US1677774A - Art of cracking hydrocarbon oils - Google Patents

Description

July 17, 1928.

Filed June 22, 1926 2 Sheets-Sheet wAuOln INVENTOR ATTORNEYS i `Iuly 17, 1928. 1,677,774

E. C. HERTHEL ET AL ART oF cRAcxING HYnRocAnoN o'ILs Filed June 2.2, 192s "2' sneet-sheet 2 Tf .trot/f ffl/wr TANK r 0 Patented July 17, 1928.`

UNITED STATES PATENT OFFICE.

EUGENE C. HERTHEL `ANI) THOMAS DE COLON TIFFI, OF CHICAGO, ILLINOIS, .AS-

SIGNORS TO SINCLAIR REFINING COMPANY, QE NEW YORK, N. Y., A CORPORATION 0F MAINE,

ART OF CRACKING HYDROCARBON OILS.

Application led .Tune 22,

This invention relates to improvements in the cracking of higher boiling hydrocarbon oils, such as gas oil, to produce therefrom lower boiling hydrocarbon oils, suoli as gasoline and pressure distillate.

This invention relates particularly to improvements in operations in which hydrocarbon oils are cracked by distillation under pressure and in which residual oil withdrawn undistilled from the pressure distillation is expanded at a lower pressure for the further separation of oilconstituents as vapors therefrom. The invention has several important advantages in heat economies, in features of control, and in the maintenance of conditions which permit prolongation of the useful period of operation without sacrifice of efficiency. The invention is of special value and application in connection with the operation of pressure cracking stills of the type described in Patent No. 1,285,- E200 issued November' 19, 1918 to the Sinclair Refining Company on an application to Edward lV. Isom, and it will be described particularly in connection therewith, but in certain aspects it has advantages which are of more general application.

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 ofi' from the stillare subjected to a relluxing operation in a reflux tower from which reiiuX is returned to the still, and thevapors remaining uncondensed from the reliuxing operation are condensed. The operation is carried out in a continuous manner by supplying fresh oil to the pressure still charge and withdrawing unvaporized oil containing the pitch formed by cracking during the operation and regulating the rate ofA supply of fresh oil and the rate of withdrawal of pitch-laden oil so that the concentration of pitch in the still charge is kept below the .saturation point. The pitch-laden oil withdrawn from the still charge is expanded by reducing the pressure thereon and is thereby separated into an unvaporized residue and an oil fraction driven oill as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 1926. Serial No. 117,698.

separation advantageously being effected simply by 'the heat contained in the pitchladen oil withdrawn from the pressure still. The vapors vseparated from this withdrawn oil are subjected to a fractionating operation in a fractionating tower, part of the vapors entering the tower being condensed therein and part escaping therefrom uncondensed.

In accordance with the present invention, the operation of the fractionating tower, into which the vapors separated from the pitchladen oil withdrawn from the still are passed, is controlled so that the fraction eseaping therefrom uncondensed corresponds in character to that escaping uncondensed from the refluxing operation to which the vapors from the pressure still are subjected, and this fraction is collected with the pressure distillate vapors from the refiuX tower on the pressure still to form a composite distillate product. An improved recovery of the desired lower boiling hydrocarbons is thus effected. Hydrocarbon constituents suitable as components of the desired product which may be retained unvaporized in the pitch-laden oil withdrawn from thepressure still are separated therefrom in a particularly advantageous manner, and such constituents are prevented from being returned to the pressure still where it so returned they might be subjected .to overcracking through further heating under the conditions maintained in the pressure still.

