US1741277A - Art of cracking hydrocarbons - Google Patents

Description

Dec. 31, 1929. J. E. BELL ART OF CRACKING HYDROCARBONS Filed Jan. 22, 1925 IIIL , n u l;

@SSX a im ATTORN EYS f /ZW/ L Patented Dec. 31, 1929 UNITED A STATES PATENT OFFICE JOHN E. BELL, DECEASECD, LATE F BROOKLYN, NEW YORK, BY LOLA R. BELL, EXECU- TRIX, OF BROOKLYN, NEW YORK, ASSIGNOR T0 SINCLAIR REFINING COMPANY, OF NEW YORK, N. Y., A CORPORATION OF MAINE ART OF CRACKING HYDROCARBONS Application tiled January 22, 1925. Serial No. 3,987.

operation of reflux or fractionating towersemplo ed in conjunction with pressure'cracking stills.

When heavy hydrocarbons are dlstllled under pressure, they are cracked with the production of lighter oils. In the commercial operation of a pressure still, some definite product or group of products, for example gasoline or pressure' distillate, is usually desred but the vapors escaping from the still itself may include heavier constituents in addition to the constituents desired in the pressure distillate. The vapors from the pressure still are commonl subjected to a refluxing operation before veing condensed to effeet, to a greater or less extent, the return of such heavier vaporized constituents to the still for further'treatment therein,`- but, as ordinarily practised, such methods have nevertheless resulted in the production of pressure distillates containing large amounts of constituents heavier than the desired pressure distillate. For example, in treating gas oil for the production of gasoline by such cracking methods, the pressure distillate usually includes a considerable amount of constituents of a `kerosene character and others even heavier, so that it is necessary to subject a relatively large amount of crude.

pressure distillate to redistillation to fractionate it into merchantable products and to separate the heavier components.

It is'one of the objects of the present invention to eliminate such redistillation of the pressure distillate as a separate operation and to save heat usually employed for such redistillation. A Other and further objects will appear more fully as the description proceeds.

According to the present invention, the heat of the pressure distillate vapors escaping from the pressure still is employed to -fractionate the pressure distillate in anim- 60 proved manner, .and it may also be employed in an advantageous way for :tractionating at the same time other oils or distillates including constituents suitable as components of lthe desired productor products.

According to the present invention, the vapors from the pressure still are passed successively through two towers, charging stock to the still is introducedv directly into the tower which the vapors first enter and reflux and admixed charging stock from this tower arev returned to the pressure still, and an oil or distillate including constituents suitable as components of the desired distillate is introduced directly into 'the second tower which the vapors escaping from the first enter.

In the first tower, the tower which the vapors rst enter, the vapors are contacted with the charging stock introduced therein, the charging stock acting as a refluxing agent and refluxing the heavier constituents of the vapors to the still for further treatment in the still, while the charging stock is at the same time preheated. The first tower-thus acts to effect an initial separation ofthe heavier cons'tituents and return them to the still and also to return to the still for useful application in the cracking operation therein a part of the heat of the escaping vapors. The vapors es`- caping from the first tower may comprise the normal pressure distillate constituents, that is the components o f the desired product associated with some heavier constituents but :freed of the heaviest constituents.

In the second tower, the tower which the vapors escaping from the first tower enter, the vapors are contacted with an oil or distillate including constituents suitable as components of the desired distillate which constituents are thereby vaporized. The vapors entering the second tower are partly cooled in the first tower and the vaporlzation ofcthe lighter constituents of the oil introduced into the second tower further cools them. The heavier constituents of the entering vapors are thus condensed a d mix with the unvaporized constituents of the introduced oil, collecting as tower condensate. The vapors es-A caping from the second tower include the lighter constituents 'of the vapors entering from the first tower and the light r constitmnL . densed in the usual Way. An accurate fractionation of the vapors from the still, and

likewise of the introduced oil, is thus eiected by the heat of the pressure distillate vapors, the condensate of the vapors escaping rom the second tower comprisingI the desired pressure distillate substantially free from heavier constituents, and the tower condensate comprising the intermediate constituents heavier than the desired pressure distillate components and lighter than the constituents reluXed to the pressure still from the first tower.

As compared to operations in which it is attempted to reflux directly to the still from a reluXtower thereon (for example the first tower described herein) all constituents heavier than lthe desired pressure distillate, the process of the present invention accomplishes a marked heat economy. Where heavier constituents having a boiling point close to the temperatures maintained in the pressure still.

are refluxed to the still theyv are cracked, with the production of additional amounts of the desired light constituents before they' are vaporized in the still; but wherev intermediate constituents, heavier than desiredvrevaporizing in a cyclic manner these intermediate constituentswithout cracking with a resulting decrease in therate of cracking and the capacity of the pressure still.

