Patent Application
20230158513
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 continuously washed off by both an irrigating film of liquid 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 poor equipment performance with requires deleterious downtime and unnecessary expense in an effort to remove them. This has been seen in 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 industry challenge that degrades performance for all WESP styles and designs.
Current industrial practice has been to try to clean the build-up in the WESP with warm water (100-130° F.), caustic solution, or a weak acid solution. In almost all cases the cleaning solution is injected into the WESP through stationary nozzles that cover a broad area to cover all surfaces of the WESP using a minimum number of nozzles to reduce cost. This spreads the mass flux of the liquid across a large area (e.g., 0.05 to 0.25 lbs/(ft2*s)) so there is not much energy hitting the dirty surfaces. Therefore, loose material can be removed, but material that is adhered to the surfaces is not removed. Also, since the spray is typically sprayed at a wide angle (90 degrees), very little of the spray penetrates to a depth of more than a foot in the honeycomb structure.
Accordingly, a method of maintaining the collecting tubes and electrodes in a clean condition with minimal manual cleaning required would be highly beneficial.
It is therefore an object of embodiments disclosed herein to incorporate multiple components in a WESP to provide a much greater impaction energy over areas expected to collect most of the particulate and therefore expected to get the dirtiest.
It is a further object of embodiments disclosed herein to minimize the amount of liquid used to clean a WESP.
Problems of the prior art have been addressed by embodiments disclosed herein, which provide a method and apparatus for cleaning pollution control equipment, such as particulate removal devices, including wet electrostatic precipitators, and to provide a particulate removal device including such cleaning apparatus. In certain embodiments, the WESP includes a housing having a chamber, at least one gas inlet in fluid communication with the chamber, a gas outlet spaced from the at least one gas inlet and in fluid communication with the chamber, one or more ionizing electrodes in the housing and one or more collecting electrodes or surfaces in the housing. In some embodiments, the collecting electrodes include a bundle of tubes or cells, which may be cylindrical or hexagonal in cross-section. In some embodiments, bundle of hexagonal in cross-section. In some embodiments, the bundle of tubes forms a honeycomb pattern of hexagonal collecting zones or cells. In certain embodiments, the housing may be placed in fluid communication with a washing liquid source, such as a water source.
In certain embodiments, a particulate removal device, such as a WESP, having movable spray nozzles is provided, wherein the movement of the nozzles is designed so that fluid expelled therefrom impacts all or substantially all of the regions in the WESP where particulate build-up deleterious to the electrostatic performance of the WESP is expected or observed. Efficient and substantially homogeneous cleaning of the collection surfaces is achieved, such as by impact of a mass flux of a washing liquid on each surface element of the particulate collection surfaces over a certain impact time. In some embodiments, the mass flux comprises a spray emitted from the nozzles, which may be a flat fan spray that concentrates a high mass of liquid moving at a moderate velocity (e.g., 30-120 ft/sec) in a small area. In certain embodiments, the particulate removal device is an upflow WESP, and one or more lower movable spray nozzles is provided in a lower plenum upstream of the particulate collection surfaces and is capable of spraying washing liquid towards the collection surfaces to cause impaction cleaning of the same. In some embodiments, one or more upper spray nozzles is provided, which may be movable, positioned downstream of the particulate collection surfaces. The primary function of the one or more upper spray nozzles is to rinse the collection surfaces, and/or to introduce cleaning agents such as sodium hydroxide or sulfuric acid to enhance cleaning.
Embodiments disclosed herein include a particulate removal device for removing particulate from a process gas, the device comprising: a housing comprising a lower plenum having a gas inlet for the introduction of process gas into the housing; a gas outlet for discharge of treated process gas from the housing; at least one ionizing electrode; at least one particulate collection electrode; the lower plenum being in fluid communication with the at least one ionizing electrode and the at least one particulate collection electrode; an upper support frame; a lower support frame connected to the upper support frame and comprising at least one electrode support beam supporting the at least one ionizing electrode; and at least one movable nozzle in the lower plenum for discharging washing liquid towards the at least one collection electrode to dislodge particulate matter from the at least one collection electrode. Preferably the at least one particulate collection electrode is tubular.
