US2884049A - Spray drying apparatus - Google Patents

Description

April 28, 1959 M. E: BARZELAY SPRAY DRYING APPARATUS 2 Sheets- Sheet. 1

Filed Jan. 17, 1955 INVENTOR. MARTIN BEAR ZELAY BY ATZDRNEY April 28, 1959' Filed Jan. 17, 1955 M. E. BARZELAYY: 2,334 049 SPRAY DRYING-APPARATUS 2 sheets sheet 2 HVVENTUR.

ATTORNEY MARTIN E .EARZIELAY This invention relates to apparatus for spray drying liquids containing solids, such as milk in a condensed state, and more particularly relates to improvements in the nozzle construction for delivering a heated drying medium into a spray drying chamber.

In spray drying of liquids, it has been the practice to deliver a heated drying medium into a drying chamber through one or more nozzles, at the mouth of which are centrally disposed liquid spraying devices for atomizing the liquid containing solids in the path of the flow of eated drying medium. For efficient drying action, it is desirable to employ a drying medium such as heated air, the temperature of which is as high as the solids can withstand without injury, in order to promote substantially instantaneous evaporation, and further, as in the case of milk, to enhance the production of a coarse powder. In an application Serial No. 474,457, filed December 10, 1954, issued as Patent #2,835,597 on May 20, 1958, there is disclosed a drying process wherein by temperature gradation in the drying medium in the region of evaporation, the advantage of rapid evaporation through utilization of a high temperature evaporating medium with the resulting promotion of coarse powder production is set forth.

In the usual drying medium nozzles employed in spray drying, there is sometimes a tendency for powder to deposit upon the internal nozzle surface by reason of eddy currents in the region of the merging of the mouth of the nozzle with the drying chamber. The collection of small amounts of dried powder on the nozzle causes such powder to be subjected over extended periods to the heat of the blast of the drying medium delivered through the nozzle, and causes scorching and burning of the powder. Such powder upon dislodging mixes with the powder deposited in the drying chamber, or. is air-borne through the chamber exhaust, and spoils the quality of the powder produced by the apparatus, which might otherwise be of a premium grade. Additionally the collection of powder on the nozzle surfaces creates a fire hazard, and has been known to smolder or to burst into flame and disrupt the operation, which would otherwise be continuous. Such collection requires shutting down the apparatus for cleaning of the nozzle surfaces.

T o forestall such tendency for the powder to deposit, a number of solutions have been proposed and tried, each of which has given no improvement or resulted in other detrimental effects. Decreasing the drying medium nozzle diameter to increase velocity has caused even worse fire hazards and deposits. Increasing milk nozzle size to give a wet spray has resulted in sticking of particles to the drying chamber walls and undesirably high moisture content in the final product without curing nozzle deposit. Increasing liquid temperature, or reducing drying medium temperature have also been proposed, but have a detrimental effect on the final dried powder produced, as will appear from a consideration of the pending application to which reference has been made.

The present invention is directed to an arrangement for 2, preventing the powder from contacting the nozzle sur faces, and more particularly embodies means for establishing adjacent to substantially the entire internal surface of the nozzle, a flow of drying medium controlled both as to velocity and temperature, and moving in the direction of the nozzle air blast. The flow acts as an impenetrable surface curtain within the nozzle, which is effective to prevent powder from contacting the nozzle. The apparatus establishes a boundary layer of air flowing along and immediately adjacent to the internal surface of the nozzle. More particularly, in a practical embodiment of the invention, there is employed an inner wall in the form of a spaced liner within the nozzle, such wall having a plurality of arcuate louvres for discharging air along the internal surface of the liner, the liner wall, and nozzle forming an annular chamber for receiving air under controlled pressure and temperature and discharging such air through the louvres. The boundary layer of air thus provided may in practice he of a lower temperature than the temperature of the drying medium, and because of its impenetrable protective effect over the nozzle surface, higher drying medium temperatures may be utilized in the main nozzle blast.

As a further explanation of the protective layer referred to, when fluid flows along and in contact with a wall, it is retarded at the surface of the wall by the viscous forces present in all fluids. In fact, at the wall the velocity is zero but a short distance out from the wall, the fluid stream has the free stream velocity. The retarded layer of fluid is called the boundary layer. In a nozzle, the flow in the boundary layer continues to thicken in the direction of flow, and finally there is a reversal of flow along the wall, a breaking away of the boundary layer from the wall and turbulence. This retardation and reversal of flow is due to energy losses associated with the wall friction. By reenergizing the boundary layer with fluid introduced parallel to the wall, the adverse eflfect of the boundary layer is overcome, and reversal prevented. In the case of milk spray drying, this reversal of flow in the boundary layer is particularly detrimental since already dried particles, or partially dried particles of milk are carried along in the reverse stream and adhere to the nozzle wall aspreviously set forth.

