US2008550A - Process of cracking petroleum oils - Google Patents

Description

July 16, 1935- R. A. HALLORAN ET AL 2,008,550

PROCESS O CRACKNG PETROLEUM OILS Y Filed Oct. lO, 1928 2 Sheets-Sheet l July 16, 1935. R. A. HALLORAN ET AL PROCESS OF CRCKING PETROLEUM OILS Filed Oct. lO, 1928 2 Sheets-Sheet Patented July 16, 1935 PATENT i OFFICE PROCESS OF CRACKING PETROLEUM OILS Ralph A. Halloran and Archie L. Strout, Berkeley, Calif., assignors to Standard Oil Compa-ny` of California, San Francisco, Calif., a corporation of Delaware vApplication October 10, 1928, Serial No. 311,467

2' Claims.

This invention relates to the art of decomposing or cracking oils, such as petroleum oils, by means of high temperature and pressure above atmospheric, commonly referred to as the pyro- 5 genetic cracking of oils, to produce low boiling point, low specic gravity, oils from relatively higher boiling point oils, and particularly to produce low boiling point oils adapted for use as fuel in internal combustion engines.

More specifically the invention relates to a pyrogenetic oil cracking process of the type in which oils, after being heated to a desired cracking or decomposing temperature, are passed into a vaporization zone from which the vapors are withdrawn as distillation products thus separating them from the unvaporized oils.

In cracking processes of this type, the operation has generally been so carried on that there is excessive coke or carbon formation in the evaporating chamber and the resulting residual oil Withdrawn from the system contains such an amount of free carbon or sediment as tomaterially reduce the value of such residual oil as a commercial fuel oil.

An object of the invention is to provide a cracking process by which a highyield of loW boiling point fractions may be obtained, While at the same time the production and precipitation of coke, carbon or carbonaceous material in the respective parts of the apparatus may be minimized and controlled or substantially avoided, and the sediment content of the residual oil reduced to a minimum, thereby rendering such residual oil satisfactory for a commercial fuel oil.

Heretofore it has been common practice to maintain in the evaporating chamber for relatively long periods of time a very considerable volume of the heated unvaporized oils discharged from the heating zone or coil, in order to secure a material amount of cracking reaction or conversion of such oils into lower boiling point oil. When the cracking reaction is thus allowed to continue while vaporization takes place and before the residual oil is Withdrawn from the system digestion of the ingredients whichv are capable of yielding further low boiling products in substantial quantity takes place in the presence of the heavier derivatives of decomposition or cracking. The result has been rapidV and excessive degeneration of the heavier derivatives oi' the cracking reaction, With the consequent production and precipitation of excessive amounts of carbon and sediment in such chamber.

This invention comprehends a process whereby oil may be rapidly raised tothe reaction temperature and then the heavy residuents` of the cracking or decomposing reaction separated from the v oil after their formation, with suiiicient celerity to avoid their degeneration into coke and the formation of sediment, While desired portions of the insufficiently cracked oils remaining after such separation may be further decomposed Without supplying further heat thereto, `whereby the production and the precipitation of carbon or coker or carbonaceous material in the apparatus may be substantially avoided or reduced to a minimum while recovering a high yield of the desired low boiling point oils.

An object of the invention is to provide a process whereby there is obtained a high yield of low boiling point oils without reliance, as a` controlling factor for the desired high yield, upon digestion of the unvaporized oils remaining in the evaporating chamber being conducted in the presence of the heavy residuents of the cracking l or decomposing reaction, thereby reducing to a minimum or substantially avoiding the production and precipitation of carbon or coke or carbonaceous material in the apparatus. The invention contemplates a process in which digestion of insufficiently cracked portions capable of yielding a further material amount of low boiling point products, i. e., their further decomposition Without further heat input, is substantially confnedto acondensate from vapors, The invention also contemplates the dilution, before 4theirremoval from the zone of reaction, of the heavy residuents of cracking With a portion of intermediate constituents capable of yielding a further material quantity of low boiling point products and the return of such intermediate constituents to the heating zone free from such heavy derivatives of cracking.

