JP2012148214A - Wet electrostatic precipitator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve dust collection efficiency by making an applied voltage higher while suppressing occurrence of a spark discharge.SOLUTION: A wet electrostatic precipitator includes a DC high-voltage generation part 3 which generates a DC high voltage, a DC high-voltage input part 2 which has a capacitor 41 smoothing the DC high voltage V generated by the DC high-voltage generation part 3, a discharge electrode which is applied with the DC high voltage output from the DC high-voltage input part 2, and a dust collection electrode which collects fine particles by a negative corona discharge generated with the discharge electrode based upon the DC high voltage. The capacity of the capacitor 41 is set based upon the voltage ripple rate between the discharge electrode and dust collection electrode.

Description

  The present invention relates to a wet electrostatic precipitator that removes dust and the like from waste gas. In particular, the present invention improves the dust collection efficiency of dust containing heavy metals by increasing the voltage applied to the discharge electrode more than before (for example, increasing to about 70 to 80 kV) while suppressing the occurrence frequency of spark discharge. The present invention relates to a wet type electrostatic precipitator that can be used.

  Conventionally, wet electrostatic precipitators (see, for example, Patent Documents 1 to 3) capture harmful dust and mist from waste gas generated in waste incineration processes as well as sulfuric acid mist treatment and aluminum refining exhaust gas treatment. It is used for collecting purposes. As described above, the wet type electrostatic precipitator is widely used as a useful device from the viewpoint of air pollution prevention and environmental protection.

  In addition to harmful dust and mist, the waste gas to be treated that is processed by the wet electrostatic precipitator may contain so-called corrosive substances such as hydrofluoric acid and sulfurous acid gas. For this reason, in recent years, conductive fiber reinforced plastic (FRP, Fiber Reinforced Plastic, hereinafter referred to as FRP) has been used as a material constituting gas contact parts such as casings and dust collecting electrodes of wet electrostatic precipitators. Is called). By adopting FRP, corrosion resistance is mainly strengthened and it is possible to manufacture at a lower cost than a high corrosion resistance metal material.

  In such a wet electrostatic precipitator, it is required to increase the dust collection efficiency of dust containing heavy metals. As a general method for increasing the dust collection efficiency, a method for increasing the voltage between the dust collection electrode and the discharge electrode, that is, the voltage applied to the discharge electrode is known.

JP 2007-196159 A JP 2002-119889 A Japanese Patent Publication No. 6-91965

However, as the voltage applied to the discharge electrode is increased, corona discharge increases and eventually spark discharge (spark) may occur. Furthermore, in the operation state in which the washing water inside the wet electrostatic precipitator is continuously sprayed, the frequency of occurrence of spark discharge increases due to the presence of the water droplets.
When such spark discharge occurs, stable operation of the wet electrostatic precipitator is hindered. For this reason, during the operation of the wet type electrostatic precipitator, it is required to maintain a stable operation state without generating a spark discharge while spraying cleaning water.
Therefore, in order to meet such a demand using conventional wet electrostatic precipitators including Patent Documents 1 to 3, it is necessary to suppress the applied voltage and increase the dust collection efficiency of dust containing heavy metals. It is a situation that must be sacrificed. For example, according to Patent Document 2, in order to suppress the occurrence of spark discharge, the effective voltage of the applied voltage must be stopped at about 40 kV to 60 kV, and the dust collection efficiency must be lowered.

  The present invention has been made in view of such a situation, and by suppressing the occurrence frequency of spark discharge, by increasing the applied voltage to the discharge electrode than before (for example, up to about 70 to 80 kV), The purpose is to improve the dust collection efficiency of dust containing heavy metals.

An electric dust collector according to one aspect of the present invention,
A high voltage generator for generating DC high voltage;
A high voltage input unit that inputs a DC high voltage generated by the high voltage generation unit, smooths the DC high voltage using a capacitor, and outputs the DC high voltage;
A discharge electrode to which a DC high voltage output from the high voltage input unit is applied;
A dust collecting electrode for collecting fine particles by a negative corona discharge generated between the discharge electrode and the DC high voltage;
With
The capacity of the capacitor is set based on a voltage ripple rate between the discharge electrode and the dust collecting electrode,
It is characterized by that.

In this case, the dust collection electrode is constituted by an assembly of a plurality of the units, with a polygonal cylinder having an opening of a predetermined shape as a unit.
The discharge electrode is accommodated in each of the plurality of units constituting the dust collection electrode.
Can be.

  According to the present invention, the dust collection efficiency of dust containing heavy metals is improved by increasing the voltage applied to the discharge electrode (eg, increasing to about 70 to 80 kV) while suppressing the frequency of occurrence of spark discharge. Can be planned.

It is sectional drawing which shows schematic structure of the wet electric dust collector which concerns on one Embodiment of this invention. It is a perspective view which shows schematic structure inside the housing of the dust collector main-body part of FIG. It is a fragmentary sectional view which shows the detail of the schematic structure of the direct current high voltage input part 2 and the direct current high voltage generation part 3 among the wet electric dust collectors of FIG. The timing chart of the DC high voltage V applied to the conventional wet electric dust collector is shown. The timing chart of direct-current high voltage Vc applied to the wet electric dust collector of this embodiment is shown. The relationship between the applied voltage with respect to a wet electric dust collector and the electric current corresponding to it is shown. FIG. 3 is an equivalent circuit diagram of the wet electrostatic precipitator according to the present embodiment on which the capacitor of FIG. 2 is mounted. It is a figure which shows the effect of the wet electric dust collector of this embodiment. Among the wet type electrostatic precipitator according to another embodiment of the present invention, the inside of the housing of the dust collector main body having a rectangular tube-shaped dust collecting electrode whose opening has a hexagonal shape as a “chamber” It is a perspective view which shows schematic structure of these.

