JPH0773685B2 - Electrostatic precipitator for use in electrofilters - Google Patents

Abstract

An electrostatic precipitator intended for use with electrofilters comprises a plurality of electrically conductive or semi-conductive plate-like or lamella-like precipitation electrodes (1, 2) which are arranged in mutually parallel spaced relationship. The electrodes (1, 2) are connected alternately to the one and the other terminal of a d.c. voltage source (3) by bringing an edge-surface part of those electrodes which are connected to one and the same terminal into pressure-contact with one side of a sheet-like or strip-like member (4 or 5) which is made of a highly resistive, antistatic material. The opposite side of the member (4, 5) has provided thereon an electric contact means (6 or 7) which is connected electrically to the relevant terminal of the d.c. voltage source (3), preferably through a high ohmic resistance (8 or 9).

Description

The present invention relates to electrostatic filters, electrostatic precipitators for use in so-called electrofilters.

In principle, electrostatic precipitators are electrically conductive or semi-conductive,
An air capacitor connected to both terminals of a DC voltage source that includes a plurality of electrode plates or electrode plates that are arranged in parallel with each other and electrically connected alternately to each terminal of the DC voltage source. Make a structural device similar to. An electrostatic precipitator of this kind is placed in the air flow passage or duct of an electrofilter in such a way that the electrode plates or lamellas extend across the air duct or air flow passage in which the filter is placed, The side surface of the electrode plate is parallel to the direction of the air flow passing through the duct. The airflow in which aerosol pollutants, which are present in the form of solid particles or liquid droplets, are purified is carried through airflow ducts, and blowers or fans, natural airflow, forced ventilation, or electric ionic wind (International Patent Through the dust collector by means of the aid of application PCT / SE85 / 00538). The electrofilter incorporates electrostatic precipitator means upstream in order to electrically charge the aerosol pollutants present in the air stream by some suitable known method, for example by means of a corona discharge generating atmospheric ions. . The purpose of an electrostatic precipitator is to produce electrically charged contaminants in the air flow through the precipitator between its various plate electrodes, between adjacent electrodes, and essentially perpendicular to the direction of the air flow. It is brought under the electrostatic induction of an electric field that extends into the electrode, so that contaminants migrate to one or the other of the electrodes and settle on it, depending on the electrical polarity of the contaminant. And purify the air stream from the contaminants.

In order for this type of electrostatic precipitator to function with a high degree of efficiency, i.e. to be able to extract a significant proportion of the pollutants present in the flowing atmosphere, it is necessary to have a high It is necessary to generate an electric field strength, i.e. a small space between the electrodes to generate a high voltage between adjacent electrodes. However, with today's electrostatic precipitator construction, these requirements are very difficult to achieve. In the known electrostatic precipitators, the small space between adjacent electrodes and the high voltage result in an unacceptably high risk of glow discharge from the electrodes. Such glow discharges occur especially at the edges of electrodes, which are usually made of thin sheet metal, and this phenomenon is angular or uneven as a result of the method used to manufacture the electrodes. This is sometimes a particular problem, and is further increased by dirt that inevitably collects on the dust collecting electrode when the dust collector is used. Such glow discharges cause high disturbing noise levels (cracking and rattling) and also generate ozone at undesired and sometimes unacceptable levels. It will also be appreciated that the electrostatic precipitator must be held in the required distance in some way. If this is achieved with the aid of electrically insulating spacers placed between the respective electrodes, the spacers are inevitably soiled during use of the dust collector, resulting in creep currents on the soiled surfaces of the spacers. This creep current gradually destroys the spacer insulator unless a very high quality insulator is used. Therefore, the usual practice with known electrostatic precipitators of this kind is to use relatively complex and therefore expensive structures in order to avoid as much as possible the need for electrically insulating spacer elements with short creep current paths. That is.

