EA037157B1 - Device for production of glow-discharge plasma - Google Patents

Abstract

The invention relates to the field of machine engineering, in particular, to gas discharge devices, and can be used in hydrocarbon feed conversion systems, plasma chemistry, laser technology, modification of powder materials, etc. The objective of the claimed technical solution is to increase the device efficiency due to higher plasma density. Said objective is attained by provision of a device for production of glow-discharge plasma, comprising a vertically mounted operation chamber, an anode assembly located in the top part of the chamber, and a cathode assembly located in its bottom part and made as a fine-meshed screen coated with a layer of conducting powder, a gas feeding and discharge system, and a power supply system, wherein the device further includes an electromagnetic system with its poles covering the operation chamber, so that the magnetic induction vector is perpendicular to the gas flow direction, and an AC power supply energizing the electromagnetic system. The essence of the claimed technical solution consists in increasing the number of particle collisions due to an increase in their path length. The increased total number of collisions leads to an increase in the number of effective collisions and ensures higher efficiency.

Description

(54) DEVICE FOR OBTAINING GLOW DISCHARGE PLASMA

(43) 2020.11.30 (56) BY-C1-22302 (96) 2019 / ЕА / 0053 (BY) 2019.05.17 US-A1-20190135633 US-A-4287040 (71) (73) Applicant and patentee: RU-C2-23 97948 SCIENTIFIC RESEARCH RU-C2-2333619 ESTABLISHMENT OF THE INSTITUTE OF NUCLEAR PROBLEMS OF THE BELARUSIAN STATE UNIVERSITY (BY) (72) Inventor: Martynyuk Viktor Ivanovich, Zelenin Viktor Alekseevich, Senko Sergey Fedorovich, Bychenok Dmitry Sergeevich, Savitskiy Aleksandr Aleksandrovich, Lyubimov Aleksandr Gennadievich (BY) GB-A-2344212

037157 B1

037157 Bl (57) The invention relates to the field of mechanical engineering, in particular to gas-discharge devices, and can be used in systems for the conversion of hydrocarbons, plasma chemistry, laser technology, modification of powder materials, etc. The task of the proposed technical solution is to increase the efficiency of the device by increasing the density plasma. The problem is solved by the fact that a device for producing a glow discharge plasma containing a vertically installed working chamber, an anode assembly located in its upper part, and a cathode assembly located in its lower part and made in the form of a fine-mesh lattice with a layer of electrically conductive powder on it, the system for supplying and removing gases and the power supply system, additionally contains an electromagnetic system covering the working chamber with poles so that the magnetic field induction vector is perpendicular to the direction of the gas flow, and its power supply source with alternating current. The essence of the proposed technical solution is to increase the number of collisions between particles by increasing the length of their trajectory. An increase in the total number of collisions leads to an increase in the number of effective collisions and provides an increase in efficiency.

The invention relates to the field of mechanical engineering, in particular to gas-discharge devices, and can be used in systems for the conversion of hydrocarbon feedstock, plasma chemistry, laser technology, modification of powder materials, etc.

A device for producing plasma at atmospheric pressure is known, comprising a chamber, an anode assembly, a cathode assembly with a dielectric and capillaries, a gas supply system, and a power source. The distance between the electrodes is no more than 1 cm, and the plasma is ignited in the capillary channels made of dielectric.

The disadvantage of the analogue is the too small volume of generated plasma, which imposes significant restrictions on the area of its use. An increase in the interelectrode distance requires the application of high voltages to obtain a gas discharge and, accordingly, rather sophisticated electronic equipment. The small volume of the produced plasma predetermines the extremely low productivity of the analogue, for example, in the conversion of hydrocarbons, and the low efficiency of the device.

It is also known a device for producing glow discharge plasma at atmospheric pressure, containing a working chamber, anode and cathode assemblies, a cathode cooling system, a system for supplying and removing gases and a power supply system. As follows from his description, the plasma is ignited by contacting the electrodes. After plasma ignition, the electrodes are separated to the required distance, while the power consumption of the device can reach 5 kW.

