JPH08252479A - 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 a reverse electric dissociation phenomenon in the electric collection of dust having a high electric resistance value. CONSTITUTION: The second dust collecting electrode 6 is installed at a position close to a discharge electrode 2 to which direct current high voltage is applied and also close to one or both ends of a grounded main dust collecting electrode 4, to maintain the conductivity of the surface of the electrode 6. In this way, the ionic charge of charged dust accumulated on the main electrode 4 is discharged along the surface of the electrode 6 so that the grounding electric potential of the surface of the electrode 4 is maintained substantially.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to electric dust collection of dust in the air, and more particularly to electric dust 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 performed in Japan and abroad for a long time.

The principle of electrostatic precipitating is to apply a high DC voltage, usually a negative DC high voltage, to a discharge electrode having a wide area and normally forming a sharp angle with respect to a grounded dust collecting electrode. A corona discharge is generated and dust passes through it. At that time, the dust adsorbs negative ions and free electrons (hereinafter simply referred to as ions) generated between both electrodes due to high voltage and is negatively charged, and strongly repels the discharge electrode due to Coulomb force. It flies toward the dust collecting pole between the two, collides with and adheres to the dust collecting pole. 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 amount of generated ions increases as the amount of current increases, and thus the amount of generated ions increases as the voltage applied to the discharge electrode increases. 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 raised and the electric field strength is raised too much, a spark will be generated, and an arc discharge will not be generated, and a uniform corona discharge will not be formed. Flows, which may damage the power supply or damage 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 that has collided with the dust collecting electrode releases the electric charge of the adsorbed ions and loses the Coulomb force. However, if the dust itself has an electric insulating property, it is relatively weak due to the Van der Waals force. It adheres to the dust collecting electrode and accumulates. Even if the accumulated dust has electrical insulation, if it has an appropriate conductivity, the polarity of the dust electrode surface, that is, the ground potential is maintained, so that new negatively charged dust collects dust. Can collide with, discharge and attach. 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, its conductivity is recovered and the dust is collected. The work can be continued stably. That is, when the electric resistance value is appropriate (usually approximately 10 ⁴ to 10 ¹¹ Ω-cm), high electric dust 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 several tens to several thousand times the size of the dust before the collision. Therefore, the dust collection electrode should be set at an appropriate frequency depending on the dust concentration.
Usually, if hammering is performed once every few minutes, the accumulated and enlarged dust is separated from the dust collecting electrode, overcomes the wind speed and falls due to gravity, so that even sub-micron particles are collected by the dust collector. It is possible to collect the hopper in the lower part.

However, in the case of dust such as silicates or polymer resins having an excessively high electric resistance value, the electric resistance value on the surface of the dust collecting electrode gradually increases as the dust accumulates, and the discharge from the colliding dust is smooth. No longer done. Further, due to the shape of the dust collecting electrode, the strength of hammering, the frequency and the direction, the dust is not evenly peeled off, and a part of the dust collecting electrode where no dust adheres and a part where dust remains remain. In this case, since the ionic charge of the dust discharges along the surface of the separated portion or the surface of the dust that is electrostatically shielded and has little dust adhesion, the dust collection efficiency is greatly reduced, but the dust collection 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 having the same polarity as 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 is reduced. . Therefore, a large amount of uncharged dust is generated, the dust does not approach the dust collecting electrode, and even if a part of 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 greatly reduced. Therefore, when 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 electrical resistance of dust finally exceeds the breakdown voltage locally, and the electrical resistance value of that part drops extremely. A discharge is formed. Therefore, the electric resistance value between both electrodes decreases extremely,
Therefore, a larger current than usual flows, but since the corona discharge is not uniformly formed, the ions do not uniformly collide with the dust, the charge rate of the dust is reduced, and the dust collection efficiency is significantly reduced. In addition, since the accumulated dust adheres with Coulomb force, a strong impact is required for peeling, so hammering causes a large amount of dust to escape and reduces dust collection efficiency. This phenomenon is generally called the reverse ionization phenomenon, and as described above, dust with a large electric resistance value covers the entire surface of the dust collecting electrode, and it occurs when the applied voltage locally exceeds the breakdown voltage of the dust. Dust efficiency was greatly reduced.

