Patent Publication Number: US-4321067-A

Title: Corona-discharge electrode system

Description:
FIELD OF THE INVENTION 
     Our present invention relates to a corona-discharge electrode system for a high-temperature, high-pressure electrostatic precipitator and, more particularly, to an electrostatic precipitator of the type which comprises a circular section housing inclined upwardly at an angle of 50 to 70 degrees from the horizontal and including at least one array of vertical plate-like collecting electrodes, which extend substantially throughout the gas-flow area. 
     BACKGROUND OF THE INVENTION 
     Because electrostatic precipitators of this type are operated under high pressures of around 3 to 30 bars and at high temperatures of about 300° to 1200° C., structural problems and problems with materials are encountered. Satisfactory solutions to these problems have not been made apparent prior to our work in this field. 
     For instance, the precipitator housings at least of industrial electrostatic precipitators must be circular in cross-section for reasons of strength, and it is desired much more than in other electrostatic precipitators to utilize the gas-flow area as fully as possible for the installation of corona discharge and collecting electrodes. For this reason, the precipitator housing is upwardly inclined at such an angle that the collected dust can be automatically discharged by gravity. 
     For this purpose the flow behavior of the dust under the operating conditions must be known. Such an arrangement will eliminate the need for installed dust conveyors which anyway would be operative only with restrictions in such precipitators. 
     The shape of the precipitator housing, its upwardly inclined position and the high pressures and temperatures necessitate special designs of the collecting and corona-discharge electrodes. The corona discharge electrodes must be suspended so as to be electrically insulated from the housing and must be spaced equal distances apart from the collecting electrodes everywhere so that the electrostatic field which is built up will result in a most effective collection of dust. 
     For this purpose it is essential to stress mechanically the corona-discharge electrodes, which have only a small cross section to enable them to satisfy their electrical functions. Whereas only the weight of the collector electrodes must be considered in their design, internal mechanical stresses must be allowed for in the design of corona-discharge electrode systems. 
     This gives rise to additional difficulties because the material from which such electrodes are made has only a relatively low strength at the high operating temperatures. 
     OBJECTS OF THE INVENTION 
     It is an important object of the invention to provide a corona-discharge electrode system which operates satisfactorily and effectively under the design and operating conditions stated. 
     Yet another object is to provide an electrostatic precipitator of long life and high reliability in operation because such precipitators are used only in large and expensive plants so that it is essential to minimize the standstill times. 
     Another object of the invention is to provide an improved electrostatic precipitator and especially a corona-discharge electrode system therefor which is reliable, of simple and economic construction and is free from disadvantages found in prior-art systems. 
     SUMMARY OF THE INVENTION 
     These objects and others which will become apparent hereinafter are attained, in accordance with the present invention, in an electrostatic precipitator operating at high temperatures and pressures, preferably temperatures of 300° to 1200° C. and pressures of 3 to 30 bars, which comprises an elongated upwardly inclined round-section housing defining a gas-flow duct which is provided with at least one array of substantially vertical plate-like collecting electrodes extending through the duct over a dust-collecting region thereof. 
     According to the invention, a pair of grid-like frames flank the array of collecting electrodes and are spaced apart in the gas flow direction, each frame comprising at least two horizontal main carriers or bars and a plurality of vertical auxiliary carriers or bars. 
     Each frame is held in the duct by means of a carrying structure for each frame and each carrying structure in turn comprises a pair of vertical carriers and two inclined carriers extending out of the plane of the vertical carriers. The carriers are suspended in the duct by insulators advantageously disposed at the top of the housing so that the angle between the inclined carriers and the vertical carriers is such that tension forces upon the corona-discharge electrodes can be taken up without a rigid connection between the frames. 
     The corona-discharge electrodes are formed as wire-like members parallel to the direction of gas flow and are secured to the downstream upper auxiliary carriers and pass over the upstream lower auxiliary carriers and tensioned by weights. 
     Advantageously, the weights have centers of mass which are eccentric with respect to the points at which the wire electrodes engage the lower auxiliary carriers. 
     For example, the weights may have centers of mass offset from the centers of pulleys over which the wire electrodes are guided. Alternatively, the weights may form part of a lever system anchored to the wire electrodes. For example, the lever system may comprise a bell-cranking lever, one arm of which is connected to a corona electrode wire while the other arm is formed with the weight. In another alternative, the lever itself may be pivoted or fulcrumed at one end to the lower auxiliary carrier while its other end engages the corona electrode, the center of mass being located between these ends so as to tension the wires. 
     In yet another alternative, using a lever approach with a mass eccentric to the fulcrum, a pulley forms the weight on a free end of the lever arm and the corona-discharge wire electrode passes around this pulley to be anchored at another location to the lever or at the fulcrum or even elsewhere on the frame of which the lower auxiliary carrier forms a part. 
     The weight may also be formed as an eccentric, i.e. a generally round body which bears upon the corona discharge wire electrode or about which this electrode is guided, or a more complex arrangement which may be provided whereby the wire electrode passes between a pair of pins on a weighting lever. 
     According to yet another feature of the invention, the frames and carrying structure are composed of hollow (tubular) members of circular or other cross section through which a cooling fluid is circulated. 
     The weighting means, comprising levers and/or eccentric members and/or pulleys, are advantageously composed of a ceramic material so as to be highly refractory and practically unaffected by elevated temperatures. 
     It has also been found to be advantageous to coat the frames and carrying structure with a heat-insulating coating or covering. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     The above and other objects, features and advantages will become more readily apparent from the following description, reference being made to the accompanying drawing in which: 
     FIG. 1 is a highly diagrammatic side-elevational view showing a high-temperature, high-pressure electrostatic precipitator according to the invention; 
     FIG. 2 is an enlarged vertical sectional view taken along section line II--II of FIG. 1; 
     FIG. 3 is a fragmentary sectional view taken along section line III--III in FIG. 2; and 
     FIGS. 4A-4F are diagrams which show details of the means for tensioning the corona-discharge electrodes. 
    
