US 3669414 A
Apparatus for mixing solid material with a liquid wherein a mixer device comprising a casing and an impeller is mounted below an outlet at the bottom of a subsidiary vessel. Liquid and solid material are continuously supplied to the subsidiary vessel, separately or together. Material within the casing is expelled outwardly by the impeller and is subjected to thorough mixing and disintegration. Further material, drawn downwardly in the subsidiary vessel, is directed towards the mixer casing by inwardly and downwardly sloping side walls of the subsidiary vessel.
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Description (OCR text may contain errors)
United States Patent Love 1 June 13, I972  MIXING APPARATUS 2.635359 4/1953 Dreyfus ..259/26 X i 2.882,l49 4/l959 Willemsm. ..259l66 X  E2532 3. 3,417,968 I2/l968 Schlecht .259/23 x 3.502.305 3/1970 Grun ..259/8  Filed: March 19, I969 Primary Eraminer-Waiter A. Scheel 1 Appl' 808399 Assl'slant E.taminer-Alan I. Cantor Anorney- Delio & Montgomery  Foreign Application Priority Data March 25, 1968 Great Britain ..l4,363/68 Amer Apparatus for mixing solid material with a liquid wherein a I52] U.b. LL... ..259/8, 259/96 i er device comprising a casing and an impeller is mounted  Int. Cl. ..B0lf 7/26 be|ow an out) at the bonom f a subsidiaty vemL Liquid  new of "259/661 and solid material are continuously supplied to the subsidiary 259/23 7 vessel. separately or together. Material within the casing is expelled outwardly by the impeller and is subjected to thorough  and mixing and disintegration. Further material, drawn UNITED STATES PATENTS downwardly in the subsidiary VCSSQI, i8 directed IPWflIdB lllC 3 62 89 I, 968 R h al 259/96 X mixer casing by inwardly and downwardly sloping slde walls of ,3 ,6 l 01 man et the subsidi vessel 3,423,075 H1969 Knudsen et a]. ..259/96 X ary 3.489356 1/1970 Combs et al. ..259/96 X 13 Claims, 2 Drawing Figures L\ I7 F 2, /I1
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INVENTOR Gordon U. Love,
D f Ms M W 1 w mma:
MIXING xrmnxrus BACKGROUND OF THE INVENTION This invention relates to mixing apparatus.
In mixing a powder with a liquid it is known to mount a mixing device within a vessel containing the liquid and to apply a charge of the powder to the surface of the liquid. Frequently, however, the powder tends to float on the surface of the liquid and difficulty is experienced in wetting" the powder as a preliminary to its being mixed and dispersed throughout the volume of the liquid. it is found that the particles of the powder coagulate, forming lumps which are wetted on the outside but dry inside. These lumps float on the surface for a long time before they are drawn down by the vortex action of the mixing device. Unfortunately, however, the vortex also draws air or other surrounding gaseous medium into the volume of the liquid, and the greater the surface area of the liquid the greater is the required vortex action and the greater the amount of gaseous medium introduced.
in mixing a solid which is readily wetted with a liquid there is a problem in ensuring that all of the solid is drawn through the mixing device and is thereby subjected to mixing and disintegration. Accordingly, it has been proposed to carry out the mixing in a pipeline within which there is provided an apertured partition wall and a mixing device which is arranged on the outlet side of the partition wall and receives all of the material flowing through the aperture in the wall. Even with this apparatus solid material may separate out from the liquid on the inlet side of the partition wall and this may cause a blockage in the pipeline.
STATEMENT OF THE INVENTION The present invention includes apparatus for mixing solid material with a liquid, comprising a mixer casing having an inlet aperture and outlet aperture means, an impeller which is adapted, upon rotation, to expel material within the casing outwardly via the aperture means, thereby effecting mixing of the solid material with the liquid, and a subsidiary vessel having inlet means for the continuous supply of liquid and solid material thereto and an outlet which, in use of the apparatus, is disposed in a lower part of the subsidiary vessel and provides a flow of liquid and solid material to the inlet aperture of the casing, the side walls of the subsidiary vessel being so arranged that material at each location within the subsidiary vessel is drawn downwardly within the vessel and is directed towards the inlet aperture in the casing upon rotation of the impeller.
