DE202023101768U1 - Particle filter arrangement with at least one approximately point-shaped spray electrode as a pre-ionizer - Google Patents

Abstract

Particle filter arrangement (20), through which a gas stream to be cleaned of particles, in particular an air stream to be cleaned, flows, with:
i) an ionizer unit as a pre-ionizer, which has one or more approximately point-shaped spray ionization sources (10) arranged within the air flow and acted upon by one or more different electrical ionizer potentials, wherein at least one of the spray ionization sources (10) consists essentially of a bundle of electrically conductive fibers (14) is formed, the electrically conductive fibers (14) of the spray ionization source (10) being at least partially provided with a metallic coating (16),
ii) at least one counter electrode (24, 24 ') spaced from the spray ionization source or sources (10) of the ionizer unit, each of which is subjected to one or more different counter potentials that deviate from the ionizer potential or potentials, and with
ii) a fiber-containing or sponge-like particle separation unit (26) arranged downstream of the ionizer unit, which can also contain activated carbon-containing material.

Description

The present invention relates to a particle filter arrangement with at least one approximately point-shaped spray electrode as a pre-ionizer. In particular, the invention relates to a particle filter arrangement for cleaning a gas stream, in particular an air stream, with spray or so-called pre-ionization electrodes with high efficiency and extended service life.

Particle filters with conventional filter media (i.e. e.g. fiber-containing filter media or activated carbon filters, i.e. not exclusive electrostatic filters) are used for a wide range of applications in the area of air purification and in the area of purification of other gases, e.g. in the area of air purification for residential and commercial spaces, in connection with the cleaning of Exhaust air such as kitchen extractor hoods, vacuum cleaners, for flue gas cleaning in the industrial or private sector as well as for automotive applications, e.g. for HVAC systems for vehicle interiors.

In recent years it has been recognized what serious effects airborne particles with an aerodynamic diameter of 10 µm or less - the so-called fine dust - or aerosols - especially bioaerosols, think of the spread of the coronavirus through aerosols, have on humans health, which has further increased the importance of highly efficient and compact particle filters.

It is known that different filter media are used for particle filters depending on the application profile, such as fiber filters, in particular electret filters, suspended matter filters or HEPA filters, activated carbon filters, metal filters, etc.

It is known in the prior art that the separation rate in the filter media can fundamentally be improved by pre-ionization of the particles to be separated.

For such pre-ionization, for example, conductive needle-shaped spray ionization sources arranged in the air path in front of the filter medium are subjected to a high voltage of several kV (typically in the order of approx. 8 kV), so that there are conductive components (e.g. the housing) located at ground potential between them ) forms an electric field, whereby the peak effect of the needle-shaped spray ionization sources results in a high field strength and, accordingly, a continuous (corona) discharge due to local field ionization.

This corona discharge initially generates positively (or negatively) ionized gas molecules in a spatially limited zone around the ionizer (so-called corona plasma region), which move towards the counterpotential and, on their further path outside the corona zone, interact with the (fine dust) to be separated. - Particles or aerosols collide or collide and also charge them.

The charged particles can then be separated better and more stably on conventional filters, especially on charged, fiber-containing filter materials, such as electret filters.

Overall, the filter efficiency can be significantly increased through pre-ionization, so that, for example, the performance of an existing filter assembly can be increased or the construction volume of a filter assembly can be reduced while maintaining the same performance requirement.

Pre-ionization also has the advantage that biologically active substances (such as some viruses, especially the coronavirus) are immediately biologically inactivated at high electric field strengths.

In addition to positive ionizer potentials (analogous to the so-called Penney principle in electrical precipitators), the use of negative ionizer potentials is also conceivable in the prior art and within the scope of the present disclosure.

Positive ionizer potentials lead to increased ionizer wear due to the electron bombardment of the spray ionization source, although the ozone generation rate is lower with positive ionization potentials.

Negative ionizer potentials lead to significantly higher ozone generation rates - despite a tendency to slightly improve ionization efficiency - but on the other hand, ionizer wear is only low. However, with negative ionizer potentials, an undesirable deposit of silicon dioxide forms over time - at least on needle-shaped ionizers - which, due to its shielding effect, negatively influences the ionizer properties in the long term.

Instead of needle tips, the use of spray ionization sources based on conductive fiber bundles, in particular containing graphite-containing fiber filaments, is also known in electrical separators, cf WO 2021/185418 A1 or the US 10,384,517 B2 .

The peak effect of the thin filament ends results in high local field strengths achieved with simultaneously small radii of curvature, which is favorable with regard to the ratio of deposition rate / ozone production rate, since small radii of curvature lead to high local field strengths and these in turn lead to a small corona plasma region, which, as mentioned, results in lower ozone production.

