Electrostatic spray nozzle assembly and electrostatic spray system

Abstract

An electrostatic spray nozzle assembly (130) is described that includes an induction ring (210) and a fluid tip (280). The induction ring generates an electric field for inducing charge on droplets of feed liquid from the fluid tip that pass through an opening (215) in the induction ring. The induction ring is electrically coupled to an electric induction field source (250) through a first conductive path provided by conductive surfaces of a nozzle head (230) that holds the induction ring and a purge gas tube (240) that holds the nozzle head. Feedstock flowing through the fluid tip is electrically coupled to a charge carrier source (275) through a second conductive path provided by at least a conductive surface of a fluid tube (285) that is coupled to the fluid tip. The first and second conductive paths are electrically isolated by an insulating barrier.

Description

[Technical field]

[0001] [CROSS REFERENCE TO RELATED APPLICATIONS]

[0001] This patent application claims the benefit of U.S. Provisional Patent Application No. 63 / 325,709, filed March 31, 2022, entitled "ELECTROSTATIC SPRAY NOZZLE INCLUDING INDUCTION RING," the entirety of which is expressly incorporated by reference into this specification, including any references therein.

[0002] [Technical field]

[0002] The present disclosure relates to electrostatic sprayer systems. More particularly, the present disclosure relates to an arrangement for delivering an electrostatically charged spray using an induction ring in an electrostatic spray drying system. [Background technology]

[0003] In known electrostatic sprayer systems, the liquid feedstock is charged to a potential of tens of thousands of volts (e.g., 30 kilovolts) and discharged at a spray outlet. The high potential causes the resulting charged spray droplets to repel each other, thereby ensuring a wide and uniform distribution of the spray droplets, thereby facilitating efficient and complete drying of solids suspended in the liquid feedstock during the spraying operation.

[0004] In such known electrostatic sprayer systems, during operation, charging of the liquid feedstock occurs before the feedstock is converted into a spray at the nozzle exit opening. Such a configuration results in the presence of high voltage extending from the feedstock's exit point at the spray nozzle tip to the tank containing the liquid feedstock. As a result, the entire feedstock tank and the entire feedstock path from the tank to the spray nozzle exit opening must be electrically insulated to avoid short circuits and loss of charge. This approach therefore requires specially configured components along the path of the charged feedstock, including pumps, flow meters, pressure sensors, nozzle opening actuators, etc.

[0005]

[0005] As an alternative to the electrostatic sprayer configurations described above, in which the entire feedstock is charged before it leaves the spray nozzle, there are electrostatic spray systems that include an inductor ring positioned proximate the exit opening of the spray nozzle to induce an electric charge on the spray droplets exiting the spray nozzle. The inductor ring, positioned at the exit point of the spray nozzle, is maintained at a high magnitude (either positive or negative) voltage, creating a high magnitude electric field potential that attracts (or repels, in the case of a strong negative electric field) electrons from the liquid feedstock exiting the spray nozzle. The attracted (or repelled) electrons result in a negative (or positive) charge being carried by the droplets exiting the spray nozzle.

[0006] An example of the use of an induction ring to charge the spray after it leaves the nozzle is provided, for example, in U.S. Pat. No. 4,343,433 for "Internal Atomizing Spray Head with Secondary Annulus Suitable for Use with Induction Charging Electrode." Summary of the Invention

[0007] An induction ring based electrostatic spray nozzle for use in an electrostatic sprayer system is provided herein. The arrangement includes an induction ring and a fluid tip. The induction ring generates an electric field for inducing charge on droplets of feed liquid from the fluid tip passing through an opening in the induction ring. The induction ring is electrically coupled to an electric induction field source via a first conductive path provided by a conductive surface of a nozzle head that holds the induction ring and a purge gas tube that holds the nozzle head. Feedstock flowing through the fluid tip is electrically coupled to a charge carrier source via a second conductive path provided by a conductive surface of at least a fluid tube that is coupled to the fluid tip. The first conductive path and the second conductive path are electrically isolated by an insulating barrier.