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[Configuration of wet electrostatic precipitator]
FIG. 1 is a cross-sectional view showing a schematic configuration of a wet electrostatic precipitator according to an embodiment of the present invention.
Specifically, FIG. 1 (A) and FIG. 1 (B) are cross-sectional views showing the schematic configuration of the external appearance of the wet type electrostatic precipitator, and are cross-sectional views seen from different directions substantially perpendicular to each other.

  The wet electrostatic precipitator includes a dust collector main body 1, a direct current high voltage input unit 2, and a direct current high voltage generator 3. Although not shown, a DC high voltage controller for controlling the DC high voltage generator 3 and the like are appropriately provided as components of the wet electrostatic precipitator.

  The dust collector main body 1 is provided with an upper casing 11, a dust collecting electrode 12 that also functions as a side casing, a lower casing 13, and a frame 14.

  The upper casing 11, the dust collecting electrode 12, and the lower casing 13 are combined in that order from above, whereby the housing of the dust collector main body 1 is configured. The housing of the dust collector main body 1 is fixed by a frame 14 so as to be spaced upward by a predetermined distance from the ground. In this embodiment, conductive FRP is adopted as the material of the casing of the dust collector main body 1.

FIG. 2 is a perspective view showing a schematic configuration inside the housing of the dust collector main body 1.
As shown in FIG. 2, inside the housing of the dust collector main body 1, an upper grid 21, the above-described dust collection electrode 12, a lower grid 23, an electrode rod 24, a discharge wire 25, a weight 26, An upward spray nozzle 27 and a cleaning pipe 28 are provided.

  As shown in FIG. 2, the upper grid 21, the dust collection electrode 12, and the lower grid 23 are spaced apart from each other by a predetermined distance in that order from above, and are substantially parallel to each other in the horizontal direction. It is arranged.

As shown in FIG. 2, the dust collection electrode 12 is configured by repeatedly arranging a plurality of “chambers” with a rectangular tube as a unit (hereinafter, such units are referred to as “chambers”). .
Specifically, hereinafter, one of the substantially horizontal directions is referred to as “vertical direction”, and a direction perpendicular to the vertical direction is referred to as “lateral direction”. In this case, by repeatedly arranging N units in the vertical direction and repeating M units in the horizontal direction (hereinafter referred to as “N × M”), the dust collection electrode 12 is configured.
Here, N and M are arbitrary independent integer values. In the present embodiment, as shown in FIG. 2, the number of “chambers” of the dust collection electrode 12 is N × M = 9 × 9. ing.
In this embodiment, conductive FRP is adopted as the material of the dust collection electrode 12.

In this embodiment, the discharge electrode for the dust collecting electrode 12 is constituted by an electrode rod 24 and a discharge wire 25.
As shown in FIG. 2, the electrode rod 24 is disposed so as to penetrate the center inside of a predetermined “chamber” of the dust collecting electrode 12 in a substantially vertical direction, and has an upper end fixed to the upper grid 21 and a lower end. Is fixed to the lower grid 23.
As shown in FIG. 2, the discharge line 25 is suspended from the upper grid 21 and is disposed so as to penetrate the center inside of a predetermined “chamber” of the dust collecting electrode 12 in a substantially vertical direction. The discharge line 25 is also connected to a weight 26 provided on the upper part of the lower grid 23 so as to have a tension that does not loosen.

  A negative DC high voltage generated by the DC high voltage generator 3 of FIG. 1 and supplied via the DC high voltage input unit 2 of FIG. 1 is directly applied to the electrode rod 24. On the other hand, the negative DC high voltage is applied to the discharge line 25 via the electrode rod 24 and the upper grid 21.

  The upward spray nozzle 27 is disposed above the four corners of each “chamber” of the dust collecting electrode 12 and ejects cleaning water flowing through the cleaning pipe 28 as a fine mist in a substantially vertical upward direction. Thereby, fine particles such as mist and dust adhering to the dust collecting electrode 12 can be cleaned and removed.

FIG. 3 is a partial cross-sectional view showing details of schematic configurations of the DC high voltage input unit 2 and the DC high voltage generation unit 3 in the wet electrostatic precipitator of FIG.
Specifically, FIG. 3A and FIG. 3B are cross-sectional views showing the details of the schematic configuration of the external appearance of the DC high voltage input unit 2 and the DC high voltage generation unit 3, which are substantially perpendicular to each other. It is sectional drawing seen from a different direction.

  As shown in FIG. 3, the direct current high voltage input unit 2 includes a capacitor box 31, a bus duct 32, and an insulator chamber 33.

  A capacitor 41, a protective resistor 42, and a protective resistor 43 are provided inside the capacitor box 31.

