US2311564A - Handling finely divided materials - Google Patents

Description

Feb. 16, 1943. J. c. MUNDAY HANDLING FINELY-DIVIDED MATERIALS Filed Nov. 2, 1940 Patented Feb. 16, 1943 2,311,564 I HANDLING mam mvman MATERIALS John C. Munday, Cranford, N. J., assignor to Standard Oil Development Company, a corporation of Delaware Application November 2, 1940, Serial No. 364,085

4 Claims.

This invention relates to a method of handling finely-divided materials and pertains more particularly to a method of imposing a pressure on such material. I

In many types of industrial processes in which powdered materials are involved, it is desirable to place the powder under substantial pressure.

One example is catalytic operations in which powdered catalysts are employed. In such operations, suflicient pressure must be imposed on the powder to feed the same into the stream of reactant gases which in turn must be under a pressure adequate to force the resulting mixture through the reaction zone. Also, it may be desirable in many instances to carry out the operation under a substantial pressure.

The main object of the present invention is to provide an improved method of building up pressure on powdered material.

It has heretofore been proposed to place powdered material under a positive pressure by mechanical means, such as, for example, by the use of a compression screw. However, this method gives rise to certain inherent mechanical dimculties. Perhaps the most serious objection to this method is the amount of power required to build up the pressure. The power required increases at a disproportionately greater rate with increase of pressure across the compression screw. In many instance the compression screw becomes seriously eroded or abraded by the powdered material which necessitates frequent replacements. In other cases the application of mechanical pressure may adversely afiect the character of the powder being compressed. For

example, in catalytic operations involving the use of acid treated clay, it has been found that the use of compression screws tends to agglomerate the clay particles into spheres.

In lieu of a compression screw or other similar mechanical devices, it has also been a practice in some cases to build up the required pressure by means of pressure hoppers in which the powdered material is placed and the required pressure built up by means of a gas imposed above the level of the material in the hopper. This method, however, is objectionable in many cases. For example, in processe which operate continuously requiring continuous removal of the material from the hopper, additional receptacles must be provided so that some may be placed under pressure while the material is being withdrawn from others.

It has also been proposed in isolated cases to build up the required pressure on powdered material by means of avertical column of said powder, By maintaining the powder within the column in a'freely flowing state, a static pressure similar to hydrostatic pressure in the case of liquids may be developed'at the bottom of the column. However, there are practical limitations with respect to the height of the column which may be employed for building up pressure in this manner.

In accordance with the present invention, a plurality of columns or standpipes is provided and a substantial portion or the static pressure" developed from one column is carried over or transferred into a second column in which further pressure is built' up. Therefore, by provision of sufiicient number of such columns any desired pressure may be imposed on the powder. The present invention is made possible by the fact that finely-divided powdery materials under certain conditions may be made to behave as a liquid.

For a more complete understanding, the invention will be now described in more detail in which reference will be-made to the accompanying drawing which is a diagrammatic illustration of an apparatus which may be employed for carrying the invention into effect.

For illustrative purposes, the invention will be described as applied to catalytic processes employing powdered catalysts and more specifically to catalytic cracking of oils in which the invention has found particular application. It will be understood, however, that the invention in its broader phases is not so limited.

Referring to the drawing, the reference character l i designates a hopper for the powdered material employed in the process. The powdered catalyst from the hopper ll discharges into a vertical tandpipe l2 of a height sufficient to develop a substantial pressure at the bottom thereof; To insure that the powdered material in the standpipe i2 is in freely flowing condition so that the pressure is transmitted to the bottom of said column, a fluidizing gas from the manifold line I3 may be introduced into the standpipe l2 through one or more lines I4 [5 and IS.

