EP4000738B1 - Filter for cleaning a gas flow - Google Patents

Description

The invention relates to an electrostatic filter with an ionization unit and a separation unit for cleaning a gas flow.

Electrostatic filters are used to remove various types of contaminants in the form of particles, dust, airborne particles or droplets from gas streams. Electrostatic filters are used in air conditioning and ventilation systems. An important area of application for the filters is the treatment of air contaminated by industrial processes. Electrostatic filters work on the principle of separation. In a first step, the ionization unit is used to electrically charge particles or particles that are to be separated and that are located in a gas stream or gas mixture stream to be cleaned. In a second step, the charged particles are separated from the gas flow in the separation unit.

From the EP 2 105 205 B1 discloses an electrostatic filter with an ionization unit and separation unit, the ionization unit having a wire-shaped ionization element extending along a longitudinal axis and a counter-electrode for generating an electric field, in order to ionize the particles present in the gas flow. The longitudinal axis of the circular ionization element runs orthogonally to an inflow direction along which the gas stream flows through the ionization unit. The counter-electrode has several flat electrode plates, which extend essentially parallel to the inflow direction of the gas stream. A voltage is applied between the ionization element and the counter-electrode so that the particles flowing through the ionization unit pass through an electric field. The voltage between the ionization element and the counter-electrode is adjusted in such a way that the ionization element emits electrons which collide with the particles and charge them electrically. The particles charged in this way then reach the separation unit, where they can then be separated from the gas flow due to the charging.

The ionization of the particles is of particular relevance for the efficiency or degree of separation of electrostatic filters. A high number of ionized particles and a high ionization strength per particle can be achieved by advantageous measures, which promotes efficient separation. The number of ionized particles and the ionization strength per particle can be set, for example, via the electrical voltage between the ionization element and the counter-electrode, with limits being set here by spark flashovers that are to be avoided. the EP 2 105 205 B1 proposes, in order to increase the efficiency, to design the ionization element in the form of a spray wire with sharp edges, which promotes good spraying behavior. However, the formation of the sharp edges of the spray wire is associated with increased production costs.

From the DE 10 2017 214 495 A1 an electrostatic filter is known in which the counter electrode is formed in the form of a cylindrical spiral. The longitudinal axis of the wire-shaped ionization element coincides with the central axis of the cylindrical spiral. The counter-electrode completely spirals around the ionization element. The complex structure can be seen as a disadvantage of such a filter.

the JP S60 187357 A discloses an electrostatic filter for cleaning a gas flow with an ionization unit. The ionization unit has an electrode plate which is parallel to the inflow direction of the Gas flow extends. The electrode plate has a front edge and a rear edge, both of which are positioned in front of the ionization element, viewed in the direction of flow. The electrode plate and the ionization element have the same charge, so that no electric field is established between the electrode plate and the ionization element. An electric field between the ionization element and the upstream electrode plate on the one hand and between the precipitation plates and a net-like counter-electrode on the other hand, both of which are behind the ionization element viewed in the flow direction, ensures the ionization of the gas flow.

the JP S60 187358 A discloses another electrostatic filter with an ionization element and an electrode plate positioned upstream of the ionization element and having the same charge as the ionization element. An electrical field for ionization is set between the downstream precipitation plates, viewed in the direction of flow, and the combination of ionization element/electrode plate.

the JP H08 84939 A discloses another electrostatic filter having a plurality of ionization elements and a counter-electrode having a plurality of electrode plates. Provision is made for the ionization elements to be movable. The ionization elements and electrode plates can therefore be moved relative to one another, so that the electrode plates can also be positioned with a rear edge in front of the ionization elements by being displaced in the direction of flow. An electric field is formed between the counter-electrode with the electrode plates and the ionization element.

The present invention is therefore based on the object of providing a simply constructed electrostatic filter which has a high level of efficiency.

This object is achieved by an electrostatic filter having the features of patent claim 1.

Advantageous refinements and developments of the invention are the subject matter of the dependent claims.

The object on which the invention is based is achieved in that the electrode plate has a front edge and a rear edge, viewed in the direction of flow, which are positioned in front of the ionization element, viewed in the direction of flow. In particular, the rear edge of the electrode plate is also arranged in front of the ionization element. In the inflow direction, the rear edge is located in front of a plane in which the ionization element is located and which extends perpendicularly to the inflow direction. According to the invention, a voltage is present between the ionization element and the electrode plate, so that an electric field is present.

