Patent Publication Number: US-6663696-B1

Title: Earth conductor for earthing systems

Description:
This is a 371 of PCT/EP00/06669 filed Jul. 13, 2000 (International filing date). 
     The invention relates to an earth conductor for earthing systems, in particular of electrostatic separators, such as dry, semi-dry or wet electrostatic filters, consisting of an electrically conductive core with a plastic or rubber sheath. 
     BACKGROUND OF THE INVENTION 
     Moist, saturated gases are nowadays widely cleaned using wet electrostatic filters, on the precipitation electrodes of which a liquid film forms under the influence of the electric field and runs off continuously. Any particles of dust present are thereby removed as a suspension. If necessary, an additional system of continuously operating mist nozzles can be provided for gas saturation. The moist atmosphere necessitates the use of earth conductors that are good electrical conductors and are made from corrosion resistant materials in order to ensure that the current is safely conducted away from the electrodes. If the earth conductor should be destroyed, the current is conducted away via plastic parts or via the rubber covering of the filter housing, with the result that not insignificant damage occurs, which may lead to the electrostatic filter systems being shut down for extended periods. 
     DE-C-12 31 216 describes a wet electrostatic separator for cleaning moist chlorine gas or waste gases containing chlorine gas, which, for conducting away the electrical charge of the conductive liquid collecting in the drainage channels, has wick-like, liquid-absorbing cords or ropes produced using a ceramic substance or from glass fibres and connected to an earth conductor. 
     DE-C-15 57 162 describes a device for the corrosion resistant earthing of precipitation electrodes made from non-conductive material in wet tubular electrostatic dust separators. The lower part of the precipitation electrode tube is rendered electrically conductive by a paint or coating by means of an electrically conductive material and has an earth conductor wound around it in a loop. The strands of the earth conductor in the loop are separated from one another by a spacer made from non-conductive material. 
     DE-A-43 28 438 discloses an earth conductor for earthing systems of electrostatic separators which has a core made from carbon, e.g. graphite cords, which is encased with a layer of plastic or rubber and which is said to have high corrosion resistance over long operating periods. On use of earth conductors of this type—even in the case of a reduced pressure prevailing in the housing of the electrostatic filter—the capillary action of the earth conductor means that liquid is drawn out of the housing of the electrostatic filter to the screw connections attaching the earth conductor to the earthing system, where it causes considerable corrosion, which leads to destruction of the screw connections with increasing operating time and thus to damage to and shutdown of the electrostatic separator. 
     SUMMARY OF THE INVENTION 
     The object of the present invention is to provide an earth conductor for earthing systems, in particular of electrostatic separators, which is simple to install, which is flexible and chemically resistant, and which prevents escape of liquid from the housing of the electrostatic separator so that corrosion of the contact zone between the earth conductor and the earthing system does not occur. 
     The use of the earth conductor according to the invention is particularly suitable for tubular electrostatic filters, which consist of a housing with plastic tubes arranged in parallel and vertically therein, with electrodes running in the centre of each tube, each tube being connected at both ends to the corresponding current-side conductor part of the earth conductor. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention is described in greater detail with and by way of example below. In the drawing: 
     FIG. 1 shows a diagrammatic longitudinal section through a tubular electrostatic filter; 
     FIG. 2 an enlarged depiction of detail X in FIG.  1 . 
    
    
     DETAILED DESCRIPTION 
     The tubular electrostatic filter ( 1 ) consists of a rubber-covered steel or plastic housing ( 2 ) with tubes ( 3 ) having a circular cross section arranged in parallel and vertically therein serving as precipitation electrodes, in the centre of which the discharge electrodes ( 4 ) are suspended in an insulated manner. The tubes ( 3 ), which consist of plastic, are suspended and sealed in a tube carrier base ( 5 ) which is arranged in the upper part of the tubular electrostatic filter ( 1 ). The lower ends of the tubes are spaced by a grid, which is not shown. The gas direction ( 6 ) is generally selected to be from top to bottom. The current transport takes place in the liquid film on the specially prepared surface of the electrically non-conductive plastic of the tubes ( 3 ). The plastic tubes ( 3 ) serving as precipitation electrodes are thus merely carriers of the conductive liquid film. The electrical current is conducted away from the liquid film to the earthing system from the upper and lower ends of the plastic tubes ( 3 ), which are edged at both ends from the outside by an electrically conductive strip ( 7 ), which in each case leads to a terminal block ( 8 ). From the terminal blocks ( 8 ), an earth conductor ( 10 ) leads to the earth ( 11 ) through corresponding openings ( 9 ) in the housing ( 2 ) of the tubular electrostatic filter ( 1 ). The earth conductor ( 10 ) in each case consists of a current source side conductor part and an earth side conductor part ( 12 ,  13 ), which are built up from an electrically conductive core ( 14 ,  15 ) having a rectangular cross section made from graphite fibre braiding with a butyl rubber sheath ( 16 ,  17 ). The two conductor parts ( 12 ,  13 ) are connected by a liquid-tight, cuboid graphite piece ( 18 ), which is permanently pressed against unsheathed sections of the cores ( 14 ,  15 ) in a parallel overlapping manner in such a way that the longitudinal axes of the cores ( 14 ,  15 ) run parallel to the longitudinal axis of the graphite piece ( 18 ). The graphite piece ( 18 ), the unsheathed sections of the cores ( 14 ,  15 ) of the earth conductor ( 10 ) which are pressed against it, and the zones of the sheaths ( 16 ,  17 ) adjacent to these sections are embedded in a plastic body ( 20 ) cast in a hollow, plastic cylinder ( 19 ). The earth conductor ( 10 ) is inserted into the opening ( 9 ) in the housing ( 2 ) of the tubular electrostatic filter ( 1 ) via a flange ( 21 ) running around the circumference of the hollow cylinder ( 19 ) and is bolted, with the insertion of the sealing ring ( 25 ), to the corresponding flange ( 23 ) of the tube connector ( 24 ) installed in the wall of the tubular electrostatic filter ( 1 ). 
     The earth conductor designed in accordance with the invention has high flexibility, is simple to install, and reliably prevents the passage of liquid from the housing of the tubular electrostatic filter to the connecting point with the external earth connection.