Patent Application
20230276562
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The present invention relates to high-temperature plasma torches and in particular to a high-power plasma torch using a dielectric resonator.
Plasma torches, which produce a jet of high-temperature plasma, are used for cutting, plasma spraying, waste disposal, and the like. In a common design, a gas passes through an arc between electrodes and the energy of the arc converts the gas to a plasma exiting from the torch as a jet. The electrodes of such systems are subject to erosion, especially at high power, and corrosion by the carrier gas.
U.S. Pat. No. 9,706,635 entitled: “Plasma generator using dielectric resonator” describes a method of plasma generation using intense electrical fields produced by a circumferentially excited dielectric resonator. Such an approach eliminates arc electrodes and the associated problems of electrode wear and contamination of the plasma from such electrodes.
The present invention increases the power that can be output by a dielectric resonator plasma torch by multipoint excitation of the dielectric element, for example, using a branched waveguide. By exciting the dielectric at multiple points, asymmetrical current flow and heating of the dielectric material is reduced increasing power handling by the dielectric within desired temperature limits and improving the uniformity of plasma density and temperature. In addition or separately, a combination of spiral and linear airflow thermally isolates the intense plasma from the dielectric material allowing desirably higher intensity electrical fields possible with smaller dielectric channel sizes. Axially opposed choke tubes integrate into this torch assembly to both provide support for a torch tube guiding the plasma and the desired spiral and linear airflows, while greatly reducing emitted microwave radiation for improved efficiency and safety.
In one embodiment, the invention provides a plasma torch including at least one radiofrequency energy source, a dielectric ring providing a central opening extending along an axis, and a gas port for introducing plasma feeder gas along the axis through the central opening. A waveguide conducts radiofrequency energy from the at least one radiofrequency energy source to circumferentially separated points along the dielectric ring, the phase shift of radiofrequency energy at the circumferentially separated points matching a phase shift of current flow through the dielectric ring during resonant circumferential current flow through the dielectric ring.
It is thus a feature of at least one embodiment of the invention to increase the current handling capability of the dielectric ring and to improve the uniformity of plasma density and temperature by identifying and correcting points of excess energy dissipation.
The waveguide may provide a three-port, E-type junction having a first channel communicating with a waveguide entrance and splitting to a second and third channel communicating with a first and second waveguide exit at the circumferentially separated points to provide at the first and second waveguide exits a relative phase shift of 180° in the exiting radiofrequency energy, and wherein the circumferentially separated points are diametrically opposed about the dielectric ring with respect to the axis.
It is thus a feature of at least one embodiment of the invention to employ a simple waveguide structure to generate proper phasing and separation of the excitation points.
The second and third channels may curve inwardly about the axis.
It is thus a feature of at least one embodiment of the invention to modify a standard waveguide shape to minimize waveguide length and dissipation.
The first channel may include a set of stepped constrictions providing an impedance matching between the radiofrequency energy source and the dielectric ring.
It is thus a feature of at least one embodiment of the invention to allow the waveguide structure to also perform impedance matching.
The waveguide may support a transverse electromagnetic radio field having perpendicular E and H directions, and the waveguide maybe releasably separable across the H direction.
It is thus a feature of at least one embodiment of the invention to provide a waveguide structure that can be readily manufactured without inaccessible internal voids while also minimizing the disruption in the waveguide structure caused by such separability by separating across the low current H direction.
The plasma torch may further include a tuned cavity defining a substantially cylindrical volume holding the dielectric ring and providing opposed openings at opposed bases of the cylindrical volume along the axis and aligned with the central opening and providing the circumferentially separated points around the circumference of the cylindrical volume.
It is thus a feature of at least one embodiment of the invention to promote coupling between the waveguide and the dielectric ring through a containing tuned cavity.
The tune cavity may include a set of washer-shaped conductive shims releasably insertable into the tuned cavity to tune the tuned cavity to a resonant frequency of the dielectric ring.
It is thus a feature of at least one embodiment of the invention to provide a simple mechanism for accurately tuning the cavity to the dielectric resonator.
The dielectric ring may include multiple dielectric ring elements aligned and spaced along the axis.
It is thus a feature of at least one embodiment of the invention to allowing arbitrary scaling of power through the use of axially-stacked dielectric rings.
