WO2015085054A1

WO2015085054A1 - Bidirectional rapping apparatus for electrostatic precipitator electrodes

Info

Publication number: WO2015085054A1
Application number: PCT/US2014/068539
Authority: WO
Inventors: Hajrudin Pasic; Khairul Alam
Original assignee: Ohio University
Priority date: 2013-12-04
Filing date: 2014-12-04
Publication date: 2015-06-11

Abstract

Electrostatic precipitator electrodes are lightweight, thin metal plates and/or bidirectional composite ply sheets. Such lightweight sheets or plates are more efficiently cleaned, because the rapping force requirement is reduced relative to larger conventional electrodes. The mechanism to dislodge dust from the electrode is motion within the plane of the collection surface. A frame is mounted around the collection electrode having upper and lower support members at opposite electrode sides and first and second vertical support members at opposite electrode sides. The upper support member is displaced by application of a tensile force, thereby causing deformation of the electrode due to biaxial tensile stress. In one embodiment, a second tensile loader applies tensile force to a vertical support member.

Description

TITLE

BIDIRECTIONAL RAPPING APPARATUS FOR ELECTROSTATIC PRECIPITATOR ELECTRODES BACKGROUND OF THE INVENTION

[0001] The invention relates generally to electrostatic precipitators, and more specifically to an apparatus for "rapping", which is applying a sharp, sudden force to, the electrodes thereof to dislodge accumulated dust.

[0002] Electrostatic precipitators (ESPs) are described in detail in existing patents, such as United States Patent No. 4,276,056 and United States Patent No. 6,231,643, both of which are incorporated herein by reference. In an ESP, fly ash and other particles are suspended in a gas that flows between electrically charged discharge electrodes and typically electrically grounded collector electrodes on which the dust is collected after being charged by the discharge electrodes. ESPs are widely used in many pollution- control industries. For example, more than 90% of the fly ash produced by coal-burning power plants in the USA is collected and handled in the dry state.

[0003] Collector electrodes are conventionally made of parallel steel plates, about one foot apart, thirty feet tall by ten feet long, about one millimeter thick, reinforced by vertical stiffening ribs about every two feet. The stiffening ribs add to the weight and stiffness of the collector plates. In dry ESPs, after dust is collected, the top edges of the plates are periodically struck by hammers, typically every five to ten minutes, to shake off collected dust into hoppers beneath. Conventional collector plates require a strong, heavy mechanism for vibrating the plates ("rapping") and the ESP system requires strong foundations to support such weight. Both plates and hammers are heavy and expensive in conventional ESPs.

[0004] In United States Patent No. 4,276,056, a system of dislodging dust from a collector plate is described in which collector plates are rapped by pulling (tension) rather than pushing on the top of the collector plates. High frequency stress waves are produced in a collector plate when it is under rapidly induced tensile loading. These stress waves produce strains on the plate that dislodge the dust layer on one or both sides of the plate. Large forces are required when applying such tensile forces to thick, stiff collector plates. Tensile loading can also be difficult to use with thin collector plates because thin plates tend to wrinkle, which is movement perpendicular to the plate's plane, due to contraction in the horizontal direction when pulled vertically, or vice versa. This phenomenon is due to the fact that a vertical tension producing vertical lengthening simultaneously causes horizontal contraction of the plate due to Poisson' s effect, which is well known to those in the field of solid mechanics. Such lateral movement perpendicular to the plate's plane tends to dislodge the collected ash and/or dust too far, thereby pushing it back into the gas flow, which is detrimental to the collection efficiency of the system.

[0005] Therefore, the need exists for an improved collection electrode and/or collection electrode rapping mechanism.

BRIEF SUMMARY OF THE INVENTION

[0006] A lightweight ESP with lower overall cost is achieved by replacing heavy and expensive steel collector electrodes with lightweight, thin metal plates and/or bidirectional composite ply sheets woven with tapes, fibers, fiber tows, strands or other configurations. All of these lightweight plates or sheets can be more efficiently cleaned with light and inexpensive cyclical tension-inducing rapping mechanisms, referred to herein as "shakers". Such lightweight plates and sheets do not require stiffeners in the new rapping mechanisms, so the rapping force requirement is drastically reduced. Therefore, the heavy rapping mechanism can be replaced by lighter, less expensive systems such as pneumatic hammers, for example. The new technology can be used in power plants and numerous other pollution-control industries.

