EP2105205B1 - Ionisation element and electrostatic filter - Google Patents

Abstract

The ionization element has a spraying wire (13) with a radius of curvature smaller than 0.2 millimeter and an elongated carrier (12), which serves for the adjustment or positioning of the spraying wire in an electrostatic filter. The spraying wire and the carrier are formed in a single piece. An independent claim is included for an electrostatic filter.

Description

The invention relates to an ionization element for an electrostatic filter, which has at least one spray wire with a radius of curvature r smaller than 0.2 mm and an elongate carrier, which serves for fixing or positioning of the spray wire in the filter. Moreover, the invention relates to an electrostatic filter which is equipped with such an ionizing element.

Electrostatic filters operate on the principle that particles to be separated by the filter or dirt particles are charged in a medium to be cleaned such as polluted air in a first stage when they pass between two electrical conductors, for example between the spray wire and two sheets arranged on both sides of the spray wire , The sheets on the one hand and the spray wire on the other hand are applied to different electrical voltages. The difference in the voltages is designed so that the spray wire emits electrons, which encounter the particles or dirt particles and charge them electrically. Such a charged particle is then deposited in a second stage, for example between two sheets of different electrical voltage from the air flow. In this case, the particle is attracted to the deposition electrode, which has a polarity opposite to the particle.

Of particular relevance to the degree of separation or efficiency of such an electrostatic filter is the so-called spray behavior of the spray wire. By increasing the voltage, more electrons are emitted, which basically increases the efficiency, but at the same time the danger of a flashover also increases. Also, high voltages promote ozone formation, which is particularly detrimental when the purified air stream is returned to a closed space.

From the DE 10 2008 031 888 A1 For example, an ionization element is known which has a spray wire with a radius of curvature r of 0.015 mm. This spray wire is wound around a stretched cylindrical support in the form of a helical or a helical spring. The carrier serves to fix the spray wire in the electrostatic filter or to hold in position.

By the spray wire in the form of a helix, on the one hand, there is a considerable enlargement of the active surface of the spray wire within the flow channel of the electrostatic filter. On the other hand, since the wearer supports the spray wire and holds in place, it can be very fine, allowing a small radius of curvature, which positively affects the spray behavior. However, the production of the ionizing element is associated with a certain effort, since the spray wire and the carrier must first be made separately from each other, and finally the spray wire must be wound around the carrier or pushed axially over it.

From the DE 43 26 895 C1 For example, an ionizing element is known that consists of a support on the outside of which a fabric with crossed and twisted yarns of carbon fibers is arranged. A carbon fiber corresponds to a spray wire, wherein in the DE 43 26 895 C1 a diameter of 5 - 10 microns are given for a carbon fiber. Again, to be achieved by the large number of carbon fibers, each having a small radius of curvature, a good spray behavior of the ionizing element. But even here, the production is complicated, since after Production of the carbon fibers they must be processed into a fabric, and then to pull this tissue over the carrier.

The US 2008/0066620 A1 relates to an electrostatic dust collecting device having a dust charging unit and a dust collecting unit. The charging unit comprises a star-shaped ionizing element.

The invention is therefore based on the object to provide an ionizing element, which has a favorable with regard to the efficiency of an electrostatic filter spray behavior and can be easily produced.

This object of the invention is achieved with the feature combination according to claim 1. Preferred embodiments may be taken from the dependent claims of claim 1.

Another object of the invention to provide an efficient electrostatic filter is solved by claim 14. Preferred embodiments may be taken from the subclaims 15 and 16.

In the ionization element according to claim 1, the spray wire and the carrier are integrally formed. For example, due to their integral nature, the spray wire and carrier can be drawn from a blank or base wire of a single material, such as tungsten. The integral nature of the spray wire and carrier enables simple and inexpensive production of the ionization element. Due to the radius of curvature r of the spray wire, which should be less than 0.2 mm, the ionizing element has at least one sharp edge, which promotes good spray behavior

Due to the integral nature of the carrier and the spray wire, the latter can also be referred to as spray elevation, which is formed on the carrier and forms a sharp edge due to its small radius of curvature r.

The at least one spray wire may be substantially parallel to a longitudinal axis of the carrier. Compared to a spray wire that is wound around the carrier, the ionization element is easier to clean, as possible depressions or gaps run axially. Purification of the ionizing element is usually necessary at certain intervals to deposits to dissolve the spray wire, which negatively affect the spray behavior.

The carrier has in cross section a convex basic shape with an edge or circumference on which the spray wire is arranged. Under convex basic form is to be understood a form in which a connecting line between any two points within this basic shape is completely in the basic form and does not cut the edge of the basic shape However, the carrier in cross-section also have a non-convex basic shape, such as a kidney shape or a bone shape, which lies outside the invention.

