US1675558A - Art of cracking hydrocarbons - Google Patents

Description

July 3, 1928.

E. W. lSOM EVAL ART 0F CRACKING HYDROCARBONS Filed March 3. 1923 .w mm

NNJOOU M15-1 mmv NMLUQI wml Nul-GCU Patented July 3, 1928.

UNITED STATES 1,575,558 PATENT OFFICE.

EDWARD W. ISOM, OF WINNETKA, ILLINOIS. AND CHARLES L. PARMELEE, OF ORANGE,

NEW JERSEY, ASSIGNORS TO SINCLAIR REFINING COMPANY, OF CHICAGO, ILLI- NOIS, A CORPORATION 0F MAINE.

ART 0F CBXACXING HYDROCARBONS.

Application iledarch 3, 1923. Serial No. 622,508.

Since the extensive use ol' the intemal combustion engine has increased the demand lor gasoline beyond what can well be. supplied by distillation from petroleum by methods formerly in use, many refineries have adopted the practice of converting the loss valuable fractions, such as gas oil, into the more valuable lighter gasoline fraction b v distilling them under pressure at such temperatures that the more complex, heavier hydrocarbons are largely broken down into the lighter hydrocarbons of the group which constitute rgasoline` as adapted to use in the ordinary form of internal combustion engine.. One of the main diiliculties encountered in the cracking operation is due to the deposition of carbon on the walls through which heat is imparted to the oil, forming a hard layer thereon which insulates the Walls from the coolingr effect of the oil so that they are liable to become overheated and seriously impaired and sometimes ruptured them with disastrous results. Moreover the deposition of carbon renders it necessary at short intervals to interrupt the operation of the cracking apparatus for the purpose of removing the carbon incrustatons and as this consumes considerable time by reason of the hardness of the carbon layer and the necessity of cooling ofi' the apparatus before i he removal can be attempted and heating it up again in resuming operation the eliiciency of the cracking units is greatly reduced.

In practicing cracking operations in one form of cracking apparatus7 which is that to which our invention more particularly relates, thel oil is heated and cracked while flowing in a continuous stream through a heated conduit, specifically a coil of pipe in a furnace. In carrying out cracking operations in prior apparatus of this character the deposition of carbon in the tubes has seriously interfered with the economical operation thereof. 1t is one of the purposes of our invention to provide a process and apparatus of this character in which the deposition of carbon in the cracking tubes is largely avoided. It appears that in the cracking operation the formation of coke on the pipe Walls is the result of two distinct steps or processes. The first of these steps which innnediatelyv follows as a result of cracking is the formation of a heavyy tar which is to a. certain extent soluble in the oil. So long as the oil is not saturated there is no deposition upon the walls of the tubes. It. is only when the oil becomes super-saturated with the tar that the latter is deposited on the walls of the tubes. There it is super-heated and converted into hard carbon which foims the objectionable lining on the tubes referred to above. 1n our improved process, in order to avoid carbon deposition we. prevent super-saturation of the oil with the heavy tarry matter by adding to the oil being cracked in the heating zone a solvent oil of character and in quantities dependent largely on the nature of the oil being treated. As an example it may be said that we have found that in treating gas oil, kerosene oil or oil differing slightly therefrom in specific gravity is suitable for use as a solvent as it is decomposed only at a temperature substantially higher than that employed for cracking the gas oil and so passes through the process substantially unchanged, maintaining its solvent action throughout and can be separated from the processed oil and re-used if desired. Preferably the solvent is only added after cracking has taken place to a greater or less extent but before the point of saturation has been reached. If added too soon, by diluting the oil it absorbs a portion of the available heat and retards the heating of the hydro-carbon to be cracked. If added too late more or less carbon deposition may take place before the solvent becomes effective. All of the solvent may be. added to the stream of hydro-carbon oil being cracked at one point in it course through the heating zone. Preferably, however, it is added at two or more points as the accumulation of tar in the stream due to the progress of the cracking operation demands lVhere the solvent, is added at a pluralit of points it may bc all of the same speci e gravity. lVe have found it desirable, however, that successive additions of solvent to the stream be 0f higher gravity, that is to say, lighter. Preferably the solvent is heated before being added to the stream of hydro-ca1bons being cracked.