The object of the invention is to provide a nozzle on which depositing of the desiccated material is prevented and in which elevated air blast temperatures may be employed safely, withoutfire hazard and Without contamina-' tion of the product by scorched or burned particles.

The above features and other objects of the invention will appear more fully hereinafter from the following detailed description when taken in conjunction with the accompanying drawings. It is expressly understood that the drawings are employed for purposes of illustration only and are not designed as a definition of the limits of the invention, reference. being had for this purpose to the appended claims.

In the drawings wherein like reference characters indicate like parts:

Figure 1 is a sectional view through a single nozzle embodying the invention, and mounted in the end wall of a drying chamber, with a spray jet associated therewith;

Figure 2 is a perspective view of the nozzle with portions thereof cut away; and

Figure 3 is any enlarged fragmentary perspective view of a segmental portion of the nozzle.

In Figure 1, there is shown a drying chamber 10, having an end wall 12, in. which is mounted one or more nozzles 14 of generally frusto-conical shape, the mouth 16 of the nozzle discharging into the drying chamber and the inlet end 18. of the nozzle coupling with a hot air supply duct or plenum chamber 20, having a wall 22.

Extending through the center of the nozzle thus shown is a solids containing liquid supply tube 24 terminating in an atomizing spray jet 26, such tube extending through a protective sleeve 28, which in practice may serve as heat insulation between the tube and hot blast passing through the nozzle. The jet may be of the centrifugal or other type, and the atomization pattern may vary from that shown.

The nozzle comprises an outer tapered wall 30, to which there is applied in spaced relation an inner wall or spaced liner 32, thus forming an annular chamber 33. The liner wall is provided with an outwardly extending flange 34, at the entrance end thereof adapted to be secured to the supply duct wall, and an outwardly extending flange 36 at the mouth thereof, which flange is secured to a supporting annular plate 38 having its rim overlying and secured to the wall 12 of the drying chamber.

The liner wall is provided with a multiplicity of louvrelike openings 39 extending in an arcuate segmental manner around the liner wall, each of such louvre-like openings comprising an inwardly struck deflector 41 suitably inclined to direct air emerging from the chamber 33 in a direction along the internal wall of the liner, toward the mouth of the nozzle. The chamber 33 is supplied with air under pressure by an annular manifold 40 having a plurality of ducts 42 connecting with ports 43 in the end flange 34 of the liner wall 32. Such manifold is supplied with air under pressure through a suitable control valve 44.

In practice, a heated drying medium, such as air, enters the nozzle and flows in the general direction of arrows A. The blast of air is accelerated by the throat effect of the nozzle, and emerges from the mouth thereof to impinge upon the fog of atomized liquid 46 from the spray jet 26. The heated air rapidly evaporates the moisture from the particles suspended by the atomization of the liquid containing the solids, and the dried particles either drop upon the chamber bottom for collection, or are air borne to a centrifugal separator for collection in the drying chamber exhaust (not shown). The temperature of the air blast passing through the nozzle may be in the order of 420 F. or substantially higher in the case of milk drying. It is to be understood that the temperature depends upon the nature of the solids from which the moisture is to be evaported. For other types of liquids in solids, it will be possible to similarly sub stantially raise the drying temperature, and thus increase process efi'iciency, without detrimental sticking, burning and scorching.

Without the liner 32, the hot air blast in passing through the nozzle has a tendency to heat the nozzle to the temperature of the air of the blast, and should particles of solids being dried, or in a dried state come in contact therewith and become temporarily lodged thereon as a result of eddy currents at the mouth of the nozzle, such particles would be subjected to extended heating, suflicient to scorch the particles. Should such particles deposit upon the nozzle internal wall in suflicient quantity, the heat may cause ignition and burning of the particles. The scorched or burned particles, on burning become dislodged and are carried into the chamber and intermix with the dried product, contaminating the product and rendering the same unfit to meet the standards set up for commercial purposes.

