US2921019A - Conversion of hydrocarbons - Google Patents

Description

United States Patent 2,921,019 :CONVERSION OF HYDROCARBONS JamesA. Hart, Munster,"Ind., assignor to Socony Mobil O1l'Company,Inc., New York, N.Y., a corporation of New York 1 Application March 29,1956, Serial No. 574,-660

3 Claims. (Cl. 208-169) This invention relates to a method and apparatus'for the conversion of hydrocarbons in thepresencebf a moving particle-form catalytic contact mass. More particularly, the present invention isjdirected to a-method whereby separate degrees of severity may he applied to portions of the hydrocarbon charge stock having different boiling points, and whereby said degrees 'of severity may be varied in response to seasonal demands for the products formed, while treating all of the charging stock in the same column of contact mass for purposes and advantages-which will hereinafter be explained.

A well known method of hydrocarbon conversion, contacts a continuous moving, stream of mixed phase hydrocarbons heated to conversion-temperature with a continuously -moving-stream of catalyst. In this method, the reaction is carried out in a vessel throughwhich the catalytic contact mass'descends as a moving bed or substantially compact column. The hydrocarbons to be reacted are passed into this vessel at reaction temperature, and spent catalyst material is discharged from the bottom-of the reactor and is reactivated by treating with air in a separate regeneration chamber.

In the usual operation of this process during the summer months, it is desirable to make as much gasoline as possible. The process described provides-adequate flexibility with regardto temperature control, space velocity, and catalyst to oil ratio control, to perfect attainment of the desired high gasoline yields. A desirable balance is to recover from about 40 to 43 percent of the charge as gasoline and from about 20 to 25 percent No. 2 fuel oil. In winter months, however, it often becomes desirable to decrease gasoline yields and increase the yield of No. 2 fueloil. The attainment of low gasoline yields and high yields (as much as 35 percent) of No. 2 fuel oil will present no problem when operating on 100 .percent vaporized feed stock.

The terms gasoline and No. 2 fuel oil have the common meaning of the prior art when employed herein, gasoline being a product distilling, for example, with percent overhead at about 150 F. and 90 percent overhead at 390 F., while No. 2 fuel oil, for example, might have 1-0 percent overhead at 430 F. and 90 percent overhead at 590 F. I

It has been found that when the process described above is carried out with a mixed feed, for example, part vapor and part liquid feed, the required flexibility is not available. Under these conditions a large amount of coke is produced due to liquid feed, and this requires high catalyst circulation rates (i.e., high catalyst to oil ratio) which in turn tends to promote high gasoline yield. High gasoline yields are also promoted by charging 100 percent virgin crude oil tothe unit without any recycling as is sometimes required in normal refinery operations.

When operating with liquid feeds, it is necessary to maintain thev reactortemperature quite high in order to prevent loss of excess amounts of liquid hydrocarbons with thespen't catalyst leaving the bottom of the 2 reactor. These high temperatures, of course, also promote high gasoline yields.

Because of the abovefa'ctorscausing high gasoline production, as explained above, the lowratio of gasoline to No. 2 fuel oil-dictated by market demand cannot be obtained during the winter months from the catalytic cracking unit which employs both liquid and vapor feed. This is true even when the reactionbed height'is reduced to the lowest levelnormally provided in commercial design. It is possible to 1 provide suiiicient storage facilities to carry over fuel oil made -in -'the summer into the winter and'thereby' balance the total yearly demand. However, such facilities are expensive and fuel oilstored for such long'aperiods frequently deteriorates.

This invention enables the refinery to maintain the production of gasoline and fuel oil in the same ratio as the market demand for them during all seasons of the year.

A major object of this invention isthe'provision in a system for the conversion of both liquid and vapor phase hydrocarbons, of animproved'method and apparatus for introducing --hydrocarbons and contact material to the conversion zonewhich avoids the diificulties hereinabove described.

A specific object is the provision-of a method and apparatus permitting flexible control of the gasoline and fuel oil outputs of catalytic cracking operation in response to'seasonal'demands when converting high boiling liquid "and vapor phase hydrocarbon charges in a continuous 'cy'clic :process to lower boiling hydrocarbon products.

