Patent ID: 12189406

DETAILED DESCRIPTION

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 gas 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 collecting electrodes or plates that attract and remove electrically-charged particulate matter and intermixed liquid droplets from the gas stream; and a source of sealing liquid. The purpose of the sealing liquid is to create a barrier to prevent gas flow. Any liquid could be used provided it has a high enough density that the level of the liquid is sufficient to create a pressure differential greater than the gas flow can overcome. In certain embodiments, the one or more collecting surfaces includes one or more elongated tubes or cells. In some embodiments, the tubes or cells are hexagonal in cross-section.

Referring now toFIGS.1and1A, an exemplary WESP unit100is shown and is an upflow design having a vertical orientation. An upflow design has certain advantages, which include eliminating the need for demisting at the outlet, allowing for liquid and solid contaminants to collect by gravity before they reach (and potentially contaminate) the collection electrodes, and enabling a simplified layout if exhausting directly to a stack. A further advantage of an upflow device is that any water droplets present are carried upward by the airflow, and eventually caused to collect on the collecting surfaces. As a result, the upflow device functions as a demister, preventing any droplets from becoming entrained in the gas flow that exits the device. Similarly, during a flush cycle of a particular compartment, where the gas flow ceases, water droplets cannot become entrained because no gas flow is leaving the compartment being flushed. However, other designs may be used, including downflow designs.

In some embodiments, the unit100has one or more lower process gas inlets12and one or more upper outlets or exhausts14spaced from the one or more lower process gas inlets12. The one or more lower process gas inlets12may be in fluid communication with suitable ducting or the like to direct process gas in a generally upward flow to be treated by the unit100towards collection surfaces that may include an array30of a plurality of cells30A (FIG.1A). In certain embodiments, the location of the one or more process gas inlets12in the chamber10is below or upstream, in the direction of process gas flow, of the array30of cells, and is located so that the chamber can be flooded with liquid in amount sufficient to submerge the one or more inlets12and stop gas flowing therefrom.

Preferably the cells30A in the WESP are hexagonal in cross-section. The array30of cells30A is provided in the unit100in a region between the one or more inlets12and the outlet14. The array30of cells30A can be supported in the unit100by any suitable means, such as from the side and/or the bottom by supporting the outer perimeter of the array30with the use of angle irons36or similar supports. In certain embodiments, the array30may be formed by coupling individual plates or walls in the desired shape such as by welding. As can be seen in the embodiment ofFIG.1A, adjacent cells30A share common walls and form an array. The number of cells30A in an array30is not particularly limited; any array size is suitable, although smaller arrays are easier to ship in an assembled condition. In the embodiment shown, the array30is a 5/6×7 array (the term “5/6” is used to indicate that the rows of cells alternate between 5 and 6 cells or tubes per row).

In certain embodiments, an upper high voltage frame40and a lower high voltage frame41are suspended from the top wall46of the unit100with suitable supports including one or more support rods (three shown as45A,45B and45C). The lower high voltage frame41is supported from the upper high voltage frame40by one or more support electrodes37, preferably four, and supports a plurality of electrodes or masts50. Each of the plurality of masts50may be generally elongated and rod-shaped and extends upwardly into a respective cell30A, and is preferably positioned in the center of each cell30A and is coaxial therewith. In certain embodiments, the volume of each cell30A defined by its outer wall or walls is empty except for a mast50. In some embodiments each of the masts50is attached to the lower high voltage frame grid with a single bolt or other fastener, and each mast50can be pre-aligned prior to assembly into the unit100. In some embodiments, suitable position adjusters can be provided on the masts50to properly position them in the unit100. By supporting the masts50from the bottom rather than the top, cleaning of the collection surfaces is not inhibited, and better access to the unit for maintenance is provided because there are minimal high voltage members above the array30of cells30A. In addition, it allows for increasing the surface area of the collection surfaces if desired. The masts50, when positioned within each cell30A, maintain the array30of cells30A at a desired voltage. In certain embodiments, the potential difference between the masts50and 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, washing liquid such as water can be periodically introduced into the unit and applied to the array30of cells30A to dislodge particular matter that has collected on the collection surfaces. The washing liquid may or may not be the same as the sealing liquid provided that they are compatible because the washing and sealing liquid will mix with each other. For example, it may be desirable for the washing liquid to have additives that will dissolve the material to removed. These additives would not be required in the sealing liquid. In certain embodiments, a source of wash liquid (not shown), which may include a plurality of nozzles, may be positioned above (downstream of) the collecting tubes15and may be placed in fluid communication with a liquid source such as water.