It is also understood that electrostatic precipitators exhibit considerable capacitance. If the dust collector electrodes are touched unintentionally,
Naturally, a strong capacitive discharge current is emitted. This current is very unpleasant and can even be dangerous. Therefore, if this type of retro filter is used in a human environment, such as a home or work environment, the electrostatic precipitator should be ensured not to be touched unintentionally. This often poses a conflict in the construction of eletro filters with other structural requirements such as small size, low airflow resistance and the like.

Accordingly, one object of the present invention is to overcome the aforementioned problems and difficulties and to provide an electrostatic precipitator of the type described in the introductory part, which is due to between the adjacent electrodes of said precipitator. Higher voltages and even smaller mutual spacings are possible, which makes the separation of electrically charged aerosol pollutants from the air flow through a dust collector or filter more efficient than can be achieved with known electrofilters of this kind. Can be achieved.

For this purpose, at least the electrodes connected to one terminal of the DC voltage source are individually connected to said terminals instead of being directly connected to each other one by one as in the electrostatic precipitators known to date. It is achieved according to the present invention in that it is connected to each other. A separate connection of the electrodes or of the dust-collecting element to the one pole is made by making the lateral edge portion of each electrode made of a highly resistive material and electrically connected to the relevant terminal of the DC voltage source. This is accomplished by placing the members, such as lamellas, or strips, which are in contact with the electrodes by separate electrical contacting means, against the individual sides of the members. Certain advantages are obtained if the remaining electrodes are connected to the other terminal of the voltage source in a similar manner. One terminal of the high voltage source is normally grounded, with which the electrodes connected to the high voltage terminal of the DC voltage source are connected at least individually in the manner described above, and each to itself to the power source. .

The above-mentioned highly resistive materials are expediently referred to as highly resistive plastics, so-called antistatic plastics or plastics which have been treated to be antistatic, for example semiconductors so that the parts are protected against the influence of electrostatic voltages. Includes plastic materials of the type used to package components. Such antistatic, or antistatic treated, plastic materials are available in the market,
It usually has a surface resistivity of 10 ⁹ to 10 ¹⁵ Ω, approximately 10 ¹³ Ω.

According to the invention, the electrode connected to one terminal of the DC voltage source, i.e. the ungrounded high-voltage terminal of said source, is at least electrically connected to said terminal and to each other via a very high resistance. ing. These currents, which can occur as a result of electrical discharges from the electrodes or as a result of creep currents along the electrically insulating spacer members between adjacent electrodes having different voltages, are very small values, for example approximately Limited to values of 10 to 100 nA. Therefore, the above-mentioned discharges are too small or negligible to produce audible noise or an undesirable level of ozone,
And any creep current that may be generated is too small to have a detrimental effect on the insulating material.
In practice, each electrode of the electrostatic precipitator assembled according to the present invention will respond to a very mild discharge and / or a very low creep current along the electrically insulating spacer member to individual voltage levels. Adjusted automatically. Even a direct short circuit between two adjacent electrodes does not produce a harmful short circuit current and does not affect the voltage level of the remaining electrodes, so the dust collector can continue to function practically without interference. it can. The present invention also eliminates the possibility of strong relative discharge currents resulting from physical contact of the electrodes, thereby eliminating the risk and discomfort that such unintended contact may otherwise cause. .

The present invention will now be described in more detail with respect to an exemplary embodiment of an electrostatic precipitator assembled according to the present invention and with reference to the accompanying drawings.

The only figure in the accompanying drawings is a schematic view of the electrostatic precipitator of the present invention viewed in the direction of the air flow through the precipitator or electrofilter. The air duct in which the dust collector is located has been omitted from the drawing for the sake of brevity and clarity.

