US1714090A - Art of cracking hydrocarbons - Google Patents

Description

May 21, 1929.

E. C. HERTHEL ET AL ART 0F CRACKING HYDROCARBONS Filed June l1, 1927 E@ @ii Eugene wu SSN y L. Heizer ATTORN EYS Patented May 21,` 1929,

UNITED STATESPATENT',OFFICE.

:EUGENE c. IIIIMHEL, F CHICAGO, ILLINOIS, AND HARRY L. InLznR, or HIGHLAND,

INDIANA, AssIGNoRs To sINcLAIa :aEIIN'ING ooIIrANY, or NEW YORK, N. Y,

A. CORPORATION 0F MAINE.

4Annu or CRACKING IIYDRocABBoNs.'

Application med June 11,

This invention relates to improvements in the cracking of heavier and higher, boiling f` hydrocarbon oils, such as gas oil, for the production of lighter and lower boiling hydrocarbody of oil is maintained at a cracking tem-y perature and vapors including vapors of the cracked product are taken off from the body under pressure. Heat for maintaining the cracking temperature and for'supplying the heat required in the cracking operation is supplied to this body in two ways, both externally and internally. Oil is circulated and recir culated from the body through heating tubes and back to the body and the circulating oil l is heated in the heating tubes by heating gases passed thereover. Likewise, a gaseous heating medium heated to a cracking temperature is introduced directly into the body of oil l The heat exchange with the gaseous heating medium so introduced is direct and involvesl no heat transfer through the walls of tubes 25 or the like( The burden of heat transfer through the heating tubes is thus relieved by the heat so supplied to the body of oil. Further to protect the heatin tubes, a bed of finely divided filtering or a sorbent material is also maintained in'the body of oil in the path of the oil circulating and recirculating through the heating tubes. l

In addition to the desired lighter and lower boilingl hydrocarbon oils,.the products of the cracking reaction include pitch-like or asphaltic constituents which tend to separate upon externally heated surfaces with resulting formation off carbonaceous deposits on such heating surfaces which impede heat transfer from the heating surface to the oil and consequently tend to cause local and extreme overheating. The formation of such carbonaceous deposits, in part at least, is dependent upon the rate of heat transfer, the tendency to formation of such deposits being less at lower rates of heat transfer, and such deposits moreover are less objectionable where they occur on surfaces throu h which the rate of heat transfer is relative low.

In the cracking operation of tlie present in- 1927. seriINo. 198,252.

ventionthe oil is heated, in part, by circulation through 'externally heated heatlng tubes, but the burden of heat transfer through these tubes is reduced by the direct introduction of a gaseous heating medium. AThe tendency toward formation of lcarbonaceous deposits in the heating tubes is thus reduced, and the objectionable effects of any such deposits that may occur are also minimized. At the same time, these heating tubes arefu'rther protected by reducing the concentrationv of such pitch-like or asphaltic constituentsin the oil circulating through the heating tubes by circulating this'oil also through a bed of filtering or absorbent material. The concentration of such pitch-like and asphaltic constituents in the circulatingcharge of oil in the pressure still may be further controlled: and regulated, as described in Letters Patent No. 1,598,136 issued August 31, 1926, by the discharge of pitch-laden oil or tar and the supply of raw oil and the conjoint regulation. of the discharge of pitch-laden oil or tar and the supply of raw oil to maintain the concentration of such constituents in the still charge below saturation, or below an objectionable value.

The gaseous heating medium may with advantage consist of a hydrocarbon gas mixture, such as the gas mixture remaining uncondensed after separation ofthe condensed distillate product or after scrubbing or other suitable treatment for recovery of condensible constituents of the uncondensed gas mixture as initially separated from the'distillate product. One advantageous absorbent and filtering material is fullers earth. Other absorbent earths and clays may be used in a similar way. Finely divided carbonaceous materials such as pulverized coke, however, are particularly advantageous. The gaseous heating medium, particularly where it con- -sists of a hydrocarbon gas mixture, is ad- Icol partly in suspension, in the body of oil the finely divided material, thus assisting in promoting intimate contact between the finely divided material and the still charge and in maintaining free circulation of the still charge. If a hydrocarbon gas mixture containing reactive constituents is used as a gaseous heating medium, the introduction of ythe gaseous heating medium at a cracking temperature may also promote further reaction and combination of such constituents with constituents of the still charge. By introducing the gaseous heating medium beneath the bed of finely divided material, any surface or catalytic action of such finely divided material efl'ective to promote such reaction or combination is utilized. Where the gas mixture remaining uncondensed from the cracking operation is returned as the gaseous heating medium, for example, it may contain substantial proportions of reactive constituents, particularly unsaturated constituents, which so reintroduced into the still charge may ,assist in improving yield or quality of product.

