JPH0549970A - Apparatus for electrostatic classification - Google Patents

Abstract

PURPOSE:To provide an apparatus for electrostatic classification which can treat a large amount of aerosol and has an excellent mono-dispersibility for an optional particle size and an improved space efficiency by forming a unit main body of a flat rectangular tube. CONSTITUTION:Each of electrostatic classification units 10 comprises a unit main body 11 of a flat rectangular tube forming a downstream passage for charged aerosol particles in it, an electrode 14 of a plane plate generating an electric field perpendicular to the flat surface of the unit main body 11 in the downstream passage, an aerosol supply part 13 forming an aerosol supply slit 13A, and an aerosol collecting part 15 forming an aerosol collecting slit 15A in parallel with the aerosol supply slit 13A. The electrostatic classification units 10 are arranged so that the flat planes of the units confront each other. The aerosol particles having a constant particle size and electric charge are moved in the direction perpendicular to the flat plane of the unit main body 11, forming a narrow flow. The particles are lastly corrected into the aerosol collecting slit 15A.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrostatic classification device characterized in that a plurality of electrostatic classification units are arranged so that their flat surfaces face each other.

[0002]

2. Description of the Related Art For example, in performance tests such as a precision test of dust collection efficiency of an air filter for a clean room and a precision test of particle size resolution of a dust counter, an aerosol having a certain particle size is used. Therefore, in order to perform an accurate performance test, it is necessary to use an aerosol whose particle size distribution is as narrow as possible, that is, an aerosol having an excellent monodispersity of particle size. Then, in order to obtain such an aerosol excellent in monodispersity, it is known to classify aerosol particles by an electrostatic classifier.

FIG. 9 is an explanatory view showing a conventional electrostatic classifier. The electrostatic classifier of this example is a double cylinder type electrostatic classifier, 91 is an inner cylinder made of a cylindrical electrode, 92 is an outer cylinder having a cylindrical electrode, 93 is an aerosol introduction port having an aerosol introduction port 93A. And 94, an aerosol collecting part having an aerosol collecting port 94A, 95 an inlet for sheath air, and 96 an exhaust port for excess air.

An aerosol having a wide particle size distribution generated by an aerosol generator (not shown) is neutralized by a neutralizer (not shown).
And is introduced into the electrostatic classifier from the aerosol introduction port 93A. A constant voltage is applied between the inner cylinder 91 and the outer cylinder 92, and an electric field of a constant intensity is generated in the space defined by the inner cylinder 91 and the outer cylinder 92 (region indicated by L in FIG. 9). is doing. The aerosol particles P introduced into the electrostatic classifier flow down in this space while moving from the inner wall side of the outer cylinder 92 to the inner cylinder 91 side. Then, by changing the flow rate of the sheath air and the applied voltage, the aerosol particles having a predetermined particle size are classified and collected from the aerosol collecting port 94A.

According to the electrostatic classifier of this example, 0.01 to 0.5
Aerosol particles of any particle size can be obtained within the range of μm, and in particular, in the range of 0.01 to 0.05 μm, classification can be performed at intervals of 0.01 μm.

Here, the concentration of the aerosol particles introduced from the aerosol introduction port 93A is, for example, 10 ⁶ particles / cm 2.
It is about ³ . If this concentration is exceeded, agglomeration of aerosol particles tends to occur. The concentration of the aerosol that is classified and collected in the aerosol collecting port 94A is, for example, about 10 ³ particles / cm ³ , although it depends on the set particle size.

[0007]

However, when the aerosol is classified by the conventional double cylinder type electrostatic classifier, the amount of the aerosol obtained by the classifying process is small, and the performance test of the air filter is difficult. Therefore, there is a problem that a sufficient amount cannot be supplied.

