Dielectric barrier discharge device

Abstract

A dielectric barrier discharge (DBD) device for removing gas components is provided. The DBD device comprises: a first electrode and a second electrode, with a dielectric barrier between the first electrode and the second electrode, capable, in use, of establishing an electric field between the first electrode and the second electrode; and a gas flow path passing between the first electrode and the second electrode, at least one of the electrodes having one or more discharge nodes positioned along the gas flow path. Each location where the at least one discharge node is located along the gas flow path is an ionization region and has an adjacent recombination region downstream of the respective ionization region.

Description

Technical Field

[0001] The present disclosure relates to apparatus and methods for reducing the amount of a component in a gas using a dielectric barrier discharge. Typically, this is achieved by managing temperature and / or ionization parameters. Background Art

[0002] There is growing concern about pollutant emissions from the use of fossil fuels and other processes, which lead to poor air quality, environmental damage, and harm to human health. This has led to increased attention to air quality and emission regulations, and the need to provide means to eliminate or reduce the concentration of pollutants emitted into the atmosphere.

[0003] Hydrocarbons represent a pollutant whose release into the atmosphere is desirable to minimize or eliminate. In particular, it is desirable to minimize methane (CH4, CH4) emissions because methane is a potent greenhouse gas and therefore of concern due to its contribution to global temperature increases.

[0004] Liquefied natural gas (LNG), which has methane as its main component, has attracted attention as an alternative fuel to petroleum and light oil, and has been used as a fuel to power engines on board ships, for example. From the perspective of air quality, LNG fuel has many advantages over conventional (marine) fuels. Due to the low or absent sulfur content of the gas, sulfur dioxide (SO2, SO2) emissions are low. The low sulfur content and the absence of fuel aromatics also contribute to low particle formation levels. In addition, the most widely used marine LNG engines have significantly less nitrogen oxides (NOx, NOx) than conventional marine diesel engines. x )emission.

[0005] Since the beginning of the 21st century, the use of LNG as a marine fuel has increased significantly. However, many LNG engines currently produced have the problem of unburned methane flowing through the engine and being discharged with the exhaust. This is known as "unburned engine." Therefore, due to the impact of methane leakage on the environment, climate, and human health, it is desirable to remove methane from LNG engine exhaust upstream of its release into the atmosphere.

[0006] Engine manufacturers are developing methods to reduce methane leakage from LNG engines. This has been moderately successful, but there appear to be limitations to reducing escape through engine design measures. Therefore, other post-engine methods are needed to eliminate methane leakage.

[0007] Typically, hydrocarbons (including methane) are removed from gases at high temperatures or by adsorption processes using catalysts such as platinum, palladium or rhodium. Methane is a relatively stable molecule and therefore typically requires temperatures of at least 400 degrees Celsius (°C) to oxidize over catalysts based on precious metals. There are devices that remove methane from exhaust gases at temperatures below 400°C using catalysts with high loadings of platinum and palladium. However, palladium-based catalysts are sensitive to SO2 and deactivate when the concentration of SO2 in the exhaust stream is very low. High concentrations of CO2 and H2O in the exhaust gas also limit the activity of (methane) oxidation catalysts. Therefore, there remains a need for methane slip removal methods that overcome the limitations of precious metal-based catalyst materials.

[0008] Electron beam flue gas treatment (EBFGT) is a catalyst-free technology used to treat flue emissions from fossil fuel burning facilities (e.g., power plants) and municipal solid waste incinerators. EBFGT removes sulfur oxides (SOx, SO x ) and NOx. This is achieved by converting ammonia (NH3, NH3) into non-toxic ammonium sulfate-nitrate, which can be used as agricultural fertilizer. The technology involves passing humidified flue gas through an electron beam reactor, where high-energy electrons bombard nitrogen, water, and oxygen to produce strong reagents that react with sulfur oxides and nitrogen oxides to form sulfuric acid and nitric acid.

[0009] In an EBFGT, the electron beam reactor consists of an electron beam accelerator, specifically a double-grid quadrupole gun in which the cathode housing is located within a vacuum housing. Free electrons are generated in an ultra-clean environment (called an ultra-high vacuum) at a pressure approximately 12 orders of magnitude lower than atmospheric pressure. The electrons are then accelerated and passed through an aluminum or titanium membrane that separates the ultra-high vacuum from the flue gas, where pollutant gases flow. Electrons passing through the aluminum membrane collide with gas molecules, initiating a chemical chain reaction that removes pollutants.

[0010] The implementation of such an EBFGT system requires significant capital costs due to the installation of electron accelerators. Electron accelerators also require frequent maintenance and extreme safety requirements, which are undesirable or impossible at the reactor site. Furthermore, multiple accelerators must be implemented for redundancy. The need for ultra-high vacuum increases costs and can lead to accelerator failure. Furthermore, the use of this technology for mobile applications is undesirable due to the heavy radiation shielding required to protect against at least X-ray emission and ionizing radiation.

[0011] Therefore, the use of EBFGTs is not an ideal alternative to catalyst-based methane slip removal.Therefore, there is a need for a practical device for exhaust gas purification that can advantageously oxidize the unburned components (eg, methane) of a fuel (eg, LNG).

[0012] Dielectric barrier discharge (DBD) devices are known for removing unwanted components from gases. These electrodes typically take the form of parallel plate electrodes or coaxial cylindrical or rod-shaped electrodes, with a dielectric barrier positioned between them. When an electric field with a strength above the breakdown threshold of the gas is applied between the electrodes, a plasma is formed by the electrical discharge between the electrodes. The generation of the plasma drives reactions in the gas to remove various components.

[0013] The goal has always been to provide a uniformly distributed discharge within a DBD device to achieve a uniform plasma density, allowing chemical reactions to be driven throughout the volume between the electrodes. This goal has been difficult to achieve satisfactorily because even slight imperfections in the electrodes that focus the electric field disrupt the distribution of the discharge and negatively impact the uniformity of the plasma density. This limits the value of DBD in removing unwanted components of a gas to a reasonable level of efficiency. Summary of the Invention

[0014] According to a first aspect, a dielectric barrier discharge device for (i.e., suitable for) removing gas components is provided, comprising: a first electrode and a second electrode, with a dielectric barrier between the first electrode and the second electrode, and an electric field can be established between the first electrode and the second electrode during use; and a gas flow path passing between the first electrode and the second electrode, at least one electrode having one or more discharge nodes positioned along the gas flow path, each position where at least one discharge node is positioned along the gas flow path is an ionization region and has an adjacent recombination region downstream of the respective ionization region.

[0015] Instead of seeking to further improve plasma density uniformity, the DBD device according to the first aspect enhances the concentration of reactive species in the partially ionized gas. By increasing the concentration of reactive species, the efficiency of gas component removal is improved. Consequently, when the same or similar amount of energy is applied to a standard DBD device with a uniform electric field, a greater amount of components can be removed from the gas than is achievable using conventional DBD devices.

[0016] The invention is intended to be responsive to the presence of an electric field between a first electrode and a second electrode so as to enable an electrical discharge to be established between one or more discharge nodes (and thereby at least one electrode) and another electrode. Due to the arrangement of the first electrode and the second electrode and the dielectric barrier, the discharge can be established between the one or more discharge nodes (and thereby at least one electrode) and the dielectric barrier. Such a discharge (also referred to as an electrical discharge) typically generates electrons. It is known that such electrons generated during a discharge in a gas interact with the gas to generate reactive species. These reactive species are typically in the form of free radicals and ions (as well as additional electrons ionized, excited, and ionized by electron impacts of background gas molecules). These reactive species oxidize, reduce, or decompose components of the gas, including pollutant molecules that may be present in the gas, such as CH4, SOx, and NOx.

[0017] In known discharge devices, there is a uniform (i.e., homogeneous) volume distribution of the electrical discharge, which produces electrons with an energy distribution typically between 1 and 10 electron volts (eV). In contrast, the DBD device according to the first aspect is a form of "graded" dielectric barrier discharge device. This is because it provides one or more locations in the form of one or more discharge nodes, and thus multiple stages along the length at which discharge occurs in use, as well as intermediate locations where the probability of discharge occurring is lower.

[0018] Other forms of hierarchical DBD devices may be provided, and thus, in its most general form, a hierarchical DBD device is provided. Such a hierarchical DBD device may exclude one or more of the features mentioned above with respect to the first aspect. This can be achieved while still providing the ability to generate a discharge at one or more locations along a path through which a gas or another fluid can pass during use. This, therefore, provides the aforementioned advantages of the DBD device according to the first aspect.

[0019] The term "discharge" refers to some form of electrical discharge, such as one that produces plasma. Generally, this means the release and transfer of electrical energy through a medium, such as a gas, in an applied electric field. This is typically achieved by a stream of electrons in the form of filaments that move from one location to another or between two points. The electron stream is typically a transient stream of electrons in the form of filaments. This is intended to refer to the electron flow in microdischarges or filaments during an electrical discharge, with each individual discharge ignition event lasting only a short time. Of course, if the appropriate conditions are maintained, many filaments may be present over time. Electrical discharges allow for the transfer of electricity through a gas in an applied electric field.

[0020] By the term "recombination region," it is intended that there be a region of reduced ionization occurring within the ionization region. This may be due to ion recombination of ions generated within the ionization region or plasma dissipation of plasma generated within the ionization region. This may be achieved by reaction of the plasma or ions with themselves and / or other species present (e.g., with gas components).

[0021] Electrical discharge can be used to remove CH4 by converting it into one or more other substances. It has been found that the high-energy electrons generated during the staged discharge remove CH4 from a CH4-containing gas. This provides an enhanced process by which CH4 can be removed from a gas using known techniques. The method reduces the amount of CH4 present in the treated gas. Before removal begins, the CH4 may be at most 10,000 ppmv, at most 5,000 ppmv, at most 2,500 ppmv, or at most 2,000 ppmv, and may be at most 100 ppmv or 1,250 ppmv.

[0022] Any form of electrical discharge can be suitable for removing CH from gas, such as pulse, corona, electron beam, radio frequency, microwave, ultraviolet radiation discharge, brush, glow, arc, static electricity, partial discharge, streamer, vacuum arc, Townsend discharge, field emission of electrons or discharge in gas, lead (or spark), St. Elmo's fire or lightning. However, generally, the electrical discharge can be a barrier electrical discharge. We have found that barrier discharge can be used to reduce the CH content in the gas, thereby allowing it to be used to reduce CH from air and / or point sources (such as exhaust gas). The presence of dielectric does not allow arc or spark to occur (that is, a discharge that produces a continuous current between electrodes). Instead, it only allows micro-discharges to occur, which usually only last for a few microseconds. This provides the necessary energy and components to help decompose the chemical reaction path of CH while limiting the amount of power required to provide a continuous discharge.

[0023] Each discharge node may include or may be a recess, recess edge, edge, corner, tip, point or textured portion of each electrode. Typically, each discharge node is at least one protrusion, such as a plurality of protrusions, from a respective electrode, with at least one component of the respective electrode (each protrusion having) being oriented toward the other electrode. By having a discharge node be (or include) a protrusion (or multiple protrusions), the distance between the electrodes is reduced, thereby reducing the field strength requirements of the electric field for the discharge to occur. This therefore reduces the stress on the electrical components, making them less likely to fail and extending their lifespan. In addition, each protrusion provides an asymmetry in the electric field, which promotes electrical breakdown at that point. This is typically because each protrusion can taper to a point or tip or have a tapered portion to a point or tip.

[0024] There can be up to 12 bumps, the number of bumps can be a multiple of 3, and typically there can be 6 bumps. When each discharge node has multiple bumps, in addition to the above advantages of at least one bump, the multiple bumps have advantages corresponding to those explained below with respect to the second aspect.

[0025] The phrase "towards the other electrode" is intended to mean that if the first electrode has at least one protrusion, the protrusion is oriented to have a component facing the second electrode. Correspondingly, if the second electrode has at least one protrusion, the protrusion is oriented to have a component facing the first electrode.

[0026] The at least one protrusion may be a protrusion from the first electrode and / or the second electrode.

[0027] There may be (only) a single discharge node. However, typically, the one or more discharge nodes are multiple discharge nodes located along the gas flow path. We have found that as the number of discharge nodes increases, the amount of gas component removal increases. A limiting factor may be the length of the electrode on which the discharge node is located. Thus, at least one electrode may have a discharge node located along the discharge length of the electrode, which is the length of the electrode over which a discharge is established in use when the electric field strength is equal to or above a threshold strength.

[0028] Each recombination region may separate the respective ionization region from a downstream ionization region (or from the electrode end).

[0029] The distribution of discharge nodes can be uniform, asymmetric, symmetric, clustered / grouped, or random. We have found that a uniform distribution (i.e., consistent spacing between adjacent discharge nodes) provides suitable gas component removal. Regardless of the distribution, adjacent discharge nodes are typically separated by a distance corresponding to at least 60% of the height of at least one protrusion and / or at most 150% of the height of at least one protrusion.

[0030] The spacing may be at least 80% of the height of at least one protrusion, or may be at least 85% of the height of at least one protrusion. Additionally or alternatively, the spacing may be at most 130% of the height of at least one protrusion, at most 110% of the height of at least one protrusion, or at most 90%.

[0031] By the height of a protrusion it is intended to mean the distance from the base of the protrusion at the electrode to the opposite end of the protrusion.

[0032] We have found that by providing such spacing of the discharge nodes within these standards, removal of gaseous components is enhanced.

[0033] The first electrode and the proximal side of the dielectric barrier may be separated by a first distance. Additionally or alternatively, the second electrode may abut the distal side of the dielectric barrier to the first electrode.

[0034] Each protrusion may have a height between 10% and 50% of the first distance. Each protrusion may have a height of at least 11% of the first distance, at least 12% of the first distance, or at least 13% of the first distance. Each protrusion may have a height of at most 45% of the first distance, or at most 40% of the first distance.

[0035] The height of each protrusion affects the field strength required to provide a discharge and back pressure on the gas passing along the gas flow path. We have found that each protrusion having a height within the stated range provides an optimal balance between back pressure and field strength along the gas flow path, protecting electronic devices by limiting the pressure applied to them and minimizing the number of devices required to remove components from a given volume of gas.

[0036] Each discharge node may take any suitable form. Typically, each discharge node is a structure for (ie, suitable for) electric field enhancement for use in a dielectric barrier discharge device.

[0037] The term "structure" herein is intended to mean a selected form, such as an intentional and / or repeatable, predetermined or specific form. This is intended to replace forms that are simply non-repeatable or only produce random forms in the same (within manufacturing tolerances) form, such as a rough surface where the roughness or texture is provided naturally or by using, for example, sandpaper. This means that in some cases, the discharge node as a structure is a more specific form of a discharge node. In some forms, the discharge node may simply be a point, area, region, feature, part, location or element that is more preferred for the occurrence of discharge, or at which discharge occurs more reliably / repeatably, or that discharge occurs only relative to where no discharge node is present. In this form, this may be natural or may have been prepared.

[0038] The structure may comprise a ring comprising at least one tip extending along a first radial axis passing through a center of the ring, wherein in use, the ring is arranged around a first electrode of a discharge device, a gap is present between the structure and an opposing electrode of the discharge device, the at least one tip limiting a minimum gap between the structure and the opposing electrode, thereby increasing a probability of electrical breakdown occurring at the tip when an electric field is applied between the first electrode and the opposing electrode.

[0039] Independent of the first aspect, according to the second aspect, there is provided a structure for (i.e., suitable for) electric field enhancement for use in a dielectric barrier discharge device, the structure comprising: a ring including at least one tip extending along a first radial axis passing through the center of the ring, wherein, in use, the ring is arranged around a first electrode of the discharge device, a gap is present between the structure and an opposing electrode of the discharge device, the at least one tip limiting the minimum gap between the structure and the opposing electrode, thereby increasing the probability of electrical breakdown occurring at the tip when an electric field is applied between the first electrode and the opposing electrode.

[0040] Whether a structure for electric field enhancement is provided as part of the first aspect or as part of the second aspect, the structure provided for electric field enhancement provides various benefits in increasing the rate at which a discharge device (e.g., a dielectric discharge device) removes pollutants from exhaust gases. In use, a ring is arranged around a first electrode, and the structure is further arranged, in such a way that a gap is formed between the opposing electrode and the structure. The presence of the structure introduces an asymmetry in the electric field applied between the first electrode and the opposing electrode. This results in a higher concentration of active species near the structure relative to conventional discharge devices. Therefore, the structure promotes oxidation of gases passing through the discharge device in use. Specifically, the radially extending tip reduces the gap between the structure and the opposing electrode at the location of the tip. This concentrates the applied electric field at the tip. This increases the generation of active species at the tip, so that gases near the tip are more likely to be oxidized.

[0041] Furthermore, due to the inherent geometry of the tip, ie, because the tip typically terminates in a sharp point, the tip contributes to the formation of a plasma stream when contaminants pass through the discharge device in use.

[0042] It has been observed that, in use, discharge devices including such structures remove contaminants with greater efficiency than similar devices without such structures.

[0043] All of these benefits are achieved without the need to provide any additional energy. That is, the electric field typically applied to a conventional discharge device can be applied to a staging device having a structure that provides improved pollutant removal efficiency.

[0044] In addition, the presence of a catalyst is not necessarily required to achieve improved pollutant removal rates. If a catalyst is used, this will still provide further improvements, but without the need for a catalyst. If the option of using a catalyst is implemented, it is combined with discharge. This will contribute to the existing ability to purify gases (such as air and flue emissions) from combustion engines, power plants, and incinerators in, for example, ships and other vehicles.

[0045] In another optional example, the electric field enhancing structure further comprises a channel extending from the center of the ring to the exterior of the ring along a second radial axis, wherein the second radial axis is not aligned with the first radial axis.

[0046] In some optional examples, the width of the channel can be 1 millimeter (mm).

[0047] The presence of the channel facilitates easy installation and removal of the structure surrounding the first electrode. This effectively makes it easier to replace the structure, for example, if it fails. The width of the channel also provides space for the structure to expand and contract, for example, due to heating by the gas flowing through the discharge device during use. This further improves the reliability of the structure.

[0048] In some examples, the ring has a body, and at least one tip is connected to the body.

[0049] In some advantageous examples, the body may have a radial thickness of 3.6 mm.

[0050] The radial thickness of the ring increases the structural integrity of the structure. For example, the structure is less likely to bend out of shape.

[0051] A ring with a radial thickness of 3.6 mm provides the best compromise between structural strength and ensuring that the structure is not overly bulky.

[0052] An electric field enhancing structure as claimed in any preceding claim, wherein at least one tip comprises two side surfaces meeting at a point and forming a first angle therebetween to form the tip.

[0053] Additionally, the first angle may be 69 degrees.

[0054] This is optimal for contaminant removal (e.g., methane) during use. Furthermore, this angle ensures that the tip has a minimum level of structural integrity. Tips having a first angle of at least 69 degrees are less susceptible to breakage than more pointed tips. The specified first angle also allows for easy and repeatable manufacturing of the tip with a high level of accuracy and precision.

[0055] In an advantageous example, the at least one tip of the electric field enhancing structure comprises a plurality of tips, each tip of the plurality of tips being arranged on an outer edge of the ring.

[0056] Multiple tips can further improve the contaminant removal rate during use. That is, multiple tips provide additional sites for gas electrical breakdown to occur. This means that more gas can be processed compared to a structure with a single tip.

[0057] In some further examples, the plurality of tips may each extend along a respective radial axis that is not aligned with the second radial axis.

[0058] This effectively means that each of the multiple tips extends in a different radial direction. This means that the tips will be distributed somewhat along the outer edge of the ring. Consequently, the tips' impact is less likely to overlap, and the tips will therefore complement each other. That is, in use, each tip encounters a different portion of the gas flowing through the discharge device.

[0059] Furthermore, in some examples, it may be advantageous to have the multiple tips evenly distributed over the outer edge of the ring.

[0060] The uniform distribution of the tips further improves the efficiency of contaminant removal in use.By requiring a plurality of uniformly distributed tips, it is ensured that every portion of the gas flowing through the discharge device in use has some opportunity to be treated.

[0061] Note that by uniform distribution, it is intended that the material is uniformly distributed around the ring at the tip, rather than the entire 360 ​​degree structure. For example, a channel may provide a break in the ring.

[0062] In some examples, the plurality of tips may include 3 tips.

[0063] In other examples, the plurality of tips may include 21 tips.

[0064] A specific number of tips can effectively remove contaminants during use.

[0065] In certain advantageous examples, the plurality of tips may generally include six tips.

[0066] The plurality of tips may also consist of 6 tips (ie only 6 tips).

[0067] A configuration having six tips has been found to be optimal for removing contaminants such as methane from the gas flowing through the discharge device in use.

[0068] The second radial axis may bisect a second angle between two adjacent tips on either side of the passage, the first angle being measured between adjacent sides of the two tips.

[0069] The electric field enhancement structure according to claim 11, wherein the second angle is 135.6 degrees.

[0070] This further defines the configuration of the structure. The channel bisects two adjacent channels and is therefore intended to be positioned midway between two adjacent tips. This can further increase the usefulness of the channel for easily replacing the structure.

[0071] In some optional examples, adjacent tips in the plurality of tips other than two adjacent tips on either side of the channel may be separated by a third angle measured between adjacent sides of the adjacent tips, preferably wherein the third angle is 127.6 degrees.

[0072] Therefore, the configuration of the structure is further specified. The above arrangement of multiple tips may be particularly effective for removing contaminants such as methane during use. The specified angles between the tips may also improve structural integrity and ensure that the tips can be manufactured repeatedly with high precision.

[0073] In some useful examples, the axial thickness of the structure may be 1 mm.

[0074] The axial thickness of the structure ensures that the structural integrity of the structure is not easily compromised. The minimum axial thickness of 1mm makes it more difficult to bend the structure out of shape.

[0075] The arrangement of the first electrode and the second electrode can be any of a variety of arrangements, such as a parallel plate arrangement in which the first electrode and the second electrode are each a plate that is at least partially aligned with each other and has at least components that are parallel to each other. Alternatively, the first electrode and the second electrode are concentrically arranged with parallel longitudinal axes, with the second electrode positioned at least partially around the first electrode. In some forms, the concentric arrangement can be such that the longitudinal axes of each of the first electrode and the second electrode are coaxial. We have found that by providing a concentric arrangement, there is a more uniform discharge distribution along the length of the electrodes, resulting in a more uniform heat distribution and a driven reaction to more consistently remove gas components throughout the area where the electric field is applied (e.g., within the discharge length).

