JP4447176B2 - Electric dust collector - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an electric dust collector capable of efficiently cleaning an electrode surface on which dust is collected by utilizing a discharge phenomenon.
[0002]
[Prior art]
The air in the tunnel of the motorway is contaminated with submicron-order suspended particulates such as harmful gas in the exhaust gas exhausted from the automobile, soot, and tire dust generated when the automobile travels, and road asphalt wear dust.
[0003]
In order to remove such smoke particles in the contaminated air, an air purification facility using a corona discharge type two-stage electric dust collector constituted by a charging part and a dust collecting part has been put into practical use.
[0004]
The corona discharge type two-stage electrostatic dust collector has a high dust collection rate even with respect to nanometer particles, and is suitable for a large flow rate treatment. However, almost no harmful gas in the gas can be removed, and there is a demand for the development of an apparatus that performs this with high efficiency.
[0005]
In recent years, silent discharge type electrostatic dust collectors that simultaneously remove harmful gases as well as suspended particles have been proposed. Since this silent discharge type electrostatic precipitator can remove suspended particles and harmful gas at the same time, it can also be expected to have sterilization and deodorizing effects.
[0006]
[Problems to be solved by the invention]
In the corona discharge type two-stage electrostatic precipitator, the particles collected on the surface of the dust collecting electrode are generally removed by water washing. This is a system in which high-pressure water spray is generated from a nozzle previously installed in an electrostatic precipitator and particles collected on the electrode surface are removed.
[0007]
However, there is a problem in water washing that a large-scale water washing auxiliary equipment such as a washing water tank, a sewage pit, a sewage storage tank, a filtration device, a drainage compressor, an operation air source unit and various pumps is required.
[0008]
On the other hand, in the silent discharge type electrostatic precipitator, as a method of removing particles collected on the electrode surface, it is considered to apply a water washing method similar to the corona discharge type two-stage electrostatic precipitator, Large-scale cleaning equipment is required.
[0009]
Accordingly, an object of the present invention is to provide an electric dust collector capable of simplifying the cleaning system and reducing the size of the cleaning equipment.
[0010]
[Means for Solving the Problems]
The present invention relates to an electrostatic precipitator that collects particles suspended in the air by utilizing a discharge phenomenon between electrodes, wherein the frequency of the AC high voltage applied to the electrodes When cleaning is performed by removing particles adhering to the surface of the electrode while the flow of the contained gas flow is stopped, the particles floating in the air are collected using a discharge phenomenon between the electrodes. The electrostatic precipitator is configured by providing a high-frequency applying means for making the frequency higher than the operating frequency.
[0011]
Here, the frequency of the AC high voltage applied to the electrode during the cleaning may be several hundred Hz or more.
[0012]
The voltage value of the alternating high voltage applied to the electrode during the cleaning may be the same voltage value as during operation .
[0013]
The voltage value of the AC high voltage applied to the electrode during the cleaning may be a voltage value higher than the voltage applied during the operation.
[0014]
The high voltage may be several kV or higher.
[0016]
The means for generating a discharge phenomenon between the electrodes may be configured as a silent discharge generating means for generating a silent discharge or a corona discharge generating means for generating a corona discharge.
[0017]
An operation control means for periodically switching between the operation at the time of operation and the operation at the time of cleaning according to the amount of dust may be further provided.
[0018]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
[0019]
[First example]
A first embodiment of the present invention will be described with reference to FIGS.
[0020]
In this example, a silent discharge type electric dust collector capable of generating a large amount of radicals and removing harmful gases with high efficiency will be described as an example of the electric dust collector.
[0021]
(Device configuration)
First, the overall configuration of the silent discharge type electric dust collector will be described with reference to FIG.
[0022]
As shown in FIG. 6, this apparatus includes a charging unit 1 and a dust collection unit 2.
[0023]
The charging unit 1 is composed of two flat plate-like discharge electrodes 3 and is arranged to face each other as a parallel plate structure. Each discharge electrode 3 includes a flat dielectric 4 and a metal electrode 5 covered with the dielectric 4.
