US1705077A - Art of cracking hydrocarbons - Google Patents

Description

March 12, 1929." Q H, TABER, JR i 1,705,077

ART 0F CRACKING HYDROCARBONS Filed Nov. 26, 1927 2 Sheets-Sheet l` March 12, 1929. Q H, TABER, JR 1,705,077

ART oF cnAcKING HYDRoc/mows l Filed Ngv. 2e, 1927 '2 sheets-snee: 2

y E n ATTORNEYS Patented Mar. 12, 192.9.l

UNITED STATES 1,105,017 PATENT oFFlcE. f

GEORGE H TABER, JR., OF RYE, NEW YORK, ASSIGNOR TO SIN'CLAIR REFINING COM- PAN Y, OF NEW YORK, N. Y.,

A CORPORATION oF MAINE AAIR/1.* OF CRACKING HYDROCAYRBONS.

Application led November 26, 1927. Serial No. 235,86.

This invention relates more particularly to improvements in cracking operations carried out to produce lighter and lower boiling hydrocarbon oils, such as gasoline, from heavier and higher boilinghydrocarbon oils, suoli as kerosene, gas oil, fuel oil and the like. The invention is of special value in connection with distillation operations carried out under superatmospheric pressure, 1o but it is also useful inconnection withl other types of operations, such as those in Which the oil to be cracked is heated to a. cracking temperature in the vapor-phase either at approximately atmospheric pressure or at higher pressures and those in which the oil is heated to a cracking temperature, usually under very high pressures, Without complete separation of vapors and unvaporized liquids in the cracking operation itself. 20. `In cracking operations in lWhich the cracked products are taken off as a .mixtureof vapors and gases, either from the crack! ing operation itself or from some subsequent operation carried out to separate the lighter cracked products from residues the constituents of which are unsuitable as components of the desired product, the gas-vapor'mixture usually includes gases incondensable except under high pressures and at low temperatures aswell as vapors of the desired lighter lower boiling hydrocarbon oils. In the usual vcondensing operation, a -certain amount of the constituents suitable as components of the desired product are carried off uncondensed with such incondensable gases. The recovery of condensable constituents suitable as components of the desired product escaping with the gas-vapor mixture remaining uncondensed from the condensing 4o operation is of course desirable to improve the yield secured from the cracking operation. This invention provides an "improved method of recovering such condensablc constituents from such gas-vapor mixtures.

According to the present invention, the

gas-vapor mixture from the cracking operation is subjected to a fractionating operation, the gas-vapor mixture remaining from the -fractionating operation is subjected toa 5o condensing operation, the gas-vapor mixture remaining. uncondensed from the lcondensing operation is subjected to a scrubbing treatment with a higher boiling oil fraction from the fractionating operation, and the oil containing constituents absorbed from the gassvapor mixture in the scrubbing operation isA reintroduced into the fractionating operation. The relatively 10W boiling condensable constituents separated in the scrubbing operation from the gas-vapor mix? ture remaining uncondensed from the condensing operation are thus condensed together' with a relatively large proportion of higher boiling constituents to form a stable condensate While the heat of the gas-vapor mixture from the cracking operation given up in the fractionating operation is utilized to effect stripping of the absorbed constituents from the scrubbing oil. The higher boiling oil containing absorbed constituents from the scrubbing operationmay with advantage be preheated, for example, by heat exchange with the gas-vapor mixture escaping from the fractionating operation, before reintroduction into the fractionating operation. To assist in the recovery of low boiling condensable constituents, vthe condensing operation and the fractionating operation may be carried out under pressure substantially above atmospheric pressure.

The invention Will be further described in connection with the accompanying drawings, which diagrammatically illustrateone form of apparatus adapted for carrying out the process of the invention. Fig. 1 illustrates a form of apparatus for carrying out the invention in conjunction with various types of cracking operations, and Fig. 2

illustrates this form of apparatus as em-l bodied in a. system for carr ing out one type of cracking operation. t will be appreciated that different types of apparatus may be employed to carry out the various steps effected 1n the apparatus shown, that the process of the invention is useful in con nection with types of cracking operation other than that particularly illustrated, and that a recovery system such as that illustrated may be employed' in connection with one or several cracking units.

