EP2772309B1 - Device for separating particles from a gas flow charged with particles and method - Google Patents

Description

The invention relates to a device for separating particles from a particle-laden gas stream, in particular an electrostatic precipitator and a method for separating particles from a particle-laden gas stream.

Background of the invention

For the purification of a particle-laden gas stream, electrostatic precipitators in various forms are known in the prior art, for example as tube electrostatic precipitators or as plate electrostatic precipitators. When operating the devices, so-called corona quenching occurs at high particle concentrations, which reduces the separation efficiency.

One way to improve the separation efficiency is a bipolar charging of the gas stream or aerosol to achieve an agglomeration. For example, it is known to charge the aerosol bipolarly by means of separate high-voltage electrodes. The separate electrodes are either installed in a common channel or in separate channels, with the differently charged gas streams subsequently being mixed. Furthermore, an embodiment is known, wherein the separate electrodes are arranged one behind the other and after passing through the electrodes a subsequent mixing takes place. It is also known to accelerate the agglomeration by superimposed alternating fields.

An apparatus and method for bipolar charging of an aerosol is disclosed in the document DE 44 00 827 C1 known. The aerosol is passed through a flow channel in which at least one pair of electrodes is arranged. One electrode of the pair is earth-free connected to the positive pole of a voltage source and the other electrode is connected to the negative pole floating. The tips of the electrodes face each other. Between the electrodes, a corona discharge is formed, whereby the aerosol is charged almost symmetrically bipolar. However, a symmetrical loading of the aerosol with positive and negative ions only achieves a low net charge of the aerosol, which is insufficient for rapid deposition. The latter is also undesirable in the agglomeration process according to the prior art, since here the agglomeration product is to be transported away with the gas phase.

In the document US 7,452,411 B2 a device for separating an aerosol is described. The device comprises a first electrode, which bears against a first potential, and a second electrode, which bears against a second potential. The first electrode is configured to form a corona discharge, thereby charging the aerosol. Charged particles of the aerosol settle on the second electrode and are excreted.

The document DE 36 09 698 A1 discloses an apparatus and method for ionizing or neutralizing a gas stream. In separate zones, ions of both polarities are generated. The gas stream flows out of the device in positive and negative layers.

The document DE 195 24 214 A1 discloses an electrostatic filter with negative corona in the entrance area. This ammonia is filtered from flue gas.

The document DE 10 2008 009 258 A1 discloses a method and apparatus for energetically optimized separation of aerosols in a two-stage electrostatic precipitator.

Summary of the invention

The object of the invention is to provide improved technologies for the separation of particles. The influence of the corona quenching is to be overcome in order to achieve a good separation in a small construction volume.

The object is achieved by a device for separating particles from a particle-laden gas stream according to independent claim 1 and a method according to independent claim 12. Advantageous embodiments of the invention are the subject of dependent claims.

According to one aspect of the invention, an apparatus for separating particles from a particle-laden gas stream is provided, in particular an electrostatic precipitator. The device has a flow channel, with an inlet region into which the particle-laden gas stream enters, and an outlet region from which the gas stream, which is at least partially purified from the particles, emerges. Arranged in the flow channel is a spray electrode, which is electrically connected to a high voltage source, such that when a high voltage is applied, a first corona discharge at the spray electrode is trained. Furthermore, a precipitation electrode is formed, which is applied to the ground potential, and at which electrically charged particles are deposited from the gas stream. In the flow channel at least one counter electrode is arranged, which is electrically connected to the collecting electrode and is also at earth potential. The at least one counterelectrode is configured to form a second corona discharge when a boundary field strength of the electric field is exceeded due to a particle space charge in the region of the counterelectrode, which is polarized opposite to the first corona discharge.

A kit for retrofitting an electrostatic precipitator is disclosed wherein the electrostatic precipitator includes a flow channel, a spray electrode, and a precipitation electrode. The kit includes at least one counter electrode which is installable in the flow channel, electrically connected after installation to the collecting electrode and at the ground potential. The at least one counterelectrode is configured to form a corona discharge when a boundary field strength of the electric field is exceeded due to a particle space charge in the region of the counterelectrode, which is polarized opposite to a corona discharge of the spray electrode.

