GB690650A - Process for cracking heavy hydrocarbon oils - Google Patents

Abstract

<PICT:0690650/III/1> Heavy hydrocarbon oils are cracked by contacting the oil with a fluidized bed of catalytically-inert solid particles in a cracking zone maintained at a temperature of about 900 DEG -950 DEG F to give cracked gases and vapours, and to deposit an uncracked hydrocarbonaceous residue and coke on the solid particles; the charged solid particles so obtained are then fluidized in a second cracking zone, maintained at 1000 DEG -1100 DEG F, whereupon the residue is cracked to give further gases and vapours. In order to increase the proportion of motor fuel range hydrocarbons in the products, the cracked gases and vapours from the first cracking zone are introduced into the second zone, or a gas oil fraction, separated from the volatile products from the first zone, is introduced in the second zone. The solid particles may be sand, coke, pumice or a spent clay. The coke on the solids withdrawn from the second zone, is submitted to combustion; and the hot solids so obtained are returned to the cracing zones. A heavy oil residue is supplied at a temperature of 500 DEG to 600 DEG F to line 1, where it is mixed with petroleum coke particles (50-200 microns) at 1050 DEG -1100 DEG F, introduced from standpipe 3, so as to establish a temperature of 825 DEG -900 DEG F. The mixture passes through line 5 where a dilute suspension of petroleum coke in steam, or gaseous hydrocarbons, at 1150 DEG -1800 DEG F, is added from line 7 in order to obtain a temperature for the total mixture of between 900 DEG and 950 DEG F. The mixture then passes into reactor 9 where a dense, turbulent mass M9 of solids in rising vapours, is formed, the upper level L9 of which is controlled, by solids-overflow pipe 13, so that the residence-time of the solids in reactor 9 is 1/2 to 5 minutes. Under these conditions 50-80 per cent of the feed is converted into gas oil, gasoline and gases; and the remainder is dispersed on the coke particles withdrawn through pipe 13. The volatile products are withdrawn from reactor 9 through pipe 13. The volatile products are withdrawn from reactor 9 through cyclone 19 and line 17. The coke particles flow down pipe 13 to reactor 25, where a dense suspension M25 at 1050 DEG -1100 DEG F is maintained by means of a dilute suspension of coke particles in steam or gaseous hydrocarbons, at 1150-1800 DEG F, introduced through line 27. A portion of the products in line 17 is passed through lines 65 and 27 to reactor 25. Solids are withdrawn from reactor 25 through standpipe 3 for recirculation and, if desired, through pipe 31 for coke recovery. The supply of solids to reactor 25 through lines 13 and 27, and the withdrawal through pipes 3 and 31, are balanced so that the residence time is at least 5 minutes. The gas oil, gasoline and gases produced in reactor 25, are withdrawn through line 33, cyclone 35 and line 37. A portion of the solids in standpipe 3 is supplied to line 1, and the remainder is passed through standpipe 41 to line 43 wherein it is carried by air, introduced through line 45 into burner-heater 49 where a dense hurbulent suspension M49 at 1150 DEG -1800 DEG F is maintained. Highly-heated solids are withdrawn from heater 49 through standpipe 59, and are carried to lines 7 and 27 by steam or hydrocarbon gases introduced through line 63. In a modification, provision is made for quenching the volatile products from the first reactor almost immediately after they are formed; and the second reactor is of the upflow type.