In one embodiment, the plasma torch may include a first conduit passing along the axis through the central opening in receiving the plasma feeder gas. A second gas port may be provided introducing inner cooling gas into the first conduit at an angle to the axis to promote a spiral flow of inner cooling gas around the plasma feeder gas along the axis, and a third gas port may be provided for introducing outer cooling gas into a second conduit coaxially around the first conduit for flow along the axis in a sheath around the first conduit.
It is thus a feature of at least one embodiment of the invention to provide two tailored air-cooling mechanisms to protect the dielectric ring. A first spiral gas within the first conduit envelops and separates the plasma of the plasma feeder gas from the conduit wall. This spiral gas may be coordinated with the speed of the plasma feeder gas. Outside of the conduit, a much higher speed linear flow may be adopted to scavenge heat leaking through the first conduit and to remove the heat from the inner surface of the dielectric ring by forced convection. The first conduit allows separate control of these two different streams.
The plasma torch may further include a manifold providing a circumferential passageway around the first conduit having a circumferential cross-sectional area at least twice an axial cross-sectional area between the first and second conduits.
It is thus a feature of at least one embodiment of the invention to provide uniform cooling airflow on all sides of the first conduit through a smoothing manifold structure.
The outer cooling gas may exit the second conduit before an end of the first conduit through openings directing the outer cooling gas radially with respect to the axis.
It is thus a feature of at least one embodiment of the invention to permit independent control of the plasma-involved gases and the outer cooling gas.
In one embodiment, the openings may direct the outer cooling gas away from the axis.
It is thus a feature of at least one embodiment of the invention to eliminate interference between the high-velocity cooling gas and the plasma plume stability.
The first conduit may extend outside of the tuned cavity and be supported at first and second ends at points beyond the tuned cavity by conductive metal sleeves surrounding the outer cooling flow, the metal sleeves centering the first conduit within the central opening and opposed openings and extending axially from the bases by at least 1 cm.
It is thus a feature of at least one embodiment of the invention to provide a microwave choke structure serving multiple purposes including reducing emitted microwave energy, supporting the first conduit, and providing the walls of the second conduit.
The dielectric ring may comprise multiple dielectric ring elements aligned and spaced along the axis by an insulating support providing a smooth central lumen forming an inner wall of the second conduit.
It is thus a feature of at least one embodiment of the invention to allow the outer cooling flow to flow closely adjacent to the dielectric structure for improved cooling with closer proximity of the dielectric current flow to the generated plasma.
These particular objects and advantages may apply to only some embodiments falling within the claims and thus do not define the scope of the invention.
Referring now to
The torch tube 12 communicates at an inlet side 15 with a source of plasma feeder gas 16, for example, initially providing argon or the like and then transitioning to nitrogen or air. Before being received by the torch tube 12, the feeder gas 16 may pass through a spark unit 18 providing a high-voltage electrode imparting an initial ionization of the feeder gas 16 received by the torch tube 12.
The torch tube 12 extends from the inlet side 15 along the axis 14 through a waveguide cavity 20 operating to expose the feeder gas 16 in the torch tube 12 to an intense alternating electrical field stripping the electrons from the gas to create the plasma state. The resulting plasma 22 may exit the torch tube 12 at an exit side 25 as a driven flow of the feeder gas 16.
The waveguide cavity 20 communicates through an input arm 24 extending perpendicularly from the axis 14 with a microwave system 26. This microwave system 26 generally provides a source of high frequency microwave energy, for example, in excess of 2.5 GHz, and may provide a power in excess of 1 kW. The microwave system 26, for example, may provide a microwave generator, such as a magnetron with an isolator, 28 receiving a source of electrical power 31 to generate microwave energy which is then passed through a bidirectional power meter 32 and then through a stub tuner 34 of conventional design. The bidirectional power meter 32 measuring input energy from the magnetron 28 and reflected energy from the waveguide cavity 20 allows assessment of impedance matching between the magnetron 28 and the waveguide cavity 20. This impedance may be adjusted using the stub tuner 34 to maximize transfer of power from the magnetron 28 to the waveguide cavity 20.
Referring now also to
The connection plane is selected, 29 as depicted, to be generally parallel to the electrical field of a transverse electromagnetic wave passing through the channels 30, 36a and 36b, and thereby reduces the need for current flow between the halves of the waveguide cavity during operation as a waveguide, and thus minimizing the need for good electrical communication between the halves.
