JP3629894B2 - Electrostatic air purifier - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an electrostatic air cleaner, and more particularly to an electrostatic air cleaner provided with an electrode for applying a high voltage.
[0002]
[Prior art]
The electrostatic air cleaner is a two-stage system consisting of a charging unit that charges dust in the air with ions generated by corona discharge and a dust collecting unit that collects the charged dust with a parallel plate to which a high DC voltage is applied. Many electric dust collector structures are used. In addition, a single-stage electrostatic precipitator having a charging part and a dust collecting part may be used, such as an electrostatic precipitator used for a thermal power plant or industrial use. In both types of electrostatic air cleaners, the casing is often open on the air suction side, the blow side, or both.
[0003]
[Problems to be solved by the invention]
The dust collector has a higher dust removal performance as the applied voltage is higher. However, if it is too high, a spark discharge occurs between the electrodes, so that the operation is performed with the applied voltage set slightly lower than the spark voltage. Nevertheless, spark discharge may occur due to the dust attached to the electrode and the vibration of the discharge electrode. In the case of an electrostatic air cleaner, an insect such as a moth or a mosquito may enter to generate a spark discharge. Since such a spark discharge is accompanied by a rapid current change, a strong electromagnetic wave is emitted as noise. The above-mentioned industrial dust collectors for industrial and thermal power plants are entirely surrounded by a metal casing, so that electromagnetic noise generated by spark discharge never leaked to the outside.
[0004]
On the other hand, since the electrostatic air cleaner has an opening, electromagnetic noise is radiated to the outside. If an electronic device is placed in the vicinity of the electrostatic air cleaner, there is a risk of causing trouble in operation due to electromagnetic noise.
Therefore, a conventional electrostatic air cleaner is applied with a voltage much lower than the spark voltage and is operated with a low dust removal performance, or several discharge current control means as described below have been considered.
That is, the one disclosed in Japanese Patent Laid-Open No. 1-194554 has an arc discharge detection circuit, and is configured to stop the high voltage generation circuit when arc discharge continues between electrodes for a certain time. This method controls the high voltage generation circuit only for continuous arc discharge without determining that the arc discharge is discretely generated as an abnormal state. However, an electronic device or the like placed around an electrostatic air cleaner may be affected even by a single radiated electromagnetic wave, which is insufficient as a countermeasure.
[0005]
On the other hand, a current limiting element such as a resistor or an inductance is interposed between the high voltage power source and the electrode as disclosed in Japanese Utility Model Publication No. 54-20692, Japanese Patent Application Laid-Open No. 5-31398 and Japanese Patent Application Laid-Open No. 7-132249. Thus, a method for suppressing the discharge current when a spark occurs is disclosed. Examples thereof are shown in FIGS. 7, 8 and 9.
The resistor 102 in FIG. 7, the resistor 114 in FIG. 8, and the inductance 124 in FIG. 9 are current limiting elements, and are inserted in order to suppress the discharge current when a spark discharge occurs. By suppressing the discharge current by using these current limiting elements, it is intended to reduce the radiated electromagnetic wave intensity at the time of spark generation and the sound generated by the discharge.
However, even when the above measures were taken, when the radiated electromagnetic wave intensity was measured, a clear suppression effect could not be recognized. Certainly, the current flowing from the high-voltage power source to the electrode was suppressed, but the intensity of the radiated electromagnetic wave was hardly suppressed.
[0006]
Next, consider this reason. As described in JP-A-7-132249, electrodes to which a high voltage is applied (103 and 105 in FIG. 7, 111 in FIG. 8, 120 and 121 in FIG. 9), and an electrode on the ground side (FIG. 7). 101, 112 in FIG. 8 and 122) in FIG. 9 play the role of an air capacitor, and a high voltage is applied between both electrodes during operation, so that electric charges are accumulated. In Japanese Patent Application Laid-Open No. 7-132249, when a spark discharge occurs, the electric charge stored between the electrodes is instantaneously released. Since the discharge of the charge at this time appears as a spark current, it is necessary to suppress the discharge of the charge. A measure for stopping the discharge of the charge is the inductance 124 of the current limiting element shown in FIG.
We agree with the idea that the sudden flow of charge stored between the electrodes is the spark discharge current. Then, the current flowing from the electrode to the high voltage power source or the current flowing from the high voltage power source to the electrode is suppressed by the effect of the current limiting element. This is common to the above three examples, and was confirmed in experiments.
[0007]
However, the electric charge stored in the electrode constituting the air capacitor is not discharged outside the electrode during the spark discharge but is neutralized in the electrode through the spark discharge path. At this time, the current flowing through the spark discharge path is the spark discharge current. The model is shown in FIG. 2, which is equivalent to the dielectric breakdown of the air capacitor through the spark point. Therefore, the spark discharge current cannot be captured by a current detector attached outside the electrode, and cannot be suppressed by a current limiting element provided outside. It only limits the current flowing into the electrode from the high voltage power supply. Therefore, since the spark discharge current cannot be suppressed, the intensity of the radiated electromagnetic wave cannot be suppressed.
