US1923526A - Treating hydrocarbon oils - Google Patents

Description

Au 22, 1933. o. BEHIMER I TREATING HYDROCARBON OILS Filed Aug. 13, 1925 Suvemtoz MAM/v1 Patented Aug. 22, 1933 UNITED STATES TREATING HYDROCARBON OILS Otto Behimer, Port Arthur, ,Tex.,tassignor, by mesne assignments, to The Texas Company, New York, N. IL, a Corporation of Delaware Application August 13, 1925. Serial No. 49,915

1 Claim.

This invention relates to the conversion of higher boiling hydrocarbons into lower boiling ones for the production of gasoline and similar products.

' One of the objects of the inventionis to provide a method of cracking hydrocarbon oils that is adapted to be operated in a given apparatus for extended periods of time thus avoiding the v disadvantages incident to many existing systems which require frequent shut-downs for the purpose of removing carbon and coke accumulated during a run. My experiments have shown that cracking or molecular decompositionof hydrocarbons can be carried on for a time without the formation of carbon. It appears that in the first stages of the cracking operation the hy-: drocarbon compounds are broken down to yield lighter or lower boiling constituents, such as gasoline, some intermediate fractions and certain higher boiling or heavier products of greater molecular weight than any of the constituents in the original oil treated. These heavier products appear to be polymerized constituentsand are readily converted into carbon or coke upon the further application of heat. My experiments indicate clearly that it is these polymers or heavy carbon-forming compounds produced in the cracking reaction that in common methods of operation aredecomposed to form free carbon. 1 have found that by arresting the decomposition at or before the critical point at which these heavy carbon-forming oils are converted into carbon or coke that higher boiling hydrocarbons may be converted into lower boiling ones without the production of any material quantity of carbon or coke. In this way it is possible to operate in a given. apparatus for long periods of time.

Broadly and generally my invention contemplates passing oil through a cracking zone and arresting the decomposition at approximately the critical point at which free carbon is formed. It is to be observed that in the practice of my invention I do not carry the cracking operation,

as applied to a givencharge of oil through the converter, to completion but on the contrary subject the oil to cracking until the oil reaches provided careis taken in designing the heating,

true that in some of the existing cracking sys- Rterns oil or residue is withdrawn from the conbecause these products are in solution with the rest of the .oil in the converter. My experience with prior cracking-processes has been that it" is imposs ble in a continuous process to efiect a clean separation between the polymers or high carbon-forming oils and the rest of the oil and that as a run continues, evenfthough liq uid be regularly withdrawn from the cracking zone in the customary manner, there is a tendency for these carbon-forming products to collect in thecracking zone causing increased quantities ofcarbon and coke to accumulate therein. One of the primary objects of .my invention is to provide acontinuous method of operation of such nature that the heavy carbon-forming oils may be separated from the restof the oil before being decomposed into carbon. In practicing the invention the polymers or high carbonforming compounds are removed from the cracking zone practically as soon as formed and are immediately separated from the rest of the oil. I have found thathydrocarbon oils vary considerably in carbon-forming capacity. Thus in, the case of some oils carbon begins to form as soon as the oil has been decomposed sufliciently to yield about 5% or of gasoline. With other oils it is possible to produce in a batch' operation or or even moregasoline without any appreciable formation of carbon.

apparatus so as to avoid, 'or at least reduce to a minimum, localized overheating and resultant 'carbonization. In practicing my invention I subject a given oil in passage through the converter to that degree or extent of decomposition, which has been determined by experiment can be applied to such oil without any appreciable formation of carbon and then remove the oil from the cracking zone. The process is preferably conducted in a continuous manner, the charging stock being passed through the cracking zone at such a rate that the required degree of cracking will takenplace and the oil being then continuously removed fromthe cracking zone. The time of travel of the oil through the cracking zone is sov regulated that the oil will be cracked to the critical point of carbon precipitation and the oil is then rapidly removed from the cracking zone.

In accordance with one aspect of the inven- 1 .mers or high carbon-forming oils, since it has been separated therefrom by distillation, and

thus may with advantage be returned to the cracking. zone so that it may ultimately be converted to gasoline or other light product desired.

I preferably employ the cycle stock in proportions somewhat in accordance with the carbonforming qualities of the initial charging stock used. Thus in the case of an oil that yields carbon with say only 10% of cracked gasoline the cycle stock is used in maximum proportions,

-while with, an oil that does not yield carbon until say 25%. of gasoline is formed the proportions of cycle stock used may beconsiderably less. In general, the greater the carbon-forming capacity of the oil, that is, the greater the readiness with which it car'honizes, the greater the proportion of cycle stock employed, and the more resistant the oil is to carbonization, the smaller the proportion of cycle oil required. In

most cases it is desirable to so operate as to provide quantities of cycle stock in excess of the amount of initial charge.- And the cyclic re.- turn of oil to the cracking zone, in quantities exceeding that of the initial charge, is an important feature of one phase of the invention.