Therefore, various methods have been tried in order to prevent the reverse ionization phenomenon. For example, a method of flowing water on the surface of the dust collecting electrode to maintain the conductivity of the surface of the dust collecting electrode, a method of scraping off the dust on the surface of the dust collecting electrode with a brush or the like are used. Although these methods are effective in preventing reverse ionization, volume efficiency is low and the device cost is high, and the device structure is complicated, so not only maintenance cost is high, but also the air to be processed is In case of high temperature air such as incinerator, it was difficult to apply. Further, as the high voltage waveform applied to the discharge electrode, not only a simple DC high voltage but also a DC pulse high voltage, a DC high voltage superimposed with a DC pulse high voltage, and the like are used. When the pulse waveform voltage is applied to the discharge electrode, the electric field strength required to form the arc discharge increases, so that the maximum applied voltage can be increased. Therefore, although the effect of improving the dust collection efficiency can be obtained to some extent, the effect is not only small in comparison with the increase in the power supply cost, but on the other hand, the applied voltage is increased to increase the electric field strength, and the electric field strength near the arc discharge is generated. If it is removed, the amount of harmful gas generated is significantly increased, which is not preferable. In addition, since the dust adheres with a strong Coulomb force, a strong impact must be given when hammering, resulting in a decrease in efficiency.

In view of the problems of the prior art, the present invention is applied to air containing dust having a high electric resistance value so that reverse ionization does not occur, and therefore the dust collection efficiency is not reduced even if the voltage is not increased specially. An electric dust collecting method and an electric dust collecting apparatus are provided.

[0008]

In order to solve the problem, the means provided by the present invention is to apply a high DC voltage to a vertically arranged discharge electrode so that a grounded main collecting electrode faces the discharge electrode. In a vertical dust collecting operation, a second dust collecting electrode, which is formed by a thin line or a narrow surface and is grounded, is placed vertically near one or both ends of the main dust collecting electrode. Is provided, and the conductivity of the surface of the second dust collecting electrode is always maintained, and the means for removing the dust on the surface of the second dust collecting electrode to maintain the conductivity is The second dust collecting electrode rotates about the vertical axis and is scraped by a scraper, and the dust on the surface of the fixed second dust collecting electrode is scraped by a scraper rotating about the vertical axis. It includes things that are things.

[0009]

According to the above-mentioned means, since the second dust collecting electrode which always maintains the conductivity is arranged near the end of the main dust collecting electrode, the electric resistance which collides with the surface of the main dust collecting electrode. Even if the dust having a high value covers and deposits on the entire surface of the main dust collecting electrode, the electric charges of the ions attached to the dust are always discharged toward the second dust collecting electrode due to the creeping discharge. Therefore, reverse ionization does not occur. Therefore, dust adheres, grows and deposits on the main dust collecting electrode with a weak force due to the Van der Waals force. Therefore, it is easily peeled off and dropped by hammering, and is collected in the hopper. On the other hand, since the dust on the surface of the second dust collecting electrode is removed by a scraper or the like, its conductivity is not lost, and the dust separated from the second dust collecting electrode is recharged by the ions from the discharge electrode. Or collides with charged dust and grows toward the main dust collecting pole. Further, since the area of the second dust collecting electrode is smaller than that of the main dust collecting electrode, a dust collecting device having high volume efficiency can be obtained.

The operation of the second dust collecting electrode according to the present invention will be described in more detail based on the following examples. That is, FIG.
Is a horizontal sectional view showing an embodiment of rotating the second dust collecting electrode in the present invention, and FIG. 2 is a horizontal sectional view showing an embodiment of rotating the scraping machine.