In carrying out the present invention,

useless consumption of heat in revaporizing such intermediate constituents is avoided while' the heat of the vapors is nevertheless employed to advantage in fractionating the I vapors for the separation of apressure distillate of the desiredwcharacter. The heavier constituents of the vapors, susceptible to furly ther cracking in the pressure still, are refluXed to the pressure still from the first tower, and the intermediate constituents heavier than suitable as components of the desired distillate are separated from the vapors in the second tower. The condensate collecting in the second tower may be subjected to further cracking treatment, for example in a pressure still operated at a higher pressure or in vapor phase. cracking apparatus, or'it may be disposed of otherwise;

The oil introduced into the second tower may be an oil or distillate independent of the pressure still operation, or it may advantageously be a part of the final pressure distillate produced-in the operation ras the condensatepf the vapors escaping from the second tower. Vhe're an independent oil or distillate is employed it is in effect fractionally distilled in the second towerby the heat of the vapors, the vaporized .constituents escaping with the uncondensed pressure distillate vapors and the heavier unvaporized constituents collecting in admixture with the pressure distillate vapor constituents condensed by the cooling effect of the vaporization.

Where a part of the pressure distillate condensate is introduced, the introduced oil is more or less completely vaporized, only the heaviest constituents, 'if any,'remaining unvaporized, while the cooling effect of the vaporization ell'ects a sharp reluxing of the heavier constituents of the pressure distillate vapors, particularly of the constituents heavier than the vaporized constituents. A close fractionation between constituents suitable as components of the desired pressure distillate and the heavier constituents is thus effected.- Where a part of the pressure distillate is so employed, the oil introduced into the second tower contains no substantial amount of constituents heavier than the desired pressure distillate components and no heavier constituents can get into the pressure distillate from that source while the part of the pressure distillate returned is an effective refluXing agent. In this way, by regulating the amount of pressure distillate'introduced into the second tower, the character of the pressure distillate 9 as well as of the tower condensate can be closely controlled.

The inventian will be further described in connection with the accompanying drawings which show, in a 4somewhat diagrammatic and vconventional manner, an apparatus stapt-cd for the practice of the process of the rivention; but it is intended and will be understood that the invention is n'ot limited to the specific methods of operation described in connection with this particular apparatus.

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The accompanying drawings represent, in Y V elevation and partly in section, a pressure still system adapted for the practice of the process" of the invention. The pressure cracking still illustrated in the drawings is of the general construction and operation described and illustrated in United States Letters Patent No. 1,285,200 granted to the 'Sinclair Refining Company, November 19, 1918 on the application of Edward W. Isom. It will be apparent that theprocess of the invention may be carried'out in connection with pressure` cracking stills of other and different types.

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The pressure still illustrated comprises the bulk supply tank 1 located away. from the heating furnace, the vertically arranged heating tubes 2 located in the heating ilue of the furnace, and circulating pipes 3, 4 and 5 connecting successively the bulk supply tank, the

circulating pump 6, the lower end of the heating tubes, and the upper end-of the heating tubes and the bulk supply tank. A circulating pump may, with advantage, be employed for circulating the oil from the bulk supply tank through the heating tubes and back to the bulk supply tank; or the circulating pump may be omitted and thermosiphonic action relied upon for maintaining circulation but with decreased still capacity. Arranged above the bulk supply tank is the re- Hux tower 7 having a series of bailes therein and connected with the vapor dome of the bulk supply tank through the vapor line 8. 10 The pump 9 is arranged for introducing fresh charging stock into the upper end of the reflux tower through connections 10 and 11; and the return reflux line 12 is arranged for returning reflux and admixed fresh oil from 15. the lower end of the reflux tower to the circulating connection 3 on the suction side of P the circulating pump. A connection 13 is also provided for introducing Jfresh charging stock into the circulating oil through the bearings of the circulating pump. A connection 14 is arranged at the lower part of the circulating connect-ion for pumping out and charging the still, and a tar draw-off connection for use during the operation of the still is provided at 15.

