EP1545785B1 - Electrostatically operating filter and method for separating particles from a gas - Google Patents

Abstract

The invention relates to an electrostatically operating filter for separating particles from a gas, comprising at least one electrode (4) connected to a high voltage source and at least one earthed or oppositely poled electrode (5) between which the gas charged with particles is guided. In order to improve the cleaning performance of the filter, at least one of the electrodes (4,5) is provided with a space (9) in which the particles can enter and in whose extension essentially no electric potential difference prevails. The invention also relates to a method for separating particles from a gas by means of an electrostatically operating filter.

Description

The invention relates to an electrostatic filter for the separation of particles from a gas having at least one electrode connected to a high voltage source and at least one grounded or oppositely poled electrode, between which the gas laden with the particles can be passed. Document DE 28 02 965 A discloses such an electrostatic filter.

Furthermore, the invention relates to a method for separating particles from a gas by means of an electrostatic filter.

Electrostatically operating filters of the generic type are known, for example, from EP 0 847 806 B1. They are used for the electrostatic separation of any particles and droplets from different gases in many process engineering processes, in particular for gas dedusting. In this case, the gas to be purified flows through a gas-arranged register of precipitation electrodes, each of which is substantially shaped as a plate. Spray electrodes are arranged centrally in each lane formed by the collecting electrodes. Between the spray electrodes and the collecting electrodes, a high DC voltage is applied, which is above the corona threshold voltage. This ensures that the discharge electrodes emit electrons that are so strongly accelerated in the immediate vicinity of the high-voltage discharge electrodes due to the prevailing high electric field strength that their kinetic energy is sufficient to knock out more electrons from neutral gas atoms and / or molecules and in this way to create an electron cloud. On the way to the (grounded) precipitation electrode, the electric field strength decreases rapidly, so that the kinetic energy of the electrons falls below the limit at which the electrons are bound by neutral gas molecules or atoms to form negative gas ions.

In the further course of the deposition mechanism, these negative gas ions preferably accumulate on the dust particles and thus share with them an electrical charge, as a result of which the thus charged dust particles experience an accelerating force action in the direction of the collecting electrode in the electric field. There, they are collected in a layer of dust, through which the charge carriers flow to the grounded precipitation electrode, agglomerated and preferably by vibrations of the electrodes, for example caused by knocking, cleaned and fed by gravity of the dust collection and Staubaustragsvorrichtung.

A special type of electrostatic filter is described in DE 3 723 544 A1. Here, a "patterned deposition electrode" is shown as a deposition electrode facing the spray electrode. The structuring can be different in many ways. It always serves for mechanical binding and storage of the electrostatically separated dust particles.

A deduction of the dust during filter operation from the system is not provided in this type. The dust is disposed of by incineration in the filter or by replacement or cleaning of the filters outside of the filter operation.

If the structure-forming elements of the precipitation electrode precede a closed metal plate, then a field-free space is created within the precipitation electrode, which is not described in its dimensions, since it is irrelevant to the function of the precipitation electrode: By design, a Faraday cage occurs by design. Decisive for the function of this type of filter, however, are the porous structure-forming elements, which are intended to ensure binding and storage of the separated dust.

With the mentioned principle, dust particles and droplets of different types of gas streams can be deposited in many applications. The deposition efficiency is strongly influenced by the particles, but also by the gas properties. The gas composition decisively determines the solubility of the Gases and thus the number of gas ions, which is available for charging, ie for the electrical loading of the dust particles. In the dust particles, especially the specific electrical dust resistance is known as a significant dust property, because of this size, the amount of the effluent to the collecting electrode charge carriers is limited.

Regardless of the boundary conditions, which are given by the gas and dust properties, by an appropriate regulation of the voltage source (HS aggregate) always trying to provide the possible for a particular constellation and meaningful maximum amount of charge (current). In this case, it is accepted that the maximum current flow also generates a usually deposition-inhibiting turbulence, a so-called electric wind, in the gas.

In order to avoid the electric wind, EP 0 847 806 B1 proposes a method in which the charging of the dust particles and their deposition is carried out procedurally in decoupled partial steps. In a first charging zone, the dust particles are electrically charged with as high a charge carrier as possible, even at the cost of high gas turbulence. In a subsequent second zone, the deposition zone, the electrically charged dust particles are deposited in an electric field whose voltage is below the corona threshold voltage. As a result, the excitation of the electric wind is avoided.

