Rotary atomizer with porous gas bearings

Abstract

The rotary atomizer includes 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 for the shaft, and a rotating disk mounted at a lower end of the shaft, the rotating disk configured to atomize liquid in fine particles. A clearance detection system monitors the distance between the porous gas bearings and the vertical shaft. A bushing on the motor housing helps maintain precise alignment of the rotor during installation and maintenance.

Description

[Technical field]

[0001] [CROSS REFERENCE TO RELATED APPLICATIONS] This application claims priority to U.S. Provisional Application Serial No. 63 / 338,507, filed May 5, 2022, the entire contents of which are hereby incorporated by reference in their entirety.

[0002] [Technical field] The present invention relates generally to a rotating disk atomizer for use in a spray dryer or spray freezer, and more specifically to a rotary atomizer having a porous gas bearing. [Background technology]

[0003] Spray drying is a method of producing dry powders / particles from a slurry or liquid by rapidly drying the liquid with a stream of hot gas. Spray drying is the preferred method for drying many heat-sensitive materials such as food and pharmaceuticals. Consistent particle size distribution is the reason some industrial products are spray dried such as catalysts and other chemicals. Usually air is the heated drying medium, but nitrogen may be used if the liquid being sprayed is a flammable solvent (e.g. ethanol) or if the product is oxygen sensitive.

[0004] Generally speaking, spray dryers use atomizers to disperse liquid into a spray of controlled droplet size. Common types of atomizers used in spray drying include spinning disks and single-fluid pressure swirl nozzles. Alternatively, for some applications, two-fluid nozzles or ultrasonic nozzles may be used. Depending on the process and / or product needs, droplet sizes of 10 to 500 micrometers may be achieved by appropriate selection. However, common applications are often in the range of 100 to 200 micrometers in diameter. Summary of the Invention [Problem to be solved by the invention]

[0005] The present application discloses systems and methods for improving the performance and efficiency of rotary sprayers and reducing maintenance and repair costs. [Means for solving the problem]

[0006] According to a first aspect of the present invention, a rotary sprayer comprises an electric motor having a stator and a permanent magnet rotor capable of outputting a rotational force, a vertically arranged shaft having a desired length, the shaft being capable of being rotated by the rotational force, one or more porous gas bearings for providing frictionless support of the shaft in the radial and axial directions, and a rotating disk provided at the lower end of the shaft for spraying liquid in the form of fine droplets.

[0007] According to a second aspect of the present invention, a method for atomizing a slurry material includes the steps of feeding a slurry material to a rotary atomizer, wherein the rotary atomizer has an electric motor capable of rotating a shaft at a constant speed; outputting liquid material in the form of atomized droplets using the rotary atomizer; and circulating the atomized droplets with a process gas to produce substantially dry particles. [Brief description of the drawings]

[0008] These and other advantages of the present invention will be readily understood with reference to the following specification and accompanying drawings.

[0009] [Figure 1] FIG. 1 is a perspective view of a rotary atomizer according to the present invention.

[0010] [Diagram 2] FIG. 2 is a cutaway side view of a rotary atomizer according to the present invention showing the gas passageways inside the machine.

[0011] [Diagram 3]FIG. 3 is a cutaway side view of a rotary atomizer according to the present invention showing the gas supply bushings supplying the radial pads.

[0012] [Figure 4] FIG. 4 is a cutaway side view of a rotary atomizer according to the present invention further illustrating components of the porous gas bearing of the present invention.

[0013] [Diagram 5] FIG. 5 is a cutaway side view of a rotary sprayer according to the present invention further illustrating a gap detection embodiment of the present invention.

[0014] [Figure 6] FIG. 6 is an enlarged view of callout A from FIG. 5, showing the detector of mechanical resistance temperature.

[0015] [Figure 7] FIG. 7 is an enlarged view of callout B from FIG. 5 showing the mechanical spring contacting the thrust bearing pad. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below with reference to the accompanying drawings. In the following description, well-known functions or constructions will not be described in detail, as they may unnecessarily obscure the details of the present invention.

