Combustible waste gas treatment method

Abstract

The invention relates to the technical field of low-temperature plasma, and discloses a combustible waste gas treatment method. The method comprises the steps that combustible waste gas and rare gas are mixed, the obtained mixed gas is injected into a plasma treatment device from a gas inlet to be treated, one of the outermost plasma reaction tube and the innermost plasma reaction tube in the more than two plasma reaction tubes (4) is provided with a gas inlet, and the other one of the outermost plasma reaction tube and the innermost plasma reaction tube is provided with a gas outlet. The other plasma reaction tube is provided with a gas outlet, and two adjacent plasma reaction tubes are communicated with each other; and in each plasma reaction tube, the mixed gas enters the plasma reaction tube from one end, and enters another plasma reaction tube adjacent to the plasma reaction tube from the other end or is discharged. According to the technical scheme, the safety of the plasma reaction is realized, and the VOCs degradation performance of the plasma is improved.

Description

Technical Field

[0001] This invention relates to the field of low-temperature plasma technology, and more specifically to a method for treating combustible waste gas. Background Technology

[0002] Low-temperature plasma technology is a technique that uses a high-voltage electric field to ionize a gas, generating highly chemically active particles (including electrons, positive and negative ions, and neutral particles). These particles participate in chemical reactions to achieve specific functions, and the technology has broad application prospects. Examples include plasma sterilization, plasma material surface modification, and the treatment of toxic and harmful gases. Among these, volatile organic compounds (VOCs) are a significant category of pollutants. The dual-medium barrier low-temperature plasma reactors commonly used in industry operate at an energy level of 5-20 mJ, far exceeding the ignition energy of major VOCs. When the concentration reaches the lower explosive limit in air, an explosion can occur, posing a safety hazard. Therefore, the key issue in promoting the application of dual-medium barrier low-temperature plasma technology for treating this type of gas is how to balance safety risks and treatment efficiency, i.e., how to safely and efficiently achieve the harmless treatment of combustible waste gases.

[0003] To address safety hazards, researchers have developed accurate and rapid-response monitoring systems for total hydrocarbon concentration in waste gas. These systems control VOCs entering the plasma reactor to levels well below their explosive limits, as demonstrated in patent applications CN106918637B, CN107064281B, and CN107024377B. Furthermore, by optimizing the plasma device's process flow, high-concentration waste gas can be rapidly diluted, as illustrated in patent applications CN108970346B and CN109308042B. However, while optimizing the safety control system based on the total hydrocarbon monitoring system is an effective measure to reduce VOCs combustion and explosion accidents, its effectiveness is limited by the operator's ability to perform standardized operations, preventing it from fundamentally eliminating safety risks.

[0004] To improve the treatment efficiency of VOCs, low-temperature plasma has a high degradation efficiency for most VOCs, such as alkenes, alkynes, aromatic hydrocarbons, aldehydes, alcohols, and acids; however, its efficiency is very low for VOCs such as ketones and small molecule alkanes. Researchers mainly use the method of embedding catalysts in the discharge zone. The active particles in the plasma generate more reactive active centers on the catalyst surface. On the one hand, VOCs are adsorbed on the catalyst surface, prolonging the reaction time with the active particles; on the other hand, the reaction rate is faster, improving the degradation efficiency and mineralization efficiency of VOCs, as shown in patent applications CN103638761B, CN103657403B, and CN105080302A. However, embedding catalysts also increases the operating energy consumption of the device, and the use and regeneration of catalysts also increase operating costs. Patent application CN104069721B discloses a variable-diameter dielectric barrier reactor for treating volatile organic pollutants; the reactor consists of an outer electrode, an inner electrode, and inner and outer discharge spaces formed by inner and outer dielectric layers. Although the invention improves the conversion rate and mineralization rate, it cannot extend the discharge area and cannot improve the treatment effect of combustible waste gas while ensuring safety.

[0005] Therefore, there is an urgent need to develop a method for treating combustible waste gas that can safely and efficiently achieve the harmless treatment of combustible waste gas, while reducing the operating energy consumption of plasma devices and lowering the operating cost of waste gas treatment systems. Summary of the Invention

[0006] The purpose of this invention is to overcome the problems of safety risks and difficulty in balancing treatment efficiency in existing technologies for volatile organic gas (VOC) treatment, as well as high energy consumption and high cost of equipment operation. This invention provides a method for treating combustible waste gas by incorporating a high volume concentration of rare gases into the organic waste gas. This not only reduces the discharge voltage and saves energy, but also lowers the oxygen concentration in the discharge space to below 6%, achieving intrinsic safety in the plasma reaction process. In the plasma treatment device of this invention, multiple cavities (i.e., multiple plasma reaction tubes) are coaxially arranged. A certain proportion of mixed gas generates an extended discharge space during the discharge process, significantly extending the discharge space and increasing the discharge intensity, effectively improving plasma degradation efficiency. This invention simultaneously achieves the dual enhancement of intrinsic safety in the plasma reaction process and improved performance in plasma degradation of VOCs.

[0007] To achieve the aforementioned objectives, this invention provides a method for treating combustible waste gas. The method includes: mixing the combustible waste gas with a rare gas, and then injecting the resulting mixed gas into a plasma treatment device through an inlet for treatment. The plasma treatment device includes a high-voltage electrode, a ground electrode, and two or more plasma reaction tubes arranged coaxially. The high-voltage electrode is arranged along the central axis of the innermost plasma reaction tube, and the ground electrode is arranged along the outer wall of the outermost plasma reaction tube. The ratio of the gap between the inner and outer plasma reaction tubes is 0.3-0.8:1, preferably 0.4-0.6:1. In the two or more plasma reaction tubes, one of the outermost and innermost plasma reaction tubes is provided with an inlet, and the other with an outlet. Adjacent plasma reaction tubes are interconnected. In each plasma reaction tube, the mixed gas enters from one end and enters or exits from the other end into another plasma reaction tube adjacent to it.

