Ozone generation system and method

Abstract

To provide a technology capable of improving the efficiency of ozone generation in an ozone generation system. [Solution] The ozone generation system includes an ozone generator having a pair of electrodes arranged opposite each other across a discharge space through which gas can flow, and which generates ozone gas by causing a discharge in the discharge space through which a raw material gas containing oxygen and nitrogen flows, and a switching means which can switch the gas flow state in the discharge space between a first state and a second state in which the gas flow directions are opposite to each other.

Description

[Technical Field]

[0001] The present invention relates to an ozone generation system and a method for producing ozone. [Background technology]

[0002] In recent years, the strong oxidizing action of ozone has been utilized in some water treatment processes, such as decolorization, deodorization, sterilization, and decomposition of organic matter in water supply, sewage, and wastewater. Specifically, for example, an ozone generator has been proposed that generates a gas containing ozone (ozone gas) by generating a discharge between a pair of opposing electrodes while a raw material gas containing oxygen is circulated between the electrodes (see Patent Document 1). In this regard, it is known that the ozone concentration can be increased by using a mixed gas obtained by adding nitrogen to oxygen gas as the raw material gas (see Patent Documents 1 and 2).

[0003] It is also known that ozone is decomposed by metal oxides such as Ni oxide (Non-Patent Document 1). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] International Publication No. 2019 / 229865 [Patent Document 2] Patent No. 6714018 [Patent Document 3] Patent No. 5693787 [Non-patent literature]

[0005] [Non-Patent Document 1] S. Gong, “Heterostructured Ni / NiO Nanocatalysts for Ozone Decomposition”, 2019 Summary of the Invention [Problem to be solved by the invention]

[0006] The above-described ozone generator has a problem in that the efficiency of ozone generation is reduced as a result of ozone being decomposed by metal oxides that adhere to the surfaces of the electrodes due to discharge.

[0007] The technology disclosed herein has been made in consideration of the above-described circumstances, and aims to improve the efficiency of ozone generation in an ozone generation system. [Means for solving the problem]

[0008] In order to solve the above problems, the technology disclosed herein employs the following configuration: That is, the technology disclosed herein is an ozone generation system including an ozone generator having a pair of electrodes arranged opposite each other across a discharge space through which gas can flow, the ozone generator generating ozone gas by causing discharge in the discharge space through which a raw material gas containing oxygen and nitrogen flows, and a switching means capable of switching the gas flow state in the discharge space between a first state and a second state in which the gas flows in opposite directions. [Effects of the Invention]

[0009] According to the technology of the present disclosure, it is possible to improve the ozone generation efficiency in an ozone generation system. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 is a diagram showing the configuration of an ozone generation system 1000 according to the first embodiment. [Figure 2] FIG. 2 is a cross-sectional view illustrating the ozone generator 100 according to the first embodiment. [Figure 3] FIG. 3 is a diagram showing the flow path configuration of the ozone generation system 1000 according to the first embodiment. [Figure 4] FIG. 4 is a diagram illustrating an example of a flow path configuration of the ozone generation system 1000 in the first state (forward flow state). [Figure 5]FIG. 5 is a diagram illustrating an example of the flow path configuration of the ozone generation system 1000 in the second state (counterflow state). [Figure 6] FIG. 6 is a diagram illustrating the hardware configuration of the control device 600 according to the first embodiment. [Figure 7] FIG. 7 is a flowchart illustrating the ozone generation process according to the first embodiment. [Figure 8] FIG. 8 is a diagram showing the configuration of an ozone generation system 1000A according to the second embodiment. [Figure 9] FIG. 9 is a flowchart illustrating the ozone generation process according to the second embodiment. [Figure 10] FIG. 10 is a diagram showing the configuration of an ozone generation system 1000B according to the third embodiment. [Figure 11] FIG. 11 is a flowchart illustrating the ozone generation process according to the third embodiment. [Figure 12] FIG. 12 is a table showing the evaluation results of the amount of metal oxide adhesion. [Figure 13] FIG. 13 is a table showing the evaluation results of the amount of nitrogen oxides attached. DETAILED DESCRIPTION OF THE INVENTION

[0011] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. However, such descriptions should not be interpreted in a limiting sense, and do not limit the subject matter described in the claims. Furthermore, various changes, substitutions, and modifications can be made without departing from the spirit and scope of the present disclosure. Furthermore, different embodiments can be combined as appropriate.

[0012] [Ozone generation system 1000 according to embodiment 1] First, a description will be given of an ozone generation system according to embodiment 1. Fig. 1 is a diagram showing the configuration of an ozone generation system 1000 according to embodiment 1. Note that the dashed lines in Fig. 1 indicate representative control lines.

[0013] The ozone generation system 1000 generates ozone gas containing ozone from a raw material gas containing, for example, oxygen and nitrogen. The ozone gas generated by the ozone generation system 1000 is supplied to downstream equipment (not shown), such as a water treatment system or a storage tank, and is used for water treatment such as decolorization, deodorization, and sterilization in water supply and sewage systems. However, the use of the ozone generation system 1000 is not limited to this. In this specification, when the raw material gas and ozone gas are described without distinction, they may be collectively referred to as "gas."

[0014] The source gas may be any gas that contains oxygen and nitrogen and can generate ozone gas by discharge. Examples of the source gas include a mixed gas in which a small amount of nitrogen gas is added to oxygen gas, and air. The source gas may contain components other than oxygen and nitrogen. The nitrogen addition rate (content) in the source gas is not particularly limited.

[0015] 1, an ozone generation system 1000 according to the first embodiment includes, for example, an ozone generator 100, a switching means 200, a raw material gas supplying device 300, a refrigerant supplying device 400, a power supplying device 500, a control device 600, a first main flow path 700, a second main flow path 800, a first bypass flow path B1, and a second bypass flow path B2. Each component of the ozone generation system 1000 will be described below.

[0016] [Ozone Generator 100] Fig. 2 is a cross-sectional view illustrating the ozone generator 100 according to the first embodiment. Fig. 2 shows a cross section along the gas flow direction indicated by the symbols D1 and D2. Symbol G indicates the gas flow, and symbol R indicates the cooling medium flow.

[0017] Ozone generator 100 has, for example, a pair of electrodes 1 and 2 arranged opposite each other with a dielectric 3 interposed therebetween to form a discharge space 5 through which a gas can flow. Ozone generator 100 is, for example, a silent discharge type ozone generator that generates ozone gas by applying a voltage (AC voltage) to discharge space 5 through which a raw material gas flows, thereby causing a discharge. The electrodes of ozone generator 100 can be of various types, such as a parallel plate type or a cylindrical tube type, but here, an ozone generator having cylindrical tube type electrodes such as the pair of electrodes 1 and 2 shown in FIG. 2 will be described as an example.

[0018] As shown in FIG. 2, the ozone generator 100 includes, for example, a pair of electrodes 1 and 2, a dielectric 3, a housing 4, a discharge space 5, refrigerant flow paths 6 and 7, a first communication port 8, and a second communication port 9.

[0019] The pair of electrodes 1, 2 includes, for example, a cylindrical inner electrode 1 disposed on the inside as a high-voltage electrode and a cylindrical outer electrode 2 disposed on the outside as a ground electrode, and are arranged opposite each other across a cylindrical discharge space 5. The inner electrode 1 and the outer electrode 2 are, for example, stainless steel metal tubes with open ends, and are installed so as to extend along the gas flow direction. The metal material constituting the pair of electrodes 1, 2 is not particularly limited, and examples include aluminum, chromium, titanium, nickel, alloys containing these, and stainless steel. The length of the pair of electrodes 1, 2 in the extension direction (axial direction) is also not particularly limited, but can be, for example, 1500 mm.

