CN111970807A - Device for exciting microwave plasma based on sliding arc discharge - Google Patents

Abstract

The invention discloses a device for exciting microwave plasma based on sliding arc discharge. A microwave electric field is generated in the waveguide; the non-metallic discharge tube is fixed in the microwave waveguide; the high-voltage power supply is connected to two metal electrodes; the two metal electrodes are symmetrically bent and distributed in the cyclone device; the air outlet of the cyclone device is opposite to one end of the non-metal discharge tube. The ends of the two metal electrodes do not protrude into the microwave waveguide. One end of the non-metal discharge tube is fixed on the surface of the cyclone device, and the other end extends out of the microwave waveguide. The invention is based on a device for exciting microwave plasma by sliding arc discharge, has high excitation success rate, stable excitation, simple device and convenient use, can realize the excitation and maintenance of microwave plasma under atmospheric pressure, and can be applied in large-scale industrial production.

Description

A device for exciting microwave plasma based on gliding arc discharge

technical field

The invention belongs to the technical field of microwave plasma excitation, and particularly relates to a device for exciting microwave plasma based on sliding arc discharge.

Background technique

Microwaves propagate inside the waveguide, and when the electromagnetic power is large enough, it will cause strong gas ionization to generate microwave plasma. Microwave plasma has the advantages of no electrode, instantaneous high temperature, and high energy density, so it has application prospects in solid waste treatment, gas waste treatment, metallurgy, metal welding, etc. The excitation field strength of microwave plasma is 777kV/m, which is much higher than the sustaining field strength. In conventional applications, the entire cavity is composed of waveguides, transition waveguides and compressed waveguides. Although the compressed waveguides can improve the electric field strength to a certain extent, they cannot meet the requirements of the excitation field strength. Therefore, in the process of microwave plasma excitation, auxiliary excitation is also required.

At present, there are three methods of assisted excitation. One is the metal probe method, that is, the ignition method in the form of a metal wire or a metal nozzle. The existing document for reference is the invention application document with publication number CN104507249A, which discloses a rectangular waveguide microwave plasma source generating device. A copper probe is arranged in the reaction zone of the rectangular waveguide resonator to excite the microwave plasma . However, due to the extremely high temperature of the reaction zone, the copper probe is melted or ablated after one use, and the process is accompanied by the problem of metal contamination, and the microwave plasma cannot be quickly reignited when it is accidentally extinguished.

Another method is the DBD method, that is, dielectric barrier discharge. The existing document for reference is the Chinese invention application document with publication number CN107801286A, which introduces an excitation system for exciting microwave plasma based on dielectric barrier discharge. Electrons blown into the cavity act as seed electrons to excite the microwave plasma. This method requires argon as the ionized gas, and the lower end of the non-metallic pre-ionized jet tube is relatively close to the plasma area, which is prone to melting and cannot successfully excite the microwave plasma again. At the same time, the method has high cost, complicated system and inconvenient use, and is difficult to be applied on a large scale in industry.

There is also a method of fixing a metal conductor at the inner wall of a non-metallic discharge tube. The existing documents available for reference include the Chinese invention application document with the publication number of CN109104808A, which uses a conductor to absorb microwave energy to generate a flashover by placing a radius-matched spiral or grid-shaped high-temperature conductive material in a non-metallic discharge tube. Seed electrons are generated, which in turn excite the microwave plasma. Although the device is simple, the excitation is unstable and the metal conductor ablation phenomenon is prone to occur.

The invention mainly solves the problems of difficult excitation of microwave plasma, unstable excitation and complicated excitation device.

SUMMARY OF THE INVENTION

The purpose of the present invention is to provide a device for exciting microwave plasma based on sliding arc discharge, which has high excitation success rate, stable excitation, simple device and convenient use, and can realize the excitation and maintenance of microwave plasma under atmospheric pressure, and can be applied on a large scale in industrial production.

The technical scheme of the present invention is:

A device for exciting microwave plasma based on sliding arc discharge, comprising a microwave generator, a microwave waveguide, a non-metallic discharge tube, a high-voltage power supply, a metal electrode and a cyclone device, wherein:

A microwave generator, which emits microwaves and generates a microwave electric field in the microwave waveguide;

Non-metallic discharge tubes, fixed in microwave waveguides;

High voltage power supply, connect two metal electrodes;

Two metal electrodes, symmetrically bent and distributed in the cyclone device;

Cyclone device, the air outlet of which is opposite to one end of the non-metallic discharge tube.

Preferably, the ends of the two metal electrodes do not extend into the microwave waveguide.

Preferably, one end of the non-metal discharge tube is fixed on the surface of the cyclone device, the other end extends out of the microwave waveguide, and the middle part traverses the inside of the microwave waveguide.

Preferably, the parameters of the high-voltage power supply are between 10kV-30kV, and the operating frequency is a high-frequency AC sine wave ranging from DC to several tens of kHz.