A simple and preferred basic form represents a circle. However, the convex basic shape can also be a polygon (for example, a triangle, quadrangle) or an oval. The edges of a polygon can be the same length, but they can also be different, as would be the case for a flat rectangle.

In a preferred embodiment, the spray wire is in cross-section substantially a circular section defined by a circular arc having a radius R corresponding to the radius of curvature r and by a chord forming part of the periphery of the basic shape. The tendon is essentially a straight line or a line with a curvature that is substantially less than the curvature of the circular arc. For example, if the basic shape of the carrier is a circle with a diameter D, then this diameter D is many times larger than the radius R. Preferably, the diameter D 8, 12, even 15 times larger than the radius R.

The radius of curvature r or the radius R may be less than 0.1 mm. Particularly good results in use in the electrostatic filter have been found when the radius R is less than 0.05, for example, 0.03 mm. In particular, this not only good efficiencies can be achieved, but also announce an undesirable formation of ozone as far as possible.

The area of the circular section with the radius R may be smaller than a corresponding semicircular area. In a preferred embodiment, the area of the circular arc corresponds to less than 70% of the semicircular area with the radius R. In other words, a height h of the circular section is smaller than the radius R. As a result, a "compact" cross section for the ionizing element can be achieved Spray wire is flat, but still has a very small radius of curvature.

A preferred alternative is that the cross section of the spray wire in addition to the circular section has a base with a height H. This base makes the spray wire stand out more clearly from the wearer.

The area of the basic shape is smaller than 0.5 mm ² . In preferred embodiments, the area of the basic shape is less than 0.3 mm ² . In a circular basic shape with a diameter D equal to 0.4 mm results in an area of only 0.126 mm ² . However, even smaller diameters can be realized, which then lead to correspondingly smaller areas than 0.126 mm ² . For example, here is a circular basic shape with a diameter of 0.25 mm mentioned, which has an area of 0.049 mm ² .

Preferably, a plurality of spray wires are provided, which are arranged at the edge of the basic shape. They can be evenly spaced from each other. In the case of a circular basic shape, it is possible, for example, to provide 12 spray wires, which are each offset by 30 ° on the circumference of the circular basic shape. Due to the large number of spray wires with correspondingly small radii of curvature, a high spray density is achieved, which enables high efficiencies. Also, it has been found here that the voltage in this embodiment can be lowered so far that at almost constant efficiencies ozone formation can be virtually eliminated.

Between two adjacent Sprühdrähten a rounding radius R may be _{approximately} provided adjacent a smooth transition between the To achieve spray wires in cross section. Due to the rounding radius R _round the cross section of the spray wire is slightly changed, but the basic shape of the spray wire is not significantly affected. Thus, it should continue to be a circular section for the cross section of the spray wire to one, even if this is no longer completely limited by a circular arc and a tendon in the strict sense, since now also parts of the boundary are formed by the rounding radius R _round .

In addition, the surface of the spray wire or of the ionization element can be roughened. This can be realized by suitable methods such as by etching.

A preferred embodiment of the electrostatic filter according to claim 14 is that the ionization element is arranged in a charging step of the electrostatic filter between two spaced plate-shaped counter-electrodes. The pitch of these counter plate-shaped electrodes is preferably 20 to 50 mm.

In a deposition stage of the electrostatic filter deposition electrodes may be arranged, each facing an intermediate electrode of a different polarity. Thus, electrodes of different polarity face each other at a small distance as in a capacitor for generating an electric field.

Figur 1

einen elektrostatischen Filter in schematischer Darstellung;

Figur 2

einen Querschnitt eines ersten Ausführungsbeispiels für das erfindungsgemäße Ionisierungselement;

Figur 3

einen vergrößerten Ausschnitt X der Figur 2;

Figur 4

den Querschnitt eines zweiten Ausführungsbeispiels;

Figur 5

den Querschnitt eines dritten Ausführungsbeispiels;

Figur 6

den Querschnitt eines vierten Ausführungsbeispiels; und

Figur 7

den Querschnitt eines nicht erfindungsgemäßen lonisierungsele- ments.

Reference to the embodiments illustrated in the drawings, the invention is explained in detail. Show it:

FIG. 1

an electrostatic filter in a schematic representation;

FIG. 2

a cross section of a first embodiment of the ionization element according to the invention;

FIG. 3

an enlarged section X of the FIG. 2 ;

FIG. 4

the cross section of a second embodiment;

FIG. 5

the cross section of a third embodiment;

FIG. 6

the cross section of a fourth embodiment; and

FIG. 7

the cross section of an ionizing element not according to the invention.