The two halves of the waveguide cavity 20, after machining, may be assembled together by means of machine screws (not shown) engaging threaded bolt holes 33 cut and tapped in the outer and inner walls 21 of one half of the waveguide cavity 20 (aligned with corresponding bores in the other half) defining the channels 30, 36a and 36b.
The inner and outer walls 21 define the first channel 30 to extend along a longitudinal axis 38 perpendicular to the axis 14 within the input arm 24 between the microwave system 26 and the torch tube 12. This channel 30 provides a transverse electric mode of transmission of microwave energy with an orientation of the electric field 39 aligned with the plane 29 (the arrow showing the reference direction for the electric field intensity vector) as discussed above facilitating construction of the waveguide cavity 20.
The inner surface of the channel 30 may include a series of stepped reductions 41 as one moves from the microwave system 26 toward the torch tube 12 providing impedance matching of a type generally understood in the art.
The channel 30 terminates before reaching the torch tube 12 at a T-junction 35 where it splits into a left (upper as depicted) and right (lower as depicted) channel 36a and 36b providing a so-called “E-type waveguide” junction in which the conducted radiofrequency energy separates to pass equally down the left and right channels 36a and 36b but with a relative 180° phase shift between the electrical polarization of the radiofrequency energy passing through channels 36a and 36b.
The left and right channels 36a and 36b initially diverge perpendicularly from the channel 30 at the T-junction 35 but then follow a curve of constant radius about the axis 14 symmetrical about the longitudinal axis 38 to termination points adjacent to opposite sides of a periphery of a tuned cavity 40. Generally, the width of each of the channels 36 in the depicted E-plane of
Mutually opposed and facing openings 42a and 42b are provided between cavity 40 and respective left channel 36a and right channels 36b. The width of each of the openings 42 in the depicted E-plane of
The openings 42a and 42b allow the energy from the left channel 36a and right channel 36b, as previously phase shifted, to enter the cavity 40 on opposite sides with opposite electromagnetic phase.
Centered within the cavity 40 about the axis 14 and torch tube 12 is a dielectric resonator 46 being, in one embodiment, an annular ring symmetric about the axis 14. As so positioned, the opposite of electrical field polarities of electrical energy from each of the openings 42a and 42b induce opposite currents 48a and 48b on opposite sides of the dielectric resonator 46 to promote cyclic current flow therethrough at the frequency of the radiofrequency energy. The dimensions of the dielectric resonator 46 and of the cavity 40 holding the dielectric resonator 46 are adjusted to encourage an oscillating current flow within the dielectric resonator 46 at the frequency of the microwave power. By separate and opposite excitation of the dielectric resonator 46 through openings 42a and 42b more uniform current flow through the dielectric resonator 46 is possible, reducing peak heating of the dielectric resonator 46 and providing a more uniform induced electrical field within the plasma 22 and thus a more uniform and stable plasma 22. The process of generating plasma through a concentrated yet highly uniform electrical field within a dielectric resonator is described in more detail in U.S. Pat. Nos. 9,706,635 and 9,491,841, assigned to the assignee of the present application and cited above and hereby incorporated by reference.
The material of the dielectric resonator 46 desirably has any one or more of the qualities of: a quality factor of greater than 100, an electrical resistivity greater than 1×1010 Ωcm, a dielectric constant with a loss tangent of less than 0.01, and a dielectric constant (relative permittivity) greater than five.
Referring now to
The holes 52 may have internal opposed counterbores which receive an insulating end of an axially extending insulating tube 54, for example, constructed of a fluorinated hydrocarbon such as Teflon®. Desirably the insulating tube 54 provides high electrical insulation with a low relative permittivity of less than four and has a diameter sized to fit tightly within the counterbores to be held fixedly therein centered on axis 14.
Central openings in one or more annular dielectric resonators 46a and 46b have the same diameter as the inner diameter of tubes 54 to be aligned thereby with axis 14 and held in spaced separation by hooks 56 extending radially from the outer surface of the tube 54, for example, at a spacing of 120°, capturing the sides of the dielectric resonators 46. The tube 54 and hooks 56 may be assembled from multiple components but desirably from a substantially smooth and continuous inner bore 58 to facilitate the flow of air therethrough (for example, between the inner bore 58 and an outer surface of the torch tube 12) with minimized turbulence.