[0007] In the traditional rapping process, plates produce buckle and produce lateral, out-of-plane motion perpendicular to the plane of the plate, leading to dust re- entrainment into the gas flow. In contrast, the mechanisms disclosed herein to dislodge the dust include relative motion within the plane of the collection surface sheet, membrane or ply. Therefore, the new design reduces re-entrainment of the collected dust.

[0008] In one of the embodiments of the new collection electrode, the material is based on the construction of a ply used in the composite fabrication industry, which is a fabric-like layer that can be made by weaving tows or ravings of fibers, or by weaving tapes of already formed composites or other materials, including metal or other conductive strips. Composite tapes can be made by using a polymer matrix with electrically conductive carbon fibers reinforcing the matrix. Regardless of its material composition, the ply is deformed during rapping to produce relative motion between the tapes and thereby dislodge the collected dust.

[0009] The new technology contemplates replacing conventional steel plates with a lighter, thinner collector plate made of metal or any other conductive material, including polymer-based composites. The novel aspect of the design is to apply tension to the collector plate in two different directions (biaxial) simultaneously, so that no buckling occurs in the collector plate. The resulting biaxial stress waves produce strains in two directions and increase the effectiveness of dust dislodgement from the plate. The preferred directions of pulling are vertical and horizontal but others are also contemplated. Ideally constant tension is applied biaxially to avoid buckling, but this tension can be varied at times to induce relative motion among tapes or other independently movable structures woven together.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

[0010] Fig. 1 is a schematic view illustrating an embodiment of the present invention using a thin plate subjected to vertical and horizontal tension.

[0011] Fig. 2 is a schematic side view illustrating the weave pattern of a composite tape.

[0012] Fig. 3 is a schematic view illustrating a magnified section of a composite collection electrode made of woven tapes.

[0013] Fig. 4 is a schematic view illustrating an alternative embodiment of the present invention using a woven collector electrode with a mechanism for providing bidirectional tension.

[0014] Fig. 5 is a front view illustrating an experimental embodiment of the present invention.

[0015] Fig. 6 is a schematic view illustrating another alternative embodiment of the present invention in which the tapes are at a different angle relative to the rapping mechanism compared to the embodiment of Fig. 4.

[0016] Fig. 7 is a schematic view illustrating the details of an alternative embodiment of the rapping mechanism with additional slots and pins to maintain the vertical support bars substantially parallel at all times, thereby mitigating or eliminating buckling of the electrode. [0017] In describing the preferred embodiment of the invention which is illustrated in the drawings, specific terminology will be resorted to for the sake of clarity. However, it is not intended that the invention be limited to the specific term so selected and it is to be understood that each specific term includes all technical equivalents which operate in a similar manner to accomplish a similar purpose. For example, the word connected or terms similar thereto are often used. They are not limited to direct connection, but include connection through other elements where such connection is recognized as being equivalent by those skilled in the art. DETAILED DESCRIPTION OF THE INVENTION

[0018] U.S. Provisional Application No. 61/911,560 filed December 4, 2013 is incorporated in this application by reference.

[0019] In the embodiment shown in Fig. 1, a thin (e.g., up to about 1.0 mm), preferably rectangular collector plate 10 electrode is attached to a rigid horizontal member, such as the support bar 12 all along the lower (in the orientation shown in Fig. 1) edge of the plate 10. The plate 10 can be made of any conductive material, but metals, such as stainless steel and other corrosion-resistant alloys (e.g., sold under the trademark HASTELLOY), are normally preferred. The support bar 12, along with all other support bars described herein, is preferably made of steel or another very strong material that is not readily deformed substantially under tension and that is not substantially corroded in the environment in which it is used. The support bar 12 is preferably mounted to the plate 10 using rivets, bolts, adhesives, a clamping mechanism, or any other fastener that rigidly attaches the thin plate 10 to the support bar 12. In a preferred embodiment, the support bar 12 is mounted to a very strong structure in the ESP, such as a metal or concrete base. This configuration prevents movement of the support bar 12 relative to the ESP. Of course, the support bar 12 and the base can be a single component as will be appreciated by the person of ordinary skill.

