US2111717A

US2111717A - Hydrocarbon conversion process

Info

Publication number: US2111717A
Application number: US162692A
Authority: US
Inventors: Young Rex
Original assignee: MAX G COHEN
Current assignee: MAX G COHEN
Priority date: 1937-09-07
Filing date: 1937-09-07
Publication date: 1938-03-22
Anticipated expiration: 1955-03-22

Description

' March 22, -l938. R. YOUNG mnnnocmuaon CONVERSION PROCESS Filed Sept. 7,- 1957 2 Sheets-Shegt 1 oNH l-llll INVENTOR v 165x Ka /v6 7 1 ATTORNEY March 22,1938. yQUNG 2,111,717

' HYDROCARBQN CONVERSION PROCESS- Filed Se t. 7, 1957 2 Sheets-Sheet 2 u msfi OIL- 4 \36 28 LIQUID P-HA 5E PRODUCTS 'INVENTQR Fax Ydu/V y ATTORNEY HEAVY .LIQUID' roamed Mars. 22, was

NlTED STAT i HYDROCARBON CONVERSIQN PRQC'ESQ Rex Young, Grandfleld, Okla, assigi'nor to Max G.

Cohen, Tulsa, Okla.

Application september 1,1937, Serial No. 162,692

7 Claims.

This invention is directed particularly to improvements in the so called liquid-phase crack-- ing" process for converting relatively high boiling petroleum hydrocarbons to lower boiling hydrocarbons largely in the gasoline boiling range. In the conventional liquid phase cracking process, highboiling hydrocarbons are first heated to a decomposing temperature in a heating step and are then maintained at such decomposing temperature for a period of time sufilcient to effect substantial decomposition of the hydrocarbons.

During the heating and reaction periods, the hy-,

drocarbons are maintained under pressure sufficiently high to prevent substantial vaporization of the products during these periods. Thereafter, the pressure on the products is reduced to permit vaporization and separation of lighter products from heavy carbonaceous products, and the vaporized lighter products are then fractionated to separate same into desired fractions, while the 9.; heavier carbonaceous products are removed from the system. a

A well known process of this type is the Dubbs cracking process, wherein petroleum oil to be cracked is heated in a tubular cracking still to a cracking temperature and the heated oil is then transferred to an enlarged reaction zone, generally unheated, wherein the heated oil is retained en masse at the cracking temperatures and for a period of time sufficient to effect further cracking 5 of the charge. A relatively. high pressure is maintained on the oil in the tubes and in the reaction zone in order to prevent substantial vaporization of any of the products. At the completion ofthe reaction period the products are transferred into the lower portion of a separating chamber where the temperature.

and the pressure are sharply reduced to halt the reaction to thereby prevent excessive over-decomposition of the products. The reduction inspres- 3 sures inthe separating chambers in conjunction 'jwith heat retained in the products, results in vaporization of the lighter products of the cracking reaction and the separation thereof from unvaporized and condensed heavy products containing undesirable carbonaceous matter, which are withdrawn inliquid state'from the lower portion of the chamber, the vaporized products being separately withdrawn from the upper portion of the chamber.

The major problems encountered in a cracking process of the type described are those of carbon or coke formation and deposit in the separating chamber 'and of the complete removal of particles of free carbon or highly carbonaceous constituents from the vaporized products removed from the separating chamber. Since these vaporized products include unconverted charge and intermediate boiling range products both of which are desirable for re-cycling in the process, the presence of highly carbonaceous materials therein proves very detrimental to the cycling process, in that such materials decompose to free carbon in the heating tubes and other parts of the apparatus, resulting in frequent shut-downs of the apparatus and other detrimental results well understood in the art. e.

Heretofore in the conventional process above described, these problems have been solved more 'or less successfully by sharply reducing the pressure on the products entering the separating chamber to allow rapid vaporization and separation of the lighter products from heavier products and the rapid escape of these products from the separating chamber, thereby reducing to a minimum the period of time during which these vaporsare subjected to the relatively high temperatures in the separating chamber and thereby reducing the danger of erccessive decomposition of the products At the same time the temperature of the products also is sharply reduced and the cracking reaction halted by in reducing relatively cool oil into intimate contact th the products in the separating chamber.