The disadvantage of this analogue is also its low efficiency, due to the small volume of generated plasma at high power consumption. At the root of these shortcomings are the features of the electric discharge in gases. The volume of the generated plasma is determined by the distance between the electrodes and the cross section of the discharge. Since the breakdown of a gas gap 1 cm long at atmospheric pressure requires a voltage of the order of ~ 10 kV, which imposes significant restrictions on the design of the power supply for electrical insulation, then in practice small interelectrode distances are used. To obtain the required plasma efficiency, the operating currents are increased, which, in turn, leads to its uncontrolled heating and contraction of the gas discharge, i.e. lacing of the current and the subsequent occurrence of an electric arc. The use of a cooling system partly solves this problem, but this further reduces the efficiency of the device, since most of its power is spent on heating parts.

The closest to the claimed technical solution, its prototype is a device for producing glow discharge plasma, containing a working chamber, placed in it anode and cathode units, a gas supply and exhaust system and a power supply system, while the working chamber is installed vertically, the cathode unit is located in it the lower part and is made in the form of a fine-mesh lattice with a layer of electrically conductive powder located on it.

The supply of the working gas leads to the boiling of the layer of electrically conductive powder at the cathode, which makes it possible to significantly reduce the operating voltage and multiply the volume of the generated plasma. The use of a boiling cathode makes it possible to significantly increase the efficiency of the device in comparison with the above analogs and, due to this, significantly expand its technical capabilities.

The disadvantage of the prototype is the insufficiently high efficiency of the device associated with the features of the trajectory of charged particles in the interelectrode space. The efficiency, for example, of the gas conversion process is determined by the fraction of effective collisions of atoms, i.e. such collisions, which lead to the occurrence of their chemical interaction with the formation of a conversion product. In the general case, the fraction of effective collisions depends on the ion energy, determined by the voltage between the electrodes, and increases with increasing voltage. However, an increase in the voltage between the electrodes leads to contraction of the discharge, heating of the plasma, and a decrease in the efficiency due to a decrease in the plasma volume and the occurrence of a reverse chemical reaction. The total number of collisions depends on the length of the ion trajectory in the interelectrode space. Stirring the fluidized bed with an ascending gas flow noticeably increases this length due to turbulence, which gives the prototype advantages over analogues. However, the constant voltage between the electrodes during the operation of the device leads to the minimization of the path length of charged particles as they move from the cathode to the anode, the ions tend to overcome this distance in a straight line. The plasma density, determined by the number of charged particles per unit of its volume, turns out to be lower than the realistically possible one, which does not allow reaching the maximum efficiency.

Thus, the peculiarities of the trajectory of charged particles during the operation of the prototype do not allow achieving the maximum efficiency of plasma combustion and lead to a decrease in the efficiency.

The objective of the proposed technical solution is to increase the efficiency of the device by increasing the plasma density.

The problem is solved by the fact that a device for producing a glow discharge plasma containing a vertically installed working chamber, an anode assembly located in its upper part, and a cathode assembly located in its lower part and made in the form of a fine-mesh lattice with a layer of electrically conductive powder on it, a gas supply and exhaust system and a power supply system, additionally contains an electromagnetic system, covering the working chamber with poles so,

- 1 037157 that the vector of the magnetic field induction is perpendicular to the direction of the gas flow, and the source of its power supply is alternating current.

The essence of the proposed technical solution is to increase the number of collisions between particles by increasing the length of their trajectory. An increase in the total number of collisions leads to an increase in the number of effective collisions and provides an increase in efficiency.

Equipping the working chamber with an electromagnetic system with a magnetic field induction vector perpendicular to the direction of the gas flow leads to an additional effect on the moving charged particles of the working gas plasma. The trajectory of their movement in an alternating magnetic field becomes spiral-shaped and, due to this, lengthens. This leads to an increase in the number of collisions between individual ions and radicals, the number of elementary acts of interaction and, accordingly, to an increase in the plasma density. As a result, the efficiency of the device increases. An additional advantage of the inventive device is an increase in the discharge resistance to contraction, which allows the use of higher current densities and thereby increase the productivity of the conversion process.

The specific characteristics of the alternating magnetic field are set on the basis of the dimensions of the working chamber, the type and composition of the working gas, as well as depending on the material (magnetic properties) and dispersion of the powder particles. A positive effect is achieved already at values of the magnetic field strength H ~ 0.5 A-m ^-1 . With increasing H, the positive effect is enhanced. The upper limit of the H values is limited only by the design features of the electromagnets compatible with specific working chambers. The frequency of the magnetic field also does not play a special role, since a positive effect is observed already at rather low frequencies (on the order of several tens of Hz). High frequencies requiring special power supplies can be used in special cases of plasma formation. In this case, the magnetic system can contain one or more electromagnets, both equipped with magnetic circuits (pole pieces), and without them.

