US1859510A - Art of cracking hydrocarbon oils - Google Patents

Description

May 24, 1932. E. c. HERTHEI. ET Al. 1,859,510

ART OF CRACKING HYDROCARBON OILS Filed June 7, 1928 2 Sheets-Sheet l May 24, E932. E. c. HERTHEL-ET AL ART OF CRACKING HYDROCARBON OILS Filed June '7, 1928 2 Sheets-Sheet 2 vNN.

l Patented May 24, 1932 UNITED STATES 'PATENT OFFICE EUGENE C. HERTHEL AND THOMAS DE COLON TIFFT, 0F CHICAGO, ILLINOIS, ASSIGNORS T0 SINCLAIR REFIN ING COMPANY, OF NEW YORK, N. Y., A CORPORATION OF MAINE ABT OF CRACKING HYDROCARBON Application filed June 7, 1528. Serial No. 283,516.A

`Thi vention relates to improvements in the cracking of'higher boiling hydrocarbon oils, such as gas oil, to produce therefrom lundistilled from the pressure distillation is expanded at a lower pressure for the further serration of oil constituents as vapors therefrom. The invention has several important advantages in heat economies, in features of control, and in the maintenance of vconditions which permit prolongation of the useful period-of operation without sacrifice of efficiency.

In carrying out the present invention, the

' oil to be cracked is subjected to distillation under pressure at a cracking temperature in a pressure still. The vapors driven off from the still are subjected to a reiiuxing operation in a reflux tower from which reflux is returned to the still, and Athe-vapors remaining uncondcnsed from the reluxing operation are condensed to forni the distillate product. The operation is carried 4out in a continuous manner by supplying fresh oil to the pressure still charge and withdrawino` unvapor'- ized oil containing the pitch ormed by cracking during the operation. The pitch laden oil withdrawn from the still charge is expanded' by reducing the pressure thereon and is thereby separated into an unvaporized residue and an oil fraction driven olf as vapors. The pitch content of the unvaporized oil Withdrawn from the pressure still charge is separated in this residue and the oil components of the withdrawn material, or the greater part of them, are separated as vapors, this separation advantageously being effected simply by the heat contained in the pitch laden oil from the pressure still. In accordance with the present invention, the oil vapors separated from the pitch laden oil withdrawn from the pressure still are passed through a tower through which fresh oil to be supplied to the -plressure still is passed in indirect heat exchanging relation with these vapors. This fresh oil is thus heated and the vapors cooled. The heavier components of the vapors are condensed and the condensate is introduced while hot directly into the pressure still. Lighter constituents such as those f suitable as components of the distillate product remain uncondensed andare withdrawn and separately condensed. The thus heated fresh oil is then introduced into the .reflux tower through which the vapors from the pressure still are passed.l To control or assist in controlling the reiuxing action in the tower through which the vapors separated from the unvaporized oil withdrawn from the pressure still are passedpart of the fresh A oil may be by-passedaround this tower. To Y control or assist in controlling the refluxing action in the tower through which the vaporsdriven off from the pressure still are passed, the fresh oil heated by heat exchan e with the vapors in the other tower may e partially cooled before introduction into the pressure still reiux tower, or as before ad ditional fresh oil may be introduced into the pressure still reflux tower. Further tocontrol or assist in controlling the reflux action in either or both of the towers, a part of the distillate product or some similar light fraction may be introduced into the vapors in the towers. Light fractions so supplied to either or both of the towers are substantially completely revaporized, escaping with the vapors from th towei` to be condensed therewith. Additional fresh oil may also be su -plied directly to the pressure still charge, 1f

necessary, for example to maintain the still charge.

Fig. 1 of the accompanying drawings is a pictorial representation of theoperatlon of the process of the invention. The invention will be further described in connection with Fig. 2 of the drawings which illustrates in a diagrammatic and conventional manner, an

apparatus adapted for carrying out the process of the invention.