[0008] While the appended claims set forth the features of the present invention with particularity, the invention and its advantages are best understood from the following detailed description taken in conjunction with the accompanying drawings, in which: [Brief description of the drawings]

[0009] [Figure 1] FIG. 1 is a schematic diagram of an exemplary electrostatic spray drying system, in accordance with an illustrative example. [Figure 2A] FIG. 1 is a first cross-sectional view of an electrostatic spray nozzle assembly in accordance with an illustrative example. [Figure 2B] FIG. 1 is a second cross-sectional view of an electrostatic spray nozzle assembly in accordance with an illustrative example. [Diagram 3] FIG. 3 is a detailed cross-sectional view of the nozzle head portion, including the induction ring, of the electrostatic spray nozzle assembly shown in FIGS. 2A and 2B. [Figure 4] FIG. 2C is an exploded perspective view of the electrostatic spray nozzle assembly shown in FIGS. 2A and 2B. [Diagram 5] FIG. 2C is a cross-sectional view of a multi-nozzle spray assembly incorporating the electrostatic spray nozzle assembly shown in FIGS. 2A and 2B. [Figure 6] 1 is a further cross-sectional view of an electrostatic spray nozzle assembly according to a further illustrative example. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010]

[0015] In the present disclosure, an arrangement is provided for providing an electrostatically charged spray nozzle incorporating electrical circuitry to ensure proper operation of the electrostatic spray nozzle, including an induction ring for providing an electrostatic charge to the output spray of the electrostatic spray nozzle. Referring to FIG. 1, an exemplary electrostatic spray dryer system 100 is illustratively shown. In the illustrative example, a tank 110 holds a liquid feedstock 115. The liquid feedstock 115 is drawn from the tank 110 by a motor-driven pump 120 into a supply line 125 through the supply line 125 and discharged at an electrostatic spray nozzle 130 in a spray-drying chamber 135. Importantly, the spray nozzle includes an induction ring 140. The induction ring 140 is positioned at the exit opening of the electrostatic spray nozzle such that, during operation, a high voltage electric field (e.g., 3000 volts) generated by the induction ring applies and establishes an electrostatic charge potential to droplets in the spray created from the liquid feedstock 115 discharged from the electrostatic spray nozzle 130.

[0011]

[0016] One aspect of the specific configuration of the electrostatic spray nozzle 130 including the induction ring 140 makes the electrostatic spray nozzle 130 particularly adapted and configured for use in spray drying of feedstock. In particular, a sufficient voltage difference is applied between the induction ring 140 and the feedstock at the exit opening of the nozzle 130 to promote droplet formation from the feedstock material due to induced charges present in the liquid passing from the exit opening of the nozzle 130. Such a voltage may be 3,000 volts to 4,000 volts, which is significantly (e.g., an order of magnitude) lower than known electrostatic spray systems that operate at, for example, 30,000 volts. Furthermore, considering the variation in the conductivity of the feedstock, a closed loop control configuration is contemplated in the illustrative example to facilitate automatic setting of the voltage difference between the induction ring 140 and the exit opening of the electrostatic spray nozzle 130 to ensure that sufficient voltage is applied to ensure promoted / desired droplet formation without excessive voltage being applied. Such a feedback arrangement may be implemented, for example, by incorporating a current sensor into the induction circuit that senses both too little current (i.e., the magnitude of the induced electric field needs to be increased) and too much current (i.e., the magnitude of the induced electric field needs to be decreased).

[0012]

[0017] A controlled liquid feedstock delivery system including a pump 120 delivers a specified flow rate of the liquid feedstock 115 to the spray nozzle 130. The motor-driven pump 120 is controlled by a controller 145 (e.g., a programmable logic controller) according to a specified set point and a currently sensed flow rate. An operator specifies a flow rate set point, e.g., via a human machine interface (HMI), and then activates the motor-driven pump 120. The controller 145 then monitors (via a sensor input signal) the flow rate of the liquid feedstock and adjusts (via a motor control signal) the motor speed of the motor-driven pump 120 to maintain the set / specified flow rate of the liquid feedstock 115 to the spray nozzle 130. To maintain the desired flow, the controller 145 continuously receives a measurement signal indicative of the instantaneous flow rate of the liquid feedstock through the supply line to the spray nozzle. An in-line flow meter 150 measures the instantaneous flow rate of the liquid feedstock 115 through a pipe section 155 to which the in-line flow meter 150 is operably attached. The in-line flow meter 150 then maintains a historical record of the sensed flow and provides a signal to the controller 145 that provides control of the overall operation of the electrostatic spray dryer system 100 (including the speed of the motor-driven pump 130).