Preferably, the cyclone device comprises a cylindrical cyclone casing and an air pump, one end of the cyclone casing is closed, and the other end is provided with an air outlet, and two metal electrodes penetrate into the cyclone casing from the closed end through a high-voltage insulating medium; the cyclone casing is distributed along the circumference There are several air guide holes, which are respectively connected with the air pump.

Preferably, the air guide holes are flush with the inner wall of the cyclone casing, and the included angle with the axis of the cyclone casing is 10-80 degrees; the number of the air guide holes is 2 or more, and the center extension line of each air guide hole is in line with the cyclone casing. The axes are in different planes.

Preferably, the central axis of the non-metallic discharge tube is located at a distance λ/4+kλ from the end face of the microwave waveguide, where λ is the wavelength of the microwave in the system, and k is an integer not less than 0.

Preferably, the high-voltage power supply causes the two metal electrodes to break down at the narrowest distance to form an arc. Under the action of the airflow of the cyclone device, the arc slides toward the air outlet, and the charged particles are sent to the non-metal discharge through the airflow. In the tube, the microwave plasma is excited.

Preferably, the length of the arc increases in the process of sliding towards the air outlet. When the arc length increases beyond the limit that the power supply can sustain the discharge, the arc is extinguished, but a new arc is formed at the shortest distance, and so on.

Preferably, the charged particles are sent into a non-metal discharge tube to excite microwave plasma to form a stable microwave plasma torch, and then turn off the high-voltage power supply. If the microwave plasma torch is accidentally extinguished, turn on the high-voltage power supply again.

The advantages of the present invention are:

The invention is based on a device for exciting microwave plasma by sliding arc discharge, has high excitation success rate, stable excitation, simple device and convenient use, can realize the excitation and maintenance of microwave plasma under atmospheric pressure, and can be applied in large-scale industrial production.

Description of drawings

Below in conjunction with accompanying drawing and embodiment, the present invention is further described:

FIG. 1 is a schematic structural diagram of a device for exciting microwave plasma based on gliding arc discharge according to the present invention.

Among them: 1. Microwave waveguide; 2. Non-metal discharge tube; 3. Microwave generator; 4. Microwave power supply; 5. Cooling fan; 6. Cyclone shell; 7. Air hole; 8. Air pump; 9. High voltage power supply; 10 , High voltage insulating medium; 11. Metal electrode.

Detailed ways

As shown in FIG. 1 , the device for exciting microwave plasma based on sliding arc discharge of the present invention includes a microwave waveguide 1, a non-metallic discharge tube 2, a microwave generator 3, a microwave power source 4, a cooling fan 5, a cyclone device, and a high-voltage power source. 9. A high-voltage insulating medium 10 and a metal electrode 11 ; the cyclone device includes a cyclone casing 6 , an air hole 7 , and an air pump 8 .

When in use, the microwave waveguide 1 is connected to the microwave generator 3, and the microwave power supply 4 of the microwave generator 3 is connected, so that a microwave electric field is generated inside the microwave waveguide 1, and the microwave electric field is increased by compressing the waveguide, and the microwave electric field is increased in the distance. The maximum field strength is formed at the short-circuit end face λ/4+kλ, where k is an integer not less than 0. Then, the high-voltage power supply 9 causes a breakdown at the narrowest distance between the two metal electrodes 11 to form an arc. Under the action of the airflow, the arc slides outwards and increases in length at the same time. When the arc length increases beyond the power supply can sustain the discharge At the limit, the arc is extinguished, but a new arc is formed at the shortest distance, and so on. Although the two metal electrodes 11 do not penetrate deep into the microwave waveguide 1 , when the arc slides outward, a part of the arc will penetrate into the non-metallic discharge tube 2 , so as to act as seed electrons to excite the microwave plasma.

Since the metal electrode does not penetrate deep into the microwave waveguide, the metal electrode will not be ablated by the high-temperature microwave plasma torch during the excitation of the microwave plasma and the operation of the microwave plasma, so as to avoid the loss of the metal electrode, and then Extend the service life of sliding arc metal electrodes.

The gas is passed into the cyclone casing 6 through the air pump 8 to form a vortex gas, which is called the carrier gas of the microwave plasma device. Since the generation of microwave plasma does not require high gas, usually argon, helium, nitrogen or air can be introduced as the carrier gas. According to the needs of different applications, other gases can also be selected as the carrier gas to excite the microwave plasma. .

The parameters of the high-voltage power supply used to generate the sliding arc are between 10kV and 30kV, and the operating frequency can range from DC to high-frequency AC sine waves of several tens of kHz, and high-frequency sinusoidal AC signals are the best.