FIG. 1 shows a schematic representation of an electrostatic filter, which is designated in its entirety by 1. The filter 1 is used for cleaning a gaseous, particle-laden medium, the filter 1 according to the arrows 2 in the illustration of FIG. 1 flows through from left to right. The medium to be filtered is guided by a plurality of parallel, gap-like flow channels 3, which are each limited mainly by mutually parallel and spaced deposition electrodes 4, 5. The deposition electrodes 4, 5 are formed as sheets, which are fastened in a frame not shown here and thus held in position.

In a charging stage 7, at least one ionization element 6 is provided for each flow channel 3, which extends perpendicular to the flow direction 2 and is arranged between two plate-like counterelectrodes 16, 17. It is a wire-shaped ionization element that extends into the plane of the drawing. The detailed structure of the ionization element 6 in different embodiments is in the FIGS. 2 to 7 shown in more detail.

In deviation from the schematic representation of FIG. 1 Both electrodes 4 and 16 and the electrodes 5 and 17 may be integrally formed. In this case, for example, the precipitation electrode 4, which would then run longer, would extend into the charging stage and simultaneously serve as counterelectrode, which would reduce the number of components in the filter 1. An advantage of in FIG. 1 However, the arrangement shown is that the distance between the counter electrodes 16, 17 and thus the distance of the counter electrodes 16, 17 to the centrally arranged ionizing element 6 can be adjusted independently of the distance of the deposition electrodes 4, 5.

The ionization element 6 and counterelectrodes are connected to a high voltage generator 8, wherein the ionization element 6 is positively poled and the counter electrodes 16, 17 are at ground potential. It results between the counter electrodes 16, 17, a highly inhomogeneous electric field with very high field strengths in the immediate vicinity of the ionizing element 6. Separating occurring free electrons are strongly accelerated towards the ionization element 6, where they first encounter gas molecules. From these individual electrodes can be knocked out, with the gas molecules becoming positive ions. These positive ions then hit the entrained particles and give up. Hit her charge. The thus positively charged particles are transported to a separation stage 9 due to the pressure conditions set in the filter 1. In this deposition stage 9, the positively charged particles are attracted to the earth electrode lying on Abscheidideelektroden 4.5 and are deposited there.

In addition to the deposition electrodes 4, 5 already described above, a further deposition electrode 10 is provided which has the same polarity as the deposition electrodes 4, 5. Between the Abscheideelektrode 4 and the Abscheideelektrode 10 and between the Abscheideetektrode 10 and the Abscheideelektrode 5 is an intermediate electrode 11 is provided in each case, which is positively charged as the ionizing element 6. While a voltage U _{1 is} set between the counterelectrodes 16, 17 and the ionization element 6, there is a voltage U ₂ between the precipitation electrodes 4, 5, 10 and the intermediate electrode 11. The high voltage U ₂ is lower than the high voltage U ₁ is used to generate electric fields in the separation stage 9. In the FIG. 1 are corresponding connections to the high voltage generator 8 and to the earth for the sake of simplicity only for a flow channel 3 shown.

FIG. 2 shows in cross section a first embodiment of the ionization element 6 according to the invention.

FIG. 3 shows on an enlarged scale a section X of the FIG. 2 ,

The ionization element 6 has a circular cross-section support 12 with a diameter D. At the edge or on the circumference of the carrier 12 a plurality of approximately semicircular in cross-section spray wires 13 are arranged. The evenly distributed on the circumference of spray wires 13 and the carrier 12 are integrally formed. In the following, therefore, the spray wires 13 are referred to as spray elevations 13.

Again FIG. 3 can be removed, the cross section of a spray elevation 13 (or spray wire 13) by a circular arc 14 with a radius R and by a portion 15 of the circumference of the support 12 is limited, wherein the portion 15 relative to the radius R, which is much smaller than the diameter D is, can be considered as a rectilinear tendon. Between two adjacent wires 13, 13 a, a rounding radius R is provided _around , through which a smooth transition between the spray wires 13, 13 a is ensured.

The diameter D of the circular cross-section support 12 is for example 0.36 mm, while an outer diameter D _A , as in FIG. 2 is shown and can be considered as the envelope of the individual spray lifts 13, 0.4 mm. The radius R of each spray lift is 0.03 mm, while the radius of curvature R is _{approximately} half that and thus 0.015 mm.