However, the graphite-based conductive fiber bundles do not have the desired durability and service life for many applications, especially when they are subjected to higher voltages than those commonly used in the prior art, i.e. with voltages ≥ 8 kV, typically even with more than 10 kV, or even with approx. 12 kV or more (e.g. ≥ 15 kV or ≥ 20 kV), but partly also due to the mechanical and general material requirements (e.g. aging of the material with embrittlement and breaking of the fibers).

At times - especially at high voltages and field strengths, whereby the parameters are of course chosen so that electrical flashovers are avoided - a surprisingly rapid and severe wear of the fiber bundles is observed, which leads to a rapid decrease in separation performance, increased ozone production and undesirable noise.

This wear and tear is primarily attributed to so-called streaming effects. The streaming effects in question are attributed to the fact that high local field strengths cause electrons and negative gas ions, which cannot be transported away quickly enough, to impact the surface of the spray electrode (anode) with high kinetic energy, tearing out material there and thus forming microscopic “craters”. with sharp edges.

These sharp edges can in turn generate such high electric field strengths that the so-called “streamers” occur.

Furthermore, it is assumed that the reactive species emitted during a corona discharge, such as O ⁺ , O ²⁺ , NO ⁺ , also promote electrode erosion due to their reactivity.

Such streaming effects cause unwanted noise, lead to increased ozone production, electromagnetic interference and greatly accelerated ionizer wear. Without specific measures, such spray ionization sources can be worn out after just a few weeks of continuous operation; normally desired service lives of typically several years cannot be reliably achieved.

These streaming effects are undesirable and there is a need to eliminate or at least minimize them in order to prevent premature wear of the spray ionization sources.

Furthermore, as already mentioned, the general mechanical durability of graphite-containing fiber filament tufts as pre-ionizers cannot always be reliably guaranteed under harsh environmental conditions, such as in automotive applications with their specific NVH properties (noise vibration harshness) or in the presence of abrasive particles in the gas stream to be cleaned .

One object of the present invention is to provide a particle filter arrangement of the type mentioned at the outset with highly efficient and robust pre-ionization.

The aforementioned problem is solved by means of a particle filter arrangement according to the features of the independent claims.

Advantageous embodiments of the invention are explained in the dependent claims.

• i) eine lonisatoreinheit als Vorionisator, die ein oder mehrere innerhalb des Luftstroms angeordnete, mit einem oder mit mehreren unterschiedlichen elektrischen lonisatorpotentialen beaufschlagte, näherungsweise punktförmige Sprühionisationsquellen aufweist, wobei wenigstens eine der Sprühionisationsquellen im Wesentlichen aus einem Bündel elektrisch leitfähiger Fasern gebildet ist, wobei die elektrisch leitfähigen Fasern der Sprühionisationsquelle wenigstens teilweise mit einer metallischen Beschichtung versehen sind,
• ii) wenigstens eine von der oder den Sprühionisationsquellen der lonisatoreinheit beabstandete Gegenelektrode, die jeweils mit einem oder mit mehreren unterschiedlichen, von dem lonisatorpotential oder den lonisatorpotentialen abweichenden Gegenpotential beaufschlagt ist, sowie
• ii) eine stromabwärts der lonisatoreinheit angeordnete faserhaltige oder schwammartige Partikelabscheideeinheit, die auch aktivkohlehaltiges Material enthalten kann.

To solve the aforementioned problem, a particle filter arrangement through which a gas stream to be cleaned of particles, in particular an air stream to be cleaned, flows has the following:

• i) an ionizer unit as a pre-ionizer, which has one or more approximately point-shaped spray ionization sources arranged within the air flow and acted upon by one or more different electrical ionizer potentials, wherein at least one of the spray ionization sources is essentially formed from a bundle of electrically conductive fibers, wherein the electrically conductive fibers of the spray ionization source are at least partially provided with a metallic coating,
• ii) at least one counter electrode spaced from the spray ionization source or sources of the ionizer unit, each of which is subjected to one or more different counter potentials that deviate from the ionizer potential or potentials, and
• ii) a fiber-containing or sponge-like particle separation unit arranged downstream of the ionizer unit, which can also contain activated carbon-containing material.

• - Gewebefilter aus Kunststofffasern, Glasfasern, Textilfasern, alle ggf. mit zusätzlich eingewirkten Metallfasern und/oder Metallfasern, und/oder
• - Elektretfilter, ggf. mit zusätzlich eingewirkten Metallfasern, und/oder
• - Aktivkohlefilter, und/oder
• - schwammartige Filter.