[0024]
The discharge electrode 3 has a sandwich structure in which a metal electrode 5 is sandwiched between two flat dielectrics 4. In this case, it is necessary to design the metal electrode 5 so that it is completely covered with the dielectric 4 and no gap or the like exists between the metal electrode 5 and the dielectric 4.
[0025]
The dielectric 4 can be made of, for example, a photocatalytic material such as titanium oxide (TiO ₂ ), and has a thickness of about several millimeters when ordinary glass is used.
[0026]
In this example, the dielectric 4 is used for both of the discharge electrodes 3 facing each other in parallel. However, the present invention is not limited to this, and one discharge electrode 3 may be covered with the dielectric 4. Good.
[0027]
An AC high voltage power source 6 (commercial frequency: 50 Hz or 60 Hz) is connected between the metal electrodes 5 during operation. An AC high voltage (about 14 kV) is applied between the metal electrodes 5 by the AC high voltage power source 6 to generate a silent discharge 7. The silent discharge 7 is also called ozonizer discharge or dielectric barrier discharge.
[0028]
The dust collection part 2 is comprised by the two flat metal electrode plates 8, and is opposingly arranged as a parallel plate structure.
[0029]
A DC high voltage power source 9 is connected between the metal electrode plates 8. A direct current high voltage is applied between the metal electrode plates 8 by the direct current high voltage power source 9, and one of them becomes a positive electrode (+) and the other becomes a negative electrode (-) to adsorb charged particles.
[0030]
And the discharge electrode 3 is arrange | positioned in the upstream of the flow direction of the gas flow A containing a dust particle and harmful gas. The metal electrode plate 8 is disposed on the downstream side of the discharge electrode 3. Here, dust particles and harmful gases are shown as particles 10.
[0031]
The configuration described above shows a basic configuration during operation for actually performing dust collection processing.
[0032]
(High frequency high voltage generator)
FIG. 1 shows a configuration in which a high-frequency high-voltage generator 100 according to the present invention is provided in the charging unit 1 during cleaning.
[0033]
The high-frequency and high-voltage generation unit 100 stores a high-frequency generation unit 110, a high-voltage generation unit 120, a CPU 130 that performs overall control of the apparatus, a timer unit 140, a control program according to the present invention, and the like. It includes a ROM 150, a RAM 160 that executes various arithmetic processes, and a sensor unit 170 that measures the amount of dust.
[0034]
The high frequency generator 110 has a function of applying a high frequency different from the commercial frequency during operation, that is, a frequency of several hundred Hz or more. Thereby, dust particles adhering to the surface of the discharge electrode 3 can be efficiently removed.
[0035]
The high voltage generator 120 has a function of applying a high voltage different from the operating voltage, that is, a voltage of several tens of kV or more. Thereby, dust particles adhering to the surface of the discharge electrode 3 can be efficiently removed.
[0036]
CPU 130 intermittently controls the operation of high-frequency and high-voltage generation unit 100 based on the time measured by timer unit 140.
[0037]
The sensor unit 170 is constituted by optical detection means such as a photodetector, and measures the amount of dust floating in the air. The measurement result is sent to the CPU 130 and used as a judgment material for intermittent control of operation or cleaning.
[0038]
Here, a numerical example of control in the high-frequency and high-voltage generator 100 will be given. The frequency ranges from several Hz to 1 KHz, and the voltage ranges from 5 mm to several kV to 30 kV. The voltage varies depending on the electrode interval. When the electrode interval is 10 mm, the voltage is doubled. The maximum value of the electrode interval is about 20 mm.
[0039]
In addition, by providing this device with a communication function, it is possible to perform remote operation. By measuring the cleaning history, etc., it is possible to accurately grasp the maintenance time and efficiently perform repairs and inspections. Effective when installed on the ground.
[0040]
In this example, the AC high-voltage power supply 6 at the time of operation shown in FIG. 6 and the high-frequency high-voltage generator 100 at the time of cleaning shown in FIG. 1 are separately configured. Both functions may be configured together.
