US1675575A - Method for cracking oils - Google Patents

Description

July '3, T928.

C. L. PARMELEE ET AL METHOD FOR CRACKING OILS Filed Aug. 13, 1923 INVENTOR s la-au.

BY` MA., m W

ATTORNEY`S` `Patented .my 3, 192s. l

UNITED STATES vWATENT 'ori-"ICE,

CARLES L. IARMELEE, OF ORANGE, NEW JERSEY, AND EDWARD W. ISOM, OF WIN- NETKA. ILLINOIS, ASSIGNORS TO SINCLAIR REFINING COMPANY, OF CHICAGO, ILLINOIS, A. CORPORATION OF MAINE.

METHOD FOB CRACEING OILSY.

Application sled August 1a, 1923. se-nai No. 656,990.

This' invention relates to an improved method for `cracking heavier .hydrocarbon oils for the production of lighter hydro'- carbon oils therefrom. More' particularly, the invention relates to an improved method of cracking heavier oils ordistillatcs of a kerosene like character in a continuous manner in a` tubular cracking still, and to an improved tubular cracking still adapted for use inl the carrying out of the p-rocess.

In the cracking of heavier o ils in a tubular cracking still, orin a tubular cracking still of the sofcalled tube and tank construction, the heavier oil is passed through a tubular cracking still With the tubes ar` ranged in a furnace or heating flue and with the oil progressively heated during its passage therethrough. When the oil is heated to thecracking temperature it -undergoes cracking in 'a progressive manner. The cracking operation may be completed in the tubes so that the cracked oil is discharged directly from the tubular still to a Vaporizing still or chamber or to 'a condenser for the condensation of the cracked oil in the form of a so-called synthetic crude; or the cracking operationmay be in part carried out during the passage of the oil through fthe tubes and in part in a reaction or d igestion chamber into which the oil from the `heating and cracking coil is discharged and in which the oil is maintained at the cracking temperaturev to permit further cracking before Jthe cracked oil is discharged from the still. t

In the operation of such tubular cracking stills, the cracking of the oil results in the formation of tar Which tends to separate out on the heated Walls of the still and to form a deposit of, carbon thereon which interferes with the heating of the oil in theV tubes and-tends to cause overheating ofthe tubes or hot tubes. In order to reduce this objectionable carbon deposit in the heating tubes, digestion orreaction chambers have been .combined with the heating Icoil to refI are not used, and when the cracking operation is completed in the heating tubes, the

-eXtent to `Which the cracking can be per'- mitted to take place-is limited by the formation of tar and carbon deposit on the walls of the tubes, particularly in the tubes through which the oil flows afterconsiderable cracking has taken place therein and a considerable amount of tar has been formed,

so that it is necessary to limit the extent to which cracking is permitted to take place in the tubes to avoid objectionable carbon deposit therein.

According to the present invention, the operation of such tubular cracking stills is improved, so that the stills can be operated for longer periods of time before cleaning is required and so that the oil can be maintained in the still for longer periods of time, and the cracking carried to a'further extent thansivould otherwisebe feasible.

According to the presentinvention, Wev

improve the operation of tubular cracking stills by the uintroductiontherein, at an intermediate point, or at intermediate points, of the coils of the tubular still, of a solvent oil, or of solvent oils, which Will mingle with the partially cracked oil lflowing through the tubular still and which will permit the degree of crackingto be continued over a longer period of time or carried to an increased degree. Such solvent oil or oils will dilute the partially cracked oil in the still, as Well as exert a solvent action thereon and particularly upon the tarryV constituents, holding them in solution .While further cracking takes place. The increased amount of oil also gives an increased velocity through the tubes 'which further tends to reduce the Vdanger of objectionable carbon deposit upon the tube Walls. The increased time during Which the oil can be maintained in the cracking coil and under cracking conditions Wit-hout objectionable carlnn'deposit permits the time factor of crac ing to be takenadvantage of to a greater extent than would otherwise be possible, and the cracking of the initial oil can be carried to a correspondingly increased degree during the passagp of the oil through the tubular cracking stil The oil used as charging stock the process and apparatus of the present invention can be varied and heavierpetroleum y ,the present invention includes the `introduction ofi a'solvent oil at one or more stages of progression of oil through thecracking coil,- Whether the oil so introduced is of the same character as the initial charging stock or of a diiferent character.

