Electrostatic precipitator

Abstract

The present invention provides an electrostatic precipitator for treating a gas stream carrying particulate matter. The electrostatic precipitator comprises a housing defining a chamber, the housing comprising an inlet configured to enable the gas stream carrying particulate matter to enter the chamber, and an outlet configured to enable the treated gas stream to exit the chamber. The electrostatic precipitator further comprises a charging electrode arranged within the chamber towards the inlet, a filter element arranged within the chamber towards the outlet such that to reach the outlet the gas stream passes through the filter element, an insulator element arranged between the charging electrode and the filter element, and a collection electrode configured to be held at electrical earth. The charging electrode is configured to be held at a first high voltage potential such that particulate matter in the gas stream becomes charged as it passes the charging electrode, and the filter element is configured to be held at a second high voltage potential that is greater than the first high voltage potential, such that when the gas stream is conveyed through the filter element to the outlet, charged particulate matter is repelled from the filter element towards the collection electrode. The invention further provides a method for removing particulate matter from a gas stream.

Description

[0001] Electrostatic precipitator

[0002] Field

[0003] The present invention relates to an electrostatic precipitator for treating a gas stream carrying particulate. The present invention also relates to a method for removing particulate matter from a gas stream.

[0004] Background

[0005] Electrostatic precipitators are configured to remove dust and particulate contaminants from gas, for example, from air or from exhaust gases formed as part of an industrial process.

[0006] Typical electrostatic precipitators comprise a collection electrode which is electrically grounded, and a charging electrode to which a high voltage is applied. When a high voltage is applied to the charging electrode, a corona discharge forms between the charging electrode and the collection electrode. As a result, particulates become charged and may be attracted to appropriately grounded collection electrodes by electrostatic force. There is a desire for electrostatic precipitators that can remove particulate matter from a gas stream more efficiently.

[0007] Particulate build up within an electrostatic precipitator can have a detrimental impact upon efficient operation of an electrostatic precipitator device. A build-up of particulate matter can cause short circuiting and / or a corona discharge to form in a manner which does not support efficient overall operation of the electrostatic precipitator device. There is a desire for electrostatic precipitators where the build-up of particulate matter is avoided.

[0008] The present invention aims to solve, at least in part, these and other problems associated with electrostatic precipitators of the prior art.

[0009] Summary

[0010] In an aspect, the present invention provides an electrostatic precipitator for treating a gas stream carrying particulate matter. The electrostatic precipitator comprises a housing defining a chamber. The housing comprises an inlet configured to enable the gas stream carrying particulate matter to enter the chamber. The housing further comprises an outlet configured to enable the treated gas stream to exit the chamber.

[0011] The electrostatic precipitator further comprises a charging electrode arranged within the chamber towards the inlet. The electrostatic precipitator further comprises a filter element arranged within the chamber towards the outlet such that to reach the outlet the gas stream passes through the filter element. The electrostatic precipitator further comprises an insulator element arranged between the charging electrode and the filter element. The electrostatic precipitator further comprises a collection electrode. The collection electrode is configured to be held at electrical earth.

[0012] The charging electrode is configured to be held at a first high voltage potential such that particulate matter in the gas stream becomes charged as it passes the charging electrode. The filter element is configured to be held at a second high voltage potential that is greater than the first high voltage potential such that when the gas stream is conveyed through the filter element to the outlet, the charged particulate matter is repelled from the filter element towards the collection electrode.

[0013] Advantageously, embodiments according to the present invention may provide efficient filtering of particulate matter from the gas stream. The electrostatic precipitator may effectively protect downstream devices, for example catalysts, from fouling by removing particulate matter from the gas stream. This may be particularly beneficial in instances wherein the downstream device is costly to repair or replace, and / or wherein the downstream device is prone to fouling. The electrostatic precipitator of the present invention may increase the mean time between servicing.

[0014] The gas stream may be an exhaust gas stream from an industrial process. For example, the gas stream may be an exhaust gas stream from a deposition process. It will be appreciated that the composition of the particulate matter may depend on the application. The particulate matter may comprise solid particles. In some cases, the particulate matter may comprise silica particles. Typically, the gas stream may be carrying fine particulate matter. For the purposes of the present invention, fine particulate matter may consist of particles that are less than 2.5 micrometres in diameter (i.e. PM2.5). In some cases, the fine particulate matter may be defined as particles having a diameter of from about 0.1 micrometre to about 1 micrometre.