Those and other objects of this 'invention are accornplished by supplying liquid feed to the upper portion of the reactor 'in the conventional manner. Vapor 'feed is supplied tothe -reactor at a level which-is chosen to give the ratio of gasoline to No. 2 fuel oil production dictated byexisting market requirements. The level of vapor feed supply is varied in response 'to seasonal demand, 'being raised to increase the ratio and lowered to decrease it. i

The method of operation with which this invention is concerned may be understood mostreadily by reference to the drawing attached hereto, in which Figure d is an elevationa-l view, partlyin section, show ing a modified-form of my invention, and

Figure 2 is an elevational view, partially in section, showing a preferred form of the invention.

Turning now to Figure l, we find a diagrammatic flow sketch of a hydrocarbon conversion process. In Figure 1, there is shown a converter 17, a supply hopper 18 located thereabove to which is transferred hot contact material particles from the regenerator. Extending across the upper section of vessel 17 is a partition 21 which serves to provide a seal chamber 22 in the upper end of vessel 17 and a conversion chamber 23 therebelow. -A plurality of spaced conduits 24, depend from partition 21 to a level therebelow in the conversion chamber 23. It will be noted that the conduits 24 serve as passages for solidflow from seal chamber '22 to the surface 25 of the contact material column within the conversion chamber and that the conduits extend only through that portion of the horizontal cross-sectional area of the upper portion of the chamber which is near the outer periphery of said chamber. Another conduit 26 extends downwardly from a central portion of partition 21 to a level in the upper section of gas space 27 in the conversion chamber. A flow throttling device is provided below the lowerend of the conduit 26.

The flow throttling device broadly consists of a plate 28 having a hole 29 therein and a receiving funnel 30 positioned around they hole and a slide plate 31 there- Patented Jan. 12, 1960 flow toward the center of the chamber.

below which may be adjusted so that a hole 33 therein coincides partially or entirely with the hole 29 in plate 28 or so as to entirely block the flow through hole 29. A rod 34 is connected to the slide plate 31 and passes through stufiing box 35 on the vesselshell to permit adjustment of the throttling device from a. point outside the vessel '17. The throttling device is supported by means of angle irons 36 and 37 which extend across the chamber in a direction perpendicular to the face of the drawing. Also supported by the angle irons 36 and 37 is a skirt 38, which is open on either end and positioned centrally with its axis vertical within the vessel 17. The skirt 38 tapers inwardly slightly so as to direct solid A conical shaped baffle 39 is supported by rods 40 substantially centrally within the skirt 38 and below the flow throttling device. The diameter of the base of the baffle 39 is less than that of the skirt 38 so as to provide an annular space for solid flow therebetween.

' A liquid spray device 41 is positioned substantially centrally of the vessel cross-sectional area adjacent the.

lower end of skirt 38. Liquid hydrocarbon charge is supplied to the spray device 41 through pipe 42. Gableroofed vapor feed pipes '14, 15 and 16 are provided at a lower level in conversion chamber 23 and are manifolded into the vapor inlet pipe 13. In addition, a vapor feed pipe 70 extends from the same manifold into reactor 17 at a-level above the lower ends of pipes 24. A catalyst material gravity feed leg 45 extends between hopper 18 and seal chamber 22 and a conduit 46 connects into seal chamber 22 for introduction of an inert gas thereinto. A second gravity feed leg descends from hopper 18 and delivers catalyst particles to intermediate levels of the conversion chamber 23, through branch pipes 11 and 12.

In the lower section of the vessel 17 there is provided a gable-roofed gas collecting trough 48. Adjacent troughs are'connected by means of nipples 50 and outlet pipe 51 connects into the-end trough. Below the levels of the collector troughs are provided three spaced partitions 54, 55 and 56. A plurality of uniformly distributed circular rows of nipples 57 depend from the uppermost partition 54 and a lesser number of rows of nipples 58 depend from the next lower partition 55. The nipples 58 are horizontally staggered proportionately be tween the nipples 57 thereabove. A circular row of holes 59 are provided in the lowermost partition 56, the row of holes being horizontally staggered with respect to the rows of nipples 58 thereabove. An outlet conduit 60 hearing flow control valve 61 is provided on the lower end of the vessel 17. a v

In operation, catalyst material particles are supplied from hopper 18 through leg 45 into the seal chamber 22. The contact material passes from the seal chamber 22, through'conduits 24, directly onto the surface of the column of contact material within the conversion chamber 23. The temperature of the contact'material so supplied to the conversion chamber should be suitable for supporting the intended hvdrocarbon conversion. The liquid phase of the hydrocarbon charge .is sprayed into the gas space 27 from spray device '41." A typical liquid hydrocarbon charge boils within the range about 800 F. to 1000 F. and is heated to, for example, 790 F. before introduction into the reactor 17.

