RU2486719C1 - Gas cleaning, destruction and conversion method - Google Patents

Abstract

FIELD: machine building.

SUBSTANCE: in gas cleaning, destruction and conversion method, action of high-voltage pulse periodic ring discharge is performed on gas, which leads to formation of low-temperature plasma and UV radiation, which initiate plasma chemical reactions, creation of an impact wave, gas heating, creation of convective flows and gas cleaning from microparticles. Gas cleaning is performed by a plasma jet created with microwave radiation; at that, gas quickly passes to a hot plasma area, where plasma chemical reactions are implemented, and is supplied to cold area, thus ensuring tempering of products of plasma chemical reactions.

EFFECT: invention allows improving action efficiency of a plasmatron and a high-voltage pulse-periodic ring discharge, channels of destructions of different types of impurities in gases, which are specific for ultra-high frequency.

3 cl, 3 dwg

Description

The invention relates to the gas and chemical industries and is intended for the purification of gases from solid, liquid, vapor and gaseous inorganic and organic substances, the destruction and conversion of gases.

There are many methods of gas purification: filtration, absorption, sorption, catalytic, thermal, etc. (Rodionov A.I., Klushin V.N., Torocheshnikov N.S. Environmental protection technology. M: Chemistry, 1989, 512 p.).

Recently, much attention has been paid to the development of electrophysical, electric-discharge methods of purification, destruction, and gas conversion. A known method of cleaning a device containing an annular multielectrode discharge system in communication with a pulse-periodic generator of high voltage pulses. The device operates by the method of plasma-chemical, gas-dynamic gas exposure, based on the use of a ring, multi-electrode, high-voltage pulse-periodic discharge (decomposition and transformation of the freon component of a high-pressure gas mixture with a laser spark and a sliding surface discharge. (Z.G. Akhvlediani, E.M. . Barkhudarov, G.V. Gelashvili, etc. // Plasma Physics. 1996, T22. - No. 5 - S.470-477).

A feature of the device is the following:

- the arrester works in all gaseous media in a wide pressure range (from 10 ^-3 Torr to above atmospheric);

- the plasma is localized in the form of small formations with a high electron concentration (N _e ≥10 ¹⁶ cm ³ ) with a gas and electron temperature T _g = (3-5) 10 ³ K and T _e = 3-5 eV, respectively;

- generation of intense epithermal UV radiation (γ≤185 nm);

- the formation of photoplasma near the center of the ring (N _e ≈10 ¹¹ -10 ¹² cm ³ );

- the generation of converging cumulative shock waves (shock waves) at pressures close to atmospheric.

Known methods of plasma chemical exposure to gases using a microwave plasma torch (RU 83682 U1, 03/27/2009; RU 80450 U1, 03/10/2008; RU 8044903 U1, 03/10/2008).

Gas processing is carried out by a plasma jet (torch) excited by microwave radiation emerging from the coaxial. High gas temperature (T _g = (4-5) 10 ^-3 K), electron concentration (N _e ≈3 · 10 ¹⁴ -10 ¹⁶ cm ^-3 ) and electron temperature (T _e = 4-5 eV), as well as plasma nonequilibrium (T _e >> T _g ) provide a high plasma-chemical effect on harmful impurities in gases and gas transformation.

A known method using a multi-electrode spark gap with pumping non-combustible gas (air, nitrogen, argon, etc.) through the interelectrode space, with the help of which a high-voltage pulse-periodic discharge is realized in a liquid (water and its solutions) in order to influence its microbiological, organic and chemical constituents (US 6558638 B2, publ. 07.02.2002).

A device placed in a liquid is structurally the following: on the outer surface of a dielectric cylindrical tube, covering it, there are "n" cylindrical ring electrodes (stainless steel, copper, titanium, etc.) with the same gap between them. The end part of the electrodes is working, the outer cylindrical surface of the electrodes is covered with an insulator. There are several small ≤1 mm holes in the walls of the dielectric tube in the interelectrode space through which gas bubbles enter the liquid from the tube cavity. High-voltage voltage is supplied to two extreme electrodes: one directly, and the second with the help of a return conductor passing through the tube cavity. A discharge formed in gas bubbles is a source of powerful ultraviolet radiation and active particles (O ₃ , H ₂ O _2. OH, O, etc.).

