US1787981A - Art of cracking hydrocarbons - Google Patents

Description

Jan. 6; 1931. E. c. HERTHEL ET AL 1,787,981

ART OF CRACKING HYDROCARBQNS Filed Jun 11, 1927 INVENTOR 6 i'l/jenc C f/er M l I flarr L. Feller BY 5 5; W $2M ATTORNEYS Patented Jan. 6, 1931 UNITED STATES PATENT OFFICE EUGENE C. HERTfiELQOF CHICAGO, ILLINOIS, AND HARRY L PELZER, OF HIGHLAND, INDIANA, ASSIGNORS T0 SINCLAIR REFINING COMPANY, OF NEW YORK, N. Y.,

CORPORATION OF MAINE ART OF CRACKING HYDROCARBONS Application filed June 11,

This invention relates to improvements in the cracking of heavier and higher boiling hydrocarbon oils, such as gas oil, to produce therefrom lighter and lower-boiling hydrocarbon oils, such as gasoline and gasolinecontaining pressure distillates. This invention relates particularly to improvements in the operation and arrangement of externally heated pressure cracking stills, that is pressure cracking stills in which the heat for the cracking operation is supplied by heating gases passed externally over the heating surfaces of the still from a firebox in which fuel is burned. The invention includes improvements in both method and apparatus.

The products of the cracking reaction'inelude, in addition to the desiredlighter and lower boiling hydrocarbon oils, asphaltic and pitch-like constituents which tend to deposit upon the heating surfaces of externally heated pressure'stills. Such deposits obstruct heat transfer and tend to cause extreme overheating because of this obstruction of heat transfer, necessitating periodic shut down of the pressure still for cleaning, thus limit-ing the useful period of operation. -As the concentration of such asphaltic and pitch-like constituents in the charge of oil in the pressure still increases, the tendency toward deposition of such materials also increases. This invention provides for reduction'in the concentration of asphaltic and "pitch-like constituentsin the oil in-contact with the heating surfaces of the still, and for tempering of the heating gases passing over the heating surfaces through which heat is transferred to that portion of the charge containing the greater concentration of such constituents by a corresponding absorption of heat from the heating gases by heat exchange with oil substantially free from such constituents and of a character such that the tendency toward the formation of such constituents is materially reduced, as well as for particularly advantageous treatment of relatively refractory stocks; thus providing improved continuity of operation with accompanying increase in still capacity and in efficiency of operation.

According to the present invention, a body 1927. Serial No. 198,248.

of oil is maintained at a cracking temperature under pressure in a vaporizing zone, the oil being heated to a cracking. temperature in heating tubes through which it is circulated from the body and back to the body, and a bed of finely divided absorbent or filtering material is maintained within the body of oil in the vaporizing zone so that the circulating oil is caused to pass through it. Vapors taken over the heating tubes through which oil from the body in the vaporizing zone is repeatedly circulated. The concentration of asphaltic or pitch-like materials in the oil circulated and recirculated from the vaporizing zone through the first mentioned heating tubes and back to the vaporizing zone is thus reduced by the act-ion of the bed. of absorbent or filtering material. At the same time, the heating gases are tempered before they come in contact with these heating tubes over which the heating gases first pass. These separate heating tubes are thus exposed to the heating gases while at highest temperature, but the oil circulated through these heating tubes is substantially free from asphaltic or pitchlike constituents and, this reflux condensate being relatively refractory, the formation of asphaltic or pitch-like constituents in the oil circulated through the separate heating tubes is reduced or retarded while this relatively refractory stock is subjected to particularly advantageous cracking conditions for further production of .desired lighter and lower boiling hydrocarbon oils. The oil supplied thereto advantageously is circulated but once or in a single'pass through the separate heating tubes.

F ullers earth, or a similar absorbent earth A in the Cracking o eration, which appear to be relatively smal in amount as compared materials, are also useful in carrying out the invention, but fullers earth is particularly eflicacions, apparently combining in itself valuable selective absorbent, desul hurizing and other properties which favora ly affect and benefit the pressure still operation. For example, fullers earth seems to have a selective affinity for the more objectionable as phaltic and pitch-like constituents formed by the cracking operation.