Here, an outline of the reason for mounting the capacitor 41 will be described.
That is, the DC high voltage V generated from the DC high voltage generator 3 and input to the DC high voltage input unit 2 is converted from AC to DC (hereinafter referred to as “rectification”) by a silicon rectifier 71 described later. Although done, it is hard to say that it is fully rectified.
For this reason, in the DC high voltage V generated from the DC high voltage generator 3, the peak-to-peak voltage difference ΔE is very large, and the peak voltage Vp becomes very high with respect to the effective voltage Er. Therefore, when the DC high voltage V is applied to the discharge electrode as it is, the occurrence frequency of spark discharge may increase. In the present embodiment, the “discharge electrode” means a collection of the electrode rod 24 and the discharge line 25 shown in FIG. 2 as described above.
Therefore, in the present embodiment, the capacitor 41 further reduces the DC pulsating flow for the DC high voltage V generated from the DC high voltage generator 3 (hereinafter referred to as “smoothing”). By reducing the peak-to-peak voltage difference ΔE, it is possible to suppress the peak voltage Vp while increasing the effective voltage Er.
That is, in the DC high voltage Vc after being smoothed by the capacitor 41, the peak voltage Vp is suppressed while the effective voltage Er increases. An increase in the effective voltage Er means that the dust collection efficiency of the wet electrostatic precipitator can be increased. On the other hand, suppressing the peak voltage Vp means that the occurrence frequency of spark discharge in the electrostatic precipitator can be suppressed.
As a result, even when an applied voltage having an effective voltage Er higher than that of the conventional one is used, stable operation in which the frequency of occurrence of spark discharge is suppressed becomes possible, and as a result, dust containing heavy metals is efficiently collected.
Further details of the capacitor 41 and its effects will be described later with reference to the drawings after FIG.

The protective resistor 42 is connected between the capacitor 41 and a high voltage output terminal 72 of a DC high voltage generator 3 described later.
The protective resistor 43 is connected between the high voltage output terminal 72 and a bus bar 51 described later of the bus duct 32 for overvoltage protection.

A bus bar 51, a wall penetrating insulator 52, and a closing plate 53 are provided inside the bus duct 32.
The bus bar 51 connects one end of the protective resistor 43 (the end opposite to the end to which the high voltage output terminal 72 is connected) and one end of the wall penetration insulator 52.
The wall penetrating insulator 52 is arranged so as to pass through the closing plate 53 as its name, and one end thereof is connected to the above-described bus bar 51 and the other end is a supporting insulator 61 described later in the insulator chamber 33. Connected to.
The closing plate 53 is installed between the bus duct 32 and the insulator chamber 33 for the purpose of blocking the intrusion of the gas to be processed into the bus duct 32.

  One end of the support insulator 61 provided in the insulator chamber 33 is connected to the above-described wall penetrating insulator 52, and the other end is connected to the electrode rod 24 (FIG. 2) which is a part of the discharge electrode. .

The DC high voltage generator 3 boosts an AC voltage from an AC power source (not shown in FIG. 3) (AC power source Vo in FIG. 7) by a transformer (not shown in FIG. 3) (transformer Tr in FIG. 7). , By performing a series of processes such as rectification by the silicon rectifier 71 (however, as described above, the rectification is insufficient in terms of a large pulsating flow), the high voltage output terminal 72 is converted into the DC high voltage V. Output from.
The DC high voltage V output from the high voltage output terminal 72 is input to the DC high voltage input unit 2 and applied to the discharge electrode through the protective resistor 43, the bus bar 51, the wall penetration insulator 52, and the support insulator 61. Is done. In other words, the DC high voltage V feeding path output from the high voltage output terminal 72 includes the high voltage output terminal 72, the protective resistor 43, the bus bar 51, the wall penetrating insulator 52, and the support insulator 61.

[Operation of wet electrostatic precipitator]
Next, the operation of the wet electrostatic precipitator of the present embodiment having the above configuration will be described.
With the dust collecting electrode 12 (FIG. 2) grounded, the negative DC high voltage V generated from the DC high voltage generator 3 (FIG. 3) is converted into a capacitor 41 in the DC high voltage input unit 2 (FIG. 3). Is sufficiently smoothed, and as a result, is applied to the discharge electrode as a DC high voltage Vc. The discharge electrode is a collection of the electrode rod 24 and the discharge line 25 (FIG. 2) as described above.
When the value of the DC high voltage Vc increases, a negative corona discharge is generated between the discharge electrode and each side surface of the “chamber” of the dust collection electrode 12 surrounding the discharge electrode, and as a result, from the discharge electrode to the dust collection electrode. Negative ions move in the direction toward each of the side surfaces of the twelve “chambers” and an ion wind is generated in the same direction.

Thus, in the wet electric dust collector of the present embodiment, the internal space of each “chamber” of the dust collecting electrode 12 becomes an ion space. Therefore, as shown in FIG. 1, the gas G1 containing fine particles such as mist and dust is supplied to the lower part of the casing of the wet electrostatic precipitator, and from the opening at the lower end of each “chamber” of the dust collecting electrode 12. When flowing toward the opening at the upper end, the fine particles are charged by the collision of negative ions.
The charged fine particles move from the discharge electrode by a direct current electric field inside each “chamber” of the dust collecting electrode 12 in a direction toward each side surface of each “chamber” of the dust collecting electrode 12 to collect the particles. It adheres to the side surface of each “chamber” of the dust electrode 12.
In this way, fine particles are removed from the gas G1. The gas G2 from which the fine particles have been removed from the gas G1 is released from the upper end of each “chamber” of the dust collecting electrode 12, and further, as shown in FIG. 1, the upper part of the casing of the wet electrostatic precipitator of the present embodiment. Discharged from.