[0015] The chamber may be defined by an inwardly facing surface of the housing. Preferably, the chamber may be generally cylindrical. However, it will be appreciated that the chamber may be any suitable shape. Preferably, the chamber may be arranged such that a central axis of the chamber is generally vertically aligned when in use. Preferably, when in use, the inlet may be arranged below the outlet. Preferably, when in use, the inlet may be arranged at or towards the bottom of the chamber, and / or outlet may be arranged at or towards the top of the chamber.

[0016] For the purposes of the present invention, the gas stream being “treated” may refer to the removal of some or all of the particulate matter from the gas stream. In some embodiments, the gas stream being treated may refer to the removal of some or all of the fine particulate matter from the gas stream.

[0017] The charging electrode may be arranged at or towards the inlet of the housing. Preferably, a central axis of the charging electrode is coaxial with the central axis of the chamber. The charging electrode may be separated from the surface defining the chamber by a gap. It will be appreciated that the shape, number, and location of the charging electrode may be changed to improve the system characteristics. Preferably, the charging electrode may comprise one or more protrusions. The protrusion(s) may have a needle-like or wire construction. The protrusion(s) may have a generally circular cross-section, preferably having a diameter of from about 0.3 mm to about 4 mm. The protrusion(s) may have a length of from about 5 mm to about 30 mm.

[0018] The charging electrode may be coupled to a power supply. The housing may comprise an electrical feed-through to enable the charging electrode to be coupled to a power supply.

[0019] The filter element may be arranged at or towards the outlet of the housing. Preferably, a central axis of the filter element may be coaxial with the central axis of the chamber. Additionally, or alternatively, the central axis of the filter element may be coaxial with the central axis of the charging electrode. Preferably, the filter element may be connected to the charging electrode. The filter element may be electrically isolated from the charging electrode by the insulator element.

[0020] The filter element may be an openwork porous or mesh structure. The filter element may be configured to allow gas to pass through it. Whilst the particulate matter may be small enough to theoretically pass through the filter element, the high voltage potential at which the filter element is held during use may repel the charged particulate matter. The filter element may act as a physical barrier to prevent larger particulate matter from passing through.

[0021] The insulator element may comprise an electrical insulator. The insulator element may be configured to electrically separate the charging electrode from the filter element. The insulator element may be configured to couple the charging electrode and the filter element. The dimensions and features of the insulator elements may depend on various factors including the charging electrode, the filter element, their respective voltage potentials. The insulator element may comprise one or more electrical feedthroughs.

[0022] The collection electrode may be maintained at electrical earth (i.e. about 0V) during operation of the electrostatic separator. In other words, the collection electrode may be grounded. The collection electrode may be separated from the charging electrode by a gap.

[0023] The charging electrode may be configured to generate electrons by means of corona discharge. The generated electrons may ionise the molecules of the gas stream. Ionised gas molecules within the electrostatic precipitator device combine with particulate matter carried in the gas stream. As a result, the particulate matter may become charged.

[0024] Some of the charged particulate matter may be attracted to the collection electrode as soon as it is charged. When the charged particulate matter nears the filter element, it may be repelled away from the filter element due to the high voltage potential. The filter element may be configured to repel charged particulate matter and prevent it passing through the filter. The filter element may be configured to repel the charged particulate matter away from the outlet. The filter element may be configured to repel the charged particulate matter generally radially outwardly. The charged particulate matter may stick to the collection electrode.

[0025] Advantageously, the filter element may provide an electrical field barrier that may substantially prevent the particulate matter from leaving the chamber through the outlet. This may provide more effective treatment of the gas stream. Additionally, the filter element may provide a physical barrier to particulate matter leaving the chamber through the outlet, although this mechanism is not the preferred method of treating the gas stream.

[0026] Typically, a surface of the housing defining the chamber may provide the collection electrode. Preferably, the inner surface of the housing may provide the collection electrode. Additionally, or alternatively, a coating or layer attached to the housing may provide the collection layer. Advantageously, this may provide a space efficient arrangement by integrating the collection electrode into the housing surface.

