GB724117A - Improvements in or relating to the cracking of heavy hydrocarbon residues - Google Patents

Abstract

Heavy petroleum residues such as reduced crude, pitch or asphalt, are converted into motor fuels by contacting the feed with a dense fluidized bed of hot inert particles (e.g. coke particles) under <PICT:0724117/III/1> such conditions that vapours are formed while coke and ash are deposited on the particles; the evolved vapours are immediately mixed with a high proportion of hot cracking catalyst particles, and the mixture is passed through a tube (transfer line reactor), the residence time of the vapours in the reactor being short (less than 30 seconds) but sufficient to convert the higher boiling components into gasoline. The heat evolved in the regeneration of the catalyst is employed for heating the inert particles. Suitable catalysts are activated clays, activated alumina, and synthetic composites of silica gel with alumina, magnesia, and/or boria. In the Fig. the initial coking is effected in coker 11, the catalytic reaction is effected in horizontal transfer line 23 which has a length/diameter ratio of at least 12 and the catalyst is regenerated in regenerator 37. Coker 11 contains a dense fluidized bed of coke particles (50-150 microns) at a temperature of 850 DEG -1050 DEG F. The particles are fluidized by steam or hydrocarbon gases introduced through line 15. The bed of particles has an upper interface L. A vacuum residuum (API gravity 12 DEG , Conradson carbon 17 per cent) is supplied through line 1 at a temperature of 300 DEG -500 DEG F., and is preheated to 500 DEG -700 DEG F. in heat-exchanger 3. The preheated feed is sprayed through nozzle 7 into coker 11, the feed rate being 0.5 to 10 barrels per hour per ton of solids hold-up in coker 11. About 90 per cent. of the feed is converted into vapours, the remainder being deposited as coke and ash on the particles. Coke particles grown to non-fluidizable size by deposition of coke and ash are withdrawn from the coker through standpipe 16. A portion of this coke is withdrawn as a product through line 18; and the remainder is ground in grinder 20 and returned to coker 11 via lines 22 and 15. The vapours evolved in the coker are passed through separator 17 and line 21 into horizontal tube 23. A portion of the cracking catalyst particles, admixed with carrier gas and at a temperature of 800 DEG -1050 DEG F., is introduced into line 21 through line 25; the remainder of the catalyst being supplied through line 23 via line 27. The total catalyst feed rate should be about 300 to 5000 lbs. per barrel of residuum. The vapour velocity in line 23 is about 10 to 20 ft./sec. The mixture discharges from tube 23 into cyclone 31 after a residence time in the tube of 4 to 8 seconds. A mixture of cracked products and carrier gas is withdrawn from the cyclone through line 33, and passed to recovery equipment. In addition to gasoline (octane number 90-96), the products include gas rich in propylene, heating oil boiling between 430 DEG and 650 DEG F., and a bottoms cut boiling above 650 DEG F. which may be recycled. Contaminated catalyst separated in cyclone 31 passes through dip-pipe 35 into regenerator 37, which is supplied with air through line 39. The coke on the catalyst burns off, and the flue gases leave the regenerator through separator 43 and line 45. In the regenerator is disposed a coil 51 which is connected to coker 11 via lines 53 and 55; and a gas such as steam is injected through taps t in order to circulate coke particles from the coker, through the coil 51, and back to the coker. In this way the coke particles in the coker are maintained at about 850 DEG -1050 DEG F., and the catalyst particles in the regenerator are maintained at about 1000 DEG -1150 DEG F. Regenerated catalyst is withdrawn from the regenerator through line 57, and is cooled to 800 DEG -1050 DEG F. in heat-exchanger 3. The catalyst in line 57 is stripped and aerated by inert gas injected through lines 59; and is returned to lines 25 and 27 via line 29 which is supplied with carrier gas through line 63. Other inert solids referred to are sand, pumice, spent clays and silica gel. Specification 710,144 is referred to.