Patent Application
20230173507
Pollution control equipment, such as wet electrostatic precipitators (WESP) are used to remove dust, acid mist and other particulates from water-saturated air and other gases by electrostatic means. For example, particulates and/or mist laden water-saturated air flows in a region of the precipitator between discharge and collecting electrodes, where the particulates and/or mist is electrically charged by corona emitted from the high voltage discharge electrodes. As the water-saturated gas flows further within the precipitator, the charged particulate matter and/or mist is electrostatically attracted to grounded collecting plates or electrodes where it is collected. The accumulated materials are continuous washed off by both an irrigating film of water and periodic flushing to a discharge drain or the like.
Such systems are typically used to remove pollutants from the gas streams exhausting from various industrial sources, such as incinerators, coke ovens, glass furnaces, non-ferrous metallurgical plants, coal-fired generation plants, forest product facilities, food drying plants, wood product manufacturing and petrochemical plants.
In wood product manufacturing in particular, for example, maintenance issues are problematic, particularly due to material build-up on the collectors and on electrodes. Sticky particulates, condensation products, etc. tend to adhere to and accumulate on equipment internals, resulting in deleterious downtime and unnecessary expense in an effort to remove them. This has been seen not only in the manufacture of wood products such as panelboard, for example, but also in the biofuel and other markets. Manual intervention is often necessary to adequately clean the equipment internals from the build-up of contaminants, which is highly undesirable. Dirty WESP tubes and electrodes are thus a persistent wood products industry challenge that degrades performance for all WESP styles and designs.
In almost all existing industrial WESP or dry ESP design, the majority of the particulate collection occurs at the inlet of the precipitator. This is more pronounced as the design efficiency of the precipitator increases. A removal efficiency of 90-98% is a typical range for a single stage WESP in many present applications. Using the standard Deutsch-Anderson equation for estimating WESP performance in this range it can be shown that the first ¼ of WESP removes approximately 49-64% of the particulate and the last ¼ of the WESP removes only 3-9% of the particulate. There are other factors that influence this distribution, but this is a reasonable estimate. Current industry standards use tube lengths in the 7 to 20 foot range, with 12 to 14 feet most common. In order to provide modular and shippable systems, tube length is ideally limited to 10 feet in height, and therefore achieving the equivalent tube height of more than 10 feet in the given space is desirable. In addition, the shorter the tube is, the shorter the emitting electrode is (often a rod or pipe with spikes or discs). Shorter electrodes are mechanically stiffer, creating less oscillation from airflow and are easier to align. Good alignment or centering of electrodes is critical to any electrostatic collector.
It therefore would be desirable to increase the effectiveness of the collection surfaces such as collection electrode tubes in an electrostatic collector, without substantially increasing the height of the collection surfaces (or the collector). One advantage of doing so would be the provision of a modular electrostatic collector unit that is readily shippable without sacrificing particulate collection efficiency.
Problems of the prior art have been addressed by the embodiments disclosed herein, which provide an electrostatic collector or precipitator with improved effectiveness of electrode collectors, and a method of removing particulate from a process stream with such an electrostatic collector. In certain embodiments, a wet electrostatic precipitator is disclosed, which includes a housing, at least one gas inlet in fluid communication with the housing, at least one gas outlet or exhaust spaced from the at least one gas inlet and in fluid communication with the housing, one or more ionizing electrodes or current emitters in the housing adapted to be connected to a high voltage source, and one or more collection electrodes in the housing, wherein the one or more ionizing electrodes are spaced from the one or more collection electrodes to effect a corona discharge between them. In certain embodiments, the one or more collection electrodes may include a bundle or array of elongated tubes or cells, which may be, for example, circular, square, rectangular or hexagonal in cross-section, or may be plate type, and one or more collection electrode extensions or surface area enhancing members in electrical communication with at least one respective collection electrode. In some embodiments, the collection electrodes form an array of cells, and the number of collection electrode extensions equals the number of cells in the array. In some embodiments the number of collection electrode extensions may be less than the number of cells in the array. In some embodiments the cells are hexagonal in cross-section and form a honeycomb pattern of repeating, hexagonal collecting zones or cells, and the collection electrode extensions also have a hexagonal cross-section. In certain embodiments, each of the ionizing electrodes is supported from the bottom and extends vertically upwardly into a respective one of the collection electrodes. In various embodiments, a lower high voltage grid or support may be used to support the one or more ionizing electrode masts. This lower high voltage grid may be supported from insulators mounted to the top wall or roof of the WESP using one or more of the ionizing electrodes as a support, or from insulators mounted in the side walls of the WESP located below the collecting electrodes, or from an upper high voltage grid that is in turn supported from insulators mounted in either the top wall (roof) or side wall of the WESP above the collection electrodes.
