US1980839A - Process of and apparatus for cracking hydrocarbon oils - Google Patents

Description

J. B. WEBRE 1,980,839

PROCESS OF AND APPARATUS FOR CRACKING HYDROCARBON OILS Nov. 13, 1934.

Filed Feb, 18, 1931 INVENTOR ATTORNEY r: 1 ur:

Patented Nov. 13, 1934 PATENT OFFICE PROCESS OF AND APPARATUS FOR CRACK- ING HYDROCARBON OILS Joseph B. Webre, Port Arthur, Tex., assignor to v The Texas Company, New York, N. Y., a corporation of Delaware Application February 18, 1931, Serial No. 516,567

6 Claims.

This invention relates to an improved process of and apparatus for the pyrogenous conversion of hydrocarbon oil having a relatively high boiling point into lower boiling oils such as the type commercially known as gasoline, and broadly.

relates to a process in which the oil is subjected to conversion under conditions of temperature and pressure such that tarry constituents which are formed during the conversion of the oil and which ordinarily precipitate and settle out into a relatively undisturbed portion of the conversion zone wherein they may be substantially transformed into coke, are maintained suspended within the main body of oil which is being treated to thereby undergo decomposition into desirable liquid fractions without substantial conversion to coke or solid carbonaceous material.

The invention contemplates a process for the conversion of hydrocarbon oil into desirable low boiling fractions and a relatively higher boiling residual portion which comprises heating the oil to a cracking temperature, introducing the heated oil to a plurality of conversion vessels through which it may flow in succession and in which substantial bodies of the oil are maintained under uniform cracking conditions, continuously recycling through the vessels in succession a portion of the oil undergoing conversion therein to effect turbulent intermingling of the oil in order to maintain the tarry and potential coke-forming constitutents formed during conversion and which normally tend to settle out of the bodies of oil, suspended therein to undergo substantial and more advanced conversion into desirable liquid fractions without substantial coke formation, and to maintain a substantially uniform temperature therein whereby a uniform rate of cracking is maintained in all of the stills. The residual and heavier liquid fractions resulting from the conversion and which accumulate within the vessels may be continuously withdrawn from the system, while the vapors generated within the vessels are withdrawn therefrom to be subjected to dephlegmation to form a desired vapor fraction and a reflux condensate which may be returned to the system for further treatment.

During the pyrogenic decomposition of hydrocarbon oil the production of low boiling fractions of the order of gasoline is usually accompanied by the formation of relatively heavier fractions which as the reaction proceeds are converted or transformed into tarry or relatively heavier material which ordinarily tends to precipitate and settle out from the'ma n ody of (C1. 19e 4s oil undergoing conversion. When this tarry matter is permitted to accumulate and collect in a. relatively quiescent or undisturbed portion of the conversion zone, it tends" to readily undergo substantially complete transformation into coke or solid carbonaceous matter. The reaction may be one of polymerization or of chemical condensation of the constituents of the tarry matter to form a relatively high melting pointpitch which, under further or continued exposure to high temperatures and pressures, is largely converted to the form of coke. Ordinarily the formation and accumulation of these tarry cokeforming constituents and their subsequent transformation into coke may progress at a relatively rapid rate so that it becomes necessary to discontinue the cracking operation at frequent and regular intervals in order to remove the coke and solid matter which has accumulated within theconversion vessels or stills.

In cracking apparatus of the coil and. drum type wherein the oil to be cracked is preheated to a cracking temperature and introduced to the first of a series of reaction chambers through which it may flow in succession and in which substantial bodies of oil may be maintained under cracking conditions, it is found that the accumulation of tarry matter and carbonaceous material'occurs for the most part in the last vessels or stills of the series and that, at the completion of a run, the last vessel of the series may be substantially filled with coke while the preceding vessels contain correspondingly smaller amounts, the first vessel probably containing a negligible amount of such material.