Referring more particularly to Fig. 1, the gas-vapor mixture from the cracking operation enters fractionating tower 3 through connection 4. The 4gas-vapor mixture remaining from the fractionating operation escapes through connections 5 and 6 to condenser 7, passing on the Way through heat exchanger 8. Condenser 7 discharges through connection 9 int`o receiving tank 10. From tank 10, the condensate is discharged either through connection 11 or through connection 12 after passing through separating tank 13. The uncondensed gas-vapor mixture from receiving ltank 10, together with any uncondensed vapors and gases separated in tank 13, escapes to scrubbing tower 15 through connection 14. Other hydrocarbon gas-vapor mixtures containing condensable constituents of correspondin character may also be supplied to scrub ing tower 15 through connection 16 by means of compresser or blower 17. Part of the higher boiling oil'eollecting in the lower end of fractionating tower 3 is, circulated through cooler 18 and then introduced into scrubbing tower l5 through connection 19 by means of pump 20. The scrubbing oil containing absorbed constituents from scrubbing tower 15 is reintroduced into the fractionating tower 3 through connection 21 or connection 22 or both of these connections by means of pump 23 after passing through heat exchanger 8. The gas or gas-vapor-mixture remaining from the scrubbing operation escapes through connection 24. The eondensable constituents absorbed in the scrubbing oil in the scrubbing tower 15-are stripped from this oil in the ractionating tower 3 to be condensed in condenser 7 together with the major part of the eondensable constituents of the gasvapor mixture from the fractionating operation. Part of the higher boiling oil collecting in the lower end of fractionating tower 3 may be discharged through connection 25 and cooler 26. An intermediate cut may also ,be discharged from the ractionating tower lation with the gas-vapor mixture in the.

upper end thereof, or by the direct introduction into the upper end thereof of part of the distillate product or a fraction of corresponding character, or by the directintroduction of higher boiling oil which then escapes with higher boiling fractions separated in the tower. Part of the cooling required, in some eases even all of it, is supplied by the introduction of the charged scrubbing oil from the scrubbing operation. Except where atmospheric cooling is relied upon, it is usually advantageous to lag or thermally insulate fraetionating tower 3.

Although cooler 18 may in some cases be dispensed with, the absorbent capacity of the scrubbing oil is increased by cooling it as it circulates from the fractionating operation to the scrubbing operation. In the process of the invention, it is particularly `advantageous to preheat the charged scrubbing oil from the scrubbing operation before reintroduction into the fraetionating operation. This preheating is with advantageV effected by heat exchange with the gas-vapor mixture from the fractionating operation, as in heat exchanger 8. As the degree of preheating increases, with a fractionating tower such as that illustrated, the charged scrubbing oil may be introduced at a lowei point or the proportion of the charged scrubbing: oil introduced at the lower of two or more points may be increased.

While the fractionating operation and the subsequent condensing operation may be carried out under approximately atmospheric pressure, substantially higher pressures may be maintained on these operations to assist. in the recovery of low boiling eondensable constituents. In conjunction with pressure distillation cracking operations, for example, substantially the still pressure may be maintained through fraetionating tower 3 and condenser 7 or the fraetionating tower and condenser may be operated under an intermediate pressure above atmospheric. Likewise, the fraetionating tower may be operated under a pressure higher than that maintained in the condenser. Where condenser 7, in the apparatus illustrated, is operated under approximately atmospheric pressure, separating tank 13 may be dispensed with; its use is not essential in any case. Where condenser is operated under a pressure substantially higher than atmospheric, however, it is advantageous to maintain receiving tank 10 under substantially the same pressure maintained in condenser 7 and to reduce the pressure on the condensate approximately to atmospheric as it is discharged into a separating tank 13 as shown.