According to another aspect of the invention, there is provided a method of separating particles from a particle-laden gas stream. The method comprises the steps of: introducing the particulate laden gas stream into a flow channel through an entrance region, forming a first corona discharge by means of a spray electrode disposed in the flow channel and electrically connected to a high voltage source, charging the particles in the first corona discharge so that the charged particles depositing on a precipitation electrode adjacent to the ground potential, forming a second corona discharge, which is poled opposite to the first corona discharge when a field strength limit of the electric field due to a particle space charge in the region of the collecting electrode is exceeded, and discharging the at least partially purified from the particles gas stream the flow channel through an exit area. For example, at least one counterelectrode can be arranged in the flow channel, which is electrically connected to the collecting electrode and is at earth potential. The at least one counterelectrode can be arranged in the vicinity of the precipitation electrode or connected directly to it. The at least one counterelectrode can be configured to form the second corona discharge when a limiting field strength of the electric field is exceeded due to a particle space charge in the region of the counterelectrode.

The particle-laden gas stream forms an aerosol. The particles may be in solid or liquid state. On the way of the gas flow through the flow channel, the particles are at least partially removed from the gas stream. In the first corona discharge emanating from the spray electrode, the gas particles are ionized. The gas ions accumulate on the particles in the gas stream, so that charged particles are formed. The charged particles migrate to the collecting electrode and settle there, for example in the form of a dust layer. The cleaning of the precipitation electrode can be used as dry cleaning, for example, by tapping, or wet cleaning, for example by rinsing with water done.

Depending on the concentration of the particles in the gas stream, different operating conditions may occur. At low concentrations, the electric field in the flow channel is essentially determined by the static field of the spray electrode and the space charge field of the gas ions. The particle space charge formed by the charged particles is low at low concentrations and has little effect on the electric field and operation of the device. Under these conditions, no second corona discharge is triggered at the at least one counterelectrode yet.

At a high particle concentration, many charged particles collect at the precipitation electrode. As a result, the particle space charge increases sharply in the region of the collecting electrode and the current consumption of the spray electrode is suppressed. It comes to a so-called "Corona Quenching". If the field strength emanating from the particle space charge exceeds a limiting field strength in the region of the at least one counterelectrode, a second corona discharge, which is opposite to the first corona discharge, is formed on the counterelectrode. There is a bipolar corona discharge between the spray electrode and the at least one counter electrode.

As a result, gas ions are formed in the region of the at least one counterelectrode, which are charged opposite to the gas ions formed in the first corona discharge. The oppositely charged gas ions accumulate on the particles, so that a polarity charged with opposite polarity space charge arises. The opposite-polar space charges attract each other and there is a very rapid mixing of the oppositely charged aerosols. As a result, the total space charge is reduced very quickly. The oppositely charged particles move alternately and agglomerate to larger, electrically neutral particles. An agglomeration process is thus carried out in parallel with the quenched operation. The total particle concentration decreases as a result, and the larger particles are easier to deposit. Reducing the total space charge at least partially reverses corona quenching and the spray electrode can recharge the gas stream. As soon as the particle concentration has decreased by the agglomeration process so much that the corona quenching decreases sharply or even ends, the second corona discharge is terminated at the at least one counter electrode. The counterelectrode automatically returns to an "inactive" state. An energy-intensive agglomeration Bipolar charging of the aerosol is thus triggered accurately and only if the concentration of the particles is so great that corona quenching occurs.

At least for liquid aerosols, the construction volume of a device according to the invention is smaller by a factor of 2 to 4 than the construction volume of an electrostatic precipitator known from the prior art which operates exclusively in unipolar operation (and under quenched conditions).

The configuration of the at least one counterelectrode is effected by a suitable choice of the shape and the associated dimensions, for example diameter, length and surface radii.

The spray electrode may be arranged, for example, in the center of the flow channel. Alternatively it can be provided that the spray electrode is arranged deviating from the center of the flow channel. The spray electrode may be formed as a single wire. Alternatively or additionally, the spray electrode may be formed star-shaped or from plates which are arranged at an angle to each other. A positive or a negative high voltage can be applied to the spray electrode by means of the high-voltage source. It is also possible to arrange a plurality of spray electrodes in the flow channel, which can all have the same shape or a combination of the aforementioned shapes.

According to one embodiment it can be provided that the at least one counter electrode is arranged in the input region of the flow channel. The high particle concentrations, which lead to corona quenching, usually occur in the entrance area. The adverse effects of the quenched operation can be counteracted by suitable placement of the at least one counter electrode. It can be provided that the output region of the flow channel is free of counterelectrodes in order to save material and energy during operation of the device.

According to a development it is provided that the at least one counterelectrode is formed as a tip or edge. A pointed counter electrode is in the form of a pin, the length of the electrode being larger than the diameter. An end of the tip projecting into the flow channel has a rounding diameter that is smaller than the diameter of the electrode shaft. The counter electrode may be formed as an elongate edge of a surface which projects into the flow channel. The tip or edge can be arranged directly on the collecting electrode.

