CENTRIFUGAL ATOMIZER

Abstract: A centrifugal atomizer comprises an atomizer wheel (29) mounted on a driven shaft (28) and defining an acceleration chamber (35), where liquid is fed in said acceleration chamber through a stationary, annular distribution member (30) and a corresponding annular opening (27) in the atomizer wheel. The liquid is ejected in form of a spray from the atomizer wheel (29) through openings (16) distributed in circumferential direction. A sealing means is associated with passages (36, 37) provided between the distribution members (30) and the respective sides of the corresponding opening (27) in the atomizer wheel (29). The sealing means comprises a stationary, circumferential and projecting rib (40, 41), which projects radially inwards into a quantity of a sealing liquid in an annular groove (38, 39). The annular groove is adapted to rotate together with the atomizer wheel (29), means being provided for feeding said groove with sealing liquid and removing said sealing liquid again, respectively, during operation.

Description: Title: Centrifugal atomizer. Technical Field. The invention relates to a centrifugal atomizer comprising an atomizer wheel mounted on a driven shaft and defining an acceleration chamber, where liquid is fed to said acceleration chamber through a stationary, annular distribution member and a correspondingly annular opening in the atomizer wheel, and where said liquid is ejected from said acceleration chamber in form of a spray through openings distributed in the circumferential direction. Background Art Centrifugal atomizers are known where the atomizer wheel is driven by a vertically extending shaft which is driven by means of a suitable actuating means and is mounted by means of oiled bearings. The atomizer wheel includes an acceleration chamber which is supplied with a liquid through a stationary annular distribution member projecting into an annular opening in the upper face of said atomizer wheel. As the atomizer wheel is ordinarily caused to rotate at very high numbers of revolutions, often in the range of 5,000 to 15,000 revolutions per minute, rather substantial oscillations of the vertical straightening of the shaft and the atomizer wheel mounted thereon may occur. In this connection it should be noted that both higher and lower numbers of revolutions compared to the said numbers may apply. The said oscilla- tions can be limited by manufacturing the shaft with large, but inappropriate dimensions. Another possibility is to mount the shaft in a guide bearing positioned relatively close to the atomizer wheel, said guide bearing being adapted to absorb the forces applying especially when the shaft exceeds a critical number of revolutions. The latter guide bearing is usually manufactured as a slide bearing of a material producing weak frictional forces at contact with the shaft. The latter solution is often preferred in order to allow a manufacture of the shaft as a relatively thin, resilient structure. However, such a structure implies that the natural vibration of the shaft is considerably lower than the operational number of revolutions, and therefore it is necessary to exceed critical numbers of revolutions during the starting and stopping of the plant. No matter how carefully the plant is structured, an exceeding of critical numbers of revolutions for the shaft will result in an oscillation of the atomizer wheel from the geometric centre line thereof. These oscillations necessitate a predetermined clearance between the distribution member and the adjacent parts of the atomizer wheel in the annular opening thereof. These clearances must be of a size sufficient for avoiding a metallic contact between the rotating and the stationary parts, but on the other hand they must also be as narrow as possible. A gap width in the range of 0.5 to 1.0 mm is not unusual in order to restrict the number of draw-backs optionally arising. The liquid passing through the distribution member and into the acceleration chamber of the atomizer wheel is accelerated to speeds in the range of 100 to 200 m per second before it leaves again through the openings of said atomizer wheel provided along the circumference of said atomizer wheel and is atomized. As a result, a very turbulent state is caused in the acceleration chamber. As a result, drops from the acceleration chamber can be ejected through the slit between the external side of the distribution member and the adjacent part of the atomizer wheel so as subsequently to spread over the upper face of the atomizer wheel and the lower face of the adjacent stationary parts of the centrifugal atomizer, where they can deposit in form of a dried out product layer. This product layer may in time become discoloured or assimilate undesirable properties in another way, and can be torn loose from time to time because under some circumstances a product layer can be formed which is so thick that an actual wearing off takes place. On the other hand, the rotating atomizer wheel possesses due to its geometry a predetermined ability to pump out air in the same manner as a centrifugal ventilators and therefore a negative pressure arises in the interior of the wheel, said negative pressure having the effect that said impurities can be pulled into the acceleration chamber of the wheel again through said slit between the distribution member and the atomizer wheel. As a result, impurities are mixed into the pure atomization liquid and consequently a risk applies