The chief disadvantage in the type above described, is that in order to prevent carcracking reaction must be halted sharply and in accomplishing this in the manner described, the cracking reaction is halted of necessity before completion, thereby reducing the possible yield per pass of-light products from the original charge. On the other hand, while the tempera of operation bon formation in the separating chamber, the

ture must be reduced in the separating chamber to a point at which the cracking reaction will be halted or greatly reduced, nevertheless, in order to .compensate for the loss in yield per pass, it

becomes necessary to recover from the products as much as possible of the clean relatively high 1 boiling products suitable for re-cycling to the cracking step. This requires that a temperature be maintained in the separating chamber which will be sufliciently high to vaporize the maximum amount of these relatively high boiling products and separate them from the highly carbonaceousproducts. Such a temperature, however, is'stiil CPI within the range in which over decomposition of the cracked products and coke formation would occur if the products are'permitted to remain at such temperature for even a short period of time, and in spite of the precautions taken heretofore, some carbon formation and deposit still occurs in the separating chamber with detrimental results to the operation of the process.

It is a principal object of this invention to provide an improved method of operating the sepa ration step of processes of the type heretofore used as above described, whereby, separation of light products from heavy products may be effectively accomplished at temperatures andpressure such that increased yields of light products of higher anti-knock value may be obtained, through-put capacity increased, and such carbon or coke as may be formed may be effectively removed from the separating zone and from the vaporized products, thereby lengthening the period of time during which the cracking apparatus may be kept in continuous operation.

Generally speaking, the process of this inven tion comprises introducing the hot mixture of products from a liquid phase decomposition process into the upper portion of an enlarged separating chamber into substantially uniformly distributed wall-washing relationship with the walls of the chamber, whereby, the products will continuously wash down the walls of the chamber and remove carbon deposits which tend to form thereon.

By continuously washing the walls of the separating chamber in this manner, it is found that temperatures and pressures may be maintained in the chamber which are higher than those hitherto considered practical and are sufficiently high to effect additional cracking of the heavier constituents of the charge.

The washing of the separating chamber walls is supplemented by introducing a relatively cool oil above the point of entry of the liquid phase products and distributing the relatively cool oil in a substantially uniform manner over the transverse area of the chamber and into contact with the walls of the chamber. In this way the portion of the chamber Walls above that washed by the liquid phase products will also be washed to prevent adherence thereto of carbonaceous matter. At the same time the oil will act as a liquid screen or baifle through which the vapor products are forced to pass when being withdrawn from the chamber, resulting in scrubbing of the vapors with removal of carbonaceous particles suspended therein.

Other objects and advantages of my new process will become apparent from the following description when read in conjunction with the accompanying drawings which illustrate diagrammatically a form of apparatus suitable for practicing the improved process of this invention.

In the drawings:

Fig. 1 illustrates the flow of the process of the present invention.

Fig. 2 is a detail. of the separating chamber utilized in this invention.

Referring to the drawings, relatively heavy hydrocarbon oil, such as crude oil, gas oil, topped crude' or other relatively heavy charging stock to be thermally decomposed into lighter hydrocarbons such as gasoline, is introduced through a pipe I and a valve 2 into a conventional fractionator 3, wherein the charge is partially heated by heat exchange with hot vapors, produced in the process. The heated charge is withdrawn from the lower portion of fractionator 3 through a pipe 4 by a pump 5 which discharges the heated charge through pipe 6 and thence through a heating coil I mounted in a furnace 8 wherein sufficient heat is imparted to the charge traversing coil I to heat the charge to a suitable decomposition temperature. The charge is then discharged from coil 1 through a pipe 9, in which is mounted a pressure release valve In, into the upper portion of a conventional reaction chamber I I. By suitable manipulation of valve I0 sufficient pressure is maintained in coil Ito retain the charge in the liquid phase while it is in coil I.

Reaction chamber II is of sufficient capacityto retain the heated charge therein at a decomposing temperature for a period of time sufficient to permit the decomposition reaction to proceed to the desired point, whereupon the reaction products are discharged from the lower portion of reaction chamber I I through a pipe I2, in which is mounted a pressure release valve I3, into the upper portion of a separating chamber I4. By suitable manipulation of valve I 3, pressure, sufficient to keep the reaction products in the liquid phase, is maintained in reaction chamber II.

The products of the liquid phase decomposition are then separated in separating chamber I4 into vapor and liquid products in a manner to be more fully described hereinafter. The liquid products thus separated, collect in the lowermost portion of J separating chamber I4 and are withdrawn as rapidly as they collect through a pipe I5 and a valve I6, and thence through a cooler I! wherein these liquid products are cooled to a suitable storage temperature and discharged through a pipe :1

I8 to storage, not shown.

The vapor products separated in separating chamber I4, are withdrawn from the upper portion thereof through a pipe I9, in which is mounted a pressure release valve 20, into fractionator 3, wherein the vapor products are fractionated to produce a vapor product, generally of the gasoline boiling range, which is discharged from the upper portion of fractionator 3 through a pipe 2| and a valve 22 to conventional condensing and storage equipment, not shown.

