EP1930081B1 - Optimised electrostatic separator - Google Patents

Description

The invention relates to an exhaust gas purification system according to the preamble of independent claim 1.

Furthermore, the invention relates to an electrostatic precipitator according to the preamble of independent claim 5.

Due to emissions from heating systems and global efforts to reduce such emissions - see, for example, the Kyoto Protocol - heating systems use appropriate emission control systems. These are to filter out in particular the harmful substances and particles in exhaust gases, so that the remaining, purified exhaust gas can be safely released to the environment. In particular, such emission control systems are used in biomass heating systems, where in addition to otherwise economic and environmental benefits increased emissions of pollutants in the exhaust gases can occur. Especially the relatively high emission of particulate matter as a pollutant component is a problem in biomass heating systems.

From the EP 1 193 445 A2 An emission control system is known, which is used for biomass heating systems to reduce particulate matter emission. The device described therein can be installed in a flue gas channel and for this purpose has a lid which can be placed gas-tight on an associated opening on a flue gas channel. On the inside of the lid, a spray electrode, for example in the form of a tensioned rod, is held over an insulating holder. A high-voltage transformer with rectifier function allows the construction of a high DC voltage between the wire and the lid, which is electrically connected to the furnace tube, so that it acts as a collector electrode.

Such an electrostatic precipitator with spray electrode and collector electrode is also known as an electrostatic precipitator. This is used for exhaust gas purification in an exhaust pipe of a heating system. In this case, a capacitor is formed by the spray, which runs approximately centrally through the exhaust pipe and therefore also referred to as the center electrode, and a peripheral surface of the exhaust pipe, which is also referred to as a cylindrical capacitor in a cylindrical tube-shaped design of the exhaust pipe. The spray or center electrode generally has a circular cross section in the flow direction of the exhaust gas, wherein the diameter of the cross section or the radius of curvature is generally formed relatively small (for example, less than 0.4 mm). In order to separate the pollutants, more precisely the particles of the exhaust gas that are not released to the environment, from the exhaust gas flow, a field extending transversely to the flow direction is formed by the center electrode and the collector electrode formed by the lateral surface with field lines from the center electrode to the collector electrode. For this purpose, a high voltage is applied to the center electrode, for example in the range of 15 kV. As a result, a corona discharge is formed, through which the particles flowing through the field in the exhaust gas are charged in a unipolar manner. Due to this charge, the particles move through the electrostatic Coulomb forces to the inner wall of the exhaust pipe, which serves as a collector electrode.

The high voltage applied to the center electrode is supplied from outside to the center electrode via a high voltage supply. This generally runs transversely to the flow direction of the exhaust gas, preferably radially to the center electrode. In order to prevent an early penetration of the high voltage to the inner wall of the exhaust pipe, the high voltage supply is covered with an insulator.

It has been shown that the exhaust gas produced at biomass heating systems can have (condensing) water, which can be deposited on the insulator at least in a cold phase of the precipitator. In addition, a further disadvantage of this insulation is that exhaust particles settle in the form of ash on the insulation. With an appropriate number of these ashes, particles can form an electrically conductive surface on the insulator since ash easily bonds to the condensate and thus can lead to a discharge of the center electrodes. This leads to failure of the electrostatic precipitator.

The invention has for its object to provide an emission control system and an electrostatic precipitator, which overcomes this disadvantage and in particular prevents or reduces a precipitation of water and a deposit of particles on the insulator to increase the service life of the electrostatic precipitator.

An exhaust gas purification system for solving the inventive task has the features of independent claim 1. Advantageous developments can be found in the dependent claims.

Such an exhaust gas purification system comprises an electrostatic precipitator in a flow passage having a passage wall and a passage inside which a particulate containing exhaust gas flows in a flow direction, an electrode extending in the passage inside a substantially flow direction, and an electrode lead for feeding the electrode the electrode feed is at least partially encased with an insulator, and wherein on and / or in the insulator (5, 5 ') a Partikelabweisemittel (6, 7) as Thermophorese-Partikelabweisemittel (6) is integrated, wherein the Partikelabweisemittel a heating device (6 ).