According to another development, it is provided that the at least one counterelectrode is formed as a tensioned wire or as a wire grid. The counterelectrode in the form of a wire or wire grid may be arranged in the flow channel such that it is spaced from the collecting electrode.

The concrete shape and design of the at least one counter electrode should be in relation to the design of the device. When the counter electrode is shaped as a tip, its length may be about 2% to 10% of the diameter or cross-section of the flow channel. For example, the diameter of the tip may be between 0.5 and 5 mm and the tip radius between 0.05 mm and 0.5 mm. The values for the diameter and the tip radius are preferably less than or equal to the corresponding values for the spray electrode.

When a plurality of counter electrodes are formed in the device, the above-mentioned shapes for the counter electrodes can be arbitrarily combined with each other. Alternatively it can be provided that all counter-electrodes have the same shape.

It can be provided that a current measuring device is connected to the at least one counterelectrode in order to measure the current flowing out via the counterelectrode. This allows monitoring of the operating state of the counter electrode, from which measures for process control can be derived. For example, can be displayed by means of a display device that the counter electrode has activated and a corona discharge takes place.

According to a further embodiment, the flow channel is formed within a tube. This corresponds to the construction of a tubular electrostatic precipitator. The tube may have, for example, a circular, an oval, a square or a rectangular cross-section. In addition, further cross sections are conceivable. It can be provided that a plurality of counter electrodes are arranged symmetrically with respect to the cross section of the tube. For example, three counterelectrodes may be arranged along the inner wall of the tube with a uniform spacing. Alternatively, a plurality of counter electrodes may not be arranged symmetrically with respect to the cross section of the tube. A non-symmetrical arrangement can lead to improved cross-mixing of the aerosol. Furthermore, it can be provided that the distance between the spray electrode and the collecting electrode is smaller than the distance between the spray electrode and the at least one counter electrode. This arrangement is especially for rectangular or square Cross-sections advantageous because flashovers between the at least one counter electrode and the spray electrode are thereby prevented.

According to another embodiment, it is provided that the flow channel is bounded by a first plate and a second plate, which are opposite, and wherein at least one counter electrode is arranged on the first and second plate. Such an arrangement is also referred to as a plate electrostatic precipitator. It can be provided that a plurality of counter electrodes arranged on the first plate are arranged offset along the flow direction to a plurality of counter electrodes arranged on the second plate. The staggered arrangement of the counter electrodes improves the cross-mixing of the aerosol and reduces the risk of flashover between the spray electrode and the counter electrodes.

The aforementioned features apply to the kit for retrofitting an electrostatic precipitator accordingly. The method can be carried out with a device having the aforementioned features.

Description of exemplary embodiments

Fig. 1

eine schematische Darstellung eines Rohrelektroabscheiders,

Fig. 2

einen qualitativen Verlauf der elektrischen Feldstärke in einem Rohrelektroabscheider,

Fig. 3

eine schematische Darstellung eines Querschnitts eines Rohrelektroabscheiders,

Fig. 4

den Querschnitt aus Fig. 3 mit Zonen der Raumladungen,

Fig. 5

eine schematische Darstellung eines Querschnitts eines weiteren Rohrelektroabscheiders,

Fig. 6

eine schematische Darstellung eines Querschnitts noch eines weiteren Rohrelektroabscheiders,

Fig. 7

eine schematische Darstellung eines Querschnitts eines rechteckigen Elektroabscheiders,

Fig. 8

eine schematische Darstellung eines Querschnitts eines weiteren rechteckigen Elektroabscheiders,

Fig. 9

eine schematische Darstellung eines Querschnitts noch eines weiteren rechteckigen Elektroabscheiders,

Fig. 10

eine schematische Darstellung eines Plattenelektroabscheiders und

Fig. 11

eine schematische Darstellung eines weiteren Plattenelektroabscheiders.

In the following the invention will be explained in more detail by means of exemplary embodiments with reference to figures of a drawing. Hereby show:

Fig. 1

a schematic representation of a Rohrelektroabscheiders,

Fig. 2

a qualitative course of the electric field strength in a tube electrostatic precipitator,

Fig. 3

a schematic representation of a cross section of a pipe electrode,

Fig. 4

the cross section Fig. 3 with zones of space charges,

Fig. 5

a schematic representation of a cross section of another pipe electrode,

Fig. 6

a schematic representation of a cross section of yet another tubular electrostatic precipitator,

Fig. 7

a schematic representation of a cross section of a rectangular electrostatic precipitator,

Fig. 8

a schematic representation of a cross section of another rectangular Elektroabscheiders,

Fig. 9

a schematic representation of a cross section of yet another rectangular electrostatic precipitator,

Fig. 10

a schematic representation of a Plattenelektroabscheiders and

Fig. 11

a schematic representation of another plate electrostatic precipitator.