[0020] The inner electrode 1 functions as a high-voltage electrode by being electrically connected to a power supply device 500 for applying a high AC voltage, for example.

[0021] The internal space of the inner electrode 1 is formed as, for example, a coolant flow path 6 for cooling the inner electrode 1. A coolant such as cooling water can flow through the coolant flow path 6. Furthermore, for example, a coolant inlet 11 is formed at one end of the inner electrode 1, and a coolant outlet 12 is formed at the other end.

[0022] The outer electrode 2 has, for example, a larger diameter than the inner electrode 1 and is disposed so as to surround the inner electrode 1. More specifically, the outer electrode 2 is disposed concentrically with the inner electrode 1 so that, for example, its inner peripheral surface faces the outer peripheral surface of the inner electrode 1 with a gap therebetween. This forms a cylindrical discharge space 5 between the inner electrode 1 and the outer electrode 2. The outer electrode 2 functions as a ground electrode by, for example, being grounded.

[0023] In this embodiment, the inner electrode 1 is used as a high-voltage electrode and the outer electrode 2 is used as a ground electrode, but the technology according to the present disclosure is not limited to this. For example, the inner electrode 1 may be grounded as a ground electrode, and the outer electrode 2 may be electrically connected to the power supply device 500 as a high-voltage electrode.

[0024] The dielectric 3 is formed into a cylindrical shape from a dielectric material such as glass, and is interposed between the pair of electrodes 1 and 2. Specifically, the dielectric 3 is, for example, a glass tube, and is provided integrally with the outer electrode 2 so as to cover the inner peripheral surface of the outer electrode 2. Therefore, the space between the outer peripheral surface of the inner electrode 1 and the inner peripheral surface of the dielectric 3 forms a discharge space 5. Note that the dielectric 3 only needs to be interposed between the inner electrode 1 and the outer electrode 2, and may, for example, be provided integrally with the inner electrode 1 so as to cover the outer peripheral surface of the inner electrode 1.

[0025] The housing 4 has tube plates 41 and 42 that respectively support both ends of the outer electrode 2. The tube plates 41 and 42 are metal plates made of stainless steel, for example, and both ends of the outer electrode 2 pass through them.

[0026] The space surrounded by the outer electrode 2, the tube sheet 41, and the tube sheet 42 is formed, for example, as a coolant flow path 7 for cooling the outer electrode 2. The coolant flow path 7 is formed, for example, in a cylindrical shape surrounding the outer electrode 2 and extends along the axial direction of the outer electrode 2. A cooling medium such as cooling water can flow through the coolant flow path 7. The coolant flow path 7 also has, for example, an inlet (not shown) and an outlet (not shown) for the cooling medium.

[0027] The first communication port 8 and the second communication port 9 are, for example, gas inlet / outlet ports for the ozone generator 100 and communicate with the discharge space 5. For example, in the extension direction of the discharge space 5, the first communication port 8 is provided at one end of the discharge space 5, and the second communication port 9 is provided at the other end of the discharge space 5. As will be described in detail later, gas flowing through the discharge space 5 flows into the discharge space 5 through one of the first communication port 8 and the second communication port 9 and flows out of the discharge space 5 through the other. For example, the flow direction of the gas from the first communication port 8 to the second communication port 9 is defined as a first direction D1 (forward flow direction), and the flow direction opposite thereto, i.e., the flow direction of the gas from the second communication port 9 to the first communication port 8, is defined as a second direction D2 (backward flow direction).

[0028] As will be described in more detail later, the gas flow state in the discharge space 5 can be switched by the switching means 200 between a first state (forward flow state) in which the gas flows in a first direction D1 and a second state (backward flow state) in which the gas flows in a second direction D2.

[0029] Next, the operation of ozone generation by the ozone generator 100 will be described. A predetermined AC voltage is applied between the pair of electrodes 1 and 2 by the power supply device 500, generating silent discharge in the discharge space 5. While the source gas is flowing through the discharge space 5 in the first direction D1 or the second direction D2, silent discharge occurs in the discharge space 5, causing oxygen molecules contained in the discharge source gas to dissociate and recombine, generating ozone. Ozone gas containing ozone is then discharged from the ozone generator 100. At this time, the pair of electrodes 1 and 2 are cooled by a cooling medium flowing through the refrigerant channels 6 and 7, thereby suppressing thermal decomposition of ozone caused by heat generated by the silent discharge. The direction R in which the cooling medium flows through the refrigerant channels 6 and 7 is not particularly limited, but from the perspective of cooling efficiency, it is preferably opposite to the gas flow direction. For example, when the gas mainly flows in the first direction D1 in the ozone generation process described below, it is preferable to flow the cooling medium in the direction opposite to the first direction D1 (i.e., the second direction D2).

[0030] Generally, it has been confirmed that when an ozone generator generates ozone, adding a small amount of nitrogen gas to oxygen gas improves the efficiency of ozone generation compared to when only oxygen gas is used as the raw material gas. In ozone generation, the small amount of nitrogen gas added to oxygen gas or the nitrogen gas in the raw material air is also oxidized by electrical discharge to generate nitrogen oxide gas.

[0031] [Source gas supply device 300] 1 is, for example, a supply source of a raw material gas to be supplied to the ozone generator 100. For example, when a mixed gas obtained by adding a small amount of nitrogen gas to oxygen gas is used as the raw material gas, a cylinder filled with the mixed gas can be used as the raw material gas supply device 300. Furthermore, when air is used as the raw material gas, a compressor, a blower, or the like can be used as the raw material gas supply device 300.

[0032] [Refrigerant supply device 400] 1 is, for example, a supply source of a cooling medium for cooling the pair of electrodes 1 and 2. The cooling medium supply device 400 has a circulation pump (not shown) that circulates the cooling medium between the ozone generator 100 and the cooling medium supply device 400, and a cooler (not shown) that cools the cooling medium recovered from the ozone generator 100. The cooling medium supplied from the cooling medium supply device 400 to the ozone generator 100 flows through the cooling medium flow paths 6 and 7 while absorbing heat generated by silent discharge, and is then recovered by the cooling medium supply device 400. The cooling medium is not particularly limited, and may be, for example, cooling water such as tap water, ion-exchanged water, or pure water, or a cooling gas.

[0033] [Power supply unit 500] 1 applies, for example, a high AC voltage (for example, about 10 kV) between a pair of electrodes 1 and 2 to generate a silent discharge in a discharge space 5. The power supply device 500 is configured to include, for example, a rectifier circuit, an inverter circuit, a transformer, and the like.

[0034] [First main channel 700] 1 is, for example, a flow path through which a raw material gas supplied from the raw material gas supply device 300 flows. The first main flow path 700 is formed, for example, by a pipe that connects the raw material gas supply device 300 and the ozone generator 100, and is connected to a first communication port 8 of the ozone generator 100. For example, the first main flow path 700 supplies the raw material gas to the ozone generator 100 in a first state (see FIG. 4), and supplies the raw material gas to a first bypass flow path B1 in a second state (see FIG. 5).

[0035] [Second main channel 800] 1 is, for example, a flow path through which ozone gas discharged from the ozone generator 100 flows. The second main flow path 800 is formed, for example, by a pipe that connects the ozone generator 100 with downstream equipment (not shown), and is connected to a second communication port 9 of the ozone generator 100. For example, the second main flow path 800 discharges ozone gas from the ozone generator 100 in a first state (see FIG. 4), and discharges ozone gas from a second bypass flow path B2 in a second state (see FIG. 5).