[0008] Preferably, the number of plasma reaction tubes (4) is 2, and the air inlet and air outlet are located on the same side of the plasma reaction tubes (4).

[0009] Preferably, the gap between the inner plasma reaction tubes is less than 20 mm.

[0010] Preferably, the gap between the outer plasma reaction tubes is less than 40 mm.

[0011] Preferably, two adjacent plasma reaction tubes (4) are connected by a vent (3).

[0012] Preferably, the high-voltage electrode (1) is a metal rod; or the high-voltage electrode (1) is a metal tube; or the high-voltage electrode (1) includes an insulating dielectric tube and conductive metal powder filled in the insulating dielectric tube; or the high-voltage electrode (1) includes an insulating dielectric tube and a conductive metal rod or conductive metal tube embedded in the insulating dielectric tube; wherein the insulating dielectric tube is made of quartz, ceramic, corundum or polytetrafluoroethylene.

[0013] Preferably, the ground electrode (2) is a high-temperature resistant conductive metal.

[0014] Preferably, the conductivity of the ground electrode (2) at 25°C is 10. 5 -10 8 S / m.

[0015] Preferably, the plasma reaction tube (4) is an insulating dielectric tube made of any one of the following materials: quartz, ceramic, corundum, or polytetrafluoroethylene.

[0016] Preferably, the wall thickness of the plasma reaction tube (4) is no more than 5 mm.

[0017] Preferably, the rare gas accounts for more than 70% of the volume of the mixed gas, and more preferably 80-95%.

[0018] Preferably, the volume percentage of combustible components in the combustible waste gas is less than 40%, and more preferably 0.1-5%.

[0019] Compared with the prior art, the technical solution of the present invention has the following advantages:

[0020] (1) According to the plasma treatment device of the present invention, multiple plasma discharge zones can be formed in the same plasma reactor by coaxially arranging multiple cavities (i.e. multiple plasma reaction tubes), thereby extending the residence time of combustible waste gas in the plasma discharge zone. This not only improves the VOCs degradation performance of the plasma reactor, but also significantly reduces energy consumption.

[0021] (2) According to the method for treating combustible waste gas of the present invention, the combustible waste gas is diluted by rare gas (especially the volume ratio of rare gas in the mixed gas is more than 70%). On the one hand, the oxygen concentration in the combustible gas can be significantly reduced, and the plasma degradation of combustible VOCs can be made inherently safe. On the other hand, since rare gas is more easily ionized than air, a more uniform and stable discharge space can be obtained with less discharge power, which can significantly reduce energy consumption.

[0022] (3) According to the method for treating combustible waste gas of the present invention, depending on the difficulty of plasma treatment of combustible VOCs waste gas, a higher degradation performance can be obtained by adjusting the mixing ratio of rare gases and the gas inlet method of the inner and outer reaction tubes.

[0023] The technical solution of this invention can be applied to industries that emit organic waste gas, such as petrochemicals, spraying, printing and dyeing, municipal wastewater treatment, and pharmaceuticals. The plasma treatment device of this invention has a low discharge initiation voltage and, through the coaxial arrangement of multiple cavities (i.e., multiple plasma reaction tubes), can achieve high-throughput treatment of combustible VOCs waste gas, making it suitable for the treatment of scattered, distributed pollution sources. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the plasma processing device described in this invention;

[0025] Figure 2 This is a schematic diagram of a discharge state of the plasma processing device described in this invention.

[0026] Figure 3 This is a schematic diagram of another discharge state of the plasma processing device described in this invention;

[0027] Figure 4 This is a schematic diagram of another discharge state of the plasma processing device described in this invention.

[0028] Explanation of reference numerals in the attached figures

[0029] 1. High-voltage electrode; 2. Ground electrode; 3. Pore; 4. Plasma reaction tube; 5. Plasma discharge zone. Detailed Implementation

[0030] The following provides a detailed description of specific embodiments of the present invention. It should be understood that the specific embodiments described herein are for illustrative and explanatory purposes only and are not intended to limit the scope of the invention.

[0031] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0032] The method for treating combustible waste gas according to the present invention includes: mixing combustible waste gas with a rare gas, and then injecting the resulting mixed gas into a plasma treatment device through an inlet for treatment, wherein, as... Figure 1 As shown, the plasma processing device includes a high-voltage electrode 1, a ground electrode 2, and two or more plasma reaction tubes 4 arranged coaxially. The high-voltage electrode 1 is arranged along the central axis of the innermost plasma reaction tube 4, and the ground electrode 2 is arranged along the outer wall of the outermost plasma reaction tube. Among the two or more plasma reaction tubes 4, one of the outermost plasma reaction tube and the innermost plasma reaction tube is provided with an inlet, and the other is provided with an outlet. Adjacent plasma reaction tubes are interconnected. In each plasma reaction tube, the mixed gas enters the plasma reaction tube from one end and enters or exits from the other end into another plasma reaction tube adjacent to the plasma reaction tube.

[0033] According to the method described in this invention, by diluting the combustible waste gas with rare gas and making the volume ratio of rare gas in the mixed gas exceed 70%, the oxygen concentration in the mixed gas can be reduced to below 6%, which is far below the minimum oxygen concentration required for the explosion of most combustible components, thus achieving intrinsic safety in the plasma degradation of combustible components process; moreover, it improves the VOCs degradation performance of the plasma reactor and significantly reduces energy consumption.

[0034] In the plasma treatment device described in this invention, two or more plasma reaction tubes 4 are coaxially arranged, and there are gaps between adjacent plasma reaction tubes, thereby forming multiple cavities. Under operating conditions (i.e., when high voltage is applied), these cavities can form multiple plasma discharge zones. Moreover, by connecting these cavities in series from the inside to the outside (or from the outside to the inside), the residence time of combustible waste gas in the plasma discharge zone can be extended. This not only improves the VOCs degradation performance of the plasma reactor but also significantly reduces energy consumption.