For example, in the above double cylinder type electrostatic classifier, as described above, for example, an aerosol having a concentration of about 10 ³ particles / cm ³ can only be obtained at a rate of about 1 to several liters per minute. However, a real air filter, for example 610mm x 61
When performing a precision test of dust collection efficiency using a 0 mm air filter, 10 to 1000 liters of aerosol with a concentration of about 10 ³ particles / cm ³ are required. Therefore, it takes a considerable amount of time to obtain such an amount of aerosol with the above electrostatic classifier, which is not practical. Furthermore, in order to increase the classification processing amount, if the outer circumference of the inner cylinder 91 is multiplied by n while the distance between the inner wall of the outer cylinder 92 and the inner cylinder 91 (distance between the electrode plates) is fixed, the cross-sectional area of the device becomes n ² times. In combination with the dead space occupied by the inner cylinder 91, the space efficiency of the device becomes extremely low.

The present invention has been made based on the above circumstances, and an object thereof is to classify a large amount of aerosols to obtain a large amount of aerosols having excellent monodispersity at an arbitrary particle size. Another object of the present invention is to provide an electrostatic classification device that is capable of achieving high space efficiency.

[0010]

The electrostatic classification device of the present invention is an electrostatic classification device comprising a plurality of electrostatic classification units, wherein each of the plurality of electrostatic classification units has charged aerosol particles inside. The flat rectangular cylindrical unit body that forms the flow path of the unit, the flat electrode that generates an electric field in the direction perpendicular to the flat surface of the unit body, and the slit-shaped aerosol introduction in the flow path of the charged aerosol particles. An aerosol introducing part having a mouth and an aerosol collecting part having a slit-shaped aerosol collecting port parallel to the aerosol introducing port are formed, and the plurality of electrostatic classification units face each other with a flat surface. It is characterized by being arranged as follows.

[0011]

[Effect] In each electrostatic classification unit, among the aerosol particles introduced from the slit-shaped aerosol introduction port, those having a constant particle size and electric charge form a narrow band-like flow by the electric field from the flat electrode. While moving in a direction perpendicular to the flat surface of the unit main body, it flows down while maintaining this state and is collected by the slit-shaped aerosol collecting port. Therefore, a large amount of aerosol can be classified as compared with the conventional double cylinder type electrostatic classifier. Since the electrodes are flat, the cross-sectional area of the electrostatic classification unit is only n times larger even if the lateral length is increased by n times with the distance between the electrodes fixed. The processing capacity per space is higher than that of the conventional double cylinder type electrostatic classifier. Since the plurality of electrostatic classification units are arranged so that the flat surfaces of the respective unit bodies face each other, a large amount of aerosol can be classified in a small space.

[0012]

EXAMPLES Examples of the present invention will be described below, but the present invention is not limited thereto. FIG. 1 is an explanatory diagram showing an embodiment of the electrostatic classification device of the present invention.

In FIG. 1, reference numeral 1 denotes an electrostatic classification device composed of 10 electrostatic classification units 10 arranged, and 2 denotes neutralization of charged aerosol particles having a predetermined particle size classified by the electrostatic classification device 1. A neutralizer for treatment 3 is a neutralizer for neutralizing the introduced aerosol particles. In the neutralizer 3, americium ( ²⁴¹ Am) or polonium ( ²¹⁰ Po) as an α-ray source and krypton ( ⁸⁵ K as a β-ray source)
r) or lead ( ²¹⁰ Pb) or the like is arranged.

2 and 3 are a perspective view and a sectional view of an electrostatic classification unit 10 constituting the electrostatic classification device 1, respectively.

Reference numeral 11 denotes a flat rectangular cylindrical unit main body, and inside the unit main body 11, a flow path for charged aerosol particles is formed.

