CN112973399A

CN112973399A - Method for confirming efficient harmless degradation of SF6 waste gas through dielectric barrier discharge

Info

Publication number: CN112973399A
Application number: CN202110179253.XA
Authority: CN
Inventors: 张英; 王明伟; 刘喆; 牧灝; 张晓星; 余鹏程
Original assignee: Guizhou Power Grid Co Ltd
Current assignee: Guizhou Power Grid Co Ltd
Priority date: 2021-02-09
Filing date: 2021-02-09
Publication date: 2021-06-18

Abstract

The invention discloses a confirmation method for degrading SF6 waste gas by dielectric barrier discharge in a high-efficiency and harmless manner, which comprises the following steps: building an experiment platform; obtaining DBD reactor degradation SF using experimental platform₆Discharge parameters and experimental parameters of (a); for background gas and SF₆Distributing gas; by controlling variables to promote SF₆Forward decomposition experimental study to obtain decomposed SF₆The optimum condition of (2); SF (sulfur factor) by combining density functional theory and chemical reaction kinetics analysis₆Chemical reaction mechanism of gas under discharge degradation; establishment of dielectric barrier discharge degradation SF₆According to various basic physical coefficients of the physical model. The invention degrades SF by dielectric barrier discharge₆System pair SF₆Full degradation of gas and analysis and detection of SF₆The degraded product is comprehensively detected and analyzed to obtain the best degraded ginsengThe configuration is more scientific and the degradation energy efficiency is higher.

Description

Method for confirming efficient harmless degradation of SF6 waste gas through dielectric barrier discharge

Technical Field

The invention relates to a confirmation method for degrading SF6 waste gas by dielectric barrier discharge in an efficient and harmless manner, and belongs to the technical field of SF6 waste gas degradation.

Background

SF₆The gas is widely applied to industries such as electric power, metal smelting, semiconductor manufacturing, aerospace and the like due to unique physicochemical properties of the gas. However, SF₆The gas is an extremely strong greenhouse gas, and the potential value GWP (global Warming potential) of the greenhouse effect is CO₂23500 times of SF, and a lifetime in the atmosphere of about 3200 years, the last 5 years, SF₆The content in the global atmosphere has increased by 20%. The joint nations climate Change convention contracting party signed in 1997 in Kyoto Protocol (SF)₆The gas is listed as one of six limiting greenhouse gases. The Paris convention, signed at the end of 2015, strives to control the global average temperature rise to within 2 ℃ of the pre-industrialization level and strives not to exceed 1.52 ℃ of the pre-industrialization level.

To solve the problem of SF₆Greenhouse effect caused by gases, SF has been already known in Europe, North America, Australia and parts of Asia₆The use of gas is initially subject to emission taxes to control and progressively limit SF₆The use of a gas. But with economic development, for SF₆The demand for gas has increased or decreased. The reduction of carbon emission and the increasing demand for environmental protection will lead to the development of new environmental-friendly insulating gases and devices (e.g., Alston and ABB, national Relay, etc.), which will generate a large amount of SF in the future₆Exhaust gas, whereas SF₆80% of the applications are in the power industry, and thus the power industry is directed to SF₆The treatment of exhaust gases is particularly important.

At present, for SF at home and abroad₆The treatments have been studied, and the methods of pyrolysis, photolysis, dielectric barrier discharge and the like are all used for treating SF₆And (4) exhaust gas. Among them, the Dielectric Barrier Discharge (DBD) technology is most efficient and economical, and is suitable for industrial applications. The researchers divideThe research is carried out from the aspects of discharge conditions, gas components, gas flow rate, catalysts, reactor design and the like, and a certain rule is summarized from one or more aspects, but the research point is single, the degradation energy efficiency is low, the research is on a laboratory scale, and the industrial application level is not reached.

Disclosure of Invention

The technical problem to be solved by the invention is as follows: the method for confirming the efficient harmless degradation of SF6 waste gas by dielectric barrier discharge is provided, so as to solve the technical problems in the prior art.