of such impurities appearing in the ready-dried product and thereby deteriorate the quality thereof. It is known to limit this draw-back by feeding pure air to the area adjacent the said slit in such a manner that particles present outside this area are not carried into the acceleration chamber through said slit. However, the latter does not prevent product residues torn loose in the area closest the slit from being carried into the acceleration chamber. Another draw-back is found in the fact that the pumping effect of the atomizer wheel can imply that ventilation air is also sucked downwards along the shaft and into the acceleration chamber through the slit between the inner side of the distribution mem- ber and the atomizer wheel. This air may contain lubricating oil aerosols from the oiled bearings and solid particles from the said guide bearing. A risk further applies that such impurities end up in the finished product. Finally, the ventilating air can carry bacteria and other micro-organisms into the acceleration chamber through both the outer and the inner slit or through the ventila- tion path and thereby pollute the liquid to be atomized. It goes without saying that the above draw-backs are particularly undesirable irrespective of the quantity within for instance the food industry and the pharmaceutical industry. Brief Description of the Invention The object of the invention is to provide a centrifugal atomizer avoiding the above draw-backs, and whereby the need for a regular dismounting and manual cleaning of the atomizer wheel and the adjacent parts and consequently an interruption of the production has been reduced. The centrifugal atomizer according to the invention is characterised in that a sealing means is associated with passages provided between the distribution member and the respective sides of the corresponding opening in the atomizer wheel, said sealing means comprising a stationary, circumferential and projecting rib which projects radially into a quantity of a sealing liquid in an annular groove adapted to rotate together with said atomizer wheel, means being provided for feeding said grooves with sealing liquid and for removing, respectively, said sealing liquid from said grooves. As a result, all kinds of impurities must pass such a liquid seal and cannot consequently flow directly into the acceleration chamber of the atomizer wheel. The said impurities can all be dissolved in, suspended in, precipitated in, emulsified in and chemically reacted with or collect on the surface of a sealing liquid which can be suitably chosen in accordance with the liquid to be treated in the centrifugal atomizer. According to the invention the sealing means may particularly advantageously be provided between the annular distribution member and the adjacent side of the opening in the atomizer wheel, the grooves being formed directly on said atomizer wheel and the ribs on the distribution member in such a manner that the sealing and consequently the removal of the impurities is carried out as close as possible to the acceleration chamber. According to the invention the means for feeding and removing the sealing fluid may comprise a plurality of outlet openings and inlet openings provided on the ribs, said outlet openings and said inlet openings being arranged on the outer periphery of the ribs and on the side of said ribs, respectively, being farthest away from the accelera- tion chamber. As a result, the polluted portion of the sealing liquid is quickly removed before the portion of said sealing liquid closest to the acceleration chamber is polluted. According to the invention, the means for feeding and removing sealing liquid may comprise pumping devices adapted to feed more sealing liquid than is removed with the result that it is possible always to flush the portions of said passages adjacent the acceleration chamber and thereby remove deposits deriving from the liquid to be treated in the centrifugal atomizer. The grooves of the sealing means on the side adjacent the acceleration chamber may according to the invention particularly advantageously be defined by a ring secured on the atomizer wheel, and at least the ring present on the outer side of the distribution member when seen in the radial direction may be secured to said atomizer wheel through an additional separately secured ring defining the side of the groove being farthest away from said acceleration chamber. In this manner it is possible in a relatively easy manner to assemble and disassemble the parts in question in connection inter alia with a cleaning. According to the invention, the distribution member adjacent at least one of the grooves of the sealing means may comprise a member projecting into the acceleration chamber, said member protecting the groove against direct splashes of liquid from said acceleration chamber. Finally, the said protecting member may according to the invention be a separate ring secured on the distribution member in such a manner that said protecting member also can be easily disassembled in connection inter alia with a cleaning. Brief Description of the Drawings The invention is explained in greater detail below with reference to the accompanying drawings, in which Fig. 1 is a diagrammatic view, partly in section of a known centrifugal atomizer, and Fig. 2 is a radial sectional view through a preferred embodiment of the area adjacent the atomizer wheel of a centrifugal atomizer according to the invention. Best Mode for