JP2016049466A - Wet electrostatic precipitator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enhance the collection efficiency of dust containing heavy metals by increasing applied voltage to a discharge electrode and regulating minimum current density while suppressing the occurrence frequency of spark discharge.SOLUTION: A wet electrostatic precipitator comprises: a high voltage generation unit generating a DC high voltage; a discharge electrode applied with the DC high voltage generated by the high voltage generation unit; and a dust collection electrode performing the dust collection of fine particles by negative corona discharge generated between the discharge electrode and the dust collection electrode based on the DC high voltage. The discharge electrode is composed of an electrode rod and a barbed wire-like discharge wire 25 and the current density of a current flowing to the dust collection electrode is regulated. A pitch showing a distance between a pair of barbed wires 252 at the discharge wire 25 is set according to the regulated current density.SELECTED DRAWING: Figure 3

Description

The present invention relates to a wet electrostatic precipitator that removes dust and the like from waste gas. In particular, the present invention increases the applied voltage to the discharge electrode (eg, rises to 65 kV or more) and suppresses the frequency of occurrence of spark discharge, and defines the current density (eg, 0.1 mA / m ²⁾ . ) To improve the dust collection efficiency of dust containing heavy metals.

  Conventionally, wet electrostatic precipitators (see, for example, Patent Documents 1 to 3) remove 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 in the mining industry. It is used for the purpose of collecting. 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.

  To-be-processed waste gas processed by a wet electrostatic precipitator contains harmful substances such as lead, cadmium and arsenic and heavy metals. For this reason, in such a wet electrostatic precipitator, it is required to increase the dust collection efficiency of dust containing harmful substances and heavy metals.

The wet type electrostatic precipitator generally has a dust collecting electrode having a smooth surface composed of two flat plate types or a cylindrical shape such as a cylindrical shape or a rectangular tube shape, and a linear shape provided in the dust collecting electrode. The discharge line is configured to be included.
When dust and mist are removed by such a wet electrostatic precipitator, a high voltage is applied between the discharge electrode side and the grounded dust collection electrode side. As a result, a strong current electric field is formed between the discharge electrode side and the grounded dust collection electrode side, and a strong corona discharge is generated from the discharge electrode side as the voltage rises. The dust collection space between the two is filled with negative ions and electrons. When exhaust gas is introduced into the dust collection space, dust and mist in the exhaust gas are negatively charged, move toward the dust collection electrode by the Coulomb force with an electrostatic aggregating action, and adhere to the dust collection electrode. The adhering dust or mist loses a negative charge at the dust collecting electrode, is peeled off from the dust collecting electrode by the washing water and its own weight supplied to the dust collecting electrode, and is discharged to the outside of the electric dust collector.
In this way, the wet electrostatic precipitator can collect various types of solids, fine particles such as liquid fine particles, etc. with high dust collection efficiency.

  In such a wet electrostatic precipitator, a technique for increasing the applied voltage between the discharge electrode and the dust collecting electrode is known in order to increase the dust collection efficiency of dust containing heavy metals.

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

However, when the applied voltage between the discharge electrode of the wet electrostatic precipitator and the dust collecting electrode voltage is increased, corona discharge increases, and spark discharge (spark) may eventually occur.
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.
For this reason, 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.

  In addition to the applied voltage between the discharge electrode and the dust collecting electrode, there is also a current that determines the efficiency of such a wet electrostatic precipitator. However, in the conventional wet electrostatic precipitator including Patent Documents 1 to 3, sufficient consideration for the current has not been made.

The present invention has been made in view of such a situation, and while suppressing the occurrence frequency of spark discharge, the applied voltage to the discharge electrode is increased more than before (for example, increased to 65 kV or more), and the current density is specified. The purpose is to improve the dust collection efficiency of dust containing heavy metals by (for example, specified at 0.1 mA / m ² ).

