US2729544A - Contact apparatus with rotating discs - Google Patents

Description

Jan. 3, 1956 w. J. PIETERS 2,729,544

CONTACT APPARATUS WITH ROTATING DISCS Filed Sept. 7, 1951 g I g u a .l

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WILLEM J. PlEJERs BY W/v M HIS ATTORNEY United States Patent-(*3 CONTACT APPARATUS WITH ROTATING DISCS Willem Johan Pieters, Amsterdam, Netherlands, assignor to Shell Development Company, Emeryville, Calif., a corporation of Delaware Application September 7, 1951,'Serial No. 245,507

Claims priority, application Netherlands September 13, 1950 6 Claims. (Cl. 23-2705) This invention relates to contactors for intimately contacting two or more fluent phases that are at least partially immiscible, e. g., immiscible or partially miscible, and is, more particularly, concerned with improvements in contactors provided with rotating discs mounted in alternation with stationary baffie rings that are fixed to the inner wall of an at least partially upright, preferably vertical column or tube. Such apparatus is suitable for effecting intimate contact between fluent material conducted through the device either concurrently or countercurrently and may be applied, for example, to solvent extraction of liquid mixtures, such as mineral or fatty or essential oils, with one or more selective solvents, or for bringing reagents into intimate contact when carrying out chemical reactions, such as reactions between higher olefins and sulfuric acid. The fluent materials or phases are, as a rule, a pair of liquids. or a liquid and a gas; one of the phases may, however, be a solid phase, such as finely comminuted solid.

Contactors having rotating discs are already known.

Briefly, they comprise a stationary tube or shell which is at least partly upright, is provided with inlets and outlets for fluent materials, and is subdivided into a plurality of compartments, which may be substantially identical in size and shape, by stationary annular bafiles or rings extending to the tube wall and having central openings at the tube axis; each compartment has at least one rotor disc and the several rotor discs situated in different compartments are fixed to a common rotor shaft which is coaxial with the tube or different groups of rotor discs are mounted to different rotor shafts extending longitudinally through the tube, the rotor discs being preferably located to be substantially at the centers of the respective compartments. Such a device will herein be referred to as a contactor of the character described.

When the fluent materials are admitted to the tube either at the same end or at opposite ends, andare withdrawnat ends opposite to their respective points of introduction, they flow successively through the contacting compartmentsand form separate phases therein.- Rotation of the rotor shaft and discs thereon imparts a further movement to the phases, which is importantfor effecting intimate contact between them: The rotor discs cause the phases to rotate about the tube axis and the resulting.

centrifugal force induces the phases at the .level of the discs to move radially outwards from the shaft as outward currents along a somewhat spiral path toward the tube wall; upon reaching the latter the fluent material changes direction, one part moving upwards andthe other downwards, and returns as two inward currents withineach' compartment, in the neighborhood of each stationary baffle; Hence the motion of the phases, apart from their fiow through the successive compartments, is generally toroidaL but with themajor part transverse to the axis of the shaft, forming vortex patterns,

In contactors of the character described that have a plurality of rotor shafts, .each compartment generally has a plurality of rotor discs, all rotor discswithin any.

2,729,544 l atehted Jan. 3, 1956 shafts being in such case situated in a circle surrounding the tube axis and alternate shafts are rotated in a common direction which is opposite to the direction or rotation of the intervening shafts. Such contactors are described in Netherlands patent application Serial Number 148,854, filed September 22, 1949.

The present invention relates to an improvement in contactors of the character described and has for its object to avoid or minimize the occurrence of undesired tubulence, which has the result of lowering the contacting efficiency of the device.

In summary, according to this invention streamlining bodies are provided in contactors of the character described at one or more of the places where the vortical currents of fluent material change their directionsof flow. These bodies have contours conforming as far as possible to the pattern of the flat vortices created in the compartments.

Thus, streamlining bodies in the nature of fillets may be provided at the dihedral angles formed by the rotor discs with the rotor shaft and/ or in the dihedral angles formed by the stator rings with the inner wall of the tube of column, which bodies locally modify the wall contour bounding the currents in the contacting compartments so as to better adapt the contour for the formation of the desired vortex systems to be created in the operation of the contactor. The bodies near the rotor shaft may be integral with the rotor shaft or rotor discs while those near the tube or column wall maybe integral with the column or with the stator baffles; however separate bodies may be employed. If these bodies are not present, dead angles occur in the apparatus in the places indicated which may give rise to undesirable turbulence. If, for example, an extraction is carried out with the apparatus, the useful effect thereof will decrease as a result of this turbulence.