[0036] [First bypass flow path B1 and second bypass flow path B2] Fig. 3 is a diagram showing the flow path configuration of the ozone generation system 1000 according to embodiment 1. As shown in Fig. 3, the first bypass flow path B1 and the second bypass flow path B2 are, for example, flow paths that bypass the ozone generator 100 and connect the first main flow path 700 and the second main flow path 800. The first bypass flow path B1 and the second bypass flow path B2 are, for example, formed by piping that connects the first main flow path 700 and the second main flow path 800.

[0037] 3, for example, the connection portion between the first main flow path 700 and the first bypass flow path B1 is designated as connection portion C11, and the connection portion between the second main flow path 800 and the first bypass flow path B1 is designated as connection portion C21. Furthermore, for example, the connection portion between the first main flow path 700 and the second bypass flow path B2 is designated as connection portion C12, and the connection portion between the second main flow path 800 and the second bypass flow path B2 is designated as connection portion C22. Here, connection portion C12 is located between connection portion C11 and the first communication port 8 in the first main flow path 700. Furthermore, connection portion C21 is located between the second communication port 9 and connection portion C22 in the second main flow path 800.

[0038] [Switching means 200] The switching means 200 is, for example, a mechanism for switching the gas flow state in the discharge space 5 between a first state and a second state in which the gas flows in opposite directions. Specifically, as shown in FIG. 3 , the switching means 200 includes a first on-off valve V1 provided in the first main flow path 700, a second on-off valve V2 provided in the second main flow path 800, bypass on-off valves V3 and V4 provided in the first bypass flow path B1, and bypass on-off valves V5 and V6 provided in the second bypass flow path B2. These on-off valves V1 to V6 are, for example, solenoid valves that can be switched between open and closed states under the control of the control device 600. However, the on-off valves according to the present disclosure are not limited to electrically operated valves and may be, for example, manual valves. Furthermore, the switching means according to the present disclosure is not limited to those that use on-off valves as long as they are capable of switching the gas flow direction in the discharge space.

[0039] 3, the first on-off valve V1 is disposed, for example, in the first main flow path 700, between the connection points C11 and C12. The second on-off valve V2 is disposed, for example, in the second main flow path 800, between the connection points C21 and C22. The bypass on-off valve V3 is disposed, for example, near the connection point C11 in the first bypass flow path B1, and the bypass on-off valve V4 is disposed, for example, near the connection point C21 in the first bypass flow path B1. The bypass on-off valve V5 is disposed, for example, near the connection point C12 in the second bypass flow path B2, and the bypass on-off valve V6 is disposed, for example, near the connection point C22 in the second bypass flow path B2.

[0040] FIG. 4 is a diagram illustrating an example of a flow path configuration of the ozone generation system 1000 in a first state (forward flow state). FIG. 5 is a diagram illustrating an example of a flow path configuration of the ozone generation system 1000 in a second state (reverse flow state). In FIGS. 4 and 5, flow paths indicated by solid lines are open (i.e., gas can flow), and flow paths indicated by dashed lines are blocked (i.e., gas cannot flow). In FIGS. 4 and 5, symbol G1 indicates the flow of raw material gas supplied to the ozone generator 100, and symbol G2 indicates the flow of ozone gas discharged from 100. In FIGS. 4 and 5, open valves indicate an open state (hereinafter also referred to as an open state), and black valves indicate a closed state (hereinafter also referred to as a closed state). That is, the open state includes, for example, a state in which the valve is fully open (fully open state). In addition, the closed state is, for example, a state in which the valve is fully closed (fully closed state).

[0041] The switching means 200 can switch the gas flow state in the discharge space 5 between a first state in which the gas flows in a first direction D1 as shown in Figure 4 and a second state in which the gas flows in a second direction D2 as shown in Figure 5, for example, by switching the opening and closing of each on-off valve in accordance with the control of the control device 600.

[0042] 4, the switching means 200 sets the first state by, for example, opening the first on-off valve V1 and the second on-off valve V2 and closing the bypass on-off valves V3 to V6. Therefore, in the first state, for example, the first main flow path 700 is opened from the raw material gas supply device 300 (not shown) to the first communication port 8 of the ozone generator 100, the second main flow path 800 is opened from the second communication port 9 of the ozone generator 100 to downstream equipment (not shown), and the first bypass flow path B1 and the second bypass flow path B2 are blocked. As a result, in the first state, gas flow paths are formed so that, for example, the raw material gas flows into the discharge space 5 through the first communication port 8 and the ozone gas is discharged from the discharge space 5 through the second communication port 9.

[0043] Specifically, the gas flow in the first state will be described with reference to Fig. 4. In the first state, the raw material gas supplied from the raw material gas supply device 300 (not shown) flows through the first main channel 700 toward the ozone generator 100 and reaches the first communication port 8 of the ozone generator 100 without flowing into the first bypass channel B1. The raw material gas that flows into the discharge space 5 from the first communication port 8 flows in the first direction D1 within the discharge space 5. Then, the ozone gas generated by the discharge in the discharge space 5 flows in the first direction D1 within the discharge space 5 and reaches the second communication port 9. The ozone gas discharged from the second communication port 9 to the second main channel 800 flows through the second main channel 800 toward a downstream equipment (not shown) and is supplied to the downstream equipment without flowing into the second bypass channel B2.

[0044] 5, the switching means 200 establishes the second state, for example, by closing the first on-off valve V1 and the second on-off valve V2 and opening the bypass on-off valves V3 to V6. Therefore, in the second state, the first main flow path 700 is blocked by the first on-off valve V1, the second main flow path 800 is blocked by the second on-off valve V2, and the first bypass flow path B1 and the second bypass flow path B2 are open. As a result, in the second state, gas flow paths are formed so that the raw material gas flows into the discharge space 5 through the second communication port 9 and the ozone gas is discharged from the discharge space 5 through the first communication port 8.

[0045] Specifically, the gas flow in the second state will be described with reference to FIG. 5. In the second state, the raw material gas supplied from the raw material gas supply device 300 (not shown) flows through the first main channel 700 toward the ozone generator 100 and flows into the first bypass channel B1 via a connection C11 between the first main channel 700 and the first bypass channel B1 without reaching the first communication port 8. The raw material gas that flows into the first bypass channel B1 from the connection C11 flows through the first bypass channel B1 and into the second main channel 800 via the connection C21. The raw material gas that flows into the second main channel 800 from the connection C21 flows through the second main channel 800 toward the ozone generator 100 without reaching downstream equipment (not shown) and reaches the second communication port 9 of the ozone generator 100. The raw material gas that flows into the discharge space 5 from the second communication port 9 flows in the second direction D2 within the discharge space 5. The ozone gas generated by the discharge in the discharge space 5 flows in the second direction D2 within the discharge space 5 and reaches the first communication port 8. The ozone gas discharged from the first communication port 8 to the first main channel 700 flows through the first main channel 700 toward the raw material gas supply device 300 and flows into the second bypass channel B2 via a connection C12 between the first main channel 700 and the second bypass channel B2 without reaching the raw material gas supply device 300. The raw material gas that flows into the second bypass channel B2 from the connection C12 flows through the second bypass channel B2 and into the second main channel 800 via the connection C22. The ozone gas that flows into the second main channel 800 from the connection C22 flows through the second main channel 800 toward the downstream equipment and is supplied to the downstream equipment.

