DEVICE IN AN ELECTROSTATIC PRECIPITATOR FOR THE SUSPENDING, CONTROLLING AND RAPPING OF COLLECTING ELECTRODES

Abstract: A device in an electrostatic precipitator for suspending, controlling and rapping one or more collecting electrodes (2) arranged essentially vertically in one or more substantially parallel rows (1), said device comprising for each row (1) a substantially horizontally oriented carrier element (3), to which the upper ends of the collecting electrodes (2) are attached, connecting elements (4a, 4b) which connect the carrier element to the casing (5) of the electrostatic precipitator, control means (11a, 11b, 12a, 12b, 13, 14a, 14b) for controlling the motion of each row (1) of collecting electrodes in the transverse and/or longitudinal direction of the electrostatic precipitator, and a rapping mechanism (6) for rapping the collecting electrodes (2) of each row, comprising a rapping means (7), such as a rapping hammer, and an anvil (9) connected to the carrier element (3). The carrier element (3) of each row is separately suspended by means of said connecting elements (4a, 4b), thereby permitting, during rapping, a minimum horizontal pivoting motion restricted to each row (1) of collecting electrodes and occurring in the longitudinal direction of the electrostatic precipitator.

Description: DEVICE IN AN ELECTROSTATIC PRECIPITATOR FOR THE SUSPENDING. CONTROLLING AND RAPPING OF COLLECTING ELECTRODES The present invention relates to a device in an electrostatic precipitator for the sus¬ pending, controlling and rapping of one or more collecting electrodes arranged essen¬ tially vertically in one or more substantially parallel rows and comprising for each row a substantially horizontally oriented carrier element to which the upper ends of the collecting electrodes are attached, connecting elements which connect the carrier element to the casing ofthe electrostatic precipitator, control means for controlling the motion of each row of collecting electrodes in the transverse and/or longitudinal direction ofthe electrostatic precipitator, and a rapping mechanism for rapping the collecting electrodes of each row and comprising a rapping means, such as a rapping hammer, and an anvil connected to the carrier element. Electrostatic precipitators are usually composed of a plurality of successive precipi¬ tation fields through which dust-laden gas is passed to be cleaned. Each ofthe preci- pitation fields is divided into a plurality of parallel gas passages by means of a plura¬ lity of juxtaposed, earthed collecting electrodes vertically arranged in rows . These are usually in the foπn of rectangular, substantially plate-shaped, sectional metal sheets. Vertical discharge electrodes, to which a negative voltage is supplied, are arranged in each gas passage. Owing to corona discharges at the discharge electrodes, the dust- laden gas is ionised in the electric field in the gas passages. The negative ions are attracted by the collecting electrodes and, while moving towards these, collide with the dust particles ofthe gas, which are then charged and separated from the gas by being attracted by the closest collecting electrode, on which they are deposited and build up a dust layer. At regular intervals, the dust layer is loosened, by vibrations, from the collecting electrodes by these being mechanically affected by means of a rapping mechanism. The dust particles then fall into a collecting hopper associated with the respective precipitation fields. The rapping mechanism can either be arranged at the top or at the bottom of each row of collecting electrodes and usually comprises a rapping hammer acting in a vertical plane about a rotary shaft which extends horizontally in the transverse direction ofthe electrostatic precipitator and to which the rapping hammer thus is connected, and an anvil. The rapping force for cleaning each row of collecting electrodes is generated by the rapping hammer giving a horizontally directed rap via the anvil to a rapping means cooperating with the collecting electrodes, whereby a horizontal motion is imparted to the rapping means. This motion is transferred to the collecting electrodes in the form of a shock wave which spreads across these. Thus, the dust layer accumu- lated on the collecting electrodes is loosened. A greater or smaller amount ofthe rapping force is absorbed by the suspension ofthe collecting electrodes during the cleaning operation. The amount of absorbed rapping force depends on the manner of connecting the collecting electrodes to the suspension and on the manner in which the suspension is connected to the casing ofthe electro¬ static precipitator. The collecting electrodes are usually controlled in the longitudinal as well as in the transverse direction ofthe electrostatic precipitator so as to be kept in exact positions and, thus, prevent flashovers. There have been suggested various solutions of a device in an electrostatic precipita¬ tor for the suspending, controlling and rapping of its collecting electrodes. For instance, EP 0 584 880 discloses a device for cleaning collecting electrodes in an electrostatic precipitator by rapping, the collecting electrodes being vertically arrang¬ ed, successively in parallel rows. The collecting electrodes of each rows are, at their upper ends, attached between a pair of horizontally arranged longitudinal rapping beams and suspended from these, said beams thus also serving as carrier