ELECTRODE MOVING TYPE ELECTROSTATIC PRECIPITATOR
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an electrostatic precipitator, and more particularly to an electrode moving type electrostatic precipitator.
2. Description of the Related Art
As shown in Fig. 9, in this type of the electrode moving type electrostatic precipitators, conventionally, both the ends of each of a plurality of dust collection electrode plates 1, 1, ... are coupled with a pair of endless chains 2, 2, and the dust collection electrode plates 1, 1 are circularly moved by circularly moving the endless chains 2, 2. A discharge electrodes 3 isdisposedtothe circularly moving dust collection electrode plates 1, 1, ... at a predetermined interval, and a corona discharge is generated from the discharge electrodes 3 by applying a high voltage thereto. Dusts in a gas are electrostatically charged by the corona discharge and captured by the dust collection electrode plates 1, 1, ....
Rotary brushes 4 are fixedly disposed in the moving paths of the dust collection electrode plates 1, 1,... , and the dusts capturedby the dust collection electrode plates 1 are exfoliated and removed by the rotary brushes 4 each time the dust collection
electrode plates 1 pass through the position of the rotary brushes 4. Thus, the dusts captured by the dust collection electrode plates 1, 1, ... are maintained only to a predetermined thickness or less. Accordingly, the electrode moving type electrostatic precipitator is particularly useful as an electrostatic precipitator for high resistant dusts the dust collecting performance of which is greatly deteriorated by a back corona phenomenon when dusts are deposited more than a predetermined thickness. [0004]
A discharge current, which is caused to flow in the dust collection electrode plates 1, 1, ... by the corona discharge, is grounded through the endless chains 2, 2. That is, driving sprockets 5 for circularly moving the endless chains 2, 2, driven rollers 6, and the rotary brushes 4 are grounded through cables 7, 8, and 9, respectively. Accordingly, the discharge current flowing in the dust collection electrode plates 1, 1,... flows to any of the driving sprockets 5, the driven rollers 6, and the rotary brushes 4 through the endless chains 2, 2 and is grounded through the cables 7, 8, and 9. [0005]
Incidentally, since this type of the electrode moving type electrostatic precipitators have a lot of moving components, they are disadvantageous in that the endless chains 2, 2, the driving sprockets 5, the driven rollers 6, and the like are greatly worn and the life of use thereof is short. Contemplated as the reason of the wear are wear due to a mechanical factor

and wear due to partial electrolytic corrosion which is caused when the discharge current flows, and the wear due to the electrolytic corrosion occupies a considerably large ratio of the reason. [0006]
Patent document 1 discloses a technical idea for extending the life of use of driving sprockets and driven rollers of this type of the electrode moving type electrostatic precipitators by suppress wear due to electrolytic corrosion in such a manner that a discharge current flowing in endless chains is prevented from reaching the driving sprockets and the driven rollers.
[Patent Document 1] Japanese Patent Application Laid-open (JP-A) No. 5-64754 [Disclosure of the Invention] [Problem to be solved by the Invention] [0007]
However, the technical idea disclosed in patent document 1 cannot suppress the discharge current flowing in the endless chains although it can extend the life of use of the driving sprockets and the driven rollers. Accordingly, the technical idea has a problem in that electrolytic corrosion due to the discharge current still progresses in the endless chains themselves and the operation of the dust collector is hindered by the extension of the endless chains caused by wear . Although the extension of the endless chains can be suppressed when the duct collector is operated so as to reduce the discharge current flowing in the endless chains, a voltage applied to a discharge

electrode must be reduced by the amount of reduction of the discharge current. As a result, a dust collecting performance is lowered. [0008]
An obj ect of the present invention is to improve the defect of the conventional technique and to provide an electrode moving type electrostatic precipitator capable of reducing extension of endless chains even if the dust collector is operated for a long period and increasing a dust collecting performance. [Means for solving problem] [0009]
To achieve the above object, an electrode moving type electrostatic precipitator according to the present invention^ which captures dusts in a gas to dust collection electrode plates by the corona discharge from discharge electrodes by circularly moving endless chains to which the dust collection electrode plates are suspended so that the dust collection electrode plates are circularly moved, is characterized in that the ripple ratio of a voltage applied to the discharge electrodes is set to 10% or less.
[Effect of the Invention] [0010]
When the high voltage direct current power supply having the ripple ratio of 10% or less is used for the moving electrode type electrostatic precipitator, a discharge current caused by a peak voltage can be greatly lowered even if the same average voltage is applied to the discharge electrodes. As a result.