Strong acoustic waves generated during the discharge process, as well as shock waves (shock waves) generated as a result of the collapse of the bubbles, are an additional factor affecting the microbial, organic, and chemical constituents of the liquid.

The disadvantages of this method are:

1) the linear geometry of the discharge device eliminates the possibility of focusing UV radiation and acoustic waves generated by the discharge;

2) the difficulties and inconveniences associated with the placement of a spark gap and communication systems in the water to supply high voltage and gas to the spark gap; when operating a spark gap in a stream, the discharge system creates additional resistance to the flow of liquid;

3) with a vertical arrangement of the discharge device in the fluid flow due to hydrostatic pressure, an uneven flow of gas occurs through openings located along the discharge device, which can affect the stability and uniformity of the discharge channels;

4) sufficient design complexity as a whole.

The technical result of the invention is to increase the effectiveness of the impact of specific for the microwave plasmatron and high-voltage pulse-periodic ring discharge channels of destruction of various types of pollution in gases, their destruction and conversion.

The invention consists in the combined use of two methods of plasma-chemical effects on gases:

1) a multi-electrode pulse periodic high-voltage discharge;

2) microwave coaxial plasmatron (microwave torch).

The combination of these two methods leads to a synergistic effect, which ensures high gas exposure.

The technical result is achieved by the fact that in the proposed method of purification, destruction, conversion of gases, a plasma-chemical and gas-dynamic effect on the gas is carried out, while they are affected by a high-voltage pulse-periodic ring discharge, which leads to the formation of low-temperature plasma and UV radiation, initiating plasma-chemical reactions, creating a shock wave , heating gas, creating convection flows and purifying gas from microparticles, in addition, the gas is treated with a plasma jet created by mic wave radiation, the gas sequentially passes quickly into a "hot" region of the plasma where the plasma-chemical reactions are realized, and supplied to the "cold" area, providing a "hardened" product plasma-chemical reactions.

A method of purification, destruction, gas conversion, in which a combined plasma-chemical and gas-dynamic effect on a gas is carried out using a high-voltage ring discharge and a microwave plasma jet simultaneously in one area of space.

A method of purification, destruction, gas conversion, in which the plasma-chemical and gas-dynamic effects on gas are carried out using a high-voltage ring discharge and a microwave plasma jet in series.

Figure 1 presents the device that implements the proposed method.

Figure 2 - ring discharge system.

Figure 3 - plasmatron.

Low-temperature plasma is nonequilibrium, and plasma-chemical reactions and processes are significantly different from reactions of traditional chemistry.

Nonequilibrium plasma-chemical processes determines the final product of exposure. Plasma-chemical reactions can occur either as a result of strong heating followed by rapid quenching of the reaction products, or by nonequilibrium excitation of vibrational and electronic degrees of freedom of molecules.

The essence of the method consists in the combined use of two different realizations of the plasma-chemical and gas-dynamic effects on gases. The method involves the use of a ring high-voltage multi-electrode pulse-periodic discharge in combination with a microwave coaxial plasmatron, which differ from each other in spatial, temporal plasma characteristics, specific energy input, degree and nature of plasma nonequilibrium. Therefore, the effect of each of these methods on gas and gas mixtures is different. The simultaneous use of these two methods significantly increases the efficiency of exposure to gases and gas mixtures.

The proposed method, in particular, can be implemented according to the scheme shown in figure 1. The cylindrical pipeline 1 is made of two sections 3 and 8, which are reactors. The pipeline is equipped with a gas pumping system having a gas supply channel 4 and gas sampling channels 5 and 11 for analysis and a channel 10 for the scrubber. In the first section 3, at least one ring multi-electrode discharge system 2 is placed, which is in communication with a pulse-periodic high-voltage pulse generator 13, and in the second section 8, a microwave plasma torch 7 is installed, having an electric ignition system and in communication with a magnetron 12.