The dust collector shown consists of a plurality of thin plate-like or polar plate-like electrodes 1 and 2 arranged in parallel with each other and spaced apart from one another, the sides of the electrodes 1 and 2 being airflow. Lie parallel to the direction of, ie perpendicular to the plane of the drawing. These electrodes, or dust collecting elements, are electrically conductive or semi-conductive. In this respect,
It is observed that the current carried by the electrodes is very small because it corresponds exclusively to the electrical charging of contaminants that settle on the electrodes and to the electrical charging of atmospheric ions that may discharge in the vicinity of the electrodes. Thus, the electrodes 1, 2 can be made of metal, or of a weakly conductive or semiconductive material, such as a semiconductive paper or paperboard structure. Each alternating electrode 1 of the dust collector,
2 is electrically connected to each terminal or pole of the DC voltage source 3. In the case of the exemplary preferred embodiment of the electrostatic precipitator of the present invention, the dust collecting electrodes 1, 2 are respectively connected to one of the two terminals of the voltage source 3 on one side of each electrode. A sheet-like or strip-like member 4 made of a highly resistant material on the edge surface, or at least part of said lateral edge surface, for example so-called antistatic plastic, or antistatic plastic. Alternatively, it is achieved by pressing one side of each of the five. Such antistatic or antistatic treated materials are well known per se and are especially used to wrap semiconductor components to protect them from electrostatic voltage during shipping and storage. It is being appreciated. These plastic materials are 10 ⁹ to 1
It has a surface resistivity of 0 ¹⁵ Ω, usually around 10 ¹³ Ω. MPA
It has been found that the antistatic material sold by MAGNAB of the name C, Nykoping, Sweden is very suitable for the requirements of this invention. The plastic parts 4, 5 may for example have a thickness of 1 to 5 mm,
The sides of the electrodes 1, 2 are a little elastic or stretchable so that they can make firm abutment with one surface of the respective plastic member with the help of a suitable applied pressure. On respective side surfaces of the plastic parts 4, 5 facing each other, respective electrical contact means 6, 7 are provided, for example in the form of metal wires, metal strips, metal plates, etc., on the surface of each plastic part. They are pressed against each other and are suitably electrically connected to their respective terminals of the DC voltage source 3 through high ohmic resistors 8 and 9, respectively. Relatively soft and elastic antistatic plastic members 4, 5 are provided with respective rigid holders 10 and made of good quality insulating plastic material.
Supported by 11, it offers certain advantages.

As a result of the arrangement according to the invention, each of the dust collecting electrodes 1, 2 is connected to the relevant terminal of the DC voltage source 3 via the very high resistance formed by the respective antistatic plastic members 4 and 5. Individually electrically connected. Besides being present between the plate electrodes 1, 2 and the associated terminals of the power supply 3, this high resistance is present between the various electrodes 1, 2 which are commonly connected to the same terminal of the voltage source 3. To do. Therefore, these possible electrical discharges at the edges of the electrodes 1, 2 are completely inaudible and do not generate appreciable amounts of ozone. Similarly, the creep currents that may occur along the electrically insulating spacer member between the respective electrodes 1 and 2 are limited to very low values, leaving the insulator material unaffected. Furthermore, as a result of the invention, very low short-circuit currents can occur as a result of the direct short circuit between two adjacent electrodes 1 and 2. In practice, each individual electrode 1, 2 is automatically adjusted to a voltage level at which the general discharge current, creep current and short circuit current through the associated electrode is accidental. Reducing the voltage level of a given electrode does not affect the voltage level of the remaining electrodes and therefore does not have any appreciable effect on the performance or efficiency of the electrostatic precipitator.

The particular construction of the electrostatic precipitator of the present invention ensures that large, dangerous or unpleasant discharge currents do not occur as a result of unintentional physical contact with the electrodes 1,2.

The main purpose of the high ohmic resistors 8, 9 is to prevent a large short-circuit current from occurring if one of the plastic parts 4, 5 becomes short-circuited, for example as a result of unintentional contact with water.