[0011]

1 and 2, 2 is a discharge electrode, 4 is a main dust collecting electrode, 5 is an end of the main dust collecting electrode 4, and 6 is a second dust collecting electrode. Further, 8 is a scraping machine, which is arranged inside the dust collector 10. Reference numeral 20 is a DC high voltage power supply, and 22 is a flow direction of air.

The discharge electrode 2 is formed of a thin wire such as a stainless wire or a piano wire, and is disposed so as to face the surface of the main dust collecting electrode 4. The number of discharge electrodes 2 is determined according to the amount of air to be processed. Further, a negative DC high voltage is applied to the discharge electrode 2 by a DC power source 20 according to a standard method. In this case, discharge electrode 2
It is not necessary to particularly increase the voltage applied to the device, and it is sufficient to set the electric field strength to the extent that corona discharge is formed and the spark is not reliably generated. Further, in the present invention, since reverse ionization does not occur, it is sufficient to apply a DC high voltage having a flat waveform, but the present invention is not limited to this, and a pulse in which a pulse high voltage having a DC high voltage as a base voltage is superimposed is superimposed. High voltage may also be used. However, also in that case, it is preferable that the electric field strength formed by the maximum voltage applied is such that sparks are not reliably generated, since harmful substances are not generated.

The main dust collecting electrode 4 is made of a steel plate and is grounded.
It is arranged in the vertical direction in parallel with the air flow direction 20. The shape of the main dust collecting electrode 4 may be a flat plate or a rectangular cross section in addition to the embodiments shown in FIGS. 1 and 2. In any case, if the portion near the second dust collecting electrode 6 is formed so as to have the sharp tip 5, the creeping discharge from the surface of the main dust collecting electrode 4 to the second dust collecting electrode 6 can be performed more smoothly. It is preferable because it is displayed. The size of the main dust collecting electrode 4 in the air advancing direction, that is, the size in the longitudinal direction may be changed according to the dust concentration and the amount of air, but it is normally about twice the distance from the discharge electrode, and therefore the high volume is high. Efficiency is obtained. The number of main dust collecting electrodes 4 and the number of discharge electrodes 2 may be appropriately determined as in the past depending on the amount of air and the dust concentration. Further, the main dust collecting electrode 4 is regularly and usually impacted several times per minute by a hammering device (not shown), and the dust collecting device 10
Although it is collected in a hopper (not shown) arranged in the lower part of the, since dust is attached by the Van der Waals force,
There is no need to give a particularly strong impact. Therefore, instead of intermittent hammering, continuous high-speed vibration or continuous weak impact can be applied, and the hopper can continuously collect.

The second dust collecting electrode 6 is made of a conductive material and is arranged in parallel to the discharge electrode and near the end 5 of the main dust collecting electrode 4. The number of the second dust collecting electrodes 6 is at least 1 for each discharge electrode.
I need one. Various means can be used as means for maintaining the conductivity of the surface. That is, FIG. 1 shows an example in which the second dust collecting electrode 6 is rotated, the scraping machine 8 is fixed, and the second dust collecting electrode 6 is brought into contact with the surface of the second dust collecting electrode 6 to remove dust. In this case, the diameter of the second dust collecting electrode is not limited to a particularly large diameter as long as it can withstand the rotating torque. Therefore, high volume efficiency can be obtained. Further, a metal brush is embedded in the contact end of the scraping machine 8 so that dust can be reliably removed. Second dust collector 6
Is continuously or intermittently rotated by a rotating device (not shown). In this case, the scraper can also use the end part 5 of the main dust collecting electrode 4 by contacting it with the second dust collecting electrode 6, and thus a higher volumetric efficiency can be obtained. 2 is the second
The dust collecting electrode 6 is made to coincide with the end 5 of the main dust collecting electrode 4, and the area of the second dust collecting electrode 6 is smaller than that of the main dust collecting electrode 4, so that high volumetric efficiency can be obtained. In this case, the maintenance of conductivity is achieved by rotating the scraper 8 made of a metal brush. In the case of both FIG. 1 and FIG. 2, the effect of peeling off the dust on the surface of the second dust collecting electrode 6 is greater as the rotation speed is larger, and usually 10 or more times per minute are required. This is preferable because the rotation surely removes dust. Further, the second dust collecting electrode 6 is hardly deposited because the dust is constantly removed by the scraper 8, but
If an electrostatic shield is used to shield the lines of electric force from the discharge electrode, the adhesion of dust can be prevented more reliably.