The electrode plate is arranged in such a way that it is aligned parallel to the gas flow, so that the gas flow or the air flow first hits the front edge, then flows past the two long, flat main surfaces of the plate and finally passes the rear edge. The electrode plate offers a favorable flow profile and low flow resistance. The ionization element, whose longitudinal axis is perpendicular to the inflow direction, can be designed as a wire with a preferably round cross section. The gas flow preferably flows against the ionization element over the entire length. The gas flow is preferably applied to the electrostatic filter with the aid of a blower which is connected upstream or downstream of the ionization unit.

The particles transported in the gas flow are ionized by the electric field. Ionization means that the particles are electrically charged, so that each particle has an excess of electrons, for example.

The gas flow can be an air flow. In addition, it can also be other gaseous media or mixtures. The gas flow contains particles that are transported along with it. Particles can be dirt or dust particles that arise in industrial processes such as metal-cutting shaping (e.g. turning and milling using coolants). The particles can also be fine dust or the finest particles, right down to microscopically small suspended matter or particles. A particle can also be a liquid substance. Accordingly, particles can also be droplets or aerosols. Droplets or aerosols can also be carriers of viruses or bacteria, so that the filter according to the invention can be used to filter viruses or bacteria. Ozone, which can form in the ionization unit, can advantageously be used to kill viruses or bacteria.

The filter can be used in extractors, air conditioners, room fans or ventilation systems.

An advantageous arrangement of ionization element and counter-electrode is realized by the invention. The position of the electrode plate with its rear edge makes it possible for the ionization and the associated flow of electrons between the ionization element and counter-electrode to take place in front of the ionization element, viewed in the flow direction. The sharp contour of the rear edge promotes the desired ionization. In addition, an advantageous flow behavior of the gas flow can be adjusted by the electrode plate connected upstream of the ionization element. For example, the counter-electrode can be positioned in such a way that the particles are exposed to the ionization for a long time and thus an efficient ionization takes place. The direction of the gas flow and the particles is preferably aligned and/or calmed by the electrode plate. For example, a turbulent gas flow can be converted into a directed gas flow by flowing around the electrode plate. The gas flow and the particles preferably do not experience any turbulence. The configuration can also prevent stagnation points.

Stagnation points are points at which flow-related particles are deposited because there is no air movement in the stagnation point. A further advantage is the simple design of the counter-electrode on the basis of plates or metal sheets, as a result of which the filter can be manufactured at low cost.

The rear edge of the electrode plate is preferably arranged in front of the ionization element over its entire length. However, it is also conceivable that the rear edge is only partially arranged in front of the ionization element.

According to the invention, it is provided that the rear edge of the electrode plate runs parallel to the longitudinal axis of the ionization element. A constant distance from the rear edge of the electrode plate can thus be set over the entire length of the ionization element. This enables continuous and efficient ionization to be achieved over the entire length of the ionization element.

According to one embodiment, the counter-electrode has at least two electrode plates, the rear edges of which are each arranged in front of the ionization element and are at the same distance from the ionization element at least in a plane perpendicular to the longitudinal axis of the ionization element. Due to the same distance, the same boundary conditions for the interaction between the ionization element and the electrode plates are established between the ionization element and the at least two electrode plates. If this distance is set optimally, a particularly effective ionization results. To the extent that the rear edges of the electrode plates run parallel to the longitudinal axis of the ionization element, the rear edges lie on the lateral surface of an imaginary cylinder whose central axis coincides with the longitudinal axis of the ionization element.

The requirement of the same distance is said to be met if the distance between the rear edge of one electrode plate does not differ by more than 2 mm from the distance between the rear edge of the other electrode plate. in one Embodiment of the invention, the corresponding distances differ from each other by a maximum of 1 mm. Insofar as it is assumed below that the distances to the ionization element are the same, such equality should exist if the values differ by a maximum of 2 mm.