To prevent the occurrence of particles reaching the nozzle wall, air under pressure is introduced into the chamber 33 from the manifold 40, which air is emitted from the louvres 39 in the direction indicated by arrows B and caused to flow along the internal surface of the liner wall, the air thus introduced traveling along with the blast or at a velocity slightly greater than the blast in the annular region 47 generally defined by the line 46, the inner wall surface of the liner wall, and the extension thereof as indicated by the line 48. A layer of inter-mixing of the air thus introduced and that of the 4 air blast takes place in the region 51 defined by the line 46 and the line 50.

The air supplied through the control valve 44 to the manifold 40 should preferably be unheated air. Its temperature may be somewhat elevated, however, by flow through the manifold and ducts which are exposed to the temperature within the supply duct 20. Thus the central region 53 of the main blast of air as it leaves the nozzle will be undisturbed so far as its temperature is concerned, but the region 51 or intermixed air will evidence a somewhat lower temperature, whereas the air in the outer region 47 will evidence a still lower temperature. The overall effect of the apparatus is to produce a blast of air, the temperature of which shows a gradient, the hottest air being directed into the central portion of the atomization fog, close to the jet 26 Where the moisture density is greatest.

The apparatus as thus provided and when operated under the conditions set forth above, provides a means whereby extremely high blast temperatures may be employed, for example, as high as the fog suspended solids can accommodate, whereby substantially instantaneous drying is effected. At the same time the nozzle is protected against solids collecting upon the nozzle surfaces, and the outer cooler region of the blast operates to complete the drying of any solids, the evaporation of which has not been efiected in the central region.

In the case of milk drying, the apparatus permits the use of a spray of concentrated milk whose temperature at the spray jet is maintained relatively low for beneficial reasons as set forth in the herein above referred to application, since the temperature of the air blast can be elevated not only to compensate for a low temperature of the concentrated supply, but to a higher temperature to provide more rapid and substantially instantaneous drying. At the same time, there is present a boundary layer of protection against deposit of dried particles upon the nozzle, and thus protection from possible scorching, burning or ignition, which would ultimately result from such deposit. Further, the apparatus is rendered continuous in its operation, since shutdowns to clean the nozzles is made unnecessary.

Although a single embodiment of the invention has been illustrated and described, it is to be understood that the invention is not limited thereto. As various changes in the construction and arrangements may be made without departing from the spirit of the invention, as will be apparent to those skilled in the art, reference will be had to the appended claims for a definition of the limits of the invention.

What is claimed is:

1. In a spray drying apparatus, a drying chamber, a drying medium nozzle mounted in a wall of the chamber for introducing heated drying medium into the chamber, means for delivering a blast of heated drying medium into the chamber through the nozzle, a source of additional drying medium independent of said blast delivering means, and means for admitting said additional drying medium into the nozzle along the internal surface thereof to energize a boundary layer moving with the blast over substantially the entire nozzle inner surface.

2. In a spray drying apparatus, a drying chamber, a drying medium nozzle mounted in a wall of the chamber for introducing heated drying medium into the chamber, a spray head for liquids containing solids mounted centrally with respect to the nozzle and in the region adjacent the chamber end of the nozzle, means for delivering a blast of heated drying medium into the chamber through the nozzle, a source of additional drying medium independent of said blast delivering means, and means for admitting said additional drying medium into the nozzle along the internal surface thereof to energize a boundary layer over substantially the entire nozzle inner surface.

3. In a spray drying apparatus, a drying chamber, a drying medium nozzle mounted in a Wall of the chamber for introducing heated drying medium into the chamber, said nozzle being tapered and reducing in crosssection toward the chamber end, means for delivering a blast of heated drying medium into the chamber through the nozzle, a source of additional drying medium independent of said blast delivering means, and means for admitting said additional drying medium of a lower temperature into the nozzle through and along the internal surface thereof to energize a boundary layer over substantially the entire nozzle surface.

4. In a spray drying apparatus, a drying chamber, a drying medium nozzle mounted in a wall of the chamber for introducing heated drying medium into the chamber, said nozzle gradually reducing in cross section toward the chamber end, a spray head for liquids containing solids mounted centrally with respect to the nozzle and in the region adjacent the chamber end of the nozzle, means for delivering a blast of heated drying medium into the chamber through the nozzle, a source of additional drying medium independent of said blast delivering means, and means for admitting said additional drying medium of a lower temperature into the nozzle through and along the internal surface thereof to energize a boundary layer over substantially the entire nozzle surface.