[0013]

[0018] The general structural details of the electrostatic spray drying system 100, including the controller 145, are well known to those skilled in the art and therefore will not be described in detail herein. Rather, attention is directed to an exemplary electrical / structural configuration of a spray nozzle including a directing ring mounted proximate its exit opening for delivering a stream of electrostatically charged droplets of a liquid feedstock, according to an illustrative example of the present disclosure.

[0014]

[0019] As a first specific example, the spray nozzle 130 is a specially configured nozzle assembly that exhibits certain electrical characteristics that facilitate the generation of a continuous stream of electrostatically charged spray droplets during operation. Referring to FIG. 2A, an exemplary electrostatic spray nozzle configuration is illustratively shown in which electrostatic charging of the spray droplets is achieved by electrical circuitry including an induction ring 210 (corresponding to induction ring 140 of FIG. 1) provided in the form of a conductive metal retaining cap disposed at the outlet opening of the spray nozzle 130. The opening 215 of the induction ring 210 is wide enough to avoid excessive accumulation of liquid feedstock emitted from the opening of the atomizing gas cap 220 passing through the opening 215 in droplet form with the aid of a purge gas flow. By way of example, the opening 215 has an inner diameter on the order of less than 1 inch for an applied electric field having a voltage of 3,000-4,000 volts (3-4 kilovolts). More specifically, the opening 215 has a diameter of about 0.7 inches. However, according to various spray drying applications, the diameter of the opening 215 and / or the applied voltage (electric field potential between the guide ring 215 and the liquid feedstock exiting the nozzle) are varied according to the spray pattern (wide / narrow spray field), nozzle opening position (linear displacement along the path of the spray field) with respect to the opening 215 of the guide ring 210. In an illustrative example, the atomizing gas cap 220 is a non-conductive insulating material (e.g., a hard plastic material).

[0015]

[0020] A first conductive path is provided for generating an electrostatic field at the opening 215 of the induction ring 210 for electrostatically charging the droplets of feedstock released from the atomizing gas cap. To that end, the induction ring 210 physically and conductively engages (by complementary threading) with a conductive surface of the nozzle head 230. The first conductive path is further provided by a further physical and conductive engagement of the nozzle head 230 with the purge gas tube 240. As an example, the nozzle head 230 and the purge gas tube 240 are physically and conductively engaged at 242 by complementary threaded surfaces. The purge gas tube 240 is also provided with a conductive surface that provides a conductive path from the nozzle head 230 to the induction field (high voltage) electrode 250 from a high voltage field signal source (not shown).

[0016]

[0021] In an illustrative example, the outer surface of the conductive component (e.g., induction ring 210) is coated with an electrically insulating layer to reduce the possibility of arcing in the spray environment. Thus, only the inner surface (or a portion thereof) of the exposed surface of induction ring 210 (as opposed to the unexposed threaded surface of induction ring 210, which is also an electrically conductive surface) is an electrically conductive surface. Such an electrically insulating layer is provided, for example, by a polytetrafluoroethylene (PTFE) coating.

[0017]

[0022] In yet a further illustrative example, all exposed surfaces of the conductive components, even the inner exposed surface of the induction ring 210, are coated with a ferroelectric material (e.g., PTFE) to provide an electrical insulating barrier between the high (magnitude) voltage of the induction ring 210 and the low (magnitude) voltage of the feedstock, as well as any potential source of ground connection that the feedstock contacts before exiting the spray nozzle. Such a configuration facilitates preventing and minimizing current flow from the induction ring during operation of the illustrative electrostatic spray drying system.