We consider it more advantageous, however,vto use a heavier charging stock initially and to introduce a lighter solvent oil after the heavier oil has undergone a partial cracking and in order to permit a further cracking of the heavier oil without objectionable carbon deposit on the tube walls. In particular, the solvent oils may be lighter distillates or fractions which Will be cracked only to a limited extent and which will accordingly remain as more or less inert 'solvents while permitting continued cracking of heavier oil constituents. The solvent oil may however be one which will' itself be cracked to a greater or less extent and may nevertheless exert a diluting and solvent ac,

tion, updn the oil flowingv through the tubular cracking still.

The present invention relates more particularly to so-called liquid phase cracking of oils with the maintenance of a sufticient pressure upon the tubular cracking stillto keep the oil or thergreater part of it in a liquid state. The pressure employed can accordingly be varied with vdifferent oils devpendingupon the boiling point of the oil and the pressure necessary to maintain the oil to the necesary extent in a liquid state. Vaporization however may take. placeto a greater or less extent during the' passage of the oil through the tubular still, and lighter vapors and gases may also be formed as a result of the cracking operation and remain in part in a gaseous state and bey carried along through the coil with the liquid oil. Where the solvent oil is a lighter oil than the initial charging stock, the pressure should in general be suiiicient to keep the solvent oil to a greateror less extent as a liquid. Lower pressures around to 195 lbs. can be used with some oils While higher pressures of around 300 lbs. or even around variedlin its construction. For example, it may consist of a single-pass coil of alsuicient length to complete the cracking operation during the flow of the oil through the coil and the solvent oil may be introduced at one or more stages of the progression of the oil through the coil; or a plurality of coils may be employed, either in series or in parallel, andarranged in the same or separate furnaces, With provision for introduction of solvent o1l at mtermechate points of the coil or coils;

There the cracking operation is comeration in the coil itself, the partiallyV cracked oil may be introduced into an insulated chamber or into a heated chamber and maintained at the cracking temperature and pressure to'continue the cracking operation, after which the cracked oil may be cooled to give a synthetic crude or discharged to a vaporizing still or chamber and the heat of the oil utilized `tor vaporizing the lighter fractions ot the oil, for example, asfabove mentioned. Vhere the solvent oil is introduced at one or more intermediate points of the cracking coil, the cracking operation can be carried to a much further extent in the coil without objectionablecarbon deposit, and, in addition, the cracking operation can be still further continued in the digestion chamber by holding the cracked oil therein for a further period of time.

It will be evident that the size of the coil and the point or points of introduction of .-sol-ventoil, as well as the amount of such yoil or oils introduced, can be varied, de-

Y 600 to Y700 lbs. or higher maybe used for' the cracking` of diferent oils.

TheV tubular cracking still itself can be pending upon the pressure and temperature of the oil, the character of the oil and vsolvent, and the time factor necessary for the most efficient cracking of the chargin stock under the conditions of operation. iferent charging stocks will require somewhat different .conditions of pressure and temperature for efficient cracking and will stand cracking to varying degrees, but in general the introduction of solvent oil, according top the present invention, will -permit the cracking operation to be continued beyond the point otherwise feasible While neverthelue less permitting the maintenance of the necf essary conditions of temperature and pressure. `The rate of circulation can also be,

varied, depending upon the character' of the oil, the size of the c oil, the amount of the solvent oil and the time required to carry the cracking operation to the desired degree.

The rate of circulation will however increase p distilled and fractionally condensed, the` with the introduction of the solvent oil and thisincreased velocity will further tend to reduce the danger of carbon'deposit on the tubes.

Where the cracked oil is vaporized or apparatus embodying the invention and adapted for the practice of the process of the invention; but it will beunderstood that `the invention is illustrated thereby but is not limited thereto. The showing of the drawing is largely diagrammatic and conventionaland not to scale, being partly inthe nature of a iow sheet.

In the apparatus illustrated, a series of three coils 1, 2 and 3 vis arranged in a single furnace together with a preheating coil 4, each of these coils being made up of a series of pipes connected at their ends by return bends (not shown) and so arrangedthat the oil flows in a single-pass successively through the individual pipes of the coil.