In one exemplary embodiment, the at least one movable nozzle is rotatable about a vertical axis. In some aspects the particulate removal device further comprises a support shaft in the lower plenum and having a longitudinal axis, the support shaft supporting one or more rotational arms having at least one nozzle positioned thereon, and wherein the one or more rotational arms is adapted to rotate about the longitudinal axis. In some aspects, there are plurality of nozzles positioned on the one or more rotational arms. In some aspects, one of the plurality of nozzles is angled relative to vertical to provide hydraulic motive energy to the one or more rotational arms, whereby discharging liquid through the angled nozzle causes rotation of the one or more rotational arms.
In another exemplary embodiment, there is an upper nozzle assembly positioned in the housing downstream, in the direction of process gas flow from the inlet to the outlet, of the at least one particulate collection electrode.
In some embodiments, disclosed is a method for cleaning a collection surface of a particulate separation device, in which the collection surface is sprayed with a washing liquid over a cleaning interval, wherein a partial region of the collection surface is sprayed with a minimum quantity of washing liquid for a minimum treatment period, and wherein the washing liquid acts on the partial region with a momentum which varies in time over the minimum treatment period and is effective for dislodging particulate matter adhered to the collection surface.
In some embodiments, the angle of action of the washing liquid relative to a surface normal to the partial region does not remain constant over the minimum treatment period; e.g., it is varied.
In some embodiments, the at least one nozzle is moved or is movable relative to the partial region in such a way that a distance between the at least one nozzle and the partial region varies over the minimum treatment time. In some embodiments, the at least one nozzle is moved or is movable relative to a surface normal to the partial region in such a way that a liquid jet is emitted from the at least one nozzle at an angle varying with the surface normal to the partial region during the minimum treatment period. In some embodiments, the mass flow of the washing liquid is not constant over the minimum treatment period; e.g., it is varied. In some embodiments, the washing liquid is supplied to the one or more nozzles with a varying pressure and/or volume flow. In some embodiments, the outflow from the one or more nozzles varies in time and/or location. In some embodiments, the at least one movable nozzle is mounted on a nozzle device and is movable in at least one degree of freedom with respect to the nozzle device. In some embodiments, the at least one nozzle comprises a fluidic oscillator.
In certain embodiments, a method of removing particulate matter from a contaminated gas supply is disclosed, the method comprising supplying washing liquid to at least one of movable nozzle in a plenum of a particulate removal device comprising one or more ionizing electrodes, one or more particulate collection electrodes or surfaces, at least one inlet for the contaminated air and at least one outlet, the plenum being in fluid communication with the one or more ionizing electrodes and the one or more particulate collection electrodes, and discharging said washing liquid from said nozzle towards said one or more collection electrodes impacting regions of said one or more particulate collection electrodes with said washing fluid emitted from said at least one or more movable nozzles to dislodge particulate from said particulate collection electrodes to clean the same. In some embodiments, the plurality of movable nozzles is upstream, in the direct of gas flow from the inlet to the outlet during operation of said particulate removal device. A source of high voltage for charging the one or more ionizing electrodes may be provided.
In certain embodiments, there are a plurality of electrode support beams and a plurality of ionizing electrodes each having a free end and a supported end supported on one of the plurality of electrode support beams, wherein the free end is downstream, in the direction of process gas flow from the gas inlet to the gas outlet during operation of the device, of the supported end.
In certain embodiments, the particulate removal device is an up-flow WESP, where gas is introduced below the one or more ionizing electrodes and flows vertically upwardly in the device.
