JPH08252482A - Method for electric dust collection and apparatus therefor - Google Patents

Abstract

PURPOSE: To carry out dust collection work by low electric field strength without efficiency lowering while preventing reverse electric dissociation in the electric collection of dust having a high electric resistance value. CONSTITUTION: A part of a dust collecting electrode 4 arranged vertically is shielded electrically by a shielding material 8 to form a shielded surface 6 which is not affected by the electric line of force of a discharge electrode 2. Hammering is carried out before the entire surface 6 being covered to prevent, the accumulation of dust on the surface 6, and conductivity is maintained so that discharge from dust accumulated on a dust surface 5 to the shielded surface 6 is secured.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to the electrostatic collection of dust in the air, and more particularly to the electrostatic collection of fine dust having a high electric resistance value.

[0002]

2. Description of the Related Art As a method of collecting fine dust floating in the air, electrostatic dust collection has been widely used in Japan and abroad since ancient times.

The principle of electrostatic precipitating is that a negative DC high voltage is usually applied to a discharge electrode having a wide area and a tip that forms an acute angle with respect to a dusting electrode that is normally grounded to cause corona discharge. generate. At that time, negative ions and free electrons generated between both electrodes (hereinafter simply referred to as ions)
Is adsorbed on dust to be charged, and is caused to fly between both electrodes by Coulomb force to collect dust. Therefore, if the discharge electrode and the dust collecting electrode are arranged at right angles to the direction of the air flow or the direction of the dust, the generated ions will surely collide with the dust and thus be uniformly charged. Further, the charging rate becomes higher as the amount of generated ions increases, so that high dust collection efficiency can be obtained. However, the larger the amount of current, the larger the amount of generated ions. Therefore, the higher the voltage applied to the discharge electrode, the larger the amount of generated ions. Also, the higher the applied voltage, the stronger the electric field strength, and the stronger the Coulomb force against the charged dust. That is, the voltage exerts a double effect and enhances the dust collection efficiency. However, if the voltage is increased and the electric field strength is excessively increased, a spark will be generated and an arc discharge will not be generated, and a uniform corona discharge will not be formed.Conversely, the dust charge rate will decrease and not only the dust collection efficiency will decrease, but also a large An electric current will flow and damage the power supply or the electrodes. Even if arc discharge or spark does not occur, if the voltage is raised and the electric field strength is excessively increased, the gas in the air is decomposed and harmful gas is generated.Therefore, it is desired to collect the dust at the lowest electric field strength. There is.

By the way, the dust which is transported by air and has come close to the dust collecting portion of the dust collector is strongly repelled by the Coulomb force to the dust collecting electrode when adsorbed and charged with the ions generated from the discharge electrode. Fly and collide. At that time, the dust that collides with the dust collecting electrode releases the electric charge of the adsorbed ions. The dust that has released the electric charge and lost the Coulomb force adheres to the dust collecting electrode and is deposited by a relatively weak force due to the Van der Waals force if it has electrical insulation. Even if the accumulated dust has electrical insulation, if it has some conductivity, it maintains the polarity of the surface of the dust collecting electrode, that is, the ground potential, so new charged dust collides with the dust collecting electrode. Can then be discharged and attached. Therefore, as the dust collection work progresses, the accumulated dust gradually increases the electric resistance value in proportion to the thickness, but if the dust is peeled off at an appropriate time interval by hammering, the conductivity is recovered and the dust is collected. The work can be continued stably.
That is, a moderate electric resistance value (usually about 10 ⁴ to 10 ¹¹⁾
Ω-cm), high electrostatic collection efficiency can be obtained. Further, if each dust has the above-mentioned appropriate electric resistance value, it adheres by the Van der Waals force and increases its particle size. Therefore, as the dust collection operation progresses, the size of the accumulated dust particles grows to several tens to several thousand times the size of the dust before collision. Therefore, if the dust collecting electrode is hammered at an appropriate frequency according to the dust concentration, usually once every few minutes, the accumulated dust is separated from the dust collecting electrode, overcomes the wind speed, and falls due to gravity. Therefore, it becomes possible to collect even submicron particles in the hopper provided in the lower part of the dust collector. However, since hammering causes dust to be re-scattered and the dust collection efficiency to be reduced, the frequency of dust collection is reduced as much as possible.