The powdered catalyst from the bottom of the standpipe I2 is fed through any suitable valve l1 into a return leg l8 into which a carrier gas is introduced through line I9 leading from the manifold line 20. The amount of carrier gas introduced into the return leg l8 should be sufficient to considerably reduce the bulk density of the stream flowing therein. The diluted stream of powder and gas of low bulk density is transferred from the bottom of the standpipe l2 through ascending leg ll into the top section 2| of a second standpipe 22. The upper portion of the hopper section 2| may be provided with a suitable separator for segregating solids from gases, such as a cyclone separator 22. The fluidi zing gas separated from the catalyst in the cyclone separator 22 is removed therefrom through line 24. The catalyst from the hopper section 2| feeds into the vertical column or standpipe 22 throughwhich a fiuidizing as from manifold line 25 may be introduced through one or more lines 22, 21 and 22 so as to maintain the powder in the second standpipe 22 in a freely flowing state. If desired, a portion of the fluidizing gas from manifold 25 may be introduced at one or more spaced points in return leg ll fluidity, since the density under freely flowing conditions determines the pressure developed per linear foot of standpipe for any given material. Similarly, since the back pressure developed in the up-flowing leg depends on the density of the powder, it is advantageous to employ a large amountof gas therein. The amount of pressure produced in each U-tube maybe conveniently through lines 21' and 22'. Additional pressure is developed by the catalyst at the bottom of .the standpipe 22. The bottom of.the second standpipe 22 is also provided with a suitable valve 22 through which the catalyst is fedinto a return leg 22 in whichit intermingles with additional carrier gas introduced through line 2|. By reducing the density of the powdered material in the return leg 22, the catalyst may be returned to another separator 24 in hopper 22 located at the top of a third standpipe 22. The .fluidizing gasseparated from the catalyst in the cyclone separator 24 is removed therefrom through line 22 and may be rejected from the system through line 22. However, this gas is normally at a higher pressure than the gas introduced into the first return leg II. In accordance with one of the specific features of the present invention, the gas separated in the cyclone separator 24 may be used as a carrier for the catalyst in the return leg 12 and, if desired. it may also be used for maintaining the catalyst in the initial standpipe l2 in a freely flowing condition. To this end, apart. or all of theme withdrawn from the cyclone.

separator 24 through line 25 may be passed through lines 21 and 22 into line ll leading to the leg ll. Also, a portion of this gas may be fed through line 29 into manifold line II, from whence it may be passed into the initial standconditions, a fiuidizing gas from line 42 may be introduced at one or more spaced lines ll, 42 and 42.

The apparatus hereinbefore described forms in efiect a series of U-tubcs with the powdered material flowing downwardly in one leg of the tube and upwardly in the other. The progressive building up of pressure on the catalyst is obtained by reducing the density of the catalyst in the upfiowing leg of the U-tubes. The pressure developed by each of the standpipes I2, 22 and 22 depends upon. the height and density of the powder therein. The density of the powder in turn depends upon the specific gravity of the material and to some extent upon the size of the particles. In order for the column to transmit its pressure throughout its.length, it must be maintained in a fluidized state. This. in most cases, requires the addition of a fluidizing gas to prevent packing of the column. This will reduce the bulk density of the material therein. It is generally preferred to introduce the minimum amount of fiuidizing gas which ensures perfect controlled by the relative amounts of gas introduced into the two legs. It has been found that in the case of activated clays the maximum density under freely flowing conditions may be of the order of 25 to 35 pounds per cubic foot. In such case, from 4 to 6 linear feet of standpipe may be required for each pound per square inch of pressure developed. It will thus be apparent that for buildings. pressure of. only a few atmospheres in a single standpipe, towers of extreme height would be required. However, by building up the pressure progressively in a series of standpipes as described, a material saving in structural steel and other materials may be. realized.

The carrier gas used for reducing the density in return legs I. and 20 and the gas introduced at various points in the standpipes I2, 22 and 22 may be an inert carrier gas or it may be an active gas capable of undergoing reactions in the presence of the powder or capable of modifying the character of the powder. For example, it may be an oxidizing gas capable of reacting with carbonaceous deposits formed on the catalyst during the cracking operation.

Furthermore, while the carrier gas and fluidizing gas are illustrated as coming from a common. manifold 20, it will be understood that the gas introduced into the standpipe for fiuidizing may be of a different character than that used as a carrier in the return legs I! and 22.

Returning to the drawing, the powdered material from the bottom of the third standpipe 22 may be passed through a suitable valve ll into a stream ,of gases introduced into the system through line ll. These gases may be of any type which it is desired to contact with the powdered material from the column' 22. In many.

the latter instance .the gas introduced through line ll may be a relatively inert gas utilized as a carrier gas for conveying the catalyst through a heat exchange zone.

