EP2072141B1 - Electrostatic precipitator with safety device - Google Patents

Description

The invention relates to an electrostatic precipitator, in particular for an exhaust pipe of a heating system, according to the preamble of claim 1. Furthermore, the invention relates to a heating system for generating energy by burning an energy source with an electrostatic precipitator according to the preamble of claim 8. In addition concerns The invention relates to a method for the protection against uncontrolled discharges of an electric field-generating electrode of an electrostatic precipitator of a heating system according to claim 7.

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 in particular to filter out the harmful substances and particles from 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. Biomass heating systems currently represent an economically and ecologically improved alternative to oil and gas heating systems. Such biomass heating systems are, for example, log wood or Holzpelletheiz-plants, which occupy a high proportion of space heating systems. The current biomass heating systems emit - in some cases only in certain operating states - relatively large amounts of fine dust in the heat generation. The fine dust from the biomass combustion, in contrast to the dust from the combustion of fossil fuels mainly from salts such as potassium and calcium compounds. Due to the large amount of fine dust emissions and legal regulations for wood combustion systems such as the Federal Immission Control Act (BlmSchG), the limit values for fine particulate emissions are to be lowered. The required particulate matter reduction can be achieved, for example, by means of exhaust gas aftertreatment with electrostatic precipitators be achieved. Such electrostatic precipitators are characterized in particular by a low pressure loss, a high separation efficiency, ie a high proportion of separated exhaust particles from a particle stream, and low operating costs.

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 filter with a spray electrode and a collector electrode is 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 now to deposit the pollutants, more precisely the particles not to be discharged to the environment, of the exhaust gas 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, most of the particles migrate through the electrostatic Coulomb forces to the inner wall of the exhaust pipe, which serves as a collector electrode.

As mentioned above, the particles are electrostatically charged by the corona discharge which forms along the surface of the electrode. This is done at the molecular level by the following process: Is the electrode z. B. compared to the exhaust pipe to negative high voltage, so a large number of gas molecules is negatively charged. They move in the electric field applied by the electrode and the exhaust pipe in the direction of the exhaust pipe. If these meet on their way through the exhaust pipe to electrically neutral particles, they stick to these and charge the previously neutral particles also negative. The charged particles flow, driven by electrostatic deflection forces, to the inner wall of the exhaust pipe. Here the particles stick, lose their charge and are safely removed from the exhaust stream. This is the core process of an electrostatic precipitator and, depending on the geometry, height of the corona current, electrode shape, etc., leads to deposition rates of up to more than 90%. This core process can be disturbed by the following effects:

Burning produces bipolar charged particles. By means of Boltzmann distribution, the proportion of single or multiply charged particles can be estimated. The distribution is symmetrical, ie, there are the same number of positive and negative charged particles. For conditions such as those present in the exhaust gas of biomass heating systems, between 15 and 20% of the particles carry an elementary electric charge. Although the number of charged particles is reduced by approx. 10% per second due to coagulation, there are still more than 10% charged particles at the electrostatic precipitator (corresponding to about one to two seconds of particle flying time from the place of combustion). Now get the charged particles in the vicinity of the lying on negative high voltage electrode of the charger (unit exhaust pipe, electrode), the negative particles will flow away from the electrode towards the exhaust pipe inside. The positive particles, on the other hand, flow towards the electrode. Of this, a part is neutralized or negatively charged while flowing through the charger, but the rest of the particles reaches the electrode and deposits there. Over the service life it comes therefore to function restrictions of the electrostatic deflector. Because the fine dust deposited on the electrode locally prevents the formation of the corona. As a result, the electrical charge of the particles deteriorates. The deposition efficiency of the system is degraded. In addition, in the immediate vicinity of the corona (within a radius of a few millimeters around the electrode) there is a bipolar charge area. Electrically neutral particles which flow through this area can also be positively charged by a negative electrode. They then flow to the electrode. One part is neutralized or negatively charged by the corona, but a small remainder reaches the electrode and also deposits there. To maintain the functionality of the electrode, it must therefore be removed from its ready-to-use position and cleaned.

A disadvantage of the electrostatic precipitators according to the prior art is that after a longer operating time, a continuous degradation of the corona current can occur at a constant high voltage. As a result, the charging efficiency of the electrode decreases, which in turn reduces the separation efficiency of the entire system. The electrode must be cleaned manually or automatically. This can lead to damage, since the charge supply to the electrode is not always interrupted or the electrode is not always charge-free when moving out of its ready position.

The, as in the US 3,733,783 , disclosed possibility to interrupt a voltage source through a door contact is also unsatisfactory, it should be broken or the separator is not housed.