[0076] "At least partially surrounding" means that in at least or only one plane, the second electrode partially or completely surrounds the first electrode. Typically, the second electrode is completely (i.e., completely) located around the first electrode, thereby meaning that the second electrode completely surrounds the first electrode in at least one plane (and typically only in a single plane, which plane may be perpendicular to the longitudinal axis of the first electrode and / or the second electrode).

[0077] The dielectric barrier can be a coating on one of the electrodes, or can be positioned independently of the first and / or second electrodes (i.e., with a spacing or gap therebetween). Typically, the dielectric barrier is arranged concentrically with the first and second electrodes and has a longitudinal axis parallel to the longitudinal axis (i.e., axis) of each of the first and second electrodes, with the second electrode mounted on the distal side of the dielectric barrier from the first electrode and at least partially surrounding the dielectric barrier around its circumference. This minimizes the structural rigidity required for the second electrode and provides a structure for the DBD device that simplifies device construction and manufacture.

[0078] The second electrode may pass around the entire circumference of the dielectric barrier, thereby completely surrounding the dielectric barrier around its circumference.

[0079] The dielectric barrier may have a thickness between about 0.1 millimeters (mm) and 10 mm, such as about 2 mm.

[0080] The dielectric barrier may be one or more of mica, quartz, fused silica, alumina, titanium dioxide, barium titanate, fused silica, titanium dioxide silicate, silicon nitride, hafnium oxide, a polymer, or a ceramic. In this context, by the phrase "one or more of," it is intended to mean a combination of two or more of the specified materials when two or more of these are used.

[0081] Typically, the dielectric barrier is (glass) quartz. This is because quartz is readily available, low-cost, can be processed in large quantities, and can have high resistance to thermal stress. The dielectric barrier can alternatively be mica. Mica is beneficial in that it has a slightly higher dielectric constant than other dielectric materials (such as glass).

[0082] The second electrode can be a foil, such as a solid sheet of grounded foil. This allows for minimal use of second electrode material and minimizes complexity. Alternatively, the second electrode can be a thicker sheet, mesh, rod, coating, cast, or molded component. We have found that coatings are unreliable for long-term use, and meshes are inefficient relative to plasma processing. When the second electrode is located on or mounted on the dielectric barrier, the second electrode can be applied as a foil.

[0083] Typically, the second electrode is steel, such as stainless steel, such as SS 316L. Alternatively, the second electrode may be aluminum. Each of these materials allows the second electrode to be electrically conductive.

[0084] The second electrode may be held in position on the dielectric barrier by one or more constant force springs. This allows for a simple design and avoids puncturing the desired electrode (and thus the foil that may form the electrode). Alternatively, alternative fixings such as adhesives, bonds or coatings may be provided.

[0085] There may be five constant force springs. While there may be more or fewer constant force springs, having more makes the total weight of the springs excessively heavy and makes the device difficult to manufacture. If there are smaller constant force springs, the second electrode may move or shift over time.

[0086] A spacing may exist between an axial end of the second electrode and an axial end of the dielectric barrier. In other words, each end of the second electrode may be axially offset from a corresponding end of the dielectric barrier. This helps minimize voltage creep by providing an area where discharge is less likely to occur at the end of the DBD device.

[0087] There may be an axial offset between the or each discharge node and the proximal axial end of the dielectric barrier. For the same reasons, this also minimises voltage creep.

[0088] The axial offset between the end of the second electrode and / or each discharge node and the corresponding axial end of the dielectric barrier can be at least 4% of the axial length of the dielectric barrier, such as at least 5% of the axial length of the dielectric barrier, 6% of the axial length of the dielectric barrier and / or 7% of the axial length of the dielectric barrier.

[0089] The first electrode is typically a rod, but can be a sheet, foil, such as a ground foil, mesh, coating, cast, or molded part. The rod can have a diameter between 5 mm and 10 mm, for example, 8 mm. Typically, the first electrode is steel, such as stainless steel, such as SS 316L. The combination of the first electrode being a rod of the stated material and the stated diameter limits the bending radius of the first electrode to within the mechanical tolerances of the device over a certain length, such as about 800 mm or longer. This means that the first electrode will not bend during use, thereby avoiding changes in the applied electric field caused by bending of the first electrode, which could disrupt undesirable discharge concentration.

[0090] The dielectric barrier may be a cylinder having an outwardly oriented collar offset from an end of the cylinder, the end of the second electrode abutting the collar in use. The outwardly oriented collar prevents the second electrode from passing through the collar, thereby helping to prevent the electrode from sliding relative to the dielectric barrier when the collar is oriented under the electrode under the influence of gravity.

[0091] "Outwardly oriented" means facing or oriented outward, such as on the outer surface of a cylinder. In an arrangement where the second electrode is mounted on a distal surface of the dielectric barrier relative to the location of the first electrode, the outwardly oriented collar is located on the same distal side of the dielectric barrier. The phrase "offset from the end of the cylinder" is intended to mean that the collar is located near the end of the cylinder but spaced apart from the end of the cylinder, for example, at a distance of at most 10%, 8%, or 7% of the length of the cylinder from the end of the cylinder.

[0092] The first electrode can be kept separate from the second electrode and the dielectric barrier. This can be achieved using a connector that provides an insulated connection to the dielectric barrier and the second electrode, with the connector located at opposite ends of the dielectric barrier and the gas flow path through the connector. This suspends the first electrode in the space between it and the second electrode, minimizing the engagement along the length of the first electrode. This also allows the first electrode to be centered between the second electrode and the dielectric barrier.

[0093] The connectors may each include three spokes extending between the rim and the hub of each connector. This is the most structurally stable configuration while maximizing the passage of gas along the gas flow path. While fewer spokes may be used, using, for example, two spokes has been found to be less advantageous due to vibrations occurring in the spokes leading to structural failure.

[0094] These connectors, also referred to herein as "end cups," can be of any suitable (eg, insulating) material. Typically, they are alumina, such as green alumina.

[0095] Each connector can be molded, extruded, or machined. Typically, each connector is machined and then sintered. All or part of each connector surface can then be glazed. Green alumina represents the material's pre-sintering state and consists of aluminum oxide grit with a binder that allows for machining. The binder is typically burned off after sintering. Made from alumina, the thermal expansion of each connector is similar to or matches that of the dielectric cell.

[0096] Each connector can have a minimum thickness between 1 mm and 5 mm, such as 2 mm. This is a balance between size and fragility. At a minimum thickness of 2 mm, each connector will become too fragile.

[0097] The connection between the first electrode and the at least one connector is provided by a spring. The spring allows for thermal expansion and contraction of the first electrode while maintaining the structural integrity of the device. The spring can be a compression spring, but can also be an extension spring.

[0098] The first electrode can be configured as a cathode during use, and the second electrode can be configured as an anode. The first electrode and the second electrode can be a cathode-anode pair relative to each other. Thus, the first electrode can be the anode in a different cathode-anode pair, and / or the second electrode can be the cathode in another cathode-anode pair. The second electrode, acting as an anode, directs the discharge inward, which is safer and reduces the need for shielding of the device.

[0099] The gas may be air or gas from any local, remote, ambient, environmental or artificial source. The gas may typically be exhaust gas, although the gas may be any gas from any source, or may simply be a locally available gas such as air. The gas may be gas from an engine.

[0100] Additionally or alternatively, the gas may be a gas containing CH 4 .This allows the use of electrical discharge to reduce CH 4 in exhaust gases (such as flue gases) from, for example, internal combustion engines in ships and other vehicles, power plants and incinerators, and in air.

[0101] Instead of a gas flow path, a fluid flow path may be provided, typically a flow path for a gas, but a flow path may be provided for another type of fluid, such as a liquid.

[0102] The first electrode and the second electrode may be any suitable material for providing electrodes that allow an electric field to be established therebetween. Typically, the electrodes may be made of a conductive metal.

[0103] Each discharge node can be any form of appropriately sized structure. Typically, each discharge node provides a point, such as being shaped to form a point, a pointed structure, or a taper to a point, such as a cone or triangle. This enhances the electric field at the peak or vertex of the point, thereby increasing the probability of a discharge occurring at that location compared to when a flat or blunt geometry is used instead of such a sharp geometry.

[0104] There may be a power source connected to each of the first electrode and the second electrode and arranged, in use, to establish an electric field between the first electrode and the second electrode.

[0105] The power supply can also be arranged to provide an adjustable amount of active power to the fluid present between the first electrode and the second electrode in use. The phrase "active power" is intended to refer to the instantaneous power (p(t)) provided to the DBD device averaged over a period of applied voltage (e.g., T0), where the period is generally the period from the start of excitation or the start of a power window to the start of the next power window. Active power (P) can be calculated as shown in Equation 1:

[0106]

[0107] Where "t" is time, and "t0" is the time when the stimulus starts or the power window begins.

[0108] In terms of active power, we also intend to express the ratio of the production of high-energy electrons in the fluid present between the first electrode and the second electrode to the undesirable losses involved in the process. We aim to provide a conversion of electrical energy (e.g., from a drive circuit) to chemical energy (e.g., in the fluid between the electrodes during use). The overall intention is to minimize losses to maximize the production rate of high-energy electrons.

[0109] When there are multiple discharge nodes, the discharge node may be connected to at least one of the first electrode and the second electrode and / or the dielectric barrier. By this, we intend to mean that at least one discharge node is connected to at least one of the first or second electrode or the dielectric barrier. This means that more than one of the first and second electrodes and / or the dielectric barrier may have one or more discharge nodes connected thereto. Of course, there may be multiple discharge nodes, each connected to one of the first or second electrodes or the dielectric barrier, for example all discharge nodes are connected to only one of the first or second electrodes or to only the dielectric barrier; or one or both of the first and second electrodes and / or the dielectric barrier are connected to one or more discharge nodes. It is intended that when a discharge node is connected to an electrode or the dielectric barrier, the discharge node is only connected to the respective electrode or dielectric portion and not also to one or the other electrode or dielectric portion (when connected to an electrode).

[0110] The power supply may maintain active power by any suitable means, such as by providing a set amount of constant power supply from some form of DC power source, or by providing a constant or modulated AC power or continuous power supply in a sinusoidal waveform at a predetermined frequency.

[0111] The power supply may be a drive circuit as detailed in WO 2022 / 106622, which is incorporated herein by reference. This may be a drive circuit for (i.e., suitable for) a dielectric barrier discharge device, the drive circuit comprising: a power supply connectable, in use, across a dielectric discharge gap, the dielectric discharge gap providing capacitance; and an inductance between the power supply and the dielectric discharge gap when connected, thereby establishing, in use, a resonant tank circuit, wherein power is supplied to the tank circuit in bursts and only during the bursts, the pulse frequency of each burst being tunable, in use, to the resonant frequency of the tank circuit, the power supplied by each burst charging the tank circuit and maintaining the tank circuit to a threshold at which discharge ignition occurs (at the dielectric discharge gap), the discharge ignition events for each burst (such as those occurring during a period of any one burst) being limited to a maximum number based on the drive circuit being arranged, in use, to inhibit each burst from delivering power to the resonant tank circuit after the maximum number has occurred.

[0112] By providing a train of power pulses to the resonant tank circuit, the amount of energy stored in the resonant tank circuit increases over the duration of each pulse train, also known as "charging" the resonant tank circuit. When the potential difference across the gap reaches a threshold value (Vth), a dielectric barrier discharge occurs across the dielectric discharge gap. By tuning the pulse frequency of the pulse train (by pulse frequency, it is intended to mean the period between individual pulses within the pulse train or the inverse of the cycle period of the pulses) to the resonant frequency of the tank circuit, the charging process results in a rapid increase in the amplitude of the potential difference. This increases the potential difference amplitude to a threshold value in, for example, less than ten cycles, to reach a threshold value at which a dielectric barrier discharge occurs (which may also be referred to as the "ignition threshold").

[0113] The described drive circuit is used to provide a limitation on the stress exerted by the current. This arrangement achieves this limitation by accumulating a potential difference reaching a threshold value within a cycle (i.e., individual pulses) during a pulse train, via the voltage gain of the resonant tank circuit, thereby reducing power losses in the drive circuit. In conventional pulsed plasma systems, providing a plasma discharge using a single pulse requires a high step-up transformer, resulting in higher currents and, consequently, increased stress caused by the current on the primary winding side.

[0114] Furthermore, the power supply is protected from short circuits without the need for overcurrent detection, since the inductance of the resonant tank circuit provides sufficient impedance to limit the current when the output terminals of the power supply are shorted (e.g., due to a short circuit fault at the dielectric barrier).

[0115] Additionally, by limiting the number of discharge ignition events, energy dissipation is reduced to heating or producing only a small amount of reactive species. In fact, we have found that by implementing this hybrid of resonant AC and limited pulse excitation, we can provide effective pollutant reduction while also having high power conversion efficiency.

[0116] Thus, in summary, by using the described driving circuit, power transmission in a DBD device is achieved with high efficiency (due to resonant operation), while also limiting stress caused by current flow and preventing short circuits in order to protect circuit components.

[0117] The gap between the first electrode and the second electrode can provide a dielectric discharge gap. The dielectric discharge gap is intended to serve as a gap between the electrodes of the DBD device. When an electric field is established between the first electrode and the second electrode, this typically provides capacitance due to the gap, with another capacitance provided by the dielectric barrier. Of course, when a power source is connected across the discharge gap, since the edges / sides of the gap are provided by the electrodes, the power source is intended to be connected (i.e., electrically connected) to at least one electrode in a manner that allows the power source to provide current to the electrodes and establish a potential difference across the electrodes. In various examples, the power source can still be connected to both ends of the dielectric discharge gap by connecting to wires or wiring connected to the electrodes that form a closed circuit including the power source and the dielectric discharge gap.

[0118] The cycle period of the power supplied by a resonant tank circuit is intended to refer to the time period during which the current and / or voltage passes through (only) a single oscillation cycle determined by the frequency. In other words, this is intended to be the time it takes for the current and / or voltage to pass through (only) a single wavelength.

[0119] The presence of a dielectric barrier at the dielectric discharge gap typically does not allow arcing or sparking (i.e., a discharge that produces a sustained current between the electrodes). Instead, it typically only allows microdischarges to occur, which typically last only a few microseconds. This provides the necessary energy and components to facilitate chemical reaction pathways to decompose compounds in the medium through which the discharge passes, while limiting the amount of power required to provide a sustained discharge.

[0120] The process of a discharge caused by a power supply can be thought of as initially not occurring before reaching the ignition threshold. This means that the gas in the discharge gap (e.g., between the electrodes) is not ionized, there is no discharge, and, more importantly, no power is delivered to the gas. However, once the threshold is reached, a discharge occurs, which can be referred to as a "discharge ignition event." This results in the formation of transient filaments (each representing a microdischarge) from a single point (such as some form of discharge node on the surface of an electrode defining one side of the discharge gap). The lifetime of each filament (i.e., the time period during which the corresponding filament exists) is on the order of tens of nanoseconds. Only during the lifetime of these transient microdischarges are high-energy electrons formed in the discharge gap. When accelerated by the applied electric field, the electrons gain kinetic energy. The electrons then transfer this energy through collisions, which can be elastic (kinetic energy conservation) or inelastic (transferring internal energy to molecules and reactions). The energy transferred by the generated high-energy electrons can trigger the decomposition of pollutants because the energy levels are sufficient to initiate chemical reactions.

[0121] Maintaining the discharge gap at the voltage threshold indefinitely leads to charge accumulation on the surfaces of the dielectric barrier and electrodes of the DBD device's dielectric discharge gap. This can be avoided by using pulses. Due to the alternating polarity provided by the pulses, the pulses can be considered to limit the amount of time that the instantaneous voltage at the discharge gap remains at the ignition threshold to a period on the order of a few microseconds. This means that transient filaments can only be generated during this time. Therefore, the period during which microdischarges can occur can be considered limited to the amount of time that the instantaneous voltage at the discharge gap remains at the ignition threshold, and the sum of those transient filaments can be considered a "macrodischarge" or "discharge event."

[0122] Therefore, the term "discharge ignition event" is intended to refer to the start of a macroscopic discharge or discharge event; or in other words, the beginning of a period during which microdischarges in the form of transient filaments can occur, i.e., when a threshold is reached. This threshold is typically a voltage threshold, such as the voltage threshold at a dielectric discharge gap, for example, in the form of a potential difference (e.g., a voltage change or difference ΔV) between an electrode and an electrode / dielectric layer defining the gap. Strictly speaking, in practice, we are referring to an electric field threshold, where the voltage threshold is determined by the electric field strength and the electrode spacing.

[0123] The pulse frequency of the pulse train that can be tuned to the resonant frequency (also referred to as the "resonant frequency") of the tank circuit in use is intended to mean that the pulse frequency can be tuned to one or more of a plurality of frequencies that can be considered to be resonant frequencies. These include a theoretical resonant frequency (i.e., a frequency that would be calculated as the resonant frequency when real-world effects are not taken into account), or a practically applicable resonant frequency, such as a frequency that takes into account real-world effects, which may include one or more of inductance and / or resistance, damping, or impedance in wiring and / or other components. Thus, as further detailed below, zero voltage switching frequency.

[0124] The maximum number of discharge ignition events can typically be between one and five events, such as between one and three events, including (only) one, two, or three events. By limiting the number of discharge events to so few, we have found that this produces the most energy-efficient and efficient pollutant decomposition. This is because the energy transfer that occurs due to the discharge ignition events limits the transfer to the medium in the discharge gap, thereby directing a higher proportion of energy to cause the decomposition of compounds in the medium.

[0125] The drive circuit may further comprise a phase meter in communication with the tank circuit and arranged to identify, in use, such as by monitoring, a phase shift in power supplied to the tank circuit during each pulse train, the phase shift corresponding to the occurrence of a discharge ignition event, and wherein the drive circuit may further be arranged to determine, in use, when a maximum number of discharge ignition events has occurred based on the number of pulses in the respective pulse trains since each discharge ignition event.

[0126] We have discovered that this phase shift indicates the start of a discharge, and therefore, the number of discharge ignition events that have occurred from that point can be identified (such as by counting or knowing the number of pulses in a pulse train starting from that point). This means that it can be determined when a maximum number of discharge ignition events has been reached to stop further discharge ignition events from occurring. The first discharge ignition event can be detected by monitoring, for example, the voltage-current phase shift at the input of a resonant tank circuit (such as the voltage-current phase shift measured at the terminals of an H-bridge, the relevance of which is further detailed below). During the charging period of the resonant tank circuit (e.g., rapid voltage accumulation), there is typically a near-zero phase shift (excited at resonance). However, once the plasma is ignited as part of the discharge ignition event, there is typically a shift in the resonant frequency due to the increase in capacitance imposed by the "ignited" discharge gap. When monitored, this resonant frequency shift can be immediately detected by monitoring the phase shift.

[0127] Such a phase meter (eg, phase detection unit) as described above may be provided by a controller, a processor, a microprocessor or a microcontroller or another such device capable of monitoring the phase of at least two signals.

[0128] In addition to or as an alternative to phase monitoring or using a phase meter, each pulse train can have a pre-tuned or optimized number of pulses (i.e., the number of pulses within the pulse train). It is typically possible to calculate or model how many pulses will be required to charge the resonant tank circuit, and typically there will be (only) a single discharge ignition event per pulse, or at least it is possible to calculate how many discharge ignition events each pulse will cause. This allows the number of pulses in a pulse train to be set to at least the maximum number of discharge ignition events required plus the number of pulses required to charge the tank circuit. If this approach is used, it is of course possible to include additional pulses in each pulse train, such as when using pulses to discharge the resonant tank circuit. If this approach is used, these can also be included in the calculation of how many pulses are required for each pulse train.

[0129] The drive circuit may also include an energy storage device connected across the power supply, the energy storage device being arranged to receive and store power released from the tank circuit (i.e., power discharged from the tank circuit) after each pulse train (or after a maximum number of discharge ignition events have occurred) in use. This provides a means for storing / retrieving power within the drive circuit that would otherwise be lost due to energy dissipation in the resonant tank circuit. This reduces energy losses between pulse trains and allows the stored energy to contribute to the formation of the next high voltage pulse train, thereby improving efficiency.

[0130] Energy or electrical energy recovery can be achieved by passive or active means. Typically, an active device is used, such as a drive circuit that is typically arranged to shift the phase of the pulse train (the pulses in it) by 180 degrees (°) after a maximum number of discharge ignition events have occurred in use. When passive means for energy recovery (and possibly any other active means) are not possible, such as due to the use of a loosely coupled air-core transformer, energy recovery can be achieved by implementing this mechanism. This thereby allows the efficiency gains achievable from energy recovery to still be achieved. For the same number of pulses as the number of pulses in the pulse train used to charge the resonant tank circuit to the threshold, the phase shift can be set to an appropriate position, although a phase shift can be applied to a different number of pulses. This maintains similar power flow when charging and discharging the resonant tank circuit.

[0131] The drive circuit may also include an inverter between the power supply and the tank circuit, the inverter being arranged to modulate the power supplied from the power supply to the tank circuit in use. This allows the characteristics and properties of the power supplied to the resonant tank circuit to be determined by components within the drive circuit rather than by any input to the drive circuit. This provides for a greater degree of customisation and variation than would be possible if this were determined by the power supplied at the circuit input.

[0132] The inverter can be any suitable type of inverter. Typically, the inverter is an H-bridge or half-bridge. This provides a simple mechanism for providing the inverter function while also allowing direct and easy control of the output from the inverter to enable passive and / or active recovery of energy stored in the tank circuit at the end of each pulse train.

[0133] When an H-bridge or half-bridge is used, the switches used in the bridge inverter can be any suitable switches, such as mechanical switches or power transistor switches. Typically, each switch of the inverter can be a silicon or silicon carbide (metal oxide semiconductor field effect transistor, MOSFET) switch, a silicon insulated gate bipolar transistor (IGBT) switch, or a gallium nitride power transistor (FET) switch. Silicon MOSFET switches typically have a blocking voltage of approximately 650V; silicon carbide (SiC) MOSFET switches typically have a blocking voltage of approximately 1.2kV; silicon IGBT switches typically have a blocking voltage of approximately 650V or approximately 1.2kV; and gallium nitride FET switches typically have a blocking voltage of approximately 650V. It is also possible to use multi-level bridge branches with several low-voltage devices connected in series to achieve high (higher) blocking voltage bridge branches. However, a mechanism is usually required to ensure that the voltage is shared equally between the switches, which makes things complicated and less reliable. This is why a two-level H-bridge is often used in the drive circuit according to the first aspect. Using the above switches in the inverter also allows the components to be kept simple. Wide bandgap (WBG) semiconductors, such as SiC and GaN, are often used because they perform better than Si-based power semiconductors.