The invention will be further described in connection with the accompanying drawings which illustrate, in a diagrammatic and conventional manner, in elevation and partly in section and with parts broken away, one form of apparatus adapted for carrying out the process of the-invention, but it will be understood that the process of the invention can be carried out in other and dierent apparatus and that the apparatus specifically illustrated is intended for the purpose of illustration only.

Referring to the drawings, the pressure still illustrated comprises a bulk supply drum 1, a battery of heating tubes 2, arranged in theheating flue of a furnace and circulating connections 3, 4 and 5 including a circulating pump 6 for circulating oil from the bulk supply drum upwardly through the heating tubes and back to the bulk supply drum. Ar-

' ranged in the bulk supply druml, beneath the normal liquid level therein and entirely across the path of the circulating-still charge between the circulating connections 3 to the heating tubes and the circulating connect-ions 5 from the heating tubes is a bed 7 of finely 'divided absorbent or filtering material. This bed of finely divided material is supported upon a suitable supporting means 8 adapted to retain the finely divided material butto permit freepassage of oil. This supporting means mayconsist, for example, of one or more screens of appropriate mesh arranged between perforated,plates,or arranged between gratings as described in application 'seri/a1 No.iisiaec sied April 16, 1927. This latter construction is particularly advantageous for use 'in practicing they present invention.l` Arranged in the bulk supply'drum beneath the supporting means 8 is a perforated pipe or pipes 9. Connection 10 communicates with this perforated pipe, Heating coil 11, arranged in another heating furnace, is connected to the perforated pipe 9 and a compressor or other forcing means is provided for forcing a gaseous heating medium through thisheating coil into the still charge through perforated pipe 9.

Vapors from the bulk supply drum 1 escape through connection 12 to the lower end of the reflux tower and vapors remaining uncondensed escape from the upper end of the reflux tower through connection 14 to the condenser 15 arranged to discharge into the receiver 16. The distillate product is discharged from this receiver through connection 17 and uncon'densed vapors and gases through connection 18. Pressure in the system is maintained and regulated by means of valve 19, or by suitable valves arranged beyond the condenser or receiver. Connection 20 is provided for introducing raw oil into the upper end of the reflux tower 13. Reflux condensate, together with any admixed unvaporize'd raw oil, is returned to the circulating still charge, from the lower end of the reflux tower through connection 21. Connection 22 is provided for discharging tar or pitch-laden oil during operation. onnection 23 is provided for supplying cool oil to the bearings of the circulating pump 6. Raw oil in excess of that required to cool and lubricate the pump bearings may be forced into the circulating still charge through the pump bearings through this connection. Connection 24 is provided for pumping out the still at the end of a run and for initially charging the still at the beginning of a run.

In operation, fuel is burned in the firebox 25 of the furnace 26 and the hot products of combustion are passed over the heating tubes 2 through the heating flue in which these heating tubes are arranged. Part of the heating gases may be recirculated through this heating flue in admixture with fresh hot products of combustion from t-he firebox by means of return flue 27 provided with suitable forcing means, such as the steam jet blower illustrated. Fuel is also burned in the furnace 28 for heating the gaseous heating medium forced through the heating coil 11.

In a pressure still of the type illustrated, in which the normal operating charge is about 10,000 gallons, the bed of finely divided material may consist, for example, of from 4 to tons of 15-30 mesh fullers earth 'or similar absorbent earth or clay, or of from 3 to.

5 tons of 15-30 mesh pulverized coke.v Agitation due to the introduction of the gaseous heating medium may effect the discharge of a part of the finely divided material in suspension in the discharged pitch-laden oil or 1,714,ooo I 3 tar, during operation, and to make up for any such discharge of the finely divided absorbent or filtering material additions of suchmaterial may b e made in suspension in raw oilsupplied to the operation.