[0017] 1-7 illustrate an exemplary rotary sprayer system 100 that allows for improved reliability and increased RPM and disk speeds. Rather than employing an induction rotor as used in most existing rotary sprayer systems, the rotary sprayer system uses an electric motor 102 with a permanent magnet rotor 104, resulting in a more efficient motor that requires less physical space for a given power output. The electric motor 102 receives power via a power electrical receptacle and generally includes a motor housing 106, a permanent magnet rotor 104, a stator 110, and a shaft 108. Typically, the smaller the motor size, the closer the disks can be to the lower radial bearing assembly 112. The motor 102 is preferably constructed using stainless steel, which is both corrosion resistant and has good heat dissipation. Other materials, such as aluminum or other metals, are contemplated. As a result of the closer proximity, the motor 102 can operate throughout its speed range while remaining below the first critical speed of the shaft 108. The rotating shaft may flex during rotation, as shown in FIG. 4, even in the absence of an external load. The combination of the weight of the shaft 108 and the weight of the disks 114 often causes deflection and produces resonant vibrations above a certain speed known as the critical speed. Therefore, to function properly, the motor 102 should be operated below the critical speed. This motor configuration also allows for the use of smaller disk diameters, which are generally less expensive and easier to operate, and leaves enough free space around the motor for placement of the liquid supply tube(s).

[0018] The permanent magnet rotor 104 offers many advantages over its AC counterparts (e.g., induction motors or asynchronous motors). For example, the permanent magnet rotor 104 generally provides higher speed and torque output while improving power efficiency by eliminating the need for unnecessary current flowing through the rotor windings of a conventional induction motor. Another advantage of using a permanent magnet rotor 104 is increased power density (i.e., the power that can be extracted from a given space). Generally speaking, the permanent magnet motor 102 typically produces 30% to 40% higher power density than a conventional similarly sized AC asynchronous motor. The increased power density provides an opportunity to improve performance without requiring additional space for a larger motor, or to reduce the size and weight of the motor while maintaining the original performance. The reduced motor power size and power consumption can lead to lower operating temperatures and less effort required to cool the motor and / or motor system. The permanent magnet rotor 104 of the embodiment has a conical interference fit with the shaft 108 for ease of maintenance and rebuilds.

[0019] The rotary sprayer system 100 may further employ one or more porous gas bearings, including an upper radial bearing assembly 116 and a lower radial bearing assembly 112, which may be supported by one or more upper / lower bearing housings to allow frictionless support of the shaft 108, rotor 104, and disks 114. However, in certain embodiments, bearing housings may not be necessary. For example, a single housing may surround both the bearings and the stator 110. The advantage of the porous gas bearings 112 and 116 is that they are non-contact and therefore do not require lubrication or speed limitations in the electric motor. The porous gas bearings 112 and 116 may also provide both primary radial and axial support for the shaft 108, rotor 104, and disks 114. Thus, the sprayer system 100 of the present invention may operate at higher RPMs, resulting in increased disk speeds. Additionally, the segmented porous gas bearings 112 and 116 of the present invention offer several advantages over known systems, including, but not limited to, providing a passive system that uses only gas pressure, using smaller housings, using larger shaft diameters, allowing for higher loads, eliminating the need for backup bearings, allowing for radial thermal expansion of the shaft, and allowing for uniform gas loading across the entire contact surface.

[0020] In certain embodiments, the porous gas bearings 112 and 116 are radial bearings mounted in a cartridge 117 having a common gas supply 118. Advantages of the common gas supply 118 include reduced complexity of implementing gas supplies to the individual pads, fewer points of failure due to loss of gas supply, etc. In some embodiments, the gas supplied to the bearings may be 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 combination of gases.

[0021] In some embodiments, the porous gas bearings 116 and 118 comprise graphite, which is porous in nature, bonded to a stainless steel housing. In other embodiments, the porous gas bearings comprise other naturally porous materials, composite materials having a porous structure, or bearing-type materials having a large number of discreet machined holes that provide the desired porosity characteristics.

[0022] In some embodiments, the rotary sprayer 100 further comprises a porous gas bearing arrangement including an upper thrust bearing 120 and a lower thrust bearing 122 arranged radially relative to the shaft 108 such that the porous gas bearings form a discontinuous surface over the entirety of the rotating shaft (e.g., forming a slot, groove, hole, or other gap). In other embodiments, the porous gas bearings 120 and 122 are arranged axially relative to the shaft 108 in a manner that provides either a continuous or discontinuous surface over a portion of the rotating shaft 108 (e.g., forming a slot, groove, hole, or other gap). In some embodiments, the porous gas bearings 120 and 122 are arranged axially relative to a collar portion of the shaft. Without being bound to any particular theory, the present invention allows for the arrangement of the porous gas bearings 120 and 122 in close proximity to the rotating shaft, which allows for improved heat dissipation and sprayer performance characteristics.