[0018]

[0023] A second conductive path is provided to establish a complementary electrical (e.g., ground) path from the conductive feed line through which the feedstock travels from the tank 110 (see FIG. 1 ) to the atomizing gas cap 220. The second conductive path provides a source for inducing an electric charge (opposite to the electric field potential generated at the opening 215) in droplets passing through the electric field at the opening 215 from the fluid tip 280, which has an electrically grounded conductive surface in contact with the feedstock. The second conductive path continues in the physical and electrical connection between the fluid tip 280 and the fluid tube 285, which supplies the feedstock to the fluid tip 280. The outer surfaces of the fluid tip 280 and the fluid tube 285, as well as the outer surface of the induction ring, are coated with an electrically insulating layer (e.g., PTFE).

[0019]

[0024] An atomized gas tube 290 supplies atomized gas to the atomized gas cap 220. The atomized gas tube 290 is, by way of example, made of a non-conductive material (e.g., hard plastic, ceramic, etc.) configured to provide a sealing engagement with the atomized gas cap 220. Alternatively, the atomized gas tube 290 includes a conductive material coated with an electrically insulating material. Thus, the atomized gas tube 290 and the atomized gas cap 220 provide an electrically insulating barrier between the first and second conductive paths described herein above. It should be noted that such electrically insulating properties may alternatively be achieved by coating the exposed surfaces with an insulating coating (e.g., PTFE).

[0020]

[0025] As shown in FIG. 2A, the nozzle body 260 is physically configured with several receptacles / openings for maintaining physical / electrical engagement between components of the spray nozzle 130 illustratively shown herein. In the illustrative example, the nozzle body 260 includes an induction field electrode receptacle 255 that holds an induction field electrode 250 in conductive engagement with a conductive surface of the purge gas tube 240. The nozzle body 260 includes a ground electrode receptacle 270 that holds an electrical ground electrode 275 in conductive engagement with a conductive surface of the fluid tube 285. An induction ring purge gas port 277 provides an opening for supplying purge gas flowing through the purge gas tube 240 to the opening 215 in the induction ring 210. As further shown in FIG. 2B (a further cross-sectional view rotated 90 degrees from the view shown in FIG. 2A), the nozzle body 260 further includes an atomization gas port 295 that provides an opening for supplying atomization gas to the atomization gas tube 290.

[0021]

[0026] As shown in FIG. 2A, the nozzle body 260 includes a cylindrical receptacle having a threaded surface at 265 for holding in place a purge gas tube 240 having a complementary threaded exterior surface.

[0022]

[0027] With reference to Figure 3, a further detailed view of the nozzle head portion of the spray nozzle shown in Figures 2A and 2B is provided to allow a clearer view of the various physical relationships shown in Figures 2A and 2B and the corresponding description provided above. Additionally, Figure 4 provides an exploded perspective view of the electrostatic spray nozzle assembly shown in Figures 2A and 2B to provide additional visual detail of an illustrative example of an electrostatic spray nozzle according to the present disclosure.

[0023]

[0028] 5, an exemplary multi-head assembly is provided in cross-section to show details of one of the multiple spray nozzles incorporated in the multi-nozzle assembly. In the illustrative example, a (grounded) fluid tip 580 receives feedstock fluid from a feedstock delivery manifold 584, provided by a fluid tube 585, which is also grounded to form a second (grounded) conductive path through which the feedstock passes before being atomized and ejected from one of a plurality of openings (such as opening 515) of a plurality of spray nozzle openings (such as opening 516 proximate to induction ring 510). As with the single nozzle configuration described above, multiple threaded receptacles are provided in the nozzle head 530 (electrically connected to induction ring 510) (one per induction) to hold a corresponding induction ring (e.g., induction ring 510) and provide a portion of the first conductive path from the induction ring to the electrical induction field source described herein above with respect to the single spray nozzle configuration. Nozzle head 530 is electrically connected to a purge gas tube 540 providing a further segment of the first conductive pathway.