As previously mentioned, for illustratiwe purposes. it will be assumed that the powdered material is a cracking catalyst which has been contaminated with carbonaceous deposits in the cracking of hydrocarbon ofl and that it is desired to regenerate the catalyst by treating with an oxidizing medium such as air. "Hie invention is especially useful in such processes because of the increased burning rate and the increased heat transfer rate which result from increase in pressure. The gas preheated to the requiredgas, it is desirable to pass the reactant mixture through the treating vessel at relatively low velocities so that there is a general tendency for the powdered material to settle out of the gases during the passage therethrough. When operating in this manner, the time of residence of the powdered material within the treating vessel will be materially greater than the time of residence of the gases therein.

The stream of powdered material suspended in the gas is withdrawn from the vessel 41 through line 43. In some cases it may be desirable to return a portion of the catalyst directly to the treating zone without any intermediate treatment. For example, the conditioned catalyst may be cooled and recycled to the treating zone where, by reason of its heat capacity it is of assistance in maintaining heat control there in. The mixture may, therefore, be transferred through lines 48, 48 and h or'5l or both to the inlet of either separator 23 or 34 in the top of the standpipes 22 and 33, depending on the pressure drop obtained in line 46, zone 41 and lines 43 and 43. The catalyst recycled in this manner is discharged from ' separator 23 or 34 directly into standpipe 22 or 33.

A part or all of the stream of gaseous products and catalyst removed from the reaction zone 41 through line 48 may be passed through line 52 to a cyclone separator 53 or other equivalent separating devices for removing the gaseous reaction products from the powdered catalyst. The gases separated in the separator 53 are removed overhead through line 56 and may be withdrawn through line 81, or they may be passed through lines 58 and 3| and utilized as a fluidizing and conveying gas in the up-flowing leg 30, or by way of cross-over line 59 and lines 38 and IS in the up-flowing leg ll. If it is desired to allow a considerable time of contact between the gases separated in separator 53 and the up-flowing catalyst, leg 30 may be enlarged to form a reaction vessel similar to vessel 41 in the up-flowing legs 46 and 48. Similiarly, a reaction vessel may be built into up-leg I8. The passage of gas separated in separator 34 through lines 31, 38 and II into the stream of catalyst flowing upward in leg II has already been described.

The catalyst separated in the cyclone separator 53 may feed directly into a further standpipe 55 in which a fiuidizing gas for maintaining the catalyst in freely flowing condition may be introduced at any one or more spaced points through lines 60, 6| and 62.

The catalyst from the standpipe 55 may be fed at the desired pressure through a suitable pressure control valve 63 into a stream of fluidizing and reactant gas introduced through line 64. This gas may, for example, be hydrocarbon vapors which it is desired to crack. The resulting suspension of vapors and catalyst then passes through line 65 to a chamber 66 which in the specific case illustrated constitutes a reaction zone. The flow of vapors and catalyst through the reaction zone 66 may be at relatively low velocities as previously described with respect to the conditioning vessel or zone 41 so as to effect intimate mixing between the catalyst and the gas to be treated therewith. Also, as previously mentioned, in such case the time of residence of the gas in the reaction zone is materially less than the time of residence of the catalyst therein. As a result there is a'constant intermixing between the catalyst and the gas which in turn results in maintaining a substantially uniform temperature throughout the full length of the reaction zone.

The contaminated catalyst together with the cracked products passes from the reaction zone f 68 through lines 61 and 63 to the cyclone separator 6! located at the top of the initial standpipe II. In this case, the catalyst separated from the vapors in the separator 63 passes directly to the initial standpipe i2 for returnvto the regeneration zone.

Reaction products separated from the catalyst in separator 89 are removed therefrom through line 10 and are subjected to further fractionation and purification of the final product in apparatus not shown.