Here, the wet electrostatic precipitator of this embodiment is compared with a conventional wet electrostatic precipitator.
The conventional wet electrostatic precipitator here is a device in which the DC high voltage V generated from the DC high voltage generator 3 is directly applied to the discharge electrode, that is, the capacitor 41 of the present embodiment is not mounted. Refers to the device.

FIG. 4 shows a timing chart of a DC high voltage V (hereinafter referred to as “applied voltage V” as appropriate) applied to a conventional wet electrostatic precipitator.
In FIG. 4, the vertical axis represents the applied voltage V (kV), and the horizontal axis represents time t.
In the applied voltage V shown in FIG. 4, the peak-to-peak voltage difference ΔE is very large at about 75 kV. This is because, as described above, in the DC high voltage generator 3, only the rectification by the silicon rectifier 71 is performed, but this alone is insufficient for rectification (meaning that the pulsating current is large).
As described above, in the conventional wet electrostatic precipitator, the peak-to-peak voltage difference ΔE becomes very large. Therefore, although the effective voltage Er of the applied voltage V is about 60 kV, the peak voltage Vp is It becomes very high at about 100 kV. At such a high peak voltage value Ep, the frequency of occurrence of spark discharge (spark) increases.
For this reason, in the conventional wet electrostatic precipitator, in order to suppress spark discharge and maintain a stable operation state, as described above, the effective voltage Er of the applied voltage V is further lowered to about 40 to 60 kV. I had to stop and drive. However, sufficient dust collection efficiency could not be obtained with such a low applied voltage V.

FIG. 5 shows a timing chart of the DC high voltage Vc (hereinafter referred to as “applied voltage Vc” as appropriate) applied to the wet type electrostatic precipitator of the present embodiment.
In FIG. 5, the vertical axis indicates the applied voltage Vc (kV), and the horizontal axis indicates time t.
In the applied voltage Vc shown in FIG. 5, it can be seen that the peak-to-peak voltage difference ΔE is about 10 kV, which is much smaller than the conventional one. This is because the DC high voltage V output from the DC high voltage generator 3 is further smoothed by the capacitor 41 as described above.
Thus, in this embodiment, since the capacitor 41 is mounted, the peak-to-peak voltage difference ΔE is much smaller than that of the conventional one, and as a result, the effective voltage Er of the applied voltage Vc is about 75 kV. Even if it is set higher than before, the peak voltage Vp can be suppressed to about 80 kV, which is lower than before.
An increase in the effective voltage Er means that the dust collection efficiency of the wet electrostatic precipitator can be improved. On the other hand, suppressing the peak voltage Vp means that the occurrence frequency of spark discharge in the electrostatic precipitator can be suppressed.
Thereby, in the wet type electrostatic precipitator of this embodiment, even if it raises to the applied voltage Vc higher than before, more specifically to the applied voltage Vc = 70-80 kV, it is a stable driving | operation which suppressed spark discharge. The state can be maintained, and as a result, dust containing heavy metals can be collected efficiently.

FIG. 6 shows the relationship between the voltage applied to the wet electrostatic precipitator and the current corresponding thereto.
In FIG. 6, the vertical axis represents the current corresponding to the applied voltage (output current of an equivalent circuit of FIG. 7 described later) (mA), and the horizontal axis represents the applied voltage (output voltage of the equivalent circuit 2C of FIG. 7 described later). The effective voltage Er of Vc) is shown.
Here, whether it is the wet electrostatic precipitator of this embodiment or the conventional wet electrostatic precipitator (the device in which the capacitor 41 of this embodiment is not mounted as described above) The relationship with the corresponding current is substantially the same.
For this reason, the point Pa shows an actual measurement value for a conventional wet electrostatic precipitator, and spark discharge occurred when the effective voltage Er of the applied voltage V was about 72 kV (current is about 12 mA). It has been confirmed.
A point Pb shows an actual measurement value of the wet electrostatic precipitator of the present embodiment, and no spark discharge occurred even when the effective voltage Er of the applied voltage Vc was about 86 kV (current was about 22 mA). It has been confirmed.
Here, it should be noted that the only difference between the wet electrostatic precipitator of the present embodiment and the conventional wet electrostatic precipitator used for the actual measurement in FIG. 6 is the presence or absence of the capacitor 41 and the protective resistor 42. . This is because, as a result of the actual measurement shown in FIG. 6, when the capacitor 41 is not mounted, a spark discharge occurs at about 72 kV. It means that it does not occur.
As described above, by adopting the wet electrostatic precipitator according to the present embodiment equipped with the capacitor 41, the effective voltage Er of the applied voltage is set to about 14 kV (= 86 kV-72 kV) higher than the conventional one. However, it was confirmed that operation is possible, that is, dust containing heavy metals can be collected efficiently.

