Particle filter arrangement with at least an approximately point-shaped spray electrode as pre-ioniser

Abstract

The invention relates to a particle filter arrangement (20), which is flowed through by a gas flow which is to be cleaned of particles, in particular an air flow which is to be cleaned, having: an ioniser unit as a pre-ioniser, which has one or more at least approximately point-shaped spray ionisation sources (10) which are arranged within the air flow and to which different electric ioniser potentials are applied, wherein at least one of the spray ionisation sources (10) is formed substantially from a bundle of electrically conductive fibres (14), wherein the electrically conductive fibres (14) of the spray ionisation source (10) are provided, at least partially, with a metal coating, in particular a nickel coating (16); at least one counter electrode (24, 24') spaced apart from the spray ionisation source or spray ionisation sources (10), one counter potential or several different counter potentials, which differs or differ from the ioniser potential or ioniser potentials, being applied to each of the counter electrodes; and a fibre-containing or sponge-like particle separation unit (26) which is arranged downstream of the ioniser unit and can also contain activated-carbon-containing material.

Description

[0001] PARTICLE FILTER ARRANGEMENT WITH AT LEAST ONE APPROXIMATELY POINT-SHAPED SPRAY ELECTRODE AS PRE-IONIZER

[0002] The present invention relates to a particle filter assembly with at least one approximately point-shaped spray electrode as a pre-ionizer. In particular, the invention relates to a particle filter assembly for purifying a gas stream, in particular an air stream, with spray or so-called pre-ionization electrodes with high efficiency and extended service life.

[0003] Particle filters with conventional filter media (e.g. fiber-containing filter media or activated carbon filters, ie not exclusively electrostatic precipitators) are used for a wide variety of applications in the field of air purification and in the field of cleaning other gases, e.g. in the field of air purification for residential and commercial premises, in connection with the cleaning of exhaust air such as in kitchen extractor hoods, in vacuum cleaners, for flue gas cleaning in the industrial or private sector and for automotive applications, e.g. for HVAC systems for vehicle interiors.

[0004] In recent years, it has been recognized what serious impact airborne particles with an aerodynamic diameter of 10 pm or less – so-called fine dust – or aerosols – especially bioaerosols, one thinks of the spread of the coronavirus through aerosols – can have on human health, which has once again increased the importance of highly efficient and compact particle filters.

[0005] For particle filters, different filter media are used depending on the application profile, such as fiber filters, in particular electret filters, particulate matter filters or HEPA filters, activated carbon filters, metal filters, etc.

[0006] It is known in the state of the art that the separation rate in the filter media can be fundamentally improved by pre-ionization of the particles to be separated.

[0007] For such pre-ionization, 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 magnitude of approximately 8 kV), so that an electric field is formed between these and conductive components at a ground potential (e.g. the housing), whereby a high field strength is created by the peak effect of the needle-shaped spray ionization sources and accordingly a continuous (corona) discharge is created by local field ionization.

[0008] This corona discharge initially generates positively (or negatively) ionized gas molecules in a spatially narrow zone around the ionizer (so-called corona plasma region), which move towards the counter potential and, on their further path outside the corona zone, collide with the (fine dust) particles or aerosols to be separated and also charge them.

[0009] 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.

[0010] Overall, pre-ionization can significantly increase filter efficiency, so that, for example, the performance of an existing filter assembly can be increased or the volume of a filter assembly can be reduced while maintaining the same performance requirement.

[0011] 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.

[0012] In addition to positive ionizer potentials (analogous to the so-called Penney principle in electrostatic precipitators), the use of negative ionizer potentials is also conceivable in the prior art and within the scope of the present disclosure.

[0013] Positive ionizer potentials lead to increased ionizer wear due to the electron bombardment of the spray ionization source, but the ozone generation rate is lower at positive ionization potentials.

[0014] Negative ionizer potentials lead to significantly higher ozone generation rates, despite a somewhat improved ionization efficiency, but ionizer wear is minimal. However, at negative ionizer potentials, an undesirable silicon dioxide deposit forms over time—at least on needle-shaped ionizers—which, due to its shielding effect, negatively impacts the ionizer properties in the long term.

[0015] 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 electrostatic precipitators, cf. WO 2021 / 185418 A1 or US 10 384 517 B2.

[0016] Due to the tip effect of the thin filament ends, high local field strengths are achieved with small radii of curvature, which is favorable with regard to the ratio of deposition rate to 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.