In some embodiments, a gas distribution device, such as a perforated plate70, may be provided downstream of the lower high voltage grid41and masts50, to help distribute the process gas evenly through the cells30A, with similar residence times in each.

In certain embodiments, the device is compartmentalized, or modularized, wherein there are two or more units100in a single particulate removal device such as a WESP. In some embodiments, there are three or more such modules.

One advantage of an up-flow device is that any water droplets present are carried upward by the airflow, and are eventually caused to collect on the collection plates. As a result, the up-flow device functions as a demister, preventing any droplets from becoming entrained in the gas flow that exits the device. Similarly, during a flush cycle of a particular compartment, which causes the gas flow to cease, water droplets cannot become entrained because no gas flow is leaving the compartment being flushed.

In certain embodiments, the internal volume of the bottom chamber region10below or upstream (in the direction of gas flow during normal operation) of the collection electrodes30A can be reduced, such as by including a half-pipe or barrel member76or the like, which occupies volume that would otherwise be occupied by sealing liquid during a flushing cycle. In some embodiments, no liquid can occupy the region underneath the half-pipe or barrel member76.

FIG.2illustrates the flow of process gas during operation of the WESP100in accordance with certain embodiments. In the embodiment shown, there are a plurality of wave-reducing baffles310that may be shaped to accommodate the half-pipe76. In some embodiments, the baffles310are spaced from one another along the length of the half pipe76, and are generally parallel with the front and rear walls of the unit100(see alsoFIG.2A). Each of the baffles310may have a semi-circular cut-out that that allows it to accommodate the half=pipe76as shown. An additional baffle311may be positioned orthogonal to the baffles310and may bisect each baffle310as shown. The baffle arrangement helps reduce wave formation as the chamber region10of the module is flooded with liquid in an amount effective to stop gas flow into the module, and may also help direct flow of the process gas towards the collection electrodes as shown by the arrows312inFIG.2. Waves can inhibit the speed at which the seal is achieved by allowing a gas flow path until the valley of the waves is of sufficient height to inhibit flow. Those skilled in the art will appreciate that other baffle arrangements may be used to achieve acceptable process gas flow distribution and/or wave formation inhibition.

FIG.2also illustrates a pair of spaced side chambers450(one shown) having a plurality of flow diverter baffles or vanes400. In certain embodiments, the flow diverter baffles400include a plurality of spaced plates that extend vertically from the base or floor105of the WESP100. A portion of one or more of the diverter baffles400, such as the upper portion, may be angled or bent as shown, such at about a 45aangle, and terminates in a free end. Arrays of spaced diverter baffles400may be positioned in each of the side chambers450on opposite sides of the WESP100, such as along the opposite side walls100′,100″, with each array adjacent to a divider wall122. Each divider wall122is spaced from a respective side wall100′,100″, and delimits a side chamber450. A generally horizontally extending top wall123extends from the top of each divider wall122towards a respective side wall100′,100″. Each divider wall122extends downwardly from the top wall123, and terminates above the base or floor105of the WESP100. Accordingly, the diverter baffles400function by diverting process gas flow to the region between the bottom of each diverter wall122and the floor105, out of the side chamber105and towards the baffles310, as illustrated by arrows401. The diverter baffles400create a gas flow direction change that encourages particulate drop out before the gas reaches the collection tubes. One or more of the top walls123may have an access opening124for maintenance purposes. If present, the access opening124should be closed and sealed during operation so that the water seal functions properly. In a preferred option said access opening124can be designed as openable and closable sealable door, hatch or cover or covered/closed by a removable sealing plate.

