KR101179650B1 - An innovative hollow electrodes plasma torch with permanent magnet fields applied in the anode region - Google Patents

Abstract

The present invention relates to a cavity-type plasma torch used in pyrolysis processes such as a large-capacity waste disposal process. An axial magnetic field applied by mounting a permanent magnet at a specific position around an anode of a torch and a radial current formed inside the torch are applied. By circumferential Lorentz force generated from the combination of the components, the arc and thermal plasma are strongly rotated to mitigate electrode erosion to prolong the life, and to facilitate the mixing between the thermal plasma flame and the treated object in the reactor region outside the torch. It is designed to improve pyrolysis efficiency without additional power consumption.

Description

Cavity plasma torch improves performance by applying permanent magnetic field around anode {AN INNOVATIVE HOLLOW ELECTRODES PLASMA TORCH WITH PERMANENT MAGNET FIELDS APPLIED IN THE ANODE REGION}

The present invention relates to a cavity type plasma torch used to pyrolyze a hardly decomposable waste or the like at a large capacity.

The present invention relates to a cavity-type plasma torch used to thermally decompose a hardly decomposable waste material in a large capacity. The present invention relates to an electrode nozzle mitigation by rotating an arc point while maintaining a stable discharge by inserting a permanent magnet at a specific position around the anode nozzle. It is designed to improve the thermal decomposition efficiency of the gas to be treated without additional power consumption.

Thermal plasma generated by using electric energy has a temperature of tens of thousands at the arc center inside the torch and a temperature of flame emitted to the outside of the torch. Temperature limits can easily be overcome. These thermal plasma flames are widely used in industries such as machining, new material synthesis, and nano powder manufacture because they have characteristics such as high heat capacity, high speed, and chemical reaction control as well as ultra high temperature characteristics. It is used as a clean technology to replace the existing combustion method for pyrolysis treatment of harmful environmental substances in the ultra-high temperature environment, such as used for the treatment of the hard-degradable greenhouse gas generated in.

Plasma torch, a device that generates thermal plasma, can be classified in various ways according to the type of input power, whether or not the arc is transferred, and the shape of the electrode. In the case of the DC non-feeding cavity type torch used in the present invention, The arc generated by the inside of the plasma torch is not transferred to the substrate to be treated, and the shape of the electrode composed of the cathode and the anode forms a hollow in the center. In the non-feeding torch operation, since arc discharge is generated inside the torch to generate a high temperature thermal plasma flame, the discharge can be maintained regardless of the type and state of the substance to be injected into the thermal plasma flame from the outside of the torch. It has the advantage of continuous processing. In the electrode configuration composed of a rod-shaped or button-type cathode and an anode nozzle, arc discharge is performed by hot electron emission. In this case, when an oxygen-containing material such as air or water vapor is used as a discharge gas, the surface of the cathode is oxidized, resulting in hot electron emission. It is difficult to maintain a stable discharge and to re-ignite because it is not smooth. On the other hand, when a cavity type electrode is used, it is known that arc discharge is performed on the principle of field emission irrespective of oxidation of the surface of the electrode. Therefore, oxygen is included in the pyrolysis process to convert the material to be converted into a stable oxide form. The discharge gas can be freely applied. With this advantage, the cavity-type torch is easy to increase the output compared to other plasma torches, and can generate a relatively large high temperature area from a large diameter electrode, which is suitable for effectively processing a large object.

However, a sufficient high temperature range for pyrolysis of the object to be treated is directly influenced by the temperature distribution characteristics of the thermal plasma flame generated from the torch, which exhibits a very high temperature of several thousand degrees in the flame center region of the torch outlet, but from this radius. As the distance increases in the direction and the axial direction, the temperature drops sharply. Therefore, for efficient pyrolysis process, the object to be treated should be strongly injected toward the center of the flame or a large diameter electrode should be used. In order to strongly inject the object in the pyrolysis process, an additional mechanical device capable of applying a high pressure is required for this purpose, and the life of the additional equipment is drastically reduced when treating a corrosive waste such as a waste product of a semiconductor manufacturing process. There is a disadvantage that the maintenance and repair costs are increased. In addition, as mentioned above, a cavity torch may have a larger electrode diameter than a rod-nozzle type or button-nozzle type torch, but there is a fundamental limit to expanding the high temperature region in the reactor region because the electrode diameter is limited depending on the torch operating conditions. There is. Due to these problems, the treatment object that is not included in the temperature range sufficient for pyrolysis, such as in the outer flame, is not completely decomposed, and the processing object does not enter the flame center region where the temperature is sufficiently high, so unnecessary power is not supplied. It is being consumed.