Suitably, the mixer casing, the impeller, and the outlet of the subsidiary vessel are disposed within a main vessel adapted to contain a large volume of the said liquid and solid material, and the surface area of liquid within the subsidiary vessel which is exposed to the surrounding gaseous medium is substantially smaller than the exposed surface area of liquid in the main vessel when the mixer casing and impeller are immersed in the liquid in the main vessel, whereby solid particles at each location on the surface of the liquid in the subsidiary vessel are drawn downwardly by the impeller and are accompanied by a reduced amount of the said gaseous medium.
Alternatively, an apparatus according to the invention further comprises an inlet conduit for the continuous supply of liquid and solid material to an upper part of the subsidiary vessel, and an outlet conduit into which material is expelled by the impeller via the outlet aperture means in the mixer casing.
BRIEF DESCRIPTION OF THE DRAWINGS The invention will now be described, by way of example, with reference to the accompanying drawings, in which:
FIG. 1 is a vertical section of an apparatus according to the invention;
FIG. 2 is a side elevation of a second apparatus according to the invention.
2 DESCRIPTION OF THE PREFERRED EMBODIMENTS The mixing apparatus shown in FIG. 1 of the drawings is suitable for use in mixing a powder such as carboxymethyl cellulose with a large volume of a liquid such as water without introducing undesirable quantities of air or other surrounding gmeous medium into the mixture.
This apparatus includes a main, cylindrical vessel 1 which serves as a container for the liquid and a small, subsidiary vessel 3 which is mounted within the main vessel 1 and is used for introducing the powder into the liquid therein. Associated with the subsidiary vessel 3 are mixing devices 5 and 7, each including a casing and an impeller, and an electric motor 9 for driving the impellers.
The subsidiary vessel 3 of the present apparatus has a cylindrical upper part 11, a tapering intennediate part 13. and a lower neck part 15 of reduced diameter. The vessel 3 is open at the top and bottom thereof.
For mounting purposes a horizontally extending bracket 17 is welded to the top of the subsidiary vessel 3 and extends outwardly therefrom. in its mounted position the subsidiary vessel 3 is arranged with the bracket I7 resting on a peripheral rim 19 at the top of the main vessel 1 and fixedly secured to the rim by suitable clamping means (not shown). The subsidiary vessel 3 then extends downwardly into the main vessel 1 with the lower part 15, the intermediate part I3 and approximately half of the upper part 11 of the subsidiary vessel below the surface of the liquid in the main vessel.
An inlet aperture 21 for liquid is formed in the cylindrical upper part 11 of the subsidiary vessel 3 and is arranged below the level of liquid in the main vessel 1, as hereinafter described.
The above-mentioned mixer devices 5 and 7 are mounted at the lower end of the subsidiary vessel 3, each having a casing which is secured relative to the vessel 3 and an impeller which is mounted on a shaft 23 extending downwardly through the vessel 3, coaxially thereof. At its upper end the impeller shaft 23 is coupled to an output shaft of the electric motor 9, which is mounted on a cross-member 25 extending diametrically of the upper, open end of the vessel 3.
For mounting the casings of the mixer devices 5 and 7 a mounting ring 27 is welded to the outside of the neck part 15 of the subsidiary vessel 3, coaxially thereof, and an annular mounting plate 29 having a diameter greater than the diameter of the ring 27 is secured to the undersurface of the ring by four screws 31.
A casing 33 of the upper mixing device 5 is formed of a cylindrical side wall having an outer, peripheral flange which is secured to the undersurface of the mounting plate 29 by means of screws 35. The casing 33 is arranged coaxially of the neck part 15 of the subsidiary vessel 3 so that an open, upper end thereof receives material flowing downwardly from that vessel. Outlet apertures 37 are formed in the cylindrical side wall of the casing 33.
