Plasma Activated Fluid Treatment Systems

Abstract

The present invention relates to a plasma activated fluid treatment system, comprising: an alternating current (AC) power supply (10), a reaction chamber (14), wherein the one reaction chamber comprises a plurality of reaction electrodes (11) and corresponding ground electrodes (12), each reaction electrode being separated from the corresponding ground electrode by a gap; or a plurality of reaction chambers (14), wherein each reaction chamber comprises at least one reaction electrode (11) and a corresponding ground electrode, the reaction electrode being separated from the corresponding ground electrode by a gap; wherein the AC power supply is electrically connected in parallel with each ground electrode on one side and in parallel with each reaction electrode on the other side, wherein each reaction electrode is connected to the ground (13) via a capacitor (21), and wherein an inductor (20) is arranged between each reaction electrode and the AC power supply.

Description

Technical Field

[0001] The present invention relates to a system and method for treating a fluid using plasma. Examples of such plasma activated fluid treatments include plasma activated water synthesis, and treating a gas containing nitrogen and oxygen (eg, air) for nitrogen fixation. Background Art

[0002] Water can be "activated" by applying plasma in contact with the water, for example by generating plasma in the water (forming bubbles in the water) or along the surface of the water. Plasma activated water (PAW) typically contains hydrogen peroxide, nitrates, nitrites, wherein peroxynitrite is formed due to the reaction of nitrite and hydrogen peroxide in an acidic environment and is present in the PAW for about 15 minutes after activation. In addition, the pH value of PAW is generally in the range of 0 to 7. The composition and low pH of PAW have been shown to have a synergistic antimicrobial effect on bacteria, biofilms, yeasts and other microorganisms. PAW can be used as a natural fertilizer, which enhances seed germination and stimulates plant growth.

[0003] The production of nitrates by the activation process has proven to be very energy-efficient and can be used as an energy-efficient alternative to the production of nitrogen components in fertilizers currently produced by the energy-intensive Haber-Bosch process. The activation process has also proven to be highly efficient for the production of hydrogen peroxide.

[0004] Nitrogen fixation (NF) is the process of converting nitrogen molecules (N2) in air or nitrogen gas (relatively inactive molecules) into nitrogen-containing compounds. Plasma in air can generate reactive nitrogen and oxygen species, which form nitric acid and nitrous acid in an aqueous environment.

[0005] The Birkeland-Eyde arc nitrogen fixation process was developed in 1903. The process consists of multiple steps. First, an arc plasma is applied to convert nitrogen / oxygen into nitric oxide (NO), which is then further oxidized to nitrogen dioxide (NO2) by cooling the hot gas and mixing it with atmospheric oxygen. Finally, the NO2 is converted to nitric acid (HNO3) by absorption in water.

[0006] In the context of this description, the term "nitrogen fixation" will refer to the formation of any nitrogen-containing compound other than N2.

[0007] Plasma activated fluid treatment can be achieved by thermal plasma or non-thermal plasma, which can be generated by connecting an alternating current (AC) or direct current (DC) power source to a circuit including a reaction electrode (sometimes referred to as a high voltage (HV) electrode) and a ground electrode, between which a plasma will be generated. The electrode is located within a reaction chamber, which generally has an inlet and an outlet for the fluid to be treated.

[0008] In the case of PAW synthesis, there will be inlets and outlets for water and air, in the case of NF, inlets and outlets for gas will suffice.

[0009] Published application WO 01 / 37619 A1 discloses an electric arc furnace. For efficient reignition, a second energy supply is provided.

[0010] A cold plasma device for surface plasma treatment is disclosed in DE 10 2006 019664 A1. All disclosed embodiments comprise only a single reaction electrode.

[0011] WO 2016 / 096751 A1 discloses a thermal plasma and non-thermal plasma activated water reactor system.

[0012] US Patent 5 977 715 discloses a handheld atmospheric pressure glow discharge plasma source. The embodiment comprises only a single reaction electrode.

[0013] A problem with current plasma activated fluid processing equipment for PAW and / or NF is upgrading the equipment to use multiple reactive electrodes connected in parallel to the same power source. When plasma ignites in the gap between a reactive electrode and a grounded electrode, the current will travel exclusively through that plasma due to the low resistance of the plasma, making it impossible to ignite plasma at other reactive electrodes.