[0023] In certain embodiments, the rotary sprayer 100 of the present invention includes a gap detection system 124 that monitors one or more parameters related to bearing health and performance, as depicted in Figure 5. For example, in one embodiment, the gap detection system 124 includes components that measure a resistance related to the distance between the upper radial bearing assembly 116 and the rotatable shaft 108, such that the gap detection system 124 stops operation of the rotary sprayer 100 when a resistance threshold is reached or exceeded. For example, in some embodiments, a current source is supplied to the rotatable shaft 108 through a ground ring, and one or more of the porous gas bearings 114 or 116 are electrically connected to a panel mounted programmable logic controller (PLC), which monitors whether the supplied current bridges to the gas bearing pads 120 or 122. As depicted in FIG. 7 , a mechanical spring 132 contacting the thrust pad along with an electrical wire 134 may form a leg of an electrical resistance circuit used to detect whether the shaft 108 contacts the lower thrust bearing 122 or the upper thrust bearing 120.

[0024] In another embodiment, the gap detection system 124 includes components that measure the temperature of the bearing pads 114 or 116, either by an infrared sensor or a spring-loaded contact temperature sensor, such that the gap detection system stops operation of the rotary atomizer 100 when a temperature threshold is reached or exceeded. For example, as depicted in Figure 6, a metallic resistance temperature detector (RTD) 126 is pushed through a spring 128 into contact with a radial bearing pad along with an electrical wire 130. When the temperature detected by the RTD 126 exceeds a predetermined threshold, rotation of the shaft 108 is stopped by the gap detection system 124.

[0025] The gap detection system 124 provides several advantages, including minimizing the total machine downtime due to repairs that may be required if the rotary sprayer 100 is operated in an unsafe condition that causes damage to systems and components therein. Additional advantages of the gap detection system 124 include longer life of internal components, improved system reliability, etc. In some embodiments, a resistance level is determined when there is contact between the shaft and the porous gas bearing, and a resistance threshold level is determined when there is no contact between the shaft and the porous gas bearing, which indicates the relative distance between the shaft and the porous gas bearing. Without being bound to a particular theory, this resistance threshold level can provide information regarding the operation of the sprayer 100. This information can be used to prevent operation of the sprayer 100 when a certain resistance threshold or percentage thereof is reached (e.g., shutting down when 75% of the resistance threshold is reached).

[0026] In some embodiments, due to the magnetic attraction of the rotor 104 to the metallic stator laminations, the rotary sprayer 100 of the present invention includes integral guide bushings including an upper shaft guide bushing 132, a rotor guide bushing 134 and a lower shaft guide bushing 136 that are radially disposed relative to the shaft 108 and rotor 104, allowing for 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 elaborate / additional tooling, thereby reducing resources required for maintenance and repair of the rotary sprayer 100.

[0027] The use of the porous gas bearings 112 and 116 in the present invention achieves several efficiencies and advantages over other known rotary sprayers. For example, unlike sprayers using magnetic bearings, the sprayers of the present invention do not need to use frictional backup bearings. Similarly, the porous gas bearings 112 and 116 used in the sprayers of the present invention do not require centralized magnetic tuning, which is necessary for the various disk designs used in the various magnetic bearing rotary sprayer embodiments. The porous gas bearings 112 and 116 further improve the operation of the rotary sprayer 100, including withstanding higher unbalanced forces on the disk 114, increased radial load capacity, and increased shaft size. The design of the gas bearings 112 and 116, along with the guide bushes 132, 134, and 136, are designed to prevent any damage to the sprayer internals (motor, shaft, etc.) in the event of loss of gas pressure, i.e. loss of the bearing mechanism, and to rub against the rotating shaft 108 to help the machine spin down quickly due to braking action.