[0035] In the plasma treatment device described in this invention, the number of plasma reaction tubes 4 can be two or more, specifically, two, three, four, or more. In practical applications, the more plasma reaction tubes 4 there are, the better the VOCs degradation performance of the plasma treatment device, but at the same time, the difficulty of voltage control and the design cost of the device are also higher. Considering both the treatment effect and cost of the plasma treatment device, the number of plasma reaction tubes 4 is preferably two. When there are two plasma reaction tubes 4, the plasma reaction tube located on the inner side is called the inner reaction tube, and the plasma reaction tube located on the outer side is called the outer reaction tube. The inlet and outlet are respectively located on the same side of the inner and outer reaction tubes. In operation, the mixed gas enters one reaction tube (such as the inner reaction tube) from the inlet, undergoes plasma treatment in the reaction tube, and then enters another reaction tube (such as the outer reaction tube) from the opposite end to the inlet. Plasma treatment continues in the other reaction tube, and the treated gas is discharged through the outlet.

[0036] In some embodiments, when there are three plasma reaction tubes 4, the air inlet can be located at one end of the innermost plasma reaction tube or the outermost plasma reaction tube, and the air outlet is correspondingly located at one end of the outermost plasma reaction tube or the innermost plasma reaction tube. In one example, there are three plasma reaction tubes 4, with the air inlet located at one end of the innermost plasma reaction tube and the air outlet located at one end of the outermost plasma reaction tube. The air inlet and air outlet are respectively located on both sides of the plasma processing device. In operation, the mixed gas enters the innermost plasma reaction tube through the air inlet and undergoes plasma processing. Then, the processed gas enters the middle layer plasma reaction tube from the other end of the innermost plasma reaction tube opposite to the air inlet and continues to undergo plasma processing. The mixed gas flows through the entire middle layer plasma reaction tube, and then enters the outermost plasma reaction tube from the other end opposite to the air inlet and continues to undergo plasma processing. The mixed gas flows through the entire outermost plasma reaction tube and then exits from the air outlet.

[0037] In the plasma processing apparatus of the present invention, two adjacent plasma reaction tubes 4 can be connected by a vent 3. The vent 3 is formed on the tube wall between two adjacent cavities.

[0038] In the plasma treatment apparatus of the present invention, gaps exist between adjacent plasma reaction tubes, thereby forming cavities. Preferably, the gaps between the plasma reaction tubes gradually increase from the inside to the outside. More preferably, the ratio of the gap between the inner and outer plasma reaction tubes is 0.3-0.8:1, more preferably 0.3-0.7:1, and even more preferably 0.4-0.6:1. In this preferred embodiment, the plasma treatment apparatus can achieve better VOCs degradation performance.

[0039] In the plasma processing apparatus of the present invention, when the number of plasma reaction tubes 4 is two, the gap between the inner reaction tubes can be less than 20 mm, preferably 1-18 mm, more preferably 3-15 mm, and even more preferably 4.5-12 mm; the gap between the outer reaction tubes can be less than 40 mm, preferably 10-30 mm, more preferably 13-25 mm, and even more preferably 15-20 mm.

[0040] In the plasma processing apparatus of this invention, the high-voltage electrode 1 can be connected to a high-voltage power supply; the voltage of the high-voltage power supply can be 25-36kV, preferably 30-35kV. The ground electrode 2 can be grounded. A potential difference can be formed between the high-voltage electrode 1 and the ground electrode 2. Both the high-voltage electrode 1 and the ground electrode 2 can be made of high-temperature resistant conductive metal. In a preferred embodiment, the conductivity of both the high-voltage electrode 1 and the ground electrode 2 at 25°C is 10. 5 -10 8 S / m.

[0041] In the plasma processing apparatus of the present invention, there is no particular limitation on the shape of the high-voltage electrode 1, and it can be an electrode of various shapes conventionally used in the art. In the present invention, preferably, the high-voltage electrode 1 is tubular or rod-shaped.

[0042] In some embodiments, when the high-voltage electrode 1 is rod-shaped, it can be a metal rod. The metal rod has a conductivity of 10⁻⁶ at 25°C. 5 -10 8 S / m.

[0043] In other embodiments, when the high-voltage electrode 1 is tubular, the high-voltage electrode 1 can be a metal tube. The outer diameter of the metal tube can be 1-10 mm, preferably 3-6 mm; the inner diameter of the metal tube can be 1-8 mm, preferably 1-4 mm.

[0044] In other embodiments, when the high-voltage electrode 1 is tubular, it may include an insulating dielectric tube and conductive metal powder filled within the insulating dielectric tube. The insulating dielectric tube may be made of quartz, ceramic, corundum, or polytetrafluoroethylene, and the conductive metal powder may be at least one of iron, copper, or magnesium. Preferably, the outer diameter of the high-voltage electrode 1 is 3-5 mm, and the inner diameter of the tubular high-voltage electrode 1 is 1.5-2.5 mm. In one specific embodiment of the invention, the high-voltage electrode 1 includes a quartz tube and iron powder filled within it. Those skilled in the art may also select other conductive metal powders to fill the insulating dielectric tube as the high-voltage electrode 1 as needed.

[0045] In other embodiments, when the high-voltage electrode 1 is tubular, the high-voltage electrode 1 may include an insulating dielectric tube and a conductive metal rod or conductive metal tube embedded within the insulating dielectric tube; wherein, the insulating dielectric tube may be made of quartz, ceramic, corundum, or polytetrafluoroethylene. In a specific embodiment of the present invention, the high-voltage electrode 1 includes a quartz tube and a conductive metal tube filled within the quartz tube.