Referring still to
It will be appreciated that an arbitrary number of dielectric resonators 46 may be arrayed along the tube 54 with corresponding increases in the height of the cavity 40, for example, when higher power plasma torches are required.
Referring now to
Referring to
One of the conductive metal sleeves 80b provides a manifold portion for receiving cooling air 70 through a first inlet 84. This manifold portion is sized to produce a low resistance to airflow circumferentially around the torch tube 12 within the manifold portion so that air may be uniformly received on all sides of the tube 12 for uniform axial flow. In this regard, the cross-sectional area of the manifold portion of the sleeve 80b defining a passage of airflow around the tube 12 (and thus measured in a plane perpendicular to that airflow) will be at least twice and desirably more than five times the cross-sectional area between the outer surface of the tube 12 and the inner surface of the tube 54 perpendicular to the axis 14.
The remaining conductive metal sleeve 80a, in contrast, and as previously discussed, will provide a smooth continuation of the inner surface of the tube 54 which together with the inner surface of the hole 52 promotes low turbulence flow of air 70 axially toward the exit side 25. Radially directed openings 86 at the distal end of the metal sleeve 80a are distributed circumferentially around the distal end of the metal sleeve 80a to discharge the high transfer cooling air 70 radially away from the axis 14 to reduce interference with the plasma 22 exiting the torch tube 12.
Referring still to
The secondary manifold assembly 100 provides a volume communicating with a second gas cooling inlet 104 receiving a cooling gas 110, such as air, steam, methane, carbon-dioxide, hydrogen, argon, helium, or any combination thereof, generally at a tangent to the axis 14 and further communicating with a plasma feeder gas inlet 106 generally aligned with the axis 14 receiving plasma feeder gas 16 (shown in
By providing segregated spiral cooling gas 110 through second gas cooling inlet 104 and cooling gas 70 through inlet 84, the benefits of a spiral flow shielding the inner surface of the torch tube 12 together with a higher velocity a direct linear flow of cooling gas 70 can be provided without the need for similar gas flow velocities such as can be non-optimal for these different flow purposes and patterns. Thus, for example, the high transfer cooling air 70 may be pumped at about 200 L per minute to maintain a peak temperature of less than 90° C. in contrast to the cooling gas 110 and plasma feeder gas 16 passing at 100 L per minute but reaching temperatures of over 3000° C.
Referring now to
Referring again to
Certain terminology is used herein for purposes of reference only, and thus is not intended to be limiting. For example, terms such as “upper”, “lower”, “above”, and “below” refer to directions in the drawings to which reference is made. Terms such as “front”, “back”, “rear”, “bottom” and “side”, describe the orientation of portions of the component within a consistent but arbitrary frame of reference which is made clear by reference to the text and the associated drawings describing the component under discussion. Such terminology may include the words specifically mentioned above, derivatives thereof, and words of similar import. Similarly, the terms “first”, “second” and other such numerical terms referring to structures do not imply a sequence or order unless clearly indicated by the context.
When introducing elements or features of the present disclosure and the exemplary embodiments, the articles “a”, “an”, “the” and “said” are intended to mean that there are one or more of such elements or features. The terms “comprising”, “including” and “having” are intended to be inclusive and mean that there may be additional elements or features other than those specifically noted. It is further to be understood that the method steps, processes, and operations described herein are not to be construed as necessarily requiring their performance in the particular order discussed or illustrated, unless specifically identified as an order of performance. It is also to be understood that additional or alternative steps may be employed.
It is specifically intended that the present invention not be limited to the embodiments and illustrations contained herein and the claims should be understood to include modified forms of those embodiments including portions of the embodiments and combinations of elements of different embodiments as come within the scope of the following claims. All of the publications described herein, including patents and non-patent publications, are hereby incorporated herein by reference in their entireties
To aid the Patent Office and any readers of any patent issued on this application in interpreting the claims appended hereto, applicants wish to note that they do not intend any of the appended claims or claim elements to invoke 35 U.S.C. 112(f) unless the words “means for” or “step for” are explicitly used in the particular claim.