The scrubbing operation may be carried out under atmospheric pressure or under a slightly higher pressure, :tor exam le, sufficient to force the stripped gas from the scrubbing operation 4to storage or to burners or to other point of disposition.

rllhe system illustrated in Fig. 2 comprises 'a pressure rstill of the general type described and illustrated in Letters Patent No. 1,285,200 granted November 19, 1918, to the Sinclair Retining Co. on the application of Edward Isom.v The still comprises a bulk supply drum located away from a battery of vertical tubes in a heating furnace and connections Aincludingr a circulating pump for circulating oil from the bulk supply drum upwardly through the heating tubes and back to the bulk supply drum. Vapors and gases escape from the bulk supply drum to a reflux tower 29 from which the gas-vapor mixture remaining uncondensed lescapes through connections 30, 31 and 4 to the apparatus for carrying out the present invention. The same parts illustrated in Fig. 1 and described in connection therewith are in Fig. 2 designatedby the same reference character with a prime ap pended.

The operation of scrubbing tower 3, heat exchanger 8, condenser 7, receiving tank 10', 4separating tank 13'; cooler 18', and' The condensate discharged from receiving' tank 10 may be discharged to separating tank 13 either-directly through connection 34 or' through cooler 35. Connection 36 is provided for introducing any gases and vapors from the separating tank 13 into the scrubbing tower 15 through connection 16' by means of blower or compressor 17', for example, where thescrubbingtower is operated under a, pressure higher than that prevailing in the separating tank.

Connection 37 is provided for discharging stripped gases from the scrubbing tower 15 to a gas holder and connection 38 is provided for discharging these gases, for example, ,to burners for supplying heat to the cracking operation. Traps for the separation of an liquid from the gas mixture passing throng the associated'connections are shown at 39 and 40.

In addition to the gas-vapor mixture from the cracking operation introduced into scrubbing tower 15 through connection 14', other reiner`y\g'ases may be lntroduced into the i scrubbing tower, tor example, through connection 41, and similarly gases produced during distillation oftars or residues from cracking operations may also be introduced into the scrubbing tower, through connection 42 in the apparatus illustrated in Fig. 2.

The apparatus for distilling tar, d ischarged during, operation of the pressure cracking still illustrated in Fig. 2 comprises an evaporating towe43 anda-ractionating tower 44. Tar discharged from the pressure cracking still is introduced while hot into' the lower end of tower 43 through connection 45, a pressure being maintained in tower 43 substantially lower than that prevailing `in the pressure cracking still so that the lower boiling components of the tar are distilled by the self-contained heat of the tar on reduction in pressure. The residue from tower 43is discharged through cooler 46. The separated vapors and gases escape through connection 47 to fractionating tower 44. Connection 48 and pump 49 are provided for introducin a low boiling oil into tower 44 to control t e :Eractionating operation therein. Low boiling oils escape from tower 44 as vapors to condenser 50 and higher boiling oils condensed in the tower are discharged through cooler 51. Any gas or gas-vapor mixture separating from the distillates discharged from condenser 50 and cooler 51 escape through connection 42.

In the operation of t-he pressure cracking still illustrated, raw oil is introduced into the upper end of the reiiux tower through connection 52, there assisting in effecting and controlling the refluxing operation, and through the bearings ot'- the circulating pump 53 through connection 54 there assisting in cooling and lubricating the pump bearings. Pump 55 is provided for charging the still through connection 56 at the beginning of a run. At the end of a run the chargev remaining in the still is pumped out through connection 56 and cooler 57 by means of pump 58. Where the tar from a number of cracking operations is discharged into tower 43, the tar so pumped out of the still at the end of a run may be introduced into tower 43 through connection 59 there to be distilled.

Condenser 60 and connections 61 and 62,

cracking units.

The operation of the'fractionating towers 3 and 44, in the apparatus illustrated in` Fig. 2, may be controlled so that the higher boiling fractions separated therein and discharged throughconnections 77 and 78 are available as charging stock again to be introduced in to the pressure .cracking still.

Connections 79 and 80 are provided igor this purpose. To improve heat economy in such operation by-pass 81 is provided around cooler 26 to permit the return of this fraction, or asbmuch of it as can be so returned without excessively increasing the temperature of the oil entering the pressure cracking still, in a heated state. A by-pass around cooler 51 may be similarly arranged and operated.