In prior art electrostatic filters, which are also referred to as electrostatic precipitators, a relatively high energy expenditure is required for efficient separation of the particles or droplets from the gas. Furthermore, the problem generally arises that the generated electric wind generates deposition-inhibiting turbulence. At high electrical resistivity of the dust, the dust layer at the collecting electrodes increasingly acts as a limiting factor for the current and the separation efficiency.

The invention is therefore based on the object to overcome the aforementioned disadvantages and to propose an electrostatic precipitator and a method for its operation, which are characterized by a high separation efficiency with low energy consumption. Furthermore, the formation of electric wind should be minimized and the limiting effect of the specific electrical dust resistance should be removed.

This object is achieved by an electrostatic filter according to claim 1 or the method for depositing particles according to claim 14.

Finally, in contrast to DE 3 723 544 A1, the construction should be designed so that a continuous or quasi-continuous withdrawal of the separated particles is ensured during the ongoing operation of the filter.

The solution of this problem by the invention is characterized in that the electrostatic precipitator contains no spray electrode and the electrodes (4,5) with a grid-like conversions, quasi field-free, in its longitudinal extent at least at one end open space (9) are formed in the the particles can enter via grid openings and exit at the open end.

In this case, the use of a spray electrode is dispensed with, ie an electrode on which extreme field strength peaks are generated by small radii or other geometric points. Since the electrodes of both polarities then act as precipitation or deposition electrodes, it is therefore only possible to differentiate between high-voltage and grounded electrodes. High voltage can be the positive or negative electrode.

According to one embodiment, it is provided that only the at least one electrode connected to the high-voltage source, preferably all electrodes connected to the high-voltage source, contains or contains such a space. However, it can also be provided that only the at least one grounded electrode, preferably all grounded electrodes, contain or contain such a space. Finally, both the at least one electrode connected to the high-voltage source and the at least one grounded electrode, preferably all electrodes, may contain such a space.

Advantageously, this space is at least partially bounded by a grid, mesh or the like and a Abscheideblech, the electrically conductively connected to each other, form the electrode. The grid has inlet openings for the particles.

In this case, the grid, mesh or the like is an obstruction of the projected electrode surface (= area of the Abscheidebleches) of a maximum of 10%. It has in no way the function of a mechanical separator or a memory for the deposited particles.

The quasi-field-free space formed between the grid, mesh or the like and the Abscheideblech is designed so that the incoming particles are slowed down so that they do not adhere to the Abscheideblech for a long time after the impact, but continuously fall down and be removed ,

The grid, mesh or the like can be formed from a number of interconnected mutually parallel rods, which are electrically connected to the plate-shaped Abscheideblech. However, it can also be provided, for example, that the grid is formed from a number of mutually connected mutually parallel rings, these being electrically conductively connected to a cylindrical or hollow-cylindrical deposition plate, forming the electrode.

The electrostatically operating filter may be formed as a "plate electrostatic filter" in which a number of planar box-shaped electrodes are arranged parallel to each other. It is equally possible that it is designed as a tubular electrostatic filter in which at least two cylindrical or hollow cylindrical electrodes are arranged coaxially with each other.

For improved discharge of the filtered particles can be provided that at least one electrode has a discharge channel for particles adjacent to the electrically largely field-free space.

The method of separating particles from a gas by means of an electrostatic filter is characterized in that
that the particles are deflected to one of the two electrodes (4, 5), and that the particles pass into a lattice-like space (5) of the electrode, in the extension of which no electrical potential difference prevails, and are deposited there, the filter without a Spray electrode is operated.

It is one of the features of this filter design that the high-voltage leading and the grounded electrodes can be designed structurally similar. Therefore, a quasi-homogeneous electric field perpendicular to the flow direction of the particle-laden gas forms between the electrodes - without field strength peak, as in the previously known systems with spray electrodes. In contrast to the previously known electrostatic filter types, the separation of particles from the gas at the electrodes of both polarities can take place in the same way.