The spray of liquid hydrocarbons is limited to the central portion of the vessel cross-sectional area. On the other hand, the conduits 24 through which the hot catalyst material charge enters the upper section of the convertor are positioned only along the outer periphery of the chamber instead of being uniformly spaced throughout the cross-sectional area of the chamber. In this manner, contact between liquid charge and hot 'metal surfaces in the gas space 27 'is limited so as to avoid the tendency for coke formation on such surfaces. It has H 5,521,019 1" H 'f," i f A been found that the tendency for such coke formation may be still further avoided and the distribution of the liquid charge on the contact material may be greatly improved by also introducing contact material into the upper section of gas space 27 through conduit 26 at a rate controlled by the slide valve therebelow.

The contact material passing from the conduit 26 which is horizontally centrally positioned falls onto the conical shaped baflle 39 and falls therefrom between the annular space between baflie 39 and skirt 38 as a shower of freely falling particles, which shower is restricted by means of the baffling substantially to only a central portion of the gas space 27 until the particles reach the surface 25 of the contact material column therebelow. Liquid hydrocarbon charge from spray device 41 is sprayed into that central portion of the gas space 27 within which said shower of particles is maintained so that the liquid hydrocarbon charge is uniformly deposited upon the showering contact material particles and prevented from reaching the hot metal surfaces adjacent the outer periphery of space 27. The contact material particles from the shower soon uniformly distribute themselves across the entire column cross-sectional area so as to provide uniform contacting of the liquid hydrocarbons with all the contact material.

The vapor feed is introduced into the reactor either at the upper end of the bed through passage 70 or below the bed surface at any one of several selected levels through feed pipes 14, 15 or 16. In this manner, the liquid feed which has a long residence time in the convertor is heavily cracked, while the degree to which the vapor feed, which constitutes the greatest portion of the total charge, is cracked, can be varied by selective choice among passages 14, 15, 16 and 70. A typical vapor feed boils within the range 600 F. to 850 F. and is heated above its end boiling point before introduction.

Only a portion of the fresh hot catalyst from hopper '18 is supplied to the upper section of the converter through feed leg 45 and conduits 24. The remainder of the catalyst is bypassed through feed leg 10 and branch pipes 11 and 12 to injection points in the lower section of convertor 23 above the vapor feed outlet or at least above the catalyst purge section. This method of operation reduces overcracking of the liquid feed in the upper portion of the catalyst bed by decreasing the catalyst to oil ratio through the conversion portion of the reactor. Introduction of hot fresh catalyst near the reactor outlet also accomplishes good purging of the spent catalyst. The contact material and liquid hydrocarbons pass downwardly through the conversion zone and the liquidhydrocarbons are converted to gaseous hydrocarbon'products. It will be understood that the term gaseous as used herein in describing and in claiming this invention is used in a broad sense as meaning material in the gaseous phase under existing operating conditions, regardless of the normal phase of that material under ordinary atmospheric conditions.

Gaseous conversion products are separately withdrawn from the lower section of the conversion zone through collector troughs 48 and pipe 51; Used contact material flows downwardly through the partition arrangement 57, 58 and 59 in the lower end of vessel 17 and is withdrawn through outlet conduit 60 at a rate controlled by valve 61. The partition arrangement 57, 58 and 59 is such as will insure uniform withdrawal of contact material from all portions of the chamber cross-sectional area in the conversion zone thereabove. It will benoted that the rate of contact material withdrawal through conduit 60 is equal to the sum of the rate of contact material introduction through conduit 26 and through conduits 24, 11 and 12. Usually, it is preferable to introduce the major portion of the contact material charge through the conduits 11 and 12, since a large proportion of the material charged to th? reactor is vapor feed and enters through conduit 13. For-example, the liquid feed may amountto only 1500 to2500 barrels :per day, whereas the vapor feed can amount to about 10,000-t'o 13,000 barrels per day.

