Plasma device for improving gas conversion performance and gas reforming method

Abstract

The application provides a plasma device and a gas reforming method for improving gas conversion performance, the tail ends of three quartz tubes are communicated with each other, an outer electrode is attached to the outside of each quartz tube, the three outer electrodes are connected with each other through metal wires, an inner electrode is arranged in each quartz tube, an air outlet is arranged on the first quartz tube, a first air inlet and a second air inlet are arranged on the second quartz tube and the third quartz tube respectively, the first inner electrode is connected with high voltage, and the second inner electrode and the third inner electrode are grounded. The application utilizes dielectric barrier discharge plasma technology to form a two-section compact plasma reaction system, uses two-section discharge, makes the reaction gas change from a ground state molecule to an excited state molecule in the left and right end discharge areas, and makes the reaction gas in different energy levels, so that the gas reforming reaction is more likely to occur, the energy consumption is reduced, and these steps are integrated in the same reaction, the device volume is reduced, and the reaction conversion performance is improved.

Description

Technical Field

[0001] The present invention relates to improving gas conversion performance, and in particular to a plasma device and a gas reforming method for improving gas conversion performance. Background Art

[0002] Currently, the main methods for gas reforming reactions include thermal catalysis, electrochemistry, and plasma catalysis. While thermal catalysis offers a simple process, it suffers from high energy consumption and the high temperatures that can easily lead to catalyst sintering and deactivation. While electrochemical methods improve conversion efficiency, they also suffer from complex processes, high equipment costs, and poor economic efficiency. Plasma technology, on the other hand, utilizes the large number of high-energy charged particles and active particles contained in plasma to initiate a series of reactions with gas molecules, allowing reactions to proceed at room temperature and pressure.

[0003] Plasma is a non-equilibrium plasma generated at atmospheric pressure, with an overall temperature close to room temperature. Plasma contains a large number of active species, such as high-energy electrons, excited atoms, and free radicals. These active species can collide with the reactant gas, breaking the chemical bonds of the gas molecules and generating a series of reactions.

[0004] Glow discharge has low gas pressure, low power density and low gas conversion rate; corona discharge is weak, and the electric field strength and electron density are unevenly distributed, and the gas processing efficiency is greatly affected by the electrode structure.

[0005] Dielectric barrier discharge (DBD) involves inserting an insulating dielectric into the discharge space between two electrodes. The strong electric field ionizes and accelerates the gas molecules between the electrodes, ultimately creating an ionization channel that runs through the entire space. The insulating dielectric hinders the movement of charged particles toward the electrodes, preventing the discharge from transitioning to sparks or arcs. Its advantages include a wide pressure range, a wide range of discharge frequencies, a simple structure, and uniform and stable discharge. However, DBD requires a high-power power supply, resulting in unnecessary energy waste.

[0006] For example, the device for reducing carbon dioxide to prepare multi-carbon products by using a low-temperature plasma in series with an electrolytic cell as described in patent CN115466970A combines a plasma reactor with an electrolytic cell module, resulting in excessive energy input and excessive energy consumption.

[0007] For example, the array-type multi-needle coaxial high-efficiency low-temperature plasma reactor described in patent CN114832590B uses a flow monitor, an electric three-way ball valve, a guide ring, etc., which increases the complexity of the device and the operating cost.

[0008] For example, the multi-chamber plasma reaction generating device for treating malodorous gases described in patent CN216418877U utilizes guide plates to increase the gas flow path, but the reaction temperature also places higher requirements on the material and pressure resistance of the guide plates. Summary of the Invention

[0009] 1. Technical problems to be solved:

[0010] How to improve the gas reforming conversion performance?

[0011] 2. Technical solution:

[0012] To solve the above problems, the present invention provides a plasma device for improving gas conversion performance, comprising three quartz tubes, the tail ends of the three quartz tubes being internally connected, an external electrode wrapped and attached to the outside of each quartz tube, a first external electrode outside the first quartz tube, a second external electrode outside the second quartz tube, and a third external electrode outside the third quartz tube, the three external electrodes being connected to each other by metal wires, an internal electrode being provided in each quartz tube, an air outlet being provided on the first quartz tube, a first air inlet being provided on the second quartz tube, and a second air inlet being provided on the third quartz tube, respectively, the first internal electrode in the first quartz tube being connected to a high-voltage power supply, the second internal electrode in the second quartz tube, and the third internal electrode in the third quartz tube being grounded.

[0013] Each quartz tube is provided with a polytetrafluoroethylene tube for fixing the inner electrode in the quartz tube.