By the process disclosed in the pending application of Ralph A. Halloran and Archie L. Strout, Serial Number 176,990, filed March 21, 1927, the production of such carbon and sediment may be effectively controlled and reduced to a minimum or substantially avoided, thereby reducing or substantially avoiding precipitation thereof in the evaporating chamber. However, with such a process as that disclosed in said application, in order to secure the desired high yield of l'ow boiling point oils, it has been necessary to compensate for the decrease in digestion taking place in vaporization chamber by increasing to a greater or less degree the temperature to which the oil undergoing treatment is raised in the heating zone or coil. Corrosion of the equipment is a materialfactor in the commercial operation of such process. Higher coil temperatures increase corrosion. It is one of the objects of this invention to provide a process by which the same high yield may be obtained without resort to such higher coil temperature, and in fact by a reduction in the coil temperature, thus avoiding such increased corrosion or experiencing a reduction in the amount of corrosion.

,Another embodiment of this invention comprehends a process or method whereby relatively high boiling point, high specific gravity oils may be economically cracked or decomposed by rapid passage through a relatively long heating coil in which such oils are subjected to pressure materially above atmospheric while being quickly raised to a relatively high cracking temperature whereby a relatively rapid cracking rate is securediwithin the coil and from which heating coil the intermingled cil and vapors are discharged into a vaporization or separation chamber, (preferably maintained under substantially the same pressure as the oil and vapors in vsaid coils), wherein the vaporized'fractions are quickly separated from the oil fractions unvaporized'at the tem erature and pressure of the operation, and in which the temperature of said unvaporized oils rapidly drops materially below the exit temperature from the coil, subjecting the resultant vapors to reflux condensation, (preferably under substantially the pressure of the operation), subjecting the liquid oils condensed thereby to digesting or cracking reaction, preferably under the contained heat thereof, and under pressure -above atmospheric, recovering the vapors from such digestion or cracking operation, passing the residuum from such last named cracking or conversion operation to the heating coil for .re-treatment, maintaining a substantially constant but :relatively small volume of unvaporized oils in said evaporating chamber by continually dis- ;charging the unvaporized voils ytherefrom to a distillation chamber (preferably by maintaining la substantially uniform rate of flow into vand yseparate discharge of vapors and unvaporized -oils from said vaporizing chamber), wherein the eration, readily decomposed to coke, and returning said last named condensate together with fresh feed, either directly or indirectly, to the heating coil; preferably maintaining in such vavporizing chamber such a relation of pressure toVV i temperature therein as to provide dilution of the heavy residuents of cracking with a proportion vof lighter oils not readily decomposed into carbonaceous material under the time, pressure and .temperature conditions of the operation.

An essential feature ofthis invention resides ,in subjecting the condensate from the reflux and without the production of products in such residuum which when passed through the heating coil will undergo extensive decomposition to coke, carbon or carbonaceous matter or precipitation therein.

The invention may be more readily and fully understood by reference to a description of a preferred embodiment as utilized in actual practice taken in connection with the accompanying drawings diagrammatically illustrating the apparatus employed, and in which Fig. l. is a diagrammatic illustration of such an apparatus; Fig. 2 showing modifications'of the apparatus in connection with the digestion or cracking reaction of the condensate.V

In the drawings, 2 indicates a heating coil, suitably mounted within a furnace 3 to be heated thereby to the desired temperature. The furnace is fired in the usual or any preferred manner. This coil E is preferably of such length and dimensions and so mounted in the furnace 3 as to provide a relatively long ,passage of the oil through the .heating zone, so that the oil to be cracked or ,decomposed Vmay be rapidly forced through the coil and raised to andsubjected to ,l

the desired cracking temperature while within the coil, at the same time being moved therethrough with such rapidity as to substantially prevent the formation or precipitation of coke or carbonaceous matter in the cracking coil. i indicates a dischargeV line leading from the cracking coil to a separating or evaporating chamber 5. Preferably this discharge line discharges into such chamber 5 at the top thereof. t indicates a vapor line by means of which the vapors are conducted from such separating or evaporating chamber 5 and discharged into a fractionating tower l. This fractionatingstower 'i may be of the ordinary or any preferred construction, such as the well-known Vbubble or doughnut-and-pan tower.

indicates a vapor line leading from the fractionating towerl into a suitable condenser 3 from which the condensed oil maybe discharged into a suitable receiver It. il represents a gas discharge line by means of which any fixed gas or uncondensed vapor may be discharged. This line ii is providedwith a valve l2, asindicated. i3 indicates a line by which the oil may be withdrawn from the receiver lil to storage. i3 is controlled by a suitable valve Ul. If desired a branch I3 in the line i3 may be connected to a pump I5 by which a portion of suchdistiilateV ,may be returned from the receiver It to the upper part of the fractionating tower l and This line therein used as a cooling agent for the ascending vapors. .Any well-known cooling Vmedium or `means may be used, however, to control the fractionating tower .'l.