The fiber-containing or sponge-like particle separation unit can preferably be one of the following units or a combination tion of corresponding units - as far as technically possible - act:

• - Fabric filters made of plastic fibers, glass fibers, textile fibers, all possibly with additional metal fibers and/or metal fibers, and/or
• - Electret filter, possibly with additional metal fibers, and/or
• - activated carbon filter, and/or
• - sponge-like filters.

Thus, the pre-ionizers according to the invention with the metal-coated conductive fibers can be combined with a variety of common filter technologies, including typical HEPA filters or so-called composite filters, i.e. pleated fiber filters, the filter material of which has been soaked with a solution containing activated carbon.

In this context, the fiber-containing and/or activated carbon-containing particle separation unit can be designed, for example, as a mat filter, possibly with pleated filter material, or as a pocket filter.

• - in Strömungsrichtung vor der lonisatoreinheit, und/oder
• - zwischen lonisatoreinheit und Partikelabscheideeinheit, und/oder
• - in die Partikelabscheideeinheit integriert, und/oder
• - in Strömungsrichtung hinter der Partikelabscheideeinheit.

In a preferred embodiment, the counter electrode or at least one of several counter electrodes can be arranged as follows:

• - in the direction of flow in front of the ionizer unit, and/or
• - between ionizer unit and particle separation unit, and/or
• - integrated into the particle separation unit, and/or
• - in the direction of flow behind the particle separation unit.

Furthermore, the at least one counter electrode can be formed by at least part of a housing forming the flow path.

With regard to possible details of the counterelectrode design, please refer to WO 2021/185418 A1 referred to, which is incorporated herein by reference.

The edge counter electrodes described there for an electrical separator or the upstream collector elements described can also be used advantageously for the present particle filter arrangement, including the arcuate configurations of the electrodes described there.

The counter electrode can - as mentioned above - also be made completely or partially integral with the particle separation unit, for example by integrating conductive fibers into the filter material, which are then placed at a corresponding counter potential to the spray ionization potential. In the embodiment in which a counter electrode is arranged only behind the particle separation unit, the electric field created by the ionization source passes through the particle separation unit itself, which may additionally improve the filter effect due to electrostatic charge effects.

The (at least partial) metallic coating of the conductive fibers in the pre-ionizer is intended to achieve a significant reduction in wear and extension of the service life of the spray ionization sources used as a pre-ionizer due to streaming effects, which can mean that due to the at least partial metallic coating of the electrically conductive fibers, a typical service life of a Spray ionization source in a separator that is operated with relatively high ionization voltages of ≥ 8 kV is achieved by at least one year (preferably at least approx. 3 years), whereas the spray ionization source without the metallic coating already expires in such a separator due to streaming effects would be worn out after just a few weeks of continuous operation.

Furthermore, the mechanical stability and chemical resilience of the fibers is increased.

The metallic coating preferably consists essentially of nickel or at least a nickel alloy, preferably with more than 50% nickel content. For example, a nickel/chrome alloy can be used as the nickel alloy, with nickel as the main component.

Chromium can be contained in such a nickel/chrome alloy either in a relatively high proportion (between 10% to less than 50%) or in a proportion lower than 10%. Such chromium addition tends to increase oxidation resistance.

As is known in metallurgy, a nickel/chrome alloy can also contain other components such as aluminum, silicon, manganese, cobalt, hafnium, rhenium or other rare earth metals such as yttrium, which can be added in small proportions to improve the strength, oxidation and corrosion properties are preferably nickel and - to a lesser extent - chromium remain the main components. The term “nickel/chrome alloy” is not intended to exclude additional alloy additions, although pure nickel/chrome alloys can also be used.

However, it is also conceivable that other conductive metals or metal alloys are used for such a coating, for example precious metals such as gold, silver, platinum, iridium, palladium, or semi-precious metals such as copper or subgroup elements such as chromium, molybdenum or tungsten or alloys of these elements or other elements.

However, the coating preferably consists of pure nickel, which is preferably applied to the fibers by means of chemical vapor deposition.

The electrically conductive fibers are preferably carbon or graphite filaments or possibly fibers spun from such filaments, with bundles or tufts of individual filaments (as opposed to multifilament fibers) preferably being used.

Carbon or graphite filaments - these terms should be understood synonymously here - are fibers made from carbon-containing starting materials that are converted into fiber form via chemical processes into graphite-like carbon, which is known to have very favorable mechanical properties in the so-called anisotropic types preferred here can be achieved with very good conductivity at the same time.