Vl'hile the above is the best explanation we can now give of the principle of our invention and we believe it to be accurate. our invention is not dependent upon the correctness of the theory given for exemplitication thereof. By practicing the process of the invention as described it is possible to greatly reduce the deposition of carbon, increase the efficiency of and prolong the cracking operation in so-called continuous tube stills before shutting down for the removal of carbon.

In the drawing accompanying and forming a part of this specification we have shown, in part diagrammatically, an effective and preferred embodiment of the apparatus of the invention adapted for practicing the process invention and have described the same in detail hereinafter. It is to be understood, however, that the specific disclosure is for the purpose of exemplification only and that the scope of the invention is defined in the following claims in which we have endeavored to distinguish it from the prior art so far as known to us without, however, relinquishing or abandoning any portion or feature thereof.

The drawing shows the apparatus diagrammatically, the heater being shown partly in central vertical section.

Referring now to the drawing the furnace is shown conventionally as comprising a fire box 1, a stack 2, and a zig zag flue divided by alternately opposite partitions into a series of four heating chambers 4, 5, 6 and 7. A greater or less number of heating chambers may be employed if desired. Each chamber contains a battery or group of coils or pipe lengths shown as extending horizontally across the furnace. The pipe lengths of each group are connected in series and the number of pipes in the respective groups depends upon the character of oil to be treated, the rate of flow desired, etc. If desired, the various groups of pipes may extend through and be heated in separate furnaces, but the construction shown is economical and efficient and well adapted for the treatment of gas oil, the material from which the cracked gasoline is usually made, and by the treatment of which the present invention will be exemplified herein.

The gas oil or other material to be treated is pumped from a storage tank or receptacle 8 to the coil 9 in the last pass 7 of the furnace where it receives heat from the relativel cool gases and is pre-heated but preferabfy not to the cracking temperature. This pre-heating, while desirable, is not essential. We have shown at 10 a pump for forcing the oil to the pre-heating coil andL the pum may be of any well known or approved esign capable of forcing the oil into the coil against the pressure maintained therein which may be as much as eighty pounds or more for cracking gas oil. With li hter stocks higher pressures may be emp oyed. A meter 11 may be employed in the oil line connecting the pump and the preheating coil. From the preheating coil the oil fiows through pipe 13 to the rearmost pipe length in the lowermost row of the battery 14 occupyin the first and hottest pass of the furnace. n this coil oil is heated preferably to a cracking temperature or substantially so, and then flows by pipes 15, 16 and 17 to the rearmost pipe of the upper row of coil 18 in the second pass of the furnace. After traversing the pipes of this group the oil leaves the first pipe in the lowermost row thereof by pipes 19, 20, 21, flowing to the first pipe in the lowermost row of group or coil 22 in chamber 6 where it is still further heated. From the last tube of the uppermost row of this group the oil Hows away by pipe 23. Before leaving the furnace the cracking of the oil is substantially completed and it may be disposed of in any way found desirable as a synthetic crude oil. Preferably it is conducted by pipes 23 and 24 to an expansion chamber 25 passing through a pressure reducing valve 26 in pipe 24 by means of which the desired degree of pressure is maintained in the cracking tubes. The valve 26 may be a hand valve or any other apparatus by which the pressure may be conveniently maintained and regulated.