Insuch an operation, it is important to maintain the levelqof the-surface ofthe column of contact material substantially constant within the conversion zone. This is automatically accomplished in the operation described hereinbelow, sincethe contact material flow inpipes 24 is automatically throttled only by the column surface level. Thus, only as much contact material passes through conduits 24 as is required to maintain the column surface level substantially at 25, as shown. In order to prevent escapeof hydrocarbon vapors from :the conversion zone into seal chamber 22, .an inert seal gas, a

such as steam or flue gas, may be introduced through conduit 46 into the seal chamber 22 at a rate so .controlled as to maintain an inert gaseous atmosphere in zone 22 at a .pressure slightly higher '(for example M1- /2 lb. per square inch) than the pressure in gas space '27. An inert purge gas such as steam or flue 'gas may be introduced through conduit 67 below partition 54 to strip hydrocarbons from the outflowing contact material. Spent or used contact material passes via conduit 60 to the regenerator.

It should be understood that the invention is not considered to be limited to the specific apparatus construction described hereinabove. Reaction vessels "having cross-sectional shapes other than circular, as shown, may be employed. In such cases the shape of skirt 38 and bafiie39 shouldbe modified accordingly. Moreover, the other bafile systems than the skirt and cone system described hereinabove are contemplated, for example, systems in which liquid charge is injected directly into the upper section of thereaction bed. Also, several inlet jets may be spaced uniformly at a given single level within the lower section of curtain 38 to replace the single jet 41, and the distribution system for introducing the vapor feed and fresh catalyst to the intermediate section of the reactor may be modified.

Moreover, other suitable apparatus adapted for separate withdrawal of gaseous conversion products and other suitable apparatus adapted to control uniform withdrawal of solid material from all sections of the vessel crosssectional area may be substituted for the apparatus specifically shown in Figure 1. I p

A preferred form of my invention may be seen in Figure 2, wherein identical numerals. identify structural features similar to those illustrated in Figure 1. In this arrangement there is no introduction of catalyst directly into the intermediate section of the convertor chamber 23. All catalyst must pass into the convertor through conduits 24 or 26 and travel the entire length of the convertor chamber. Again, in this arrangement, the vapor feed is introduced into the convertor at any one of several possible locations positioned within the central portion of space 23, choice among these locations being made on the basis of market demand for gasoline and fuel oil. The major portion of the vapor feed will flow downwardly as described above and be withdrawn from the outlet 51 at the bottom of the reactor. However, a controlled minor fraction of the vapor feed passes upwardly and is withdrawn from the top of the reactor at outlet 7 along with cracked products from the liquid feed. The relative amounts of flow through outlet conduits 7 and 51 is controlled by the valves in these conduits. This method of operation permits control of the severity of liquid feed cracking as the contact time of the cracked reaction products with catalyst is regulated by the upward rate of gas flow through space 23. Another advantage of this modification of my invention is that the liquid charge and the vapor charge which flows upwardly, are subjected to very hot catalyst. The contact time in this region may be easily controlled by regulation of the amount of vapor feed flowing upwardly and as a result of the high temperatureof reaction, a high octanezgasoline will issue from pipe 7, While fuel .oil and lower octane gasoline issue from pipe 51. fI'hus, this process may automatically act to separate high octane gasoline from the remainder of the ,product without useof expensive fractionation.

I The exact dimensions of the several elements which make up the improved apparatus combination described hereinabove-will, of course,-be dependent to a certain extent upon the particular operation and operating conditions for which the apparatus is to be employed. In general, it has been found desirable to provide a vertical distance ofthe order of 5 to 15 feetbetween the contact material baffling, such as baffles 38 and 39 of Figure 1, and the level at which the contact material column is to be maintained in the conversion chamber. The relative dimensions of the skirt 38 and bafile 39 and the vessel 17 will, of course, vary withthe dimensions of the vessel 17 and the desired rate of contact material flow.