However, the point to be noted here is that the capacitor 41 is simply mounted and the above-described effects cannot be sufficiently achieved. In other words, the above-described effects can be sufficiently achieved only when a capacitor having an appropriate capacity is employed as the capacitor 41.
Therefore, referring to FIG. 7, a method for setting an appropriate capacitance for the capacitor 41 will be described below.

[How to set the capacity of capacitors mounted on wet electrostatic precipitators]
FIG. 7 is a diagram illustrating an equivalent circuit of the wet electrostatic precipitator according to the present embodiment in which the capacitor 41 is mounted.
As shown in FIG. 7, the equivalent circuit of the wet electrostatic precipitator of the present embodiment mainly includes an equivalent circuit 3 </ b> C for the DC high voltage generation unit 3, and an equivalent circuit 2 </ b> C mainly for the DC high voltage input unit 2. In addition, an equivalent circuit 1C for the dust collector main body 1 is mainly connected.
Here, “mainly” is described, for example, so that the total capacity C described later cannot be determined only from the elements of the dust collector main body 1, This is because it cannot be clearly separated as each equivalent circuit of the DC high voltage generator 3.

  In the equivalent circuit 3C, the AC voltage from the AC power supply Vo is boosted by the transformer Tr and further rectified by the silicon rectifier 71 (however, as described above, the rectification is insufficient), the DC high voltage V Is input to the equivalent circuit 2C.

The equivalent circuit 2C is configured as a T-type four-terminal circuit as shown in FIG. In the equivalent circuit 2C, the equivalent circuit 3C is connected to the two ends of the input, and the equivalent circuit 1C is connected to the two ends of the output. One end (the lower end in FIG. 4) of the input and output of the equivalent circuit 2C is grounded. The input voltage of the equivalent circuit 2C (potential difference between the two terminals of the input) is the DC high voltage V output from the DC high voltage generator 3, and the output voltage of the equivalent circuit 2C (potential difference between the two terminals of the output) is The voltage Vc applied to the discharge electrode of the dust collector main body 1.
The two ends of the series connection of the capacitor 41 and the protective resistor 42 of the DC high voltage input unit 2 are connected to the two ends of the input of the equivalent circuit 2C, respectively. The protective resistor 43 of the DC high-voltage input unit 2 is connected between one end of the series connection (end opposite to the ground end) and one end of output of the equivalent circuit 2C (end opposite to the ground end). Is connected.

  As shown in FIG. 7, the equivalent circuit 1 </ b> C is configured by a specific capacitance C <b> 1 of the wet electrostatic precipitator according to the present embodiment.

  Here, the rated voltage of the output voltage Vc of the equivalent circuit 2C, that is, the applied voltage Vc to the discharge electrode of the dust collector main body 1 is described as Eo. The rated current at the output of the equivalent circuit 2C is described as Io.

Regarding the output voltage Vc of the equivalent circuit 2C (the applied voltage Vc to the discharge electrode of the dust collector main body 1), the difference between the maximum value and the minimum value of the AC voltage component, that is, the peak-to-peak voltage difference ΔE is It is represented by Formula (1).
ΔE = Io / 2fC (1)
In Expression (1), f represents the frequency of the AC power supply Vo, and C represents the sum of C1 and C2 (C = C1 + C2), which is hereinafter referred to as “total capacity”. C1 represents the specific capacitance of the wet electrostatic precipitator as described above, and C2 represents the capacitance of the capacitor 41 of the DC high-voltage input unit 2.

In this case, the peak voltage Vp of the output voltage Vc of the equivalent circuit 2C (applied voltage Vc to the discharge electrode of the dust collector main body 1) is expressed by the following equation (2).
Vp = Eo + ΔE / 2 (2)

Here, the voltage ripple rate is described as Mv, and is defined as the following equation (3).
Mv = Vp / Eo
= (Eo + ΔE / 2) / Eo
= 1 + ΔE / (2 × Eo) (3)

Here, the rated voltage Eo is known, and when the voltage ripple rate Mv is determined, the peak-to-peak voltage difference ΔE can be obtained according to the following equation (4).
ΔE = (2 × Eo) × (Mv−1) (4)

The total capacity C is obtained by substituting the calculated value of Expression (4) into Expression (1) described above. In this case, the capacitance C2 of the capacitor 41 of the DC high voltage input unit 2 is obtained by the following equation (5).
C2 = C−C1 (5)

Here, the intrinsic capacitance C1 of the dust collector main body 1 is the capacitance between the dust collecting electrode 12 and the discharge electrode, and between the electric circuit (bus bar 51) and the bus duct 32 in the DC high voltage input unit 2. The sum with the capacitance can be approximately obtained by a known equation.
It should be noted that the resistance value Ro of the protective resistor 43 and the resistance value Rc of the protective resistor 42 are less than the allowable current of the equipment when the electric circuit of the wet electrostatic precipitator, for example, the discharge wire and the dust collecting electrode 12 is short-circuited. Should be selected.