An electric dust collector according to one aspect of the present invention,
A high voltage generator for generating DC high voltage;
A discharge electrode to which a DC high voltage generated by the high voltage generator 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 discharge electrode is composed of an electrode rod and a barbed wire-like discharge wire,
The current density of the current flowing through the dust collecting electrode is defined,
The pitch indicating the distance between the two stab pairs of the discharge lines is set according to the defined current density,
It is characterized by that.

  In this case, the dust collecting 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, and the discharge electrode is the plurality of units constituting the dust collecting electrode. Can be housed in each of the.

  The fine particles may be collected from an exhaust gas containing at least one of lead, cadmium, arsenic, and mercury.

According to the present invention, while suppressing the frequency of occurrence of spark discharge, the voltage applied to the discharge electrode is increased (for example, increased to 65 kV or more) than before, and the current density is defined (for example, defined at 0.1 mA / m ²⁾ . ), It is possible to improve the dust collection efficiency of dust containing heavy metals.

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 figure which shows the specific example of the shape of the barbed wire-like discharge line of the dust collector of FIG. It is a figure which shows the specific example of the shape of the electricity supply line of FIG. It is a figure which shows the relationship between the overvoltage of the wet electric dust collector of FIG. 1, and dust collection efficiency. It is a figure which shows the relationship between the current density and dust collection efficiency of the wet electric dust collector of FIG. It is a figure which shows the relationship between the barbed wire-like discharge line of FIG. 3 and the current density of the wet electrostatic precipitator of FIG.

  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.
Moreover, the chamber of the present embodiment is a square tube having sides with a length of 35 to 50 cm. The reason why the length of the side is 35 to 50 cm will be described later.
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.

FIG. 3 is a diagram showing a specific example of the shape of the barbed wire-like discharge wire 25 of the present embodiment.
The discharge line 25 is composed of a linear energization line 251 and a plurality of paired wire pairs 252 provided in pairs from one end to the other end of the energization line 251.
The plurality of stab wire pairs 252 are provided at equal intervals along the longitudinal direction of the conductive wire 251. Here, an interval between adjacent pair of stabs 252, that is, a distance between two pair of stabs 252 is hereinafter referred to as “pitch P”. As will be described later, the pitch P is set to an appropriate length according to the current density with respect to the dust collecting electrode 2.

FIG. 4 is a diagram illustrating a specific example of the shape of the energization line 251.
The current-carrying wire 251 has a cross-sectional shape orthogonal to the longitudinal direction of a round shape as shown in FIG. 4 (a), a square shape as shown in FIG. 4 (b), or any shape. Although it is good, it is preferably a star shape as shown in FIG. Furthermore, it is more preferable that the cross-sectional shape of the energization line 251 is a star shape having six vertices, and the adjacent vertices are curved in a concave shape.

Each stab wire pair 252 is composed of two stab wires that are sharp at both ends and bent into an L shape. The thinner the stab wire, the easier it is to generate corona discharge. Therefore, in the present embodiment, the stab wire is formed with a diameter of about 3 mm. These two stab wires are fixed to both side surfaces of the energizing wire so as to face each other with the energizing wire 251 interposed therebetween.
The method for fixing the stab wire to the energizing wire 251 is not particularly limited, but is preferably attached by welding. Thereby, the durable barbed wire-like discharge wire 25 with little variation in quality can be easily mass-produced.
At the time of welding the piercing wire, first, the substantially central portion of the piercing wire is bent into an L shape, and a bent portion formed at the substantially central portion of the L-shaped piercing wire is welded to the electric wire 251. Thereby, even if the stabbing line is thin, the deformation of the stabbing line can be suppressed and the plurality of stab line pairs 252 can be arranged in a uniform shape. In addition, attachment of the stab wire and the conductive wire 251 is performed by fixing the portion of the conductive wire 251 that is curved in the above-described concave shape so that the convex curved portion of the stab wire is aligned. preferable.