[0046] [Control device 600] The control device 600 shown in FIG. 1 controls the switching means 200, the raw material gas supply device 300, the refrigerant supply device 400, and the power supply device 500, for example, to operate the ozone generation system 1000.

[0047] Specifically, the control device 600 performs an ozone gas generation process (hereinafter also referred to as an ozone generation process) by the ozone generator 100 by controlling, for example, the switching of the flow state by the switching means 200, the supply of raw material gas by the raw material gas supply device 300, the supply of cooling medium by the refrigerant supply device 400, and the power supply by the power supply device 500.

[0048] In addition, in the control of switching the flow state (hereinafter also referred to as flow direction switching control), the control device 600 switches the flow state to the first state or the second state, for example, based on the generation time of ozone gas in each of the first state and the second state.

[0049] Specifically, the control device 600 switches the flow state based on, for example, the elapsed time since the generation of ozone gas began in each of the first and second states (hereinafter also referred to as continuous generation time) as the generation time. Here, the continuous generation time in each flow state is, for example, the elapsed time from the point in time when ozone gas generation began after the previous switching of the flow state, when the flow state is switched. In other words, the continuous generation time is the time continuously performed from the start of ozone gas generation in each flow state to the present time. The continuous generation time may be, for example, the time elapsed since switching to the first state or the second state, or the time elapsed since discharge began in the first state or the second state.

[0050] For example, when ozone gas is being generated in the first state, the control device 600 switches from the first state to the second state when the continuous generation time t1 in the first state reaches a predetermined time T1 (t1≧T1). Also, when ozone gas is being generated in the second state, the control device 600 switches from the second state to the first state when the continuous generation time t2 in the second state reaches a predetermined time T2 (t2≧T2). The predetermined times T1 and T2 are not particularly limited.

[0051] In addition, for example, when the flow state is switched multiple times, the control device 600 may switch the flow state according to the cumulative total time for which ozone gas has been generated in each of the first state and the second state (hereinafter also referred to as cumulative generation time) as the generation time.

[0052] The control device 600 may also switch the flow state in accordance with the concentration of ozone gas in the discharge space 5 or the amount of ozone generated, as in the second and third embodiments described below. The control device according to the present disclosure may control the switching means in accordance with, for example, at least one of the time for generating ozone gas in the first and second states and the ozone concentration and amount of ozone generated in the discharge space. The control device 600 may also control the power output of the power supply device 500 in accordance with, for example, a change in the amount of ozone required due to a change in the water quality of downstream equipment.

[0053] Fig. 6 is a diagram illustrating the hardware configuration of a control device 600 according to the first embodiment. As shown in Fig. 4, the control device 600 is, for example, an electronic device having an electronic circuit. More specifically, the control device 600 is, for example, a computer device having a CPU 601 which is a processor, a memory 602, a communication device 603, and a storage medium 604. Each unit is connected to each other via, for example, a bus 605.

[0054] The storage medium 604 has, for example, a program storage area (not shown) that stores a program 610 for controlling the ozone generation process. The storage medium 604 also has, for example, an information storage area 620 that stores information used when performing the ozone generation process. The storage medium 604 may be, for example, a hard disk drive (HDD) or a solid state drive (SSD).

[0055] The CPU 601 performs control for the ozone generation process by executing the program 210 loaded into the memory 602 from the storage medium 604, for example.

[0056] The communication device 603 accesses an operation terminal (not shown) through which an operator inputs necessary information, for example, via a network (not shown) such as the Internet.

[0057] The electronic circuitry of the control device 600 may be, for example, a field programmable gate array (FPGA) or an application specific integrated circuit (ASIC). The ozone generation process may be performed by, for example, the FPGA or the ASIC.

[0058] [Ozone generation treatment] The ozone generation process executed by the control device 600 in the first embodiment will be described below. FIG. 7 is a flowchart illustrating the ozone generation process according to the first embodiment. In the present embodiment, as an example, the flow direction switching control is automatically executed by the control device 600, but the present disclosure is not limited to this. The flow direction switching control may be executed, for example, by an operator manually operating an on-off valve. Furthermore, although the following describes a case where the ozone generation process is started from the first state (forward flow), the ozone generation process may also be started from the second state (reverse flow).

[0059] First, the control device 600 starts generating ozone gas in the first state (step S1 in FIG. 7). Specifically, the generation of ozone gas starts when, for example, a flow path in the first state is formed as shown in FIG. 4. The control device 600 starts generating ozone gas based on, for example, an operator's operation received by the communication device 603. In step S1, for example, based on the control of the control device 600, the raw material gas is supplied from the raw material gas supply device 300 to the discharge space 5, and a high AC voltage is applied from the power supply device 500 to the pair of electrodes 1 and 2. This causes a silent discharge in the discharge space 5 in which the raw material gas is flowing, and the generation of ozone gas in the first state starts. Also, in step S1, for example, based on the control of the control device 600, a cooling medium is supplied from the refrigerant supply device 400 to the refrigerant flow paths 6 and 7, thereby cooling the pair of electrodes 1 and 2. Also, in step S1, for example, the control device 600 starts measuring the elapsed time (continuous generation time t1) since the generation of ozone gas in the first state started.

[0060] Next, the control device 600 determines, for example, whether a predetermined end condition is satisfied (step S2 in FIG. 7). The predetermined end condition may be, for example, whether the elapsed time since the operation of the ozone generation system 1000 started has reached a predetermined time, whether the number of times of ozone generation in the first state or the second state has reached a predetermined number of times, or whether the amount of generated ozone gas has reached a predetermined amount, etc. In step S2, when the end condition is satisfied (step S2: YES), the control device 600 stops the operation of the ozone generation system 1000 and ends the ozone generation process, for example.

[0061] In step S2, when the end condition is not satisfied (step S2: NO), the control device 600 proceeds to step S3, for example. In step S3, the control device 600 determines, for example, whether a predetermined time has elapsed since the generation of ozone gas in the first state started (step S3 in FIG. 7). Specifically, in step S3, for example, it is determined whether the continuous generation time t1 in the first state has reached the predetermined time T1 (whether t1 ≧ T1). When t1 < T1, that is, when the predetermined time has not elapsed (step S3: NO), for example, the process does not proceed to step S4 and the generation of ozone gas in the first state is continued (return to step S2).

[0062] In step S3, when t1 ≥ T1, that is, when a predetermined time has elapsed (step S3: YES), the control device 600 switches, for example, the flow state from the first state to the second state (step S4 in FIG. 7). In step S4, first, the control device 600 temporarily stops generating ozone gas, for example, before switching to the second state (i.e., in the first state). In step S4, next, the control device 600 controls the switching means 200 in a state where the generation of ozone gas has stopped, and forms a flow path in the second state as shown in FIG. 5, for example, by switching the opening and closing of each on-off valve. In step S4, next, the control device 600 resumes generating ozone gas, for example. Thereby, in step S4, the generation of ozone gas in the second state is started. Also, in step S4, the control device 600 starts measuring, for example, the elapsed time (continuous generation time t2) since the generation of ozone gas in the second state was started. Also, in step S4, the nitrogen addition rate of the raw material gas supplied in the second state may be set higher than the nitrogen addition rate of the raw material gas supplied in the first state, for example.

[0063] Next, the control device 600 determines whether a predetermined end condition is satisfied, for example, in the same manner as in step S2 (step S5 in FIG. 7). In step S5, when the end condition is satisfied (step S5: YES), the control device 600 stops the operation of the ozone generation system 1000 and ends the ozone generation process, for example.