I6 indicates a discharge line for the withdrawal of the unvaporized oils from the vaporization chamber 5 and discharges into a flashing ,chamber l?. IS indicates a suitable valve by which the release of pressure is controlled.l i9 represents a discharge line from the bottom of the flashing chamber il controlled by a valve 2U leading to suitable storage for the fuel oil produced. 2l represents a line for drawing off the .vapors from the flashing chamber I'l and leads through a heat exchanger 22 to a jet condenser 23, The heat exchanger 22 may be-of any ordinary or preferred construction. Only one heat exchanger is indicated in the drawings. Any desired number may be used, VThe jet condenser may be of` any ordinary or preferred construction charges into the fractionating tower l.

and is.` indicated as provided With the usual bafe plates. The condenser is provided with a line 24 controlled by a valve 25, by which, the incondensible gases may be withdrawn and discharged. Y

. 23 indicates the fresh feed line through which the fresh oil to be treated may be. introduced to the jet condenser and sprayed` therein, thereby elfecting a jet condensation or" the vapors from thev dashing chamber il'. 2 represents an outlet line from the 'jet condenser connected'with the'suction side of a feed pump 28 which delivers into the line 28 through heat exchanger 22 and to the branch feed line 29 which is connected with the pipe or line 3Q connected to the suction side of the feed pump 3l. arranged to deliver through the line 32 tothe heating coil 2. Interposed in the branch feed line 2S is a suitable control valve 33. 34 indicatesa .second branch of the feed line 28', controlled by the valve 35 and discharging into the fractionating tower l, thereby spraying a porti on of the feed into the uprising vapors in the fractionating tower l. 1t is obvious that either the branch E9 or 3d of the feed beof the ordinary or any preferred construction v and may be arranged horizontally, as indicated in the drawings, or vertically. It is preferable to utilize a horizontally disposed digester 3l of comparatively small cross section and of considerable length, in order to provide directional` flo-w through such digester,` as thereby the time of treatment of the oils passing into and through such digester may be more accurately controlled. The line 3u connects the outlet end ofthe digester 3? with the suction of the pump 3l 38 indicates a vapor line by means of which the vapors produced in the digester 31 may be withdrawn.` As indicated in thetdrawngs, this vapor line 33 dis- It is obvious that if desired a separate condensermay be used for these vapors, andl they may be separately discharged to suitable storage. 4@ indicates a compartment in the digesteryl formed by baliles 4l. ft2 indicates a line through which gas or steam may be passed to this compartment as an aid to distillation therein. 39 indicates a vapor line passing to fractionating tower 3. A line 44 leads from the fractionating column 43 to condenser d which may be of any practical type. d8' indicates a line for conducting condensate from condenser Il?. to suitable storage or to a naphtha recovery system. Interposed in line isis trap t from which line :i5 provided with valve il leads to fractionating tower i3 for conducting thereto apart of the condensate.

As an example of an operation of a. process embodying this invention with a, particular type or size of equipment, we have used as a charging stock or fresh feed to the system a 26 A. P; I. gas oil cut from California crude. This oil was pumped at the desired rate into the upper part ofthe jet condenser 23; In descending over the baffle plates Vof this condenser this cooled feed contacted with the cycle stock vapors from the distillation chamber l'l and condensed the said vapors. The commingled feed oil and condensed cycle stock were `withdrawn from the condenser chamber 23 through the feed line 2l by the pump 28. Inasmuch as the cycle stock had been cooled by passage through the heat exchangers indicated (at 22,v and further cooled by contact with the in.-

coming fresh feed in the chamber 23, thetemperature` of i the mixture. flowing throughv the pump 28 was relatively low. As this mixed feed was forced `through the feed line 28 by the pump 28, it passed through the heat exchanger '22, and