However, in the case of dust such as silicates having an excessively high electric resistance value, the electric resistance value on the surface of the dust collecting electrode gradually increases due to the accumulation of dust, and the discharge from the colliding dust cannot be performed smoothly. Further, depending on the shape of the dust collecting electrode, the strength of hammering, and the frequency, the dust is not evenly peeled off, and a part where the dust does not adhere and a part where the dust remains remain on one part of the dust collecting electrode. In this case, the electric charge of the ions contained in the dust is discharged to the separated portion or the surface that is electrostatically shielded and has a small amount of dust attached, so that the dust collecting efficiency is greatly reduced, but the dust collecting effect is maintained. However, with the lapse of time, those portions are also covered with dust having high insulating properties, and finally covered entirely. Therefore, electric charges that make the polarity equal to that of the discharge electrode are gradually accumulated on the surface of the dust collecting electrode, and the spatial electric field strength between the discharge electrode and the surface of the dust collecting electrode decreases, so that the amount of ions generated from the discharge electrode decreases, and No discharge occurs and the amount of discharge current drops sharply. Therefore, a large amount of uncharged dust is generated, the dust does not approach the dust collecting electrode, and even if the charged dust approaches the dust collecting electrode, it is repelled and does not collide with the dust collecting electrode. Therefore, the dust collection efficiency is significantly reduced. Therefore, if the voltage applied to the discharge electrode is increased, the repulsive force on the surface of the dust collecting electrode is overcome to increase the discharge current and the deposition proceeds. However, when the applied voltage is gradually increased, the electric resistance of dust finally exceeds the breakdown voltage locally, and the electric resistance value of that part drops extremely, so a kind of arc discharge occurs in that part. Is formed. Therefore, the electric resistance value between both electrodes is extremely reduced, and thus a larger current than usual flows, but since the corona discharge is not formed uniformly, the ions do not uniformly collide with dust,
Therefore, the charge rate of dust is reduced, and the dust collection efficiency is significantly reduced. In addition, even if the voltage is adjusted to the limit of the spark voltage, not only is the adjustment practically difficult, but the Coulomb force between the charged dust and the dust collection electrode increases in proportion to the square of the voltage. A strong impact force was required for peeling, and the amount of charged dust escaping into the air flow due to hammering also increased dramatically, resulting in reduced efficiency. This phenomenon is generally called a reverse ionization phenomenon, and occurs when the dust having a large electric resistance covers the entire surface of the dust collecting electrode as described above and the applied voltage locally exceeds the breakdown voltage of the dust. When this phenomenon occurs, the dust collection efficiency is greatly reduced, so that a huge device is required as compared with the case of collecting dust having an appropriate electric resistance value, and the device cost and the maintenance cost are significantly increased.

The mode of occurrence of the reverse ionization phenomenon is as described above.
In addition to the electric resistance value of dust, it changes depending on the electrode shape, the concentration of dust, etc., and in particular, the shape of the dust collecting electrode is electrostatically shielded as shown in FIG. A significant difference has occurred. That is, the dust collection efficiency is reduced because the dust is not uniformly charged, but the electric charge of the ions on the surface of the dust collection electrode is a creeping discharge on the shielded surface with less dust adhesion, and the dust collection effect is maintained. Because.

For example, as shown in FIG. 3 (a), a baffle plate 25 is attached to the flat plate type dust collecting electrode surface 4 to prevent dust from re-scattering, and a shielded surface 26 is formed. . Further, as shown in FIG. 3B, a dust collecting electrode having a baffle plate 25 provided with a leak gap and preventing re-scattering of dust is in practical use. Further, as shown in FIG. 3 (c), a dust collecting electrode is provided which has a pocket for dropping dust and prevents re-scattering. In these cases, due to the electrostatic shielding effect of the baffle plate 25 and the pocket forming material 25, that is, the Faraday cage effect, the portion 26 where dust does not adhere is formed. Further, as shown in FIG. 3D, a dust collecting electrode unit having a bent plate structure is used by being rotated 180 degrees and continuously connected. In this case, in the dust collecting electrode unit 4, the bent portion 25 acts as an electrostatic shielding material with respect to the discharge electrode 2, and the inside 26 thereof becomes a shielded surface. However, the discharge electrode 21
With respect to, the electrostatic collecting member and the shielded surface are not formed on the dust collecting electrode unit 24.

When a dust collecting electrode having such a structure is used, a creeping discharge is generated on a shielded surface to which less dust adheres, so that reverse ionization occurs with a delay and is therefore higher than a simple flat plate type dust collecting electrode. Dust collection efficiency can be obtained. However, neither of these conventional dust collecting pole shapes and the shielding material is intended for electrostatic shielding, and therefore a shielded surface having a sufficient width is not formed.
With the lapse of the dust collection work time, these shielded surfaces were gradually covered with dust to increase the insulating property, and finally the creeping discharge stopped and the reverse ionization occurred.