- In accordance with my invention the cracking operation is preferably carried on under a comparatively high pressure so that when decomposition is arrested by a'loweringv of the temperature, the pressure also may be reduced to efiect distillation whereby the heavy polymers or-high carbon-forming compounds may be removed from the system as a residue while substantially all of the remaining products are vaporized. The vapor products contain the gasoline or naphtha desired and the cycle oil which is separated out and returned to the converter to dilute the initial charge.

An important feature of my invention consists in carrying on' the cracking or decomposition of the oil while in motion and under such conditions that the decomposition may be terminated at the precise point desired. Thus the oil being converted may be transmitted through atubular converter or conduit of restricted cross section, the rate of flow of the oil being so regulated with respect to its particular composition and the temperature employedthat the desired extent of decomposition is obtained when the oil reaches the end nf the conduit. The resulting products are thereupon rapidly discharged into another vessel wherein the conditions are so altered that further, decomposition is arrested or retarded. Best results and economy of opera tion are obtained by having a high rate of flow through the converter and maintaining a high rate of decomposition.

In existing cracking processes it is customary for .the residue, commonly referred to as pres-.

sure bottoms", to contain quantities of gasoline, and also kerosene andgas oil fractions suitable for rerunning in the pressure stills,

'ly to the cracking or reaction coil 14.

and in order to recover these valuable fractions from these residues it has been common practice to remove the pressure still residues from the cracking units and subsequently distill these residues in separate distilling equipment. It is an important object of my invention to provide a continuous cracking and distilling process in which no subsequent distillation of the pressure bottoms is necessary, the oil being converted to gasoline and tar or residue substantially free from lighter products, in one complete continuous operation, as is hereinafter more fully set forth.

For the purpose of describing the invention in detail reference will now, be had to the accompanying drawing which is a diagrammatic sectional elevation of one form of apparatus adapted for the practice of the invention and constituting an embodiment thereof. 10 indicates a furnace which may be an oil fired or gas fired furnace and which is adapted to supply high temperature heat to a coil 11. The furnace is provided with a flue 12 which leads to a chamber 13 containing a cracking coil 14. The flue 12 may be equipped with a damper to regulate the passage of spent combustion gases from the furnace 10 to the heating chamber 13, and may also be equipped, if desired, with auxiliary burners 15 for supplying additional heat to the gases leaving the furnace 10. The heating chamber 13 may well be arranged to accommodate, inaddition to the cracking coil 14, a preheating or economizer coil 16 arranged to be heated by the spent gases that have been used in heating the coil 14.

The oil to be treated is drawn from a suitable source by a pump 17 and charged through a line 18 to such preheating or heat exchange elements as may be desired. Thus a portion or all of the oil may be charged through an exchanger supplied with the heat from tar or residue obtained in the process; or the charge or a portion of it may be brought into heat exchange with vapors evolved in the process. Charging stock may, for example, be introduced into an apparatus employed in dephlegmating or fractionating the vapors, the charge thus being. preheated and at the same time serving as a cooling or reflux medium to aid in the condensation or fractionation of the vapors. It is of course desirable to preheat the charge by some such heat exchange system but for simplicity of illustration the pipe 18 is shown as communicating directly with the economizer coil 16. A conduit 19 connects the economizer coil 16 with the heating coil 11. The function of the coil 11 is to supply the oil with a material quantity of theheat required for the cracking operation and it is generally preferable to heat the oil in-this coil to a temperature ap roximating a cracking temperature. An outlet pipe 20 conducts the oil from the heating coil 11 direct- Here the oil is removed from the direct application of furnace heat, such as is supplied to the coil 11 in the furnace 10, the heat required for maintaining the oil in the coil 14 at the desired cracking temperature being supplied by the flue gases passing through the flue 12 together with such additional heat, supplied by the burners 15, as may be desired. If desired, the chamber 13 may be lightly fired, but it is generally pref-- erable to rely on convected heat, that is, heat supplied by hot gases entering the chamber, for

maintaining the @1 14 at the desired cracking temperature.

A pipe 21 is adapted to conduct the oil from the cracking coil 14 to the separating drum or] coming into direct contact withtheliquid collectjed in the lower portion of the still. The liquid obtained in the still 22,,which may be withdrawn by means ,of the tar line 23, is substantially free from contamination with the lighter prod- "ucts contained in the fluid conveyedto the still.

The still22 may also-be equipped with a steam line 22a forsupplylngsteam toassist'in the distillation and to produce agitation. of the contents.

so as to maintain in admixture with liquid being withdrawn any carbon or coke formed andprevent coke deposits inthe still.- Mechanical means. may be employed, if desired, to stir or agitate the contents of the still.