[0020] At the top edge of the plate 10, another strong, stiff horizontal support bar

16 is similarly attached to the opposite edge of the plate 10 and a base 18 of the ESP. The base 18 is preferably, or is at least similar to, a structure to which conventional, much thicker, collection electrodes hang in a conventional ESP. For example, if the invention is used in a retro-fitted conventional ESP, the base 18 will be the structure that previously held the much heavier collection electrodes. [0021] Tensile loaders 20 and 21 , which are prime movers, such as pneumatic rams or electromotors, are interposed between the support bar 16 and the base 18 to vary the tension applied to the support bar 16 and the base 18. The loaders 20 and 21 apply a tensile bias continuously to the support bar 16 during operation, and periodically applying an impulse tensile force of increased magnitude to the support bar 16 to dislodge particulate matter from the plate 10 as is explained below and in the patents incorporated herein by reference. The tensile loaders 20 and 21 are thus variable in quantity of tension applied. The tensile loaders 20 and 21 pull on the support bar 16 to apply a tensile force to the plate 10 in the vertical direction. The plate 10 can be pre-tensioned by a turnbuckle or other similar mechanical mechanism attached to the upper support bar 16 through pins 3 and 4 extending into the slotted holes 3' and 4' to permit relative vertical movement.

[0022] On the opposing lateral sides of the plate 10, vertical support bars 30 and

32 are mounted to opposite edges of the plate 10 similarly to the upper and lower support bars 12 and 16. The vertical support bars 30 and 32 are preferably mounted to the plate 10 using rivets, bolts, adhesives, a clamping mechanism, or any other fastener that attaches the thin plate 10 to the vertical support bars. The vertical support bars 30 and 32 are disposed with their inwardly-facing edges spaced a very small amount (millimeters, or fractions thereof, away from) or in physical contact, but not attached to, the two horizontal support bars 12 and 16. Preferably, the opposing ends of the lower support bar 12 contact, or are close to contacting, the inwardly facing surfaces of the support bars 30 and 32 near the lower ends of the support bars 30 and 32 as shown in Fig. 1. Preferably, the opposing ends of the upper support bar 16 contact, or are close to contacting, the inwardly facing surfaces of the vertical support bars 30 and 32 at the upper ends of the support bars 30 and 32. In this configuration, contacting surfaces can slide relative to one another, and these contacting surfaces can be enhanced in their ability to slide by adding roller bearings, low friction material or any other known bearing surface enhancement.

[0023] There is small vertical movement of the collector plate 10 when it is strained by sufficient vertical tension. Even though the vertical support bars 30 and 32 are in close contact with the horizontal support bars 12 and 16, the lack of a bond or any mechanical attachment between the support bars allows small relative movement of the upper support bar 16 away from the lower support bar 12. This enhances the stresses and strains in the collector plate 10 in a uniform manner as described herein. [0024] Some attachments of support bars to the collector plate 10 are designed to allow small relative movements between the support bars and the collector plate 10 in a specific direction only. For example, a slotted hole (not visible) for each of the rivets 6 connecting the collector plate 10 to the vertical support bar 30 allows small relative movement of the plate 10 in the vertical direction relative to the support bar 30 but not in the horizontal direction. Such a configuration can enhance the stress waves in the collector plate 10 that dislodge the collected particles on the collector plate 10.

[0025] The configuration shown and described in Fig. 1 allows vertical movement of the horizontal support bar 16 relative to the horizontal support bar 12 and the vertical support bars 30 and 32, but prevents any substantial horizontal, inward movement by the vertical support bars 30 and 32 past the ends of the horizontal support bars 12 and 16. Thus, upon the application of a vertical force by the tensile loaders 20 and 21 , the plate 10 is placed in vertical tension, but little to no horizontal contraction occurs due to the limitations on inward movement by the vertical support bars 30 and 32 by the ends of the horizontal support bars 12 and 16. This induces horizontal tension in the plate 10 that reduces or eliminates movement transverse to the plane of the plate 10 that would cause re-entrainment of the collected dust. If the plate 10 is pre-tensioned in the horizontal direction before the vertical support bars 30 and 32 are mounted on it, the plate 10, upon the application of a vertical force will always remain in tension in both vertical and horizontal direction, irrespective of whether the vertical and the horizontal support bars are in contact.