It is believed that the oil undergoes what may be considered a primary or elementary stage of cracking or decomposition in the first vessels of the series wherein the resulting products of the reaction may consist of a relatively large amount of volatile fractions and. a relatively small proportion of fractions having a boiling point inter mediate that of the volatile fractions and that of the ultimate residual tar or pitch which is withdrawn from the system. As the partially decomposed oil flows through the remaining conversion vessels, wherein it remains at substantially the same temperature, the reaction is of a more advanced nature in which the aforementioned heavier products resulting from the initial conversion of the oil are subjected tofurther decomposition and in which the resulting products of the reaction may comprise a relatively small amount of volatile fractions and a relatively larger proportion of extremely heavy tarry material which is exceedingly rich in carbon and correspondingly leanwith respect to hydrogen.

It is believed that this heavy tarry material when permitted to precipitate from the main body of oil undergoing conversion and settle out or accumulate in a relatively undisturbed portion of the conversion zone where it continues to remain exposed to the influence of high temperatures and pressures, tends to be converted into coky or solid carbonaceous matter, possibly as a result of polymerization or chemical condensation. I

Also since the volume of the volatile fractions: generated within the bodies of oil in the last stills of the system is relatively small compared to that generated in the preceding stills, there is therefore, under ordinary operating conditions, correspondingly less agitation within the last stills of the system and wherein the oil is more viscous in nature and in fact the body of oil in the last still may actually remain in a substantially quiescent state which condition is, of course, extremely favorable to the settling out of the heavy tarry constituents and their subsequent conversion into coke, as already explained. The purpose of my invention is to maintain a positive circulationthrough the successive conversion vessels of a substantial portion of the oil undergoing conversion therein in order to effeet a continual turbulent intermingling of the oil in the successive vessels and thereby maintain the heavy tarry particles which normally tend tosettle out, suspended uniformly throughout the bodies of oil within'the vessels, whereby these particles are subjected to further conversion while in intimate or immediate contact'with relatively lighter or partially decomposed oil which tends to exert a solvent effect upon the particles and under which conditions the latter may be subjected to further and substantial conversion into desirable liquid fractions comprising low boiling fractions of the order of gasoline and/or somewhat heavier fractions which may eventually be converted into valuable products upon continued treatment within the system. Thus, as'a result of my invention whereby the heavy tarry constituents are maintained in suspension within the main bodies of oil rather than being permitted to coalesce and accumulate in the relatively undisturbed portions of the cracking zone, as is ordinari'ly the case, the ultimate yield of valuable light products may be materially increased while the formation of coke within the vessels is materially inhibited and, furthermore, the residual oil which is withdrawn from the system may contain materially'less particles of coke or carbon suspended therein and therefore comprises a residual oil or pitch of more uniform quality free from undesirable solid matter.

. Moreover, as a result of maintaining the oil in all of the stills of a more uniform character by continuously recycling through the successive stills a substantial portion of the oil undergoing cracking therein so that the tarry matter is maintained uniformly disposed throughout all of the vessels, such coke as may gradually be formed during the conversion of the oil accumulates substantially uniformly in all of the stills thereby increasing the extent of the useful operating time and reducing the frequency of shutdowns in order to remove the deposited matter from the conversion vessels or stills.

A further object of my invention consists in maintaining a more uniform temperature throughout the successive conversion vessels.

Ordinarily when the heated charge is introduced to the first of the series of vessels through which it fiows in succession, there is a progressive dropping off in temperature in succeeding vessels irrespective of whether the vessels are protected against heat losses as a result of vaporization as well as by convection and radiation to the surroundings, either by coverings of heat insulating material, or by the direct application of mod-- erate external heating, which latter must be of limited intensity in order to avoid heating the walls of the vessels above certain safe temperature limits and which may not appreciably exceed thereaction temperatures. Where the stills are externally heated in this way, it is not unusual for the oil in a succeeding vessel to be 5 F. or 10 lower in temperature than that in a preceding vessel, and this differential may be appreciably greater in the case where coverings of heat insulating material only are depended upon for counteracting the above mentioned. heat losses.

' I am able to substantially compensate for this reduction in temperature by conuningling the I oil, whichis being recycled with a stream of. the

charge to the "system which may have been heated to a temperature higher than that necessary to normally effect its subsequent conversion and thereby reheat the partially converted oil which is being recycled. comprise the fresh charge or a mixture of fresh This heating medium may 1 charge and reflux condensate being introduced to the. stills or may preferably comprise a selected portion of the oil undergoing conversion as, for

example, the reflux'co-ndensate, which is of a drawing which is a diagrammatic sectional elevation of an apparatus constructed in accordance with the invention and constituting ment thereof.