Here, in order to suppress the peak voltage Vp while increasing the above-described effect, that is, increasing the effective voltage Er (for example, increasing to about 70 to 80 kV), it is necessary to suppress the peak-to-peak voltage difference ΔE. . In other words, the required peak-to-peak voltage difference ΔE is determined to some extent by the required effective voltage Er and peak voltage Vp.
Therefore, a designer or the like may determine a peak-to-peak voltage difference ΔE as a design concept so that a desired effect can be obtained.
Here, the peak-to-peak voltage difference ΔE can be obtained by the above-described equation (4). According to the equation (4), the value that can be freely changed by the designer or the like is the voltage ripple rate Mv. When the voltage ripple rate Mv is determined, the peak to peak are automatically The voltage difference ΔE is obtained.
From the above, in order to obtain a desired effect, a designer or the like may first determine the voltage ripple rate Mv as a design value. For example, in order to obtain the effect shown in FIG. 5 described above, a value of 1.15 (15%), preferably 1.10 (10%) or less may be determined as the voltage ripple rate Mv.

  Thus, if the voltage ripple rate Mv is determined, the peak-to-peak voltage difference ΔE can be obtained from the above-described equation (4). Further, the total capacity C is obtained by substituting the peak-to-peak voltage difference ΔE thus obtained into the above-described equation (1). Then, by substituting the total capacitance C into the above-described equation (5), an appropriate capacitance C2 of the capacitor 41 to obtain a desired effect is obtained.

[Elements that contribute to dust collection efficiency of wet electrostatic precipitators]
As described above, the effect of improving the dust collection efficiency of the wet type electrostatic dust collector can be obtained by increasing the applied voltage Vc to the discharge electrode of the dust collector main body 1 from the conventional level (for example, by raising the applied voltage Vc to about 70 to 80 kV). I explained that.
However, the applied voltage Vc is not the only factor contributing to the dust collection efficiency of the wet electrostatic precipitator. This will be briefly described below.
That is, in order to increase the dust collection efficiency, in other words, in order to efficiently remove dust, mist, etc. from the exhaust gas, it is necessary to increase the strength of the electric field between the two electrodes of the dust collection electrode 12 and the discharge electrode as much as possible. There is.
In general, it is known that when the potential difference (applied voltage Vc) between two electrodes increases, the strength of the electric field increases, whereas when the distance between the two electrodes increases, the strength of the electric field decreases. That is, it is known that there are not only the applied voltage Vc but also a distance between two electrodes as elements contributing to the dust collection efficiency of the wet type electrostatic precipitator.
From the above, since the strength of the electric field is increased by shortening the distance between the two electrodes, the dust collection efficiency can be increased accordingly. However, if the distance between the two electrodes is excessively shortened, dielectric breakdown occurs between the two electrodes, and as a result, spark discharge occurs. For this reason, it is not a good idea to shorten the distance between the two electrodes, and it is necessary to keep it within an appropriate range. Therefore, an appropriate distance between the two electrodes will be described below.

[Distance between the two electrodes of the dust collector and discharge electrode of the wet electrostatic precipitator]
In general, the sustaining voltage of the corona discharge when no spark discharge occurs is about 4 kV (about 4 kV / cm) per 1 cm distance between the two electrodes.
Accordingly, the appropriate distance d between the two electrodes is determined by the potential difference between the two electrodes, that is, the applied voltage Vc (kV). Specifically, an appropriate distance d between the two electrodes is as shown in the following formula (6).
d (cm) = Vc (kV) / 4 (kv / cm) (6)
For example, if 70 kV is required as the applied voltage Vc, 17.5 cm is appropriate as the distance d between the two electrodes from Equation (6).

Therefore, by setting the distance d between the two electrodes to 17.5 cm and mounting the above-described capacitor 41, it is theoretically possible to operate with the applied voltage Vc = 70 kV without generating a spark voltage.
This is true regardless of the shape of the electrode. For example, as shown in Patent Document 3, a capacitor 41 is mounted on a conventional dust collector main body having a linear discharge electrode and a planar dust collecting electrode (hereinafter referred to as “planar electrode”). If the DC high voltage input unit 2 and the DC high voltage generation unit 3 of the present embodiment are applied and the distance d between the two electrodes is 17.5 cm, the applied voltage Vc (kV) is theoretically Even if the voltage is raised to 70 kV, it is possible to realize a stable operation state without causing spark discharge. That is, due to the effect of the capacitor 41, it is theoretically possible to improve the dust collection efficiency even with a flat electrode.

However, when FRP is adopted as the material of the planar electrode, the planar electrode is deformed in a shape such as “sledge” or “bend” due to aging or influence of heat.
Even if the “sledge”, “bend”, or the like occurs in a part of the planar electrode, the distance between the two electrodes in the part is reduced by that amount. Therefore, even with the same applied voltage Vc, Strength increases. In other words, the spark discharge voltage decreases as the distance between the two electrodes is shortened by “sledge”, “bend”, etc., and therefore, when the initial applied voltage Vc = 70 kV is applied, the spark discharge occurs. Occur frequently, and stable operation cannot be continued.
For example, if the flat plate of the FRP is deformed such as “sledge” or “bend” at a rate of 3% of the total length due to aging or heat, the flat plate electrode having a length of 315 cm is 9.45 cm. Deformation such as “sledge” and “bend” (= 315 cm × 0.03) occurs. Since the initial distance d between the two poles is 17.5 cm, the distance between the two poles after the deformation is shortened to 8.05 cm (= 17.5 cm−9.45 cm).
Therefore, in order to suppress the occurrence of spark discharge, the applied voltage Vc must be reduced to 32.2 kV (= 8.05 cm × 4 kV / cm).
Therefore, in the conventional planar electrode, the applied voltage Vc as a specification is reduced to 32.2 kV in advance in consideration of changes such as “sledge” and “bend” due to changes over time and heat, etc. It is necessary to design the distance between the two electrodes long in advance, including the shortening of the distance due to change, heat, or the like.
If the applied voltage Vc is reduced to 32.2 kV as a specification, it will be very difficult to ensure the required dust collection efficiency. On the other hand, if the distance between the two electrodes is designed to be long, only that much. The wet electrostatic precipitator increases in size and causes problems in various aspects such as cost and installation.