In one advantageous way of carrying out the invention, the fresh oil, or a part of the fresh oil, to be supplied to the pressure dis` tillation `may be employed to promote the condensation effected in the fractionating tower, and heat so absorbed from the vapors in this fresh oil may, in whole or in part, be returned to the pressure distillation. Fresh oil employed for this purpose may be intro-- duced into the fractionating tower in direct contact with the vapors passing therethrough. If the amount of fresh oil required by the Vpressure distillation is at least suflicient to effect the necessarycondensation in the fractionating tower, the operation of the fractionating tower may be controlled by regulating the rate at which fresh oil is supplied thereto. Usually, however, it is advantageous to employ in addition to the fresh oil some supplemental condensing agent, and one such particularly advan- Q ha tageous condensing agent is a part of the distillate product or a fraction of corresponding character. Likewise, and with advantage, the condensation in the fractionating tower can `be effected entirely by returning a partof the distillate productor supplying a fraction of 4similar character to the fractionating tower and introducing it into direct contact with the vapors therein, and the operation can be controlled by regulating the vrate at which this condensing agent is supplied. VBy employing a part of the distillate product or a fraction of similarl character, improved fractionation is obtained and the fraction so supplied is substantially completelyl revaporized escaping with the vapors from the towerto be condensed therewith. Vhere fresh oil is introduced into direct contact with the vapors in the fractionating tower vany constituents of the fresh oil suitable as components of the desired dis-4 tillate product are also vaporized and es- V cape with the vaporsl from the fractionating tower. Y

The condensate separated from the vapors entering thel fractionating tower, or admixed condensate and fresh oil vif fresh oil `is introducedl into direct'contact with the vapors in the fractionating tower,'is supplied ,to the pressure distillation. This mixture, for example, may be introduced intoV the reflux towcx to which the vapors from the pressure still are passed, or it may be introduced into the pressure still directly, or part of it may be supplied in each of these ways. Before being returned to the ressure distillation, the condensate or the a mixed fresh oil and condensate may be cooled or partially cooled, or` if part of it is supplied to the pressure still directly and part of it to the reflux tower on the pressure still only that part of'it supplied to the reflux tower may be cooled. Additional fresh oil may Yalso be supplied to the reflux tower on the pressure still, and further to promote and control the refluxing operation "a part of the distillate product or la fraction of vcorresponding character may also be introduced into the reflux tower on the pressure still.

F 1 of the accompanying drawings is a pictorial representation of the operation 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 processV of the invention. i

Referring to Fig. 2 of the drawings, the pressure still illustrated is of the type described in Patent No. 1,285,200, referred to above. The pressure still comprises abulk supply Ytank 8 located away from the heat-` furnace d, battery of vertical heating tubes arranged 1n the'heating furnace, and circulating connections 6,7 and 8 and acircubulk supply tank. supply Vtank escape through connection 10 lating pump 9 arranged to withdraw oil from Y the bulk supply tank and force it upwardly through the heating tubes and back to the TJapors from the bulk and pass upwardly through the reflux tower 117 uncondensed vapors escaping from the upper end ofthe reflux tower through connection 12 to the condenser 13 in which theyy are condensed, the condensate collecting in receiver' 14. A connection is provided for the discharge of uncondensed vapors and gases and a connection 1G for discharge of the condensate. mixed unvaporized oil introduced into the refiux tower, are returned from the refiux tower 11 to the circulating line connecting the bulk supply tank with-the suction side of the circulating pump through connection through connection 22 to the cooler 23. lThe vapors from the expander pass upwardly through vthe expander tower 24, uncondeused vapors escaping from the upper end of the tower throi'igh connection 25 to the condenser 26 in which ythey are condensed,

the condensate collecting inv receiver 27.

which is provided with a discharge connection 28 foruncondensed vapors and gases and connection 29 for the discharge of condensatc. Y pump 30 to the upper end of the expander tower 24 through connections 31 and 32. A part of the fresh oil so supplied may also be introduced into the upper end of thereflux tower 11v through connection The condensate and admixed fresh oil collecting in the lower end of expander tower 24 is withdrawn. through connection `34. This mixture maybe introduced into the upper end of the reliux tower llthrough connections 35, 3G and 37 by n-ieans of pump 38; or through connection 39. the cooler 40 and connections rlll, 3G andBT by means of pump 38. A part ofv the'mixture may be returned directly to the circulating connection supplyirreI oil to the lower end of the heating tubes in the pressure still through connections 42 and L13 by means of pump 44. As a supplemental refluxing or condensing agent or controlling medium, a part of the distillate product can be reintroduced .by means of pump l5 either into .iefiux, and anyV ad-V Fresh cil is supplied by means ofV loo Iliff llc the upper end of the reflux tower 11 through connection 46 or into the upper end of expanderl tower 24 through connection 47. The distillates collecting in the receivers 14 and 27 are discharged together through connections 53 and 511 into a common distillate tank to form the composite distillate product. The still pressure `may be rerluced and regulated byvalve 52 located between the reflux and tinal condenser or regulated by valves located beyond the condenser '13. The hot parts of the appara- `tus and the hot connections may with ad vantage be lagged or insulated to `prevent heat loss, particularly the expander 19. To promote condensation, the expander tower 24 may be uninsulated, although control of the operation is somewhat facilitated by insulating this tower as well.