[0046] In some embodiments, the ground electrode 2 is a conductive metal mesh or a conductive metal sheet. In one specific embodiment of the present invention, the ground electrode 2 is a 306 stainless steel mesh.

[0047] In the plasma processing apparatus of the present invention, the plasma reaction tube 4 can be an insulating dielectric tube made of any one of the following materials: quartz, ceramic, corundum, or polytetrafluoroethylene. The wall thickness of the plasma reaction tube 4 can be no more than 5 mm, preferably 0.5-2 mm. When the wall thickness of each plasma reaction tube 4 is the same, the wall thickness of the plasma reaction tube 4 is preferably 0.5-2 mm. When the wall thickness of each plasma reaction tube 4 is different, the wall thickness of the plasma reaction tube gradually increases from the inside to the outside. In a specific embodiment, when the number of plasma reaction tubes 4 is two, the plasma reaction tube 4 is a quartz glass tube, the wall thickness of the inner plasma reaction tube is 0.5-1.2 mm, and the wall thickness of the outer plasma reaction tube is 1-1.5 mm.

[0048] In the plasma treatment device of the present invention, in order to ensure VOCs degradation performance while reducing design costs, the ratio of the length of the ground electrode 2 to the length of the plasma reaction tube 4 is preferably 0.2-0.9, more preferably 0.3-0.6.

[0049] In the method described in this invention, the volume percentage of the rare gas in the mixed gas is preferably 70% or more, more preferably 75% or more, further preferably 80% or more, and even more preferably 80-95%. Specifically, for example, it can be 80%, 82%, 85%, 87%, 90%, 93%, or 95%. In this preferred case, the intrinsic safety of the plasma degradation process of combustible VOCs can be ensured, while significantly reducing energy consumption.

[0050] In the method described in this invention, the rare gas can be at least one selected from argon, neon, helium, krypton, and xenon, preferably argon. In this invention, the purity of the rare gas can be 99.9% or higher, preferably 99.9-99.999 wt%.

[0051] In the method described in this invention, the combustible waste gas may contain combustible components and air. The main components of the air are nitrogen and oxygen. The volume percentage of oxygen in the combustible waste gas is generally around 20%. The volume percentage of combustible components in the combustible waste gas can be below 40%, preferably 0.1-5%. In this preferred case, by controlling the content of oxygen and combustible components, the intrinsic safety of the plasma degradation process of combustible VOCs can be ensured.

[0052] In the method described in this invention, in order to obtain higher VOCs degradation performance, the flow rate of the mixed gas in the plasma treatment device described in this invention is preferably 0.5-3 L / min, more preferably 0.8-1.5 L / min.

[0053] In the method described in this invention, when a high voltage is applied to the high voltage electrode 1, different plasma discharge zones 5 will be generated in the inner plasma reaction tube and the outer plasma reaction tube according to the ratio of the gap between the inner plasma reaction tube and the outer plasma reaction tube and the composition of the mixed gas.

[0054] In the method described in this invention, when no rare gas is added to the mixed gas, the discharge state of the inner and outer plasma reaction tubes is limited to the area covered by the high-voltage electrode, such as... Figure 2 As shown.

[0055] In the method described in this invention, when the gap ratio between the inner and outer plasma reaction tubes is 0.3-0.5, and combustible waste gas is mixed with rare gas, the plasma discharge region 5 of the outer plasma reaction tube is mainly concentrated in the inner plasma reaction tube. Figure 3 As shown.

[0056] In the method described in this invention, when the gap ratio between the inner and outer plasma reaction tubes is 0.5-0.8, and the volume of the rare gas accounts for 85-95% of the mixed gas, the plasma discharge region 5 of the outer plasma reaction tube is mainly concentrated in the inner plasma reaction tube and the trapezoidal plasma discharge region 5 of the outer plasma reaction tube, such as... Figure 4 As shown.

[0057] In the method described in this invention, when the gap ratio between the inner and outer plasma reaction tubes is 0.5-0.8, and the volume of the rare gas accounts for 70-85% of the mixed gas, the plasma discharge region 5 of the outer plasma reaction tube is mainly concentrated in the inner plasma reaction tube, such as... Figure 3 As shown.

[0058] In the method described in this invention, for recalcitrant or highly concentrated combustible waste gas, the recalcitrant or highly concentrated combustible waste gas is mixed with a rare gas. The resulting mixed gas enters from one end of the outermost plasma reaction tube and from the other end into another plasma reaction tube adjacent to it. The mixed gas exits through the outlet at the other end of the innermost plasma reaction tube. The recalcitrant combustible waste gas contains benzene compounds and / or small molecule alkanes. The highly concentrated combustible waste gas has a combustible component volume percentage of 1-5%. When the volume percentage of the rare gas in the mixed gas of recalcitrant or highly concentrated combustible waste gas and rare gas is 90-95%, a plasma discharge zone 5 is formed in both the inner and outer plasma reaction tubes.

[0059] In the method described in this invention, for easily degradable or low-concentration combustible waste gas, the easily degradable or low-concentration combustible waste gas is mixed with a rare gas, and the resulting mixed gas enters from one end of the innermost plasma reaction tube and from the other end into another plasma reaction tube adjacent to it. The mixed gas is discharged from the outlet at the other end of the outermost plasma reaction tube. The easily degradable combustible waste gas contains at least one of alcohols, aldehydes, and olefins. The low-concentration combustible waste gas is defined as a combustible component comprising 0.1-1% of the volume of the combustible waste gas. When the volume percentage of the rare gas in the mixed gas of easily degradable or low-concentration combustible waste gas and rare gas is 80-90%, a plasma discharge zone 5 is formed in the innermost plasma reaction tube.