[0024]

[0029] With continued reference to FIG. 5, the atomizing gas cap 520 and the atomizing gas tube 290 provide an electrical insulating barrier between the first and second conductive paths described herein above with respect to the exemplary multi-spray nozzle head structure according to the present disclosure.

[0025]

[0030] 6, a further cross-sectional view of an electrostatic spray nozzle assembly 600 is shown according to a further provided illustrative example. In an alternative exemplary configuration, the second conductive path (through which the feedstock traverses and which is electrically coupled to electrical ground) and the insulating barrier between the second conductive path and the first conductive path are substantially the same as the illustrative example provided in FIG.

[0026]

[0031] However, in the illustrative example provided by FIG. 6, the conductive components of the first conductive path are physically shielded from the environment outside the electrostatic spray nozzle 600 by the nozzle mount / shell components. In the illustrative example, an air atomizer is provided inside the circumference of the induction ring 610. The purge air flow is provided by a stainless steel tube 620 that connects the induction ring 610 (e.g., at electrode 630) to a high (magnitude) voltage source. In the illustrative example, the air atomizer components can be replaced with any of a variety of nozzles including purely hydraulic nozzles, internal mix air atomizers, ultrasonic atomizers, etc. Importantly, the nozzle mount / shell components provide a physical and electrically insulating barrier between the induction ring 610 and the chamber that contains the dust created by the dried feedstock.

[0027]

[0032] Additionally, while illustrative examples are shown and described with respect to exemplary electrostatic spray nozzle assembly configurations, the present disclosure is not limited to such assemblies. In light of the present disclosure, it will be readily appreciated that the advantages of the present disclosure are also applicable to a variety of electrostatic spray systems that include induction rings. Thus, the present disclosure is intended to be applied to a wide variety of electrostatic spray nozzle configurations, with appropriate adjustments to the above-described structures to accommodate the variances of a particular electrostatic spray application.

[0028]

[0033] All references cited in this specification, including publications, patent applications, and patents, are herein incorporated by reference to the same extent as if each reference was individually and specifically indicated to be incorporated by reference and was set forth in its entirety herein.

[0029]

[0034] Use of the terms "a" and "an" and "the" and "at least one" and similar referents in the context of describing the invention (particularly in the context of the claims which follow) should be construed to encompass both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. Use of the term "at least one" followed by a list of one or more items (e.g., "at least one of A and B") should be construed to mean one item selected from the listed items (A or B) or any combination of two or more of the listed items (A and B), unless otherwise indicated herein or clearly contradicted by context. The terms "comprising," "having," "including," and "containing" should be construed as open-ended terms (i.e., meaning "including, but not limited to"), unless otherwise indicated herein or clearly contradicted by context. The recitation of ranges of values ​​herein is merely intended to serve as a shorthand method of individually referring to each separate value falling within the range, unless otherwise indicated herein, and each separate value is incorporated herein as if it were individually recited herein. All methods described herein can be performed in any suitable order, unless otherwise indicated herein or clearly contradicted by context. Any and all examples provided herein, or the use of exemplary language (e.g., "such as"), are intended merely to better illustrate the invention, and do not present a limitation on the scope of the invention unless otherwise claimed. No language in this specification should be construed as indicating any non-claimed element as essential to the practice of the invention.

[0030]

[0035] Preferred embodiments of the present invention are described herein, including the best mode known to the inventors for carrying out the invention. Variations of these preferred embodiments may become apparent to those skilled in the art upon reading the foregoing description. The inventors expect that such variations will be utilized by those skilled in the art as appropriate, and the inventors intend for the invention to be practiced otherwise than as specifically described herein. Accordingly, this invention includes all modifications and equivalents of the subject matter recited in the claims appended hereto as permitted by applicable law. Moreover, any combination of all possible variations of the above-described elements is encompassed by the present invention unless otherwise indicated herein or clearly contradicted by context.

