JP7106491B2 - Electrostatic precipitator - Google Patents

Description

The present invention relates to an electrostatic precipitator.

2. Description of the Related Art As a conventional electrostatic precipitator, there is known one having flat plate-like dust collection electrodes arranged in parallel along a gas flow and a discharge electrode having a corona discharge portion arranged in the center thereof. The shape of the corona discharge part of the discharge electrode has a protruding shape to generate electric field concentration to ensure corona discharge. In general industrial electrostatic precipitators, a structure with a protruding corona discharge part is the mainstream in order to ensure stable corona discharge even if the electrode is dirty. Assuming structure.

In an electric dust collector, a DC high voltage is applied between a dust collection electrode and a discharge electrode, and a stable corona discharge is performed at a corona discharge portion of the discharge electrode, thereby charging dust in a gas flow. The conventional dust collection theory explains that charged dust is collected by the dust collection electrode due to the action of the Coulomb force acting on the dust under the electric field between the discharge electrode and the dust collection electrode.

By the way, the electric dust collectors of Patent Documents 1 and 2 are provided with a plurality of through-holes for allowing dust to pass through, and are provided with a dust collection electrode having a closed space inside for collecting dust. In Patent Literatures 1 and 2, dust is confined in a closed space through the through-hole, thereby making it difficult for collected dust to scatter again.

The electrostatic precipitator of Patent Document 3 includes a dust collection electrode including a ground electrode having an aperture ratio of 65% to 85% and a dust collection filter layer for collecting gas. By providing such a dust collection electrode, in Patent Document 3, an ion wind is generated in a cross section perpendicular to the gas flow, and a spiral gas flow circulating between the discharge electrode and the dust collection electrode is generated. , to efficiently collect dust. In Patent Literature 3, ion wind is actively used, but this case is intended to collect dust mainly in the dust collection filter layer.

Japanese Patent No. 5761461 Japanese Patent No. 5705461 Japanese Patent No. 4823691

The dust collection efficiency η in the electrostatic precipitator can be calculated by the well-known Deutsche formula (formula (1)) below. w is the dust collection index (moving speed of particulate matter), and f is the dust collection area per unit amount of gas.
η=1−exp(−w×f) (1)

In the above formula (1), the moving speed w of dust (particulate matter) is determined by the relationship between the Coulomb force and the viscous resistance of the gas. Deutsche's equation (equation (1) above) assumes that dust migrates from the discharge electrode in the electric field, and the ionic wind is not directly considered in its impact on performance. However, the premise that the distribution of dust concentration, which is the premise of the performance design, is always uniform within the cross section of the dust collection space between the discharge electrode and the dust collection electrode perpendicular to the gas flow of the electrostatic precipitator. The ionic wind is thought to be one of the factors that cause gas turbulence and make the dust concentration uniform.

The ion wind is generated by negative ions generated by corona discharge at the discharge electrode when a negative voltage is applied between the electrodes, and is generated by positive ions in the case of a positive voltage. Hereinafter, in this specification, since an industrial electrostatic precipitator is considered as a base, a case of applying a negative voltage will be described, but the same applies to a positive voltage.

In an electrostatic precipitator in which an electrode group is arranged along a gas flow, an ion wind generated at the discharge electrode flows across the gas flow toward the dust collection electrode. The ion wind reaching the dust collection electrode is reversed at the dust collection electrode to change the flow direction. This creates a spiral turbulent flow between the electrodes.

Among the turbulent flows, the flow from the discharge electrode to the dust collection electrode has the effect of carrying dust to the vicinity of the dust collection electrode. Dust brought to the vicinity of the dust collection pole is finally collected by the Coulomb force.

However, the ion wind reversed at the dust collection electrode moves the dust in a direction away from the dust collection electrode, which is a collector, and thus has the effect of hindering dust collection. Therefore, it is effective to provide an opening in the dust collection electrode to prevent the reversal of the ion wind.

Patent Literature 3 describes an electrostatic precipitator that also considers the effect of ion wind. However, in this case, the structure is such that the ion wind is fed into the filter layer behind the dust collection electrode with openings, and the purpose is to collect dust in places that are not affected by the main gas. It was complicated, and it was difficult to separate and collect the adhering dust in the dry method.