[0060] In some embodiments, the method for treating combustible waste gas according to the present invention is carried out in the plasma treatment apparatus described above, and the method includes:

[0061] Combustible waste gas is mixed with a rare gas, and the resulting mixture is introduced into a reaction tube (e.g., an inner reaction tube) at a flow rate of 0.5-3 L / min. After plasma treatment within this reaction tube, the mixture enters another reaction tube (e.g., an outer reaction tube) from the opposite end of the inlet. Further plasma treatment is performed in this outer reaction tube, and the treated gas is discharged through an outlet. The combustible waste gas contains combustible components and air. The volume percentage of the combustible components in the combustible waste gas is less than 40%, and the volume percentage of oxygen is generally around 20%. The gap ratio between the inner and outer reaction tubes is 0.3-0.5. The plasma discharge region 5 of the outer reaction tube is mainly concentrated in the inner reaction tube. Figure 3 As shown.

[0062] In other embodiments, the method for treating combustible waste gas according to the present invention is carried out in the plasma treatment device described above, wherein the number of plasma reaction tubes 4 in the device is two, and the method includes:

[0063] Combustible waste gas is mixed with a rare gas, and the resulting mixture is introduced into a reaction tube (e.g., an inner reaction tube) at a flow rate of 0.5-3 L / min. After plasma treatment within this reaction tube, the mixture enters another reaction tube (e.g., an outer reaction tube) from the opposite end of the inlet. Further plasma treatment is performed in this outer reaction tube, and the treated gas is discharged through an outlet. The combustible waste gas contains combustible components and air. The volume percentage of the combustible components in the combustible waste gas is 0.1-5%, and the oxygen volume percentage is generally around 20%. The gap ratio between the inner and outer reaction tubes is 0.5-0.8. When the volume percentage of the rare gas in the mixture is 70-85%, the outer reaction tube mainly concentrates its volume in the inner reaction tube. Figure 3 As shown.

[0064] In other embodiments, the method for treating combustible waste gas according to the present invention is carried out in the plasma treatment device described above, wherein the number of plasma reaction tubes 4 in the device is two, and the method includes:

[0065] Combustible waste gas is mixed with a rare gas, and the resulting mixed gas is introduced into a reaction tube (e.g., an inner reaction tube) from the inlet at a flow rate of 0.8-1.5 L / min. After plasma treatment within this reaction tube, the gas enters another reaction tube (e.g., an outer reaction tube) from the opposite end of the inlet. Plasma treatment continues in this outer reaction tube, and the treated gas is discharged through the outlet. The combustible waste gas contains combustible components and air. The volume percentage of the combustible components in the combustible waste gas is 0.1-5%, and the oxygen volume percentage is generally around 20%. The gap ratio between the inner and outer reaction tubes is 0.5-0.8. When the volume percentage of the rare gas in the mixed gas is 85-95%, the plasma discharge region 5 of the outer reaction tube is mainly concentrated in the trapezoidal plasma discharge regions 5 of the inner and outer reaction tubes. Figure 4 As shown.

[0066] In some embodiments, the method for treating combustible waste gas according to the present invention is carried out in the plasma treatment device described above, wherein the number of plasma reaction tubes 4 in the device is two, and the method includes:

[0067] A mixture of recalcitrant or highly concentrated combustible waste gas and a rare gas is introduced into a reaction tube (e.g., an inner reaction tube) at a flow rate of 0.5-3 L / min. After plasma treatment within this reaction tube, the gas enters another reaction tube (e.g., an outer reaction tube) from the opposite end of the inlet. Further plasma treatment is performed in this outer reaction tube, and the treated gas is discharged through an outlet. The combustible waste gas contains combustible components and air. The volume percentage of the combustible components in the combustible waste gas is less than 40%, and the volume percentage of oxygen in the combustible waste gas is more than 20%. The gap ratio between the inner and outer reaction tubes is 0.3-0.8. The recalcitrant combustible waste gas contains benzene compounds and / or small molecule alkanes. The highly concentrated combustible waste gas has a combustible component volume percentage of 1-5%. In a mixture of combustible waste gas and rare gas with high concentration or low degradation, the volume percentage of the rare gas is 90-95%, and a plasma discharge zone 5 is formed in the inner and outer reaction tubes.

[0068] In other embodiments, the method for treating combustible waste gas according to the present invention is carried out in the plasma treatment device described above, wherein the number of plasma reaction tubes 4 in the device is two, and the method includes:

[0069] Easily degradable or low-concentration combustible waste gas is mixed with a rare gas. The resulting mixed gas is then introduced into a reaction tube (e.g., an inner reaction tube) at a flow rate of 0.5-3 L / min through an inlet. After plasma treatment within this reaction tube, the gas enters another reaction tube (e.g., an outer reaction tube) from the opposite end of the inlet. Further plasma treatment is performed in this outer reaction tube, and the treated gas is discharged through an outlet. The combustible waste gas contains combustible components and air. The volume percentage of the combustible components in the combustible waste gas is less than 40%, and the volume percentage of oxygen in the combustible waste gas is more than 20%. The gap ratio between the inner and outer reaction tubes is 0.3-0.8. The easily degradable combustible waste gas contains at least one of alcohols, aldehydes, and olefins. The low-concentration combustible waste gas refers to the combustible components comprising 0.1-1% of the combustible waste gas by volume. When the volume percentage of the rare gas in a mixture of easily degradable or low-concentration combustible waste gas and rare gas is 80-90%, a plasma discharge zone 5 is formed in the inner tube of the reaction.

[0070] The following examples further illustrate the method for treating combustible waste gas according to the present invention. These examples are implemented based on the technical solution of the present invention, providing detailed implementation methods and specific operating procedures; however, the scope of protection of the present invention is not limited to the following examples.

[0071] Unless otherwise specified, the experimental methods used in the following embodiments are conventional methods in the art. Unless otherwise specified, the experimental materials used in the following embodiments are commercially available.

