GB757769A - Improvements in or relating to cracking hydrocarbon oils - Google Patents

Abstract

<PICT:0757769/III/1> Hydrocarbon oils such as whole-, topped- or reducedcrudes are treated to obtain naphtha and coke by first distilling the oil to separate gas oil and heavy bottoms, submitting the gas oil to cracking in the presence of fluidized particles of of cracking catalyst, coking the bottoms in the presence of a dense fluidized bed of hot inert solid particles, and introducing the effluent vapours from the cracking unit and from the coker into a common fractionator from which naphtha is withdrawn as product while the bottoms material is passed to the coking zone. Topped crude is fed through line 10 into vacuum tower 11. The vapours passing overhead from the tower are condensed; and the condensate is introduced through line 21 into vessel 100 which contains hot fluidized cracking catalyst, supplied through line 102. The bottoms residuum from tower 11 is lead through lines 23 and 25 to coking vessel 35 which contains a bed of coke particles (50 to 400 microns average diameter) at 900 DEG -1500 DEG F. fluidized by steam introduced through line 48. The residuum is injected into the fluidized bed through nozzles 31 and 33. The vapours withdrawn from vessels 35 and 100 are united in line 55, and introduced into the lower part of fractionator 50. The liquid in the bottom of the fractionator is quenched to keep its temperature below about 700 DEG F. to avoid coking. Naphtha and gas oil are withdrawn from the fractionator through lines 93 and 95 respectively, and light gases are taken off overhead. The gas oil is sent to the catalytic cracking vessel 100. The bottoms withdrawn from the base of fractionator 50 are passed through line 97 to the coker. Coke particles, carrying fresh coke deposits, are withdrawn from the coking zone into stripping zone 37, which is supplied with steam through line 59. The finer particles then pass through coarse screening device 63 into line 65, and are conveyed by steam up standpipe 71 into heater 47. Large coke particles are withdrawn from the system through valves 69 and 70. Oxidizing gas is introduced into heater 47 through line 77 in order to fluidize the particles and raise their temperature by combustion of coke. The heat of combustion may, if desired, be supplemented by hot fuel gas introduced through line 79. The heated particles flow over a notched weir 85, and are returned to the coker through lines 89 and 45. In an alternative embodiment, vacuum tower 11 may be dispensed with; the fresh feed is then introduced into fractionator 50 through line 90.