The air guide hole is flush with the inner wall of the entire cyclone device, and the included angle with the axis of the cyclone device is 10-80 degrees. At the same time, the air holes on a cyclone device are evenly distributed along the circumference, the number of air holes should be more than 2, and the center extension line of the air hole and the axis of the cyclone device are in different planes, so that a vortex gas can be formed better.

One end of the non-metallic discharge tube is fixed on the surface of the cyclone device, and the other end extends out of the microwave waveguide.

The above-mentioned non-metal discharge tubes and metal electrodes used to generate sliding arcs are preferably high temperature resistant materials.

The steps of exciting microwave plasma in the present invention are as follows:

Step 1: Turn on the air pump, so that the carrier gas forms a vortex gas and passes into the non-metal discharge tube;

Step 2: Turn on the cooling fan and prepare to cool the microwave generator;

Step 3: turn on the microwave power supply and supply power to the microwave generator, so that a microwave electric field is generated in the microwave waveguide;

Step 4: turn on the high-voltage power supply, generate a sliding arc, and send the charged particles into the non-metallic discharge tube 4 through the airflow to excite the microwave plasma;

Step 5: Turn off the high-voltage power supply after the microwave plasma torch is stable;

Step 6: If the microwave plasma torch is accidentally extinguished, repeat steps 4 and 5.

The above-mentioned embodiments are only intended to illustrate the technical concept and characteristics of the present invention, and the purpose thereof is to enable those skilled in the art to understand the contents of the present invention and implement them accordingly, and cannot limit the protection scope of the present invention. All modifications made according to the spirit and essence of the main technical solutions of the present invention should be covered within the protection scope of the present invention.

Claims (10)

1. The utility model provides a device based on slip arc discharges and arouses microwave plasma which characterized in that, includes microwave generator, microwave waveguide, non-metallic discharge tube, still includes high voltage power supply, metal electrode and cyclone, wherein:

a microwave generator for emitting microwaves and generating a microwave electric field in the microwave waveguide;

the non-metal discharge tube is fixed in the microwave waveguide tube;

the high-voltage power supply is connected with the two metal electrodes;

the two metal electrodes are symmetrically bent and distributed in the cyclone device;

and the air outlet of the cyclone device is opposite to one end of the non-metal discharge tube.

2. The sliding arc discharge based microwave plasma excitation device according to claim 1, wherein the ends of the two metal electrodes do not extend into the interior of the microwave waveguide.

3. The device for exciting a microwave plasma based on sliding arc discharge of claim 2, wherein the non-metallic discharge tube is fixed at one end to the surface of the cyclone device, and extends out of the microwave waveguide tube at the other end, and the middle part of the non-metallic discharge tube traverses the inside of the microwave waveguide tube.

4. The device for exciting microwave plasma based on sliding arc discharge according to claim 3, wherein the high voltage power supply has parameters between 10kV and 30kV and has an operating frequency of high frequency AC sine wave from DC to tens of kHz.

5. The device for exciting microwave plasma based on sliding arc discharge as claimed in claim 3, wherein the cyclone device comprises a cylindrical cyclone casing and an air pump, the cyclone casing is closed at one end, an air outlet is arranged at the other end, and two metal electrodes penetrate into the cyclone casing from the closed end through a high-pressure insulating medium; a plurality of air guide holes are distributed on the cyclone shell along the circumference and are respectively communicated with the air pump.

6. The device for exciting microwave plasma based on sliding arc discharge according to claim 5, wherein the air guide hole is flush with the inner wall of the cyclone shell and forms an angle of 10-80 degrees with the axis of the cyclone shell; the number of the air guide holes is 2 or more, and the central extension line of each air guide hole and the axis of the cyclone shell are in different planes.

7. The sliding arc discharge based microwave plasma excitation device according to claim 3, wherein the non-metallic discharge tube has a central axis located at a distance of λ/4+ k λ from the end surface of the microwave waveguide, λ being a wavelength of the microwaves in the system, and k being an integer not less than 0.

8. The device for exciting microwave plasma based on sliding arc discharge according to claim 1, wherein the high voltage power supply causes the two metal electrodes to break down at the narrowest distance to form an arc, the arc slides towards the air outlet under the action of the air flow of the cyclone device, and charged particles are fed into the non-metal discharge tube through the air flow to excite the microwave plasma.

9. The device for exciting a microwave plasma based on sliding arc discharge according to claim 8, wherein the length of the arc increases during the sliding process towards the air outlet, when the length of the arc increases beyond the limit of the power supply capable of maintaining discharge, the arc is extinguished, but a new arc is formed at the shortest distance, and the process is repeated.

10. The sliding arc discharge based microwave plasma excitation device according to claim 9, wherein the charged particles are fed into the non-metallic discharge tube to excite the microwave plasma, and the high voltage power supply is turned off after the stable microwave plasma torch is formed, and is turned back on if the microwave plasma torch is accidentally extinguished.

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