Rotary sprayer 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 on May 5, 2022, the entire content of which is hereby incorporated by reference in its entirety.

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

Background Art

[0003] Spray drying is a method of producing dried powder / particles from a slurry or liquid by rapidly drying the liquid using a flow of hot gas. Spray drying is a preferred method for drying many heat - sensitive materials such as foods and pharmaceuticals. A uniform particle size distribution is a reason for spray - drying some industrial products such as catalysts and other chemicals. Usually, air is the heating drying medium, but nitrogen may be used when the liquid being sprayed is a flammable solvent (e.g., ethanol) or when the product is sensitive to oxygen.

[0004] Generally speaking, a spray dryer uses an atomizer to disperse the liquid into a spray of controlled droplet size. Common types of atomizers used in spray drying include a rotary disk and a single - fluid pressure swirl nozzle. Alternatively, for some applications, a two - fluid nozzle or an ultrasonic nozzle may be used. Depending on the process and / or product needs, appropriate selection may achieve a droplet size of 10 to 500 micrometers. However, common applications are often in the range of 100 to 200 micrometers in diameter.

Summary of the Invention

Problems to be Solved by the Invention

[0005] This application discloses a system and method for improving the function and efficiency of a rotary sprayer 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 rotational force; a shaft that is vertically mounted and of a desired length and capable of rotating by the rotational force; one or more porous gas bearings for enabling frictionless radial and axial support of the shaft; 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 spraying a slurry material includes the steps of: supplying the slurry material to a rotary sprayer, the rotary sprayer comprising an electric motor that enables the rotary sprayer to rotate a shaft at a constant speed; using the rotary sprayer to output the liquid material in the form of atomized droplets; and circulating the atomized droplets with a process gas to produce substantially dry particles. [Brief explanation of the drawing]

[0008] These and other advantages of the present invention will be readily apparent from the following specification and accompanying drawings.

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

[0010] [Figure 2] Figure 2 is a cross-sectional side view of the rotary sprayer according to the present invention, showing the gas passages inside the machine.

[0011] [Figure 3]Figure 3 is a cross-sectional side view of a rotary sprayer according to the present invention, showing a gas supply bushing that supplies radial pads.

[0012] [Figure 4] Figure 4 is a cross-sectional side view of a rotary sprayer according to the present invention, which further illustrates the components of the porous gas bearing of the present invention.

[0013] [Figure 5] Figure 5 is a cross-sectional side view of a rotary sprayer according to the present invention, further illustrating an embodiment of the gap detection method of the present invention.

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

[0015] [Figure 7] Figure 7 is an enlarged view of the blowout B from Figure 5, showing the mechanical spring that contacts the thrust bearing pad. [Modes for carrying out the invention]

[0016] Preferred embodiments of the present invention will be described below with reference to the accompanying drawings. In the following description, well-known functions or structures will not be described in detail, as this may unnecessarily obscure the details of the present invention.

[0017] Figures 1-7 illustrate an exemplary rotary sprayer system 100 that enables improved reliability and increased RPM and disk speed. Instead of 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 with less physical space required for a given 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 disk can be to the lower radial bearing assembly 112. The motor 102 is preferably constructed from stainless steel, which has both corrosion resistance and good heat dissipation. Other materials such as aluminum or other metals are also considered. As a result of being able to move closer, the motor 102 can operate across its entire speed range while remaining below the primary critical speed of the shaft 108. The rotating shaft can deflect during rotation, even without external load, as shown in Figure 4. The combined weight of shaft 108 and disk 114 often causes deflection and resonant vibrations above a certain speed known as the critical speed. Therefore, for proper functioning, motor 102 should be operated at speeds 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 sufficient space around the motor to accommodate (multiple) fluid supply pipes.

[0018] The permanent magnet rotor 104 offers several advantages over its AC equivalent (e.g., induction motor or asynchronous motor). For example, the permanent magnet rotor 104 generally delivers higher speed and torque output while improving power efficiency by eliminating the need for unwanted current flowing through the rotor windings of a conventional induction motor. Another advantage of using the permanent magnet rotor 104 is the increased power density (i.e., the power that can be extracted from a given space). Generally speaking, a permanent magnet motor 102 typically produces a power density 30% to 40% higher than a conventional AC asynchronous motor of similar size. The increased power density offers 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 power size and power consumption of the motor lead to lower operating temperatures, which can reduce the effort required to cool the motor and / or motor system. The permanent magnet rotor 104 of this embodiment has a conical interference fit with the shaft 108 to facilitate maintenance and rebuilding.

[0019] The rotary sprayer system 100 can further employ one or more porous gas bearings including an upper radial bearing assembly 116 and a lower radial bearing assembly 112, which are supported by one or more upper / lower bearing housings and can enable frictionless support of the shaft 108, rotor 104, and disk 114. However, in certain embodiments, the bearing housing may not be necessary. For example, just one housing may surround both the bearing and the stator 110. The advantages of the porous gas bearings 112 and 116 are that they are non-contact and thus do not require lubricants or have no speed limitations in an 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 disk 114. Thus, the sprayer system 100 of the present invention can operate at higher RPMs and result in an increase in disk speed. Further, the segmented porous gas bearings 112 and 116 of the present invention provide several advantages over known systems (including providing a passive system that uses only gas pressure, using a smaller housing, using a larger shaft diameter, generating a higher load, eliminating the need for backup bearings, allowing for radial thermal expansion of the shaft, and allowing for a uniform gas load across the contact surface, but not limited to these).

