PLASMA SYSTEM AND A NON-THERMAL PLASMA-BASED GAS-TREATMENT SYS¬

TEM COMPRISING SUCH PLASMA ELECTRODE CONFIGURATION

FIELD OF THE INVENTION

The invention relates to a plasma electrode configuration for a high-voltage non-thermal plasma system. The invention further relates to a plasma reaction chamber comprising such plasma electrode configuration. The invention also relates to a high-voltage non- thermal plasma system comprising such plasma reaction chamber. Finally, the invention further relates to a non-thermal plasma-based gas-treatment system comprising such plasma reaction chamber or high-voltage non-thermal plasma system.

BACKGROUND OF THE INVENTION

Systems and solutions for air pollution control are known and widely used to reduce odours, limit particle emission to the ambient, and to reduce or remove the emission of chemical substances.

Air pollution control measures are taken in a wide range of industries. Some industries or polluters are limited by official regulations, other choose to deal with issues to maintain a good relationship with their surroundings. Large factories may have polluted air (gas) flows of several hundred thousand cubic meters of exhaust per hour, hence the required gas-treatment capacity is also large. A variety of gas-treatment systems are present in the market, some based on biological or chemical processes, others on adsorption and/or filtration technologies. Non-thermal plasma-based solutions have been available for industrial applications for at least 25 years. Two different approaches: injection of ozone- or radical enriched gas into an exhaust airstream, or alternatively, treatment of the exhaust directly in a non-thermal plasma reaction chamber.

The current technologies have various limiting factors in terms of capacity, size, operating costs, and abatement efficiency.

Improved efficiency, lower energy costs, and less environmental impact are factors playing an important role when deciding what solution to choose, especially when regulations are tightening up.

In view of the above is the inventors earlier identified need to further develop gas-treatment systems, such that they get larger treatment capacities at lower financial and environmental costs, in particular non-thermal plasma-based gas treatment systems.

The inventors disclosed improved gas-treatment systems in non-prepublished patent publications PCT/N 02021/050229 and PCT/N02021/050230, filed on the same day. As these publications are non-prepublished at the time of filing this specification, parts of their contents are included in this specification.

The systems disclosed in these patent publications have been further developed, which lead to the current invention.

SUMMARY OF THE INVENTION

The invention has for its object to remedy or to reduce at least one of the drawbacks of the prior art, or at least provide a useful alternative to prior art. The inventor(s) identified the need for further developing their own gas-treatment technology to increase the performance.

The object is achieved through features which are specified in the description below and in the claims that follow.

The invention is defined by the independent patent claims. The dependent claims define advantageous embodiments of the invention.

In a first aspect the invention relates to a plasma electrode configuration for a high-voltage non-thermal plasma system. The plasma electrode configuration comprises: a first electrical input terminal for receiving a first output voltage signal in operational use and a second electrical input terminal for receiving a second output voltage signal in operational use. The plasma electrode configuration further comprises: a first ground electrode and a second ground electrode spaced apart from the first ground electrode so as to define a electrode space there between; a first set of high-voltage plasma electrodes electrically connected with the first electrical input terminal, and a second set of high-voltage plasma electrodes electrically connected with the second electrical input terminal.

The high-voltage plasma electrodes are placed within the electrode space and spaced apart from the ground electrodes, wherein the high-voltage plasma electrodes are placed such that a shortest distance between respective plasma electrodes of one of the sets and respective plasma electrodes of the other one of the sets is smaller than a further shortest distance between respective plasma electrodes of each set individually, wherein said distances are measured in a plane orthogonal to an axial direction of said high-voltage plasma electrodes.

The effects of the features of the plasma electrode configuration in accordance with the invention are as follows. The use of ground electrodes, as such, is well known from the prior art. The ground electrodes can be plate-formed, mesh-formed or even comb-structured. Conventionally these ground electrodes are oriented parallel to each other, but this is not essential to the invention. One could intentionally place these ground electrodes under an angle with each other, for instance non-rectangular plasma chamber, or where there is a need for non-uniform electric fields.

However, a first key feature of the invention is that there are now two groups (sets) of high-voltage plasma electrodes, which are both placed between the same ground electrodes. The first group is electrically connected to the first electrical input terminal for receiving the first output voltage signal, in operational use. The second group is electrically connected to the second electrical input terminal for receiving the second output voltage signal, in operational use. As simple as this feature may sound, it does open up a completely new design space, which will be elaborated upon and further illustrated in view of the detailed description of the embodiments.

A second key feature of the invention concerns the placement of the two groups of high- voltage electrodes. High-voltage plasma electrodes conventionally have an elongate shape (or at least a part of the electrode, not being the yoke, has this, for instance the legs in a comb-structured electrode) and thereby an axial direction of the elongate shape is defined as well. In the invention the high-voltage plasma electrodes are placed such that the shortest distance between respective plasma electrodes of one of the sets and respective plasma electrodes of the other one of the sets is smaller than a further shortest distance between respective plasma electrodes of each set individually. Important to note that in this somewhat complex definition the distances are measured in a plane extending in a radial direction of said high-voltage plasma electrodes. This plane may be orthogonal to the axial direction of the high-voltage plasma electrodes or under an angle with it. This is also dependent on the shapes of the electrodes, which may have protruding elements and the like. What is important that the distances are in effect “effective distances” that are measured between the plasma electrodes including its protruding parts.