• - die elektrisch leitenden Fasern des Faserbündels sind als Graphit- oder Carbonfilamente oder als aus derartigen Filamenten gesponnene Fasern ausgebildet; und/oder
• - die elektrisch leitenden Fasern sind als synthetische Fasern aus einem leitfähigen Polymer oder aus einem Polymer mit leitfähigkeitserhöhenden Zuschlägen ausgebildet; und/oder
• - die einzelnen Fasern weisen einen Faserdicke von jeweils weniger als 20 µm auf; und/oder
• - das Faserbündel besteht aus 16 Einzelfasern oder mehr, bevorzugt bis zu 96.000 Fasern, ganz besonders bevorzugt zwischen 3.000 und 48.000 Fasern; und/oder
• - die freie Faserlänge zwischen dem Austritt aus einer das Bündel zusammenhaltenden Fassung und dem Stirnende der Fasern liegt für die Mehrzahl der Fasern des Faserbündels jeweils zwischen 2 mm bis 25 mm, bevorzugt jeweils zwischen 5 mm bis 12 mm; und/oder
• - die Bündel sind in Strömungsrichtung oder entgegen der Strömungsrichtung orientiert.

In a preferred embodiment, the bundles of electrically conductive fibers of the spray ionization source also have one or more of the following properties:

• - the electrically conductive fibers of the fiber bundle are designed as graphite or carbon filaments or as fibers spun from such filaments; and or
• - the electrically conductive fibers are designed as synthetic fibers made of a conductive polymer or of a polymer with conductivity-increasing additives; and or
• - the individual fibers each have a fiber thickness of less than 20 µm; and or
• - the fiber bundle consists of 16 individual fibers or more, preferably up to 96,000 fibers, very particularly preferably between 3,000 and 48,000 fibers; and or
• - the free fiber length between the exit from a socket holding the bundle together and the front end of the fibers is between 2 mm and 25 mm, preferably between 5 mm and 12 mm, for the majority of the fibers of the fiber bundle; and or
• - the bundles are oriented in the direction of flow or against the direction of flow.

In addition to or instead of pure carbon filaments or fibers, other conductive fibers can also be used, for example electrically so-called self-conducting polymers or, for example, graphite-reinforced plastics (Carbon Fiber Reinforced Plastics, CFRP).

Overall, the fibers of the fiber bundles are preferably quite delicate due to a preferred diameter of less than 20 μm and the relatively large free fiber length of several millimeters compared to the diameter.

The term “fiber bundle” or “fiber tuft” further implies that the individual fibers of the bundle - starting from a common socket - diverge like tufts as the distance from the socket increases, so that the fiber ends do not form a coherent surface.

The intrinsic conductivity of the fibers does not necessarily have to be very high - although this is actually quite high for the preferred carbon fibers - because the metallic coating can also contribute to the conductivity of the fibers.

The fibers of the fiber bundle particularly preferably have a diameter of 5 μm to 20 μm, preferably between 5 μm and 10 μm.

The (average) metal coating thickness can preferably be between 0.05 µm and 1.0 µm, preferably between 0.2 µm and 0.5 µm.

Particularly preferably, the fibers of the fiber bundle are coated with metal essentially along the fiber circumferential sides, at least in the spatial proximity of the free ends, whereas the end faces of the free ends are preferably uncoated, so that the coating can take place before the fibers are assembled.

In one embodiment, at least one spray ionization source or preferably all of the spray ionization sources can be supplied with a relatively high ionizer potential of at least 8 kV, preferably more than 10 kV, and most preferably more than 12 kV.

In one embodiment of the invention, the ionization current per spray ionization source can be limited to less than 100 µA.

Furthermore, the spatial distance of each spray ionization source from the corresponding counter electrode or from another on which The electrode located at the most opposite potential (eg the conductive outer walls of the flow channel located at ground potential) is preferably at least approximately 75 mm, whereby this value is to be understood as an example and depends on many design parameters.

Furthermore, within the scope of the invention, a spray ionization source made of a bundle of electrically conductive fibers with a metallic coating as described above is proposed, which is accordingly intended - if necessary as a replaceable part - for use in a particle filter arrangement as described above.

In addition to the bundle of coated conductive fibers, this spray ionization source can of course also have other elements, such as an electrically conductive socket for holding the fiber bundle or fiber tuft and, if necessary, an insulated electrical supply line.