The invention has for its object to provide an electrostatic precipitator, which overcomes this disadvantage and in particular allows a safe moving out of the electrode from its ready position, without causing uncontrolled discharge or charge transfer from the electrode. Further, the invention has for its object to provide a heating system with a separator according to the invention, which allows reliable electrode maintenance. In addition, the invention has for its object to provide a method by which a safe electrode maintenance is realized.

This is achieved by the objects with the features of claim 1 and of claim 7 and by a method having the features according to claim 8. Advantageous developments can be found in the dependent claims.

The electrostatic precipitator according to the invention is characterized in that in an electrostatic precipitator, in particular for an exhaust pipe of a heating system, with a flow channel having a channel wall and a channel inside, through which a particulate-containing exhaust gas flows in a flow direction, and in the channel interior substantially extending in the flow direction, from the

Flow channel removable electrode, to form an electric field between the electrode and the channel wall. In this case, the electrode is detachably attached to the channel wall via an electrode holder contacting the channel wall. Furthermore, a safety device is included, which prevents electrical charge from being applied when a contact between the electrode holder and the channel wall of the electrode is removed, and the safety device further comprises a discharge device which causes at least partial discharge of the electrode when the contact is removed. Due to this discharge device residual charge, which is located at the electrode, discharged controlled, so that a safe moving out of the electrode is possible.

In a further embodiment it is provided that the discharge device is designed as a short-circuiting means to effect a short circuit between the electrode and a grounded part. The grounded part may be the channel wall or any other grounded component. The short circuit realizes a complete discharge of the electrode.

In yet another embodiment, it is provided that the securing device has a contact monitoring unit which monitors the contact between the electrode holder and the channel wall and signals a cancellation of the contact. As a result, each release of the electrode is detected and appropriate measures for safe removal of the electrode can be initiated.

An embodiment provides that the contact monitoring unit comprises at least one sensor. This is selected from the group comprising capacitance sensors for measuring an electrical capacitance, acoustic sensors for acoustic measurement, optical sensors for optical measurement, magnetic sensors for magnetic measurement and the like. Yet another embodiment provides that the securing device is designed as a switch, which interrupts a charge supply feeding the electrode when the contact is removed. As a result, a charge supply is immediately interrupted and a discharge of the remaining charge to the electrode can be initiated and carried out. An embodiment of the invention provides that the securing device has a control unit, via which the charge supply supplying the electrode is controllable, in particular lockable.

The heating system is characterized in that for generating energy by burning of an energy source such as biomass with a particulate matter emitting heating system, such as a biomass heating system, for burning the energy carrier, wherein particle-containing exhaust gases are formed, and comprising an electrostatic precipitator in an exhaust pipe a flow channel having a channel wall and a channel inside, through which the particle-containing exhaust gas flows in a flow direction, an electrode extending in the channel interior substantially in the flow direction and an electrode feed to feed the electrode is provided. In this case, the electrode feed is at least partially encased with an insulator. The electrostatic precipitator is formed according to the electrostatic precipitator according to the invention, namely with a safety device which prevents electrical charge being applied when the contact between the electrode holder and the channel wall of the electrode is removed, and the electrode is at least partially discharged.

The inventive method is characterized in that in the method for protecting against uncontrolled discharges of an electrode of an electrostatic precipitator, in particular when releasing the held over an electrode holder spray electrode of a channel wall of a flow channel, the steps of: monitoring a contact between the electrode holder and the Kanalwandung and interrupting a charge supply to the electrode at a cancellation of the contact and discharging the electrode after a release of the contact.

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

The securing device reliably and reliably detects detachment of the electrode. During operation, the electrode is securely arranged in the flow channel. For example, for maintenance, the electrode is released and must be moved out of the flow channel. Upon release, the contact between the electrode holder and the channel wall is canceled. The electrode must be disconnected from a charge source, such as a high voltage power supply, and the rest of the charge removed from the electrode to prevent uncontrolled discharge and possible damage. This is realized by the securing device. With this safety device, an automatic charge supply interruption and a discharge can be realized, so that the electrode can be safely moved out of the flow channel. The securing device can be realized in various embodiments. Some embodiments of the device according to the invention and of the method according to the invention are briefly described below:

In one embodiment, the electrode, more precisely the electrode holder, is designed as an electrical switch. Here, the electrode holder of the electrode is attached to a flow channel formed as a stovepipe, for example by means of screws, gluing or the like. The furnace tube and the electrode holder are preferably metallic in their contact region and the metallic contact is used as a switch. Once the electrode holder is removed from the stovepipe, the high voltage supply to the electrode is automatically shut off and the electrode grounded accordingly. The electrode can be moved out of the furnace tube with the electrode holder be, the electrode has a voltage at ground level. As a result, an uncontrolled discharge of the electrode is prevented.