Similarly, it is sometimes advantageous, particularly in the case of contactors of large diameter, to fit streamlining bodies on the rotor shaft approximately midway adjacent rotor discs (i. e., at about the level of the stator baffles) and/or on the tube or column wall approximately midway between the stator baflles (i.'e., at about the level of the rotor disc). These bodies function in the nature of current dividers and will be herein so designated; they will in general be smaller than the fillet-like bodies mentioned in the foregoing paragraph and extend outwardly from the rotor shaft and column wall, respectively, for short radial distances.

According to the invention any of such streamlining bodies or combination thereof may be employed. In

the illustrative embodiment to be described herein all four types of bodies are shown.

The invention will be described further with reference to the accompanying drawing forming a part of this specification and illustrating one preferred embodiment by way of example, wherein:

Fig. 1 is a vertical central section through a contactor embodying the invention; and

Fig. 2 is a transverse section taken on line 2-2 of Fig. 1.

In the drawings a vertical column or tube of circular imperforate rotor discs 6 made of thin metal or other' rigid material are fixed to the rotor shaft for rotation therewith with their plane surfaces perpendicular to the shaft. axis. The innerwall. of the column. is equipped with annular horizontal stator rings or baffles 7, likewise made of thin material but having central circular openings concentric with the rotor shaft and discs, the diameter of the circular openings being materially greater than the diameter of the shaft and, preferably, also greater than the diameter of the rotor discs. The stator baffles thereby subdivide the column into a vertical series of compartments, the heights of which are determined by the vertical intervals between the bafiies. These intervals may be uniform throughout the height of the column, but this is not in every case essential. The rotor discs 6 are situated half-way between each pair of adjoining stator baffles. Suitable inlets and outlets for the fluent material are provided; when the column is intended for countercurrent contacting the inlets 8 and 9 are at the top and bottom, respectively, being advantageously located beyond the stator bafiies but displaced somewhat in from the ends of the column, while the outlets 10 and 11 are located near the extreme ends of the column.

As regards the optimum dimensions to be used in constructing the contactor, reference is made to U. S. Patent No. 2,601,674 to Gerrit H. Reman, wherein it is shown thatbest results are obtained when, in each compartment of the contactor, the diameter of the rotor discs is less than the diameter of the central opening in the stator battles; when the ratio of the internal column diameter to the diameter of the rotor disc is between about 1.5 and 3.0; and when the ratio of the internal column diameter to the compartment height (the height being equal to the interval between stator baflles) is between about 2 and 8. The instant invention is not, however, limited to contactors conforming to any or all of those relative dimensions. In fact, it was found that in the case of columns of large diameters, e. g., those with internal diameters in excess of 50 cm., higher values for the ratios of the last two relations are desirable for mechanical reasons; thus, with large diameter columns, such as those from one-half to two meters in diameter, ratios of column diameter to rotor disc diameter above 5, e. g., to 10, may be employed without appreciably decreasing operating efiiciencies, while ratios of internal column diameter to compartment height in excess of 8, e. g., up to 20, may be used to advantage. No claim to sole inventorship is made as to any of the dimensional relations given in this paragraph.

Various modifications in the construction of contactors of the character described, details concerning operation and auxiliary equipment are further set forth in the said Reman patent and need not be repeated herein in extenso.

Now according to the instant invention streamlining bodies are provided at any of the following places: (a) at the juncture of the rotor discs 6 and the rotor shaft, shown at 12; (b) at the juncture of the stator bafiles 7 and the vessel wall, shown at 13; (c) on the rotor shaft between the rotor discs, shown at 14; and (d) on the vessel wall between the stationary baffles, shown at 15. These may be formed, for example, as follows:

Each rotor disc 6 is thickened both at the top and bottom at the radially innermost part thereof to provide a pair of annular fillets 12, one above and the other beneath the rotor disc. These fillets have concave surfaces of revolution; in cross section these surfaces are arcuate and the intermediate part thereof may be substantially circular while the nearly vertical and horizontal parts may be given progressively longer radii to merge smoothly with the shaft and rotor disc faces. It will be noted that in the preferred construction shown the upper and lower faces of each rotor disc are flat for the major part of the radial extent thereof. These flat faces as well as the fillets should, for best results, be smooth so as to cause as far as possible a dispersion wherein the dispersed droplets have uniform sizes.