[0014] The first inner electrode is inserted into the first polytetrafluoroethylene tube, the second inner electrode is inserted into the second polytetrafluoroethylene tube, and the third inner electrode is inserted into the third polytetrafluoroethylene tube. Each inner electrode is coaxial with the corresponding polytetrafluoroethylene tube.

[0015] Each of the inner electrodes is a metal rod, a metal threaded tube or a metal mace.

[0016] The metal is one of stainless steel, copper and aluminum.

[0017] The three quartz tubes are arranged in a Y shape.

[0018] The intake gases of the first and second air inlets are any combination of CO2 and CH4, CO2 and H2, CH4 and O2, N2 and H2, and CH4 and H2O.

[0019] The present invention also provides a method for gas reforming using the plasma device for improving gas conversion performance, comprising the following steps:

[0020] Step S01: The first inner electrode is connected to high voltage, forming a strong electric field in the first quartz tube, thereby forming a first discharge region inside the first quartz tube where the first outer electrode is located. The electric field of the first discharge region is partially transmitted to the second discharge region inside the second quartz tube where the second outer electrode is located, and to the third discharge region inside the third quartz tube where the third outer electrode is located, thereby forming a secondary discharge.

[0021] Step S02: Gas enters the second discharge region 8 and the third discharge region 9 from the first gas inlet and the second gas inlet respectively.

[0022] Step S03: the molecules in the second discharge region and the third discharge region undergo ionization and dissociation reactions with the high-energy electrons, and the gas changes from ground-state molecules to excited-state molecules, and active substances are generated.

[0023] Step S04: the active material and part of the undecomposed gas produced in step S03 are introduced into the first discharge region 7 to react, thereby completing the reforming of the gases and producing additional chemical products.

[0024] When the intake gas is any combination of CO2 and CH4, CO2 and H2, CH4 and O2, CH4 and H2O, the additional chemical products produced are methanol, ethanol, acetic acid, etc. When the intake gas is N2 and H2, the additional chemical product is NH3.

[0025] 3.Beneficial effects:

[0026] The present invention utilizes dielectric barrier discharge plasma technology to form a two-stage compact plasma reaction system. Using two-stage coordinated discharge, the reaction gas is first converted from ground state molecules to excited state molecules in the left and right discharge areas. The reaction gas is at different energy levels, making the gas reforming reaction more likely to occur and reducing energy consumption. In addition, these steps are integrated into the same reaction, reducing the device volume and improving the conversion performance of the reaction. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 It is a structural schematic diagram of the present invention.

[0028] Figure 2 This is a schematic diagram of a quartz tube.

[0029] Figure 3 Schematic diagram of threaded pipe.

[0030] Figure 4 It is a flow chart of the device operation method.

[0031] Figure 5 This is a schematic diagram of the CO2 and CH4 conversion rates in Example 1.

[0032] Figure 6 Schematic diagram of energy efficiency of the Y-type tube in Example 1.

[0033] Figure 7 This is a schematic diagram of the energy efficiency of a single tube in Example 1.

[0034] Explanation of the accompanying drawings: 101. First inner electrode; 102. Second inner electrode; 103. Third inner electrode; 201. Second outer electrode; 202. First outer electrode; 203. Third outer electrode; 301. First gas inlet; 302. Second gas inlet; 4. Gas outlet; 5. Quartz tube; 6. Metal wire; 7. First region; 8. Second region; 9. Third region; 10. Second polytetrafluoroethylene tube; 11. Third polytetrafluoroethylene tube; 12. First polytetrafluoroethylene tube. DETAILED DESCRIPTION

[0035] The present invention is described in detail below with reference to the accompanying drawings and embodiments.

[0036] like Figure 1 As shown, a plasma device for improving gas conversion performance includes three quartz tubes 5, the tail ends of the three quartz tubes 5 are internally connected, and an external electrode is wrapped and attached to the outside of each quartz tube 5. The outside of the first quartz tube is a first external electrode 202, the outside of the second quartz tube is a second external electrode 201, and the outside of the third quartz tube is a third external electrode 203. The three external electrodes are connected to each other by a metal wire 6. An internal electrode is provided in each quartz tube, the first quartz tube is provided with a gas outlet 4, and the second and third quartz tubes are provided with a first gas inlet 301 and a second gas inlet 302, respectively. The first internal electrode 101 in the first quartz tube is connected to a high-voltage power supply, and the second internal electrode 102 in the second quartz tube and the third internal electrode 103 in the third quartz tube are grounded.

