US3356348A

US3356348A - Breaking foam

Info

Publication number: US3356348A
Application number: US517223A
Authority: US
Inventors: Jr Frank W Paul
Original assignee: Mixing Equipment Co Inc
Current assignee: Mixing Equipment Co Inc
Priority date: 1965-12-29
Filing date: 1965-12-29
Publication date: 1967-12-05
Anticipated expiration: 1984-12-05

Description

F. W. PAUL, JR

BREAKING FOAM Dec. 5, 1967 Filed Dec. 29, 1965 q co o INVENTOR. FRANK W- PAUL,JR. BY QiuUW-W- FIG.2

ATTORNEYS United States Patent 3,356,348 BREAKING FOAM Frank W. Paul, Jr., Macedon, N.Y., assignor to Mixing Equipment Co., Inc., Rochester, N.Y., a corporation of New York Filed Dec. 29, 1965, Ser. No. 517,223 5 Claims. (Cl. 259108) ABSTRACT OF THE DISCLOSURE Foam is broken by a high speed impeller having an axial flow barrier and rotated on a vertical axis above the foam area to draw up foam, break it, and accelerate it radially outward in a sheet-like stream of gas and liquid falling over the foam area.

This invention relates to ways and means for breaking or destroying foam.

The production of copious quantities of foam in many liquid treatment processes continues to be a major problem in spite of numerous chemical and mechanical inventions aimed at solving the problem. Advances have been made with chemical additives that inhibit foam generation, but such additives are generally expensive and in some instances should not be present in the ultimate product. Mechanical devices heretofore developed for breaking foam have not been effective, particularly for tenacious foams, and, even where reasonably effective, have been expensive to build and to operate. A definite need exists, therefore, for improvement in Ways and means for breaking foam.

A general object of this invention is to provide such an improvement.

A specific object of this invention is to provide improved ways and means for breaking foam mechanically.

Another specific object of this invention is to break foam by means that are simple and economical to manufacture and operate.

These and other objects which may appear as this specification proceeds are achieved by this invention.

This invention, in summary, comprises a process for breaking foam within a generally horizontal, foam area such as, for example, that presented by an agitated body of liquid in a tank. The process is practised by rotating an impeller above the foam area under special conditions which result in foam being broken without being impacted to any substantial extent.

One of the conditions is that the impeller be rotated in a gas. Usually it is air. The gas is at any suitable ambient pressure and temperature. In the case of air the pressure is usually atmospheric and the temperature is generally in a range from about 0 to about 100 C.

Another condition is that the speed of rotation of the impeller in general be sufiicient to form a tornado-like flow of gas from beyond one side of the impeller into the region of the impeller, and to accelerate said gas radially outwardly from said region, but insuflicient to effect substantial impacting by the impeller of foam and foam residue in said region.

Still another condition is that the axial distance of the impeller from foam in the area and the speed of rotation of the impeller within the foregoing range be selected so that the tornado-like flow of gas entrains into the region of the impeller at least a substantial portion of the foam.

Yet another condition is that the position of the impeller be selected so that any impingement of foam residue traveling outwardly from said region of the impeller on surfaces at a foam generation velocity is at a minimum and preferably less than substantial. Satisfactory results have 3,356,348 Patented Dec. 5, 1967 been achieved in the case of impellers with vertically oriented axes with the impeller in each case being spaced by at least substantially four times the maximum radius of the impeller from any substantial, generally upright surface.

As a result of these conditions a substantial portion of any foam in the area is entrained in the tornado-like, rising stream of gas and becomes broken in its travel into the region of the impeller and radially outwardly from the region, forming foam residue.

A preferred condition is that the axis of rotation of the impeller be vertically positioned. Under this condition, foam residue falls in an umbrella-like pattern over the underlying area. This fall-out helps to depress foam in that area. Of course, if the foam residue strikes vertically disposed surfacessuch as those presented by tank walls and the like, it runs down the surfaces without being regenerated to a substantial extent into foam.

Another preferred condition is that on the axis in the region of the impeller there be an axial flow barrier structure to minimize flow of gas and of foam about the axis of rotation through and considerably beyond the impeller. Preferably, the barrier structure is part of the impeller.

The impeller comprises at least one impeller blade. In preferred embodiments of this invention the blade is a flat or plate like element, the plane of which is positioned relative to the axis of rotation in a range from substantially an axial plane to a swept-back plane parallel to the axis of rotation. Swept-back as used herein is relative to the direction of rotation of the impeller. The area of the impeller blade is selected generally in accordance with the foam area and the volume of foam to be handled per unit of time, the greater the area and volume per unit of time, the greater the blade area.

In preferred embodiments of this invention the impeller comprises a plurality of impeller blades evenly or circumferentially equidistantly spaced about an axis of rotation. Preferably, each impeller blade has substantially the same dimensions and position relative to each other and the axis of rotation. The number of impeller blades is preferably 4-8. However, lesser and greater numbers of blades are within the broader concepts of this invention.

