US 3117849 A
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Description (OCR text may contain errors)
Jan. 14, 1964 w. A. SELKE AIR CLEANER Filed Aug. 22, 1961 4 II II & 1 L
i l/r INVENTOR.
& r 4% M United States Patent 3,117,849 Am CLEANER William A. $81129, Stockbridge, Mass, assignor to Kimberly-Clml: Corporation, Neenah, Wis., a corporation of Delaware Filed Aug. 22, 1961, Ser. No. 133,188 4 Claims. (Cl. 55-131) This invention relates to air cleaners, and more particularly to air cleaners which combine the ellects of mechanical filtration and electrostatic precipitation.
Mechanical filters, generally fabricated of a fibrous material, have the advantage of being small and cheap, but have been found to be relatively inefiective in removing very small particles, such as cigarette smoke, from the air. Electrostatic precipitators, on the other hand, are effective against extremely small particles, but have numerous other disadvantages. Precipitators are generally large and expensive in relation to filters, they require a high voltage for charging the collector plates or electrodes of the precipitator, they require an ionizer in advance of the collector plates for charging the particles to be removed from the air, and they require rather elaborate cleaning systems for removing the particles which accumulate on the plates.
It has been suggested to combine the advantages of mechanical filters and electrostatic precipitators and thus eliminate some of the disadvantages of each. Such fibrous electrostatic cleaners have been found to be much more encient than either filters or precipitators, since lower voltages can be used to charge the electrodes and no ionizer is required. However, a problem which remains is that of removing the accumulation of particles deposited on the air cleaner. This problem is particularly acute since the fibrous material cannot readily be cleaned.
It is a general object of the present invention to alleviate this and other problems by providing a fibrous electrostatic cleaner in which the collector plates or electrodes are disposable. Toward this end, the collector plates are formed of fibrous, and hence porous, electrically conductive sheets. Preferably, these sheets are electrically conductive paper. Since the fibrous sheets are porous, they serve to mechanically filter the air, and since they can be charged electrically, they serve, at the same time, as electrostatic precipitators. The outstanding advanta e of using electrically conductive paper or the like is that it is cheap enough to be discarded, once it becomes clogged with particles filtered and precipitated out of the air, and replaced by similar sheets. The problem of leaning the filter and precipitator elements is eliminated, consequently.
It is another object of the invention to provide the electrically conductive fibrous sheets in the form of a mulilayer web extending across the flow of air to be cleaned, the web being movable longitudinally in order to move a particle-filled portion of the web out of the air stream and a fresh portion of the Web into the flow of air.
It is a further object of the invention to provide a multilayer electrically conductive web wherein the layers comprise adjacent discontinuous conductive regions separated by narrow transverse non-conductive regions so that in the event of a short circuit between electrically conductive layers, only a limited region of the web will be affected.
t is still another object of the invention to provide a multilayer electrically conductive web wherein the electrically conductive layers are laterally offset so that brushes connected to an electrical source can make constant electrical contact with each of said conductive layers respectively in order to produce an electrical field bet een the layers.
It is yet a further object to provide a multilayer paper web including outer electrically conductive layers separated by an inner nonconductive layer wherein the inner layer and one of the outer layers are formed as a single sheet of paper.
Other objects and advantages will be apparent in the following description in which reference is made to the accompanying drawings.
In the drawings:
FIGURE 1 is a schematic view of an illustrative air cleaner made according to the present invention;
FIGURE 2 is a cross-sectional view taken on line 22 of FIGURE 1;
FIGURE 3 is a face view of one of the electrically conductive sheets; and
FIGURE 4 is an enlarged cross-sectional view of a composite conductive and nonconductive sheet.
The air cleaner chosen for illustration comprises gen orally a multilayer web 10 adapted to be unwound from a supply roll 11 and rewound upon a take-up roll 12. The rolls l1 and 12 are arranged on either side of a duct 13 carrying the air to be cleaned, and the web 10 passes through the duct transversely to it so that all the air flowing in the duct must pass through the web.
The web is fabricated of porous fibrous material, such as paper, and in the present illustration is formed of three layers or sheets (see FIGURE 2). The outer sheets 14 and 15 of the Web are capable of conducting electricity. If the sheets are paper, they may be made electrically conductive during the paper-making process by, for example, including electrically conductive fibers in the slurry from which the paper is made. The intermediate sheet 18 is nonconductive and serves to separate the outer conductive sheets 14 and 15. The outer sheets could be separated by air; however, in the present embodiment wherein the web is wound upon the rolls 11 and 12 it is more convenient to employ a nonconductive sheet 18 to maintain the separation between the conductive sheets.