[0027] The second high voltage potential may be up to about 4 kV greater than the first high voltage potential. Preferably, the second high voltage potential may be from about 1 kV to about 4 kV greater than the first high voltage potential. Advantageously, this may improve the ability of the filter element to repel the charged particulate matter during use.

[0028] Typically, the first high voltage potential may be from about 20 kV to about 25 kV. Preferably, the first high voltage potential may be about 22 kV. Additionally, or alternatively, the second high voltage potential may be up to about 30 kV.

[0029] Typically, during use, the electric field generated may be from about 300 kV / m to about 400 kV / m.

[0030] Typically, the electrostatic precipitator may further comprise an outlet duct. The outlet duct may be configured to convey the treated gas stream to the outlet. The outlet duct may comprise a substantially electrically insulating material. The outlet duct may be connected to the filter element. Preferably, the outlet duct may consist of a substantially electrically insulating material. Preferably, the outlet duct may comprise a glass. The outlet duct may be a generally tubular duct. Preferably, the outlet duct may be a glass generally tubular duct. The outlet duct may be connected at a first end to the filter element, and at a second end to the housing. Advantageously, the outlet duct being an insulator material may electrically isolate the filter element from the grounded housing. Furthermore, the outlet duct being an insulator may reduce the likelihood of the charged particulate matter sticking to the outlet duct.

[0031] Build-up of wet particulate matter on the outlet duct between the filter element and the collection electrode may result in electrical breakdown (i.e. shorting). Therefore, in some embodiments a purge gas flow may be conveyed onto the outlet duct to prevent particulate build-up thereon.

[0032] Preferably, the electrical feedthrough(s) may be arranged on the “clean” side of the filter element. More preferably, the electrical feedthrough(s) may pass through the “clean” side of the outlet duct. In other words, the electrical feedthrough(s) may be arranged such that the particulate matter substantially doesn’t contact the electrical feedthrough. Advantageously, this may reduce the need to perform an insulator purge.

[0033] Typically, the filter element may comprise a generally tubular filter element. It will be appreciated that the filter element may be any alternative geometry, size and configuration. At a first end, the generally tubular filter element may be coupled to the outlet duct. At a second end, the generally tubular filter element may be coupled to the insulator element. Preferably, the filter element may comprise a plurality of concentrically arranged generally tubular layers.

[0034] Preferably, the generally tubular filter element may be arranged such that the central axis of the filter is concentric with the central axis of the chamber. The generally tubular filter element may arranged such that, during use, the gas stream may flow generally radially inwardly through the filter element.

[0035] Typically, the filter element comprises a porous filter element. In some embodiments, the filter element may comprise a metallic foam. Preferably, the metallic foam may be an open cell metallic foam. For example, the metallic foam may comprise a nickel alloy, an iron alloy, or an aluminium alloy.

[0036] Typically, the filter element may comprise a sintered wire element. Preferably, at least one layer of the filter element may comprise a sintered wire element. The wire may be a metallic wire. The wire may be an electrically conductive wire. For example, the wire may comprise stainless steel.

[0037] Typically, the wire may have a generally circular cross-section, or a generally rectangular cross-sectional area. In some embodiments, the wire may include protrusions configured to separate the coils of the wire when coiled to enable gas flow.

[0038] Preferably, the sintered wire element may be a woven sintered wire element. Preferably, one or more layers of the filter element may comprise a Dutch weave. Preferably, one or more layers of the filter element may comprise a helically wound sintered wire element.

[0039] The filter element may be self-cleaning. In other words, the filter may be arranged to have a mechanism to remove particulate build-up from the surface. Whilst the electrostatic precipitator according to the present invention should not suffer from significant particulate build-up on the filter element, it is unlikely to be entirely preventable. The self-cleaning mechanism may comprise stretching and / or compressing and / or twisting and / or rotating the filter element. For example, in some embodiments the self-cleaning mechanism may comprise the application of a tensile force to the filter element, causing the dimensions of the openwork mesh to change. This change may loosen any particulate matter or agglomerates from the surface of the filter element.

[0040] In some embodiments, the filter element may be cleanable by “back-flushing”. In such embodiments, gas may be flowed in a reverse direction through the electrostatic precipitator (i.e. from the outlet to the inlet).