According to the invention, the separating unit has at least one precipitation plate with a front edge and a rear edge in the inflow direction, as well as at least one intermediate plate which extends parallel to the precipitation plate. When voltage is applied, an electric field is set up between the precipitation plate and the intermediate plate, as a result of which the particles previously ionized or charged in the ionization unit are repelled by the intermediate plate and attracted by the precipitation plate. The particles are deposited on the precipitation plate and are thus separated from the gas or air flow. Particles that have settled on the precipitation plate can be transported away by any mechanism. Preferably, gravity and the resulting gravitational forces can be used. For example, particles can be transported downwards on vertically running plates. According to the invention, the longitudinal axis of the ionization element, the electrode plate of the counter-electrode and the precipitation plate of the separating unit run parallel to one another, preferably in the vertical direction, when the filter according to the invention is in the operational position.

Analogously to the electrode plates, the precipitation plates also have the additional function of specifying the direction of gas flow and particles through the plate. The electrode plate and the precipitation plate can advantageously be matched to one another, for example by lying in one plane and thus providing a good flow profile. Furthermore, ozone that has formed on the ionization element can be transported away or broken down by the precipitation plates. The precipitation plate is particularly easy to clean thanks to its flat sheet design. It is also conceivable for the ozone and/or for particles which could not or could not be separated from the gas flow in the separation unit could be dismantled to provide a downstream after-treatment. This can include the use of an activated carbon filter. Filter media made of glass fibers can also be used here.

The precipitation plate has the front edge, which is arranged behind the ionization element as seen in the inflow direction and whose distance from the ionization element corresponds according to the invention to the distance from the rear edge of the electrode plate of the counter-electrode to the ionization element. Thus, the rear edge of the electrode plate of the counter-electrode and the front edge of the collecting electrode lie on the circumference of a circle whose center coincides with the longitudinal axis of the ionization element and whose radius corresponds to the distance. The precipitation plate is therefore not only used to separate the particles from the gas flow, but can also contribute to the ionization of the particles.

According to a further embodiment, the separating unit has at least two precipitation plates (for example 2, 3 or 4 precipitation plates), the front edges of which are at the same distance from the ionization element.

In addition to the at least one electrode plate, the counter-electrode can include at least one additional electrode plate, which runs parallel to the direction of flow and has a front edge and a rear edge, with the rear edge of the additional electrode plate being positioned behind the ionization element or at the same height as the ionization element, viewed in the direction of flow. If the trailing edge is at the same height as the ionization element, the trailing edge and the ionization element lie in the same plane, which extends perpendicularly to the inflow direction. The rear edge of the additional electrode plate preferably runs parallel to the longitudinal axis of the ionization element.

According to one embodiment of the invention, the counter-electrode has at least two additional electrode plates, the ratio of one The distance between the two additional electrode plates and the distance between the ionization element and the rear edge of the electrode plate is 1.5 to 2.5, preferably 1.8 to 2.2. If the counter-electrode has more than two additional electrode plates, the distance described here is the distance between two adjacent additional electrode plates. It has been found that with the above ratio, a compact ionization unit with good efficiency can be implemented.

The additional electrode plate can form an outer plate of the counter electrode. Two additional electrode plates are preferably provided, each of which forms an outer plate or an outside of the ionization unit. The outer plates can also be used for shielding, for example against external electrical fields and against unwanted air currents or objects that penetrate the filter on the outside. Furthermore, the outer plates can prevent the charged particles from escaping from the filter before they have even reached the separation unit.

According to a further embodiment, the ionization unit is equipped with a large number of ionization elements, for example 2 to 20 and preferably 3 to 10, which can be arranged at the same height as seen in the direction of flow, with at least one additional electrode plate of the counter-electrode being arranged between each two ionization elements.

According to a further embodiment, the electrode plate of the counter-electrode has an edge profile running along the rear edge. The edge profile can be designed as a sawtooth profile, wave profile or stepped profile. This edge profile provides the trailing edge with several sharp, exposed corners and peaks that promote ionization.

Alternatively or additionally, the electrode plate can converge in a pointed shape at the rear edge. This also leads to a sharper expression the trailing edge, which promotes ionization. Not only the rear edge of the electrode plate, but also the front edge of the precipitation plate of the separating unit can have the edge profiles described above and/or the pointed shape mentioned.