[0014] An obvious solution is to use multiple power supplies, one for each electrode. However, this solution is more expensive than using a single larger power supply. The present invention seeks to provide an alternative solution to this problem. Summary of the invention

[0015] According to a first aspect, the present invention provides a plasma activated fluid treatment system comprising:

[0016] - an alternating current (AC) power source (10),

[0017] - a reaction chamber (14), wherein the reaction chamber comprises a plurality of reaction electrodes (11) and corresponding ground electrodes (12), each reaction electrode and the corresponding ground electrode being separated by a gap;

[0018] or

[0019] - a plurality of reaction chambers (14), wherein each reaction chamber comprises at least one reaction electrode (11) and a corresponding ground electrode, and the reaction electrode and the corresponding ground electrode are separated by a gap;

[0020] wherein an AC power source is electrically connected in parallel with each ground electrode on one side and in parallel with each reaction electrode on the other side, wherein each reaction electrode is connected to ground (13) via a capacitor (21), and wherein an inductor (20) is provided between each reaction electrode and the AC power source. Advantageously, the system is thus able to power all reaction electrodes using a single AC power source. In a reaction chamber having more than one reaction electrode, the ground electrode may be a common ground electrode for the plurality of reaction electrodes. The corresponding ground electrode may be a common ground electrode for each reaction electrode in the reaction chamber. Alternatively, each reaction electrode may have its own corresponding reaction electrode

[0021] The inductor and capacitor form an LC circuit for each electrode. The inductor can be a coil or other electronic component. When the plasma ignites, the LC circuit will suppress the discharge current to prevent low load impedance to the power supply. Therefore, other electrodes can also ignite, overcoming the starting problem of multi-electrode configuration.

[0022] In an embodiment according to the invention, the frequency of the AC power source is close to the resonant frequency of the inductor-capacitor circuit. "Close" means that the match is sufficient for good coupling between the AC power source and the LC circuit. When close to resonance, the LC circuit can be excited, so the voltage on the reaction electrode can be amplified to the starting voltage of the plasma.

[0023] In an embodiment according to the invention, the system comprises a plurality of inductors, each inductor being connected to a corresponding reactive electrode, wherein the inductors are arranged in a symmetrical manner, preferably in a point-symmetrical manner. The configuration with symmetrical stray capacitance ensures that the resonant frequency of all electrode circuits is the same. It can also advantageously reduce the need for shielding between inductors.

[0024] Since the stray capacitance of an inductor is usually the dominant factor in the total capacitance, using (point) symmetrical inductors is a good way to promote symmetrical stray capacitance. A further improvement would include a symmetrical arrangement of other (stray) capacitance sources (e.g. electrodes).

[0025] In an embodiment according to the invention, the system comprises a voltage measurement unit configured to determine the voltage gain of the fluid treatment system, more specifically, the voltage gain of the plasma generation portion of the fluid treatment system, and to continuously adjust the AC power frequency to maximize the voltage gain. This allows the system to track the resonant frequency, even when it shifts due to changes in impedance caused by igniting the plasma. In an embodiment, a single capacitive voltage sensor is placed in the center of or around the concentric coil structure, or in the center of or around the (symmetrically arranged) electrodes, so that the average gain of the entire system can be monitored. By maximizing the gain, the output power coupled into the system can be maximized.

[0026] In a further embodiment, a matching circuit is provided between the AC power source and the parallel LC circuit. The matching circuit is configured to match the impedance of the power source with the impedance of the parallel connected LC circuit to achieve optimal power transfer.

[0027] In an embodiment according to the invention, the capacitor is formed by the intrinsic capacitance of the system. The intrinsic capacitance may include the stray capacitance of the reactive electrodes and / or the stray / self capacitance of the inductor.

[0028] In an embodiment according to the invention, the AC power supply is provided with a controller for periodically controlling the voltage and / or frequency and / or waveform of the AC power supply output. The controller can be used, for example, to manipulate the plasma between a thermal operating mode and a non-thermal operating mode.