[0017] However, the conductive graphite-based 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 state of the art, i.e. voltages > 8 kV, typically even more than 10 kV, or even approx.

[0018] 12 kV or more (e.g. > 15 kV or > 20 kV), but partly also due to the mechanical and general material requirements (e.g. material aging with embrittlement and fiber breakage).

[0019] At times - especially at high voltages and field strengths, where, of course, the parameters are selected to avoid electrical arcing - a surprisingly rapid and severe wear of the fiber bundles is observed, which leads to a rapidly decreasing separation efficiency, increased ozone production and undesirable noise generation.

[0020] This wear is primarily attributed to so-called streaming effects. These streaming effects are attributed to the fact that high local field strengths cause electrons and negative gas ions that cannot be transported away quickly enough to collide with the surface of the discharge electrode (anode) with high kinetic energy, tearing out material and thus creating microscopic "craters" with sharp edges.

[0021] These sharp edges can in turn generate such high electric field strengths that the so-called "streamers 1 ' appear.

[0022] It is also assumed that the reactive species emitted during a corona discharge, such as O + , O 2+ , NO + , which further 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 wear out after just a few weeks of continuous operation; the normally desired service life of typically several years cannot be reliably achieved.

[0023] 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.

[0024] Furthermore, as already mentioned, the general mechanical durability of graphite-containing fiber filament tufts as pre-ionizers under harsh environmental conditions, such as in automotive applications with their specific NVH (Noise Vibration Harshness) properties or in the presence of abrasive particles in the gas stream to be cleaned, cannot always be guaranteed.

[0025] An object of the present invention is to provide a particle filter arrangement of the type mentioned above with highly efficient and robust pre-ionization.

[0026] The above-mentioned object is achieved by means of a particle filter arrangement according to the features of the independent claims.

[0027] Advantageous embodiments of the invention are explained in the dependent claims.

[0028] To achieve the above-mentioned object, a particle filter arrangement through which a gas stream to be purified of particles, in particular an air stream to be purified, flows comprises 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 stream and subjected to 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(s) of the ionizer unit, each of which is subjected to one or more different counter potentials deviating from the ionizer potential(s),and ii) a fibrous or sponge-like particle separation unit arranged downstream of the ionizer unit, which may also contain activated carbon material.

[0029] The fibrous or sponge-like particle separation unit may preferably be one of the following units or a combination of corresponding units - as far as technically possible:

[0030] Fabric filters made of plastic fibers, glass fibers, textile fibers, all possibly with additionally woven metal fibers and / or metal fibers, and / or

[0031] Electret filters, possibly with additionally woven metal fibers, and / or

[0032] Activated carbon filters and / or sponge-like filters.

[0033] 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 whose filter material has been impregnated with a solution containing activated carbon.

[0034] In this context, the particle separation unit containing fiber and / or activated carbon can be designed, for example, as a mat filter, possibly with pleated filter material, or as a pocket filter.

[0035] In a preferred embodiment, the counter electrode or at least one of several counter electrodes can be arranged as follows: in the flow direction upstream of the ionizer unit, and / or between the ionizer unit and the particle separation unit, and / or integrated into the particle separation unit, and / or in the flow direction downstream of the particle separation unit.

[0036] Furthermore, the at least one counter electrode can be formed by at least a portion of a housing forming the flow path. For possible details of the counter electrode design, reference is made to WO 2021 / 185418 A1, which is incorporated herein by reference.

[0037] The edge counter electrodes or the upstream collector elements described therein for an electrostatic precipitator can also be advantageously used for the present particle filter arrangement, including the arcuate configurations of the electrodes described therein.

[0038] As mentioned above, the counter electrode can also be designed entirely or partially integral with the particle separation unit, e.g., 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 generated by the ionization source permeates the particle separation unit itself, which can possibly further improve the filtering effect due to electrostatic charging effects.

[0039] The (at least partial) metallic coating of the conductive fibers in the pre-ionizer is intended to achieve a significant reduction in wear and an extension of the service life of the spray ionization sources used as pre-ionizers due to streaming effects. This 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 operated with relatively high ionization voltages of > 8 kV is achieved of at least one year (preferably at least approximately 3 years), whereas the spray ionization source without the metallic coating would be worn out after only a few weeks of continuous operation due to streaming effects in such a separator.