[0041]
(During operation: dust collection)
Next, the overall flow of dust collection processing during normal operation will be described.
As shown in FIG. 6, in the charging unit 1, an AC voltage of about 14 kV at a commercial frequency is applied between the metal electrodes 5 of the discharge electrode 3 by an AC high voltage power source 6. Thereby, a silent discharge 7 is generated in the space between the electrodes.
[0042]
In this state, when particles 10 containing dust particles such as dust particles and NOx flow into the charging unit 1 along the direction of the gas flow A, harmful gases such as NOx are removed by the discharge chemical reaction in the discharge space. Is done.
[0043]
At this time, active oxygen species are generated on the electrode surface of the dielectric 4 made of the photocatalytic medium, and this active oxygen species chemically reacts with NOx to remove NOx and the like. Therefore, harmful gases such as NOx are removed not only in the discharge space but also in the vicinity of the electrode surface of the dielectric 4.
[0044]
Thereafter, the particles 10 (hereinafter referred to as charged particles) charged positively or negatively by the silent discharge of the charging unit 1 are guided to the dust collection unit 2 downstream. In the dust collection portion 2, since the DC high voltage V is applied between the metal electrode plates 8 by the DC high voltage power source 9, the charged particles 10 are adsorbed.
[0045]
As described above, the discharge chemical reaction by the photocatalyst medium constituting the dielectric 4 is used to convert light generated by silent discharge and the energy of active species into the electrode surface energy of the dielectric 4, and dust particles, NOx, etc. Of harmful gases can be collected more efficiently.
[0046]
In this example, the electric dust collector is composed of two parts, that is, the charging unit 1 and the dust collecting unit 2. However, the electric dust collecting device may have only the charging unit 1 from which the dust collecting unit 2 is removed.
[0047]
(During cleaning: removal of dust particles)
Next, dust particle removal processing during cleaning will be described.
As described above, when the electrostatic precipitator is operated at an AC high voltage near the commercial frequency, dust particles are collected and deposited on the surface of the discharge electrode 3 of the charging unit 1.
[0048]
In FIG. 1, in order to remove the accumulated dust particles, a high frequency high voltage of several hundred Hz or more is applied between the parallel flat discharge electrodes 3 to generate a high frequency silent discharge. For example, the AC voltage has a value of about 14 kV, which is the same as that during operation, but a high frequency silent discharge is generated by applying the voltage for about 90 minutes in a state where the frequency is increased from a commercial frequency to a high frequency of 400 Hz. By this high frequency silent discharge, dust particles collected on the surface of the discharge electrode 3 can be efficiently removed.
[0049]
In addition to changing to a high frequency such as 400 Hz, the AC voltage may be increased from about 14 KV during operation to several tens of kV or more. As described above, the dust particles collected on the electrode surface can be more efficiently obtained by appropriately changing and combining the frequency value by the high frequency application unit 110 and the voltage value by the high frequency voltage unit 120 in the high frequency high voltage generation unit 100. Can be removed. The cleaning mechanism of dust particles collected by high-frequency silent discharge is thought to be due to the combustion of dust particles, but the details are not clear at this time.
[0050]
(Cleaning example)
Next, an example of cleaning on the electrode surface will be described.
FIG. 2A shows a state in which the surface state of the discharge electrode 3 is imaged using an imaging device (digital camera or the like) as a result of applying a high voltage of about 14 kV at 50 Hz during operation. In this case, the electrode surface is observed as black over the entire surface of the electrode as indicated by P due to dust particles collected during operation.
[0051]
In contrast, in FIG. 2B, a high voltage of about 14 kV is applied at 50 Hz for 30 minutes, and then a high frequency silent discharge of 400 Hz is generated by the high frequency application unit 110 of the high frequency high voltage generation unit 100 for 90 minutes. The state of observing the surface state of the discharge electrode 3 when washed using an imaging device (digital camera or the like) is shown. In this case, dust particles are not observed on the electrode surface. From this, it can be seen that the dust particles collected during operation are almost completely removed from the electrode surface by applying the high frequency high voltage.