The second tower 16 is arranged beside the reflux tower 7 and a vapor connection 17 is provided for conducting vapors from the upper end of the reflux tower to the lower of the second, or vfractionating, tower. The

vapors escape from the top of the second tower through the vapor line 18 to the condenser 19 which is arranged to discharge into the receiver 20. From the receiver, the con- 5densed pressure distillate is discharged through valved connection 21 and the uncondensed vapors and gases through the valved connection 22. From the receiver, the condensed distillate may be discharged into the pressure distillate tank 23, or through connection 24. ,The pump 25' is arranged for introducing a refluxing agent into the upper end of the fractionating tower through connecr tion 26. The refluxing agent so supplied may o be pressure distillate withdrawn from the tank 23 withdrawn through vco-nnection 27 or it may be supplied through a separate source from connection 28. A connection 30 is arranged for discharging the condensate mixture produced in the fractionating tower 16 from the lower end of the fractionating tower.

The pressure may be regulated and reduced by means of a regulating valve 29 interposed between the fractionating tower and the condenser, or the still pressure may be maintained through the condenser and the pressure regulated and controlled by a suitable eo valve or valves arranged beyond the condenser.

In carrying out the process of the invention in the apparatus illustrated, the pressure still is charged and brought to the cracking conditions of temperature and pressure in the usual way. As cracked vapors escape from the still additional charging stock is introduced through the reflux tower 7 and the charging stock and admixed relluxed constituents are returned to the still from the reflux tower. Tai' may be withdrawn as the operation proceeds, and the rate of tar withdrawal and the rate of supply of fresh charging stock may advantageously be regulated to maintain the concentration of pitch constituents in the charge below saturation. The vapors escaping from the reflux tower 7 enter the fractionating tower 16 where they are directly contacted with an oil refluxing agent introduced through connection 26. The suply of refluxing agent is regulated to control the character of the vapors escaping from the fractionating tower and to condense in the fractionating tower the vapor constituents heavier than those suitable as components of the desired pressure distillate. The condensed constituents of the yvapors and the unvaporized constituents of the refluxing agent are withdrawn through connection 30.

The vapors escaping from the fractionating tower are condensed in the condenser 19 and the condensate collected as the desired pressure distillate.

In cracking gas oil for the production of gasoline, for example, the still is initially charged with gas oil and additional gas oil charging stock is introduced through the reflux tower as the operation proceeds. The reflux returned to the still from the reflux tower includes any gas oil character constituents of the vapors and may also include heavier kerosene character constituents but 1S substantially free of gasoline constituents. The vapors, including the gasoline constituents, escape to the fractionating towerand a refluxing agent including gasoline constituents is introduced into direct contact with the vapors in the fractionating tower.

introduced into the fractionating tower are vaporized by the heat of the vapors from the reflux tower and the vaporization of these constituents cools the vapors in the fraction ating tower. The supply of refluxmg'agent is regulated to absorb suflicient heat, 1n vaporization of the lighter constituents thereof, to condense the vapor constituents heavier than gasoline without `condensing the gasoline components. The heavier constituents are thus condensed in the fractionating tower, and the gasoline constituents of the cracked vapors together with the gasoline constituents of the reliuxing agent escape and are condensed as the desired pressure distillate. A gasoline character pressure distillate is thus produced directly.

For the production of gasoline, the refluxing agent may, for example, be a part of the pressure distillate, or a naphtha character fraction including gasoline constituents and The gasoline constituents of the refluxing agent heavier components such as kerosene constituents, or a gasoline fraction such as a straight run gasoline to be blended with the pressure distillate may be employed as the reiuXing agent. Very close fractionation can be obtained by employing a part of the pressure distillate itself, the reintroduced pressure distillatebeing substantially completely revaporized in the fractionatlng tower, the heat absorbed by the vaporization being available therein to effect the desired fractional condensation. Where a naphtha character fraction is used, such as a crude pressure distillate as ordinarily produced in running for gasoline containin upwards of about 50% gasoline the napht a isl also fractionated in the fractionating tower, the heavier constituents of the naphtha collecting with the condensate in the tower and the gasoline con' stituents escaping with the gasoline constituents of the pressure still vapors. The operation of a pressure still in accordance with the present invention may thus be combined with advantage with other pressure still op ing the pressure distillate.

