Improvements in or relating to the coking of residual petroleum oils

摘要

PICT:0714210/III/1 In a method of coking heavy residual petroleum oils in the presence of a fluidized bed of inert solid particles at a temperature of 800 DEG -1200 DEG F., the temperature of the bed is maintained by withdrawing particles therefrom, stripping the particles, contacting the stripped particles in a transfer line with flue gas from a combustion zone at a temperature of from 1300 DEG F. to 3500 DEG F., the velocity of the gas in the transfer line being such that the particles are carried in turbulent suspension through the transfer line and are rapidly heated therein to 900 DEG -1500 DEG F. by the flue gas, separating the reheated particles from the gas and returning them at least in part to the fluidized bed in the coking zone to supply heat thereto. In a preferred embodiment, reheated particles are also added to the stripping zone. The particles may be of coke, sand, spent cracking catalyst, pumice, kieselguhr, or carborundum. The method may be used for cracking tar, pitch, crude residuum, and heavy bottoms. The oil is passed through coil 12 in furnace 14, wherein it is preheated to about 850 DEG F. The preheated oil is mixed in line 16 with superheated steam, introduced through line 28; and the mixture is sprayed into a dense fluidized bed 22 of coke particles (20-200 microns) at 850 DEG F., in vessel 18. The bed is maintained in a dense fluidized state by the introduction of superheated steam through line 38. There are preferably twelve lines 16 for introducing the feed into the coke bed. The vaporous products pass through cyclone 32 and line 36 to a fractionator, from which gasoline and heavy oil (boiling range 430 DEG -950 DEG F.) are withdrawn. Heavy bottoms are also withdrawn from the fractionator, and these are recycled to the feed line 10. Coke particles are collected in zone 44 of vessel 18, and stripped therein by superheated steam introduced through line 52. Some of the stripped particles are withdrawn as coke product through line 54. Particles to be heated are withdrawn from stripping zone 44 through line 72, and are introduced into the lower part of transfer line 68 (40 feet long, 4 feet diameter) where they are contacted with flue gas at about 3000 DEG F. from gas burner 58. The hot gas flows through line 68 at about 40 feet per second, and carries the particles up the line as a turbulent suspension, simultaneously heating them to about 1100 DEG F. The suspension is passed to cyclone 78, and the solids separated therein are returned, via standpipe 82 and line 88, to the fluidized bed 22. Another line 92, having a slide valve 94, communicates with standpipe 82 for delivering hot solids to the upper portion of the stripping zone 44 to maintain the temperature therein at about 975 DEG F., in order to ensure the complete coking of the particles in the stripping zone before they are withdrawn therefrom. Part of the coke particles may be withdrawn from zone 44 through line 98, raised through line 106 by means of air or steam, introduced through line 104, and then injected into transfer line 68 at a substantial distance above the point of injection of the coke particles from line 72.