FIGS.3-5illustrate exemplary configurations of the gas inlet(s)12. In certain embodiments, the gas inlet(s)12should be configured to allow flooding of the chamber with sealing liquid while gas is flowing, such that the sealing liquid ultimately overwhelms the gas flow and results in shutoff of that flow into the chamber. For example, in the embodiment shown inFIGS.3A and3B, gas inlet pipe11A is elbow shaped, and has an outlet opening111A facing towards the bottom of the WESP chamber10, such that the gas flow through the gas inlet pipe11A and out the outlet opening111A is as depicted by the arrows. Once sufficient sealing liquid200submerges the outlet opening111A to a sufficient extent, the gas flow out the outlet opening111A ceases. The sealing liquid overwhelms the gas flow by increasing the resistance to this flow. Resistance to flow through a device is measured by pressure drop. The higher pressure drop, the greater the resistance. Pressure drop through a WESP is usually measured in units of inches (or millimeters) of water column (wc) with a typical range of 1 to 4 inches (25 to 101 millimeters). During normal operation with a multiple module system the gas flow and pressure drop through each module will be approximately equal. As sealing liquid is introduced to one module, the pressure drop in that module increases and more gas flow will go to other modules to balance the pressure drop. When the level of sealing liquid the gas would have to flow through exceeds the pressure drop of all the gas flowing through the other modules the gas flow through this module will cease.

For example, consider a three-module system in which the pressure drop through each module is typically 2 inches of water column. A first module begins filling with sealing liquid, forcing more gas flow through the second and third modules. Eventually all of the gas flow through needs to flow through the second and third modules, increasing the flow through each of these by 50%. Using the square law of flow vs. pressure in the turbulent flow regime, this will increase the pressure drop through the second and third modules by the square of the increase in flow. In this example, the pressure drop would increase to 4.5 inches of water column (2 inches×1.52). Once the sealing liquid level the gas would need to flow through exceeds 4.5 inches of water column, gas flow through the first module will cease.

In the embodiment shown inFIGS.4A and4B, gas inlet pipe11B has a plurality of nozzles111B that function as outlet openings facing downwardly towards the bottom of the chamber10, such that the gas flow through the gas inlet pipe11B and out the nozzles111B is as depicted by the arrows. Once sealing liquid200submerges the nozzles111bto a sufficient extent, the gas flow out the nozzles111bceases. In certain embodiments, there are two arrays of nozzles111B, the nozzles in each array being linearly aligned.

In the embodiment shown inFIG.5, gas inlet pipe11C has an open end111C, and a spaced hood112C is positioned over the open end111C as shown. The region between the hood112C and the open end111C allows for inlet gas to flow into the chamber, as depicted by the arrows. Once sealing liquid200submerges the region between the hood112and the open end111C to a sufficient extent, the gas flow out ceases.

In certain embodiments, the process gas inlet pipe or pipes is positioned in the WESP in a region of the chamber where a sufficient level of liquid can be introduced so as to ultimately submerge the process gas inlet pipe opening(s) and cease gas flow emanating therefrom.

FIGS.6A-6Cshow schematically the reduction and eventual complete cessation of gas flow as a result of a liquid flush in accordance with certain embodiments. As shown inFIG.6A, chamber10has two spaced inlet openings12that allow for gas flow into the outer regions10A of the chamber10, as depicted by the arrows. Gas flows uninhibited from the outer regions10A, under the dividing walls122and into the center10B of the chamber10, as shown by arrows500. InFIG.6B, the introduction of sealing liquid200has begun, and the sealing liquid200begins to accumulate at the base (in this embodiment shown as sloped) in the chamber10and begins to flood the chamber. Some gas is still able to flow from the outer regions10A, percolate through the sealing liquid200, flow under the dividing walls122and enter the center10B of chamber10, but there is a reduction in gas flow due to the presence of the sealing liquid200. InFIG.6C, the dividing walls122are now sufficiently submerged in the sealing liquid200, preventing gas flow from the outer regions10A to the center10B of chamber10. Due to the modular design of the apparatus, all gas flow is now directed into the one or more additional units that are not undergoing a flushing cycle. The module undergoing the flush may be isolated from the remaining module(s) for an extended period of time, without losing significant efficiency in the overall particulate matter removal process as compared to cleaning a module online, where the particulate removal efficiency of that module approaches 0% during the cleaning cycle.

In certain embodiments, sealing liquid may enter the chamber of the WESP such as by one or more wash liquid inlets211(FIG.1, two shown) that are in fluid communication with a sealing liquid source.

