GB761501A - Improvements in the catalytic cracking of hydrocarbon oils - Google Patents

Abstract

<PICT:0761501/III/1> In a process for the catalytic cracking of heavy hydrocarbon oils employing the heat-balanced fluidized catalyst technique, hot gas oil separated from the cracked products is cooled and then mixed with hot regenerated catalyst to produce a suspension of catalyst in oil vapours having a temperature above the cracking temperature (but not above 1050 DEG F.); this suspension is passed through a transfer line into the bottom of the fluidized catalyst bed in the reaction zone; and the fresh feed oil, preheated to a temperature below the cracking temperature, is separately introduced into the bottom of the fluidized catalyst bed, wherein the two streams intermingle to produce a suspension of catalyst in oil vapour at the cracking temperature. The process produces good quality gasoline, and obviates overcracking of the feed. The relative depth of cracking may be varied by the amount of cooling and heating, respectively, of the two streams fed to the reaction zone. The apparatus shown comprises a preheating furnace 9, a reactor 2, a product fractionator 6 to which are connected sidestrippers 7 and 8, a cooler 10 connected to the lower end of a riser 5 which leads up into the bottom of reactor 2, and a regenerator 1 which is connected to the lower end of riser 5 by standpipe 3. Gas oil at 600 DEG F. removed from the sidestrippers is passed through line 14 to cooler 10 where it is cooled to 180 DEG F. This recycle gas oil is then introduced into riser 5 where it mixes with regenerated catalyst at 1100 DEG F. from standpipe 3 to form a suspension of catalyst in oil vapours at about 1000 DEG F., which flows up the riser to reactor 2. Virgin gas oil is preheated in furnace 9 to 740 DEG F., and is then discharged through line 15 into the reactor at the top of riser 5. The feed rate ratio of virgin gas oil to recycle gas oil is 2:1; and the temperature of the mixture where it mingles with the fluidized bed of catalyst in reactor 2 is about 900 DEG F. A pressure of 11 p.s.i.g. is maintained in the reactor. The product vapours, issuing from the reactor through line 11, are passed to fractionator 6. Gasoline and gases are withdrawn from the head of the fractionator, and gas oil fractions are taken off into side-strippers 7 and 8. Spent catalyst leaves reactor 2 through line 4, and is regenerated in regenerator 1 which is maintained at a pressure of 16 p.s.i.g.