US2661984A - Centrifugal atomizer - Google Patents

Description

Dec. 8, 1953 D. D. PE EBLES ETI'AL 2,661,984

CENTRIFUGAL ATOMIZER Filed Jan. 16. 1951 F'IIE I INVENTORJ Dav/d D. eeb/es Clarence P Turner ATTORNE Y5 Patented Dec. 8, 1953 UNITED .I'STLATE CENTRIFUGAL ATOMIZER.

David D. Peebles, Hillsborough, and Clarence P. Turner, Petaluma, Calif., assignors to Western Condensing Company, San Francisco, Calif., a corporation of California Application January '16, 1951, Serial No. 206,162

3 Claims. (01.299-453) This invention relates generally to centrifugal atomizers and atomizing methods suitable for use-with spray driers.

Centrifugal atomizing devices for spray driers generally employ an atomizing head mounted upon a shaft and rotated at a relatively high rate of speed. The material to be atomized is fed to the head and as it is thrown outwardly by centrifugal force, it is acted upon by atomizing means such as a plurality of circumferentially spaced impact bars. A centrifugal atomizer of this type has undesirable features, particularly when used for certain types of serv ice. For example, there is a tendency toward lack of uniformity of the particle size of the atomized material, and the average size of the particles may be larger than is desirable in the spray drying of many products. There is also a tendency forsuch atomizers to discharge coarser particles at relatively high tangential velocity, with the result that such particles tend to directly impact the side wallsof the desiccating chamber, rather than to be entrained in the drying gas. In addition to the disadvantages just mentioned there is a tendency for the circumferentially spaced impact bars to be subject to excessive wear.

It is an object of the present invention to provide a. centrifugal atomizer and method which will overcome the difficulties pointed out above.- v 7 Another object of the invention is to provide an atomizer and method capable of relatively fine and uniform atomization of various fluid feed materials, and which will facilitate entrainment of the atomized material in drying gas. 3

Another object of the invention is to provide an atomizing device and method which will avoid the use of impact bars or like mechanical impacting means for effecting a substantial amount of atomization. l

Additional objects of the invention will appear from the following description in which the preferred embodiment has been set forth in detail in conjunction with the accompanying drawing.

Referring to the drawing: 7 Figure 1 is a side elevational view in section illustrating an atomizing device incorporating the present'invention. 7

Figure 2 is a cross-sectional detail taken along the line 2-2 of Figure l. I

Figure 3 is a cross-sectional detail takenalong the line 33 of Figure 1. g a V v Figure 4 is a detail looking toward one peripheral surface of the atomizing head.

Figure5 is a detail serving to diagrammati: cally illustrate the method.

The atomizing device illustrated in the draw-' ing consists generally of an atomizing head I 0- which is circular in contour, and which is attached to the rotatable shaft I I. In the particular construction illustrated the shaft is made hollow and in'two coupled sections I la and I lb. The mounting means for journaling thisshaft may consist of the ,ball'bearing assemblies l2 and [3, which are carried by the mounting rings 16 and I1. These rings are connected by the concentric tubes !8, l9, which are dimensioned to provide a space 2! for circulating cooling liquid. The upper mounting ring It can be attached to the top wall (not shown) of a desiccating chamber. The shaft is shown being driven by suitable means such as the pulley 22.

A feed tube 26 extends downwardly through the longitudinal shaft passage 21. The upper end of this tube is carried by the support bracket 28. At one point along. its length the tube is steadied by the ball bearing assembly 29.

As illustrated it is desirable for the feed tube 26 to have a small spacing or clearance with respect to the surrounding shaft.

The atomizer head consists of a hub 3| which carries the disc- like plates 32 and 33. The lower plate 33 is secured to the hub by suitable means such as the dowels 34 and the locking nut 36. The inner periphery of the upper plate 32 is shown seated upon the annular shoulder 31 formed on the hub. The two plates are clamped together by suitable means such as the circumferentially spaced screws 38.

The hub 3| is bored to provide the annular chamber 39, and a plurality of openings 4| in the lower end portion of the shaft serve to connect this chamber with the lower portion 42 of the passage 21 through the vertical drive shaft. Another series of circumferentially spaced opening's 43 are formed in the hub and serve to deliver material from the annular chamber 39 into the space 44 between the plates 32 and 33. The openings 43 are regularly spaced about the hub (see Figures 1 and 2) to secure uniform distribu' tion of material into the space 44.

The peripheral marginof the lower plate 33 is formed to provide a plurality of circumferentially spaced slots 46. Theseslots extend in a general radial direction, although as illustrated in Figure 3 it is desirable that they be at a small angle to radii from the center of rotation. In the specific proportioning illustrated this angle is 5, and the outer end of each slot is ofiset toward the direction of rotation.

tion 411) is of gradually reduced height to terminate at 69 flush with the adjacent face ii of the plate 33.

The lower face of the upper plate 32 is slotted in a manner similar to the lower plate 33. Thus 7 the outer margin of the upper plate 32 is provided with the rectangularly contoured slots 52, which are separated by the circumferentially spaced intervening ribs 53. The bottoms .of the slots are coincident with the surface 54, which is planar and parallel to surface 58. The two portions 53a and 53b of the ribs 53 correspond to and are shaped likethe rib portions 41a and 41?) previously described.

