ELECTROSTATIC PRECIPITATOR SYSTEM HAVING A GRID FOR COLLECTION OF PARTICLES

Abstract

The present invention relates to an electrostatic precipitator (ESP) system (1) for removal of particles from a flue gas flowing in a flow passage (4) being delimited by a primary collection in the form of a collection plate (5). The system comprises a discharge electrode (11) arranged in the flow passage and connected to a high voltage generator (12) providing for an electric field around the discharge electrode. The system further has a secondary collection electrode in the form of a grid (101) arranged within the collection plate and made of an electrically conductive material. The presence of such a grid improves the efficiency of the precipitator. In some embodiments, the ESP system comprises an actuator (112) for moving the grid upwards and letting it drop onto an internal bottom structure (109). The movement between the collection plate and the grid as well as the impact force imparted to the dropping grid both result in a removal of collected particles.

Claims

1. An electrostatic precipitator system for dry particle precipitation comprising: a flue gas inlet for receiving a flow of flue gas, a flue gas outlet for venting the flow of flue gas, a flow passage extending between the flue gas inlet and the flue gas outlet, part of the flow passage being delimited by a primary collection electrode in the form of a collection plate, a discharge electrode connected to a high voltage generator providing for an electric field being generated around the discharge electrode, when the high voltage generator is turned on, the discharge electrode being arranged inside the part of the flow passage being delimited by the collection plate, and a secondary collection electrode in the form of a grid being arranged within the collection plate, the grid comprising a mesh-like structure, the mesh-like structure of the grid being made of an electrically conductive material, and the grid being dimensioned, shaped and configured such that it extends along and at a distance from the collection plate.

2. The electrostatic precipitator system according to claim 1, wherein the collection plate comprises a flat shape, which further extends into a curved shape to form a tubular cylinder segment.

3. The electrostatic precipitator system according to claim 1, wherein the grid comprises a corrosion-resistant material.

4. The electrostatic precipitator system according to claim 1, wherein the mesh-like structure of the grid comprises openings with a vertical dimension of 15-30 mm.

5. The electrostatic precipitator system according to claim 1, further comprising an actuator configured to provide a force to the grid so as to move the grid relative to the collection plate, when the actuator is in operation.

6. The electrostatic precipitator system according to claim 5, wherein the force provided by the actuator is an upwards force so as to move the grid upwards, so that the grid, after being moved upwards, drops from a height due to gravity resulting in the grid impacting on an internal bottom structure of the electrostatic precipitator system.

7. The electrostatic precipitator system according to claim 6, wherein the grid is resting on the internal bottom structure of the electrostatic precipitator system when not being moved upwards.

8. The electrostatic precipitator system according to claim 6, wherein the grid, when being moved upwards, is moved upwards a distance at least equal to, the vertical dimension of the openings in the grid.

9. The electrostatic precipitator system according to claim 5, further comprising a control system, which controls when the actuator is in operation and for how long, such that the actuator, when in operation, runs for a period of time during which the grid is moved a number of times.

10. The electrostatic precipitator system according to claim 5, wherein the electrical field generated by the discharge electrode is turned off, while the actuator is in operation.

11. The electrostatic precipitator system according to claim 5, wherein the grid comprises a contacting means which extends from the grid, the grid being moved upwards by the contacting means on the grid making contact with a cam being rotated by a motor, when the actuator is in operation.

12. The electrostatic precipitator system according to claim 11, wherein the cam, when seen along the axis of rotation, has a shape that is generally rectangular with two rounded corners, the rounded corners being opposite each other in both directions, such that the slope of the rounded corners extend to a sharp edge.

13. The electrostatic precipitator system according to claim 1, wherein the discharge electrode comprises: a discharge electrode connector, which is connected to the high voltage generator, and a first and a second wire connectors, which are connected to and separated a distance apart by a support rod, the first and second wire connectors having at least one wire suspended between them, and wherein the discharge electrode connector, the first and second wire connectors, the support rod, and the at least one wire are all made of electrically conductive material.

14. The electrostatic precipitator system according to claim 13, wherein the discharge electrode comprises a plurality of wires, and wherein a first end of the support rod is mounted within a central region of the first wire connector, and a second end of the support rod is mounted within a central region of the second wire connector, such that the plurality of wires are arranged around the support rod.

15. The electrostatic precipitator system according to claim 13, wherein each of the first and second wire connectors is shaped as a disk and has a shape in the horizontal plane corresponding to that of a horizontal cross-section of the flow passage delimited by the collection plate when viewed in the vertical direction.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0060] The electrostatic precipitator system according to the invention will now be described in more detail with regard to the accompanying figures. The figures show one way of implementing the present invention and is not to be construed as being limiting to other possible embodiments falling within the scope of the attached claim set.