In the flow channel, an electric field is generated in the channel interior by the electrode fed with high voltage and acting as counter electrode channel wall, wherein the field lines extend transversely to the flow direction of the exhaust gas, preferably perpendicular to the electrode. Arranged transversely to the electrode is an electrode feed which supplies the electrode with high voltage from an external voltage source. So that no discharge of the electrode takes place via the electrode feed, this is at least partially encased with an insulator. The insulator is preferably formed of an insulating material comprising ceramics and the like.

In one embodiment, the flow channel is formed as a tube, preferably as a tube with a circular cross section in the flow or longitudinal direction. The electrode preferably extends centrally in this tube in the flow direction and is therefore also called center electrode. The center electrode is preferably formed in wire form with a likewise circular cross-section in the flow direction. Thus, electrode and tube form a kind of cylindrical toridor. The radius of the cross section of the center electrode is relatively small as compared with the radius of the cross section of the pipe, and is preferably in a range of 0.5 mm or less. The voltage applied to the electrode via the electrode lead is a high voltage and is preferably in a range around 15 kV.

In the electric field in the channel interior, the particles are deflected from their flow direction in the direction of the channel wall and are deposited on the channel wall. In order to prevent particles from depositing on the insulator, which projects into the channel interior to the electrode, a Partikelabweisemittel is provided. This effectively prevents particles deflected from their flow direction from depositing on the insulator or reduces the number of particles depositing on the insulator per unit of time.

The Partikelabweisemittel is formed on and / or integrated in the insulator. On the one hand, the particle-repelling agent may be formed around the insulator in order to form a kind of cladding layer at least partially around the insulator, which does not allow particles to pass to the insulator or only to a small extent. In this case, the Partikelabweisemittel is formed on the insulator. On the other hand, the particle-repelling agent can be formed in the insulator, whereby likewise a cladding layer can be produced, which at least partially surrounds the insulator. Of course, the particle-repelling agent can also be designed as a combination of both variants.

The particle repelling agent is designed as a thermophoresis particle repelling agent. By thermophoresis is meant, in particular, an effect which occurs in the case of aerosols in air, as occurs, for example, in a corresponding application of the electrostatic precipitator according to the invention in an exhaust gas line. In this case, a dust particle from all sides impinging on the middle uniform air molecules. A static fluctuation leads to a Brownian motion of the particles, the motion being random and undirected. If these particles are in a temperature gradient (such as a temperature field), faster molecules hit the particle on the hotter side than on the colder side. Learns through this the particle gives a net impulse towards the colder side. The movement is still essentially statistical. However, over a period of time, the particle moves toward the colder side.

This effect is used in the thermophoresis particle repellent. That is, the thermophoresis particle repelling agent is formed to repel the particles from the insulator by the effect of thermophoresis.

That the thermophoresis particle repelling agent is formed as a heater, in particular as a heating wire or the like. This heater is configured to at least partially heat the surface of the insulator in the particulate exhaust stream. The heater may be formed both on the surface of the insulator, as well as be formed in the insulator. Combinations are also possible. The heating device preferably designed as a heating wire preferably runs in the insulator.

An embodiment provides that the heating device is adapted to heat an outer surface of the insulator to a temperature required for a thermophoresis, which is correspondingly higher than that of the surrounding exhaust gas. Preferably, this required temperature or more precisely the temperature difference between exhaust gas temperature and surface temperature in a range of> = 50 to <= 400 K, more preferably approximately in the range of 100 K above the exhaust gas temperature. This produces a temperature field whose temperature gradient to the surrounding exhaust gas reliably prevents the deposition of particles, in particular of small, clearly submicron particles in a range of about 200 nm and smaller.

Another embodiment provides that the heating device is designed to heat the insulator to a temperature for burning off particles located on the insulator. Despite the particle repelling agent, it can happen that some particles are deposited on the insulator. In order to remove them, that is, to deflect them from the insulator, the heating device is designed so that a temperature can be generated on the surface of the insulator, which makes it possible to burn off the particles.

For this purpose, a control unit can be provided which, for example, causes the insulator, which is preferably designed as a ceramic insulator, is increased at least on its surface to a burning temperature, which preferably in a range of 550 ° C to 750 ° C, more preferably about 600 ° C and above is formed. Upon reaching the burn-off temperature, the combustible, deposited particles burn on the insulator. Non-combustible particles remain on the insulator, the non-combustible particles are not electrically conductive and thus are not critical to the functioning of the electrostatic precipitator.