[0052]
(Washing: Frequency dependence)
Next, frequency dependency during cleaning will be described.
FIG. 3 shows the frequency dependence of the dust amount on the electrode surface with respect to time characteristics.
[0053]
As measurement conditions, the applied voltage is constant (14 kV in this case), and the amount of dust adhering to the electrode surface (mg / m ² ) at the initial stage of cleaning is almost equal. The gas flow rate is 0 m / sec, and no new dust adheres to the electrode surface.
[0054]
When the applied voltage is constant at 14 kV and the frequency is changed in the range of several tens of Hz to several kHz (here, 50 Hz, 100 Hz, 400 Hz, 800 Hz, 1 kHz), the amount of change in the amount of dust on the electrode surface Check out.
[0055]
A curve with a frequency of 50 Hz corresponds to a conventional cleaning. In contrast, it can be seen that the amount of dust on the electrode surface at the same time (minute) decreases as the frequency increases. Moreover, although the dust amount on the electrode surface decreases with the passage of time, it can be seen that the dust is removed more rapidly as the frequency increases.
[0056]
(Washing: Applied voltage dependence)
Next, the applied voltage dependency during cleaning will be described.
FIG. 4 shows the applied voltage dependence on the time characteristics of the dust amount on the electrode surface.
[0057]
As measurement conditions, the applied voltage is equal to or higher than the discharge start voltage (14 kV in this case), and the amount of dust adhering to the electrode surface (mg / m ² ) at the initial stage of cleaning is almost equal. The gas flow rate is 0 m / sec, and no new dust adheres to the electrode surface.
[0058]
Then, when the frequency is constant at 400 Hz and the applied voltage is changed in the range of several kV to several tens of kV (here, 10 kV, 14 kV, 20 kV, 30 kV), the amount of change in the dust amount on the electrode surface is examined. .
[0059]
It can be seen that the amount of dust on the electrode surface at the same time (minutes) decreases as the applied voltage increases with respect to the curve of the applied voltage of 10 kV. Moreover, although the dust amount on the electrode surface decreases with the passage of time, it can be seen that the dust is removed more rapidly as the applied voltage is larger.
[0060]
(Intermittent control)
Next, intermittent control during operation and cleaning will be described.
FIG. 5 shows an example of intermittent control when the present apparatus is installed on the ceiling in the tunnel.
[0061]
In step S1, the timer 140 is started and the operation time is measured.
[0062]
In step S2, it is checked whether or not there is an abnormality in operation. If there is no abnormality, the process proceeds to step S3, where normal operation is performed, and dust particles and harmful gas are removed. On the other hand, if there is an abnormality, the operation is stopped.
[0063]
In step S4, it is checked whether or not the measured driving time exceeds 15 hours. If it is more than 15 hours, it will progress to step S6 and the high frequency high voltage generation part 100 will perform a washing process. On the other hand, if it is less than 15 hours, it will progress to step S5.
[0064]
Although the operation time is 15 hours, it is not limited to this, and may be changed according to the period of use or the service life of the apparatus.
[0065]
In step S5, it is detected by the sensor unit 170 whether or not the amount of dust exceeds a reference value. When the amount exceeds the reference value, the process proceeds to step S6 to perform a cleaning process, and when it is less than the reference value, the process returns to step S2.
[0066]
This amount of dust can be measured, for example, by using optical means to measure the amount of dust particles, etc. floating in the air, and when the amount of transmission falls below a certain value, it is determined that the amount exceeds the reference value. Perform the cleaning process. The measurement of the amount of dust is not limited to optical means, and other well-known techniques such as other sensors may be used.
[0067]
In step S6, a cleaning process between the electrodes is performed, and the process proceeds to step S7 to check whether or not the cleaning time has exceeded 90 minutes. When it is 90 minutes or longer, the cleaning process is terminated and the process proceeds to step S8.