In addition, due to the corona discharge generated from the corona discharge portion protruding from the main body of the discharge electrode, the ion wind flows along with the corona current toward the collecting electrode side, but the collector on the side opposite to the corona discharge portion of the discharge electrode is not provided with the corona discharge portion. Since corona discharge does not occur between dust poles, ionic wind cannot be used. On the other side where the corona discharge part is not provided, the amount of charge in the dust collection space due to corona current and charged dust is smaller than that in the corona discharge part. It is smaller than the part side, and the dust collecting action due to the Coulomb force is also weak. For this reason, the inventors of the present invention focused on the active use of the dust collecting electrode on the opposite side of the corona discharge portion.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an electrostatic precipitator capable of effectively collecting dust even at the collecting electrode on the opposite side of the corona discharge section. and

An electrostatic precipitator according to an aspect of the present invention includes a plurality of discharge electrodes each having a body portion and a corona discharge portion for corona discharge protruding from the body portion, and arranged along a gas flow direction; A discharge-side dust collection electrode disposed along the gas flow direction and positioned on the corona discharge section side, and a discharge-side dust collection electrode disposed along the gas flow direction and on the opposite side of the discharge-side dust collection electrode with the discharge electrode interposed therebetween. a plurality of the corona discharge parts are arranged along the gas flow direction, and two of the corona discharge parts adjacent to each other along the gas flow direction project in a direction of The corona discharge portion protrudes only toward the discharge-side dust collection electrode, and the center of the main body portion of the discharge electrode is an arrangement position passing through the center of the discharge-side dust collection electrode. The corona discharge is located in a direction away from the discharge side dust collection electrode than a central position between a certain first center axis and a second center axis that is an arrangement position passing through the center of the opposite side dust collection electrode. A corona discharge is generated on the side of the discharge side dust collection electrode rather than the opposite side dust collection electrode, and an ion wind is generated from the tip of the corona discharge portion toward the opposing discharge side dust collection electrode .

The discharge electrode has a corona discharge portion protruding toward only one discharge-side dust collection electrode of the dust collection electrodes. As a result, an ion wind can be caused to flow only from the corona discharge part toward the discharge-side dust collection electrode by causing corona discharge. This method eliminates the interference of the ion wind between the opposing discharge electrodes with the dust collection electrode in between, compared to the method in which the ion wind flows on both sides by having the corona discharge parts on both sides of the normal discharge electrode. There are benefits you can get.
However, since the dust collection electrode on the opposite side of the discharge electrode, that is, on the opposite side of the corona discharge portion does not face the corona discharge portion, almost no corona discharge occurs. However, since the center of the main body of the discharge electrode is located in a direction away from the discharge-side dust collection electrode than the center position between the discharge-side dust collection electrode and the opposite side dust collection electrode, the main body of the discharge electrode The dust collecting electrode on the opposite side comes close. As a result, the electric field intensity between the body of the discharge electrode and the dust collection electrode on the opposite side can be increased, and the dust collection efficiency can be improved by improving the Coulomb force on the opposite electrode as well.
For example, when the distance between the discharge-side dust-collecting electrode and the opposite-side dust-collecting electrode is 300 mm or more and 500 mm or less, the center of the main body of the discharge electrode is positioned at a distance of 10 mm or more toward the opposite-side dust-collecting electrode. It is preferable that
As the dust collection electrode, for example, there is a discrete dust collection electrode in which a plurality of rigid members are arranged at predetermined intervals. As a rigid member, for example, a member having a pipe-shaped main body can be used. Another type of dust collecting electrode includes, for example, a flat plate-like dust collecting electrode having a plurality of through holes. For example, a punching metal or a wire mesh is used as the flat dust collecting electrode.

Furthermore, in the electrostatic precipitator according to one aspect of the present invention, the distance between the center of the body portion of the discharge electrode and the first central axis of the discharge-side dust collection electrode is D1, and the When the distance between the center of the main body and the second central axis of the opposite dust collecting electrode is D2, 1.1 ≤ D1/D2 ≤ 2.0.

By setting 1.1 ≤ D1/D2 ≤ 2.0, the electric field intensity between the body portion of the discharge electrode and the dust collection electrode on the opposite side is increased, and the electric field intensity is increased between the corona discharge portion and the dust collection electrode on the discharge side. The electric field strength between the poles can be approximated. Compared to the case of 1.1>D1/D2, the dust collection performance is improved, and unlike the case of D1/D2>2.0, the occurrence of spark discharge can be prevented.