erations carried out in the usual manner, and the crude pressure distillate from one or more other pressure stills fractionated, or redistilled, in conjunction with the pressure still operation of the present invention. The amount of crude pressure distillate which can be so fractionated will depend upon the relative proportion of gasoline constituents in the crude pressure distillate as well as upon the concentration of asoline constituents in the vapors entering t e fractionating tower. A blending operation may also be advantageously combined with the process of the present invention and the gasoline, or gasoline fraction, for blending at, the same time utilized for fractionating the pressure dis-1 tillate vapors. In such a combined blending operation, any heavier constituents of the asoline for blending may also be eliminated rom the composite pressure distillate. It will thus be seen that the present invention enables the direct production of a pressure distillate substantially free from constituents heavier `than those suitableas components of the desired pressure distillate. The .v

elimination of such heavier constituents from the pressure distillate, or the increased concentration of the desired constituents in the pressure distillate, reduces the cost of refin- Redistillation may be avoided. The amount of pressure distillate that must be handled for each gallon of the desired product is also reduced. This in turn reduces thel amount of equipment, labor and chemicals required for subsequent chemical treatment, and also reduces the amount of equipment, labor and fuel required if the pressure distillateis redistilled. The improved fractionation effected 'also substantially eliminates from the pressure distillate any entrained heavier constituents of the charging stock introduced into theiirst tower on the still such as might carry with them objectionable impurities or otherwise inter- The" improved fractionation effected may also ac` fere with subsequent refiningoperations.

all constituents heavier than desired as com-r y ponents of the pressure distillate. The cooling of the pressure distillate vapors in the second tower also assistsv in reducing the amount of cooling water employed for condensing the pressure distillate.

Another important advantage of the present invention is that it does not require the use of bubble towers or other fractionating towers in which the iiow of vapors is materially restricted. One of the disadvantages of such fractionating towers when employed in conjunction with pressure stills is the possibility of development of excessive pressures because of the restriction lof vapor -flow and, moreover, if the conditions in the tower are disturbed a more or less prolonged period is required to bring the tower back to normal operation. In carrying out the present inven-tion, on` the other hand, the second tower. maygibe of ordinary baille construction prO- viding'a relatively large area for the free iiow of the vapors. The path through such a tower is also relatively short and the heat exchanging relations in the tower are comparatively simple and subject to' direct and immediate control. An'easil controlled and simple operation is thus provided while at the same time the direct introduction of part of the pressure distillate orof an oil containlng constituent suitable as components of the pressure distillate" enables close fraction of the pressure, distillate and the substantial elimination otheavier consituents therefrom. Where an ordinary baiie towerl is so employed, a wide range of roducts can also be produced without ehangmg the design of the tower regulating the amount and 'character of the reiuxing .medium introduced into the tower. y

It will also be-seen that the present invention provides an improved method of frac` tionating pressure distillate, which in eiect may be considered a redistillation `of the pressure distillate in .which the heat of the pressure distillate vapors is em loyed in a particularly advantageous way gdr carrying out the redstillation. In the direct producf be improved, heavier constituents of the vapors escaping from the pressure stillsusceptible to further cracking treatment therein being refluxed tothe still and part of the heat of the vapors being returned to the pressure still in thefresh charging stock for further application. to the cracking operation therein, and intermediate constituents which might cause an excessive consumption of heat in revaporization without useful cracking if returnedv directly to the still charge being separated from the pressure distillate vapors without being returned to the pressure still.

What is claimed as new and desired to be secured byl Letters Patent of the United States is:

'1.An improved method of cracking gas oil for the production of gasoline, which comprises heatmg a body of gas oil at the cracking temperature by circulating oil from theV body through heating tubes and back to the body and distillng off vapors generated ation in direct contact with an oil including constituents suitable as components of the desired pressure distillate, withdrawing an intermediate condensate including kerosene constituents from the fractionating operation whereby the boiling range of the condensates returned to the distillng operation is restricted, condensing the vapors escaping from the fractionating operation, and supplying part wofthe condensate so produced to the fractionating operation as the oil including pressure distillate constituents.

I aix my signature.

LOLA It. BELL,

Emea/,trim Qf tu'e Last Will ami Testamtefnt of JOLWE'. Bell, Deceased.

In testimony whereof thereby under pressure, subjecting the vapors from the distillng operation to a reluXing operationin direct contact with fresh gas oil charging stock, returning the reflux and admiXed gas oil constituents lto the distillng operation, subjecting the vapors from the reluxing operation to a fractionating operation in direct contact with an oil containing gasoline constituents, withdrawing an intermediate condensate including kerosene constituents from the fractionating operation whereby the boiling range of the condensatesreturned to the distillng operation is restricted, withdrawing the gasoline constituents from the fractionating operation as vapors and condensing them, and supplying part of the condensate so produced to the fractionating operation as the oil containing gasoline constituents.

2. An improved method of cracking heavier hydrocarbon oils for the production thereby'under pressure, subjecting the vapors from the distillng operation to a reiuxing operation, returning the reflux to the distilling operation, subjecting the vapors from the reiluxingkoperation to a fractionating oper-

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