Therefore, in the dust collection electrode 12 of the present embodiment, a “room” unit is introduced, a plurality of “rooms” are repeatedly arranged in succession, and the four corners of each “room” are firmly fixed, so ”,“ Bend ”, and the like are less likely to be deformed.
Here, in the present embodiment, as shown in FIG. 2, the number of “chambers” of the dust collection electrode 12 is 81 (= 9 × 9). Therefore, if the length of one side in the substantially horizontal direction of the entire dust collecting electrode 12 is set to 315 cm, which is the same as the length of the conventional planar electrode in the above example, a square opening of 35 cm × 35 cm is provided. A room should be prepared.
In this case, if such a “chamber” is made of an FRP plate in which deformation such as “sledge” or “bend” occurs in the central portion at a rate of 3% of the total length, similar to the above-described planar electrode, The length of one side in one “chamber” is reduced only by about 1 cm (= 35 cm × 0.03).
Accordingly, the distance from the discharge electrode in one “chamber”, that is, the distance between the two poles is 16.5 cm (= 17.5 cm−1 cm). In this case, the applied voltage Vc may be a slight decrease of about 66 kV (= 18.5 cm × 4 kV / cm).
Furthermore, as described above, in the present embodiment, the four corners of each “room” are firmly fixed, so that it can be expected that such deformations as “sledge” and “bend” are less likely to occur. In this case, it can be expected that the decrease in the applied voltage Vc can be further reduced.
As described above, in the present embodiment, the plurality of “chambers” are repeatedly and continuously arranged to constitute the dust collecting electrode 12, so that changes such as “sledge” and “bend” due to secular change, heat, etc. Even without much consideration, the wet electrostatic precipitator can be designed and manufactured by directly adopting a desired voltage (70 kV in the above example) as the applied voltage Vc as a specification.
Even if designed and manufactured in such a manner, deformation such as “sledge” and “bend” does not occur so much. Therefore, even if it is used for a long period of time, it is possible to operate while maintaining the initial applied voltage Vc (70 kV in the above example) substantially without causing spark discharge.

[Relationship with protection circuit of wet electrostatic precipitator]
By the way, although not shown, a protection circuit as disclosed in Patent Document 3 may be applied to the wet type electrostatic precipitator of the present embodiment for the purpose of safety.
That is, when a spark discharge occurs, the spark discharge may reach the surface portion of the dust collection electrode 12. In such a case, in the part of the dust collecting electrode 12 where the spark discharge has arrived, damage such as peeling of the FRP resin or fiber due to the spark discharge occurs, the corrosion resistant layer of the conductive FRP deteriorates, and the conductive There arises a problem that the corrosion resistance of FRP is lowered.
In order to solve such a problem, Patent Document 3 discloses a protection circuit that executes automatic control for suppressing the occurrence of a continuous spark discharge once a spark discharge has occurred. . Specifically, the voltage applied from the high voltage generator (DC high voltage generator 3 of the present embodiment) (conventionally applied voltage V and applied voltage Vc in the present embodiment) is instantaneously reduced to a voltage at which no spark is generated. Patent Document 3 discloses a protection circuit that performs automatic control such that the spark discharge is stopped by lowering the voltage and then the voltage is increased again to the original applied voltage.
However, the state in which such a protection circuit is activated (automatic control is performed) and the applied voltage is reduced means that the dust collection efficiency of the wet electrostatic precipitator is reduced. It is not preferable to discharge the waste gas to be processed to the next process in such a state that the dust collection efficiency is lowered, although it is instantaneous.
However, in the wet electrostatic precipitator of this embodiment, as described above, the effective applied voltage Er is increased more than before and the peak voltage Vp is decreased more than before due to the smoothing effect of the capacitor 41. Can do. For this reason, since the frequency of occurrence of spark discharge becomes very low, the frequency at which the protection circuit operates, that is, the frequency at which the waste gas to be treated is discharged to the next process in a state where the dust collection efficiency is reduced, is also very low. Can be expected.

[Effects of wet electrostatic precipitator of this embodiment]
In summary, the wet electrostatic precipitator according to the present embodiment can provide the following advantageous effects (1) to (3) as compared with the conventional wet electrostatic precipitator.

(1) Conventionally, the output voltage V of the DC high voltage generator 3, that is, the output voltage V in a state where rectification is insufficient (a state where the pulsating flow is large) is applied as it is to the discharge electrode as it is. On the other hand, in the present embodiment, the output voltage V of the DC high voltage generation unit 3 passes through the DC high voltage input unit 2 on which the capacitor 41 is mounted, and becomes a further smoothed output voltage Vc. An output voltage Vc is applied to the discharge electrode.
As a result, the peak voltage Vp of the applied voltage Vc is increased while the effective voltage Er of the applied voltage Vc is increased as compared to the conventional voltage (for example, the conventional voltage is increased from about 40 to 60 kV to about 70 to 80 kV). It becomes possible to suppress more. Increasing the effective voltage Er of the applied voltage Vc means increasing the dust collection efficiency, and suppressing the peak voltage Vp of the applied voltage Vc means reducing the frequency of occurrence of spark discharge.

