US2934325A - Contacting apparatus for gases and liquids - Google Patents

Description

April 26, 1960 G. HAGLUND 2,934,325

CONTACTING APPARATUS FOR GASES AND LIQUIDS Filed Aug. 6, 1956 A tomeys CONTACTDIG APPARATUS FOR GASES AND LIQUIDS Gustaf Haglund, Enskede, Stockholm, Sweden, assiguor to AB Hedemora Verkstiider, Hedemora, Sweden vapours and liquids of the type which comprises a container having a liquid space and on top thereof a .gas

space as well as more than one rotor arranged for the achievement of the contact. Each of these rotors consists of a rotary shaft on which are mounted spreading members, for instance discs, sectors, or arms, in such a way that during a portion of their rotation with the shaft they are submerged or dipped into the liquid. By this type of contact apparatus it is often of great importance that not only gas and liquid are properly mixed in the gas space but also that liquids or liquids containing solid particles suspended therein are kept in a uniform state during the operation so that its composition remains essentially equal throughout the liquid space. This is particularly important in case the liquid contains suspended solids which are liable to deposit on the bottom. Contact apparatus of the current kind are when properly designed, well suited for the absorption, cleaning or condensing of gases or vapours in liquids. In these operations, besides physical processes, also chemical reactions may take place even during very much varying temperature conditions. It has been noted that a great many physical and chemical operations have been diflicult to carry out practically in available apparatus of the present type which is thought to be due to the fact that it has not been possible to keep the liquid in the liquid space homogeneous. It is also important that the gases be kept mixed with one another. Previous apparatus have not proved fully satisfactory in this respect, and the object of the present invention is to achieve a contact apparatus of the above type which fully meets the demands one has to place upon it in order to be able to carry out therein such physical and chemical operations which require great accuracy. It is thus an object of the invention to construct and arrange the rotors so that liquids and suspension treated in the container will become so uniform that the composition will be substantially equal in all parts thereof, even in parts thereof thrown up in the gas space by the rotors.

To obtain these and other objects the invention consists in providing at least two rotors for eftectuating the contact and arranging the rotors in the container so that their shafts which should be substantially parallel to each other, will be positioned substantially perpendicular to the longitudinal direction of the container, e.g. the side walls thereof, and so that at least one rotor will be located substantially only within one longitudinal half of said container extending from the side walls about half way to the opposite side wall and at least one rotor located substantially only within the other longitudinal half of the container extending from said opposite side wall about half way to the first mentioned side wall at least one of the last mentioned rotors being adapted to rotate in opposite direction to the rotational direction of at least one of the first mentioned rotors. The rotors may thus extend /3 to /3 of the way from the one side wall to the opposite side wall. Preferably all rotors in one rates Patent P 2,934,325 Patented Apr. 26, 1960 ICC of the halvesof the container are arranged to rotate in the same direction. In this way all rotors may be made to propel the liquid ina closed path around the container. In some cases it is advantageous to place a partition wall between the longitudinal halves along a ,portion of the length of the container so as to promote "a proper circulation of the liquid and avoid sedimentation at central areas of the bottom.

The invention will now be described more in detail in connection with the attached drawing showing one of many possible embodiments. The drawing will also illustrate and exemplify various ways to arrange the rotors according to the invention. In the drawing:

Fig. 1 shows a plan sectional view, and Fig. 2 a vertical sectional view of an apparatus or arrangement according to the inventiomwhereas Fig. 3 shows a rotor in longitudinal section.

In the side walls of a container 1 of elongated rectangular configuration, a number of shafts 2 are supported in bearings 3. The shafts 2 extend normally approximately to the centre line of the container only, but as shown in Fig. 1, a shaft at one end of the container may according to the invention reach some distance beyond the centre line. One shaft 2a is extended straight across the whole of the container cross section and is supported in hearings in both side walls. The shafts 2 are, all along their whole lengths, and the shaft 2a along half its length, equipped with spreading discs 5 which may be exchangeable. In this way it is possible, when required, to alter the spreading members with regard to diameter and/or length. It is also possible to vary the number of discs. It is favourable to arrange the rotors in staggered relationship to one another so that a rotor at one side is situated just opposite the space between two adjacent rotors at the other side but, one may also, as shown on the drawing, arrange them straight opposite one another. With this arrangement many possibilities of variation are given from which one may be chosen in order to meet special requirements. Moreover, a further possibility of variation is offered through the proposition of controlling the rotary speed of the rotors and possibly the changing of the direction of rotation as is implied by the invention. It is often suitable, as shown in the drawing, to cause all the rotors on one side run in the same direction but opposite to those on the other side.

