Classifications

• • H—ELECTRICITY
  • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
  • H05H—PLASMA TECHNIQUE; PRODUCTION OF ACCELERATED ELECTRICALLY-CHARGED PARTICLES OR OF NEUTRONS; PRODUCTION OR ACCELERATION OF NEUTRAL MOLECULAR OR ATOMIC BEAMS
  • H05H1/00—Generating plasma; Handling plasma
  • H05H1/24—Generating plasma
  • H05H1/26—Plasma torches
  • H05H1/32—Plasma torches using an arc
  • H05H1/44—Plasma torches using an arc using more than one torch
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
  • H01J37/00—Discharge tubes with provision for introducing objects or material to be exposed to the discharge, e.g. for the purpose of examination or processing thereof
  • H01J37/32—Gas-filled discharge tubes
• • H—ELECTRICITY
  • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
  • H05H—PLASMA TECHNIQUE; PRODUCTION OF ACCELERATED ELECTRICALLY-CHARGED PARTICLES OR OF NEUTRONS; PRODUCTION OR ACCELERATION OF NEUTRAL MOLECULAR OR ATOMIC BEAMS
  • H05H1/00—Generating plasma; Handling plasma
  • H05H1/24—Generating plasma
  • H05H1/26—Plasma torches
  • H05H1/32—Plasma torches using an arc
  • H05H1/34—Details, e.g. electrodes, nozzles
  • H05H1/36—Circuit arrangements

Definitions

• the present invention relates generally to Alternating Current (AC) thermal plasma generators. More particularly, this invention 0 pertains to three-phase, AC thermal plasma generators.
• AC Alternating Current
• Thermal plasma is generally defined as a state of matter, which exhibits many properties similar to gas, contains 5 substantially equal numbers of positive and negative ions and radicals, and is a good conductor of electricity.
• Thermal plasma may be created by increasing the internal energy of matter.
• the internal energy of matter may be increased by exposing matter to an electric arc in such a way that the electrical energy from the electric arc is 0 transferred to the matter.
• thermal plasma generation systems Different technique s for generating thermal plasma have been researched for many years. As a result, several different types of thermal plasma generation systems have been developed. One such example is the 5 thermal plasma, metal cutting, torch. Each system differs in the way that the electric arc is initiated and sustained.
• Thermal plasma has been created using both direct current and alternating current devices.
• Low power direct current (DC) and inductive coupling (IC) thermal plasma generators are currently used in semiconductor, film deposition, and other high technical applications.
• Alternating current (AC) thermal plasma generators are ideal for such applications as radioactive materials vitrification, decontamination of pathogenic materials and substances (e.g., hospital waste), and reduction and/or safe decomposition of hazardous waste or difficult to destroy materials.
• AC thermal plasma generators may be used in chemical processes that require the heating of materials in the absence of oxygen or to reduce or de-compose waste materials into clean energy fuel. In all DC arc-generating systems, the arc is initiated between a cathode and an anode.
• a substance being treated In a transferred arc system, a substance being treated, a molten metal for example, is used as one of the electrodes. In a non-transferred arc system, the electrodes are independent of the treated substance.
• AC thermal plasma generators are more efficient and less expensive than DC thermal plasma generators because complicated and expensive rectifier equipment is not necessary.
• AC thermal plasma generators have disadvantages as well.
• Single-phase AC thermal plasma generators have been found to be inherently unstable due to the fact that the electric arc is extinguished every half cycle. As a result, the electric arc must be initiated 120 times per second. Three-phase AC thermal plasma generators overcome this instability problem. A three-phase AC thermal plasma generator is described in
• the primary electrode arrangement in the '489 patent provides small arc-working areas on each primary electrode. As a result, the primary electrodes wear out in a short time period and must be replaced. This is a time-consuming and expensive process.
• Another disadvantage of the '489 patent is the fact that the primary electrodes are fixed in place. As the primary electrodes wear down due to the small arc-working areas on each electrode, the gap between the primary electrodes increases. As the gap increases, the voltage necessary to initiate an arc across the gap increases and generator efficiency is reduced.
• Still another disadvantage of the '489 patent is the use of a single pneumatic ring, located adjacent to the primary electrodes, to introduce the working stream into the arcing chamber. As a result, a non-uniform thermal plasma steam is produced, having hot and cold spots, which reduces generator efficiency.
• the thermal plasma generator of this invention is powered with alternating current directly from a conventional electric utility network or from a generator system.
• a significant improvement in efficiency over DC generators is obtained by using alternating current because of reduced losses that would otherwise occur in the power supply.
• the process of convective heat-exchange takes place because of the rapid movement of the arcs within the chamber, high turbulence stream flow, and diffusion of the arc inside the chamber.