[0134] The frequency of the pulses supplied to the resonant tank circuit (if supplied as a pulse train, such as the frequency of the voltage waveform) can be exactly the resonant frequency of the resonant tank, such as the frequency of the first harmonic (i.e., the fundamental frequency or natural frequency), or can be near the resonant frequency, such as within the range of the resonant frequency. If higher-order harmonics are used, then since the resonant tank circuit typically has a low-pass characteristic, harmonics higher than the first harmonic are attenuated or damped. This is why, even though the excitation is typically provided as a square wave, the resulting current and voltage across the dielectric discharge gap are almost perfectly sinusoidal.

[0135] When using an inverter using switches such as an H-bridge or half-bridge inverter, the pulse frequency of each pulse train can be a zero voltage switching (ZVS) frequency. This is typically slightly higher than the exact resonant frequency of the tank circuit, such as from about 5% to about 10% higher than the exact resonant frequency, and no more than about 10%, depending on the quality (Q) factor of the drive circuit. This reduces losses caused by the switching action and reduces electromagnetic interference (EMI) caused by the switching action, thereby making the inverter more efficient and reducing the noise generated by the inverter.

[0136] The drive circuit may further include a transformer, the secondary winding of which forms part of the resonant tank circuit, and the transformer is a step-up transformer. This reduces the voltage level (i.e., V) required to achieve dielectric barrier discharge in the resonant tank circuit by increasing the voltage input level. th ) requires a minimum voltage gain. Additionally, the use of a transformer reduces ground currents (currents flowing in the parasitic capacitance between the electrodes of the DBD device and any surrounding metal housing), thereby reducing EMI. While the transformer can be located within the drive circuit, where the primary winding, rather than the secondary winding, forms part of the resonant tank circuit, the kilovolt-ampere (kVA) rating of the transformer can be reduced in arrangements where the secondary winding forms part of the resonant tank circuit. In this case, the reactive power of the DBD device can be compensated.

[0137] When a transformer is used, the drive circuit can be arranged to short-circuit the primary transformer winding after each pulse train, in use. When energy is recovered / reclaimed from the tank circuit, the short-circuit of the primary winding is typically applied after the energy is recovered, for example after the respective pulse train. Short-circuiting the primary winding reduces ringing that may occur due to the components that make up the resonant tank circuit. When an inverter is used, short-circuiting the transformer primary winding can be achieved in use by switching on either the low side or the high side of the inverter. This avoids the need to include additional components in the drive circuit, thereby limiting the number of components.

[0138] The inductance of the resonant tank circuit can be provided or contributed by one or more components and can be provided by the inductance in the wiring or cabling between components within the drive circuit. At least a portion of the inductance (such as some or all of the inductance) can be provided by a transformer. This uses a characteristic of the transformer that is generally not desirable, thereby allowing that characteristic to be used as a contribution to the function of the drive circuit. Any inductance provided by the transformer can be the leakage inductance (also known as stray inductance) of the transformer. In some cases, this can allow the resonant tank circuit to not need to also include an inductor as a specific component.

[0139] As explained in more detail below, the transformer can be an air-core transformer. When an air-core transformer is used, it is possible to have a magnetic coupling of up to 60% between the windings. Using an air-core transformer (such as one with 60% magnetic coupling between the windings) increases the inductance that the transformer can provide, thereby reducing the need for the resonant tank circuit to have any additional inductance. Additionally, when an air-core transformer is used, the resonant inductance, and thus the resonant frequency of the resonant tank circuit, can be tuned by adjusting the distance between the primary winding (also known as the transmit coil) and the secondary winding (also known as the receive coil). This reduces the need to place additional capacitors in the drive circuit, as is known to be done in existing systems, thereby reducing component count. This is possible due to the planar inductive power transfer that occurs when using an air-core transformer. Other arrangements that allow for the implementation of an air-core transformer are also possible.

[0140] Compared to other transformers (i.e., non-air-core or solid-core transformers), air-core transformer windings have low coupling. This allows the secondary (i.e., high-voltage) side of the transformer to oscillate freely when no voltage is applied from the primary side (such as when all switches are off and the body diode is not conducting). The means for active energy recovery detailed above (i.e., 180° phase shifting of some pulses) eliminates these oscillations and avoids the power loss associated with using air-core transformers.

[0141] The transformer may have a step-up ratio of the primary transformer winding to the secondary transformer winding of about 1:1 to about 1:10, such as about 1:5. By applying this arrangement, the following equation holds (Equation 2), which is not typically used in known systems:

[0142]

[0143] Where V dc is the voltage provided by the DC link power supply, n is the turns ratio of the transformer (i.e., N1 / N2, corresponding to the number of primary windings divided by the number of secondary windings), and V th is the firing voltage or discharge threshold of the DBD device. As described in the next paragraph, this reduces the gain requirements.

[0144] For a dielectric barrier discharge ignition voltage threshold in a DBD device of approximately 20 kV, this means that a step-up ratio of approximately 1:5 requires a minimum resonant tank circuit voltage gain of approximately 5 times when the input voltage to the driver circuit is approximately 800 V. This achieves an optimized balance between transformer step-up and resonant tank circuit voltage gain, significantly reducing the current stress on the driver circuit compared to conventional pulse power and resonant converter systems that rely primarily on high step-up transformers (1:20 or higher) to achieve the required discharge voltage levels.

[0145] Before the discharge threshold is reached, there is minimal damping in the resonant tank circuit. This is because there is no load on the resonant tank during charging (such as power transfer to the medium in the discharge gap). In contrast to known resonant systems, in such systems, there is usually always a load because there is a continuous or extended discharge that creates the load.

[0146] The lack of a load on the resonant tank circuit of the drive circuit according to the first aspect results in a very high voltage gain compared to known systems (such as a gain with a Q value greater than 50). Unlike known systems, the achievable voltage gain of the resonant tank circuit does not depend on the load (which, as described above, generally corresponds to the power delivered to the gas when a dielectric discharge occurs). Instead, it depends (only) on the parasitic resistance of the resonant tank circuit (such as the parasitic resistance caused by the resistance of the magnetic element and the electrodes).

[0147] Furthermore, due to the lack of load, this allows for faster charging, with the pulse frequency of the pulse train being as close as possible to the true resonant frequency of the tank circuit (such as the theoretical resonant frequency without taking into account the damping effects that are typically present in reality). This is because the amount of damping is so low that minimal damping needs to be taken into account when setting the pulse frequency. This enhances energy transfer capabilities, making the drive circuit more efficient.

[0148] When a transformer is present, the required size of the transformer step-up turns ratio (i.e., the specification set for the transformer step-up turns ratio) also depends solely on the parasitic resistance of the resonant tank circuit. If there is also a load to consider, the size of the transformer step-up turns ratio will also need to take this into account. This allows the losses from the transformer to be kept to a minimum, thereby reducing the impact of using a transformer on the efficiency of the drive circuit compared to when the load needs to be considered.

[0149] As an alternative or in addition to a transformer providing inductance, at least a portion of the inductance (such as some or all of the inductance) can be provided by an inductor. This provides a component designed to provide the inductance to be used, thereby optimizing the drive circuit. Where the inductance is partially or fully provided by an inductor and a transformer, each contributes to the inductance between the power supply and the dielectric discharge gap, and thus to the inductance of the resonant tank circuit.

[0150] When separate transformers and inductors are provided, there are several possible arrangements for the drive circuit. One arrangement is to connect the inductor to the input of the resonant tank circuit (such as the output of an inverter), which in turn is connected to the primary winding of the transformer; the secondary winding of the transformer is then connected across the dielectric discharge gap. Another arrangement is to connect the input of the resonant tank circuit to the primary winding of the transformer; the secondary winding is connected to the inductor, which is connected in series with the dielectric discharge gap. In each of these arrangements, the leakage or stray inductance of the transformer contributes to the resonant inductance value (i.e., inductance) of the resonant tank circuit. Naturally, if the resonant tank circuit is placed after the transformer, the kVA rating of the transformer is reduced because the oscillating reactive power of the dielectric discharge device does not pass through the transformer.

[0151] Another arrangement is to connect the input of the resonant tank circuit to the primary winding of a transformer; and the secondary winding of the transformer is connected across the dielectric discharge gap. In this arrangement, since no separate inductor component is provided, the leakage or stray inductance of the transformer will need to be large enough to compensate for the load on the dielectric discharge gap at the desired resonant frequency. This can be achieved with a transformer with very low coupling between the windings, as is the case with air-core transformers (i.e., without a magnetic core) as discussed in more detail below.

[0152] The device may also include a controller connected to the drive circuit, the controller being arranged to adjust the power supplied to the tank circuit of the drive circuit based on input provided to the controller. This allows the power supplied to the resonant tank circuit to be modified during use, thereby providing the ability to make changes when parameters within the system change during use, thereby causing characteristic shifts within the system. For example, changes in the fluid passing between the electrodes may cause changes in the capacitance of the resonant tank circuit, thereby changing the resonant frequency. The controller can then be used to adjust the frequency of the pulses supplied to the resonant tank circuit during the pulse train.

[0153] The controller may be arranged to adjust / modulate the pulse frequency (such as the frequency of the voltage waveform or current waveform) and / or the pulse train frequency (such as the frequency of the pulse train, i.e. the frequency at which the pulse train occurs, which can also be referred to as the pulse train repetition frequency) and / or the number of pulses in each pulse train and / or the number of pulse trains (such as the number in a series of electrical pulse trains) during use. This provides a wide range of adjustments that can be made to allow the power provided to be tailored to provide optimal dielectric barrier discharge generation during use of the system.

[0154] The input provided to the controller may include one or more relevant parameters. Typically, the input includes the voltage and current at the output of the driver circuit (such as the output of an inverter). This allows the calculation of the phase angle between the supplied voltage and current and the average phase of the pulse train. This can be used to optimize the pulse frequency provided during the pulse train. Therefore, the controller can be arranged to determine (by which we intend to mean "calculate") the phase difference between the voltage and current in use. This can of course be determined by another component.

[0155] As mentioned above, this phase difference can also be used to detect the onset of the occurrence of a dielectric barrier discharge. Detecting this can allow, after a defined number of discharge ignition events, to identify it when the pulse train transitions from providing energy to, for example, recovering energy. Also as mentioned above, the occurrence of a dielectric barrier discharge in the discharge gap increases the effective capacitance. This leads to a decrease in the resonant frequency and, therefore, an increase in the measurable phase difference for a given drive frequency (such as the pulse frequency of the pulse train). In view of this, it can be seen that the phase meter and the controller of the drive circuit can be identical components to each other. Alternatively, the controller and the phase meter can communicate with each other, or the controller can be combined with the phase meter, for example, the phase meter is a component of the controller.

[0156] As described above, the drive circuit may include an inverter between the power supply and the resonant tank circuit of the drive circuit. In this case, the voltage and current can be provided from the output of the inverter. Due to the higher frequencies that can be achieved using the inverter, this allows the level of control provided to the output of the resonant tank circuit to be finer (i.e., more precise) than the level of control that can be achieved if the AC power supply is simply connected to the resonant tank circuit to power it. In addition, the higher AC frequencies that can be achieved using the inverter can provide shorter dielectric barrier discharges. This allows for simpler limiting of the maximum number of discharge ignition events and faster control than using a standard AC power supply to maintain the efficiency gains achieved by limiting the number of discharge ignition events.

[0157] The controller may also be connected to the dielectric barrier discharge device, with inputs including one or more characteristics of the fluid passing through the device in use. This allows the characteristics of the fluid to be taken into account when seeking to optimise the performance of the system.

[0158] According to a third aspect, a system for providing a dielectric barrier discharge is provided, wherein the system comprises: a plurality of dielectric barrier discharge devices according to the first or second aspects, including a drive circuit according to any combination of the features of the drive circuits described above; and a controller connected to each drive circuit, the controller being arranged to regulate the power supplied to the tank circuit of each drive circuit based on input provided to the controller. This allows the system to be scaled to accommodate various volumes of fluid passing through it, such as various sizes of engines passing through the exhaust gas to be cleaned. Furthermore, this provides the advantages of the controller described above.

[0159] The controller may be just a single controller. Whether there is a single controller (connected to all the drive circuits) or a plurality of controllers (each connected to a respective drive circuit), the controller or each controller may provide any combination of the features of the controllers described above. For example, the controller may be arranged to adjust the pulse frequency, and / or the pulse train repetition frequency, and / or the number of pulse trains, and / or the number of pulses in a pulse train, in use; the inputs may include the voltage and current at the output of each drive circuit; when each drive circuit includes an inverter between the power supply and the tank circuit, the inverter may be arranged to modulate the power supply from the power supply to the tank circuit in use, with the voltage and current being provided from the output of the inverter; the controller may be arranged to determine the phase difference between the voltage and current in use; the controller may also be connected to each dielectric barrier discharge device, the inputs including one or more characteristics of the fluid passing through the device in use; and / or only a single power supply may be arranged to power all the drive circuits in use.

[0160] According to another aspect, a method for controlling a dielectric barrier discharge in a dielectric barrier discharge device according to the first aspect, according to the second aspect, or as part of a system according to the third aspect may be provided, the method comprising: providing power to a resonant tank using a series of electrical pulse trains, the pulse frequency of each pulse train being tuned to the resonant frequency of a tank circuit, the resonant tank being connected across a gap between a first electrode and a second electrode in the dielectric discharge device, the capacitance of the tank circuit being provided by the dielectric discharge device, the power provided by each pulse train charging the tank circuit and maintaining the tank circuit to a threshold at which discharge ignition occurs; providing a maximum number of discharge ignition events for each pulse train by prohibiting each pulse train from transmitting power to the resonant tank after the maximum number of discharge ignition events has occurred; and prohibiting power transmission to the tank circuit between pulse trains.

[0161] The term "inhibit" is intended to mean passively or actively inhibiting the transfer of electrical energy to the tank circuit, such as by not providing a path by which electrical energy can be transferred to the tank circuit or by diverting the path to an alternate circuit, respectively.

[0162] As mentioned above, the maximum number of discharge ignition events may be between 1 (one) and 5 (five) events.

[0163] The method may also include identifying a phase shift in the power supplied to the tank circuit during each pulse train, the phase shift corresponding to the occurrence of a discharge ignition event; and determining when a maximum number of discharge ignition events has occurred based on the number of pulses in the pulse train since each discharge ignition event. This provides an accurate means of avoiding exceeding the maximum number of events.

[0164] Each electrical pulse train may be a voltage pulse train.By this we intend to mean that the electrical pulse train may be provided by a voltage pulse train, such as a voltage waveform that may be used as an excitation waveform for a resonant tank circuit and that may induce a current waveform in the resonant tank circuit.

[0165] The method may also include modulating the pulse frequency, and / or the frequency of the pulse train, and / or the number of pulse trains in a series of electrical pulse trains, and / or the number of pulses in each pulse train. It is noteworthy that the power frequency can be modulated by modulating the power or a component of the power (such as voltage and / or current). The frequency of the power is twice the frequency of the voltage waveform that contributes to the power (the frequency that the pulse frequency is intended to represent), which is typically the case for power supply systems. If the voltage and current are each sinusoidal waveforms, the power will be the square of the sinusoidal waveform (i.e., Sin^2), and spectral decomposition will show a fundamental frequency that is twice the excitation (i.e., voltage) frequency.

[0166] The modulation may be based on a phase difference in characteristics of the power supplied to the resonant tank circuit and / or one or more characteristics of the fluid flowing through the device.

[0167] The resonant tank circuit may be powered via a transformer, the method further comprising short-circuiting the transformer primary winding between the repeated pulse trains. This prevents (ie, mitigates) unwanted oscillations between the magnetizing inductance of the transformer and the capacitance of the DBD reactor.

[0168] The pulse frequency of each pulse train supplied to the resonant tank circuit can be set by switching action in the circuit between the power supply and the resonant tank circuit.

[0169] For each pulse train, after a maximum number of discharge firing events have occurred, the resonant tank circuit can be discharged (i.e., depleted). This can be achieved by active or passive recycling. In this case, the method can also include storing the energy transferred from the resonant tank circuit by the discharge. Recycling energy in this way significantly improves the energy efficiency of the method.

[0170] There is usually a time difference between the end of one pulse train and the start of the next pulse train. In other words, there may usually be a period of time without pulses between the end of one pulse train and the start of the next pulse train, which allows distinguishing one pulse train from the next and avoiding any concurrent parts or overlaps between consecutive pulse trains.

[0171] The first electrode and / or the second electrode may be any suitable material for providing an electrode that allows an electric field to be established therebetween. Typically, the electrodes may be made of a conductive metal.

[0172] As described above, the dielectric barrier can be connected to the second electrode and / or each discharge node can be connected to the first electrode. This allows the dielectric barrier and discharge node to be applied independently to their respective electrodes. This avoids the possibility of damaging the discharge node or dielectric barrier during the processes of applying the dielectric barrier to the electrodes and the discharge node to the electrodes, respectively. This simplifies the device manufacturing process and reduces the failure rate during manufacturing.

[0173] The dielectric barrier may provide a covering of at least a portion of the or each electrode to which it is connected. The dielectric barrier may be a coating on at least a portion of the surface of the or each electrode to which it is connected. For example, the dielectric barrier may coat the entire surface of the or each electrode to which it is connected.

[0174] By "a dielectric barrier is connected to at least one electrode," we mean that each electrode to which the dielectric barrier is connected is independent of every other dielectric barrier and electrode connected to the dielectric barrier. This means that there can be multiple dielectric barriers. Each dielectric barrier can be connected to only a single electrode.

[0175] Each discharge node may be any form of suitably sized structure that provides a point of discharge.

[0176] According to a fourth aspect, there is provided a dielectric barrier discharge device operating at a temperature between 160°C and 500°C.

[0177] This can be achieved using any form of dielectric barrier discharge device without the specific features disclosed herein. In general, the device according to the second aspect can be a device comprising a pair of electrodes (or a first electrode and a second electrode) and a gas flow path passing between the pair of electrodes, with a dielectric barrier between the pair of electrodes, and an electric field can be established between the pair of electrodes in use.

[0178] The DBD device may be operated at a temperature of at least 180°C.

[0179] The DBD device may operate at a temperature of up to (eg, at most) 450°C.

[0180] Of course, the dielectric barrier discharge device according to the first aspect can also be a device according to the fourth aspect, and vice versa, as part of a system according to the third aspect. Thus, the device according to the first aspect can be operated at a temperature between 160° C. and 500° C. In other words, the device according to the first aspect can be arranged to operate at a temperature between 160 degrees Celsius (° C.) and 500° C. during use.

[0181] According to a fifth aspect, a method for removing gas components is provided. The method includes passing a gas having a maximum of 10,000 ppmv of methane along a gas flow path between a first electrode and a second electrode, wherein a dielectric barrier is provided between the first electrode and the second electrode; and establishing an electric field between the first electrode and the second electrode, at least one electrode having one or more discharge nodes positioned along the gas flow path, each location along the gas flow path where at least one discharge node is positioned is an ionization region and has an adjacent recombination region downstream of the respective ionization region. By establishing the electric field, a discharge occurs at the one or more discharge nodes, thereby generating ionization and thereby forming active species / plasma. Gas components including methane react with the active species / plasma, thereby causing recombination in the recombination region and removing contaminants from the gas. The method can be implemented using the apparatus of the first, second, and / or fourth aspects of the system according to the third aspect.

[0182] According to a sixth aspect, there may be provided use of the apparatus according to the first aspect for removing methane from a gas. According to a seventh aspect, there may be provided use of the apparatus according to the first aspect for removing methane from a gas, wherein the gas contains at most 10,000 ppmv of methane.

[0183] As mentioned above, the gas mentioned in each of the fifth, sixth and / or seventh aspects may contain up to 5,000 ppmv, 2,500 ppmv, 2,000 ppmv of methane, and may be at least 100 ppmv or at least 1,250 ppmv. BRIEF DESCRIPTION OF THE DRAWINGS

[0184] Example devices and methods are described in detail below with reference to the accompanying drawings, in which:

[0185] Figure 1 A. Figure 1 B and Figure 1 C shows a DBD device according to the prior art and a corresponding plasma density diagram, as well as a diagram showing the concentration of reactive species compared to the concentration of pollutants according to the prior art;

[0186] Figure 2 A. Figure 2 B and Figure 2C shows a first example DBD device and a corresponding plasma density map, showing the concentration of reactive species compared to the concentration of contaminants;

[0187] Figure 3 shows a schematic diagram of a first example DBD device;

[0188] Figure 4 A first example DBD device is shown along Figure 3 A cross-sectional view of plane AA in FIG.

[0189] Figure 5 A schematic diagram showing components of a first example DBD device;

[0190] Figure 6 A first example DBD device is shown along Figure 3 and Figure 4 A cross-sectional view of plane BB in FIG;

[0191] Figure 7 A schematic diagram illustrating another component of the first example DBD device;

[0192] Figure 8 An example graph showing the variation of power and specific energy input (SEI) with respect to CH4 for different discharge node forms is shown;

[0193] Figure 9 shows an example graph of power versus CH4 removal efficiency for different second electrode and dielectric barrier parameters;

[0194] Figure 10 shows example graphs of power versus CH4 removal efficiency for different variations of discharge nodes;

[0195] Figure 11 Example graphs of power versus CH4 removal and SEI versus CH4 removal are shown for different variations of a discharge node;

[0196] Figure 12 shows an example graph of power versus CH4 removal efficiency for different electrode parameters;

[0197] Figure 13A and Figure 13B shows example graphs of power versus CH4 removal for different environments and electrode parameters;

[0198] Figure 14 A second example DBD device is shown;

[0199] Figure 15 An alternative embodiment of a second example DBD device is shown;

[0200] Figure 16 An example high voltage electrode of an alternative embodiment of a second example DBD device is shown;

[0201] Figure 17 An example graph showing gap spacing and rod width of an example high voltage electrode relative to reduction in SO2;

[0202] Figure 18 An example graph showing voltage and current in a pulse train according to a prior art device;

[0203] Figure 19 A schematic diagram illustrating the principles of electron irradiation and dielectric barrier discharge purification technology in an example dielectric barrier discharge device is shown;

[0204] Figure 20 shows example graphs of voltage, current, and power applied in an example circuit;

[0205] Figure 21 shows an example graph of voltage versus time comparing an applied gap voltage to an output voltage and a corresponding graph with a zoomed portion of output current versus time;

[0206] Figure 22 An example circuit is shown;

[0207] Figure 23 Another example circuit is shown;

[0208] Figure 24 Another example circuit is shown;

[0209] Figure 25 An example method of operating an example circuit is shown;

[0210] Figure 26 shows example graphs of switching sequences over time and resulting voltages over time;

[0211] Figure 27 shows an example graph of voltage over time versus power transfer rate;

[0212] Figure 28 An example controller for an example circuit is shown;

[0213] Figure 29 shows another example graph of voltage and current over time during an example pulse train;

[0214] Figure 30 Another example controller is shown;

[0215] Figure 31a and Figure 31bshows an example graph of a switching sequence over time and the resulting voltage over time;

[0216] Figure 32 shows example graphs of resonant tank circuit input voltage and current and resulting DBD device voltage versus time without energy recovery; and

[0217] Figure 33 Example graphs of resonant tank circuit input voltage and current with energy recovery and resulting DBD device voltage versus time are shown. DETAILED DESCRIPTION

[0218] Various aspects described herein allow for the removal of one or more contaminants or components of a gas by using a dielectric barrier discharge in a DBD device.