The means for removing dust accumulated on the surface of the second dust collecting electrode 6 is not limited to the above, and the second dust collecting electrode 6 may be peeled off by continuous high-speed vibration or impact. In this case, it is preferable that the diameter of the second dust collecting electrode 6 is as small as possible, because the attached dust can be easily separated. Alternatively, the end surface of the flat plate-type main dust collecting electrode may be peeled off by a claw that moves up and down. In this case, the portion separated by the claw becomes the second dust collecting electrode. Further, when the dust is polymer resin or the like, it is also possible to use air blow with compressed air.

In the present invention, the surface of the main dust collecting electrode 4 may be covered with an insulating material so that the reverse ionization phenomenon does not occur, and the second dust collecting electrode 6 is separated from the main dust collecting electrode 4. Then, when dust having a low electric resistance value is collected, the jumping phenomenon does not occur. Therefore, when dust with a high electric resistance value and dust with a low electric resistance value are collected simultaneously or alternately, or when the resistance value of the dust changes significantly during the dust collection work, neither jumping nor reverse ionization phenomenon occurs, so high dust collection Efficiency is obtained.

[0017]

According to the present invention, the surface of the second dust collecting electrode 6 always maintains conductivity, and the charges from the ions of the dust accumulated on the surface of the main dust collecting electrode 4 are absorbed by the creeping discharge. Reverse ionization phenomenon does not occur. Therefore, the dust collection efficiency is significantly improved. Moreover, since the voltage applied to the discharge electrode 2 is set so that the electric field strength is such that corona discharge is generated and the spark is not reliably generated, no harmful gas is generated. Further, since the area of the second dust collecting electrode is smaller than that of the main dust collecting electrode, a high volume efficiency electrostatic precipitator can be obtained.

[Brief description of drawings]

FIG. 1 is a diagram showing an embodiment in which a second dust collecting electrode is rotated.

FIG. 2 is a diagram showing an embodiment in which the scraper is a rotary type.

[Explanation of symbols]

 2, discharge electrode 4, main dust collecting electrode 5, main dust collecting extreme part 6, second dust collecting electrode 8, scraper

Claims (4)

[Claims] 1. An electrostatic precipitator in which a DC high voltage is applied to a vertically arranged discharge electrode and a grounded main dust collecting electrode is arranged vertically in opposition to the discharge electrode. The second dust collecting electrode, which is formed by a thin line or a narrow surface and is grounded, is vertically arranged near one or both ends of the dust collecting electrode, and the conductivity of the surface of the second dust collecting electrode is always maintained. An electrostatic precipitating method characterized by being held 2. A main dust collecting electrode that is grounded, a discharge electrode to which a high DC voltage is applied, and a second dust collecting electrode that is arranged near one or both ends of the main dust collecting electrode and is grounded. An electrostatic precipitator comprising means for removing dust adhering to the surface of the second dust collector 3. The means for removing dust on the surface of the second dust collecting electrode is characterized in that the second dust collecting electrode rotates around a vertical axis and is scraped by a scraping machine. Electrostatic precipitator described in 4. The means for removing the dust on the surface of the second dust collecting electrode scrapes off the dust on the surface of the fixed second dust collecting electrode by a scraping machine which rotates around a vertical axis. The electrostatic precipitator according to claim 2.