[0072] The processes of the combustible waste gas treatment methods in Examples 1-8 and Comparative Example 1 are as follows: Figure 1 The plasma treatment device shown is implemented in a plasma treatment apparatus. Specifically, the apparatus includes a high-voltage electrode 1, a ground electrode 2, and two plasma reaction tubes 4 arranged coaxially. The high-voltage electrode 1 is arranged along the central axis of the inner reaction tube, and the ground electrode 2 is arranged along the outer wall of the outer reaction tube. One of the outer and inner reaction tubes has an inlet, and the other has an outlet. The inlet and outlet are located on the same side of the plasma reaction tubes 4, and the two plasma reaction tubes 4 are connected by a vent 3. The mixed gas enters one reaction tube (e.g., the inner reaction tube) through the inlet, undergoes plasma treatment within the reaction tube, and then enters the other reaction tube (e.g., the outer reaction tube) from the opposite end of the inlet. Plasma treatment continues in the other reaction tube, and the treated gas is discharged through the outlet. The high-voltage electrode 1 is connected to a high-voltage power supply and comprises a quartz tube filled with iron powder. The outer diameter of the high-voltage electrode 1 is 4 mm, and the inner diameter is 2 mm. The conductivity of both the high-voltage electrode 1 and the ground electrode 2 at 25°C is 10. 8S / m, the ground electrode 2 is a 306 stainless steel mesh with a length of 100mm, the ratio of the gap between the inner reaction tube and the gap between the outer reaction tube is 0.53:1, the gap between the inner reaction tube is 10mm, the gap between the outer reaction tube is 19mm, the plasma reaction tube 4 is an insulating dielectric tube made of quartz, the wall thickness of the plasma reaction tube 4 is 1mm, and the length of the plasma reaction tube 4 is 300mm.

[0073] Example 1

[0074] Diethylbenzene and air (with diethylbenzene comprising 1% of the combustible waste gas by volume) are passed into a rare gas mixture to obtain a 90% rare gas by volume. The mixture flows in from the outer plasma reaction tube at a flow rate of 1 L / min and out from the inner plasma reaction tube. The plasma discharge zone is as follows: Figure 4 As shown, when the driving power supply applies a voltage of 32kV, the degradation rate of diethylbenzene is 90%, and the mineralization rate is 85%.

[0075] Example 2

[0076] Diethylbenzene and air (with diethylbenzene comprising 1% of the combustible waste gas by volume) are passed into a rare gas mixture to obtain a 70% rare gas by volume. The mixture flows into the reactor from the outer plasma reaction tube at a flow rate of 1 L / min and exits from the inner plasma reaction tube. The plasma discharge zone is as follows: Figure 3 As shown, when a driving power supply applied a voltage of 32kV, the degradation rate of diethylbenzene was 74%, and the mineralization rate was 65%. Compared with Example 1, the volume percentage of rare gases in the mixed gas decreased, forming... Figure 3 When the discharge state is reached, the degradation effect of difficult-to-degrade combustible waste gas decreases.

[0077] Example 3

[0078] Ethylene and air (with ethylene comprising 4% of the combustible waste gas by volume) are passed through a rare gas mixture to obtain a 90% rare gas volume. The mixture flows into the reactor from the outer plasma reaction tube at a flow rate of 1 L / min and exits from the inner plasma reaction tube. The plasma discharge region is as follows: Figure 4 As shown, when the driving power supply applies a voltage of 32kV, the degradation rate of ethylene is 94% and the mineralization rate is 80%. The degradation effect of high-concentration combustible waste gas is better when it moves from the outer plasma reaction tube to the inner plasma reaction tube.

[0079] Example 4

[0080] Ethylene and air (with ethylene comprising 4% of the combustible waste gas by volume) are passed through a rare gas mixture to obtain a 90% rare gas volume. The mixture flows into the reactor from the inner plasma reaction tube at a flow rate of 1 L / min and exits from the outer plasma reaction tube. The plasma discharge region is as follows: Figure 4 As shown, when the driving power supply applies a voltage of 32kV, the degradation rate of ethylene is 85% and the mineralization rate is 58%. Compared with Example 3, the degradation effect of high-concentration combustible waste gas from the inner plasma reaction tube to the outer plasma reaction tube is poor.

[0081] Example 5

[0082] Ethylene and air (with ethylene comprising 0.5% of the combustible waste gas by volume) are passed through a rare gas mixture to obtain a 75% rare gas by volume. The mixture flows in from the inner plasma reaction tube at a flow rate of 1 L / min and out from the outer plasma reaction tube. The plasma discharge zone is as follows: Figure 3 As shown, when a driving power supply applies a voltage of 30kV, the degradation rate of ethylene is 98%, the mineralization rate is 90%, and the byproduct NO... x Not detected. Low-concentration combustible waste gas showed better degradation effects from the inner plasma reaction tube to the outer plasma reaction tube.

[0083] Example 6

[0084] Ethylene and air (with ethylene comprising 0.5% of the combustible waste gas by volume) are passed through a rare gas mixture to obtain a 95% rare gas volume mixture. The mixture flows in from the outer plasma reaction tube at a flow rate of 1 L / min and out from the inner plasma reaction tube. The plasma discharge region is as follows: Figure 4 As shown, when a driving power supply applies a voltage of 32kV, the degradation rate of ethylene is 90%, and the mineralization rate is 86%. Byproduct NO x The concentration was 688 ppm. Compared with Example 5, the degradation energy consumption of the low-concentration combustible waste gas from the outer plasma reaction tube to the inner plasma reaction tube was higher, and by-products were generated, causing secondary pollution.

[0085] Example 7

[0086] A mixture of diethylbenzene (1% by volume) and air is introduced into the reactor to obtain a rare gas mixture, which comprises 70% of the total volume. The mixture flows into the reactor from the outer plasma reaction tube at a flow rate of 0.8 L / min and exits from the inner plasma reaction tube. The plasma discharge zone is as follows: Figure 3 As shown, when the driving power supply applies a voltage of 30kV, the degradation rate of diethylbenzene is 71%, and the mineralization rate is 62%.