A further embodiment provides that the contact between the electrode holder and the stovepipe is permanently detected via the high-voltage supply by detecting the electrical capacitance of the earth potential. When the electrode holder is removed from the furnace tube, the electrical capacitance of the ground potential changes due to the change in the metallic mass of the electrode holder relative to the system electrode support stovepipe. Upon detection of a corresponding change, the high voltage power supply is turned off and the charge dissipated, that is grounded.

In a further embodiment, the contact between the electrode holder and the furnace tube is acoustically detected. Through a sounder, such as an ultrasound generator, the system is excited electrode holder stovepipe with appropriate vibrations. When the electrode holder is detached from the furnace tube, the resonance frequency of the oscillating, excited system changes. This change is detected and generates a corresponding signal. On the basis of this signal, the charge supply is interrupted and existing charge dissipated. In yet another embodiment, the contact between the holder and the furnace tube is optically monitored. Upon release of the electrode holder from the furnace tube, the optical change is detected and the release signaled accordingly. On the basis of signaling, a charge supply interruption and a grounding occur.

The procedure can be used for manual maintenance as well as for automated maintenance. After detaching the electrode holder from the furnace tube, the electrode must be moved out of the furnace tube for maintenance. This is preferably done through an opening in the furnace tube. The opening can be loosely closed by a closure element which is electrically conductive with the furnace tube, for example a loose wire mesh. When moving out of the electrode, the electrode forcibly contacts the closure element, so that a short circuit is caused by the electrical connection with the grounded stovepipe. Due to the short circuit between the electrode and the furnace tube, a discharge or a kind of forced earthing takes place. In addition to this short circuit, the contact between the closure element and the electrode additionally removes the adhering fine dust. The fine dust is stripped off from the electrode by contact with the closure element, which is designed in the manner of a curtain.

The drawing shows an embodiment of the invention and shows in the single figure schematically a longitudinal cross section through a section of an embodiment of an electrostatic precipitator according to the invention.

The figure shows schematically a longitudinal cross section through a section of an embodiment of an electrostatic precipitator 1 according to the invention. The electrostatic precipitator 1 is integrated as part of an exhaust pipe 2 (shown only partially) of a heating system not shown here and comprises a flow channel 3. The flow channel 3 is as formed through the flow channel 3, shown here by three arrows P, particulate-containing exhaust gas flows in the flow direction also shown by the arrows P. In the exemplary embodiment illustrated, the channel wall 4 has a channel wall 4 of equal thickness along the flow direction P, that is, the wall thickness of the channel wall 4 is substantially constant along the flow direction P. In the flow direction P, an electrode 6, which is also referred to as a center electrode or corona electrode, extends in the interior of the flow channel 3. The flow channel 3 is preferably formed in cross section in the flow direction P rotationally symmetrical about a central axis A, wherein the cross section is formed at least in the illustrated section constant along the flow direction P. The electrode 6 extends along this central axis A. After prolonged operation, particles 6 can adhere to the electrode 6, forming a dust layer 6a around the electrode 6, which can impair the performance of the electrostatic precipitator 1. The electrode 6 is fed via an electrode feed 7, which is covered with an insulator 8. Together with the channel wall 4, the electrode 6 forms a charging unit, in which particles can be charged electrically. To this end, the electrode 6 forms an electric field with the channel wall 4 while applying a high voltage, the field lines of which extend essentially radially to the electrode 6 or the channel wall 4, essentially transversely, more precisely at right angles, to the flow direction P.