• 1a,b eine schematische isometrische Ansicht sowie eine Draufsicht auf ein Beispiel einer erfindungsgemäßen Sprühionisationsquelle bzw. eines Vorionisators;
• 2a,b schematische Darstellungen zum Abnutzungsverhalten (vorher - nachher) bei einem unbeschichteten Karbonfilament;
• 3a,b schematische Darstellungen zum Abnutzungsverhalten (vorher - nachher) bei einem nickelbeschichteten Karbonfilament;
• 4a,b schematische Schnittansichten einer Partikelfilteranordnung mit in (4a) bzw. gegen die Strömungsrichtung (4b) orientierten Vorionisatoren sowie mit einer zwischen Vorionisatoren und Partikelabscheideeinheit angeordneten Gegenelektrode;
• 5a,b schematische Schnittansichten einer Partikelfilteranordnung mit in (5a) bzw. gegen die Strömungsrichtung (5b) orientierten Vorionisatoren sowie mit einer in Strömungsrichtung vor den Vorionisatoren angeordneten Gegenelektrode;
• 6 eine schematische Schnittansicht einer Partikelfilteranordnung mit in Strömungsrichtung orientierten Vorionisatoren sowie mit einer zwischen Vorionisatoren und Partikelabscheideeinheit angeordneten Gegenelektrode mit bogenförmigen Elementen;
• 7 eine schematische Schnittansicht einer Partikelfilteranordnung mit in Strömungsrichtung orientierten Vorionisatoren sowie mit einer in Strömungsrichtung hinter der Partikelabscheideeinheit angeordneten Gegenelektrode;
• 8 einen Elektroabscheider mit Sprühionisationsquellen und Rand-Gegenelektroden sowie Stromaufwärts-Kollektorelementen;
• 9a,b mikroskopische Aufnahmen zum Abnutzungsverhalten (vorher - nachher) bei einem unbeschichteten Karbonfilamentbündel; und
• 10a,b mikroskopische Aufnahmen zum Abnutzungsverhalten (vorher - nachher) bei einem nickelbeschichteten Karbonfilamentbündel.

The invention is explained in more detail below using the exemplary embodiments shown in the drawings. Show it:

• 1a,b a schematic isometric view and a top view of an example of a spray ionization source or a pre-ionizer according to the invention;
• 2a,b schematic representations of the wear behavior (before - after) of an uncoated carbon filament;
• 3a,b schematic representations of the wear behavior (before - after) of a nickel-coated carbon filament;
• 4a,b schematic sectional views of a particle filter arrangement with in ( 4a) or against the direction of flow ( 4b) oriented pre-ionizers and with a counter electrode arranged between the pre-ionizers and the particle separation unit;
• 5a,b schematic sectional views of a particle filter arrangement with in ( 5a) or against the direction of flow ( 5b) oriented pre-ionizers and with a counter electrode arranged in the direction of flow in front of the pre-ionizers;
• 6 a schematic sectional view of a particle filter arrangement with pre-ionizers oriented in the flow direction and with a counter electrode with arcuate elements arranged between the pre-ionizers and the particle separation unit;
• 7 a schematic sectional view of a particle filter arrangement with pre-ionizers oriented in the flow direction and with a counter electrode arranged behind the particle separation unit in the flow direction;
• 8th an electrostatic precipitator with spray ionization sources and edge counter electrodes as well as upstream collector elements;
• 9a,b microscopic images of the wear behavior (before - after) of an uncoated carbon filament bundle; and
• 10a,b Microscopic images of the wear behavior (before - after) of a nickel-coated carbon filament bundle.

An essential element of the particle filter arrangement according to the invention are the approximately point-shaped spray electrode or pre-ionizers 10, which are subjected to a positive high-voltage potential in the following examples (the high-voltage source and supply lines are not shown), which are the ends of a bundle of thin conductive fibers Usually graphite filaments, also known as carbon fibers or carbon fibers, are used, as in the 1a and 1b shown schematically.

A positive high voltage application tends to be preferred over negative ionization in the context of the invention (although negative ionization can also be used) because - as mentioned at the beginning - this minimizes the ozone generation rate and the long-term formation of silicon oxide deposits, such as those that occur with negative ionization would be avoided.

At the same time, the metallic coating of the fibers according to the invention effectively protects against premature wear of the electrodes, even at higher operating voltages.

Further referring to the 1a and 1b an approximately point-shaped spray ionization source 10 with a graphite fiber filament tuft or fiber bundle is shown schematically in an isometric view and in a top view. The individual fibers are designated 14, although the number and diameter of the filaments are not to scale.

The term “approximately point-like” is intended to express that the spray ionization originates from a tip of a fiber-like element with a very small radius of curvature (compared to the other dimensions of the device), so that due to the electrical tip effect, the corresponding electric field and the ionization effect are approximate primarily as can be viewed as starting from one point (or many points in the case of several diverging fiber tips), although the point here obviously represents a mathematical idealization.

The spray ionization source 10 is held by a holder or a socket 12, which is also designed to be electrically conductive and applies the ionizer potential to the individual fibers 14 via a high-voltage source (not shown here).