[0040] Furthermore, the mechanical stability and chemical resilience of the fibers is increased.

[0041] The metallic coating preferably consists essentially of nickel or at least a nickel alloy, preferably with a nickel content of more than 50%. A nickel-chromium alloy, for example, with nickel as the main component, can be used as the nickel alloy.

[0042] Chromium can be present in such a nickel-chromium alloy either in a relatively high proportion (between 10% and less than 50%) or in a proportion less than 10%. Such a chromium addition tends to increase oxidation resistance.

[0043] As is well known in metallurgy, a nickel-chromium alloy can also contain other components, such as aluminum, silicon, manganese, cobalt, hafnium, rhenium, or other rare earth metals such as yttrium, in small amounts to improve strength, oxidation, and corrosion properties. Nickel and, to a lesser extent, chromium remain the primary components. The term "nickel-chromium alloy" is not intended to exclude other alloying additions, although pure nickel-chromium alloys can also be used.

[0044] However, it is also conceivable that other conductive metals or metal alloys are used for such a coating, e.g. 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.

[0045] However, the coating preferably consists of pure nickel, which is preferably applied to the fibers by chemical vapor deposition.

[0046] The electrically conductive fibers are preferably carbon or graphite filaments or, if appropriate, fibers spun from such filaments, with bundles or tufts of single filaments (as opposed to multifilament fibers) being used.

[0047] Carbon or graphite filaments - these terms should be understood synonymously here - are fibers made from carbon-containing starting materials that are converted into graphite-like carbon in fiber form by chemical processes, whereby the so-called anisotropic types preferred here are known to achieve very favorable mechanical properties combined with very good conductivity.

[0048] In a preferred embodiment, the bundles of electrically conductive fibers of the spray ionization source additionally have one or more of the following properties: the electrically conductive fibers of the fiber bundle are formed as graphite or carbon filaments or as fibers spun from such filaments; and / or the electrically conductive fibers are formed 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 pm; 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 holder holding the bundle together and the front end of the fibers is, for the majority of the fibers of the fiber bundle, between 2 mm and 25 mm, preferably between 5 mm and 12 mm; and / or the bundles are oriented in the direction of flow or against the direction of flow.

[0049] Thus, in addition to or instead of pure carbon filaments or fibers, other conductive fibers can also be used, e.g. electrically so-called self-conducting polymers or, for example, graphite-reinforced plastics (Carbon Fiber Reinforced Plastics, CFRP).

[0050] Overall, the fibers of the fiber bundles are preferably quite filigree due to a preferred diameter of less than 20 pm and the relatively large free fiber length of several millimeters compared to the diameter.

[0051] The term "fiber bundle" or "fiber tuft" further implies that the individual fibers of the bundle - starting from a common socket - diverge in a tuft-like manner with increasing distance from the socket, so that the fiber ends do not form a continuous surface.

[0052] The intrinsic conductivity of the fibers does not necessarily have to be very high—although it is indeed quite high in the preferred carbon fibers—because the metallic coating can also contribute to the fibers' conductivity. Particularly preferably, the fibers of the fiber bundle have a diameter of 5 pm to 20 pm, preferably between 5 pm and 10 pm.

[0053] The (average) metal coating thickness may preferably be between 0.05 pm and 1.0 pm, preferably between 0.2 pm and 0.5 pm.

[0054] Particularly preferably, the fibers of the fiber bundle are metallically coated substantially along the fiber circumferential sides, at least in the spatial vicinity of the free ends, whereby the ends of the free ends are preferably uncoated, so that the coating can be carried out before the fibers are assembled.

[0055] In one embodiment, at least one spray ionization source or preferably all of the spray ionization sources are subjected to a relatively high ionizer potential of at least 8 kV each, preferably more than 10 kV, and most preferably more than 12 kV.

[0056] In one embodiment of the invention, the ionization current per spray ionization source can be limited to less than 100 pA.

[0057] Furthermore, the spatial distance of each spray ionization source from the corresponding counter electrode or from another electrode located at the most opposite potential (e.g. 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.

[0058] Furthermore, within the scope of the invention, a spray ionization source comprising a bundle of electrically conductive fibers with a metallic coating as described above is proposed, which is accordingly intended - possibly as a replaceable part - for use in a particle filter arrangement as described above.