elements for the collecting electrodes. The rapping beams rest freely on a pair of supporting beams, between which the upper ends ofthe collecting electrodes are arranged. The pair of supporting beams rests, in turn, on a frame pertaining to the casing ofthe electrostatic precipitator. The pair of rapping beams thus is arranged so as to be able to slide, during rapping, horizontally on the supporting beams in the longitudinal direction of the electrostatic precipitator. During cleaning by rapping, the rapping force is transfer¬ red in the form of a shock wave by means of a rapping hammer to all the collecting electrodes of a row via an anvil, which is fixedly mounted on the pair of rapping beams of each row. On each side ofthe ends ofthe pair of rapping beams, laminated springs are mounted in the casing and cooperate with transverse so-called stop pins arranged at each end ofthe pair of rapping beams. A spring-back motion ofthe pair of rapping beams to its original position is permitted in connection with the rapping before the anvil is again hit by the rapping hammer. As a result, the laminated springs control the row of collecting electrodes in the longitudinal direction ofthe electrosta¬ tic precipitator. The laminated springs also serve as control means in the transverse direction ofthe electrostatic precipitator. A drawback ofthe thus disclosed device is that a relatively great amount ofthe rapping force is absorbed by the casing during rapping and, thus, is lost. Besides, for each row of collecting electrodes, the device consists of a large number of components, which makes it mechanically complicated. The mounting ofthe respective rows is carried out in such a manner that the upper ends ofthe collecting electrodes are first inserted between the pair ofthe supporting beams and are temporarily mounted therein by means of bolts. Each rapping beam is tiien arranged on both sides ofthe upwardly extending ends ofthe collecting elec¬ trodes and is mounted therein by means of bolts, whereupon the bolts in the pair of supporting beams are removed. The mounting procedure accomplished in this manner thus is complicated and time-consuming. The mounting of each row will probably also take place inside the electrostatic precipitator, which is a drawback compared with the technique of mounting the row outside the electrostatic precipitator so as to be inserted afterwards. One object ofthe present invention thus is, in view of that stated above, to provide a new and improved device in an electrostatic precipitator for suspending, controlling and rapping its collecting electrodes, said device allowing a more efficient use ofthe generated rapping force when cleaning the collecting electrodes. A further object of the present invention is to provide a device for suspending, controlling and rapping, which is mechanically simpler and, consequently, easier to mount. These objects are achieved by a device which is ofthe type stated by way of introduc¬ tion and which according to the present invention is characterised in that the carrier element of each row is suspended separately by means of connecting elements, which as stated above connect the carrier element to the casing ofthe electrostatic precipita- tor, thereby permitting a minimum horizontal pivoting motion restricted to each col¬ lecting electrode row and occurring in the longitudinal direction ofthe electrostatic precipitator. The pivoting motion arising in rapping occurs owing to the separate sus¬ pension and thus fully independently ofthe remaining rows. By a restricted, mmimum pivot motion is meant a pivoting motion which is less than about 5 mm ofthe carrier element in its longitudinal direction. According to the present invention, the connecting elements ofthe carrier element preferably comprise two elongate rods, each making an angle α, relative to a vertical axis extending through each rod, in the range of about 5-35°, especially in the range of about 5-15°, in such a manner that said rods are positioned substantially in the plane of the row such that the distance between their lower ends is smaller than between their upper ends. In consequence ofthe carrier element being separately suspended in the above-mentioned fashion, the row of collecting electrodes will be self-centred after rapping, i.e. the row will immediately return to its correct original position. The smaller the angle the more movable the actual suspension, which means that a greater amount ofthe rapping force, relatively seen, will be absorbed by the casing, which results in poorer cleaning. On the other hand, the greater the angle α, the more unresilient the suspension, which also results in poorer cleaning. To achieve optimum cleaning, i.e. to transfer as great an amount as possible ofthe rapping force to the col¬ lecting electrodes, the angle is adjusted according to the present invention so that as small an amount as possible ofthe rapping force is absorbed by the casing. Moreover, the angle α should be adjusted so as to prevent too great a pivoting motion ofthe col¬ lecting electrodes. By such suspension, which is mechanically simple and easy to mount, a more efficient cleaning ofthe collecting electrodes is provided. According to the present invention, the control means ofthe device consist of upper control elements cooperating with the carrier element, and/or lower control elements cooperating with the lower ends ofthe collecting electrodes. The