[0061] FIG. 1 shows schematically an embodiment of the invention. FIG. 1.a shows a top view, and FIG. 1.b shows a cross-sectional view along section A-A in FIG. 1.a. FIG. 1.c shows a partial cross-sectional view of the region around the insulator.

[0062] FIG. 2 shows the collection plate and grid of the system in FIG. 1.

[0063] FIG. 3 shows schematically an ESP system having two compartments each being in the form of a tubular cylindrical segment.

[0064] FIG. 4 shows schematically a three-dimensional partial view of an embodiment of the invention.

[0065] FIG. 5 shows schematically a part of a system according to an embodiment of the invention; the system comprising an actuator having a motor used to rotate a cam.

[0066] FIG. 6 shows schematically the cam of the actuator in FIG. 5.

[0067] FIG. 7 shows schematically a discharge electrode of an embodiment of the invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENT

[0068] FIG. 1 shows schematically an electrostatic precipitator (ESP) system 1 according to the present invention; FIG. 1.a shows a top view, and FIG. 1.b shows the system in cross-sectional view along line A-A in FIG. 1.a. The system 1 is designed to be arranged on a chimney of e.g. a wood combustion stove in order to remove particulate matter from the flue gasses from wood combustion. However, it can also be used for other applications where it is desired to remove particles from a flue gas. The ESP system 1 comprises a flue gas inlet 2 for receiving a flow of flue gas, a flue gas outlet 3 for venting the flow of flue gas, and a flow passage 4 extending between the flue gas inlet 2 and the flue gas outlet 3. At least a part of the flow passage 4 is delimited by a primary collection electrode in the form of a collection plate 5. The ESP system 1 also comprises a secondary collection electrode in the form of a grid 101 arranged within the collection plate 5. The collection plate 5 and the grid 101 in combination form the collection electrode of the ESP system 1. The collection plate 5 and the grid 101 of the system in FIG. 1 are shown arranged next to each other in three-dimensional view in FIG. 2 showing that the collection plate 5 comprises a flat shape which extends into a curved shape to form a tubular cylinder segment. The grid 101 has a corresponding shape. This shape is particularly interesting in an embodiment of the invention as shown in FIG. 3, where parts of the ESP system 1 to be protected from the high temperatures in the flue gas are arranged in a separate second compartment 7 also being of a tubular cylinder segment and forming a protective shielding. The matching first compartment 6 is established either by the collection plate 5 itself, or by an outer housing surrounding the collection plate 5. By suitable dimensioning and arranging the two tubular cylinder segments, it is possible to obtain the overall appearance of a circular cylinder. In the embodiments in FIG. 2 and the following figures, the flat part of the collection plate 5 as well as the flat part of the second compartment 7 and the flat part of the first compartment 6, each comprises a lateral opening 16 providing a passage for the components of the system extending between the first and the second compartments 6,7.

[0069] The ESP system 1 may be of a type having a forced draft obtained by arranging a motor-driven impeller 8 located upstream of the outlet 3; such an embodiment is shown schematically and in cross-sectional partial view in FIG. 4. The motor 9 for driving the impeller 8 can be arranged in the second compartment 7. As shown in FIGS. 3 and 4, there is an air gap 10 between the two compartments to improve the protection of the electric and electronic parts arranged in the second compartment 7 from the hot flue gas.

[0070] As shown in FIG. 1, the ESP system 1 further comprises a discharge electrode 11 connected to a high voltage generator 12 providing for an electric field being generated around the discharge electrode 11, when the high voltage generator 12 is turned on. In the presently preferred embodiments, the voltage is in the order of 20-50 kV when the system is in use. The discharge electrode 11 is arranged inside the part of the flow passage 4 being delimited by the collection plate 5 so that a strong electric field is established in the flow passage 4 causing the flue gas around the discharge electrode 11 to become ionized. In the embodiment in FIG. 4, the high voltage generator 12 is arranged in the second compartment 7. The discharge electrode 11 is further connected to an insulator 13 arranged between the high voltage generator 12 and the discharge electrode 11. In the illustrated embodiment, this connection is made via a high voltage connector 14 which passes partly through the insulator 13 as shown in FIG. 1.c. When the discharge electrode 11 is of the type shown in further details in FIG. 7, see description below, the connection can be established by letting the discharge electrode connector 204 in the form of a tube slide over the high voltage connector 14. The rod-shaped high voltage connector 14 can then be fastened inside the discharge electrode connector 204 e.g. by screwing a screw through the discharge connector 204 that then reaches the high voltage connector 14 inside it. The insulator 13 is arranged between the discharge electrode 11 (negative polarity) and where the insulator 13 is mounted on the body of the ESP (groundedpositive polarity). It prevents the shortcut between two poles (i.e. the discharge electrode and the collection electrode). As shown schematically in FIG. 1.c, a high voltage cable 15 passes through the insulator 13 and connects to the high voltage connector 14, and the other end of this cable 15 is connected to the high voltage generator 12 as shown in FIG. 1.b.

