GB689280A - Catalytic cracking heat exchange process - Google Patents

Abstract

<PICT:0689280/III/1> In a process for the cracking of a petroleum oil fraction such as gas oil using fluidized catalyst, followed by fractionation of the cracked products, the oil feed supplied to the reactor and the catalyst-in-heavy-oil slurry withdrawn from the base of the fractionating column are passed in heat-exchange relationship; and the gummy material deposited in the heat-exchanger by the oil feed is removed by periodically interchanging the flow-paths of the two streams within the heat-exchanger so that the slurry flows through (and cleans) the path formerly traversed by the oil feed, and vice versa. The apparatus shown in the Figure represents a fluidized, dense-bed catalytic cracking unit comprising a reactor 1, catalyst-regenerator 2, and a column 10 in which the products (which contain a small amount of entrained catalyst) withdrawn from reactor 1 through line 5, are fractionated. The upper part of column 10 contains plates 11, and the lower part contains disc and donut packing 12. An over-head fraction is withdrawn from column 10, and side streams are withdrawn through lines 14 and 15. A slurry containing about 0.4 lbs. of catalyst per gallon of heavy oil, at a temperature of about 650 DEG F, is withdrawn from the base of column 10 through line 16, and is subdivided into two streams. One stream of the hot slurry is passed through heat-exchanger 17, wherein it is cooled by water (which is vaporized to steam); the cooled slurry is then re-introduced into column 10 through line 19. The other stream of hot slurry is passed through the coils 20 of heat-exchanger 18, while the oil feed at about 250 DEG F is pumped via line 21 around the outside of coils 20 on its way to reactor 1. By this means the slurry is cooled to about 450 DEG F, and the oil is heated to about 400 DEG F. The cooled slurry withdrawn from heat-exchanger 18 is in part discarded from the system and in part recycled to fractionator 10 through line 19. After about 15 days of operation, the outsides of coils 20 become fouled, and the flows of slurry and oil are interchanged (see dashed lines on Figure) so that the slurry passes around the coils while the oil passes through them. The slurry takes about 48 hours to clean the outsides of the coils, after which the original flow-paths are operated again.