' The three cracking coils and the preheatin'g coil are arranged in four flues or heating chambers 5, 6, 7 and 8 of a furnace having a fire-box 9 with oil or gas burner 11 and having an outlet connection 10 to the fiue or stack. A side connection 12 permits the return of part of the stack gases from near the outlet of the furnace chamber 5 and their reintroduction into the vertical flue 13 where they will mix with the products of combustion from the fire-box thus giving a low tempera/ture of the gases where they first come in Contact with the tubes and giving an increased velocity of the gases over the tubes, thus increasing the heating effect and maintaining a more nearly constant temperature in the coils of the first pass ofthe furnace in the chamber 5. The return of av regulated amount of fluefgas can be effected by a steam jet. or blower (not shown). i

Feed oil is supplied to the preheating coil through the feed line 15. The preheated oil fiows from the preheater coil to the first cracking coil 1 through the connecting pipe 14. Regulatingjv'alves 16 and 17 permit b passing of partI of the feed directly Ito t e first cracking coilwhere this is desired,

while by closing the valve 17 lthe feed will lthrough the cracking coilv 1.

all pass first through the .preheater and then From the cracking coil 1, the oil flows through connecting pipes 18 and 19 tothe second coil 2 and from thence through connecting pipes 20 and 21 to the third cracking coil from which the cracked oil fiows through the line 24.

Provision is made vfor introducing a solvent oil into the cracking still through the line 22, this oil mixing with the oil fiowing from the first coil 1 to the second coil 2. Provision is also made for the addition of a further amount of solvent oil through the line 23 to the oil passing from the second to the third cracking coil.

The cracked oil leaving the tubular cracking still through the line 24 passes through the expansion valve 25 ywhere its pressure is reduced to atmosphericor to a predetermined pressure above atmospheric and the expanded oil and vapors pass to the expansion chamber 26. In this expansion chain- Sti ber which is conventionally shown, butf which in practice will be of appropriate size, the heat of the cracked oil is used in Vaporizing thelighter constituents which pass off through the heat exchangers 39 and 38 and the connecting pipes 31, 40 and 41 to. the condenser 42. From the condenser the distillate from the synthetic crude passes through the gas separator 43 and the pipe 45 to a place of storage, while the gases pass off through the line 44 to a place of gas storage or use (not shown).

The unvaporized portion of the cracked oil is drawn off from the expansion chamber through the'line 27 to the cooler 28 andv is then pumped by the pump 29 to a storage tank 30. This unvaporized residue or tar may be further `fractionated or distilled for the recovery of heavier distillates, etc., therefrom.

The charging stock and solvent oil are supplied from suitable storage or supply tanks indicated at 33. 35 and 37., The charging stock in the tank 33 is indicated as a cut or fraction of 35 Bc. which may be obtained from the distillation of crude oil or in part from the synthetic crude produced by the cracking process or by other cracking proc'- ess. This charging stock is pumped by the pump 32 to the supply line 15 and thence to the preheating coilgin the furnace. The solvent oil in tanks 35 and 37 is indicated respectively as at 38o B.. cut or fraction and a 4lo B. fraction. The solvent oil indicated flow through the first cracking coil 1. The' .pump 36 and is forced through the heat exvpumped into the rerun still 47 from .which the successive fractions are condensed in a condenser 50 andcollected in a receiver 51. The distillate from this rerun still may be cut into fractions corresponding to the desired gasoline fraction and the fractions indicated respectively as 41 B. cut, 389/136, out and 35 B. cut, these respective cuts or fractions heilig distributed through the lines 55, 54, 53 and 52 respectively from the receiver 37. Additional charging stock and solvent oil may be supplied from extraneous sources, such as from distillates from crude oil or distillates from other cracking processes. The residue from the rerun `still is drawn ofi' through 57 to a fuel storage 58.

When the still is first charged, and before the oil has been heated sufiicicntly to cause cracking to take place, the oil may be returned to the storage tank 33 by closing the valve 25 and opening the valve 59 which permits the oil to return through the cooler 60 to the storage tank 33. When the desired temperature and pressure have been reached in the cracking coils, the valve 59 is closed and the valve 25 gradually opened to permit discharge of the synthetic crude or cracked oil into the expansion chamber 26.

The cracking operation, when once established. may be continued for relatively long periods of time. The charging stock will-be supplied throughy the line 15 to the pre-heating coil from which the preheated oil will oil .partly cracked in'this coil is then admixed with solvent o il of 38 B. supplied through the vline 22 and the resulting mixture passes through the cracking coil 2. The` cracked oil flowing from the second coil 2 is then vadmired with further solvent oil of 41 B. supplied fromthe tank 37 through the lin'e 23 and the resulting admixture then passes through the third cracking coil where the cracking operation is completed. The

resulting cracked oil or'synthetic crude is then cooled to give a synthetic crude or is partially vaporized by utilizing the heat which it contains and the vapors separately condensed.

