A microwave plasma jet device, method and application

Abstract

The present invention relates to a microwave plasma jet device, method and application, which includes a rectangular waveguide and a circular waveguide. A plurality of the rectangular waveguides are communicatively arranged with one circular waveguide, and the microwave emitting device is arranged at the port of the rectangular waveguide; a circular ridge and a quartz tube are arranged in the circular waveguide. The quartz tube is a hollow through-tube, and the circular ridge and the quartz tube are arranged along the length direction of the circular waveguide. One end of the quartz tube is connected to a gas supply device, and the other end of the quartz tube penetrates out of the circular waveguide. The gas supply device is used to introduce a gas that can be broken down into the quartz tube; the circular ridge is used to compress the electric field in the circular waveguide. The purpose is to compress the high electric field intensity, concentrate the microwave energy, and break down the gas discharge to form a plasma jet.

Description

Technical Field

[0001] The present invention belongs to the field of microwave technology, and in particular relates to a microwave plasma jet device, method and application. Background Art

[0002] In recent years, microwave plasma has been widely used in the fields of organic pollutant degradation, hazardous solid waste and wastewater and waste gas treatment. With the improvement of the reliability of microwave devices and the energy conversion efficiency of magnetrons, microwaves are used in industry to excite and obtain plasma with high-density excited states and active particles. Compared with other traditional plasmas, microwave plasma has a higher degree of ionization and decomposition, can maintain plasma under high pressure, and does not require electrodes. Microwave plasma equipment has a longer service life.

[0003] In order to efficiently excite a microwave plasma torch, Zhang Guixin and others optimized the nozzle to concentrate the electromagnetic field energy at the nozzle to break through the electric field, thereby exciting a microwave plasma torch at normal pressure. They used simulation software to test the effects of different nozzle diameters, different nozzle angles, different nozzle orifice sizes, and different nozzle lengths (relative to the distance from the waveguide wall) on the electric field intensity at the nozzle. Chen Ying designed a new atmospheric pressure microwave plasma torch and analyzed the effects of probe length, probe diameter, coupled waveguide width and height on the central electric field distribution and intensity through simulation results. The dual-gas flow-stabilized atmospheric pressure microwave plasma torch designed by Xu Maochun found through experiments that the two factors, the position of the wave to the cutoff surface and the gas flow, have a great influence on the stability of the microwave plasma torch. Researchers have been continuously optimizing the excitation factors, and the microwave plasma excitation devices have been gradually improved. However, due to factors such as the small concentration range of the electric field intensity inside the nozzle, probe and other devices, and the limitation of the microwave energy input at a single port, most microwave plasmas are small in size, with a small jet diameter and a length of only 30mm to 40mm. The excited plasma gas flow rate is only 0.3 to 1L / min, making it difficult to achieve efficient conversion of microwave energy into microwave plasma. A high external heat dissipation capability is required, and large-scale plasma processing applications cannot be realized. Summary of the invention

[0004] In order to solve the problem that the existing microwave plasma excitation device has a small jet diameter and a low height, and cannot realize large-scale plasma processing applications, a microwave plasma jet device, method and application are provided. The circular ridge waveguide is fed into a dual-port or multi-port rectangular waveguide, which effectively improves the input microwave power, and compresses the electric field through its internal circular ridge to increase the concentration range of the electric field intensity. The reaction gas enters the quartz tube in a cyclonic intake manner, thereby efficiently exciting an atmospheric flow, high-length and stable microwave plasma jet.

[0005] The technical solution adopted by the present invention is: a microwave plasma jet device, comprising a rectangular waveguide and a circular waveguide, wherein several rectangular waveguides are connected to a circular waveguide, and the microwave emitting device is arranged at the port of the rectangular waveguide; a circular ridge and a quartz tube are arranged in the circular waveguide, and the quartz tube is a hollow through tube, and the circular ridge and the quartz tube are arranged along the length direction of the circular waveguide, one end of the quartz tube is connected to a ventilation device, and the other end of the quartz tube passes through the circular waveguide, and the ventilation device is used to introduce a breakdown gas into the quartz tube; the circular ridge is used to compress the electric field in the circular waveguide.

[0006] Preferably, the ventilation device is a cyclonic ventilation device, and the cyclonic ventilation device is used to generate cyclonic gas that enters the interior of the quartz tube.