An impeller 39 of this first mixing device includes an annular plate 4| formed on its lower surface with an apertured boss and on the upper surface thereof with four upstanding, radially extending blades 43. The external diameter of the annular plate 41 and of the volume swept out by the blades 43 upon rotation thereof is slightly less than the internal diameter of the side wall of the casing 33 and the blades 43 are arranged at the same vertical location as the outlet apertures 37 in that side wall. The inlet to the casing 33, which is defined by the annular space between the shaft 23 and the neck part 15 of the vessel 3, has a cross-sectional area substantially smaller than the cross sectional area of the volume swept out by the impeller blades.
For securing a casing 45 of the second mixer device 7 relative to the subsidiary vessel 3 a cylindrical mounting element 47 is clamped between the undersurface of the above-mentioned, annular mounting plate 29 and a lower annular, mounting plate 49 by means of axially extending screws 51, each screw 5| extending upwardly through an aperture in the plate 49 and having its upper end threadably engaged in an aperture in the plate 29. The cylindrical element 47 and the upper and lower annular plate 29 and 49, respectively, together form a cylindrical chamber 53 into which material emerges from the casing 33 of the first mixer device 5.
The casing 45 of the lower mixing device 7 includes a cylindrical mesh screen 55 which is arranged coaxially of the lower annular plate 49 with an outer flange at the upper end of the screen 55 contacting the undersurface of the plate 49 and secured thereto by screws 57. Each of these screws 57 extends upwardly through a bottom wall in a housing 59 which is also secured below the lower annular plate 49 and supports a bearing 61 for the lower end of the impeller shaft 23. This housing 59 is formed with a series of apertures 63 to allow material flowing through the mesh screen 55 to pass to the exterior of the housing.
An impeller 65 of the lower mixing device 7 is similar to the impeller 39 of the upper device 5, having an annular plate 67 which is secured to the impeller shaft 23 and four upstanding blades 69 disposed adjacent to the mesh screen 55 forming the side wall of the casing 45.
Secured to the element 45 is a tube 71 which receives liquid flowing outwardly through the mesh screen 55 and the apertures 63. An outlet of the tube 71 is disposed at a predetermined location in the main vessel 1.
An additional impeller 73 is secured to the shaft 23, within the subsidiary vessel 3.
in use of the present apparatus the main vessel 1 is filled with liquid to a level above the inlet aperture 21 in the side wall of the subsidiary vessel 3 as described above. The electric motor 9 is then energized to rotate the impeller shaft 23 and the three impellers mounted thereon and, finally, the powder is fed into the upper end of the subsidiary vessel 3 at a predetermined rate.
Rotation of the bladed impeller 39 of the upper mixing device causes liquid and powder within the subsidiary vesel 3 to be drawn downwardly through the aperture at the lower end of the vessel and into the mixer casing 33. Downward flow of material is assisted by the rotating impeller 73. Material is expelled radially outwardly through the apertured side wall of the casing 33 and into the chamber 53 surrounding this casing by the rotating impeller blades 43. In passing through the narrow, annular gap between the blades 43 and the side wall of the casing 33 the material is subjected to large shearing forces which effect thorough mixing and disintegration of the particles.
Fresh liquid flows into the subsidiary vessel 3 from the main vessel 1, via the inlet aperture 21, and fresh powder is supplied to the upper end of the vessel 3 as mentioned above.
Material entering the chamber 53 is drawn downwardly through the chamber by the action of the impeller 65 of the lower mixing device 7. The material then passes into the casing 45 of the device 7 and is expelled outwardly through the mesh screen 55 by the rotating impeller blades 69. From the screen 55 the material travels through the apertures 63 in the bearing housing 59 and into the tube 71, from which it travels into the main volume of liquid in the main vessel 1. The mixture is again subjected to thorough mixing and disintegration in passing through the gap between the blades 69 of the impeller 65 and the mesh screen of the device 7.