[0219] Among known discharge devices, there is an electrical discharge that produces a uniform (i.e., homogeneous) volume distribution of electrons with an energy distribution typically between 1 electron volt (eV) and 10 eV. It is known that the electrons generated during the discharge in a gas interact with the gas to produce reactive species in the form of free radicals and ions (as well as additional electrons generated by electron impact ionization, excitation, and ionization of background gas molecules). These reactive species (free radicals and ions) oxidize, reduce, or decompose molecules (and in some cases, pollutants) present in the gas, such as methane.

[0220] Examples of such known discharge devices are Figure 1 A DBD device is shown generally at 100. This shows a known uniformly distributed discharge device.

[0221] Figure 1 The device 100 shown in Figure A comprises a first electrode 101, an opposing second electrode 105, and a dielectric barrier 102. In use, an electric field is applied between the first and second electrodes. Under the correct circumstances, a discharge occurs between the first and second electrodes. The presence of the electric field and discharge generates a (non-thermal, low-temperature) plasma 103 between the first electrode and the dielectric barrier.

[0222] like Figure 1 B, the plasma is uniformly distributed throughout the device 100. Line 106 on the graph represents the plasma density along the entire length of the device, with the plasma density remaining at the same level from a first location 108 aligned with the upstream end of the device to a second location 110 aligned with the downstream end of the device.

[0223] As a result of this realization, Figure 1 C shows a graph 115 which provides a representation of the concentration of active substance in the device 100 (measured on the left Y-axis). Figure 1 The concentration of the active substance in C is indicated by the solid line 109, and the concentration of the contaminant, for example (measured on the right Y-axis), is indicated by the dashed line 107. The concentration of the active substance is shown to be negligible up to a first position X1 aligned with the first position 108. During use of the device, at position X1, the concentration of the active substance rises to a first concentration that is constant throughout the rest of the device up to the second position 110. As for the concentration of the contaminant, from Figure 1 As can be seen from C, the concentration starts at a first concentration N0 and remains constant upstream of the first location X1. The concentration of the active pollutant then decreases linearly to a minimum concentration N at the second location. min This reduction is caused by the interaction of the gas containing the contaminants with the plasma as the gas passes through the device. It will therefore be appreciated that, in use, the known discharge device 100 removes contaminants along its length.

[0224] In contrast, as an example of an apparatus according to aspects disclosed herein, Figure 2 Shown in Figure 2 A corresponds to details of a hierarchical DBD device shown generally at 200. The hierarchical DBD device has Figure 1 The DBD device 100 shown in A has a first electrode 201 , an opposite second electrode 205 , and a dielectric barrier 202 arranged identically.

[0225] Figure 2 The exemplary hierarchical DBD device shown in A also has a plurality of discharge nodes 204 in the form of electric field enhancement structures. The discharge nodes are arranged along the length of the first electrode 201 with spaces between adjacent nodes. Figure 2 In the example shown in A, the discharge nodes are shown as being evenly spaced along the first electrode. In other examples, the spacing may be different and / or may be non-uniform.

[0226] Similar to Figure 1 In use, an electric field is applied to the hierarchical DBD device 200 between the first electrode 201 and the second electrode 205. Under the correct conditions, a discharge occurs between the first electrode and the second electrode. The presence of the electric field and discharge generates a (non-thermal, low-temperature) plasma 203 between the first electrode and the dielectric barrier 202.

[0227] Figure 2 B shows Figure 2 Illustrative graph 206 of plasma density distribution in the graded DBD device 200 of FIG. A. The solid line 207 in the graph shows the plasma density along the length of the graded DBD device, and the dashed line 208 shows the average plasma density in the graded discharge device.

[0228] exist Figure 2 In FIG. 2B , solid line 207 has three peaks. The center of each of the three peaks is aligned with the centerline 212, 213, or 214 of each of the discharge nodes 204. This indicates that plasma 203 is highly concentrated around each discharge node. Plasma exists only at a low level in the region between the discharge nodes (and between the discharge nodes and the ends of the hierarchical DBD device 200).

[0229] Graph 206 shows that the density of the plasma 203 has step changes at short distances upstream and downstream of each discharge node centerline 212, 213, 214. In practice, instead of step changes, the plasma density may be a smooth or curved profile with the center and / or peak aligned with the centerline of the discharge node 204. In any case, as shown by the dashed line 208, this provides a similar Figure 1 The average plasma density of the DBD device 100 shown in A is substantially the same average plasma density.

[0230] Fluctuations in the density of the plasma 203 along the length of the graded DBD device 200 affect the concentration of reactive species and components such as contaminants along the length of the graded DBD device. Figure 2 C shows the description Figure 2 A is a graph 209 showing the concentration of active species (measured on the left Y-axis) and the concentration of contaminants (measured on the right Y-axis) in a hierarchical DBD device.

[0231] exist Figure 2 In C, the solid line 210 represents the concentration of active substances, and the dotted line 211 represents the concentration of pollutants. It can be seen that the concentration of active substances reaches a peak near the center lines 212, 213, and 214 of each discharge node 204. Figure 2 In the example shown in C, the peak of each spike in active material concentration is aligned with the centerline of the respective discharge node. In other examples, the peak is slightly upstream or slightly downstream of the respective centerline.

[0232] Figure 2The solid line 210 and the dashed line 211 in the graph 209 of C show that the concentration of the contaminant starts from a certain initial concentration P0 and is constant until it reaches the first discharge node 204, coinciding with the peak of the plasma density. The concentration of the contaminant then decays sharply (in this example, linearly). When it reaches the second discharge node along the length of the graded DBD device 200, the plasma density reaches a peak again, causing the concentration of the active species to increase again. At this point, the concentration of the contaminant continues to decrease, but at a less steep rate because the concentration is already below the initial concentration. Upon passing the third discharge node, the increase in plasma density and active species concentration causes a further decrease in the concentration of the contaminant, but at a more gradual rate (i.e., a less steep, less dramatic decay). This decay continues until the concentration of the contaminant reaches its lowest P min level.

[0233] It has been observed that from hierarchical DBD devices (e.g. Figure 2 The exemplary hierarchical DBD device shown in Figure 4 removes contaminants at a rate greater than that from conventional discharge devices (e.g. Figure 1 This is evident from the fact that, using the discharge node 204, the rate of contamination removal is greater than that of conventional devices. In addition, the concentration of contaminants, P min Lower than the concentration N that can be achieved by conventional devices min .

[0234] The reason for this is that an increase in the concentration of active species in the known gas increases the efficiency of pollutant removal from the gas. Furthermore, generating discharges only at periodic points along the length of the graded DBD device 200 allows for ionization regions (i.e., where active species are generated) and recombination regions (i.e., where active species react with pollutants, or in other words, species generated in the ionization regions react with each other or with other gas components present, thereby reducing the amount of (remaining) ionization). The repeated ionization regions can be viewed as "replenishing" or "regenerating" the concentration of active species in the graded discharge device. In the absence of these graded ionization regions, the concentration of uniformly generated active species, as established in known discharge devices, can be lower by comparison. This is because the active species may suffer from non-specific reactions or thermal degradation. Therefore, re-establishing a high concentration of active species in the discharge device is beneficial to pollutant removal efficiency.

[0235] Given the hierarchical DBD device concept we have developed, we have further developed a method to generate a large number of high-energy electrons, atoms, and free radicals to remove pollutant molecules from the gas. This is achieved using discharge technology that has been found to remove pollutant molecules from the gas, including but not limited to particulate matter, SOx, NOx, CO2, mercury (Hg), volatile organic compounds (VOC), and hydrocarbons (HC).

[0236] As a general overview, an apparatus and method for removing CH4 from a gas by discharge has been developed. The same ability to remove gas components also applies to other gas components, such as SOx and CO2. A gas stream containing a harmful or pollutant gas (e.g., CH4) is introduced into the apparatus. The apparatus is provided with a plurality of electrodes (typically an anode and cathode pair). The electrodes are separated by a gas space and a dielectric barrier.

[0237] Where reference is made herein to a cathode and an anode, it is intended to refer to two electrodes facing each other across an air or gas gap with no other intervening electrodes.

[0238] In the presence of an electric field between the electrodes, as gas passes between them, it is instantly ionized to form high-energy electrons, atoms, and free radicals. Taking CH₄ as an example, as a gas stream passes from the gas inlet at one end of the device through the discharge reaction zone (i.e., between the electrode pair), a portion of the CH₄ in the gas is converted into carbon monoxide (CO) and water (H₂O, H₂O). This is possible due to the electric field established between the electrodes.

[0239] Once passed between the electrode pairs, the gas stream is discharged to the gas inlet through an outlet provided at the opposite end of the device. The composition of the gas after the device contains a portion of the original CH4 as well as CO and H2O.

[0240] When using a graded discharge, a high voltage alternating current can be applied to electrodes that are typically separated by a gas space and a dielectric barrier or insulator. Other types of discharge devices include, but are not limited to, pulse, corona, and electron beam discharges, as well as radio frequency, microwave, and ultraviolet radiation sources. Of the available discharge devices, high temperature, graded barrier discharges, and many other named energy sources are not known to be used to remove CH from air or previous point sources of CH, such as flue gas or exhaust from engines and industrial plants. It is surprising and unexpected that these parameters can be used for these applications.

[0241] The use of a dielectric barrier allows sufficient energy to be provided to convert CH4 into CO and H2O. A dielectric material is applied to the entire surface of one or both of the cathode and anode. In various examples, the dielectric portion uses quartz as the dielectric material, but other materials, such as alumina, may also be used.

[0242] In some examples, the anode is a metal mesh. When the anode is a metal mesh, in various examples, a dielectric portion is coated onto the mesh to maintain the mesh structure. In other words, the dielectric coating is provided with holes that align with the holes in the mesh.

[0243] There are examples in which the anode and cathode are flat plates facing each other with a dielectric material between them (such as coated on each anode). In some of these examples, the plates can be mounted in an upright (such as vertical) position to prevent clogging by particulate matter. The rows of plates are supported by a mechanical structure and suspended from the top of the housing by insulators so that the planes of the plates can be parallel to the direction of flow of the flue gas within the housing in which the plates are located. In this way, the maximum amount of flue gas is processed by discharge with minimal pressure drop across the device. In some examples, multiple rows of plates are mechanically fastened together, one row on top of the other, to form a stack that extends substantially from the top to the bottom of the housing.

[0244] Although a planar anode and cathode configuration may be a preferred arrangement in some examples, different arrangements are possible. Such arrangements include a cylindrical cathode electrode and a planar anode electrode, and a cylindrical cathode electrode centered in the middle of a cylindrical anode electrode. In various of these example arrangements, the cathode electrode and the anode electrode have the same construction (e.g., one set of electrodes has one or more electric field enhancing structures thereon, while the other set of electrodes has a dielectric portion thereon).

[0245] In some examples, a coaxial tubular reactor arrangement is used. In several examples using a coaxial tubular reactor arrangement, one electrode is provided by a conductive tube, a central electrode is fixed inside along the central longitudinal axis of the conductive tube, and a dielectric material is disposed between the electrodes within the tube. In various examples, the tubes are arranged in a bundle.

[0246] When multiple tubes or tube bundles are present, the actual number of bundles stacked side-by-side and stacked together is typically an engineering decision based on the requirements of the system in which the device is to be used. In some of these examples, multiple coaxial electrode tubes are typically secured in spaced relation to one another using a rectangular configuration. Various examples include wire electrodes secured inside the coaxial electrodes along the central longitudinal axis of the tubes. Although the term "wire" is used, these electrodes may alternatively be rods or other shaped materials that are smaller than the inner diameter of the tubes.

[0247] Coaxial reactors have improved dielectric barrier discharge performance over flat-plate electrodes. This is because it is generally easier to establish a barrier discharge across the entire discharge area in a coaxial reactor than in a flat-plate reactor. Additionally, the temperature gradient between the top and bottom of a flat-plate reactor generally provides for an uneven reaction, which reduces reactor efficiency. This is because in a flat-plate reactor, the discharge causes the top of the plate to be hotter than the bottom, and the middle to be hotter than the sides. On the other hand, a coaxial reactor tends to "ignite" (i.e., produce a discharge) more evenly throughout the tube once the temperature and power requirements reach a threshold for a particular reactor geometry. This makes the reaction more uniform. The result is that more gas is exposed to the barrier discharge, meaning more gas is processed.

[0248] The gas can be pre-treated before passing through the equipment. For example, the gas can be passed through an electrostatic precipitator to remove particulate material. The gas can also be cooled, for example using a heat exchanger or by spraying or atomizing cold water or another liquid or solution through it.

[0249] Figure 3 and Figure 4 An example apparatus according to aspects disclosed herein is shown, generally at 400. This provides a staged DBD device in the form of a coaxial reactor.

[0250] The exemplary graded DBD device 400 includes a first electrode 304 and a second electrode 310 having a dielectric barrier 311 and a conductive material 312. Figure 3 and Figure 4 In the example shown, the dielectric barrier is a cylinder, specifically, in this example, a straight, hollow cylinder that is open at opposite ends. This provides a chamber 30 within the dielectric barrier. During use, a gas or air flow can enter and / or pass through the cylinder. In other examples, the cylinder can have a different shape and can be non-straight and / or at least partially filled.

[0251] Conductive material 312 is provided around the outside of a portion of dielectric barrier cylinder 311. In some examples, this is provided around the entire circumference of the cylinder. In other examples, the conductive material can be provided around only a portion of the circumference of the cylinder.

[0252] In some examples, the conductive material 312 extends along the entire length of the dielectric barrier cylinder 311. However, in Figure 3 and Figure 4 In the example shown, the conductive material is located only along a portion of the length of the dielectric barrier cylinder. This portion is approximately in the middle of the cylinder.

[0253] For various examples, the conductive material 312 is a coating on the dielectric barrier cylinder 311. Thus, it is intended to be non-removably attached to the cylinder. Figure 3 and Figure 4 In the example shown, the conductive material 312 is a detachable component. To hold the conductive material in place, a plurality of (in Figure 3 and Figure 4 In the example shown in , five) ring-shaped constant force springs 403 are located around the conductive material, with one constant force spring located at each end of the conductive material and the others evenly distributed along the length of the conductive material.

[0254] exist Figure 3 and Figure 4 In the example shown, the first electrode 304 is an elongated rod. In this example, the rod has a circular cross-section and is positioned through the cavity 30 of the dielectric barrier cylinder 311. This means that at least a portion of each of the first electrode and the conductive material 312 is aligned along the length of the cylinder.

[0255] The first electrode 304 has a plurality of discharge nodes 300 arranged along at least a portion of its length. Figure 3 and Figure 4 In the example shown in , the discharge node is arranged along a length portion of the first electrode that is aligned with the conductive material 312 .

[0256] In addition to the first electrode 304, the associated discharge node 300, the dielectric barrier cylinder 311, the conductive layer 312 and the constant force spring 403, Figure 3 and Figure 4 The exemplary graded DBD device shown also includes end cups 401. There is an end cup that mates with each end of the barrel. Figure 3 and Figure 4 In the example shown, the end cups are also circular, with the interior of the rim 42 of each cup fitting around the exterior of the cylinder.

[0257] As follows about Figure 7 To elaborate in more detail, between the rim 42 and the hub 43 of each end cup 401, there is a channel 41. The channel is intended to allow gas to flow through the end cup.

[0258] End cups 401 are included to provide a means for retaining first electrode 304 in position relative to dielectric barrier cylinder 311 and conductive material 312. This is achieved by positioning the first electrode at hub 43 of each end cup. The hub is located at the center of each end cup. Thus, the first electrode is retained at the center of the cylinder by the end cup. This results in the longitudinal axes of each of the first electrode, cylinder, and conductive material being aligned and, in effect, coaxial.

[0259] exist Figure 3 and Figure 4 In the example shown, one end of the first electrode 304 is in direct contact with an end cup 401. Figure 3 and Figure 4 In the examples, the end of the first electrode is shown extending beyond the end cup. In other examples, the end of the first electrode is aligned with or located at the end cup. Regardless of the relative placement of the end of the first electrode and the end cup, in some examples, the contact is a fixed contact, wherein the end of the electrode is held in a predetermined position by the end cup.

[0260] At the opposite end of the first electrode 304, there is a connection to another end cup 401. Instead of direct contact between the first electrode and the end cup, the connection at this end of the first electrode is provided by indirect contact. This is due to a compression spring 402 connected between the first electrode and the end cup. Other types of springs are used in other examples.

[0261] A compression spring 402 connecting one end of the first electrode 304 to one end cup allows the length of the first electrode to change relative to the length of the dielectric barrier cylinder due to, for example, thermal expansion. This reduces the likelihood that one or both end cups will be pulled away from the cylinder due to thermal expansion of the first electrode.

[0262] exist Figure 3 and Figure 4 In the example shown, there is a collar 31 that forms part of a dielectric barrier cylinder 311. The collar is located near the end of the conductive material 312. Thus, the collar is offset from the proximal end of the cylinder. The collar provides a ring that projects radially outward from the cylinder and has a larger outer diameter than the rest of the cylinder.

[0263] In some examples, the collar 31 is located at the end of the dielectric barrier cylinder 311 opposite the end where the compression spring 402 is located. Figure 3 and Figure 4 As shown, the collar is located axially offset from the end of the barrel to which it is closest.

[0264] In several examples, the graded DBD device 400 is arranged in an upright orientation, with the length of the first electrode 304 aligned with a vertical or upright axis. In some such examples, a collar 31 is positioned at the lower end of the dielectric barrier cylinder 311. Exemplary graded DBD devices are held in a predetermined position by passing the lower end through a circular hole in a plate or grid. In these examples, the collar rests against the plate, thereby preventing the graded DBD device from moving through the hole under the influence of gravity. In various examples, the opposite end of the graded DBD device is placed through a similar hole to help secure the graded DBD device's position. In use, multiple graded DBD devices can be arranged adjacent to each other to form a graded DBD device cassette.

[0265] In the upright orientation, the collar 31 provides a surface against which the conductive material 312 and the at least one constant force spring 403 can bear. This also helps to hold the conductive material in a predetermined position.

[0266] The hierarchical DBD device 400 can be connected to a power source, such as the drive circuit disclosed in WO 2022 / 106622, including the claims or appended claims of WO 2022 / 106622. Figures 5 to 7 . When connected to a power source, one of the first electrode 304 and the second electrode 310 is a high-voltage electrode, while the other is a low-voltage electrode. In various examples, the first electrode is a high-voltage electrode, and the second electrode is a low-voltage electrode. As described in more detail below, a discharge occurs between the electrodes under appropriate circumstances. This discharge is intended to occur only at a discharge node 300 arranged along a portion of the first electrode.

[0267] like Figure 4 As shown, in various examples, a creepage distance 4 is provided between the endmost discharge node 300 at each end of the portion along which the discharge node is located and the end of the dielectric barrier cylinder 311 closest to the respective discharge node. This is provided to minimize discharge in this area, thereby limiting the short circuit that this may cause.

[0268] Going to the details of the example discharge node, the example discharge node is Figure 5 300 in the form of an electric field enhancement structure. The exemplary electric field enhancement structure includes a ring 301 and at least one tip 302. It should be understood that although Figure 5 Six tips are shown in FIG, but the structure requires only one tip to operate.

[0269] In use, the ring 301 is arranged around the first electrode 304. This can be achieved by allowing the electric field enhancement structure 300 to deform so as to fit securely around the first electrode in the groove or channel 303. Other ways of arranging the ring around the first electrode are possible. For example, the first electrode can be integral with the structure. Such a structure can be formed, for example, by cutting or milling material.

[0270] As can be seen, at least one tip 302 extends along a radial axis passing through the center of the structure 300. In use, and as described below, the tip limits the minimum distance between the structure and the opposing electrode. That is, the tip effectively creates a region where the distance between the opposing electrode and the structure is less than it would be without the tip. In practice, this can be achieved by using a cylindrical opposing electrode.

[0271] In some examples, such as the example shown in the figure, the discharge node 300 includes a plurality of tips 302 arranged on the (radial) outer edge of the ring 301. The plurality of tips can be distributed on the outer ring in any suitable manner. However, it may be advantageous for each of the plurality of tips 302 to extend along a respective radial axis. By this, we intend to mean that each tip 302 extends in a unique radial direction (radial directions separated by a 180-degree rotation are still considered unique to each other). Typically, no tip 302 will extend along the same radial axis as the channel 303, because the channel 303 creates a break in the material of the ring 301.

[0272] Figure 5 The exemplary discharge node's multiple tips 302 are shown evenly distributed around the outer edge of ring 301. By this, we intend to indicate that the multiple tips 302 are evenly distributed across the material at the outer edge of the ring. This eliminates the need for channels 303. This even distribution of tips 302 is effective in ensuring that as much gas as possible passing through the discharge device has a chance to be processed. In other words, evenly distributed tips can overcome issues caused by tips being crowded together.

[0273] As described above, in various examples, channel 303 allows structure 300 to be assembled onto the first electrode during use and to counteract issues that may arise due to thermal expansion or contraction. The channel extends along a second radial axis from the center of ring 301 to the exterior of ring 301. The second radial axis is not aligned with at least one of the tips 302. When structure 300 includes multiple tips, channel 303 is not aligned with the axis of any of the tips. In other words, channel 303 does not overlap with any of the tips.

[0274] In some examples, channel 303 has a width of 1 mm, and typically, channel 303 has a width of 0.8 mm. Regarding ring 301, in various examples, ring 301 has a body to which at least one tip 302 is connected. Thus, in the case of multiple tips, each tip would be connected to the body. The body has a radial thickness, which in some examples is 3.6 mm. In other examples, the radial thickness of the body of ring 301 is 3.56 mm or 3.46 mm, or any value within a range between 3.46 mm and 3.56 mm.