In order to solve this problem, in the present invention, a permanent magnet is inserted around the anode of the cavity-type torch to generate a Lorentz force that rotates the anode arc point to pyrolyze in the reactor through the rotational direction of the thermal plasma flame ejected to the outside of the torch. In order to improve the pyrolysis treatment efficiency without additional power consumption, it is possible to extend the high temperature region sufficient to increase the turbulent mixing with the object to be treated. However, a method of applying a magnetic field to the torch by using a mechanism such as a magnet or a solenoid is widely used as a method for increasing the life of an electrode, and is also partially employed to change the flow characteristics of a thermal plasma flame as in the present invention. . In general, however, in the cavity type torch, a method of improving a cathode life by dispersing locally applied heat load by applying a magnetic field only to a fixed cathode arc point is used. At this time, the magnetic field application method by the solenoid is generally adopted, but there is a disadvantage that the device size is large, the structure is complicated, and additional power is required. In addition, the method of changing the flow characteristics of the thermal plasma flame by applying a magnetic field to the anode region is a part of the rod-nozzle type torch, which is easy to maintain stable discharge in spite of the sudden movement of the anode arc point due to the high current-low voltage torch operation characteristic. Although it is being used, in the case of a cavity-type torch operated at a relatively low current-high voltage, an unstable arc discharge is easily induced due to the rapid arc point movement, and therefore, a simple method of applying a proper magnetic field in consideration of this and an application to a high efficiency pyrolysis process are required.

In order to solve the above problems, computer simulation is performed on the condition of the size and position of a permanent magnet which can easily apply a magnetic field to the anode region while maintaining a stable arc discharge in a cavity-type torch suitable for a large capacity pyrolysis process. And the experimental method, and from this, the electrode life is extended along with the arc point rotation, and the flow of flame ejected to the outside of the torch is increased to increase the mixing between the thermal plasma and the object to be treated. It aims to improve efficiency.

In order to achieve the object as described above, the present invention

A hollow cathode 1;

An anode nozzle 2 having a length l ;

A gas injection ring allowing the discharge gas 10 to be injected into the vortex between the two electrodes;

Providing a bipolar magnetic field applied cavity type plasma torch including a permanent magnet (100) located around the anode from a point of l / 2 or more toward the torch outlet direction from the gas inlet,

In order to prove the effect of the positive electrode magnetic field applied cavity type plasma torch through the waste gas pyrolysis process,

A reactor (4) coupled to a lower portion of the plasma torch to inject a waste body (40) and to separate a reaction zone from the outside;

It is installed inside the reactor to form a flow path of the waste body, so that the waste body can be mixed and injected into the thermal plasma flame near the torch outlet, and confined inside the reactor that functions to reduce the loss of heat by spatially limiting the reaction zone Provide a tube (3).

Anodic field applying cavity type plasma torch by permanent magnet according to the present invention is simpler than the application by electromagnet and requires no additional power, and can use reactive gas containing oxygen as discharge gas, stable anode arc In addition to the effect of electrode life from the rotation of the point to generate the vortex motion of the thermal plasma to increase the mixing with the object to be treated can improve the processing efficiency of the large-capacity pyrolysis process without additional power consumption.

1 is a cross-sectional view showing the configuration of a permanent magnet-mounted bipolar magnetic field applied cavity type torch and a reactor according to the present invention.
2 is a voltage measurement data showing a list-like phenomenon in the cavity-type torch used in the present invention.
Figure 3 is a computer simulation data showing the temperature distribution at the anode arc point position according to the arc length in the cavity-type torch used in the present invention.
Figure 4 is a computerized data of the magnetic field strength on the inner surface of the anode nozzle according to the present invention.
5 is a shape change measurement data over time of the thermal plasma flame generated from the cavity-type torch when the present invention is not applied.
Figure 6 is a measurement of the shape change over time of the thermal plasma flame generated from the cavity-type torch applied magnetic field to the anode region according to the present invention.

Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.

1 is a schematic cross-sectional view of a pyrolysis system composed of a positive electrode magnetic field applied cavity torch and a reactor by a permanent magnet according to the present invention. The anode magnetic field type cavity type torch is the same as a general cavity type torch and discharges the arc gas 20 by vortexing the discharge gas 10 between the cavity type cathode 1 and the nozzle type anode 2. It is operated on the principle of spraying the thermal plasma jet 30 generated therefrom to the outside while forming and maintaining, and the permanent magnet 100 is half of the length l of the anode from the gas inlet to rotate the anode arc point 22. It is characterized in that it is located at least l / 2 away. Unlike the plasma torches having a bar or button type cathode, the cavity torch can directly use oxygen-containing gas as a discharge gas, has a relatively large electrode diameter, and is easy to increase output, thereby pyrolyzing and stabilizing a large amount of waste gas. It is suitable for chemical conversion into a substance. However, the arc discharge causes erosion of the inner surface of the anode, and the generated thermal plasma jet 30 is limited in size by the inner diameter of the anode 2, which is an electrode located at the outlet side of the torch. When the waste is injected in the vertical direction of the thermal plasma flow under the torch exit surface, the mixture of the thermal plasma and the waste 50 should be smoothly to pyrolyze the efficient waste pyrolysis process inside the confinement pipe 3 inside the reactor. 60) can be expected.

The mixing of the thermal plasma flame ejected from the torch at high speed and the surrounding gases surrounding it is known to be caused by turbulent mixing due to the rapid velocity gradient of the boundary layer in the narrow area between the two gas layers. The vortex that is enclosed in the surroundings of the plasma flame to the center of the flame due to inertia and density difference occurs frequently on a large scale, and the two gases are well mixed. Therefore, in order to increase the velocity gradient in the boundary layer, it is necessary to improve the injection speed of the thermal plasma by increasing the output of the torch and the flow rate of the discharge gas. In this case, additional power and discharge gas are consumed, which is not suitable for economic pyrolysis process. Therefore, in the present invention, the velocity gradient in the boundary layer is basically formed in the axial direction ( z direction) of the torch and reactor, which are the flow direction of the thermal plasma, and is permanent so that it can be strengthened in the rotational direction ( θ direction) about this axis. The magnet 100 was mounted around the anode 2.

In the thermal plasma torch, the anode arc point 22 is rotated at a certain speed by the discharge gas 10 injected into the vortex. In addition, the axial magnetic field component induced by the rotational current component generated from the movement of the anode arc point 22 and the radius that is away from the central axis of the torch and the reactor according to the shape of the arc column 20 near the anode point. The rotational Lorentz force acts on the anode arc point 22 by the current component formed in the direction ( r direction). That is, even without applying an external magnetic field, the anode arc point 22 is rotated, and the thermal plasma jet that is thermally expanded by the arcs 20, 21, 22 also rotates together. By the way, since the magnetic fields can overlap each other and act larger, when the external magnetic field is applied around the anode with the permanent magnet 100, the movement of the anode arc point 22 becomes more active and the arc point is fixed to the anode surface. To mitigate erosion that occurs. Of course, the cathode arc point 21 can also be rotated on the same principle, but since the cathode arc point is far from the torch outlet and the ultra-high temperature plasma has high viscosity, the thermal plasma emitted to the torch outlet even if the cathode arc point rotates. The influence on the rotation of the flame 30 is insignificant.

The direction of the magnetic field applied by the permanent magnet 100 should take into account the direction of the magnetic field in which the anode arc point 22 is rotated and self-induced without an external magnetic field. When the gas 100 is injected in the counterclockwise direction (+ θ direction) and the movement of the initial anode arc point 22 is formed in the + θ direction, an axial magnetic field from the torch to the reactor direction (+ z direction) is induced, In the same direction, the externally applied magnetic field must be superimposed. That is, in the case of injecting the discharge gas in the + θ direction, the polarity of the ring-shaped permanent magnet 100 located around the anode should be the S pole toward the reactor 4 and the cathode 1 toward the cathode. The viewing surface becomes the N pole so that the magnetic field in the + z direction is applied at the anode arc point to enhance the rotational direction of the anode arc point 22 and the thermal plasma jet 30.