[0026] There are also multiple "shield bars" 24 that are preferably rigidly mounted to the lower support bar 12 and preferably slidably mounted to the upper support bar 16 to prevent dust dislodgement by the flow of exhaust gases over the plate 10 during and after rapping. The shield bars 24 extend along the height of the plate 10 and preferably prevent exhaust gas flow from dislodging the dust layer on the collector metal plate during normal operation. The shield bars 24 perform the dust re-entrainment avoiding function of stiffeners in traditional ESP collector plates. However, rather than being mounted to the plate 10, the shield bars 24 are rigidly attached to the lower support bar 12, and are held loosely in slots found in the top support bar 16. This configuration allows the shield bars 24 to slide relative to both the upper support bar 16 and the plate 10 during elongation of the plate 10. The shield bars 24 are preferably spaced from the plate 10 by a small distance, such as one millimeter to a few millimeters, thereby forming a gap between the shield bars 24 and the plate 10.

[0027] When the plate 10 is stretched by the force F (see Fig. 1) applied periodically by the variable tensile loaders 20 and 21, the shield bars 24 remain vertical and parallel to each other as they slide within the slots formed in the upper support bar 16. The shield bars 24 do not cause any substantial resistance to vertical movement of the upper support bar 16 relative to the lower support bar 12.

[0028] The variable tensile loaders 20 and 21 produce vertical lengthening (strain) of the plate 10 during rapping, and, due to the configuration of the support bars, there is no substantial horizontal contraction of the collector plate 10 caused by Poisson's effect. Virtually any tendency to contract horizontally is prevented, or at least substantially mitigated, by the vertical support bars 30 and 32 butting against the ends of the horizontal support bars 12 and 16. Therefore, any tendency to contract inwardly horizontally, resulting from the vertical elongation, creates forces applied by the vertical support bars 30 and 32 opposing the inward contraction, thereby resulting in horizontal tension on the plate 10. Therefore, the net effect of the arrangement of the support bars 12, 16, 30 and 32 is to produce simultaneous biaxial tension of the plate 10 so that high frequency stress waves are generated in both vertical and horizontal directions. The high frequency stress waves on the collector plates in two directions can dislodge the collected dust layer on the plates more effectively and without buckling, so the dust collection efficiency is higher.

[0029] Membrane and single material collector plates can be very thin, and the thickness is based on design life of the collector plate material in the corrosive environment of the ESP. Typically, such collector plates can be made of metal, but they can also be non-metal. The collector plates can be made of an electrically conductive composite material, such as carbon fiber-reinforced polymer. Light collector plates can be made from polymer matrix composites impregnated with conductive powder, fibers or wire. The conductive material can be carbon fibers, including nanofibers, or carbon powder, among others. Furthermore, the material selection for the horizontal and vertical support bars takes into consideration the thermal expansion coefficient so as to optimize the contact between them at the operating temperature of the ESP.

[0030] The tensile force required of the tensile loaders 20 and 21 is smaller than that of the prior art, because of a lack of stiffeners in the plate 10. Such smaller forces can be provided by inexpensive pneumatic hammers. For a retrofit of a conventional ESP, such smaller forces can be applied by new equipment, or the tensile load can be provided by simple modification of the traditional rapping system to produce an upward, instead of a downward, force that generates the tensile load. This can be accomplished by levers, gearing and many other common mechanical devices that reverse the direction of the forces applied by the traditional rapping system.

[0031] In an alternative embodiment shown in Figs. 2-4, a lightweight and very strong bidirectional composite is used. This is preferably a single sheet 40 (Fig. 2) made of woven composite tapes in which the tapes 42, 44, 46 and 48 in the ply have a range of movement relative to each other. This relative movement may occur due to stretching or deformation of the sheet, resulting in shearing forces on the dust deposited on the sheet and dislodging of the dust from the ply without buckling of the sheet. Utilization of this special bidirectional material makes it possible to apply simple, inexpensive means for dislodging the dust, instead of using heavy steel collection electrodes and heavy and expensive hammers to clean them.