was raised to va temperature of approximately,

50W-606 E'. and passed into the fractionating tower The length ofthe heating coil 2 was so proportioned to the furnace conditions that the 4oil passed therethrough with sufficient rapidity to be progressively and not too abruptly raised to the m xirnum temperature. through the cracking coil,V the oil was raised to a temperature of about 875 l. under a pressure between 275-299 pounds. WithY such an operation the temperature of the vapors discharged through the transfer line 4 approximated 875 F. The evaporating chamber was suitably insulated to avoid excessive heat radiationand the teinperature of the unvaporized oil collecting inthe bottom of the vaporizing chamber was approximately 79()Q F. The fractionating tower 'l was so constructed and operated as to produce from the vapor discharged through the vapor line B'the desired distillate. The refiux condensate from this fractionating tower hada temperature of 785 F. The pressure maintained in the fractionating tower approximated 270 pounds. The temperature of the oils entering "the digestion chamber was approximately 785 F. and the residual therefrom was drawn through the pump 3i at a temperature of approximately '275 F. The pressure in the digestion chamber 3l in such operation approximated 270 pounds.

From the evaporator chamber 5 the unvaporl ized oils were discharged through the line I6 to the hashing chamber il', pressure being released by the valve I8 to effect flash distillation. These oils were distilled in the hashing chamber il by their contained heat and all those constituents suitable for further decomposition recovered as vapors, Vand were utilized as a charging stock. The liquid oil, (containing the heavy derivatives of the. cracking reaction) remaining from such flash distillation was discharged from the-chamber Il at a gravity of approximately l0 to 12 A. P. I. and was substantially free from sediment and carbon or coke, and available as a good liquid fuel.

With certain oils or certain operations, the entire pressure may be released upon the delivery of the unvaporized oils to the hash chamber l1 and with certain operations advantage may be had by actually creating a partial vacuum in such chamber H by means of a vacuum' pump (not shown in the drawings), thus inducing additional distillation therein.

Degeneration of the heavy derivatives of cracking to colte and carbonaceous material was controlled by regulating the time during which the unvaporized oils from the cracking coil and the heavier derivatives of cracking were subjected to decomposition conditions in the vaporization chamber passing such residuals out of the ByV its passage` vaporization chamber before such excessive decomposition or degeneration could take'place.

The best results were obtained by maintaining a relatively small amount of liquid oils within the Yvaporization chamber. 5. By reducing the amountA of unvaporized oils within the vaporisation chamber 5 and 'by maintaininga substantially uniform rate of ow into and separate discharge of vaporsand unvaporized oils from the vaporizing chamber 5, substantial degeneration of the heavy out these lighter fractions.

Y into coke, etc., under the temperature and pres-.

sure of the operation. Therefore, specific illustrations of the particular time element preferable in such operation are not given, as these must be related to the volume of oil undergoing treatment, the volumetriccapacity of the apparatus, temperatures, pressures, etc. The rate of discharge of such diluted unvaporized oils from the evaporating chamber should. however. be at such rate as not to maintain any given portion thereof therein for a sufficient period of time to permit degeneration to or precipitation therein of coke,

etc. Y

gester a drop in temperature occurs between the inlet and outlet ends due in part to the endothermic reaction of the cracking process and in part to the heat of vaporization absorbed in the production of vapors in this element. Inasmuch as lighter fractions are produced within the body of the oil, not all of the light fractions produced may be distilledv off under the constant pressure conditions. If these fractions are not removed from the oil they pass to the heating element and may be partially cracked to gas and undesirably further broken down. Their presence in the oils passing to the cracking coil may also cause too early vaporization therein, and their vapors will exert their partial pressure effect within the system, and also, due to the formation of such vapors, will `tend to cause an over-all expansion of the material passing through the coil and thereby for the same thruput shorten the time of eX- posure under the established temperatures.. This shortening of time will tend to reduce the amount of cracking for any given temperature and for the same yield or production make it necessary to carry higher temperatures than would be the case if the lighter fractions were not present.

. Where such light fractions would otherwise remain in the residuum discharged from the digester 31 into the feed line to the heating coil 2, provision is preferably made for their removal from the residuum either beforeV the residuum is discharged from the digester 31 or before suchV residuum is passed into the feed to the coil. In Fig. 1 there is illustrateda method of stripping Distillation is facilitated by the gas or steam introduced through line l41 and the vapors evolved in compartment 4B are passed through line 3S to fractionating tower 43 equipped with or accompanied by the necessary facilities for proper fractionating and for condensing the desired product from said vapors. While it is indicated in the drawings that a part of the condensate may be returned to the fractionating column d3, it is evident that various types of fractionating tower with the return of the necessary fractions for cooling may be utilized. Reflux from the column is preferably returned to the residuum passing to the heating coil 2 as by a reflux line 45. Instead of utilizing a separate condenser, the vapors rising from the compartment 40 may be conducted (as indicated in dotted lines) into the vapor line 38.

