Patent Publication Number: US-4097252-A

Title: Electrostatic precipitator

Description:
FIELD OF THE INVENTION 
     The invention relates to a horizontal flow electrostatic precipitator or filter, for flue gas. 
     BACKGROUND OF THE INVENTION 
     It is known that such filters for purifying the flue gases of a steam boiler installation may be subdivided in the direction of flow by one or more gastight partitions and have separate connection ducts for the admission and the discharge of different partial amounts of flue gas so that distinct and separate chamber spaces are defined. In each of these collection and discharge electrodes are installed in such a manner that they form a plurality of electrically independent precipitation fields which are connected to respective and separately controlled high-tension rectifier units. The fields in each chamber are passed through seriatim by the flowing gas. The collection electrodes are usually of strip metal form and the discharge electrodes of wire. 
     Because of the ever-increasing outputs of boilers, electrostatic filters of this kind must likewise be increased in capacity in order to be able to comply with legal requirements concerning the purity of the waste gases which are finally discharged. The problem of providing space for these electrostatic filter plants has therefore become increasingly difficult, since capacity has been a function of size. In determining the size of such plants a main essential factor is the legal requirement that even in the event of the failure of one of the electric fields the prescribed dust content of the purified gas must not be exceeded. This is possible only if in electrostatic filter units of increasingly large size there has been a greater subdivision into a larger number of electrically separate precipitation fields within each chamber of the filter. 
     Under these conditions the speeds of flow necessary for complying with the guarantee must be kept within certain limits within the electrical precipitation fields in dependence on the type of firing and the composition of the fuel (for example between 1.0 and 1.3 meter per second for mineral coal firing and between 1.6 and 2 meters per second for brown coal firing). Thus, the cross-sections of electrostatic filters have become increasingly great, and because the optimum cross-sectional heights of the electric fields customary at the present time, that is to say a maximum of 13.5 meters, will scarcely be able to be exceeded in the future, this implies increasing the width of the filter as a whole which also can only be done up to a certain limit. 
     The necessary enlargement of the volume of an electrostatic filter is therefore most expediently made only by increasing the length of the filter traversed by the gas in its horizontal flow. But then, where space is restricted it may not be possible to accommodate such a large electrostatic filter with the ground plan arrangement hitherto customary (as shown in FIG. 1) with its longitudinal axis in the direction of flow, within the distance between the boiler house and the chimney. 
     SUMMARY OF THE INVENTION 
     The present invention therefore seeks to construct a horizontal flow electrostatic filter in such a manner that in order to achieve a greater saving of space it can be installed with its longitudinal axis at right angles, in ground plan, to the distance between the boiler house and the chimney. This means that in a given said distance an electrostatic filter can be installed, on one level, which is of greater capacity than would have been possible in the prior art. 
     According to the invention flue gas inlet ducts for respective ones of the plurality of separate chambers and the corresponding outlet ducts therefrom are connected at opposite ends of the electrostatic filter casings in such a manner that the separate chambers are to be passed through in opposite directions by fractions of the total throughput of the flue gas. 
     To further increase the capacity of the installation the electrostatic filter of the invention may be connected in parallel to a second horizontal-flow flue gas electrostatic filter and can be disposed above the latter. 
    
    
     DESCRIPTION OF THE DRAWINGS 
     In the accompanying drawings, which are somewhat diagrammatic: 
     FIG. 1 shows a customary prior art ground plan arrangement and construction of a horizontal-flow flue gas electrostatic filter between a boiler house and a chimney, and 
     FIG. 2 shows the ground plan arrangement and construction of the electrostatic filter embodying the invention. 
    
    
     DESCRIPTION OF PRIOR ART 
     The prior art arrangement, seen in FIG. 1, has a boiler 1 in a boiler house 3, with its flue gases passing through rotary regenerative preheaters 2 and then in parallel through an electrostatic filter 4. The gases are divided between separate chambers of the filter 4 and in each chamber flow in the same direction, shown by arrows F, which is also the direction of the shortest distance between boiler house 3 and chimney 6. Draught fans 5 are in the base of the chimney 6. 
     DESCRIPTION OF A PREFERRED EMBODIMENT 
     FIG. 2 also shows part of the steam boiler 1, at whose flue gas outlet two regenerative air preheaters 2a, 2b are disposed inside a boiler house 3. Half of the flue gases flow from the right-hand regenerative air preheater 2a through a right-hand gas inlet duct 8 and then from right to left in a first chamber 9 of electrostatic filter 7 which is longitudinally divided into separate and horizontally side-by-side chambers by longitudinal wall 10. The electrostatic filter 7 is installed with its longitudinal axis side disposed transversely to, preferably at right angles to, the distance between the boiler house 3 and a chimney 6. From the left-hand end of the first chamber 9 of the electrostatic filter 7 one half of the purified flue gas flows through the left-hand gas outlet duct 11 and the induced draught fan 5a into the chimney 6. Similarly, the inlet of the second chamber 12 of the electrostatic filter 7 is connected by inlet duct 13 to the left-hand regenerative air preheater 2b. The gas flows through the chamber 12 from left to right, as shown by arrows F&#34; i.e. in the opposite direction to the flow F&#39; in the first chamber, and at its outlet this second chamber 12 is connected by outlet duct 14 to the right-hand induced draught fan 5b. 
     Each of the chambers 9 and 12 has a plurality of arrays (7a and 7b respectively) of collection and discharge passed through in series by the gas flows, such arrays being separately electrically supplied and controlled. 
     A first electrostatic filter arranged thus may be superposed on or lie vertically under a second electrostatic filter arrangement which may be of conventional type and lie with its longitudinal axis at right angles to that of the first. 
     It can be seen that inlet an outlet ducts for separate chambers of the electrostatic filter casing may in many cases be disposed and installed in a spatially more favourable manner than has been possible in the prior art and that in conjunction therewith the arrangement of the electrostatic filter embodying the invention makes it possible for the filter to be accommodated in a relatively short distance between the boiler house and the chimney.