By manipulation of valve 20, pressure is maintained in separating chamber l4 which is somewhat lower than that maintained in reaction chamber I I. ing chamber I4 is maintained sufiiciently high to prevent immediate discharge of the vapor products from chamber I4 and thus provide an additional period of time during which the product may undergo further decomposition in chamber I4, at the temperature which is maintained therein in a manner to be described in greater detail hereinafter.

In fractionator 3 the vapor products supply heat to the incoming charging stock as previously described, and will also strip lighter fractions therefrom, and those lighter fractions are then fractionated together with the vapor products. Those fractions in the gasoline boiling range will be discharged with the corresponding fractions of the vapor products from the upper portion of fractionator 3 through pipe 2|. The heavier fractions of the charge together with those fractions of the products which are suitable for recycling to the process will be removed from the lower portion of fractionator 3 through pipe 4, and sent to the heating coil and reaction chamber. also as previously described.

An intermediate boiling range fraction, such However, the pressure in separat- I as light gas oil or distillate, will be withdrawn where this fraction will be'cooled to a comparatively low temperature and will then be pumped by means of a pump 25 through a pipe 23 thence through a nozzle 21 intov the upper portion of .separating chamber i4 and discharged therein at a point above the point of entry into chamber it of the liquid phase products. Nozzle 21 is equipped with a valve 23 by means of which the quantity oi. cool oil introduced into chamber it may be regulated to control the temperature of the products within the chamber.

The foregoing description is that of a more or less conventional liquid phase decomposition process, with the exception of that portion of the process involving the method of operation of separating chamber M, which will now be described with reference particularly to Fig. 2 of the drawings. v

' In the above process, the charging stock is heated in passage through coil 1 to a temperature of approximately 910 F., under a pressure of approximately 500 pounds per square inch gage, and is then retained in reaction chamber ii at approximately the same temperature and under a pressure of approximately 250 pounds per square inch gage, and for a time suflicient to allow the decomposition reactions to proceed to the desired point. The pressure maintained in reaction chamber ii is sufliciently'high to prevent substantial vaporizationof any of the products.

At the completion of the reaction period, the highly heated products are discharged from reaction chamber il through pipe l2 into the upper 'portion of separating chamber i4. The prodbets are introduced into chamber I4 through a nozzle 23 the discharge end of which is centrally located withinchamber i4 at a point well above the axial mid-point ofthe chamber. The discharge end of nozzle 23 is fitted with an annular horizontally arranged flange 33 to which is attached a registering plate 3 I, which is spaced vertically from flange 33, thereby providing a narrow annular orifice 32 between the flanges. The highly heated reaction products are discharged through orifice 32 under the relatively high pressure of chamber II and due to the shape of the orifice, enter chamber i4 in the form of a thin radially extending sheet of mixed liquid and vapor, which, under the existing pressure, is forced into contact with the walls of chamber M in a substantially uniformly distributed manner. The

pressure in chamber i4 is reducedbelow that in chamber ii, and in the above example will be approximately 125 pounds per square inch gage.

, As a result of this reduction in pressure, the lightiii er constituents of the entering products will vaporize and separate from the heavier constituents as the mixture is injected into chamber id and flows down the walls thereof. The unvaporized products will flow down the walls of the chamber, and because of their uniform distribution thereon, will provide a liquid film, indicated by the numeral 33, over the portion of the walls of the chamber belowthe level at which the entering sheet of products impinges on the walls. The liquid film 33, in flowing down the walls of the chamber, will continuously flush from the walls any carbonaceous matter which-would ordinarily tend to deposit thereon. The down flowing liquid products will collect in the lower portion of chamber i4 and will be substantially immediately withdrawn therefrom through pipe l3 and valve i3 in order that such liquid products, which are path of highly carbonaceous, will not be subjected for any substantial period of time to the temperature conditions maintained in chamber M. \I

As a result of the partial vaporization of the heated products, the temperature of the products will be reduced but not sufliciently to prevent further decomposition of the heavier constituents of the vaporized products. Ordinarily under these conditions, the additional decomposition would result in the formation of carbonaceous matter which would deposit in the upper portion of chamber 14 above the level of entering liquid sheet. To prevent this and to control the temperature of the products in chamber i4, the rela* tively cool liquid hydrocarbons withdrawn from fractionator 3 through pipe 23, will be introduced into chamber i4 through pipe 23, which connects with valve 23 and nozzle 21 which extends axially into chamber i4 to a point above the liquid sheet introduced into the chamber through orifice 32.