In certain embodiments, the device is compartmentalized, or modularized, wherein there are two or more units 100 in a single particulate removal device such as a WESP. In certain embodiments, the WESP has three or more modules. In some embodiments, one of the plurality of modules can be isolated from the others, taken offline and subjected to a cleaning cycle, while the remaining module or modules continue to operate to remove particulate from the process gas stream.
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 openended 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.
In certain embodiments, an upper or downstream (in the direction of process gas flow from the inlet 12 to the exhaust 14) high voltage frame 40 (
In some embodiments, where the lower high voltage frame 41 is supported from the upper high voltage frame 40, it may be so supported by one or more support electrodes 37, preferably four, and supports a plurality of rigid electrode support beams 49, which in turn support electrodes or masts 50. In certain embodiments, the rigid electrode support beams 49 are spaced and positioned in a parallel horizontal array, each respectively supporting a plurality of masts 50. Each of the plurality of masts 50 may be generally elongated and rod-shaped and extends upwardly into a respective cell 30A, and is preferably positioned in the center of each cell 30A and is coaxial therewith. Since in this embodiment the masts 50 are supported from the bottom by the plurality of rigid electrode support beams 49, their free ends are downstream, in the direction of process gas flow form the inlet to the outlet, of their supported ends. Preferably the masts 50 are relatively short (e.g., less than 12 feet long, e.g., 10-12 feet long) to minimize deflection. To further minimize deflection, the walls of the masts 50 may be thicker than conventional, e.g., 0.083 inches thick. Further still, cross-bracing may be used to prevent sway of the support structure, e.g., insulated rods or struts connecting the upper high voltage frame 40 and/or lower high voltage frame 41 to a wall of the WESP. In certain embodiments, the volume of each cell 30A defined by its outer wall or walls is empty except for a mast 50. As can be seen in
By supporting the masts 50 from the bottom rather than the top, cleaning of the collecting surfaces is not inhibited, and better access to the unit for maintenance is provided because there are minimal high voltage members above the array 30 of cells 30A. The masts 50, when positioned within each cell 30A and connected to a high voltage source, maintain the array 30 of cells 30A at a desired voltage. In certain embodiments, the electrical 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 other embodiments, the lower high voltage frame 41 may be supported from top wall mounted insulators, or may be supported from electrical insulators mounted in insulator compartments on the side walls of the WESP, below the at least one collection electrode.
As seen in
In some embodiments the movement of the movement assembly 52 may be adjusted manually. In other embodiments, an automatic control scheme may be used, such as an actuator which may be selected from a hydraulic actuator, a pneumatic actuator, an electro-static actuator, an electro-magnetic actuator, a piezoelectric actuator, an electro-mechanic actuator, an electric motor, and other actuators being capable of a remote activation. In some embodiments, the actuator may be a battery operated sealed electric motor attached to the nozzle that receives a signal to rotate the nozzle to adjust the nozzle speed. Such a signal may be transmitted wirelessly. In other embodiments, a mechanical method such as a pivot arm or a spring loaded moving sleeve using the centrifugal force of the spray system to partially block the hydraulic energy and therefore self-regulate the rotational speed may be used. For example, as shown in
In some embodiments, the nozzle movement assembly 52 is designed for operation in a particulate laden environment, without fouling of the bearings or other components of the movement system. In certain embodiments, large clearances in the movement assembly 52 are designed to allow for this. These clearances take advantage of the fact that minor leakage of the cleaning liquid is not an issue in the design. The nozzle movement assembly 52 also should be capable of operation within a temperature range of about 40 to 200° F.
In certain embodiments, the nozzle movement assembly 52 includes a support shaft 201 and one or more elongated rotational arms 202 supported by the support shaft 201. Suitable bearings are provided so that the elongated rotational arm 202 can rotate about central hub 203 of the support shaft 201. As seen in
Accordingly, in certain embodiments, the bearings may be designed with loose tolerances to allow movement in a dirty environment, minimizing friction losses and taking advantage of the fact that leaks through bearing seals are tolerated and not an issue to the operation of the nozzle movement assembly 52.