The fact that the inlet to the casing 33 has a cross-sectional area substantially smaller than the cross-sectional area of the volume swept out by the impeller blade 43 reduces the vortex action which would otherwise be exerted on material above the inlet to the casing 33.
in using the present apparatus, however, it is only necessary for the impeller 39 to set up a small vortex action for powder to be drawn downwardly from all parts of the surface of the liquid in the vessel 3, since the downwardly tapering part 13 of the vessel 3 ensures that all of this powder is directed towards the device 5. The vortex action is not sufficient to drawn down large quantities of air. Efficient mixing is therefore obtained without undue aeration of the mixture. If the subsidiary vessel 3 were not present and the mixing device 5 were simply immersed in the liquid within the main vessel 1 it would only be possible to draw powder from allparts of the liquid surface by increasing the size or speed of rotation of the impeller 39. This would result in undue aeration.
The mixing device 7 provides a second mixing of material from the first device 5, the mesh screen 55 leading to a further reduction in particle size. in cases where aeration can be tolerated the impeller 73, whose position on the shaft 23 is adjustable, increases the vortex action and provides rapid wetting of large quantities of material.
It will be appreciated that the above apparatus can be modified by removing the mixing device 7 and allowing material from the device 5 to travel directly into the liquid in the main vessel 1. Alternatively, one or more further mixing devices may be provided below the device 7 so as to ensure even more mixing of material from the subsidiary vessel 3. Each of these further devices is provided with an inlet chamber which receives material flowing from the preceding device, in the manner of the above-described chamber 53 between the devices 5 and 7.
In another apparatus according to the invention a further mixing device below the devices 5 and 7 has both its inlet and outlet communicating with the liquid in the main vessel 1. This further device therefore provides additional mixing of material already in the main vessel. With the subsidiary vessel 3 mounted at one side of the main vessel 1, as described above, the provision of the further mixing device has the further advantage of causing a general circulation of liquid around the main vessel l, thereby improving dispersion of the solid particles through the main vessel.
The impeller 73 can be replaced by a worm.
In the apparatus shown in FIG. 1. the subsidiary vessel 3 is approximately 20 inches in diameter and has an overall depth of approximately 2 feet. The main vessel 1 has a diameter of approximately 20 feet and a depth of approximately 20 feet. The volume of the main vessel 1 is therefore approximately 700 times the volume of the subsidiary vessel 3 and the surface area is approximately 150 times that of the subsidiary vessel. It will be appreciated that the maximum size of subsidiary vessel 3, or the minimum value of the above ratios, which will give an acceptable result depends upon the amount of aeration which can be tolerated. In general, however, it would be expected that although any reduction in surface area over which the powder is dispersed is desirable it would be usual to effect a reduction of at least five times and preferably at least 10 to 20 times.
The apparatus shown in H6. 2 of the drawings is for use in disintegrating solid material and thoroughly mixing the material with a liquid.
This apparatus includes a subsidiary vessel 103 which corresponds to the above-described vessel 3 except for the omission of the inlet aperture 21 in the side wall of vessel 3. Mounted below the subsidiary vessel I03 are mixing devices 105 and 107 respectively corresponding to the above-mentioned mixing devices 5 and 7. Each of these devices 105 and 107 includes a mixer casing and an impeller which is mounted on a shafi 109, driven by an electric motor 1 l I.
The subsidiary vessel 3 and the mixing devices 105 and 107 are disposed between an upper, inlet conduit [13 and a lower outlet conduit 115.
Liquid and solid material flow into the open top of the vessel 103 from the inlet conduit 113 and the mixing devices 105 and 107 are immersed in liquid in the outlet conduit 115.
in use of the present apparatus, liquid and solid material are continuously supplied to the vessel 103 from the conduit "3. Rotation of the impellers in the device I05 and 107 expels material through the casings of these devices, causing thorough mixing and disintegration of the solid material. From the device 107 the mixture of liquid and solid material is ex pelled into conduit 115. Material in the vessel 103 is drawn downwardly by the impeller in the device 105, the downwardly tapering section of the vessel 103 ensuring that material at each location in the vessel is directed towards the outlet at the bottom of the vessel.
