GB773524A - A combined process for distilling and cracking petroleum oils - Google Patents

Abstract

<PICT:0773524/III/1> <PICT:0773524/III/2> Reduced crude petroleum oil containing gas-oil contituents is subjected to a combined distillation and cracking process by passing the reduced crude into a fractionation zone, removing from the fractionation zone above the point of introduction of the reduced crude a gas-oil fraction, subjecting the gas-oil fraction to a catalytic cracking operation and introducing the total effluent of the cracking operation into a fractionation/stripping section of the fractionation zone which is situated below the point of introduction of the reduced crude and in which section the cracked products are passed through a series of fractionation stages. Crude oil from line 1 is pumped via a heat-exchanger 6 and a coil in a furnace 7 to a still 10. There is removed from the still 10 (1) light virgin naphtha (b.p below 250 DEG F.) which is passed via line 16 and a preheater coil in a reforming furnace to the lower part of section A of a fractionator 40 (Fig. 1A), (2) a heavy naphtha (b.p. 250 DEG -500 DEG F.) which is passed via line 28 to a reforming furnace 30 the output of which is passed via line 34 and a pressure release valve 36 into the lower part of section A, (3) kerosene (b.p. 400 DEG -700 DEG F.) which is drawn off through line 20 and (4) reduced crude which is passed via line 22 to the upper part of section A. From the top of section A a gas oil (b.p. 600 DEG -1100 DEG F.) is withdrawn via line 42, part of which is refluxed via line 44, part of which is withdrawn through line 48 for blending with diesel oil and the rest of which is passed via line 46 to a catalytic cracker 50 (Fig. 1) which may be of the fixed bed, moving bed, "fluid" or suspension type. The effluent of cracker 50 is returned via line 52 to an intermediate part of section A of fractionator 40. This section has a number of bubblecap trays between lines 22 and 52 and in it the upwardly rising vapour strip the downwardly flowing gas oil cut, reduced crude and cracked liquid products of substantially all their distillable constituents and a vapour mixture passes at 700 DEG -750 DEG F. into a fractionation-absorption section B of fractionator 40. From the bottom of section A heavy material is withdrawn via line 47, part recycled via a cooler 53 and line 55 and the rest passed to filter 90 from which solids are removed via line 92 or passed to a catalyst recovery system while a fuel oil grade residuium is recovered via line 94. In section B, rising vapours are cooled by contact with cool heating oil entering the top of section B via line 68 and the heating oil together with material condensed is withdrawn via line 56 from which waste is returned to section B via cooler 58 and line 62 whilst the rest is passed to a stripper 57 the vapours from which are returned to section B via line 59 while the liquid is in part taken via 78 to product (as heating or light diesel oil) and in part passed through lines 78, 83, 81 and 55 as a refluxing oil to the heavy residue in the bottom of the tower. Product vapours above inlet line 68 (section B) comprising naphtha fractions and gas fractions containing a large quantity of C4, C5 and C6 hydrocarbons are fractionated by reflux introduced via line 76. Vapours are withdrawn through line 66, compressor 69, condenser 72 and stripper 73 the naphtha from which is in part refluxed via line 76 and in part sent to storage via line 70. Gas and light fractions from stripper 73 are led back into the absorber portion of section B via line 77 where C5+ components are absorbed in the cooled heating oil introduced at line 62. Gas in withdrawn from the top of the fractionator via line 64. Part of the bottoms in line 47 may be subjected in unit 82 to vis breaking and/or coking and passed to stripper 84 from which heavy materials are passed to filter 90 whilst lighter materials are returned to section A via line 88.