In addition to reflux'condensate, raw oil may also with advantage be circulated through the separate heating tubes arranged in advance of those through which oil is circulated and recirculated from the vaporizing zone. Such raw oil may be'supplied directly to the separate heating tubes in ad mixture with the returned reflux condensate,

or, .and this is a particularly advantageous method of operation, the raw oil, or part of it, may be introduced into the refluxing operation for promoting or controlling the refluxing operation and for preheating the raw oil. Admixed reflux condensate and unvaporized raw oil ma then be supplied to the separate heating tn 5 from the refluxing operation. Additional raw oil may also be supplied directly to the charge of oil circulating through the vaporizing zone, and part of the reflux condensate, or admixed raw oil and refluxed condensate, from the refluxing operation may also be supplied directly to the body of oil circulating through the vaporizing zone as required without first being passed through the separate heating tubes.

The present invention thus provides improved protection for all of the externally heated heating surfaces of the pressure still. The heating tubes with which the heating gases first contact and which accordingly are exposed to the heating gases while at highest temperature are protected. by circulation therethrough of relatively refractory stock and stock which is substantially free from asphaltic and pitch-like constituents formed in the cracking operation, the stock circulated through these first heating tubes being either reflux condensate or a mixture of reflux condensate and raw oil. The remaining heating tubes are protected in a dual manner; they are protected by the action of the bed of finely divided. absorbent or filtering material in reducing the concentration of asphaltic and pitch-like constituents in the oil circulating therethrough, and they are further protected by the tempering of the heating gases effected by heat absorption in the first heating tubes. The. reflux condensate circulated through the first heating tubes is also subjected to advantageous cracking conditions, this reflux condensate being relatively refr'ac tory with respect to the cracking conditions to which the body of oil circulated and recirculated through the remaining' heating Referring to the drawings, the pressure still illustrated comprises a bulk supply drum 1, a battery of heating tubes 2 and circulating connections 3, 4 and 5 including a circulating pump 6 arranged to provide for circulation of oil from the bulk supply drum through the heating tubes 2 'and back to the bulk supply drum. Arranged in the bulk supply drumand below the normal liquid level therein is a bed 7 of finely divided absorbent o'r filtering material. This bed is supported on a suitable support 8 adapted to retain the finely divided solid material but to permit free passage of oil therethrough. The support may consist, for example, of one or more screens arranged between perforated plates or between suitable gratings; The support 8 and the bed offinely divided solid material thereon are arranged in the bulk supply drum 1 extending entirely across the -bulk supply drum and between the circulat- 1ng connections 3 to the circulating tubes 2 and the circulating connections 5 from the heating tubes so that oil circulating and re- I furnace in the flue betweenthe firebox 10 and the heating tubes 2 so that heating gases from the firebox must pass over these heating tubes 12 before contacting with the heating tubes 2. Further-to assist in tempering the heating gases passing. over the heating tubes,

means for clrculating over the heating tubes a portion ofthelescaping' waste heating gases in admixture with fresh hot products of comoustion from the firebox may be provided, as shown at 13.

Arranged above the bulk supply ,drum 1 is a refluxtower 14. Vapors from the bulk supply drum enter the lower end of this reflux tower through vapor line 15. Vapors remaininguncondensed escape from the upper end of this reflux tower through vapor line 16 to the condenser 17 arranged to discharge into the receiver 18. The distillate product is discharged from the receiver 18 through the connection 19 and uncondensed vapors and gases through the connection 20. The pressure in the'system may be maintained and regulated by means of the valve 21 or by means of suitable valves arranged beyond the condenser or receiver. Reflux condensate from the reflux tower 14 is conveyed to the reservoir 22 through connection 23. A supplemental vaporline between the upper end of the reservoir 22 and a point in the reflux tower above the outlet for reflux condensate is provided at 24. From the reservoir 22, reflux condensate is circulated through the heating tubes 12 by means of connection 25 or pump 26 and connection 27. The hot oil products from the heating tubes 12 are discharged into the bulk supply drum 1 through connections 28 and 5. Feed line 29 is provided for introducing raw oil into the upper end of the reflux tower 14. Raw oil so introduced into the reflux tower 14 passes to the reservoir 22 and continues in admixture with the reflux condensate. Additional raw oil may be supplied directly to the heating tubes 12 through connection 30. An overflow connection for reflux condensate, or reflux condensate and admixed unvaporized raw oil, in excess of that discharged through connection 23 is provided at 31. Oil may also be discharged from the reservoir 22 into the upper end of the circulating connection 3 through connection 32. If for any reason the supply of oil to the heating-tubes 12 from reservoir 22 is insufficient, as in starting the operation, a part of the recirculating charge of oil in the pressure still may be supplied thereto through connection 33, or other oil may be supplied through connection 30.