Hereinafter, like reference numerals are used for like components.

Fig. 1 shows a schematic representation of a Rohrelektroabscheiders. A flow channel 1 has an inlet region 2, into which a particle-laden gas stream enters the separator. The gas stream, which is at least partially cleaned of particles, exits the separator again via an outlet region 3.

In the flow channel 1, a star-shaped spray electrode 4 is suspended, which is connected to a high voltage source (not shown). The high voltage source may provide a positive or a negative high voltage. The spray electrode 4 may alternatively be formed as a wire or from each other arranged in angled plates. When a sufficiently high voltage is applied to the spray electrode 4, a first corona discharge is formed. Gas particles ionize in the first corona discharge and accumulate on particles, forming charged particles.

On the inner wall of the tube, a precipitation electrode 5 is formed, which abuts the ground potential. The charged particles collect on the precipitation electrode 5 and are removed from the gas stream. On the collecting electrode 5 a plurality of counter electrodes 6 are fixed, which protrude into the flow channel 1. If, at a high particle concentration, the electric field strength exceeds a critical value in the region of the counterelectrodes 6, a respective second corona discharge forms at the counterelectrodes 6, which is polarized opposite to the first corona discharge of the spray electrode 4. This leads to a bipolar agglomeration of differently charged particles. Particles excreted from the gas stream are discharged by means of an opening 7.

The counterelectrodes 6 are preferably arranged in the input region 2. The agglomeration and the favorable cross-mixing increase the separation efficiency of the separator.

In Fig. 2 is the qualitative, radial course of the electric field strength in a Rohrelektroabscheider shown under different operating conditions. The curves 8 and 9 relate to a conventional separator having no counter electrodes. Curve 8 shows the course at a low particle concentration. The course at a high particle concentration is shown by curve 9. Here comes the Corona Quenching. The influence of the at least one counterelectrode on the inner wall of the separator (ie at maximum radius) on the course at high particle concentrations is shown in FIG. 10.

Fig. 3 shows the cross section of a tube electrodepositioner with a spray electrode 4, a collecting electrode 5 and three counter electrodes 6, which are formed on the collecting electrode 5. The spray electrode 4 is in the form of a thin wire. The counter electrodes 6 are formed as sharp points. With sufficiently high field strength in the region of the counter electrodes 6, these are activated automatically.

Fig. 4 shows the zones of negative space charge 11 and positive space charge 12 for the separator after Fig. 3 at high particle concentrations, when 6 corona discharges occur at the counter electrodes.

Fig. 5 shows another tube electrode. Here, the spray electrode 4 is not positioned in the center. The counter electrode 6 is located at a greater distance from the spray electrode 4 than in the Fig. 3 illustrated embodiment. This is advantageous at low aerosol concentrations since electrical flashovers occur later. In addition, this design favors the transport of oppositely charged particles to each other.

In the Fig. 6 illustrated embodiment has an improved cross-mixing. The spray electrode 4 is formed from mutually angled plates, for example, from sharp-edged sheet metal. Due to the staggered arrangement of the electrodes, a directed circulation flow 13 is generated in the radial direction, which leads to rapid mixing and agglomeration of the oppositely charged particles.

In Fig. 7 a rectangular electrostatic precipitator is shown. Here, the counter electrode can be attached to different locations. Suitable placement points for one or more counter electrodes are labeled a, b and c. Advantageously, the counterelectrodes 6 are farther away from the spraying electrode 4 than the distance between the spraying electrode 4 and the precipitating electrode 5 formed on the wall in order to exclude flashovers between the counterelectrodes 6 and the spraying electrode 4.

Fig. 8 shows another simple geometry of the counter electrode 6 in a rectangular electrostatic precipitator. The counter electrode 6 is formed as a thin, parallel to the collecting electrode 5 stretched wire. Alternatively, the counter electrode 6 may be formed as a grid fixed on the collecting electrode 5.

In order to determine the operating state of the counterelectrode 6 (active / inactive) and to derive therefrom measures for process control, individual or several counterelectrodes can be instrumented by measuring the current flowing away via the counterelectrode 6 by means of an ammeter 14 or by exceeding a threshold value a display device is displayed. This is in Fig. 9 shown. If the current exceeds a certain value, it is indicated, for example, that the counter electrode 6 has activated and a corona discharge takes place.