upper control ele- ments preferably consist of upper cam control elements cooperating with the end por¬ tions ofthe carrier element. Advantageously, the cam control elements extend sub¬ stantially horizontally in the transverse direction ofthe electrostatic precipitator through a plurality of rows and thus prevent each row of collecting electrodes from moving in said direction. The upper control elements also serve as control means in the longitudinal direction ofthe electrostatic precipitator, especially in case of small angles α. By means of these upper control elements, which are mechanically simple and easy to mount, efficient control is achieved. To further improve the control, in addition to the control provided by means ofthe upper control elements, lower control elements are preferably arranged at the bottom of each row and cooperate, as stated above, with the lower ends ofthe collecting elec¬ trodes. According to a preferred embodiment ofthe inventive device, the lower ends ofthe collecting electrodes are loosely controlled by the lower control elements on the one hand in the transverse direction ofthe electrostatic precipitator by means of a longi- tudinally oriented, horizontal pair of rods, between which the lower ends ofthe col¬ lecting electrodes are arranged and, on the other hand, in the longitudinal direction ofthe electrostatic precipitator by means of spacer members arranged before, after and/or between the collecting electrodes. A further alternative preferred embodiment ofthe inventive device is characterised in that the lower ends ofthe collecting electrodes are firmly controlled by the lower con¬ trol elements in the transverse as well as longitudinal direction ofthe electric preci¬ pitator by means of longitudinally oriented, horizontal rods, to which the lower ends ofthe collecting electrodes are attached, preferably by means of bolts or rivets. A common feature ofthe lower control is that each row of collecting electrodes is controlled in the transverse direction ofthe electrostatic precipitator by means of transversely oriented lower cam control elements arranged at the ends of said rods. The cam control elements advantageously extend substantially vertically in the transverse direction ofthe electrostatic precipitator through a number of rows and thus prevent the respective rows of collecting electrodes from moving in said direc¬ tion. By means of these lower control elements, which are mechanically simple and easy to mount, efficient control is achieved. The lower and the upper control accord¬ ing to the invention is further designed with regard to thermal expansion. According to the present invention, the anvil ofthe rapping mechanism is preferably directly fixedly mounted on the upper side ofthe carrier element and comprises a rap¬ ping shoulder, which is the rapping point ofthe rapping means, which is arranged in such a manner that the rapping point is located above the horizontal centre line ofthe canier element. According to an alternative embodiment, the anvil can also extend across at least two rows of collecting electrodes in the transverse direction ofthe elec¬ trostatic precipitator. In this case, the anvil, which consists of e.g. a flat iron bar, is also directly fixedly mounted on the upper side ofthe carrier element of each row. The rapping means ofthe rapping mechanism preferably acts in a vertical plane about a rotary shaft connected thereto and extending horizontally in the transverse direction ofthe electric precipitator, the rapping means giving the anvil a horizontally directed rap during rapping. In dependence on the embodiment, the rap is given to the anvil either directly or indirectly via the above-mentioned rapping shoulder. A general advantage ofthe inventive device is that each row of collecting electrodes can be mounted outside the electrostatic precipitator and then be inserted. The invention will now be described in more detail with reference to the accompany¬ ing drawings, in which: Fig. 1 is a schematic vertical section of a device according to the invention in parallel with a row of collecting electrodes in an electrostatic pre¬ cipitator. Fig. 2 is a horizontal section towards the collecting electrodes taken along line B-B in Fig. 1. Fig. 3 is an enlarged view of a lower control element in Fig. 2. Fig. 4 is a vertical section towards the collecting electrodes taken along line A-A in Fig. 1. Fig. 1 thus is a schematic vertical section in parallel with a row 1 of collecting electrodes 2 in an electrostatic precipitator, which for each row 1 is provided with a device for suspending, controlling and rapping the collecting electrodes 2. The electrostatic precipitator comprises a plurality of successive precipitation fields, each field consisting of a plurality of parallel rows 1 of earthed collecting electrodes 2, which are vertically arranged in succession in the respective rows. Each row 1 of collecting electrodes consists of substantially plate-shaped, sectional metal sheets, which between themselves thus form gas passages for the dust-laden gas to be clean¬ ed. The gas flow in the electrostatic precipitator occurs horizontally as indicated by arrow G. Between each row 1 of collecting electrodes 2, discharge electrodes (not shown) are accommodated, which are connected to a negative voltage. As indicated in Fig. 1, the collecting electrodes 2 of each row are at their upper ends attached by means of rivets or bolts