Therefore, various methods have been tried in order to prevent the reverse ionization phenomenon. For example, a method of maintaining conductivity of the surface of the dust collecting electrode by flowing water on the surface of the dust collecting electrode or mechanically scraping the accumulated dust is used. Although these methods are effective in preventing reverse ionization, it is difficult to use water when the air to be treated is high temperature air such as in an incinerator, and the mechanical scraping method is not Since it is difficult to evenly scrape a thin dust film due to thermal distortion, the device cost and maintenance cost are extremely high, and therefore it cannot be used. Further, a method for preventing sparks by applying a pulsed voltage waveform to the discharge electrode has been used, but this is not preferable because the applied voltage increases and the amount of harmful gas generated increases.

In view of the conventional problems, the present invention prevents reverse ionization in the electrostatic collection of air containing dust having a high electric resistance value, and maintains high dust collection efficiency without using a specially high voltage. The present invention provides an electrostatic precipitating method and device.

[0011]

In order to solve the problem, the means provided by the present invention is to dispose a discharge electrode formed of a thin conductive wire in an air flow containing dust, and to discharge the discharge electrode by an electrostatic shield. A dust collecting electrode having a shielded surface electrostatically shielded and a wide dust collecting surface continuous to the shielded surface is arranged in the vertical direction so that the lines of electric force from the electrodes do not reach, and In the electric dust collection performed by applying a DC high voltage between the dust electrode and the discharge electrode, the dust collecting electrode is hammered into the dust collecting electrode before the whole surface of the shielded surface is covered with dust. Is peeled off and dropped.

[0012]

According to the above means, when the discharge electrode 2 is arranged in the horizontal air flow 20 as shown in FIG. 1, the dust collecting electrode 4 is electrostatically charged by the electrostatic shield 8. Shielded shielded surface 6
Therefore, the dust adheres and accumulates on the dust collecting surface 5 of the dust collecting electrode 4, but the dust does not easily enter the shielded surface 6. Even if dust enters the shielded surface 6, the hammering device 32 performs hammering according to a program installed in the operation panel 30 before the entire surface is covered and deposited, so that the conductivity of the shielded surface 6 is maintained. It At that time, since the dust accumulated on the surface of the shielded surface 6 adheres with a weak force due to the Van der Waals force, it can be reliably separated. On the other hand, since the dust collecting surface 5 is continuous with the shielded surface 6, the electric charge of the dust accumulated on the dust collecting surface 5 is the electric force line 36 by the discharge electrode and the electric force line formed by the electric charge of the dust itself. 38 causes creeping discharge to the shielded surface 6. Therefore, the reverse ionization phenomenon does not occur. Dust collecting surface 5
Since no electric charge is accumulated on the dust collecting surface 5, new charged dust can collide with and adhere to the dust collecting surface 5, increasing the amount of accumulation. Further, since a large amount of dust attached and accumulated on the dust collecting surface 5 is attached by a weak Van der Waals force, it is easily peeled off and dropped by hammering.
Therefore, the dust collection efficiency does not decrease.

[0013]

Embodiments and operations of the dust collecting electrode 4 having a shielded surface 6 according to the present invention will be described in more detail below based on embodiments.

FIG. 1 shows an example of a horizontal section of the dust collecting electrode 4 and the discharge electrode 2 showing an embodiment of the present invention. FIG.
2 is a discharge electrode, which is formed of a thin wire such as a piano wire or a stainless wire, is vertically arranged in the dust collecting device, is electrically insulated from the dust collecting electrode 4, and has a DC high-voltage power supply (not shown). It is connected. 4 is a dust collecting electrode, which is grounded. 5 is a dust collecting surface of the dust collecting electrode 4, 6 is a shielded surface of the dust collecting electrode 4, and 8 is an electrostatic shielding material. Again 30
Is an operation panel and has a built-in program for timing when hammering the dust collecting electrode. 20 shows the flow direction of air.

The shielded surface 6 and the dust collecting surface 5 of the dust collecting electrode 4 are made of a steel plate, and are appropriately reinforced and integrated so as to have a strength to withstand impact. The wider the shielded surface 6, the longer the time required to cover the entire surface, and the less frequently hammering is performed, which is preferable because high efficiency can be obtained. Further, the dust collecting surface 5 may be covered with an insulating material, which is preferable because the dust can be uniformly separated and dropped by hammering.