The catalyst removed from the cracked products in separator 63 discharges into hopper H from whence a part or all may be passed to the conditioning vessel 41 through standpipes I2, 22 and 33 and return legs I! and 30. The fluidizing gas introduced into standpipes I2, 22 and 33 and the carrier gas introduced into the return legs l8 and will remove vaporizable hydrocarbons adsorbed or otherwise retained on the catalyst separated in the cyclone separator 89.

In cases where only a portion of the catalyst. removed from the cracked products in separator- 68 is subjected to conditioning treatment in conditioning vessel 41, the remainder may be returned to the reaction zone 66 through line 1| having a valve 12. When employing this method. for reasons of safety the fluidizing gas introduced into standpipe I2 and up-leg It should not be incompatible with the vapors undergoing reaction in zone 66.

Fresh makeup catalyst may be introduced into the circuit through hopper 13.

It will be understood that, whereas in the above-described example it is preferable to conduct the catalyst conditioning treatment at a higher pressure than the reaction pressure, in some cases the pressures will be substantially equal, and in other cases the reaction pressure will be the higher.

From the foregoing, it will be apparent that the present invention has provided a means for building up the desired pressure on powdered materials without the use of any moving parts. It will also be apparent that by the present invention it is possible to treat gas or vapor with a powder concurrently in each of several stages, the overall flow of powder being toward increasing pressure and the overall flow of gas being toward decreasing pressure. In the regeneration of catalystsby burning with air, this offers a distinct advantage in that theburning is more easily controlled, since toward the end of regeneration when the coke content is relatively low the burning rate is favored by the increase in pressure, while in the early stages of regenera- 1 tion when the coke content is high the oxygen partial pressure is relatively low. This modification of the invention may also be applied in the catalytic cracking of certain hydrocarbon oils in which a higher pressure is employed during early stages of cracking than during later stages. Another application is in the cracking of oils wherein it is desired to treat the cracked products or the gasoline constituents thereof with additional catalyst at the same or at a lower temperature in order to reduce acid heat.

Still another application is in the reforming oi naphtha in the presence of hydrogen, wherein the naphtha after being reformed in a later stage is utilized together with the hydrogen in an earlier stage as'a fluidizing and conveying gas at a lower temperature whereupon the gum content of the naphtha is reduced by hydroflning. It will of course be understood thatthe temperature of standpipes and of up-legs ofthe U-tubes can be controlled at will by suitably placed heat exchangers or by enclosure in heat exchange baths.

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

What is desired to be protected by Letters Patent is:

1. A process for imposing pressure on flnelydivided solids which comprises flowing a stream of said finely-divided solid alternately upwardly and downwardly in a sinuous path, maintaining each downwardly flowing stream at a materially higher density than the next succeeding upwardly flowing stream whereby staticpressure developed at the bottom of said downwardly flowing streams is substantially greater than the static pressure at the bottom of the next adjacent upwardly flowing stream and transmitting excess static pressure from the bottom of each preceding downwardly flowing stream to the top of the next succeeding downwardly flowing stream to build up successive increments of pressure on said finely-divided solid.

2. In the method deflned by claim 1, the further improvement which comprises introducing a gaseous diluent into the upwardly flowing streams of said flnely-divided material to reduce the density and static pressure of the upwardly flowing streams and separating the gaseous diluent from said solids before passing the latter downwardly into the next succeeding stream.

3. Ina process for the conversion of hydrocarbon oils wherein the oil in vapor form is converted in the presence of a finely-divided conversion catalyst and'wherein it is necessary to develop a positive pressure on the finely-divided catalyst to feed the same into the oil vapors; the improvement in the method of imposing the desired pressure on the catalyst which comprises flowing a stream of said finely-divided conversion catalyst alternately upwardly and downwardly in a sinuous path, maintaining each downwardly flowing stream at a materially higher density than the next succeeding upwardly flowing stream whereby the static pressure developed at the bottom of the downwardly flowing streams is substantially greater than the pressure at the bottom of the next succeeding upwardly flowing stream, transmitting excess static pressure from the bottom of each preceding downwardly flowing stream to the top of the next succeedin downwardly flowing stream to build up the de-, sired positive pressure in successive increments.

'4. In the process deflned by claim 3, the further improvement which comprises adding a catalyst to the next succeeding downwardly flowing stream.

- JOHN .C. MUNDAY.

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