In order to strongly rotate the thermal plasma jet from the rotation of the anode arc point 22, the strength of the permanent magnet 100 is high, and it may be advantageous to be located all around the anode, but in this case, the operation of the plasma torch is caused by unstable arc discharge. This stops and the pyrolysis process does not proceed smoothly because of the list-like phenomena inherent in the arc discharge of the plasma torch. As shown in FIG. 2, the wrist-like phenomenon refers to a phenomenon in which the arc voltage constantly increases and then suddenly drops in the operation of the plasma torch, which is caused by the movement of the anode arc point 22 as follows. Due to the hydrodynamic drag due to the flow of thermal plasma, the anode arc point 22 is extended in the direction of the torch exit. At this time, the voltage and output increase together, and the temperature near the discharge gas inlet is high enough to increase the electrical resistance. When it is reduced below a certain value, the anode arc point 22 is moved to the vicinity of the discharge gas inlet momentarily. Therefore, the voltage decreases rapidly along with the length of the arc pillar 20, and the phenomenon in which the voltage increases as the length of the arc increases again is repeated. Since the DC power of the plasma torch is generally a constant current source, as shown in FIG. 2, the power applied to the torch is also changed as the arc voltage is changed. The maximum and minimum values of the power according to the repetition of the List-Like phenomenon are about 2 times. Leads to In other words, if the arc length is short, the input power to the torch is reduced. On the contrary, if the arc length is increased, the input power is increased to change the thermal plasma characteristics inside the torch. 3 shows a three-dimensional computational analysis of the thermal plasma temperature distribution inside the torch according to the arc length, and then shows a temperature distribution cross section at the anode arc point. As shown in FIG. 3A, when the arc length is short, the input power is relatively small, thereby showing a lower temperature distribution than the case of the long arc length of (b). The thermal plasma temperature inside the torch is highest at the arc pillar 20 and arc points 21 and 22 and lowers toward the periphery, so that the inner wall of the arc pillar 20 and the anode nozzle 2 near the central axis of the torch is High temperature is shown at the attached anode arc point 22. In the case of a cavity-type torch discharge gas such as air or nitrogen, the electrical conductivity rapidly increases as the temperature increases from about 6,000 K or more. If the anode arc point 22 is not sufficiently developed as shown in FIG. ) Rotates strongly by an externally applied magnetic field, the arc point moves to a low temperature range, and the arc discharge may be interrupted due to insufficient electric conductivity. On the contrary, if the arc length is long and a sufficiently high temperature distribution is formed as shown in FIG. 3 (b), even if the position of the arc point suddenly changes in the rotational direction, stable arc discharge can be maintained. Actually, in the present invention, an anode nozzle having a length of 175 mm was used. As a result of experiments by changing the axial position of the permanent magnet 100, the permanent magnet 100 should be positioned at least 90 mm away from the gas inlet without interruption of arc discharge. Stable torch operation was possible.

For the above reason, in the present invention, the permanent magnet 100 is positioned from the discharge gas inlet to the torch outlet in a direction of 100 mm, and has a ring-shaped neodium magnet having a different thickness to determine a desired magnetic field strength and magnetic field application period. Was used. When the thickness of the magnet is 10, 20, 30 mm, respectively, the strength of the magnetic field acting on the inner wall of the anode nozzle 2 to which the anode arc point 22 is attached is shown in FIG. 4. Since the permanent magnet 100 is positioned from -75 mm 100 mm away from -175 mm, which is the injection position of the discharge gas 10 in FIG. 4, the axial center points of the magnets are -70, -65, and -60 mm, respectively. The axial magnetic field acting on the anode arc point 22 at this position exhibits the highest value. It can be seen from the computer simulation results of FIG. 4 that the thicker the permanent magnet 100 is, the stronger and longer the magnetic field can be applied to the anode arc point 22. However, when the permanent magnet 100 had a thickness of 40 mm, the pyrolysis process could not proceed smoothly due to unstable discharge, which means that the external magnetic field should not be too strong in the anode magnetic field applied cavity torch, and the anode arc point The maximum value of the axial magnetic field strength applied to (22) should be less than 1,000 gauss as shown in FIG. Therefore, in the present invention, the magnet is installed at any point from the half point of the anode length to the end, regardless of the point, and the magnetic field is 1000 even more than 1/2 point no matter how long. Should be less than Gaussian.