Figur 1:

ein Ausführungsbeispiel für einen nicht-erfindungsgemäßen Filter in einer Schnittdarstellung;

Figur 2:

einen weiteren nicht-erfindungsgemäßen Filter mit drei Ionisierungselementen;

Figur 3:

ein Ausführungsbeispiel für einen erfindungsgemäßen Filter mit einem gegenüber Figur 1 und Figur 2 leicht geänderten Aufbau.

Further advantageous configurations and details of the invention are explained below using exemplary embodiments and with reference to the accompanying drawings. Show it:

Figure 1:

an embodiment of a filter not according to the invention in a sectional view;

Figure 2:

a further filter not according to the invention with three ionization elements;

Figure 3:

an embodiment of a filter according to the invention with a opposite figure 1 and figure 2 slightly modified structure.

figure 1 1 shows parts of an electrostatic filter 1 in a simplified sectional view. The filter 1 comprises an ionization unit 2 and a separation unit 3. The ionization unit 2 has a wire-shaped ionization element 4 that extends along a longitudinal axis 5. In the representation of figure 1 the ionization element 4 extends perpendicularly to the plane of the drawing. Furthermore, the ionization unit 2 has a counter-electrode 6 which has three electrode plates 7 and two further additional electrode plates 8 .

The separating unit 3 has three precipitation plates 9 and two intermediate plates 10 which are arranged between two adjacent precipitation plates. The precipitation plates 9 and the intermediate plates 10 are in the figure 1 shown only partially and therefore in a shortened form.

The ionization element 4 is designed as a round or essentially round spray wire, the diameter of which is from 0.1 to 1 mm can accept. The length of the ionization element 4 can be in a range from 10 to 90 cm, preferably from 15 to 70 cm. A height of the filter 1 corresponds approximately to the length of the ionization element 4 and is therefore also in a range from 10 to 90 cm.

A length L of the filter 1 is preferably in a range of 10 to 40 cm. In the figure 1 The width B shown can assume values of 15 to 60 mm. Since a section of the filter 1 is only shown schematically here and a filter can be composed of a large number of these sections, the width of the filter can be a multiple of B.

A gas flow 11 with an inflow direction 12 flows against the ionization unit 2 . The gas flow 11 contains particles that are to be separated by the filter 1 . Due to the arrangement of the plates of the filter 1, the gas stream 11 flows through both the ionization unit 2 and the separation unit 3 without changing direction. Correspondingly, the gas flow 11 first enters the ionization unit 2 and flows past the electrode plates 7 and additional electrode plates 8 . The electrode plate 7 has a front edge 13 and a rear edge 14 . It can be seen that both the front edge 13 and the rear edge 14 of the electrode plate 7 lie in front of the ionization element 4 as viewed in the direction of flow 12 . The edges 13, 14 or the electrode plates 7 in their entirety are thus located in front of a plane E in which the longitudinal axis 5 of the ionization element 4 lies and whose extension is indicated by the dot-dash line in figure 1 becomes clear. The plane E extends perpendicularly to the direction of flow 12. The extent of the electrode plate 7 in the direction of flow 12 (distance between the front edge 13 and the rear edge 14) can be greater than 4 mm, preferably greater than 6 mm.

Next is the figure 1 it can be seen that the rear edges 14 of the three electrode plates 7 lie on the circumference of a circle 15 whose center coincides with the longitudinal axis 5 of the ionization element 4 and which has a radius R. The radius R corresponds to a distance between the respective rear edge 14 of the electrode plate 7. Since the rear edges 14 should run parallel to the longitudinal axis 5 (the electrode plates 7 extend on the one hand between the front edge 13 and rear edge 14 and on the other hand parallel to the ionization element 4), the rear edges 14 lie on top a lateral surface of a cylinder whose central axis coincides with the longitudinal axis 5 of the ionization element 4 .

The radius R or the distance between the rear edge 14 and the ionization element 4 is preferably 8 to 20 mm. In one embodiment, the radius R is 12 to 14 mm. Since the circle 15 touches the additional electrode plates 8, this results in a distance between the additional electrode plates 8 which corresponds to the diameter of the circle 15 or twice the radius R.