A tar line for discharging tar or pitch laden oil from the pressure still during operation is provided at 34. A connection for.

pumping out and for initially charging the still is shown at 35. Oil for cooling and lubricating the bearings of the circulating pump 6 may be supplied through connection 36, or raw oil in excess of the amount required for cooling and lubricating the pump bearings may be supplied to the recirculating still charge through this connection and forced in through the pump bearings.

The bulk supply drum 1, the reservoir 22, and the several hot connections are all advantageously lagged or insulated to prevent or reduce heat loss. Where the refluxing operation is effected by heat exchange with raw oil, as inthe apparatus illustrated, it is also advantageous to lag or insulate the reflux tower 14.

In starting operation, the still system 'is charged with oil and gradually brought to cracking conditions of temperature and pressure in the usual manner. While the still is being brought to cracking conditions, or until an adequate supply of reflux condensate is available, a portion of the oil discharged recirculating through the heating tubes 2 will 0 in general be the temperature corresponding to the. pressure used; but the oil circulating through the heating tubes 12 may be superheated to a considerably higher temperature. For example, if the oil body in the bulk supply drum 1 is at a temperature in the neigh borhood of 750 to 775 F., the hot oil products from the heating tubes 12 as discharged through connection 28 may be at atemperature of from 775 to upwards of 825 F. The refluxin operation may be controlled by regulated mtroduction of raw oil through connection 29; for example, the temperature at which the vapors remaining uncondensed escape from the upper end of the reflux tower may be maintained at some appropriate predetermined temperature b regulating the introduction of raw oil. Kdditional raw oil supplied to the operation may be introduced through connection 36 or in part through connection 36 or through connection 30 or in part through connection 30. In a' pressure still of the type illustrate in which the bulk supply drum 1 is adapted to contain a normal operating charge in the neighborhood of 10,000 gallons, the bed of finely divided solid material 7 may with advantage consist of from four to seven tons of fullers earth. It is advantageous to use relatively coarse earth, say from 15. to 30 mesh, although finer earth may be used. The

tar line 34 is advantageously arranged, as

illustrated,'to discharge pitch-laden oil from the body-of oil in the bulk supply drum 1 from above the bed-of finely divided filtering or absorbent material, although it may be the still charge.

the repeated passage of the circulating oil through the bed of absorbent or filtering material 7. This bed of filtering or absorbent material is entirely submer ed in and directly exposed ,to the body of oil in the bulk supply drum 1 so as to exert its maximum effect upon The concentration of asphaltic and pitch-like constituents in the charge of oil circulating through the bulk supply drum 1 is further ;controlled by the discharge of tar or pitch-laden oil through connection 34 in conjunction with the supply of raw oil to the operation. During the operation, the oil circulated through the battery of heatin tubes 2 will nevertheless contain some asp altic and pitch-like constituents but these heating tubes are further protected by the tempering of the heating gases effected by the heat absorption by the separate bank of heatingtubes 12.

The heating gases including fresh hot products of combustion from the firebox pass first over the separate bank of heating tubes 12 and then over the battery of heating tubes 2 so that the reduction in temperature of the heating gases as they pass over the heating tubes 12 reduces the temperature of the heating gases as they contact with the heating tubes 2. The separate bankof heating tubes 12 are protected by the circulation of oil substantially free from asphaltic and pitch-like constituents therethrough, either reflux 'con densate from the reflux tower ,14 or such reflux condensate admixed with raw oil. 1 The relatively refractory character of the reflux condensate, moreover, assists in further reducing or retarding the formation of as- .phaltic or pitch-like constituents in' the heating tubes 12, that is the heating tubes subjected to highest temperatures. 7

The hot oil products discharged from the separate bank of heating tubes 12 may assist in heating, internally, the charge of oil in the bulk supply drum 1'. Where the hot 011 products are heated in the heating tubes 12 to a temperature substantially higher than that prevailing in the bulk suppl drum 1, the reduction of tem erature of t e hot oil products discharged om the separate'bank of heating tubes 12 as they are introduced into the body of oil in the bulk supply drum 1 may also assist in arresting any tendency toward overcracking.