As a result of measuring the average input power to the torch under various operating conditions of the bipolar field-applied cavity type plasma torch according to the present invention, it was confirmed that almost the same power was consumed regardless of whether the permanent magnet 100 was installed and the thickness thereof. In addition, as a result of experimental measurement using a high speed camera, when the permanent magnet 100 was not inserted, the maximum rotation speed of the anode arc point 22 was 8.9 m / s, and the permanent magnet 100 having a thickness of 10, 20, or 30 mm was installed. In this case, the maximum rotation speed of the anode arc point 22 was rapidly improved to 84.7, 127.0, and 140.4 m / s, respectively. In the bipolar magnetic field applied cavity type torch according to the present invention, when there is no permanent magnet 100 and when the permanent magnet 100 having a thickness of 20 mm is mounted, thermal plasma is generated to show the shape of the flame measured by the high speed camera. 5 and FIG. 6. As can be seen in FIG. 5, when the permanent magnet 100 is not installed, the length of the ultra-high temperature flame of the thermal plasma is steadily increasing to 3.25 ms, just before the next list rise, while the input power continuously rises after the list rise. On the other hand, in Fig. 6, the length of the arc was increased and the list-like occurred at 3.25 ms. Even though the input power increased until 3.25 ms, the flame length of the ultra-high temperature region did not increase by a certain length, which is the anode arc point 22. This is because the thermal plasma rotates due to the strong rotation of, and the ultra high temperature region is reduced as it is mixed with cold gas around the flame.

From the above experimental results, it can be expected that the efficiency of the pyrolysis process can be improved without additional power consumption when applying the bipolar field-applied cavity type plasma torch by the permanent magnet. Decomposition and removal efficiency was measured by quadrupole mass spectrometry (QMS), while actual pyrolysis process experiments were carried out on waste sludge with 400 slpm containing 1% of CF ₄ , a non-degradable greenhouse gas. When the permanent magnet 100 was not installed at the average input power of about kW, the throughput was 45.4%, but when the permanent magnets 100 having thicknesses of 10, 20, and 30 mm were installed, the throughput was 52.3, 55.4, and 62.3%. Was improved.

<Explanation of symbols for the main parts of the drawings>
1: cavity anode 2: cavity anode (nozzle)
3: reactor inner conduit tube 4: reactor
10: discharge gas 20: arc pillar
21: cathode arc point 22: anode arc point
30: thermal plasma 40: target gas
50: Mixed area of thermal plasma and gas to be treated
60: pyrolysis zone 100: permanent magnet
l : length of cavity anode

Claims (4)

A bipolar magnetic field applied cavity plasma torch,
By rotating the anode arc point near the torch exit surface while maintaining a stable arc discharge, it prevents electrode erosion and generates vortex movement of thermal plasma flame ejected into the reactor.
In order to extend the anode life and increase the mixing between the thermal plasma and the treated object in the reactor,
A ring-shaped permanent magnet is mounted on the outer circumference of the anode nozzle of the cavity plasma torch.
The permanent magnet is a positive electrode magnetic field applied cavity plasma torch, characterized in that located at least half (( l / 2) of the anode nozzle length in the direction of the torch outlet from the gas inlet located between the cathode and the anode of the plasma torch .
delete The method of claim 1,
When the discharge gas is injected during the vortex movement by a gas injection ring having a plurality of holes which are inclined at predetermined intervals at equal intervals in the circumferential direction,
When you look inside the torch from the torch exit,
If the direction of the vortex movement is counterclockwise, position the S pole of the permanent magnet toward the torch exit direction.
And if the direction of the vortex movement is clockwise, the N pole of the permanent magnet is positioned so as to face the torch exit direction.
4. The bipolar magnetic field applied cavity plasma torch of claim 3, wherein an axial intensity of an externally applied magnetic field by the permanent magnet is limited to less than 1000 gauss at an anode nozzle inner wall at which the anode arc point is located.

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