[0032] The invention shown in Fig. 4 utilizes a bidirectional composite ply sheet

100 made of composite tapes or fibers and a frame apparatus 110 to produce relative movement between the tapes or fibers in the two directions. The bidirectional ply sheet 100 construction allows relative movement of tapes with respect to each other and makes it possible to dislodge the dust very easily from the surface of the sheet.

[0033] The tapes in the sheet 100 can be individual composite tapes 42-48, in which a thermoplastic or thermoset matrix is reinforced with electrically conductive fibers, such as carbon fibers. Alternatively, the tapes can be metal strips or other conductive materials. Fibers with bidirectional weave in a single sheet can also be used. The weave in the sheet and the material composition of the composite sheet 100 can be selected to optimize the friction forces of relative movement of the tapes or fibers in transverse directions. One significant feature of the invention is the relative movement in two different, and preferably perpendicular, directions within the bidirectional ply sheet to enhance the removal of the dust collected on the ply.

[0034] The composite ply can be made of tapes woven bidirectionally, which is along two directions, such as horizontal and vertical in the orientation shown in Fig. 3. The tapes can also be "braided tape", where each tape is about 5-10 mm wide, and a portion of each group of the tapes is woven at ±45 degrees (see Fig. 2), or any other suitable angle, relative to the other portion of tapes. That is, the horizontal group of tapes 42, 46 is woven to a vertical group 44, 48 of tapes, and the horizontal group is angled at about 90 degrees relative to the vertical group of tapes.

[0035] All candidate materials for the composite sheet must be light, strong, and rigid (i.e., large elastic modulus - e.g., 20 GPa). Such candidates must also endure high loads and high temperatures (e.g., up to about 500 degrees F), and they are preferably relatively inexpensive in order to be economically feasible for use. For example, tapes made of polyimide polymer or Polyphenylene Sulfide (PPS) thermoplastic polymer with carbon fiber and/or graphite particulate filler are candidates for this application. Thermoset tapes and other conductive fibers are also candidates.

[0036] Carbon-fiber based composite unitapes are candidates for this application, and braided bidirectional plies made from these tapes are available on the market for the fabrication of composite structures. The tapes can be designed with a proper combination of matrix material and carbon fibers for the acceptable range of friction forces and surface resistivity. Carbon fibers are strong and inexpensive and some of the composite tapes can operate at elevated temperatures.

[0037] The layout of the alternative collecting electrode and shaking mechanism is presented in Fig. 4. The composite sheet 100 is attached to a frame 110 that has a lower horizontal support bar 112, an upper horizontal support bar 116, a right vertical support bar 130 and a left vertical support bar 132. The support bars 112, 116, 130 and 132 are preferably made of steel or another very strong material that is not readily deformed substantially under tension and that is not damaged by a corrosive environment. In a preferred embodiment, the support bar 112 is integral to a very strong structure in the ESP, such as a metal or concrete base 114. This configuration prevents movement of the support bar 112 relative to the ESP. At the top edge of the sheet 100, the strong, stiff horizontal support bar 116 is similarly attached to the opposite edge of the sheet 100 and a base 118 of the ESP. The base 118 is preferably a structure from which conventional thicker collection electrodes would hang, or is similar thereto.

[0038] The support bars 112, 116, 130 and 132 are preferably mounted to the sheet 100 using rivets, bolts, adhesives, a clamping mechanism, or any other fastener that attaches the sheet 100 to the respective support bar. In a contemplated embodiment, the fibers, tapes or strands of the sheet 100 may be wrapped around the support bars 112, 116, 130 and 132 and adhered or clamped to fix to the support bars. [0039] Preferably a variable tensile loader 120 is interposed between the support bar 116 and the base 118. The loader 120 applies a tensile bias continuously to the support bar 116 during operation, and periodically applies an impulse tensile force of increased magnitude to the support bar 116 to dislodge particulate matter from the sheet 100. The sheet 100 can thereby be put in tension along the vertical direction by the tensile loader 120 pulling on the support bar 116. The sheet 100 can be pre-tensioned by a turnbuckle or other similar mechanical mechanism (not visible) attached to the upper support bar 116. The tensile loader 120 may be a motor with a driveshaft that is attached to the support bar 116 along an axis offset from the driveshaft' s axis (not visible). The electrode shaking slide-crank mechanism, or other suitable mechanism (e.g. shaker), is mounted to the support bar 116 and is driven by an electromotor or a hydraulic or pneumatic motor. The tensile loader 120 is preferably variable in the tension that it can apply.