An alternative embodiment of a particle-repelling agent provides that the particle-repelling means is designed as a deflection means in order to deflect the path of the particles in the flow channel accordingly. In this case, the particle means is designed such that the particles are selectively deflected by a directed effect force of their path in the flow direction and are directed away from the insulator. Of course, a combination of deflection and thermophoresis Partikelabweisemittel is possible.

For directional deflection of the particles, it is provided that the deflection means is designed as fluid fluid in order to deflect the path of the particles in the flow channel by a fluid accordingly. The fluid is introduced into the flow channel in such a way that a flow is created which entrains the exhaust gas particles in a direction away from the insulator.

Furthermore, the inventive task is solved by an electrostatic precipitator having the features of independent claim 5. This is arranged in a flow channel of an exhaust pipe and includes an at least partially encased by an insulator electrode feed, wherein on and / or in the insulator, a heater is designed as a particle deflector integrated.

• Durch das Partikelabweisemittel wird weitestgehend verhindert, dass sich Wasser und Partikel auf der Isolatoroberfläche ablagern. Hierdurch kann eine Entladung über Wasser bzw. wasserenthaltende Partikel entlang des Isolators verhindert werden und somit lässt sich die Funktionsfähigkeit des elektrostatischen Abscheiders wirkungsvoll verbessern. Die Partikelabweisemittel sind einfach aufgebaut und lassen sich leicht realisieren.

With the electrostatic precipitator according to the invention and the heating system according to the invention, the following advantages are realized in particular:

• The particle repelling agent largely prevents water and particles from settling on the insulator surface. As a result, a discharge via water or water-containing particles along the insulator can be prevented and thus the functionality of the electrostatic precipitator can be effectively improved. The particle repellents are simple and easy to implement.

• Fig. 1 zeigt schematisch einen Ausschnitt eines erfindungsgemäßen elektrostatischen Abscheiders in einer Schnittansicht, mit einem als Heizeinrichtung ausgebildetem Partikelabweisemittel und
• Fig. 2 zeigt schematisch ein zweites Ausführungsbeispiel eines Ausschnitts eines erfindungsgemäßen elektrostatischen Abscheiders in einer Schnittansicht, mit einem als Fluidströmungsmittel ausgebildetem Partikelabweisemittel.

The drawings illustrate two embodiments of the invention and show the following:

• Fig. 1 schematically shows a section of an electrostatic precipitator according to the invention in a sectional view, with a trained as a heater particle repelling agent and
• Fig. 2 schematically shows a second embodiment of a section of an electrostatic precipitator according to the invention in a sectional view, with a designed as a fluid fluid particle repellent.

Fig. 1 schematically shows a section of an electrostatic precipitator 1 according to the invention, which is arranged in an exhaust pipe of an exhaust gas purification system (not shown). The exhaust pipe has a flow channel 2, which essentially consists of a channel wall 2a and a channel interior 2b. In operation, a particle-containing exhaust gas from a heater (not shown) flows through the flow channel 2. The electrostatic precipitator 1 comprises an electrode 3 extending in the flow direction in the channel interior 2b and an electrode feed 4. The electrode feed 4, which in this case runs approximately perpendicular to the electrode 3, is encased with a ceramic insulator 5. This electrode lead 4 is electrically connected to the electrode 3 and supplies it with an external voltage supply source (not shown) having a high voltage. The channel wall 2a and the electrode 3 form a kind of capacitor, wherein forms an electric field between the surfaces of the electrode and the channel wall 2a. In order to prevent discharges from the electrode 3 to the channel wall 2a via the electrode feed 4, the electrode feed is coated with an insulator, here the ceramic insulator 5 in an insulating manner.

In order to prevent particles from the flowing exhaust gas stream from depositing on the ceramic insulator 5 and possibly forming a conductive surface, which leads to a discharge of the electrode 3 along this conductive surface to the channel wall 2 a, a particle-deflecting means designed as a heating device 6 is integrated into the ceramic insulator 5. The heater 6 is formed of a plurality of heating wires 6 a (two of which are shown) extending in paths in the ceramic insulator 5. These heating wires 6 a are adapted to heat the outer surface of the ceramic insulator 5 to a temperature which is suitable by means of thermophoresis effect to reject particles from the ceramic insulator 5. An example of conditions that are present in an application area for the electrostatic precipitator are the following: Exhaust heat when entering the flow channel 2: about 220 ° C Flow rate of the exhaust gas: about 2 m / s Diameter of the ceramic insulator 5: about 10 mm Length of the ceramic insulator 5: about 35 mm Heating capacity: about 10 - 20 W

Thus, a heating power of a heater 6, which is formed, for example, as an electrical resistance heater, sufficient to reject particles from the ceramic insulator 5. In order to remove possibly deposited on the ceramic insulator 5 particles, the heater 6 is formed to generate temperatures of about 600 ° C and more at the surface of the ceramic insulator 5.