  Returning to FIG. 2, a negative DC high voltage generated by the DC high voltage generating unit 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 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.

In the wet electrostatic precipitator 1 of the present embodiment, the washing water is ejected from the upward spray nozzle 27 as a fine mist in a substantially vertical upward direction. Thereby, since dispersion | distribution of washing water becomes good, the quantity of washing water used can be reduced from the quantity of water used conventionally.
Specifically, when the area of the dust collecting electrode is 126 m ² , the conventional wet electric dust collector required a cleaning water amount of 150 L / min. In 1, the amount of cleaning water used is 15 L / min.
Further, spark (spark discharge) is more likely to occur as a large amount of washing water passes around the discharge electrode. In this regard, the wet electrostatic precipitator 1 according to the present embodiment can significantly reduce the amount of cleaning water used compared to the conventional wet electrostatic precipitator, thereby greatly suppressing the occurrence of sparks. can do.
Furthermore, in the wet electrostatic precipitator 1 of this embodiment, since the wash water is ejected as a fine mist, the particle size of the wash water when passing around the discharge electrode is that of the conventional wet electrostatic precipitator. Since it is smaller than that of sparks, the occurrence of sparks can be further suppressed.
That is, the upward spray nozzle 27 is a component that contributes to an increase in negative DC high voltage applied to the electrode rod 24 and the discharge line 25.

[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 (not shown) is smoothed and applied to the discharge electrode as a DC high voltage Vc. Is done. 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.

FIG. 5 is a diagram illustrating the relationship between the overvoltage and the dust collection efficiency of the wet type electrostatic precipitator according to the present embodiment.
In FIG. 5, the vertical axis indicates the dust collection efficiency (%), and the horizontal axis indicates the applied voltage (kV).
In the conventional wet electrostatic precipitator, the applied voltage is about 40 to 60 kV, so the dust collection efficiency is about 99.6% at the maximum, and arsenic (As) is 98% at the applied voltage of 50 kV. It is a low value such as not reaching.
On the other hand, in the wet type electrostatic precipitator of the present embodiment, the applied voltage Vc can be increased by 65 kV or more (in the example of FIG. 5, up to 80 kV, but up to about 100 kV). ), Cadmium (Cd), and arsenic (As), the dust collection efficiency is very high such as 99.8 to 99.9%.

[Elements that contribute to dust collection efficiency of wet electrostatic precipitators]
Thus, the dust collection efficiency of the wet electrostatic precipitator can be improved by raising the applied voltage Vc to the discharge electrode of the dust collector main body 1 from the conventional level (for example, raising the voltage to about 65 to 100 kV). .
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.

[Relationship with current of wet electrostatic precipitator]
Furthermore, as described above in the background art, there is also a current flowing through the dust collecting electrode 2 in addition to the applied voltage Vc between the discharge electrode and the dust collecting electrode, which determines the efficiency of the wet electrostatic precipitator. More specifically, the electric field generated by the applied voltage Vc contributes to the charging of particles such as dust and mist and the transport of charged particles (charged particles) to the dust collecting electrode 2. On the other hand, the current contributes to the charging of the particles and the pressure bonding of the particles to the dust collection electrode 2.
For this reason, if at least one of the voltage and the current is insufficient, the dust collection efficiency of the wet electrostatic precipitator is greatly reduced.

FIG. 6 is a diagram showing the relationship between the current density and the dust collection efficiency of the wet electric dust collector of this embodiment.
In FIG. 6, the vertical axis indicates the dust collection efficiency (%), and the horizontal axis indicates the current density (mA / m 2).
As described above, in the conventional wet electrostatic precipitator, since the current density is not particularly considered, the dust collection efficiency depends only on the applied voltage, and the dust collection efficiency becomes low depending on the current density. It was.
On the other hand, in the wet type electrostatic precipitator of this embodiment, any current collection of dust, lead (Pb), cadmium (Cd), and arsenic (As) is defined by defining the current density to 0.1 mA / m2. As for dust efficiency, it is possible to secure a very high value exceeding 99.3 to 99.9%.
Here, it is possible to define the current density to a value exceeding 0.1 mA / m 2, but as shown in FIG. 6, if it exceeds 0.1 mA / m 2, the dust collection efficiency becomes almost flat. In particular, it is not necessary to exceed 0.1 mA / m2. In other words, the current density is preferably 0.1 mA / m2.

