Electronic fine dust separator

Abstract

A method and to a device for the electrostatic separation of fine dust particles from gases that flow through a housing (1) containing perforated plates (6) and electrodes (4, 5). An electric field is created between the electrode (4) on the inflow opening side and the electrode or electrodes (5) having positive polarity on the outflow side. The removal of negatively charged fine dust particles (9) is carried out by deposition on the inflow side of the perforated plates (6), and the removal of positively charged fine dust particles (11) is carried out on the outflow side. Fine dust particles without charge (10) are charged after the last perforated plate (6) in an ionization chamber (8) and deposit on the outflow side of the last perforated plate (6).

Claims

1. A method for electrostatic separation of fine dust particles from a gas containing fine dust particles in a housing having an inlet side and an outlet side and a direction of flow defined between the inlet side and the outlet side, an electrode at the inlet side, an electrode at the outlet side, non-conductive perforated plates arranged between the electrode at the inlet side and the electrode at the outlet side and transverse to the direction of flow, the perforated plates each having an inflow side and an outflow side, the perforated plates comprising openings for the gas flow and deposition surfaces on the inflow and outflow side for fine dust particles, wherein the openings of adjacent perforated plates are arranged staggered in relation to each other in the direction of flow, the method comprising: establishing an electric field between the electrode at the inlet side of the housing and the electrode at the outlet side of the housing, wherein the electrode at the inlet side has negative polarity or is grounded, and the electrode at the outlet side is has positive polarity, or the electrode at the inlet side is has positive polarity and the electrode at the outlet side has negative polarity or is grounded, flowing said gas along a direction of flow between the inlet side of the housing and the outlet side of the housing, electrostatically depositing fine charged dust particles on the inflow and outflow sides of the perforated plates, wherein the depositing of negatively charged fine dust particles is achieved through electrostatic deposition on the inflow side deposition surfaces of the non-conductive perforated plates and the depositing of positively charge fine dust particles is achieved through electrostatic deposition on the outflow side deposition surfaces of the non-conductive perforated plates in the case that the electrode at the inlet side has negative polarity or is grounded and the electrode at the outlet side is has positive polarity, or the depositing of positively charged fine dust particles is achieved through electrostatic deposition on the inflow side deposition surfaces of the non-conductive perforated plates and the depositing of negatively charged fine dust particles is achieved through electrostatic deposition on the outflow side deposition surfaces of the non-conductive perforated plates in the case that the electrode at the inlet side has positive polarity and the electrode at the outlet side is has negative polarity or is grounded wherein the gas flow which emerges from the openings of a non-conductive perforated plates (6) plate strikes the deposition surface of a subsequent perforated plate producing a suction towards the deposition surface upon striking the deposition surface of the subsequent perforated plate, and wherein non-charged fine dust particles or fine dust particles which passed through the last perforated plate are charged in an ionization chamber between the last perforated plate and the electrode at the outlet side and deposited on the outflow side deposition surface of the last perforated plate.

2. The method according to claim 1, wherein the polarity of the electrodes is alternated, as a result of which the deposition surfaces are coated with fine dust particles opposite in sign and ozone is eliminated on the outlet side of the separator.

3. The method according to claim 1, wherein gas relaxation takes place in the ionization chamber due to a larger through-flow area of the electrodes compared with the last perforated plate, in the area of the outflow opening, with the result that the time available for ionization increases.

4. The method according to claim 1, wherein the charging of non-charged fine dust particles or of fine dust particles with too low a charge is conducted in the ionization chamber through diffusion charging.