[0007] Preferably, the swirl gas generated from the gas outlet of the swirl ventilation device adheres to the inner wall of the quartz tube and swirls to the other end of the quartz tube.

[0008] Preferably, the cross-section of the circular ridge is trapezoidal, and the longer bottom surface of the circular ridge is connected to the inner wall of the circular waveguide; the circular ridge is symmetrically arranged in two along the axial direction of the circular waveguide, and the quartz tube is arranged between the two circular ridges.

[0009] Preferably, the rectangular waveguide is a BJ26 rectangular waveguide, and the circular waveguide is a BY25 circular waveguide; two rectangular waveguides are provided, and the two rectangular waveguides are respectively located at two ends or both sides of the circular waveguide; and the breakdown gas is air or argon.

[0010] Preferably, a cooling mechanism is provided on the outside of the quartz tube, the cooling mechanism is fitted to the quartz tube, the cooling mechanism is a cooling tube, and cooling water is passed through the cooling tube.

[0011] Preferably, the cooling tube is a spiral tube, which is spirally wound on the outer wall of the quartz tube; or, the cooling tube is a straight tube, and several cooling tubes are evenly distributed and attached to the outer wall of the quartz tube, and the length direction of the straight tube is consistent with the length direction of the quartz tube.

[0012] A microwave plasma jet method, comprising a plurality of rectangular waveguides and a circular waveguide, wherein the plurality of rectangular waveguides are connected to a circular waveguide; a circular ridge and a quartz tube are arranged in the circular waveguide, and one end of the quartz tube is connected to a ventilation device;

[0013] The microwaves emitted by the microwave transmitting device enter from the mouths of several rectangular waveguides and are finally fed into the circular waveguide. The electric field is compressed by the circular ridge inside the circular waveguide, increasing the concentration range of the electric field intensity. The plasma moment is formed by breaking through the gas inside the quartz tube, so that the jet height of the plasma moment reaches 300-400mm.

[0014] Preferably, inside the circular waveguide, a cooling mechanism is arranged outside the quartz tube, and the cooling mechanism is made of metal. The quartz tube is cooled by the cooling mechanism, while the electric field focusing energy is increased and the electric field concentration range is expanded.

[0015] An application of a microwave plasma jet device, including the above-mentioned microwave plasma jet device based on circular ridge waveguide, wherein the microwave plasma jet device based on circular ridge waveguide is applied in treating hazardous solid waste, degrading organic pollutants and treating wastewater and waste gas.

[0016] The present invention has the following beneficial effects:

[0017] 1) Microwaves are fed into the circular ridge waveguide through a dual-port rectangular waveguide, and the circular ridge inside the waveguide compresses the electric field to increase the concentration range of the electric field intensity. The reaction gas enters the quartz tube in a cyclonic inlet mode to excite the plasma jet. The microwave power is 2kW, the jet height is 400mm, and the maximum gas flow rate can reach 37L / min. The larger the gas flow rate, on the one hand, the larger the gas volume broken down by the electric field, the larger the size of the plasma torch generated, and the more sufficient the treatment of solid waste and waste gas, the higher the stability and efficiency; on the other hand, the fast air flow rate is conducive to the heat dissipation of the quartz tube, so that the energy utilization rate reaches 88%; In view of the problems of low plasma efficiency, insufficient processing capacity, short processing range, unstable discharge, discharge pollution, and strict requirements on gas pressure level in industrial applications, solutions and methods are proposed;

[0018] 2) The present invention introduces swirl gas into the quartz tube through a swirl ventilation device, and the airflow spirally rises to prevent the hot zone problem (due to different electric field distributions in the quartz tube, the temperature and heat in different areas of the quartz tube are also different), improve the utilization rate of microwave energy, and generate plasma in the quartz tube; because the swirl gas flows closely to the inner wall of the quartz tube, the swirl reaction gas molecules can flow through the upper, lower, left and right areas of the quartz tube, thereby alleviating the negative impact of the hot zone effect;