In the drawing a coil and drum or a tube and tank cracking system is shown but it is to be understood that the invention is not limited to this particular type of cracking operation, since it may well be practiced in any method of cracking in which the oil is distilled in two or more stills or where separate bodies of oil are subjected to the cracking operation.

A pump 1 is adapted to draw charging stock from a suitable source and introduce it tov a section 2 of a heating coil within a furnace adapted to heat the oil to a suitable cracking temperature and from which the oil may flow through a transfer line 4, having a valve 5, terminating in branch pipes 6a and 612 having valves 7a and 7b, respectively, and leading to the lower portions of the first two stills of a battery consisting of stills 8. By closing the valve 5 the oil may, if desired, flow through the valve 9 into the section of the heating coil wherein it may be mixed with a returning stream of reflux condensate, as will be described presently in more detail, and therein subjected to further heating following which the admixture is passed through a pipe 10 leading to the previously mentioned transfer line l.

The stills 8 may be either heat insulated or mounted in asuitable furnace. (The upper poran emboditions of these stills are interconnected by vapor equalizing lines 12 and liquid equalizing lines 13. A vapor line 14 conducts the vapors generated within the stills to a dephlegmator or bubble tower 15 wherein they are subjected to fractionation to form a desired vapor fraction and a reflux condensate. The vapor fraction is withdrawn from the dephlegmator through a line 17 leading to a condenser18 from which'thecondense-d material may bewithdrawn through the pipe 19, having a pressure control valve 20, into a receiving tank 21.

The surplus reflux condensate collecting in the bottom of the tower 15 is withdrawn through a pipe 22 by a pump 23 and introduced to the section 3 of the heating coil, as already mentioned, I

wherein it may be mixed with the fresh charge leaving the section 2 of the heating coil.

The residual oil being formed or collecting within the conversion chambersor stills may be withdrawn from the bottom of the stills-through draw-off pipes 24, having valves 25, into a main draw-off line 26, having a .valve 27, which may lead to storage tanks or preferably to a stripping unit wherein the residual oil may be sub-.

jected to further distillation and fractionation to strip out light gasoline constituents which may remain admixed therewith as well as to recover valuable and relatively heavier gas oil fractions i which may be subsequently returned to the system to undergo further conversion.

Liquid outlet pipes 23, having valves 29, are provided through which partially converted oil may be withdrawn from a lower or intermediate I portion of the last two stills and discharged into a pipe 30, having a valve 31, leading to the suction side of an injector or jet pump 32 interposed in the pipe 10 through which the heated mixture of fresh charge and reflux condensate is conducted to the first stills, and wherein the par and illustrated, it is contemplated that a reciprocating pump or other suitable pumping means may equally well be substituted therefor, if desired, with which to draw oil out of the last stills and return it to the first stills of the series or to withdraw oil from a succeeding still and return it to a preceding still of the series, and thereby effect the desired degree of recycling.

In practicing the invention, the fresh charge oil is conducted through the section 2 of the heating coil wherein it may be preheated to a suitable temperature following which it may then be passed through the section 3 of the heater coil together with the reflux condensate being returned to the system through the pipe 22 and heated therein to a predetermined crackingitemperature which may range from 800 F. to 950 F. or higher. The heated admixture of fresh charge and reflux condensate is then passed through the injector 32, creating a suction therein where by oil is withdrawn from either or both of the last two of the stills 8 and is commingled therein with the heated mixture and returned to the lower portion of either or both of the first two stills. The oil flows upward through these stills and overflows through the liquid equalizing lines 13 into succeeding stills. The quantity of partially converted oil being recycled through the succeeding stills may be several times the volume of mixed charge entering the stills from the section 3 of the heating coil, and is preferably adjusted so as to maintain a high volume of flow through the stills'and thereby produce a sufficiently high degree of turbulence and in,- termingling of the oil within the conversion vessels so that the heavy tarry fractions which are formed, particularly during the latter stages of conversion of the oil, are kept suspended within the main bodiesof oil in the upper and major portions of the vessels. Thus, the precipitation of these tarry materials is retarded or delayed while they undergo further or advanced conversion under conditions which are productive of desirable liquid fractions and inhibitory of their transformation into coke. The heavy pitchy material resulting from this advanced conversion, being too heavy to remain in suspension in the lighter oil, then settles down in the bottom and relatively small portions of the stills from which it may be withdrawn as a residual pitch-like material, approximately as rapidly as it accumulates without remaining in this undisturbed zone for appreciable periods of time at relativelyv high temperatures and pressures during which it would otherwise undergo trans formation into a coke-like formation.