It is further explained in dependent claims and the detailed description of this specification what embodiments fall within the scope of the claim. The aspect of the invention concerning the placement of the high-voltage plasma electrodes could also be expressed differently, namely that each plasma electrode of one set has a plasma electrode of the other set as its closest electrode.

The special placement of the high-voltage electrodes opens up for the possibility to increase the electric field between the neighbouring pairs of high-voltage electrodes, wherein pairs are defined as the respective high-voltage electrode of one set in combination with its closest neighbour from the other set. As the detailed description will elaborate upon, in some embodiments there may be two or more closest neighbours of the other set. Then still we define the pairs as having one of each set.

Further embodiments and aspects of the invention illustrate that the electric field between the neighbouring pairs of electrodes can be enhanced by making the first output voltage signal and the second output voltage signal such that their AC-components are in antiphase (180 degrees phase shifted) with the second output voltage signal. In an embodiment of the invention the DC-components of said signals are the same. The first output voltage signal and the second output voltage signal may also be referred to as dual-phase signals.

In order to facilitate understanding of the invention one or more expressions are further defined hereinafter.

Throughout this specification, the wording “electrode configuration” must be interpreted as equivalent to “electrode assembly”, “electrode set-up”, electrode arrangement, etc. Throughout the description the wording “set” must be interpreted as “at least one” or “one or more”.

The wording “high-voltage” must be interpreted as voltages of at least 1000 V for alternating current (AC) and at least 1500 V for direct current. This definition complies with the standards set by the International Electrotechnical Commission and its national counterparts (IET, IEEE. VDE, etc.). The typical output voltages in the current invention will be well above these levels.

Throughout this specification the wording “non-thermal plasma” is to be interpreted as a plasma which is not in thermodynamic equilibrium, because the electron temperature is much hotter than the temperature of heavy species (ions and neutrals). Alternative words for non-thermal plasma are cold plasma or non-equilibrium plasma.

Throughout this specification the wording “magnetic core” must be interpreted as a core built from material that can be magnetized, thus soft-magnetic material.

The wording “full-wave rectifier circuit” must be interpreted as a rectifier circuit, which rectifies both positive and negative cycles of alternating-current (AC) voltages on its input. In contrast, the wording “half-wave rectifier circuit” is a rectifier circuit, which rectifies either the positive cycle or the negative cycle of alternating-current (AC) voltages.

In an embodiment of the plasma electrode configuration according to the invention all high-voltage plasma electrodes are placed parallel. This additional feature covers all embodiments discussed in the detailed description. The advantage of this group of embodiments is that it allows for a homogenous electric field strength along the length of the electrodes. It must be noted that this embodiment does not exclude comb-shaped electrode structures, wherein the legs are parallel, yet connected with a yoke on one or two sides.

In an embodiment of the plasma electrode configuration according to the invention neighbouring electrodes of each set are placed equidistantly. This additional feature covers all embodiments discussed in the detailed description. The advantage of this group of embodiments is that the electric fields between neighbouring plasma electrodes of the same set are more homogenous along the plasma chamber.

In an embodiment of the plasma electrode configuration according to the invention all neighbouring electrodes with the first set as well as the second set are placed equidistantly. This additional feature covers a subset of the embodiments discussed in the detail description. This leads to a very regular electrode configuration, either in plane or in different planes.

In an embodiment of the plasma electrode configuration according to the invention neighbouring electrodes of each set are placed with non-uniform distance. The advantage of this embodiment is that different zones can be created in the electrode space, which may each be designed with different characters due to chemical process in terms of activation, sustaining, quenching, etc.

In an embodiment of the plasma electrode configuration according to the invention the high-voltage plasma electrodes are all placed within a same plane. In this embodiment the plasma electrodes are effectively placed in a line formation when seen from the axial direction of the plasma electrodes.

In an embodiment of the plasma electrode configuration according to the invention the first set of high-voltage plasma electrodes is placed within a first plane, and the second set of high-voltage plasma electrodes is placed within a second plane, the second plane spaced apart from the first plane and being parallel thereto. In this embodiment the plasma electrodes may be placed in a zigzag formation when seen from the axial direction of the plasma electrodes or the respective sets may be in aligned positions. For both variants embodiments will be discussed in the detailed description.

In a second aspect the invention relates to a plasma reaction chamber comprising a housing defining a contained volume for receiving polluted gas to be treated, and further comprising a plasma reaction chamber electrode configuration in accordance with the first aspect of the invention, wherein the plasma reaction chamber electrode configuration is placed within the housing.

