IL109265A

IL109265A - Electrostatic method and apparatus for separating particles from a fluid stream

Info

Publication number: IL109265A
Application number: IL109265A
Authority: IL
Inventors: Chaim Gutfinger; David Pnueli; Mati Fichman; Leonid Moldavsky
Original assignee: Technion Res & Dev Foundation
Priority date: 1994-04-08
Filing date: 1994-04-08
Publication date: 1998-04-05
Also published as: IL109265A0; WO1995027565A1

Description

ELECTROSTATIC METHOD AND APPARATUS FOR SEPARATING PARTICLES FROM A FLUID STREAM TECHNION RESEARCH AND DEVELOPMENT FOUNDATION LTD.

Inventors: Chaim Gutfinger David Pnueli Mati Fichman inD'g Tin Leonid Moldavsky C: 18329 ELECTROSTATIC METHOD AND APPARATUS FOR SEPARATING PARTICLES FROM A FLUID STREAM The present invention relates to a filtering method and apparatus, and particularly to an electrostatic filtering method and apparatus for separating particles from a fluid stream. The particles may be solid particles, and/or liquid drops, and/or soft doughlike particles, melted material, etc.; and the fluid may be gaseous (e.g., separation of dust particles from an air stream), or vapor, or liquid, or a mixture of these.

Conventional mechanical filters include a fluid-permeable filtering element across the outlet which removes the particles from the fluid stream flowing through the outlet. The particles thus accumulate in the fluid-permeable filtering element and must therefore be periodically removed (as by mechanical shaking, water rinsing, or the like), or the filtering element must be periodically replaced.

An object of the present invention is to provide a filtering method and apparatus free from the need for periodical cleaning or replacing the filtering element.

According to one aspect of the present invention, a method is provided for separating particles from a fluid stream which flows along a flow path from an inlet to an outlet, comprising: electrostatically charging the particles with charges of one polarity while the fluid stream flows through an electrostatically charging zone in the flow path; locating a fluid-permeable electrode across the outlet; and electrostatically charging the fluid-permeable electrode with a charge of the same polarity as the charged particles to repel from the fluid outlet the charged particles in the fluid flowing through the fluid-permeable electrode to the fluid outlet.

According to further features in the described preferred embodiment, the method also includes electrostatically charging a precipitating electrode with a charge of the opposite polarity as that of the charged particles to attract the charged particles thereto.

According to still further features in the preferred embodiments of the invention described below, the particles are charged with the one polarity by a corona discharge.

Two embodiments of the invention are described below for purposes of example.

According to one described embodiment, the precipitating electrode is located outside of the flow path from the inlet to the outlet. In addition, the electrostatic charging zone is enclosed by an annular (circular or of other geometrical shape) electrode through which the flow path passes from the inlet to the outlet, and electrically connected to the fluid-permeable filtering electrode .

According to a second described embodiment, the precipitating electrode is located laterally of the flow path from the inlet to the outlet. In addition, the electrostatic charging zone is defined by an electrostatically charging electrode through which passes the flow path, and the precipitating electrode is of annular (circular or of other geometrical shape) configura ion located around the electrostatically charging electrode, such that the flow passes between the two electrodes.

The invention also provides apparatus for separating particles from a fluid stream in accordance with the above method.

As will be described more particularly below, the method and apparatus of the present invention are effective to block the particles from reaching the filtering element, such as the fluid-permeable electrode which also serves as the filtering element, or a separate mechanical filtering element provided on the downstream side of such a fluid-permeable electrode, thereby negating the need for periodically cleaning the filtering element or periodically replacing it.

The present invention is to be sharply distinguished from the conventional electrostatic filtering or precipitation method. In such conventional method, the particles are electrostatically charged with charges of one polarity, and the precipitating electrode is electrostatically charged with a charge of the opposite polarity to attract the charged particles thereto; but such a method does not include a fluid-permeable electrode across the outlet which is electrostatically charged with a charge of the same polarity as the charged particles to repel from the fluid outlet the charged particles in the fluid flowing through the fluid-permeable electrode.

The novel method of the present invention is also to be sharply distinguished from that described in Arbesi US Patent 5,203,993, Yeh US Patent 4,066,526, and Masuda US Patent 3,930,815. The Arbesi patent relates to a method and apparatus for removing salt from sea water in which a repelling electrode is also provided carrying a charge of the same polarity as that on the particles, but there the repelling electrode is located parallel to the outlet and not across the outlet. The Yeh patent relates to a method which also includes a repelling electrode, but the same electrode also produces a corona discharge for electrostatically charging the particles. The method of the Masuda patent also includes repelling electrodes for repelling the particles, but there the repelling electrodes are located in the path of the fluid stream, and not across the fluid outlet to block the fluid particles from reaching the fluid outlet.

Further features and advantages of the invention will be apparent from the description below.