[0029] In an embodiment according to the invention, the ground electrode is provided with a water interface barrier and / or a dielectric barrier. In a process step involving liquids and gases (e.g., water and air), the liquid can efficiently form a dielectric barrier. In the case of gas processing, a dielectric barrier can be added to the ground electrode. The dielectric barrier can act as an inert surface (e.g., glass, ceramic) while being able to transmit the discharge current.

[0030] In an embodiment according to the present invention, the system includes a plurality of reaction chambers, each reaction chamber having at least one reaction electrode and a ground electrode connected in parallel to an AC power source.

[0031] In an embodiment according to the present invention, each reaction chamber is provided with a plurality of reaction electrodes connected in parallel to an AC power source.

[0032] In an embodiment according to the invention, the plasma activated fluid treatment system further comprises a gas inlet and / or a gas outlet, a fluid inlet and a fluid outlet. The fluid inlet and the fluid and gas outlets may be connected to a reservoir.

[0033] In an embodiment according to the invention, the AC operating frequency is between 10 kHz and 50 MHz, preferably between 20 kHz and 15 MHz. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Embodiments of the present invention will be described hereinafter by way of example only with reference to the accompanying drawings, which are schematic in nature and are not necessarily drawn to scale. In addition, like reference numerals in the drawings refer to like elements.

[0035] Figures 1A to 1E Schematically illustrating plasma activated fluid processing systems in various configurations according to embodiments of the present invention;

[0036] Figure 2schematically illustrates a circuit of a plasma activated fluid treatment system according to an embodiment of the present invention; and

[0037] FIG. 3A to FIG. 3B The configuration of an inductor according to an embodiment of the present invention is schematically shown. DETAILED DESCRIPTION

[0038] Figures 1A to 1E Schematic diagrams of plasma activated fluid processing systems in various configurations according to embodiments of the present invention are shown. Details of electrical components are mostly omitted; see Figure 2 . Figure 1A A basic example with only one reaction electrode 11 in one reaction chamber 14 is depicted, wherein an AC power source 10 (e.g., a high voltage power source and / or an RF power source) provides electrical power to a single reaction electrode (sometimes also referred to as a high voltage electrode) 11 within the reaction chamber 14. The reaction chamber 14 also includes a ground electrode 12 electrically connected to a ground 13 and the power source 10. It should be understood that other configurations are also possible, for example, two pointed electrodes may be used instead of the pointed reaction electrode 11 and the surface ground electrode 12. Those skilled in the art may use not only pointed electrodes but also disk electrodes and other types of electrodes.

[0039] In operation, the reaction chamber will be filled with one or more fluids. In the case of PAW synthesis, this may be a mixture of water (located in the lower portion of the reaction chamber, submerging the ground electrode 12) and air (located in the upper portion of the reaction chamber). In the case of nitrogen fixation, the fluids may include air or pure nitrogen as well as other fluids that include molecules used in the nitrogen fixation process (e.g., water, water vapor, oxygen, atmospheric air, etc.).

[0040] When the power supply 10 supplies sufficient power and voltage to the electrode 11, thermal plasma or non-thermal plasma can be generated between the electrode 11 and the ground electrode 12. In the presence of plasma, there is actually a closed circuit involving the power supply 10, the reaction electrode 11, the plasma and the ground electrode 12.

[0041] In the presence of plasma, PAW synthesis and / or nitrogen fixation occurs. The PAW production method can use non-thermal (or cold) plasma or thermal plasma. PAW is synthesized by generating plasma in air, or in a nitrogen / oxygen mixture in a fluid, or in a nitrogen / oxygen mixture close to or in contact with a fluid (e.g., plasma in bubbles, discharge in the presence of fluid / steam, discharge in contact with a fluid, or spray / aerosol in close contact with plasma and / or gas). Plasma essentially generates reactive oxygen species and reactive nitrogen species (ROS, RNS) in the gas phase, which result in the formation of products in water.