While the fresh charge maybe commingled with the reflux condensate and heated to cracking temperatures in the section 3 of the heating coil and the combined charge then conducted to the conversion vessels, it is contemplated that in some cases it may be desirable to heat the fresh charge and the returning reflux condensate in separate coils. It has been found undesirable in many instances to initially subject the fresh charge, particularly when it comprises a relatively heavy oil, to needlessly high cracking temperatures, due to the resulting incipient formation of heavy tar-like fractions which are apt to be immediately transformed into coke under the. influence of high temperature upon coming into contact with the metallic walls of the heating coil, or to subsequently undergo such transformation when introduced to the cracking vessels. The reflux condensate, on the other hand, comprises a distillate material, free from tarry matter, of appreciably lower boiling range than the charge, and which is therefore more refractory towards decomposition and consequently may be, and actually requires to be, heated to a relatively higher temperature in order to effect its subsequent conversion, and which conversion may be accomplished without the production of material quantities of the undesirable tar or coke-forming materials.

Accordingly, in the practice of my invention,

wherein it is desired to maintain more nearly uniform temperatures throughout the succeeding vessels and compensate for heating losses, the reflux condensate may be separately heated in the coil section 3 to a cracking. temperature in 3;

excess of that normally required to effect its sub-- sequent conversion following which it is passed through the transfer line 10 to the injector 32 wherein oil is entrained from the last stills and heat is imparted to the entrained oil from the relatively hotter reflux condensate in order to reheat the recycled liquid to a desired extent and thus compensate for the cooling of the oil within the vessels. While under ordinary circumstances all of the reflux condensate may be passed through the injector 32, it may be desirable in some instances to regulate the amount of impelling liquid flowing through the injector in which case a'jump-over connection 33, having a valve 34, is provided through which any desired proportion of theheated reflux condensate may be by-passed around the injector into the transfer line 4 through which the fresh preheated charge is being introduced to the system.

Although the preferred embodiment of the invention has been set forth in conection with apparatus having a particular construction and arrangement of parts and mode of operation, it is obvious that various changes and modifications may be made therein, while securing to a greater generated within the stills and conducting them 7 to a dephlegmator to form therein a desired va por fraction which is drawn off to condensing means and a reflux condensate, withdrawing the reflux condensate and reheating it in a separate heating coil to a cracking temperature, passing the heated reflux condensate through an injector pump adapted to withdraw unvaporized residual oil from the last stills of the series and commingle it with the heated reflux condensate, conducting the resulting admixture to the first stills of the series, thereby recycling through the stills a substantial portion of the oil undergoingconversion therein so as to effect turbulent intermingling of the oil in said bodies in order to main tain tarry constituents which ordinarly settle out in the lower portion of the stills to form coke suspended within the bodies of oil wherein they undergo substantial conversion'into desirable liquid fractions and to maintain a substantially uniform temperature in all of the stills, whereby a uniform rate of cracking is maintained. 1