The plasma reaction chamber of this aspect may benefit from the plasma electrode configuration in accordance with the first aspect as it opens up for an improved performance of the plasma chamber by providing the right voltage signals on the different sets of electrodes.

In a third aspect the invention relates to a high-voltage non-thermal plasma system comprising the plasma reaction chamber according to the second aspect of the invention, and further comprising a high-voltage generation unit for generating the first output voltage signal and the second output voltage signal. The high-voltage generation circuit forms an important ingredient of a non-thermal plasma-based gas-treatment system and, additionally, allows for the generation of the required voltage signals for the different sets of plasma electrodes.

In an embodiment of the high-voltage non-thermal plasma system according to the invention the first output voltage signal and the second output voltage signal are 180 degrees phase-shifted relative with each other. This technical feature leads in combination with the plasma electrode configuration of the invention to the increased electric fields between the pairs of electrodes as will be elaborated upon in the detailed description of the embodiments.

In an embodiment of the high-voltage non-thermal plasma system according to the invention the first output voltage signal and the second output voltage signal each are built up of a same high-voltage DC component with a high-voltage AC component superimposed thereon, wherein the respective high-voltage AC components are in anti-phase with each other. This embodiment constitutes a convenient way of making the output voltage signals such that they are in anti-phase with each other.

In an embodiment of the high-voltage non-thermal plasma system according to the invention the respective high-voltage AC-components each have a same amplitude that is smaller than an absolute value of the respective high-voltage DC component.

In an embodiment of the high-voltage non-thermal plasma system according to the invention the high-voltage generation unit comprises a high-voltage generation circuit comprising: a transformer having a primary coil and a secondary coil that are magnetically coupled, wherein the primary coil and the secondary coil have a turns ratio lower than 1, wherein the primary coil has input terminals for receiving an input voltage, wherein the secondary coil has a first terminal at a first end and a second terminal at an opposite end, the first and second terminals being configured for delivering an amplified output voltage; a multi-stage rectifier circuit having a first terminal coupled to the first terminal of the secondary coil and a second terminal coupled to the second terminal of the secondary coil, the rectifier circuit having at least one and a half multiplier stages connected in series and coupled to the first terminal and the second terminal, the rectifier circuit having a DC- output terminal coupled to the last stage in the series of multiplier stages; a ground terminal coupled to the rectifier circuit for providing a ground potential to the rectifier circuit, and a generator output being coupled to the rectifier circuit and being configured for supplying the amplified output voltage to the non-thermal plasma chamber electrode, wherein the ground terminal is coupled to the DC-output terminal of the rectifier circuit, and in that the generator output is coupled to one of the first and second terminals of the rectifier circuit, wherein the multi-stage rectifier circuit comprises full-wave rectifier stages, wherein the high-voltage generation circuit further comprises a further generator output being coupled to the other one of the first and second terminals of the rectifier circuit. The high-voltage generation circuit of this embodiment complies with an embodiment of the high-voltage generation circuits presented in non-prepublished patent publications PCT/N02021/050229 and PCT/N02021/050230. It is exactly this embodiment which is very advantageous in combination with the electrode configuration of the current invention, as the high-voltage generation circuit already produces the signals that can be used for the different sets of high-voltage plasma electrodes.

In a fourth aspect the invention relates to a non-thermal plasma-based gas-treatment system comprising the plasma reaction chamber according to the second aspect of the invention.

In a fifth aspect the invention relates to a non-thermal plasma-based gas-treatment system comprising the high-voltage non-thermal plasma system according to the third aspect of the invention.

A non-thermal plasma-based gas-treatment system in accordance with the fourth and fifth aspect of the invention may typically comprise a gas-treatment apparatus. The gas-treatment apparatus comprises a gas inlet, a plasma chamber in fluid communication with the gas inlet, and a gas outlet in fluid communication with the plasma chamber. The plasma chamber comprises said high-voltage plasma chamber electrodes for creating a corona for treating gas that flows through the plasma chamber in operational use. Non-thermal plasma-based gas-treatment device, when based on high-density non-thermal plasma (corona discharge), can be easily designed with gas-treatment capacities between 40000- 60000 m ³ /hour per module as the inventor’s prototype showed.

BRIEF INTRODUCTION OF THE FIGURES

In the following is described examples of embodiments illustrated in the accompanying figures, wherein: Fig. 1a shows a perspective view of a non-thermal plasma-based gas-treatment system in accordance with an embodiment of the invention;

Fig. 1b shows a front-view of the non-thermal plasma-based gas-treatment system of Fig. 1a;

Fig. 2 shows a high-voltage non-thermal plasma system of non-prepublished patent publications PCT/N02021/050229 and PCT/N02021/050230, which is very advantageous for the current invention;

Fig. 3 shows an example of a plasma electrode configuration known from the prior art;

Fig. 4 illustrates an example of a known voltage signal to be applied to the plasma electrodes in Fig. 3;

Fig. 5 illustrates a top view of the plasma electrode configuration of Fig. 3 together with a voltage profile along paths in two orthogonal directions;

