US2414852A - Catalytic process and apparatus - Google Patents

Description

Jan. 28, 1947. H. w. BURNSIDE ErAL 2,

cn'rgunc *rnoc:-:S AND APPARATUS Filed April 11, 1944 2 Sheets-Sheet 1 14 1D FRACTIONATING EQUIPMENT Hamel E. W. bumside Henry J. Oqorzalq INVENTUQS Jan. 28, 1947. H. E. w. B URNSIDE EI'AL- 2,414,352

CATALYTIC PRQCESS AND APPARATUS Filed April 11, 1944 2 Sheets-Sheet 2 &

Harveq EM. burrgsidq INVENTORS Heart; J.

Patented Jan. 28, 1947 v 2,414,852 UNITED STATES. PATENT orrlcs CATALYTIC PROCESS AND APPARATUS Harvey E. W. Burnside and Henry J. Og'orzaly,

Elizabeth, N. 1., assignors to Standard Oil Development Company, a corporation of Delaware Application April 11, 1944, Serial No. 530,450

. 10 Claims.

This invention relates to catalytic processes and pertains more particularly to a catalytic process in which a finely divided catalyst is caused to circulate continuously through a treating zone.

While the invention in its broader aspects has a more general application, it is especially adapted to processes and apparatus for the catalytic cracking of hydrocarbon oil wherein the catalyst is continuously circulated through a reaction zone and a regenerating zone.

One method now employed for cracking hydrocarbon oil to form motor fuel is to crack the oil in the presence of a finely divided cracking catalyst which is continuously circulated through the cracking and regenerating zones by the pressure generated by a column or a plurality of columns of catalytic material in which the catalyst is maintained in a relatively dense, fluid state similar to aliquid and capable of developing ahydrostatic pressure.

According to present practices, the rate of.circulation of the powder through the cracking and regenerating zones is regulated by control valves usually positioned at the base of-the column or standpipe. In order to permit substantial variations in the rate of flow and also provide an effective seal between the cracking and regenerating zones, the apparatus is normally designed to provide from 2 to 5 pounds pressure drop across the valves and in some operations an even greater pressure drop is desirable.

One of the objects to provide a method of the general character above outlined wherein the height of the columns or standpipe may be reduced.

It is also a practice, when carrying out a cata lytic process as above outlined, to pass the oil vapors upwardl through the cracking zone at a velocity controlled to maintain a relatively dense fluidized layer of catalytic material in the bottom portion of the cracking or regenerating zone. It has been found, for example, that under properly controlled conditions the catalyst remains largely segregated in a relatively dense layer at the bottom of the cracking or regenerating zone and this layer is superimposed by a free space wherein the gases being treated contain only a relatively small amount 'of entrained catalyst particles.

A broader object of the present invention is to provide an improved process for circulating a powder through a treating zone.

A more specific object of the invention is to for the catalytic conversion of hydrocarbon oils.

Another object of our invention is to provide an improved apparatus for circulating catalytic or other finely divided contact materials through a treating zone, Other objects and advantages of the invention will be apparent from the de- -in the form of an enlarged vertical reaction vessel. For illustrative purposes, the invention will be described as applied to the catalytic cracking of hydrocarbon oils, it being understood that in its broader phases the inventionmay have a more general application as previously pointed out.

The oil to be cracked in admixture with a finely divided cracking catalyst is introduced into the bottom section of chamber In through line 1 ll. Any type of solid material capable of exofthe'"present invention is erting the desired catalytic effect on the oil vapors may be employed in the operation. Par-,- ticularly suitable catalysts comprise acid-treated bentonite clays or synthetic siliceous gels oi the same or different composition. The catalyst is preferably in finely divided form, having a particle size generally smaller than 200 mesh.

The bottom portion of the chamber 10 may take the form of an inverted cone forming a. distribution zone for distribution of the oil and catalyst over the full cross-sectional area of the reactor. It is also preferable to provide a per forated grid in the bottom section of, the reactor for insuring more thorough distribution of the provide a more simple and inexpensive method I catalyst andoil vapors therein.