to a horizontally oriented, flexurally rigid carrier element in the form of a U-beam 3. The U-beam 3 is in turn separately and movably suspended by means of connecting elements, which in the embodiment illustrated consist of two inclined, elongate round bars 4a, 4b. The round bars 4a, 4b are posi¬ tioned in the plane ofthe row and are oriented in such a manner that their lower ends face each other and make an angle oc of about 10° relative to a vertical axis V extend¬ ing through the respective round bars. The lower ends ofthe round bars 4a, 4b are secured to the end portions ofthe U-beam 3 in the upper flange thereof, and the upper ends ofthe round bars are secured to the casing 5. Because of this, according to the invention, special suspension ofthe U-beam 3 and the fact that the collecting elec¬ trodes 2 are in direct contact with the U-beam 3, a very small amount ofthe rapping force is absorbed by the casing 5, which results in efficient cleaning. Besides, the horizontal pivoting motion ofthe row 1 of collecting electrodes arising during clean¬ ing will be minimal. In the illustrated embodiment, the rapping mechanism 6 for cleaning the collecting electrodes 2 of each row is arranged in the centre ofthe U-beam 3 and comprises a rapping hammer 7, which acts in a vertical plane about a rotary shaft 8 extending horizontally in the transverse direction ofthe electrostatic precipitator, and an anvil 9. As shown in Fig. 1, the anvil 9 in the form of an L-beam is directly fixedly mounted by means of bolts on the upper side ofthe U-beam 3 and comprises a rapping shoul¬ der 10. The U-beam 3 thus serves as carrier element as well as rapping means for the collecting electrodes 2. During cleaning, the U-beam 3 is subjected to a horizontally directed motion by the rapping hammer 7 giving the rapping shoulder 10 arranged on the anvil 9 a rap, which is transferred in the form of a shock wave to the collecting electrodes 2 via the carrier beam 3. The rapping point ofthe rapping hammer 7 thus is placed in such a manner that it is located above the horizontal centre line C ofthe U-beam 3, which is also evident from Fig. 4. The shock wave spreads downwards along all the collecting electrodes 2 ofthe row 1, which are thus caused to vibrate, whereupon the dust layer is loosened by the vibrations. The dust particles then fall into a collecting hopper (not shown) pertaining to the respective precipitation fields. The illustrated device further comprises control means which consist of upper and lower control elements for controlling the motion of each row 1 of collecting elec- trodes in the transverse as well as longitudinal direction ofthe electrostatic preci¬ pitator. In order to prevent, during the cleaning operation, flashover because ofthe motion ofthe row 1 in the transverse direction ofthe electrostatic precipitator, the U-beam 3 is provided with upper control elements in the form of upper cam control elements I la, l ib, which at each end ofthe U-beam 3 cooperate with the web there- of. The upper cam control elements 1 la, 1 lb also constitute a certain control ofthe carrier element 3 ofthe row, and thus the row, in the longitudinal direction ofthe electrostatic precipitator, especially at small angles α. In the embodiment illustrated, the upper cam control elements I la, l ib extend horizontally through a plurality of rows in the transverse direction ofthe electrostatic precipitator. In the embodiment illustrated, the lower ends ofthe collecting electrodes 2 are for each row loosely controlled in the longitudinal as well as transverse direction ofthe electrostatic precipitator by means of lower control elements, which will appear from the following description. As shown in Figs 1 and 2, the lower ends ofthe collecting electrodes are inserted between a pair of rods in the form of flat iron rods 12a, 12b horizontally oriented in the longitudinal direction. In this manner, the flat iron rods prevent the motion ofthe collecting electrodes 2 in the transverse direction ofthe electrostatic precipitator. The control ofthe collecting electrodes 2 in the longitudinal direction ofthe electrostatic precipitator is carried out by means of spacer members 13 arranged before, after and between the collecting electrodes 2. The spacer members 13 are fixedly mounted in the transverse direction across the rods 12a, 12b as shown in Fig. 3. Moreover, the row 1 of collecting electrodes is controlled in the transverse direction ofthe electro¬ static precipitator by means of lower cam control elements 14a, 14b which are verti¬ cally oriented in the transverse direction and arranged at the ends of said pairs of rods. The rods 12a, 12b are further provided with a supporting suspension 15 in the centre ofthe row 1. The control described above is designed with regard to thermal expan¬ sion. The distance between the pair of rods is fixed by spacer members (not shown), which in suitable positions are arranged between the rods. The invention is, of course, not restricted to the embodiments described above and can be modified in various ways within the scope ofthe appended claims. For instance, the lower ends ofthe collecting electrodes 2 can be firmly controlled instead of loosely controlled. For instance, the anvil 9 can be designed so as to extend across at least two successive parallel rows 1 of collecting electrodes 2 in the transverse direction ofthe electrostatic precipitator, instead of across a single row.