Fig. 6 illustrates dual-phase voltage signals in accordance with an embodiment of the invention;

Fig. 7 shows a high-voltage non-thermal plasma system comprising a first embodiment of a plasma electrode configuration in accordance with the invention;

Fig. 8 illustrates a top view of the plasma electrode configuration of Fig. 7 together with a voltage profile along a path in a first direction;

Fig. 9 illustrates a voltage profile of the plasma electrode configuration of Fig. 8 along a path in a second direction orthogonal to the first direction;

Fig. 10 illustrates a top view of a second embodiment of the plasma electrode configuration in accordance with the invention together with a voltage profile along a first path in a first direction;

Fig. 11 illustrates a voltage profile of the plasma electrode configuration of Fig. 10 along a path in a second direction orthogonal to the first direction; Fig. 12 illustrates a top view of a third embodiment of the plasma electrode configuration in accordance with the invention together with a voltage profile along a first path in a first direction;

Fig. 13 illustrates a voltage profile of the plasma electrode configuration of Fig. 12 along a path in a second direction orthogonal to the first direction;

Fig. 14 illustrates a top view of a fourth embodiment of the plasma electrode configuration in accordance with the invention, and

Fig. 15 shows part of an example of a plasma electrode, which may be used in the invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Various illustrative embodiments of the present subject matter are described below. In the interest of clarity, not all features of an actual implementation are described in this specification. It will of course be appreciated that in the development of any such actual embodiment, numerous implementation-specific decisions must be made to achieve the developers’ specific goals, such as compliance with system-related and business-related constraints, which will vary from one implementation to another. Moreover, it will be appreciated that such a development effort might be complex and time-consuming but would nevertheless be a routine undertaking for those of ordinary skill in the art having the benefit of this disclosure.

The present subject matter will now be described with reference to the attached figures. Various systems, structures, and devices are schematically depicted in the figures for purposes of explanation only and to not obscure the present disclosure with details that are well known to those skilled in the art. Nevertheless, the attached figures are included to describe and explain illustrative examples of the present disclosure. The words and phrases used herein should be understood and interpreted to have a meaning consistent with the understanding of those words and phrases by those skilled in the relevant art. No special definition of a term or phrase, i.e. , a definition that is different from the ordinary and customary meaning as understood by those skilled in the art, is intended to be implied by consistent usage of the term or phrase herein. To the extent that a term or phrase is intended to have a special meaning, i.e., a meaning other than that understood by skilled artisans, such a special definition will be expressly set forth in the specification in a definitional manner that directly and unequivocally provides the special definition for the term or phrase.

The current invention falls within the field of electrification of various chemical processes (known from the prior art) for air treatment for: i) reducing pollutant emission, ii) air pollutant upcycling to synthetic, iii) reforming, or iv) other chemical production processes.

The invention builds further upon non-prepublished patent publications PCT/N02021/050229 and PCT/N02021/050230. For any details concerning features taken from those documents, these documents can be accessed. This is particularly so for the high-voltage generation part of the current invention. Yet, it must be noted that also other high-voltage generators from the prior art may be used to create the dual-phase output voltage signals.

The invention will be discussed in more detail with reference to the figures. The figures will be mainly discussed in as far as they differ from previous figures.

Fig. 1a shows a perspective view of a non-thermal plasma-based gas-treatment system 1 in accordance with an embodiment of the invention. Fig. 1b shows a front-view of the non- thermal plasma-based gas-treatment system 1 of Fig. 1a. The gas-treatment system 1 comprises a gas-treatment apparatus 10 as illustrated on the right side of the drawing.

The gas-treatment apparatus 10 comprises an inlet 12, a plasma chamber 15 in fluid communication with the inlet 12, and an outlet 18 in fluid communication with the plasma chamber 15. Fig. 1b further illustrates a location of a housing 15h of the plasma reaction chamber 15. It is within this housing 15h that the earlier-mentioned high-voltage plasma electrodes are mounted.

The plasma chamber 15 is fed with high-voltage through high-voltage supply cables 30-1 , 30-2 as illustrated. A shielded interface cabinet may be provided to cover the supply cables, but this part is not shown in figure 1. The high-voltage supply cables 30-1 , 30-2 are supplying high voltages to the plasma chamber 15, which voltages are generated by a high-voltage unit 20. The high-voltage unit 20 comprises a high-voltage generation circuit (not shown in Figs. 1a and 1b). The system 1 in Figs. 1a and 1 b is operated as follows. During operation polluted gas 99d is sucked or pumped into inlet 12 as illustrated by the thick arrow at the bottom of the drawing. In order to achieve this gas flow a pump or a fan may be implemented either inside the system 1 or outside. Gas flow may be achieved with one or more fans creating pressure difference resulting in a gas flow through the plasma reaction chamber. The fans may be installed upstream or downstream of the plasma chamber. After entering the inlet 12 the polluted gas 99d flows to the plasma chamber 15, where it is treated with non-thermal plasma, i.e. , corona discharge. This plasma treatment purifies the gas, i.e., removes impurities and odour, and thus turns it into clean gas (or treated gas) 99c, which is then flowing to the outlet 18 and leaves the gas-treatment system 1 as illustrated by the large arrow at the top.