[0037] By applying a high voltage to the inner electrode 101, a strong electric field is formed in the first discharge region 7. This electric field ionizes the surrounding gas molecules or atoms. The ionization process produces positive ions and free electrons. Positive ions, due to their large mass and relatively slow movement, are accelerated in the electric field and attracted to the electrode. Free electrons are also accelerated by the electric field, forming a space charge region near the electrode. When there are sufficient free electrons in the space charge region, they can gain sufficient energy to overcome the ionization energy of the gas molecules, leading to more ionization reactions. This triggers an electron cascade discharge process, generating a plasma. Electrons and ions in the plasma collide and recombine, generating high energy, which forms a primary discharge within the quartz tube where the first outer electrode 202 is located in the first discharge region 7. The second and third outer electrodes 201 and 203 are connected to the first outer electrode 202 via metal wires 6. Part of the discharge is transported to the second discharge region 8 within the second quartz tube where the second outer electrode 201 is located, and to the third discharge region 9 within the third quartz tube where the third outer electrode 203 is located, respectively, to form secondary discharges.

[0038] The plasma device for improving gas conversion performance of the present invention can also be used for the ammonia synthesis reaction of N2 and H2. N2 and H2 are first introduced into the dielectrically-barrier first discharge region 8 and second discharge region 9 at the left and right ends to partially activate them. The partially activated active materials in these two discharge regions, along with the unactivated N2 and H2, are then introduced into the second dielectrically-barrier first discharge region 7 to undergo the ammonia synthesis reaction. This pre-ionizes the reactant gases, increasing the amount of intermediate products and thereby improving the yield of the target product. The device can also be used for reactions of CO2 and H2, CH4 and O2, and CH4 and H2O (water vapor).

[0039] Gas is introduced into the first gas inlet 301 and the second gas inlet 302 respectively, and is activated and decomposed in the first discharge region 8 and the second discharge region 9 of the two plasma discharges respectively. The gas is converted from ground state molecules to excited state molecules. Then, some active substances and some undecomposed gases enter the first discharge region 7 of the second plasma stage to react and prepare additional chemical products.

[0040] In one embodiment, the three quartz tubes are arranged in a Y-shape. The Y-shaped quartz tubes form a compact device structure. The two dielectric barrier discharge plasma reaction zones are integrated into one device, reducing the overall device volume and improving energy efficiency.

[0041] In one embodiment, the inner electrode is a metal rod, a metal threaded tube or a metal mace, and the metal includes stainless steel, copper, aluminum, etc. Figure 3 The figure shows a schematic diagram of a metal threaded pipe.

[0042] In one embodiment, each quartz tube is provided with a polytetrafluoroethylene tube for fixing the inner electrode in the quartz tube. The first inner electrode 101 is inserted into the first polytetrafluoroethylene tube 12, the second inner electrode 102 is inserted into the second polytetrafluoroethylene tube 10, and the third inner electrode 103 is inserted into the third polytetrafluoroethylene tube 11, each inner electrode and the corresponding polytetrafluoroethylene tube are coaxial.

[0043] The following describes a method for improving the gas conversion performance of the plasma device for gas reforming, taking the first gas inlet 301 and the second gas inlet 302 as examples, respectively introducing CO2 and CH4, as shown in Figure 2 The method comprises the following steps:

[0044] Step S01: As shown in Figure 2 The first inner electrode 101 is connected to high voltage, forming a strong electric field in the first quartz tube, thereby forming a first discharge area 7 inside the first quartz tube where the first outer electrode 202 is located. The electric field of the first discharge area 7 is partially transmitted to the inside of the second discharge area 8 in the second quartz tube where the second outer electrode 201 is located and the third discharge area 9 in the third quartz tube where the third outer electrode 203 is located to form a secondary discharge.

[0045] Step S02: When CO2 and CH4 gases enter the quartz tube from the first gas inlet 301 and the second gas inlet 302 respectively, dielectric barrier discharge plasma is generated between the second inner electrode 102 and the second outer electrode 201 and between the third inner electrode 103 and the third outer electrode 203, respectively, to process the reaction gas. The plasma has high reactivity and can achieve rapid reaction at normal temperature and pressure, thus greatly reducing the manufacturing cost of the device.

[0046] Step S03: In the second discharge area 8 and the third discharge area 9, molecules and high-energy electrons ionize, and due to the high activation of the plasma, CO2 and CH4 molecules ionize and dissociate with high-energy electrons, respectively producing active substances. The gas changes from a ground state molecule to an excited state molecule.

[0047] Step S04: The active substances produced in step S03 and part of the undecomposed gas enter the first discharge area 7 to react, complete the reforming of the gas, and produce additional chemical products.

[0048] The two-stage discharge is used at the same time, and the two-stage discharge can make the gas change from a ground state molecule to an excited state molecule, making the CO2 and CH4 reforming reaction easier to proceed, reducing energy consumption, and integrating these steps in the same reaction, reducing the size of the device and improving the conversion performance of the reaction.