The liquid space 6 is filled with liquid through the inlet 7 and the liquid leaves through the outlet 8. The gas enters through the gas inlet 9 and is taken out through the outlet 10. The inlets and outlets can be so arranged that gas and liquid pass each other principally counter currently. By means of a level controller, shown in the drawing in the form of an overflow weir 15 the level of the liquid space may be varied and thus still another variation possibility be offered. If desired the rotors may be designed so as to be raised or lowered, preferably individually. This may be done as indicated in Fig. 2 by having the bearings for the shaft 2 vertically adjustable. Thus, for example, the shaft bearings may be shifted between an upper position as at 3 in Fig. 2 and a lower position as at 3a. In this way it is possible to control the suspension effect of the apparatus inasmuch as this effect depends to a great extent upon the vertical distance between the spreading member, such as a disc, and the bottom of the container.

In order to assist in maintaining the circulation path of the liquid around the container in the direction indicated by the arrows in Fig. l, a vertical partition 16 may be installed longitudinally within the container parallel to and intermediate the side walls of the container and between the rotors in opposite longitudinal halves of the container. The partition 16 extends to the bottom of the container but the ends of the partition terminate short of the end walls of the container so as to enable the circulating liquid to go around the ends of the partition as the flowing liquid reaches one end of the container and starts back in the opposite direction in the opposite longitudinal half of the container. I s

In one of its aspects the invention thus consists in positioning the rotor in the container at such a small vertical distance above the bottom thereof that in water filling out said liquid space of the container the portions of the water nearest said bottom and vertically below said rotor will be caused to flow violently as a result of the rotation of the rotor in said water. Thereby solids will be prevented from settling on the bottom, provided that the flow is sufficiently strong for the particular goods suspended. Thus, if, for example, finely divided lime, magnesium carbonate (magnesite) or dolomite is sus- V pended, as for the manufacture of cooking acid for the sulphite cellulose process, the distance must be so small that the flow of the suspension is strong enough for keeping the particles of these substances suspended. The strength of the flow, it is true, depends also upon the diameter of the spreading discs or the like and the rotary speed thereof, but it has been ascertained by experiments that the depth gradient of the flow of the liquid below a rotary disc varies relatively little within the limits of disc diameters and velocities used in practice, whereas the horizontal velocity of the liquid near the edge of the disc varies considerably.

The spreading members are suitably arranged in greater or smaller sections, each comprising a tube 11 having an inside diameter which is a. little larger than the diameter of the shaft 2, 2a onto which it is to be mounted. The length of the tube 11 is made so that one or more sections may be put on to the shaft as desired. Onto this tube there are secured a number of discs 5 or carrying members of some other suitable shape for lifting liquid up into the gas space and propelling the liquid in the tank. The radial dimensions of these carrying members as well as the distances between them are made to suit the requirements according to the treatment called for. The tube 11 is equipped with flanges 13 and sockets 14 enabling the spreading sections to be mounted on the shaft in the number and place wanted. The mechanical design of the spreading sections and the way of fixing them onto the shaft may be varied without influencing thereby the functional results.

It should be understood that the apparatus as illustrated and described is only an example and any combination of two or more rotors as illustrated may be used, provided that there are at least two rotors, one in each half of the container, rotating in opposite directions.

In this connection it should be understood that a spreading device according to the invention is not equal to, or the same as an ordinary turbulator or propeller working down in the liquid. The present spreaders are working both in the liquid and in the gas space simultaneously. They should be made to work at varying depths of liquid and thus also with varying volume in the gas space. One may exchange spreading members and alter the rotation velocity or the direction of rotation in order to accomplish the results demanded by the prevailing conditions. The spreading principle, as such, is conventional as is the employment of plain, corrugated or otherwise formed circular rotary discs, bars or other kinds of carrying members which are rotated, but, according to the invention these spreading elements are applied in a new and more efiicient way than previously.

It is thus obvious that according to the invention the spreading devices, as a principle, are not allowed to extend across the whole of the width of the absorption apparatus but only over substantially half of the width. In this way the spreading devices will work or operate each on its own side of the liquid and gas spaces of the apparatus. When these spreading devices are rotated at adequately determined velocities and directions of rotation and at a desired depth in the liquid and at adequate distance from the bottom, movements in the liquid and gas of the apparatus may be achieved which cannot be arrived at in any other way hitherto known and, which movements have a strong and eflicient influence on the reaction cycles. The liquid may, for example, move as shown by the arrows in the drawing.

In order to illustrate how the objects of the invention can be obtained by an arrangement according to this invention an example will now be given.

In a rectangular closed container of a length of 2.25 meters, a width of 1.5 meter and a height of 2 meters two rotors were arranged, each extending 0.75 meter from opposite side walls near opposite end walls. Each rotor carried ten discs evenly distributed on the rotor shaft. The rotors could be displaced vertically.

In one test discs of a diameter of 0.6 meter were used and the rotors were set so that the lower-most edge of each disc was about 0.15 meter from the bottom of the container. The container was charged with water to a height corresponding to a submersion depth of the discs of 0.1 meter. The rotors were made to rotate in opposite directions at a speed of 610 revolutions per minute in order to propel the liquid along the side from which the respective rotor extended. Powdered lime was added in a quantity corresponding to 2 percent by weight of the water. Samples taken from the spray in the gas space, from a surface layer of the suspension, and from a layer near the bottom gave different values of lime percentage, and some lime settled on the bottom.