[0064] In step S5, when the end condition is not satisfied (step S5: NO), the control device 600 proceeds to step S6, for example. In step S6, the control device 600 determines whether a predetermined time has elapsed since the generation of ozone gas in the second state was started, for example (step S6 in FIG. 7). Specifically, in step S6, for example, it is determined whether the continuous generation time t2 in the second state has reached a predetermined time T2 (whether t2 ≥ T2). When t2 < T2, that is, when the predetermined time has not elapsed (step S6: NO), for example, the process does not proceed to step S7, and the generation of ozone gas in the second state is continued (return to step S5).

[0065] In step S6, if t2≧T2, that is, if a predetermined time has elapsed (step S6: YES), the control device 600, for example, switches the flow state from the second state to the first state (step S7 in FIG. 7). In step S7, similar to step S4, the control device 600, for example, controls the switching means 200 while the generation of ozone gas is stopped to form a flow path in the first state, and restarts the generation of ozone gas. As a result, in step S7, the generation of ozone gas in the first state is started. Also, in step S7, similar to step S4, the control device 600, for example, starts measuring the continuous generation time t1. After step S7, the process returns to step S2.

[0066] The control device 600 repeats the loop from step S2 to step S7 until, for example, the termination condition is satisfied in step S2 or step S5. As described above, in the ozone generation process, ozone generation in the first state (forward flow state) and ozone generation in the second state (backward flow state) are alternately performed until the termination condition is satisfied in the first state (forward flow state) or the second state (backward flow state). Note that the threshold value (T1, T2) for the continuous generation time may be changed depending on the number of times ozone generation is performed in the first state or the second state, and may, for example, increase as the number of times increases.

[0067] Furthermore, in the above-described ozone generation process, flow direction switching control may be performed so that ozone generation in the first state (forward flow state) is the primary mode, and ozone generation in the second state (reverse flow state) is the intermittent conditioning (maintenance) mode for uniformizing nitrogen oxides on the electrode surface. In this case, for example, the operation time (ozone generation time) in the second state may be shorter than the operation time in the first state, e.g., T1 = 100 [h], T2 = 5 [h]. Furthermore, flow direction switching control may be performed so that ozone generation in the first state (forward flow state) and ozone generation in the second state (reverse flow state) are both primary, with a 50:50 ratio. In this case, for example, T1 = T2.

[0068] [Actions and Effects] As described above, the ozone generation system 1000 according to this embodiment includes the ozone generator 100 and the switching means 200. The ozone generator 100 has a pair of electrodes 1, 2 arranged opposite to each other across the discharge space 5 through which gas can flow, and generates ozone gas by generating a discharge in the discharge space 5 through which a raw material gas containing oxygen and nitrogen flows. The switching means 200 can switch the gas flow state in the discharge space 5 between a first state and a second state in which the gas flows in opposite directions.

[0069] In silent discharge ozone generation, metal oxides derived from the electrode material are generated by silent discharge and adhere to the surfaces of the electrodes and dielectrics. In this example, metal oxides adhere to the surfaces of the inner electrode 1 and dielectric 3 exposed to the discharge space 5. These metal oxides decompose ozone. On the other hand, in silent discharge ozone generation, when ozone gas is generated from a source gas containing oxygen and nitrogen, nitrogen oxides (e.g., dinitrogen pentoxide (N2O5)) are by-produced as ozone is generated. When these nitrogen oxides adhere to the surfaces of the electrodes and dielectrics and coexist with the metal oxides, the contact area between the metal oxides and ozone is reduced, thereby suppressing ozone decomposition by the metal oxides. By suppressing the ozone decomposition reaction by the metal oxides, gas with a relatively high ozone concentration can be generated.

[0070] However, when the raw material gas is flowed in one direction through the discharge space 5, the amount of metal oxides that adhere to the electrode surfaces is not uniform in the gas flow direction in the discharge space 5, and tends to be greater on the upstream side than on the downstream side. Also, when the raw material gas is flowed in one direction through the discharge space 5, the amount of nitrogen oxides that adhere to the electrode surfaces is not uniform in the gas flow in the discharge space 5, and tends to be greater on the downstream side than on the upstream side. Specifically, for example, in the first state, the amount of metal oxides that adheres increases from the second communication port 9, which serves as the ozone gas outlet, toward the first communication port 8, which serves as the raw material gas inlet (i.e., toward the second direction D2), and the amount of nitrogen oxides increases from the first communication port 8 toward the second communication port 9 (i.e., toward the first direction D1). Conversely, for example, in the second state, the amount of metal oxides increases from the first communication port, which is the outlet for ozone gas, toward the second communication port 9, which is the inlet for raw material gas (i.e., toward the first direction D1), and the amount of nitrogen oxides increases from the second communication port 9 toward the first communication port 8 (i.e., toward the second direction D2).

[0071] Therefore, for example, if ozone generation in the first state is carried out continuously for a long period of time without switching to the second state, the amount of metal oxides on the electrode surface will be greater on the first communication port 8 side than on the second communication port 9 side, while the amount of nitrogen oxides on the electrode surface will be less on the first communication port 8 side than on the second communication port 9 side. Therefore, ozone decomposition by metal oxides on the first communication port 8 side cannot be sufficiently suppressed, and as a result, there is a concern that the ozone concentration in the generated ozone gas will decrease and the ozone generation efficiency will decrease.

[0072] In contrast, as described above, the ozone generation system 1000 according to this embodiment can switch the gas flow state in the discharge space 5 between a first state and a second state in which the gas flows in opposite directions. This allows the nitrogen oxides adhering to the electrode surface to be uniformly distributed, for example, by performing discharge in the first state and then switching to the second state and performing discharge again. Specifically, in the first state, more nitrogen oxides adhere to the second communication port 9 side than to the first communication port 8 side, and in the second state, more nitrogen oxides adhere to the first communication port 8 side than to the second communication port 9 side. As a result, after ozone generation in the first state and ozone generation in the second state, nitrogen oxides are uniformly distributed on the electrode surface, suppressing ozone decomposition by metal oxides and restoring the ozone concentration. As a result, the ozone generation system 1000 according to this embodiment can suppress a decrease in ozone generation efficiency.

[0073] The ozone generation system 1000 according to this embodiment further includes a first main channel 700 that supplies a raw material gas to the ozone generator 100 in the first state, a second main channel 800 that discharges ozone gas from the ozone generator 100 in the first state, and a first bypass channel B1 and a second bypass channel B2 that connect the first main channel 700 and the second main channel 800 while bypassing the ozone generator 100. The switching means 200 establishes the first state by opening the first main channel 700 and the second main channel 800 and blocking the first bypass channel B1 and the second bypass channel B2, and establishes the second state by blocking the first main channel 700 and the second main channel 800 and opening the first bypass channel B1 and the second bypass channel B2.