The proposed method utilizes the effect of an electric field between two electrodes on non-ionized by a technical device dust particles or targeted ionized dust particles in a gas stream. The electrodes are preferably under a voltage which is below the corona threshold voltage. The particles are deflected in the electric field depending on the polarity to one of the two electrodes.

The electrostatic filter can be constructed as a horizontally flow-through filter in which a cascade of box-shaped electrodes is used. Each second box-shaped electrode is either connected to the high voltage source or grounded or polar oppositely. In the same way, it is also possible to provide a design which leads to a vertically flown through tube or honeycomb electrostatic precipitator. Likewise, the proposed principle is applicable to a wet electrostatic precipitator.

The invention makes use of the fact that in the proposed embodiment of the electrodes with a quasi electric field-free space dust particles can enter the room due to their kinetic energy in this but then exposed to no further external electrostatic force and therefore separated using gravity and off the system is continuously discharged.

Advantageously, the proposed electrostatic precipitator has a highly efficient separation ability of particles and droplets from any gas stream, with only a small amount of energy is required. The emergence of an electric wind is largely avoided.

In free-flowing or free-flowing particles, the cleaning of the electrodes, as described, takes place automatically. If, on the other hand, particles with adhesive or adhesive properties are concerned, the filtered particles can be cleaned from the walls of the electrostatic precipitator and / or the electrodes in a manner known per se by knocking the electrodes, with the particles falling down predominantly in a largely electric field-free space he follows. Depending on the properties of the particles and their rinsing - ie a wet filtration - during operation is possible.

The deposition of particles on / in the electrodes (between the deposition plates and the grids / rods / or the like which together form the electrodes) is also substantially dependent on the field strength existing between the high voltage electrode and the grounded electrode. The field line of maximum field strength is perpendicular to the polarity between the electrodes; this also applies in principle to known filters with earthed Abscheideblechen and lying on high voltage potential Sprühelektroden. In order to increase the effectiveness of the invention, it is desirable to increase the distance between the electrodes of different polarity.

This is achieved by the fact that of the opposing electrodes of different polarity mutually electrically conductive, with the corresponding Conductively connected electrodes, bodies - eg wires - in the space between the electrodes protrude. These bodies can be arranged parallel or perpendicular or obliquely to the flow direction of the gases to be cleaned.

This results in maximum field strengths firstly between the bodies and the opposing electrodes and secondly between the bodies of different polarity. The maximum field strengths depend on the structural arrangement and can therefore have different values and directions. The angles between the maximum field strengths (body - electrode or body - body) can assume all values between 0 ° and 180 °.

Fig. 1

eine perspektivische Darstellung eines elektrostatisch arbeitenden Filters, der als horizontal durchströmter Filter ausgebildet ist;

Fig. 2

eine perspektivische Darstellung eines vertikal durchströmten Röhrenfilters;

Fig. 3a,3b

Querschnitte durch die Elektroden des Filters; und

Fig.4

eine perspektivische Darstellung einer Filtergasse eines horizontal durchströmten Filters, dessen Elektroden mit feldfreien Räumen und mit zusätzlichen Körpern (hier Drahtbügeln) versehen sind

In the following drawings embodiments of the invention are shown. Show it:

Fig. 1

a perspective view of an electrostatic filter, which is designed as a horizontally flowed through filter;

Fig. 2

a perspective view of a vertical flow-through tube filter;

Fig. 3a, 3b

Cross sections through the electrodes of the filter; and

Figure 4

a perspective view of a filter alley of a horizontally flowed through filter whose electrodes are provided with field-free spaces and with additional bodies (here wire brackets)

In Fig. 1, an electrostatic filter is shown, which is suitable for filtering particles and / or droplets from a gas stream. The particulate contaminated gas entering the filter is indicated by an arrow numbered 1. The gas stream flows through the filter, whereby the particles in the gas are filtered out and removed. The outflowing, cleaned gas is indicated by the arrow with the reference numeral 2. Downstream, the flow of deposited particles 3 exits the filter.

To clean a larger gas flow, a cascade of electrodes is used. As can be seen in Fig. 1, a number of box-shaped electrodes 4 and 5 are arranged parallel to each other. Between the electrodes 4, 5 lanes 8 are provided, through which the gas to be purified 1 is passed. The electrodes 4, 5 are alternately connected either to a high voltage source (namely, the electrodes 4) or grounded (namely, the electrodes 5).