When it comes down to non-thermal plasma treatment of gas, it is important to note that there are different ways of doing so. The applicant developed a system, which is a corona radical shower (CRS) system, which generates a certain type of Non-Thermal Plasma (NTP). “Corona discharge” is a name of one discharge process that leads to NTP. The applicant developed a pulsed-plasma system, which is capable of generating high-density NTP.

It must be noted that the gas that is released from the plasma system may need some post- treatment (for example UV treatment, gas-washing, gas-scrubbing, or gas filtering) before it can be released into nature.

Fig. 2 shows a high-voltage non-thermal plasma system of non-prepublished patent publications PCT/N02021/050229 and PCT/N02021/050230, which is very advantageous for the current invention. The figure shows a high-voltage non-thermal plasma system 200 comprising the high-voltage generation circuit 100 of these two patent publications driving two high-voltage non-thermal plasma chamber electrodes EL1A, EL2A.

The high-voltage generation circuit 100 comprises of a (modified) transformer T having a primary coil L1 and a secondary coil L2 that are magnetically coupled via a magnetizable core, which is connected with its secondary side to a multi-stage full-wave rectifier circuit MS comprising stages with diodes D and capacitors C. The special thing with this rectifier circuit MS is that it is modified and actually connected in a rather non-straightforward way. The original output To of the rectifier circuit is connected to a ground terminal GND as illustrated. The inputs of the rectifier circuit, which also are connected with the secondary side of the transformer T now become the outputs To1 , To2 of the high-voltage generation circuit 100. But rather than producing a large positive voltage, as the original output To would do, these new outputs To1 , To2 push the voltage towards large negative values. The inventors realized this works the same for creating plasma. The non-thermal plasma system 200 comprises both the high-voltage generation circuit 100 as well as the plasma electrodes. Conventionally, in a pulsed non-thermal plasma gas-treatment system, the plasma chamber (not shown) typically comprises electrode pairs, each having one high-voltage non-thermal plasma chamber electrode EL1A, EL2A (connected to the respective output terminals To1 , To2 of the high-voltage generation circuit 100 as illustrated) and one ground electrode EL1 B, EL2B (connected to the ground terminal GND as illustrated). It is the very circuit of Fig. 2, which opens up an interesting possibility.

The AC-signals on the respective output terminals To1 , To2 are in anti-phase. It is exactly because of these feature that, when the loads on the outputs of the high-voltage generation circuit are balanced, the load current Io (charging- and discharging current) that runs between said parasitic capacitances main runs through the secondary coil L2 and not through the capacitance network defined by the capacitors C. This is a huge gain as it relaxes the requirements for the high-voltage generation circuit. Another convenient property is that an uneven power distribution between the two loads will not create a DC-magnetic field in the transformer, as is the case without the half-stage of the multiplier.

On the input side of the high-voltage generation circuit there must be put a rectangular- wave form. This has not been discussed in detail so far. A driver circuit (not shown) is required which drives the primary coil L1 of the transformer T. This driver circuit typically generates the required square-wave form.

On a sidenote, moving the transformer to the high-voltage side of the multiplying network introduces several important advantages, but also creates a need for the transformer to support the total output voltage between primary and secondary. In addition, when the load sparks in one of the load banks, it causes the secondary coil seeing full output voltage between the secondary coil terminals.

In addition to immersing the transformer in oil and paying attention to insulation and creepage distances, several measures were taken to make a transformer that is rugged enough to tolerate those voltages. Some of these measures are quite innovative:

Measure 1 Making the secondary winding out of Teflon-insulated wire. Teflon/PTFE has very high electric field breakdown properties and is mineral oil resistant. Alternatives for Teflon are Kapton, Nomex, or the like. These alternative materials apply for any part mentioned in this description that is made of Teflon. Measure 2 Design and use a secondary winding bobbin strictly organising the winding in defined portions.

Measure 3 Use a primary winding bobbin giving insulation distance to the core.

Measure 4 Bias the magnetic core to a voltage level between GND and output, typically the DC-voltage of one of the intermediate nodes (see DC1 , DC2 in Fig. 10) on the middle line.

Measure 5 Introduce two perpendicular foils (rolls) of insulation sheet, one separating the secondary windings from the magnetic cores and primary winding, and one separating the secondary windings from the primary windings.

More information on the high-voltage generation circuit is found in non-prepublished patent publications PCT/N02021/050229 and PCT/N02021/050230.

Fig. 3 shows an example of a plasma electrode configuration known from the prior art.