    
     SPECIFIC DESCRIPTION 
     FIG. 1 shows an inclined precipitator housing 8, which is supported by a carrying structure 20, 21. 
     The precipitator housing 8, which has the form of a duct, is provided with a generally horizonal gas-inlet pipe 18 at the lower end and axially extending gas-outlet pipe 19. 
     Dust bins 14 with discharge devices 14a (represented diagrammatically) are provided on the underside of the precipitator housing. 
     Housings 15, 16, 17 are mounted on top of the precipitator housing 8 and accommodate the insulators 7 for carrying the corona discharge electrode system. 
     The housings 15 are associated with vertical carriers 5 (see FIG. 3). The housings 16 are associated with the inclined carriers 6, which are directed upwards out of the collection region in the direction of gas flow. The housings 17 are associated with the inclined carriers 6, which are directed upwards out of the system opposite to the direction of gas flow, i.e. the carriers 6 of housings 16 and 17 diverge (see FIG. 3). High voltage is applied through housings 17. 
     The precipitator housing has an elliptical contour in the vertical sectional view shown in FIG. 2. The housings 15 contain the insulators 7 for vertically supporting the gridlike frame 1 by means of the carriers 5. The frame 1 consists of two horizontal main carriers 2 and a plurality of vertical auxiliary carriers 3. 
     The fragmentary sectional view of FIG. 3 indicates how the corona discharge electrode field is supported. 
     Platelike collecting electrodes 22 extend substantially parallel to the direction of gas flow in vertical planes and divide the entire flow area into discrete passages, in which the tensioned corona discharge electrodes 9 extend parallel to the direction of gas flow. 
     The corona discharge electrodes 9 are secured to the upper vertical auxiliary carriers 3 and pass over elements on the lower auxiliary carriers 13 and tensioned by weights. See FIGS. 4A-4F. 
     The auxiliary carriers 3, 13 and the main carriers 2 constitute frames, which are suspended in the housings 15 by means of vertical carriers 5 and interposed insulators and are spaced a predetermined distance apart by means of inclined carriers 6, which are directed out of the region and are secured in the housings 16 and 17 by insulators 7. 
     The angle between the carriers 5 and 6 is so selected that the weight and the tensile forces of the corona discharge electrode system can be taken up without a rigid connection between the frames. High voltage is applied through the housing 17. Dust-collecting bins 14 are provided on the underside of the precipitator housing 8. 
     Various arrangements comprising weights 10 for tensioning the corona wires 9 are shown in FIGS. 4A-4F. In all of these FIGURES the vertical auxiliary carrier is designated 13. 
     In accordance with FIG. 4A, the corona wire 9 is guided around a pulley 11, which is rotatably mounted on the auxiliary carrier 13, and is tensioned by a weight 10 which is secured to the corona wire 9. The center of mass of weight 10 is thus offset from the pulley axis. 
     In accordance with FIG. 4B, the corona wire 9 is secured to one arm of a bell-crank lever 12 and a weight 10b for tensioning the corona wire is carried by the other arm of the lever, which is fulcrumed between these arms to the auxiliary carrier 13. 
     In accordance with FIG. 4C, the corona wire 9 is directly connected to an elliptical weight 10c, whose center of mass is offset from the pivot by which this weight is rotatably mounted on the auxiliary carrier 13. 
     In FIG. 4D, the weight 10d consists of a pulley, which is pivoted to the auxiliary carrier 13 by a lever 12d. The corona wire 9 is secured in this case at the pivoted axis or fulcrum. 
     In FIG. 4E, the corona wire 9 is also secured at the pivot and an elliptical weight 10e is provided. In accordance with FIG. 4F the corona wire 9 is secured directly to the auxiliary carrier 13 and an angled weight 10f having two wire-deflecting pins is suspended from the wire to tension the same. 
     As can be seen from FIG. 4A, the members 13 of the frame, like all of the members of the upper and lower frames can be hollow and connected in a closed circulating system 50 for a coolant, this system including a pump 51 and a heat exchanger 52 for removing heat from the coolant which can be water. The external surfaces 53 of the members are coated with a ceramic such as alumina or other thermally insulating material while the tensioning members 10, 10b-10f, 11, 12 and 12d can be composed of ceramic as well.