JPS60212255A - Electrostatic filter apparatus - Google Patents

Abstract

PURPOSE:To supplement the lowering in the collection efficiency of a fibrous charged filter, in an electrostatic filter apparatus, by forming the fibrous charged filter in a two-layered structure and arranging a charge part to the upstream side thereof. CONSTITUTION:Dirty air is introduced into a duct 10 from an arrow C and passes through a charge part 11 consisting of a discharge electrode 12 and an earthing electrode 13. Plus corona discharge is performed between the discharge electrode 12 and the earthing electrode 13 to charge dust while the charged dust is introduced into a collection part 20 and collected by the upstream side filter 15 or downstream side filter 16 of a fibrous charged filter brought to an electret state. Because two filters are used as mentioned above, the downstream side filter performs mechanical collection when the collection efficiency of the upstream side filter is lowered and the upstream side filter performs mechanical collection when the efficiency of the downstream side filter is lowered and collection efficiency is kept high as a whole.

Description

[Detailed Description of the Invention] Industrial Field of Application The present invention relates to an electrostatic filter device used in clean rooms, etc., in which a two-layer fibrous charged filter made of electret material is used in the collection section. .

Conventional configurations and their problems There have been many types of dust collectors for removing dust from gases such as air. It is already known to use an electret fibrous charged filter as a furnace material in the collection section. Its typical configuration is shown in FIGS. 1 and 2. FIG. 1 shows that the fibrous charged filter 2 is installed inside a circular or rectangular cylindrical duct 1, and contaminated air is introduced from arrow a and is purified by passing through the fibrous charged filter 2. is ejected in the direction of In FIG. 2, a charging section 3 for electrically charging dust in contaminated air is provided upstream of the fibrous charged filter 2, and the charging section 3 connects a discharge electrode 4 and a ground electrode 5 to the inside of the duct 1. They are arranged at equal intervals, and a DC high voltage power source 6 is connected to both ends of the discharge electrode 4 and the ground electrode 5.

In the above configuration, the dust of contaminated air is charged in the charging section 3, and the charged dust is transferred to the fibrous charged filter 2.
It will be collected by. Also, Figures 1 and 2
The collection efficiency shown in the figure is better in the configuration shown in FIG. 2 having the charging section 3. However, the change in collection efficiency over time is
As shown in the figure, as the dust collection progresses, it decreases from the initial stage. The reason for this is that dust adheres to the surface of the fibers of the fibrous charged filter 2, and the electrostatic effect weakens. However, after that, if it drops to a certain point, it will rise again. This is due to mechanical trapping effects rather than electrostatic effects.

As is clear from the above explanation, fibrous charged filters have the disadvantage that in areas that require high cleanliness, such as clean rooms, the collection efficiency decreases, making it difficult to maintain cleanliness. OBJECT OF THE INVENTION Therefore, the present invention aims to compensate for the decrease in collection efficiency of the fibrous charged filter and to apply it to places where high cleanliness is required.

Structure of the Invention In order to achieve this object, the present invention has two layers of fibrous charged filters, and a charging section is provided on the upstream side of the fibrous charged filter, thereby reducing the collection efficiency of the fibrous charged filter on the upstream side. When the collection efficiency of the fibrous charged filter on the downstream side decreases, the collection efficiency of the fibrous charged filter on the upstream side is not compensated for. DESCRIPTION OF EMBODIMENT 0 DESCRIPTION OF THE EMBODIMENTS DESCRIPTION OF EMBODIMENTS DESCRIPTION OF EMBODIMENTS OF THE INVENTION An embodiment of the present invention will be described below with reference to the accompanying drawings. Fourth
In the figure, 1o is a circular or rectangular cylindrical duct which has inside thereof a charging section 11 for charging dust contained in contaminated air and a collection section 2o on the downstream side thereof. In the charging section 11, a discharge electrode 12 and a ground electrode 13 are uniformly arranged within the duct 10. A DC high-voltage power supply 14 is connected between the discharge electrode 12 and the ground electrode 13. The collecting section 2o on the downstream side is connected to an upstream filter 16 using an electret fibrous charged filter. In the above configuration, the contaminated air is ducted from the direction of arrow C).
10 is introduced inside. Dust in contaminated air first passes through the charging section 11. In the zero charging section 11, positive corona discharge is occurring between the discharge electrode 12 and the grounding electrode 13, so the dust passes through the charging section 11. During this period, it becomes positively charged. Next, the charged dust is introduced into the collection section 20. In the collection section 20, the particles are collected by the upstream filter 16 or the downstream filter 16, which is an electret fibrous charged filter. Its collection efficiency is
This is what is obtained as shown in FIG. Curve e is the collection efficiency of the upstream filter 16, from the initial stage to p e/.
As the dust collection progresses, the collection efficiency decreases. The reason for this is, as mentioned above, that dust adheres to the surface of the fibers of the fibrous charged filter, which weakens the electrostatic effect. Beyond e', the collection efficiency increases due to the mechanical collection effect due to the reduction of the passing gap due to dust adhesion. The problem is that in the worst case, the value drops to e', and to compensate for this, the downstream filter 16 is provided. The change in collection efficiency of the downstream filter 16 is shown by a curve f. Due to the effect of the upstream filter 16, the amount of dust passing through is small, so the reduction in collection efficiency is slower and smoother than in the curve e, and the lowest point f' is reached with a time delay. When the efficiency of the downstream filter 16 decreases, the efficiency decrease is prevented by mechanical collection of the upstream filter 16. Therefore, due to the combined effect of the upstream filter 15 and the downstream filter 16, the collection efficiency in the collection section 20 is as shown by the curve q, and when the collection efficiency of the upstream filter 15 decreases, the downstream filter 1
When the collection efficiency of the downstream filter 16 decreases, the upstream filter 15 does not compensate, and the collection efficiency as a whole can be maintained at a high level.

Effects of the Invention As is clear from the above explanation, the present invention uses two layers of electret fibrous charged filters in the collection section, one upstream and one downstream, to compensate for each other's decrease in collection efficiency. Since it is a material, it is possible to maintain a high level of collection efficiency.

[Brief Description of the Drawings] Figures 1 and 2 are cross-sectional views of conventional electrostatic filters;
Figure 3 is a graph showing the collection efficiency of conventional electrostatic filters.
FIG. 4 is a sectional view showing an embodiment of the electrostatic filter of the present invention, and FIG. 6 is a graph showing the collection efficiency of the electrostatic filter of the present invention. ...
...Discharge electrode, 13...Ground electrode, 14...
・DC high voltage power supply, 15... Fibrous charged filter (upstream filter), 16... Fibrous charged filter (downstream filter), 2o... Collection section 0

Claims (2)

[Claims] (1) An electrostatic filter device in which electret fibrous charged filters are arranged in two layers, upstream and downstream, inside a cylindrical duct. (2) A charging section that charges dust is provided on the upstream side of the two-layer electret fibrous charged filter.