[0068]
Although the cleaning time is set to 90 minutes, the cleaning time may be changed according to the amount of dust. In addition, the cleaning is not controlled by time, but it may be determined whether to continue the process according to the degree of cleaning.
[0069]
After performing the cleaning process, the process proceeds to step S8, where it is determined whether or not normal operation is to be resumed. When restarting, the process returns to step S1 to continue the process.
[0070]
[Second example]
Next, a second embodiment of the present invention will be described with reference to FIGS. In addition, about the same part as the 1st example mentioned above, the description is abbreviate | omitted and the same code | symbol is attached | subjected.
[0071]
This example is an example in which a corona discharge type electrostatic dust collector is used as the electrostatic dust collector.
[0072]
FIG. 7 shows the configuration of the corona discharge electrode.
[0073]
The discharge electrode 20 as a corona discharge electrode is composed of two flat plate electrodes 21 and a linear line electrode 22 disposed between the flat plate electrodes 21. The striped electrode 23 made of a photocatalytic substance is formed on the surface on the opposite side of the plate electrode 21, but this need not be formed.
[0074]
The electrode spacing is in the range of 3.7 cm to 5.0 cm. The applied voltage between the plate electrode 21 and the line electrode 22 at the time of cleaning is in the range of 11 kV to 15 kV.
[0075]
During operation, a DC high voltage V is applied between the line electrode 22 and the two plate electrodes 21. In this case, the line electrode 22 is a positive electrode, and the flat plate electrode 21 is a negative electrode, which is grounded.
[0076]
At the time of cleaning after operation, the high-frequency and high-voltage generating unit 100 according to the present invention is connected between the two flat plate electrodes 21 or between the flat plate electrode 21 and the line electrode 22. Thereby, dust particles adhering to the surface of the discharge electrode 3 can be efficiently removed during cleaning.
[0077]
In this example, the DC high-voltage generator during operation and the high-frequency high-voltage generator 100 during cleaning are configured separately, but the present invention is not limited to this, and both functions are combined into one device. It may be configured.
[0078]
When a DC high voltage is applied during operation, a corona discharge is formed only in the vicinity of the periphery of the line electrode 22, and the chemical process for treating harmful gas such as NOx by the photocatalyst in the discharge space is the first process described above. This is the same as the silent discharge in the example. Since the discharge space is limited to the vicinity of the periphery of the line electrode 22 and the amount of discharge light emission is small, the harmful gas removal rate is lower than that of the silent discharge type.
[0079]
(Comparative example)
Next, cleaning examples in silent discharge type and corona discharge type electric dust collectors will be compared and described.
[0080]
FIG. 8 shows the dust removal characteristics of the electrode surface in comparison between the silent discharge type and the corona discharge type.
[0081]
As measurement conditions, the frequency is constant and the amount of dust adhering to the electrode surface (mg / m ² ) at the initial stage is almost equal. The gas flow rate is 0 m / sec, and no new dust adheres to the electrode surface.
[0082]
Of the four curves, the solid line 200 represents the silent discharge type of the present invention, the solid line 300 represents the corona discharge type of the present invention, the broken line 250 represents the conventional silent discharge type, and the broken line 350 represents the conventional corona discharge type. It is a characteristic.
[0083]
First, the silent discharge type of the solid line 200 according to the present invention and the corona discharge type of the solid line 300 are compared. It can be seen that the dust amount on the electrode surface decreases with the passage of time in any of the electrostatic precipitators. In this case, the corona discharge type has a lower removal rate than the silent discharge type, but dust on the electrode surface can be removed by applying a high frequency high voltage.
[0084]
Next, the present invention will be compared with a conventional example. In the silent discharge type, it can be seen that the solid line 200 according to the present invention significantly reduces the amount of dust on the electrode surface as compared with the conventional broken line 250. On the other hand, in the corona discharge type, the solid line 300 according to the present invention shows a difference in the amount of dust on the electrode surface over time as compared to the conventional broken line 350.