The dust collecting electrode 4 is provided with a hammering device 32 which is normally used, and hammers before dust is deposited on the shielded surface 6. The adhesion speed and therefore the adhesion amount largely change depending on the electric resistance value, the concentration, the temperature of the dust, and the structure of the dust collecting electrode 4, but when hammering the dust collecting 4, the dust completely covers the shielded surface 6. Must be done before. Therefore, you have to know the exact timing,
You can do the following: (A) If the property and temperature of dust do not change significantly during dust collection work, the time required to cover the entire surface 6 to be shielded is generally determined. Check it visually and hammer it at a shorter time interval. Good. Further, when the reverse ionization phenomenon occurs, the light emission due to the corona discharge is extinguished, so that it can be confirmed that the shielded surface 6 is entirely covered. (B) When the shielded surface 6 is entirely covered, the average amount of current is significantly reduced unless the applied voltage is changed. However, in the case of the dust collecting electrode 4 of the present invention, since the current amount does not suddenly decrease, hammering may be performed when the current value decreases to a certain constant value. Further, if both (A) and (B) are used together, it will be more reliable. This program may be built in the operation panel 30 to automatically perform hammering. Further, instead of the peeling by intermittent hammering, the peeling may be performed by continuous fine vibration. Alternatively, the program may be performed according to a program that combines continuous micro-vibration and intermittent hammering.

As the shape of the electrostatic shield surface 6 of the dust collecting electrode 4 of the present invention, not only FIG. 1 but also FIGS. That is, FIG. 2A shows an example in which the electrostatic shielding material 8 is arranged at a right angle to the shielded surface 6. In FIG. 2B, the electrostatic shielding material 8 also serves as the dust collecting surface 5. Further, in FIG. 2C, the electrostatic shielding material 8 is not provided alone, but the distance between the two dust collecting surfaces 5 is short and the electrostatic shielding surface 6 is substantially used. In this case, the dust collecting surface 5 and the shielded surface 6 are not directly continuous, but the distance between the discharge electrode 2 and the dust collecting surface 5 is large, while the distance between the tip of the dust collecting surface 5 and the shielded surface 6 is large. Since it is short and therefore substantially continuous, the ionic charges on the dust collecting surface 5 are discharged to the shielded surface 6. Further, FIG. 2D shows an example in which the discharge electrodes are arranged in the vertical direction and the shielded surface is formed in the horizontal direction. Figure 2
In (d), 3 indicates a weight for pulling the discharge electrode in the vertical direction.

In the present invention, a high DC voltage having a flat waveform is applied to the discharge electrode 2, but the present invention is not limited to this. That is, a pulsating current obtained by rectifying an alternating current or a direct current pulse high voltage having a direct current high voltage as a base voltage can be used. However, even if these voltage waveforms are used, it is not necessary to excessively increase the electric field strength formed by the highest voltage for dust collection in incinerators, etc., and no harmful substances are generated when the electric field strength does not generate sparks. Therefore, it is preferable.

[0019]

According to the present invention, since the dust collecting electrode 4 is composed of the dust collecting surface 5 and the shielded surface 6, and the shielded surface 6 is shielded against the lines of electric force from the discharge electrode 2. Dust does not enter the shielded surface 6, and even if it enters, it does not accumulate because it is hammered and peeled off before it is entirely covered. Therefore, the conductivity of the surface is maintained. Moreover, since the shielded surface 6 is continuous with the dust collecting surface 5, the electric charges from the ions of the dust accumulated on the dust collecting surface 5 can be stably absorbed by the creeping discharge. Therefore, the reverse ionization phenomenon does not occur, and the dust collection efficiency is significantly improved. Moreover, no harmful gas is generated because only a voltage enough to generate corona discharge is applied to the discharge electrode 2.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing an embodiment of the present invention.

2A to 2D are horizontal sectional views showing another embodiment of the present invention.

FIG. 3A to FIG. 3D are diagrams showing a conventional example.

[Explanation of symbols]

 2, discharge electrode 4, dust collecting electrode 5, dust collecting surface 6, shielded surface 8, shielding material 30, operation panel 32, hammering device

Claims (2)

[Claims] 1. A discharge electrode formed of a thin conductive wire is provided in an air flow containing dust, and is electrostatically shielded by an electrostatic shielding material so that an electric force line from the discharge electrode does not reach. A dust collecting electrode having an electrostatic shielded surface and a wide dust collecting surface continuous with the electrostatic shielded surface is disposed in the vertical direction, and a DC high voltage is provided between the dust collecting electrode and the discharge electrode. In the electric dust collection performed by applying a voltage, before the dust is deposited and covered on the entire surface of the electrostatic shield, the dust collector is hammered to separate and drop the dust. Dust method 2. A dust collecting electrode having a discharge electrode formed of a thin conductive wire, an electrostatic shielded surface electrostatically shielded by an electrostatic shield, and a wide dust collecting surface continuous with the electrostatic shielded surface. And a hammering device for removing dust accumulated on the dust collecting electrode, and an operation including a program for hammering the dust collecting electrode before the dust is deposited and covered on the entire surface to be shielded. Electric dust collector equipped with a panel