Patent GB-775790-A (GB)
Title: Catalytic cracking of hydrocarbon oils
IPC: B01J8/00
Filed: 1954-12-21
Abstract: <PICT:0775790/III/1> Hydrocarbon oils such as gas oil are cracked by passing a suspension of hot catalyst particles in the hydrocarbon vapours upwards through a reactor 10 at a velocity of at least 6 feet per second and separating the cracked products from the spent catalyst.  The carbonaceous deposit is burned off the spent catalyst by passing it with oxygen-containing gas through regenerator 40 at a velocity of at least 6 feet per second; a major proportion of the hot regenerated catalyst is recycled to the inlet of the regenerator, and the remainder is mixed with fresh hydrocarbon feed flowing to the reactor.  Because the hydrocarbon vapours expand in volume as cracking proceeds, reactor 10 is made in the shape of a slender inverted cone.  The catalyst may be synthetic silica-alumina, silica-magnesia boria-alumina or natural clay, and preferably has a particle size of 20 to 100 microns.  Gas oil, preheated to about 675 DEG F., is introduced into the system through conduit 13, and is vaporized by hot regenerated catalyst (5 to 6 parts per part by weight of oil) flowing through conduit 11.  The mixture of catalyst and hydrocarbon vapours then passes upwardly at a superficial velocity of about 10 ft./sec. through reactor 10 where the pressure is about 10-25 p.s.i.g., the temperature about 850 DEG -1000 DEG F., and the density of the mixture about 6 lbs./cubic foot.  There is about 55 per cent conversion in the reactor.  The mixture flows out through rough cut cyclone 15, which contains moving vanes, into separation chamber 16.  The catalyst particles are thrown tangentially outwards into the lower portion of this chamber; and residual catalyst is separated from the hydrocarbon vapours by cyclone 18.  The hydrocarbon vapours are introduced through conduit 22 into fractionating equipment (not shown) to separate gasoline and other products.  The catalyst is withdrawn from chamber 16 through conduit 17, and flows to stripper 30 which contains baffles and is supplied with steam through conduit 31. The steam flows up through the downwardly-cascading catalyst, and strips entrained hydrocarbons therefrom.  The steam and hydrocarbon vapours are introduced into chamber 16.  The stripped spent catalyst flows down conduit 34, and is conveyed into the bottom of regenerator 40 by air introduced through conduit 35. Hot regenerated catalyst is introduced into the bottom of the regenerator through conduit 41.  The ratio of recycle catalyst to spent catalyst is about 3 : 1.  Auxiliary burner 42 at the base of the regenerator is normally used only during the starting-up of the plant, when the burner is supplied with fuel through line 43. Air is supplied to the burner through line 45, and the flow of air through this line is continued during on-stream operation.  The mixture of catalyst and air flows upwards through the regenerator at a superficial velocity of about 10 ft./sec.  The average temperature in the regenerator is 1000 DEG -1200 DEG F., the average pressure is 5 to 15 p.s.i.g. and the density of the catalyst/air mixture is about 8 lbs./cubic foot.  The hot regenerated catalyst and flue gases pass through rough cut cyclone 48 into separation-chamber 47.  The flue gases finally flow out through cyclone 50.  The separated catalyst passes through conduit 49 into hopper 60.  About threequarters of this hot regenerated catalyst is recycled to the regenerator through conduit 41, and the remainder flows through conduit 11 to reactor 10.  The flow of catalyst through conduit 41 is controlled by the amount of aeration gas introduced therein through conduit 65, which is controlled by valve 66.  In order to overcome loss of catalytic activity due to metallic deposition, part of the catalyst is withdrawn from the system through line 80, and is replaced by fresh catalyst introduced into conduit 65.  Hopper 70 contains the fresh catalyst, and this is introduced into the cracking system through line 76 and conduit 78, fluidizing air being introduced through lines 73 and 79.  About 12 per cent of the total catalyst in the system is replaced by fresh catalyst per day. Specifications 558,879 and 716,242 are referred to.