[0019] 3) A cooling mechanism is installed on the outside of the quartz tube. The cooling mechanism is made of metal and fits the outer wall of the quartz tube. Cooling water is introduced into the cooling mechanism. On the one hand, the metal can increase the cooling speed, thereby cooling and dissipating the heat of the quartz tube as a whole. On the other hand, the metal cooling mechanism can further increase the electric field strength in the quartz tube, expand the electric field concentration range, reduce the gradient value of the axial distribution of the electric field, and further promote the excitation of the plasma torch. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0021] Figure 1 It is a structural schematic diagram of the present invention;

[0022] Figure 2 It is a schematic diagram of the structure of the circular ridge of the present invention;

[0023] Figure 3 is a streamline diagram of the swirl gas of the present invention;

[0024] Figure 4 is a schematic diagram of electric field intensity distribution;

[0025] Figure 5 The schematic diagram of the structure of the cooling tube is a spiral tube;

[0026] Figure 6 This is a comparison diagram of the electric field distribution after adding the spiral tube;

[0027] Figure 7 The schematic diagram of the structure of the cooling pipe is a straight pipe;

[0028] Figure 8 This is a comparison diagram of the electric field distribution after adding the straight tube;

[0029] In the figure: 1- rectangular waveguide; 2- circular waveguide; 3- circular ridge; 4- quartz tube; 5- cooling tube. DETAILED DESCRIPTION

[0030] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0031] like Figure 1-4 As shown, the present invention is suitable for working in the microwave frequency band of 2.45 GHz. A microwave plasma jet device includes a rectangular waveguide 1 and a circular waveguide 2. Based on the microwave frequency band of 2.45 GHz, the rectangular waveguide 1 in the present invention is a BJ26 rectangular waveguide, and the circular waveguide 2 is a BY25 circular waveguide.

[0032] Several rectangular waveguides 1 are connected to a circular waveguide 2, and the number of rectangular waveguides 1 can be selected as needed. In the present invention, two or four rectangular waveguides 1 are used. Figure 1In the second embodiment, two rectangular waveguides 1 are respectively arranged at the upper and lower ends of the circular waveguide 2, or they can be arranged on both sides of the circular waveguide 2 along the axis of the circular waveguide 2; Figure 5 In the embodiment of four embodiments, four rectangular waveguides 1 are arranged on the circumference of the circular waveguide 2 along the axis of the circular waveguide 2 .

[0033] The microwave emitting device is arranged at the port of the rectangular waveguide 1; a circular ridge 3 and a quartz tube 4 are arranged in the circular waveguide 2, and the quartz tube 4 is a hollow through tube. The circular ridge 3 and the quartz tube 4 are arranged along the length direction of the circular waveguide 2, one end of the quartz tube 4 is connected to the ventilation device, and the other end of the quartz tube 4 passes through the circular waveguide 2 to the outside and is connected to the atmosphere. The ventilation device is used to introduce a breakdown gas into the quartz tube 4. In this embodiment, the breakdown gas is air or argon; the circular ridge 3 is used to compress the electric field in the circular waveguide 2 and increase the concentration range of the electric field intensity.

[0034] The ventilation device in the present invention adopts a swirl ventilation device, which is used to generate swirl gas entering the interior of the quartz tube 4. In the swirl ventilation device, the air flow radially flows into the quartz tube wall from the side, and the spiral upward air flow is maintained in the quartz tube. The swirl gas generated from the air outlet of the swirl ventilation device adheres to the inner wall of the quartz tube 4 and swirls to the other end of the quartz tube 4. Figure 3 As shown, it is a streamline diagram of swirl gas. The swirl gas flow device has a certain angle with the axis of the circular waveguide 2 through the air inlet, and exhausts gas toward the inner wall of the quartz tube 4. Multiple (more than two) air inlets have the same angle and are arranged clockwise or counterclockwise, so as to ensure the generation of swirl gas. Through the swirl air intake, the gas rises slowly, and the gas can fully absorb microwave energy in the quartz tube to carry out chemical reactions of gas breakdown and particle collisions. The airflow has been rising in a spiral manner, with strong fluidity, and the cold and hot airflows interact, avoiding the adverse reactions caused by the hot zone effect.