[0020] In certain embodiments, the porous gas bearings 112 and 116 are radial bearings mounted within a cartridge 117 having a common gas supply 118. The advantages of the common gas supply 118 include reducing the complexity of performing gas supply to individual pads and reducing the number of failure points due to loss of gas supply. In some embodiments, the gas supplied to the bearings can be from the compressed process gas associated with the operation of the rotary sprayer. In other embodiments, the gas supply can include a specific gas (e.g., nitrogen) or a combination of gases.

[0021] In some embodiments, porous gas bearings 116 and 118 include graphite that is porous in its natural form and is adhered to a stainless steel housing. In other embodiments, the porous gas bearings include other natural porous materials, composite materials having a porous structure, or bearing-type materials having a number of unobtrusive machined holes with desired porosity characteristics.

[0022] In some embodiments, the rotary atomizer 100 further comprises a configuration of porous gas bearings including upper thrust bearing 120 and lower thrust bearing 122 that are radially disposed with respect to shaft 108 such that the porous gas bearings form a discontinuous surface (e.g., forming slots, grooves, holes, or other gaps) that covers the entire rotating shaft. In other embodiments, porous gas bearings 120 and 122 are axially configured with respect to shaft 108 in a manner that provides either a continuous or discontinuous surface (e.g., forming slots, grooves, holes, or other gaps) that covers a portion of the rotating shaft 108. In some embodiments, porous gas bearings 120 and 122 are axially configured with respect to the collar portion of the shaft. Without being bound by any particular theory, the present invention enables the configuration of porous gas bearings 120 and 122 in proximity to the rotating shaft, which enables heat dissipation and an improvement in the performance characteristics of the atomizer.

[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 the integrity and performance of the bearings, as shown in Figure 5. For example, in one embodiment, the gap detection system 124 includes a component that measures resistance related to the distance between the upper radial bearing assembly 116 and the rotary shaft 108, thereby causing the gap detection system 124 to stop the operation of the rotary sprayer 100 if a resistance threshold is reached or exceeded. For example, in some embodiments, a current source is supplied to the rotary 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), which monitors whether the supplied current bridges to the gas bearing pads 120 or 122. As shown in Figure 7, the mechanical spring 132, which contacts the thrust pad together with the electric wire 134, may form a leg of an electrical resistance circuit used to detect whether the shaft 108 is in contact with the lower thrust bearing 122 or the upper thrust bearing 120.

[0024] In another embodiment, the gap detection system 124 includes a component that measures the temperature of the bearing pad 114 or 116 by either an infrared sensor or a spring-loaded contact temperature sensor, thereby stopping the operation of the rotary sprayer 100 when a temperature threshold is reached or exceeded. For example, as shown in Figure 6, a metal resistance temperature detector (RTD) 126 is pressed via a spring 128 and contacts the radial bearing pad together with an electrical wire 130. If the temperature detected by the RTD 126 exceeds a predetermined threshold, the rotation of the shaft 108 is stopped by the gap detection system 124.

[0025] The gap detection system 124 offers several advantages, including minimizing the total downtime of the machine due to repairs that may be necessary if the rotary sprayer 100 operates in a dangerous condition that could cause damage to its systems and components. Additional advantages of the gap detection system 124 include extended lifespan of internal components and improved system reliability. 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, indicating the relative distance between the shaft and the porous gas bearing. While not bound by any particular theory, this resistance threshold level can provide information regarding the operation of the sprayer 100. This information can be used to prevent the operation of the sprayer 100 when a specific resistance threshold or a percentage thereof is reached (for example, to stop it when it reaches 75% of the resistance threshold).

[0026] In some embodiments, the magnetic attraction of the rotor 104 to the metal stator laminate allows the rotary sprayer 100 of the present invention to feature integrated guide bushings, including an upper shaft guide bushing 132, a rotor guide bushing 134, and a lower shaft guide bushing 136, which are radially positioned relative to the shaft 108 and rotor 104, enabling efficient replacement of the porous gas bearings 112 and 116 without the need for shaft alignment tools. An additional advantage of the integrated guide bushings 132, 134, and 136 is that they guide the shaft assembly during initial installation / assembly without the need for elaborate / additional tools, thereby reducing the resources required for maintenance and repair of the rotary sprayer 100.

[0027] The use of porous gas bearings 112 and 116 in the present invention achieves several efficiencies and advantages of other known rotary sprayers. For example, unlike sprayers using magnetic bearings, the sprayer of the present invention does not require the use of friction backup bearings. Similarly, the porous gas bearings 112 and 116 used in the sprayer of the present invention do not require the intensive magnetic adjustment required for the various disk designs used in 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, increasing radial load capacity, and increasing shaft size. The design of the gas bearings 112 and 116, together with the guide bushings 132, 134, and 136, is designed to prevent any damage to the inside of the sprayer (motor, shaft, etc.) in the event of gas pressure loss, i.e., bearing mechanism loss, and to help rapidly reduce the machine's spin by rubbing against the rotating shaft 108 as a brake.

