GB762091A - Improvements in or relating to combination distillation and hydrocarbon conversion process - Google Patents

Abstract

<PICT:0762091/III/1> Reduced crude petroleum containing a substantial quantity of gas oil hydrocarbons is distilled in a fractionating zone, a gas oil fraction is withdrawn from the fractionating zone and is subjected to catalytic cracking at a temperature of 850 DEG to 1000 DEG F., a major proportion of the product vapours from the cracking zone is introduced into the fractionating zone at a level below the inlet of the reduced crude, the remainder of the cracked product vapours is partially condensed in a by-pass fractionating zone, a bottoms fraction boiling above 600 DEG F. is withdrawn from the by-pass fractionating zone and is discarded from the process, the overload vapours from the by-pass fractionating zone are passed to the main fractionating zone at a level above the withdrawal outlet of the gas oil fraction, and gasoline and other desired products are withdrawn from the main fractionating zone. The process selectively removes aromatic, coke-forming constituents from the system with minimum loss of heat and virgin feed. Crude petroleum is pumped through line 20 to furnace 26 where a substantial portion of the oil is vaporized. The heated material is introduced through line 28 into a lower section of column-still 10. Light naphtha is withdrawn from the head of still 10 heavy naphtha (B.R. 250 DEG -400 DEG F.) is removed through line 40; kerosene is withdrawn through line 42; and reduced crude, boiling above 700 DEG -800 DEG F., is removed from the base. The reduced crude is introduced through line 44 into fractionator 14. The light naphtha is passed through line 36 to furnace 46, where it is heated to 800 DEG -1000 DEG F., and is then passed via line 47 to the lower section 74 of fractionator 14, which contains disc- and doughnut-type baffles. The upper section 76 contains bubble cap plates. The heavy naphtha is subjected to thermal reforming in tube furnace 12 at about 1000 DEG F. and a pressure of 200-1000 p.s.i.g. The reformed naphtha is passed through line 52 and valve 54 into the lower section of fractionator 14. Gas oil (B.R. 650 DEG -1000 DEG F.) is withdrawn from section 76 through line 56, and is passed to fluid catalytic cracking stage 16 which contains an activated montmorillonite clay, a silica-alumina gel or a silica-magnesia gel, at 800 DEG -1000 DEG F. and a pressure of 25 p.s.i.g. About five sixths of the vapours discharged from stage 16 are passed through line 62 and valve 64 into the lower section of fractionator 14. A temperature of about 800 DEG F. is maintained in the base of the fractionator while that at the top of section 74 is about 750 DEG F., the pressure therein being 5 to 15 p.s.i.g. Part of the gas oil withdrawn through line 56 is cooled and supplied to the top of section 74 as reflux. The remainder of the vapours from cracking stage 16 is passed through line 98 to tower 102, which is supplied with steam through inlet 108, and is maintained at a pressure of 6 to 8 p.s.i.g. Reflux liquid for tower 102 is withdrawn from fractionator 14 via line 112 and cooler 116. Vapours at 600 DEG -650 DEG F, are withdrawn overhead from tower 102, and are passed through line 118 into the upper section of fractionator 14. The oil withdrawn from the base of tower 102 is discarded. The top of fractionator 14 is maintained at a pressure of about 4 p.s.i.g., and the vapours leaving through line 132 contain appreciable amounts of normally gaseous hydrocarbons. The vapours are passed to condenser 134, and the effluent therefrom is passed to gas-separator 136. Gasoline collects in separator 136; part is withdrawn as product through line 142 and the remainder is returned via line 144 as reflux to fractionator 14. The gases withdrawn from separator 136 through line 146 are passed to a gasoline recovery system. Heating oil is withdrawn from fractionator 14 through line 148. Heavy oil is withdrawn from the base of the fractionator through line 84. Part or all of this material may be subjected in furnace 154 to vis breaking and/or coking. The product from furnace 154 is treated with steam in stripper 156. Heavy residuum and coke are withdrawn from the base of the stripper, while the vapours withdrawn overhead are passed to fractionator 14. Catalytic reforming may be employed in place of thermal reforming stage 12.