst fines are removed; the remainder of the catalyst fines are removed from the flue gas by electrical precipitators 70.  The flue gas is finally discharged into the atmosphere via stack 74.  The catalyst fines are returned to regenerator 411.