Reference numeral 12 is a sheath air rectification box connected to the upper end of the unit body 11. The sheath air, which is the rectifying gas of the aerosol, is supplied from the sheath air inlet 121 into the sheath air rectifying box 12, and is supplied into the unit main body 11 via the inside of the sheath air rectifying box 12. As shown in FIG. 4, a HEPA filter 122 is provided at the connecting portion between the sheath air rectifying box 12 and the unit main body 11, whereby the sheath air forms a rectified band-shaped flow while the unit main body 11 is being formed. Supplied within. In the figure, 123 is a wire net that supports the HEPA filter 122, and 124 is a gasket made of, for example, silicone rubber.

Reference numeral 13 denotes an aerosol introducing portion provided at an upper portion of one end side of the unit main body 11, and the aerosol introducing portion 13 is
As shown in FIG. 5, it comprises an introduction box 131, a 1 mm thick copper partition plate 132, and a 1 mm thick spacer 133.
The unit main body 11 is provided so as to sandwich the side plate 111 on one end side. Then, the tip (lower end) of the partition plate 132 and the side plate 11
The slit-shaped aerosol introducing port 13A is formed by 1 and. Reference numerals 112 are communication holes formed in the side plate 111 at equal intervals so as to connect the inside of the unit body 11 and the inside of the introduction box 131. The partition plate 132 is provided so that its tip is located at a level 50 mm below the center of the communication hole 112. As a result, the aerosol introduced from the communication hole 112 does not immediately associate with the sheath air, the so-called approach distance of the aerosol particles is secured, and velocity components other than the downflow velocity are reduced to zero.
Can be The aerosol particles neutralized by the neutralizer 3 are introduced into the introduction box 131 from the aerosol inlet 134.
Is supplied to the unit main body 11 through the communication hole 112.
It is introduced into the inside and forms a rectified band-like flow as it flows down the approach distance, and is associated with the sheath air at the aerosol introduction port 13A. The partition plate 132 forms a smooth taper on the flow path side of the sheath air,
And the tip is sharply polished. As a result, the spread and turbulence of the aerosol are prevented at the portion where the aerosol and the sheath air meet.

Reference numeral 14 denotes a flat surface (side plate 111 and side plate 113) of the unit main body 11 in the flow path of neutralized aerosol particles.
Is a flat plate-shaped electrode provided along the surface of the plate.
The flat electrode 14 charges the aerosol particles P charged.
Flows down while moving in a direction perpendicular to the flat surface of the unit main body 11. The partition plate 132 has a flat plate-shaped electrode.
The same voltage as that of the electrode plate on the side plate 111 side of 14 is applied.

Reference numeral 15 denotes an aerosol collecting portion provided on the lower part of the other end side of the unit main body 11, and the aerosol collecting portion 15
Is a collection box 151, a 1 mm thick copper partition plate 152, 1
The unit main body 11
Is provided so as to sandwich the side plate 113 on the other end side. Then, the tip end (upper end) of the partition plate 152 and the side plate 113 on the other end side form a slit-shaped aerosol collecting port 15A parallel to the aerosol introducing port 13A. The structure of the aerosol collecting unit 15 is almost the same as that of the aerosol introducing unit 13, but since it is not necessary to consider the approach distance of the aerosol, the partition plate 15
The length of 2 is shorter than the length of the partition plate 132. The charged aerosol particles P having a predetermined particle diameter flow down while maintaining a narrow band-like flow, and the aerosol collecting port 15
It is collected from A into the collection box 151.

Reference numeral 16 denotes an exhaust box connected to the lower end of the unit main body 11, and sheath air is exhausted from the exhaust box 16. A HEPA filter 162 is provided at the connection between the exhaust box 16 and the unit body 11.

In each of the electrostatic classifying units 10, the aerosol particles having a predetermined particle size and electric charge, which are collected in the collection box 151, are introduced into the neutralizer 2 and are neutralized, and then are aimed at. Used accordingly. Americium ( ²⁴¹ Am) is arranged in the neutralizer 2, and the charged aerosol particles are recovered after being neutralized by α rays emitted from the americium ( ²⁴¹ Am). This prevents electrostatic aggregation of the collected aerosol particles.