The rotors were now lowered so that the lower-most edges of the disc was 0.10 meter. Samples from the places mentioned now showed practically the same percentages of lime and no deposits were obtained.

Tests were also made with discs of 0.5 meter diameter and relations between rotary speed, submersion depth, and distance from bottom for obtaining uniform suspension could easily be ascertained.

Obviously the relations between disc diameter, rotary speed, submersion depth, and distance from bottom varies according to the material to be suspended.

Generally, however, in an apparatus according to the invention the number and diameters of the spreading members on each rotor, the depth of submersion of said spreading-members below the liquid level in said liquid space, and the vertical distance of said rotors above the bottom of said container are so correlated to each other that the horizontal velocity of a liquid filling out said liquid space is substantially equal over the entire vertical cross section in each longitudinal half of the container when the rotors are rotated at working speed. It has been ascertained that up to a given speed the efliciency of a given apparatus in making the liquid uniform and the depth to which the eificient stirring effect reaches increases materially. Above that given speed, however, an increase of the speed will not materially improve the homogenizing of the liquid. The critical range of velocity depends on the structure of the apparatus and can be easily ascertained for a given apparatus. The working speed should, of course, be at least somewhat below the critical velocity and it will be determined to a great extent by the requirements for an effective spraying of the liquid into the gas space of the apparatus and the economical gain by an increase of velocity.

The distance between the rotor and the bottom of the container can also be defined by reference to the behavior of water or a given suspension, such as of finely divided lime or magnesite, filling out the liquid space. Thus, the apparatus should be such that the portions of the water nearest said bottom and vertically below said rotor will be caused as a result of the rotation at working speed of the rotor submerged in said water to a depth equal to at least /3 of its radius to flow practically immediately upon the starting of said rotation. With reference to a suspension the particles suspended near the bottom should be caused under said circumstances to move and be kept suspended, so that no sedimentation will take place.

In case the spreading members are in the form of, for instance, sectors or arms their diameters are to be reckoned as the radial distances of the outermost points of the sectors or arms, respectively, from the centre of the rotors.

What is claimed is:

1. Apparatus for effecting contact between a gas and a liquid containing particulate matter suspended therein, said apparatus comprising a closed container of essentially rectangular configuration having top and bottom walls, side Walls and end walls connecting said side walls, a liquid inlet to said container and a liquid outlet from said container, means for maintaining the liquid in said container at a given level above the bottom wall thereof thereby to establish a gas space above the surface of the liquid, a gas inlet to said gas space and a gas outlet from said gas space, a plurality of rotors for spraying the liquid into said gas space, each said rotor comprising a rotatable shaft equipped with a plurality of spreading members distributed along the length thereof and extending normal to the shaft axis, the length of such portions of said rotors as are equipped with said spreading members being not more than one-half the distance between opposite side wall of said container, means mounting at least one of said rotors with the spreading member equipped portion thereof located on one side of a center line extending longitudinally through said container, means mounting at least one of said rotors with the spreading member equipped portion thereof located on the other side of said center line, said spreading members of said rotors being parallel with said side walls and being partially submerged in the liquid during a portion of their rotation, the shafts of said rotors being parallel to each other and parallel to the bottom wall of said contamer and extending inwardly respectively from opposite side walls of said container, means for rotating all of the spreading members located on one side of said center line in the same direction, means for rotating all of the spreading members located on the other side of said center line in the same direction but in a direction opposite to that in which the spreading members on the opposite side of said center line rotate thereby to elfect a spraying of the liquid from said rotating spreading members into said gas space and to establish a closed path for circulation of the liquid in opposite directions respectively through the longitudinal halves of said container which lie at opposite sides respectively of said center line, the number and size of said spreading members on each said rotor, the depth of submersion of said spreading members in the liquid, the distance between the lowermost edges of said spreading members and said bottom wall of said container and the rotational speed of said spreading members being so correlated with respect to each other and with respect to the character of the liquid that the horizontal velocity of the liquid is substantially equal over the entire vertical cross-section of the liquid in each said longitudinal half of said con tainer thereby to maintain the particulate matter suspended uniformly in the liquid and thereby prevent settling out of any of the particular matter on said bottom Wall of said container.

2. Gas-liquid contact apparatus as defined in claim 1 whererin said container is elongated and which includes a plurality of rotors in each longitudinal half of said container.

3. Gas-liquid contact apparatus as defined in claim 2 wherein a rotor in one longitudinal half of said container is located opposite the interspace between two adjacent rotors in the other longitudinal half of said container.

4. Gas-liquid contact apparatus as defined in claim 1 wherein said container is elongated and which further includes a partition wall extending along said center line for separating said longitudinal halves thereof.

References Cited in the file of this patent UNITED STATES PATENTS 1,253,401 Lorimer Jan. 15, 1918 1,592,231 Stroder July 13, 1926 1,848,202 Scott Mar. 8, 1932 2,094,456 Lattner Sept. 28, 1937 2,237,482 Faber Apr. 8, 1941 2,397,818 Tausch -1 Apr. 2, 1946

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