The first section of the pipeline 1 can be made in the form of separate sections made of a dielectric, on the inner surface of each of which electrodes of the ring discharge system 2 are installed symmetrically about the pipe axis (Fig. 2).

The second section 3 may be made of dielectric or metal.

At the walls of the dielectric cylindrical pipe 1 or directly on it at the same distance from each other with the same gap between them, electrodes 15 are located, one of the electrodes is grounded, and a high-voltage pulse is supplied to the other, symmetrically located. The remaining electrodes are grounded through capacitance 16 (Figure 2), the value of which is significantly less than the capacitance of the storage capacitor of the high-voltage generator. After a quick process of closing the discharge gaps 14, the main discharge current is formed, which flows in two opposite directions.

The parameters of the high-voltage generator are as follows: the number of channels 5, the voltage U≤20 kV, the pulse repetition rate f≤100 Hz, the capacitance of the storage capacitor of one channel C = 10 ^-8 F, the discharge current I≤300 A for a duration τ = 3-5 μs, average generator power N = 1 kW.

An annular pulse-periodic discharge operates in all gas mixtures in a wide pressure range from 10 ^-3 Torr to above atmospheric pressure.

Of particular interest is the high-pressure region. In this case, the nonequilibrium discharge plasma is localized in the form of small formations with a high electron concentration N _e ≥10 ¹⁶ cm ^-3 and the temperature of the gas and electrons, respectively, T _g = (3-5) 10 ³ K and T _e = (3-5) 10 ⁴ K. Due to this, plasma formations are a source of powerful UV radiation, which ensures the occurrence of photoionization and photo-dissociation processes in the outside of the discharge region, initiating a number of plasma-chemical processes. A relatively low gas temperature outside the discharge region (T≤10 ³ K) can ensure the occurrence of plasma-chemical processes associated with the presence of molecules in a vibrationally excited state. The ring geometry of the discharge system provides focusing of UV radiation and the formation of an electron concentration of 10 ¹² -10 ¹³ cm ^-3 in the off-discharge region of the plasma. The short duration of the current pulse (2-5 μs) and the large energy input per pulse (2-20 J) provide the generation of convergent toroidal cumulative shock waves, which leads to gas heating and the creation of convection flows, providing effective mixing of gas flows. In addition, the shock wave helps to purify the gas from the microparticles contained in it.

The design of the plasma torch, shown in Fig.3.

The essence of the modification is the use of a multi-electrode ring spark gap to initiate a microwave discharge. For this purpose, an annular discharge system 2 is located directly near the nozzle 17 (FIG. 3) of the inner electrode 15.

The magnetron and its power system are widely used in household appliances, (microwave) frequency f = 2.45 GHz, average power N = 1 kW. A half-wave alternating voltage rectifier (50 Hz) provides a high-voltage voltage to the magnetron anode and generation of microwave radiation in the form of a sequence of pulses with a duration of τ = 8 ms, the pause between pulses is 12 ms.

Gas processing is carried out by a plasma jet (torch) created by microwave radiation. The energy of a microwave wave is extremely efficiently transformed into plasma energy. An important role in the implementation of plasma-chemical processes is played by the spatial structure of the torch. Near the nozzle of the plasma torch, a brightly luminous region (1-1.5 cm) is formed, surrounded by a less bright region, whose dimensions are an order of magnitude higher. The plasma parameters in the first region are N _e ≈10 ¹⁶ cm ^-3 , T _e ≈5 eV, in the second region Ne _e ≈ (1-3) 10 ¹⁴ cm ^-3 , T _e ≈1-1.5 eV, the gas temperature the first and second regions T ₁ ≈5 kK and T ₂ ≈ 2.5 kK, respectively.