[0087] Example 8

[0088] Ethylene and air (4% by volume) are passed into a rare gas mixture to obtain a 95% rare gas volume ratio. The mixture flows into the reactor from the outer plasma reaction tube at a flow rate of 1.5 L / min and exits from the inner plasma reaction tube. The plasma discharge region is as follows: Figure 4 As shown, when the driving power supply applies a voltage of 35kV, the degradation rate of ethylene is 92% and the mineralization rate is 76%.

[0089] Comparative Example 1

[0090] Diethylbenzene and air (in which the volume percentage of diethylbenzene in the combustible waste gas is 1%) flowed into the outer plasma reaction tube at a flow rate of 1 L / min. When the maximum voltage applied by the driving power supply was about 36 kV, no plasma discharge light zone appeared.

[0091] The following comparisons of the combustible waste gas treatment methods in Examples 2-5 are as follows: Figure 1 The plasma treatment apparatus shown is implemented in a specific manner. Specifically, the apparatus includes a high-voltage electrode 1, a ground electrode 2, and two plasma reaction tubes 4 arranged coaxially. The high-voltage electrode 1 is positioned along the central axis of the inner reaction tube, and the ground electrode 2 is positioned along the outer wall of the outer reaction tube. One of the outer and inner reaction tubes has an inlet, and the other has an outlet. The inlet and outlet are located on the same side of each plasma reaction tube 4, and the two plasma reaction tubes 4 are connected by a vent 3. The mixed gas enters one reaction tube (e.g., the inner reaction tube) through the inlet, undergoes plasma treatment within the reaction tube, and then enters the other reaction tube (e.g., the outer reaction tube) from the opposite end of the inlet. Plasma treatment continues in the other reaction tube, and the treated gas is discharged through the outlet. The high-voltage electrode 1 is connected to a high-voltage power supply. The high-voltage electrode 1 is a metal tube with an outer diameter of 1.5 mm and an inner diameter of 0.5 mm. The conductivity of both the high-voltage electrode 1 and the ground electrode 2 at 25°C is 10. 5 S / m, the ground electrode 2 is a 306 stainless steel mesh with a length of 100mm, the ratio of the gap between the inner reaction tube and the gap between the outer reaction tube is 0.26:1, the gap between the inner reaction tube is 4.5mm, the gap between the outer reaction tube is 17mm, the plasma reaction tube 4 is an insulating dielectric tube made of quartz, the wall thickness of the inner reaction tube is 1mm, the wall thickness of the outer reaction tube is 1.5mm, and the length of the plasma reaction tube 4 is 300mm.

[0092] Comparative Example 2

[0093] Benzene and air (with benzene comprising 0.5% of the combustible exhaust gas by volume) are passed into a rare gas mixture to obtain a 90% rare gas by volume. The mixture flows in from the outer plasma reaction tube at a flow rate of 1 L / min and out from the inner plasma reaction tube. The plasma discharge zone is as follows: Figure 4 As shown, when a driving power supply applies a voltage of 32kV, the degradation rate of benzene is 80%, the mineralization rate is 70%, and the byproduct NO... x The concentration was 1480 ppm, causing secondary pollution.

[0094] Comparative Example 3

[0095] Benzene and air (with benzene accounting for 0.5% of the volume in the combustible waste gas) flowed into the outer plasma reaction tube at a flow rate of 1 L / min and flowed out from the inner plasma reaction tube. When the maximum voltage of the driving power supply used was 36 kV, no plasma discharge light zone appeared.

[0096] Comparative Example 4

[0097] Ethylene and air (with ethylene comprising 4% of the combustible waste gas by volume) are passed through a rare gas mixture to obtain a 90% rare gas volume. The mixture flows into the reactor from the inner plasma reaction tube at a flow rate of 1 L / min and exits from the outer plasma reaction tube. The plasma discharge region is as follows: Figure 4 As shown, when a driving power supply applies a voltage of 33kV, the degradation rate of ethylene is 83%, the mineralization rate is 51%, and the byproduct NO... x The concentration was 1506 ppm, causing secondary pollution.

[0098] Comparative Example 5

[0099] Ethylene and air (with ethylene accounting for 4% of the volume in the combustible waste gas) flowed into the inner plasma reaction tube at a flow rate of 1 L / min and flowed out from the outer plasma reaction tube. When the maximum voltage of the driving power supply used was 36 kV, no plasma discharge light zone appeared.

[0100] Example 9

[0101] The plasma processing apparatus used in this embodiment is the same as that used in Comparative Example 2, except that the ratio of the gap between the inner and outer reaction tubes is replaced by a ratio of 0.75:1 instead of 0.26:1. Specifically, the high-voltage electrode 1 is a metal tube with an outer diameter of 1.5 mm and an inner diameter of 0.5 mm. The conductivity of both the high-voltage electrode 1 and the ground electrode 2 at 25°C is 10. 5S / m, the ground electrode 2 is a 306 stainless steel mesh with a length of 100mm, the ratio of the gap between the inner reaction tube and the gap between the outer reaction tube is 0.75:1, the gap between the inner reaction tube is 6mm, the gap between the outer reaction tube is 8mm, the plasma reaction tube 4 is an insulating dielectric tube made of quartz, the wall thickness of the inner reaction tube is 1mm, the wall thickness of the outer reaction tube is 1mm, and the length of the plasma reaction tube 4 is 300mm.