• the use of relatively low voltage alternating current eliminates the need for an additional high-voltage direct current power supply thus reducing the cost of fabrication and maintenance.
• the primary electrodes are positioned so that a portion of each electrode forms a narrow gap with respect to a portion of each of the other two electrodes, and another portion of each electrode forms a wider gap with respect to another portion of each of the other two electrodes. This configuration results in a larger electrode arc- working area and extends the life of the electrodes.
• Electrodes configured to provide a large arc- working area and the application of the rail gun effect (the movement of the arc under the influence of its own magnetic field) allows the use of electrodes cooled by water with the operational advantage of several hundreds of hours without maintenance.
• Two types of electrodes can be used: tubular water-cooled electrodes made of copper and rod electrodes made of tungsten alloy and cooled with stream.
• the plasma generator of the present invention utilizes a novel adjustable arrangement and configuration of electrodes that provides a large arc- working area and redistributes thermal load on the electrodes by rapidly moving the arc along the electrodes.
• the large arc-working area and redistribution extends the life of the electrode.
• the adjustment mechanism ensures that the gap between each electrode remains constant and, as a result, maintains generator efficiency.
• a high quality, uniform plasma is obtained by injecting the working stream into the arcing chamber of the generator through multiple stream rings. The use of multiple rings improves the mixing of the working stream.
• FIG. 1 is a block schematic diagram that generally shows the electrical and stream interconnections among the various components of the system
• FIG. 2 is a cutaway side view of a preferred mechanical embodiment of the plasma generator of the present invention.
• FIG. 3 is an enlarged side view of one of the primary electrodes, 33a, used in the plasma generator of FIG. 2.
• FIG. 4 is an enlarged cutaway side view of the high voltage plasma injector used in the plasma generator of Fig. 2.
• FIG. 5 is a flowchart illustrating the control sequence of a preferred embodiment of the control circuits.
• the plasma generator system 10 comprises six major components: a plasma generator 30, an injector stream manifold 19, a working stream manifold 18, a cooling stream manifold 20, control circuits 15, and an electric power supply 14. Some of these components, such as the control circuits 15, are enclosed in steel cabinets (not shown).
• the thermal plasma generator 30 includes a housing 31 in which are mounted the operative components.
• High voltage operating power for an injector 34 is fed from the secondary of injector high power transformer 16 (FIG. 1) to first and second injector electrode terminals 38 and 39 on injector 34 which passes through an end wall of the housing 31.
• the primary side of injector transformer 16 is connected through an automatic power switch 48 (FIG. 1) across one phase of a 3-phase 480 VAC power network.
• the 3-phase 480 VAC power network is represented by the electric power supply 14 illustrated in Fig. 1.
• the thermal plasma generator housing 31 is actually a shell with an internal stream jacket to provide for stream cooling.
• a faceplate 32 is attached to housing 31 by a spacer ring 37 to form an interior arcing chamber 40 which contains the primary arcs.
• a circular opening 42 is formed in the center of the faceplate 32 from which the thermal plasma stream is exhausted from within chamber 40.
• Faceplate 32 and spacer ring 37 also have stream jackets in their respective outside walls for cooling purposes. Accordingly, brass tubes having an axial orientation are arranged peripherally around the mating surfaces of faceplate 32 and spacer ring 37 to provide passages between the jackets of housing 31, faceplate 32, and spacer ring 37. Cooling stream enters, the jacket system through housing cooling water hose 44.
• Three primary electrodes 33a, 33b, and 33c are circumferentially positioned around the chamber 40 (see also FIG. 3). Each electrode is positioned adjacent each other electrode such that narrow gaps are formed between each electrode adjacent to the end wall of the housing 31. The other end of each electrode extends laterally toward the faceplate 32 such that the gap between each electrode increases when moving toward the faceplate 32.
• Each of the electrodes 33a-c are adjustably connected to the housing 31 using an electrode adjustment assembly.
• Each electrode adjustment assembly is independently adjustable to ensure that the narrow gap between each electrode remains substantially constant.
• the electrode adjustment assembly 50 includes a dielectric plate 52 connected to electrode holders 54 and 56 of electrode 33a.
• the dielectric plate is generally a thin rectangular sheet of metal having a threaded hole 58 (not shown) in the middle thereof.
• a bolt 60 passes through the threaded hole 58 (not shown) and is rotatably attached to the housing 31.
• Similar electrode adjustment assemblies (not shown) are used to connect electrodes 33b and 33c.
• the electrodes 33a-c are powered directly through reactors 17a,
• the electrodes 33a, b, and c are hollow copper tubes so that they can be cooled internally by stream routed through cooling stream hose 44 from cooling stream manifold 20 (FIG. 1). Insulators
• Ring 35a is adjacent the end wall of the chamber 31 and introduces the working stream into the chamber 40 intermediate the end wall and the working area of the electrodes 33a, b, and c.