The technical scheme adopted by the invention is as follows: a method for confirming efficient harmless degradation of SF6 waste gas by dielectric barrier discharge comprises the following steps:

(1) building dielectric barrier discharge degradation SF₆The experimental platform of (1);

(2) obtaining dielectric barrier discharge degradation SF₆The DBD reactor of the experimental platform degrades SF₆The discharge parameters comprise external voltage, external power supply and electrode material, and the experiment parameters comprise initial concentration, external gas type and proportion thereof, catalyst type and morphology;

(3) SF of DBD reactor by gas distribution system₆Gas and background gas distribution;

(4) by using a controlled variable method, SF influencing dielectric barrier discharge decomposition is changed₆Are contributing to SF₆The forward decomposition experimental study shows that all factors comprise background gas, reduced field intensity, gas flow, different additional gases, external medium of the reactor and different filling media, the experimental rule is summarized, and decomposed SF is obtained₆The optimum conditions of (2): degrading SF by dielectric barrier discharge built₆On the experimental platform of (2), a large amount of SF is carried out₆Degradation experiment to obtain SF under the action of dielectric barrier discharge₆The degradation rules of different background gases, reduced field intensity, gas flow, external gas and environment medium are analyzed, and the influence mechanism of experimental parameters is analyzed to obtain the optimal background gas type, reduced field intensity in the discharge area of the reactor, reaction gas flow, external gas type and DBD counter reactionAn environment for placing the reactor and a filling medium;

(5) SF (sulfur factor) by combining density functional theory and chemical reaction kinetics analysis₆Chemical reaction mechanism of gas under discharge degradation:

analyzing the energy change of the plasma discharge reaction by adopting a density functional theory, and specifically using DMol in the Material Studio (MS)4.3 software of molecular dynamics simulation software³Module implementation of SF under dielectric barrier discharge₆The thermodynamic parameters of the degradation reaction of the gas are corrected under limited conditions, and the calculation formula after correction is as follows:

ΔE＝∑(E₁+H_1(298.15))-∑(E₀+H_0(298.15)) (1)

wherein E₁And E₀The single point energies, H, of the product and reactant at vacuum and absolute zero, respectively_1(298.15)And H_0(298.15)The enthalpy value correction values of the product and the reactant at 1atm and 298.15K are respectively;

(6) establishment of dielectric barrier discharge degradation SF₆According to various basic physical coefficients of the physical model, the parameters of the electron energy distribution characteristic, the electron density and the space-time distribution of other particle densities of the plasma discharge under different conditions are obtained through numerical calculation; determining the type and energy state of the active particles using emission spectroscopy; SF by using Fourier infrared spectrometry and gas chromatography-mass spectrometry₆The degradation products were analyzed; SOF also using gas chromatography/mass spectrometer₄、SO₂F₂、SOF₂And SO₂These four products were quantitatively determined and their selectivities were calculated using equation (2):

in the formula, K represents the name of the product, C_KTo degrade the concentration of products in the exhaust gas, C_inIs SF₆Gas input concentration in ppm or%, C_outIs SF₆Residual concentration of gas, singlyThe bit is ppm or%.

The acquisition method for obtaining the discharge physical parameters by solving the Boltzmann equation by using the BOLSIG + computer program package comprises the following steps:

reading an electron-neutral particle collision cross section and corresponding electron energy from an input file;

inputting input parameter values of reduced field intensity, angular frequency and particle number ratio of alternating electric field, gas temperature, gas component mole fraction and ionization degree, setting electric field form, electron growth mode and ionization energy distribution model, selecting grid model, setting energy interval, number of points of numerical energy grid and solving precision;

calculating the physical parameters of plasma discharge under different conditions, and directly outputting the obtained result in a data file format.

Preferably, the dielectric barrier discharge degrades SF₆The experimental platform comprises a gas distribution system, a DBD reactor and a power supply system, wherein a gas outlet of the gas distribution system is connected to a gas inlet of the DBD reactor, and the DBD reactor is connected with the power supply system.

Preferably, the dielectric barrier discharge degrades SF₆The test platform of (a) is also connected to an analytical detection system.

Preferably, the analysis and detection system comprises an electrical parameter detection system, a chemical parameter detection system and an optical parameter detection system.

Preferably, the analysis and detection system includes an oscilloscope, a Gas Chromatograph (GC), a Fourier Transform Infrared Spectrometer (FTIR), a Gas Chromatograph/Mass Spectrometer (GC/MS), and a Spectrometer.

Preferably, the gas distribution system comprises a plurality of standard gas distribution bottles and a gas distribution instrument, wherein the plurality of standard gas distribution bottles are connected to the gas distribution instrument, and the gas distribution instrument is connected to the DBD reactor; the standard gas distribution cylinders are an Ar gas cylinder, an SF6 gas cylinder and an O2 gas cylinder.

Preferably, the outlet of the DBD reactor is also connected to an alkaline liquid tank and a KDHF03A adsorption box in sequence.