At relatively high ionizer potentials from about 8 kV, but preferably about 10 kV or about 12 kV or more, the streaming or streamer effects mentioned above occur over time when using uncoated graphite filaments, so that the service life of the spray ionization sources is unsatisfactory .

Based on the microscope images in the 9a and 9b , the graphite filaments in their original state ( 9a) compared to fibers affected by streaming effects ( 9b) show, can be seen - especially from the lowest fiber in 9b - that the originally “round” fiber tip is now asymmetrical. A fiber end that is “pointed” in this way no longer has the required mechanical stability and tends to develop streaming effects, especially since the intensity of wear increases due to the even stronger electrical peak effect.

Against this background, within the scope of the invention, a metallic coating of the fibers, preferably with a nickel layer, or with a nickel alloy layer, is proposed, in the example of the microscopic illustrations (according to 10a and 10b) a pure nickel coating was used.

The corresponding before and after comparison is in the 10a and 10b shown, with the corresponding fibers in the 9a,b and 10a,b comparable parameters (discharge geometry, ionization voltage, service life, etc.). In the 10b Recognizable coated fibers still have a “round” tip shape even after a long period of time, so that there are no self-reinforcing streaming effects.

• Bei dem in den 2a (vorher) und 2b (nachher) dargestellten unbeschichteten Faserende 14 setzt der Verschleiß durch die Entladungsprozesse an der schwarz markierten oberen Kante ein und führt zu einer „Zuspitzung“ der Geometrie, die hier symmetrisch ist, aber in der Praxis, wie aus 9b ersichtlich, auch asymmetrisch verlaufen kann und zu den erwähnten Streamer-Effekten führt.

The inventors suspect that the better stability is largely due to the 2a,b or. 3a,b schematically illustrated different wear behavior is based:

• With the one in the 2a (before) and 2b (after) shown uncoated fiber end 14, the wear caused by the discharge processes begins on the black marked upper edge and leads to a “pointing out” of the geometry, which is symmetrical here, but in practice, as shown 9b As can be seen, it can also be asymmetrical and lead to the streamer effects mentioned.

With a nickel-coated fiber end 14 according to 3a (before) and 3b (after) - the nickel coating is not shown in dashed lines to scale, marked 16 - the front edge is protected from wear, so that overall there is more even wear without “pointing out”, as in 3b indicated. Against this background, a metallic coating of the end face of the fiber is not absolutely necessary (this would also be quite complex in terms of production technology, because the filaments would then have to be coated in ready-made form), because edge protection is essential to achieve the inventive effect.

Furthermore, it is conceivable that the wear-protective effect of a nickel coating (or a coating with a nickel alloy) is related to the formation of a protective oxide layer on the metal (“passivation”).

According to current theories, the formation of a metal oxide takes place either at the inner (facing the metal) or at the outer (facing the ambient air) interface of the oxide layer. If the mobility of the metal cations in the metal oxide is much greater than the mobility of the oxygen anions - which is the case in the case of nickel at room temperature conditions and natural oxygen partial pressures - then the oxidation is theorized to take place essentially at the outer interface.

Under living and indoor conditions, a stable, passive and outwardly growing oxide layer forms on a nickel-coated electrode surface.

This is believed to provide a dielectric barrier (insulation) to the current and protection against further oxidation.

• Zum einen Erosion durch sog. ionen- und elektroneninduziertes Sputtern, also Stoß der Elektronen oder der Ionen mit der Oberfläche, wobei dieser Vorgang aufgrund der erforderlichen Aktivierungsenergien eine deutliche Temperaturabhängigkeit aufweist.

Two main mechanisms are assumed for the erosion of metal-coated fibers, as used in the present pre-ionizers:

• On the one hand, erosion caused by so-called ion- and electron-induced sputtering, i.e. collision of electrons or ions with the surface, whereby this process has a clear temperature dependence due to the required activation energies.

On the other hand, erosion effects caused by reactive species emitted during a corona discharge, such as O ⁺ , O ²⁺ or NO ⁺ . The latter effect is only slightly dependent on temperature and tends to depend more on the generation rate of the reactive species, i.e. primarily on the ionization current.

Therefore, both effects can be fundamentally differentiated from one another experimentally by varying the temperature and ionization current.

Such experiments suggest that nickel passivation is particularly effective at attenuating or preventing the erosion effects caused by the reactive species emitted by a corona discharge.

Furthermore, experiments have suggested that in the case of oxide layer-forming materials such as nickel, those alloys - for example nickel/chrome alloys - provide particularly high wear resistance whose oxide layers grow slowly in the initial stage, passivate quickly and which form good adhesion to the metal surface.