From a practical point of view, the most convenient electromagnets are powered by a standard AC 220 V and 50 Hz through a step-down transformer. In the overwhelming majority of cases, this makes it possible to create simple and rather effective devices for obtaining a stable glow discharge plasma at atmospheric pressure.

Thus, the alternating magnetic field created by the electromagnetic system increases the length of the trajectory of charged particles in the interelectrode space and increases the number of collisions between them, leading to an increase in the yield of the conversion product, i.e. to increase efficiency.

The essence of the proposed technical solution is illustrated by the drawings of FIG. 1 and 2, which shows a schematic representation of the device (side and top views, respectively). The following designations are adopted in the drawings:

- working chamber;

- lattice;

- powder;

- anode;

- power supply;

- gas supply fitting;

- gas outlet fitting;

- base;

- pole piece;

- electromagnet;

- electromagnet power supply;

- magnetic circuit.

As can be seen from the drawings, the inventive device consists of a vertically installed working chamber 1, in the lower part of which a grating 2 is mounted with a powder 3 located on it and together forming a cathode, and an anode 4 is located in the upper part. both solid and in the form of a lattice. In the case of a solid anode, a channel is left between it and the walls of the working chamber for the gases to escape. The grid 2 and the anode 4 are supplied with voltage from the power supply 5. The working gas is supplied through the gas supply 6 located in the lower part of the working chamber 1. After processing, the gas is removed from the working chamber 1 through the gas outlet 7 located behind the anode 4. In to avoid overheating of the thin lattice 2 during operation, it is equipped with a massive metal base 8, which serves as a heat sink. The working chamber 1 is installed between the pole pieces 9 of the electromagnets 10, which are supplied with an alternating voltage from the power source of the electromagnet 11. The pole pieces 9 are connected by a magnetic circuit 12 (not shown in Fig. 1 to avoid obstruction) to form a closed magnetic system.

The device works as follows. Lattice 2 is connected to the negative electrode of the power supply, and the anode 4 is connected to the positive one. In the first version, by turning on the power supply 5, an operating voltage is applied to the electrodes, while the powder 3 is charged negatively. Since the distance between the grating 2 with the layer of powder 3 and the anode 4 is currently large - 2 037157 ko, the current does not flow through the device. Then, gas (gas mixture) is supplied to the working chamber 1 through the gas supply connection 6. Under the action of the gas flow, the powder 3 boils, the distance between the negatively charged powder 3 and the positively charged anode 4 is significantly reduced, and an electrical breakdown occurs, which ionizes the processed gas. At the next moment in time, due to avalanche ionization of the gas in the interelectrode space of the working chamber 1, plasma ignites. In the second version, a gas mixture is first fed through the gas supply nozzle 6 into the working chamber 1, and after the powder 3 has boiled, a high voltage pulse is supplied to the electrodes, providing a breakdown of the gas gap. The resulting discharge due to the presence of a fluidized bed leads to the subsequent ionization of the entire interelectrode space and the ignition of the plasma. After that, the voltage across the electrodes drops to a stationary value. The plasma combustion mode is set in accordance with the requirements of the technical process and is regulated by the gas flow rate, voltage between the electrodes and the strength of the flowing current. After passing the anode, the reaction products through the gas outlet 7 are discharged into the atmosphere (for example, in the case of afterburning of exhaust gases), or fed into the working area of another technical process (for example, during ozonation), or collected in a special container (not shown in the drawing) for further use. The released heat is utilized due to the flow of the gas mixture and heating of the base 8, which prevents burnout of the grating 2. The alternating magnetic field created in the volume of the working chamber 1 between the pole pieces 9 of the electromagnets 10 leads to an increase in the length of the trajectory of charged particles in the interelectrode space. Electric charges, for example, electrons e, located in the volume of the working chamber 1, are affected by a constant electric field vector E, determined by the operating voltage and directed from the anode to the cathode, and a variable magnetic induction vector B, determined by the frequency of the operating voltage of electromagnets 10 and directed perpendicularly to E from from the south pole to the north pole. This leads to a change in the trajectory of electrons from rectilinear to spiral, an increase in the plasma density and stabilization of its combustion during the entire technological cycle. The control of the characteristics of the alternating magnetic field is carried out using the power source of the electromagnet 11. In the simplest case, a laboratory step-down transformer (LATR) equipped with a voltmeter and an ammeter can be used as this source.

