US1760357A - Art of cracking hydrocarbon oils - Google Patents

Description

May 27, 1930. E. c. HERTHEL El A 1,760,357

ART OF CRACKING HYDROCARBON OILS v Filed Jan. -5, 1928 4/ Pressure flistz'lmte INVENTORS i'ugezleCf/erzfbel 7g/ amas dC. fifft 155 1, QM' V ATTORNEYS Patented May 27, 1930 -NIT ED STATES PATENT OFFICE EUGENE c. nnnrn'nr. AND mourns DE conon 'rrrrr, or cmcaeo, ILLINOIS, ASSIGN- ons 'ro SINCLAIR nnrmme oomrm, or NEW YORK, 1v. xi, A conronn'rrou or AB! 01 CRACKING HYDBOOARBON" OILS Application filed January 5, 1928. Serial no. M4583.

I have been subjected to results;

special absorbent condensable constituents are subsequently tinuation of an application filed June 22,

1926, Serial No. 117,697 which has eventuated into Patent 1,677,773.

In addition to desired lower boiling oils, the products of cracking operations as usually carried out include gases incondensable except under high pressures and at low temperatures. These incondensable gases tend to carry with them uncondensed but condensable lower boiling constituents suitable as components of the desired lower boiling oil product- The recovery of such uncondensed but condensable constituents is of course desirable to improve the, yield secured from the cracking operation, and a number of schemes have been used for this purpose.

For example, such gas mixtures have been subjected to scrubbin operations with media rom which absorbed separated and recovered by distillation from the absorbent. Likewise, such gas mixtures scrubbing treatment with raw oil to be sup lied to the cracking operation so that absor able constituents are returned to the cracking operation in the raw oil again to escape with from the cracking operation. Where such condensableconstituents are reintroduced directly into the cracking operation proper, overcracking of such constituents frequently This overc-racking can be avoided, for example, by introducing the raw oil, containing such absorbed condensable constituents into .a refluxing operation to which the vapors and gases from the cracking operation are subjected so that absorbed condensable constituents are separated before the raw oil reaches the crackingiopera-tion proper, but this involvesloss of heat which otherwise proper. I

k In continuous cracking operations, residual oil is usually withdrawn undistilled from the cracking operation proper. Such residtion,

the gases and vapors in the cracking operation ual oils are with advantage expanded at lower pressure for separation of oil constituents as vapors therefrom and these vapors in turn subjected to a refluxing operation able to be returned to the cracking operation",

Part of the heat of such residual discharged from the craclu'ng 'opera- 1 for condensation of heavier components suitproper. oils, as tion, has been returned to the cracking operation proper by various expedients, but complete recovery of this heat is at least unusual in practical operation.

According to the present invention, uncondensed vapors and gases including condensable constituents, for example, gasoline components, are subjected to scrubbing treatment with raw oil to be supplied to the cracking operation and, before t e. raw oil with constituents absorbed in the scrubbing operation reaches the cracking operation proper,

the heat of residual oil discharged from the cracking operation is utilized to distill such absorbed condens'able constituents from the raw oil. Any possibility of overcracking such low boiling condensable constituents is thus avoided at the same time that an important heat economy is eflt'ected. This invenmoreover, provides a particularly advantageous way of effecting the heat transfer from residual oil to raw oil containing 4 absorbed constituents.

According to the present invention, the residual oil discharged from cracking operation is expanded at a lower pressure for the separation of oil constituents as vapors therefrom, leaving a pitchy or coky residue, and the resulting vapors are subjected to a refluxing operation into which raw oil containing absorbed condensable constituents from the scrubbing treatment is directly introduced, lower boiling components of these vapors being taken off and condensed together with the condensable constituents vaporized from the raw oil while the absorption of heat in such vaporlzation asslsts' 1n condensing the higher boiling components of the vapors being subjected to the refluxing operation, the unvaporized portion, of the raw oil at the same time being preheated anprlbthereby assisting in condensing the higher iling components of the vapors and forming with the reflux condensate a hot oil mixture suitable to be supplied to the cracking operation proper.

"Objectionable constituents of the residual oil discharged from the cracking operation are not included in this oil mixture as they are separated in the-initial expansion of the residual oil.

The invention will be further described in connection with the accompanying drawings which illustrate, in a diagrammatic and conventional manner, an apparatus adapted for carrying out the process of the invention.

The pressure still illustrated is of the general type described in Letters Patent No. 1,285,200 issued November 19, 1918, to the Sinclair Refining Company on an application o'f'Edward W. Isom. This particular type of pressure still is used simply for the purposes of illustration.