[0041] It will be appreciated that the filter element may comprise a plurality of concentrically arranged layers, which may be substantially the same or different. Adjacent layers may be interconnected or they may be separate.

[0042] Typically, the collection electrode may be a substantially tubular surface. Preferably, the charging electrode may be arranged along a central axis of the collection electrode. There may be a gap between the charging electrode and the collection electrode. The gap may define the shortest distance between the charging electrode and the collection electrode. Typically, the gap between the charging electrode and the collection electrode may be from about 40 mm to about 100 mm. Preferably, the gap may be from about 45 mm to about 70 mm. In embodiments wherein the collection electrode is a substantially tubular surface and the charging electrode is arranged along a central axis thereof, the gap may be measured in a radial direction. Preferably, the gap may be substantially uniform about the charging electrode.

[0043] The size of the gap and the potential voltage applied to the charging electrode may at least in part determine the characteristics of the electric field generated within the electrostatic precipitator. It will be appreciated that these and other features may be varied to optimise the performance of the electrostatic precipitator.

[0044] Preferably, the electrostatic precipitator may further comprise a liquid inlet for conveying liquid into the chamber to provide a liquid curtain on the collection electrode. In other words, the electrostatic precipitator may be a wet electrostatic precipitator (WESP). During use, a flow of liquid may be directed through the liquid inlet onto the collection electrode to provide a liquid curtain. The liquid curtain may clean at least a part of the collection electrode to remove particulate matter or agglomerates thereof. In some embodiments, the flow of liquid may comprise a continuous or pulsed flow of gas configured to clean at least one collection electrode surface in the electrostatic precipitator. The liquid may comprise, for example, water or an aqueous solution.

[0045] Advantageously, this may improve the efficiency of the electrostatic precipitator. Buildup of particulate matter on the collection electrode may be detrimental to the performance of the electrostatic precipitator. Particulate build-up may reduce the size of the gap between the collection electrode and the charging electrode, which may lead to intermittent electrical arcing, or a full electrical shortage.

[0046] Typically, the electrostatic precipitator may further comprise a purge gas inlet. The purge gas inlet may be configured to convey a purge gas into the chamber. Preferably, the purge gas inlet is configured to convey a purge gas onto the outlet duct of the chamber. The purge gas inlet may be configured to substantially prevent particulate build-up on the outlet duct. Particularly, in embodiments wherein the electrostatic precipitator is a wet electrostatic precipitator, the purge gas inlet may be configured to keep the glass outlet duct dry.

[0047] In some embodiments, the electrostatic precipitator may comprise a first power source connected to the charging electrode, and a separate second power source connected to the filter element.

[0048] In a further aspect, the present invention provides a method for removing particulate matter from a gas stream. The method comprises the steps of providing an electrostatic precipitator according to any preceding aspect or embodiment. The method further comprises the step of generating a first high voltage potential at the charging electrode and a second high voltage potential at the filter element. The method further comprises the step of conveying a gas stream carrying particulate matter into the chamber through the inlet. The method further comprises the step of conveying the gas stream carrying particulate matter across the charging electrode. The method further comprises the step of conveying the gas stream through the filter element such that charged particulate matter is repelled from the filter element towards the collection electrode. The method further comprises the step of conveying the treated gas stream through the outlet.

[0049] Advantages and further features of the method may be as set out in relation to embodiments of the previous aspect.

[0050] The method may further comprise the step of conveying liquid into the chamber to provide a liquid curtain on the collection electrode. Preferably, this step may occur whenever the gas stream carrying particulate matter is being conveyed into the chamber.

[0051] Further particular and preferred aspects are set out in the accompanying independent and dependent claims. Features of the dependent claims may be combined with features of the independent claims as appropriate, and in combinations other than those explicitly set out in the claims. Where an apparatus feature is described as being operable to provide a function, it will be appreciated that this includes an apparatus feature which provides that function or which is adapted or configured to provide that function.

[0052] Brief Description of Figures

[0053] Preferred features of the present invention will now be described, with reference to the following figures in which:

[0054] Figure 1 shows a cross-sectional view of an electrostatic precipitator in accordance with an embodiment of the present invention;

[0055] Figure 2 shows a flow diagram of a method in accordance with an embodiment of the present invention.

