GB723149A - Cracking heavy hydrocarbons - Google Patents

Abstract

<PICT:0723149/III/1> In a process for converting heavy hydrocarbon oils wherein the oil is cracked in the presence of a hot bed of inert solid particles and the vapours so formed are contacted with a hot bed of catalytic solid particles, the vapours are scrubbed with relatively cool oil (e.g. the oil to be cracked) before they are introduced into the catalytic bed in order to remove entrained particles (from the inert bed) and vaporous coke-forming components which would otherwise contaminate the catalytic bed. The two beds are preferably of the densely-fluidized type; and both beds may be arranged in the same vessel with a pool of scrubbing liquid between them. The first bed may be operated as a coking zone, and may comprise particles of petroleum coke, sand, pumice, Kieselguhr, carborundum, alumina, spent clay catalyst, or spent synthetic silica-alumina catalyst. The second bed may comprise particles of cracking catalyst such as activated clay, activated alumina, or synthetic composites of silica with alumina, magnesia and/or boria. The solids in the second bed may also contain a reforming catalyst such as activated carbon, clay or bauxite, whereby the octane number of naphtha produced in the coker may be improved. Whole or reduced crude petroleum, pitches, tar, asphalts, and the clarified bottoms from the recovery system of another cracking process, may be cracked by the process. Reduced crude is passed through line 201 to coil 202, which is immersed in the fluidized bed in catalyst regenerator 203; and is thereby preheated to 600 DEG -700 DEG F. The preheated feed is introduced through lines 204, 210 onto perforated plate 211. This plate, and also the plate 213 below, are disposed above the upper level 218 of a dense fluidized bed 205 of coke particles, but below a dense fluidized bed 220 of catalyst particles. The oil flows from plate 211 via downcomer 212 to plate 213; and is then introduced via line 214 and nozzles 209 into the coke bed 205, which is maintained at 850 DEG -1100 DEG F. by means of heating coil 236. The coke particles are fluidized by steam introduced through line 217. The oil is vaporized and partially coked in bed 205, without converting any substantial fraction of the feed into naphtha or gasoline; and the vapours flow up through the liquid pools on plates 213 and 211. The pool on plate 211 is maintained between 600 DEG and 800 DEG F.; a portion of the effluent (temperature about 850 DEG F.) from plate 213 being recycled, through line 215 and cooler 216, to the upper plate 211 in order to control the temperature. The building-up of coke fines in the scrubbing section is prevented by means of slurry settler 221. Oil withdrawn from the scrubbing section may be returned to the coking bed 205. Coke particles are withdrawn from bed 205 through line 222; a portion thereof is ground down and recycled to the bed, while the remainder is withdrawn as a product. From plate 211 the vapours rise through perforated plate 219 into the fluidized catalytic bed 220, which comprises clay or silica/alumina particles maintained at 950 DEG -1100 DEG F. The effluent vapours from this second bed are passed through cyclone 223 and line 224 to a product fractionation system. Spent catalyst is withdrawn from bed 220 through standpipe 227, and is hydraulically lifted into regenerator 203 by means of air admitted through pipe 228. The catalyst particles form a dense fluidized bed in the regenerator, the temperature being maintained at 1050 DEG -1250 DEG F. Hot regenerated catalyst may be recycled from the regenerator to the catalytic bed 220 via line 234 and steam generator 245. Some of the hot regenerated catalyst is recycled to catalyst bed 220 via line 235 and coil 236, which is submerged in coke bed 205, in order to supply the required heat for the coking stage. Heat may also be exchanged directly by mixing coke and hot regenerated catalyst particles of different size, and then separating the two kinds of particles from the mixture by elutriation. Another embodiment is described wherein the coke bed is maintained at a high temperature (up to 1300F DEG .) whereby gasoline is formed in addition to heavier vaporous components. These heavier components are removed in the scrubbing zone, which is maintained below 600 DEG F.; and the gasoline vapours leaving the scrubbing zone are contacted with silica/alumina catalyst at about 750 DEG F. in order to remove olefines and increase the stability. A process which employs three contact beds-for coking, catalytic cracking, and catalytic up-grading -is also referred to. Specification 714,210 is referred to.