This pressure still comprises a bulk supply drum 1, a battery of vertical heating tubes 2, arranged in a heating furnace, and circulating connections 3, 4, and 5 including a circulating pump which is arranged to force oil from the bulk supply drum upwardly through the heating tubes and back to the bulk supply drum. Vapors from the bulk supply druin escape through connection 7 to pass upwardly through reflux tower 8, uncondensed vapors escaping from the upper end of the reflux tower through connection 9 to condenser 12. This condenser discharges into receiver 13 from which the condensate is discharged through connection 14, uncondensed vapors and gases escaping through connection 15. Raw oil may be introduced into the upper end of reflux tower 8 through connection 16. Some other refluxing medium, for example, a light oil vaporizing substantially completely under the pressure and at the temperature prevailing in the reflux tower, may be introduced through connection 17. The refluxing operation in reflux tower 8 may beefi'ected or controlled by either or both of these means. Reflux, and any admixed unvaporized oil introduced into the reflux tower, is returned from reflux tower 8 to the circulatin'g connection 3 through connection 18. Residual oil is discharged from' the bulk supply drum through connection 19 arranged to discharge into expander 20. Connection 21 is also provided for the introduction of oilinto the pressure still. Cool oil for cooling and lubricating the bearings of the circulating pump issupplied through connection 22.

Connection 23 is provided for initially charg ing the still at the beginning of a run and for pumping out the still at the end of a run.

Uncondensed vapors and gases escaping through connection 15 are discharged into the lower end of scrubbing tower 24 through connections 25'and' 26. Other hydrocarbon gas mixtures including, for example,'gasoplied to the cracking operation is introduced into the upper end of scrubbing tower 24 through connections 31 and 32 by means of pump 33. After passing through the scrubbing tower the raw oil, containing constitucuts-absorbed in the scrubbing tower, flows through connection 34 to tank 35, this tank being provided to give flexibility to the operation. Additional raw oil may also be supplied to tank 35 through connection 36.

A pressure reducing valve 37 is provided in. connection 19, advantageously at a point adjacent the pressure still, to control and release the pressure between the still and the expander 20. To promote the consequent vaporization in the expander, steam, or other hot gaseous medium may be introduced into the expander. Several baflies'are arranged in the upper end of expander 20 to inhibit entrainment. Vapors escape through this expander through connection 38 into the lower end of tower 39 and unvaporized material is discharged through connection 40. The vapors from the expander pass upwardly through tower 39 and are subjected to reflux condensation therein, low boiling vapors escaping from the upper end of this tower through connection 41 to condenser 42. This condenser discharges into receiver 43 provided with a condensate outlet 44 andgan outlet 45 for any uncondensed vapors and gases.

Raw oil'containing condensable constituents absorbed in the scrubbing treatment is introduced into the upper end of tower 39 from tank 35 through connections 46 and 47 by means of pump 48. Some supplemental refluxing medium, for example, a light oil vaporizing substantially completely at the temperature and under the pressure prevailing in the tower, may also be introduced through connection 49. The absorbed condensable constituents are vaporized from the raw oil by the heat of thevapors esca ing from expander 20, this vaporization o absorbed condensable constituents assisting in cooling and condensing the vapors from the expander 20, the latter vapors at the same time being further cooled and condensed by heat absorbed in preheating the 'unvaporized raw oil. Any low boiling components of these vapors and the absorbed. condensable constitutents vaporized from the raw oil escape through condenser 42 in which they are condensed, the

condensate being collected in receiver 43.

Any uncondensed vapors and gases remaining may also be subjected'to the scrubbing I the hot oil mixture not introduce treatment, passing to the lower end of scrubbing tower 24 through connections 45, 25 and 26. The oil mixture collecting in the lower end of tower 39 is introduced into the pres sure still by means of pump 50, either through connections 51 and 16 or through connection 21, or partly through each. of these connections. It is advantageous to introduce as much as possible of this oil mixture through connection 16, but if the oil mixture is too hot more than a certain amount cannot be introduced into the upper end of reflux tower 8 while maintaining an appropriate temperature at the top of this tower, unless the vapors in the reflux tower are subjected to sup lemental cooling. Such supplemental coo mg may be supplied by introducing additlonal raw oil through connections 31, 52 and 16 or by introducing a supplemental refluxing medium through connection 17. An ,part of through connection 16 may be introduced into the pressure still'through connection 21.

Usually, asingle scrubbing tower 24;, expander 20, expander reflux tower 39, and associated condenser and receiver 42 and 4.3 may with advantage be combined with a number of cracking units. Connections 53, 54, 55, 56 and 57 are provided for connecting the recovery system, including the expander and expander tower, to a batter of pressure stills, each with an associated re paratus as wellas hot connections are advantageously lagged or heat insulated to prevent heat loss.