[0074] The ozone generation system 1000 according to this embodiment also has a first communication port 8 that communicates with the discharge space 5 and is connected to the first main flow path 700, and a second communication port 9 that communicates with the discharge space 5 and is connected to the second main flow path 800. The switching means 200 also has a first on-off valve V1 that is provided in the first main flow path 700 and can be switched between open and closed, a second on-off valve V2 that is provided in the second main flow path 800 and can be switched between open and closed, and bypass on-off valves V3 to V6 that are provided in the first bypass flow path B1 and the second bypass flow path B2 and can be switched between open and closed. Furthermore, a connection portion C12 between the first main flow path 700 and the second bypass flow path B2 is located between a connection portion C11 between the first main flow path 700 and the first bypass flow path and the first communication port 8, and a connection portion C21 between the second main flow path 800 and the first bypass flow path B1 is located between a connection portion C22 between the second main flow path 800 and the second bypass flow path B2 and the second communication port 9. Furthermore, the first on-off valve V1 is disposed between the connection portion C11 and the connection portion C12, and the second on-off valve V2 is disposed between the connection portion C21 and the connection portion C22. The switching means 200 sets the first state by opening the first on-off valve V1 and the second on-off valve V2 and closing the bypass on-off valves V3 to V6, and sets the second state by closing the first on-off valve V1 and the second on-off valve V2 and opening the bypass on-off valves V3 to V6.

[0075] This allows the gas flow to be switched simply by switching the flow path without rearranging the piping connected to the ozone generator 100, thereby realizing the ozone generation system 1000 with a simple structure. Also, by simply providing a bypass flow path in an existing ozone generation facility, the ozone generator 100 can be realized at low cost.

[0076] For example, ozone generation in the second state may be performed as conditioning to homogenize nitrogen oxides on the electrode surface, and the ozone generation time in the second state may be shorter than the ozone generation time in the first state. In this case, for example, the bypass flow paths B1 and B2 may use piping with a smaller diameter than the first main flow path 700 and the second main flow path 800. Furthermore, when ozone generation in the second state is performed as conditioning, the nitrogen addition rate of the source gas may be higher than the nitrogen addition rate in the first state in order to generate a large amount of nitrogen oxides in a short time in the second state. This allows a relatively large amount of ozone to be generated in the first state, and conditioning to be performed in a short time in the second state. For example, the nitrogen addition rate of the source gas in the first state may be 3%, which provides high ozone generation efficiency, and 10%, which provides high ozone generation efficiency, in the second state.

[0077] The ozone generation system 1000 according to this embodiment further includes a control device 600 that controls the switching means 200 in accordance with the generation time of ozone gas in each of the first and second states. This allows automatic control of flow direction switching to be performed in accordance with the generation time of ozone gas.

[0078] [Modification of the first embodiment] Next, an ozone generation process according to a modification of embodiment 1 will be described. In the above-described ozone generation process, flow direction switching control is performed according to the continuous generation time, but in the modification of embodiment 1, flow direction switching control is performed according to the cumulative generation time (the cumulative total time during which ozone gas is generated in each of the first state and the second state).

[0079] For example, the cumulative generation time in the first state (forward flow state) is tc1, and the cumulative generation time in the second state (backward flow state) is tc2. Furthermore, the threshold value of the cumulative generation time for switching from the first state to the second state the nth time (n is a natural number) after the start of the ozone generation process is Tc1(n), and the threshold value of the cumulative generation time for switching from the second state to the first state the nth time is Tc2(n). Tc1(n) and Tc2(n) are set to increase as n increases, i.e., as the number of times increases.

[0080] In the ozone generation process according to the modification of the first embodiment, the control device 600 determines whether the cumulative generation time tc1 in the first state has reached a predetermined time Tc1(n) in step S3 of Fig. 7, and if so (tc1 ≥ Tc1(n)), switches from the first state to the second state in step S4. Then, the control device 600 determines whether the cumulative generation time tc2 in the second state has reached a predetermined time Tc2(n) in step S6 of Fig. 7, and if so (tc2 ≥ Tc2(n)), switches from the second state to the first state in step S7.

[0081] In the modification of the first embodiment, flow direction switching control may be performed so that ozone generation in the first state (forward flow state) is the main ozone generation and ozone generation in the second state (backward flow state) is the conditioning ozone generation, in which case, for example, Tc1(n) > Tc2(n) may be satisfied. Furthermore, flow direction switching control may be performed so that ozone generation in the first state and ozone generation in the second state are both main ozone generation at a 50:50 ratio, in which case, for example, Tc1(n) = Tc2(n) may be satisfied.

[0082] [Ozone generation system 1000A according to embodiment 2] Next, an ozone generation system according to embodiment 2 will be described. Fig. 8 is a diagram showing the configuration of an ozone generation system 1000A according to embodiment 2. Note that the dashed lines in Fig. 8 indicate representative control lines. Hereinafter, the ozone generation system 1000A according to embodiment 2 will be described, mainly focusing on the differences from the ozone generation system 1000 according to embodiment 1, and similar components will be denoted by the same reference numerals and will not be described in detail.

[0083] As shown in FIG. 8, an ozone generation system 1000A according to the second embodiment differs from the above-described ozone generation system 1000 in that, for example, an ozone concentration sensor 900 is further provided.

[0084] The ozone concentration sensor 900 is, for example, an ozone monitor that detects the ozone concentration in the discharge space 5 and outputs the result to the control device 600. The ozone concentration sensor 900 may be provided, for example, in the second main flow path 800, and may measure the ozone concentration of ozone gas discharged from the ozone generator 100 in the first state, thereby outputting the ozone concentration in the discharge space 5 in the first state to the control device 600. The ozone concentration sensor 900 may also be provided, for example, in the first main flow path 700 or the second main flow path 800, and may measure the ozone concentration of ozone gas discharged from the ozone generator 100 in the second state, thereby outputting the ozone concentration in the discharge space 5 in the second state to the control device 600. Specifically, the ozone concentration sensor 900 may be installed between the connection C12 (the connection portion between the first main flow path 700 and the second bypass flow path B2) in the first main flow path 700 and the first communication port 8, or between the connection C22 (the connection portion between the second main flow path 800 and the second bypass flow path B2) in the second main flow path 800 and the downstream equipment. However, the installation location of the ozone concentration sensor 900 is not limited to the above.

[0085] The control device 600 according to the second embodiment switches the flow state of the discharge space 5 by controlling the switching means 200 in accordance with the detected value of the ozone concentration obtained from the ozone concentration sensor 900, for example.

[0086] The following describes the ozone generation process executed by the control device 600 in embodiment 2. Fig. 9 is a flowchart illustrating the ozone generation process according to embodiment 2. Note that, among the processes shown in Fig. 9, the description of the same processes as those in Fig. 7 will be omitted.

[0087] In the ozone generation process according to the second embodiment, for example, in step S203 of Fig. 9, the control device 600 determines whether the ozone concentration of the ozone gas discharged from the discharge space 5 in the first state has fallen below a predetermined concentration. If the ozone concentration is not below the predetermined concentration (step S203: NO), the control device 600 does not proceed to step S4, but if the ozone gas concentration has fallen below the predetermined concentration due to ozone decomposition by metal oxides (step S203: YES), the control device 600 proceeds to step S4 and switches to the second state. By switching to the second state, nitrogen oxides are uniformly attached to the electrodes, which suppresses ozone decomposition by metal oxides and restores the ozone concentration.

[0088] 9, for example, the control device 600 determines whether the concentration of ozone gas in the discharge space 5 in the second state has reached a predetermined concentration. If the concentration of ozone gas has not reached the predetermined concentration (step S206: NO), the control device 600 does not proceed to step S7, but if the concentration of ozone gas has reached the predetermined concentration (step S206: YES), the control device 600 proceeds to step S7 and switches to the first state. Note that in step S206, if the concentration of ozone gas reaches the predetermined concentration and then decreases again to fall below the predetermined concentration, the control device 600 may proceed to step S7.