A further exemplary embodiment of the ionization element 6 according to the invention is shown FIG. 4 in cross section, wherein components / features that are identical or similar to components / features of the embodiments of the previous figures, are provided with the same reference numerals. The embodiment of FIG. 4 differs from the embodiment of the FIG. 3 for the same diameter D for the carrier 12 and the same outer diameter D _A in the number of Sprüherhebungen 13, which are arranged on the circumference of the carrier 12. Also, the radius R of each spray lift 13 is 0.036 mm larger than in the embodiment of FIG FIG. 3 , The rounding radius R _{approximately} equal to 0.014 mm corresponds approximately to the radius of curvature of the embodiment of FIG. 3 ,

FIG. 5 and 6 Ionisterungselemente 6 each with circular in cross-section carriers 12 and three spray lifts 13. The spray elevations 13 are arranged offset by 120 degrees on the circumference of the carrier 12. In the embodiment of the FIG. 5 For example, each spray elevation 13 is in the form of a circular segment delimited by the circular arc 14 having the radius R and the approximately straight segment 15. In the embodiment of FIG. 6 in contrast, each spray elevation 13 is composed of a circular section and a base 18, which - if one looks approximately from the rounding of the circular support 12 with the diameter D - is rectangular and has a height H. Due to the height H (for example, 0.01 mm large) is the outer diameter D _A in the FIG. 6 with otherwise the same dimensions for the carrier 12 and the radius R greater than the outer diameter D _A in the FIG. 5 , The Figures 5 and 6 also show that no rounding radii are provided between adjacent spray elevations 13 or between a spray elevation 13 and the edge of the carrier 12.

FIG. 7 shows an ionizing element, in which the carrier 12 is not circular in cross-section, but essentially by two adjacent Krelse 19 is formed with a diameter D, between the circles 19 constrictions 20 lead to a non-convex basic shape. On the circumference of a circle 19, three spray elevations 13 are arranged in the form of a circular section with a radius R at a distance of 90 degrees. Due to the two adjacent circles 19 with the diameter D results in two different sized outer diameter D _A1 and D _A2 , the outer diameter D _A1 is composed of twice the diameter D plus twice the radius R, while the outer diameter D _{A2 of} the sum of the simple Diameter D and twice the radius R corresponds.

The number of spray wires 13, the outer diameter D _A and the diameter D of the carrier 12 and the radius R of each spray lift and also the rounding radius R _round can be set arbitrarily within the scope of the invention For example, it is possible for a first group of spray wires to choose a radius R that differs from a radius R 'for a second group of spray wires.

LIST OF REFERENCE NUMBERS

1

filter

2

arrow

3

flow channel

4

deposition electrode

5

deposition electrode

6

Ionisierungselement

7

charging stage

8th

High voltage generator

9

separating stage

10

deposition electrode

11

intermediate electrode

12

carrier

13

Spray wire / spray lift

14

arc

15

section

16

counter electrode

17

counter electrode

18

Base

19

circle

20

constriction

Claims (14)

1. Ionisation element (6) for an electrostatic filter (1), which ionisation element comprises at least one emitting wire (13) with a radius of curvature of less than 0.2 mm and an elongate support (12) that serves for fixing or positioning the emitting wire (13) in the filter (1), the cross-section of the support having a convex basic shape with a rim on which the emitting wire (13) is disposed, wherein the surface area of the basic shape is less than 0.5 mm² and the emitting wire (13) and the support (12) are formed in one piece.
2. Ionisation element (6) according to claim 1, characterised in that the at least one emitting wire (13) extends substantially parallel to a longitudinal axis of the support (12).
3. lonisation element (6) according to any one of the claims 1 or 2, characterised in that the basic shape is a circle.
4. lonisation element (6) according to any one of the claims 1 to 3, characterised in that the cross-section of the emitting wire (13) is substantially a circle segment limited by a circle arc (14) with a radius (R) that corresponds to the radius of curvature, and by a chord (15) that is part of the rim of the basic shape.
5. Ionisation element (6) according to any one of the claims 1 to 4, characterised in that the radius of curvature is less than 0.1 mm.
6. Ionisation element (6) according to claim 4 or 5, characterised in that a surface area of the circle segment is smaller than a semi-circle surface area with the radius (R).
7. lonisation element (6) according to claim 6, characterised in that the surface area of the circle segment is less than 70% of the semi-circle surface area with the radius (R).
8. lonisation element (6) according to claim 4 or 5, characterised in that the emitting wire additionally has a base (18) with a height (H).
9. lonisation element (6) according to any one of the claims 1 to 8, characterised in that several emitting wires (13) are provided that are disposed, uniformly spaced apart from one another, on the rim of the basic shape.
10. lonisation element (6) according to any one of the claims 1 to 9, characterised in that a fillet radius (R_rund) is provided between adjacent projections (13, 13a).
11. lonisation element (6) according to any one of the claims 1 to 10, characterised in that the surface of the ionisation element is roughened.
12. Electrostatic filter (1) with an ionisation element (6) according to any one of the claims 1 to 11.
13. Electrostatic filter (1) according to claim 12, characterised in that the ionisation element (6) is disposed in a charging stage (7) of the filter (1) between two spaced-apart plate-shaped counter electrodes (16, 17).
14. Electrostatic filter (1) according to claim 13, characterised in that separation electrodes (4, 5, 10), which are respectively opposite to an intermediate electrode (11), are disposed in a separation stage (9) of the filter (1).

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