sparks are unlikely to be generated, and the endless chains can be suppressed from being worn by electrolytic corrosion. Accordingly, the average voltage of the high voltage direct current power supply applied to the discharge electrodes can be increased, which enables the improvement of the dust collecting performance.
[Best mode for carrying out the Invention] [0011]
Fig. 1 is a front elevational view showing an embodiment of an electrode moving type electrostatic precipitator according to the present invention. The components in Fig. 1, which are denoted by the same reference numerals as those of Fig. 6, are the same components as those of the conventional technology, and the explanation thereof is omitted. In the embodiment, a plurality of moving electrode mechanisms shown in Fig. 6 are disposed in parallel with each other at a predetermined interval, and discharge electrodes 3 are also disposed between the respective moving electrode mechanisms. [0012]
The respective discharge electrodes 3 are connected to a power supply unit 11 through a power supply cable 10. A high voltage having a ripple ratio of 10% or less is applied to the respective discharge electrodes 3 by the power supplied from the power supply unit 11, and corona discharge is generated from the respective discharge electrodes 3. [0013]
The ripple ratio is a percentage calculated by ripple

ratio = (Vp - Vb) /Vav,  wherein Vav denotes an average voltage, Vp denotes a peak voltage, and Vb denotes a bottom voltage in a direct current voltage waveform shown in Fig. 2. [0014]
In the electrostatic precipitator, higher voltage applied to a discharge electrode more increases the electric field strength in a dust collecting space, whereby a dust collecting performance can be improved. The average voltage Vav shown in Fig. 2 is practically used as the voltage to be applied to the discharge electrode. Incidentally, according to a result of examination of the inventors, it has been found that extension of endless chains 2 due to wear is greatly changed in the electrode moving type electrostatic precipitator by the ripple ratio of the voltage applied to the discharge electrodes 3. [0015]
A high voltage direct current power supply having a frequency of 100 to 120 Hz, which is obtained by subjecting a single-phase frequency (50 to 60 Hz) of a commercially available power supply to half-wave rectification, is used as a power supply of conventional moving electrostatic precipitators. However, the high voltage direct current power supply obtained by simply subjecting the commercially available power supply to the half-wave rectification has a very high ripple ratio of about 80% because the difference between a peak voltage and a bottom voltage is increased as shown in a voltage waveform A of Fig. 3. Accordingly, when the high voltage direct

current power supply is applied to the discharge electrodes 3 in an average voltage of, for example, 70 kV, the peak voltage becomes about 98 kV. [0016]
That is, in the moving electrode electrostatic precipitator using the high voltage direct current power supply described above, a discharge current caused by the high peak voltage flows to the endless chains through dust collecting electrode plates 1 at a frequency of about 10 ms (milliseconds) . Thus, the endless chains are electrolytically corroded by the repeated application of the discharge current, which results in acceleration of the wear of the endless chains. Further, since the power supply having the high peak voltage is liable to generate sparks between the discharge electrodes 3 and the dust collection electrode plates 1, the portions of the endless chains, in which the endless chains are in contact with each other, are electrolytically corroded by a large spark discharge current which flows when the sparks are generated, which results in acceleration of the wear of the endless chains. More increasing the average voltage of the high voltage direct current power supply applied to the discharge electrodes 3 to increase the dust collecting performance more accelerates electrolytic corrosion of the endless chains. [0017]
In contrast, a high voltage direct current power supply having a ripple ratio of about 8% as shown in a voltage waveform B of Fig. 3 has a small peak voltage. Even if it is applied

to the discharge electrodes 3 in an average voltage of, for example, 70 kV, the peak voltage is about 73 kV. Accordingly, when a high voltage direct current power supply having the ripple ratio of 10% or less as described above is used to the moving electrode type electrostatic precipitator, the discharge current caused by the peak voltage can be greatly lowered even if the same average voltage is applied to the discharge electrodes 3. As a result, since sparks are unlike to be generated, the endless chains 2 can be suppressed from being worn by electrolytic corrosion. This enables to increase the average voltage of the high voltage direct current power supply applied to the discharge electrodes 3, and to improve the dust collecting performance.
Note that a radio frequency high voltage generator provided with a semiconductor switch, for example, can be used as a power supply unit for obtaining a high voltage direct current power supply having the ripple ratio of 10% or less.
[Example]
[0018]
An experiment device similar to the moving type electrode electrostatic precipitator shown in Fig. 6 was used to examine the relation between the ripple ratio of a high voltage direct current power supply applied to the discharge electrode 3 and the frequency of generation of sparks . In the experiment device, the center distance between a driving sprocket 5 and a driven roller 6 was set to 5 m, and 12 dust collection electrode plates 1 (width 2 m X height 1 m) were suspended by a pair of endless