Carrying Out the Invention The centrifugal atomizer shown in Fig. 1 comprises a so-called atomizer body 1 mounted on a motor 2 which drives a shaft or a stem 4 through a gear arrangement 3. This shaft is mounted in oiled bearings 5, and at the end it carries an atomizer wheel 6. In order to prevent the lubricating oil necessary for the operation of the bearings 5 from running along the shaft and downwards into the atomizer wheel, this shaft is provided with an oil ejecting ring 7 carrying the used lubricating oil downwards into a reservoir 8. From the reservoir the lubricating oil can be removed at suitable intervals or by means of an automatically controlled pump. A guide bearing 9 in form of a slide bearing is mounted between the lower bearing 5 and the atomizer wheel 6, said guide bearing being adapted to limit the movements of the free shaft end 10, especially while passing critical numbers of revolutions during the starting and stopping of the atomizer wheel 6. A liquid to be atomized in the centrifugal atomizer is fed into a feeding pipe 11 , and through this feeding pipe the liquid is carried through the bottom plate 12 of the atomizer body and further down into an annular liquid distributor 13 permanently mounted on said bottom plate. The liquid flows through one or more openings 14 in the fluid distributor 13 and downwards into an acceleration chamber 15 in the atomizer wheel 6. In the acceleration chamber 15 the liquid is accelerated by way of friction so as finally to be ejected through openings 16 distributed along the periphery of the atomizer wheel. As illustrated in Fig. 1 , the annular liquid distributor 13 projects through an annular opening 19 in the upper face of the atomizer wheel 6 and a short distance into the acceleration chamber 15 of said atomizer wheel 6. As a result, a slit or passage 17 and 18, respectively, is left between the inner face and the outer side of the fluid distributor 13 and the adjacent parts of the atomizer wheel 6. This slit or passage 17 and 18, respectively, is formed with a suitable clearance in order to ensure a possibility of the lower end of the shaft 10 and the atomizer wheel 6 connected thereto moving without the distributor 13 hitting the sides of the opening 19. Pure air is carried through a pipe 20 downwards into the cavity 21 above the atomizer wheel 6 in order to prevent air both from being pulled in from the outside through the opening 19 and from entraining the impurities from the area outside the orifice of the pipe 20 through the opening 19. Fig. 2 is a sectional view in greater detail of the lower portion of a centrifugal atomizer according to the invention. The portion not shown of the centrifugal atomizer corresponds substantially to the known centrifugal atomizer of Fig. 1 and corresponding parts are designated the same reference numerals. An atomizer wheel 29 is mounted on the lower portion of the shaft 28 in the centrifugal atomizer according to the invention, and an annular liquid distributor 30 is mounted on the stationary atomizer bottom plate 31. The liquid to be atomized is carried through a pipe 32 into an annular chamber 33. From this annular chamber 33 the liquid is carried out into the acceleration chamber 35 of the atomizer wheel 29 through channels 34 in the wall of the liquid distributor 30. Thus the liquid distributor 30 projects through an annular opening 27 in the upper face of the atomizer wheel 29. As a result, passages 36 and 37, respectively, are defined on the inner side and the outer side of the liquid distributor 30, said passages allowing the above movement of the shaft end 28 and the atomizer wheel 29. A sealing means comprising an annular chamber or an annular groove 38 and 39, respectively, is provided in connection with each of these passages 36, 37, said sealing means being permanently connected to the atomizer wheel 29. These passages 36 and 37 are further associated with a circumferential, projecting rib 40 and 41 , respectively, which in turn is permanently connected to the liquid distributor 30. These ribs project radially outwards from the liquid distributor and into their respective annular grooves 38 and 39, respectively, in such a manner that a substantially U-shaped branching when seen in cross section in the respective passages 36, 37 is defined between the ribs 40, 41 and the walls of the corresponding groove 38, 39. During use of the centrifugal atomizer a quantity of liquid is maintained in this U-shaped branching by means of the rotation of the atomizer wheel 29. This liquid functions as a sealing liquid in relation to the impurities passing through the respective passages 36, 37. This liquid is fed to the U-shaped chambers through channels 42, 43 extending from sources (not shown) and associated pumps (not shown) through the atomizer body 1 and further through the liquid distributor 30 and the respective ribs 40, 41 and ending at the outer periphery thereof where said channels form outlet openings 44 and 45 , respectively, for the sealing liquid. Correspondingly, inlet openings (not shown), channels (not shown) and pumps (not shown) are provided for draining off the sealing liquid from the U-shaped chambers. These inlet openings are provided on the side of the ribs 40, 41 facing away from the acceleration chamber 35 in such a manner that the impurities passing from the outside and into the sealing fluid are removed as fast as possible before the quantity of sealing liquid present at the bottom of the respective