The velocity of the oil vapors passing upwardly through the reactor I0 is preferably controlled to permit the catalyst to segregate into a relatively dense layer inthe bottom section of the chamber as illustrated. When employing catalytic materials of the type above mentioned, a velocity of the order of 0.5- to 5 feet per second may be employed. It will be-understood that the velocities here mentioned have-reference to the normal linear velocities which the oil vapors would attain in the absence of the solid material within the reactor.

It is preferable to construct the reactor ll) of suflicient height to provide a substantial free space above the level ofcatalytic material in the reactor Ill so as to reduce the amount of--catalyst entrained in the gases leaving the reactor, For this purpose a free space of from 4 to 10 or more feet is desirable. I

The reactor I0 is maintatined under cracking temperatures ranging from 750 F. to 1000 F. or more. This temperature may be maintained by the introduction of hot catalytic material into the oil vapors as later described.

The cracked vapors, after passing through the reaction zone, may be passed through a suitable regenerator l'l. wardly through the grid intermixes with the separating device such as a cyclone separator l2 for removing entrained catalytic material therefrom. The catalyst separated from the cracked vapors in the cyclone separator I2 is returned to the reactor through tube l3 below the level of the dens fluidized mass of catalytic material therein. The cracked vapors after passin through the cyclone separator I2 are withdrawn from the reactor l through-line l4 and may be passed to suitable fractionating equipment which, for simplicity, has not been shown on the drawings.

The reaction chamber I0 is also provided with 9. depending conduit 15 having a portion thereof extending into the main body of the reaction chamber for continuously withdrawing a portion of the catalytic material therefrom. The conduit I5 discharges through a tube l6 extending into the regenerator ll. The tube It projects into the regenerator ll to a point below the level of a dense fluidized layer of catalytic material undergoing regeneration therein. The conduit l5 and the tube 16 form a standpipe or column positioned to build up or generate a pressure equal to the pressure difierence'between the reactionand the regenerating zone,

A stripping gas such as steam, spent combustion gases or the like may be introduced into the bottom portion of the conduit l5 to remove vaporizable hydrocarbon constituents from the catalyst passing into the regenerating zone.

It is also'desirable to maintain the catalytic material in the conduit and the tube It in a freely flowing, fluidized state to prevent packing 0r bridging of the catalyst therein and to this end a small amount of an aerating or fluidizing gas may be introduced at one or more spaced points into the conduit l5 and the pipe IS. The amount of fluidizing gas so introduced is relatively small and only suilicient to form a thin film of gas around the individual particles within the conduit.

The regeneration chamber I1 is constructed in the same general manner as the reaction chamber Ill, The air for regenerating the catalyst by burning up the combustible deposits therefrom is introduced into the bottom section of the regenerator I! through line 18. Regenerator l'l may be provided with an inverted conical bottom forming a distributing zone for distributing gas into the regenerating chamber,

The regenerating chamber may also b vided with a perforated grid in the bottom portion thereof through which the gas or other oxidizing medium passes into the main body of the Th oxidizing gas passing upflnely divided spent catalytic material introduced into the regenerator I] through line l6 and serves to burn the combustible deposits therefrom.

As previously described with reference to the reaction chamber III, the velocity of the oxidizing gas passing upwardly through the regenerator I1 is preferably controlled to maintain the catalytic material within the regenerator in a relatively dense, turbulent layer in the bottom section thereof. This velocity may be of the order of from 0.5 to 5 feet per second.

The spent combustion gases after passing through the layer of catalytic material in the bottom portion of regenerator I! may be passed through suitable separating device such as oyclone separator l9 inwhich catalytic material entrained in the gases may be removed. The catalyst separated from the regenerating gas is 4 returned to the bottom portion of the regenerator l1 through tube 2 I.

The spent combustion gas is removed from the regenerator I! through line 22, having a pressure control valve or other means of pressure con-' trol 23 actuated as later described to maintain a predetermined pressure difference between the reaction chamber and the regeneration chamber. A stream of regenerated catalytic material is continuously withdrawn from the regenerating chamber ll through the conduit 24 which extends upwardly into the body of the reactor similar to the conduit l5 as previously described.

The conduit 24 is provided with a suitable control valve such as the slide valve 25 for regulating the amount of catalytic material withdrawn from the regenerator. The stripping or fluidizing gas is introduced into the conduit 24 at one or more spaced points to maintain the catalytic material in a fluid, liquid-like state. In some cases it may be desirable to provide cooling tubes or other cooling elements in the conduit 24 in order to extract excess heat liberated during regeneration of the catalyst.