We claim:

1. An improved method of cracking hydrocarbon oils, which comprises circulating .oil

from a body of oil in a vaporizing zone through heating tubes and back to the and heating it to a cracking temperature in the heating tub'es, maintaining a bed of fine- 1y divided solid absorbent material within said body of oil so that the circulating oil-is caused to pass therethrough, taking off vapors from said vaporizing zone under superatmospher c pressure and subjecting'themto from a body of oil in a vaporizing zone through heating tubes and back to the body and heating it to a cracking temperature in the heating tubes, maintaining a bed'of finely divided solid material within said body of oil so that the circulating oil is caused to pass therethrough, taking ofi vapors from said vaporizing zone under superatmospheric pressure and subjecting them to a refluxing operation, introducing raw oil into direct contact with the vapors in the-refluxing operation, circulating admixed reflux condensate and unvaporized raw oil from said refluxing operation through separate heating tubes into said vaporizing zone, and passing heating gases from afirebox in which fuel is burned for supplying heat to the cracking operation first over said separate heating tubes through which admixed reflux condensate and unvaporized raw oil is circulated and thenover the first mentioned heating tubes.

3. An improved method of cracking hydrocarbon oils-which comprises circulating oil from a body of oil a vaporizing zone through heating tubes and back to the body and heating it to a cracking temperature in the heating tubes, maintaining a bed of finely divided solid material within said body of oil so that the circulating oil is caused to pass therethrough, taking ofi vapors from said vaporizing zone under superatmoipheric uxing pressure and subjecting them'to a re operation, circulating reflux-condensate from vaporizing zone, and passing heating gases from a firebox in which fuel is burned for supplying heat to the cracking operation first over said separate heating. tubes through through heating tubes and bac to the body .and heating it to a cracking temperature in the heating tubes, maintaining a bed of finely divided solid material within said body of oil so that the circulating oil is caused to pass therethrough, taking off vapors from said vaporizing zone under superatmospheric pressure and subjecting them to a re-- said refluxing operation together with raw .oil through separate heating tubes into said first over said separate heating tu fluxing operation, circulating reflux condensate from said refluxin operation through separate heating tubes 1nto said vaporizing zone, discharging pitch-laden oil from thebody of oil in said vaporizing zone and supplying raw oil, and passing heating gases from a firebox in which fuel is burned for supplying heat to the crackin operation through which reflux condensate is circulated and then over the first mentioned heating tubes.

5. An improved method of cracking hydrocarbon oils, which'comprises circulating oil from a body of oil in a vaporizing zone through heating tubes and back to the body and heating it to a. cracking temperature in the heating tubes, maintaining a bed 1 of fullers earth within said body of oil so that the circulating oil is caused to pass therethrough, taking off vapors from said vaporiz'ing zone under superatmospheric pressure and subjecting them to a refluxing operation, recirculating reflux condensate fromsaid refluxing operation through separate heating tubes into said vaporizing zone, and passing heating gases from a firebox in which fuel is turning'reflux condensate from the refluxing operation to said heating coil, maintaining a bed of finely divided solid material within said body of oil, circulating unvaporized oil in said conversion chamber through the bed .of finely divided'solid material and thereburned for supplying heat to the cracking oporation first over said separate heating tubes through which reflux condensate is circulated and theno-ver the first-mentioned heating tubes.

6. An improved apparatus for cracking hydrocarbon oils, com rising a heating furnace having a heating iiiie, a firebox connected to one end thereof and a stack flue to the other,

a bulk supply drum and a battery of heatingtubes arranged in the heating flue' of the heating furnace and circulating connections for circulating oil from the bulk supply drum through the heating tubes and back to the bulk supply drum, a bed of finely'divided s0l-.

id material arranged in the bulk supply drum below the normal liquid level therein and extending entirely across the bulksupply drum s between the circulating connection from thesaid heating tubes and the circulating connecv tion to-the said heating tubes, a reflux tower and a vapor line from the bulk supply drum to the reflux tower, a separate bank of heating tubes arrangedin the heating flue of the heating furnace between the firebox and thefirst mentioned bank of heating tubes, and circulating connections forcirculating reflux condensate from said reflux tower through said separate bank of heating tubes back to the bulk supply drum.

v 7. An improved method of cracking hydrocarbon oil which comprises passing the oil through a heating co'ilwherein it is subjected to a conversion temperature, discharging the heated oil into an enlarged conversion chamber and maintaining a body of oil therein, taking ofl vapors fromsaid conversion cham ber under superatmospheric pressure and subjecting them to a refluxing operation, re-

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