Fig. 10 shows a equipped with counter electrodes 6 Plattenelektroabscheider. The advantageous staggered arrangement of the counter electrodes 6 improves the cross-mixing of the gas flow and reduces the risk of flashover between the spray electrode 4 and the counter electrodes 6.

In Fig. 11 Another plate electrostatic precipitator is shown. The flow direction of the gas stream to be cleaned is indicated by arrows. The counter electrodes 6 are realized here by a wire mesh or by tensioned wires. The precipitation electrodes 5 can be omitted in the area with the counterelectrodes 6, since no wall is required for guiding the gas flow or for delimiting the adjacent gas flows. Advantageously, the counterelectrodes 6 are used only in the input area 2 and / or in the vicinity of the raw gas inlet (where a high aerosol concentration is to be expected). In contrast, the use of counterelectrodes 6 is advantageously dispensed with in the vicinity of the clean gas outlet 3. On the wall, the counter electrodes 6 are attached to the collecting electrode 5.

The features of the invention disclosed in the description, the figures and the claims may be of importance for the realization of the invention both individually and in combination with one another.

Claims (12)

1. A device for the precipitation of particles from a gas flow charged with particles, with:

   - a flow channel (1) with an entry region (2), into which the gas flow charged with particles enters, and an exit region (3), from which the gas flow, at least partially cleaned of particles, exits,

   - a discharge electrode (4), arranged in the flow channel (1), which is electrically connected with a high-voltage source such that with the application of a high voltage a first corona discharge is formed on the discharge electrode (4),

   - a collector electrode (5) for the accumulation of electrically charged particles from the gas flow, which electrode is at earth potential, and

   - at least one counter electrode (6) arranged in the flow channel (1),

   characterised in that,

   - the at least one counter electrode is electrically connected with the collector electrode (5), and is likewise at earth potential,

   and in that

   - the at least one counter electrode (6) is configured so as to form, in the event of a limiting field strength of the electric field being exceeded by virtue of a particle space charge in the vicinity of the counter electrode (6), a second corona discharge, which is of opposite polarity to that of the first corona discharge.
2. The device in accordance with Claim 1, wherein
   the at least one counter electrode (6) is arranged in the entry region of the flow channel.
3. The device in accordance with Claim 1 or 2, wherein
   the at least one counter electrode (6) is formed as a point, or an edge.
4. The device in accordance with Claim 1 or 2, wherein
   the at least one counter electrode (6) is formed as a wire under tension, or as a wire mesh.
5. The device in accordance with one of the preceding claims, wherein
   a current measurement device (14) is connected to the at least one counter electrode (6) so as to measure the current flowing out via the counter electrode (6).
6. The device in accordance with one of the preceding claims, wherein
   the flow channel (1) is formed within a pipe.
7. The device in accordance with Claim 6, wherein
   a plurality of counter electrodes (6) are arranged symmetrically with respect to the cross-section of the pipe.
8. The device in accordance with Claim 6, wherein
   a plurality of counter electrodes (6) are not arranged symmetrically with respect to the cross-section of the pipe.
9. The device in accordance with Claim 6, wherein
   the distance between the discharge electrode (4) and the collector electrode (5) is less than the distance between the discharge electrode (4) and the at least one counter electrode (6).
10. The device in accordance with one of the Claims 1 to 5, wherein
    the flow channel (1) is bounded by a first plate and a second plate, which are located opposite one another, and wherein
    at least one counter electrode (6) is arranged on the first and second plates in each case.
11. The device in accordance with Claim 10, wherein
    a plurality of counter electrodes (6) arranged on the first plate are arranged along the direction of flow, displaced relative to a plurality of counter electrodes (6) arranged on the second plate.
12. A method for the precipitation of particles from a gas flow charged with particles, with the following steps:

    - introduction of the gas flow charged with particles into a flow channel (1) through an entry region (2),

    - formation of a first corona discharge by means of a discharge electrode (4) arranged in the flow channel (1) and electrically connected with a high-voltage source,

    - charging of the particles in the first corona discharge so that the charged particles discharge onto a collector electrode (5) located at earth potential,

    - formation of a second corona discharge on a counter electrode (6) arranged in the flow channel (1), wherein

    - the counter electrode (6) is electrically connected with the collector electrode (5), and is likewise at earth potential, and wherein

    - the second corona discharge is of opposite polarity to that of the first corona discharge, if a limiting field strength of the electric field is exceeded by virtue of a particle space charge in the vicinity of the collector electrode (5), and

    - removal of the gas flow, at least partially cleaned of particles, from the flow channel (1) through an exit region (3).

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