The separating drum or still 22 is provided with a vapor line "24' for conducting the vapors.

tosuitable fractionating equipment 25. which may be a packed tower, bubble tower,.or the; like.

The fraction'ating tower is preferably equipped with a vapor line 26 leading to a refluxlcondenser 27 provided with'a cooling boxf27a. The reflux condenser may be cooled in any convenient manner. Thus for example the charging stock or a portion thereof may be admitted to the cooling 'box 27a" and then either introduced into the fractio'nating tower 25 or admitted to other heat exchange elements or passed directly.

tothe coil 16' or coil 11. g A reflux line 28 is provided to conduct reflux or condensate from the reflux condenser 27 to the fractionating tower 25. A vapor line 29 extends from the re: flux condenser to a condenser coil 30 and a receiving drum 31 is provided for receiving distillate obtained from the condenser 30. The receiving drum is preferably equipped with a valved gas outlet32 and a valved distillate outlet 33.

A pipe 34 is adapted tosupply liquid collected in the fractionating device 25 to a hot oil pump 35 which serves to return this liquid to the heat 'ing coil 11 through theline 36. The liquid thus returne dtothe heating coil 11 comprises insuf- 'flciently j converted fractions or ,"fractions of higher boiling point than that desired in the ultimate distillate and when the charging stock is admitted into the fractionating tower 25 the liduid thus collected therein and pumped to the f coil 11 by the pump 35 consists of amixture of preheated charge and condensed vapors. A bypass line 37 connecting the pipes 23 and 34 may be provided so that liquid collected in the drum or.still 22 may be cycled back tothe heating,

coil 11. This is a desirable expedient when the apparatus is being brought under, operating con- "ditions', although in the normal operation of the process the line 37 is not used after operating conditions have been established. In practicing the invention with the apparatus illustrated the oil to be converted is charged through the pipe 18 and economizer coil 16 into the heating coil 11 wherein the oil is heated to approximately a cracking temperature. The oil in transit through the coil 11 may be heated so that it is discharged therefrom at a somewhat higher cracking temperature than is desired to be maintained in the cracking coil 14. The higher the oil is heated in the heating coil 11 the lower the temperature required in the heatmg chamber is and theiess the heatdiflerential between the chamber 13 and oil. in the coil 14 with the consequent reduction in liability of locally overheating the coil 14 and causing excess localized decomposition therein. It is preferable to so regulate the lengthot the time that 'a'given portion of oil is in the coil 11 that there will be .little or no decomposition or the oil while in this coil. The 'oil is then. passed into the cracking coil '14 wherepractically all thedecomposition takes place. It is desirable to maintain the oil in thefcoils l1 and 14 under a. considerable ,presi be gained by using pressures inexcess of around 2000 lbs. The oil in transit through the coil 11 is generally'ra'ised to temperatures approximati'ng 800. F. to 900 F. Ordinarily a temperature around 850 F. in the outlet of the coil'll will be found most satisfactory. 'Ili e temperatures used in the cracking coill4 will generally'run from about 850 F. to 1000" F., the preferred temperature being approximately 900 F.

'As decomposition is carried on in the. coil 14 with resultant production or heavy polymerized products. which as has heretofore been explained are readily decomposedto form free carbon, the necessity of avoiding any material decomposition of these products is apparent. By. reason of the fact that the bulk of the heat required for the cracking operation'is supplied to the oil while in passage through the coil 11. it is possible to supply to the oil, while in the coil 14. the additional amount of heat required for maintaining the oil at the desired cracking temperature without having'an excessive heat gradient between the heat supplying medium and .the oilinthe coil. Thus the bulk of thheat. having been suppliedby the high ..temperature' furnace 10 before the oil leaves thecoil. 11, the remainder oflthe heat may readily be provided by means difference in temperature between the heated gases about the coil 14 and-the oil contained therein should becomparatively small so that the danger of locally overheating any portions .of the coil is practically eliminated.

The length of the cairn is so arranged with respect tothe products it is desired totreat and with respect to the velocity at i which it 1 is desired to'charge the oil through the system. that the oil willbe discharged from the coil into the still or separating drum 22 before any material portion of the heavy polymers is 'decomposed into free carbon.