[0056] Detailed Description of Figures

[0057] Figure 1 illustrates a cross-sectional view of an electrostatic precipitator (1 ) in accordance with an embodiment of the present invention.

[0058] The electrostatic precipitator (1 ) is configured to treat a gas stream carrying particulate matter. The electrostatic precipitator (1 ) comprises a housing (2) defining a chamber. In this embodiment, the chamber defined by the housing (2) is generally cylindrical. The housing (2) comprises an inlet (3). The inlet (3) is arranged at a first end of the chamber. During operation, the gas stream carrying particulate matter is conveyed into the chamber through the inlet (3).

[0059] The housing further comprises an outlet duct (4). The outlet duct (4) is configured to convey the treated gas stream to the outlet of the chamber. The outlet duct (4) is arranged at a second end of the chamber, opposite the inlet (3). In this embodiment, the outlet duct (4) comprises a glass duct.

[0060] The electrostatic precipitator (1 ) further comprises a charging electrode (5). The charging electrode (5) is arranged within the chamber towards the inlet (3). The charging electrode (5) is configured to be held at a first high voltage potential during operation. Preferably, the charging electrode (5) is held at a first high voltage potential of about 22 kV. The charging electrode (5) has protrusions extending generally radially outwardly. The electrostatic precipitator (1 ) further comprises a filter element (6). The filter element (6) is arranged within the chamber towards the outlet duct (4). The filter element (6) is configured to be held at a second high voltage potential during operation. The second high voltage potential is greater than the first high voltage potential. Preferably, the filter element (6) is held at a second high voltage potential of about 26 kV during operation.

[0061] The filter element (6) is a generally tubular filter element. In this embodiment, the filter element (6) comprises a sintered metallic wire mesh.

[0062] The electrostatic precipitator (1 ) further comprises a collection electrode (7). In this embodiment, the inner surface of the housing (2) defines the collection electrode (7). The collection electrode (7) is configured to be held at electrical earth during operation (i.e. ~0 V). The charging electrode (5) is separate from the surface of the housing (2) defining the collection electrode (7) by a gap (G).

[0063] The charging electrode (5) and filter element (6) are separated by an insulator element (8). The insulator element (8) is configured to electrically insulate the charging electrode (5) from the filter element (6).

[0064] During operation, an electric field is generated in the gap because of the potential difference between the charging electrode (5) and the collection electrode (7). A gas stream carrying particulate matter is conveyed into the chamber through the inlet (3). The gas stream is conveyed through the gap (G) between the charging electrode (5) and the collection electrode (7). This leads to a corona discharge effect as the gas stream is conveyed through the gap, ionising molecules of the gas stream. In turn, this results in particulate matter carried by the gas stream becoming charged.

[0065] The gas stream carrying the charged particulate matter is conveyed towards the filter element (6). As a result of the filter element (6) being held at the second high voltage potential, the charged particulate matter is repelled from the filter element (6) towards the collection electrode (2). The “treated” gas stream (i.e. substantially particulate free) then passes through the filter element (6) and exits the chamber through the outlet (4). In this embodiment, the inlet (3), the outlet duct (4), the charging electrode (5) and the filter element (6) are all coaxially aligned with the central axis of the chamber defined by the housing (2).

[0066] Figure 2 illustrates a flow diagram of a method in accordance with an embodiment of the present invention.

[0067] The method comprises the step of providing an electrostatic precipitator according to any embodiment as described elsewhere herein (9). For example, the electrostatic precipitator as described in relation to Figure 1 may be provided.

[0068] The method further comprises the step of generating a first high voltage potential at the charging electrode and a second high voltage potential at the filter element (10). Preferably, the second high voltage potential may be greater than the first high voltage potential. More preferably, the second high voltage potential may be from about 1 kV to about 4 kV greater than the first high voltage potential.

[0069] The method further comprises the step of conveying a gas stream carrying particulate matter into the chamber through the inlet (11 ).

[0070] The method further comprises the step of conveying the gas stream carrying particulate matter across the charging electrode (12). As the gas stream is conveyed across the charging electrode, the particulate matter in the gas stream becomes charged due to the corona discharge present in the gap between the charging electrode and the collection electrode.