[0275] Furthermore, the surface of the ring may be continuous. By this, we intend to mean that the material forming the ring is solid, without any gaps extending through the ring in the axial direction. For the sake of completeness, in examples where the structure includes a channel, the channel is separate from the ring and does not form part of the solid surface of the ring.

[0276] The radial thickness of the body can also be expressed as a percentage of the radius from the center of the ring 301 to the outer edge of the ring. In some examples, the radial thickness of the body is between 55% and 65% of the radius from the center of the ring to the outer edge of the ring. A more specific range is for the radial thickness of the body to be between 60.2% and 62.2% of the radius of the ring.

[0277] In various examples, the inner diameter of the ring 301 is 7.9 mm, such as 7.90 mm, and in some examples has a tolerance of minus 0.1 mm, such as 0.10 mm. In several examples, combined with the radial thickness of the body, the outer diameter of the body is 11.5 mm, such as 11.46 mm.

[0278] In some examples, each tip 302 extends the outer diameter of the ring to 18.0 mm, such as 18.00 mm, at the point of each tip. This means that each tip typically has a height of 6.5 mm in the radial direction between its point on the body of the ring and its radially closest point, such as 6.54 mm. These sizes may vary between examples, but generally, ratios of these dimensions or similar ratios will continue to apply.

[0279] from Figure 5 As can be seen from the examples shown, at least one tip, and typically more than one tip, such as all tips, includes two (typically straight) sides that intersect at a point. In some examples, the point is a sharp point. The sharpness of the point can be understood based on the angle at which the two sides intersect. In various examples, the two sides of at least one tip 302 are at a first angle of 68.9 degrees (°) (at Figure 5 intersect (marked A in FIG) (such as at an angle of 68.89°).

[0280] It has been discussed that multiple tips may be particularly effective in neutralizing contaminants. In some examples, the multiple tips are six tips. The six tips may be evenly distributed, as described above.

[0281] By stating that the plurality of vertices is 6 vertices, this may mean that the plurality of vertices comprises 6 vertices. That is, there are at least 6 vertices.

[0282] However, other examples are envisioned in which the plurality of tips consists of 6 tips. That is, the ring 301 of the structure 300 can have exactly 6 tips, only 6 tips, or only 6 tips.

[0283] In examples where the discharge node 300 includes multiple tips and a channel 303, then the second radial axis (i.e., the axis along which the channel 303 extends) bisects a second angle measured between adjacent sides of two adjacent tips on either side of the channel 303. Figure 3A second angle, labeled B in FIG, is measured between two adjacent sides of two adjacent tips. In various examples, the second angle is 135.6°, such as 135.63°.

[0284] In the case where the discharge node 300 includes multiple tips 302, in addition to the second angle already discussed, the third angle measured between adjacent tips is 127.6°, such as 127.55° in some examples. Figure 5 Shown as angle C.

[0285] In some examples, such as Figure 5 As shown, the space between adjacent tips 305 is circular. This can help avoid creating additional breakdown sites. In various examples, this area 305 between adjacent tips has a radius of curvature, and the radius of curvature is 0.5 mm. In various examples, for the same reason, the space between channels 303 is also circular.

[0286] The discharge node 300 also has a thickness in the axial direction. In some examples, the axial thickness is 1 mm, such as 1.0 mm. Competing factors in determining the axial thickness of the structure are structural integrity and manufacturing cost. A 1 mm thick structure meets the structural integrity requirement without incurring excessive manufacturing costs. Furthermore, this allows the number of discharge nodes to be maximized within the available space in the hierarchical DBD device 400.

[0287] Go to Figure 6 , shows an example discharge node 300 in the form of an electric field enhancement structure, along with a first electrode 304 and an opposing second electrode 310. A ring 301 is arranged around the first electrode 304, and the first electrode 304 has a circular cross-section. As described above, a dielectric barrier cylinder 311 provides support surrounded by a conductive material 312.

[0288] Figure 4 It is shown that the presence of at least one tip 302 limits the minimum gap between the discharge node 300 and the opposite electrode 310. It can be seen that the minimum distance 1 between the end of the tip and the opposite electrode 310 (also in FIG. Figure 4 (marked in the middle) is less than the maximum distance 2 between the relative electrode 310 and the position without a tip on the discharge node.

[0289] In some examples, the minimum distance 1 , which is the gap between the sharp point of the tip 302 and the opposing electrode 310 , measures 8 mm.

[0290] Now consider the cup, one of which is Figure 7 The wheel is generally shown at 401. As described above, it has a rim 42 and a hub 43. The hub is held in a predetermined position in the center of the rim by spokes 44.

[0291] exist Figure 7 In the example shown, there are three spokes. While there may be different numbers of spokes in other examples, we have found that three spokes provides a balance between providing the maximum possible space for the channel 41 (i.e., minimizing area obstruction), being structurally sound in view of the vibrations that the end cup may experience in use, and minimizing the amount of material used.

[0292] The three spokes 44 are evenly spaced around the rim 42 and hub 43. This allows the load to be evenly distributed between the spokes.

[0293] To allow the first electrode 304 to pass through the hub 43, in various examples, the hub has a hole therein (such as a through hole). In some examples, the hole in one end cup is a blind hole. The hole typically has a diameter of 8.1 mm, for example 8.10 mm.

[0294] In some examples, the end cup has a depth (the distance between opposing faces) of 18 mm, such as 18.0 mm or 18.00 mm. One face has a recessed portion surrounded by a thin portion of rim 42. The recessed portion has a depth of approximately 8 mm, such as 8.0 mm or 8.00 mm. The recessed portion is provided as a portion of the end cup into which the end of dielectric barrier cylinder 311 can be positioned when assembling the graded DBD device 400.

[0295] In some examples, the end cup is made of green alumina. This material is used because it is somewhat electrically insulating and has a similar coefficient of thermal expansion as the dielectric barrier cylinder 311.

[0296] The end cups 401 are typically machined. However, these can be manufactured in some other way.

[0297] In various examples, the dielectric barrier is quartz glass, which is typically transparent. In some examples, the first electrode 304 is stainless steel, such as 316L stainless steel. In several examples, the conductive material 312 is a foil, such as a machined foil. This can be aluminum foil or stainless steel foil. If the conductive material is provided as stainless steel, this is typically 316L stainless steel. Some exemplary electric field enhancement structures 300 are stainless steel, such as 316L stainless steel. The constant force spring is a nickel-chromium based alloy, such as For example X750 (and alloys containing Al, C, Co, Cr, Cu, Fe, Mn, Nb, Ni, S, Si and Ti).

[0298] In some examples, the first electrode 304 is approximately 875 mm long and has a diameter of approximately 8 mm. The material and dimensions of the first electrode 304, as well as how the first electrode is held by the end cup 401, mean that the bend radius of the first electrode is maintained within a tolerance over its length. In various examples, this tolerance is such that the bend results in a maximum deviation of the rod from a straight line of up to 1 mm.

[0299] There are examples where dielectric barrier cylinder 311 is about 800 mm long and has an outer diameter of about 38 mm, with the inner diameter of the wall providing chamber 30 being about 34 mm. In various examples, collar 31 has one side near the proximal end of the cylinder that is located about 45 mm from the proximal end of the cylinder. The opposite side of the collar is about 51 mm from the proximal end of the cylinder.

[0300] Typically, the conductive material 312 is about 690 mm long. In some examples, this is grounded foil, which has been found to be more reliable than mesh or coating. Only five constant force springs are used as a balance between the material that can be made from the material these springs are made of, the extra material for added weight, and the ability to hold the conductive material in a predetermined position (e.g., against the dielectric barrier cylinder 311).

[0301] As described above, the discharge nodes 300 typically have a maximum diameter of about 18 mm, which in some examples provides a minimum distance 1 of about 8 mm from the closest point of each electric field enhancement structure to the dielectric barrier cylinder. As described below, we have found that the discharge nodes are spaced a distance 3 (e.g., Figure 4 As shown, a distance between two adjacent discharge nodes) of about 15 mm, such as 15.0 mm or 15.00 mm is optimal.

[0302] The creepage distance 4 as described above is between about 50 mm and 60 mm, for example 58 mm (including 58.0 mm or 58.00 mm) or 51 mm (including 51.0 mm and 51.00 mm). The creepage distance may be different for both ends, for example 58 mm for one end and 51 mm for the other end.

[0303] Turning to the use and functionality of the graded DBD device 400, the goal is to pass gas through the graded DBD device. When an electric field is applied between the first electrode 304 and the conductive material 312, the goal is to remove components of the gas passing through the graded DBD device. This is achieved by providing an electric field of at or above a threshold strength and / or a potential difference at or above a threshold between the first electrode and the conductive material to induce a dielectric barrier discharge. In some examples, the threshold is achieved by providing a pulsed signal (such as the pulsed power disclosed in WO 2022 / 106622), as described in more detail below. Once the threshold is reached, one or more discharge nodes cause a discharge to occur only at one or more of these graded points in the device.

[0304] The specific threshold for initiating discharge is determined by the specific geometry and dimensions of the implemented graded DBD device 400. However, by having a graded DBD device where the grading is provided by the discharge nodes 300, the discharge is concentrated at the discharge nodes, meaning that discharge occurs only at intervals along the device. This is because the discharge nodes create an inhomogeneous electric field by providing locations where the electric field is enhanced, thereby reducing the power required to initiate the discharge. In other words, the discharge nodes create a heterogeneous volume distribution of the discharge. This results in peak plasma density at these periodic points in the device, which provides the ionization region.

[0305] As described above, plasma is generated in the ionization region. A recombination region exists between the ionization region and an adjacent ionization region where no discharge node 300 is adjacent to another ionization region, such as at the end of the portion of the first electrode 301 along which the discharge nodes are arranged.

[0306] As the gas passes through the hierarchical DBD device 400, reactive species in the plasma in the ionization region cause components in the gas to decompose. These reactions continue in the recombination region, where the plasma also recombines along the length of the recombination region.

[0307] Because the discharge nodes 300 protrude radially outward from the surface of the first electrode 301 into the chamber 30, they provide a partial obstruction along the dielectric barrier cylinder 311. This induces back pressure in the gas, thereby slowing the flow of the gas. However, we have found that an optimal balance between back pressure and gas component removal is achieved by adjusting the ratio of the discharge node outer diameter, tip shape, and placement to the cylinder inner diameter.

[0308] We have tested the performance of hierarchical DBD devices according to aspects disclosed herein against other similar configurations. The results of this testing are Figure 8 to Figure 1 3. Multiple tests were performed using replicate compositions of exhaust gas from an LNG-fueled engine with various pollutants.

[0309] The composition comprises approximately:

[0310] Methane (CH4): 1500ppmv

[0311] Sulfur dioxide (SO2): 20ppmv

[0312] Carbon monoxide (CO): 185 ppmv

[0313] Nitrogen oxides (NOx): 165ppmv

[0314] Carbon dioxide (CO2): 4% by volume

[0315] Oxygen (O2): 14% by volume

[0316] Water vapor (H2O): 10% by volume

[0317] Nitrogen (N2): The remaining balance provides 100%

[0318] This composition, while representative of exhaust from an LNG-fueled engine, has a significantly lower methane concentration (since it is in the ppmv range, e.g., up to 10,000 ppmv, up to 5,000 ppmv, 2,500 ppmv, or 2,000 ppmv). This means that it is not desirable or even desirable to remove such low starting levels of methane using known techniques and systems. However, first consider Figure 8 , which provides a graph 600 showing methane reductions achieved in discharge devices having different configurations using the power supply disclosed in WO 2022 / 106622 as the power supply. This power supply was also used to generate the data for the later graphs and, unless otherwise stated, is used in generating the data for the later graphs. Figure 8 Each of the graphs 600 shows three data sets related to methane reduction versus power and specific energy input (SEI) for different configurations of the first electrode described above, using the same setup and conditions. Figure 8 In the graph shown, the cross-marked line 601 shows how the methane reduction varies with power when the first electrode is formed as a rod with a diameter of 16 mm. It should be noted that this is as described above with respect to Figure 4 The diameter of the first electrode in question is twice the typical size, however the size of the gap between the first electrode and the counter electrode is the same as in the configuration of the electrode with the electric field enhancing structure.

[0319] Line 603 shows how methane emission reduction changes when the discharge device is provided with 10 discharge nodes, each with 6 tips, as described above with respect to Figure 5 It can be seen that the electric field enhanced structure outperforms the rod with a diameter of 16 mm by having higher methane reduction at the same power and SEI.

[0320] Graph 600 demonstrates proof of concept that an electric field enhancement structure can outperform alternative configurations because methane, a significant component to be removed, can be effectively removed from the gas composition by employing this arrangement.

[0321] Using the same gas mix and power supply parameters as above, different diameters of the dielectric barrier cylinder 311 were also tested. A discharge node with 12 tips was used to maintain the distance between the discharge node 300 and the inner diameter of the cylinder.

[0322] Figure 9A graph 900 is shown, which illustrates four data sets related to the variation of methane removal efficiency with respect to power. The four data sets are for different outer diameters (OD) of dielectric barrier cylinders of 38 mm (labeled "A"), 42 mm (labeled "B"), 46 mm (labeled "C"), and 50 mm (labeled "D"). As can be seen from the graph, at powers of 30 W and lower, all cylinder sizes perform similarly. Within this power range, the OD 38 mm cylinder performs slightly better than the other diameters studied. However, at powers greater than 30 W, this slightly enhanced performance declines, with the OD 38 mm cylinder performing significantly worse than the other OD diameters tested.

[0323] Considering the number of tips on each discharge node 300, Figure 10 Graph 700 is shown. Figure 10 The methane removal efficiency of the variants of the discharge node with different numbers of tips is shown in FIG. Figure 9 The results shown are for tests where the same gas mix and power parameters were used Figure 10 Tests with results shown.

[0324] Figure 10 Graph 700 shows how the methane reduction efficiency varies with the power of the discharge node for different numbers of tips. In particular, discharge nodes with 6, 9, 16, and 19 tips were tested. Notably, from about 50W and more significantly from 100W, the 6-tip variant outperforms all other variants. The 6-tip variant exhibits particularly high efficiency at about 120W, achieving a methane removal efficiency of about 60%, which is about 5% higher than the next most efficient variant. Below 50W, all variants of the discharge node have relatively similar performance except for the 9-tip variant, which drops below the performance of the other tips at about 40W.

[0325] In short, Figure 10 It is shown that the number of tips of the discharge node makes little difference to the efficiency of methane reduction at most of the operating powers tested, but at powers between 80W and 120W the 6-tip variant outperforms all other variants.

[0326] based on Figure 10 The results for the 6-tip variant shown in , it is expected that higher plasma energy per flow element in this variant will trigger higher methane removal efficiency. To test this, the same gas mixture and the same gas mixture as above were used. Figure 8 Same power parameters, comparing the 6-tip variant to the 3-tip variant.

[0327] The results of this test are shown in Figure 11Graph 800 shows how methane reduction performance varies with power for a configuration with six tips and a configuration with three tips. It can be seen that the six-tip variant, represented by line 801, outperforms the three-tip variant, represented by line 802, between 0 and 100 watts. Between 100 and 160 watts, they perform roughly the same, and between 160 and 200 watts, the three-tip variant outperforms the six-tip variant.

[0328] Graph 800 shows that increasing the energy of the formed line stream does not necessarily affect methane removal. Thus, methane removal is higher for the 6-tip dart star. Furthermore, we found that the sharpness of the tip had no significant effect on performance under the conditions applied during testing.

[0329] In addition to evaluating the optimal number of tips at each discharge node, the number and spacing of discharge nodes along a given length were also considered. First, the spacing of discharge nodes along a given length was considered. The discharge nodes were arranged on the first electrode 304 with distances of 8 mm, 16 mm, and 32 mm between adjacent discharge nodes. The discharge nodes were arranged along an electrode length of 224 mm.

[0330] Use the 6-tip variant of the discharge node. Figure 12 A graph 1200 is shown showing the results of this evaluation in terms of power versus methane removal efficiency. The discharge nodes with 8 mm spacing are represented by line 1202, the discharge nodes with 16 mm spacing are represented by line 1204, and the discharge nodes with 32 mm spacing are represented by line 1206. In general, from Figure 12 It can be seen that the intervals of 16mm and 8mm are the most effective. Figure 12 The standard deviation for all points in graph 1200 is less than 5%, so there is no noticeable difference in performance by varying the distance between discharge nodes. However, it is noted that a distance of 16 mm between discharge nodes results in slightly higher methane removal and less nitrogenous products (NOx and N2O) production. These evaluations were repeated at different power supply parameters and 330°C, and similar trends were observed, confirming that there is no interaction between discharge node separation distance and temperature or power supply parameters.

[0331] The volume of the area where the discharge nodes are arranged and the gas residence time are expected to be two important parameters that are expected to affect the lifetime and amount of active species for methane removal. This is particularly relevant at larger scales where the gas flow rates are significantly high and the role of gas residence time is crucial. In order to simulate the conditions at larger scales, we reduced the number of discharge nodes to have a lower gas residence time in the ionization region and studied its effect on methane removal. In some examples, this was evaluated at two different temperatures (200°C and 330°C) to cover the temperature range in which the device can operate, and the results were Figure 13A and 13B This is shown in Figures 1300 and 1301 .

[0332] Figure 13A and 13B Graphs 1300 and 1301 in FIG. 1 show power versus methane removal efficiency in percent and ppm. These graphs show the results of four variations of the evaluation setup. In each graph, lines 1310, 1311 are for one discharge node, lines 1320, 1321 are for two discharge nodes, lines 1330, 1331 are for five discharge nodes, and lines 1340, 1341 are for ten discharge nodes. Each evaluation was run using the same power supply parameters, and Figure 13A The graph shows the results for the run at 330°C. Figure 13B The graph shows the results of a run performed at 220°C using a discharge node with 6 tips.

[0333] exist Figure 13A and Figure 13BWith standard deviations of less than 5% for each point in graphs 1300 and 1301, these figures show that methane removal is highly temperature-dependent and slightly dependent on the number of discharge nodes. Higher temperatures trigger nearly double methane removal at powers below 30 W for all discharge node numbers. Generally speaking, a larger number of discharge nodes slightly improves methane removal at 330°C but does not affect performance at 200°C, except for the case associated with a single dart star. The graphs reveal unusual behavior that requires further investigation. However, a possible explanation is the formation of an energetic plasma stream at the tip of a single discharge node. Contrary to standard behavior, at 330°C, above 20 W, methane removal is generally flat for all discharge node numbers, with removal efficiency increasing between 0 W and 20 W. The graphs also show that, across the entire power range, a larger number of discharge nodes leads to higher efficiency. At 200°C, the removal efficiency for all single discharge node arrangements is grouped together within the evaluated power range of approximately 80 W. The removal efficiency is generally linear, with an upward gradient between 0 W and 80 W. The single discharge node at 200 °C has a steeper gradient and reaches a peak at a point where the efficiency difference between the single discharge node and the other number of discharge nodes is greater than about 20%, where the removal efficiency of the single discharge node is higher than 55% and the removal efficiency of the other number of discharge nodes is less than 35%.

[0334] Based on the evaluations conducted, the optimal conditions that allow the hierarchical DBD device to operate at low power while still being effective at methane removal are a gas temperature of approximately 330°C, six tips per discharge node, and as many discharge nodes as possible over the available length.

[0335] These are optimal conditions without any catalyst. In some examples, a hierarchical DBD device is used with a catalyst. The catalyst can be positioned in various locations relative to or within the hierarchical DBD device. For example, the catalyst can be positioned upstream of the hierarchical DBD device ("before plasma"), downstream of the hierarchical DBD device ("after plasma"), or within the hierarchical DBD device ("in plasma"). When the catalyst is within the hierarchical DBD device, the catalyst can be positioned in the ionization region and / or the recombination region.

[0336] It is believed that further improvements can be achieved by using a hierarchical DBD device in conjunction with a catalyst. For example, the power and voltage required to establish the discharge can be reduced while allowing CH4 to be removed from the gas. In addition, when a hierarchical DBD device is used in conjunction with a catalyst, the overall efficiency is improved.

[0337] Hierarchical DBD devices are compatible with a variety of catalysts, and suitable catalysts are known. These can include one or more components such as cobalt, rhodium, iridium, nickel (such as nickel oxide), copper, palladium, platinum, silver, gold, manganese, aluminum, vanadium (such as vanadium oxide), chromium (such as chromium trioxide), zinc (such as zinc oxide), titanium (such as titanium dioxide), and tungsten (such as tungsten trioxide). The catalyst can be a composite material comprising CuO and MnO or Al2O3 and CuZnO.

[0338] Typically, the catalyst, if used or present, is palladium or platinum, as these exhibit particular efficiencies for methane removal.

[0339] Figures 2 to 7 The coaxial graded DBD device is generally discussed. The principles are also applicable to other forms of graded DBD devices. One such form of these principles is applicable to plate-based graded DBD devices. Figures 14 to 17 Generally relates to such plate-based hierarchical DBD devices.

[0340] Figure 14 A plate based hierarchical DBD device is shown generally at 1400. This has a first plate electrode 1402 and a second plate electrode 1404 separated by a chamber 1406. The chamber provides a gas flow path 1408 along which a gas can pass in use.

[0341] A dielectric barrier 1410 is located on the second plate electrode 1404, on the chamber side of the second plate electrode. The first electrode has discharge nodes 1412 spaced at regular intervals along the length of the gas flow path 1408. These are typically (micro)needles in an array.

[0342] In use, Figure 14 In the example shown, first electrode 1402 is configured as a high-voltage electrode, and second electrode 1404 is configured as a corresponding low-voltage electrode. Under suitable conditions, when an electric field is established between the electrodes, a dielectric barrier discharge occurs. Due to the positioning of the discharge nodes, ionization regions 1414 are generated at the discharge nodes, and recombination regions exist adjacent to each ionization region.

[0343] Figure 14 The hierarchical DBD device 1400 of the illustrated example can be connected to a power source in a manner similar to how the above examples are connected to a power source. This is typically the case when an electric field is established between the electrodes and the appropriate conditions are provided for a discharge to occur.

[0344] Figure 15 A second exemplary plate-based hierarchical DBD device 1500 is shown. Figure 14In the example of FIG, this has a first plate electrode 1502 located between two second plate electrodes 1504. The first plate electrode is separated from the second plate electrodes, and a chamber is provided between the first plate electrode and the second plate electrode, through which a gas flow path 1506 is provided.

[0345] exist Figure 15 In the example shown, the second electrode 1504 has a first dielectric layer 1508 and a second dielectric layer 1509 in a stack between each second electrode and the first electrode 1502. The first electrode has a discharge node 1510 disposed thereon.