In order to achieve a high current density such as 0.1 mA / m 2, in the present embodiment, the shape of the discharge wire 25 in FIG. 1 is a barbed wire shape as shown in FIG.
That is, when the applied voltage Vc is increased, the electric field strength in the vicinity of the discharge electrode is increased and ionization is actively performed, and at the same time, the ionization region is increased and the number of ions generated is increased. This increases the current collection efficiency.
The same effect can be obtained by reducing the diameter of the discharge electrode. However, if the discharge electrode is too fine, there is a risk of disconnection. For this reason, the shape of the discharge line 25 in FIG. 1 is shown in FIG. 3 in the present embodiment so that the equivalent discharge electrode diameter obtained from the discharge characteristics is reduced while the cross section is actually large and the mechanical strength is high. It is formed in such a barbed wire shape.
In this respect, the shape of the discharge wire 25 is not limited to the barbed wire shape, and may be a blade-type electrode. However, as shown below, by forming the discharge wire 25 into a barbed wire shape as in the present embodiment, the current Density can be variably set.

FIG. 7 is a diagram showing the relationship between the barbed wire-like discharge line 25 of the wet electrostatic precipitator of the present embodiment and the current density.
In FIG. 7, the vertical axis represents the current value (current density) (mA / m 2), and the horizontal axis represents the thorn number.
Here, the thorn means one stab pair 252 (FIG. 3) formed on the linear energization line 251. Since the length of the linear conducting wire 251 is constant, an increase in the number of thorns means that the pitch P (FIG. 3) is narrowed.
As shown in FIG. 7, it can be seen that the current value (current density) (mA / m 2) increases as the number of thorns increases, that is, the pitch P decreases. This is because narrowing the pitch P increases the charging efficiency of the suspended fine particles.
That is, if the current density is to be varied while the applied voltage Vc is kept constant at 65 kV or higher (in the example of FIG. 5, it is shown up to 80 kV but up to about 100 kV), the pitch P may be changed.
That is, in this embodiment, the current density is defined as 0.1 mA / m2. This is because the pitch P is set such that the current density is 0.1 mA / m2. Therefore, if the specified current density is changed, the setting of the pitch P is also changed according to the specified current density.

  However, if the pitch P is narrower than a predetermined interval, the discharge currents emitted from the stabs constituting the stab pair 252 interfere with each other between the adjacent pair 252. As a result, the discharge current (current density) per discharge line decreases, and as a result, the dust collection performance deteriorates.

  In order to make the current collecting effect remarkable, the wet electrostatic precipitator is preferably one that removes dust and mist from exhaust gas containing at least one kind of lead, cadmium, and arsenic.

  It should be noted that the present invention is not limited to the above-described embodiment, and modifications, improvements, etc. within a 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”.

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 251 ... Discharge wire 252 ... Stinging pair

Claims (3)

A high voltage generator for generating DC high voltage;
A discharge electrode to which a DC high voltage generated by the high voltage generator 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 discharge electrode is composed of an electrode rod and a barbed wire-like discharge wire,
The current density of the current flowing through the dust collecting electrode is defined,
The pitch indicating the distance between the two stab pairs of the discharge lines is set according to the defined current density,
A wet type electrostatic precipitator. 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 wet electrostatic precipitator according to claim 1. The fine particles are collected from an exhaust gas containing at least one kind of lead, cadmium, and arsenic.
The wet electrostatic precipitator according to claim 1 or 2.

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