[0102] Ethylene and air (with ethylene comprising 0.5% of the combustible waste gas by volume) are passed through a rare gas mixture to obtain a 75% rare gas by volume. The mixture flows in from the inner plasma reaction tube at a flow rate of 1 L / min and out from the outer plasma reaction tube. The plasma discharge zone is as follows: Figure 3 As shown, when a driving power supply applies a voltage of 30kV, the degradation rate of ethylene is 93%, the mineralization rate is 84%, and the byproduct NO... x Not detected.

[0103] Comparative Example 6

[0104] The plasma processing apparatus used in this comparative example is the same as the plasma processing apparatus used in Example 9.

[0105] Ethylene and air (with ethylene comprising 0.5% of the combustible waste gas by volume) flow into the inner plasma reaction tube at a flow rate of 1 L / min and out through the outer plasma reaction tube. The plasma discharge zone is as follows: Figure 3 As shown, no plasma discharge light region appeared when the maximum voltage of the driving power supply of 36kV was applied.

[0106] Comparative Example 7

[0107] The plasma processing apparatus used in this comparative example is the same as that used in Comparative Example 2, except that the ratio of the gap between the inner and outer reaction tubes is replaced by a ratio of 0.18:1 instead of 0.26:1. Specifically, the high-voltage electrode 1 is a metal tube with an outer diameter of 1.5 mm and an inner diameter of 0.5 mm. The conductivity of both the high-voltage electrode 1 and the ground electrode 2 at 25°C is 10. 5 S / m, the ground electrode 2 is a 306 stainless steel mesh with a length of 100mm, the ratio of the gap between the inner reaction tube and the gap between the outer reaction tube is 0.18:1, the gap between the inner reaction tube is 4.5mm, the gap between the outer reaction tube is 25mm, the plasma reaction tube 4 is an insulating dielectric tube made of quartz, the wall thickness of the inner reaction tube is 1mm, the wall thickness of the outer reaction tube is 1.5mm, and the length of the plasma reaction tube 4 is 300mm.

[0108] Ethylene and air (with ethylene comprising 0.5% of the combustible waste gas by volume) are passed through a rare gas mixture to obtain a 75% rare gas by volume. The mixture flows in from the inner plasma reaction tube at a flow rate of 1 L / min and out from the outer plasma reaction tube. The plasma discharge zone is as follows: Figure 3 As shown, when the driving power supply applies a voltage of 33kV, the degradation rate of ethylene is 55%, the mineralization rate is 36%, and the byproduct NO... x The concentration was 537 ppm, causing secondary pollution.

[0109] Comparative Example 8

[0110] The plasma processing apparatus used in this comparative example is the same as the plasma processing apparatus used in Comparative Example 5.

[0111] Ethylene and air (with ethylene comprising 0.5% of the combustible waste gas by volume) flow into the inner plasma reaction tube at a flow rate of 1 L / min and out through the outer plasma reaction tube. The plasma discharge zone is as follows: Figure 3 As shown, no plasma discharge light region appeared when the maximum voltage of the driving power supply of 36kV was applied.

[0112] The embodiments of the combustible waste gas treatment method described in this invention all have high degradation rates and low energy consumption under high degradation performance.

[0113] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A method for treating combustible waste gas, characterized in that, The method includes: mixing combustible waste gas with rare gas, and then injecting the resulting mixed gas into a plasma treatment device through an inlet for treatment. The plasma processing device includes a high-voltage electrode (1), a ground electrode (2), and two or more plasma reaction tubes (4) arranged coaxially. The high-voltage electrode (1) is arranged along the central axis of the innermost plasma reaction tube (4), and the ground electrode (2) is arranged along the outer wall of the outermost plasma reaction tube. The ratio of the gap between the inner plasma reaction tubes to the gap between the outer plasma reaction tubes is 0.3-0.8:1, preferably 0.4-0.6:

1. In the two or more plasma reaction tubes (4), one of the outermost plasma reaction tube and the innermost plasma reaction tube is provided with an air inlet, and the other is provided with an air outlet. The two adjacent plasma reaction tubes are interconnected. In each plasma reaction tube, the mixed gas enters the plasma reaction tube from one end and enters or exits from the other end into another plasma reaction tube adjacent to the plasma reaction tube.

2. The method according to claim 1, characterized in that, The number of plasma reaction tubes (4) is 2, and the air inlet and air outlet are located on the same side of the plasma reaction tubes (4).

3. The method according to claim 2, characterized in that, The gap between the inner plasma reaction tubes is less than 20 mm.

4. The method according to claim 2, characterized in that, The gap between the outer plasma reaction tubes is less than 40 mm.

5. The method according to any one of claims 1-4, characterized in that, The two adjacent plasma reaction tubes (4) are connected by a vent (3).

6. The method according to claim 1, characterized in that, The high-voltage electrode (1) is a metal rod; or The high-voltage electrode (1) is a metal tube; or The high-voltage electrode (1) comprises an insulating dielectric tube and conductive metal powder filled within the insulating dielectric tube; or The high-voltage electrode (1) includes an insulating dielectric tube and a conductive metal rod or conductive metal tube embedded in the insulating dielectric tube. The insulating dielectric tube is made of quartz, ceramic, corundum, or polytetrafluoroethylene.

7. The method according to claim 1, characterized in that, The ground electrode (2) is made of high-temperature resistant conductive metal.

8. The method according to claim 1 or 6, characterized in that, The conductivity of the ground electrode (2) at 25°C is 10. 5 -10 8 S / m.

9. The method according to any one of claims 1-8, characterized in that, The plasma reaction tube (4) is an insulating dielectric tube made of any one of the following materials: quartz, ceramic, corundum or polytetrafluoroethylene; Preferably, the wall thickness of the plasma reaction tube (4) is no more than 5 mm.

10. The method according to claim 1, characterized in that, In the mixed gas, the volume percentage of the rare gas is 70% or more, preferably 80-95%; Preferably, the volume percentage of combustible components in the combustible waste gas is less than 40%, and more preferably 0.1-5%.

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