To give an example of the dimensions of the electrostatic classification unit 10 which constitutes the above electrostatic classification device, the height H of the electrostatic classification unit 10 is 1000 mm and the width of the unit body 11 is W: 1000 mm. Gap between inner walls 10 mm Here, the gap between the inner walls of the side plate 111 and the side plate 113 is 3 to 20.
It is preferably about mm. If this thickness exceeds 10 mm, turbulent aerosol flow may occur in the unit main body 11, and if it is less than 3 mm, sheath air is difficult to flow, and manufacturing problems such as inner wall machining accuracy tend to occur. The space in the thickness direction occupied by one unit of the electrostatic classification unit 10 is about 100 mm. Therefore, the size of the electrostatic classification device 1 configured by arranging 10 units of this is about 1 m x 1 m.
It becomes × 1 m, which is excellent in space efficiency.

According to the electrostatic classification device of this embodiment, 30 to several
Aerosols of about 100 liters / minute can be classified, and this has a processing capacity of about 10 to 100 times that of the double cylinder type.

The aerosol particles that can be classified by the electrostatic classification device of the present invention are not particularly limited as long as they are electrically charged particles, and may be liquid particles, for example.

<Experimental example> In order to confirm the flowing state of the aerosol particles in the electrostatic classification device of the present embodiment, the electrostatic classification unit 10 (unit body 11) constituting the electrostatic classification device 1 is confirmed.
The width W of 20 mm) was used for the following experiment. [Visualization by smoke] Incense stick smoke was introduced at a rate of 2 liters per minute from the aerosol introduction port 13A, sheath air was supplied at different flow rates, and the smoke was allowed to flow down without applying an electric field. The smoke thickness was measured. The results are shown in Table 1.

[0026]

[Table 1]

From the results in Table 1, it is understood that the smoke thickness becomes smaller as the sheath air flow rate increases, and that the smoke thickness tends to become slightly thicker as the sheath air flow rate decreases. The thickness of smoke at both ends was 2-3 times the thickness at the center. this is,
It is considered that this is mainly due to the shape of the edge of the portion that meets the sheath air, but in the apparatus of this embodiment, the width W of the unit main body 11 can be lengthened, so such a spread can be ignored.

[Visualization with methylene blue particles] An aerosol containing methylene blue particles is introduced into the aerosol introduction port.
13A is introduced at a different flow rate, and sheath air is supplied at a different flow rate to allow the aerosol to flow down without applying an electric field. The unit body 11 and the exhaust box 16
The thickness of the strip-shaped aerosol was measured from the traces of methylene blue remaining on the HEPA filter 162 provided at the connection portion with. An example of the trace of methylene blue is shown in FIG. 6, and the average thickness of the trace corresponding to the thickness of the strip-shaped aerosol is shown in Table 2.

[0029]

[Table 2]

As shown in FIG. 6, although a trace of turbulent flow was observed at both ends, the trace of methylene blue was almost linear, and there was no mixing with the sheath air, and a band-like laminar flow state was maintained. It was confirmed that Further, from the results of Table 2, when the flow rate of the sheath air is constant, the thickness of the trace increases as the flow rate of the aerosol increases, and when the flow rate of the aerosol is constant, the flow rate of the sheath air increases. It is understood that the thickness of the trace is reduced. Here, in FIG. 6 and Table 2,
(e) is the case where the sheath air and the aerosol have the same linear velocity, and the average thickness of the trace under these conditions is in good agreement with the slit width (1 mm) of the aerosol introduction port 13A. When the above visualization experiment was performed using the electrostatic classification unit 10 having the width W of the unit body 11 of 30 mm,
A similar trend was confirmed.