The invention has the beneficial effects that: compared with the prior art, the invention has the following effects:

(1) the invention degrades SF by dielectric barrier discharge₆System pair SF₆Full degradation experiment of gas and analysis and detection system for SF₆The degraded product is subjected to comprehensive detection and analysis to obtain optimal degradation parameter configuration and degradation equipment configuration, the configuration is more scientific, the degradation efficiency is higher, and the industrial application level is conveniently reached;

(2) the optimal conditions were obtained through the test platform:

under different background gases, SF₆The degradation effect of (a) follows the following sequence: ar (Ar)>He>N₂Is approximately equal to air. At SF₆/H₂In the O/Ar plasma system, the average electron energy and the electron number density are both maintained at a high level, which is the reason why Ar has the best effect as the background gas;

increased intensity of the reduced field in the discharge region of the reactor increases the average electron energy of the plasma, promoting SF₆The increase in degradation rate, when the reduced field strength exceeds 126Td, shortens the SF₆Time to complete degradation. But the change in the reduced field strength has less effect on the energy effect. The reduction field strength should be increased as much as possible under the condition of meeting the manufacturing process in the design process of the reactor;

thirdly, under the same plasma equivalent density, the increase of the reaction gas flow in a certain range is beneficial to SF₆The degradation rate of (2) is increased, but when the gas flow rate is too large, the SF is caused by too short a gas residence time₆The degradation rate decreases. In the aspect of energy efficiency, the energy efficiency is reduced due to too low airflow, so that the flow rate of argon is finally selected to be 3L/min, and the flow rate of sulfur hexafluoride is finally selected to be 1.5L/min;

0.5% water gas as external gas to degrade SF₆Is good, and secondly is low concentration of oxygen. SF with increasing oxygen concentration₆The degradation rate and energy efficiency of (a) are rather reduced. NH (NH)₃Although the addition of (A) can greatly improve the SF₆The degradation rate and the energy efficiency are reduced, but the solid product is separated out at the same time, the continuous degradation is not facilitated, so that the water with the concentration of 0.5 percent is used as the raw materialSuitable for the external gas;

fifth, when the reactor is placed in oil-immersed environment, the plasma discharge power is higher than that when the reactor is placed in air environment, the temperature rise of the reactor is lower, and more energy is used for degrading SF₆Instead of heating the reactor, so that SF₆The degradation effect is better;

filling medium improves electric field distribution of reactor greatly, degradation rate and energy efficiency, and has no filling system and glass beads and gamma-Al₂O₃Particulate media comparison, glass beads and gamma-Al₂O₃The particle filling enables the energy efficiency ratio of a non-filling system to be respectively higher by 76.80 percent and 115.14 percent, and the gamma-Al₂O₃The particles are more energy efficient as filling medium.

Drawings

FIG. 1 is a schematic diagram of the present invention;

FIG. 2 shows degradation of SF by dielectric barrier discharge₆Experimental platform structure diagram.

FIG. 3 is SF₆And its low fluoride loses the dissociation energy diagram of the F atom, the unit is kcal/mol in the figure;

FIG. 4 is SF₆/H₂Emission spectrum of O/Ar plasma system;

FIG. 5 is SF₆/H₂An emission spectrum of an O/Ar plasma system, wherein (a) is 300-450 nm; (b) 450-680 nm;

FIG. 6 is an FTIR spectrum of degradation products at a moisture concentration of 0.5%;

FIG. 7 is a graph comparing the selectivity of major sulfur-containing degradation products under water-gas conditions.

Detailed Description

The invention is further described with reference to the accompanying drawings and specific embodiments.

Example 1: as shown in figures 1-2, the equipment adopted by the method for confirming the efficient harmless degradation of SF6 waste gas by dielectric barrier discharge comprises the steps of degrading SF6 by dielectric barrier discharge₆The experiment platform and the analysis and detection system, and the dielectric barrier discharge degradation SF₆The system comprises a gas distribution system, a DBD reactor and a power supply system, wherein a gas outlet of the gas distribution system is connected to the DBD reactorThe analysis and detection system comprises an electrical parameter detection system, a chemical parameter detection system and an optical parameter detection system; the analysis and detection system comprises an oscilloscope, a Gas Chromatograph (GC), a Fourier Transform Infrared Spectrometer (FTIR), a Gas Chromatograph/Mass Spectrometer (GC/MS) and a Spectrometer; the gas distribution system comprises a plurality of standard gas distribution bottles and a gas distribution instrument, wherein the plurality of standard gas distribution bottles are connected to the gas distribution instrument, and the gas distribution instrument is connected to the DBD reactor; the standard gas distribution cylinder is Ar gas cylinder or SF gas cylinder₆Gas cylinder and O₂A gas cylinder; a water tank (or NH) is additionally arranged between the gas distribution system and the DBD reactor₃A gas cylinder); the DBD reactor was also connected to an alkaline solution tank and KDHF03A adsorption cassette in turn.