[0040] Vertical support bars 130 and 132 are mounted, such as by clamps, bolts or other fasteners to opposite edges of the membrane 100 as with the upper and lower support bars 112 and 116. In a preferred embodiment, four linkages 122, 124, 126 and 128 are pivotably mounted where the upper and lower support bars 112 and 116 and the vertical support bars 130 and 132 would intersect if they were slightly longer. Where the linkages 122, 124, 126 and 128 overlap the support bars 112, 116, 130 and 132, there are axle pins that extend rotatably through at least one of the two structures to permit relative pivoting between each linkage and each respective connected support bar. The lower support 112 is fixed at the bottom (in the orientation shown in Fig. 4) to the ESP structure 114, while the upper support bar 116 is mounted with pins that slide within the slots 134 and 136 formed in the surrounding structure in the ESP main frame to maintain the lateral position of the support bar 116. The pins that extend into the slots 134 and 136 are preferably extensions of, or are coaxial with, the pins that permit relative pivoting between the linkages 122 and 128 and the upper horizontal support bar 116.

[0041] All of the linkages 122, 124, 126 and 128 connecting the vertical and horizontal support bars 112, 116, 130 and 132 make the same angle, Θ with the horizontal support bars 112 and 116. This angle, Θ can vary in order to optimize the apparatus. Hence, when an upward vertical force is exerted by the tensile loader 120 to the upper support bar 116, the support bar 116 remains horizontal as the sheet 100 is elongated in the vertical direction. The vertical support bars 130 and 132 remain substantially vertical and parallel as they move slightly towards each other, allowing the sheet 100 to contract inwardly in the horizontal direction as the linkages 122-128 pivot to accommodate the inward movement of the vertical support bars 130 and 132.

[0042] When the constant tensile force applied in the upward direction in the illustration of Fig. 4 is subsequently reduced, the vertical support bars 130 and 132 remain substantially vertical and parallel, and move away from each other. This thereby stretches the sheet 100 in the horizontal direction, while contracting it in the vertical direction from the extreme vertical elongation that occurs at maximum vertical tension. This cycle starts again and then continues as the tensile loader 120 applies a maximum tensile force upwardly in Fig. 4. Hence, for each complete cycle of the tensile loader 120, which can be for each revolution of a crank mechanism, the "ply electrode" sheet 100 is stretched once in the vertical direction and once in the horizontal direction. If an electromotor is used to drive a slider-crank mechanism, and the electromotor rotates at 1000 revolutions per minute (i.e., about 16 times per second), the collection electrode 100 is stretched 16 times in both directions every second. Therefore, the new "rapping" process is effective in dislodging the dust within a few seconds.

[0043] The present invention has numerous advantages, including the significant reduction in weight of the collecting electrodes, the rapping mechanisms and of the whole supporting ESP structure that previously bore the weight of these heavy structures. The collection electrodes are loaded in tension only, unlike conventional collecting electrodes where buckling occurs due to tensile loading along only one line, and therefore there is no buckling in the invention to produce substantial re-entrainment of collected dust. The shaking ("rapping") mechanism of the lightweight collection electrode is inexpensive, simple and small in size.

[0044] It is also apparent that the collection electrodes are cleaned better than in the prior art due to two effects. First, the electrodes are rapped and/or shaken tens of times in a single second, which is a substantial increase over the prior art. Second, the relative motion of the tapes of one embodiment in two directions (e.g. horizontal and vertical) relative to each other distributes the dislodgement motion of the composite over the entire electrode rather than in localized areas as in the prior art.