Claims: CLAIMS 1. A device in an electrostatic precipitator for the suspending, controlling and rapping of one or more collecting electrodes (2) arranged essentially vertically in one or more substantially parallel rows (1), said device comprising for each row (1) a substantially horizontally oriented carrier element (3) to which the upper ends ofthe collecting electrodes (2) are attached, connecting elements (4a, 4b) which connect the carrier element (3) to the casing (5) ofthe electrostatic precipitator, control means (1 la, 1 lb, 12a, 12b, 13 , 14a, 14b) for controlling the motion of each row ( 1 ) of collecting elec¬ trodes in the transverse and/or longitudinal direction ofthe electrostatic precipitator, and a rapping mechanism (6) for rapping the collecting electrodes (2) of each row and comprising a rapping means (7), such as a rapping hammer, and an anvil (9) connect¬ ed to the carrier element (3), c h a r a c t e r i s e d in that the carrier element (3) of each row is separately suspended by means of said connecting elements (4a, 4b), thereby permitting, during rapping, a minimum horizontal pivoting motion restricted to each row (1) of collecting electrodes and occurring in the longitudinal direction ofthe electrostatic precipitator. 2. The device as claimed in claim 1, c h a r a c t e r i s e d in that the connect¬ ing elements ofthe carrier element (3) comprises two elongate rods (4a, 4b), each making an angle α, relative to a vertical axis (V) extending through each rod, in the range of about 5-35°, preferably in the range of about 5-15°, in such a manner that said rods (4a, 4b) are positioned substantially in the plane ofthe row such that the distance between their lower ends is smaller than between their upper ends. 3. The device as claimed in claims 1 and 2, c h a r a c t e r i s e d in that the control means consist of upper control elements (Ila, lib) cooperating with the car¬ rier element (3), and/or lower control elements (12a, 12b, 13, 14a, 14b) cooperating with the lower ends ofthe collecting electrodes (2). 4. The device as claimed in claim 3, c h a r a c t e r i s e d in that the upper control elements consist of upper cam control elements (Ila, lib) cooperating with the end portions ofthe carrier element, said cam control elements extending substan- tially horizontally in the transverse direction ofthe electrostatic precipitator. 5. The device as claimed in claim 3 or 4, c h a r a c t e r i s e d in that the lower ends ofthe collecting electrodes are loosely controlled by the lower control ele¬ ments (12a, 12b, 13, 14a, 14b) on the one hand in the transverse direction ofthe elec¬ trostatic precipitator by means of a longitudinally oriented, horizontal pair of rods (12a, 12b), such as flat iron rods, between which the lower ends ofthe collecting elec¬ trodes are arranged and, on the other hand, in the longitudinal direction ofthe electric precipitator by means of spacer members (13) arranged before, after and/or between the collecting electrodes (2). 6. The device as claimed in claim 3 or 4, c h a r a c t e r i s e d in that the lower ends ofthe collecting electrodes are firmly controlled by the lower control ele¬ ments (12a, 12b) in the transverse as well as longitudinal direction ofthe electric pre¬ cipitator by means of longitudinally oriented, horizontal rods, to which the lower ends ofthe collecting electrodes are attached. 7. The device as claimed in claim 5 or 6, c h a r a c t e r i s e d in that each row (1) is controlled in the transverse direction ofthe electrostatic precipitator by means of transversely oriented lower cam control elements (14a, 14b) arranged at the ends of said rods. 8. The device as claimed in any one of claims 1-7, c h a r a c t e r i s e d in that the anvil (9) is directly fixedly mounted on the upper side ofthe carrier element and comprises a rapping shoulder (10) which is the rapping point ofthe rapping means (7) which is arranged in such a manner that the rapping point is located above the horizontal centre line (C) ofthe carrier element. 9. The device as claimed in any one of claims 1-7, c h a r a c t e r i s e d in that the anvil (9) extends across at least two rows (1) of collecting electrodes (2) in the transverse direction ofthe electrostatic precipitator and is directly fixedly mounted on the upper side ofthe carrier element (3) of each row. 10. The device as claimed in claim 8 or 9, c h a r a c t e r i s e d in that the rapping means (7) acts in a vertical plane about a rotary shaft (8) extending substan¬ tially horizontally in the transverse direction ofthe electric precipitator, the rapping means giving the anvil (9) a horizontally directed rap during rapping.

Inventors: KNUTSSON FILIP, KNUTSSON, FILIP
Applicants: FLAEKT AB, KNUTSSON FILIP, ABB FLAEKT AKTIEBOLAG, KNUTSSON, FILIP
Application year: 1996
Main classification: B03C3
IPC codes: B03C3