5. The method according to claim 1, wherein the fine dust particles are in the range of 0.05-0.5 m.

6. A device for electrostatic separation of fine dust particles from gas containing fine dust particles in a housing having an inflow opening and an outflow opening and a direction of flow between the inflow opening and the outflow opening, wherein at least the following listed elements are located consecutively in the direction of flow and spaced apart in said housing: a first electrode earthed or having a negative polarity and oriented transversely to the direction of gas flow, two or more adjacent perforated plates occupying the housing and oriented transversely to the direction of the gas flow, wherein said adjacent perforated plates each have perforation openings and an inflow side deposition surface and an outflow side deposition surface for deposition of fine dust particles, wherein the openings of said adjacent perforated plates are staggered in said direction of the gas flow, one or more second electrodes having a positive polarity, an electric field between the first and second electrodes and passing through the two or more adjacent perforated plates, and an ionization chamber between the last perforated plate in the direction of flow and at least one of said one or more second electrodes in which ionization chamber fine dust particles that pass through the last perforated plate in the direction of flow become charged for electrostatic deposition on the outflow side deposition surface of said last perforated plate in the direction of flow.

7. The device according to claim 6, wherein the electrodes and are configured in form of a sieve or a net.

8. The device according to claim 6, wherein impact ionization is produced in the ionization chamber between the last perforated plate and the first electrode by voltage applied to the one or more electrodes.

9. The device according to claim 6, wherein distance between adjacent perforated plates and the perforation size are such that the exiting gas flow, on striking the deposition surface of the following perforated plate, creates a suction towards the deposition surface.

10. The device according to claim 6, wherein the surface of the perforated plates is rough.

11. The device according to claim 6, wherein the electrodes and are configured in form of a sieve or a net forming a flat surface.

12. The device according to claim 6, wherein the perforated plates consist of a plastic.

13. The device according to claim 6, wherein the fine dust particles are in the range of 0.05-0.5 m.

Description

(1) The fine dust separator is to be explained by an embodiment example, where:

(2) FIG. 1 shows the cross-section in the direction of flow,

(3) FIG. 2 shows the deposition of fine dust particles,

(4) FIG. 3 shows the ionization chamber and

(5) FIG. 4 shows the concentration profile of fine dust particles before and after the separator when the separator is switched on and following the shutdown of the separator.

(6) FIG. 1 shows the cross-section of a preferred embodiment of the device for the electrostatic separation of fine dust particles 9, 10, 11 from exhaust air containing fine dust particles from copying technology in the direction of flow 14.

(7) In the housing 1, the following are arranged one after another and spaced apart in the direction of flow 14 between the inflow opening 2 and the outflow opening 3: an electrode 4 which is earthed or has negative polarity, four perforated plates 6 occupying the housing 1 transversely to the direction of flow 14, wherein the openings 7 of adjacent perforated plates 6.1,6.2; 6.2,6.3 and 6.3,6.4 are staggered in the direction of flow 14, and four electrodes 5 have positive polarity.

(8) An electric field exists between the electrodes 4 and 5 due to the voltage of 8-14 KV applied to the electrodes.

(9) The distance (a) between the plastic plates 6 in this embodiment example is 2-3 mm and the width (b) of the ionization chamber 8 is 2-4 mm.

(10) The electrodes 4 and 5 are sieves with sieve wire diameters of 0.05 mm and smaller, each of which form a flat surface.

(11) Due to the voltage of 8-14 KV applied to the electrodes 5, impact ionization can be produced in the ionization chamber 8 between the last perforated plate 6.4 and the electrodes 5.

(12) The perforated plates 6 are made of an electrically non-conductive plastic, where the surface of the perforated plates 6 is roughened. The perforation diameter of the openings 7 of the perforated plates 6 is 1.5-2.2 mm, preferably 1.8-2 mm, and the distance between the centers of adjacent openings 7 from one another is approx. 6 mm.

(13) The description indicates that the fine dust separator has a compact form. Despite this relatively small spatial extent of approx. 15-25 mm in the direction of flow 14, the separator allows e.g. fine dust adsorption during the production of around 100,000 copies, without the need for maintenance.

(14) The mode of operation is to be explained with reference to FIG. 2 and FIG. 3.