The discharge end of nozzle 21 is equipped with a horizontally arranged annular flange 33 below which is a registering plate 31 which is fix edly attached to a stem 33, which extends axially through nozzle 21 and valve 23 to the exterior of the chamber. A lever 33 is operatively connected to the outer end of stem 33 and extends at an angle thereto and is pivotally supported on a brace 43 mounted on valve 23. A weight 4i is suspended on lever 33 and is adjustable laterally thereon. By shifting the position of weight 4i on lever 33, the position of plate 31 may be adjusted with respect to flange 33 to provide an annular orifice 42 between plate 31 and flange 33.

The relatively cool hydrocarbon liquid will then be injected under pressure of pump 23 into the upper portion of chamber i4 through orifice 42 in the form of a thin radially extending sheet of liquid and will form a liquid baiiie through which the vapor products must pass in flowing to pipe i3 for exit from the chamber. Sufficient pressure is applied to the cool liquid to cause the sheet thereof discharged from orifice 42 to impinge on the walls of chamber i4, above the level at which the liquid phase'decomposition products impinge thereon, and. will thus provide a wall-washing film of oil for that portion of the chamber walls above the point at which the flim 33 begins. The volume of cool oil introduced into.chamber l4 in this manner will be regulated to control the temperature within chamber M. In the process described, the temperature thus maintained in chamber it will be 825 E.

By the described method of conducting the separation of the liquid phase products, a higher temperature of separation maybe maintained than was heretofore considered practical for this type of process, thus permitting vaporization of a larger proportion of the liquid phase products.

Similarly, higher pressures may be maintained in chamber it and the combination of higher temperature and pressure to which the vaporized products are subjected produces additional decomposition of these products, under vapor phase decomposition conditions, and results, in an increased yield per pass of light products from the original charge and the light products so produced will have a relatively high anti-knock value. 'At the same time the washing of the walls of chamber 4 by liquid materials will keep the walls free oi carbon deposits. By interposing the liquid screen of relatively cool oil in the withdrawal of the vapors, further decomposition oi the vapors is halted and the vapors are scrubbed clean of any entrained heavy carbonaceous matter, so that when later condensed in fractionator 3, the products will be free of such materials which would otherwise be detrimental to the continuation of the process.

It is found most advantageous to introduce the liquid phase products into separating chamber M at a point well above the midpoint of the chambor. For example, in the case of a conventional chamber 40 feet in length, the liquid phase products will be introduced approximately '7 feet from the top or about two thirds'of the distance above the midpoint of the chamber. The cool wash liquid is introduced at a point about 4 feet above' the point of discharge of the liquid phase products into the chamber. Both of these distances may be varied somewhat, but in any case, it is desirable that there be as much free area as possible below the point of entry of the liquid phase products to enable the separated vapors to drop any entrained liquid particles, and that the cool oil screen be interposed above the screen of liquid phase products and in the path of the vapors rising above the latter.

The various temperature and pressure conditions given above. are merely exemplary and in practice will be varied depending largely upon the nature of the charging stock to 'be treated.

By the described method of operation, it has been found that temperatures from 75f to 100 F. higher than in the conventional operation can be successfully maintained in the separating chamber and that the pressure therein can likewise be maintained from 75 to 100 pounds per square inch greater than heretofore found practical. Theseincreased temperatures and pressures may be utilized with the advantages cited heretofore without producing deleterious carbonaceous deposits in the apparatus.

The increased yield per pass of light products obtained as a result of the described operation, provides a substantial increase in the daily through-put capacity of the apparatus.

In an operation conducted at the temperatures and pressures cited in the foregoing detailed description, the yield of gasoline from a Mid- Continent topped crude oil, has been increased as much as two per cent, and the gasoline so produced has an octane value from one to two points higher than the gasoline produced in conventional processes. At the same time the through-put capacity of the apparatus was increased about ten per cent.

It will be understood that numerous modifications and alterations may be made in the details of this process without departing from the scope of the invention as set forth in the appended claims.

What I claim and desire to secure by Letters Patent is:

1. In the process for the thermal decomposition of hydrocarbons which comprises effecting decomposition of hydrocarbons under liquid phase conditions of temperature and pressure and thereafter separating the products of the decomposition into vapor products and-liquid products, the improvements which comprise, introducing the heated liquid phase products into the upper portion of an elongated separating zone of enlarged cross sectional area, discharging said products into substantially uniformly distributed wall-washing relationship with the inner walls of said zone, therein separating said products into vapor products and liquid products, withdrawing said liquid products from the lower portion of said zone as rapidly as they collect therein, retaining said vapor products in said zone at a temperature and for a time sufiicient to effect additional decomposition of said vapor products, withdrawing said vapor products from the upper portion of said zone, interposing a screen of relatively cool liquid in the path of withdrawal of said vapor products and into wall-washing relationship with the walls of said zone above the point of discharge therein of said liquid phase products.