Ln order to charge the conductive sheets or electrodes 14 and 15 so as to create an electrical field between them, a pair of brushes or shoes 19 and 20 are provided, the shoes being electrically connected to the opposite poles of a source of direct current, such as the battery 21. Alternatively, a simple half-wave rectifier connected to a source of alternating current could be used in place of the battery 21. Under some circumstances the paper electrodes could be energized with alternating current, but for most cases direct current is preferable. The shoes 19 and 2t) engage the web It) along its opposite lateral edges. In order that each shoe will contact only one of the outer conductive sheets 14 and 15, the outer sheets are laterally ofiset, as may be seen in FIGURE 2. Preferably, the intermediate sheet 18 is wider than either of the outer sheets so that it extends across the full width of the web. It will be seen that as the margins of the web 10 move past the shoes 19 and 20, the shoes will maintain constant electrical contact with their respective electrically conductive sheets 14 and 15. An electric motor 22 may be provided for rotating the rolls 11 and 12 in the direction of the arrows in FIGURE 1.
In use, the air to be cleaned carried by the duct 13, indicated by the arrows in FIGURE 2, passes through the web 10. The particles carried by the air are thus subjected to mechanical filtration and electrostatic precipitation simultaneously. The fact that the web 10 is fabricated of fibrous material gives rise to the mechanical filtration. The presence of an electrical field between the outer sheets 14 and 15 causes the particles, which carry small naturally existing charges, to be attracted to and precipitated upon one or the other of the electrically conductive sheets 14 and 15. During the air cleaning operation, the motor 22 is either constantly or intermittently run so as to move particle-filled portions of the web 19 out of the duct 13 and on to the take-up roll 12, and fresh portions of the web from the supply roll 11 into the duct 13. Since the paper used in the present air cleaner is relatively inexpensive, the entire web it) may be discarded once used and replaced by a clean Web. Consequently, the present invention eliminates the need for expensive and cumbersome cleaning apparatus, and a time consuming cleaning operation.
It is possible that the intermediate nonconductive sheet 18 might, by chance, contain a metallic inclusion, in which case a short circuit would develop between the outer charged sheets 14 and 15. This could be avoided by connecting the lateral margins of the web lit to a high current source before the web is used, so as to burn away the metallic fault in the sheet 18. Alternatively, one or both of the outer conductive sheets 14 and 15 could be provided with narrow nonconductive regions extending transversely of the sheet between its opposite lateral edges. The result, as indicated in FIGURE 3, is a series of discontinuous conductive regions 23 insulated from one another by narrow nonconductive regions 24. Consequently, if a short circuit develops in any particular region 23, the short circuit will be opened as soon as that region moves past the shoes 19 and 29.
It is also contemplated that if the sheets 14, 1S, and 18 are made of paper, the nonconductive sheet 18 and one of the conductive sheets, for example the sheet 15, may be made as a single sheet by use of, for example, a multiple headbox system. Thus, as shown in FIGURE 4, a single sheet 25 would be employed which varies across its thickness from an electrically conductive portion 15a to a nonconductive portion 18a. To form the web 10, a second sheet of electrically conductive paper would be placed against the face of the portion 18a.
Where higher levels of filtration are required, and in the case of higher air velocities, it may be desirable to form the web 10 of more than three layers. In such a case, alternate positive and negative electrically conductive sheets would be employed interleaved with nonconductive sheets.
While reference has been made to the filtering of air, it will be understood that other gases may be similarly treated, and that the term air as used herein and in the appended claims is intended to include within its significance flue gases and other gaseous media carrying solid particles which are to be separated out. Also, while the invention can be employed without pre-charging the 4 particles, there is no reason why such pre-charging should not be employed if it is thought desirable or advantageous to do so.
The invention has been shown and described in preferred form only and by way of example and many variations may be made in the invention which will still be comprised within its spirit. It is understood, therefore, that the invention is not limited to any specific form or embodiment except insofar as such limitations appear in the appended claims.
What is claimed is:
1. An air cleaner comprising a duct for carrying a fiow of air to be cleaned, a continuous multilayer fibrous web having a face extending across said duct transverse to the flow of air therethrough so that the air flows through the web, said web comprising outer electrically conductive porous paper-like fibrous layers and an inner nonconductive porous paper-like fibrous layer sandwiched between said outer layers, means for constantly applying an electrical potential of one polarity to one of said outer layers and an electrical potential of opposite polarity to the other of said outer layers in order to create an electric field between them, whereby particles in the air are collected on said web due to both mechanical filtration and electrostatic precipitation, and means for advancing said web in order to move the particle-filled portions of said web away from said duct and fresh portions of said web toward said duct.
2. An air cleaner according to claim 1 wherein said outer layers of said web are laterally olfset, and wherein said means for applying an electrical potential includes a pair of brushes connected to an electrical source engaging the free lateral edges of said layers respectively.
3. An air cleaner according to claim 1 where at least one of said outer conductive layers comprises adjacent discontinuous conductive regions.
4. An air cleaner according to claim 1 wherein the non-conductive layer and at least one of the conductive layers are integral parts of a single sheet of paper.
References Cited in the file of this patent UNITED STATES PATENTS 2,535,697 Roos Dec. 26, 1950 2,782,612 Spiegelhalter Feb. 26, 1957 2,881,859 Nutting Apr. 14, 1959 FOREIGN PATENTS 794,038 Great Britain Apr. 30, 1958