Example 2: a method for confirming efficient harmless degradation of SF6 waste gas by dielectric barrier discharge comprises the following steps:

(4) by using a controlled variable method, SF influencing dielectric barrier discharge decomposition is changed₆Are contributing to SF₆The forward decomposition experimental study shows that all factors comprise background gas, reduced field intensity, gas flow, different additional gases, external medium of the reactor and different filling media, the experimental rule is summarized, and decomposed SF is obtained₆The optimum conditions of (2): degrading SF by dielectric barrier discharge built₆On the experimental platform of (2), a large amount of SF is carried out₆Degradation experiment to obtain SF under the action of dielectric barrier discharge₆At a different placeBackground gas, reduced field intensity, gas flow, degradation rule of external gas and environment medium, and analyzing the influence mechanism of experimental parameters to obtain the optimal background gas type, reduced field intensity in the discharge area of the reactor, reaction gas flow, external gas type, DBD reactor placement environment and filling medium;

ΔE＝∑(E₁+H_1(298.15))-∑(E₀+H_0(298.15)) (1)

in the formula, K represents the name of the product, C_KTo degrade the concentration of products in the exhaust gas, C_inIs SF₆Gas input concentration in ppm or%, C_outIs SF₆The residual gas concentration means in ppm or%.

BOLSIG + is an open source, interface friendly computer package. The method for obtaining the discharge physical parameters by solving the Boltzmann equation by using the BOLSIG + comprises the following steps:

firstly, reading an electron-neutral particle collision cross section and corresponding electron energy from an Input file (an Input file of Bolsig + software, the data of a particle collision interface is stored in the software, the software is provided with an Input-example.

and thirdly, calculating the physical parameters of plasma discharge under different conditions, and directly outputting the obtained result in a data file format for access.

By using a controlled variable method, SF influencing dielectric barrier discharge decomposition is changed₆All the factors of (A) promote the forward decomposition research of the (A) to summarize the rule to obtain the decomposed SF₆The optimum condition of (2).

Degrading SF by dielectric barrier discharge built₆On the experimental platform, a large amount of SF is carried out₆Degradation experiment to obtain SF under the action of dielectric barrier discharge₆The degradation rules under different background gases, reduced field intensity, gas flow, additional gases and environment media are analyzed, the influence mechanism of the experimental parameters is analyzed, and the main conclusion is obtained as follows:

under different background gases, SF₆The degradation effect of (a) follows the following sequence: ar (Ar)>He>N₂Is approximately equal to air. At SF₆/H₂In the O/Ar plasma system, both the average electron energy and the electron number density are maintained at a high level, which is why Ar works best as a background gas.

Increased intensity of the reduced field in the discharge region of the reactor increases the average electron energy of the plasma, promoting SF₆The increase in degradation rate, when the reduced field strength exceeds 126Td, shortens the SF₆Time to complete degradation. But the change in the reduced field strength has less effect on the energy effect. The reduction field strength should be increased as much as possible during the reactor design under conditions that are compatible with the fabrication process.

Thirdly, under the same plasma equivalent density, the increase of the reaction gas flow in a certain range is beneficial to SF₆The degradation rate of (2) is increased, but when the gas flow rate is too large, the SF is caused by too short a gas residence time₆The degradation rate decreases. In terms of energy efficiency, the energy efficiency is reduced due to the fact that the flow rate of the gas flow is too low, and therefore the flow rate of argon is finally selected to be 3L/min, and the flow rate of sulfur hexafluoride is finally selected to be 1.5L/min.

0.5% water gas as external gas to degrade SF₆Is good, and secondly is low concentration of oxygen. SF with increasing oxygen concentration₆The degradation rate and energy efficiency of (a) are rather reduced. NH (NH)₃Although the addition of (A) can greatly improve the SF₆The degradation rate and the energy efficiency are low, but the solid product is separated out at the same time, so that the continuous degradation is not facilitated, and therefore, 0.5 percent of water gas is suitable as the external gas.

Fifth, when the reactor is placed in oil-immersed environment, the plasma discharge power is higher than that when the reactor is placed in air environment, the temperature rise of the reactor is lower, and more energy is used for degrading SF₆Instead of heating the reactor, so that SF₆The degradation effect is better.

Filling medium improves electric field distribution of reactor greatly, degradation rate and energy efficiency, and has no filling system and glass beads and gamma-Al₂O₃Particulate media comparison, glass beads and gamma-Al₂O₃The particle filling enables the energy efficiency ratio of a non-filling system to be respectively higher by 76.80 percent and 115.14 percent, and the gamma-Al₂O₃Made of particlesThe energy efficiency is higher for filling the medium.

SF (sulfur factor) explanation by combining density functional theory and chemical reaction kinetics₆Chemical reaction mechanism of gas under discharge degradation.