[0042] Figure 1BA variant is shown in which a single power supply 10 provides power to two reaction electrode 11 / ground electrode 12 pairs, each pair being in a separate reaction chamber 14. As mentioned in the introduction, when no special measures are taken, Figure 1B The system is difficult to start. Usually, one plasma will ignite first, such as the plasma in the left reaction chamber 14. In the presence of plasma, the circuit through the left reaction chamber will be effectively closed, and the voltage on the reaction electrode drops below the starting voltage of the plasma, so there is not enough electric field to ignite the plasma at the other electrodes. The present invention is achieved by adding suitable inductors and capacitors ( Figures 1A to 1E (not shown) to overcome this problem. Figure 2 Provides more details.

[0043] Figure 1C A single reaction chamber 14 is shown with four reaction electrodes 11 sharing one or more ground electrodes 12. Figure 2 The inductor and capacitor, the system will have the same Figure 1B A similar starting problem as described for the system of : when the plasma ignites at one electrode, it will be difficult to start the plasma at the other three electrodes.

[0044] Figure 1D Shows Figure 1B and Figure 1C has two reaction chambers, each with four electrodes. Figure 2 The inductor of this configuration may cause startup problems. It will be clear to those skilled in the art that, in general, any number of reaction chambers 14 with any number of electrodes 11 may be used as long as the plasma source is powerful enough. For example, the power supply 10 may be used with n1, n2, n3...n m m (m ≥ 1) reaction chambers of electrodes are connected, where n x represents the number of electrodes in the reaction chamber x (x≤m), and the total number of electrodes n=n1+n2+n3+...+n m If n>1, the startup problem described above may occur.

[0045] Figure 1E Again, it shows Figure 1AThe configuration of the reactor 160 now includes details of possible fluid connections. In this example, conduit 15 can be used to transport gas between reservoirs 150 and 150', depending on the settings of the valves in conduit 15. Conduit 16 can be used to bring liquid from reservoir 160 to reaction chamber 14, while conduit 17 can be used to bring liquid from reaction chamber 14 back to reservoir 160. It will be clear to those skilled in the art that the inlets, outlets, conduits, and reservoirs shown here are merely exemplary, and that those skilled in the art can provide any inlets, outlets, conduits, and reservoirs required for any plasma activated fluid process of interest.

[0046] Figure 2 The electrical circuit of a plasma activated fluid treatment system according to an embodiment of the present invention is schematically shown. The electrical components shown may be considered to form the plasma generating part of the fluid treatment system. Figure 2 The example follows Figure 1C A variant with four electrodes 11, but it should be understood that Figure 2 The example can be applied to Figures 1A to 1E Any of the variants shown in and a general variant having one or more reaction chambers 14 , each reaction chamber 14 having one or more reaction electrodes 11 .

[0047] Each electrode 11 is provided with an inductor 20 in series with the power supply 10 and a capacitor 21 connecting the electrode 11 to ground 13. The capacitor 21 may be an additional capacitor and / or an intrinsic capacitance of the electrode 11 itself and / or the inductor 20. Ignoring for the moment any plasma impedance, for each electrode 11, the inductor 20 and the capacitor 21 will form an LC circuit whose resonant angular frequency is given by the inverse of the square root of the product of the inductance L and the capacitance C:

[0048]

[0049] In an embodiment, all LC circuits (one for each of the m electrodes) have the same resonant frequency in the absence of plasma.

[0050] In operation, the AC power supply will activate the LC circuits, providing each LC circuit with its own voltage oscillation. When a plasma is ignited at one of the reaction electrodes 11, the inductor 20 connected to that electrode will suppress the current through the plasma (otherwise the current will spike due to the greatly reduced impedance of the plasma compared to the impedance of the unignited gas or liquid before ignition). This prevents excessive load on the power supply 10 due to the reduced impedance in one of the circuits. This allows other circuits to be ignited as well, overcoming the above-mentioned startup problem. When all plasmas are ignited, the current will be shunted by the inductor 20, which has a higher impedance than the plasma. As a result, each electrode 11 will receive a certain proportion of the power share from the power supply 10.

[0051] Reality is much more complex than the ideal diagram above. As mentioned earlier, initially, for example in a symmetrical system where the stray capacitances are symmetrical and equal, all circuits can be designed to have the same resonant frequency. However, when one or more electrodes are ignited, the resonant frequency shifts. That is, the plasma load impedance of the individual LC circuits can shift the resonant frequency of the entire circuit. An equation that takes into account the impedance R of the plasma (or unignited gas) between a single pair of reactive electrodes and the ground electrode is provided below:

[0052]

[0053] In practice, multiple resonant frequencies and phase shifts may occur when not all plasma loads are equal on the individual electrodes.