The separation of the electron temperature from the gas temperature determines the degree of nonequilibrium, and, consequently, the efficiency of plasma-chemical processes. The torch operates in stationary or quasi-stationary modes. In the latter case, the duration of microwave radiation is 8 ms, followed by a pause of 12 ms. Thus, the gas stream sequentially quickly passes into the hot region of the plasma and enters the region of cold gas surrounding the torch, which provides quenching of the reaction products.

The specifics of the microwave torch are as follows.

- Rapid heating of the gas followed by rapid cooling (quenching).

- Formation of thermonequilibrium plasma (nonequilibrium excitation of vibrational and electronic degrees of freedom of molecules).

- The main volume of the reaction zone is practically isolated from the walls of the chamber, being separated from them by a cold gas stream.

- The use of a plasma torch allows you to realize reactions that are unrealistic or ineffective under equilibrium conditions.

- Creates a large volume of non-equilibrium plasma with a relatively high concentration of electrons.

The above characteristics of two different methods of exposure to gases indicate that the simultaneous use of these methods significantly expands the channels of exposure to gases, can provide a synergistic effect. And this is an increase in the effectiveness of the impact and the possibility of obtaining results that cannot be obtained using both methods separately. The simultaneous effects of these methods can be combined or shared in space.

The described circuit works as follows.

Five spark gaps or part of them are connected to a pulse-periodic high-voltage pulse generator, the necessary voltage and pulse repetition rate are set, and the generator is turned on. Plasma is formed in the interelectrode gaps of the arresters.

After that, the gas to be processed enters section 3 through channel 4, through channel 6, the gas flows to the second reactor, through the tubular electrode 18 (Figure 3).

The magnetron is turned on, microwave radiation in the nozzle region forms a microwave plasma torch, then the gas through channel 10 enters the scrubber, and through channel 11 it is taken for analysis. If the formation of the plasma torch is difficult, simultaneously with the magnetron for a short time, the ring discharge system 2 is turned on (Figure 3). As a power supply for the arrester, you can use a separate generator or one of the channels of a five-channel generator. For a long simultaneous effect of a microwave and ring discharge on gas, it is possible to turn on the discharge system 2 (Figure 3) for a long time. The device comprises a magnetron 12, a coaxial tee 19, a gas supply channel 6, an external electrode 20, a central inner tubular electrode 18, a microwave torch 9, a pointed nozzle 17, an annular multi-electrode discharge system 2.

The combined use of two different plasma-chemical methods of influence on the gas being treated can provide a synergistic effect and thereby increase the effectiveness of the plasma-chemical effect on gases.

The parameters of the power sources of the annular spark gap and plasma torch can vary depending on the implementation of a specific task.

The device can be used for gas purification from various types of contaminants, gas neutralization by the method of destruction, conversion, gas transformation, as well as in solving a number of industry technological problems.

Claims (3)

1. The method of purification, destruction and conversion of gases, characterized in that they carry out plasma-chemical and gas-dynamic effects on the gas, while they are affected by a high-voltage pulse-periodic ring discharge, which leads to the formation of low-temperature plasma and UV radiation, initiating plasma-chemical reactions, creating a shock wave, heating gas, the creation of convection flows, and gas purification from microparticles, in addition, the gas is treated with a plasma jet created by microwave radiation, at The gas sequentially quickly passes into the "hot" region of the plasma, where the plasma-chemical reactions are realized, and enters the "cold" region, providing quenching of the products of the plasma-chemical reactions. 2. The method of purification, destruction and conversion of gases according to claim 1, characterized in that the plasma-chemical and gas-dynamic effects on the gas are carried out using a high-voltage ring discharge and a microwave plasma jet simultaneously in one area of space. 3. The method of purification, destruction and conversion of gases according to claim 1, characterized in that the plasma-chemical and gas-dynamic effects on the gas are carried out using a high-voltage ring discharge and a microwave plasma jet in series.

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