[0045] The motion or deformation of the electrode may be arranged to be in tension, which will occur using the weave pattern represented by the orientation of the two groups of tapes or clusters of fibers shown in Fig. 4. In this embodiment, one group of the tapes of the composite 100 is aligned (vertically) in the direction that the upwardly- directed vertical force is applied, and these tapes are preferably attached at their opposite ends to only the support bars 112 and 116. Another group of tapes is aligned (horizontally) with the force that is applied by the vertical support members 130 and 132 when a downwardly-directed vertical force is applied, and these tapes are preferably attached at their opposite ends to only the support bars 130 and 132. Thus, an increased vertical tension stresses the vertical tapes as the horizontal tapes relax inwardly. Upon release, the vertical tapes relax slightly, thus forcing the horizontal tapes outwardly very slightly (e.g., much less than 1 mm). This rapid cycling movement of the tapes relative to one another causes dislodgment of a collected dust layer.

[0046] The motion or deformation of an electrode according to the invention may be arranged to be in shear at varying angles, a, as represented by the orientation of the two groups of tapes or clusters of fibers represented in Fig. 6. In this insert, one group of tapes 300 is represented as angled to the direction that the upwardly-directed vertical force is applied, and the other group of tapes 302 is angled to the horizontal force that is applied by vertical support members when a downwardly-directed vertical force is applied. Thus, a different shear force, as compared to the Fig. 4 embodiment, is applied at one extreme deformation versus the other. In the Fig. 6 embodiment, the angles that each tape in the first group 300 has relative to each tape in the second group 302 may begin at about 90 degrees during constant tension, but changes substantially at maximum tension applied to the upper horizontal support bar of Fig. 6. This in-plane movement of the groups causes substantial dislodgement of the dust layer without buckling that causes substantial re-entrainment.

[0047] It will be appreciated that the Fig. 4 embodiment has one group of tapes that is parallel to two support bars and perpendicular to the other two support bars. In Fig. 6, both groups of tapes are angled at about 45 degrees to all support bars. The angles between the tapes and the support bars can vary between parallel and perpendicular (0 and 90 degrees). The Fig. 4 embodiment is a special case where the tapes are at extreme angles, where one group is attached to the horizontal support bars, but has no attachment to the vertical support bars, and the second group of tapes is attached to the vertical support bars, but has no attachment to the horizontal support bars. In Fig. 6, the tapes in each group attach to one each of a horizontal and a vertical support bar, which is typically the case except for in the Fig. 4 embodiment. [0048] The direction of movement of the vertical support bars 230 and 232 (Fig.

7) can be guided using slots 200, 202, 204, and 206 formed in the ESP structure and pins 200' , 202', 204', and 206' extending from the linkage members into the slots 200, 202, 204, and 206, respectively. The slots and pins of Fig. 7 maintain the substantially parallel relative orientations of the vertical support bars 230 and 232, and such a configuration can be added to the embodiments of Figs. 4 and 6 to accomplish the same purpose.

[0049] Experiments have been conducted with a small tape ply unit as shown in

Fig. 5 having tapes oriented along the directions in which tension is applied. Applicant has concluded from this experiment that it may be important for the vertical support bars 130 and 132 to hold and pull only horizontal tapes, while the support bars 112 and 116 only hold and pull on vertical tapes. The movement of the tape plies results in relative movement between the tapes in the two different directions. In addition, there is a flexing motion of tapes (in both directions) which dislodges the dust on the woven ply.

[0050] The system shown in Fig. 5 is made of a set of thermoplastic unidirectional composite tapes stretched in vertical and horizontal directions. Such membranes can be consolidated to make a light thin collector plate or membrane which can also be vibrated very easily to dislodge the dust.

[0051] The pattern/angle of the tapes with respect to the tension vector can be changed to get different types of relative motion between the tapes in the bidirectional ply. The bidirectional ply is much easier to put into uniform tension than a single flexible sheet or a membrane. A single sheet or membrane can produce undesirable buckling or "wrinkles" in the plane when under tension, and these are more readily avoided with a bidirectional ply sheet.

[0052] Dislodging the dust can be achieved by using the mechanisms in any of the embodiments described and shown, or by simply using one motor to pull one group of tapes (or a single layer in one direction), and a second motor to pull another group of tapes (or a single layer in a second, transverse, direction).