[0054] It is expected that the impedance change caused by igniting the plasma will cause such a shift in the resonant frequency that the power supply will no longer supply power at or near the resonant frequency. Surprisingly, applicants have found that the shift in the resonant frequency is relatively modest and sometimes even negligible. The inductor can act as a balancing impedance (each electrode will have a main impedance in series, which effectively distributes the power supply current to the electrodes). There can also be a strong (self-regulating) interaction between the load impedance of the plasma and the impedance of the LC circuit. A lower plasma load impedance can shift the resonant frequency, which (at a fixed power supply frequency) automatically reduces the power delivery to the plasma.

[0055] As an optional feature, for situations where the resonant frequency shift due to ignition of the plasma cannot be ignored, a power supply frequency control circuit ( Figure 2 It is advantageous to have a power supply frequency control circuit (not shown) configured to vary the frequency of the power supply to track the offset resonant frequency. In other words, after the first plasma ignites, the power supply frequency can be adjusted to the offset resonant frequency to maximize the voltage gain on the electrode that has not yet ignited. The second electrode will ignite, and the process will repeat until the remaining electrodes are ignited. The resonant frequency of the system can therefore be adjusted by shifting the power supply frequency to an optimal value that maximizes the voltage gain in the system. Measurement of the system voltage gain can be achieved by several methods, such as voltage probes on individual electrodes or a single (capacitive) voltage sensor placed in the center of or around the concentric coil structure.

[0056] As a further optional feature, after all electrodes are ignited, the power frequency may be continuously adjusted to control the output power of the plasma.

[0057] In an embodiment, the power supply 10 is provided with an optional controller ( Figure 2The power supply may be programmed to control the voltage and / or frequency and / or waveform of the power supply output (not shown). By programmatically changing these settings periodically (e.g., in 0.1 ms or 1 ms cycles), the plasma may be switched between various modes (e.g., thermal and non-thermal). This will in turn affect the reactions occurring in the plasma. The inventors have discovered that the production ratios of certain compounds found in the process fluid may be adjusted.

[0058] In an embodiment, an optional matching circuit is provided between the AC power source and the parallel LC circuit ( Figure 2 ). The matching circuit is configured to match the impedance of the power source to the impedance of the parallel connected LC circuit to achieve optimal power transfer.

[0059] FIG. 3A to FIG. 3B FIG. 2 schematically shows the configuration of the inductor 20 according to an embodiment of the present invention. Figure 3A In FIG. 1 , eight inductors 20 are arranged around point P along circle C in a point-symmetrical manner. Figure 3B In FIG. 1 , six inductors 20 are arranged in a point-symmetrical manner along a circle C around a point P. In general, any number of inductors 20 may be arranged in a point-symmetrical manner around a center point. Other types of symmetry may also be used. The same point-symmetrical configuration may also be applied to the electrodes in the reactor to produce a more symmetrical stray capacitance.

[0060] It has been found that this configuration of the inductors promotes each inductor 20 to have the same capacitance coupled to the environment and other inductors. As previously mentioned, it is important that the total capacitance in each LC circuit (of which the capacitive coupling of the inductors is a factor) is the same so that each of the resonant frequencies is the same. Using this arrangement of the inductors 20, the inventors have found that it is no longer necessary to place a grounded shield between the inductors, which is an inconvenient measure in high voltage applications.

[0061] It will be appreciated that if the distances between the groups of inductors are sufficiently far from each other, it may be sufficient to organize the arrangement symmetrically within the groups alone. For example, in a configuration with two reaction chambers 14, each reaction chamber 14 having six electrodes, a total of twelve inductors, two groups of six connected inductors are spaced a certain distance from each other, such as Figure 3B As shown, six sensors per group are sufficient.

[0062] In the foregoing description of the drawings, the invention has been described with reference to specific embodiments of the invention. However, it will be apparent that various modifications and changes may be made thereto without departing from the scope of the invention as outlined in the appended claims.