grooves 38, 39 is polluted. Thus a continuous feeding of fresh sealing liquid is ensured co-currently with a continuous renewal of said quantity of sealing liquid. In addition to the removal of impurities, an advantageous removal of frictional heat is also provided, said frictional heat being generated during the rotation of the atomizer wheel. In order to protect the sealing means against direct splashes from the acceleration chamber 35, relatively long slits 46 and 47 are provided by the shaping of the surroundings between the acceleration chamber 35 and the sealing means. The latter slit 47 is provided by means of a protecting ring 48 secured to the liquid distributor by means of screws 49. The annular groove 38 associated with the passage 36 adjacent the shaft 28 is manufactured by means of a separate ring 50 secured to the atomizer wheel 29 by means of screws 51. The groove 39 associated with the passage 37 is formed by means of a ring 52 se- cured to a second ring 53 by means of screws 54 and sealed by means of a gasket 55 , the pressure in the outer layer of the sealing liquid otherwise involving an emptying of the sealing chamber through the abutment face between said rings. The ring 53 is secured to the atomizer wheel 29 by means of screws 56. A gasket 57 corresponding to the gasket 55 is also arranged between the ring 50 and the atomizer wheel 29. The use of the described centrifugal atomizer maintains a seal in the passages 36 and 37 by establishing a quantity of sealing liquid in the respective annular grooves 38, 39. The feeding and the removal of the sealing liquid are adjusted by means of a control unit placed outside the centrifugal atomizer in such a manner that a quantity of sealing liquid is always fed which is sufficient for removing impurities, said control unit co-currently maintaining the temperature of the sealing liquid at a suitable level below its boiling point. The feeding of a quantity of sealing liquid slightly exceeding the quantity of sealing liquid being drained off has the result that the slits 46 and 47 between the rotating rings 50 and 52, respectively, and the stationary liquid distributor are advantageously flushed free of possible smudges deriving from the acceleration chamber 35. Therefore the liquid chosen as sealing liquid is not injurious to the liquid to be treated in the acceleration chamber 35. A physical distinguishing is made between several different types of impurities, said impurities being described below together with the function of the sealing means aimed at: 1. Impurities; which are dissolved in the sealing liquid or form a homogenous mixture with said sealing liquid, and which are not separated from said sealing liquid by the centrifuging. Such a pollution is removed from the sealing means during the operation by a flow as described above. 2. Impurities; which are not dissolved in or form a homogenous mixture with the sealing liquid and with a density corrresponding to or lower than the density of the sealing liquid. Such impurities are for instance in form of a particle-shaped material or lubricating oil deriving from aerosols from the interior of the centrifugal atomizer, and due to the centrifugal effect they deposit on the surface of the sealing liquid in the portion of the U-shaped chamber facing the surroundings. When the layer of impurities reaches the thickness determined by the position of the inlet opening(s), the polluted layer is continuously removed from the sealing means through said inlet opening(s). 3. Impurities; which are not dissolved in or form a homogenous mixture with the sealing liquid and have a density higher than the density of the sealing liquid. Such impurities are collected at the bottom of the respective grooves 38, 39, viz. in the outer layers of the U-shaped chamber when seen in the radial direction. Such impurities can be in form of a particle-shaped material deriving from the atomizer liquid, or be in form of material dust deriving from a wearing off in the guide bearing 9. These impurities can be removed in two ways depending on the nature thereof: 3.1 A particular liquid is fed to the sealing means optionally by way of a brief routine procedure, said liquid being known to be able to dissolve the impurities or convert said impurities into a material meeting the requirements presented in the above item 1 or 2 and which is subsequently removed as described in these items. 3.2 When a method described in 3.1. for some reason is not suitable; such as in case chemicals are required, the use of which present a risk to the employees, the equipment or the liquid to be treated by means of the atomizers; or in case the impurities in question are fed in very high quantities to the sealing means; it is possible to carry out a manual cleaning by way of an ordinary dismounting of the individual parts of the atomizer wheel 29. A continuous analysing of the liquid returning from the sealing means with respect to type and quantity of impurities renders it possible to establish a hitherto unknown monitoring of the function of the atomizer wheel during operation. It is possible to connect market available analysis apparatuses in a simple manner to the return flow from the sealing means in such a manner that the operational employees always can monitor the impurities being removed from the atomizer wheel. Such a continuous removal of impurities otherwise appearing in the final product as well as a continuous analysis of the return flow from the sealing