It will be appreciated that the apparatus of FIG. 2 can be provided with separate feed lines for liquid and solid material.
1. Apparatus for mixing solid material with a liquid, comprising a subsidiary vessel having at least one inlet in an upper part thereof and an outlet in a lower part thereof, a first mixer casing which is formed with an inlet in an upper end wall thereof and with outlet aperture means in a generally cylindrical side wall thereof, said outlet aperture means extending around said side wall, means for securing said casing to the subsidiary vessel so that all material flowing downwardly through the outlet in the subsidiary vessel enters said casing whilst material flowing outwardly from the outlet aperture means of said casing is prevented from returning to the subsidiary vessel via the outlet thereof, an impeller shaft, and a first impeller mounted on the said shaft and disposed within said casing, said impeller comprising a generally circular plate formed with a plurality of upstanding impeller blades, with their radially outer ends adjacent to the side wall of the casing, whereby, upon rotation of the shaft, the impeller forces material in said casing radially outwardly through the outlet aperture means, thereby subjecting the material to thorough mixing and disintegration, wherein the side walls of said subsidiary vessel are arranged such that material therein is directed to said inlet to said casing, and wherein said inlet to said casing has a cross-sectional area substantially smaller than the cross-section of the volume swept out by said first impeller, thereby to produce a reduced vortex action on liquid in said subsidiary vessel and to draw solid material at any location within said subsidiary vessel downwardly into the said casing, without undue aeration of the material, to replace the expelled material.
2. Apparatus as claimed in claim 1, wherein the subsidiary vessel has a part which tapers downwardly towards the outlet thereof.
3. Apparatus as claimed in claim 1, wherein said first impeller is mounted on a shaft which extends downwardly through the subsidiary vessel and additional impeller means are provided on the shaft, above said first casing and within the subsidiary vessel, for assisting in driving liquid and solid material downwardly towards said mixer casing.
4. Apparatus as claimed in claim 1, wherein said impeller shaft extends below said first mixer casing, and a second impeller is mounted on said shaft below said first mixer casing, and the said second impeller being disposed within a second mixer casing.
5. Apparatus as claimed in claim 4, wherein the outlet aperture means in said first casing opens into a chamber having an outlet at a lower end thereof, the second mixer casing has an inlet aperture arranged to receive material flowing downwardly through the said outlet, and the second impeller is adapted, upon rotation, to draw material within the chamber downwardly into the second mixer casing and to expel material outwardly through aperture means therein.
6. Apparatus as claimed in claim 5, including means for securing said second casing to said chamber so that all material forced outwardly through said outlet aperture means of said first casing is prevented from returning to said first casing.
7. Apparatus as claimed in claim 4, wherein said mixer casings, said first and second impellers, and the outlet of the subsidiary vessel are disposed within a main vessel adapted to contain a large volume of the said liquid and solid material, and the surface area of liquid within the subsidiary vessel which is exposed to the surrounding gaseous medium is substantially smaller than the exposed surface area of liquid in the main vessel when the mixer casings and impellers are immersed in the liquid in the main vessel.
8. apparatus as claimed in claim 7, wherein the subsidiary vessel, mixer casings and impellers are offset from a central position relative to the main vessel, as viewed in plan.
9. Apparatus as claimed in claim 7, wherein material expelled from the aperture means in the mixer casings is conveyed via a tube to a predetermined location in the main vessel.
10. Apparatus as claimed in claim I, wherein said impeller shaft is the output shaft of an electric motor which is mounted above the subsidiary vessel.
ll. Apparatus as claimed in claim 1, wherein a single inlet is provided in said subsidiary vessel for supply of both liquid and solid material to said vessel.
12. Apparatus as claimed in claim 1, wherein said outlet of said subsidiary vessel and said inlet to said first mixer casing are connected by a neck portion.
13. Apparatus as claimed in claim 22, wherein said neck portion is cylindrical and the diameters of said neck portion and said inlet are equal.