'When the two plates 32 and 33 are assembled as in Figure 1, adjacent slots of the two plates are substantially parallel and they are staggered as illustrated in Figure 4. Thus each slot is closed by the adjacent rib of the opposed plate. Such closed slots form elongated passages which communicate at their inner ends with the space '41 Within the head, and which at their outer ends communicate with the peripheral surface 56 of the head. Each of these passages is closed for the radial distance a (Figure '3) and inwardly from this region the passages communicate with rather than the leading side surfaces of the passages. This effect is aided by the angular positioning of the passages illustrated in Figure 3.

All of the fluid feed material is caused to form a flowing film in the manner described above, and no substantial amount of material is permitted to discharge through the passages 45, 52, in the 3 form of particles in free flight. As the feed material enters the zone of the rib portions 53b, 41b some atomization may take place by mechanical impact, but .such atomized particles are not permitted to have free flight through the passages for discharge from the atomizer head. On the contrary while passing through the radially extending passages 46, 52, such particles are necessarily caused to merge with the flowing film described above, whereby substantially all of the feed material is delivered to the peripheral surface .56 as a composite rapidly moving film.

At the peripheral surface 56 the outwardly moving films of feed material are continuously atomized due to disruptive shearing off and mechanical disintegration as the films meet the surrounding air. Such atomization provides par? ticles of relatively small and uniform particle size.

The method described above is illustrated diagrammatically in Figure 5. The outwardly flowthe space 44. For the region 17 (Figure .3) the rib portions 531) and 471) are divergent, and serve as vanes to impart rotary velocity to .fluidfeed ma-.

able peripheral velocity, such as from 450 to 650 -feet .per second. A source of fluid feed material 'tobe atomized is coupled to the upper end of the pipe "26. Feed material continuously delivered through the pipe 26 is introduced into the lower end portion 42 of the shaft passage, .and from thence it is discharged through the openings 4;! into the hub chamber 39. From chamber 39 the material is discharged through the openings 63Tinto the space 140f the rotating atomizerhead. As discharged outwardly through the space '44 the streams of material break into .the form ofa coarse spray which is uniformly distributed about the space 44. As the coarse spray reaches the region-of the ribportions 53b and 41b it is .acted upon -by these ribs whereby its rotary velocity is increased and where it is distributed into the several slots or passages Mi. As the material progresses outwardly through these passages, it islpresSed against the side surfaces of each passage 'to cause the effect of a substantially .com- .pact outwardly flowing film. This flowingfilm effect takes place upon'the side surfaces 16, 11.7 "(Figure '4) of the slots or passages' lfi, 52, assumingthe direction of rotation is as indicated. In other words it takes place upon the trailing ill matically at T8. The thickness of the film decreases outwardly due to the progressivelygreater flow velocity. Disintegration and atomization of the film takes place along the vertical edge '19 yivhich is coincident with the peripheral surface By way of example, in one particular instance the head was 20 inches in diameter, and was operated at a speed of 7,000 B. P. The slots were inch in circumferential width, inch deep, and the dimensions a and b were 1% and 2 inches, respectively. Such a head operated to secure uniform fine atomization of skim milk, and was employed with a spray drying chamber.

It will be evident from the foregoing that the present atomizer operates entirely by virtue of disintegration of an outwardly flowing film of the feedmaterial. No droplets of material produced byimpact disintegration are discharged from the head. Because of the absence of impact disintegration wear of the ribs and the other parts of the atomizer is reduced to a minimum.

We claim:

1. A centrifugal atomizing head comprising a pair of disc-like plates, a hub serving to carry said plates, means for clamping the plates into face to face relationship, means for feeding -maiterial into the interior of the hub, said plates having their opposed faces formed to provide an annular space communicating through spaced ports with the interior of the huh-whereby said space receives a coarse spray'from the hub when the -head rotates, circumferentially spaced ribs formed on the inner face of-at least one of said plates and extending from the periphery of the same toward said hub, said ribs serving to form substantially rectilinear passages between the samefor passage of --feed material, the inner end -to-form=vanes,-the other portions of the ribsbeing in contact with the other plate :for a substantial radial distance.

2. In a centrifugal atcmizer,-acircularlycontoured'head comprising apair of disc-lilge plates.

a hub to"which"the plates are secured, a rotatable shaft serving to mount the hub and having its axis coincident with the center of the head, circumferentially spaced slots formed in the opposed peripheral margins of the plates and extending in a general radial direction, the slots of said plates being in staggered relation whereby the slots of one plate are angularly displaced and ofiset with respect to the slots of the other plate, said slots forming a plurality of enclosed passages having their outer ends terminating with the peripheral surface of the head and having their inner ends communicating with the interior of the head, said passages being of substantial radial length compared to their circumferential dimensioning, a feed chamber formed within the hub and adapted to receive fluid material, said head being formed to provide a space surrounding the hub and communicating with the inner ends of the passages, andthe peripheral wall of said hub being provided with spaced openings for discharge of a coarse spray of said material from said chamber into said space, and means for delivering material into the feed chamber.

3. A centrifugal atomizing head as in claim 1 in which said ribs are formed on the inner opposed surfaces of both said plates, the opposed end faces of said ribs being in contact, the slots formed. between said ribs being in staggered relation whereby the slots of one plate are angularly displaced and ofiset with respect to the slots of the other plate.

DAVID D. PEEBLES.

CLARENCE P. TURNER.

7 References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,420,722 MacLachlan June 27, 1922 1,833,497 Prouty Nov. 24, 1931 1,939,364 Peebles et a1. Dec. 12, 1933 2,003,575 Bowen June 4, 1935 2,450,599 Kloda Oct. 5, 1948 2,607,571 I-Iession, Jr. Aug. 19, 1952 FOREIGN PATENTS Number Country Date 229,178 Great Britain Feb. 19, 1925

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