The resulting products pass through the line 21 and thence into the drum or still.22.. The valve in the line 21 is so regulated as to effect a substantial drop in pressurein thestill 22. The pressure drop. should be such that practically all of. the fluid discharged through the pipe 21, except the heavy polymerized products; will be vaporized in the still. These polymers are practically non-vaporizable, that is, in the sense that they are not vaporizable as such; heating them merely decomposes them into carbon and gas. Thus by dropping the pressure in the still the vaporizable constituents may be removed as a vapor and the non-distillate polymers withdrawn from the system as a tar or residue through the line 23. The vapors from the conof they hot gases conductedby the flue 12.. The

duit 24 are fractionated in the fractionating apparatus so as to take off in the form of vapor through'the line 2 9 the gasoline or naphtha distillate desired while the heavier products are collected at the bottom of the fractionating device'and are returned'bythe pump to the coil .11 for retreatment,

In a specific example of my invention'equipment is designed to'pr'oduce gasoline distillate,

collected in the tank 31, at the rate of 10 barrels per hour; The cracking coil 14 is a 3 inch-coil about 4000 feet long. The oil to be converted is a heavykerosene and the oil passing through the cracking coil 14'is held at a temperature of sure.

and about 51 barrels consisting of the reflux condensate obtained from the fractionatin'g device 25. 'Atthis rate of charging about-l5 minutes is required for passage through the cracking coil 14 of a unit volume of oil. Heavy tar comprising .the carbon forrning polymers is withdrawn from, 'the still -22fat the rate ,of about 5 barrels per hour. The yield of gasoline distillate, collected in the receiver 3115 approximately 66% of the initial charge.

It is tobe understood that the foregoing specific example is given merely for illustrative purposes. The various factors as to the dimensions of the equipment used and the conditions of operation will vary within comparatively wide limits. The temperatures employed in the crack-- ingcoil, the temperatures or the furnace, the

[length of the coil, its diameter, the rate of charge through "the coil-these and other fac- I [10 to'30 minutes is required for such passage;

ordinarily the time of travel will'approximate.

tors are so arranged and regulated with respect to' the particular oil being treated as to produce .the desired decomposition-to givethe maximum yield of gasoline with the minimum production of -carbon.

In general the oil is passed through the crack 'ing' coil l i at such-a rate of speed that from- 15 minutes. It is to be noted that the time factor varies considerably ,withdiiferent oils;

with some oils, such for example as some of the Oklahoma crude derivatives it is possible to carry on a veryhigh degree of cracking without decomposition of the polymers into carbon, and with other oils, such for example as products from certain Mexican crude and Gulf Coast I crudes carbon formation beginsat a very early point inthe cracking reaction.

zone will vary considerably with: the particular type of oil used and with the specific conditions of operation employed. As examples of propor tions found suitable when using a fraction of crude petroleum known commercially as gas oil it may be stated that in producing a yield of gasoline constituting approximately 66% of the initial charge'andwith a conversion into gaso line of 10% per volume put through the cracking zone the ratio ofinitial charge to cycle oil such as tosecure a substantial 'theoil in its flow oil in the stream entering the was about 1: 6; with the same ultimate yield of gasoline but with 15% conversion, pe'rvolume put through the ratio was about 1: 3,with 20% conversion per volumeput through the ratio was aboutl: 2, with 25% conversion per volume put through the ratio was about '1: 1% and with 30% conversion per volume put' through the ratio was about 1: 1%. It is to be observed'that fin each ofthese specific examples the yield of gasoline'on'the basis of the initial charge was 66% which, so iarasl am aware, is a greater but it may also be applied to the v conversion of heavier stocks.

v k especial difllculty in most of the existing cracking processes,

"Although the preferred embodiment of the invention has been set forth in connection with apparatus having a particular construction and arrangement of parts and mode of operation, it is obvious that variouschanges and modifica- ItlOll-S may be made therein, while securing. to a.

greateror less extent some or all of the benefits of the invention, without departing from the spirit. and scope thereof. Therefore, only such limitations should be imposed asare indicated in the appended claim. I claim:

'The process of convertinghigher boiling hydrocarbon oils into lower boiling hydrocarbon oils which comprises passing, the oil to beconverted in admixture with condensate oils derived'from previous conversion treatment in continuoua'tlow in a restricted stream through a heating zone in which the oil mixture is heated rapidly to a high cracking temperature, continuing the flow of oil in a restricted stream with substantially undi minished velocity through a confined passageway in a further heating zone, where it is heated only sufliciently tomaintain its crackingtemperature without substantially increasing in temperature, thetime of travel of the oil throughsaid second heatingzone being conversion,-there of tothe desired low boiling products without substantial i'ormation and deposition of free carbon, maintaining superatmosphe'ric pressure on through said heating zones, reducingthe pressure on the oil directly on leaving the second heating zon'eand passingit in indirect heat conductive contact with a body of unvaporized oil products in an enlarged chamber. and thereupon discharging the heated oil mix- The proportions of reflux condensate or back trap which are cycled through the cracking ture into said'enlarged chamber,. whereby its unvaporized constituents are admixed with the ing them to condense constituents heavier than the desired low boiling products and returning such condensate to admix and pass with fresh heating zones. O'I'IO BEHIMER.

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