Microwave plasma device with increased selectivity for nitrogen oxides and method for preparing water containing nitrogen oxides using the same

Abstract

The microwave plasma device includes: a hollow tube which is empty inside and to which microwaves are irradiated; a swirl gas injection port located at the lower end of the hollow tube into which swirl gas is injected; an axial gas injection port penetrating the lower end of the hollow tube into which axial gas is injected; and a swirl gas diaphragm located inside the hollow tube and near the injection of the swirl gas, extending in the longitudinal direction of the hollow tube. A gap (g) is formed between the swirl gas diaphragm and the hollow tube, and plasma is generated inside the hollow tube, and nitrogen oxides are generated inside the hollow tube.

Description

Technical Field

[0001] The present invention relates to a microwave plasma device with increased selectivity for nitrogen oxides and a method for preparing water containing nitrogen oxides using the device. Background Art

[0002] Since Robert Furchgott, Louis Ignarro, and Ferid Murad won the Nobel Prize in 1998 for discovering that nitric oxide (NO) in nitrogen oxides acts as a signaling molecule in living cells, interest in nitric oxide has spread rapidly in the academic community, and many benefits of nitric oxide have now been discovered in animals and plants.

[0003] In particular, since nitric oxide has the ability to activate cells, when water containing nitric oxide is regularly applied to a wound, the wound site can be rapidly regenerated, thereby healing the wound. For example, when water containing nitric oxide comes into contact with the wound site, the wound surface is cleaned, and microorganisms attached or parasitic on the wound surface are killed. In addition, due to capillary dilation, blood circulation is good, cell proliferation is active, and protein proliferation is promoted. Therefore, a large number of macrophages in the wound site increase, and fibroblasts rapidly proliferate, thereby enabling the wound to heal quickly.

[0004] In order to prepare such water containing nitrogen oxides such as nitric oxide, technologies capable of appropriately generating and controlling nitrogen oxides are being studied.

[0005] Currently, research has been conducted on generating nitrogen oxides using a microwave plasma device. However, conventional devices have low selectivity for nitrogen oxides such as nitric oxide or nitrogen dioxide. In particular, due to the turbulent flow of the axial direction gas on the wall surface of the dielectric tube (hollow tube), the conversion rate of nitrogen oxides in the axial gas is low. In addition, in the case of aerosol or particles with a large mass, the turbulent flow may be more severe. Summary of the Invention

[0006] Technical Problem

[0007] The technical problem to be solved by the present invention is to provide a device having a microwave plasma nozzle with high selectivity for nitrogen oxides.

[0008] In addition to the above technical problems, the embodiments according to the present invention can be used to achieve other technical problems not specifically mentioned.

[0009] Technical Solution

[0010] A microwave plasma device according to an embodiment includes: a hollow tube which is empty inside and to which microwaves are irradiated; a swirl gas injection port located at the lower end of the hollow tube into which swirl gas is injected; an axial gas injection port penetrating the lower end of the hollow tube into which axial gas is injected; and a swirl gas diaphragm located inside the hollow tube and near where the swirl gas is injected, extending in the longitudinal direction of the hollow tube, wherein a gap (g) is formed between the swirl gas diaphragm and the hollow tube, and plasma is generated inside the hollow tube and nitrogen oxides are generated inside the hollow tube.

[0011] The swirl gas can be supplied to the inside of the hollow tube through the gap (g).

[0012] The swirl gas can be oxygen or nitrogen.

[0013] When the swirl gas is oxygen, the axial gas can be nitrogen, and when the swirl gas is nitrogen, the axial gas can be oxygen.

[0014] A method for preparing nitrogen oxides according to an embodiment includes: the step of injecting swirl gas into a hollow tube; the step of the injected swirl gas passing through the gap formed between the swirl gas diaphragm and the hollow tube; the step of injecting axial gas into the hollow tube; the step of irradiating microwaves to the hollow tube; and the step of generating plasma and nitrogen oxide gas inside the hollow tube.

[0015] A method for preparing water containing nitrogen oxides according to an embodiment includes: the step of injecting swirl gas into a hollow tube; the step of the injected swirl gas passing through the gap formed between the swirl gas diaphragm and the hollow tube; the step of injecting axial gas into the hollow tube; the step of irradiating microwaves to the hollow tube; the step of generating plasma and nitrogen oxide gas inside the hollow tube; and the step of subjecting the generated nitrogen oxide gas to plasma treatment in distilled water to generate water containing nitrogen oxides.