[0008]
Fig. 3 shows the change over time in the voltage between the electrodes and the electric field strength of the radiated electromagnetic waves when a spark discharge is generated in a charged part consisting of a discharge wire electrode and a plate electrode using a conventional electrostatic air cleaner. It is a thing.
After the spark is generated, the voltage between the electrodes drops to zero while being damped, but when the waveform is examined in detail, a vibration with a short period is superimposed on a damped vibration with a relatively long period. Long-period vibration is a component of vibration due to the capacitance between the entire discharge line electrode and the plate electrode of the charging unit, and the inductance of the current path and spark discharge path constituting the electrode. On the other hand, it was found that the vibration with a short period was due to the capacitance and inductance that only the discharge line electrode that generated the spark had between the flat plate electrode.
[0009]
The electromagnetic field intensity shows that electromagnetic waves corresponding to a short period are radiated strongly. The size of the electrode system of the electrostatic air cleaner is very short with respect to the wavelength of the electromagnetic wave with respect to vibration with a long period, and when the electrode is considered as an antenna, the resonance frequency is greatly shifted and the radiation efficiency is low.
On the other hand, the wavelength of the electromagnetic wave with respect to the vibration having a short period is short, approaches the resonance frequency of the electrode, has high radiation efficiency, and is considered to emit a strong electromagnetic wave.
From the above experimental results, it can be seen that the means for suppressing the spark discharge current with the entire electrode taken together is ineffective to suppress the radiated electromagnetic noise. An object of the present invention is to provide an electrostatic air cleaner that has high dust removal performance at a high operating voltage and has low electromagnetic wave noise radiated even when spark discharge occurs.
[0010]
[Means for Solving the Problems]
In order to achieve the above object, an electrostatic air cleaner according to a first aspect of the present invention includes an electrode system in which discharge lines and electrodes composed of flat plates facing the discharge line are arranged, and the capacitance and self-induction of the electrode system. With respect to the characteristic impedance determined by the coefficient, each electrode has a resistance component distributed over π times the characteristic impedance per unit length, and the spark discharge current is suppressed by the resistance of the electrode itself.
The invention of claim 2 is characterized in that, in claim 1, the total resistance of each electrode is not less than 2π times the characteristic impedance and not more than 10 ⁶ Ω.
According to a third aspect of the present invention, there is provided a two-stage electrostatic air comprising a charging line electrode system comprising a discharge line and a flat plate facing the discharge line, and a dust collecting electrode system comprising a high voltage applying flat plate and a dust collecting plate. In the purifier, each electrode has a distributed resistance component more than π times the characteristic impedance per unit length with respect to the characteristic impedance determined by the capacitance of the electrode system of the charging unit and the self-induction coefficient. flat dust portion of the electrode is formed by a resistor material, per unit length, and characterized by having a capacitance and π times more resistive component of the characteristic inspiration over dance determined by the self-induction coefficient between each of the opposing flat plate To do.
According to a fourth aspect of the present invention, there is provided a two-stage electrostatic air composed of a discharge line and an electrode system of a charging portion comprising a flat plate opposed to the discharge line and an electrode system of a dust collection portion comprising a high voltage applying flat plate and a dust collecting plate. in purifier, the total resistance of each of the electrodes of the electrode system of the charging portion is higher 2π times the characteristic impedance and, together with or less 10 ⁶ Omega, flat of each of the electrodes of the particulate collection portion is molded by a resistor material, the unit It has a resistance component more than π times the characteristic impedance determined by the capacitance between each opposing flat plate and the self-induction coefficient per length.
[0011]
[Operation and effect of the invention]
According to the configuration of the present invention, by one lifting each of the electrodes is high electrical resistance, since it reduces the discharge current when the spark discharge is generated, it can greatly suppressed the intensity of the electromagnetic wave noise radiated, location neighborhood It is possible to eliminate the interference caused by electromagnetic waves on the electronic devices and the like, and to reduce the discharge noise. Moreover, since high voltage operation is possible, dust removal performance can be improved.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a structural diagram of an electrode showing an embodiment of the present invention. There is no significant difference in appearance from the conventional electrostatic air cleaner.
This example is a two-stage electrostatic precipitator, which includes a charging unit 10 and a dust collecting unit 20. The charging unit 10 includes a discharge wire 11 and a ground plate 12 that generate a corona discharge by applying a high voltage. The dust collecting unit 20 includes a dust collecting plate 22 that collects charged dust and a high voltage applying flat plate 21 that creates an electric field so that an electric force acts on the dust collecting plate 22 toward the dust collecting plate 22.