(15) FIG. 2 shows a detail of two perforated plates 6.1 and 6.2 located one behind the other. The openings 7 of the perforated plate 6.2 are staggered with respect to the openings 7 of the perforated plate 6.1.

(16) The distance (a) between the perforated plates 6.1 and 6.2 is 2-3 mm and, with the perforation size, is adjusted to the gas flow such that the exiting gas flow, on striking the deposition surface 13 of the perforated plate 6.2, creates a suction towards the deposition surface 13 at its center.

(17) After flowing through the earthed electrode 4, the exhaust air which is contaminated with fine dust particles 9, 10, 11 strikes the electrically non-conductive perforated plate 6.1 and enters the intermediate space between the perforated plates 6.1 and 6.2 through the openings 7. The fine dust particles either have a positive charge 11, a negative charge 9 or no charge 10.

(18) On flowing into the intermediate space between the perforated plates 6.1 and 6.2, the fine dust particles 9, 10, 11 collide with the inflow side of the perforated plate 6.2, with the deposition surface 13 present here.

(19) The forces of the electric field between the electrodes 4 and 5, flow forces and the suction forces explained above act on the fine dust particles 9, 10, 11.

(20) On striking the deposition surface 13 of the inflow side of the perforated plate 6.2, significant fractions of fine dust particles with a negative charge remain stuck here.

(21) The remaining fraction of fine dust particles rebounds from the deposition surface 13 and strikes the outflow side of the perforated plate 6.1. Due to the effect of the electric field, parts of the positively charged fine dust particles 11 are deposited on this outflow side on the deposition surfaces 12 present here.

(22) The remaining fraction of fine dust particles reaches the intermediate space between the perforated plates 6.2 and 6.3 through the openings 7 of the perforated plate 6.2. The separation process is repeated here in the manner described previously.

(23) A blockage of the openings 7 and the intermediate spaces respectively is avoided in that a reduction of the flow cross-section leads to greater flow rates, overcoming contact forces, and the fraction of fine dust particles flowing further into the next space increases.

(24) In summary, it can therefore be established that the removal of negatively charged fine dust particles 9 is carried out by deposition on the inflow side of the perforated plates 6, and the removal of positively charged fine dust particles 11 is carried out by deposition on the outflow side of the perforated plates 6.

(25) FIG. 3 shows the ionization chamber 8 between the last perforated plate 6.4 and the electrode 5, which has positive polarity and to which a voltage of 8-14 KV is applied.

(26) Due to the separation of positively and negatively charged fine dust particles, only particles with a very weak charge or neutral fine dust particles 10 enter the ionization chamber 8. These fine dust particles 10 and the fine dust particles with low charge are positively charged in the ionization chamber by diffusion charging, with the result that they move in the direction of the outflow side of the last perforated plate 6 and become attached here.

(27) The removal of fine dust particles without charge 10 or fine dust particles with too low a charge is therefore carried out after the last perforated plate by charging in an ionization chamber 8 and deposition on the outflow side of the last perforated plate 6.

(28) The concentration profile of fine dust particles in front of and behind the separator over time is shown in FIG. 4. Separation rates of at least 90 to 96% are achieved with the proposed separator.

(29) While the concentration of fine dust drops abruptly (graph 3) after switching on the separator and levels off at a virtually constant value (top fig.), the concentration increases significantly again when the separator is switched off (graph 3 in the bottom fig.).

LIST OF REFERENCE NUMERALS

(30) 1 Housing 2 Inflow opening 3 Outflow opening 4 Electrode earthed or having negative polarity 5 Electrodes having positive polarity. 6 Perforated plates 7 Openings of the perforated plates 8 Ionization chamber 9 Fine dust particles negatively charged 10 Fine dust particles without charge 11 Fine dust particles positively charged 12 Deposition of positively charged fine dust particles 13 Deposition of negatively charged fine dust particles 14 Direction of flow