[0028] In one embodiment of the invention depicted in FIG. 4, the porous gas bearings 112 and 116 are configured in one or more segments arranged radially along the shaft 108. The segment bearings are arranged with a central gas supply bushing 138 in a cartridge 117. In another embodiment, the porous gas bearing segments are arranged radially within the cartridge 117 on a gasket 140 (e.g., an O-ring) and configured to allow the cartridge 117 to dynamically move (and thereby the porous gas bearings to dynamically move) in response to operating conditions to maintain a desired distance between the shaft 108 and the porous gas bearings 112 and 116. The gasket 140 acts in combination as series and parallel springs in response to deflection of the shaft 108. This allows the rotary atomizer to continue to operate even if 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 during deflection. Centerlines 146 and 148 indicate the deflection of the shaft collar during normal operation and deflection, respectively. The series and parallel arrangement of gaskets 140 allows for deflection of the shaft 108 and shaft collar without requiring shutdown of the rotary sprayer system 100.

[0029] In another embodiment, the lower radial bearing assembly 112 and the upper radial bearing assembly 116 are also mounted on a gasket 140 configured to provide additional dynamic response to operating conditions to maintain a desired distance between the shaft 108 and the porous gas bearings 112 and 116. Without being bound to any particular theory, the porous gas bearings 112 and 116, the cartridge 117, and the gasket 140, along with other components of the sprayer, function to provide a dynamic response to changes in shaft position that may occur during operation of the sprayer 100, including, but not limited to, radial movement during disk load upsets or imbalances, higher vibration loads, and thermal expansion of the rotating shaft. The gasket 140 can be compressed or expanded to accommodate changes in shaft position compared to the centerline during normal operation.

[0030] For example, during normal operation of the rotary sprayer 100 of the present invention, disk imbalance may exist as a result of fluctuating loads on the disk 114, which in turn results in shaft movement (e.g., vibration, deflection, etc.). Without being bound to any particular theory, the sprayer 100 of the present invention provides increased balance tolerance. The combination of the gap detection system 124 and the porous gas bearings configured to provide a dynamic response to changes in shaft position allows the sprayer 100 of the present invention to maintain a desired distance between the shaft 108 and the bearing pads 112 and 116, resulting in reduced wear and deterioration, thereby extending the life of both the porous gas bearings 112 and 116 and other components of the sprayer 100.

[0031] The use of the permanent magnet rotor 104 in combination with the porous gas bearings 112 and 116 allows the sprayer 100 to reach a higher and more preferred operating RPM speed, thereby increasing the efficiency of spray drying and also reducing maintenance. The preferred operating speed (RPM) will vary depending on the size of the disk 114. Thus, the disk 114 is available in multiple sizes. However, smaller disk sizes may be preferred as they are generally less expensive and easier to operate. In some embodiments, the sprayer 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, a high peripheral disc tip speed (e.g., 985 ft / s (300 m / s)) is required for a particular application. Without being bound to any particular theory, the sprayer 100 of the present invention is configured to maintain the peripheral disc tip speed for a longer period of operation due to one or more factors related to the porous gas bearings 112 and 116, the gap detection system 124, and / or a combination thereof.

[0032] Although various embodiments have been described with reference to particular component arrangements, features, etc., these are not intended to exhaust all possible arrangements or features, and in fact those skilled in the art will recognize many other embodiments, modifications, and variations. It is therefore to be understood that the invention may be practiced other than as specifically described above. The above-cited patents and patent publications provide additional background information believed to be relevant to this application and are hereby incorporated by reference in their entireties.

Claims

1. an electric motor having a stator and a rotor; A vertical shaft; one or more porous gas bearings configured to provide radial and axial frictionless support for the shaft; a rotating disk provided at a lower end of the shaft, the rotating disk being configured to atomize liquid into fine particles; A rotary sprayer comprising:

2. 10. The rotary atomizer of claim 1, further comprising a guide bushing disposed radially relative to said shaft.

3. 10. The rotary atomizer of claim 1, further comprising a cartridge having a common gas supply configured to supply gas to the one or more porous gas bearings.

4. 4. The rotary sprayer of claim 3, wherein the cartridge further comprises one or more gaskets configured to enable the porous gas bearing to maintain a clearance between the porous gas bearing and the vertical shaft in response to movement of the vertical shaft during operation of the rotary sprayer.

5. 4. The rotary sprayer of claim 3, wherein the porous gas bearing further comprises one or more gaskets configured to enable the porous gas bearing to maintain a clearance between the porous gas bearing and the vertical shaft in response to movement of the vertical shaft during operation of the rotary sprayer.

6. The rotary atomizer of claim 1 , further comprising a gap detection system configured to monitor one or more parameters related to a distance between the porous gas bearing and the vertical shaft.

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

8. 7. The rotary sprayer 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 sprayer.

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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