chains 2, 2. Further, since the endless chains 2 hada circularly moving width of 46 cm and a discharge electrode 3 was disposed at the center of the circularly moving width, the interval between the dust collecting electrode plate 1 and the discharge electrode 3 was 23 cm. [0019]
An exhaust gas having a dust concentration of 5 g/m^ and a temperature of 80°C was introduced into the experiment device, and the experiment device was operated by uniformly setting the moving speed of the endless chains 2, 2 to 0.5 m/min and the average voltage of the high voltage direct current power supply to be applied to the discharge electrode 3 to 75 kV. Experiment was performed using five types of high voltage direct current power supplies having the ripple ratio set to 5%, 10%, 20%, 50%, and 80% as the high voltage direct current power supply to be applied to the discharge electrode 3. [0020]
Fig. 4 is a graph showing a result of the experiment, wherein a horizontal axis shows the ripple ratio of the high voltage direct current power supply, and a vertical axis shows the number of times of generated sparks. Note that the term "sparks" means spark discharge generated between the dust collecting electrode plate 1 and the discharge electrode 3. When the sparks are generated, a value indicated by an ammeter disposed to the power supply unit is instantly increased, and thus, the number of times of generation of the sparks can be counted. As apparent from Fig. 4, when the ripple ratio of

the high voltage direct current power supply is 5% or 10%, sparks are not almost generated, and an increase of the ripple ratio abruptly increases the number of times of sparks. It is considered that a reason why the result of the experiment is obtained resides in that a high voltage direct current power supply having a larger ripple ratio has a higher peak voltage as described above, whereby sparks are liable to be generated. Generation of the sparks instantly increases the discharge current, thereby accelerating electrolytic corrosion of an endless chain. [0021]
Fig. 5 is a model view showing the relation between the number of times of sparks and a chain extension ratio. Fig. 5 shows an estimated value when the experiment device was operated 100,000 times in the above condition, wherein a region C in Fig. 5 shows a chain extension ratio due to a mechanical wear caused when the endless chain is driven, and a region D shows a chain extension ratio due to electrolytic corrosion. It is estimated that the extension ratio due to the electrolytic corrosion increases approximately in proportion to the number of times of sparks. When the number of times of sparks is 100 times/min at the ripple ratio of 80%, the chain extension ratio reaches 1.5% which is near to the like of use of the endless chain. In contrast, when the ripple ratio is 10% or less as in the present invention, sparks are not almost generated. For this reason, the chain extension ratio is only about 0.5% due to the mechanical wear, and thus the extension ratio of the

endless chains can be suppressed to about one third the case that the ripple ratio is 80%. [Brief description of the drawings] [0022]
Fig. 1 is a front elevational view showing an embodiment of an electrode moving type electrostatic precipitator according to the present invention;
Fig. 2 is a graph explaining a ripple ratio;
Fig. 3 is an explanatory graph for comparing the voltage waveforms of a high voltage direct current power supply;
Fig. 4 is a graph showing a result of experiment;
Fig. 5 is a model view showing the relation between the number of times of sparks and a chain extension ratio; and
Fig. 6 is a perspective view showing a basic arrangement of an electrode moving type electrostatic precipitator. [Description of the reference numerals] [0023]
1. Collection electrode plate
2. Endless chain
3. Discharge electrode
4. Rotary brush
5. Driving sprocket
6. Driven roller 7.8.9. (Ground) cable

10. Power supply cable
11. Power supply unit
[Name of Document] Claim
[Claim 1]
An electrode moving type electrostatic precipitator for capturing dusts in a gas to dust collection electrode plates by the corona discharge from discharge electrodes by circularly moving endless chains to which the dust collection electrode plates are suspended so that the dust collection electrode plates are circularly moved, wherein the ripple ratio of a voltage applied to the discharge electrodes is set to 10% or less.

2. An electrode moving type electrostatic precipitator for capturing dusts in a gas to dust collection electrode plates by the corona discharge from discharge electrodes by circularly moving endless chains to which the dust collection electrode plates are suspended so that the dust collection electrode plates are circularly moved, wherein the ripple ratio of a voltage applied to the discharge electrodes is set to 10% or less by providing a primary circuit of a voltage set-up transformer with reactance adjustment means so as to adjust a reactance.
3. An electrode moving type electrostatic precipitator for capturing dusts in a gas to dust collection electrode plates by the corona discharge from discharge electrodes by circularly moving endless chains to which the dust collection electrode plates are suspended so that the dust collection electrode plates are circularly moved, wherein the ripple ratio of a voltage applied to the discharge electrodes is set to 10% or less by connecting capacitors between the dust collection electrode plates and the discharge electrodes, and providing capacitance
adjustment means of the capacitors to change the capacitances of the capacitors.
4 . An electrode moving type electrostatic precipitator for capturing dusts in a gas to dust collection electrode plates by the corona discharge from discharge electrodes by circularly moving endless chains to which the dust collection electrode plates are suspended so that the dust collection electrode plates are circularly moved, wherein the ripple ratio of a voltage applied to the discharge electrodes and the dust collecting electrodes is set to 10% or less by providing a frequency conversion unit of a voltage input from a power supply and adjusting the frequency of a voltage in a primary circuit of a step-up transformer.