Each stator ring 7 is thickened both at the top and bottom at the radially. outermost part thereof to provide a pair of annular fillets 13, one above and the other beneath the baffle. These fillets have concave surfaces of revolution and may have cross sectional shapes as described for the fillets 12, merging substantially with the vessel wall and with the flat upper and lower faces of the baffles. In the preferred construction these batfies have upper and lower faces that are flat throughout the major parts of their radial extents.

The streamlining bodies at 14 and 15 serve as current dividers in addition to guiding the currents in their changes of direction; they may be integral with the rotor shaft and vessel wall, respectively, or formed of separate rings as shown and fixed to the shaft and vessel. Each of these bodies has two concave surfaces of revolution, each surface extending smoothly substantially from the vertical to the horizontal and each pair of surfaces on the same body merging along a sharp annular edge that is advantageously situated away from the rotor shaft or vessel wall, respectively, by a distance that is a minor part of the radial extent of the neighboring rotor disc and stator baflles, respectively. Each body 14 is situated substantially midway between neighboring rotor discs, i. e., at about the level of a stationary baffle 7 and radially spaced a substantial distance therefrom to afford ample communication between compartments. Similarly, each body 15 is situated substantially midway between neighboring stationary baffles, at about the level of a rotor disc 6 and radially spaced therefrom to afford ample communication between the upper and lower regions of the respective compartment.

Operation In operating the contactor, the fluent materials may be admitted and contacted either intermittently or continuously, and either concurrently or countercurrently. In operating the contactor for countercurrent extraction heavy and light materials are introduced at the top and bottom through inlets 8 and 9, respectively, and the contactor can be operated either so that the light phase or so that the heavy phase is the continuous phase, the other phase being the dispersed phase. When the light phase is to be continuous the column is initially filled with light phase; thereafter the heavy material is introduced at the top and dispersed by the rotor discs, passing downwardly by gravity from compartment to compartment and collecting at the bottom to form a layer of settled heavy phase below the level A. By regulating the rates of feed and drawofi of the heavy phase through the outlet 10 by a suitable valve, not shown, the interface between light and heavy phases is maintained at the level A. On the other hand, when the light phase is to be dispersed the column is initially filled with heavy phase and the interface is maintained at the level B near the top of the column by similarly regulating the flow rates and the rate of discharge of heavy phase.

For greatest contacting efiiciency it is advantageous to operate the rotor at the highest speed possible without causing flooding, typically one thousand to several thousand revolutions per minute; as the flow rates are increased lower rotor speeds become necessary. Flooding occurs at higher rotor speeds because the droplets of dispersed phase become smaller with increasing rotor speeds, eventually becoming so fine that they cannot settle rapidly enough to cause the phases to flow between compartments at the required rate. Since the flood point is largely determined by the smallest droplets present in the compartment, it is advantageous to prevent the formation of any great range of droplet sizes, since this would on the one hand produce coarse droplets that are not adequately contacted with the other phase while at the same time producing very fine droplets that place a limit on the permissible rotor speed. Such non-uniformity in droplet sizes is promoted by roughness and turbulence, and it is 5 a particular "feature of this invention that the stream lining bodies minimize turbulence.

For countercurrent extractions it is desirable that the light and heavy fluent phasesfornied in the contactor have density differences that are at least 0.02 gram per cubic centimeter; it is easier to operate the column with phases having greater density difference, e. g. at least 0.08 gram per cubic centimeter.

The operation of the contactor will now be described as applied to the extraction of a light hydrocarbon oil forming the continuous phase with a heavier solvent, such as furfural or aqueous phenol, forming the dispersed extract phase. The column having been initially filled with oil, the heavier solvent is introduced continuously at the top and oil is introduced continuously at the bottom While rotating the rotor shaft and discs, resulting in a fine dispersion of the solvent in the oil, particularly at the levels of the rotating discs. The finely dispersed droplets constitute the extract or solvent phase, which is collected at the bottom and withdrawn through outlet at a controlled rate to maintain the interface at A. The continuous oil phase rises through the column and dispersed extract phase settles from it at the level above the inlet 8. The oil is then withdrawn through the outlet 11, which is preferably fully open to permit discharge of oil at the rate determined by the oil feed rate.