[0059] In addition to the bundle of coated conductive fibers, this spray ionization source can of course also comprise other elements, such as an electrically conductive holder for holding the fiber bundle or fiber tuft and, if necessary, an insulated electrical supply line.

[0060] The invention is explained in more detail below with reference to the exemplary embodiments illustrated in the drawings. Figures 1a and b show a schematic isometric view and a plan view of an example of a spray ionization source and a pre-ionizer according to the invention;

[0061] Figures 2a, b show schematic representations of the wear behavior (before - after) of an uncoated carbon filament;

[0062] Figures 3a, b show schematic representations of the wear behavior (before - after) of a nickel-coated carbon filament;

[0063] Figures 4a, b show schematic sectional views of a particle filter arrangement with pre-ionizers oriented in (Figure 4a) or against the flow direction (Figure 4b) and with a counter electrode arranged between pre-ionizers and particle separation unit;

[0064] Figures 5a, b show schematic sectional views of a particle filter arrangement with pre-ionizers oriented in (Figure 5a) or against the flow direction (Figure 5b) and with a counter electrode arranged in the flow direction in front of the pre-ionizers;

[0065] Figure 6 is 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;

[0066] Figure 7 is 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;

[0067] Figure 8 shows an electrostatic precipitator with spray ionization sources and edge counter electrodes and upstream collector elements;

[0068] Figures 9a, b microscopic images of the wear behavior (before - after) of an uncoated carbon filament bundle; and

[0069] Figures 10a, b show microscopic images of the wear behavior (before - after) of a nickel-coated carbon filament bundle.

[0070] An essential element of the particle filter arrangement according to the invention are the approximately point-shaped spray electrodes 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 in each case), which are the ends of a bundle of thin conductive fibers, usually graphite filaments, which are also referred to as carbon fibers or carbon fibers, as shown schematically in Figures 1a and 1b.

[0071] 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 above, this minimizes the ozone generation rate and avoids the long-term formation of silicon oxide deposits, which would occur with negative ionization.

[0072] 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.

[0073] Referring further to Figures 1a and 1b, an approximately point-shaped spray ionization source 10 with a graphite fiber filament tuft or fiber bundle is schematically shown in an isometric view and a plan view. The individual fibers are designated 14, with the number and diameter of the filaments not to scale.

[0074] The term "approximately point-like" is intended to express that the spray ionization emanates 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 can be regarded as approximately primarily emanating from a point (or many points in the case of several diverging fiber tips), although the point here naturally represents a mathematical idealization.

[0075] The spray ionization source 10 is held by a holder or a socket 12, which is also electrically conductive and applies the ionizer potential to the individual fibers 14 via a high-voltage source not shown here.

[0076] At relatively high ionizer potentials starting from approximately 8 kV, but preferably approximately 10 kV or approximately 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.

[0077] Based on the micrographs in Figures 9a and 9b, which show graphite filaments in their original state (Figure 9a) compared to fibers affected by streaming effects (Figure 9b), it is evident – ​​especially evident in the bottommost fiber in Figure 9b – that the originally "round" fiber tip is now asymmetrical. Such a "pointed" fiber end no longer exhibits the required mechanical stability and is prone to the development of streaming effects, especially since the even stronger electrical tip effect increases the wear intensity.

[0078] Against this background, a metallic coating of the fibers, preferably with a nickel layer or with a nickel alloy layer, is proposed within the scope of the invention, wherein in the example of the microscopic representations (according to Figures 10a and 10b) a pure nickel coating was used.

[0079] The corresponding before-and-after comparison is shown in Figures 10a and 10b, with the corresponding fibers in Figures 9a, b and 10a, b being exposed to comparable parameters (discharge geometry, ionization voltage, service life, etc.). The coated fibers visible in Figure 10b still exhibit a "round" tip shape even after extended service life, thus preventing self-reinforcing streaming effects.

[0080] The inventors suspect that the better stability is largely due to the different wear behavior schematically illustrated in Figures 2a, b and 3a, b:

[0081] In the uncoated fiber end 14 shown in Figures 2a (before) and 2b (after), wear due to the discharge processes begins at the upper edge marked in black and leads to a "tapering" of the geometry, which is symmetrical here, but in practice, as can be seen from Figure 9b, can also be asymmetrical and leads to the aforementioned streamer effects.