[0016] The method for preparing water containing nitrogen oxides may further include: the step of removing oxygen as a dissolved gas from the water containing nitrogen oxides.

[0017] The method for preparing water containing nitrogen oxides may further include: the step of cooling and storing the water containing nitrogen oxides.

[0018] Advantages of the Invention

[0019] According to an embodiment, the selectivity of nitrogen oxides can be improved, and the conversion rate of nitrogen oxides of the axial gas can be improved. Brief Description of the Drawings

[0020] Figure 1 is a side view schematically showing a microwave plasma device.

[0021] Figure 2 is a cross-sectional view schematically showing a swirling gas inlet of the microwave plasma device.

[0022] Figure 3 shows the magnitude of the circumferential velocity (in m / s) of the plasma inside the microwave plasma device -1 ).

[0023] Figure 4 shows Figure 3 the argon mass fraction inside the hollow tube of the third microwave plasma device (s-4) (left side) and the fifth microwave plasma device (s-8) (right side).

[0024] Figure 5 shows the pressure curve in the cross-sectional direction of the hollow tube of the microwave plasma device according to the presence or absence of a swirling gas diaphragm.

[0025] Figure 6 shows the concentration of nitrogen oxides generated in the microwave plasma device according to the presence or absence of a swirling gas diaphragm.

[0026] Figure 7 shows the concentration of nitrogen oxides generated in the microwave plasma device according to the presence or absence of a swirling gas diaphragm with respect to the change in the oxygen flow rate when nitrogen is used as the swirling gas and oxygen is used as the axial gas.

[0027] Figure 8 shows the concentration of nitrogen oxides generated in the microwave plasma device according to the presence or absence of a swirling gas diaphragm with respect to the change in the nitrogen flow rate when oxygen is used as the swirling gas and nitrogen is used as the axial gas. Detailed Description of the Embodiment

[0028] Embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those of ordinary skill in the art to which the present invention pertains can easily implement the present invention. The present invention can be implemented in various different ways and is not limited to the embodiments described herein. To clearly describe the present invention in the drawings, parts irrelevant to the description are omitted, and the same reference numerals denote the same or similar components throughout the specification. Additionally, if it is a well-known art, its detailed description is omitted.

[0029] In the specification, when a certain part is described as "including" a certain technical feature, unless there is a particularly contrary description, it means that other technical features may also be included, and it does not exclude other technical features.

[0030] Hereinafter, a microwave plasma device according to an embodiment will be described in detail.

[0031] Figure 1 FIG. is a side view schematically showing the microwave plasma device, Figure 2 FIG. is a cross-sectional view schematically showing the swirling gas injection port of the microwave plasma device.

[0032] Referring to Figure 1 , the microwave plasma device includes a hollow tube 10, a swirling gas injection port 20, an axial gas injection port 30, and a swirling gas diaphragm 40.

[0033] Here, the microwave plasma device generates plasma at normal pressure (atmospheric pressure). Normal pressure (atmospheric pressure) plasma has very different characteristics under various electrode structures, driving frequencies, and conditions, and has various advantages such as high-temperature and low-temperature processing, high density of active species, and fast processing time.

[0034] The hollow tube 10 is a hollow cylindrical shape inside which microwaves are irradiated. When microwaves are irradiated into the hollow tube 10, plasma will be generated from the swirling gas and the axial gas injected into the hollow tube 10 as source gases. For example, the hollow tube 10 can be made of quartz.

[0035] The swirling gas injection port 20 is located at the lower end of the hollow tube 10 and can be one or more. For example, referring to Figure 2 , the swirling gas injection port 20 is four and is formed at an angle of about 90 degrees along the circumference of the hollow tube 10. The swirling gas is injected into the hollow tube 10 in a spiral shape through the swirling gas injection port 20. For example, oxygen, nitrogen, etc. can be used as the swirling gas.

[0036] Regarding the number and shape of the swirling gas injection port 20, it can be optimized through the experiments shown in Figure 3 and Figure 4 .