[0089] According to the ozone generation system 1000A of the second embodiment, the flow direction switching control can be automatically performed according to the ozone concentration of the ozone gas. This makes it possible to maintain the ozone concentration at a certain level or higher, and to suppress a decrease in the efficiency of ozone generation.

[0090] The control device 600 may switch the flow state depending on, for example, both the generation time of the ozone gas and the ozone concentration in the discharge space 5. The above-mentioned flow direction switching control may also be performed by, for example, an operator manually operating an on-off valve.

[0091] [Ozone generation system 1000B according to embodiment 3] Next, an ozone generation system according to embodiment 3 will be described. Fig. 10 is a diagram showing the configuration of an ozone generation system 1000B according to embodiment 3. Note that the dashed lines in Fig. 10 indicate representative control lines. Hereinafter, the ozone generation system 1000B according to embodiment 3 will be described, mainly focusing on the differences from the ozone generation system 1000A according to embodiment 2, and similar components will be denoted by the same reference numerals and will not be described in detail.

[0092] As shown in FIG. 10, an ozone generation system 1000B according to the third embodiment differs from the above-described ozone generation system 1000A in that it further includes a flow meter 910, for example.

[0093] The flow meter 910 is provided, for example, in the first main flow path 700 or the second main flow path 800, and measures the flow rate of ozone gas discharged from the ozone generator 100 in each of the first state and the second state, and outputs the result to the control device 600.

[0094] The control device 600 of embodiment 3 switches the flow state of the discharge space 5, for example, by controlling the switching means 200 according to the cumulative amount of ozone generated in each of the first state (forward flow state) and the second state (backward flow state) (hereinafter also referred to as the cumulative ozone generation amount).

[0095] For example, the control device 600 calculates the cumulative amount of ozone generated based on the ozone concentration and flow rate of the ozone gas discharged from the ozone generator 100 and the operating time (cumulative generation time) of the ozone generator 100. Specifically, the cumulative amount of ozone generated can be calculated by the following formula. Cumulative ozone production [g] = ozone concentration of ozone gas [g / m 3 ] × ozone gas flow rate [m 3 / h] x operating time (cumulative generation time) [h]

[0096] For example, let m1 be the cumulative ozone generation amount in the first state (forward flow state), and m2 be the cumulative ozone generation amount in the second state (backward flow state). Furthermore, let M1(n) be the threshold for the cumulative ozone generation amount for switching from the first state to the second state the nth time (n is a natural number) after the start of the ozone generation process, and let M2(n) be the threshold for the cumulative ozone generation amount for switching from the second state to the first state the nth time. M1(n) and M2(n) are set to increase as n increases, i.e., as the number of times increases.

[0097] Fig. 11 is a flowchart illustrating an ozone generation process according to embodiment 3. Note that, among the processes shown in Fig. 11, the same processes as those in Fig. 7 and Fig. 9 will not be described.

[0098] In the ozone generation process according to the third embodiment, the control device 600 determines whether the cumulative ozone generation amount m1 in the first state has reached a predetermined amount M1(n) in step S303 of Fig. 11, and if so (m1 ≥ M1(n)), switches from the first state to the second state in step S4. Then, the control device 600 determines whether the cumulative ozone generation amount m2 in the second state has reached a predetermined amount M2(n) in step S306 of Fig. 11, and if so (m2 ≥ M2(n)), switches from the second state to the first state in step S7.

[0099] According to the ozone generation system 1000B of the third embodiment, flow direction switching control can be automatically performed in accordance with the amount of ozone generated.

[0100] In the third embodiment, flow direction switching control may also be performed so that ozone generation in the first state (forward flow state) is the main ozone generation and ozone generation in the second state (backflow state) is the conditioning ozone generation. In this case, for example, M1(n) > M2(n) may be set. For example, M1(n) = 5000 [kg] and M2(n) = 150 [kg] may be set. Furthermore, flow direction switching control may also be performed so that ozone generation in the first state and ozone generation in the second state are both main ozone generation at a 50:50 ratio. In this case, for example, M1(n) = M2(n) may be set. For example, M1(n) = M2(n) may be set.

[0101] Furthermore, the control device 600 may control the switching from the first state to the second state according to the cumulative amount of ozone generated in the first state, while controlling the switching from the second state to the first state according to the continuous generation time in the second state. Specifically, the control device 600 may switch to the second state when the cumulative amount of ozone generated m1 in the first state reaches 5000 [kg], and then switch back to the first state when the continuous generation time t2 in the second state reaches 10 [h].

[0102] [Modification of the third embodiment] Furthermore, the control device 600 may switch the flow state based on, for example, the amount of ozone continuously generated after the start of ozone gas generation in each of the first and second states (hereinafter also referred to as the continuous ozone generation amount). For example, when the flow state is switched, the continuous ozone generation amount in each flow state is the amount of ozone generated from the point at which ozone gas generation started after the previous switching. For example, the control device 600 may switch to the second state when the continuous ozone generation amount in the first state reaches a predetermined first threshold, and may switch to the first state when the continuous ozone generation amount in the second state reaches a predetermined second threshold. Furthermore, ozone generation in the first state (forward flow state) may be the main process, and ozone generation in the second state (backward flow state) may be used as conditioning. In this case, for example, the first threshold may be greater than the second threshold (n). Furthermore, for example, flow direction switching control may be performed so that ozone generation in the first state and ozone generation in the second state are both predominant at a 50:50 ratio, in which case the first threshold value may be set equal to the second threshold value. Specifically, for example, the flow state may be switched every time the continuous ozone generation amount reaches 5,000 kg. Furthermore, the threshold values ​​for the continuous ozone generation amount (first threshold value and second threshold value) may be changed depending on the number of ozone generation events in the first state or the second state, and may increase as the number of events increases, for example.

[0103] <Electrode surface evaluation test> A confirmation test was carried out to evaluate the tendency of the amount of metal oxides and nitrogen oxides attached to the electrode surface in silent discharge ozone generation.

[0104] In the test, an ozone generator equivalent to the ozone generator 100 described above was operated continuously for a predetermined period of time to generate ozone. A metal tube made of SUS304 was used as the inner electrode serving as the high-voltage electrode. Ozone was generated only in the first state, and the gas flow in the discharge space was not switched. Specifically, source gas was supplied through the first communication port (hereinafter also referred to as the inlet in this test), a discharge was induced in the discharge space, and ozone gas was discharged through the second communication port (hereinafter also referred to as the outlet in this test). Tests were also conducted for 20 hours and 240 hours of continuous operation of the ozone generator. Hereinafter, when each end of the metal tube serving as the inner electrode is described separately, the end on the inlet side of the discharge space (the first communication port side) will be referred to as the inlet end, and the end on the outlet side of the discharge space (the second communication port side) will be referred to as the outlet end.

[0105] [Metal oxide adhesion evaluation] To evaluate the amount of metal oxide attached to the electrode, the inner electrode was removed from the ozone generator after continuous operation, and each end was immersed in hydrochloric acid to obtain leachate from each end. The metal ions contained in the leachate were quantitatively analyzed using ICP (Inductively Coupled Plasma) emission spectrometry.

[0106] Figure 12 is a table showing the evaluation results of the amount of metal oxide adhesion. Figure 12 shows the concentration and composition ratio of metal ions in the leachate at the inlet end and the leachate at the outlet end. Figure 12 also shows the composition ratio of SUS304, the material of the inner electrode.