In the exemplary embodiment according to FIG. 1, all the electrodes 4, 5 are provided with a space, not designated here, into which the particles to be filtered out can enter, but in the extension of which no electrical potential difference prevails; he is therefore referred to here as a virtually electric field-free space. This space is created in the electrodes 4, 5 in that the Abscheideblech 7 is surrounded by a grid 6. Abscheideblech 7 and grid 6 are electrically connected. The grid 6 consists of a number of mutually parallel bars.

The gas laden with particles initially flows in between the electrodes 4, 5 (see gas flow 1) and there comes under the effect of the quasi-homogeneous electric field. The particles are deflected in the direction of the electrodes and enter through the grid openings. Thus, they are in a virtually electric field free space, where they are no longer exposed to any further external electrostatic force. They fall down due to gravity and can be continuously - while the filter operation - removed from the filter. The cleaned gas leaves the filter in the horizontal direction via an outlet hood (see gas flow 2).

The electrodes 4, 5 according to FIG. 1 show, by way of example, the creation of the electric-field-free space by the grid 6 composed of interconnected bars, which grid is electrically connected to the internal separator plate 7. The electrodes 4, 5 may be modular and arranged above and behind each other, as shown in Fig. 1. In this example, the electrodes on both sides of the Abscheidebleches a field-free space. Randseitige electrodes or in a filter with only one passage for the gas passage, the electrodes may also be constructed so that they only have a field-free space on one side of the Abscheidebleches. In any case, the depth of the field-free space depends on the requirements of the continuous particle withdrawal.

In Fig. 2, an alternative embodiment of this type of electric filter is sketched as a tube filter. In the example, only the grounded electrode 5 contains the virtually field-free space 9, which is bounded here by a ring grid 6 and the cylindrical deposition plate 7. The grid 6 is formed here by a number of interconnected parallel arranged metal rings, which are electrically connected to the Abscheideblech 7 and together form the electrode 5.

The aim is in all cases that to avoid the re-entry of dust into the gas stream, the electric field-free spaces 9 are formed as flow-calmed zones. This can be achieved by appropriate geometric arrangement of the bars or grid rings and / or a corresponding design of the gas inlet and the gas outlet.

FIGS. 3 a and 3 b show a few details of the configuration of the electrodes 4, 5 with the deposition plate 7, the grid 6 and the quasi electrically field-free spaces 9 defined thereby.

According to Fig. 3a, the Abscheidebleche 7 are plate-shaped and enclosed by rod-shaped grid elements which form the grid 6. Between the Abscheideblechen 7 and the grid 6, the largely electric field-free space 9 is formed in the electrodes 4, 5. The filtered particles move in the direction of arrow 3 (direction of gravity) down and can be removed from the electrostatic precipitator.

FIG. 3b shows a double-walled embodiment of the electrodes 4, 5 for assisting the discharge of the particles from the filter. The particles which are located in largely electrically field-free space 9 sink downwards due to gravity and are guided through baffles and slits of the double-walled separating plate 7 into an internally protected intermediate space, namely into a discharge channel 10. There, they can be led out of the electrostatic precipitator, uninfluenced by the outer gas flow.

The illustrated construction of the electrodes can be provided in principle in a horizontally and vertically flowed through electrostatic precipitator, with straight, curved, folded or round electrodes can be used.

The formation of the electrodes and the height of the voltage are coordinated so that no increase in the electric field strength occurs, which leads to a corona or external partial discharges.

4 shows a section of an alley of a horizontally flowed through electrostatic precipitator is shown. Before the Abscheideblech 7, the grid 6, here formed of wire hangers used. Between the grids 6, the body 11 are shown. They are constructed here of wire brackets, which are conductively connected to the respective electrodes (4,5). In the illustrated construction, the straight wires are arranged perpendicular to the gas flow. The bodies can also be arranged parallel to the gas flow or at all angles between perpendicular and parallel to the gas flow. These possible arrangements of bodies (eg wire rings or spirals) are also transferable to tubular electrodes.