[0037] Figure 3Shows the magnitude of the circumferential velocity ( / ms-1) of the plasma inside 7 microwave plasma devices. The microwave plasma devices with 1 (s-1), 2 (s-2), and 4 (s-4) swirling gas inlets are shown in sequence from the left. For example, the 2 swirling gas inlets of the second microwave plasma device (s-2) are 180 degrees apart from each other on the circumference. The 4 swirling gas inlets of the third microwave plasma device (s-4) are 90 degrees apart from each other on the circumference. The fourth microwave plasma device (s-4_45) has 4 swirling gas inlets, and all 4 are inclined 45 degrees from the axial direction. The fifth microwave plasma device (s-8) has 8 swirling gas inlets, which are 45 degrees apart from each other on the circumference. The sixth microwave plasma device (s-8_45) has 8 swirling gas inlets, and all 8 are inclined 45 degrees from the axial direction. The seventh microwave plasma device (s-12) has 12 swirling gas inlets, which are 30 degrees apart from each other on the circumference.

[0038] Refer to Figure 3 , in order to measure the coaxial co-flow effect on the stability of the plasma flow field, the circumferential velocity inside the hollow tube was measured. It is most stable at the wall of the hollow tube and most unstable near the center of the hollow tube. Therefore, the wall of the hollow tube can be protected, and the precursor / carrier gas can be unhindered by the sheath gas.

[0039] Among Figure 3 the 7 plasma devices, the best swirling flow is in the third microwave plasma device (with 4 swirling gas inlets) (s-4) and the fifth microwave plasma device (with 8 swirling gas inlets) (s-8). In the third microwave plasma device (s-4), the 4 swirling gas inlets can form a good spin flow with a high circumferential velocity near the wall of the hollow tube. However, in the fourth microwave plasma device (s-4_45), the structure where the 4 swirling gas inlets are inclined 45 degrees from the axial direction provides a downward spin with a much lower circumferential velocity. In the fifth microwave plasma device (s-8), the 8 swirling gas inlets exhibit a relatively high circumferential velocity on the wall of the hollow tube, so the co-flow gas has a well-swirled flow.

[0040] Figure 4 Shows Figure 3 the argon mass fraction inside the hollow tubes of the third microwave plasma device (s-4) (left) and the fifth microwave plasma device (s-8) (right).

[0041] Since the circumferential velocity of the third microwave plasma device (s-4) is higher than that of the fifth microwave plasma device (s-8), more carrier gas is dispersed. However, since the fifth microwave plasma device (s-8) better protects the inner wall of the hollow tube from the influence of the carrier gas, it may be the most preferred design.

[0042] The axial gas injection port 30 is formed to penetrate the center of the lower end portion of the hollow tube 10. Axial gas is injected into the inside of the hollow tube 10 through the axial gas injection port 30. For example, oxygen, nitrogen, etc. can be used as the axial gas.

[0043] In order to generate nitrogen oxides with the microwave plasma device, a mixed gas of nitrogen and oxygen, or dry air can be injected as the swirl gas. In addition, nitrogen can be used as the swirl gas and oxygen can be used as the axial gas. Or, oxygen can be used as the swirl gas and nitrogen can be used as the axial gas.

[0044] The swirl gas diaphragm 40 is formed near the injection of the swirl gas at the lower part of the hollow tube 10 and extends along the length direction of the hollow tube 10. A gap g is formed between the swirl gas diaphragm 40 and the inner wall of the hollow tube 10. The swirl gas injected into the swirl gas injection port 20 flows into the inside of the hollow tube 10 through the gap g. Due to such a gap g, the nitrogen selectivity of the microwave plasma device can be increased.

[0045] For example, the ratio of the gap g between the swirl gas diaphragm 40 and the inner wall of the hollow tube 10 to the diameter D of the swirl gas injection port 20 can satisfy the following mathematical formula 1.

[0046] [Mathematical formula 1]

[0047] 0.1 ≤ g / D ≤ 1.5

[0048] When the ratio of the gap g between the swirl gas diaphragm 40 and the inner wall of the hollow tube 10 to the diameter D of the swirl gas injection port 20 is greater than 1.5, since the injection of the swirl gas is off-tangential, the swirl flow is disrupted and may become turbulent flow. In addition, when the ratio of the gap g between the swirl gas diaphragm 40 and the hollow tube 10 to the diameter D of the swirl gas injection port 20 is less than 0.1, limitations in machining may occur.

[0049] Figure 5 Shows the pressure curves in the cross-sectional direction of the inside of the hollow tube for the microwave plasma device with and without the swirl diaphragm.

[0050] Refer to Figure 5, the farther away from the center of the microwave plasma device (radial position 0 mm), the more the internal pressure caused by the plasma flow decreases, and it increases rapidly after passing 5 mm. In particular, it can be seen that the pressure gradient in the microwave plasma device with a swirling diaphragm (with barrier) is greater than that in the microwave plasma device without a swirling diaphragm (without barrier).