Referring to Fig. 2 of the drawings, the pressure still illustrated comprises a bulk c; cbrnection 34 and returned directly to the Cil - supply tank escape through connection and pass upwardly through reflux tower 11, uncondensed vapors escaping from the upper end of the reflux tower through connection 12 to the condenser 13 in which they are condensed, the condensate collecting in receiver 14. A connection 15 is provided for discharging the uncondensed vapors and gases and a connection 16 for the discharge of the condensate. Reflux, and admixed unvaporized fresh oil introduced into the reflux tower, are returned from the reflux tower 11 to the circulating line connecting the bulk supply tank with the suction side of the.circu1ating pump throughy connection 17. Unvaporized oil is withdrawn from the bulk supply tank 3 through connection 18 arranged to discharge into expander 19. The pressure releasing valve 20 is provided in connection 18, advantageously at a point adjacent the pressure still, to control and reduce the pressure between the bulk supply tank and the expander. To promote vaporization, steam, or other hot gaseous medium, may be introduced into the expander 19, for example, steam may be injected into and admixed with the oil as it enters the expander. A s little as one percent of steam will, in many cases, materially increase the amount of vaporization over any particular pressure drop. To inhibit entrainment, several baffles are arranged in the upper end of expander 19. Vapors escape from the expander through connection 21 and unvaporized material is discharged through connection 22. The vapors from the expander pass upwardly through the expander reflux tower 24, uncondensed vapors escaping from the upper end of this tower through connection 25 to condenser 26 in which they are condensed, the condensate collectingin receiver 27 which is provided with a discharge connection 28 for uncondensed vapors and gases and a connection 29 for the discharge of condensate. Fresh oil is forced through coil 23 acting as a heat exchanger arran ed within the tower 24 and then introduced into the upper end of tower 11 through connections 31, 32, 33 and by means of pump 30. The fresh oil flowing through . connections 32 and 33 may be passed in whole or in part through` cooler 36. Fresh il may also be supplied by means of pump 30 to the upper end of the reflux tower 11 throughl connections 31. 37 and 35. The condensate collecting in the lower end of expander reux tower 24 is withdrawn through 'substantial amount is begun.

flux tower 11 through connection 40 or into the upper end of expander tower 24 through connection 41. The hot parts of the apparatus as well as the hot connectionsare ad' vantageously lagged or heat insulated to prevent heat loss, particularly the expander 19. Cool oil for cooling and lubricating thebearings of the circulating pump 9 is supplied through connection 42. Cool fresh oil in excess of thevamount required to cool and lubricate the pump bearings may also be supplied to the pressure still charge through this con-- nection. Additional fresh oil may also be supplied to the pressure still charge through connection 43.

In operation, the pressure still is charged with fresh oil and brought to cracking conditions of temperature and pressure. In a still of the type illustrated, an initial charge of about 8000 gallons of cold oil, that is oil at a temperature of about F. for example, is, commonly employed. The pressure maintained during the operati-on is determined to a large measure by the stocks to be treated and the products to be obtained. With gas oil character charging stocks, pressure up to 125 lbs. per square inch or more may be used, and with charging stocks containing large amounts of kerosene character components, much higher pressure, say up to 300 lbs. per square inch may be used. Vhen the still is brought to operating conditions fresh oil is initially introduced through connections 31, 37 and 35 and pressure distillate vapors are discharged into the condenser and condensed,

the pressure being regulated by valve 44 between the reflux tower and the condenser. The pressure may also be regulated if desired by valves beyond the condenser. During the initialperiodwof operation, unvaporized oil is not withdrawn from the pressure still, or is withdrawn in but small amount, but before the pitch concentration in the charge of oil in the pressure still reaches an objectionablevalue, the withdrawal of pitch laden oil in The pitch laden oil withdrawn is discharged into the expander 19 where a pressure substantially `lower than that prevailing within the pressure still is maintained, the pressure between i reflux tower 11 may be maintained at about A porized by its self-contained heat, but if a .essary so that lthe operation can be carried out continuously. With still pressures in the neighborhood of 100 lbs. per square inch or more, the pressure in the expander may be maintained at a value between atmospheric pressure and say lbs. per square inch or more', depending upon the amount of vaporizatin desired. When/.the withdrawal of pitch laden oil is begun, and vapors from this oil begin to pass through the expander tower, the fresh oil is passed through coil 23 on its way to the reflux tower 11. For purposes of control, part of the fresh oil supplied tothe refluxrtower 11 may still be passed through connection 37 vinstead of through coil 23 and connections 32 and 33. Fresh oil is passed through coil 23 and heated by heat exchange with the vapors in tower 24, or part v of it may also be passed for purposes of control through cooler 36 onl its way to reiux tower 11. Operating for the production of gasoline or gasoline containing pressure distillate with a gas oil lcharacter charging stock, as an example of the operation of the invention, the temperature at the top of the 550 F. and the temperature at the top of expander tower 24 at about 350 F. The pressure distillate may be taken off at a rate, for example, of about 1000 gallons per hour and pitch laden unvaporized oil withdrawn from the still charge at a rate of about 1500 gallons per hour, requiring the return to the pressure still of 2500 gallons of oil per hour vto maintain the charge. The temperature of the oil as withdrawn from the pressure still, during-l operation under a pressure in the neighborhood of 100-125 lbs. per square inch, may approximate 700-725 F., and on reduction to approximately atmospheric pressure upto about 80% or 1200 gallons per hour of this oil may be vaporized The temperature of the vapors and of the residue escaping from the expander approximates 650 F. or upwards. Since part of this vaporized fraction of' the oil withdrawn from the still charge escapes as vapors from the expander reflux tower, fresh oil in amount upwards of 1300 gallons per hour is supplied. When all of thisfresh oil is passed through the heat exchangecoil 23 in the expander reiux tower, the temperature V-of the condensate collecting irl the bottom of the expander tower may approximate 400 F. or upwards. To maintain vgadequate refluxing action in the pressure still reflux towerK 11 it is usually desirable t0 limit the temperature of the fresh oil introduced through connection 35 to a value 'not exceeding about'275-280o F. unless some supplemental refluxing agent is employed'. If no fresh oil is supplied through connection 37 or if the fresh voil supplied through connection 37 is insuflicient in amount to bring the oil mixture flowing through connection 35, including the heated fresh oil supplied through connection 33, within the desired temperature limit, the fresh oil flowing through connection 32 is partially cooled, so far as necessary, by meansof cooler-36.v The supply of oil to the pressure still reiux tower 11 is regulated with respect to the temperature of the oil to maintain the desired head temperature. If any additional fresh oil is required to maintain the still charge, it 1s supplied to the still charge directly. The condensate from the lower end of the expander reiux tower 24 is advantageously returned to the pressure still charge at as high a temperautre as is available. To maintain the desired head temperatures, part of the distillate product may be supplied to the upper ends of the pressure still reflux tower and the expander reiux tower as required.