[0346] In use, the second exemplary plate-based hierarchical DBD device 1500 can be provided with electrical energy from a power supply as described above to establish an electric field between the high voltage electrode and the low voltage electrode. Figure 15 In the example shown, these are provided by the first plate electrode 1502 and the second plate electrode 1504, respectively. Under suitable conditions, a dielectric barrier discharge can be established between the electrodes. This creates an ionized region where the discharge occurs and a recombination region therebetween to allow the establishment and recombination of a plasma with active species. Figure 14 and Figure 15 As the gas flow paths 1408, 1506 of the exemplary plate-based hierarchical DBD devices 1400, 1500 pass through, as in the above examples, components of the gas are removed from the gas due to reactions driven by the presence of reactive species. These examples can achieve the same general effects as those described above with respect to the coaxial hierarchical DBD devices.

[0347] Figure 16 A schematic diagram for a plate-based hierarchical DBD device (e.g., Figure 14 and Figure 15 An example high voltage electrode 1600 is shown, which is similar to those described above for plate-based graded DBD devices. The electrode has a ladder-like shape with side rails 1602 extending the entire length of the electrode and rods 1604 spaced at regular intervals along the length of the electrode and attached to the side rails. In some examples, the discharge nodes are included on the rods, and in other examples, the rods provide the discharge nodes.

[0348] We have found that the width of the strips 1604 in a direction parallel to the length of the electrode 1600 and the spacing between the strips affect the amount of components that can be removed from the gas by using the electrode in a plate-based hierarchical DBD device. This can be seen from Figure 17 It can be seen that Figure 17A graph 1700 is shown indicating the spacing between bars and the width of the bars relative to a measure of SO2 reduction in ppm from a gas passing through a graded DBD device including electrodes meeting the indicated parameters.

[0349] from Figure 17 As can be seen, minimizing the rod width to approximately 2 mm optimizes the rod width for gaseous component removal. An additional rod spacing of approximately 15 mm also optimizes the rod spacing. Combined, this maximizes SO removal, exceeding 2.5% over the suboptimal rod width and spacing combination of 2 mm and 10 mm. Figure 17 Other combinations are shown in FIG, where the bar width (bw) and bar spacing (bs) are 1 mm bw, 30 mm bs; 2 mm bw, 30 mm bs; 15 mm bw, 10 mm bs; 5 mm bw, 10 mm bs; and 5 mm bw, 5 mm bs. Between the maximum and minimum component removal, the component removal increased by 25% from minimum to maximum removal. The test was conducted using an electrode with a length of 33 cm and a width of 3.3 cm and an applied potential difference of 18.4 kilovolts (kV) to establish an electric field between the electrode and the low-voltage electrode.

[0350] For identification purposes, since it was originally included in Figure 17 The bars on the graph are labeled "A" through "G" relative to the scale on the right side of the graph.

[0351] Regarding providing a pulsed signal, such as the pulsed power disclosed in WO 2022 / 106622, in some examples and as described above, when using the above-described hierarchical DBD device, a pulsed system can be used. This is intended to ignite a dielectric barrier discharge between electrodes in the device.

[0352] High-voltage pulse power equipment for industrial-scale DBD systems typically employs a low-voltage pulse generation unit with a peak output pulse voltage of 400V to 1000V and a subsequent step-up transformer with a turns ratio of 1:20 to 1:40 to meet the required dielectric barrier discharge voltage level.

[0353] Figure 18 The characteristic voltage and current waveforms of a single pulse with a conventional high voltage pulse generator are shown in Figure 2. This shows two graphs of a single pulse generated using a prior art high voltage pulse modulator system for charging a large DBD device, one showing the change in voltage versus time and the other showing the change in current versus time.

[0354] It can be seen that the voltage curve starts at 0V, and then the pulse rises to a peak value of approximately 22kV in about 1 microsecond (μs). The voltage then drops from the peak to a level of approximately 12kV over the course of about another 1.5μs. The voltage then slows down to a linear decrease to 0V in about 21μs.

[0355] The drop from the peak value is caused by the natural resonance between the DBD device and the transformer parasitics. This resonance causes oscillation to begin, which can be seen during the drop from the peak value. The resonance is then stopped by stopping the pulse, thereby cutting off the supplied voltage. From this point on, a linear discharge occurs. If the pulse were not stopped, a cyclic waveform would be visible.

[0356] The corresponding current graph shows that the current increases from 0 A to a peak of about 90 A in about 0.5 μs. This then drops to about -40 A (negative 40 A) in about 1 μs, and returns to 0 A in about another 1 μs.

[0357] The change in current occurs within the same time period that the voltage takes to pass through its peak and return to 12 kV. The dielectric barrier discharge begins approximately at the point where the voltage reaches its peak and ends when the voltage returns from its peak to 12 kV. The linear slope from this point back to 0 V is due to the energy dissipation in the pulse generation unit from the energy stored in the capacitance of the DBD device after the dielectric barrier discharge occurs.

[0358] As described above, the low power factor PF, which is determined from the ratio of active power to apparent power in the DBD device, i.e., the large amount of reactive power required to recycle the voltage at the reactor and the relatively small amount of active power actually delivered to the plasma, poses a fundamental challenge to achieving high power transfer efficiency.

[0359]

[0360] As an example, a DBD device with an equivalent capacitance of 5nF ​​and a firing voltage of 20kV requires a charge / discharge current of 100A to achieve a voltage rise time of at least 1μs, according to Equation 3. If a 1:20 step-up transformer is used, a peak input current of 2kA is required, which must be processed by various electronic components and a pulse generation unit before passing through the transformer.

[0361] To overcome its negative aspects, we have developed example devices, systems, and methods described in detail below. Such devices can be used to purify exhaust gases, such as the devices disclosed above or in GB 2593786, which is incorporated herein by reference. The device utilizes functionalized electrodes having one or more electric field enhancement structures (such as submacro features) and a dielectric portion. The electric field enhancement structure is exposed to an electric field, resulting in field emission of electrons from the electric field enhancement structure and discharge of the dielectric barrier between the dielectric and the opposing electrode. The gas to be purified is then exposed to those electrons.

[0362] The phrase "functionalized electrode" is intended to mean an electrode having one or more structures (eg, a coating) thereon that have functional aspects other than serving as an electrode (ie, as an anode and / or cathode).

[0363] As an illustrative example, Figure 19 The principle of the electron irradiation and dielectric barrier discharge purification technology is schematically shown. Two electrodes (anode 10110 and cathode 10120) are positioned so that they face each other. In this example, a dielectric portion 10125 is located on the anode. This dielectric portion provides a coating on the entire surface of the anode.

[0364] Figure 19 The example in further includes an electric field enhancing structure 10130 located between the anode 10110 and the cathode 10120. In this example, the electric field enhancing structure is electrically connected to the cathode.

[0365] In some examples, the electric field enhancement structure is the electric field enhancement structure described above or a portion thereof. The electric field enhancement structure may also include or be in the form of (other) sub-macro features, such as microneedles, microneedle arrays, and / or one or more CNTs. These can function and operate in the same or similar manner as how the electric field enhancement structure described below functions.

[0366] In use, when a potential difference is established between the anode 10110 and the cathode 10120, the electric field enhancing structure 10130 and / or other sub-macroscopic features emit electrons (e-, e-) in response to the presence of the electric field between the anode 10110 and the cathode 10120. - ). The electric field between the anode and cathode also causes a dielectric barrier discharge between the dielectric portion 10125 and the cathode 10120 (in the form of a dielectric barrier discharge).

[0367] The electrodes are coupled to the housing so as to position the dielectric portion 10125 and the electric field enhancing structure 10130 near a container 10140 containing the gas (g) to be purified such that the interior of the container can be exposed to field emitted electrons and dielectric barrier discharges.

[0368] For a compact arrangement, the anode 10110 and / or cathode 10120 can be attached to the interior of a container (e.g., a flue) such that each of the surfaces of the dielectric portion 10125, the electric field enhancement structure 10130, and the cathode extend into the flue and the dielectric barrier discharge and electrons pass through a cross-section of the flue. However, many other arrangements can be envisioned. For example, the surfaces of the dielectric portion and / or the electric field enhancement structure and the cathode can be located outside of but close to the container, with a window (hole) on the container side allowing electrons to enter and a surface where the dielectric barrier discharge can begin / end. For example, such an arrangement can be selected to make it easier to retrofit the device to an existing flue, or to facilitate maintenance of the dielectric portion and / or electric field enhancement structure portion of the device. The cathode and housing need not be located in the same location.

[0369] For example, in an industrial setting, it may be more practical to use an array of electric field enhancement structures rather than a single electric field enhancement structure. Providing multiple sets of anode-dielectric-cathode-electric field enhancement structure arrangements may also be beneficial. Such larger-scale arrangements may be in a flue, and it is also contemplated to have multiple sets of anode-dielectric-cathode-single electric field enhancement structures, or where a single set of anode-dielectric-cathode-electric field enhancement structure arrays is present.

[0370] When using a DBD device, such as implementing Figure 19 We have developed methods for achieving high-frequency sinusoidal waveforms (similar to wavelet-type waveforms) with varying amplitudes using a DBD device, such as the device shown in FIG. In various examples, the wavelet is generated by connecting an inductor in series with the DBD device, which provides capacitance. This forms a series resonant circuit, also known as a series resonant tank circuit, which is capable of being excited at a resonant frequency. When repeatedly excited for several cycles at the resonant frequency using bipolar voltage pulses, this allows the DBD device to be excited at a high voltage slew rate while significantly reducing current stress and lowering the peak power handled by the power electronics. Thus, the voltage gain achieved in the resonant tank circuit provides a high ignition voltage level for the DBD device, rather than using a pulse transformer with a high turns ratio to provide the voltage gain. Therefore, the relevant properties of the resonant tank circuit are the achievable voltage gain and the ability to compensate for the reactive power of the DBD device.

[0371] Applying several consecutive bipolar voltage pulses to form a pulse train allows for low power loss (demonstrated by the high efficiency mentioned below) and higher pulse repetition frequencies, and thus significantly increases the average power delivery capability over systems using single pulses. As an example, by applying this process, the pulse repetition frequency can be increased by at least a factor of ten on such systems. This can be achieved in conjunction with the use of silicon carbide semiconductor technology, as described in more detail below.

[0372] The repetition frequency of the pulse train is limited by the maximum operating temperature of the power electronics. Typically, pulse power converter designs utilize a slow thermal response. This means that if a high pulse repetition frequency is used in a conventional pulse system, the peak power dissipated will be too high to maintain the safer operating temperature of the power electronics. This is avoided in the examples described herein by using pulse train modulation, described below. Furthermore, this is avoided by limiting the maximum number of discharge ignition events generated from a single pulse train and then allowing a cool-down period before the next pulse train.

[0373] By implementing a pulse train of several consecutive bipolar voltage pulses as described with respect to the examples set forth herein, this is achieved while providing energy transfer with very high efficiency (such as approximately 90% efficiency or higher) even if the number of discharge ignition events is limited to between one and five.

[0374] like Figure 20 As shown, the use of sequential bipolar voltage pulses results in three operating modes induced at the DBD device. Figure 20 The first mode occurring between 0 μs and time A is the charging of the resonant circuit. This establishes a potential difference between the electrodes in the DBD device. As described above, this is achieved by applying continuous bipolar voltage pulses at the resonant frequency of the resonant tank circuit.

[0375] exist Figure 20 In the graph shown, this can be seen as a sine wave at a consistent frequency with a steadily increasing amplitude for both voltage and current. This results in the instantaneous power level of the rectified sine wave (as the product of the rectangular voltage and the sinusoidal inductor current) having a steadily increasing amplitude. Figure 20 The duration of the pattern in the example shown is approximately 2.5 voltage cycles, 2.5 current cycles, and 5 power cycles (a power cycle is a transition from zero to peak and back to zero). In this example, the current waveform leads the voltage waveform by approximately 90°.

[0376] exist Figure 20 In the example graph of FIG. 1 , the second mode occurs between time A and time B. When the voltage reaches the ignition or breakdown voltage (V th ). This mode is reached when V is 0.05 V. This delivers power to the plasma and should only last for a few discharge cycles to achieve the most effective contaminant reduction. During this mode, the voltage amplitude remains above V due to the continued excitation of the resonant tank circuit at the resonant frequency. th level. As can be seen in the graph, the voltage and current continue as a sine wave with a consistent frequency. The amplitude of the wave varies slightly over the duration of the period (increasing until about halfway through the pattern duration and then beginning to decrease).

[0377] Figure 20 The example shown in is based on a DBD device with a capacitance of approximately 3.0 nF. The voltage has a peak value at approximately ±24 kV (plus or minus 24 kV), and the current is ±80 A. In other examples, the capacitance is approximately 1.0 nF, but can also be approximately 45.0 nF or higher.

[0378] The voltage and current amplitude patterns are the same for the instantaneous power, which is still a rectified sine wave. Figure 20 In the example shown, the peak instantaneous power is approximately 180 kilowatts (kW).

[0379] The duration of the second mode is about 1.5 voltage cycles, about 1.5 current cycles, and about 3 power cycles.

[0380] During the first and second modes, the resonant tank circuit is excited by supplying power to the resonant tank circuit. During the third mode, the excitation is stopped, and the resonant tank circuit is discharged by draining. In some examples, the tank circuit is actively discharged by recovering energy from the tank circuit. Passive discharge is also possible.

[0381] In the third mode, the voltage, current and power decrease to zero due to stopping the excitation and providing a discharge path. Figure 20 The example graph in FIG shows a third mode from time B onward. As in the first and second modes, the voltage and current follow sinusoidal waveforms with a consistent frequency. The power continues to be a rectified sine wave. Over a period of approximately 2.5 cycles for the voltage and 2.5 cycles for the current, the amplitudes of the voltage and current decrease toward zero.

[0382] Figure 20 The power graph shown is consistent with an example of passive discharge of a resonant tank circuit. This can be seen by the instantaneous power being inverted to become a rectified sine wave, but with a negative peak value rather than a positive value as in the first and second modes. The power amplitude decreases to zero within approximately five cycles.

[0383] These three modes form a wavelet pulse power process in the form of a pulse train achieved by exciting the resonant tank. The duration of power transfer achieved using this process is determined by the length of time the excitation pulse train is supplied to the resonant tank circuit. This is only one parameter of the excitation pulse train, which is determined by the circuitry that implements the pulse train. Figure 22 、 Figure 23 and Figure 24 Example circuits that can be used to implement one or more pulse trains are shown.

[0384] An example of the excitation applied to the resonant tank circuit is shown below. Figure 29As can be seen in this figure, in various examples, the excitation takes the form of a square wave voltage waveform comprising a plurality of successive individual pulses that together form a pulse train. This induces a sinusoidal current ( Figure 29 The current waveform shown in Figure 20 The waveform is provided at the DBD device shown.

[0385] Although Figure 29 The dielectric barrier discharge threshold is not shown, or specifically the markings separating the first, second and third modes, but it can be seen in these figures where the third mode begins. Figure 29 At time D in Figure 1, it can be seen that the voltage waveform has a peak at its maximum positive value, which has a shorter duration than the other peaks in the waveform. This occurs due to the transition from the second mode to the third mode. At this point, excitation ceases, meaning that voltage is no longer actively supplied to the resonant tank circuit and DBD device.

[0386] Depending on the action taken at this stage, such as using active or passive energy recovery, this results in a phase shift in the voltage waveform. Figure 29 Passive energy recovery was used in the simulations; therefore, the applied waveform changes were caused by the freewheeling current in the H-bridge diodes. An alternative active energy recovery method, applied in some examples, involves a 180-degree phase shift to dissipate power. These processes are described in more detail below, along with an example inverter that provides an H-bridge.

[0387] In various examples, in examples according to aspects disclosed herein, the transition to the third mode is applied after a maximum number of discharge ignition events. Several examples limit the maximum number of discharge ignition events to only a single discharge ignition event, or to up to approximately five discharge ignition events. When only a single discharge ignition event is used as the maximum number, or after the last discharge ignition event with a larger maximum number, the third mode transition occurs directly after (such as immediately after) the maximum number of discharge ignition events has occurred, or after the last discharge ignition event with a larger maximum number.

[0388] In terms of how an example stimulus applied to a DBD device is converted into a discharge, this is accomplished by Figure 21 This is demonstrated by the curves shown in . This shows an upper graph and a lower graph. The upper graph is a graph of voltage versus time, and the lower graph is a graph of current versus time.

[0389] Figure 21The upper graph shows solid and dashed lines. The solid line is a sine wave with a minimum at time zero. In this example, this line corresponds to the voltage applied across the DBD device. The dashed line is a sine wave with its maximum and minimum peaks truncated to form plateaus. Like the applied voltage curve, this line has a minimum at time zero and, in this example, corresponds to the voltage across the discharge gap.

[0390] The magnitude of the gap voltage is less than the magnitude of the applied voltage. As the applied voltage turns positive, the gap voltage increases. After about one eighth of the cycle of the applied voltage, the gap voltage becomes positive. Just before the end of the second eighth of the cycle, the magnitude of the gap voltage reaches a threshold. Figure 21 In , this occurs at time α. Figure 21 This plateau is maintained until the applied voltage reaches a maximum at time γ. At time γ, the process repeats itself, but with reversed polarity, and continues to switch between movement in the positive and negative directions as long as the applied voltage continues.

[0391] Compared to the first, second, and third modes described above, the rise in the gap voltage corresponds to, for example, a voltage rise during the second mode following a first voltage drop during the second mode. It can be understood from this that discharge can occur during this period, and therefore, the flat top in the gap voltage curve is due to reaching the threshold voltage.

[0392] Figure 21 The current graph shows the current at the gap induced by the gap voltage. At time zero, this has approximately zero amplitude. This increases in the form of a sine wave. If the gap voltage does not reach the threshold voltage (such as if Figure 21 The graph represents the voltage and current during the first mode or the third mode), then Figure 21 As shown by the dashed line in the current graph, the sine wave continues uninterrupted. However, at time α, ignition occurs because the threshold voltage has been reached. This causes the dielectric in the discharge gap to ionize and discharge to begin.

[0393] From time α, the gap current rapidly increases to a peak at time β, which corresponds to the zero-crossing point of the applied voltage. Since time α is almost at the end of a quarter of the applied voltage cycle, this is a very short period of time relative to the cycle of the current curve. Then, starting from time β, the current decreases sinusoidally to zero at time γ, at which point it returns to its original form and amplitude range. This cycle continues in parallel with the gap voltage and the applied voltage.

[0394] From this it can be seen that the magnitude of the current simply increases to the amplified level.

[0395] Figure 21The main current graph of shows a continuous curve between time α and time γ. As mentioned above, this is the time when the discharge occurs. Therefore, this period can be considered as the macroscopic discharge period, and time α is the time when the discharge ignition event occurs. However, as Figure 21 As shown in the enlarged portion of the current graph of FIG, the current curve does not have a continuous form. Instead, the curve consists of many current spikes that are so close together that they make the curve appear continuous. Each spike represents a microdischarge or transient filament that originates from a single point on one of the electrodes (such as from Figure 19 It is each of these filaments that provides the field enhancement structure 10130 on the opposite electrode (one electrode 10110 of course has a dielectric layer 10125 thereon, as shown). Figure 19 The connection between the discharge gap (shown) causes a current spike because the filament provides a current path across the discharge gap. Since these microdischarges ionize the medium in the gap and transfer high-energy electrons into the medium, there is enough energy to drive chemical reactions, such as those that break down pollutants in the medium.

[0396] exist Figure 22 、 Figure 23 and Figure 24 Shown generally at 10001 in each of the Figures is a circuit diagram of an example system for providing a dielectric barrier discharge. The system includes a DBD device 10010, also referred to as a DBD reactor.

[0397] DBD reactor 10010 Figure 22 、 Figure 23 and Figure 24 Each of the images is represented by a model. The model is provided with a voltage V in use th The power input (also called the power supply) of the diode bridge. The electrodes of the DBD device are shown in the model as connected across the diode bridge.

[0398] The electrodes (particularly, the gap between the electrodes, which may be referred to as a "dielectric discharge gap") and the dielectric barrier mounted to one of the electrodes are arranged in a manner similar to the embodiment of the present invention. Figure 22 、 Figure 23 and Figure 24 100 is represented by capacitor 10012. This is because when represented as a circuit, the electrical function provided by the gap and dielectric barrier to the system is capacitance.

[0399] The capacitance provided by the dielectric discharge gap is shown connected directly across the diode bridge. The capacitance provided by the dielectric barrier itself is shown connected at one end to a diode bridge in parallel with the capacitance provided by the gap. The other end of the capacitance provided by the dielectric barrier is not connected to the diode bridge. Instead, it is connected to a drive circuit that is arranged to drive the dielectric barrier discharge across the gap between the electrodes.

[0400] Although by Figure 22 、 Figure 23 and Figure 24 Although the model in FIG. 1 shows, the capacitance of the DBD device 10010 is primarily determined by the capacitance of the dielectric (typically a gas, such as air) in the dielectric discharge gap. This is generally due to the dielectric constant of the dielectric being approximately 1, and dielectric materials being significantly higher than 1, such as between approximately 3 and 6 (when measured at approximately 20 degrees Celsius and approximately 1 kHz). Since the dielectric and the dielectric are connected in series, the dominant capacitance is relatively small, and therefore, due to these relative dielectric constants, the effective capacitance of the DBD device is controlled by the dielectric.

[0401] Furthermore, the contribution of the capacitance of the dielectric in the gap is approximately constant and independent of the temperature of the dielectric composition in the gap. Thus, the "air gap" capacitance is approximately constant because, as explained in more detail below, the pulse trains used in examples according to the disclosed aspects limit the number of discharge ignition events to a point where this capacitance changes minimally. However, this is not true for known resonant systems. This is due to the extended nature of the discharge causing the dielectric capacitance to shift, or when the dielectric has different properties, such as when using a surface dielectric barrier discharge device.

[0402] The drive circuit Figure 22 、 Figure 23 and Figure 24 The drive circuit has a power supply 10022 connected to an inverter 10030. In the example of these figures, the power supply is provided by a DC power supply. In the example shown, this is a DC link voltage source V dc .

[0403] exist Figure 22 and Figure 23 In the example shown, inverter 10030 has a circuit loop connected across its terminals. This circuit loop has connections to electrodes of DBD device 10010, which are connected in series across the capacitance provided by the dielectric discharge gap and the dielectric barrier. This closes the circuit loop connecting the two terminals of the inverter.

[0404] Figure 24In the example shown, the inverter 10030 has a transformer 10050 connected across it. In this arrangement, the primary side 10052 of the transformer is connected across the inverter. The secondary side 10054 of the transformer has connections to the electrodes of the DBD device 10010, which are connected in series across the capacitance provided by the dielectric discharge gap and the dielectric barrier.