In certain embodiments, the electrode extensions substantially increase the surface area of the surface available for particulate collection, without substantially increasing the height of the collection electrodes. For example, the electrode extensions can include surface area increasing components, such as a plurality of spaced fins that provide additional particulate collecting surface area without requiring a corresponding increase in vertical height of the collection electrodes. In some embodiments, each collection electrode extension or surface area enhancing member(s) is positioned downstream, in the direction of process gas flow, of a respective collection electrode. In other embodiments, each collection electrode or surface area enhancing member(s) is positioned within at least a portion of the interior volume of a collection electrode, downstream, in the direction of process gas flow, of an ionizing electrode position within an interior volume region of a respective collection electrode. In this embodiment, the surface area enhancing member or members may be attached to the wall or walls of the collection electrode itself.
Thus, certain aspects relate to an electrostatic precipitator, comprising: a housing having an inlet for a gas process stream and an outlet spaced from the inlet for exhausting treated gases, a particulate collection surface comprising one or more collection electrodes positioned within the housing between the inlet and the outlet, one or more ionizing electrodes in the housing, each ionizing electrode being associated with a respective collection electrode, and at least one collection surface extension or surface area enhancing member or members in electrical communication with at least one collection electrode, the collection surface extension comprising. For example, a plurality of spaced fins. In various embodiments, a lower high voltage grid or support may be used to support the one or more ionizing electrode masts. This lower high voltage grid may be supported from insulators mounted to the top wall or roof of the WESP using one or more of the ionizing electrodes as a support, or from insulators mounted in the side walls of the WESP located below the collecting electrodes, or from an upper high voltage grid that is in turn supported from insulators mounted in either the top wall (roof) or side wall of the WESP above the collection electrodes.
In certain embodiments there are a plurality of collection electrodes having a hexagonal cross-section and forming a honeycomb array of hexagonal cells. In certain embodiments, there may be a plurality of collection surface extensions, and each collection surface extension may comprise a hexagonal perimeter. In various embodiments, each collection surface extension may be supported on a respective collection electrode and in electrical communication therewith. In some embodiments, each collection surface extension may comprise an outer wall and an inner wall spaced from said outer wall, and wherein the plurality of spaced fins extend from the outer wall to the inner wall. In some embodiments, the inner wall may be eliminated, and the fins extend from one region of the outer all to another region of the outer wall. In some embodiments, each collection electrode extension may be mechanically supported on a respective collection electrode by one or more supports providing aligned interconnections between the collection electrode and the collection electrode extension. Each such support may be a slotted cylindrical tube. In certain embodiments, each cell has a cell surface area and cell height, each collection surface extension has a collection surface extension surface area and a collection extension surface height, and the collection surface extension surface area may be at least four times greater than the cell surface area for each cell height equivalent height to the collection surface area height. In some embodiments, the collection surface extension surface area may be at least eight times greater than the cell surface area for each cell height equivalent height to the collection surface area height. In some embodiments, the collection surface extension surface area may be as much as 20 times greater than the cell surface area for each cell height equivalent height to the collection surface area height. In certain preferred embodiments the collection surface extension surface area is 8 to 12 times the cell surface area for each cell height equivalent height to the collection surface area height.