It will ordinarily be found desirable to temper the hot gases before they reach the first pass of the furnace and for this purpose we have shown a return flue 27 extending from the lower rear corner of the chamber 4 to the throat of the furnace and provided with a Venturi blower 28 (see dotted lines) for forcinr the return of a portion of the partly cooled gases to dilute the fresh productsl of combustion coming from the fire box. The cracking action in the tubes of the first group releases a certain amount of the heavy tarry soluble matter to which reference has been made above but not sufficient to saturate the oilv or cause substantial deposition of coke upon these tubes. Before the oil has the opportunity to absorb additional heat in the second pass of the furnace and thereby undergo additional cracking which might result in saturation of the oil with the heavy tar, we introduce into pipe 16 at point 29 a stream of solvent oil of such character and amount as to provide for the solution of any tarry matter which may have been formed in coil 14 of the first pass and which may be formed in the coil 18 of the second pass. The amount of solvent introduced at 29 may not be sufficient to take care of the heavy compounds formed in the coil 22 of the third pass 6 of the furnace and in order to prevent carbon deposition in the tubes of this coil we introduce into the pipe 21 at point 30 an additional stream of solvent oil. In the broader aspect of the invention the source and particular character of the solvent oils introduced is immaterial; preferably however after the operation is started the solvent oils are largely made up of fractions separated from the oil flowing from the cracking device in a manner which will be explained later on. It may be desirable to supplement the heat from the fire box in the second and third passes of the furnace and for this purpose we have indicated burners at 31 and 32 in the lowei` part thereof. 4

1n one advantageous way of carrying out the process of the invention the higher coniponents of the synthetic crude are volatilized ln expansion chamber 25 by the contained eat.

The tar flows through a pipe 61 to a cooler 62 from which it is forced by pump 63 through line 64 and meter 65 to a tar holder 37. The overhead or vapor from the expansion chamber 25 is carried to a condenser 34. Before it reaches the condenser a large portion of the heat is extracted from the vapors by the heat exchangers 35 and 36 which are employed for pre-heating the solvent supplied to the cracking coils. The condensate from condenser 34 flows to separator 38 from which any fixed gas contained in the vapors is drawn ofil through pipe 67. The condensate from the separator 38 flows through a meter 68 either to a storage tank 39, or it may be forced by pump 69 to a re-run still 40. The bottoms or tar from the re-run still may be stored in tank 70 for use as fuel or for other purposes. The overhead is carried by vapor line 71 to condenser 72. Preferably four cuts are taken from the re-run still of which the first which is a gasoline distillate is taken by pipe 73 to storage tank 41, the second, which for example may have a gravity of 41 degrees B. by pipe 74 to tank 42, the third, which for example may have a gravity of 38 degrees B. by pipe 75 to storage tank 43, and the fourth, which may approximate gas oil in composition, by pipe 76 to the storage tank 8 from which the stock to be treated in the cracker is taken.

Advantageously and as shown in the drawing, the cut from tank 43 is' used as the solvent heretofore mentioned as introduced at 29 between the first and second cracking coils. lt is forced by pump 77 through line 78. heat exchanger 36, and pipe 79 to the point of introduction 29. In case for any reason the-supply of the cut in tank 43 is insuiicient it may be supplemented by oil of a generally similar character coming from storage through pipe 80.

"he cut in tank 42 is preferably used to constitute the second injection of solvent being forced by pump 81 through pipe 82, heat exchanger 35 and pipe 83 to the point of injection 30 intermediate the second and third cracking coils. The supply from tank 42 may be augmented from storage or any suitable source through pipe 84.

Instead of treating the synthetic crude as heretofore described it may be run through a cooler 85 and conveyed to storage. For

this purpose we have shown a pi e 86 connecting pipe 23 to said cooler an provided with a hand valve 87. From the cooler synthetic crude may be led to storage through pipe 88.

ln our improved process the oil is gradually heated to the cracking temperature in the furnace coils and maintained at such temperature therein until the desired degree of cracking has been effected, carbon deposition being substantially prevented by the introduction of solvent to the extent necessary to prevent super-saturation and precipitation of the heavy tar in the coils.

We claim:

1. A process of cracking heavy hydrocarbons to produce lighter hydrocarbons comprising passing the oil through a heating zone of restricted cross section, heating it therein to a cracking temperature and adding to the oil at an intermediate point of said heating zone during its passage therethrough and before the heated oil becomes saturated with tar an oil capable of acting as a solvent for the tar formed during crackmg.