[0071] The ionization of the flue gas releases electrons that charge the particles present in the flue gas. The charged particles are pushed toward the primary collection electrode in the form of the collection plate 5 and the secondary collection electrode in the form of the grid 101, together forming the collection electrode as described above, due to the same polarity electric field, and here they precipitate and stay until they are removed by the automatic cleaning or burning as described above. In known systems, this removal of particles from the collection electrode is e.g. done by use of a brush or by rapping as described above.

[0072] The grid 101 which is arranged in the part of the flow passage 4 delimited by the collection plate 5 comprises a mesh-like structure. In the illustrated embodiment, the grid 101 is in the form of a mesh e.g. made from wire-material, but it could also be a plate with holes. The mesh-like structure of the grid 101 is of an electrically conductive material, and the grid 101 is dimensioned, shaped and arranged such that it extends along and at a distance from the collection plate 5.

[0073] The particles are collected both on the grid 101 and on the collection plate 5, and as described above, this arrangement significantly improves the efficiency of the ESP compared to similar known systems without such a grid. Both the collection plate 5 and the grid 101 can be made from low or medium carbon steel; it can also be made from stainless steel or alloy steel to obtain a higher corrosion resistance.

[0074] FIG. 2 shows schematically an embodiment of a grid 101 wherein the mesh-like structure of the grid is in the form of a wire fence comprising openings 102 with a vertical and a horizontal dimension. By vertical and horizontal reference is made to the ESP system 1 when installed on a chimney; i.e. with the inlet 2 facing downwards and the outlet 3 is facing upwards. The vertical dimension of a grid 101 may be 15-30 mm, such as 18-25 mm, such as 20-22 mm, and the horizontal dimension may be 15-30 mm, such as 18-25 mm, such as 20-22 mm. Grids 101 having openings 102 of such dimensions have been tested during the development of the present invention, but other dimensions are also covered by the scope of the claims. The wire fence sheet has been cut to the size matching the inner dimensions of the collection plate 5 and installed with a clearance 103 inside the collection plate 5 as shown in FIG. 1. Hereby it is obtained that the grid 101 can move freely, i.e. without touching the collection plate, and when it slides up and down along the collection plate 5 in the embodiment described below. Thereby, it can detach the collected particles. This part of the cleaning due to the movement is in addition to the cleaning related to the burn-off of the particles as described above.

[0075] A characteristic of some embodiments of the present invention is a built-in possibility of regularly cleaning the grid 101 by removing the particles collected thereon in order to improve the efficiency of the ESP. This cleaning can be performed by the system itself so that a chimneysweeper does not need to have direct access in order to perform the cleaning e.g. by use of a brush as is of the case in known systems. Furthermore, with an ESP system 1 according to the present invention, the cleaning can be performed regularly, such as daily, and not just once or twice a year as is typically the case with traditional systems.

[0076] In the illustrated embodiment, the cleaning of the collection electrode, in the form of the collection plate 5 and the grid 101, is established by an actuator 112 which can provide a force to the grid 101 so as to move the grid 101, when the actuator 112 is in operation. FIG. 5 shows schematically an example of such an actuator 112 comprising an electric motor 104 having an eccentric cam 105 mounted on a shaft 106 which can be rotated by the electric motor 104. The cam 105, when seen along the axis of rotation, has a shape that is generally rectangular with two rounded corners 107, the rounded corners 107 being opposite each other in both directions, such that the slope of the rounded corners 107 extends to a sharp edge 108; see FIG. 6. This shape with two sharp edges 108 has the effect of causing the grid 101 to drop as soon as the contacting means, see below, clear the sharp edge 108. This results in the most efficient accelerating effect due to gravity and thereby a high impact force when the grid 101 hits an internal bottom structure 109; see FIG. 4.

[0077] The grid 101 has a contacting means which extends from the grid 101. In the embodiment in FIGS. 1 and 2, the contacting means is a pin 110 arranged on the flat side surface of the grid 101 which pin 110 goes out through a slit 111 in the collection plate 5; see FIG. 5. In this embodiment of the invention, the electrical motor 104 with low rotational speed, such as below 100 rpm, causes the double-eccentric cam 105 to move the grid 101 upward. In tests performed with a prototype of the invention, the dimensions of the cam 105 were so that the upward movement of the grid 101 was about 25 mm. After being moved upwards, the grid 101 drops from this height due to gravity resulting in the grid 101 impacting on the internal bottom structure 109 of the ESP system 1. This internal bottom structure 109 is typically also a supporting base for the grid 101 when it is not being moved; i.e. when no cleaning due to impact is performed. In addition to the impacting action, cleaning is also established by friction between particles on the grid 101 and on the collection plate 5. The distance between the grid 101 and the collection plate 5 should preferably be chosen so that this friction is large enough to detach particles and low enough to allow the grid 101 to fall fast enough to impart the impact resulting in further removal of particles from the grid 101.

