Rotary atomizer with porous gas bearing

Abstract

The present invention relates to a rotary nebulizer comprising: an electric motor having a stator and a rotor; a vertical shaft; one or more porous gas bearings configured to provide frictionless radial and axial support to the shaft member; and a rotating disk mounted at a lower end of the shaft, the rotating disk configured to eject a liquid in the form of fine particles. A gap detection system monitors a distance between the porous gas bearing and the vertical shaft. A bushing on an engine housing helps maintain precise alignment of the rotor during installation and maintenance.

Description

[0001] Related Applications Cross Reference

[0002] This application claims priority to U.S. Provisional Application Serial No. 63 / 338,507, filed on May 5, 2022, the entire contents of which are hereby incorporated by reference in their entirety. Technical Field

[0003] The present invention relates generally to a spinning disk atomizer for use in a spray dryer or cooler, and more particularly to a spinning atomizer with a porous gas bearing. Background Art

[0004] Spray drying is a method of producing dry powders / granules from a slurry or solution liquid by rapidly drying the liquid with a stream of hot air. Spray drying is the preferred method for drying many heat-sensitive materials such as foods and pharmaceuticals. A consistent particle size distribution is the reason for spray drying some industrial products such as catalysts and other chemicals. Typically, air is the heated drying medium; however, if the liquid being atomized is a flammable solvent (e.g., ethanol) or if the product is sensitive to oxygen, nitrogen can be used.

[0005] In general, spray dryers use an atomizer to disperse liquid into a spray of controlled droplet size. Common atomizer types used in spray drying include rotating discs and single-fluid pressure swirl nozzles. Alternatively, for some applications, two-fluid or ultrasonic nozzles can be used. Depending on the process and / or product requirements, droplet sizes from 10 microns to 500 microns can be achieved by appropriate selection. However, common applications are usually in the range of 100 microns to 200 microns in diameter. Summary of the invention

[0006] The present application discloses a system and method for improving the function and efficiency of a rotary atomizer with reduced maintenance and repair costs.

[0007] According to the first aspect of the present invention, a rotary atomizer includes: an electric motor having a stator and a permanent magnet rotor capable of outputting a rotational force; a shaft member vertically mounted and having a desired length, the shaft member being capable of rotating by the rotational force; one or more porous gas bearings for achieving frictionless radial and axial support for the shaft member; and a rotating disc mounted at the lower end of the shaft member for spraying liquid into the form of fine droplets.

[0008] According to a second aspect of the invention, a method for atomizing a slurry material comprises: feeding the slurry material to a rotary atomizer, wherein the rotary atomizer comprises an electric motor capable of rotating a shaft at a specific speed; using the rotary atomizer to output liquid material in the form of atomized droplets; and circulating the atomized droplets with a process gas to produce substantially dry particles. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] These and other advantages of the present invention will be readily understood with reference to the following description and accompanying drawings, in which:

[0010] Figure 1 is a perspective view of a rotary atomizer according to the present invention.

[0011] Figure 2 is a cross-sectional side view of a rotary atomizer according to the present invention, showing the gas passages inside the machine;

[0012] Figure 3 is a cross-sectional side view of a rotary atomizer according to the present invention showing a gas supply bushing feeding a radial pad;

[0013] Figure 4 is a cross-sectional side view of a rotary atomizer according to the present invention, which further describes the porous gas bearing assembly of the present invention;

[0014] Figure 5 is a cross-sectional side view of a rotary atomizer according to the present invention, which further illustrates a gap detection embodiment of the present invention.

[0015] Figure 6 Is from Figure 5 An enlarged view of inset A showing the mechanical resistance temperature detector.

[0016] Figure 7 Is from Figure 5 An enlarged view of inset B showing the mechanical spring contacting the thrust bearing pad. DETAILED DESCRIPTION

[0017] Preferred embodiments of the present invention will be described hereinafter with reference to the accompanying drawings. In the following description, well-known functions or constructions are not described in detail since they may obscure the present invention in unnecessary detail.