• Ring 35b is positioned intermediate ring 35a and the faceplate 32, and supplies the majority of the working stream to chamber 40.
• Ring 35c is positioned intermediate ring 35b and the faceplate 32. Utilization of three separate rings substantially improves plasma dynamics within the chamber. Furthermore, each ring can be used to introduce a different working stream into the chamber 40.
• the working stream enters the chamber 40 through concentric holes in rings 35a, b, and c.
• the holes are drilled tangentially so that the working stream is directed to flow in a clockwise direction to create a highly turbulent stream flow.
• the resulting flow creates a thin layer of non-ionized stream along the inner walls of the chamber 40. This layer provides thermal protection of the walls and minimizes the tendency of arcing between ends of the electrodes 33a-c and chamber 40.
• the ring 35a is approximately 5.6 inches in diameter with six 0.1 inch diameter holes
• ring 35b is approximately 10 inches in diameter with twelve 0.1 inch diameter holes
• ring 35c is approximately 12.4 inches in diameter with six
• the holes are formed and positioned to create the tangential air injection as close as possible to the back wall of chamber 40 so that the stream reaches the electrodes 33a-c before the point where the arc is initiated. This arrangement also allows the stream to blow around the three electrodes 33a-c evenly from all sides.
• highly ionized stream generated by the high-voltage plasma injector 34 is introduced into the gap between electrodes 33a, b, and c.
• injector stream is injected into injector 34 through the stream input 45, passing adjacent injector electrodes 46a and 46b (FIG. 4).
• a high voltage arc is initiated between the injector electrodes
• the high voltage arc extends from the tip of injector electrode 46a through injector nozzle 47 and out of the injector 34, and returns into the injector 34 by passing back through injector nozzle 47 to the tip of injector electrode 46b.
• the distance at which this high voltage arc extends beyond the nozzle 47 can be increased by increasing the input stream and can be decreased by decreasing the input stream.
• the injector stream is supplied through injector stream manifold 19 (FIG. 1).
• the high voltage arc between the injector electrodes 46a and 46b causes ionized injector stream to be expelled out of injector nozzle 47 and toward primary electrodes 33a, b, and c.
• the presence of the ionized stream causes a breakdown in the gap between the primary electrodes 33a-c.
• the resulting primary arc immediately begins to move along the electrodes 33a-c due to electrodynamic movement of the arc in the magnetic field created by its own current (rail gun effect).
• the working stream introduced through the pneumatic rings 35a-c from working stream manifold 18 (FIG. 2), is then superheated by the arc into thermal plasma.
• Rail gun effect causes the arc to move rapidly along the electrodes 33a-c, distributing the heat load.
• This heat distribution, along with internal stream cooling, allows the use of materials for electrodes 33a-c having a relatively low melting point but high thermal conductivity, such as copper alloys.
• each primary electrode 33a, b, and c Due to the connection of each primary electrode 33a, b, and c to a separate phase of the supply voltage, an arc exists continuously inside the chamber 40, with each arc being 60 degrees out of phase as compared to its preceding or succeeding arc. As each arc moves along its corresponding electrode 33a, b, and c, its length increases, causing the arc voltage to increase. As soon as the voltage reaches the magnitude of the breakdown voltage of the inner-electrode gap in its narrowest place, secondary breakdown takes place and the arc becomes self-sustaining. That is, it continues in chamber 40 beyond the region of injector stream ionization. This region is filled with the working stream.
• the working stream is heated by the arc and itself ionizes, contributing to conductance within the arc and allowing it to progress further along the electrodes 33a-c.
• the gap dimensions become too large to sustain the arc and the arc is extinguished.
• a new arc is simultaneously established at the narrow gap of two adjacent electrodes as the voltage increases between the adjacent pair of electrodes. This process is repeated 120 times a second.
• the velocity of the arc is dependent on the diverging angle between the electrodes 33a-c and the magnitude of the arc current. Based on actual measurements of arc velocity along the electrodes 33a-c, as the current increases from 150 to 850 amps, the overall velocity changes from 10 m/sec to 25 m/sec.
• the arc's actual velocity for a given operating current decreases noticeably as the arc moves along the electrodes 33a-c. This is due to the Angle A (FIG. 2) between the electrodes 33a-c and can be explained by the quadratic decrease of the magnetic field associated with the arc current and with the increase in distance between electrodes 33a, b, and c at the point of the arc.
• the optimum electrode angle A (FIG. 2) is in part a function of the operating power output of the system 10, as well as the type and flow rate of the working stream. In a preferred embodiment of the system 10, when operating at different power outputs in order to achieve the longest electrode lifetime, the electrode angle will be adjusted between 10 to 170 degrees.