It will thus bev seen that this invention provides an improved method of carrying out pressure distillation processes for cracking hydrocarbon oils which effects several heat economies. The separation of unvaporized oil withdrawn from the pressure distillation into a residue; containing all of the pitch constituents of the withdrawn oil and a completelyy vaporized fraction is. effected without requiring additional heat and fur,- ther at least a part of the heat of` the fraction so vaporized is returned to the pressure distillation in a particularly advantageous way. This heat is absorbed in fresh oil which is brought in heat exchanging relation with the vapors forming this separated fraction, and is thus returned to the pressure still in the, heated fresh oil, as wellas any condensate produced from these vapors. this heat may be given off in cooling the fresh Voil,'but nevertheless some of it is. returned and made usefully available in the cracking operation whereas otherwise it would be lost Part of i fr this purpose.4 Heat so returned to the` pressure distillation assists in prolonging the period over whichv the operation can be cont1nued as 1t reduces to a corresponding extent the amount of he/at necessary to be translSuch lower furnace temperatures can be maintained efficiently by recycling part of Vthe hot gases again over the heat transferring Walls. With the withdrawal of substantial amounts of pitch laden oil from the pressure A separately returning condensate from the u distillation which if returned might be subjected to over-cracking, are separated bef-ore the condensate produced from the vapors separated from this oil under reduced pressure is returned to the pressure distillation '10 and may be combined-with the distillate product. The invention has another advantage inthat theapparatus for cooling the components of the/pitch laden oil, in accordance with the invention, can be made compact and of a type easily maintained.

l. In proleesses of cracking higher boiling hydrocarbony oils to vproduce lower boiling hydrocarbon oils by distillation under pressure at cracking temperatures in which unvaporized oil is withdrawn during the pressure distillation and subjected to further vaporization by its self-contained heat under a reduced pressure, the improvement which comprises passing the vapors from/ the pressure still into a reflux tower, passing the vapors separated from the oil withdrawn from the pressure still into another reflux tower, passing fresh oil in indirect heat exchangingrelation with the vapors in the sec ond mentioned reflux tower and thereby subjectingthe vapors to condensation and then introducing this fresh oil into direct contact with the vapors in the first mentioned reflux tower, returning reflux together with admixed unvaporized fresh oil from the first mentioned reflux tower to the pressure still and second mentioned re x tower directlyto the pressure still.

2. In processes of cracking higher-boiling l hydrocarbon oils to produce lower boiling hydrocarbon oils by distillation under pressure at cracking tem eratures in which unvapor1zed o1l 1s w1th rawn durlng the pressure distillation and subjected to further4 vaporization by its self-contained heat under a reduced pressure, the @improvement which comprises passing the vapors from the pressure still 1nto a reflux tower, passing the.

vapors separated from the oil withdrawn from the pressure still into another reflux tower, passing fresh oil in indirect heat exchanging relation with the vapors in the second mentioned reflux tower and thereby sub` jecting the vapors to condensation and then introducing this fresh oil into direct contact with the vapors 'in the first mentioned reflux tower, supplying additional fresh oil directly to the pressure still, returning reflux together with admixed unvaporized fresh oil from the first mentioned reflux towerrto the pressure still and separately `returning condensate from the second mentioned reflux tower directly to the pressure still.

3. In processesof cracking higher boiling hydrocarbon oils to produce lower boiling hydrocarbon oils by distillation under pressure at cracking temperatures in which unvaporized oil is withdrawn during the pressure distillation and subjected to further vaporization by its self-contained heatl under a reduced pressure, the improvement which comprises passing the vapors from the pressure still into a reflux tower, passing the vapors separated from the oil withdrawn from the pressure still into another refluxy tower, passing fresh oil in indirect heat exchanging relation with the vapors in the second mentioned reflux tower and thereby sub-

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