[0013]
Resistive materials are used for the discharge wire 11 and the ground plate 12 constituting the electrode of the charging unit, and the high voltage application plate 21 and the dust plate 22 constituting the electrode of the dust collecting unit, respectively. As a method of giving a resistance component to the electrodes, a structure in which all the electrodes have a resistance component or one electrode member of each electrode, that is, a discharge line or ground plate of the charging unit and a high voltage application plate or collector of the dust collection unit. Make the dust plate have a resistance component.
First, the charging unit 10 will be described. The characteristic impedance when the electrode composed of the discharge line 11 and the two flat plates 12 sandwiching the discharge line 11 is regarded as a transmission line, that is, the discharge line 11 per unit length in the vertical direction in FIG. When the capacitance between the flat plate 12 and the flat plate 12 is C and the inductance is L, the value of (L / C) ^0.5 is about 100 to 300Ω. This varies depending on the electrode structure such as the interval between the flat plates 12 and the thickness of the discharge line 11.
[0014]
Here, if the transmission line composed of each discharge line and the flat plate has a resistance component, the spark discharge current when the spark discharge is generated is suppressed. FIG. 4 shows the magnitude of the spark discharge current with the ratio of the resistance R per unit length of the transmission line R to the characteristic impedance (L / C) of ^0.5 on the horizontal axis. The suppression effect is greater as the resistance R is higher. Although it varies depending on the frequency, the vibration that occurs when an electrostatic air cleaner generates a spark discharge is predominantly the one corresponding to the resonance frequency of the lowest-order transmission path and has a resonance frequency of the second or higher. Since the corresponding vibration is hardly observed, FIG. 4 shows the lowest resonance frequency.
[0015]
When the resistance R is π (circumferential ratio) or more times the characteristic impedance, the effect of suppressing the spark discharge current becomes remarkable, and it becomes ½ or less of the case where the electrode is made of a conductor (R≈O).
Further, in the transient phenomenon of the transmission line, if the length of the transmission line (approximately equal to the length of the discharge line) is 1 (el), the resistance R per unit length is 2π (L / C) ^0.5 / l. If it becomes above, the electric current which flows into a transmission line becomes an attenuation | damping waveform which does not have a vibration component. Therefore, the vibration component having a short period appearing in FIG. 3 disappears.
R * l is the total resistance per transmission line when the discharge line 11 and the ground plate 12 sandwiching the discharge line 11 are regarded as the transmission line, and this suppresses vibration when the characteristic impedance (L / C) is 2π times or more of ^0.5. I can do it.
[0016]
The spark discharge current can be suppressed as the resistance increases, but if it is too high, the voltage drop due to the current flowing through the discharge line and the ground plate during normal operation cannot be ignored. Normally, even if the corona discharge current per discharge line is large, it is about 1 mA. Therefore, if the resistance R * l per transmission line is 10 ⁶ Ω or less, the voltage drop is about 1000 V or less. In an electrostatic air cleaner that operates at a voltage of 10,000 V or more, it is easy to take a margin for a voltage drop in the power supply voltage.
As a method for providing resistance as a transmission line, a metal wire for a resistor or an alloy wire for a thermocouple can be used as a discharge wire. Further, a material having resistance such as carbon fiber reinforced plastic, a composite plate of carbon fiber and polymer resin or glass fiber may be used for the flat plate. Only the discharge line or only the ground plane may be formed of a resistance material, or both may be formed of a resistance material.
[0017]
As described above, the spark discharge current can be reduced to ½ or less by providing a transmission line composed of each discharge line 11 and the ground plate 12 sandwiching the discharge line 11 with a resistance of π times or more of the characteristic impedance per unit length. Can do. Therefore, the energy of the radiated electromagnetic wave can be suppressed to ¼ or less. Further, if the total resistance of each transmission line is set to 2π times or more of the characteristic impedance, the vibration at the time of occurrence of spark is eliminated, and the radiation electromagnetic wave intensity can be further suppressed.
FIG. 6 shows a measurement example of the voltage between electrodes and the intensity of radiated electromagnetic waves when spark discharge occurs in the charging part of the electrostatic air cleaner according to the present invention. The resistance of the discharge electrode is about 4π times the characteristic impedance, and the others are the same as in the measurement shown in FIG. The voltage between the electrodes is not oscillated, and the electric charge stored in the capacitance is slowly discharged through the resistor. The radiated electromagnetic wave intensity is also drastically reduced and is suppressed to 1/40 or less at the maximum peak value as compared with FIG.