[0053] The invention drastically reduces the overall ESP weight and cost, because both composite tapes and their shaking mechanisms are very light. By using a very lightweight system that can be supported on springs, it is readily set into vibration to dislodge the dust. The dust removal process is a much simpler and more efficient shaking process requiring much less force than current systems. [0054] Carbon fiber composites cannot typically operate at very high temperatures unless expensive polymers are used. Therefore, the applications for the invention are contemplated to be limited to temperatures below 500 degrees F. However, this is acceptable in most industrial ESP applications.

[0055] This detailed description in connection with the drawings is intended principally as a description of the presently preferred embodiments of the invention, and is not intended to represent the only form in which the present invention may be constructed or utilized. The description sets forth the designs, functions, means, and methods of implementing the invention in connection with the illustrated embodiments. It is to be understood, however, that the same or equivalent functions and features may be accomplished by different embodiments that are also intended to be encompassed within the spirit and scope of the invention and that various modifications may be adopted without departing from the invention or scope of the following claims.

Claims

CLAIMS 1. An apparatus for dislodging particles collected on an electrostatic precipitator electrode, the apparatus comprising:

(a) a first member mounted to a first side of the electrode;

(b) a second member mounted to a second side of the electrode opposite the first side; (c) a third member mounted to a third side of the electrode;

(d) a fourth member mounted to a fourth side of the electrode opposite the third side; and

(e) a variable tensile loader connected to the first member, the loader applying a tensile bias continuously to the first member during operation, and periodically applying at least one impulse tensile force of increased magnitude to the first member to move the first member away from the second member to elongate the electrode and dislodge particulate matter from the electrode.

2. The apparatus in accordance with claim 1, wherein the first member has opposing ends that abut inwardly facing surfaces of the third and fourth members, the second member has opposing ends that abut inwardly facing surfaces of the third and fourth members, thereby permitting movement of the first member away from the second member while preventing substantial simultaneous movement of the third member toward the fourth member.

3. The apparatus in accordance with claim 2, wherein the second member is substantially parallel to the first member, and the fourth member is substantially parallel to the third member.

4. The apparatus in accordance with claim 2, further comprising at least one shield bar rigidly mounted to the second support bar and extending across the electrode to sliding attachment to the first support bar.

5. The apparatus in accordance with claim 2, wherein the electrode is a metallic membrane.

6. The apparatus in accordance with claim 2, wherein the electrode is a composite in which a plurality of reinforcing strands is encased in a matrix.

7. The apparatus in accordance with claim 6, wherein the composite electrode has a first group of strands attached only to the first and second members, and a second group of strands attached only to the third and fourth members, whereby moving the first member away from the second member elongates the first group of strands without substantially elongating the second group of strands.

8. The apparatus in accordance with claim 1, further comprising a first linkage pivotably mounted to the first member and to the third member, a second linkage pivotably mounted to the third member and to the second member, a third linkage pivotably mounted to the second member and to the fourth member, and a fourth linkage pivotably mounted to the fourth member and to the first member.

9. The apparatus in accordance with claim 8, wherein the second member is substantially parallel to the first member, and the fourth member is substantially parallel to the third member.

10. The apparatus in accordance with claim 8, wherein the electrode is a metallic membrane.

11. The apparatus in accordance with claim 8, wherein the electrode is a composite in which a plurality of reinforcing strands is encased in a matrix.

12. The apparatus in accordance with claim 11, wherein the composite electrode has a first group of strands attached only to the first and second members, and a second group of strands attached only to the third and fourth members, whereby moving the first member away from the second member elongates the first group of strands without substantially elongating the second group of strands.

13. The apparatus in accordance with claim 12, further comprising a second variable tensile loader connected to the third member, the loader applying a tensile bias continuously to the third member during operation, and periodically applying at least one impulse tensile force of increased magnitude to the third member to move the third member away from the fourth member to elongate the electrode and dislodge particulate matter from the electrode.

14. The apparatus in accordance with claim 11, wherein the composite electrode has a first group of strands interwoven with, and transverse to, a second group of strands, whereby moving the first member away from the second member moves the first group of strands relative to the second group of strands to elongate the composite electrode.