2. A process of cracking heavy hydrocarbons to produce lighter hydrocarbons which comprises passing the heavy hydrocarbons in a stream through a heating Zone of re.- stricted cross section, heating them in said heating zone to a cracking temperature and maintaining them at or above such temperature, and adding to the said hydrocarbons at in intermediate point in the heating zone before the hydrocarbons become saturated with tar a solvent for the tar produced by the cracking operation.

3. A process for cracking heavier hydrocarbons to produce lighter hydrocarbons which comprises passing the hydrocarbons to be cracked through a heating zone of restricted cross section, heating them therein to a cracking temperature and adding to the said hydrocarbons at an intermediate point in said heating zone before the said hydrocarbons become saturated with tar other hydrocarbons of lighter specific gravity than the first said hydrocarbons and which substantially resist cracking at the temperatures employed.

4. A process of cracking gas oil and the like comprising passing the oil through a heating zone in a continuous stream, heating it therein to a temperature at which a substantial portion of the gas oil is cracked to form lighter hydrocarbons and mixing with the gas oil at an intermediate point in said heating zone before the heated oil becomes Saturated with tar an oil approximately corresponding to the kerosene fraction.

5. A process of cracking heavy hydrocarbons to produce lighter hydrocarbons comprising passing the oil in a continuous stream through a zone heated to the cracking temperature wherein a portion of the hydrocarbons are progressively cracked and progressively adding to the oil in the heating zone during the cracking operation an oil capable of acting as a solvent for the heavy compounds formed during cracking whereby precipitation of carbon is prevented.

6. The vprocess of cracking heavy hydrocarbons to produce lighter hydrocarbons comprising passing the heavier hydrocarbons in a continuous stream of restricted cross section through a zone heated to a cracking temperature whereby the hydrocarbons are heated to a cracking temperature and progressively cracked, and adding to the stream at intermediate points in the heating zone successive increments of hydrocarbons lighter than the bulk of hydrocarbons to be cracked and substantially stable at the temperatures employed whereby to prevent precipitation of carbon.

7. A process of cracking heavy hydrocarbons to produce lighter hydrocarbons.which comprises passing them in a continuous stream through a zonc heated to a cracking temperature and adding at an intermediate point in said zone before the hydrocarbons become saturated with tar a lighter substantially stable hydrocarbon capable of acting as a solvent for the tar formed in sutiicient quantity to substantially prevent carbon deposition in the heated zone.

8. The process of cracking heavy hydrocarbons to produce lighter hydro ai-bons which comprises passing the hydrocarbons in a continuous stream of restricted cross section through a zone maintained at a cracking temperature and adding to the stream at an intermediate point in. said cracking zone and before the hydrocarbons become saturated with tar lighter hydrocarbons substantially stable at the temperature employed in sutiicient quantity substantially to prevent deposition of carbon within the cracking Zone.

9. A process of cracking heavy hydrocarbons to produce lighter hydrocarbons comprising passing them in a continuous stream of restricted cross section through a zone heated to a cracking temperature, adding to the stream at an intermediate point in said heating zone lighter hydrocarbons substantially stable at the temperature employed in sufficient quantity to substantially prevent carbon deposition in the heated Zone, maintaining pressure on the hydrocarbons in said heated zone, passing the hydrocarbons to an expansion chamber maintained at a lower pressure than the heated zone and removing and condensing the vapors formed in the expansion chamber.

10. A process of cracking heavy hydrocaI-, bons to produce lighter hydrocarbons comprising passing the former in a continuous stream of restricted cross section under pressure through a heated zone in which they are subjected to a cracking temperature and cracked, distilling otf the lighter portion of the hydrocarbons formed in the heating zone, fractioning the distillate and returning to the stream at an intermediate point in the heated zone an intermediate fraction of the distillate which is substantially stable at the temperature employed whereby to prevent precipitation of carbon.