The axial flow barrier structure functions under normal operative conditions to at least minimize and preferably substantially block axial flow of gas on one side of the impeller, which side in those embodiments where the axis is vertically oriented is the top side. In preferred embodiments the barrier structure is a disk substantially in a plane perpendicular to the axis of rotation of theimpeller with the axis passing through the center of the disk. The radius of the disk is substantially greater than the shaft to which the impeller is fastened and, depending on the location of the disk, can be greater than the radius of the impeller. However, in general the radius of the disk is in a range from about one fourth to about three fourths the radius of the impeller, but smaller and greater disk radii are within the broader concepts of this invention. The disk is positioned in the region of the impeller. On the tornado like flow side of the impeller,'the radiusof the disk is preferably substantially less than the radius of the impeller. In preferred embodiments of the invention the disk is part of the impeller with at least a substantial portion of the impeller blade or blades being below the disk. The impeller in such case is described as having a closed center.

It is within the concepts of this invention, particularly where a large, foam area is involved, to employ more than one or a plurality of impellers, each one being positioned and operated in accordance with the basic concepts of this invention.

This invention is further described in relation to the drawing which forms a material part of these disclosures. In the drawing:

FIG. 1 is an elevational view of a mixing tank equipped according to a preferred specific embodiment of this invention for the breaking of foam, in which view a portion or the tank has been removed in order to reveal internal structure and contents under normal operative conditions; and

FIG. 2 is a top view of a preferred specific embodiment of the rotatable impeller according to this invention, which view has been taken as indicated by the sectioning plane II'II in FIG. 1.

In greater detail, FIG. 1 illustrates a mixing tank 10. The tank comprises a cylindrical side wall or shell 12, an inverted cone bottom 14 and a cover or dome 16. The cover 16 has an access hole 17 which can be covered with a' sight glass or man hole lid, if desired. Feed means are provided for introducing liquid material into the interior of the mixing tank 10. These means comprise an infeed conduit 18 which is coupled to a feed inlet in the cover 16 and which has a shut otf and flow rate control valve 19'. Means for withdrawing material from the tank 10 are also provided. These means comprise a discharge outlet at the apex of the inverted cone bottom 14 and coupled to the outlet a discharge conduit 20 having a shut off and flow rate control valve 21. In the region of the bottom of the mixing tank 10 is a mixing impeller 22 fastened to the bottom end of a normally vertical, rotatable shaft 24. The rotatable shaft 24 extends upwardly on the vertical axis of the tank, passing through a bearing assembly 26 mounted on the tank cover 16. Above the tank cover 16 the rotatable shaft 24 is engaged with a rotatable drive assembly (not shown).

For the breaking of foam according to this invention the interior of the mixing tank 10 is provided with a closed center impeller 30. In the embodiment shown it is anchored to the bottom end of a vertically disposed, upwardly extending, rotatable shaft 32. It can be anchored to the top end of a vertically disposed, rotatable shaft extending downwardly to a drive assembly preferably located outside of the tank. In the embodiment of FIG. 1, however, the rotatable shaft 32 extends upwardly through a hole 34 in the tank cover 16 to a rotatable drive assembly 36. The drive assembly 36 has a rotatable chuck which grippingly engages the rotatable shaft 32.

The closed center impeller comprises a hub 38 with a disk 40. The radius of the disk in the embodiment shown is about half the radius of the impeller 30. The hub 38 has a bore 42 therethrough for the rotatable shaft 32. In addition, the hub 38 has a threaded radial hole in which is threadedly seated a set screw 44 for anchoring the hub 38 and thus the impeller 30 to the rotatable shaft 32. In the embodiment shown, the disk comprises a plurality of circumferentially equidistantly spaced slots 46. Seated in the slots 46, extending downwardly (see FIG. 1) from the disk 40 and fastened as by weldments to the disk 40 are impeller blades 48. In the embodiment shown the impelled blades 48 are rectangular, generally flat and substantially rigid. The impeller 30 in the embodiment shown is normally rotated in a clockwise direction as indicated in FIG. 2. The slots 46 are arranged so that the plates or blades 48 are slanted toward the counterclockwise direction. The leading faces of the blades 48 are disposed in swept-back (relative to the normal direction of rotation), vertical planes parallel to the axis of rotation of the impeller 30'.

Under normal operative conditions with liquid material 50 in the mixing tank 10, the mixing impeller 22 in rotation and foam 52 on top of the agitated body of liquid material 50, the impeller 30 is above the body of liquid material in the region of the center of the tank 10 and preferably within a circle having a radius of about one fourth the inside radius of the tank 10. The effect of the vertical surface of the rotatable mixing impeller shaft 24 is generally not substantial insofar as overall foam reduction in the mixing tank 10 is concerned.