[0082] With a nickel-coated fiber end 14 according to Figures 3a (before) and 3b (after)—the nickel coating is not shown to scale in dashed lines, designated 16—the end edge is protected from wear, resulting in more even wear overall without "tapering," as indicated in Figure 3b. Against this background, a metallic coating on 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 prefabricated form), because edge protection is essential for achieving the inventive effect.

[0083] 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").

[0084] According to current theories, the formation of a metal oxide occurs either at the inner (metal-facing) or outer (ambient air-facing) 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 for nickel at room temperature conditions and natural oxygen partial pressures—then, according to theories, oxidation occurs primarily at the outer interface.

[0085] Under living and indoor conditions, a stable, passive and outwardly growing oxide layer is formed on a nickel-coated electrode surface.

[0086] It is believed that this provides a dielectric barrier (insulation) for the current and protection against further oxidation.

[0087] Two main mechanisms are assumed for the erosion of metal-coated fibers, as used in the present pre-ionizers:

[0088] On the one hand, erosion occurs through so-called ion- and electron-induced sputtering, i.e. collision of electrons or ions with the surface, whereby this process exhibits a significant temperature dependence due to the required activation energies.

[0089] 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 shows only a slight temperature dependence and tends to depend more on the generation rate of the reactive species, i.e. primarily on the ionization current.

[0090] Therefore, both effects can be fundamentally differentiated from each other experimentally by varying temperature and ionization current.

[0091] Such experiments suggest that nickel passivation is particularly effective in mitigating or preventing the erosion effects caused by the reactive species emitted by a corona discharge. Furthermore, experiments have suggested that, for oxide-forming materials such as nickel, those alloys—for example, nickel / chromium alloys—result in particularly high wear resistance whose oxide layers grow slowly in the initial stage, passivate quickly, and adhere well to the metal surface.

[0092] In contrast to nickel, precious metals—such as platinum—form only very thin oxide layers or none at all at technically relevant temperatures and may therefore be less effective within the scope of the invention than base metals or their alloys, which form a passivating oxide layer, especially an outwardly growing passivating oxide layer. Nevertheless, more noble metals or their alloys can certainly also be used within the scope of the invention.

[0093] An example of such a coated carbon fiber filament suitable for the purposes of the invention would be a carbon fiber with a filament diameter of approximately 7 pm, coated on the outer surfaces, but not on the end faces, with a nickel coating with a thickness of approximately 0.25 pm. This coating can be applied, in particular, by means of chemical vapor deposition.

[0094] Figures 4a to 7 show various exemplary embodiments of particle filter assemblies 20, each of which includes two of the above-described pre-ionizers 10. Two pre-ionizers are only an example; any number of pre-ionizers, particularly arranged in a matrix, or just one pre-ionizer can be used.

[0095] In Figures 4a to 7, components with essentially the same function are provided with the same reference numerals. The particle filter assemblies 20 according to Figures 4a to 7 extend along a flow channel 28 that is radially bounded on all sides and preferably has a rectangular base area.

[0096] 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 is generally effected in the direction of the flow direction arrow 22, ie from left to right in the figures.

[0097] The main filtering 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 wide variety of other filters can also be used.

[0098] 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 direct voltage of approximately 8 kV or more.

[0099] In cooperation with a counter electrode 24, which in the examples is a wide-mesh metallic grid at ground potential, an electric field for spray ionization is created, which is schematically indicated in Figures 4a to 6 and designated 30. The individual embodiments of Figures 4a to 7 differ with regard to the orientation of the spray ionization brushes 10 (in Figures 4b and 5b against the direction of flow, otherwise in Figures 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 Figures 4a, b, the counter electrode 24 is located between the pre-ionizers 10 and the actual filter 26. In the embodiment according to Figures 5a, 5b, the counter electrode 24 is located in front of the pre-ionizers 10 in the direction of flow, which can be beneficial for the ionization effect, cf.the upstream collector elements of WO 2021 / 185418 A1. In the embodiment according to Figure 7, the counterelectrode 24 is located behind the filter 26 in the flow direction. Although the electrode spacing is large in this embodiment, the electric field spanned across the filter 26 (provided the filter material is dielectric, which is the case with many plastic or glass fiber-based filter materials) can enhance the separation effect through additional electrical polarization effects. In the embodiment according to Figure 6, the counterelectrode 24' additionally has arcuate sections to optimize the ionization distribution, as described in more detail in WO 2021 / 185418 A1. Of course, several differently positioned counterelectrodes can also be used in combination, provided they do not completely shield each other.Figure 8 shows the electrostatic precipitator described in more detail in WO 2021 / 185418 A1, with a collector unit 40, edge counterelectrodes 44, and upstream counterelectrodes 42 (also referred to therein as upstream collector elements), whereby the statements therein can be applied to the counterelectrodes in the present invention. List of reference symbols.