A front edge of the additional electrode 8 is denoted by 16 , while a rear edge of the additional electrode 8 is denoted by reference number 17 . In contrast to the electrode plates 7, whose rear edges 14 are in front of the ionization element 4 or in front of the plane E, the rear edge 17 of the additional electrode plate 8 is behind the ionization element 4 or behind the plane E.

The precipitation plate 9 has a front edge 19 and a rear edge 20, with the front edge 19 facing the rear edge 17 of the two additional electrode plates 8 in the case of the precipitation plates lying on the outside. A small gap 21 of a few millimeters (for example 2 to 4 mm) remains between the rear edge 17 of the additional electrode plate 8 and the front edge of the collecting electrode 9 lying on the outside. Alternatively it can also be provided that the gap 21 does not exist. In this case, the auxiliary electrode plate 8 and the outer precipitating plate 9 may be integrally formed.

The front edges 19 of all three precipitation plates 9 are at the same height or in a common plane, which is to the plane E of the ionization element 4 is spaced. The distances between the front edges 19 and the ionization element 4 are greater than the radius R.

A front edge 18 of the intermediate plate 10 is slightly recessed from the front edge 19 of the precipitation plates. It is also possible that the front edge of the intermediate plate 10 is at the same level as the front edge 19 of the precipitation plates 9.

A distance A between two adjacent electrode plates 7 essentially corresponds to a distance Z between a precipitation plate 9 and an additional plate 10. A distance A ^l between an electrode plate 7 and an additional electrode plate 8 also corresponds to the distance Z. For a symmetrical structure of the filter 1 results in a preferred embodiment as in figure 1 always shown the same (+/−1 mm) or exactly the same distances A, A ¹ and Z between adjacent plates 7, 8, 9, 10. The distances A, A ¹ and Z preferably assume values between 5 and 7 mm. A plate thickness D for the auxiliary electrode plate 8 can be in a range of 0.5 to 2 mm, with a preferred plate thickness D being 0.8 to 1.2 mm. The values for the plate thickness D can also be used for the other plates 7, 9, 10 of the filter 1, all plates used having the same plate thickness D in a preferred embodiment.

It should be pointed out that, alternatively, the rear edges 14 of the electrode plates 7 can also lie in a common plane which is aligned parallel to the plane E. In this case, the individual rear edges 14 would not be at the same distance from the ionization element 4.

The electrode plates 7 and the additional electrode plates 8 are grounded, while a voltage is applied to the ionization element. The precipitation plates are also grounded, with the intermediate plates also being subjected to a voltage.

It should be noted that the value ranges given above for preferred dimensions, distances, sizes etc. relate to a filter which is used as a decentralized filter. If the filter according to the invention is used in large, central systems with very large gas flows, the corresponding dimensions, distances, sizes, etc. can be many times larger. For example, the ionization element can also be a rod with a preferably circular cross-section, the diameter of which is greater than 1 or 2 mm.

figure 2 shows schematically another filter 1, the filter 1 shown here consisting of three filters (units) according to FIG figure 1 composed. components or features in figure 2 , belonging to components or characteristics in figure 1 are identical or similar are provided with the same reference numerals.

The longitudinal axes 5 of the three ionization elements 4 lie in the same plane E and run parallel to one another. By arranging several filters (units) in a row, the width B of the filter 1 can be varied almost at will without having to change the distances between adjacent plates or the distances between ionization elements and the front/rear edges of the plates. It should be noted that two adjacent filters (units) have a common auxiliary electrode plate 8 . In the case of a filter which has n ionization elements 4, only n+1 additional electrode plates are therefore required.

figure 3 shows an embodiment of the invention, with regard to commonalities to the filter figure 1 reference is made to the corresponding figure description. In the following, only the differences to the filter 1der figure 1 pointed out.

In contrast to the filter 1 of the figure 1 the gap 21 is between the rear edge 17 of the additional electrode plate 8 and the front edge 19 of the outer precipitation plate 9 approximately in the plane E of the ionization element 4. This means that the rear edges 17 of the Additional electrode plates 8 and also the front edges 19 of the outer precipitation plates 9 are at least approximately on the circumference of the circle 15. In addition, the front edge 19 of the central precipitation plate 9 now also lies on the circle 15. This means that all the edges of the plates that face the ionization element 4 and are grounded are at the same or approximately the same distance from the ionization element 4. This leads to a particularly intensive ionization of the particles that flow through the filter 1 along the inflow direction 12 .