The mechanism of dispersion and intimate contact within the contactor compartments may be described as follows: When the contactor is in operation there is, in the first place, a countercurrent flow through the column of light and heavy phases, caused by difference in densities of the phases. The rotation of the rotor discs imparts a rotary movement to the phases in contact therewith, and thereby sets up centrifugal forces which induce flow of the phases from the rotor shaft toward the column wall substantially in the transverse planes of the rotor discs, indicated by the dotted lines T in Fig. 1. Each outward current, upon approaching the vessel wall, is induced to change direction and divide into an upward and a downward current, which flow as separate currents toward the stationary baffles. This division and change in direction are aided by the streamlining bodies 15. The upward and downward current are again induced to change direction near their respective bafiles and to flow as separate inward currents along their respective stationary baffles as indicated by the dotted lines U1 and U2; the streamlining bodies 13 assist in bringing about this change in direction. Inward currents U1 and Us in contiguous compartments, on opposite sides of the same stationary baffie, merge when passing radially inwardly of the baflies. The merged inward currents, upon approaching the rotor shaft, are induced to change direction and divide into an upward and a downward current, which fiow as separate currents toward the rotor discs in adjoining compartments. This division and change in direction are aided by the streamlining bodies 14. The upward and downward currents are induced to change their directions near their respective rotor discs and become parts of the outward currents T. These changes in direction are aided by the streamlining bodies 12. This vortical flow resulting from the rotation of the rotor discs causes one of the phases to be reduced to a very fine state and dispersed because of the shearing stresses accompanying this flow. This flow is superimposed on the flow of the phases through the compartments. Hence, for the schematic picture of the flow of the phases we have a gravity settling of heavy drops in an ascending stream of light phase superimposed on a toroidal vortical flow, which is for the greater part in a horizontal direction. This toroidal flow causes local circulation of both liquids within each compartment and only portions of the liquid taking part in this flow pass on to the next compartment by gravity. The path of the dispersed droplets of the heavier extract or solvent phase which pass to the next compartment is indicated in Fig. l by the dotted line marked S.

should follow as far-as possible the pattern of the vortices created in these devices.

For further examples of the application of the contactor and modifications that may be made in the arrangement,=reference is made to the aforesaid earlier patentto Reman.

I claim as my invention:

1. In a contactor of the character described, having a plurality of compartments separated by centrally apertured walls and bounded by outer, substantially circular walls and containing within each compartment a rotor disc lying wholly within the compartment and spaced from the said apertured walls thereof, several rotor discs in different compartments being mountedon a shaft that extends through and is smaller than the apertures in said apertured walls, wherein,within each of said compartments, fluent material is made toflow as flat toroidal vortices that include flow of the material outwardly from the rotor disc, followed by division of the material and change in the flow direction thereof near the outer wall and flow first as separate, oppositely directed currents toward said apertured walls and thereafter inwardly along said walls, the improvement of an annular streamlining body at said outer wall situated intermediate said centrally apertured walls and substantially opposite the rotor disc, said body having a pair of concave surfaces directed toward the said apertured Walls and toward the rotor shaft.

2. A contactor according to claim 2 wherein said surfaces of the streamlining body merge along a sharp edge that is displaced inwardly from said outer wall by a distance that is a minor part of the distance from said wall to the central aperture of said apertured wall.

3. in a contactor of the character described, having a plurality of compartments separated by centrally apertured walls and bounded by outer, substantially circular walls and containing within each compartment a rotor disc lying Wholly within the compartment and spaced from the said apertured walls, several rotor discs in different compartments being mounted on a shaft that extends through and is smaller than the apertures in said apertured walls, wherein, within each of said compartments, fluent material is made to flow as fiat toroidal vortices that includes flow of the material outwardly from the rotor disc, division of the material and change in the flow direction thereof near the outer wall and flow first as separate, oppositely directed currents toward said apertured walls and thereafter inwardly along said walls, followed by merging of inwardly flowing material from adjoining compartments, division of the merged material and change in the flow direction near the shaft and consequent flow as oppositely directed currents along the shaft, the improvement of an annular streamlining body at said shaft disposed intermediate neighboring rotor discs and substantially within the central aperture of one of said apertured walls, said body having a pair of concave surfaces directed toward said neighboring discs and toward said outer wall, the greatest diameter of said body being smaller than the diameter of said aperture.