Claims

1. A guide ring, Fluid tip and An electrostatic spray nozzle assembly comprising the following: the guide ring generates an electric field for inducing an electric charge in a droplet of raw material liquid from the fluid tip passing through the opening of the guide ring; The aforementioned induction ring, A nozzle head that holds the guide ring, and Purge gas pipe that holds the nozzle head It is electrically coupled to an electric induction field source via a first conductive path provided by the conductive surface of the conductive surface, The raw material flowing through the aforementioned fluid tip is The fluid tip portion, and A fluid tube electrically coupled to the fluid tip It is electrically coupled to the charge carrier source via a second conductive path provided by the conductive surface, An electrostatic spray nozzle assembly in which the first conductive path and the second conductive path are electrically insulated by an insulating barrier.

2. The electrostatic spray nozzle assembly according to claim 1, wherein the insulating barrier is provided at least partially by an atomizing gas cap.

3. The electrostatic spray nozzle assembly according to claim 2, wherein the insulating barrier is provided at least partially by an atomizing gas pipe coupled to the atomizing gas cap.

4. The electrostatic spray nozzle assembly according to claim 1, wherein the guide ring has an inner diameter of 1 inch.

5. The electrostatic spray nozzle assembly according to claim 4, wherein the guide ring has an inner diameter of 0.7 inches.

6. The electrostatic spray nozzle assembly according to claim 1, wherein the guide ring is at least partially coated with an insulating material on its exposed surface.

7. The electrostatic spray nozzle assembly according to claim 6, wherein the insulating material is a dielectric material.

8. The electrostatic spray nozzle assembly according to claim 7, wherein the insulating material is polytetrafluoroethylene (PTFE).

9. The electrostatic spray nozzle assembly according to claim 6, wherein the inner ring surface of the guide ring is conductive.

10. The electrostatic spray nozzle assembly according to claim 1, wherein at least the externally exposed surface of the electrostatic spray nozzle is non-conductive.

11. A guide ring, Fluid tip and An electrostatic spray nozzle assembly comprising the following: the guide ring generates an electric field for inducing an electric charge in a droplet of raw material liquid from the fluid tip passing through the opening of the guide ring; The aforementioned induction ring, A nozzle head that holds the guide ring, and Purge gas pipe that holds the nozzle head It is electrically coupled to an electric induction field source via a first conductive path provided by the conductive surface of the conductive surface, The raw material flowing through the aforementioned fluid tip is The fluid tip portion, and A fluid tube electrically coupled to the fluid tip It is electrically coupled to the charge carrier source via a second conductive path provided by the conductive surface, An electrostatic spray nozzle assembly in which the first conductive path and the second conductive path are electrically insulated by an insulating barrier, A voltage source for supplying potential to the induction ring via the first conductive path and An electrostatic atomizing system, including...

12. The electrostatic atomization system according to claim 11, wherein the insulating barrier is provided at least partially by an atomizing gas cap.

13. The electrostatic atomization system according to claim 12, wherein the insulating barrier is provided at least partially by an atomizing gas pipe coupled to the atomizing gas cap.

14. The electrostatic spraying system according to claim 11, wherein the induction ring has an inner diameter of 1 inch.

15. The electrostatic spraying system according to claim 14, wherein the induction ring has an inner diameter of 0.7 inches.

16. The electrostatic spraying system according to claim 11, wherein the guide ring is at least partially coated with an insulating material on its exposed surface.

17. The electrostatic spraying system according to claim 16, wherein the insulating material is a dielectric material.

18. The electrostatic spraying system according to claim 17, wherein the insulating material is polytetrafluoroethylene (PTFE).

19. The electrostatic spraying system according to claim 16, wherein the inner ring surface of the induction ring is conductive.

20. The electrostatic spraying system according to claim 11, wherein at least the externally exposed surface of the electrostatic spraying nozzle is non-conductive.

21. The electrostatic spraying system according to claim 11, wherein the voltage supply source is configured to supply the potential at 4,000 volts or less.

22. A sensor that provides a feedback signal indicating the operation of the electrostatic spraying system, A controller that operates based on the feedback signal to adjust the aforementioned potential, The electrostatic spraying system according to claim 11, further comprising:

23. The electrostatic spraying system according to claim 22, wherein the feedback signal indicates an electric current.

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