The invention is herein described, by way of example only, with reference to the accompanying drawings, wherein: Fig. 1 schematically illustrates one form of filtering apparatus constructed in accordance with the present invention; and Fig. 2 schematically illustrates a second form of filtering apparatus constructed in accordance with the present invention.

The filtering apparatus illustrated in Fig. 1 comprises a housing, generally designated 10, formed with one or more inlets 11 , and one for more outlets 12. The housing further includes a blower 13 for producing a fluid stream of a gas (e.g., air) containing particles, which are to be removed from the fluid stream before reaching the outlet 12.

For purposes of removing the particles from the fluid stream, housing 10 further includes one or more electrostatically charging electrode 14 for electrostatically charging the particles with charges of one polarity while the fluid stream flows through an electrostatically charging zone defined by these electrodes towards the outlet 12. The filter further includes a fluid-permeable electrode 15 adjacent to and across the fluid outlet 12, such that the flow path of the fluid stream from the inlet 11 to the outlet 12 must pass through it.

Housing 10 further includes a precipitating electrode 16 on the opposite side of the inlets 11, i.e., out of the flow path of the fluid stream as it flows from the inlet 11 towards the outlet 12. Precipitating electrode 16 is electrically insulated from electrodes 14 and 15 and it receives a charge of the opposite polarity from those electrodes. When housing 10 is made of conducting material and is grounded, electrode 16 is either insulated from housing 10, or it may be connected to housing 10, i.e., grounded and not charged separately. A layer of water 17 is applied over precipitating electrode 16. As will be described below, the particles in the fluid stream are attracted towards precipitating electrode 16 and precipitate on the water layer 17 thereover, which facilitates the removal of the precipitating particles. Water layer 17 may be a static layer, but preferably is a circulating layer so as to continuously remove the precipitating particles.

As illustrated in Fig. 1, electrodes 1 and 15 are connected to a common voltage source via line 18 and lead-through insulator 10a. Precipitating electrode 16, when not grounded, is connected to another common voltage source via line 19. The voltage sources of the two lines 18 and 19 are of opposite polarity. In the example illustrated in Fig. 1, line 18 connected to electrodes 14 and 15 is of negative polarity, and line 19 connected to the precipitating electrode 16 is of ground or positive polarity.

Electrodes 14 produce a corona discharge to thereby electrostatically charge the particles within the fluid stream of one polarity, in this case of the negative polarity, while the fluid stream flows through an electrostatically charging zone between inlet 11 and the fluid-permeable electrode 15. Electrode 15 is of the same polarity as the charges applied to the particles, and thereby repels the particles so that only the fluid, without the particles, passes through the fluid-permeable electrode 15 to the outlet 12. An electrode 14a, enclosing the electrostatically charging zone between inlets 11 and the fluid-permeable electrode 15, is connected to the latter two electrodes and thereby also repels the particles, so that the particles will not precipitate on this electrode 14a.

The precipitating electrode 16, however, is of the opposite polarity as that of the charged particles and therefore attracts the charged particles towards it. These particles are deposited on the water layer 17 over electrode 16. If layer 17 is a static layer, the particles with the water may be periodically removed; and if it is a flowing layer, the particles with the water are continuously removed .

Fig. 2 illustrates another construction of electrostatic filter which operates basically in the same manner as described above with respect to Fig. 1.

The filtering apparatus illustrated in Fig. 2 also includes a housing, generally designated 20, with an inlet 21 at one end and an outlet 22 at the other end. A blower 23 located at the inlet end of the housing produces a fluid stream of a gas (e.g., air) containing particles (e.g., dust) flowing from the inlet 21 through the housing and its outlet 22.

An electrostatic-charging electrode 24 is located within housing 20 and extends continuously from its inlet 21 to its outlet 22. A fluid-permeable electrode 25 is located across the outlet 22 so as to extend across the fluid stream path through the housing 20. The fluid-permeable electrode 25 is electrically connected to the electrostatic charging electrode 24 and therefore is at the same potential as that electrode.

Housing 20 is made of metal and encloses the fluid flow path through the housing. It is electrically insulated from the fluid-permeable electrode 25 by an electrical insulator 27, and is of the opposite polarity as electrostatic electrode 24 and the fluid-permeable electrode 25. As shown in Fig. 2 for purposes of example, the fluid-permeable electrode 25 and the electrostatically-charging electrode 24 connected thereto are connected to an electrical conductor 28 of negative polarity; whereas the metal housing 20 is connected to electrical conductor 29 of ground (or positive) polarity.

Electrode 24 produces a corona discharge which electrostatically charges the particles in the fluid stream flowing through the housing 20 with charges of negative polarity. Thus, the complete volume within the housing 20 serves as an electrostatic charging zone for charging the particles in the fluid stream with charges of negative polarity. Housing 20, being of metal and charged with the opposite polarity, serves as an annular (circular or other geometrical shape) precipitating electrode located around the electrostatic charging zone and attracts thereto the negatively-charged particles in the fluid stream. Thus, the particles P within the fluid stream are repelled by both the charging electrode 24 and the fluid-permeable electrode 25, and are attracted by the precipitating electrode 20. These particles therefore traverse the trajectories shown by the curved lines T to precipitate on the inner surface of the precipitating electrode 20.