[0018] Figures 1 to 7An exemplary rotary atomizer system 100 having improved reliability and capable of producing increased RPM and disc speeds is illustrated. The rotary atomizer system uses an electric motor 102 having a permanent magnet rotor 104, rather than an induction rotor such as that used in most existing rotary atomizer systems, to produce a more efficient motor that requires less physical space for a given power output. The electric motor 102, which receives power via an electrical outlet, typically includes a motor housing 106, a permanent magnet rotor 104, a stator 110, and a shaft 108. The smaller engine size typically allows the disc to be closer to the lower radial bearing assembly 112. The motor 102 is preferably constructed of stainless steel, which is both corrosion resistant and a good heat sink. Other materials such as aluminum or other metals are also contemplated. Due to the ability to be closer, the motor 102 can operate throughout its speed range while remaining below the first critical speed of the shaft 108. The rotating shaft can deflect during rotation even in the absence of an external load, such as Figure 4 . The combined weight of the shaft 108 and the disk 114 can cause deflections that typically produce resonant vibrations above a certain speed, called the critical speed. Therefore, in order to operate properly, the engine 102 should be operated at a speed less than the critical speed. In addition, this engine configuration permits the use of a smaller disk diameter, which is generally less expensive and easier to handle, leaving enough space around the engine to place the liquid feed pipe.

[0019] The permanent magnet rotor 104 provides numerous advantages over its AC equivalent (e.g., an induction or asynchronous motor). For example, the permanent magnet rotor 104 generally produces higher speed and higher torque output while increasing power efficiency by eliminating the need for unnecessary current that would otherwise flow through the rotor windings of a conventional induction motor. Another benefit attributed to the use of the permanent magnet rotor 104 is increased power density (i.e., the power that can be extracted from a given space). In general, the permanent magnet motor 102 generally produces 30% to 40% more power density than conventional and similarly sized AC asynchronous motors. The increase in power density provides an opportunity to increase performance without requiring additional space for a larger motor, or alternatively, to reduce the size and weight of the motor while maintaining original performance. Reducing engine power size and consumption can result in lower operating temperatures, thereby reducing the effort required to cool the engine and / or engine system. The permanent magnet rotor 104 of the described embodiment has a tapered interference fit with the shaft 108 for ease of maintenance and rebuilding.

[0020] The rotary atomizer system 100 can further adopt one or more porous gas bearings including an upper radial bearing assembly 116 and a lower radial bearing assembly 112, and the upper radial bearing assembly and the lower radial bearing assembly can be supported by one or more upper / lower bearing housings to realize the frictionless support of shaft member 108, rotor 104 and disc 114. However, in a specific embodiment, a bearing housing may not be necessary. For example, a single housing may include both bearing and stator 110. The benefit of porous gas bearings 112 and 116 is that it is contactless and therefore does not require lubrication or speed restrictions on electric motors. Porous gas bearings 112 and 116 can also provide both main radial and axial support for shaft member 108, rotor 104 and disc 114. Therefore, the atomizer system 100 of the present invention can be operated with a higher RPM, thereby producing an increased disc speed. In addition, the segmented porous gas bearings 112 and 116 of the present invention provide several advantages over known systems, including but not limited to providing a passive system requiring only gas pressure, requiring a smaller housing, larger shaft diameter, generating higher loads, eliminating the need for backup bearings, allowing for thermal radial shaft expansion, and allowing for uniform gas loading across the contact surface.

[0021] In a particular embodiment, the porous gas bearings 112 and 116 are radial bearings that are mounted in a sleeve 117 with a common gas supply 118. Advantages of a common gas supply 118 include reduced complexity in running gas supplies to the individual pads, reduced number of failure points due to loss of a gas supply, and other advantages. In some embodiments, the gas supplied to the bearings may come from compressed process gas associated with the operation of the rotary atomizer. In other embodiments, the gas supply may include a specific gas (e.g., nitrogen) or a combination of gases.

[0022] In some embodiments, porous gas bearings 116 and 118 include graphite, which is porous in its natural form and is bonded to a stainless steel housing. In other embodiments, porous gas bearings include other naturally porous materials, composite materials with a porous structure, or bearing-type materials with a large number of discrete machined holes having desired porosity characteristics.

[0023] In some embodiments, the rotary atomizer 100 further includes a porous gas bearing configuration including an upper thrust bearing 120 and a lower thrust bearing 122, the upper thrust bearing and the lower thrust bearing being radially positioned relative to the shaft 108 so that the porous gas bearings form a discontinuous surface covering the entire rotating shaft (e.g., to form a slot, groove, hole or other gap). In other embodiments, the porous gas bearings 120 and 122 are axially configured relative to the shaft 108 (e.g., to form a slot, groove, hole or other gap) in a manner that provides a continuous or discontinuous surface covering a portion of the rotating shaft 108. In some embodiments, the porous gas bearings 120 and 122 are axially configured to the collar portion of the shaft. Although not being bound by a particular theory, the present invention allows for the configuration of porous gas bearings 120 and 122 close to the rotating shaft, which allows for improvements in heat dissipation and atomizer performance characteristics.