[0085]
【The invention's effect】
As described above, according to the present invention, high-frequency applying means for removing particles adhering to the electrode surface by applying a high-frequency frequency (several hundred Hz or more) different from the frequency at the time of dust collection, Since a high voltage application means for applying and removing a high voltage (several kV or more) different from the voltage at the time is provided, particles attached to the electrode surface can be removed more efficiently than in the past, Thereby, the simplification of the cleaning method and the downsizing of the cleaning equipment can be achieved.
[0086]
In addition, according to the present invention, since the operation control means for periodically switching between the operation at the time of operation and the operation at the time of cleaning according to the amount of dust is provided, dust collection processing by automatic control is performed over a long period of time. This is particularly effective in remote areas.
[Brief description of the drawings]
FIG. 1 is a perspective view showing a configuration of a silent discharge type electrostatic precipitator including a high-frequency and high-voltage generating unit according to a first embodiment of the present invention.
FIG. 2 is an explanatory view showing a surface state of a discharge electrode before and after a cleaning process.
FIG. 3 is a characteristic diagram showing the frequency dependence of the dust amount on the electrode surface with respect to time characteristics.
FIG. 4 is a characteristic diagram showing dependency of applied voltage on time characteristics of dust amount on the electrode surface.
FIG. 5 is a flowchart showing an example of intermittent control during operation and cleaning according to the present invention.
FIG. 6 is a perspective view showing a configuration of a silent discharge electrostatic precipitator during operation.
FIG. 7 is a perspective view showing a configuration of a corona discharge type electrostatic precipitator including a high-frequency high-voltage generator according to a second embodiment of the present invention.
FIG. 8 is a characteristic diagram showing a comparison of cleaning amounts between the present invention and a conventional example.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Charging part 2 Dust collection part 3 Discharge electrode 4 Dielectric (photocatalyst medium)
5 Metal electrode 6 AC high voltage power supply 7 Silent discharge 8 Metal electrode plate 9 DC high voltage power supply 10 Particles (dust particles, harmful gas)
20 Discharge electrode 21 Flat electrode 22 Line electrode 23 Photocatalyst electrode 100 High frequency high voltage generator 110 High frequency generator 120 High voltage generator 130 CPU
140 Timer section 150 ROM
160 RAM
170 Sensor Unit 200 Silent Discharge Dust Removal Characteristics 250 Conventional Silent Discharge Dust Removal Characteristics 300 Corona Discharge Dust Removal Characteristics 350 Conventional Corona Discharge Dust Removal Characteristics

Claims (8)

An electric dust collector that collects particles floating in the air using the discharge phenomenon between the electrodes,
The frequency of the alternating high voltage applied to the electrodes is a discharge between the electrodes at the time of cleaning to remove particles adhering to the surface of the electrode in a state where the flow of the gas flow containing the particles is stopped. An electric dust collector characterized by comprising high-frequency applying means for collecting particles floating in the air by using a phenomenon, which has a higher frequency than the operating frequency . 2. The electrostatic precipitator according to claim 1 , wherein the frequency of the alternating high voltage applied to the electrode during the cleaning is several hundred Hz or more. 3. The electrostatic precipitator according to claim 1, wherein the voltage value of the alternating high voltage applied to the electrode during the cleaning is the same voltage value as during the operation . 3. The electrostatic precipitator according to claim 1 , wherein a voltage value of the alternating high voltage applied to the electrode during the cleaning is a voltage value higher than a voltage value applied during the operation . 5. The electrostatic precipitator according to claim 4, wherein the high voltage value is several kV or more. Means for generating a discharge phenomenon between the electrodes, an electric precipitator according to any one of claims 1 characterized in that it is a silent discharge generating means for generating a silent discharge 5. Means for generating a discharge phenomenon between the electrodes, an electric precipitator according to any one of claims 1, characterized in that a corona discharge generating means for generating a corona discharge 5. Operations and during the operation, and an operation at the time of the cleaning, electrostatic precipitator according to a further one of claims 1 to 7, characterized in that comprises an operation control means for periodically switching in accordance with the amount of dust apparatus.

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