It will thus be seen that, as described above with respect to Fig. 1, the particles within the fluid stream in the structure of Fig. 2 are blocked from flowing through the fluid-permeable electrode 25 to the outlet 22, and precipitate on the precipitating electrode, in this case the inner surface of the metal housing 20.

In both constructions of Figs. 1 and 2, the fluid-permeable electrode, 15 and 25, respectively, may also serve as the filter element defining the filtering passageways through which the particle-free air passes to the outlet. Alternatively, conventional mechanical filter elements could be applied on the downstream side of these fluid-permeable electrodes to serve as the filtering passageways. In either case, there will be no accumulation of particles on the filtering element so that there will be no need to clean or replace it.

While the invention has been described with respect to two preferred embodiments, it will be appreciated that these are set forth merely for purposes of example, and that many other variations, modifications and applications of the invention may be made.

Claims

1. A method for separating particles from a fluid stream which flows along a flow path from an inlet to an outlet, comprising: electrostatically charging the particles with charges of one polarity while the fluid stream flows through an electrostatically charging zone in said flow path; locating a fluid-permeable electrode across said outlet; and electrostatically charging said fluid-permeable electrode with a charge of the same polarity as said charged particles to repel from said fluid outlet the charged particles in the fluid flowing through said fluid-permeable electrode to said fluid outlet.

2. The method according to Claim 1 , further including electrostatically charging a precipitating electrode with a charge of the opposite polarity as that of the charged particles to attract the charged particles thereto.

3. The method according to either of Claims 1 or 2, wherein said particles are charged with said one polarity by corona discharge.

4. The method according to any one of Claims 1-3, wherein said precipitating electrode is located outside of said flow path from the inlet to the outlet.

5. The method according to Claim 4, wherein said precipitating electrode is located adjacent to the inlet but on the side thereof opposite to that of said electrostatically charging zone.

6. The method according to either of Claims 4 or 5, wherein said electrostatically charging zone is enclosed by an electrode through which said flow path passes, from the inlet to the outlet, and electrically connected to said fluid-permeable electrode .

7. The method according to any one of Claims 4-6, wherein said precipitating electrode is covered by a liquid such that the particles are deposited on the liquid to facilitate their removal.

8. The method according to any one of Claims 1-3, wherein said precipitating electrode is located laterally of said flow path from the inlet to the outlet.

9. The method according to Claim 8, wherein said electrostatically charging zone is defined by an electrostatically charging electrode coaxial with said flow path, and said precipitating electrode is of an annular (circular or of other geometrical shape) configuration located around and coaxial with said electrostatically charging electrode.

10. The method according to Claim 9, wherein said electrostatically charging electrode produces a corona discharge.

11. Apparatus for separating particles from a fluid stream, comprising: a housing having an inlet, an outlet, and a flow path for the fluid stream from said inlet to said outlet; a charging electrode for electrostatically charging the particle with charges of one polarity while the fluid stream flows through an electrostatically charging zone in said flow path; a fluid-permeable electrode located across said flow path; and a voltage source for electrostatically charging said fluid-permeable electrode with a charge of the same polarity as said charged particles to repel from said fluid outlet the charged particles in the fluid flowing through said fluid-permeable electrode to said fluid outlet.

12. The apparatus according to Claim 11 , further including a precipitating electrode charged by said voltage source with a charge of the opposite polarity as that of the charged particles to attract the charged particles thereto.

13. The apparatus according to either of Claims 11 or 12, wherein said charging electrode charges said particles with said one polarity by corona discharge.

14. The apparatus according to any one of Claims 11-13, wherein said precipitating electrode is located outside of said flow path from the inlet to the outlet.

15. The apparatus according to Claim 14, wherein said precipitating electrode is located adjacent to the inlet but on the side thereof opposite to that of said electrostatically charging zone.

16. The apparatus according to either of Claims 14 or 15, wherein said electrostatically charging zone is enclosed by an annular (circular or of other geometrical shape) electrode coaxial with said flow path from the inlet to the outlet and electrically connected to said fluid-permeable electrode.

17. The apparatus according to any one of Claims 14-16, wherein said precipitating electrode is covered by a liquid such that the particles are deposited on the liquid to facilitate their removal.

18. The apparatus according to any one of Claims 11-13, wherein said precipitating electrode is located laterally said flow path from the inlet to the outlet.

19. The apparatus according to Claim 18, wherein said electrostatically charging zone is defined by an electrostatically charging electrode coaxial with said flow path, and said precipitating electrode is of an annular (circular or of other geometrical shape) configuration located around and coaxial with said electrostatically charging electrode.

20. The apparatus according to Claim 19, wherein said electrostatically charging electrode produces a corona discharge. Sanford T. Colb & Co. Tel-Aviv 61 230