[0035] like Figure 2 As shown, it is a stereoscopic diagram of the circular ridge 3. The cross section of the circular ridge 3 is a trapezoid. The longer bottom surface of the circular ridge 3 is connected to the inner wall of the circular waveguide 2, that is, the inner wall of the circular waveguide 2 to the circular ridge 3 is a slope transition; the circular ridge 3 is symmetrically arranged in two along the axial direction of the circular waveguide 2, and the quartz tube 4 is arranged between the two circular ridges 3. The circular ridge 3 compresses the electric field to increase the concentration range of the electric field intensity. The circular ridge 3 shortens the distance in the direction of the potential difference to increase the electric field intensity in the waveguide. In this embodiment, when the angle between the circular ridge 3 and the quartz tube 4 is 53°, the height d of the circular ridge 3 is 20mm, and the thickness a is 9mm, the port transmission efficiency is high. At this time, the electric field intensity is concentrated at the center of the ridge, and the strongest electric field intensity reaches 1.54x10 5 V / m. Figure 4As shown, it is a schematic diagram of the electric field intensity distribution after adding the circular ridge 3. The main area is concentrated in the middle position of the circular ridge 3, and a plasma jet is excited in the quartz tube cavity. Since plasma is a good microwave absorber, most of the energy input at both ends will be absorbed by the plasma.

[0036] The rectangular waveguides 1 are provided in pairs, and the two rectangular waveguides 1 are respectively located at two ends or both sides of the circular waveguide 2. In this embodiment, only the schematic diagram of the rectangular waveguides 1 being located at two ends of the circular waveguide 2 is shown.

[0037] The quartz tube 4 is provided with a cooling mechanism on the outside, and the cooling mechanism is fitted with the quartz tube 4. The cooling mechanism is a cooling tube 5. Cooling water is passed into the cooling tube 5, and the temperature is reduced by the flowing cold water. The cooling tube 5 can be made of metal. By arranging a metal cooling mechanism on the outer surface of the quartz tube 4, on the one hand, the temperature can be reduced quickly, and on the other hand, the use of a metal tube can increase the electric field focusing energy, expand the electric field concentration range, reduce the gradient value of the radial distribution of the electric field, and further promote the excitation of the plasma torch.

[0038] In the present invention, two structures of cooling tubes 5 are provided. One type of micro cooling tube 5 is a spiral tube, and the cooling tube 5 is spirally wound on the outer wall of the quartz tube 4. Figure 5 As shown, Figure 6 This is a comparison diagram of the electric field after the spiral tube is installed.

[0039] Another is that the cooling tube 5 is a straight tube, such as Figure 7 As shown, several cooling tubes 5 are evenly distributed and attached to the outer wall of the quartz tube 4, and the length direction of the straight tube is consistent with the length direction of the quartz tube 4. Figure 8 This is a comparison diagram of the electric field after installing a straight tube.

[0040] Based on the above device, the present invention also provides a microwave plasma jet method, including several rectangular waveguides 1 and circular waveguides 2, wherein several rectangular waveguides 1 are connected to a circular waveguide 2; a circular ridge 3 and a quartz tube 4 are arranged in the circular waveguide 2, and one end of the quartz tube 4 is connected to a ventilation device.

[0041] The microwaves emitted by the microwave transmitting device enter from the ports of several rectangular waveguides 1, two of which are taken as an example in the present invention, and are finally fed into the circular waveguide 2. The electric field is compressed by the circular ridge 3 inside the circular waveguide 2, the concentration range of the electric field intensity is increased, and a plasma moment is formed by breaking through the gas inside the quartz tube 4, so that the jet height of the plasma moment reaches 300-400mm.

[0042] Inside the circular waveguide 2, a cooling mechanism is arranged outside the quartz tube 4. The cooling mechanism is made of metal. The quartz tube 4 is cooled by the cooling mechanism, while the electric field focusing energy is increased and the electric field concentration range is expanded.

[0043] Utilizing the above device, the present invention also provides an application of a microwave plasma jet device, including the above-mentioned microwave plasma jet device based on circular ridge waveguide, and the application of the microwave plasma jet device based on circular ridge waveguide in the treatment of hazardous solid waste, degradation of organic pollutants and wastewater and waste gas. In particular, in the treatment of hazardous solid waste, the device of the present invention has a microwave plasma torch that can excite a large size, high power and high gas processing capacity, which can be extended to large-scale industrial applications to treat hazardous solid waste.