[0028] In one embodiment of the present invention depicted in Figure 4, the porous gas bearings 112 and 116 are comprised of one or more segments arranged radially along the shaft 108. The segment bearings are comprised of a central gas supply bushing 138 within the cartridge 117. In another embodiment, the segments of the porous gas bearing are arranged radially on a gasket 140 (e.g., an O-ring) within the cartridge 117, and are configured to allow the cartridge 117 to move dynamically (and thereby the porous gas bearings to move dynamically) in response to operating conditions in order 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 the deflection of the shaft 108. This allows the rotary sprayer to continue operating even if the shaft 108 is slightly deflected. As shown, the centerline 142 traces the axis of rotation of the shaft 108 during normal operation, and the centerline 144 traces the axis of rotation of the shaft 108 when deflected. Centerlines 146 and 148 indicate the deflection of the shaft collar during normal operation and the deflection of the shaft collar during deflection, respectively. Arranging the gaskets 140 in series and parallel allows the shaft 108 and shaft collar to be deflected without requiring the rotary sprayer system 100 to be stopped.

[0029] In other embodiments, the lower radial bearing assembly 112 and the upper radial bearing assembly 116 are also mounted on a gasket 140 configured to provide an additional dynamic response to operating conditions in order to maintain a desired distance between the shaft 108 and the porous gas bearings 112 and 116. While not bound by 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 the operation of the sprayer 100 (including, but not limited to, radial movement due to disk load misalignment or imbalance, higher vibration loads, and thermal expansion of the rotating shaft). The gasket 140 can be compressed or expanded to adapt to changes in shaft position relative to the centerline during normal operation.

[0030] For example, during normal operation of the rotary sprayer 100 of the present invention, an imbalance in the disk may exist as a result of fluctuating loads on the disk 114, which in turn leads to shaft movement (e.g., vibration, deflection, etc.). Although not bound by any particular theory, the sprayer 100 of the present invention provides an 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 the 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 lifespan of both the porous gas bearings 112 and 116 and the other components of the sprayer 100.

[0031] Using 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 simultaneously reducing maintenance. The preferred operating speed (RPM) will vary depending on the size of the disc 114. Thus, the disc 114 is available in multiple sizes. However, smaller disc sizes may be preferred because 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 is adjustable based on the application. For example, a high peripheral disc tip speed (e.g., 985 feet / second (300 m / second)) is required for a particular application. Without being bound by any particular theory, the sprayer 100 of the present invention is configured to maintain the peripheral disc tip speed over a longer operating period by one or more factors related to the porous gas bearings 112 and 116, the gap detection system 124, and / or a combination thereof.

[0032] Various embodiments have been described with reference to the arrangement and features of specific components, but these are not intended to exhaustively discuss all possible arrangements or features, and in fact, those skilled in the art will be able to find many other embodiments, modifications, and variations. Therefore, it should be understood that the present invention may be carried out in ways other than those specifically described above. The patents and publications cited above provide additional background information that is considered relevant to this application, and are incorporated herein by reference in their entirety.

Claims

1. An electric motor having a stator and a rotor, Vertical shaft and One or more porous gas bearings configured to provide friction-free radial and axial support to the vertical shaft, A rotating disk provided at the lower end of the vertical shaft, wherein the rotating disk is configured to spray a liquid in fine particles, Each of the one or more porous gas bearings includes a plurality of separate segments arranged circumferentially around the vertical shaft, and one or more gaskets arranged on each of the plurality of separate segments. A rotary sprayer, wherein the one or more gaskets are configured such that, in accordance with the movement of the vertical shaft, the one or more porous gas bearings can maintain a gap between the one or more porous gas bearings and the vertical shaft.

2. The rotary sprayer according to claim 1, further comprising a guide bush arranged radially with respect to the vertical shaft.

3. The rotary sprayer according to claim 1, further comprising a cartridge having a common gas supply unit configured to supply gas to one or more porous gas bearings.

4. The rotary sprayer according to claim 3, wherein the cartridge further includes one or more gaskets configured such that one or more porous gas bearings can maintain a gap between the one or more porous gas bearings and the vertical shaft in response to the movement of the vertical shaft during operation of the rotary sprayer.

5. The rotary sprayer according to claim 1, further comprising a gap detection system configured to monitor one or more parameters relating to the distance between one or more porous gas bearings and the vertical shaft.

6. The rotary sprayer according to claim 5, wherein the gap detection system monitors the temperature of one or more porous gas bearings.

7. The rotary sprayer according to claim 5, wherein the gap detection system monitors the resistance level related to the distance between one or more porous gas bearings and the rotating vertical shaft during the operation of the rotary sprayer.

8. The rotary sprayer according to claim 1, further comprising a housing configured to align one or more porous gas bearings with the stator.

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