11. A process of cracking heavy hydrocarbons to produce lighter hydrocarbons comprising passing the former in a continuous stream through a Zone heated to a cracking temperature thereby cracking a portion ot' the component hydrocarbons, distilling oft' the lighter hydrocarbons formed in the heated zone, tractionating the distillate into a plurality of cuts, returning a series of the cuts in the order of their gravities to the stream of hydrocarbons at intermediate points in the heated zone whereby to prevent precipitation of carbon.

12. A process of cracking heavy hydrocarbons to produce lighter hydrocarbons comprising passing the former in a continuous stream through a zone heated to a cracking temperature thereby cracking a portion of the component hydrocarbons, distilling ofi' the lighter hydrocarbons formed in the heated zone, fractionating the distillate into a plurality of cuts returning a series of the cuts in the order ot their graif'ities to the stream of hydrocarbons at intermediate points in the heated zoneand returning the heaviest cut and mixing it with the first mentioned heavy hydrocarbons before they are passed through the heated zone.

13. A process ot cracking heavy hydrocarbons to produce lighter hydrocarbons comprising passing the former through a zone heated to a cracking temperature in a continuous stream, separat-ing and fractionating the lighter hydrocarbons formed by the. cracking operation, heating a portion of the lighter cuts which are substantially stable at the temperatures employed in the cracking zone and returning the heated lighter cuts to an intermediate point in the cracking zone.

14. A process of cracking heavy hydrocarbons to produce lighter hydrocarbons comprising passing them in a continuous stream under pressure through a zone heated to a cracking temperature and thereby cracking a portion ot said hydrocarbons, reducing the pressure on the stream and leading it to an expansion chamber, distilling oii' the lighter hydrocarbons in thc expansion chamber and condensing them, fractionating the condensate into a cut corresponding to gasoline, a

cut of approximately 41 degrees BaumeJ and a cut of approximately 38 degrees Baume heating the latter two cuts and returning them to the stream of hydrocarbons at successive intermediate points in the crackingV zone.

15. The im rovement in the operation of tubular crac ing Y Ystills which comprises mechanically forcing a stream of the oil through a tubular cracking still and suboil in a tubular cracking still Which'com'- prises passing the oil in a single pass through a cracking coil and '.sub]ec`ting .thev oil thereimto a cracking temperature under a high pressure, and introducing a solventoil into thepartially cracked oil at an intermediate stage in itsA passage throughthe coil.

17. The improvement in the crackingof oils in a tubular cracking still which comprises forcing the oil in a single pass through a cracking coil and introducing solvent oil into the partially' cracked oil at a plurality of successive sta es `in the passage of the oil through the crac ing coil.`

18. The improvement in theoperation of tubular cracking stills whichvcomprises mechanically forcing the oil in a continuous stream through a cracking coil and heating the oil therein under pressure to a cracking temperature, and prolonging the cracking o eration by the introduction into the parta ly cracked oil at an intermediate point in the cracking coil of a lighter solvent oil resistant to cracking-under the conditions of temperature and pressure maintained in the cracking coil.

19. The improvement in the cracking of oil in tubular cracking stills which comprises mechanically forcing a stream of the oil under pressure throu h a series of cracking coils and heating t e oil therein to a cracking temperature, and introducina solvent oil .into the partially cracked o' at a. plurality of intermediate points in the passage of the stream of oil through said crackin coils.

20. e improvement in the cracking of oil. in tubular cracking stills which comprises passing the oil in a single-pass through a plurality of vcoils in succession, heating tl1e0il therein to a crackin temperature under' a high pressure, subjectingV said coils to heating gases at progressively lower temperatures, and introducingsolvent oil into the partially cracked oil during i-ts passage through said coils.