In contrast to nickel, noble metals - such as platinum - form only very thin or no oxide layers at technically relevant temperatures and are therefore possibly less effective in the context of the invention than base metals or their alloys, which form a passivating oxide layer, in particular one that grows outwards passivating oxide layer. Nevertheless, more noble metals or their alloys can also be used within the scope of the invention.

An example of such a coated carbon fiber filament that can be used for the purposes of the invention would be a carbon fiber with a filament diameter of approximately 7 μm, which is coated on the outer surfaces, but not on the end surfaces, with a nickel coating with a thickness of approximately 0.25 μm . This coating can be carried out in particular by means of chemical vapor deposition.

The 4a until 7 show various exemplary embodiment variants for particle filter arrangements 20, in each of which two of the pre-ionizers 10 described above are provided. Two pre-ionizers just as an example; Any number of pre-ionizers, in particular arranged in a matrix, or only one pre-ionizer can be used.

In the 4a until 7 Components that have essentially the same effect are each provided with the same reference numerals.

The particle filter arrangements 20 according to 4a until 7 extend along a radially limited flow channel 28 on all sides with a preferably rectangular base area.

By means of fan units, not shown (which - assuming electromagnetic compatibility - can also be located between the elements shown) a forced flow through the particle filter arrangement 20 in the direction of the flow direction arrow 22, i.e. from left to right in the figures, is generally effected.

The main filter effect of the particle filter arrangements 20 is achieved by a pleated filter element 26, which can advantageously be an electret filter (fiber filter with permanent electrical polarization); However, a variety of other filters can also be used.

The spray ionization sources or pre-ionizers 10 are connected via a support structure 32 to a high-voltage source, not shown, which typically supplies an approximately constant positive DC voltage of approximately 8 kV or more.

In cooperation with a counter electrode 24, which in the examples is a wide-meshed metallic grid that is at ground potential, an electric field for spray ionization is created, which is in the 4a until 6 indicated schematically and designated 30.

The individual embodiments of the 4a until 7 differ in terms of the orientation of the spray ionization tufts 10 (at the 4b and 5b against the direction of flow, otherwise at the 4a , 5a , 6 and 7 in the direction of flow) and the geometric arrangement and design of the counter electrode 24.

In the embodiment according to 4a,b the counter electrode 24 is located between the pre-ionizers 10 and the actual filter 26.

In the embodiment according to 5a , 5b the counter electrode 24 is located in the direction of flow in front of the pre-ionizers 10, which can be beneficial for the ionization effect, cf. the upstream collector elements WO 2021/185418 A1 .

In the embodiment according to 7 The counter electrode 24 is located behind the filter 26 in the direction of flow. In this embodiment, the electrode spacing is large, but on the other hand this can occur across the filter 26 A tensioned electric field (if the filter material is dielectric, which is the case with many plastic or glass fiber-based filter materials) can strengthen the separation effect through additional electrical polarization effects.

In the embodiment according to 6 the counter electrode 24' additionally has arcuate sections to optimize the ionization distribution, as in the WO 2021/185418 A1 described in more detail.

Of course, several differently positioned counter electrodes can also be used in combination, provided they do not completely shield each other.

In 8th is the one in the WO 2021/185418 A1 Electrical separator described in more detail is shown, with a collector unit 40, edge counter electrodes 44 and upstream counter electrodes 42 (also referred to there as upstream collector elements), whereby the statements there can be transferred to the counter electrodes in the present invention.

Reference symbol list

10

Spray ionization source or pre-ionizer

12

Pre-ionizer holder

14

conductive fibers

16

Metal coating

20

Particulate filter arrangement

22

Direction of flow

24.24'

counter electrodes

26

Particle separation unit / pleated filter

28

flow channel

30

Ion field

32

Holder and power supply for pre-ionizers

40

Collector unit electrostatic separator

42

Upstream counter electrodes

44

Edge counter electrodes

QUOTES INCLUDED IN THE DESCRIPTION

This list of documents listed by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• WO 2021185418 A1 [0014, 0033, 0091, 0093, 0095]
• US 10384517 B2 [0014]

Claims (13)