The energy change of the plasma discharge reaction is researched on the basis of the Density Functional Theory (DFT), and specifically, DMol in the Material Studio (MS)4.3 software of the molecular dynamics simulation software is used³And (5) module implementation.

To better simulate SF under dielectric barrier discharge₆The degradation reaction of the gas, the thermodynamic parameters are modified under defined conditions (i.e. in the case of a pressure of 1atm and a temperature of 298.15K). The modified calculation formula is as follows:

ΔE＝∑(E₁+H_1(298.15))-∑(E₀+H_0(298.15)) (1)

wherein E₁And E₀The single point energies, H, of the product and reactant at vacuum and absolute zero, respectively_1(298.15)And H_0(298.15)The corrected enthalpy values of the product and the reactant are respectively 1atm and 298.15K.

Research suggests that plasma treatment of gaseous pollutants is a rapid degradation treatment of pollutants through various electron collision reactions and chemical reactions, wherein the important role is that of active particles and pollutants.

In the invention, Ar is used as background gas and H₂O is an external gas, DBD degrades SF₆Can be generalized into three types: (1) electron collision reaction, i.e. electron and SF₆Ar and H₂Collision reaction of O; (2) collision reaction of high-energy particles, i.e. high-energy excited Ar particles with SF₆Or H₂Collision reaction of O; (3) free radical chemistry, e.g. OH groups with hypofluorosulfide SF_xThe reaction of (1). The energy change in the course of each chemical reaction is calculated, as shown in fig. 3, and the conditions required for each reaction to proceed are analyzed by the type of energy absorbed and released in the course, which is beneficial to calculating the possible reaction course in the degradation course. Treating SF at DBD₆In the course of the exhaust gas, SF is made₆Is changed into low-fluorine sulfideIs beneficial to the degradation process not only because the low-fluorine sulfide is more easily reacted with other active particles, but also because the low-fluorine sulfide is not easy to adsorb electrons so that charged particles in the space are reduced.

Establishment of dielectric barrier discharge degradation SF₆According to various basic physical coefficients, the parameters such as electron energy distribution characteristics, electron density, space-time distribution of other particle densities and the like of plasma discharge under different conditions are obtained through numerical calculation, and the DBD degradation SF is revealed₆Facilitates the realization of SF₆And (4) harmlessness of waste gas degradation.

When a substance such as a molecule, atom, ion, or radical of a substance is excited and transits from a high-energy state to a low-excitation state or a ground state, photons with different wavelengths are released, and a spectrum formed by the photons is called an emission spectrum. There are a large number of excited state active particles in the dielectric barrier discharge plasma, so the plasma discharge process can be analyzed by studying these particles. . From the measured emission spectrum, abundant plasma information can be obtained, such as excited state particle species and their concentration distribution during discharge (determined by the frequency of the emission spectrum and the intensity and intensity distribution of the spectrum), and plasma characteristic quantities such as electron density and ion temperature (determined by the line shape of the spectrum lines). The method mainly utilizes an emission spectrometry to determine the type and energy state of active particles, thereby researching the chemical behavior in plasma discharge.

The emission spectrum diagnosis system in the laboratory consists of a collimating lens, an optical fiber, a spectrometer and a computer. Light emitted by DBD plasma is collected by a collimating mirror and enters a spectrometer through an optical fiber, the spectrometer measures transmission light intensity of different wave bands, transmission light intensity data are guided into a computer through a USB data line and are processed and analyzed by special OceanView analysis software, and finally the emission spectrum of the DBD is obtained. The MX2500+ high-resolution three-channel spectrometer produced by American ocean optics company is selected, the grating is used as a light splitting element, the CCD array is used as a detector, the slit width is moderate, the response speed is high, and the change of a spectrum signal can be accurately measured.

The effect of different added gases (water, oxygen and ammonia) on the product was investigated. To illustrate the effect of water addition on the product. Measuring SF in the wave band of 300-800 nm₆/H₂Emission spectrogram of O/Ar dielectric barrier discharge system at 55V input voltage of plasma power supply, SF in reaction gas₆The initial concentration was 2%, the water gas concentration was 0.5%, and the integration time was set to 1 s. FIG. 4 is a graph of the measured emission spectra. The spectral line intensity is high due to the fact that the proportion of Ar in the reaction gas is as high as 97.5%. F atom type I line at 739.87nm, formed by SF₆The molecule is dissociated, and two specific processes are possible as follows:

SF₆→SF_x+(6-x)F (1.1)

F+e→F^*→F+hv (1.2)

or

SF₆+e→SF₅+F^*→F+hv (1.3)