The regenerated catalytic material is discharged from the conduit 24 into a stream of oil passing through line H and is returned to the reaction chamber as previously described. In order to insure continuous circulation of the catalytic material through the reacting and regenerating zone as previously described, it is important to maintain the finely divided catalyst in a freely flowing, fluidized state. To this end, a small amount of an aerating or fluidizing gas should be injected into the catalyst at any point in the circuit where there is a tendency of the catalyst to separate into a dense, compact mass.

Under these conditions the catalytic material may be caused to flow as a liquid and the laws of fluid flow may be applied. With this in mind, it will be noted that in order for the catalyst to flow from the reactor into the regenerator as described, the back pressure on the regeneration gas at the top of the regenerator must be less than the inlet pressure on the catalyst passing into the regenerator through the tube or standpipe It. On the other hand, in order to maintain a level of catalyst in the reactor Ill above the conduit l5,

it is necessary that the back pressure on the regeneration gas must be greater than the back pressure on the oil vapors above the catalyst layer in the reactor l0.

Within these limits, the level of catalyst within the reactor ID will be determined by the adjustment of the pressure control valve 23. At equilibrium conditions, the difierence between the outlet pressure on the regenerator and the outlet pressure on the oil vapors in the reactor I 0 will be equal to the hydrostatic or fluid pressure generated by the standpipe or column I6 and the superimposed layer of catalytic material located in the reactor l0 above the drawoif pipe 15. This fluid pressure will vary with the level of the catalyst in the reactor H).

In accordance with the present invention, the difference between the pressure on the gases in the free space above the catalyst layer in the regenerating chamber IT and the pressure on the vapors in the free space above the catalyst level in the reactor I0 is used for regulating the pressure control valve 23. For example, a decrease in the pressure difference between the gases and v 5 be corrected and the catalyst layer restored to the desired level by partially closing the throttle valve or pressure controller in line 22, thus increasing the back pressure on the regenerator and there- 'by reducing the rate of flow from the reactor to the regenerator until the normal level has been restored. Conversely, an increase in the pressur difference between the gases and vapors in the regenerator and reactor, respectively, indicates an increase in the depth of the catalyst layer in the reactor I 0. This, can be corrected by turning the throttle valve 23 toward the open position, thereby reducing the amount of back pressure causing an increase in the rate of flow through the standpipe I6 so as to restore the level to its original position.

The level of the catalyst layer within the reactor H] can therefore be regulated within desired limits by operating the throttle valve 23 in response to variations in the difference between the pressure on the gases in the free space above the catalyst layer in the regenerator and the pressure on the oil vapors in the free space above the catalyst layer in reactor l0. While the throttle valve 23 may be controlled manually as above outlined, it is preferred to operate the'valve by an automatic diiierential pressure controller. One simple and effective way is illustrated in the drawings wherein the upper end of the regenerator I1 is inopen communication, through line 21, with one end 28 of a U-shaped manometer .29 and the upper end of the reactor I is in open communication through line 3| with the other leg 32.

The difference in level'of the mercury in the two legs shows the pressure difierence between the two chambers.

The U-shaped manometer may be provided with suitable electrical contacts so that any predetermined fluctuations in the level of the mercury therein will cause closing of an electric circult in the operation of the control valve 23. As indicated, the level of mercury in the leg 28 will normally be lower than the level in the leg 32 due to the higher pressure in the regenerating zone. The difference in the level of the mercury in the two legs indicates the amount of hydrostatic pressure generated by the column of fluidized catalyst between the upper level of the catalyst in the reactor II] and the upper level of the catalyst in the regenerator l1, and. the amount of this hydrostatic pressure so developed depends upon the level maintained in the reactor l0.

By properly positioning the electrical contact in the U-shaped manometer, the level of catalyst in reactor Ill may be controlled within the desired limits.

When operating in accordance with the present invention, the valve 25 in the conduit 24 controls the rate of circulation of the catalyst through the cracking and regenerating zones and the throttle valve 23 in the outlet of the regenerating chamber controls the level of catalyst in the reactor l0.