[0078] With the illustrated shape of the cam 105, every rotation of the motor 104 slides the grid 101 twice against the collection plate 5, and correspondingly the grid 101 falls on the internal bottom structure 109 twice. Every time the grid 101 hits the internal bottom structure 109, its impact helps to shake the particles off the grid 101.

[0079] The cleaning process can be activated in cold conditions, where no hot flue gas is present with the high voltage generator 12 shut off to prevent elutriation of the detached particles and prompt free fall of the particles, respectively. Alternatively, when the ESP is hot, where there is hot flue gas in the chimney with the high voltage generator 12 turned on to prevent the detached particles from leaving the ESP to the outside.

[0080] Embodiments of the ESP system 1 having an actuator 112 preferably further comprises a control system (not shown), which controls when the actuator 112 is in operation and for how long; i.e. that the actuator 112, when in operation, runs for a period of time during which the grid is moved a number of times.

[0081] FIG. 7 shows schematically an example of a discharge electrode 11 which may be used in an ESP system 1 as described above. Other types of discharge electrodes providing a suitable electrical field are also covered by the scope of the present invention. The discharge electrode 11 comprises a first wire connector 201 and a second wire connector 202, which are connected to and separated a distance apart by a support rod 203. The distance between the first and second wire connectors 201,202 may be 50 to 300 mm shorter than the vertical length of the collection plate 5, such as 100-200 mm shorter. A discharge electrode 11 wherein the distance between the first and second wire connectors 201,202 was of such a dimension has been tested during the development of the present invention, but other dimensions are also covered by the scope of the claims.

[0082] A discharge electrode connector 204 is attached to the support rod 203 of the discharge electrode 11 and located at a distance from the first and second wire connectors 201,202. The optimum location of the discharge electrode connector 204 will depend on a number of parameters and possible further characteristics of the system in which the discharge electrode 11 is to be used.

[0083] In the embodiment shown in FIG. 7, the discharge electrode 11 has ten wires 205 suspended between the first and second wire connectors 201,202, but a discharge electrode 11 according to the invention may have more or less than ten wires 205 suspended between the two wire connectors 201,202. The wires 205 may have a characteristic width of 0.20-3.0 mm, such as 0.30-1.0 mm, such as 0.35-0.45 mm. Wires 205 having a diameter of 0.40 mm have been successfully used in the embodiment shown in FIG. 1, however, the optimum thickness of the wires 205 will depend on a number of parameters and possible further characteristics of the ESP system 1.

[0084] In the embodiment in FIG. 7, the first and second wire connectors 201,202 are disks each of which are shaped substantially as a circular segment. Furthermore, in the embodiment in FIG. 7, the first end 206 of the support rod 203 is mounted within a central region of the first wire connector 201 and a second end 207 of the support rod 203 is mounted within a central region of the second wire connector 202 with the wires 205 arranged around the support rod 203. In the illustrated embodiment, the wires 205 are situated at the edges of the first and second wire connectors 201,202 and distributed around the circumference of the disks with the wires 205 being substantially parallel to the support rod 203.

[0085] The discharge electrode connector 204, the first and second wire connectors 201,202, the support rod 203, and the wires 205 are all made of electrically conductive material. They may e.g. be made of corrosion-resistant material throughout or be made from another material having an outer coating of corrosion resistant material. They may also be made of different corrosion-resistant materials.

[0086] An ESP system 1 according to the present invention can e.g. be mounted on top of an existing chimney of a house, or it can be mounted to a chimney as part of the construction work when the house is being build. A grid 101 as described above, possibly movable by an actuator 112, can also be added to an existing ESP system 1 originally intended to be cleaned e.g. by use of a brush or other applied methods. The dimensions of the prototype tested during the development of the invention have been chosen for a small-scale system for use on private houses.

[0087] However, the scope of the claims are not limited to systems of this size; it also covers systems applicable for industrial large-scale use.

[0088] Although the present invention has been described in connection with the specified embodiments, it should not be construed as being in any way limited to the presented examples. The scope of the present invention is set out by the accompanying claim set. In the context of the claims, the terms comprising or comprises do not exclude other possible elements or steps. In addition, the mentioning of references such as a or an etc. should not be construed as excluding a plurality. The use of reference signs in the claims with respect to elements indicated in the figures shall also not be construed as limiting the scope of the invention. Furthermore, individual features mentioned in different claims, may possibly be advantageously combined, and the mentioning of these features in different claims does not exclude that a combination of features is not possible and advantageous.