[0107] As can be seen from Figure 12, the composition ratio of metal ions contained in each leachate after both 20 and 240 hours of operation was roughly close to that of SUS304. This suggests that the metal oxides adhering to the electrodes originated from the electrode material. Also, as can be seen from Figure 12, the concentration of metal ions contained in the leachate at the inlet end was higher than the concentration of metal ions contained in the leachate at the outlet end after both 20 and 240 hours of operation. This confirms that in silent discharge ozone generation, the amount of metal oxides adhering to the electrodes is greater on the inlet side than on the outlet side of the discharge space.

[0108] [Evaluation of nitrogen oxide adhesion amount] To evaluate the amount of nitrogen oxide (N2O5) adhering to the electrode, the inner electrode was removed from the ozone generator after continuous operation, and each end was immersed in ultrapure water to obtain leachate from each end. The nitrate nitrogen contained in the leachate was then quantitatively analyzed using ion chromatography.

[0109] Fig. 13 is a table showing the evaluation results of the amount of nitrogen oxides attached, which shows the concentrations of nitrate nitrogen in the leachate at the inlet end and the leachate at the outlet end.

[0110] As can be seen from Figure 13, the concentration of nitrate nitrogen in the leachate at the outlet end was higher than that at the inlet end after both 20 and 240 hours of operation. This confirms that in silent discharge ozone generation, the amount of nitrogen oxides adhering to the electrodes is greater on the outlet side than on the inlet side of the discharge space.

[0111] (Addendum) The present disclosure includes the following aspects. [Aspect 1] an ozone generator having a pair of electrodes arranged opposite each other across a discharge space through which a gas can flow, the ozone generator generating ozone gas by generating an electric discharge in the discharge space through which a raw material gas containing oxygen and nitrogen flows; and a switching means capable of switching the gas flow state in the discharge space between a first state and a second state in which the gas flows in opposite directions. Ozone generation system. [Aspect 2] a first main flow path that supplies the raw material gas to the ozone generator in the first state, a second main flow path that discharges the ozone gas from the ozone generator in the first state, and a first bypass flow path and a second bypass flow path that bypass the ozone generator and connect the first main flow path and the second main flow path, the switching means sets the first state by opening the first main flow path and the second main flow path and blocking the first bypass flow path and the second bypass flow path, and sets the second state by blocking the first main flow path and the second main flow path and opening the first bypass flow path and the second bypass flow path. 2. The ozone generation system of embodiment 1. [Aspect 3] the ozone generator has a first communication port that communicates with the discharge space and to which the first main flow path is connected, and a second communication port that communicates with the discharge space and to which the second main flow path is connected, the switching means includes a first on-off valve provided in the first main flow path and switchable between open and closed states, a second on-off valve provided in the second main flow path and switchable between open and closed states, and bypass on-off valves provided in the first bypass flow path and the second bypass flow path and switchable between open and closed states, a connection portion between the first main flow path and the second bypass flow path is located between the connection portion between the first main flow path and the first bypass flow path and the first communication port, a connection portion between the second main flow path and the first bypass flow path is located between the connection portion between the second main flow path and the second bypass flow path and the second communication port, the first on-off valve is disposed between a connection portion between the first main flow path and the first bypass flow path and a connection portion between the first main flow path and the second bypass flow path, the second on-off valve is disposed between a connection portion between the second main flow path and the first bypass flow path and a connection portion between the second main flow path and the second bypass flow path, the switching means sets the first state by opening the first on-off valve and the second on-off valve and closing the bypass on-off valve, and sets the second state by closing the first on-off valve and the second on-off valve and opening the bypass on-off valve. 3. The ozone generation system of embodiment 2. [Aspect 4] a control device that controls the switching means in accordance with at least one of the generation time of the ozone gas in each of the first state and the second state, the ozone concentration in the discharge space, and the generation amount of the ozone gas. 4. The ozone generation system according to any one of aspects 1 to 3. [Aspect 5] An ozone generation method using an ozone generation system that generates ozone gas from a raw material gas containing oxygen and nitrogen, comprising: The ozone generation system comprises: an ozone generator having a pair of electrodes arranged opposite to each other across a discharge space through which a gas can flow, the ozone generator generating ozone gas by generating a discharge in the discharge space while the raw material gas is flowing; a switching means for switching between a first state and a second state in which the gas flow directions in the discharge space are opposite to each other; After discharging in the first state, the state is switched to the second state and discharging is performed. Ozone generation method. [Explanation of symbols]

[0112] 1: Inner electrode 2: Outer electrode 5: Discharge space 8: 1st communication port 9: 2nd communication port 100: Ozone generator 200: Switching Method 600: Control device 700: 1st main channel 800: 2nd main channel 1000: Ozone Generating System B1: First bypass flow path B2: Second bypass flow path V1: First shutoff valve V2: Second shutoff valve V3~V6: Bypass shutoff valve

Claims

1. an ozone generator having a pair of electrodes arranged opposite each other across a discharge space through which a gas can flow, the ozone generator generating ozone gas by generating an electric discharge in the discharge space through which a raw material gas containing oxygen and nitrogen flows; a switching means for switching the gas flow state in the discharge space between a first state and a second state in which the gas flows in opposite directions to each other; Ozone generation system.

2. the apparatus further includes a first main flow path that supplies the raw material gas to the ozone generator in the first state, a second main flow path that discharges the ozone gas from the ozone generator in the first state, and a first bypass flow path and a second bypass flow path that bypass the ozone generator and connect the first main flow path and the second main flow path, the switching means sets the first state by opening the first main flow path and the second main flow path and blocking the first bypass flow path and the second bypass flow path, and sets the second state by blocking the first main flow path and the second main flow path and opening the first bypass flow path and the second bypass flow path.

10. The ozone generating system of claim 1.

3. the ozone generator has a first communication port that communicates with the discharge space and to which the first main flow path is connected, and a second communication port that communicates with the discharge space and to which the second main flow path is connected, the switching means includes a first on-off valve provided in the first main flow path and switchable between open and closed states, a second on-off valve provided in the second main flow path and switchable between open and closed states, and bypass on-off valves provided in the first bypass flow path and the second bypass flow path and switchable between open and closed states, a connection portion between the first main flow path and the second bypass flow path is located between the connection portion between the first main flow path and the first bypass flow path and the first communication port, a connection portion between the second main flow path and the first bypass flow path is located between the connection portion between the second main flow path and the second bypass flow path and the second communication port, the first on-off valve is disposed between a connection portion between the first main flow path and the first bypass flow path and a connection portion between the first main flow path and the second bypass flow path, the second on-off valve is disposed between a connection portion between the second main flow path and the first bypass flow path and a connection portion between the second main flow path and the second bypass flow path, the switching means sets the first state by opening the first on-off valve and the second on-off valve and closing the bypass on-off valve, and sets the second state by closing the first on-off valve and the second on-off valve and opening the bypass on-off valve.

3. The ozone generating system of claim 2.

4. a control device that controls the switching means in accordance with at least one of a generation time of the ozone gas in the first state and a generation amount of the ozone gas in the second state, an ozone concentration in the discharge space, and 10. The ozone generating system of claim 1.

5. An ozone generation method using an ozone generation system that generates ozone gas from a raw material gas containing oxygen and nitrogen, comprising: The ozone generation system comprises: an ozone generator having a pair of electrodes arranged opposite to each other across a discharge space through which a gas can flow, the ozone generator generating ozone gas by generating a discharge in the discharge space while the raw material gas is flowing; a switching means for switching between a first state and a second state in which the gas flow directions in the discharge space are opposite to each other; After discharging in the first state, the state is switched to the second state and discharging is performed. Ozone generation method.

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