[0049] As shown in Figure 5-Figure 7As shown in the figure, the reaction performance diagram of the single and double-stage dielectric barrier discharge device is shown. Under the same discharge power conditions, the conversion rate of CO2 and CH4 using the two-stage dielectric barrier discharge device is significantly better than that of the single-stage dielectric barrier discharge device. As the discharge power increases, when it reaches a maximum value of 25W, the conversion rates of CO2 and CH4 of the two-stage dielectric barrier discharge device reach 18.97% and 32.02% respectively, which are greatly improved compared with 11.45% and 24.89% of the single-stage dielectric barrier discharge device. In terms of energy efficiency, Figure 5-Figure 7 The two-stage dielectric barrier discharge device is significantly superior to the single-stage device. At a discharge power of 6W, the energy efficiency of the two-stage device is 0.27mmol / kJ, a significant improvement over the 0.21mmol / kJ of the single-stage device. However, as the discharge power increases, the energy efficiency decreases because more energy is used for heating.

Claims

1. A plasma device for improving gas conversion performance, characterized in that: The invention comprises three quartz tubes (5), the tail ends of the three quartz tubes are connected to each other, an external electrode is wound and attached to the outside of each quartz tube, the first external electrode (202) is outside the first quartz tube, the second external electrode (201) is outside the second quartz tube, and the third external electrode (203) is outside the third quartz tube. The three external electrodes are connected to each other by metal wires (6). An internal electrode is provided in each quartz tube, the first quartz tube is provided with an air outlet (4), the second quartz tube and the third quartz tube are provided with a first air inlet (301) and a second air inlet (302), respectively. The first internal electrode (101) in the first quartz tube is connected to a high-voltage power supply, the second internal electrode (102) in the second quartz tube and the third internal electrode (103) in the third quartz tube are grounded.

2. The plasma device for improving gas conversion performance according to claim 1, wherein: Each quartz tube is provided with a polytetrafluoroethylene tube for fixing the inner electrode in the quartz tube.

3. The plasma device for improving gas conversion performance according to claim 2, wherein: The first inner electrode (101) is inserted into the first polytetrafluoroethylene tube (12), the second inner electrode (102) is inserted into the second polytetrafluoroethylene tube (10), and the third inner electrode (103) is inserted into the third polytetrafluoroethylene tube (11), and each inner electrode and the corresponding polytetrafluoroethylene tube are coaxial.

4. The plasma reaction device for improving gas conversion performance according to claim 1, wherein: Each of the inner electrodes is a metal rod, a metal threaded tube or a metal mace.

5. The plasma device for improving gas conversion performance according to claim 4, wherein: The metal is one of stainless steel, copper and aluminum.

6. The plasma device for improving gas conversion performance according to any one of claims 1 to 5, characterized in that: The three quartz tubes are arranged in a Y shape.

7. The plasma device for improving gas conversion performance according to any one of claims 1 to 5, characterized in that: The intake gases of the first air inlet (301) and the second air inlet (302) are any combination of CO2 and CH4, CO2 and H2, CH4 and O2, N2 and H2, and CH4 and H2O.

8. A method for gas reforming using the plasma device for improving gas conversion performance according to any one of claims 1 to 5, comprising the following steps: Step S01: The first inner electrode (101) is connected to high voltage electricity to form a strong electric field in the first quartz tube, thereby forming a first discharge region (7) inside the first quartz tube where the first outer electrode (202) is located, and partially transmitting the electric field of the first discharge region (7) to the inside of the second discharge region (8) in the second quartz tube where the second outer electrode (201) is located and the inside of the third discharge region (9) in the third quartz tube where the third outer electrode (203) is located, to form a secondary discharge; Step S02: gas enters the second discharge region (8) and the third discharge region (9) from the first gas inlet (301) and the second gas inlet (302) respectively; Step S03: the molecules in the second discharge region (8) and the third discharge region (9) undergo ionization and dissociation reactions with the high-energy electrons, the gas changes from ground-state molecules to excited-state molecules, and active substances are generated; Step S04: The active material and part of the undecomposed gas produced in step S03 are introduced into the first discharge region (7) to react, thereby completing the reforming of the gases and producing additional chemical products.

9. The gas reforming method according to claim 8, wherein: When the intake gas is any combination of CO2 and CH4, CO2 and H2, CH4 and O2, CH4 and H2O, the additional chemical products produced are methanol, ethanol, and acetic acid. When the intake gas is N2 and H2, the additional chemical product is NH3.

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