In other embodiments, each surface enhancing member or members is positioned internally of a collection electrode. For example, each ionizing electrode may be associated with a respective collection electrode, each collection electrode having an internal volume having a first region occupied by its respective ionizing electrode and at least a second region unoccupied by said ionizing electrode, wherein at least a portion of the second region is occupied by surface area enhancing member or members. The wall or walls of the collection electrode may take the place of the outer wall of the collection surface extension and support the surface enhancing member or members (e.g., fins) in a similar manner as the outer wall of the collection surface extension. Accordingly, the surface enhancing member or members occupy an internal region of the collection surface electrode, downstream, in the direction of process gas flow, of the ionizing electrode that is also positioned in an internal region of the collection electrode.
In its methods aspects, disclosed herein are methods of removing particulate material from a process stream by introducing the process stream into the electrostatic precipitator described above, and causing the particulate material to collect on the collection electrodes and collection extensions.
Thus, certain aspects relate to a method of removing particulates from a process stream, comprising: providing a particulate removal device comprising a housing having at least one ionizing electrode charged by a high voltage source, at least one collection electrode, at least one inlet for said process stream, at least one outlet spaced form said inlet, and at least one collection surface extension or surface area enhancing member in electrical communication with said at least one collection electrode; creating a corona discharge between said at least one ionizing electrode and said at least one collection electrode; introducing the process stream into the inlet whereby the process stream contacts the at least one collection electrode; causing particulates in the process stream to deposit on the collection electrode and collection surface extension or surface area enhancing member(s); and removing the deposited particulates from the collection electrode and collection electrode extension or surface area enhancing member(s).
For a better understanding of the embodiments disclosed herein, reference is made to the accompanying drawings and description forming a part of this disclosure.
The embodiments disclosed herein may take form in various components and arrangements of components, and in various process operations and arrangements of process operations. The drawings are only for purposes of illustrating preferred embodiments and are not to be construed as limiting. This disclosure includes the following drawings.
A more complete understanding of the components, processes and apparatuses disclosed herein can be obtained by reference to the accompanying drawing. The figures are merely schematic representations based on convenience and the ease of demonstrating the present disclosure, and is, therefore, not intended to indicate relative size and dimensions of the devices or components thereof and/or to define or limit the scope of the exemplary embodiments.
Although specific terms are used in the following description for the sake of clarity, these terms are intended to refer only to the particular structure of the embodiments selected for illustration in the drawing, and are not intended to define or limit the scope of the disclosure. In the drawing and the following description below, it is to be understood that like numeric designations refer to components of like function.
The singular forms “a,” “an,” and “the” include plural referents unless the context clearly dictates otherwise.
As used in the specification, various devices and parts may be described as “comprising” other components. The terms “comprise(s),” “include(s),” “having,” “has,” “can,” “contain(s),” and variants thereof, as used herein, are intended to be open-ended transitional phrases, terms, or words that do not preclude the possibility of additional components.
All ranges disclosed herein are inclusive of the recited endpoint and independently combinable (for example, the range of “from 2 inches to 10 inches” is inclusive of the endpoints, 2 inches and 10 inches, and all the intermediate values).
As used herein, approximating language may be applied to modify any quantitative representation that may vary without resulting in a change in the basic function to which it is related. Accordingly, a value modified by a term or terms, such as “about” and “substantially,” may not be limited to the precise value specified, in some cases. The modifier “about” should also be considered as disclosing the range defined by the absolute values of the two endpoints. For example, the expression “from about 2 to about 4” also discloses the range “from 2 to 4.”
It should be noted that many of the terms used herein are relative terms. For example, the terms “upper” and “lower” are relative to each other in location, i.e. an upper component is located at a higher elevation than a lower component, and should not be construed as requiring a particular orientation or location of the structure. As a further example, the terms “interior”, “exterior”, “inward”, and “outward” are relative to a center, and should not be construed as requiring a particular orientation or location of the structure.
The terms “top” and “bottom” are relative to an absolute reference, i.e. the surface of the earth. Put another way, a top location is always located at a higher elevation than a bottom location, toward the surface of the earth.