In certain embodiments, one or more spray nozzles 305 are provided on each of the rotational arms 202 such that spray discharged from the spray nozzles 305 impacts the cells 30A or collecting surfaces at an impaction angle. Preferably substantially all surfaces of the collection electrode below the maximum height that can be reached by the washing liquid discharged from the spray nozzle(s) 305 (based on the angle the washing liquid is discharged from the nozzle(s) are directly impacted by the washing liquid. In certain embodiments, this angle is between about 12a and about 30° relative to vertical. Although A 90° impact angle (i.e. perpendicular) provides the greatest cleaning energy, such an angle is not achievable since spray must be introduced above or below the collecting surfaces or cells 30A. A further consideration on impact angle is the distance into each cell 30A the spray can reach. The shallower (closer to 0°) the angle of impact, the further the spray can reach, but the lower the energy that impacts the cell walls. Accordingly, an angle of 12° to 30° to vertical has been found to be preferred to provide as much energy as possible while retaining impaction energy a reasonable distance into the collection tube array 30. The distance that can be reached into a collection tube is a function of the diameter/width of the collection tube. It is preferable, therefore, to use wider and shorter tubes to maximize the cleanability of the tubes. In one preferred embodiment, 16 inch wide by 10 feet long hexagonal tubes are used with 23° impact angle of the spray system, which allows impaction cleaning approximately 3′ or approximately ⅓ of the way into the tube.
In certain embodiments, the spray nozzles 305 are spaced along the elongated rotational arms 202 to cover all of the collection surfaces in the array 30 as the rotational arms 202 rotate about the longitudinal axis of the support shaft 201. In certain embodiments, both the support shaft 201 and the one or more rotational arms 202 include an internal passage and are in fluid communication with each other, so that washing liquid from a washing liquid source introduced into the support shaft 201 with a driving force such as a pump, can flow from the support shaft 201, to the one or more rotational arms 202, and into each nozzle 305, from which the washing liquid is ultimately discharged. Preferably two rotational arms 202 extend coaxially radially outwardly from the hub 203 on each nozzle movement assembly 52, and the energy of the cleaning sprays are balanced opposite each other on the two rotational arms 202.
In various embodiments, a hydraulic pulse generator 450 (
In some embodiments as shown in
In some embodiments, rotation of the nozzle movement assembly 52, and of the rotational arms 202 in particular, may be effectuated by positioning one or more angled nozzles 210 on one or more of the rotational arms 202, so that hydraulic energy is used to drive the rotation of the rotational arms 202. Preferably the angled nozzle 210 is positioned at or near the free end of a rotational arm 202, and is positioned at an angle of 35 to 65 degrees relative to vertical. In some embodiments, there are plurality of spray nozzles 305 that are positioned at the same angle relative to vertical (e.g., 0°), and a single angled nozzle 210 that is positioned at the aforementioned angle of 35 to 65 degrees, and therefore is also angled with respect to the plurality of spray nozzles 305. Discharging washing liquid through the one or more angled nozzles 210 causes rotation of the rotational arm 202. In certain embodiments, the angle of the one or more angled nozzles 210 may be adjustable, so as to adjust the speed of rotation of the rotational arms 202. In embodiments where a spray nozzle 305 is threaded onto the rotational arm 202, the adjustment can be made by loosening or tightening the spray nozzle 305 via relative rotation of the nozzle and the rotational arm 202. Rotational speeds up to about 10 rpm are suitable. Higher speeds could be used, but do not offer any advantage and require more energy to achieve. A fluid pressure range of about 40-100 psig is suitable to achieve the objectives discussed herein.
In certain embodiments, more than one such nozzle movement assembly 52 can be positioned upstream of the cells 30A, as needed, so as to ensure spray coverage of a module effective to clean all desired surfaces.