During theprogress of the oil through the di- Y levaporator 5.

i Another method of stripping the lighter fractions from the digester 31 is illustrated in Fig. 2. In this method pressure is reduced between the digester 31 and the fractionating column 43 by means of the valve 50 in line 49 which conveys residuum from the digester 31 to the fractionating tower 43. The amount of reduction vin pressure will depend on operating conditions,

the type of stock handled, the amount of low boiling fractions carried in the digested stock and the amount of fractions it is desired to remove. Any practical fractionating equipment may be used for the purpose of stripping the lighter fractions while gas or steam may be used as an aid to distillation if found desirable. In the event it may not be necessary or desired to strip out these lighter fractions thecfractionating tower 43 and its accompanying equipment may be omitted and the residuum from digester 31 passed directly to the heating coil as indicated by dotted line 5| of Fig. 2; or by the omission of baies 4l shown in Fig. 1 Vtogether with the omission of fractionating equipment 13 as explained above.

By subjecting the refluxY condensate of the vapors, separated from the unvaporized oil delivered from the cracking coil, to a digestion or cracking reaction and distillation, and then passing the residual of such reaction back to the cracking coil a substantial yield of W boiling point oils is obtained without the production or the precipitation from this part of thev oils undergoing treatment of a material amount of coke, ctc. in the cracking coil or vaporization chainber. This digestion can be effectually Secured without the addition of heat to such condensate and may be conducted at substantially'the pressure under which such condensate is produced or at somewhat reduced pressure, or under higher pressure, and with added input of heat if desired. As the low boiling point oils thereby produced are recovered, less crackingV will be required in the heating coil and in the evaporator for the same overall yield of, low boiling point larly when treating oils containing a material sulphur content.

`In the foregoing description and drawings for a more clear understanding of ourY invention, we have described and indicated the digester- 31 asa separate mechanical element. Under some conditions of operation and installation the condensate might bepermitted to collect in the bottom of the fractionating tower (as in the lower portion of the tower 1, thus utilizing the same as a digestion chamber) and be held therein Vfor the desired time interval during which the desired decomposition takes place `before discharge of the residuum into the feed line to the cracking coil, In such case the evolved vapors of the digestion or cracking reaction distilling off would be removed before the residuum is passed to the feed line. This would also be true where the fractionating tower 1 is superposed above the In'such practice, however, there would be sacrificed the advantage of controlling parallel ow through the digestion chamber,

securable with the operation and apparatus heretofore described, because the lower boiling point fractions formed during digestion would rise through the liquid oils, causing agitation and rendering it impossible or diflicult to withdraw all portions of the residual oils or rediduum separately after the lapse of the established desired time. This sacrice, however, under certain conditions may not be of sufficient magnitude to prohibit its usej particularly in consideration of the simpler equipment involved, and our invention therefore extends to and includes both these methods of operation.

We claim:

1. A process for converting heavy hydrocarbon oil into lower boiling products which comprises passing the oil in a restricted stream rapidly through a heating zone and heating the same therein to cracking temperature under superatznospheric pressure, discharging the heated oil into a reaction zone maintained under cracking conditions of temperature and pressure and separating the same therein into vapors and unvaporized oil, removing the latter from the reac- .tion zone before any substantial quantity thereof has degenerated into coke and preventing its return to the heating zone, separately removing the vapors from the reaction Zone and dephlegmating the same under superatmospheric pressure thereby forming a reflux condensate which is at cracking temperature, digesting the reflux condensate under the superatmospheric pressure and Without application of heat thereto in a heat insulated digestion zone and effecting further conversion thereof by its contained heat, re-

moving the digested reflux condensate from the digestion zone and lowering the pressure thereon thereby separating the same into vapors and residuum, supplying said residuum to the heating Zone for retreatment -in the process, and condensing the vapors evolved from the digested reux condensate as Well asthose uncondensed by the dephlegrnation.

2. The process as dened by claim 1 further characterized in that the unvaporized oil Withdrawn from the reaction zone is flash distilled by pressure reduction, the flashed vapors dephlegmated, and resultant flash reflux introduced into contact with the initially separated vapors being dephlegrnated and Ithence into the digestion zone in admixture with said reflux condensate.

RALPH A. HALLORAN. ARCHIE L. STROUT.

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