In practice, it is desirable to position the reactor a sufficient distance above the regenerator to build upa differential pressure between the two chambers of from 3 to 10 or more pounds per square inch. When employing conventional catalysts having a fluid density of about 30 pounds per cubic foot, about 5 feet of catalyst height is required for each pound of. pressure developed. In some cases, it may be desirable to provide a safety valve in the conduit l6 which can be operated in case of any abnormal fluctuation in pressure within the circuit.

According to another phase of the invention, the velocity of the air passing upwardly through the regeneration chamber I1 is controlled so as to prevent overall recirculation of catalyst within theregenerator I1 so that the catalyst flows downwardly through the regenerator in a general direction countercurrent to the flow of the gases passing upwardly therethrough. In order to accomplish this, the velocity of the uprising vapors may be of the order of from 0.1 to 0.5 feet per second, depending upon the size of the catalyst particles and other factors. Under these conditions the concentration of carbon on the catalyst in the upper portion of the regenerator will be greater than the concentration at the bottom of the regenerator from which the regenerated cataserve as a stripping agent for reducing the amount of carbon to be burned. A part of the spent regeneration gas withdrawn from the regenerator ll may be passed through line 33 and injected into the conduit l5 as a stripping medium therefor or a separate stripping as may be introduced through line 34.

7 While in the previous description the reactor has been located at a higher level than the regenerator, in many cases it may bedesirable to position the reactor at a lower level. For example, it is desirable to maintain a back pressure on the reactor in order to pass the oil vapors through the subsequent fractionating and recovery equipment and the regenerator may be operated at substantially atmospheric pressure. The lower vessel I'l may be utilized as a reactor by introducing oil into line [8 instead of air and introducing air through line I I instead of oil and connecting line 22 with the fractionating equipment rather than line l4.

The invention-finds application in processes in which it is unnecessary to regenerate the finely divided material, but in which it is desirable to pump or otherwise continuously circulate finely divided powdered material through the treating zone. In such cases the upper chamber Ill illustrated in Fig. I mayserve. simply as a separating device for separating the powder from the gas stream passing through line H so that it may be returned to the reaction chamberlocated at the lower level.

Fig. 11 illustrates a simplified form of equipment in which a powder is continuously circulated through a reactor and in which the principles of the invention may be utilized,

Referring to Fig. II, the reference character 40 designates a reaction chamber constructed similar to the reactor [0 or regenerator l1 shown in Fig. I. The gases to be reacted 'are introduced into the reactor 40 through line 4| and pass upwardly into the main portion of the chamber rator or other suitable separating device 43 and thereafter removed from the reactor through line 44. The powder separated in the separator 43 returns to the reactor through conduit 45. A stream of finely divided powder is continuously withdrawn from the reactor 40 through fve'rtical standpipe or conduit 46 into which a small amount oi fluidizing gas may be introduced at. one or more points through lines 41 and 48 The conduit' 46 isprovided with a control valve 49 through which the powder is withdrawn from the chamber at a controlled rate and discharged into a stream of gases passing through line This stream of gases may be passed upwardly through lines 52 and 53 into the bottom of a separator 54 having a construction similar to the reaction chamber 40. The velocity of the gases passing upwardly through the separator is controlled to permit primary separation of the powder from the gas stream to form a relatively dense layer of solid material therein. This layer provides primary separation of the powder from the gases introduced into the separator. The gases may then pass to a second or final separating device such as a cyclone separator 55 positioned at the top for removing entrained powder and the gases finally vented through line 55.

The separator 54 discharges through the vertical standpipe 55 directly into the reaction chamber 40. If desired, a fluidizing gas may be introduced into the standpipe 55 through one or more pipes 51 and 58. Instead of introducing the suspension of powder and gases into the bottom section of the separator 54, the suspension may be passed through line 59 into the cyclone separator 55 and the bulk of the material separated by this separator, In the latter case, the powder-separated from the gas stream drops into the bottom portion of the separator 54 which serves as a hopper or reservoir from which the powder continuously drops through theconduit 55 into the reactor 40. As already described in connection with Fig. I, the outlet line 44 from the reactor 40 is provided with a differential pressure control valve or other means of pressure control 62 for regulating the back pressure on the reactor 40 and this control valve is preferably regulated by the differential pressure between the vapor space above the layer of powder in the separator 54 and the vapor space above the layer of powder in the reactor 40. 'This pressure control valve tends to maintain a definite level of powder in the separator 54 and maintains a seal for preventing the reaction gases from by-passing upwardly through the conduit 56.

