GB760192A - Improvements in or relating to the preparation of feedstock for catalytic cracking - Google Patents

Abstract

<PICT:0760192/III/1> Reduced crude is subjected to flash vacuum distillation at a temperature below, but within 200 DEG F. of, the temperature of thermal decomposition of the oil; the vacuum bottoms are extracted with a hydrocarbon solvent such as liquefied propane or butane to remove asphaltic components and metallic contaminants, and the de-asphalted oil is mixed with the vacuum distillate to form feedstock for a catalytic cracking reactor. Crude petroleum is fed through line 10 into atmospheric fractionator 11 where it is fractionated into the usual refinery fractions. Topped crude at a temperature of about 650 DEG F., is withdrawn from the base of the fractionator; it is heated to about 700 DEG F. in furnace 25 and then sprayed into tower 12 which is maintained at an absolute pressure of 50 to 200 mm. Hg. by ejector 51. Flash vaporization of part of the reduced crude occurs in tower 12; and the vapours are withdrawn overhead, and condensed in condenser 48, the condensate being sent via line 52 to the mixing zone. The evaporated liquid, withdrawn from the base of tower 12, is pumped through water-cooler 32, and is then introduced through line 33 into extraction-tower 13. A mixture of propane (70 per cent) and butane (30 per cent) is pumped into tower 13 via lines 35 and 36, about three volumes of solvent per volume of vacuum bottoms being employed. The extract phase leaving the top of tower 13 is passed to pressure-evaporators 39 and 40, where the solvent is volatilized at temperatures of about 210 DEG F. and 400 DEG F. respectively. The extract is then introduced into stripper 14 where the last traces of the solvent are stripped out of it by steam, supplied through line 44. The de-asphaltized oil is mixed in line 47 with the distillate from vacuum tower 12; regenerated catalyst is added from standpipe 61, and the mixture is introduced into cracker 15. The cracked products are passed through line 62 into fractionator 16 which is supplied with superheated steam through line 64. The hot gasoline product vapour, withdrawn through line 62, is used to heat evaporator 39, and is then passed through line 68 to condenser 69 and knock-out drum 70. Part of the condensed gasoline is pumped via line 67 to the head of fractionator 16. Vapours passing overhead from drum 70 are compressed, and condensed in condenser 73, the condensate being mixed with of the gasoline from drum 70 and withdrawn from the system. Heavy oil, containing catalyst particles, is withdrawn from the base of fractionator 16. Some of this hot oil is pumped through line 79 to heat the evaporator 40. The oil leaving evaporator 40 is passed, via line 80 and heat exchangers 81 and 82, either to slurry settler 83 or to line 58 for addition to the cracker feed flowing in line 47. The remainder of the hot oil from the base of fractinator 16 is pumped through water-coolers 89 and 90, and then returned to an intermediate point of the fractionator. A side stream 93 is withdrawn from the fractionator, and is recirculated to the cracker via line 47. The asphaltic raffinate withdrawn from the base of tower 13 is passed to evaporator 95 for removal of solvent; it is then stripped with steam in stripper 97, and added to the cycle oil in line 87. The catalyst slurry from settler 83 is pumped via line 101 to mix with the feed flowing to the cracker. The cycle oil from settler 83 is introduced into tower 13 through lines 105 and 106.