LIST OF REFERENCE NUMBERS

1

inflowing, particle-contaminated gas

2

escaping, purified gas

3

emerging stream of deposited particles

4

electrode connected to a high voltage source

5

grounded electrode

6

grid

7

Abscheideblech

8th

Alley between the electrodes

9

largely electric field-free space

10

discharge channel

11

Body at the electrodes

Claims (15)

1. An electrostatically operating filter for separating particles of a gas (1) which has at least one electrode (4) connected to a high voltage source and at least one earthed or opposite poled electrode (5) between which the gas laden with the particles can be guided, characterised in that the electric filter contains no spray electrode and the electrodes (4, 5) are designed with a space (9) that is constructed in the manner of a grid, is quasi field-free and is open in its longitudinal extension at least at one end, into which space the particles can be admitted via grid openings and can be discharged at the open end.
2. The electrostatically operating filter according to Claim 1, characterised in that the earthed electrodes can be constructed in a similar design to the electrodes conducting high voltage.
3. The electrostatically operating filter according to Claim 1, characterised in that the particles can be continuously discharged from the field-free spaces of the electrodes.
4. The electrostatically operating filter according to Claims 1 to 3, characterised in that at least one of the electrodes (4) connected to the high voltage source, but preferably all of the electrodes (4) connected to the high voltage source, contains or contain a quasi field-free space (9).
5. The electrostatically operating filter according to Claims 1 to 3, characterised in that at least one earthed or opposite poled electrode (5), preferably all electrodes (5), contains or contain such a space (9) .
6. The electrostatically operating filter according to Claims 1 to 3, characterised in that both at least one of the electrodes (connected to the high voltage source and at last one of the earthed or opposite poled electrodes (5), preferably all the electrodes (4, 5), contain such a space (9).
7. The electrostatically operating filter according to any one of Claims 1 to 6, characterised in that the space (9) is bounded at leas partially by a grid (6), a net or similar structure which is open for the flow of particles, in this case has only a slight narrowing of its cross-section and is connected electrically conductively to the separating plate (7), forming with this the electrode (4, 5).
8. The electrostatically operating filter according to Claim 7, characterised in that the grid (6) consists of a plurality of bars connected together and arranged parallel with each other, wherein the bars are connected electrically conductively to a separating plate (7) designed in the shape of a plate, and form with this plate the electrode (4, 5).
9. The electrostatically operating filter according to Claim 7, characterised in that the grid (6) consists of a plurality of rings connected together and arranged parallel with each other, wherein they are connected electrically conductively to a separating plate (7) that is cylindrical or hollow cylindrical in design, and form with the plate the electrode (4, 5).
10. The electrostatically operating filter according to any one of Claims 1 to 8, characterised in that it is designed as an electric plate filter wherein a plurality of plate-shaped electrodes (4, 5) are arranged parallel with each other.
11. The electrostatically operating filter according to any one of Claims 1 to 7 or 9, characterised in that it is designed as a tubular electric filter wherein at least two electrodes (4, 5) designed cylindrically or hollow cylindrically are arranged coaxially to each other.
12. The electrostatically operating filter according to any one of Claims 1 to 11, characterised in that at least one electrode (4, 5) has a discharge duct (10) for particles, which duct lies adjacent to the space (9).
13. The electrostatically operating filter according to one of Claims 1 to 12, characterised in that bodies (13) of varying polarity are arranged in the space between the electrodes, which are connected electrically conductively to one of the two adjacent electrodes (4,5) in the flow path, according to their respective polarities. Here the bodies may lie at any angle between 0° and 90° to the direction of flow.
14. A method for separating particles from a gas (1) by means of an electrostatically operating filter which has at least one electrode (4) connected to a high voltage source and at least one earthed or opposite poled electrode (5), between which the gas laden with particles is fed, characterised in that the particles are deflected to one of the two electrodes (4, 5) and in that the particles are fed to a space (5) of the electrode having a grid-like structure, in whose extension there is no electrical potential difference, and are separated there, wherein the filter is operated without a corona electrode.
15. The method according to Claim 14, characterised in that at least one of the electrodes (4) connected to the high voltage source is supplied with a voltage that is below the corona cut-off voltage.

Images