The apparatus illustrated in Fig. II is particularly suitable where it is desirable to circulate powder through a reaction chamber for the purpose of regulating the temperature therein. For example, in reactions involving strong heat effects, such as high exothermic or highly endothermic reactions, it may be desirable to extract heat from the reactor by circulating the powder through the reactor and thereafter through a heat exchanger for adding or extracting heat from the powder undergoing circulation. The heat may be extracted or added to the powder being circulated by means of a heat exchanger in the separator 54 shown in Fig. II, or a suitable heat exchanger may be placed in either the line 53 or line 59. A heat exchanger 63 has been shown in the line 59, it being understood that a similar heat exchanger may be provided in line 53 in cases where the hopper 54 serves as a primary separator as previously described.

Having described the preferred embodiment of the int ention, it will be understood that it embraces such other variations and modifications as come within the spirit and scope thereof.

We claim:

1. A method of. circulating a finely divided solid material through a treating zone which comprises maintaining a body of said finely divided material within said treating zone, passing a gas upwardly through said treatin zone, continuously withdrawing a stream of finely divided material from the bottom portion of said treating zone, introducing the finely divided material so withdrawn into a second stream of gas, transferring said last-named gas stream containing said finely divided material to a separating zone at an elevation substantially higher than said treating zone, separatingthe finely divided solid material from said'last-named gas stream, transferring the finely divided solid so separated into the top of a vertical column of said finely divided solid material, maintaining a fluidizing gas in admixture with said finely divided solid material within said column in an amount controlled to maintain said material in a fluid state capable of generating a fluid pressure, discharging finely divided material from the base of said column into said treating zone by the fluid pressure generated by said column, determining the pressure difference between said separating zone and said treating zone and controlling the back pressure on said treating zone in response to said pressure difference to regulate the rate of feed of said finely divided solid material into said treating zone.

2. A process for continuously circulating a finely divided solid material through a plurality of treatin zones which comprises maintaining a relatively dense fluidized layer of catalytic material in one of said treating zones, maintaining a second layer of finely divided solid material. in a second treating zone at an elevation substantially higher than said first-named treating zone, maintaining a confined column of said finely divided solid material between said treating zones, the upper end of said column being in open communication with said layer of material in said upper treating zone and the lower end of said column being in open communication with said layer in said lower treating zone, maintaining an aerating gas in admixture with said solids within said column in an amount controlled to maintain said column in a fluidized state capable of generating a fiuid pressure, passing a gas to be treated upwardly through said lower treating zone, continuously downwardly withdrawing finely divided material from said lower treating zone at a controlled rate, discharging the finely divided material so withdrawn into a stream of gases, passing said last-named stream of gas containing said finely divided solid material to said upper treating zone, and regulating the back pressure on said lower treating zone to control the rate of flow of said finely divided material from said upper treatin zone and through said column and maintaining the desired level in said upper treating zone.

3. In the process defined by claim 2, the further improvement which comprises controlling the back pressure on the lower treating zone in response to the pressure difference between the upper treating zone and the lower treating zone.

4. A process for the catalytic conversion of hydrocarbon oils in which finely divided catalyst is caused to circulate continuously through a conversion zone and a regenerating zone which comprises maintaining a relatively dense fluidized layer of finely divided conversion catalyst within a converison zone, passing hydrocarbons to be converted upwardly through said conversion zone at a rate controlled to prevent substantial encommunication with the zone of lower elevation, 1

maintaining the finely divided conversion catalyst in a freely flowing, fluidized state capable of generating a fluid pressure within said column, continuously downwardly withdrawing a stream of finely divided conversion catalyst from the lower of said zones, discharging the stream of catalyst so withdrawn at a controlled rate into the stream of gases passing to said upper zone and controlling the back pressure on the lower treating zone to regulate the level'of finely divided conversion catalyst in the upper treating zone.

5. In the process defined by claim'4, the further improvement which comprises positioning the conversion zone at an elevation above the regenerating zone.