At the same time, a weaker O line was also found at 777.36 nm. In order to analyze emission spectra of other particles during discharge, spectra in the ranges of 300 to 450nm and 450 to 680nm were amplified as shown in fig. 5(a) and 5(b), and a detailed plasma active component analysis was performed thereon. In the range of 300-450 nm, the main active particles detected are OH (about 308 nm) and N₂(308nm, 357.61nm and 380.46nm), O (362.77nm), F (385.14nm), Ar (402.47nm) and H (434.11 nm). In the range of 450-680 nm, main active particles detected are O (464.83nm), Ar (476.53nm and 488.80nm), S (550.91nm), OH (about 620 nm), Si (594.81nm) and H (656.33 nm). SF is detected at 450-510 nm₆The characteristic peak of the molecule is consistent with the results recorded in the literature in the prior art. The source of the OH and H radicals is the water vapor in the reaction gas, wherein OH is a group with strong oxidizing ability and plays an important role in promoting chemical reaction. Since the Si line is detected, SF is indicated₆Active F radical generated by dissociation and SiO in barrier dielectric quartz glass₂A reaction occurs, which is also referred to as an etching reaction in the semiconductor manufacturing industry. Thus, the O radical isThere may be two sources, SiO₂Etching and further decomposition of OH radicals. Absence of N in the reaction gas₂But N is detected in the emission spectrum₂Probably due to the presence of a micro-air layer between the electrode and the blocking medium. Due to the limitations of emission spectroscopy, only the above active particles are detected, but this does not mean SF₆/H₂Only these active particles are present in the O/Ar plasma.

SF₆The detection of products after the DBD degradation is not only a method for judging whether the DBD degradation technology reaches a harmless level, but also a main means for helping understanding the degradation mechanism. But SF₆The degradation product has complex components, is mostly an unusual gas, and has low content in degradation tail gas, so all SF gases are required to be treated₆Quantitative and qualitative analysis of the degradation products is very difficult. The current DBD degradation SF₆In the study of (1), SF is of great concern₆The change rule of the degradation rate is only a few to SF₆The partial degradation products of (2) were qualitatively analyzed. Since the difference of the components of the reactants is the main reason of the difference of the products in the system in the chemical reaction process, the invention adopts the SF of the Fourier infrared spectroscopy and gas chromatography-mass spectrometry combined method pair₆The degradation products were analyzed.

In this experiment, the SF is studied by adding gas and water₆The influence of degradation products. In the experiment, Ar is used as background gas, SF₆The initial concentration of the gas is 2%, the input voltage of a plasma power supply is 55V, the gas retention time is 2min, and the SF is analyzed and detected under the condition that the added gas is 0.5% of water gas₆Wherein the product is qualitatively analyzed by FTIR, SF₆FTIR detection of degradation products A10 cm Fourier Infrared Spectroscopy of Nicolet iS5 was used for secondary qualitative detection. And then carrying out quantitative analysis on the important product by GC/MS, wherein the model of the selected gas chromatography-mass spectrometer is Shimadzu PQ2010 Ultra.

FIG. 6 is an FTIR diagram of the degradation products in the presence of water vapor, and the degradation products corresponding to each characteristic peak are determined. As can be seen from FIG. 6, the plasma discharge was performed by DBDThe major degradation products after electrical treatment include SOF₂、SOF₄、SO₂F₂、SO₂、SiH₄、SiF₄、SF₄And S₂F₁₀Similar to the Lee et al study. Wherein, SF₄And S₂F₁₀Is a degraded primary product, directly from SF₆Decomposition yields, does not participate and H₂Reaction of O and its free radicals. SiH₄And SiF₄Again evidence of SiO in the quartz glass₂And (4) participating in the reaction.

In order to grasp the formation characteristics of the degradation products in detail, the SOF was also subjected to GC/MS₄、SO₂F₂、 SOF₂And SO₂The four products are quantitatively detected, the selectivity of the four products is calculated by adopting a formula (2),

in the formula, K represents the name of the product, C_KIn order to degrade the concentration of the products in the exhaust gas.

As shown in fig. 7. SOF₄The selectivity of the product is the highest and is more than 50 percent; secondly is SO₂The selectivity is also higher, above 25%, and SO₂F₂And SOF₂The yield of (a) is smaller. The following simulation will be used to analyze the formation path of each degradation product and the reason for its high and low selectivity.

