GB373239A - Improvements in or relating to cracking oils - Google Patents

Abstract

<PICT:0373239/III/1> Oils are cracked by heating them to cracking temperatures while flowing through a heating coil, passing the products directly into a coking chamber and leading the vapours evolved into contact with a spray of the crude oil in a separating chamber, from which the liquid is removed while the vapours are conducted to a fractionating tower where they are fractionated into a light fraction constituting the anti-knock spirit required and a condensate which is used as the cracking material. The heavy oils removed from the separating chamber are coked in the coking zone by contact with hot vapours from the cracking zone. Oil is vaporized and cracked by passage through coils 11, 12, 13 arranged in a furnace 10, the coils 11, 12 preferably being arranged horizontally and the coil 13 vertically. The coil 11 is heated mainly by convection heat while the coils 12, 13 are heated by radiant heat from a central downwardly extending burner. The oil is passed through the coil at high velocity e.g. 20-50 ft. per sec. with a drop of pressure of 200-400 lbs. The cracked products are introduced at 950-1200 DEG F. into coking drums 14 where the heavy residues are reduced to coke while the vapours pass to a separating chamber 15 where they are cooled to about 600-900 DEG F. by contact with the crude stock fed through a pipe 27 and by condensate introduced from the base of a tower 16 by a pump 22. Uncondensed vapours pass to the fractionating tower 16 and a heavy residue is removed through a pipe 54. From the tower 16 the desired fraction having preferably an end point below 450 DEG F. is removed and passed through a condenser 17 to collection tanks 18. Condensate formed in the tower is removed by a pump 19 to a storage tank 20 and is used as cracking stock by passing it through a pipe 21 to the furnace 10. The fractionation in the tower 16 may be controlled by introducing part of the end product from one of the tanks 18 by a pump 561. Crude oil is introduced into the system through a line 26 and is preferably preheated in a heat exchanger 24 by heat exchange with the hot residues from the separator, before introduction into the separator through the line 27 and valved pipes 28. Alternatively the crude oil may be further heated in the coil 11 before introduction into the separator by directing it through a pipe 29, the coil 11, and a pipe 30, in which case the condensate from the tower 16 is sent direct to the coil 12 through a valve 34. The condensate may be preheated by exchange of heat with the hot residues in an exchanger 23. by circulation through lines 210, 211. Residual oil from the separator 15 may be withdrawn from the system as fuel oil in which case an extraneous oil is introduced into the chambers 14 and coked there, or may be itself coked in the chamber 14 by passing it through lines 37, 38, 42 and valved pipes 43.