The height of the impeller 30 over the body of liquid material 50 and the speed of rotation of the impeller are selected in accordance with the foam density so that air flows in a swirling, tornado-like, column 54 from below the whirling impeller 30 into the region of the impeller 30 and in said region is accelerated radially outwardly without substantial impacting of foam by, the impeller blades, the velocity of the uprising, swirling air column 54 below the impeller 30 being sufiicient to cause entrainment by the column of a substantial quantity of foam 52 and carriage of the foam into said region of the impeller 30. The entrained foam is accelerated radially outwardly from the region of the impeller 30 and particularly substantially from the back sides of the impeller blades 48. During the travel of foam upwardly in the tornado-like column 54 and then radially outwardly, substantial foam breakage occurs. The position of the whirling impeller 30 in the embodiment shown is such that a substantial portion of the broken foam or foam residue accelerated radially outwardly falls in an umbrella-like pattern as depicted at 56 before reaching the tank side wall 12. and any portion of the foam residue or broken foam, that reaches the tank wall 12, strikes it at a velocity less than that velocity at which impingement results in substantial regeneration of foam.

Satisfactory results have been obtained in the practise of this invention with closed center impellers having structure like that shown in FIGS. 1 and 2. In each impeller each of the six blades were rectangular and set in the center disk in a plane parallel to the axis of rotation, the plane in each case intersecting an axial plane through the axially innermost part of the blade at an acute angle of about 60. The ratio of the length of each blade to the impeller radius was about 1:8, the ratio of the axial width of each blade to theimpeller radius was about 1:10, and the ratio of the impeller radius to the effective radius of the foam area was about 0.2. The radius of the impeller is the radial distance from the outermost point of the blades to the axis of rotation, while the effective radius of the foam area is the square root of the product equal to 1/1r times the foam area. The impeller radii ranged from about 1 and /2 inches to about 14 inches. The heights of the impellers over the foam area ranged from about 6 inches to about 4 feet while the speeds of rotation of the impellers at their peripheries were in a range from about 30 to about 225 feet per second, the particular height and speed being dependent on the foam density and impeller radius.

The foam breaking process of this invention has been found to be particularly useful in the breaking of foam that occurs in the production of phosphoric acid. It also has been found to be particularly useful in the breaking of foam generated in the oxidation treatment of black liquor, which foam is very dense and tenacious and heretofore has posed a serious problem.

A feature of advantage of this invention resides in the s mplicity of the equipment with which foam can be broken according to this invention. Thus, there is no structural conduit between the impeller and the foam area or from the impeller to any other point. There are no funct1onally close impingement surfaces, screens and the like against which foam is directed, as suggested by prior art. It has been found that such help to regenerate partially broken foam and are to be avoided in the process of this invention.

Still another feature of advantage of this invention is the ease with which the equipment can be adjusted in accordance with fairly drastic changes in foam generating conditions.

Other features, advantages and specific embodiments of this invention will be readily apparent to those in the exercise of ordinary skill in the art after reading the foregoing disclosures. All of the embodiments of this invention are within the scope of the claimed subject matter unless otherwise indicated. Also, while a specific embodiment of this invention has been described in considerable detail, variations and modifications of the specific embodiment can be effected without departing from the spirit and the scope of the invention as described and claimed.

What is claimed is:

1. A process for breaking foam within a generally horizontal, foam area, which comprises: rotating above said area in a gas an impeller on a generally vertical axis with an axial flow barrier structure disposed on said axis in the region of said impeller, said rotating being at a speed and at a height whereat there is a tornado-like flow of gas from below said impeller to said region of said impeller at a velocity sufficient to entrain in said flow at least a substantial portion of foam in said area, whereby foam is broken and foam residue formed without said impeller impacting a substantial portion of foam and foam residue in said region, said impeller being in a position relative to any substantial, vertical surface, whereat impingement of foam residue on said surface at a foam generation velocity is at a minimum.

2. A process according to claim 1 wherein said impeller comprises at least one blade, the leading face of which is substantially in a vertical plane in a range from an axial plane to a vertical plane swept-back relative to the direction of rotation of said impeller.

3. A process according to claim 2 wherein said impeller comprises a plurality of said blades with said axial flow barrier structure being a disk member of said impeller.

4. A process according to claim 3 wherein said blades are rectangular, generally flat and substantially rigid, the ratio of the length of each blade to the impeller radius is about 1:8, the ratio of the axial width of each blade to the impeller radius is about 1:10, the ratio of the impeller radius to the effective radius of the foam area is about 0:2, the impeller radius is in a range from about 1 and /2 inches to about 14 inches, the height of the impeller is in a range from about 6 inches to about 4 feet, and the speed of rotation is in a range from about 30 to about 225 feet per second.

5. A process for breaking foam within a generally horizontal, foam area, which comprises: rotating at an interface between said area and an area of gas above said foam area an impeller on a generally vertical axis with an axial flow barrier structure disposed on said axis in the region of said impeller, said rotating being at a speed and at a height whereat the foam accelerated by said impeller is broken and a sheet-like stream of gas and liquid is moved radially and horizontally in all directions from said impeller at high |velocity across substantially all of said foam area for impinging against a portion of the remainder of said foam an-d breaking the same.

References Cited UNITED STATES PATENTS 2,552,057 5/1951 Paik 259-108 X 2,637,538 5/1953 Boutros et a1 259-108 X 2,908,652 10/1959 Forrester 252-361 X 3,169,841 2/1965 Weis -36 ROBERT W. JENKINS, Primary Examiner.