The plasma electrode configuration typically comprises a first ground electrode GE1 and a second ground electrode GE2 spaced apart from the first ground electrode GE1 defining a space SP as illustrated. The ground electrodes are drawn as plate-formed electrodes in this figure and throughout the remainder of this specification. However, these ground electrodes GE1 , GE2 may also be mesh-formed or comb-structured. As long as they electrically act as a ground plane the electrode configuration will work. Both ground electrodes are connected to a ground terminal GND as illustrated. In between the ground electrodes GE1 , GE2 there are provided a plurality of high-voltage plasma electrodes E, which are all connected to the same output of a high-voltage generation unit 100p as illustrated. The upward-directed arrows in between the ground electrodes GE1 , GE2 indicate how polluted air to be cleaned is typically led along the plasma electrodes E.

Fig. 4 illustrates an example of a known voltage signal to be applied to the plasma electrodes in Fig. 3. The voltage signal is a mix of a DC-component VDC and an AC-component VAC. In this figure the AC-component has a periodic pulse-shape with two half periods, but it could also be continuous oscillating, pulsating, variable, etc. However, with pulse-shape it is at least meant that the signal returns to the DC-level before the next half period arrives. This also applies to the embodiments of the invention which are discussed later. Figure 4 defines three time instants t1 , t2, t3 within the voltage signal. Fig. 5 illustrates a top view of the plasma electrode configuration of Fig. 3 together with a voltage profile along paths in two orthogonal directions. The figure only shows the ground electrodes GE1 , GE2 and the high-voltage plasma electrodes E.

The plane PL of the paper is oriented orthogonal to an axial direction of the plasma electrodes E. Within this plane PL a first straight path is defined from one ground plane GE1 through a plasma electrode E and further to the other ground plane GE2. The voltage profile of this path is schematically drawn on the right side of the drawing and for all time instants t1 , t2, t3 as illustrated in Fig. 4. It can be observed that the high-voltage electrode E is always at the highest potential, but that the value of this potential varies with the voltage signal. It must be noted that the gradient of the voltage profile is the electric field, which is the driving force for plasma generation. It be noted that the voltage profiles are very schematic and simplified for illustration purposes.

Within the plane PL a second straight path is defined through the plasma electrodes E. The voltage profile of this path is schematically drawn on the bottom side of the drawing and for all time instants t1 , t2, t3 as illustrated in Fig. 4. It can be observed that there is no voltage gradient as all plasma electrodes E are always on the same potential. Therefore, there is no electric field between the plasma electrodes E either. It be noted here as well that the voltage profiles are very schematic and simplified for illustration purposes.

As already mentioned before, a first key feature of the invention is that the high-voltage plasma electrodes are divided in two sets of electrodes. Additionally, these two sets are merged in that each plasma electrode has a plasma electrode of the other set as its closest electrode.

Fig. 6 illustrates dual-phase voltage signals S1 , S2 in accordance with an embodiment of the invention. These dual-phase voltage signals S1 , S2 can be made in many different ways. However, the high-voltage generation circuit 100 of Fig. 2 conveniently makes these signals simultaneously, which led to the current invention. The first voltage signal S1 is similar to that illustrated in Fig. 4. The second voltage signal S2 is in anti-phase with the first voltage signal S1. Both voltage signals S1 , S2 have the same minimum voltage UMIN, maximum voltage UMAX and peak-peak voltage UAC of the AC-component VAC of the voltage signal S1 , S2. Further are illustrated the absolute value UDC of the DC- component and the amplitudes A1 , A2 of the AC-components of the first and second voltage signals S1 , S2. Both voltage signals S1 , S2 have the same DC-level, but the AC-components of the voltage signals S1 , S2 are 180 degrees phase shifted relative to the other. Fig. 7 shows a high-voltage non-thermal plasma system 200 comprising a first embodiment of a plasma electrode configuration 50 in accordance with the invention. The high- voltage generation unit 10Oi (may also be referred to as power supply), which may comprise the high-voltage generation circuit 100 of Fig. 2, but alternatively it could be any other circuits generating the voltage signals S1 , S2 of Fig. 6. The plasma electrode configuration 50 will be discussed in as far as it differs from Fig. 3. Instead of connecting all plasma electrodes to the same voltage signal, the plasma electrodes are now divided in two sets E1 , E2. Each set E1 , E2 of plasma electrodes has at least one plasma electrode. However, in this embodiment, the first set E1 has two individual plasma electrodes E1a, E1 b and the second set E2 also has two individual plasma electrodes E2a, E2b. However, it may be any number of electrodes. Also, it is very well possible to make multiple parallel ground electrode GE1 , GE2, such that multiple rows of plasma electrodes can be placed. The plasma electrode configuration of all presented embodiments is fully scalable in all dimensions.

Each respective plasma electrode E1a, E1 b of the first set E1 has its own individual plasma electrode terminal T1a, T1 b, respectively. These plasma electrode terminals T1 a, T1b are electrically connected and further electrically connected to a first electrical input terminal T1 of the plasma electrode configuration 50, as referred to in the claims.