'6. The invention defined by claim 4 wherein the regenerating zone is positioned above the conversion zone. 1

7. A process for the catalytic cracking of hydrocarbon oils wherein the oil is cracked in the presence of a finely divided catalyst which is continuously circulated through a cracking zone and a regenerating zone which comprises maintaining the cracking zone at a substantial elevation above said regenerating zone, maintaining a layer of finely divided cracking catalyst within said cracking zone, maintaining a second layer of finely divided cracking catalyst within said regenerating zone, passing an oxidizing gas upwardly through said regenerating zone at a velocity controlled to maintain a layer of said cracking catalyst in the bottom portion thereof, continuously downwardly withdrawing finely divided catalytic material from the bottom portion of said regenerating zone, discharging the catalytic material so withdrawn at a controlled rate into a stream of hydrocarbon vapors to be cracked, transferring the stream of hydrocarbon vapors containing said catalyst into said conversion zone, controlling the velocity of hydrocarbon vapors passing upwardly through said cracking zone to maintain a dense fluidized layer of catalytic material therein, maintaining a confined vertical column of said conversion catalyst between said cracking and regenerating,

zones, the upper end of said-column being in the back pressure on said regenerating zone "in responseto the diiierence in pressure between said cracking zone and said regenerating zone. 9. An apparatus'for treating gases and solids which comprises an enlarged vertical vessel adapted to contain a fluidized layer of finely divided solids, means for introducing gases to be treated into the bottom of said zone at a rate controlled to maintain a dense fluidized layer of solids therein, a conduit having an upper end in open communication with the bottom portion of said vessel and adapted to continuously withdraw finely divided solids therefrom, a valve in 'saidconduit for controlling the rate of withdrawal of said finely divided solids, separating means positioned at a substantial elevation above such vessel adapted to separate finely divided solids from gas, a pipe connecting said seperating means with said conduit and adapted to carry a suspension of solids withdrawn from said treating vessel to said separating means, a vertical column having its lower end in open communication with the interior of said treating vessel and its upper end in open communication with the interior of said separating device and adapted to transfer solid material from said separating means to said treating zone, said lastnamed conduit being adapted to sustain said solid material in a dense fluidized state therein, means for maintaining said solids within said column in a freely flowing, fluidized state capable of generating a fluid pressure, said lastnamed column being of a height 'suflicient to generate a substantial hydrostatic pressure at the base thereof, means for controlling the back pressure on said treating vessel and means responsive to the pressure difference between said separating means and said treating vessel to control said pressure control means.

10, An apparatus adapted for tne catalytic conversion of hydrocarbon oils which comprises an enlarged vertical conversion vessel, an enlarged vertical regenerating vessel supported at an elevation substantially diiferent tnan said conversion vessel,each of said vessels adapted to contain a layer of finely divided conversion catalyst therein, conduit means for continuously withdrawing a stream of finely divided conversion catalyst from the lower of said vessels, a valve in said last-named means, a pipe connecting said last-named conduit with said upper vessel and adapted to transport'any divided conversion catalyst from the bottom vessel into the upper vessel, a vertical conduit extending between said upper vessel and said lower vessel having the upper end in open communication open communication'with said cracking zone and the bottom of said column being in open communication with said regenerating zone, maintaining an aerating gas in admixture with said conversion catalyst within said column in an amount controlled to maintain said catalyst in a fluid state capable of generating a fluid pressure at the base thereof, said column being of a height suflicient to maintain a substantial pressure diflerence between said cracking zone and said regenerating zone, and controlling the back with the interior ofsaid upper vessel and the lower end in open communication with the interior of said lower vessel. means for maintaining an aerating gas in admixture with the conversion catalyst contained in' said last-named conduit in an amount controlled to maintain said conversion catalyst in a freely flowing, fluid state capable of generating a hydrostatic pressure, the

' height of said lnst-numedoonduit b81118 mimcient pressure on said regenerating zone to regulate' the flow of catalyst from said cracking zone to said regenerating zone through said column to maintain a substantial pressure differential between the upper vessel and the lower vessel, means for maintaining a back pressure on said lower vessel, means responsive to the diflerence in pressure between the upper vessel and the lower vessel for controlling said mu HARVEY E. W. BURNSIDI. HENRY J. OGORZALY.

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