The inventive device was manufactured and tested as follows. In the lower part of a hollow quartz cylinder with an inner diameter of 29 mm, a stainless steel cathode base was soldered, on which a niobium grating was mounted. The lattice contained 35x35 rows of 50x50 µm holes. Then, a funnel, also made of quartz glass, with a nozzle for gas supply was soldered. In the upper part of the cylinder, a niobium grating serving as an anode with a mesh size of 1x1 mm was soldered. The size of the cells of this lattice is chosen so that through it there is the possibility of unhindered filling of the working chamber with electrically conductive powder. The distance between the upper and lower grilles was 50 mm. Then, a gas outlet fitting was soldered over the grating in the upper part of the cylinder. The electrical leads of the gratings are brought out to the outer surface of the quartz cylinder. Through the gas outlet fitting, the resulting working chamber was filled with nickel powder of PNE GOST 9722-79 grade to a layer height of 25 mm. The lower lattice with a layer of nickel powder and a metal base formed the cathode assembly. Electrodes of the power supply of the corresponding polarity are connected to the electrical terminals of the grids. The maximum voltage of the power source was 15000 V, the maximum current was 0.1 A. As electromagnets, we used coils containing 2000 turns of 0.2 PEV wire wound on a frame made of dielectric material. The magnetic core was made of type 2212 sheet electrical steel with a thickness of 0.5 mm. The leads of the coils were connected to the leads of a LATR equipped with a voltmeter and an ammeter. The LATR was connected to an alternating current network with a voltage of 220 V and a frequency of 50 Hz.

Atmospheric air was supplied through the inlet connection using a compressor at a flow rate of 1.5-10 l / min. After the formation of a fluidized bed with a height of 30 to 48 mm, a short-term pulse with a voltage of 12000 V and a pick-up voltage of 1000 V was applied to the electrodes of the device to ignite the plasma. After that, the maximum brightness of the plasma combustion was achieved by adjusting the gas flow rate and current strength, which was 0.07 A The power consumption is thus 70 W. The volume of the luminous region was ~ 33 cm ³ . The voltage from the LATR was applied to the terminals of the electromagnets and its value was chosen such that, when exceeded, the brightness of the plasma glow did not increase. In this case, the maximum possible plasma density was achieved, providing the maximum efficiency of the device.

The gas mixture to be converted with the obtained nitrogen oxide was then fed into the absorber and passed through a bubbler with a reference volume of an aqueous solution of sodium hydroxide with the addition of phenolphthalein as a pH indicator. The efficiency of the device was evaluated by the rate of neutralization of the standard solution with nitrogen oxides and was determined by the time of its discoloration (when nitrogen oxides react with sodium hydroxide, sodium nitrate is formed, which leads to discoloration of the raspberry alkali solution). The bleaching time of the reference volume of the alkali solution was 0.50-0.55 minutes when using the prototype and 0.35-0.40 minutes when using the proposed technical solution.

- 3 037157

Thus, the proposed technical solution in comparison with the prototype can significantly increase the efficiency of the device by increasing the plasma density.

Sources of information:

1. Kunhardt E.E. Generation of Large Volume, Atmospheric Pressure, Nonequilibrium Plasmas // IEEE

Transactions on Plasma Science. - V. 28.No 1. February 2000.

2. Archipenko V.I., Zgirovsky S.M., Simonchik L.V. A device for obtaining a nonequilibrium glow discharge plasma in an atmospheric phenomenon. Patent RB 10597. Publ. 30.04.2008.

3. Martynyuk V.I., Zelenin V.A., Senko S.F., Yakovleva M.A. A device for producing glow discharge plasma. Patent RB 22302. Publ. 12/30/2018.

Claims (1)

A device for producing a glow discharge plasma containing a vertically mounted working chamber, an anode assembly located in its upper part, and a cathode assembly located in its lower part and made in the form of a fine-mesh lattice with a layer of electrically conductive powder on it, a gas supply and removal system, and a power supply system, characterized in that it additionally contains an electromagnetic system that encloses the working chamber with poles so that the magnetic field induction vector is perpendicular to the direction of the gas flow, and its power supply source with alternating current.