[0024] In certain embodiments, the rotary atomizer 100 of the present invention includes a gap detection system 124 that monitors one or more parameters associated with bearing health and performance, such as Figure 5 . For example, in one embodiment, the gap detection system 124 includes a component that measures the resistance associated with the distance between the upper radial bearing assembly 116 and the rotating shaft 108, whereby the gap detection system 124 will shut down the operation of the rotary atomizer 100 upon reaching or exceeding a resistance threshold. For example, in some embodiments, a current source is supplied to the rotating shaft 108 via a grounding ring, and one or more of the porous gas bearings 114 or 116 are electrically connected to a panel mounted programmable logic controller (PLC) that monitors whether the supply current is bridged to the gas bearing pads 120 or 122. As Figure 7 As depicted in , the mechanical spring 132 contacting the thrust pad along with the electrical conductor 134 may form a branch of a resistive circuit that is used to detect whether the shaft 108 is contacting the lower thrust bearing 122 or the upper thrust bearing 120 .

[0025] In another embodiment, the gap detection system 124 includes a component that measures the temperature of the bearing pads 114 or 116 via an infrared sensor or a spring-loaded contact temperature sensor, whereby if a temperature threshold is reached or exceeded, the gap detection system will shut down the operation of the rotary atomizer 100. For example, Figure 6 , a metallic resistance temperature detector (RTD) 126 is urged via a spring 128 and contacts the radial bearing pad along with an electrical lead 130. If the temperature detected by the RTD 126 exceeds a predetermined threshold, rotation of the shaft 108 is stopped by the gap detection system 124.

[0026] The gap detection system 124 provides several benefits, including minimizing the total downtime on the machine due to maintenance, which may be required if the rotary atomizer 100 is operated under dangerous conditions that will cause damage to the system and the components therein. Additional benefits of the gap detection system 124 include longer life of internal components, increased reliability of the system, and other benefits. In some embodiments, the resistance level is determined when there is contact between the shaft and the porous gas bearing, and the resistance threshold level is determined to indicate the relative distance between the shaft and the PGB when there is no contact between the shaft and the PGB. Although not bound by a particular theory, the resistance threshold level can provide information about the operation of the atomizer 100. When a specific resistance threshold or a percentage thereof is reached, this information can be used to prevent the operation of the atomizer 100 (for example, when 75% of the resistance threshold is reached, the atomizer is turned off).

[0027] In some embodiments, due to the magnetic attraction of the rotor 104 to the metal stator lamination, the rotary atomizer 100 of the present invention includes an integral guide bushing, including an upper shaft guide bushing 132, a rotor guide bushing 134, and a lower shaft guide bushing 136 radially positioned relative to the shaft 108 and the rotor 104, which enables efficient replacement of the porous gas bearings 112 and 116 without the need for shaft alignment tools. Additional benefits of the integral guide bushings 132, 134, and 136 include guiding the shaft assembly during initial installation / assembly without the need for any delicate / extra tools, thereby reducing the resources required to maintain and repair the rotary atomizer 100.

[0028] The use of porous gas bearings 112 and 116 in the present invention has realized several efficiencies and advantages of other known rotary atomizers.For example, unlike the atomizer using magnetic bearings, the atomizer of the present invention does not need to use friction bearings.Similarly, the porous gas bearings 112 and 116 used in the atomizer of the present invention do not need the intensive magnetic tuning required for the different disc designs used together with various magnetic bearing rotary atomizer embodiments.Porous gas bearings 112 and 116 further improve the operation of rotary atomizer 100, including bearing the higher unbalanced force on the disc 114, increasing radial load capacity and increasing shaft size.The design of gas bearings 112 and 116 makes it prevent any damage to atomizer internal components (engine, shaft etc.) together with guide bushings 132, 134 and 136 in the event of gas pressure loss (that is, bearing mechanism loss) and due to the braking action produced by friction against rotating shaft 108 to help the machine to rotate quickly and slow down.

[0029] exist Figure 4In one embodiment of the invention depicted in , the porous gas bearings 112 and 116 are arranged in one or more segments radially positioned along the shaft 108. The segmented bearings are arranged with a central gas supply bushing 138 in the sleeve 117. In other embodiments, the porous gas bearing segments are radially positioned within the sleeve 117 on washers 140 (e.g., O-rings), configured to allow the sleeve 117 (and thereby the porous gas bearings) to dynamically move in response to operating conditions to maintain the desired distance between the shaft 108 and the porous gas bearings 112 and 116. Washers 140 act in combination as springs in series and in parallel to accommodate deflection of the shaft 108. This allows the rotary atomizer to continue to operate even when the shaft 108 is slightly deflected. As shown, centerline 142 depicts the axis of rotation of the shaft 108 during normal operation, and centerline 144 depicts the axis of rotation of the shaft 108 under deflection. Center lines 146 and 148 show the deflection of the shaft collar under normal operation and under deflection, respectively.The series and parallel arrangements of washers 140 allow for deflection of the shaft 108 and shaft collar without shutting down the rotary atomizer system 100.