Similar, each respective plasma electrode E2a, E2b of the first set E2 has its own individual plasma electrode terminal T2a, T2b, respectively. These plasma electrode terminals T2a, T2b are electrically connected and further electrically connected to a second electrical input terminal T2 of the plasma electrode configuration 50, as referred to in the claims.

The first electrical input terminal T1 is electrically connected with a first output of the high- voltage generation circuit 100i, 100 via a first high-voltage connection WC1. The second electrical input terminal T2 is electrically connected with a second output of the high-voltage generation circuit 10Oi, 100 via a second high-voltage connection WC2. For completeness the ground electrodes GE1 , GE2 are each electrically connected to a ground terminal TG as illustrated, which ground terminal on its turn is connected with the high-voltage generation circuit 10Oi, 100 via a ground connection WCG. Fig. 7 also illustrates that these ground connections are all electrically connected to ground.

It must be noted that the first set E1 of plasma electrodes is visualised with crosses along a line and the second set E2 of plasma electrodes is visualised with circles along a line. This does not mean that these electrodes are necessarily different, yet it serves to be able to quickly distinguish between the sets throughout the figures. The same convention is used in the remained of the drawings. On a side note, the electrodes of the sets could be designed differently as well. The invention covers both variants.

Fig. 8 illustrates a top view of the plasma electrode configuration 50 of Fig. 7 together with a voltage profile along a path in a first direction similar to Fig. 5. Fig. 9 illustrates a voltage profile of the plasma electrode configuration 50 of Fig. 8 along a path in a second direction orthogonal to the first direction similar to Fig. 5. These figures will be discussed in as far as they differ from Fig. 5. When the voltage profiles are studied and compared with Fig. 5 it is quickly observed that in the voltage gradient, being a pure AC signal, along the second direction towards neighbouring electrodes, is present on both the first time instant t1 as well as the third time instant t3. This voltage gradient is totally absent in Fig. 5 and therefore the electrode configuration of Figs. 7 and 8 is better capable of producing plasma. For completeness, Fig. 9 also makes clear that the voltage gradient towards the ground electrodes GE1 , GE2 is not changed.

Fig. 8 serves to illustrate what is meant in the claims with the feature that a shortest distance sd12 between respective plasma electrodes E1a, E1b of one of the sets E1 and respective plasma electrodes E2a, E2b of the other one of the sets E2 is smaller than a further shortest distance sd11 , sd22 between respective plasma electrodes E1a, E1 b, E2a, E2b of each set E1 , E2 individually, wherein said distances sd11 , sd12, sd22 are measured in a plane PL3 orthogonal to an axial direction LD (Fig. 15) of said high-voltage plasma electrodes E1a, E1b, E2a, E2b.

The plane PL3 in Fig. 8 is also parallel to the paper and orthogonal to the axial direction of the plasma electrodes. A further plane PL1 is illustrated in which all plasma electrodes of the first set E1 are placed. And a similar further plane PL2 is illustrated in which all plasma electrodes of the second set E2 are placed. In this embodiment these planes PL1 , PL2 coincide, that is that all electrodes E1 , E2 are placed in the same plane PL1 , PL2. In Figs. 7 and 8 the plasma electrodes E1 , E2 are placed inline, equidistantly, and alternatingly, that is that, apart from the edge electrodes E1a, E2b, the other electrodes all see neighbouring electrodes from the other set than the respective set they belong to themselves.

The invention opens up a new design space concerning plasma reaction chambers. Different non-thermal plasma process conditions may be realised by the geometrical arrangement of the dual-phase plasma reaction chamber. Different processes crave different plasma characteristics which are achieved through: interaction (= electric field) between high-voltage electrodes E1 , E2 with the ground electrodes GE1 , GE2; interaction (= electric field) between two different types of high voltage electrodes E1 , E2; and the electrode’s distances sd11 , sd22, alignment, geometry, arrangement, etc.

With the invention it also becomes possible to create a variety of different electric fields and therefore plasma domains in one reactor setup. Thus, the plasma zones may be designed with different characters due to the chemical process in terms of activation, sustaining, quenching, etc.

Fig. 10 illustrates a top view of a second embodiment of the plasma electrode configuration 50 in accordance with the invention together with a voltage profile along a first path in a first direction. Fig. 11 illustrates a voltage profile of the plasma electrode configuration 50 of Fig. 10 along a path in a second direction orthogonal to the first direction. This embodiment will only be discussed in as far as it differs from the previous embodiments. The respective plasma electrodes E1a, E2a, E1 b, E2b, E1c, E2c are placed closer together, which is particularly advantageous because of the dual-phase voltage signals on the different sets E1 , E2 of electrodes. Figs. 10 and 11 illustrate how this reduced distance between the plasma electrodes further enhances the electric field between the plasma electrodes, still keeping the basic electrode shape and reaction chamber dimensions. Not only is the electric field enhanced, also more electrodes can be placed within the same volume.