[0051] Figure 6 Shows the concentration of nitrogen oxides generated in the microwave plasma device with and without a swirling gas diaphragm.

[0052] Refer to Figure 6 , it can be seen that the generation concentrations of nitrogen oxides NO and NO2 in the microwave plasma device with a swirling diaphragm (with barrier, “w”) are higher than those in the microwave plasma device without a swirling diaphragm (without barrier, “w / o”). The generation concentration of NOx is the sum of the generation concentrations of NO and NO2. Under the experimental conditions, g / D is 1.0, the microwave power is 500 W, nitrogen at 15 L / min is used as the swirling gas, and oxygen at 0.2 L / min is used as the axial gas.

[0053] Figure 7 Shows the concentration of nitrogen oxides generated in the microwave plasma device with and without a swirling gas diaphragm with respect to the change in the oxygen flow rate when nitrogen is used as the swirling gas and oxygen is used as the axial gas.

[0054] Refer to Figure 7 , it can be seen that the generation concentrations of nitrogen oxides NO and NO2 in the microwave plasma device with a swirling diaphragm (with barrier) are higher than those in the microwave plasma device without a swirling diaphragm (without barrier). In addition, by controlling the amount of oxygen, the selectivity of nitrogen oxides can be improved. If the generated nitrogen oxide gas is passed through water, only the nitrogen oxide gas with a high concentration can be obtained. Under the experimental conditions, g / D is 1.0, the microwave power is 500 W, nitrogen at 15 LPM is used as the swirling gas, and oxygen at 0 - 1000 sccm is used as the axial gas.

[0055] Figure 8 Shows the concentration of nitrogen oxides generated in the microwave plasma device with and without a swirling gas diaphragm with respect to the change in the nitrogen flow rate when oxygen is used as the swirling gas and nitrogen is used as the axial gas.

[0056] Refer to Figure 8, it can be seen that the production concentrations of nitrogen oxides NO and NO2 in the microwave plasma device with a swirl diaphragm (with barrier) are higher than those in the microwave plasma device without a swirl diaphragm (without barrier). Additionally, by controlling the amount of nitrogen, the selectivity of nitrogen oxides can be increased. If the generated nitrogen oxide gas is passed through water, only high-concentration nitrogen oxide gas can be obtained. Under the experimental conditions, g / D is 1.0, the microwave power is 500 W, 15 LPM of oxygen is used as the swirl gas, and 0 - 1000 sccm of nitrogen is used as the axial gas.

[0057] A method for preparing nitrogen oxides using a microwave plasma device according to an embodiment will be described in detail below.

[0058] The method for preparing nitrogen oxides includes: the step of injecting a swirl gas into a hollow tube; the step of the injected swirl gas passing through the gap formed between the swirl gas diaphragm and the hollow tube; the step of injecting an axial gas into the hollow tube; the step of irradiating microwaves to the hollow tube; and the step of generating plasma and nitrogen oxide gas inside the hollow tube.

[0059] A method for preparing water containing nitrogen oxides using a microwave plasma device according to an embodiment will be described in detail below.

[0060] The method for preparing water containing nitrogen oxides includes: the step of generating nitrogen oxide gas; the step of generating nitrogen oxide water; the step of removing oxygen as a dissolved gas; and the step of storing the nitrogen oxide water.

[0061] The step of generating nitrogen oxide gas includes the step of generating nitrogen oxides through a microwave plasma device according to an embodiment. Therefore, the selectivity of nitrogen oxides will increase.

[0062] For example, for the step of generating nitrogen oxide gas, the method for preparing nitrogen oxides includes: the step of injecting a swirl gas into a hollow tube; the step of the injected swirl gas passing through the gap formed between the swirl gas diaphragm and the hollow tube; the step of injecting an axial gas into the hollow tube; the step of irradiating microwaves to the hollow tube; and the step of generating plasma and nitrogen oxide gas inside the hollow tube.

[0063] Here, the microwave plasma device generates plasma under normal pressure (atmospheric pressure). Normal pressure (atmospheric pressure) plasma has very different characteristics under various electrode structures, driving frequencies, and conditions, and has various advantages such as high-temperature and low-temperature processing, high density of active species, fast processing time, etc.

[0064] In addition, the application fields of atmospheric pressure plasma are very extensive. Especially, since dry processing can be carried out using species with strong oxidizing power or high reactivity, it can be used in the biological / medical fields and the food industry, such as food sterilization, biofilm removal, and organic film removal.