• the arc-working area of the electrodes 33a-c is approximately 18 cm.
• the pneumatic rings, 35a-c, through which the working stream is introduced, form a whirling stream that fans the arc further, lengthening it to increase arc voltage drop.
• the incoming stream forms a cold layer near the inner walls of chamber 40 which protects the walls from the intense heat and minimizes the arcing to the chamber shell.
• power, stream temperature, and plasma generator efficiency can be adjusted by changing the working stream flow distribution of rings 35a-c.
• the tangential introduction of stream into the plasma generator chamber 40 at an optimal position as described earlier in reference to the electrodes 33a-c allows the use of a chamber 40 having a shape that is close to spherical.
• This spherical chamber design results in a more efficient heating of the working stream and better cooling of the chamber walls.
• the working stream is injected in a way so that it tends to force the plasma away from the walls of the chamber.
• the optimum working stream flow rate is between 30 and
• the system 10 will work with virtually any pure stream, stream mixture, or complex stream compound.
• An oxidizing atmosphere can be created using air or oxygen
• a reducing atmosphere can be created using hydrogen or methane
• a neutral atmosphere can be created using nitrogen, helium, or argon.
• the working stream may comprise organic compounds, inorganic compounds, or mixtures of organic and inorganic compounds.
• the design of the thermal plasma generator power supply allows it to operate using a common industrial power source (380- 480 VAC, 3-phase).
• the current-limiting reactors 17 ⁇ -c (FIG. 1) should be equipped with taps which allow regulated current selection, resulting in regulation of the plasma generator operating power.
• the taps on reactors 17 -c allow electrode current selection from 100 A to 1500 A.
• a larger system may be designed by configuring several thermal plasma generators into a single large volume reactor chamber.
• the control circuits 15 provide power, temperature, and stream flow rate regulation, sets the control parameters for thermal plasma generator operation and provide for automatic shutdown if the parameters are exceeded.
• control circuits 15 determine if the cooling stream flow rates, the cooling stream temperatures, and the working stream flow rates to the injector 34 are within preset ranges. If the cooling stream temperature exceeds 150 degrees Fahrenheit, the system will automatically shut down. If the flow rates are out of range, then the control circuits 15 prevent power from reaching the injector 34 and the system is shut down.
• the control circuits 15 supply power to the injector 34.
• the control circuits 15 determine if the cooling stream flow rates, cooling stream temperatures and working stream flow rates to the plasma generator 30 are within preset ranges. If the cooling stream temperature exceeds 150 degrees Fahrenheit, the system will automatically shut down. If the flow rates are out of range, then the control circuits 15 prevent power from reaching the primary electrodes 33a-c in the plasma generator 30 and the system 10 is shut down.
• cooling stream flow rates, cooling stream temperatures, and working stream flow rates to the plasma generator 30 are within preset ranges, then the control circuits 15 supply power to the primary electrodes 33a-c and thermal plasma generation is initiated.
• the control circuits 15 also determines whether the phase currents (not shown) in each primary reactor are within preset ranges. The phase currents will be different for different plasma generator power settings.
• the control circuits 15 will also shut down the system 10 if the doors on any of the system cabinets are open.
• the system 10 described is able to use almost any stream as the working stream during the thermal plasma generation process.
• Prior art AC thermal plasma generating systems cannot perform certain tasks because of their inherent instability and because they require a clean or even pure or noble working stream.
• this system can destroy freon gas, nerve gases, and other military, toxic, and contaminant gases which would be harmful to the environment if released.
• the gas to be treated is also the working stream for the plasma system, there is no requirement for a treatment chamber that is inefficient and can produce less than one hundred percent (100%) material destruction.
• the thermal plasma generator described in this invention can also destroy in the chamber aerosols of either a powdered solid or liquid that are introduced into the working stream flow.
• this thermal plasma generator system can be used to destroy illegal drugs, PCB laden transmission oils, or almost any other solid or liquid that can be converted into an aerosol.
• Other applications of this thermal plasma generator include the clean up of soil contaminated by organic contaminants of the type seen in gasoline spills and the destruction of sludge that may be too contaminated to dispose of in a conventional manner.

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• Physics & Mathematics (AREA)
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• Plasma & Fusion (AREA)
• Spectroscopy & Molecular Physics (AREA)
• Chemical & Material Sciences (AREA)
• Analytical Chemistry (AREA)
• Plasma Technology (AREA)

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• 2000
  • 2000-01-18 CA CA002397756A patent/CA2397756A1/en not_active Abandoned
  • 2000-01-18 WO PCT/US2000/001123 patent/WO2001054464A1/en active Application Filing
  • 2000-01-18 EP EP00902432A patent/EP1258177A4/de not_active Withdrawn

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