As an example of asatisfactoryconstruction, and with reference again to Figure 2 and my preferred method of operation, in a catalytic cracking reactor having a diameter of about 16 feet, about 24 feed pipes such as pipes 24 in Figure '1 having a diameter of about 3 /2 inches, were spaced at intervals around the periphery of the upper section of the reactor vessel. The central feed pipe 26 was about 10 inches in diameter, the conical bafile 39 measured about 42 inchesin height and 6 feet, 11 inches in diameter at its base. A vertical space of about 10 feet was-provided between the lower edge of skirt 38 and the lower ends of pipes 24. Vapor feed conduits i4, 15 and 16 may be placed about 4 to 8 feetbelow the surface of the catalyst bed. In this apparatus, the total rate of contactmaterial flow was of the order of 400 tons per hour,-of which about to '80 percent entered through the central conduit 26. In the above apparatus, the rate of fluid hydrocarbon charge was of the order of 1500 to 3000 barrels (42s) per day, and rate of vapor 'hydrocarbon'charge was of the order of 15,000 to 18,000barrels (42s) per'day. In the apparatus of the above example the catalyst falls from the annular passage between the skirt bafile and the conical bafiie as a tubular curtain of particles extending down to the bed surface. I i

The conditions of operation in the apparatus of this invention will vary widely, depending uponthe particular operational application involved. In general, the contact material should be supplied at a temperature suitableto support the conversion desired. This temperature will vary somewhat, depending upon the particular contact material to oil ratio chosen. In catalytic cracking operations on clay-type catalysts, the contact material charge to oil charge ratio may vary from about 1.0 to 20 parts by weight of contact material per part of oil. The oil space velocity may be within the range of about 0.3 to 10.0 volumes of oil (measured at 60 F.) per hour per volume of contact material column within the conversion zone. The contact material in the case of catalytic cracking operations may enter the conversion chamber at temperatures of the order of 800 F. to 1200 F., and may undergo a temperature drop of the order of 15 F. to 300 F. in passing through the conversion zone.

In general, it has been found that for preferable operation the amount of contact material entering through conduits 24 (Figure 2) should be of the order of about 20 to 50 percent of the total contact material passed through the converter, the remainder of the contact material being supplied through conduit 26. In such a process, it has been found desirable to control the contact material particle size broadly within the range 3 to mesh, and preferably within the range about 4 to 20 mesh by Tyler Standard Screen Analysis. The percentage of fines present in the contact material mass should be maintained as low as possible.

The invention may be employed for conversion of hydrocarbon charge stocks which are partially vaporizable under the conversion conditions or it may be employed for the conversion of reducedcrudes and the like, which consist for the most part of hydrocarbons boiling above the desired average conversion temperature. It is usually preferable to heat the hydrocarbon charge to a temperature of the order of 600 F. to 900 F. before introducing it into the conversion chamber.-

To achieve the desired high quantity of No. 2 fuel oil in the process of this invention, it will, in general, be desirable to introduce the vapor charge a distance beneath the contact material reaction bed surface within the range 25 to 50 percent of the total distance from the surface of said bed to the level at which products are first removed from the bed.

It is obvious that the apparatus of Figure l-could be operated without contact material flow through passage 10, and the apparatus of Figure 2 is susceptible of operation without withdrawal of vapor through passage 7. In both of these cases all of the contact material flows through the entire reaction bed and the entire product is withdrawn through passage 51. No precaution against overcracking of the liquid charge is taken. While this operation is not preferred, it is within the broad scope of this invention.

It should be understood that the particular details of apparatus construction and the examples of operating conditions and process applications of the invention given hereinaboveare intended as illustrative and are in no way to be construed as limiting the scope of this invention, except as it may be limited by the following claims.