means providing a verification of the state of the atomizer wheel during operation present particular . advantages within the food industry and the pharmaceutical industry. In addition to the sealing advantages, the centrifugal atomizer according to the invention presents furthermore the advantage that the previously critical tolerances in the passages 36, 37 now on the whole are without importance because abundant clearances can be chosen without paying regard to the function of the sealing means or to the function of the entire centrifugal atomizer. The latter is important for the cost-intensive replacement of the atomizer wheel 29 and the liquid distributor 30. Previ- ously these parts were often damaged because a metallic contact sometimes occurred due to the necessary narrow clearances, such as in connection with unexpected high unbalances. Furthermore, ventilation air is prevented from penetrating into the acceleration chamber. In connection with the known atomizers the ventilation air pene- trated into the acceleration chamber 35 and caused for instance a partial drying out of the liquid being treated therein. The sealing liquid being fed to the sealing means must be without solid particles of a density exceeding the density of said sealing liquid, and it can be chosen with respect to various requirements. Some of the preferred types of liquid can be used separately or alternately. These liquids are briefly summarized below: 1. Liquids presenting properties coinciding with the volatile part of the atomizer liquid. Examples are: Spray-drying of milk; sodium phosphate or yeast where the sealing liquid is water; or spray-drying of antibiotics dissolved in ethanole where the sealing liquid is ethanole. 2. Liquids containing or comprising ingredients killing undesired micro-organisms. Examples are: Spray-drying of an aqueous solution of dextrane where the sealing liquid is ethanole. The invention has been described with reference to a preferred embodiment. Many modifications can be carried out without thereby deviating from the scope of the invention. The sealing means adjacent the shaft 28 can for instance be accommodated between the shaft 28 and the atomizer body 1.

Claims: Claims 1. Centrifugal atomizer comprising an atomizer wheel (29) mounted on a driven shaft (28) and defining an acceleration chamber (35), where liquid is fed to said acceleration chamber through a stationary, annular distribution member (30) and a correspondingly annular opening (27) in the atomizer wheel, and where said liquid is ejected from said acceleration chamber in form of a spray through openings (16) provided in the circumferential direction, characterised in that a sealing means is associated with passages (36, 37) provided between the distribution member (30) and the respective sides of the corresponding opening (27) in the atomizer wheel (29), said sealing means comprising a stationary, circumferential and projecting rib (40, 41) which projects radially into a quantity of a sealing liquid in an annular groove (38, 39) adapted to rotate together with said atomizer wheel (29), means being provided for feeding said grooves with sealing liquid and for removing, respectively, said sealing liquid from said grooves. 2. Centrifugal atomizer as claimed in claim 1, characterised in that the sealing means are provided between the annular distribution member (30) and the adjacent side of the opening (27) in the atomizer wheel, the grooves (38, 39) being formed directly on said atomizer wheel (29) and the ribs (40, 41) on the distribution member (30). 3. Centrifugal atomizer as claimed in claim 2, characterised in that the means for feeding and removing the sealing fluid comprise a plurality of outlet openings (44, 45) and inlet openings provided on the ribs (40, 41), said outlet openings and said inlet openings being arranged on the outer periphery of the ribs (40, 41) and on the side of said ribs (40, 41), respectively, being farthest away from the acceleration chamber (35). 4. Centrifugal atomizer as claimed in claim 1,2 or 3, characterised in that the means for feeding and removing the sealing liquid comprise pumping devices adapted to feed more sealing liquid than is removed. 5. Centrifugal atomizer as claimed in claim 2, 3 or 4, characterised in that the grooves (38, 39) of the sealing means on the side adjacent the acceleration cham- ber (35) are defined by a ring (50 and 52, respectively) secured on the atomizer wheel (29), and that at least the ring (52) associated with the outer side of the distribution member (30) when seen in the radial direction is secured to the atomizer wheel (29) through an additional separately secured ring (53), which defines the side of the groove (39) in question being farthest away from the acceleration chamber. 6. Centrifugal atomizer as claimed in claim 2, 3, 4 or 5, characterised in that the distribution member (30) adjacent at least one groove (38, 39) of the sealing means comprises a part projecting in the acceleration chamber (35), said part protecting the groove against direct splashes of liquid from said acceleration chamber (35). 7. Centrifugal atomizer as claimed in claim 6, characterised in that said protecting part is a separate ring (48) secured in the distribution member (30).

Inventors: KRAGH OLE TEGLHUS, KRAGH, OLE, TEGLHUS
Applicants: APV NORDIC A S ANHYDRO, KRAGH OLE TEGLHUS, APV NORDIC A/S, ANHYDRO, KRAGH, OLE, TEGLHUS
Application year: 2000
Main classification: B05B3
IPC codes: B05B3