[0065] The step of generating nitrogen oxide water includes the step of subjecting the generated nitrogen oxide gas to plasma treatment in distilled water to generate water containing nitrogen oxides.

[0066] Traditionally, plasma has been used in wastewater treatment and post-treatment processes such as COD and BOD reduction, decolorization, and deodorization. However, distilled water or solutions treated with plasma are different in that they can be used in pretreatment processes. Distilled water treated with plasma is called plasma-treated water, which has good bactericidal power and can replace ozone water as bactericidal water. The so-called "plasma-treated water" can be generated by directly or indirectly exposing atmospheric pressure plasma to distilled water.

[0067] Atmospheric pressure plasma discharges using various discharge gases such as helium, argon, nitrogen, etc. However, the chemical species contained in the plasma-treated water to be generated depend on the discharge gas. For example, ozone or oxygen reactive species with high bactericidal power can be generated by using oxygen or a mixed gas of oxygen and other gases as the discharge gas. In addition, the chemical species dissolved in the plasma-treated water change according to the standing time. For example, synthetic nitrite required for producing meat products can be replaced with plasma-treated water. At this time, nitrite ions (Nitrite ion, NO2 - ) and nitrate ions (Nitrate ion, NO3 - ) are used as important substances. However, since the nitrite ions decrease with the increase of the standing time, the plasma-treated water can be appropriately controlled.

[0068] [Reaction formula 1] 2NO(g) + O2(g) → 2NO2(g)

[0069] [Reaction formula 2] NO + NO2 + H20 → 2NO2- + 2H +

[0070] [Reaction formula 3] 2NO2 + H2O → NO2- + NO3- + 2H +

[0071] [Reaction formula 4] 3NO2(g) + H20(l) → 2HNO3(aq) + NO(g)

[0072] [Reaction formula 5] 4NO2(g) + O2(g) H2O(l) → 4HNO3(aq)

[0073] [Reaction formula 6] NO + OH + M → HNO2 + M

[0074] [Reaction formula 7] NO2 + OH + M → HNO3 + M

[0075] Nitrous acid dissolved in plasma-treated distilled water has a pK value of 3.37. Therefore, in a solution with a pH of 3.37, 50% of the nitrous acid dissociates to form nitrite ions, and in a solution with a pH of 5.5 or higher, 99% of the nitrous acid dissociates to form nitrite ions (Reaction formula 8).

[0076] [Reaction formula 8]

[0077] According to the stoichiometric reaction formula combining Reaction formula 2 and Reaction formula 3, nitrous acid undergoes an intermediate chemical reaction and finally undergoes disproportionation to form nitric oxide, nitrate ions, hydrogen ions, and water. That is, nitrous acid decomposes over time, and its concentration decreases. The decomposition rate depends on the temperature of the solution and the initial concentration of nitrous acid. The higher the initial concentration of nitrous acid and the higher the temperature of the solution, the higher the decomposition rate. Therefore, as the standing time of the treated water increases, nitrous acid decreases, and at the same time, nitrate ions increase. The reason is the disproportionation reaction of nitrous acid, and the reaction formula is as follows.

[0078] 3HNO2 → 2NO + NO3 - +H + +H2O

[0079] In the step of removing oxygen as a dissolved gas, oxygen is removed from the prepared water containing nitrogen oxides. For example, the removal of dissolved oxygen can be carried out by a vacuum method, a nitrogen blowing method, or both. The vacuum method is a method of reducing the pressure of air using a vacuum pump. The nitrogen blowing method is a method of removing oxygen in water by blowing nitrogen gas into the gas phase.

[0080] The concentration of each chemical species changes according to the storage time. For example, in the prepared water containing nitrogen oxides, the concentration of NO, including nitrite ions, decreases, while the concentration of nitrate ions increases. The sum of nitrous acid and nitrite ions according to the oxygen concentration present in the prepared water containing nitrogen oxides decreases over time. For example, the higher the concentration of dissolved oxygen, the faster the reduction rate of nitrite and nitrite ions over time. When storing after reducing the concentration of dissolved oxygen in the water containing nitrogen oxides, the reduction rate of nitrite ions can be reduced due to preventing the reduction of nitric oxide caused by dissolved oxygen. When using low-temperature plasma (DBD, corona, etc.), dissolved ozone must also be removed.

[0081] The step of storing the water containing nitrogen oxides includes the steps of cooling and storing the water containing nitrogen oxides.