[0100] 10 Spray ionization source or pre-ionizer

[0101] 12 Pre-ionizer holder 14 Conductive fibers

[0102] 16 Metal coating

[0103] 20 Particle filter arrangement

[0104] 22 Flow direction

[0105] 24.24' Counter electrodes 26 Particle separation unit / pleated filter

[0106] 28 flow channel

[0107] 30 ion field

[0108] 32 Bracket and voltage supply pre-ionizers

[0109] 40 Collector unit electrostatic precipitator 42 Upstream counter electrodes

[0110] 44 edge counter electrodes

[0111] Patent claims

[0112] 1. Particle filter arrangement (20) through which a gas stream to be purified of particles, in particular an air stream to be purified, flows, comprising: i) an ionizer unit as a pre-ionizer, which has one or more approximately point-shaped spray ionization sources (10) arranged within the air stream and subjected to one or more different electrical ionizer potentials, wherein at least one of the spray ionization sources (10) is formed essentially from a bundle of electrically conductive fibers (14), wherein the electrically conductive fibers (14) of the spray ionization source (10) are at least partially provided with a metallic coating (16), ii) at least one counter electrode (24, 24') spaced from the spray ionization source(s) (10) of the ionizer unit, each of which is subjected to one or more different counter potentials deviating from the ionizer potential(s),and with ii) a fibrous or sponge-like particle separation unit (26) arranged downstream of the ionizer unit, which may also contain material containing activated carbon.

[0113] 2. Particle filter arrangement (20) according to claim 1, characterized in that the fibrous or sponge-like particle separation unit (26) is one of the following units or a combination of corresponding units - as far as technically possible:

[0114] Fabric filters made of plastic fibers, glass fibers, textile fibers, all possibly with additionally woven metal fibers and / or metal fibers, and / or

[0115] Electret filters, possibly with additionally woven metal fibers, and / or

[0116] Activated carbon filter and / or sponge filter.

Claims

3. Particle filter arrangement (20) according to 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, optionally with pleated filter material, or as a pocket filter.

4. Particle filter arrangement (20) according to one of claims 1 to 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.

5. Particle filter arrangement (20) according to one of claims 1 to 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 only a few weeks of continuous operation due to streaming effects in such a separator.

6. Particle filter arrangement (20) according to one of claims 1 to 5, characterized in that the metallic coating (16) consists essentially of nickel or of a nickel alloy, in particular of a nickel-chromium alloy, preferably of a nickel alloy with more than 50% nickel content.

7. Particle filter arrangement (20) according to 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.

8. Particle filter arrangement (20) according to one of claims 1 to 7, characterized in that the electrically conductive fibers (14) are carbon or graphite filaments or are formed as fibers spun from such filaments.

9. Particle filter arrangement (20) according to one of claims 1 to 8, 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 formed as graphite or carbon filaments or as fibers spun from such filaments; and / or the electrically conductive fibers (14) are formed 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 pm; 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 holder (16) holding the bundle together and the front end of the fibers (14) is between 2 mm and 25 mm for the majority of the fibers of the fiber bundle, preferably between 5 mm and 12 mm; and / or the bundles are oriented in the flow direction (22) or against the flow direction (22).

10. Particle filter arrangement (20) according to one of claims 1 to 9, characterized in that the fibers (14) of the fiber bundle have a diameter of 5 pm to 20 pm, preferably between 5 pm and 10 pm, and / or that the metal coating thickness is between 0.05 pm and 1.0 pm, preferably between 0.2 pm and 0.5 pm.

11. Particle filter arrangement (20) according to one of claims 1 to 10, characterized in that the fibers (14) of the fiber bundle are metallically coated substantially along the fiber circumferential sides, at least in the spatial vicinity of the free end faces, wherein the end faces of the free end faces are preferably uncoated.

12. Particle filter arrangement (20) according to one of claims 1 to 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 pA.

13. Use of a spray ionization source (10) which is essentially formed from a bundle of electrically conductive fibers (14), wherein the electrically conductive fibers (14) of the spray ionization source (10) are 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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