[Performance Verification of Electrostatic Classification Unit] According to the process diagram shown in FIG. 7, the electrostatic classification unit constituting the present invention
Ten performance tests were performed. In FIG. 7, 2 and 3 are neutralizers, 4 is an aerosol generator, 5 is a diffusion dryer, 6 is a condensation nucleus counter (hereinafter referred to as “CNC”) for measuring the concentration of the introduced aerosol, and 7 is an aerosol. CNC 90, which measures the trapped concentration of C., is a double cylinder type electrostatic classifier. In the double cylinder type electrostatic classifier 90, a predetermined voltage is applied to classify the aerosol particles, and the obtained aerosol particles are introduced into the electrostatic classification unit 10, and the applied voltage is changed variously to perform classification processing. The applied voltage in the electrostatic classification unit 10 was measured when the collection rate (collected concentration / introduced concentration) of the aerosol collected in the aerosol collecting section 15 was maximum. Note that NaCl was used as the aerosol particles and the sheath air flow rate was set to 27
L / min, aerosol flow rate 3 l / min
And Applied voltage V _c in the double cylindrical electrostatic classifier 90
8 shows the relationship between the applied voltage V _tmax in the electrostatic classification unit when the recovery rate is maximum.

As shown in FIG. 8, a double cylinder type electrostatic classifier
The applied voltage V _c at 90 and the applied voltage V _{tmax at the} double cylindrical electrostatic classifier 90 when the recovery rate is the maximum are in a proportional relationship, and thus the applied voltage is applied to the electrostatic classifier of the present invention. It is understood that changing the voltage can reliably classify aerosols of a given particle size.

[0033]

EFFECTS OF THE INVENTION According to the electrostatic classification device of the present invention, a large amount of aerosols having an excellent monodispersity at any particle size can be obtained by classifying a large amount of aerosols. It is also excellent in space efficiency.

Such an aerosol is industrially useful and can be suitably used for performance tests such as a test of dust collection ability of an air filter for a clean room and a test of a dust counter.

[Brief description of drawings]

FIG. 1 is an explanatory view showing an embodiment of an electrostatic classification device of the present invention.

FIG. 2 is a perspective view of an electrostatic classification unit.

FIG. 3 is a cross-sectional view of an electrostatic classification unit.

FIG. 4 is a partially cutaway perspective view showing details of a connecting portion between a sheath air rectification box and a unit main body.

FIG. 5 is a partially cutaway perspective view showing details of an aerosol introducing portion.

FIG. 6 is a diagram showing traces of methylene blue in a visualization experiment.

FIG. 7 is a process diagram for performance verification of an electrostatic classification unit.

FIG. 8 is a graph showing the relationship between the applied voltage in the double cylindrical electrostatic classifier and the applied voltage in the electrostatic classification unit when the recovery rate is maximum.

FIG. 9 is an explanatory view showing a conventional double cylindrical electrostatic classifier.

[Explanation of symbols]

1 Electrostatic classification device 2 Neutralizer 3 Neutralizer 4 Aerosol generator 5 Diffusion dryer 6 CNC 7 CNC 10 Electrostatic classification unit 11 Unit body 12 Sheath air rectification box 13 Aerosol introduction part 14 Flat plate electrode 15 Aerosol collection part 16 Exhaust box 90 Double cylinder type electrostatic classifier 91 Inner cylinder 92 Outer cylinder 93 Aerosol inlet 94 Aerosol trap 95 Sheath air inlet 96 Excess air outlet

Claims (1)

[Claims] 1. An electrostatic classification device comprising a plurality of electrostatic classification units, wherein each of the plurality of electrostatic classification units has a flat rectangular cylindrical shape that forms a flow path for charged aerosol particles therein. The unit body and the flow path of the charged aerosol particles, a flat plate-shaped electrode for generating an electric field in a direction perpendicular to the flat surface of the unit body, an aerosol introduction part having a slit-shaped aerosol introduction port, and an aerosol introduction port. And an aerosol collecting part having a slit-shaped aerosol collecting port formed in parallel with each other, wherein the plurality of electrostatic classification units are arranged so that their flat surfaces face each other. apparatus.