GB765615A - Improvements in or relating to fluidized coking process - Google Patents

Abstract

<PICT:0765615/III/1> In a process for converting heavy liquid hydrocarbons into lighter products and coke the liquid hydrocarbons are contacted with hot inert solids, e.g. coke particles, fluidized in a vertically elongated coking zone 10 by being injected from a manifold 1 at a plurality of vertically spaced levels 2, 3 and 4, the feed rate at any level being less than about 5 gallons per minute per square foot of cooking zone cross-section, and the rate of injection in the range of 0.1 to 3 weight per hour per weight of fluidized solids. The preferred feed rate is between about 0.1 to 1.5 gallons per minute/sq. ft. for cylindrical cooking zones smaller than about 10 feet in diameter, and up to about 3 gallons per minute/sq. ft. for larger coking zones up to about 15 feet in diameter. The successive feed levels are preferably spaced so that approximately equal volumes of fluidized solids will exist between them and for cylindrical zones a preferred spacement of the levels is 1 to 2 zone diameters. The hydrocarbon feed is preferably pre-heated to between 400-800 DEG F. and the inert particles mostly have a diameter of about 80 to 300 microns. Product vapours are withdrawn through line 16. The fluidized bed is maintained at a coking temperature of 800-1200 DEG F., preferably 950 DEG F., where a distillate suitable for catalytic cracking is to be the principal product. Higher temperatures may be used if ethylene or aromatics are the principal desired products. The pressure at the top of the coking zone may vary between subatmospheric and about 100 p.s.i.g. Coke particles are withdrawn from the coking zone through line 19 and passed with air to a burner 20 preferably fluidized where it is heated to at least about 100 DEG F. above the temperature of the coking zone. The thus heated coke is returned to the coking zone through lines 25, 26 and 27 arranged at levels close to the feed levels 2, 3 and 4 respectively. A portion of the coke is withdrawn through line 29 partly as product coke and partly to pass through a grinder to supply the required amount of seed coke for return to the coking zone. The coke passed to the coking zone may be activated, e.g. by treatment with superheated steam. In a modification the coke may be reheated by combustion of an extraneous fuel, e.g. oil or fuel gas. In another modification the main part of the coking zone has an inverted conical shape so that the velocity of the uprising gases will remain uniform despite the fact that volatization of the hydrocarbon feed creates additional volumes of gases. As an example the coking of a residual oil may produce about 10-20 weight per cent of coke, 7-12 weight per cent of C3 and lighter gases, about 15-25 volume per cent of a C4/430 gasoline fraction, about 45-64 volume per cent of a gas oil fraction boiling from 430-1015 DEG F., and about 0-25 volume per cent of a residual fraction.