It will be noted that the flow of the oil Ythrough each of the coils is generally counter-current to the flow of "the gases so that the hottest gases come in contact with the tubes containing the hottestoil. 4It will also be noted that there is a decreasing ternperature gradient inthe furnace such that the oil charged to the cracking coils is first subjected to the highest temperature in the coil 1 located in the heating chamber 5 while the partiallyvcrackedoil with admixed solvent oil is subjected to progressively. lower temperatures in the coils 2 and 3 and the preheating coil 4 is in theheating chamber 8 at a somewhat lower temperature. This construction and arrangement permits the highest heat to be applied to the fresh oil and permits-the partially cracked oil with admixcdsolvent oil to be subjected to heatlng gases ata somewhat lower temperature so as to prevent excessive overheating of the oil while nevertheless maintaining the oil at a cracking temperature and permitting further cracking to take place.

,The solvent oil supplied at one or more infterinediate points of the tubular cracking still may be preheated to the cracking temperature or to a somewhat lower temperature. lf it is not preheated tothe cracking temperature it will exert a cooling action on the partially cracked oil with which it is admixed. Some cooling of the partially cracked oil--may be desirable to prevent over- -heating and to reduce objectionable carbon formation; and by `regulating the tempera-- ture and amount of the solvent oil, this cooling effect, as well as the solvent action of the oil can i be regulated. By introducing the solvent oil at a temperature somewhat below that of the oil undergoing cracking and by obtaining the cooling action as well as the solvent action of the oil. a somewhat lesser quantity of the solvent oil can be used.

In the apparatus illustrated the solvent oils are heated in the heat interchangers 38 and 39 by the vapors given off from the cracked oil or synthetic crude; but it will be evident that this heating may be supplemented and the solvent oil preheated to any desired temperature by additional heating means (not shown) and its temperature and the cooling effect rupon the oil in the still thereby regulated. Where the solvent oil is preheated to the cracking temperature. it will exert its solvent action ,without cooling of the oil passing through the cracking coils.

It will be evident that the amount of solvent oil introduced can be varied, as well as the nature of the solvent oil and the stage of the progress ofthe oil through the coil at which the solventoil is introduced. In general, the amount of solvent oil should be sufficient to holdin solution all or prac-A time factor for the most eiicient'cracking of the charging stock at the desired pressure and temperature while preventing objectionable deposit of pitch and carbon during the prolongation of the cracking operation and giving as the product of the cracking operation a more or less completely cracked solution of, the charging stock in the solvent oil.

The pressure in the apparatus can be regulated by the valve between the still and expansion chamber although the presl sure will be influenced by the rate of feed of the charging stock or of the solvent oil entering the still.

The utilization of the heat of the cracked oil for eil'ecting a partial vaporization or distillation ot the oil results in economy of operation which is further increased by utilizing the heat of the vapors to preheat the solvent oil lsupplied to the still. `The cracked oil or synthetic crude, either through partial vaporization by the heat which it contains, or by condensation of the cracked oil as a whole and subsequent redistillation, can be fractionated into the desired gasoline cut and into one or more solvent oil cuts as Well as a heavier gravity cut which can be returned to the original charging stock. The cracking operation itself may thus supply part of the initial charging stock for further operation as well as solvent oil for use in the further carrying out of the process, although it will be evident that fresh charging stock and fresh solvent of operation of a coil cracking still with in' creased efficiency of thecracking operation.

It will also be seenv that the invention is of v more or less general application iin connection with tubular cracking stills Where the cracking operation is carried out in the coils of the tubular still, and that it makes possible the carrying of the cracking operation to agreater extent and fora longer period of time than `would otherwise be feasible.

ve claim': l

l. The improvement in the cracking of oil in tubular cracking stills which comprises foreing the oil in a single-pass through a cracking' coil and heating the oil therein to a cracking temperature under a high pressure, introducing a solvent oil into the partially cracked oil at one or more intermediate stages of its progressthrough the cracking coil, and preheating the solvent oil by heat linterchange with the crackedy oil or With distillates therefrom.

2. The improvement in the cracking of oil in a tubular cracking still which comprises forcing the oil in a single-pass through a cracking coil and heating the oil therein to a cracking temperature under a high pressure, introducing a solvent oil into the partially cracked oil at one or more ntermediate stages Yof its passage through the cracking coil, releasing the pressure on the cracked oil and vaporizing therefrom by its self-contained heat the lighter constituents, passing said lighter constituents into heat interchanging relation with the solvent oil to preheat the saine, and 'recovering from said constituents further amounts of charging stock and solvent oil adapted for further use in the carrying out of the process.

In testimony whereof we affix our signatures. i

CHARLES L. PARMELEE. EDWARD w. rsoM. a

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