[0405] exist Figure 22 、 Figure 23 and Figure 24 In the examples of each of the figures in FIG, the connection across the capacitance of the DBD device 10010 and the ability to connect across the capacitance enables the driver circuit 10020 to be a separate circuit from the DBD device, and in some examples a separable circuit.

[0406] exist Figure 22 and Figure 23 In the example shown, when the drive circuits 10020 and 10020' are connected to the DBD device 10010 as described above, a resonant tank circuit 10040 is formed between the inverter 10030 and the capacitor 10012 provided by the dielectric discharge gap and dielectric barrier. In this example, the inductance of the resonant tank circuit is provided by the inductor 10042 connected in series with the capacitor. Some inductance will also be provided by the wiring of the resonant tank circuit. The inverter provides power to the resonant tank circuit.

[0407] exist Figure 24 In the example shown, when the drive circuit 10020" is connected to the DBD device 10010 as described above, a resonant tank circuit 10040 is formed between the transformer 10050 and the capacitance 10012 provided by the dielectric discharge gap and the dielectric barrier. The inductance of the resonant tank circuit is provided by the inductor 10042, which is connected in series with the secondary side 10054 of the transformer, and the capacitance 10012 is provided by the dielectric barrier. Figure 24 The inductor L at reference numeral 10056 is σ represents the combined stray / leakage inductance of the transformer. Figure 24 10030 and the input to the primary side 10052 of the transformer.

[0408] Figure 24 The transformer 10050 shown in the example of FIG. 1 also has an inductor L indicated by reference numeral 10058 in the figure. m Indicates the magnetizing induction, inductor L m Connected in parallel with the primary side 10052 of the transformer.

[0409] In addition to providing step changes in voltage and current based on the turns ratio in transformer 10050, the transformer also provides galvanic isolation. This suppresses electromagnetic interference from inverter 10030 to the transformer across the resonant tank circuit. Conventional magnetic core transformers can be used in various examples. In other examples, air-core transformers (ACTs) can be used. Compared to conventional (i.e., magnetic core) transformers, ACTs can have very low coupling between windings (e.g., 40% instead of the typical 98% in magnetic core transformers). This results in higher leakage inductance than in conventional transformers. However, this is desirable in some examples because it allows several desired functions of the drive circuit as a whole to be incorporated into a single component, namely galvanic isolation for safety and EMI suppression (because the transformer provides noise blocking), boost, and resonant inductance (as discussed in more detail below). These functions can also be provided by conventional transformers, but to a lesser extent in some examples.

[0410] Turning to the inverter 10030 in more detail, Figure 22 and Figure 24 In the example shown, the inverter is provided by an H-bridge. The H-bridge has two high-side switches S 1+ and S 2+ and two low-side switches S 1- and S 2- The four switches 10032. Figure 23 In the example shown, the inverter is provided by a half bridge. This has two switches 10032 and two capacitors 10034, where the switch provides a high-side switch S 1+ and a low-side switch S 1- .

[0411] exist Figures 22 to 24 In the example shown, switches 10032 of inverter 10030 are provided by transistors. These are silicon carbide MOSFETs in the examples shown in these figures. In other examples, each switch can be provided by a MOSFET, such as an n-type MOSFET, a silicon MOSFET, or by another type of electronic switch, such as an insulated gate bipolar transistor (IGBT) (such as a silicon IGBT), a junction field effect transistor (IFET), a bipolar junction transistor (BJT), or a high electron mobility transistor (HEMT) (such as a gallium nitride (GaN) HEMT).

[0412] exist Figure 22 and 24 In the example shown, capacitor 10024 is connected in parallel with inverter 10030 and voltage source 10022. This provides the DC link capacitance for drive circuit 10020. Figure 23 In the example shown, this capacitance is provided by capacitor 10034 of the half-bridge inverter.

[0413] like Figure 25 As shown, the system is configured to provide a train of electrical pulses to a resonant tank circuit and to inhibit power delivery to the resonant tank circuit after the train of pulses. There is also a step of modulating the power characteristics to modify the pulse train before providing another pulse train, and recovering and storing energy from the resonant tank circuit after the discharge ignition event. While there are examples where energy recovery is not included in the process, it is typically included in the process. However, the step of modulating the power characteristics is optional. Details of the process, as well as further details of the power modulation and energy recovery processes, are described in greater detail below.

[0414] During the use of the system 10001, the power supplied to the DBD device 10010 needs to reach at least the dielectric barrier discharge voltage level (V th ). This is required to stimulate the discharge of the dielectric barrier at both ends of the discharge gap. Figure 22 、 Figure 23 and Figure 24 The model circuit for the DBD device shown in the figure shows that when V th The power absorbed by the DBD voltage source shown in these figures is given by the product V th and the current applied in the resonant tank circuit (when the diode is conducting) is given by . Therefore, when the voltage across the gap exceeds V th When the corresponding pair of diodes in the model circuit of the DBD device is turned on, and power is transferred to the (model) V th A voltage source represents the power transfer to the plasma. In this model, whenever a dielectric barrier discharge occurs, the voltage across the gap is clamped to V th .

[0415] The power to provide the dielectric barrier discharge voltage is provided as a pulse train by the driver circuit 10020. The power provided by the pulse train is drawn from the DC link voltage source 10022 at a level of approximately 800V. This is supplied to the inverter 10030. In other examples, when silicon carbide MOSFETs are used, the voltage provided by the DC link voltage source is up to 900V, and can be higher, such as 1.2kV to 1.3kV, when 1.7kV rated silicon carbide transistors are used.

[0416] To start a burst, use Figure 22 In the example system shown, the H-bridge is then used to excite the resonant tank circuit 10040 when power is drawn from the DC link voltage source 10022. In this example, this is achieved by the H-bridge outputting a 100% duty cycle square wave voltage for the duration of the first two modes of the pulse train (as discussed above with respect to Figure 20 as described).

[0417] The switches 10032 of the H-bridge are arranged to provide an output at a switching frequency that is tuned to excite the resonant tank circuit 10040 at its resonant frequency. This allows the H-bridge to handle only real power. To minimize switching losses, operation slightly above the resonant frequency is desirable to achieve ZVS of the switches.

[0418] As mentioned above Figure 20 As explained, once the voltage level in the resonant tank circuit 10040 reaches V th , the excitation of the resonant tank circuit 10040 causes a discharge in the dielectric barrier, which transfers power to the plasma between the electrodes in the DBD device 10010.

[0419] When the second mode of the pulse train ends, switch 10032 is opened. Figures 22 to 24 This is achieved by disconnecting the transistors except for the transistor body diodes (or external antiparallel diodes) which remain active, or by making the bridge voltage (v FB ) is achieved by phase shifting by 180 degrees (°) so as to passively or actively recover the remaining energy stored in the resonant tank circuit 10040, respectively.

[0420] The recovered energy is transferred to the DC link capacitor 10024 (when using Figure 23 The example driving circuit 10020′ shown in FIG. Figure 22 The example drive circuit 10020 shown in or Figure 24 In the example drive circuit 10020" shown in FIG, this corresponds to capacitor 10034 of inverter 10030). This is achieved by reversing the power flow via passive or active recovery described in the previous paragraph. This allows this energy to contribute to the energy for the next pulse train.

[0421] As described above, passive energy recovery is achieved by simply turning off the transistors in the inverter 10030 at the end of the second mode (i.e., when the dielectric barrier discharge is to be terminated). Due to the arrangement of the circuit in an H-bridge or half-bridge, this removes all circuit paths through the transistors and leaves a path through the transistor body diodes (e.g., Figure 22 、 Figure 23 and Figure 24 As shown, it provides connections across the transistor. Figure 22 、 Figure 23 and Figure 24 The connection of the resonant tank circuit shown relative to the diode allows energy to flow through the diode and into the DC link capacitors 10024, 10034 when the transistor is turned off.

[0422] Instead, active energy recovery is achieved by utilizing transistors to provide a 180° phase shift from the phase of the output of the inverter 10030 in the second mode. Instead of allowing energy to flow into the DC link capacitors 10024, 10034 as occurs during active energy recovery, this drives energy into the DC link capacitors.

[0423] The quality factor (Q) of the resonant tank circuit is equal to the voltage across the dielectric discharge gap (v dbd ) and the voltage gain of the bridge voltage at the resonant frequency (i.e., Q = v dbd / v FB )(Without a transformer or unity turns ratio, this would give a quality factor of Q = v dbd / (v FB / n), where n is the turns ratio of the transformer; the overall gain when using a transformer will also be determined by the transformer step-up plus the resonant gain. The effective voltage gain of the resonant tank circuit is determined by the power losses imposed by the parasitic resistances of the wires connecting the electrodes of the DBD device and the magnetic components, which provide damping to the circuit. Unlike known systems using resonant converters, in examples according to aspects disclosed herein, the effective voltage gain is not determined by the actual power delivered to the plasma because no discharge occurs during the charging of the resonant tank circuit. For this reason, a practical value of Q greater than 40 allows for dielectric barrier discharge voltages exceeding 30 kV from an 800 V DC link input voltage without the explicit need for a step-up transformer.

[0424] Therefore, it is understandable that once power is absorbed by the onset of the discharge ignition event in the DBD device, the lower voltage gain may cause self-quenching effects due to this damping and Q-value shift. However, since only a few discharge ignition events from each pulse train are required (such as between one and about five discharge ignition events), and since there is sufficient momentum in the resonant tank (the stored energy is much greater than the energy absorbed by the discharge), this does not pose any practical challenges for examples according to the aspects disclosed herein. On the other hand, known resonant converters are configured for the relatively low voltage gain resulting from the continuous power absorption of the plasma and therefore require, and are designed with, a high step-up transformer turns ratio.

[0425] The voltage across the dielectric discharge gap is determined by the capacitance of the dielectric discharge gap. This is composed of the capacitance of the dielectric and the capacitance of the gap itself. Figure 22 、 Figure 23 and Figure 24 In the example, the capacitance of the dielectric (C diel ) is usually much larger than the gap capacitance (C gap ). For example, C diel Usually higher than Cgap At least ten times larger. This also gives the gap (V gap ) and the voltage across the dielectric (V diel ) has a voltage ratio of at least 10 of the voltage across it.

[0426] Can be used Figure 23 The example drive circuit 10020' shown applies the energy recovery process in a corresponding manner. Figure 24 The example driving circuit 10020" shown can be used with Figure 22 The same process is performed for the example driving circuit 10020 shown.

[0427] The power provided by the DC link power supply is the power provided to the drive circuit averaged over the pulse train repetition interval. The energy exchanged between the DC link capacitor and the resonant tank circuit during charging of the resonant tank circuit, the transfer of power during dielectric barrier discharge, and the resonant tank circuit discharge typically result in voltage ripple across the DC link capacitor. The intervals during which power is delivered to the plasma through the dielectric barrier discharge also contribute to the generation of DC link voltage ripple.

[0428] exist Figure 24 In the example shown, transformer 10050 provides a step-up ratio of approximately 1:1 to 1:10. This lower step-up ratio of conventional pulse power circuits (example step-up ratios of which are described above) allows for limiting the current through the primary side 10052 of the transformer. When a 1:1 ratio is used, this only provides galvanic isolation, rather than providing both galvanic isolation and voltage boosting when a higher step-up ratio (such as a 1:10 ratio) is used.

[0429] exist Figure 24 The inductor 10042 used in the drive circuit 10020" can be located on the primary side or the secondary side of the transformer 10050. However, by locating the inductor on the secondary side (and therefore the high voltage side), as described above, the kVA rating of the transformer can be reduced. The reactive power of the DBD device 10010 can then be directly compensated. In this reactive load matching condition, only active power is handled by the transformer.

[0430] The galvanic isolation imposed by the transformer 10050 reduces ground currents, which are currents that flow in the parasitic capacitance between the electrodes of the DBD device 10010 and any surrounding metal enclosures. This helps meet electromagnetic compatibility (EMC) limits.

[0431] The duration of each wavelet pulse train determines the number of dielectric barrier discharge ignition events. Figure 26 It can be seen that for a given V dc , the number of excitation cycles n p(i.e. frequency cycle) defines the effective duration of the wavelet pulse train and the time required to reach V in the resonant tank. th The number of dielectric barrier discharge ignition events in the case of a burst of 1 / 4 t / 2.0 V is the number of ignition events in the dielectric barrier discharge ...

[0432] The actual power is adjusted by moving the bridge branch switching frequency away from the resonant frequency. This can be achieved by increasing the switching frequency above the resonant frequency or decreasing the switching frequency below the resonant frequency. This results in v FB and bridge current i FB The phase shift between them reduces the active power delivered to the DBD reactor.

[0433] By adopting this approach, high voltage gain is reduced and reactive power handling is increased. To maintain high voltage gain and minimize reactive power handling, instead, according to aspects of the present disclosure, the inverter 10030 can be arranged to provide excitation close to the resonant frequency in use. This is achieved by maintaining v FB and i FB The average power is adjusted by varying the repetition frequency of the wavelet pulse train (i.e., the frequency with which the wavelet pulse train is used to excite the resonant tank circuit to induce the discharge in the dielectric barrier). This allows very high part-load efficiencies to be achieved, as the resonant tank circuit is always operated at its resonance, so there is virtually no reactive power processing.

[0434] As mentioned above, the length of the pulse train is variable. Figure 26 A pulse train of one duration can be seen in . Figure 26 The pulse train shown in is a short pulse train, such as can be used with examples according to aspects disclosed herein because it produces between two and four discharge firing events.

[0435] exist Figure 26 In the pulse train, a pulse train is composed of Figure 22 or Figure 24 The example drive circuit shown generates a voltage drop. Of the two graphs shown in the figure, one graph shows the state of switches 10032 within H-bridge inverter 10030. These switches are either in the off state ("0" state) or the on state ("1" state). By operating these switches in pairs, the wave pattern shown in the lower graph of the figure can be generated at the DBD device.

[0436] The switch pair is with S 2- Switch paired S 1+ Switch and S 2+ Switch paired S 1-Switches. During the first two modes of the pulse train, the switches of each pair (i.e., the two switches within each switch pair) operate in phase, so that each switch is in the same state as the other switch of the pair. During the first two modes of the pulse train, the switch pairs operate out of phase, meaning that when one pair of switches is in one state, the other pair of switches is in the other state.

[0437] As in the conventional case of the inverter, the switch S 1+ and S 1- There is a "dead time" or "interlock time" between switching from one state to the opposite state. This dead time is the period of time during which both switches are open. This period is typically several hundred nanoseconds. This period is provided as a safety interval to avoid accidental shorting of the DC link power supply, which would cause catastrophic failure within the system.

[0438] By making the switch to S 1+ and S 2- is in the on state and the switch is on S 1- and S 2+ In the off state, this causes the positive voltage to increase. By reversing the state, the switch is 1+ and S 2- In the open state and the switch is S 1- and S 2+ is in the on-state, which causes the negative voltage to increase. By alternating this arrangement, a Figure 26 The lower graph shows a sinusoidal waveform, where the frequency of the waveform is determined by the length of time each switch pair is in the on and off states.

[0439] exist Figure 26 Each switch pair operates seven on-off cycles, where S 1+ and S 2- The pair is the first pair to be in the on state. This produces a duration of about 40 μs and a voltage of at least V th The pulse train lasts for about 1.75 cycles. When the switch-to-switch cycle stops, the third mode of the pulse train occurs until the voltage returns to 0V. Figure 26 In the pulse trains shown, the first mode and the third mode of each pulse train have approximately the same duration.

[0440] Figure 27 A mechanism for varying the amount of power delivered to the plasma is shown. As mentioned above, another mechanism for varying the amount of power delivered to the plasma is to vary the frequency of the pulse train (i.e., the number of pulse trains per unit time). This is referred to as the repetition frequency (f r ).exist Figure 27 The three graphs show three different power transmission levels.

[0441] Figure 27 Each graph in FIG shows a time period of approximately 200 μs. At low power transmission rates, such as Figure 27 In the bottom graph, there may be a pulse train that limits the f to about 5kHz. r (equivalent to the reciprocal of 200 μs), where each pulse train has a duration of approximately 40 μs. Figure 27 In the graph above this graph, f r The second graph provides a medium power transfer rate. The (very) high power transfer rate is given by Figure 27 The top graph (third graph) is an example. In this third graph, f r The frequency is about 18 kHz (equivalent to the inverse of 55 μs), and the burst duration is about 40 μs. In each of the three graphs, the bursts are distinguishable from each other because the increase and then decrease in the voltage amplitude of each burst can be determined. For each burst, when the voltage increases to at least V th Then, as the voltage drops to V th Thereafter, the discharge of the dielectric barrier stops.

[0442] Parameters within the system 10001 may change over time and / or during use. For example, the effective capacitance of the reactor is affected by process parameters such as temperature, humidity, gas flow rate, and other properties. Therefore, a feedback mechanism for monitoring and responding is used in conjunction with the DBD reactor 10010 and the drive circuits 10020, 10020', 10020". This is done as in Figure 28 The controller is provided in the form of a controller generally shown at 10200, which is connected to the drive circuit in use.

[0443] According to various examples, the controller can adjust the average power delivered to the DBD reactor 10010. This can be achieved by changing the number of pulses in the pulse train and / or the pulse repetition frequency (i.e., the repetition frequency of the pulses within the pulse train) and / or the pulse train repetition frequency. In some examples, the controller can track the resonant frequency of the resonant tank circuit. As noted, the resonant frequency can change due to the conditions of the fluid passing through the reactor and also change when power is delivered to the gas. The natural frequency can also be any frequency, damped or undamped, whose effects can be compared to the tracked frequency. In some examples, the frequency of the input to the resonant tank circuit can be adjusted over the duration of the pulse train, for example, updating the frequency after each individual pulse in the pulse train. The frequency of the input to the resonant tank circuit can also remain constant within a pulse train and only be adjusted between consecutive pulse trains.

[0444] The following describes an example monitoring and response process using controller 10200. Controller 10200 has a phase detection unit 10210. The phase detection unit is connected to the output of inverter 10030. This allows the phase detection unit to measure v FB and vi FB , and thus obtain feedback by monitoring these parameters. Based on these measurement results, the phase detection unit can calculate the phase angle The unit can then be used in a burst of n p The phase angle is averaged over the excitation period to provide the pulse train average phase Output.

[0445] In some examples, by detecting the current i FB The zero crossing (ZC) of the voltage v FB The point at which the signal is switched from negative to positive (such as time) is realized. While ZC can be used to measure voltage relative to current, since the voltage is generated by the switching action in the inverter 10030 as determined by the controller 10200, such voltage ZC measurement may not be necessary as it can be reconstructed. There are other methods closely related to this and the use of current ZC that can be used directly as a feedback mechanism. Therefore, phase control methods such as those described herein can, but need not, rely on ZC detection.

[0446] like Figure 29 As shown, can be represented by a square wave v FB The starting time of the zero crossing point X is related to the current i FB The difference in time of the zero crossing point at time Y is calculated. Figure 29 The burst averaging window (<·>) is indicated by the time window between time C and time D in w ) is the time period over which the phase angle is averaged. The time period from time C to time D begins at the beginning of the pulse train (i.e., when the excitation of the resonant tank circuit begins). This time period extends through the time period during which the resonant tank circuit charges until the firing voltage amplitude (V th ) point (ie, when the dielectric barrier discharge begins), thereby allowing power transfer to occur. This time period ends when the excitation stops.

[0447] The excitation is stopped so that the discharge ignition events stop occurring. This limits the number of discharge ignition events to the maximum number of desired discharge ignition events. In some examples, the point at which the excitation is stopped is determined based on a comparison of the number of pulses in the pulse train with a preset number of pulses for the excitation period during the pulse train. However, in a number of other examples, instead of operating based on a multiple pulse arrangement, an arrangement is used that detects when a discharge ignition event occurs. Detecting the first (and possible subsequent) occurrence of a discharge ignition event allows the number of discharge ignition events that occur in the subsequent period to be known, calculated, or predicted, and to be once. This allows the excitation to be stopped when the maximum number of discharge ignition events has been reached, whether it is one, two, three, four, five, or another number of discharge ignition events.

[0448] In order to detect when a discharge ignition event occurs, a phase shift is detected. In various examples, this is a detection of the instantaneous phase, rather than the phase shift as described above. Figure 28 As discussed above and below, the average phase is typically used when modulating the frequency of the pulses in a pulse train to track the resonant frequency. This detected phase shift is the voltage-current phase shift measured at the H-bridge terminals. During charging of the resonant tank circuit, there is a near-zero phase difference between the voltage and current at the terminals. However, once a discharge ignition event occurs (i.e., plasma ignition), the resonant frequency shifts due to the increased capacitance applied by the "ignited" DBD device. This resonant frequency shift can be immediately detected by monitoring the corresponding phase shift.

[0449] In various examples, this monitoring can be performed using the controller 10200, such as by using the phase detection unit 10210. As described above, in such examples, this is connected to the inverter terminals.

[0450] In an example where the maximum number of discharge ignition events is one discharge ignition event, energization is stopped once the first discharge ignition event is detected. In an example where the maximum number of discharge ignition events is higher (such as up to about five), energization can be stopped by counting the number of subsequent pulses and equating each pulse to, for example, one discharge ignition event. Alternatively, identification of further discharge ignition events can be achieved by continuing to monitor the phases and identifying when each discharge ignition event occurs by its effect on the voltage-current phase at the inverter terminals.

[0451] In various examples, the phase detection unit 10210 is provided by analog circuitry. In other examples, the phase detection unit is implemented digitally using a field programmable gate array (FPGA).

[0452] Using an FPGA or another (such) digital implementation of the phase detection unit 10210 enables greater flexibility than when using analog circuits, such flexibility including the ability to change the controller by upgrading the software without having to design new physical circuits and replace existing circuits when an upgrade is required.

[0453] The use of an FPGA or analog circuit also allows the phase angle to be calculated and fed by the controller 10200 after each pulse cycle in the pulse train. Figure 29 For example, such a loop is v FB A single cycle of a square wave and / or i FB This provides a higher performance system because it allows Figure 28 The PI controller 230 shown and provided in more detail below determines a new frequency set point, thereby allowing the pulse train to be adjusted during the duration of the pulse train. In contrast, by using a pulse train averaging window, the PI controller may only provide input for adjusting the characteristics of the next pulse train, rather than the pulse train currently in progress.