In operation to produce gasoline from gas o'il in apparatus such as illustrated in Fig. 2, for example, the pressure cracking still maybe operated under a'pressure in the neighborhood of'125-150 lbs. per sq. in. and at a corresponding cracking temperature. This pressure may be maintained through the reiux tower 29 and reduced 'approximately to atmospheric pressure or to an intermediate pressure by means of valve 82, `or the stlll pressure may be maintained through the fractionating tower 3'; the condenser 7, and the receiver l0. Similarly, the pressure may be initially or further reduced by means of valvev 83 betweenthe fractionating tower 3', and the-icondenser 7 operated at approximately atmospheric pressure or 'at some higher intermediate pressure. The scrubbing tower 15 ,Inay i be operated under approximately atmospheric pressure or under a higher pressure;v this pressure may be the same as that prevailing in the separating tank'13 or higher. Any pressure reduction between the receiving tank l0 and the scrubbing tower l5 may be regulated by means of valve 84, and the pressure in the scrubbing tower 15 may be regulated by means of valve 85. The gaso line, or' gasoline-containing pressure distillate produced in the operation is discharged through connection 12 or, if separating tank 13 is not used, through connectlon 11.

'r'tkerosenc or furnace oil cut may be discharged through connection 72. The operation of fractionating tower 44 may be con trolled lso that the condensate discharged through connection 74 corresponds `in character to that discharged through connection 12 or so that it includes in addition higher boiling components corresponding to the fraction discharged through connection 72. Residual fuel oil is dischargedthrough connection 76. Gas oil character fractions may be discharged through lconnections 73 vand 75 or either of them. y

`Wl1ile the invention is of special value and application as an operation combined with cracking operations, in certain aspects it includes more general applications..A rllhe invention is useful in the recovery of gasoline components from a wide varietyof hydrocarbon gas and gas-vapor mixtures. The combined scrubbing operation and :tractionating operation may also be4 carried out in conjunction with tractionating operations applied to the separation of gasoline components and higherboiling oils other than those directly associated with cracking operations with certain advantages of the invention.

l claim:

1. An improvement in cracking hydrocarbon oils which comprises subjecting the gas-vapor mixture from the cracking oper` ation to a fractionating operation and then subjecting the remaining gas-vapor mixture to a condensing operation, subjectino" the gas-vapor mixture remaining uncondensed from the condensing operation to scrubbing treatment with a higher boiling oil fraction from the ractionating operation, and reintroducing the oil containing constituents-abheated oil into the fractionating operation.

3. An improvement in cracking hydrocarbon oils whlch comprises subjecting the gas-vapor mixture from the cracking operation/to a tractionating operation and then subjecting the remaining gas-vapor mixture to a condensing operation, this fractionating operation and this condensing operation being carried out under superatmospheric pressure, subjecting the gas-vapor mixture remaining uncondensed from the condensing operation to scrubbing treatment With a higher boiling oil fraction from the fractionating operation, and reintreducing the ,Y

oil containing constituents absorbed from the gas-vapor mixture in the scrubbing operation into lthe fractionating operation.

4. An improvement in the recovery of condensable gasoline components from gasl mixtures containing the same, which com- -prises subjecting a gasoline-including Vapor mixture to a. ractionating operation and condensingcomponents` higher boiling than gasoline therein, subjecting the remaining vapor mixture to a condensing operation and condensing gasoline therein, subjecting the gasoline-including gas mixture to scrubbingtreatment with higher boiling oil from the fractionating operation and reintroducing oil containing absorbedgasoline components from the scrubbing operation into the fractionating operation, `whereby the gasoline components absorbed from the gas mixture are condensed together with the gasoline components from the lfirst mentioned vapor mixture in the said condensing operation and whereby the heat of the gaso- 1ine-including vapor mixture subjected to the fractionating operation is utilized to .strip absorbed gasoline components' from the scrubbing oil.

In testimony whereof, I have subscribed my name.

erneuern` H. TBER, JR.

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