In certain embodiments, multiple nozzle assemblies may be installed at different elevations (relative to horizonal) to allow for an overlapping spray pattern for improved cleaning without the assemblies potentially interfering with each other.
In certain embodiments the support shaft 201 may be angled up to 15° from vertical such that assembly 52 is angled up to 15° from horizontal. The purpose of this embodiment would be to allow a different angle of impaction within the tube to improve cleaning. Each of the multiple assemblies 52 may be installed at the same or different angle as necessary to achieve desired cleaning. Suitable angles include from about 3° to about 15°, more preferably from about 5° to about 10°. Thus, angles from about 3°, 4°, 5°, 6°, 7°, 8°, 9°, 10°, 11°, 12°, 13°, 14°, and 15° may be suitable.
In certain embodiments, one or more downstream nozzle assemblies 520 may be provided downstream of (e.g., above) the cells 30A or collection surfaces, as seen in
In certain embodiments, it may be desirable to optimize the spray pattern of the washing liquid discharged from the nozzles 305. The use of fan nozzles that emit flat fan sprays 300 that concentrate a high mass of liquid at moderate velocities in a small area may be used, as shown in
In an alternative embodiment, an electric motor may be used as the driving energy to drive the rotation of the rotational arms 202. Multiple pipes may be used with the spray nozzles inserted along the length of the pipe, as shown in
In an alternative embodiment, with reference to
In certain embodiments, recirculating liquid may be used in place of fresh water or other clean liquid. As shown in
In some embodiments such as that shown in
In certain embodiments, hotter liquid, such as recirculating water, may be used in the spraying system for improved cleaning. Higher temperatures increase the solubility of nearly all solids. By using higher temperature cleaning liquid, the effectiveness of the cleaning can be enhanced substantially. Typical temperature ranges of from 150 to 180° F. are suitable.
In certain embodiments, the cleaning may be performed when the process flow through the WESP module is offline. If the process is online through the WESP during a cleaning cycle, essentially no particulate is being removed because the power must be shut off during a cleaning cycle. Therefore, the cleaning cycle time must be relatively short (<5 minutes) because of regulatory or downstream process requirements. Cleaning the module offline allows the system to take extended time for cleaning while minimizing the downstream impact by maintaining the particular removal of the gas in other WESP modules in parallel with the module being cleaned. The extended offline cleaning can enhance the use of common cleaning chemicals such sodium hydroxide or sulfuric acid by allowing these chemicals time to react with the buildup before being rinsed off, which can greatly improve the removal efficiency. Another benefit of this embodiment is that none of the mist created during the washing cycle is carried downstream of the equipment, since there is no airflow during the cleaning cycle.
If the WESP is an upflow design, another embodiment is to include a rinsing flow from the top of the WESP either during or at the conclusion of the impaction cleaning performed at the bottom of the WESP. This rinsing flow can either be stationary or moving as described for the impaction cleaning sprays. The rinsing sprays provide a method of rinsing off any solids loosened and pushed up in the WESP by the lower impaction sprays.
A final rinse of the WESP with fresh water after the cleaning cycle is finished may be carried out. This final cleaning cycle serves to remove residual solids left when the recirculating water is turned off as well as to flush any residual solids out of the wash piping.
Consider a 3 module upflow WESP system treating 150,000 ACFM of polluted air. Timers in the control system initiate the cleaning cycle for one of the modules. The following steps may be performed.
This application claims priority of U.S. Provisional Application Serial No. 63/033,375 filed Jun. 2, 2020 and U.S. Provisional Application Serial No. 63/056,940 filed Jul. 27, 2020, the disclosures of which are incorporated herein by reference in their entireties.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/US2021/016729 | 2/5/2021 | WO |
| Number | Date | Country | |
|---|---|---|---|
| 63033375 | Jun 2020 | US | |
| 63056940 | Jul 2020 | US |