In Figs. 10 and 11 the plasma electrodes E1 , E2 are still placed inline, equidistantly, and alternatingly, that is that, apart from the edge electrodes E1a, E2c, the other electrodes all see neighbouring electrodes from the other set than the respective set they belong to themselves. However, the plasma electrode E1 , E2 are placed much closer as discussed.

The distance of the electrode types has now become an additional design parameter for modifying the electric field in a plasma reactor and separated the AC and DC part in a new way. It is possible for instance to have different inter-electrode distance in different zones in the reaction chamber, and thus have different plasma properties in different zones, still using the same dual feed signal all over the plasma reactor chamber. The dual-phase system is expected to become a very important tool to tune the plasma generation in order to achieve the best possible energy content/distribution (eV) of the electrons generated in the plasma, eventually in addition having different properties in different reactor zones. These are important key parameters to optimise the reactions to be run in specific applications.

Fig. 12 illustrates a top view of a third embodiment of the plasma electrode configuration 50 in accordance with the invention together with a voltage profile along a first path in a first direction. Fig. 13 illustrates a voltage profile of the plasma electrode configuration of Fig. 12 along a path in a second direction orthogonal to the first direction. This embodiment will only be discussed in as far as it differs from the previous embodiments. In this embodiment the plasma electrodes of the first set E1 are placed in a first plane PL1 and equidistantly, and the plasma electrodes of the second set E2 are placed in a second plane PL2 parallel to the first plane PL1 and equidistantly, as illustrated. This interesting part of this embodiment is that the electric field enhancement (voltage gradient) is increased in the first direction rather than the second. This is best seen from Fig. 13. This electrode configuration 50 may be a better alternative in certain applications, because of practical, mechanical, and chemical considerations.

Fig. 14 illustrates a top view of a fourth embodiment of the plasma electrode configuration 50 in accordance with the invention. This embodiment will only be discussed in as far as it differs from the previous embodiments. This embodiment still represents a multiple-plane configuration as Fig. 12, however, now the plasma electrodes E1a, E1b, E2a, E2b are placed in a zigzag formation as illustrated. This electrode configuration 50 may be a better alternative than the previous one in certain applications, because of practical, mechanical and chemical considerations.

All discussed embodiments in Fig. 7-14 show the same 2-dimensional section of the plasma reaction chamber and also have the same flow direction for gas as illustrated in Fig. 3. However, this is not essential to the invention. The direction may just as well be reversed or even have a different direction.

The electrode placement in Fig. 14 is in fact a combination of the placement Fig. 8 and Fig. 12. The asymmetrical location in Fig. 14 makes it difficult to find a straight line where electrical voltage can be meaningfully outlined in a simplified way as done for the other embodiments. However, the same locally magnified electric field will be present, in this embodiment following a zigzag line.

Fig. 15 shows part of an example of a plasma electrode E1, E2, which may be used in the invention. The figure shows an example of a section of a plasma electrode. The electrode comprises a metallic electrode body 60 having radial members 62 (here four in total) protruding away from the electrode body 60. On the radial members 62 there are provided curved protrusions 64 that extend in the same radial direction RD as the radial member 62, as illustrated. Ionization of the gas will occur on the curved protrusions 64, in operational use. The gas can flow both along and across the electrode section shown, depending on how the entire electrode is constructed. As Fig. 15 illustrates, the overall electrode shape is like a rod extending in a length direction LD as illustrated. However, it is possible to use many other electrode shapes that satisfy the above criteria, for example a comb- structured electrode configuration having a plurality of rod-shaped parallel legs connected by a yoke extending orthogonally to the legs. A high-quality electrode construction must of course also satisfy the requirements given by mechanical guidelines.

The core of the invention is an electrode system consisting of two electrode banks, so that both the ground plates and the other electrode affect the ionization. One may thus influence ionization by means of the placement of the electrodes in relation to each other. This is in addition to the effect of the placement of the ground electrodes, which is, as such, known from prior art. The distance between the electrodes and the distance from the electrodes to the ground electrodes are usually different but are chosen on the basis of the drive voltage modulation, i.e. , the ratio between the voltages UMAX and UAC in Fig. 6.

The person skilled in the art may find alternative solutions for the circuits presented here. The invention covers all these variants as long as they are covered by the independent claims. No limitations are intended to the details of construction or design herein shown, other than as described in the claims below. It is therefore evident that the particular embodiments disclosed above may be altered or modified and all such variations are considered within the scope of the invention. Accordingly, the protection sought herein is as set forth in the claims below.

It should be noted that the above-mentioned embodiments illustrate rather than limit the invention, and that those skilled in the art will be able to design many alternative embodiments without departing from the scope of the appended claims. In the claims, any reference signs placed between parentheses shall not be construed as limiting the claim. Use of the verb "comprise" and its conjugations does not exclude the presence of elements or steps other than those stated in a claim. The article "a" or "an" preceding an element does not exclude the presence of a plurality of such elements. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. The invention may be implemented by means of hardware comprising several distinct elements. In the device claims enumerating several means, several of these means may be embodied by one and the same item of hardware.