The heat of reaction of the possible reaction paths under the action of high-energy electrons was calculated based on the addition of water vapor to the reaction gas, as shown in Table 1. From the calculation results, the reaction formulas (1.4) to (1.13) are all endothermic reactions in which the heat of reaction of the reaction formulas (1.6), (1.7), and (1.8) exceeds the upper limit of the energy range of most electrons, which relatively rarely occurs. At H₂Among the several direct decomposition routes of O molecule, the energy of the reaction formula (1.5) is the lowest, only 96.64kcal/mol, and H and OH are generated^—. Reaction formula (1.7) represents H₂O molecules adsorb electrons to form H₂O-toAdhesion reaction, which requires very little energy, only 32.66kcal/mol, indicates that it is easy to occur. And H₂The energy required for the O-reparation to H and OH-is 63.99kcal/mol, which is also lower than H₂Energy of direct decomposition of O. It is therefore presumed that most of H is present in the degradation reaction₂O molecules firstly form negative ions by absorbing electrons and then are decomposed into H and OH^—。

TABLE 1, H₂Decomposition process of O and reaction heat thereof

The water molecules in the plasma reactor exist in the form of gaseous water vapor for SF₆Plays a crucial role. According to the detection of the product, the DBD treats SF under the water-gas condition₆The final degradation product of (A) is mainly SOF₂、SOF₄、SO₂F₂、SO₂、SiH₄、SiF₄、SF₄And S₂F₁₀. Wherein, SF₄From SF₆Loss of two F atoms; s₂F₁₀It is produced by two reaction pathways:

SF₄+SF₆→S₂F₁₀ (1.4)

SF₅+SF₅→S₂F₁₀ (1.5)

at the same time calculate SOF₄、SO₂F₂、SOF₂、SO₂The heat of reaction or potential barrier for the path of formation of the isoproducts is shown in Table 2 (heat of reaction, numerical signs of reaction barrier +/-indicate endotherm/exotherm, respectively, and- -if no reaction barrier is present).

TABLE 2 route of formation of water gas degradation products

SOF₄Is obtained by a reaction ofThe reactions of the formulae (1.14) and (1.15), wherein the reaction of the formula (1.14) is an endothermic reaction, the absorbed energy is only 4.51kcal/mol, but the reaction must first take place with 43.45 kcal/mol, and the reaction of the formula (1.15) is an exothermic reaction. Considering the energy of electrons in DBD plasma, and SF₅And SF₄Is SF₆The 2 reactions, which are the main intermediates of the dissociation, are carried out in large amounts, so that SOF in the degradation products₄The selectivity is the highest. In the presence of water, SO₂F₂From SOF by reaction (1.18)₄And H₂O reaction is generated, which is an exothermic reaction having a reaction barrier of 67.97kcal/mol, and it can proceed in a large amount as well.

The reaction schemes (1.16) and (1.17) are the product SOF₂The main generation mode of (1). The reaction heat is negative, and energy with different sizes can be released in the reaction process, so that the thermodynamics are favorable. But due to SF₃And SF₂At SF₆The amount of SOF produced during the process of molecular dissociation is not so large₂The amount of (2) produced is also limited. Furthermore SOF₂SO is generated by reaction with water₂And HF, as shown in the reaction formula (1.19), further reducing SOF₂The yield of (2).

The reaction formula (1.19) is an exothermic reaction, and it must first absorb 101.54kcal/mol of energy, which may occur during the degradation of the DBD. If SO₂Formed only by this reaction, and its selectivity should be less than SO₂F₂. However, the test results show that SO is generated under the water-gas condition₂Has a selectivity higher than SO₂F₂Therefore, SO can be presumed₂Another generation route of (1) is

SO₂F₂+2H→SO₂+2HF (1.20)

In addition, in all of the reaction formulas (1.14) to (1.19), HF was produced, but no HF was detected in the degradation product for the following reasons:

SiO₂+4HF→SiF₄+2H₂O (1.21)

SiH₄is due to:

SiO₂+8H→SiH₄+2H₂O (1.22)

h in formulae (1.21) and (1.22)₂The generation of O further promotes the degradation reaction process.

The analysis by the method shows that the main degradation product under the conditions of water and oxygen is SOF₄、SO₂F₂、 SO₂. The main degradation product under the ammonia condition is NH₃HF、NH₄HF₂、SO₂S, its decomposition products tend to be nontoxic, while NH₃HF、NH₄HF₂And sulfur simple substance can be attached to the surface of the glass tube, so that the pipeline is easy to block, and the continuous degradation is not facilitated. Summarizes SF₆The gas molecules participate in the generation of degradation products and active particles under the participation of different external gases, and the SF is presumed to be₆Possible decomposition reaction pathways; then, the product under the condition of discharging of the glass bead filled medium is analyzed, and the alkaline solution can absorb most of the acid gas after being washed by the alkaline solution, and only part of SO is left₂F₂The gas remains in the tail gas. In this case, the tail gas is subjected to an adsorption treatment using adsorbent particles of the KDHF03A type, which have been proven for SO in laboratory research and industrial applications₂F₂Has good adsorption effect, the adsorption performance is 0.63mol/kg, the specific surface area is 450m²/g。