FIG. 8 is a diagram showing the effect of the wet type electrostatic precipitator of the present embodiment.
In FIG. 8, the vertical axis indicates the dust collection efficiency (%), and the horizontal axis indicates the applied voltage (kV).
In the conventional wet electrostatic precipitator, as described above, since the applied voltage is about 40 to 60 kV, the dust collection efficiency is about 99.6% at the maximum, and arsenic (As) is applied. It is a low value that does not reach 98% at a voltage of 50 kV.
On the other hand, since the applied voltage Vc can be increased to 70 to 80 kV in the wet electrostatic precipitator of this embodiment, any one of dust, lead (Pb), cadmium (Cd), and arsenic (As) can be used. The dust collection efficiency is also very high such as 99.8 to 99.9%.

(2) Since the peak voltage Vp of the applied voltage Vc is suppressed, even if the effective voltage Er of the applied voltage Vc is increased to 70 to 80 kV, the frequency of occurrence of spark discharge becomes very low. For this reason, in a state where the protection circuit as in Patent Document 3 does not work frequently, that is, in a state where the possibility of exhausting the waste gas to be processed to the next process in a state where the dust collection efficiency is reduced is reduced. It is possible to suppress damage to the manufactured dust collecting electrode 12 due to spark discharge.

(3) In the dust collection electrode 12 of the present embodiment, by introducing a unit of “room”, repeatedly arranging a plurality of “rooms” continuously, and firmly fixing the four corners of each “room”, A structure in which deformation such as “sledge” and “bend” hardly occurs is realized.
As a result, even if it is used for a long period of time, the voltage at which spark discharge occurs due to the approach between the discharge electrode and the dust collecting electrode 12 can be maintained as it is without decreasing. As a result, when combined with the initial applied voltage Vc, that is, the above-described effect (1), the operating state in which the applied voltage Vc of 70 to 80 kV, which is much higher than the conventional one, is maintained for a long period of time compared to the conventional case. Is possible.

  As described above, the present invention is not limited to the above-described embodiment, and modifications, improvements, and the like within the scope that can achieve the object of the present invention are included in the present invention.

For example, as the dust collection electrode 12 of the above-described embodiment, a square tube type dust collection electrode having a square tube having a square shape as a “chamber (unit)” is employed, but is not particularly limited thereto.
Specifically, for example, the shape of the opening of each “chamber” constituting the rectangular tube-shaped dust collecting electrode is not particularly required to be a square, and may be an N-gon (N is an integer value of 3 or more), In this case, the upward spray nozzle 27 and the like may be disposed around at least one of the N corners of each “chamber”.

FIG. 9 is a perspective view showing a schematic configuration of the inside of the housing of the dust collector main body 1 having a rectangular tube-shaped dust collecting electrode whose opening is a hexagonal cylinder.
Also in the example of FIG. 9, the upper grid 21, the dust collecting electrode 12, the lower grid 23, the electrode rod 24, the discharge wire 25, the weight 26, and the upward spray are disposed inside the housing of the dust collector main body 1. A nozzle 27 and a cleaning pipe 28 are provided.
The dust collecting electrode 12 in the example of FIG. 9 is configured by repeatedly arranging a plurality of “chambers” with a cylinder having a hexagonal opening as a “chamber”.
The number of “rooms” is 10 in the example of FIG. 9, but this is only an example and may be an arbitrary number.

DESCRIPTION OF SYMBOLS 1 ... Dust collector main-body part 2 ... DC high voltage input part 3 ... DC high voltage generation part 11 ... Upper casing 12 ... Dust collection electrode 13 ... Lower casing 14 ... Frame 21 ... Upper grid 23 ... Lower grid 24 ... Electrode rod 25 ... Discharge wire 26 ... Weight 27 ... Upward spray nozzle 28 ... Cleaning pipe 31 ... Capacitor box 32 ... Bus duct 33 ... Insulator chamber 41 ... Capacitor 42 ... Protection resistor 43 ... Protection resistor 51 ... Bus bar 52 ... Wall penetration insulator 53 ... Closing plate 61 ... Support insulator 71 ... Silicon rectifier 72 ... High voltage output terminal

Claims (2)

A high voltage generator for generating DC high voltage;
A high voltage input unit that inputs a DC high voltage generated by the high voltage generation unit, smooths the DC high voltage using a capacitor, and outputs the DC high voltage;
A discharge electrode to which a DC high voltage output from the high voltage input unit is applied;
A dust collecting electrode for collecting fine particles by a negative corona discharge generated between the discharge electrode and the DC high voltage;
With
The capacity of the capacitor is set based on a voltage ripple rate between the discharge electrode and the dust collecting electrode,
Wet electric dust collector. The dust collecting electrode is composed of an assembly of a plurality of the units, with a polygonal cylinder having an opening of a predetermined shape as a unit,
The discharge electrode is accommodated in each of the plurality of units constituting the dust collection electrode.
The electrostatic precipitator according to claim 1.

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