Another significant advantage of cleaning a module offline is preventing mist carryover during the cleaning cycle. During online cleaning, some of the washing liquid is always carried out of the WESP as a mist by the gas flow through the system. Mist carryover can damage downstream equipment and/or be carried out an exhaust stack resulting in a “dirty rain”. It is therefore desirable to minimize mist carryover to the greatest extent possible.

Once sufficient time has elapsed where the module undergoing the flush is clean, the sealing liquid may be removed from the chamber10through one or more suitable drains. As the level of sealing liquid in the chamber decreases, it no longer overwhelms the gas flow into the chamber10, and the unit returns to its online status as gas flow resumes.

It will be appreciated by those skilled in the art, that isolation of the module for offline cleaning could also be accomplished by dampers to stop the gas flow. However, using sealing liquid to isolate a module has several advantages. The first is that in this dirty environment the dampers may get buildup on the sealing surfaces and may seal less effectively over time. The liquid seal will maintain a better seal over time. Another advantage is that buildup removed from the WESP during the cleaning cycle will fall into the seal liquid where it will be more readily removed from the module as the system is drained. A third advantage is eliminating the cost of a large moving component in the process gas stream.

Another preferred embodiment is that near the end of the flood cycle (the last 2 to 4 inches), the liquid level is raised quickly to achieve shut off of the process gas flow, on the order of 60 seconds or less. During this time, the final stage of the gas flow shutoff, there may be aggressive mixing between the process gas and sealing liquid. This can cause some of the sealing liquid to be entrained into the process gas and be carried into the electric field causing lower electric field strength and reduced cleaning performance during this time period. Therefore minimizing this time period is preferred.

Another preferred embodiment is to use the recirculated water that is commonly used to saturate the process gas in these applications as the source of the liquid for the liquid seal of process gas flow in the system. The advantage of using this liquid is that it does not add any additional liquid to the process system that may be needed to be discharged from the system after completing the wash cycle. Thus, In certain embodiments, recirculating liquid may be used in place of fresh water or other clean liquid. As shown inFIG.7A, recirculating liquid may be used continuously to quench the process gas to saturation temperature which is required for proper operation of the WESP. The embodiment ofFIG.7Auses fresh water from a suitable source (e.g., city water500) to supply washing fluid to the upper and/or lower spray nozzles as shown. Thus, a WESP recirculation tank502and a suitable driving force such as one or more pumps505are provided to supply the quench sprays510for quenching the process gas as it is introduced into the WESP, and a flush tank503and a suitable driving force such as one or more pumps506are provided to supply fresh water to the upper and/or lower spray nozzles. The flush tank503can be located inside of the recirculation tank502as shown inFIG.15Ato heat the flush water using the heat from the recirculating water, which is typically 10 to 15 F less than the saturated air temperature. In practice this heats the flush water to approximately 40 to 60 F less than the recirculating water. In certain embodiments, the WESP has a fluid drain512in fluid communication with the recirculation tank502through suitable ductwork or the like. The use of fresh water limits the amount of water that can be used during the flush to less than or equal to the amount of water that is evaporated by saturating the gas and the amount of water that is removed through the system blowdown507. Otherwise water will accumulate in the system.

In some embodiments such as that shown inFIG.7B, recirculating liquid also may be used as a source of washing fluid supply. Using this liquid for cleaning collection surfaces allows a much larger volume of liquid to be used for cleaning without impacting the accumulation of water in the system. The recirculating water typically has a substantial amount of solids in it (between 2-4% by weight). Accordingly, the liquid may be filtered or screened to remove larger solids (typically greater than ⅛″). Therefore, as discussed above the spraying components may be designed to function while flowing the particulate laden water. As shown inFIG.7B, Water from the recirculation tank502′ is used as the source of washing fluid to the upper and/or lower spray nozzles and to the quench sprays510′ as shown. A suitable driving force such as one or more pumps505′ are provided to supply the quench sprays510′ for quenching the process gas as it is introduced into the WESP, and to supply recirculating water to the upper and/or lower spray nozzles. In certain embodiments, the WESP has a fluid drain512′ in fluid communication with the recirculation tank502′ through suitable ductwork or the like. In this case, fresh water from a suitable source (e.g. city water500′) is only used as make-up water as needed to balance the system from evaporation losses and system blowdown507′.

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.