Reference List

1

filter

2

ionization unit

3

separation unit

4

ionization element

5

longitudinal axis

6

counter electrode

7

electrode plate

8th

additional electrode plate

9

precipitation plate

10

intermediate plate

11

gas flow

12

flow direction

13

front edge

14

back edge

15

Circle

16

front edge

17

back edge

18

front edge

19

front edge

20

back edge

21

gap

Claims (9)

1. Electrostatic filter (1) for cleaning a gas flow (11) with an ionising unit (2) and a separating unit (3), wherein during operation of the filter (1) the gas flow (11) flows along an inflow direction (12) through the ionising unit (2), wherein for generating an electrical field, the ionising unit (2) has an ionising element (4) extending along a longitudinal axis (5) and a counter electrode (6), in order to ionise particles present in the gas flow (11), wherein the longitudinal axis (5) of the ionising element (4) stands substantially orthogonally to the inflow direction (12), wherein the counter electrode (6) has at least one electrode plate (7) which extends substantially parallel to the inflow direction (12) of the gas flow (11), wherein a voltage can be applied between the ionising element (4) and the at least one electrode plate (7), such that an electrical field results, characterised in that the electrode plate (7), viewed in inflow direction (12) has a front edge (13) and a rear edge (14) which are positioned in front of the ionising element (4) viewed in inflow direction (12), wherein the separating unit (3) has at least one deposition plate (9) and at least one intermediate plate (10) which extends substantially parallel to the deposition plate (9), wherein when a voltage is applied between the deposition plate (9) and the intermediate plate (10) an electrical field is generated between the deposition plate (9) and the intermediate plate (10), wherein the deposition plate (9), viewed in inflow direction (12), has a front edge (19), the distance of which to the ionising element (4) is equal to the spacing of the rear edge (14) of the electrode plate (7) of the counter electrode (6) to the ionising element, wherein the rear edge (14) of the electrode plate (7) runs parallel to the longitudinal axis (5) of the ionising element (4), and wherein the longitudinal axis (5) of the ionising element (4), the electrode plate (7) of the counter electrode and the deposition plate (9) of the separating unit (3) run parallel to one another.
2. Electrostatic filter (1) according to claim 1, characterised in that the counter electrode (6) has at least two electrode plates (7), the rear edges (14) of which have the same distance to the ionising element (4).
3. Electrostatic filter (1) according to claim 2, characterised in that the separating unit (3) has at least two deposition plates (9), the front edges (19) of which have the same distance to the ionising element (4).
4. Electrostatic filter (1) according to any of claims 1 to 3, characterised in that the counter electrode (6) comprises at least one additional electrode plate (8) which runs parallel to the inflow direction (12) and has a front edge (16) and the rear edge (17), wherein the rear edge (17) of the additional electrode plate (8), viewed in inflow direction (12) is positioned behind the ionising element (4) or on the same level as the ionising element (4).
5. Electrostatic filter (1) according to claim 4, characterised in that the rear edge (17) of the additional electro plate (8) runs parallel to the longitudinal axis (5) of the ionising element (4).
6. Electrostatic filter (1) according to claim 4 or 5, characterised in that the counter electrode (6) has at least two additional electrode plates (8), wherein a ratio of a distance between the two additional electrode plates (8) to the distance between the ionising element (4) and the rear edge (14) of the electrode plate (7) is 1.5 to 2.5, preferably 1.8 to 2.2.
7. Electrostatic filter (1) according to claim 5 or 6 characterised in that the additional electrode plate (8) forms an outer plate of the counter electrode (6).
8. Electrostatic filter (1) according to any of claims 4 to 7, characterised in that the ionising unit (2) is equipped with a multiplicity of ionising elements (4) which are arranged in a plane (E) perpendicular to the inflow direction (12), wherein in each case the additional electric plate (8) of the counter electrode (6) is arranged between two adjacent ionising elements (4).
9. Electrostatic filter (1) according to any of claims 1 to 8, characterised in that the electric plate (7) tapers off to a point at the rear edge (14).

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