21. The improvement in the cracking of oils in tubular cracking stills which comprises v passing'in a single-pass through a. cracking coil apetroleum fraction of about 35i B. and heating the same to a cracking temperature under a high pressure, and supp l'mg successivel to the lpartially cracked o1 solvent oil -a outl 38?B.- and about 41 B.v at successive stages of progress of 'the partially cracked oil through the coil.

` 22. tubular crackin still comprising a continuous cracking coi arranged for the passage therethrough of the oil in a sin lepass, said cracking coil being made up o an plurality of coils arranged to be heated to successively lower temperatures, Ameans for.

forcing thepoil under pressure throughsaid coll and means for mechanically introducing solvent oil into the coil at one or more interl mediate points.

23. A tubular cracking still comprising a EDWARD`W. ISOM. CHARLESL. PARMELEE.

` oil in a tubular cracking still which comprises passing the oil in a single pass through a cracking coil and sub}ecting the oil therein to a cracking temperature under a high pressure, and introducing a solvent oil into the partially cracked oil at an intermediate stage in its4 passage through the coil.

17. The improvement in the cracking of oils in a tubular cracking still which comprises forcing the oil in a single pass through a cracking coil and introducing solvent oil into the partially cracked oil at a pluralit of successive sta es in the passage of the oil through the crac 'ng coil.

18. The im rovement in the operation of tubular crac 'ng stills which comprises mechanical] forcing the oil in a continuous stream irough a cracking coil and heating the oil therein under pressure to a cracking temperature, and prolonging the cracking o eration by the introduction into the parta ly cracked oil at an intermediate point in the cracking coil of a lighter solvent oil resistant to cracking under the conditions of temperature and pressure maintained in the cracking coil.

19. The improvement in the cracking of oil in tubular cracking stills which coinprises mechanically forcing a stream of the oil under pressure throu h a series of cracking coils and heating t e oil therein to a cracking temperature, and introducin a solvent oil into the partially cracked o' at a plurality of intermediate points in the passage of the stream of oil through said crackin coils.

20. e improvement in the cracking of oil in tubular crackin" stills which cornprises passing the oil in a single-pass through a plurality of coils in succession, heating tlieoil therein to a cracking temperature under a high pressure, subJectng said coils to heating gases at progressively lower temperatures, and introducing solvent oil into the partially cracked oil during its passage through said coils.

21. The improvement in the cracking of oils in tubular cracking stills which comprises passing in a single-pass through a cracking coil a petroleum fraction of about 35 B. and heating the same to a cracking temperature under a high pressure, and supplying successivel to the partially cracked oi solvent oil a out 38 B. and about 41 B. at successive stages of progress of the partially cracked oil through the coil.

22. A tubular crackin still comprising a continuous cracking coi arranged for the passage therethrough of the oil in a sin lepass, said cracking coil being made up o an plurality of coils arranged to be heated to successively lower temperatures means for forcing the oil under ressure through said coil and means for m anically introducing solvent oil into the coil at one or more intermediate points.

23. A tubular cracking still comprising a furnace having a series of crackin coils therein connected in series to permit t e passage of oil therethrough in a single-pass, each of said said coils being arranged to obtain a generally counter-current flow of oil and heating gases and the successive coils being subjected to gases at successively lower temperatures, and means for introducing solvent oil into said coils at one or more in termediate points.

EDWARD W. ISOM. CHARLES L. PARMELEE.

cnirirican: or connection.

Patent No. l, 675, 558.

Granted July 3, 1928,10

EDWARD W. lSOM ET AL.

It is hereby certified that error appears in the printedV specification of the above numbered patentrequiring correction as follows:r Page l, line 90, for the word "it" read "its"; page 5. line 66, claim 21, after the word "oil" insert the word "o"; line 72, claim 22, for the word "an" read "a", and line 83, claim 13, striked out the word "said" second occurrence; and that the seid Letten Patent should be read with these corrections therein that the same may contorni to the record of the case in the Patent Ofxice.

Signed and sealed this 20th day of November, A. D. 1928.

(Seal) M. J. Moore. Acting Comieeioner of Patente.

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