2. In the process of cracking hydrocarbon oil, the steps which comprise passing fresh, oil through a coil and heating it therein to a cracking temperature, passing the heated oil through a plurality of series-connected still chambers whereinbodies of oil are maintained under cracking conditions substantially entirely by the contained heat thereof, removing vapors generated within the stills, and conducting them to a dephlegmator to form therein a desired vapor fraction which is drawn off to condensing means and a reflux condensate, withdrawing the reflux condensate and reheating it in a separate heating coil to a cracking temperature in excess of that normally required to effect its subsequent con- ,version and above that to which said fresh oil is heated, passing the heated reflux condensate through an injector pump adapted to withdraw oil from the last stills of the series and commingle it with the heated reflux condensateto thereby reheat the, withdrawn oil, conducting the resulting admixtureto the first stills of the series, thereby recycling through the stills a substantial portion of the oil undergoing conversion therein so as to effect turbulent intermingling of the oil in said bodies in order to maintain tarry constituents which ordinarily settle out in the lower portion of the stills to form coke suspended within the bodies of oil wherein they undergo substantial conversion 1 into desirable liquid fractions and tomaintain a substantially uniform temperature in all of the stills whereby a uniform rate of cracking is maintained. o I

3. The method of converting relatively high boiling hydrocarbon oils into lower boiling hydrocarbon oils which comprises heating a flowing stream of oil to cracking temperature duringits flow through a confined heated passageway and thereafter passing the heated oil into the first of a plurality of series-connected still-chambers, whereby said oil flows successively through said chambers and undergoes cracking therein substantially entirely by its contained heat, withdrawing vaporous products from said still-chambers and subjecting them to fractionation to condenseand there-by separate, as reflux condensate, undesired" higher boiling constituents, withdrawing thefractionated vapors and condensing them to form the desireddistillate product, withdrawing; reflux condensate from said fractionating operation and passingit through a separate elongated heated passageway and heating it during its flow therethrough to a cracking temperature, thereafter passing theheated condensate to the first of said plurality of still-chambers for sim-,

bers, whereby said oil flows successively through.

said chambers and undergoes cracking therein substantially entirely by its contained heat, withdrawing vaporous products from said still-chambers and subjecting them to fractionation to con dense and thereby separate, as reflux condensate, undesired higher boiling constituents, withdrawing the fractionated vapors and condensing them to form the desired distillate product, withdrawing reflux condensate from said fractionating op,- eration and passing it through a separate elongated heated passageway and heating it during its flow therethrough to a higher cracking temperature, thereafter passing the heated condensate to the first of said plurality of still-chambers for similar flow therethr-o'ugh, withdrawing unvaporized residual products from a subsequent one of said still-chambers and introducing them directly into the stream of highly heated condensate stock subsequent to its heating in said separate elongated passageway and prior to its introduction into the said first of said series-connected still-chambers and its admixture with the said other separately heated oil.

5. Apparatus for cracking hydrocarbon oil which comprises a heating coil, means for charg- 1 chamber to a subsequent one of said, chambers;

a fractionating column, means for passing vapors from said chambers to said fractionating column, a condenser, means for passing fractionated vapors from said fractionating column to said con- 1 denser, a second heating coil, means for withdrawing refiux condensate from said fractionating column and for passing said condensate through said second heating coil, means for heating said condensate in said second coil to a cracking temperature, conduit means interconnecting the outlet of said second coil and said first of said reaction chambers, injector means interposed in said interconnecting conduit means, and means for withdrawing unvaporized products from the said subsequent reaction chamber and for introducing said withdrawn unvaporized products into said injector means whereby the said withdrawn unvaporized residues are admixed with the highly heated condensate and thereby forced into the said first reaction chamber.

6. Apparatus for cracking hydrocarbon oil which comprises a heating coil, means for charging fresh oil to said heating coil, means for heating the oil in said coil to cracking temperature, a plurality of reaction chambers, means for passing oil from said coil to the first of said chambers, means for passing oil from the said first chamber to a subsequent one of said chambers, a fractionating column, means for passing vapors from said chambers to said fractionating column, a condenser, means for passing fractionated vapors from said fractionating column tosaid condenser, a second heating coil, means for withdrawing refiux condensate from said fractionating column and for passing said condensate through said second heating coil, means for heating said condensate in said second coil to a higher cracking temperature, conduit means interconnecting the outlet of said second coil and said first of said reaction chambers, injector means interposed in said interconnecting conduit means, and means for withdrawing unvaporized products from the said subsequent reaction chamber and for introducing said withdrawn unvaporized products into said injector means, whereby the said withdrawn unvaporized residues are admixed with the highly heated condensate and thereby forced into the i said first reaction chamber.

JOSEPH B. WEBRE.

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