2. The process of thermally decomposing hydrocarbons which comprises, subjecting hydrocarbons to liquid phase decomposition conditions of temperature and pressure, introducing the heated products of said decomposition into an enlarged separating zone, utilizing said liquid phase products to wash the major portion of the inner walls of said zone, while separating vapor products from liquid products, withdrawing said liquid products from the lower portion of said zone as rapidly as they collect therein, subjecting said products while in said zone to further thermal decomposition, withdrawing said vapor products from the upper portion of said zone, interposing a screen of relatively cool hydrocarbon liquid in the path of withdrawal of said vapor products and utilizing said screen of liquid to wash that portion of the inner walls of said zone which is not washed by said liquid phase products.

3. In the process for the thermal decomposition of hydrocarbons which comprises heating hydrocarbons to a decomposing temperature under a relatively high pressure while maintaining said hydrocarbons in liquid condition and thereafter separating the products of decomposition into vapor and liquid products, the improvements which comprise introducing the heated products I into an enlarged separating zone at a point above the mid-point thereof, causing said heated products to be distributed substantially uniformly about the transverse area'of said zone and into contact with the inner walls thereof to thereby permit rapid separation of vapors from liquid and to cause said liquid to wash said walls, withdrawing said liquid from the lower portion of said zone and said vapors from the upper portion thereof, and interposing a screen of liquid in the path of said vapors above the point of entry of said products, into said zone, said screen of liquid being distributed substantially uniformly throughout the transverse area of said zone and into contact with the walls thereof.

4. The process of thermally decomposing hydrocarbons which comprises, subjecting said hydrocarbons to liquid phase decomposition conditions of temperature and pressure, introducing the products of the liquid phase decomposition including liquid and vapor constituents into an enlarged zone at an intermediate point along the vertical axis thereof, introducing said products into said zone in a manner adapted to cause the liquid constituents of said products to continuously wash the inner walls of said zone downwardly from said intermediate point while permitting the vapor constituents to separate from said liquid constituents, withdrawing said liquid constituents from the lower portion of said zone as rapidly as they collect therein, retaining said vapor constituents'in said zone at a temperature and for a time sufficient to effect substantial additional decomposition of said vapor constituents, thereafter withdrawing said vapor constituents from the upper portionof said zone, and interposing a substantially uniformly distributed termediate point and the point of withdrawal of said vapor constituents from said zone, said screen of liquid being adapted to wash the portion of the inner walls of said zone above said intermediate point.

5. Theprocess of thermally decomposing hydrocarbons which comprises; heating hydrocarbons to a decomposing temperature under pres sure while flowing in a restricted stream through a" heating zone, thence discharging the heated hydrocarbons into an enlarged vertical reaction zone maintained under decomposition conditions of temperature and pressure, withdrawing the resulting vapor and liquid products from said reaction zone and discharging same into the upper portion of an enlarged vertical separating zone and into substantially uniformly distributed wallwashing relationship with the inner walls thereof, therein separating said products into vapor products and liquid products, withdrawing said liquid products from the lower portion of said separating zone, withdrawing said vapor prod ucts from the upper portion of said separating zone, and interposing a screen of a wash liquid in the path of withdrawal of said vapor products and into wall-washing relationship with the inner walls of said separating zone above the point of discharge therein of said vapor and liquid products,

*6, The process of thermally decomposing hydrocarbons which comprises; heating hydrocarbons to a decomposing'temperature under pressure while flowing in a restricted stream through a heating zone, thence discharging the heated hydrocarbons into an enlarged vertical-reaction zone maintained under decomposition conditions of temperature and pressure, withdrawing the resulting vapor and liquid products from said reaction zone and discharging same into the upper portion of an enlarged verticalseparating zone and into substantially uniformly distributed wall-washing relationship with the inner walls thereof, therein separating said products into vapor products and liquid products, withdrawing said liquid products from the lower portion of said separating zone, withdrawing said vapor products from the upper portion of said separating zone, interposing a screen of wash liquid in the path of withdrawal of said vapor products and into wall-washing relationship with the inner walls of said separating zone above the point of discharge therein of said vapor and liquid products, and subjecting the products in said separating zone to a decomposing temperature and an elevated pressure which is substantially above atmospheric pressure but below that maintained in said reaction zone.

'I. A process as defined in claim 6 wherein the products in said separating zone are maintained at a temperature of about 825 F. under a pressure of about 125 pounds per square inch gage.

- REX YOUNG.