[0030] In other embodiments, the lower radial bearing assembly 112 and the upper radial bearing assembly 116 are also mounted on the washer 140, configured to provide additional dynamic response to operating conditions, thereby maintaining the desired distance between the shaft 108 and the porous gas bearings 112 and 116. Although not being bound by a particular theory, the porous gas bearings 112 and 116, the sleeve 117 and the washer 140, together with other atomizer components, function to provide dynamic response to shaft position changes that may occur during operation of the atomizer 100, including but not limited to radial movement during tipping or unbalanced disk loading, higher vibration loads, and thermal expansion of the rotating shaft. The washer 140 can be compressed or expanded to accommodate shaft position changes compared to the centerline under normal operation.

[0031] For example, during typical operation of the rotary atomizer 100 of the present invention, there may be a disc imbalance due to the variable load on the disc 114, which in turn causes the shaft to move (e.g., vibrate, deflect, etc.). Although not being bound by a particular theory, the atomizer 100 of the present invention provides an increased balance tolerance. The combination of the gap detection system 124 and the porous gas bearing is configured to provide a dynamic response to changes in the positioning of the shaft, allowing the atomizer 100 of the present invention to maintain the desired distance between the shaft 108 and the bearing pads 112 and 116, which results in reduced wear and degradation, thereby extending the service life of both the porous gas bearings 112 and 116 and other component parts of the atomizer 100.

[0032] The use of the permanent magnet rotor 104 in combination with the porous gas bearings 112 and 116 will allow the atomizer 100 to reach a greater and more favorable operating RPM speed, thereby increasing the spray drying efficiency while also reducing maintenance. The favorable operating speed (RPM) will vary depending on the size of the disc 114. Therefore, the disc 114 has a variety of sizes to choose from; however, a smaller disc size may be preferred because it is generally cheaper and easier to manipulate. In some embodiments, the atomizer 100 of the present invention is configured to provide a target peripheral disc tip speed that can be adjusted based on the application. For example, for a particular application, a higher peripheral disc tip speed is necessary, such as 985ft / sec (300m / s). Without being constrained by a particular theory, due to one or more factors associated with the porous gas bearings 112 and 116, the gap detection system 124 and / or its combination, the atomizer 100 of the present invention is configured to maintain the peripheral disc tip speed over a longer operating cycle.

[0033] Although various embodiments have been described with reference to particular arrangements of components, features, etc., these are not intended to be exhaustive of all possible arrangements or features, and indeed many other embodiments, modifications, and variations may be identified by those skilled in the art. Therefore, it should be understood that the present invention may be practiced otherwise than as specifically described above. The patents and patent publications cited above are hereby incorporated herein by reference in their entirety because they provide additional background information that is considered relevant to the present application.

Claims

1. A rotary atomizer, comprising: An electric motor having a stator and a rotor; Vertical shaft member; one or more porous gas bearings configured to provide frictionless radial and axial support for the shaft; and A rotating disc is mounted at the lower end of the shaft, the rotating disc being configured to spray the liquid into the form of fine particles.

2. The rotary atomizer according to claim 1, further comprising: A guide bushing is radially positioned relative to the shaft member.

3. The rotary atomizer according to claim 1, further comprising: A sleeve has a common gas supply configured to provide gas to the one or more porous gas bearings.

4. A rotary atomizer according to claim 3, wherein the sleeve further includes one or more washers, which are configured to allow the porous gas bearing to maintain a gap between the porous gas bearing and the vertical shaft in response to movement of the vertical shaft during operation of the rotary atomizer.

5. A rotary atomizer according to claim 3, wherein the porous gas bearing further comprises one or more washers, wherein the one or more washers are configured to allow the porous gas bearing to maintain a gap between the porous gas bearing and the vertical shaft in response to movement of the vertical shaft during operation of the rotary atomizer.

6. The rotary atomizer according to claim 1, further comprising: A gap detection system is configured to monitor one or more parameters associated with a distance between the porous gas bearing and the vertical shaft.

7. The rotary atomizer of claim 6, wherein the gap detection system monitors the temperature of one or more porous gas bearings.

8. The rotary atomizer of claim 6, wherein the gap detection system monitors a resistance level associated with the distance between the porous gas bearing and the rotating vertical shaft during operation of the rotary atomizer.

9. The rotary atomizer of claim 1, further comprising a housing configured to align the one or more porous gas bearings with the stator.

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