In operation, the pressure still is charged with suflicient oil and brought to cracking condition of temperature and pressure. In a still of the type illustrated, an initial charge of about 8,000 gallons of cool oil, say at a temperature of about 80 F., is commonly use The pressure maintained during the operation is determined to a largemeasure by the stocks to be treated and the products P to be obtained. With gas oil character charg- 1 ing stocks pressures up to 125 pounds .per square inch or more may be used and with charging stocks containing large amounts of kerosene character components much higher pressures, say up to 300'pounds per square inch or more, may be used in the production of gasoline. The pressure in the still system may be maintained and regulated by means of valve 58 in the vapor line between the re flux tower and the condenser, or by valves I objectionable value the discharge of residual arranged beyond the condenser or receiver. Duringthe initial period of'operation, residual oil is not discharged from the pressure still, or is discharge-d in but small amount,

but before the pitch concentration in the charge of oil in the pressure still reaches an oil is begun and the rate of discharge is regulated, with respect to the rate at which raw ux tower. It Wlllbe understood that the hot parts of the ap,

of pitch in .the pressure still charge below an objectionable value. The residual oil is discharged into expander 20 where a pressure substantiallylower than that prevailing within the pressure still is maintained, the pressure between the still and the expander being reduced by means of valve 37. Due to this reduction in pressure, the discharged residual oil is subjectedto further vaporization, vapors entering reflux tower 39 and pitchy or coky components separating in a residue remaining unvaporized. The degree of vaporization in the expander can be controlled by regulating the pressure therein. 'As much as or more of the residual oil may be so vaporized, but if a liquid residue isto be obtained it is usually not desirable to go much beyond this point and it ma be necessary to reduce the amount of vaporlzation, although a liquid residue can sometimes be obtained with vaporization of as much as 90% or more of the residual oil. Withstill pressures in the neighborhood of100 pounds per square inch or higher, the pressure in the expander may be maintained at a value between atmospheric pressure and say 50 pounds per square inch or higher, depending upon the amount of vaporization desired. In the production of gasoline from a gas oil character stock, for example, thetemperature at the top of reflux tower 8 may be maintained at about 550 F. and -the temperature at the top of expander reflux tower 39 at about 350 F. The temperature at the top of reflux tower 8 is maintained by regulated introduction. of raw'oil or the oilmixture from tower 39 through connection 16 or of a mixture of 'cool raw oil and the hot oil mixture from tower 39 through this connection, or b the introduction of some other refluxing me ium, such as a part of the distillate product, through connection 17, or by these means con-- jointly. The temperature at the top of exander reflux tower 39 is maintained by the regulated introduction of raw oil through connection 47, supplemented as may be necessary by the regulated introduction of some other refluxing medium, such as a part of the distillate product, through connection 49. The temperature of the oil mixture collecting in the bottom of expander reflux tower 39 may approximate 450-480 F., and it is usually desirable to limit the temperature of the oil or oil mixture introduced'into reflux tower 8 to a value not exceeding 2759 to 280 .F. to maintain a head temperature approxie mating 550 F., unless some supplementary refluxing medium is used in the latter tower.

While the invention has been described particularly as applied to the recovery of uncondensed but condensable constituents from gas-vapor mixtures from cracking operations, the invention is also useful in more general applications for the recovery of such uncondensed but condensable constituents from hydrocarbon gas mixtures from other sources, for example, from other refinery gases, tank gases and the like.

We claim:

1. In cracking hydrocarbon oils, the improvement which comprises heating a charge of oil to a cracking temperature under pressuretaking off vapors and gases therefrom and subjecting them to a condensing operation, subjecting uncondensed vapors and gases from the condensing operation to scrubbing treatment with raw oil to be supplied to the cracking operation, discharging residual oil from the first mentioned charge of oil and reducing the pressure thereon, thereby causing vaporization of part of said residual oil, subjecting the resulting vapors to a refluxing operation, introducing raw oil with absorbed constituents from the scrubbing treatment into direct contact with the vapors in this refluxing operation, and taking off and condensing the vapors from this refluxing operation.

2. In crackin provement whicfi hydrocarbon oils, the imcomprises heating a charge of oil to a cracking temperature underpressure, discharging residual oil from this charge of oil and'reducing pressure thereon,

thereby causing vaporization of arts of said residual oil, subjecting the resu ting vapors to a refluxing operation, subjecting a hydro-t carbon gas mixture containing uncondensed but condensable hydrocarbons to scrubbing treatment with raw oil to be supplied to the cracking operation, introducin raw oil with absorbed constituents from t is scrubbingtreatment into direct contact with the vapors in the said refluxing operation, and taking off and condensing the vapors from the said refluxing operation.

3. In cracking hydrocarbon oils, the improvement which comprises subjecting a hydrocarbon gas mixture containing uncondensed but condensable constituents to scrubbing treatment with raw oil to be supplied to the cracking operation, discharging residual oil from the cracking operation, vaporizing absorbed constituents from the raw oil from the scrubbing operation while under a lower pressure than that maintained on the oil in the cracking operation by heat given up by this discharged residual oil, condensing the resulting vapors, and su plying the raw oil after vaporization of a sorbed constituents therefrom to the cracking operation.

In witness whereof, we have subscribed our names,

EUGENE O. HERTHEL. THOMAS DE COLON TIFFT.

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