[0044] Those skilled in the art should recognize that the above embodiments are only used to illustrate the present invention and are not intended to be limiting of the present invention. As long as they are within the spirit and scope of the present invention, appropriate changes and modifications to the above embodiments are within the scope of protection claimed by the present invention.

Claims

1. A microwave plasma jet device, characterized in that: It includes a rectangular waveguide (1) and a circular waveguide (2). A plurality of the rectangular waveguides (1) are communicatively arranged with one circular waveguide (2). A microwave emitting device is arranged at the port of the rectangular waveguide (1); A circular ridge (3) and a quartz tube (4) are arranged in the circular waveguide (2). The quartz tube (4) is a hollow through-tube. The circular ridge (3) and the quartz tube (4) are arranged along the length direction of the circular waveguide (2). One end of the quartz tube (4) is connected to a ventilation device. The other end of the quartz tube (4) penetrates out of the circular waveguide (2). The ventilation device is used to introduce a gas that can be broken down into the quartz tube (4); The circular ridge (3) is used to compress the electric field in the circular waveguide (2).

2. The microwave plasma jet device according to claim 1, characterized in that: The ventilation device is a swirling ventilation device, and the swirling ventilation device is used to generate swirling gas entering the quartz tube (4).

3. The microwave plasma jet device according to claim 2, characterized in that: The swirling gas generated from the air outlet of the swirling ventilation device swirls along the inner wall of the quartz tube (4) to the other end of the quartz tube (4).

4. The microwave plasma jet device according to claim 1, characterized in that: The cross-section of the circular ridge (3) is trapezoidal, and the longer bottom surface of the circular ridge (3) is connected to the inner wall of the circular waveguide (2); The circular ridge (3) is symmetrically arranged along the axis of the circular waveguide (2) into two, and the quartz tube (4) is arranged between the two circular ridges (3).

5. The microwave plasma jet device according to claim 1, characterized in that: The rectangular waveguide (1) is a BJ26 rectangular waveguide, and the circular waveguide (2) is a BY25 circular waveguide; Two rectangular waveguides (1) are arranged. The two rectangular waveguides (1) are respectively located at both ends or both sides of the circular waveguide (2); The gas that can be broken down is air or argon.

6. The microwave plasma jet device according to claim 1, characterized in that: A cooling mechanism is sleeved outside the quartz tube (4). The cooling mechanism is in contact with the quartz tube (4). The cooling mechanism is a cooling tube (5), and cooling water is introduced into the cooling tube (5).

7. The microwave plasma jet device according to claim 6, characterized in that: The cooling tube (5) is a metal tube. The cooling tube (5) is a spiral tube, and the cooling tube (5) is spirally wound around the outer wall of the quartz tube (4); Or, the cooling tube (5) is a straight tube, and several cooling tubes (5) are evenly distributed and in contact with the outer wall of the quartz tube (4). The length direction of the straight tube is the same as the length direction of the quartz tube (4).

8. A microwave plasma jet method, characterized in that: It includes a plurality of rectangular waveguides (1) and a circular waveguide (2). A plurality of the rectangular waveguides (1) are communicatively arranged with one circular waveguide (2); A circular ridge (3) and a quartz tube (4) are arranged in the circular waveguide (2). One end of the quartz tube (4) is connected to a ventilation device; The microwaves emitted by the microwave emission device enter from the mouths of several rectangular waveguides (1) respectively and are finally fed into the interior of the circular waveguide (2). Inside the circular waveguide (2), the electric field is compressed by the circular ridge (3) to increase the range of electric field intensity concentration. A plasma plume is formed by breaking down the gas inside the quartz tube (4), so that the jet height of the plasma plume reaches 300 - 400 mm.

9. The microwave plasma jet method according to claim 8, characterized in that: Inside the circular waveguide (2), a cooling mechanism is sleeved outside the quartz tube (4). The cooling mechanism is made of metal. While cooling the quartz tube (4) through the cooling mechanism, the electric field focusing energy is increased and the electric field concentration range is expanded.

10. An application of a microwave plasma jet device, comprising the microwave plasma jet device according to any one of claims 1 - 7 above, characterized in that: The application of the microwave plasma jet device in the treatment of hazardous solid waste, organic pollutant degradation, and waste water and waste gas.

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