The terms “horizontal” and “vertical” are used to indicate direction relative to an absolute reference, i.e. ground level. However, these terms should not be construed to require structures to be absolutely parallel or absolutely perpendicular to each other.
Embodiments disclosed herein include apparatus for removing particulate matter from a process stream containing particulate matter, and may include a mist-generating member that mixes a gas stream entering the apparatus with liquid droplets; one or more ionizing electrodes that electrically charge the particulate matter and the liquid droplets; one or more collecting surfaces such as one or more collection electrodes or surface area enhancing member(s) that attracts and enables removal of electrically-charged particulate matter and intermixed liquid droplets from the gas stream; and a source of washing fluid. In certain embodiments, the one or more collecting surfaces include one or more elongated tubes or cells. In some embodiments, the tubes or cells are hexagonal in cross-section. In other embodiments, the tubes or cells are circular, rectangular or other polygonal shape in cross-section. Preferably the tubes or cells are hexagonal in cross-section, are repeating, and are configured in a bundle to form a honeycomb array. In some embodiments, each cell 30A has a diameter of 16 inches and is 10 feet in length. Preferably each cell 30A is the same size. A honeycomb arrangement is efficient in minimizes wasted space; a hexagonal structure uses the least material to create a lattice of cells within a given volume. The cells employed in the electrostatic precipitator may be constructed of any convenient construction material consistent with their function, including carbon steel, stainless steel, corrosion- and temperature-resistant alloys, lead and fiberglass reinforced plastics. In certain embodiments, the cells are at ground potential during operation of the unit. The one or more ionizing electrodes may also provide collecting surfaces.
In certain embodiments, the WESP unit 100 is an upflow design, which eliminates the need for demisting at the outlet, allows for liquid and solid contaminants to collect by gravity before they reach (and potentially contaminate) the collection electrodes, and enables a simplified layout if exhausting directly to a stack. However, other designs may be used, including downflow designs.
Referring now to
In some embodiments, the unit 100 has a lower inlet 12 and an upper outlet or exhaust 14 spaced from the lower inlet 12. The lower inlet 12 may be in fluid communication with suitable ducting or the like to direct process gas in a generally upward flow to be treated by the unit 100 towards collection surfaces that in the embodiment shown include an array 30 of a plurality of cells 30A (
In certain embodiments, the volume of each cell 30A defined by its outer wall or walls is empty (i.e., devoid of structural material) except for a mast 50. In some embodiments, the furthermost downstream region of the volume of one or more cells 30A, in the direction of process gas flow (e.g., the region near the free end of the cell 30A closest to the outlet 14 of the unit 100), is occupied by one or more surface enhancing members. In some embodiments, that portion of volume is a volume of the cell 30A that is not occupied by a mast 50. In some embodiments each mast 50 can be pre-aligned prior to assembly into the unit 100. The masts 50 when positioned within each cell 30A maintain the array 30 of cells 30A at a desired voltage. In certain embodiments, the potential difference between the masts 50 and the collection surfaces is sufficient to cause current flow by corona discharge, which causes charging of the particulate entrained in the process stream.
In certain embodiments, water can be periodically introduced into the unit and applied to the array 30 of cells 30A to dislodge particular matter that has collected on the collection surfaces. A gas distribution device, such as a perforated plate 7, may be provided to help distribute the process gas evenly through the cells 30A, with similar residence times in each.
In certain embodiments, the effective length of one or more collection surfaces such as cells 30A in the array 30 of cells 30A may be increased by providing one or more high area grounded trap collection surface extensions or surface enhancing members 90, as can be seen for example in
As seen in
In an embodiment where the surface area enhancing member or members 90 are positioned within the internal volume of a cell 30A, the wall or walls of the cell 30A itself may be used to support the surface area increasing components or fins 110, such as in the same manner as the outer slotted plates 101.
In some embodiments, the center region 115 of the extension 90 is defined by one or more inner walls which may be inner slotted plates 121, which delimit the region 115 which is devoid of fins 110. The region 115 devoid of fins 110 may be advantageously positioned at the center of the extension 90 to facilitate drainage of water downward in the WESP, which may help rid the collection surfaces of the cell 30A to which the extension is associated of debris. In other embodiments, the region 115 can be eliminated, with the fins 110 extending through the diameter of the extension 90.