As a typical example of operation in accordance with this invention in the treatment of a gas oil character charging stock to produce gasoline or a gasoline-containing pressure distillate, the pressure distillation may be carried out under a pressure in the neighn borhood of 100 to 125 pounds per square inch or higher. lith lighter charging stocks, for example charging stocks tending to a kerosene character, considerably higher prersures may be used. The pressure still may be initially charged with about 8000 gallons of cold oil. After the still charge is brought to cracking conditions of temperature and pressure, vapors of the pressure distillate are taken ofil and fresh oil is supplied through the reflux tower on the pressure still. Distillate, for example, may be taken oft' at a rate of about 1000 gallons per hour and, initially, fresh oil may kbe supplied at approximately the same rate to maintain the still charge. Before'the concentration of pitch formed by cracking in the still charge reaches the saturation point, the withdrawal of pitclrladen oil from the still charge is begun and additional fresh oil is supplied in amount corresponding approximately to the amount of pitch-laden oil withdrawn. At this point in the operation, for example, the withdrawal of pitch-laden oil at a rate of about 1500 gallons per hour may be begun, and the amount of fresh oil supplied to the still may be increased to about 2500 gallons per hour. Vhen the withdrawal of pitch-laden oil is begun, the withdrawn oil is discharged into the expander where a pressure lower than that prevailing in the pressure still is maintained and is thereby subjected to further vaporization. This vaporization, for example. may be carried to the point where as much as 80% of the withdrawn oil or more is separated as vapors. The condensate produced from these vapors in the fractionating operation to which they are then subjected may be returned to the still together with fresh oil supplied to maintain the still charge. When the withdrawal of pitch-laden oil is begun, the supply of fresh oil introduced into the redux tower on the pressure still may be diminished or diverted and the fresh oil, or part of it, supplied to the fractioning tower' on the ex- `or the relluxing or condensing operations therein supplemented by supplying thereto, in addition to fresh oil so supplied, a part of the distillate product or a fraction of corresponding character. Operating for the production of gasoline or a gasoline-contain ing distillate product, the tem Y erature of the vapors escaping from the re ux tower may `be maintained in the neighborhood of 550'o E. or somewhat less, and the temperature of the vapors escaping from the fractionating tower may be maintained in the neighborhood of 350o E. or somewhat more. The head temperature of the two towers is advantageously controlled by introducing a part of the distillate product or a fraction of corresponding character into the upper ends of the towers in amount regulated to maintain t-he desired head temperature.

lVe claim: i

In processes of cracking higher boiling hy-k drocarbon oils to produce lower boiling hydrocarbon oils by distillation under pres sure at cracking temperatures in which unvaporized oil is withdrawn from the pressure distillation during operation and sub- `iected to further vaporization by its selfcontained heat through reduction in pressure, the improvement which comprises taking olf vapors from the pressure distillation and condensing them to form a pressure distillate, subjecting the vapors separated from the unvaporized oil withdrawn from the pressure distillation to a fractionating operation, and controlling the fractionating operation by supplying1 thereto a fraction the constituents of which correspond to components of the desired distillate product to take off as vapors from the fractionating operation a fraction the constituents of which correspond to the components of the pressure distillate, and condensing this fraction.

EUGENE C. HERTHEL. THOMAS DE COLON TIFFT.

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