Particle filter arrangement (20), through which a gas stream to be cleaned of particles, in particular an air stream to be cleaned, flows, with: i) an ionizer unit as a pre-ionizer, which has one or more approximately point-shaped spray ionization sources (10) arranged within the air flow and acted upon by one or more different electrical ionizer potentials, wherein at least one of the spray ionization sources (10) consists essentially of a bundle of electrically conductive fibers (14) is formed, the electrically conductive fibers (14) of the spray ionization source (10) being at least partially provided with a metallic coating (16), ii) at least one counter electrode (24, 24 ') spaced from the spray ionization source or sources (10) of the ionizer unit, each of which is subjected to one or more different counter potentials that deviate from the ionizer potential or potentials, and with ii) a fiber-containing or sponge-like particle separation unit (26) arranged downstream of the ionizer unit, which can also contain activated carbon-containing material. Particle filter arrangement (20). Claim 1 , characterized in that the fiber-containing or sponge-like particle separation unit (26) is one of the following units or a combination of corresponding units - if technically possible: - fabric filter made of plastic fibers, glass fibers, textile fibers, all possibly with additionally incorporated metal fibers and/or metal fibers, and/or - electret filter, possibly with additional metal fibers incorporated, and/or - activated carbon filter, and/or - sponge-like filter. Particle filter arrangement (20). Claim 1 or 2 , characterized in that the fiber-containing and/or activated carbon-containing particle separation unit (26) is designed as a mat filter, possibly with pleated filter material, or as a pocket filter. Particle filter arrangement (20) according to one of the Claims 1 until 3 , characterized in that the counter electrode (24, 24 ') or at least one of several counter electrodes is arranged as follows: - in the flow direction (22) in front of the ionizer unit, and / or - between the ionizer unit and the particle separation unit (26), and / or - integrated into the particle separation unit (26), and/or - in the flow direction (22) behind the particle separation unit (26), and/or that at least one counter electrode is formed by at least part of a housing (28) forming the flow path. Particle filter arrangement (20) according to one of the Claims 1 until 4 , characterized in that due to the at least partial metallic coating of the electrically conductive fibers (14), a typical service life of the spray ionization source, which is operated with relatively high ionization voltages of ≥ 8 kV, of at least one year is achieved, whereas the spray ionization source without the metallic coating would be worn out after just a few weeks of continuous operation due to streaming effects in such a separator. Particle filter arrangement (20) according to one of the Claims 1 until 5 , characterized in that the metallic coating (16) consists essentially of nickel or of a nickel alloy, in particular of a nickel-chrome alloy, preferably of a nickel alloy with more than 50% nickel content. Particle filter arrangement (20). Claim 6 , characterized in that the coating (16) consists of pure nickel, which is preferably applied to the fibers (14) by means of chemical vapor deposition. Particle filter arrangement (20) according to one of the Claims 1 until 7 , characterized in that the electrically conductive fibers (14) are carbon or graphite filaments or are designed as fibers spun from such filaments. Particle filter arrangement (20) according to one of the Claims 1 until 8th , characterized in that the bundle of electrically conductive fibers (14) of the spray ionization source (10) has one or more of the following properties - the electrically conductive fibers (14) of the fiber bundle are designed as graphite or carbon filaments or as fibers spun from such filaments; and/or - the electrically conductive fibers (14) are designed as synthetic fibers made of a conductive polymer or of a polymer with conductivity-increasing additives; and/or - the individual fibers (14) each have a fiber thickness of less than 20 μm; and/or - the fiber bundle consists of 16 individual fibers or more, preferably up to 96,000 fibers, very particularly preferably between 3,000 and 48,000 fibers; and/or - the free fiber length between the exit from a socket that holds the bundle together (16) and the front end of the fibers (14) for the majority of the fibers of the fiber bundle is between 2 mm and 25 mm, preferably between 5 mm and 12 mm; and/or - the bundles are oriented in the flow direction (22) or against the flow direction (22). Particle filter arrangement (20) according to one of the Claims 1 until 9 , characterized in that the fibers (14) of the fiber bundle have a diameter of 5 µm to 20 µm, preferably between 5 µm and 10 µm, and/or that the metal coating thickness is between 0.05 µm and 1.0 µm, preferably between 0.2 µm and 0.5 µm. Particle filter arrangement (20) according to one of the Claims 1 until 10 , characterized in that the fibers (14) of the fiber bundle are coated with metal essentially along the fiber circumferential sides, at least in the spatial proximity of the free end faces, the end faces of the free end ends preferably being uncoated. Particle filter arrangement (20) according to one of the Claims 1 until 11 , characterized in that - the ionizer potential is at least 8 kV, preferably more than 10 kV, and most preferably more than 12 kV, and / or that - the ionization current per spray ionization source (10) is limited to less than 100 µA. Use of a spray ionization source (10), which is essentially formed from a bundle of electrically conductive fibers (14), the electrically conductive fibers (14) of the spray ionization source (10) being at least partially provided with a metallic coating (16), as a pre-ionizer for a particle filter arrangement (20) according to one of the preceding claims.

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