In some embodiments, each fin 110 has one or more end tabs 112 that facilitate attachment of the fin 110 to an inner slotted plate 121 by penetrating through a slot 113 in the plate 121, preferably two vertically spaced and aligned slots 113. Other ways to attach each fin 110 to the inner slotted plate 121 may be used, in which case the inner slotted plates may not need to be slotted and the fins may not require end tabs. The fins 110 thus extend radially from the outer slotted plates 101 to the inner slotted plates 121 as shown, and provide surface area for collection of particulates. In certain embodiments, the length of each fin 110 (e.g., from outer slotted plate 101 to inner slotted plate 121) is more than one times the height of the fin 110, preferably 2 or more times the height of each fin 110. In some embodiments, the surface area of an extension 90 is greater than eight times the surface area of the equivalent cell 30A height. An advantage of the extensions 90 is the reduction of the migration distance for particulate to travel until it contacts a collection surface, such as a reduction to less than ⅛ of the distance particulate must travel to contact a surface in a cell 30A.
In certain embodiments, the fins 110 are equally spaced. In certain embodiments, the spacing between fins 110 is such that there are no gaps greater than about 2 inches. In certain embodiments, the spacing between fins 110 is 0.125 to 1.0 inches. In some embodiments, the fins 110, when assembled in the extension 90, define a substantially flat or planar top surface as seen in
In certain embodiments the ionizing electrode mast 50, could extend through the extension 90. In this embodiment the mast would need to be covered in an insulating material such as ceramic where it passes through the extension to prevent an electrical short circuit. This is not a preferred embodiment because a conducting material, most notably water, could deposit on the outside of the insulating material and provide an electrical path between the ionizing electrode mast 50 and the extension 90 causing an electrical short circuit.
Other ways to increase the effective surface area of the collection surfaces without substantially increasing their height, such as by similarly attaching fins or other members to the ends of one or more cells 30A (or internally of one or more cells (30A) in a different configuration, e.g., concentric circles or hexagons, are contemplated and within the scope of the embodiments disclosed herein.
In certain embodiments the extensions 90 could be mounted and in electrical communication with bottom of collecting electrodes. Such an arrangement may be preferred if the process flow through the WESP was downflow. This is not a preferred embodiment in applications with high particulate loading because all of collected particulate would need to be washed through the extension and the smaller gaps in the extensions could potential plug and require manual cleaning.
Turning now to
In certain embodiments, the lower high voltage frame 41 is supported from the high voltage frame 40 by one or more support electrodes 37, preferably four. By providing the lower high voltage frame 41 in this way, the collection surface extensions 90 can be easily accommodated in the unit 100.
The support electrodes 37 may support a plurality of rigid electrode support beams 49 (
In certain embodiments, as shown in
In certain embodiments, during operation of the precipitator 100, a particulate-laden process stream is introduced into the inlet or inlets 12 of the unit and is directed upwardly towards the outlet or outlets 14. A corona discharge is effected between ionizing electrodes or masts 50 and the collection electrodes such as the array 30 of cells 30A, which causes charged particulate in the gas stream to deposit on the collection surfaces. Accumulated particulate deposits can then be removed such as by washing with a water spray.
While various aspects and embodiments have been disclosed herein, other aspects, embodiments, modifications and alterations will be apparent to those skilled in the art upon reading and understanding the preceding detailed description. The various aspects and embodiments disclosed herein are for purposes of illustration and are not intended to be limiting. It is intended that the present disclosure be construed as including all such aspects, embodiments, modifications and alterations insofar as they come within the scope of the appended claims or the equivalents thereof.
This application claims priority of U.S. Provisional Application Ser. No. 63/033,374 filed Jun. 2, 2020, the disclosure of which is incorporated herein by reference in its entirety.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/US2021/016728 | 2/5/2021 | WO |
| Number | Date | Country | |
|---|---|---|---|
| 63033374 | Jun 2020 | US |