The electrode 6, which is also referred to as a spray electrode, is fastened to the duct wall 4 via an electrode holder 9. For this purpose, the electrode holder 9 can be fixed to the channel wall 4 in a positive, frictional, force-locking and / or material-locking manner. The electrode holder 9 is attached to the channel wall 4 so that a contact between the electrode holder 9 and the channel wall 4 is formed. When the electrode holder 9 is removed from the channel wall 4 so that the contact is released, a fuse 10 interrupts a charge supply to the electrode 6. The contact is preferably formed as a metallic contact. In addition, the securing device 10 has a discharge device 11. This discharges the electrode 6 after the contact has been released, that is, after the charge supply is interrupted. For monitoring the contact, the safety device 10 further comprises a contact monitoring unit 12. The contact monitoring unit 12 permanently checks the contact between the electrode holder 9 and the channel wall 4. Once the contact is canceled, this is detected and signaled. For this purpose, the securing device 10, to be more precise the contact monitoring unit 12, has a sensor 13. The sensor 13 can monitor the contact in various ways. For example, the sensor 13 may be selected from the group comprising capacitance sensors for measuring an electrical capacitance, acoustic sensors for acoustic measurement, optical sensors for optical measurement, magnetic sensors for magnetic measurement and the like. The monitoring is carried out acoustically, optically, electrically, magnetically or in a similar manner. In addition, the securing device 10 may be formed as a switch, so that when you cancel the contact immediately a charge is switched off. Furthermore, the securing device 10 has a control unit 14. The charge supply to the electrode 6 can be regulated via this control unit 14, which is shown schematically here. For example, this allows the delay time to be regulated until the charge supply is interrupted. About the control unit 14, the discharge device 11 can be switched on. The discharge device 11 may be formed as a movable contact element, which establishes a contact between the electrode 6 and the flow channel 3 formed, for example, as a tube wall. In particular, the contact element may be formed as a curtain-like wire mesh, through which the electrode 6 must be carried out when moving out of the flow channel 3.

Claims (8)

1. Electrostatic precipitator (1), in particular for an exhaust-gas line (2) of a heating system, having a flow channel (3) with a channel wall (4) and a channel interior (5) through which a particle-containing exhaust gas (P) flows in a flow direction, and having an electrode (6), which extends in the channel interior (5) substantially in flow direction (P) and can be removed from the flow channel (3), in order to form an electric field between the electrode (6) and the channel wall (4), wherein the electrode (6) is attached to the channel wall (4) in a detachable manner by means of a electrode holder (9) which makes contact with the channel wall (4),
   characterized in that the said electrostatic precipitator further comprises a safety device (10) which prevents electrical charge from being supplied to the electrode (6) when contact between the electrode holder (9) and the channel wall (4) is broken, and the safety device (10) further comprises a discharge device (11) which causes at least partial discharge of the electrode (6) when contact is broken.
2. Electrostatic precipitator (1) according to Claim 1,
   characterized in that the discharge device (11) is in the form of a short-circuiting means in order to create a short circuit between the electrode (6) and an earthed part.
3. Electrostatic precipitator (1) according to either of Claims 1 and 2,
   characterized in that the safety device (10) has a contact-monitoring unit (12) which monitors contact between the electrode holder (9) and the channel wall (4) and indicates that contact is broken.
4. Electrostatic precipitator (1) according to Claim 3,
   characterized in that the contact-monitoring unit (12) comprises at least one sensor (13), wherein the sensor is a capacitance sensor, an acoustic sensor, an optical sensor, a magnet sensor or the like.
5. Electrostatic precipitator (1) according to one of Claims 1 to 4,
   characterized in that the safety device (10) is in the form of a switch which interrupts a charge supply, which feeds the electrode (6), when contact is broken.
6. Electrostatic precipitator (1) according to one of Claims 1 to 5,
   characterized in that the safety device (10) has a control unit (14) by means of which the charge supply which feeds the electrode (6) can be controlled, in particular can be blocked.
7. Heating system for generating energy by means of combustion of an energy carrier such as biomass, having a heating system which emits a fine dust, such as a biomass heating system, for combustion of the energy carrier, wherein particle-containing exhaust gases (P) are produced, and
   an electrostatic precipitator (1) in an exhaust-gas line (2), comprising
   a flow channel (3) with a channel wall (4) and a channel interior (5) through which the particle-containing exhaust gas (P) flows in a flow direction,
   an electrode (6) which extends in the channel interior (5) substantially in flow direction (P) and
   an electrode supply (7) in order to feed at least the electrode (6), wherein the electrode supply (7) is at least partially sheathed by an insulator (8),
   characterized in that the electrostatic precipitator (1) according to one of Claims 1 to 6 is designed with a safety device (10) which prevents electrical charge from being supplied to the electrode (6) when contact between the electrode holder (9) and the channel wall (4) is broken, and the safety device (10) further comprises a discharge device (11) which causes at least partial discharge of the electrode (6) when contact is broken.
8. Method for protecting against uncontrolled discharges of an electrode (6) of an electrostatic precipitator (1) when the spray electrode (6) which is held by means of an electrode holder (9) is detached from a channel wall (4) of a flow channel (3), comprising the steps of:

   monitoring contact between the electrode holder (9) and the channel wall (4),

   interrupting a charge supply to the electrode (6) when contact is broken, and

   discharging the electrode (6) after contact is broken.

Images