[0454] Once calculated The controller 10200 compares it with the phase reference value. Figure 28 The process control unit shown at 10220 provides This arises from the properties of the gas passing through the DBD device 10010 . Figure 28 The properties shown are the amount of NOx, the amount of SOx, the amount of CH4, the percentage of humidity (%H2O), the flow rate (liters per minute, l / min) and the temperature (°C), which in this example are provided as inputs to the process control unit. This provides further feedback by monitoring the properties and content of the gas passing through the DBD device. Although in Figure 28 Not shown, but an amount of nitrous oxide (N2O) may also be included as an input to the process control unit.

[0455] In this example, Figure 28 The quantity inputs to the process control unit 10220 in (such as the amount of NOx, SOx, CH4 and / or N2O) are provided in parts per million (ppm). Different measurement units can be used in other examples.

[0456] As Figure 28 As shown by the “…” symbol at the input of the process control unit in FIG, the amounts of other components in the gas can also be monitored and provided as input.

[0457] The expected amount of some or each of the constituent chemicals expected to be present in the gas is provided to the process control unit 10200. This allows the quantity input to be compared with the expected amount of each relevant chemical. Any difference between the quantity input and the expected amount and / or the quantity input and / or one or more other gas properties is then used to determine the output of the process control unit.

[0458] exist Figure 28 In the example shown, the output includes This is typically close to zero (such as at about 0°), or if zero voltage switching (ZVS) is applied, the phase angle is about +5° to about +15°.

[0459] and The output of the comparison between is the error in the phase angle calculated based on the monitored output from the inverter 10030. This error is input to the compensator, as Figure 28 The proportional integral (PI) controller 230 is shown in FIG. The PI controller is based on To calculate the frequency change (Δf s ).

[0460] Can be used to determine The contribution factor is the gain that can be obtained based on the phase angle and how the inverter output frequency is shifted relative to the resonant frequency.

[0461] In drive systems according to various examples described herein, the gain factor (simple multiplication) achieved is typically between about 30 and about 50. This corresponds to a gain of about 30 kV from an input of about 800 V at the DC link power supply 10022 to the dielectric barrier discharge threshold at the dielectric discharge gap. This corresponds to a gain of about 30 to about 34 decibels (dB).

[0462] The controller 10200 sets Δf based on the input to the process control unit 10120. s Added to the nominal resonant frequency feedforward term output from the unit (f sff This provides the frequency set point (f s *).

[0463] The process control unit 10220 also outputs f based on the unit inputs and the processing performed by the process control unit. r Set point (f r *) and n p Set point (n p *). f s *、f r * and n p* are provided by the controller 10200 to the modulator unit 10240. The modulator unit uses these to generate switching signals for the switches of the inverter 10030 to modulate the excitation provided to the resonant tank circuit 10040. When the inverter is an H-bridge, these switching signals are switching signals for each of the four switches (e.g. Figure 28 When the inverter is a half-bridge, these switching signals are switching signals for each of the two switches.

[0464] The switching frequency typically used in the example system is between about 100 kHz and about 10 MHz. r * Typically in the range of about 100 Hz to 50 kHz. In various examples, the latter parameter is also the rate at which the controller 10200 operates (i.e., the rate at which the controller uses and updates various parameters). This reduces the performance requirements of the controller compared to using a higher operating rate.

[0465] System 10001 can be used with a variety of different sized airflows, such as engines and boilers of various sizes. Thus, there are examples where exhaust gas purification systems or other systems employing the aforementioned driver circuits 10020, 10020', 10020" and controller 10200 are implemented in a modular manner.

[0466] In such an example, there are multiple DBD devices 10010 connected in series along the air flow. A driving circuit 10020, 10020', 10020" is typically provided for each DBD device. Figure 30 As shown, a global controller 101000 can be implemented. This applies to Figure 28 The controller 10200 described above is the same process as that described above and uses the same components. Inputs for phase detection are provided from each drive circuit. The properties of the gas are input into the global process control unit 101020. A modulator unit 10240 is provided for each drive circuit to drive the switches of the inverter of each drive circuit. Figure 28 The same type of individual setpoints for the modulator units 10240 shown are provided from the global controller to the corresponding driver circuits. This provides customized control of each driver circuit. The number of modulator units 10240 is determined by the number of driver circuits. Therefore, the number varies depending on the size of the airflow being processed.

[0467] When multiple drive circuits are used, there are examples where a single DC power supply is arranged to power all drive circuits. In other examples, each drive circuit has its own DC power supply. In examples with a single DC power supply, a single AC / DC rectifier can supply DC power to each individual drive circuit, thereby providing a single DC link power supply. As an example implementation of each drive circuit having its own DC power supply, each drive circuit can be equipped with a separate AC / DC rectifier and a three-phase AC voltage source. In such an example, the DBD devices 10010 are typically connected electrically in parallel while still being connected in series in the airflow (i.e., connected sequentially along the airflow path).

[0468] Of course, by having multiple driver circuits, various examples have multiple DBD devices. Due to these parallel arrangements, the total capacitance of the system 10001 increases as the sum of the capacitances of each DBD device. This allows for capacitances of up to 45.0 nF and potentially up to 1.0 nF, for example.

[0469] When using system 10001 to apply the example of using a step-up transformer, such as in Figure 24 In the example shown, ringing may occur between the magnetizing inductance 10058 of the transformer 10050 and the DBD device 10010 .

[0470] Ringing occurs in the timer interval between bursts. This can be Figure 31a The wave between the two pulses can be seen in the graph below. This is due to the standing wave that can be set up within the circuit.

[0471] To minimize ringing, a "freewheel" interval is introduced in some examples rather than having all switches in the off state between the end of the second mode of a burst and the start of the next burst.

[0472] This freewheeling interval is Figure 31b In this graph, it can be seen that Figure 31b After the third mode of the first pulse train (ie, the mode in which the resonant tank circuit discharges) shown in the lower graph of FIG. 1 ends, the high-side switch S 1+ and S 2+ is placed in a conducting state until the next pulse begins. This shorts the transformer winding (i.e., applies approximately 0V). The response to this in system 10001 is that the ringing is minimized / attenuated, such as by Figure 31b There is no ringing visible between the two pulses shown in the lower graph, where Figure 31a There is ringing between the two pulses shown in the lower graph.

[0473] The freewheeling interval begins after the resonant tank circuit has been de-energized (i.e., after the remaining energy in the resonant tank circuit has been transferred out of the resonant tank circuit after the pulse train has occurred). As described above, this is done by placing the high-side switch in the on state while simultaneously turning the low-side switch S 1- and S 2- The same result can be achieved by placing the low-side switch in the on-state and the high-side switch in the off-phase.

[0474] In the example using an air core transformer, ringing also occurs when no active energy recovery is applied. This can be seen, for example, from Figure 32 As can be seen in the graph shown.

[0475] exist Figure 32 In FIG. 3 , three graphs are shown. All graphs have time in milliseconds as their x-axis. The top graph shows the voltage V at the inverter terminals (i.e., the terminals connected to the primary winding of the transformer). fb The middle graph shows the corresponding current I at the inverter terminals. fb Variation with respect to time. The bottom graph shows the variation with respect to time of the voltage across the discharge gap, which voltage results from the voltage and current shown in the two other graphs of the figure.

[0476] Figure 32 Two pulse trains are shown provided by the inverter. The first pulse train starts at approximately 9.00ms. The square wave waveform V fb The excitation is in the form of a pulse train (as is typical of examples according to aspects disclosed herein). The initiation of the pulse train causes charging in the resonant tank circuit, as can be seen by a ramp up in the magnitude of the inverter terminal current and the discharge gap voltage.

[0477] Once the resonant tank circuit has charged to the threshold voltage, a discharge ignition event occurs at the discharge gap. Figure 32 This threshold in the example shown is approximately 10 kV.

[0478] The excitation is stopped shortly thereafter, depending on the maximum number of discharge firing events required. Figure 32 In the example shown, this number is between one and three discharge ignition events. The timing of the excitation cessation can be most clearly seen in the inverter terminal current graph. This shows a sudden drop in current amplitude from approximately 800A during the discharge ignition event to approximately 200A at the maximum peak in the next cycle. This occurs at approximately time 9.02ms, with charging to the threshold voltage taking until approximately time 9.01ms.

[0479] It can be seen from the inverter terminal voltage and current curves that the next pulse train then starts at about time 9.11ms. However, the voltage and discharge gap at the inverter terminals can be Figure 32 In practice, the voltage at the discharge gap decreases in amplitude only to about half the amplitude of the discharge threshold, thus about 5 kV. However, this decreases by about 1 to 2 kV in the period between the end of the excitation of the first pulse train and the beginning of the next pulse train.

[0480] Go to Figure 33 , which shows that Figure 32 Three graphs showing the changes of the inverter terminal voltage, inverter terminal current and discharge gap voltage with respect to time. Figure 33 In the example shown, the pulse train begins at time 8.00ms, as can be seen from the inverter terminal graph. The resonant tank circuit charges from this time until approximately time 8.01ms, as can be seen from the inverter terminal current and discharge gap graphs. At approximately this time, the discharge threshold is reached and a discharge ignition event occurs.

[0481] After the maximum number of discharge ignition events has occurred (which Figure 33 After the excitation is stopped (again between one and three discharge ignition events in the examples), excitation is stopped. This occurs at approximately time 8.02ms. At this point, a phase shift of 180° is applied to the inverter terminal voltage for a period of approximately 0.01ms until approximately time 8.03ms. This drives the energy in the charged resonant tank circuit out of the resonant tank circuit. As described above, in various examples, this energy is then stored. This driving of energy out of the resonant tank circuit can also be seen from the inverter terminal current graph, which, rather than showing a current with a (varying amplitude) sine wave centered around 0A, has a current wave that is offset to the negative until the end of the voltage phase shift period.

[0482] Due to this active energy recovery when using air core transformers, Figure 33 As can be seen in Figure 1 , the ringing decreases between the end of the phase shift period at approximately time 8.03 ms and the start of the next pulse train at approximately time 8.11 ms. This decrease reaches an amplitude of approximately 1 kV at the spark gap and approximately 50 V at the inverter terminals.

Claims

1. A dielectric barrier discharge device for removing gas components, comprising: a first electrode and a second electrode, with a dielectric barrier between the first electrode and the second electrode, wherein an electric field can be established between the first electrode and the second electrode in use; as well as a gas flow path passing between the first electrode and the second electrode, at least one of the electrodes having one or more discharge nodes located along the gas flow path, each location along the gas flow path where at least one discharge node is located being an ionization region and having an adjacent recombination region downstream of the respective ionization region.

2. The dielectric barrier discharge device according to claim 1, wherein: Each discharge node is at least one protrusion from a respective electrode, with at least one component oriented toward the other electrode.

3. The dielectric barrier discharge device according to claim 2, wherein: The at least one protrusion is a plurality of protrusions from respective electrodes, and each protrusion of each discharge node has at least a component oriented toward the other electrode.

4. The dielectric barrier discharge device according to any one of claims 1 to 3, wherein: The one or more discharge nodes are a plurality of discharge nodes located along the gas flow path.

5. The dielectric barrier discharge device according to claim 2 and claim 4, or claim 3 and claim 4, wherein: Adjacent discharge nodes are separated from each other by a distance corresponding to at least 60% of the height of the at least one protrusion and at most 150% of the height of the at least one protrusion.

6. The dielectric barrier discharge device according to claim 2 and claim 4, claim 3 and claim 4, or claim 5, wherein: The first electrode is separated from the proximal side of the dielectric barrier by a first distance, and the second electrode abuts the distal side of the dielectric barrier to the first electrode, and each protrusion has a height between 10% and 50% of the first distance.

7. The dielectric barrier discharge device according to claim 2, claim 2 and claim 4, claim 3 and claim 4, or claim 5 or claim 6, wherein: Each discharge node is a structure for enhancing the electric field in the dielectric barrier discharge device.

8. The dielectric barrier discharge device according to claim 7, wherein: The structure comprises a ring including at least one pointed end extending along a first radial axis passing through a center of the ring, wherein, in use, the ring is arranged around a first electrode of a discharge device, a gap is present between the structure and an opposing electrode of the discharge device, the at least one pointed end limiting a minimum gap between the structure and the opposing electrode, thereby increasing a probability of electrical breakdown occurring at the pointed end when an electric field is applied between the first electrode and the opposing electrode.

9. The dielectric barrier discharge device according to any one of the preceding claims, wherein: The first electrode and the second electrode are concentrically arranged with parallel longitudinal axes, and the second electrode is at least partially located around the first electrode.

10. The dielectric barrier discharge device according to claim 9, wherein: The dielectric barrier is arranged concentrically with the first electrode and the second electrode, and has a longitudinal axis parallel to the longitudinal axes of the first electrode and the second electrode, and the second electrode is mounted on the distal side of the dielectric barrier relative to the first electrode and at least partially surrounds the dielectric barrier around the circumference of the dielectric barrier. The dielectric barrier discharge device according to claim 10 , wherein the second electrode is a foil.

12. The dielectric barrier discharge device according to claim 10 or claim 11, wherein: The second electrode is held in position on the dielectric barrier by one or more constant force springs.

13. The dielectric barrier discharge device according to any one of claims 10 to 12, wherein: The dielectric barrier is a cylinder having an externally directed collar offset from an end of the cylinder, the end of the second electrode abutting the collar in use.

14. The dielectric barrier discharge device according to any one of claims 9 to 11, wherein: The first electrode is maintained separate from the second electrode and the dielectric barrier by a connector that provides an insulated connection to the dielectric barrier and the second electrode, the connector being located at opposite ends of the dielectric barrier and through which the gas flow path passes.

15. The dielectric barrier discharge device according to claim 12, wherein: The engagement between the first electrode and at least one connector is provided by a spring.

16. The dielectric barrier discharge device according to any one of claims 8 to 13, wherein: The first electrode is arranged as a cathode, and the second electrode is arranged as an anode, in use.

17. The dielectric barrier discharge device according to any one of the preceding claims, wherein: The apparatus is arranged to operate at a temperature of between 160°C and 500°C, in use.

18. The dielectric barrier discharge device according to any one of the preceding claims, further comprising a drive circuit, the drive circuit comprising: a power supply connected to the first electrode and the second electrode, thereby connected across a dielectric discharge gap, the dielectric discharge gap providing capacitance; as well as an inductance between the power supply and the dielectric discharge gap, thereby establishing a resonant tank circuit in use, wherein In use, power is supplied to the tank circuit in bursts and only during bursts, the pulse frequency of each pulse burst being tunable, in use, to the resonant frequency of the tank circuit, the power supplied by each pulse burst charging and maintaining the tank circuit to a threshold at which discharge ignition occurs, the discharge ignition events of each pulse burst being limited to the maximum number based on the drive circuit being arranged, in use, to inhibit each pulse burst from delivering power to the resonant tank circuit after a maximum number has occurred.

19. The dielectric barrier discharge device according to claim 18, wherein: The maximum number of discharge ignition events is between 1 event and 5 events.

20. The dielectric barrier discharge device according to claim 18 or claim 19, wherein: The drive circuit further comprises a phase meter in communication with the tank circuit and arranged to, in use, identify a phase shift in the power supplied to the tank circuit during each pulse train, the phase shift corresponding to the occurrence of a discharge ignition event, and wherein the drive circuit is further arranged to, in use, determine when a maximum number of discharge ignition events have occurred based on the number of pulses in the respective pulse trains since each discharge ignition event.

21. The dielectric barrier discharge device according to any one of claims 18 to 20, wherein: The drive circuit further comprises an energy storage device connected across the power supply and arranged, in use, to receive and store power discharged from the tank circuit after each pulse train.

22. The dielectric barrier discharge device according to claim 21, wherein: The drive circuit is arranged, in use, to shift the phase of the pulse train by 180° after a maximum number of discharge ignition events have occurred.

23. The dielectric barrier discharge device according to any one of claims 18 to 22, wherein: The drive circuit further comprises an inverter between the power supply and the tank circuit, the inverter being arranged, in use, to modulate the supply of power from the power supply to the tank circuit.

24. The dielectric barrier discharge device according to claim 23, wherein: The inverter is an H-bridge or a half-bridge.

25. The dielectric barrier discharge device according to claim 24, wherein: Each switch of the inverter is a silicon carbide switch.

26. The dielectric barrier discharge device according to any one of claims 23 to 25, wherein: The pulse frequency of each pulse train is the zero voltage switching frequency.

27. The dielectric barrier discharge device according to any one of claims 18 to 26, wherein: The drive circuit further comprises a transformer, a secondary winding of the transformer forming part of the resonant tank circuit, and the transformer is a step-up transformer.

28. The dielectric barrier discharge device according to claim 27, wherein: The drive circuit is arranged, in use, to short-circuit the primary transformer winding after each pulse train.

29. The dielectric barrier discharge device according to claim 28 when dependent on claim 24, wherein: The primary transformer winding is short-circuited in use by switching on either the low side or the high side of the inverter.

30. The dielectric barrier discharge device according to any one of claims 26 to 29, wherein: At least a portion of the inductance is provided by the transformer.

31. The dielectric barrier discharge device according to claim 30, wherein: The inductance provided by the transformer is the leakage inductance of the transformer.

32. The dielectric barrier discharge device according to claim 30 or claim 31, wherein: The transformer is an air-core transformer.

33. The dielectric barrier discharge device according to claim 32, wherein: The air core transformer has up to 60% magnetic coupling between windings.

34. The dielectric barrier discharge device according to any one of claims 27 to 33, wherein: The transformer has a step-up ratio of the primary transformer winding to the secondary transformer winding of about 1:1 to about 1:

10.

35. The dielectric barrier discharge device according to any one of claims 18 to 34, wherein: At least a portion of the inductance is provided by an inductor.

36. A dielectric barrier discharge device according to any one of claims 18 to 35, further comprising a controller connected to the drive circuit, the controller being arranged to, in use, adjust power supplied to the tank circuit of the drive circuit based on input provided to the controller.

37. The dielectric barrier discharge device according to claim 36, wherein: The controller is arranged to, in use, adjust the pulse frequency, and / or the pulse train repetition frequency, and / or the number of pulse trains, and / or the number of pulses in a pulse train.

38. The dielectric barrier discharge device according to claim 36 or claim 37, wherein: The inputs include the voltage and current at the output of the drive circuit.

39. The dielectric barrier discharge device according to claim 38, wherein: The voltage and current are provided from the output of the inverter.

40. The dielectric barrier discharge device according to claim 38 or claim 39, wherein: The controller is arranged to, in use, determine a phase difference between the voltage and current.

41. A system for providing a dielectric barrier discharge, wherein: The system comprises: a plurality of dielectric barrier discharge devices according to any one of claims 18 to 35; and A controller is connected to each drive circuit, the controller being arranged to, in use, adjust power supplied to the tank circuit of each drive circuit based on input provided to the controller.

42. The system of claim 41, wherein: The controller described is only a single controller.

43. A system according to claim 41 or claim 42, wherein The controller is arranged to, in use, adjust the pulse frequency, and / or the pulse train repetition frequency, and / or the number of pulse trains, and / or the number of pulses in a pulse train.

44. A system according to any one of claims 41 to 43, wherein The inputs include the voltage and current at the output of each driver circuit.

45. The system of claim 44, wherein: Each drive circuit comprises an inverter between the power supply and the tank circuit, the inverter being arranged, in use, to modulate the supply of power from the power supply to the tank circuit, and wherein the voltage and the current are provided from an output of the inverter.

46. ​​A system according to claim 44 or claim 45, wherein The controller is arranged to, in use, determine a phase difference between the voltage and current.

47. A system according to any one of claims 41 to 46, wherein The controller is also connected to each dielectric barrier discharge device, the inputs comprising one or more characteristics of a fluid passing through the device in use.

48. A system according to any one of claims 41 to 47, wherein There is only a single power supply which is arranged, in use, to provide power to all the drive circuits.

49. A method for controlling discharge in a dielectric discharge device, the dielectric discharge device being the dielectric discharge device according to any one of claims 1 to 40, the method comprising: providing power to a resonant tank using a series of electrical pulse trains, the pulse frequency of each pulse train being tuned to the resonant frequency of the tank circuit, the resonant tank circuit being connected across a gap between electrodes in a dielectric discharge device, the capacitance of the tank circuit being provided by the dielectric discharge device, the power provided by each pulse train charging the tank circuit and maintaining the tank circuit to a threshold at which discharge ignition occurs; providing a maximum number of discharge firing events per pulse train by disabling each pulse train from delivering power to the resonant tank circuit after the maximum number of discharge firing events has occurred; as well as Power delivery to the tank circuit is inhibited between bursts.

50. The method of claim 49, wherein The maximum number of discharge ignition events is between 1 event and 5 events.

51. The method of claim 49 or claim 50, further comprising: identifying a phase shift in power supplied to the tank circuit during each pulse train, the phase shift corresponding to an occurrence of a discharge ignition event; as well as A determination is made as to when a maximum number of discharge firing events have occurred based on the number of pulses since each respective discharge firing event.

52. The method according to any one of claims 49 to 51, wherein Each electrical pulse train is a voltage pulse train.

53. The method according to any one of claims 49 to 52 further comprises modulating the pulse frequency, and / or the frequency of the pulse train, and / or the number of pulse trains in the series of electrical pulse trains, and / or the number of pulses in each pulse train.

54. The method of claim 53, wherein: The modulation is based on a phase difference in properties of the power provided to the resonant tank circuit, and / or one or more properties of a fluid passing through the device.

55. The method according to any one of claims 49 to 54, wherein Power is provided to the resonant tank circuit via a transformer, the method further comprising short-circuiting the transformer primary winding between pulse trains.

56. The method according to any one of claims 49 to 55, wherein The pulse frequency of each pulse train supplied to the resonant tank circuit is set by switching action in the circuit between the power supply and the resonant tank circuit.

57. The method according to any one of claims 49 to 56, wherein For each pulse train, the resonant tank circuit is discharged after a maximum number of discharge firing events have occurred, the method further comprising storing energy transferred from the resonant tank circuit by the discharge.

58. The method of claim 57, wherein The tank circuit is discharged by changing the phase of the power provided by each pulse train by 180°.

59. A method for removing gas components, the method comprising: passing a gas having up to 10,000 ppmv of methane along a gas flow path between a first electrode and a second electrode with a dielectric barrier therebetween; An electric field is established between the first electrode and the second electrode, at least one of the electrodes having one or more discharge nodes located along the gas flow path, each location along the gas flow path where at least one discharge node is located is an ionization region and has an adjacent recombination region downstream of the respective ionization region.

60. Use of an apparatus according to any one of claims 1 to 17 for removing methane from a gas.

61. Use of an apparatus according to any one of claims 1 to 17 for removing methane from a gas, wherein: The gas contained up to 10,000 ppmv of methane.

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