As shown in the drawing, one terminal of the DC voltage source 3 is normally grounded. In the case of an electrostatic precipitator assembled according to the invention, it is conceivable to connect this grounded terminal of the DC voltage source 3 directly to the corresponding dust collecting electrode 2 by conventional methods. However, even in such a case, the grounded terminal of the voltage source 3 is connected to the associated electrode 2 through the highly resistive antistatic or antistatic treated plastic member 5 as shown in the drawing. It is preferable to connect.

The arrangement of the dust collecting electrodes 1, 2 of an electrostatic precipitator assembled according to the embodiment shown is such that the distance between the plastic member 4 and the electrode 2 not connected to said member is such that the electrodes 1 are adjacent to each other. It is beneficial for the distances of 2 and 2 to be greater than each other. Correspondingly, the distance between the plastic member 5 and the electrode 1 is greater than the distance between adjacent electrodes 1 and 2 to each other. This arrangement of electrodes prevents direct sparking between electrode 2 and plastic member 4 and between electrode 1 and plastic member 5.

The electrodes 1 and 2 are kept at a desired distance apart with the aid of spacer members (not shown) made of electrically insulating material. Any creep currents that may be carried through the spacer members are so small and harmless as described above, that they are used here as well as the configuration and positioning of these space members. A fairly wide range is given regarding the type of insulating material. Therefore, the spacer member can be formed of a compatible moldable, electrically insulating resin or glue and used in a suitable position between the dust collecting electrodes 1 and 2.

Since the dust collecting electrodes 1, 2 of the electrostatic precipitator can be formed of, for example, semiconductive paper or paperboard, the dust collector of the present invention can be manufactured easily and at low cost. This allows the dust collector to be intended for one-time use only, ie the electrostatic dust collector, or its part formed by the electrodes 1, 2 is such that an old dust collector or electrode pack can be used efficiently. If it is too dirty, it can be discarded and replaced with a new dust collector or a new electrode pack.

Continuation of the front page (56) References JP-A-58-64145 (JP, A) JP-A-56-76253 (JP, A) Actually opened 59-131253 (JP, U) Actual-opened 54-151965 (JP , U) Actual development Sho 48-1272 (JP, U) Actual public Sho 55-365 (JP, Y2)

Claims (7)

[Claims] 1. An electrostatic precipitator for use in an electrofilter, arranged in parallel and in spaced relation to each other, alternating with one terminal or the other terminal of a DC voltage source (3). A plurality of conductive or semi-conductive electrode plates or thin plate dust collecting electrodes (1,
2) in which the electrode (1 or 2) connected to one terminal of the voltage source (3) is at least the respective electrode (1 or 2)
Are individually connected by pressing the edge surface portions of one of them onto one side of a sheet-like or strip-like member (4 or 5) made of a high resistance material, said high resistance Of the electrical contacts means (6) which are separate from the position where their respective electrodes make contact with said members and which are electrically connected to the relevant terminals of the DC voltage source (3).
Or 7) is provided, the electrostatic precipitator. 2. Dust collector according to claim 1, characterized in that all the electrodes (1, 2) are individually connected to the respective terminals of the DC voltage source (3) in the manner described above. . 3. Highly resistive material (4, 5) comprising 10 ⁹ to 10
^A dust collector according to claim 1 or claim 2, characterized in that it comprises an antistatic plastic material having a surface resistivity of ¹⁵ Ω, preferably around 10 ¹³ Ω. 4. The terminals of the DC voltage source (3) are connected to the respective members (4 or 5) via a high ohmic resistance (8 or 9).
2. The dust collector according to claim 1, characterized in that it is electrically connected to the respective contact means (6 or 7). 5. Dust collector according to claim 1, characterized in that the high-resistive member (4, 5) is slightly elastic or soft. 6. The electrode according to claim 1, characterized in that the electrodes (1, 2) are held in their intended mutual position with the aid of spacer members which contain an electrically insulating material. Dust collector. 7. The dust collector according to claim 6, wherein the spacer member is formed of a moldable, electrically insulating plastic material or glue.