[0018]
Next, the dust collector 20 will be described. The dust collecting unit is configured by a dust collecting plate 22 for collecting charged dust and a high voltage applying flat plate 21 facing each other in parallel. These facing flat electrodes work to create an electric field that applies a Coulomb force to the charged dust, and do not need to be a conductive plate as used conventionally. Resistive materials can be used so that the charge of ions flowing from the charging unit 10 and the charge charged with dust do not accumulate on these flat electrodes. Since the current flowing through the electrode of the dust collection unit is two orders of magnitude or more smaller than that of the charging unit, the voltage drop due to the electrode using a resistance material is small, and the resistance can be made 100 times higher than that of the charging unit.
[0019]
Find the required resistance in terms of suppressing spark discharge current. Here, the distance between the high voltage applying flat plate 21 and the dust collecting plate 22 is a, and the flat plate width is b. In the case of an electrostatic air cleaner, the characteristic impedance of a parallel plate electrode made of a conductor is expressed by an approximate expression 120πa / b when a <b. In a normal electrostatic air cleaner, it is about several tens of ohms to 200 ohms. Similarly to the description of the charging unit, the spark discharge current is reduced to ½ or less by providing a pair of electrodes of the high voltage application flat plate 21 and the dust collecting plate 22 with a resistance of π times or more of this value per unit length. It can be greatly reduced. Further, if the total resistance of the pair of electrodes is 2π times or more, the vibration that causes strong electromagnetic radiation can be eliminated.
[0020]
FIG. 5 shows a modification of the flat electrode of the charging unit or the dust collecting unit. In this modification, a flat plate electrode is formed by sandwiching a metal plate from both sides with a resistor plate. Since the metal plate sandwiched between the electrodes becomes an equipotential surface, the potential distribution on the surface of the resistor plate approaches evenly. Therefore, when all are formed of a resistance material, there is a defect that potential distribution varies, and there is a place where dust removal performance is lowered in the air flow path, but this modification has an effect of eliminating this defect. .
[Brief description of the drawings]
FIG. 1 is a perspective view of an electrode configuration showing an embodiment of the present invention.
FIG. 2 is an equivalent circuit diagram showing spark discharge.
FIG. 3 is a diagram showing a measurement example of the voltage between electrodes and the intensity of radiated electromagnetic field when a conventional electrostatic air cleaner generates a spark discharge.
FIG. 4 is a diagram showing the relationship between the electrical resistance of an electrode and the magnitude of a spark discharge current.
FIG. 5 is a perspective view of a modification of a flat electrode.
FIG. 6 is a diagram showing a measurement example of an interelectrode voltage and a radiation electromagnetic field intensity when a spark discharge is generated by the electrostatic air cleaner of the present invention.
FIG. 7 is a circuit diagram showing a conventional spark discharge current suppressing method.
FIG. 8 is another circuit diagram showing a conventional spark discharge current suppressing method.
FIG. 9 is another circuit diagram showing a conventional spark discharge current suppressing method.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 ... Charging part, 11 ... Discharge wire, 20 ... Dust collection part, 21 ... High voltage application flat plate, 22 ... Dust collection board

Claims (4)

It has an electrode system in which electrodes consisting of discharge lines and flat plates facing it are arranged, and each electrode has a characteristic impedance of π per unit length with respect to the characteristic impedance determined by the capacitance and self-induction coefficient of the electrode system. An electrostatic air cleaner characterized in that a spark discharge current is suppressed by the resistance of the electrode itself having a resistance component distributed more than twice. 2. The electrostatic air cleaner according to claim 1, wherein the total resistance of each of the electrodes is not less than 2π times the characteristic impedance and not more than 10 ⁶ Ω. In a two-stage electrostatic air cleaner composed of a discharge line and an electrode system of a charging part consisting of a flat plate facing the discharge line and an electrode system of a dust collecting part consisting of a high voltage application flat plate and a dust collecting plate,
With respect to the characteristic impedance determined by the capacitance of the electrode system of the charging unit and the self-induction coefficient, each electrode has a resistance component distributed over π times the characteristic impedance per unit length, and the dust collecting unit static flat plate of the electrode is formed by a resistor material, per unit length, characterized by having a capacitance and the resistance component of the above π times the characteristic inspiration over dance determined by the self-induction coefficient between each of the opposing flat plate Electric air purifier. In a two-stage electrostatic air cleaner composed of a discharge line and an electrode system of a charging part consisting of a flat plate facing the discharge line and an electrode system of a dust collecting part consisting of a high voltage application flat plate and a dust collecting plate,
The total resistance of each electrode of the charging portion of the electrode system is more than 2π times the characteristic impedance and, together with or less 10 ⁶ Omega, flat of each of the electrodes of the dust collecting part is formed by a resistor material, unit length An electrostatic air cleaner characterized by having a resistance component that is at least π times the characteristic impedance determined by the capacitance between each opposing flat plate and the self-induction coefficient.

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