[0071] The method further comprises the step of conveying the gas stream through the filter element such that charged particulate matter is repelled from the filter element towards the collection electrode (13). The treated gas stream passes through the filter element.

[0072] The method further comprises the step conveying the treated gas stream through the outlet (14). Reference Key

[0073] 1 . Electrostatic precipitator

[0074] 2. Housing

[0075] 3. Inlet 4. Outlet

[0076] 5. Charging electrode

[0077] 6. Filter element

[0078] 7. Collection electrode

[0079] 8. Insulator element 9. Method step

[0080] 10. Method step

[0081] 11 . Method step

[0082] 12. Method step

[0083] 13. Method step 14. Method step

Claims

Claims1 . An electrostatic precipitator for treating a gas stream carrying particulate matter, the electrostatic precipitator comprising: a housing defining a chamber, the housing comprising an inlet configured to enable the gas stream carrying particulate matter to enter the chamber, and an outlet configured to enable the treated gas stream to exit the chamber; a charging electrode arranged within the chamber towards the inlet; a filter element arranged within the chamber towards the outlet such that to reach the outlet the gas stream passes through the filter element; an insulator element arranged between the charging electrode and the filter element; and a collection electrode configured to be held at electrical earth; wherein the charging electrode is configured to be held at a first high voltage potential such that particulate matter in the gas stream becomes charged as it passes the charging electrode, and wherein the filter element is configured to be held at a second high voltage potential that is greater than the first high voltage potential, such that when the gas stream is conveyed through the filter element to the outlet, charged particulate matter is repelled from the filter element towards the collection electrode.

2. The electrostatic precipitator according to claim 1 , wherein a surface of the housing defining the chamber provides the collection electrode.

3. The electrostatic precipitator according to claim 1 or 2, wherein the second high voltage potential is from about 1 kV to about 4 kV greater than the first high voltage potential.

4. The electrostatic precipitator according to any preceding claim, wherein the second high voltage potential is up to about 30 kV.

5. The electrostatic precipitator according to any preceding claim, wherein the first high voltage potential is from about 20 kV to about 25 kV, preferably about 22 kV.

6. The electrostatic precipitator according to any preceding claim, further comprising an outlet duct configured to convey the treated gas stream to the outlet, the outlet duct comprising a substantially electrically insulating material, preferably wherein the outlet duct is a tubular outlet comprising glass.

7. The electrostatic precipitator according to any preceding claim, wherein the filter element comprises a generally tubular filter element, preferably wherein the filter element comprises a plurality of concentrically arranged generally tubular layers.

8. The electrostatic precipitator according to any preceding claim, wherein the filter element comprises a sintered wire element, preferably a woven sintered wire element.

9. The electrostatic precipitator according to any preceding claim, wherein the filter element comprises a porous filter element.

10. The electrostatic precipitator according to any preceding claim, wherein the collection electrode is a substantially tubular surface, preferably wherein the charging electrode is arranged along a central axis of the collection electrode.

11. The electrostatic precipitator according to any preceding claim, wherein the gap between the charging electrode and the collection electrode is from about 40 mm to about 100 mm, preferably from about 45 mm to about 70 mm.

12. The electrostatic precipitator according to any preceding claim, further comprising a liquid inlet for conveying liquid into the chamber to provide a liquid curtain on the collection electrode.

13. The electrostatic precipitator according to any preceding claim, further comprising a purge gas inlet configured to convey a purge gas into the chamber, preferably wherein the purge gas inlet is configured to convey a purge gas onto the outlet duct of the chamber.

14. The electrostatic precipitator according to any preceding claim, further comprising a first power source connected to the charging electrode and a separate second power source connected to the filter element.

15. A method for removing particulate matter from a gas stream, comprising the steps of: providing an electrostatic precipitator according to any preceding claim; generating a first high voltage potential at the charging electrode and a second high voltage potential at the filter element; conveying a gas stream carrying particulate matter into the chamber through the inlet; conveying the gas stream carrying particulate matter across the charging electrode; conveying the gas stream through the filter element such that charged particulate matter is repelled from the filter element towards the collection electrode; and conveying the treated gas stream through the outlet.

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