In operation to produce gasoline or a gasoline-containing pressure distillate from gas oil character charging stock, for example, the

:'still -may `be Operated under a pressure in the neighborhood of 125 pounds per square inch. It will be "understood that higher or lower pressures may be used. Higher pressures, for example,up to 300 pounds per square inch or cracked vapors through the reflux tower to the condenser is begun, the introduction of raw oil through the reflux tower is started and the rate at which raw oilisso supplied is regulated to condense and 'reilurr those components of the vapors heavier f mixture such as that discharged from the operation after separation of the condensed distillate product. Other hydrocarbon gas mixtures, such as those resulting from coking operations carried out at atmospheric pressure may also be used, aloe or in admixture with such returned pressure still gas mixtures. Any of 'these gas mixtures may be subjected to scrubbing or other suitable treatment for themecovery of condensible constituents before being supplied to the operation. 'I

In carrying out the present invention, -in the apparatus illustrated for example, it will be apparent that the heat for maintaining the body of oil in the pressure still at a cracking temperature and for effecting the cracking` operation is supplied by externall heating oil. circulated from the body throug heating tubes and vback to the body and also by the direct introduction into the body of a gaseous heating medium. The heat supplied directly by the gaseous heating medium assists in relieving the burden of heat transfer through the heating tubes, thus protectingthe heating tubes against overheating. These heating tubes are further protected against overheating by the action Vof the bed of finely divided filtering or absorbent material through which the charg` of oil in the pressure still is circulated ineliminating or reducing any tendency toward the formation of carbonaceous deposits in the heating tubes. The formation of carbonaceous deposits 1n A the heating tubes may be further inhibited b the regulated supply of raw oil and disc arge of itch-laden o1l or tar, and the heating tubes urther protected by recycling over the heating tubes in admixture with fresh hot products of combustion a part of the heating gases which have passed thereover. The invention makes fpossible reduction in the strains to which the pressure still apparatus is subjected, particularly those due to very high heat transfer rates, without interfering with the capacity of the still.

. We claim:

1. An improved method of cracking hydrocarbon oils, which comprises maintaining a body of oil at acracking temperature and taking off vapors including vapors ,of the cracked product therefrom under pressure, circulating oil from the body through heating tubes externally exposed to heating gases and back to the body, maintainin a bed of finely divided filtering material in te body of oil in the path of the circulating oil, and introducing a gaseous heating medium heated to a cracking temperature into the body of oil beneath the bed of finely divided fi tering material.

2. An improved method of cracking hydrocarbon oils, which comprises maintainmg a body of oil at a cracking temperature and taking oif vapors including vapors of the cracked product therefrom under pressure, circulating oil from the body' through heating tubes externally exposed to heatm gases and back to the body, maintaining a ed of finely divided absorbent material in the body of o1l in the path of the circulating oil, and introducing a gaseous heating medium heated to a cracking temperature into the body of oil beneath the bed of finely divided absorbent material.

3. An improved method of cracking hydrocarbon oils, which comprises maintaining a body of oil at a cracking temperature and taking oil vapors including vapors of the.

cracked product therefrom under pressure, circulating oil from the body through heating tubes externally yexposed to heatin gases and back to the body, maintalning a ed of finely divided carbonaceous material in the body of oil inthe path of the circulatin oil,

.and introducing a gaseous -heating me ium heated to a Vcracking temperatureV into the body of oil beneath the bed of finely divided carbonaceous material.

4. An improved method of cracking hydrocarbon oils', which comprises maintaining a oil in the path of the circulatin oil, and inbody of oil ata cracking temperature and taktroducing hydrocarbon gases eated to a. 10 ing 0E vapors including vapors of the cracked cracking temperature into the body of oil beproduct therefrom under pressure, circulatneath the bed of finely divided carbonaoeous 5 ing oil from the body through heating tubes material.

externally exposed to heatin gases and back to the body, maintaining a ed of finely di- EUGENE C. HERTHEL. vided carbonaceous material in the body of HARRY L. PELZER.

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