5. In a spray drying apparatus, a drying chamber, a drying medium nozzle mounted in a wall of the chamber for introducing heated drying medium into the chamber, said nozzle having an internal liner and an outer wall providing an annular chamber, a spray head for liquids containing solids mounted centrally with respect to the nozzle and in the region adjacent the chamber end of the nozzle, means for delivering a blast of heated drying medium into the chamber through the nozzle, means for delivering a relatively small amount of additional drying medium of a difierent temperature into the annular chamber of the nozzle, and louvres in the liner of said nozzle inclined to direct said additional drying medium into the nozzle and in a direction toward said chamber, said louvres being located over substantially the entire surface of said liner, whereby said additional air passing through said louvres energizes the existing boundary layer travelling along the surface with the blast over substantially the entire internal surface of said liner.

6. In a spray drying apparatus, a drying chamber, a drying medium nozzle mounted in a wall of the chamber for introducing heated drying medium into the chamber, said nozzle having an internal liner and an outer wall providing an annular chamber, a spray head for liquids containing solids mounted centrally with respect to the nozzle and in the region adjacent the chamber end of the nozzle, means for delivering a blast of heated drying medium into the chamber through the nozzle, means for delivering a relatively small amount of additional drying medium into the annular chamber of the nozzle, and deflecting ports in the liner of said nozzle adapted to direct said additional drying medium into the nozzle and in a direction toward said chamber, said ports being located over substantially the entire surface of said liner, whereby said additional air passing through said ports energizes the existing boundary layer travelling along the surface with the blast over substantially the entire internal surface of said liner.

7. In a spray drying apparatus, a drying chamber, a drying medium nozzle mounted in a wall of the chamber for introducing heated drying medium into the chamber, said nozzle having an internal liner and an outer wall providing an annular chamber, means for delivering a blast of heated drying medium into the chamber through the nozzle, means for delivering a relatively small amount of additional drying medium into the annular chamber of the nozzle, and means distributed over the surface of the liner of said nozzle to direct said additional drying medium into the nozzle and in a direction toward said chamber, whereby said additional air passing through said directing means energizes the existing boundary layer travelling along the surface with the blast over substantially the entire internal surface of said liner.

8. In a spray drying apparatus, a drying chamber, a drying medium nozzle mounted in a wall of the chamber for introducing heated drying medium into the chamber, said nozzle having an internal liner and an outer wall providing an annular chamber, means for delivering a blast of heated drying medium into the chamber through the nozzle, means for delivering a relatively small amount of additional drying medium into the annular chamber of the nozzle, and louvres in the liner of said nozzle inclined to direct said additional drying medium into the nozzle and in a direction toward said chamber, said louvres being located over substantially the entire surface of said liner, whereby said additional air passing through said louvres energizes the existing boundary layer travelling along the surface with the blast over substantially the entire internal surface of said liner.

9. In a spray drying apparatus, a drying chamber, a drying medium nozzle mounted in a wall of the chamber, means for delivering under a first blast pressure a blast of heated drying medium into the chamber through the nozzle, a second source of air pressure suitably related to the blast pressure and differing from the blast pressure, and means including a multiplicity of ports over the entire internal surface of the nozzle communicating with said second source of pressure, said means serving to control the boundary layer over substantially the entire internal surface of the nozzle and prevent flow along the internal surface in a reverse direction from the main nozzle blast.

10. In a spray drying apparatus, a drying chamber, a drying medium nozzle mounted in a wall of the chamber, means for delivering under a first blast pressure a blast of heated drying medium into the chamber through the nozzle, a manifold exterior of said nozzle comprising a second source of pressure suitably related to the blast pressure and differing from the blast pressure, and means including a multiplicity of ports over the entire internal surface of the nozzle communicating with said manifold, said means serving to control the boundary layer over substantially the entire surface and prevent flow along the internal surface in a reverse direction from the main nozzle blast.

References Cited in the file of this patent UNITED STATES PATENTS 1,087,515 Sprenger Feb. 17, 1914 1,753,915 Bowen Apr. 8, 1930 1,779,516 Stevenson Oct. 28, 1930 1,829,477 Douthitt Oct. 27, 1931 2,035,673 Schultz Mar. 31, 1936 2,413,420 Stephanofi Dec. 31, 1946 2,460,546 Stephanoff Feb. 1, 1949 2,478,557 Bell et a1. Aug. 9, 1949 2,510,645 McMahan June 6, 1950

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