[0063] In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiments disclosed, but that the invention will include all embodiments falling within the scope of the appended claims.

[0064] In particular, specific features of various aspects of the invention may be combined. One aspect of the invention may be further advantageously enhanced by adding features described in relation to another aspect of the invention.

[0065] It should be understood that the present invention is limited only by the appended claims and their technical equivalents. In this document and its claims, the verb "comprise" and its variants are used in its non-restrictive sense to mean that the items following the word are included, but items not specifically mentioned are not excluded. In addition, the reference to an element with the indefinite article "a" or "an" does not exclude the possibility that more than one element is present, unless the context clearly requires the presence of one and only one element. Therefore, the indefinite article "a" or "an" generally means "at least one".

[0066] List of reference numerals:

[0067] 10: Power supply

[0068] 11: Reaction electrode (high voltage electrode)

[0069] 12: Grounding electrode

[0070] 12': Dielectric barrier / water interface

[0071] 13: Grounding

[0072] 14: Reaction Chamber

[0073] 15: Gas inlet / outlet

[0074] 16: Fluid inlet

[0075] 17: Fluid outlet

[0076] 20: Inductor

[0077] 21: Capacitor / Intrinsic Capacitance

[0078] 150, 150': Storage

[0079] 160: Storage.

Claims

1. A plasma activated fluid treatment system comprising: - an alternating current AC power source (10) operating between 10 kHz and 50 MHz, - a reaction chamber (14), wherein the reaction chamber comprises a plurality of reaction electrodes (11) and corresponding ground electrodes (12), each reaction electrode and the corresponding ground electrode being separated by a gap; or - a plurality of reaction chambers (14), wherein each reaction chamber comprises at least one reaction electrode (11) and a corresponding ground electrode, and the reaction electrode and the corresponding ground electrode are separated by a gap; wherein an AC power source is electrically connected in parallel with each ground electrode on one side and in parallel with each reaction electrode on the other side, wherein each reaction electrode is provided with a capacitor (21) connected to ground (13), and wherein an inductor (20) is provided between each reaction electrode and the AC power source, The frequency of the AC power source is close to the resonant frequency of the inductor (20)-capacitor (21) circuit.

2. The plasma activated fluid treatment system according to claim 1, comprising a plurality of inductors (20), each inductor being connected to a corresponding reaction electrode (11), wherein the inductors (20) are arranged in a symmetrical manner.

3. The plasma activated fluid treatment system of claim 2, wherein the symmetry comprises a point symmetry.

4. The plasma activated fluid treatment system according to claim 1 or 2, comprising: A voltage measurement unit is configured to determine a voltage gain of the fluid treatment system and continuously adjust the frequency of the AC power source to maximize the voltage gain.

5. The plasma activated fluid processing system according to claim 1 or 2, wherein: The capacitor (21) is formed by the intrinsic capacitance of the system.

6. The plasma activated fluid processing system of claim 5, wherein: The intrinsic capacitance includes the stray capacitance of the reaction electrode (11) and the stray capacitance of the inductor (20).

7. The plasma activated fluid processing system of claim 1 or 2, wherein: The AC power source (10) is provided with a controller for periodically controlling the voltage and / or frequency and / or waveform output by the AC power source.

8. The plasma activated fluid processing system of claim 1 or 2, wherein: The ground electrode (12) is provided with a dielectric barrier (12').

9. The plasma activated fluid treatment system of claim 1 or 2, comprising: A plurality of reaction chambers (14), each reaction chamber having a ground electrode (12) connected in parallel to the AC power source and at least one reaction electrode (11).

10. The plasma activated fluid processing system of claim 1 or 2, wherein: Each reaction chamber (14) is provided with a plurality of reaction electrodes (11) connected in parallel to the AC power source.

11. The plasma activated fluid treatment system of claim 1 or 2, further comprising: - gas inlet and / or outlet (15), -Fluid inlet (16), - Fluid outlet (17).

12. The plasma activated fluid processing system of claim 11, wherein: The fluid inlet (16) and the fluid outlet (17) are connected to a water reservoir (160) for plasma activated water.

13. The plasma activated fluid processing system of claim 1 or 2, wherein: The AC operating frequency is between 20kHz and 15MHz.

Images