4. A contactor according to claim 3 wherein said concave surfaces of the streamlining body merge along a sharp edge that is displaced radially from the shaft by a distance that is a minor part of the radius of the rotor discs.

1 having a diameter materially less than the diameters of said central openings mounted for rotation coaxially within said shell and extending through said-openings; a plurality of flat, smooth, circular rotor discs having diameters less than said central openings and fixed to said shaft perpendicularly to the axis thereof, each rotor disc being situated wholly within one of said compartments approximately midway between the stationary baflies thereof, whereby upon rotation of said rotor discs, in each compartment fluent materials are induced to move in toroidal vortices, and an annular streamlining body situated at the shell wall midway between said stationary baffles and having a pair of concave surfaces of revolution facing toward said baflles and toward the rotor shaft, said surfaces merging along an edge displaced from the shell wall toward the rotor shaft by a distance that is a minor part of the radial extent of said stationary baflles.

6. A rotating disc contactor comprising an at least partially upright tubular shell of circular cross section; vertically spaced inlet and outlet openings for fluent material; a plurality of thin, flat annular stationary baflles, fixed within the shell and spaced apart to divide the shell into compartments, each baflle extending from the shell wall to a central circular opening, whereby fluent material admitted at the inlet opening must traverse said compartments in flowing to said outlet opening; a rotor shaft having a diameter materially less than the diameters of said central openings mounted for rotation coaxially within said shell and extending through said openings; a plurality of flat, smooth, circular rotor discs having diameters less than said central openings and fixed to said shaft perpendicularly to the axis thereof, each rotor disc being situated wholly within one of said compartments approximately midway between the stationary baffles thereof, whereby upon rotation of said rotor discs, in each compartment fluent materials are induced to move in toroidal vortices; and an annular streamlining body situated on the rotor shaft Within a central opening in a stationary baffle and having a pair of concave surfaces of revolution facing toward the neighboring rotor discs and toward the shell wall, said surfaces merging along an edge displaced from the rotor shaft toward the shell wall by a distance that is a minor part of the radial extent of said rotor discs.

References Cited in the file of this patent UNITED STATES PATENTS 1,208,534 Foret Dec. 12, 1916 2,029,691 Robinson Feb. 4, 1936 2,520,424 Mills et al. Aug. 29, 1950 2,601,674 Reman June 24, 1952

Claims (1)

1. IN A CONTACTOR OF THE CHARACTER DESCRIBED, HAVING A PLURALITY OF COMPARTMENTS SEPARATED BY CENTRALLY APERTURED WALLS AND BOUNDED BY OUTER, SUBSTANTIALLY CIRCULAR WALLS AND CONTAINING WITHIN EACH COMPARTMENT A ROTOR DISC LYING WHOLLY WITHIN THE COMPARTMENT AND SPACED FROM THE SAID APERTURED WALLS THEREOF, SEVERAL ROTOR DISCS IN DIFFERENT COMPARTMENTS BEING MOUNTED ON A SHAFT THAT EXTENDS THROUGH AND IS SMALLER THAN THE APERTURES IN SAID APERTURED WALLS, WHEREIN, WITHIN EACH OF SAID COMPARTMENTS, FLUENT MATERIAL IS MADE TO FLOW AS FLAT TOROIDAL VORTICES THAT INCLUDE FLOW OF THE MATERIAL OUTWARDLY FROM THE ROTOR DISC, FOLLOWED BY DIVISION OF THE MATERIAL AND CHANGE IN THE FLOW DIRECTION THEREOF NEAR THE OUTER WALL AND FLOW FIRST AS SEPARATE, OPPOSITELY DIRECTED CURRENTS TOWARD SAID APERTURED WALLS AND THEREAFTER INWARDLY ALONG SAID WALLS, THE IMPROVEMENT OF AN ANNULAR STREAMLINING BODY AT SAID OUTER WALL SITUATED INTERMEDIATE SAID CENTRALLY APERTURED WALLS AND SUBSTANTIALLY OPPOSITE THE ROTOR DISC, SAID BODY HAVING A PAIR OF CONCAVE SURFACES DIRECTED TOWARD THE SAID APERTURED WALLS AND TOWARD THE ROTOR SHAFT.

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