I claim: I

1. Acontinuous process for the conversion of fluid hydrocarbons in the presence of granular contact material, which comprises: maintaining a downwardly gravitating, substantially compact bed of granular contact material within a confined conversion zone and continuously removing contact material from thelower section of said bed; passing a first portion of the contact material needed to supply said bed onto the upper surface of said bed; supplying a liquid hydrocarbon charge to, the upper section of said bed; injecting a vaporized hydrocarbon charge in substantially greater quantity than said liquid charge into said bed at an intermediate level therein and,rwithout varying the level of liquid charge supply, varying said level from a low levelwhich is a distance below the surface of said bed amounting to 2550 percent of the total distance from said surface to the initial level of product withdrawal'from the lower section of said bed to vary the ratio of gasoline to No. 2 fuel oil with seasonal demand, a higher level being used to increase said ratio and a lower level to decrease it; supplying a second portion of fresh, hot contactmaterial to said bed at a level immediately above the level of vapor charge injection and removing products of conversion from the lower section of said bed. g

Y 2. The process of claim 1 further limited to supplying a third portion of fresh, hot contact material to said bed at' a level immediately above the level of product removal. 3. A continuous process for the conversion of fluid hydrocarbons in the presence of granular contact material, which comprises: maintaining a downwardly gravitating, substantially compact bed of granular contact material within the lower section of a confined conversion zone; supplying contact material at a temperature suitable to effect the desired conversion to the upper section of said had; supplying liquid hydrocarbon charge to the upper section of said bed; supplying'a vaporized hydrocarbon charge to an intermediate level; passing the major portion of the vapor charge downwardly through said bed and the remainder of the vapor charge upwardly through the bed to mix with vapors formed from the liquid charge and issue from the upper end of said bed; varying the level of vapor supply to said bed to vary the ratio of gasoline to No. 2 fuel oil in response to the seasonal demand for such products, said level being raised to increase said ratio and lowered to decrease it and the level of vapor supply when said ratio is at its minimum being a distance below the surface of said bed amount- -ing to 25-50 percent of the total distance from said surface to the initial level of product removal from the lower section of said bed; removing products of conversion from the upper section of said zone above said bed and also removing products of conversion from the lower section of said bed; removing used contact material from the lower section of said bed.

References Cited in the file of this patent UNITED STATES PATENTS Sinclair Apr. 8, 1947 2,490,336 Crowley Dec. 6, 1949 7 2,499,304 Evans Feb. 28, 1950 2,606,861 Eastwood Aug. 12, 1952 2,732,331 Wesh s Jan. 24, 1956 2,741,582 Evans etal Apr. 10, 1956

Claims (1)

1. A CONTINUOUS PROCESS FOR THE CONVERSION OF FLUID HYDROCARBONS IN THE PRESENCE OF GRANULAR CONTACT MATERIAL, WHICH COMPRISES: MAINTAINING A DOWNWARDLY GRAVITATING, SUBSTANTIALLY COMPACT BED OF GRANULAR CONTACT MATERIAL WITHIN A CONFINED CONVERSION ZONE AND CONTINUOUSLY REMOVING CONTACT MATERIAL FROM TE LOWER SECTION OF SAID BED, PASSING A FIRST PORTION OF THE CONTACT MATERIAL NEEDED TO SUPPLY SAID BED ONTO THE UPPER SURFACE OF SAID BED, SUPPLYING A LIQUID HYDROCARBON CHARGE TO THE UPPER SECTION OF SAID BED, INJECTING A VAPORIZED HYDROCARBON CHARGE IN SUBSTANTIALLY GREATER QUANTITY THAN SAID LIQUID CHARGE INTO SAID BED AT AN INTERMEDIATE LEVEL THEREIN AND, WITHOUT VARYING THE LEVEL OF LIQUID CHARGE SUPPLY, VARYING SAID LEVEL FROM A LOW LEVEL WHICH IS A DISTANCE BELOW THE SURFACE OF SAID BED AMOUNTING TO 25-50 PERCENT OF THE TOTAL DISTANCE FROM SAID SURFACE TO THE INITIAL LEVEL OF PRODUCT WITHDRAWAL FROM THE LOWER SECTION OF SAID BED TO VARY THE RATIO OF GASOLINE TO NO. 2 FUEL OIL WITH SEASONAL DEMAND, A HIGHER LEVEL BEING USED TO INCREASE SAID RATIO AND A LOWER LEVEL TO DECREASE IT, SUPPLYING A SECOND PORTION OF FRESH, HOT CONTACT MATERIAL TO SAID BED AT A LEVEL IMMEDIATELY ABOVE THE LEVEL OF VAPOR CHARGE INJECTION AND REMOVING PRODUCTS OF CONVERSION FROM THE LOWER SECTION OF SAID BED.

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