GB760194A - Upgrading of heavy hydrocarbon oils - Google Patents

Abstract

<PICT:0760194/III/1> In a process of cracking heavy hydrocarbon oils wherein the oil is introduced into a fluidized bed of hot non-catalytic solid particles and the cracked vapours withdrawn from the cracking zone are fractionated to obtain naphtha, gas oil and other products, the heavy bottoms fraction withdrawn from the fractionator is recycled to a separate section of said fluidized bed or alternatively to another fluidized bed, and the pressure in the recycle cracking zone is maintained higher than that in the primary cracking zone in order to prevent vaporization of the recycle fraction before liquid-phase cracking can occur. A vacuum residuum, preheated to about 500 DEG F., is sprayed through line 1 into vessel 10 which contains a bed of coke particles, at about 950 DEG F., maintained in a fluidized state by steam introduced through line 7. The coking is effected with a pressure of about 15 p.s.i.g. in the upper part of vessel 10. The cracked vapours pass out of vessel 10 through cyclone 20, and are conveyed by line 2 to fractionator 80. Light gases, naphtha and gas oil are withdrawn from the fractionator through lines 13, 14 and 15 respectively. The residual fraction, boiling above 1100 DEG F., withdrawn from the base of the fractionator, is passed through line 6 to the lower part 30 of vessel 10. This secondary coking zone contains a bed of hot coke particles, fluidized by steam supplied through line 8. Coke particles from the main bed of vessel 10 can circulate through section 30; but baffles 50 ensure that the solids-circulation between the two zones is not too great. The secondary zone lies about 50 feet below the pseudoliquid level of the main fluidized bed, so that the pressure in the secondary zone will be about 30 p.s.i.g. The cracked vapours formed in section 30 flow upwards through the main fluidized bed to cyclone 20. The fluidized coke particles are maintained in a hot condition by heater 60. Coke particles are withdrawn from vessel 10, and are transported by steam through standpipe 3 to heater 60, where partial combustion of the particles in the presence of fluidizing air is effected. The fluidized bed of particles in heater 60 is thereby maintained at about 1100 DEG F. Hot particles are withdrawn from the heater, and transferred via lines 4 to 24 to the main and secondary fluidized beds respectively in vessel 10. The temperature in section 30 can be higher or lower than that existing in the main zone. Excess coke is withdrawn from the system as product through line 5. In a modification an entirely separate secondary coking zone is used; and the vapours therefrom are introduced into the upper part of the main zone so that they are not degraded by the main coking bed.