According to the optimized condition parameters and the mechanism analysis after decomposition, the developed dielectric barrier discharge degradation SF₆The degradation rate of the waste gas device reaches more than 96 percent, and the gas filtered by the KDHF03A adsorption box added at the tail gas does not contain acidic gas and toxic gas, and the main residual Ar gas is non-toxic and harmless to human bodies and does not influence the environment. Acid gas generated in the degradation process and Ca (OH) in a lye tank₂Reaction to form salts, SO₂F₂Absorbed by the adsorbent particles and attached to the surface of the adsorbent particles, and the alkali liquor and the adsorbent particles are replaced and recycled. The experimental results show that for SF₆The waste gas is recycled, the model machine can effectively decompose the waste gas, and the decomposed products can be absorbed and adsorbed in a targeted manner, so that the discharged waste gas is ensured not to have toxicity or influence on the environmentThereby achieving the purpose of harmless degradation.

The above description is only an embodiment of the present invention, but the scope of the present invention is not limited thereto, and any person skilled in the art can easily conceive of changes or substitutions within the technical scope of the present invention, and therefore, the scope of the present invention should be determined by the scope of the claims.

Claims

1. A method for confirming high-efficiency harmless degradation of SF6 waste gas by dielectric barrier discharge is characterized by comprising the following steps: the method comprises the following steps:

(4) by using a controlled variable method, SF influencing dielectric barrier discharge decomposition is changed₆Are contributing to SF₆The forward decomposition experimental study shows that all factors comprise background gas, reduced field intensity, gas flow, different additional gases, external medium of the reactor and different filling media, the experimental rule is summarized, and decomposed SF is obtained₆The optimum conditions of (2): degrading SF by dielectric barrier discharge built₆On the experimental platform of (2), a large amount of SF is carried out₆Degradation experiment to obtain SF under the action of dielectric barrier discharge₆Analyzing the degradation rules of experimental parameters under different background gases, reduced field strengths, gas flow rates, and degradation rules of external gases and environmental media to obtain the optimal background gas type, reduced field strengths in the discharge area of the reactor, reaction gas flow rates, external gas types, DBD reactor placement environment and filling media;

(5) bonding densityFunctional theory and chemical reaction kinetics analysis of SF₆Chemical reaction mechanism of gas under discharge degradation:

ΔE＝∑(E₁+H_1(298.15))-∑(E₀+H_0(298.15)) (1)

2. The method for confirming efficient harmless degradation of SF6 waste gas by dielectric barrier discharge as claimed in claim 1, wherein: the method for obtaining the discharge parameters by solving the Boltzmann equation by using the BOLSIG + computer program package comprises the following steps:

and thirdly, calculating plasma discharge parameters under different conditions, and directly outputting the obtained result in a data file format.

3. The method for confirming efficient harmless degradation of SF6 waste gas by dielectric barrier discharge as claimed in claim 1, wherein: dielectric barrier discharge degradation SF₆The experimental platform comprises a gas distribution system, a DBD reactor and a power supply system, wherein a gas outlet of the gas distribution system is connected to a gas inlet of the DBD reactor, and the DBD reactor is connected with the power supply system.

4. The method for confirming efficient harmless degradation of SF6 waste gas by dielectric barrier discharge as claimed in claim 1, wherein: dielectric barrier discharge degradation SF₆The test platform of (a) is also connected to an analytical detection system.

5. The method for confirming efficient harmless degradation of SF6 waste gas by dielectric barrier discharge as claimed in claim 4, wherein: the analysis detection system comprises an electrical parameter detection system, a chemical parameter detection system and an optical parameter detection system.

6. The method for confirming efficient harmless degradation of SF6 waste gas by dielectric barrier discharge as claimed in claim 4, wherein: the analysis and detection system comprises an oscilloscope, a gas chromatograph, a Fourier infrared spectrum analyzer, a gas chromatograph/mass spectrometer and a spectrometer.

7. The method for confirming efficient harmless degradation of SF6 waste gas by dielectric barrier discharge as claimed in claim 3, wherein: the gas distribution system comprises a plurality of standard gas distribution bottles and a gas distribution instrument, wherein the plurality of standard gas distribution bottles are connected to the gas distribution instrument, and the gas distribution instrument is connected to the DBD reactor; the standard gas distribution cylinder is Ar gas cylinder or SF gas cylinder₆Gas cylinder and O₂A gas cylinder.

8. The method for confirming efficient harmless degradation of SF6 waste gas by dielectric barrier discharge as claimed in claim 1, wherein: the gas outlet of the DBD reactor is also sequentially connected with an alkaline liquid box and a KDHF03A adsorption box.