[0082] The cooling temperature can be between -80 °C and 20 °C. Preferably, the water containing nitrogen oxides is cooled at a temperature between -80 °C and 0 °C. Since the decomposition rate of nitrous acid is proportional to the temperature, if the water containing nitrogen oxides is stored after the temperature is lowered, the decomposition rates of nitrous acid and nitrite ions can be reduced.

[0083] In the water containing nitrogen oxides, nitrite ions and nitrous acid exist in a specific ratio according to the pH value of the solution, so it is necessary to increase the pH value (4.5 - 13). Due to the disproportionation reaction, nitrous acid is finally decomposed into nitric oxide, nitrate ions, hydrogen ions and water, so it is necessary to increase the pH value (4.5 - 13). The decomposition rate depends on the initial concentration of nitrous acid, the storage temperature of the solution, the concentration of dissolved oxygen and the concentration of dissolved ozone, so it is necessary to remove the dissolved oxygen species.

[0084] The preferred embodiments of the present invention have been described in detail above, but the scope of the rights of the present invention is not limited to the above content. Various modifications and improvements made by those skilled in the art using the basic concepts of the present invention defined in the claims also fall within the scope of the rights of the present invention.

Claims

1. A microwave plasma device for preparing nitrogen oxides, comprising: A hollow tube, which is empty inside; A swirling gas injection port, which is located at the lower end of the hollow tube, and the swirling gas is injected into the interior of the hollow tube through the swirling gas injection port; An axial gas injection port, which penetrates the lower end of the hollow tube, and the axial gas is injected into the interior of the hollow tube in the direction of the upper end of the hollow tube; and A swirling gas diaphragm, which is located inside the hollow tube and near the injection of the swirling gas in the lower part of the hollow tube, and extends along the length direction of the hollow tube from the lower end of the hollow tube, A gap g is formed between the swirling gas diaphragm and the hollow tube, and the swirling gas injected into the swirling gas injection port flows into the interior of the hollow tube through the gap g. The hollow tube is irradiated with microwaves to generate plasma using the swirling gas and the axial gas as source gases inside the hollow tube, and nitrogen oxides are generated inside the hollow tube. The ratio of the gap g to the diameter D of the swirling gas injection port satisfies 0.1 ≤ g / D ≤ 1.

5.

2. The microwave plasma device for preparing nitrogen oxides according to claim 1, wherein, The swirling gas is oxygen or nitrogen.

3. The microwave plasma device for preparing nitrogen oxides according to claim 2, wherein, When the swirling gas is oxygen, the axial gas is nitrogen, and when the swirling gas is nitrogen, the axial gas is oxygen.

4. A method for preparing nitrogen oxides, comprising: The step of injecting a swirling gas into a hollow tube; The step in which the injected swirling gas flows into the interior of the hollow tube through a gap g formed between a swirling gas diaphragm and the hollow tube, wherein the swirling gas diaphragm extends along the length direction of the hollow tube from the lower end of the hollow tube; The step of injecting an axial gas into the hollow tube in the direction of the upper end of the hollow tube; The step of irradiating the hollow tube with microwaves; and The step of generating plasma using the swirling gas and the axial gas as source gases and generating nitrogen oxide gas inside the hollow tube, wherein the ratio of the gap g to the diameter D of the swirling gas injection port satisfies 0.1 ≤ g / D ≤ 1.

5.

5. A method for preparing water containing nitrogen oxides, comprising: The step of injecting a swirling gas into a hollow tube; The step in which the injected swirling gas flows into the interior of the hollow tube through a gap g formed between a swirling gas diaphragm and the hollow tube, wherein the swirling gas diaphragm extends along the length direction of the hollow tube from the lower end of the hollow tube; The step of injecting an axial gas into the hollow tube in the direction of the upper end of the hollow tube; The step of irradiating the hollow tube with microwaves; The step of generating plasma using the swirling gas and the axial gas as source gases and generating nitrogen oxide gas inside the hollow tube; and The step of subjecting the generated nitrogen oxide gas to plasma treatment in distilled water to generate water containing nitrogen oxides. Among them, the ratio of the gap g to the diameter D of the swirling gas injection port satisfies 0.1 ≤ g / D ≤ 1.

5.

6. The method for preparing water containing nitrogen oxides according to claim 5 further comprises: a step of removing oxygen as a dissolved gas from the water containing nitrogen oxides.

7. The method for preparing water containing nitrogen oxides according to claim 6 further comprises: a step of cooling and storing the water containing nitrogen oxides.

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