Fig. 2 schematically shows a second embodiment of a section of an electrostatic precipitator 1 'according to the invention in a sectional view. The electrostatic precipitator 1 'is also arranged in an exhaust pipe of an exhaust gas purification system (not shown). The exhaust pipe has a flow channel 2, which essentially consists of a channel wall 2a and a channel interior 2b. In operation, a particle-containing exhaust gas from a heater (not shown) flows through the flow channel 2. The electrostatic precipitator 1 comprises an electrode 3 extending in the flow direction in the channel interior 2b and an electrode feed 4. The electrode feed 4, which here also extends approximately perpendicular to the electrode 3, is encased with a ceramic insulator 5 '. The ceramic insulator 5 'penetrates, as in the embodiment according to Fig. 1 , as well as the electrode feed 4, the channel wall 2b. The electrode feed 4 is electrically conductively connected to the electrode 3 and feeds it from an external power source (not shown) with a high voltage. The canal wall 2a and the electrode 3 form a kind of capacitor, wherein forms an electric field between the surfaces of the electrode 3 and the channel wall 2a. In order to prevent discharges from the electrode 3 to the channel wall 2a via the electrode feed 4, the electrode feed 4 is coated with an insulator, in this case a ceramic insulator 5 'in an insulating manner. The ceramic insulator 5 'is here, in contrast to the cylindrical shape of the insulator in FIG Fig. 1 , conical, wherein the ceramic insulator 5 'tapers in the direction of the channel wall 2a of the channel interior 2b ago. Between channel wall 2a and ceramic insulator 5 'is formed as an annular gap 7 Partikelabweisemittel, more precisely fluid fluid formed. For example, ambient air can flow into the channel interior 2b via this annular gap 7. The annular gap 7 is designed such that particles are deflected in the exhaust gas due to the flow generated by the annular gap and the pressure conditions in the channel interior 2b and the environment so that they do not deposit on the surface of the ceramic insulator 5 '. The in the Fig. 2 Arrows indicated this deflection, with the long, vertical arrow in the Fig. 2 represents the exhaust flow without Partikelabweisemittel, the two oblique, along the ceramic insulator 5 'extending arrows represent the ambient air flow and represent the curved two remaining arrows the deflected exhaust gas flow.
Of course, a combination of different Partikelabweisemittel is possible.

Claims (5)

1. Exhaust emission control system, comprising a flow channel, through which an exhaust gas containing particles flows in a direction of flow,
   and an electrostatic separator, which is formed in this flow channel by a high-voltage electrode extending substantially in the direction of flow inside the channel, by the channel wall acting as a counter electrode and by an electrode feed, for feeding the high-voltage electrode, the electrode feed being at least partially sheathed with an insulator,
   characterized in that a particle-repelling means integrated on or in the insulator is designed as a thermophorectic particle-repelling means, the particle-repelling means comprising a heating device.
2. Exhaust emission control system according to Claim 1, characterized in that the heating device (6) is suitable for heating up an outer surface of the insulator (5) to a temperature required for thermophoresis, which is correspondingly higher than that of the surrounding exhaust gases.
3. Exhaust emission control system according to either of Claims 1 and 2, characterized in that the heating device (6) is designed to heat the insulator (5) to a temperature for burning off particles located on the insulator (5).
4. Exhaust emission control system according to one of Claims 1 to 3, characterized in that the particle-repelling means (7) is designed as a diverting means for appropriately diverting the path of the particles in the flow channel (2).
5. Electrostatic separator (1, 1') for an exhaust emission control system, which separator is arranged in a flow channel (2) of an exhaust pipe and comprises an electrode feed (4) that is at least partially sheathed by an insulator (5, 5'), characterized in that a heating device (6) is formed in an integrated manner on and/or in the insulator (5, 5') as a particle-repelling means.

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