Furthermore, in the electrostatic precipitator according to one aspect of the present invention, the plurality of discharge-side dust collection electrodes and the plurality of opposite-side dust collection electrodes are arranged along the gas flow direction, and D1 is the D2 is the distance between the center of the body of the discharge electrode and the first center axis of the discharge-side dust collection electrode, and D2 is the distance between the center of the body of the discharge electrode and the first center axis of the opposite-side dust collection electrode. It is the distance between the two central axes.

The discharge-side dust collection electrode and the opposite-side dust collection electrode are arranged along one direction, respectively, and D1 is the distance between the center of the main body of the discharge electrode and the discharge side in the direction perpendicular to the arrangement direction of the discharge-side dust collection electrode. D2 is the distance between the arrangement position of the dust collection electrodes, and D2 is the distance between the center of the main body of the discharge electrode and the arrangement position of the opposite dust collection electrodes in the direction perpendicular to the arrangement direction of the opposite dust collection electrodes. is the distance of

Furthermore, in the electrostatic precipitator according to one aspect of the present invention, the electric field strength between the discharge electrode and the discharge side dust collection electrode and the electric field strength between the discharge electrode and the opposite side dust collection electrode are considered equivalent.

By making the electric field intensity between the discharge electrode and the dust collection electrode on the discharge side equal to the electric field intensity between the discharge electrode and the dust collection electrode on the opposite side, the center of the main body of the discharge electrode The electric field intensity between the discharge electrode and the opposite electrode can be increased compared to the case where it is positioned in the middle between them.

Furthermore, in the electrostatic precipitator according to one aspect of the present invention, the tip of the corona discharge portion is located between the first center axis of the discharge side dust collection electrode and the second center axis of the opposite side dust collection electrode. It is positioned closer to the opposite dust collecting electrode than the central position between them.

By positioning the tip of the corona discharge portion closer to the opposite side of the dust collection electrode than the central position between the two dust collection electrodes, the electric field strength between the corona discharge portion and the discharge side dust collection electrode is reduced while The electric field intensity between the body of the discharge electrode and the opposite electrode can be increased.

By increasing the electric field intensity between the main body of the discharge electrode and the opposite-side dust collecting electrode, the dust-collecting efficiency can be improved by improving the Coulomb force even in the opposite-side electrode. can also collect dust more effectively.

1 is a perspective view showing an electrostatic precipitator according to one embodiment of the present invention; FIG. It is the top view which looked at the electrostatic precipitator of FIG. 1 from upper direction. It is the front view which looked at the electric dust collector of FIG. 1 from the gas flow direction. FIG. 4 is a plan view showing the positional relationship between a dust collection electrode and a discharge electrode; FIG. 4 is a cross-sectional view of a height position corresponding to a protrusion of a discharge electrode; FIG. 4 is a diagram showing electric field intensity between a discharge-side discharge electrode and a dust collection electrode without offset. FIG. 10 is a diagram showing electric field intensity between the opposite-side discharge electrode and the dust collection electrode without offset. FIG. 10 is a diagram showing the electric field strength between the discharge-side discharge electrode and the dust collection electrode when there is an offset; FIG. 10 is a diagram showing the electric field intensity between the opposite-side discharge electrode and the dust collection electrode when there is an offset; It is the front view which showed the modification of the discharge electrode. FIG. 11 is a front view showing another modification of the discharge electrode; FIG. 5 is a plan view showing a modification of the dust collecting electrode; It is the front view which showed the modification of the dust collection electrode. FIG. 11 is a plan view showing another modification of the dust collecting electrode; FIG. 10 is a front view showing another modification of the dust collecting electrode; It is a graph which shows the relationship between a dust collection performance index ratio and an offset ratio. It is a graph which shows the relationship between the electric field strength near a dust collection pole and an offset ratio. 1 is a plan view showing an electrostatic precipitator according to one embodiment of the present invention; FIG.

An embodiment of an electrostatic precipitator according to the present invention will be described below with reference to the drawings.

The electrostatic precipitator 1 is used, for example, in a thermal power plant using coal as fuel, and collects dust (particulate matter) in flue gas led from a boiler. Also, the electrostatic precipitator 1 is installed in a building, an underground space, or the like, although the size of each component is different from that for a thermal power plant, and collects fine particulate matter (for example, PM 2.5), Purify the air inside.

The electric dust collector 1 includes a plurality of conductive dust collection electrodes 4 made of metal or the like. The dust collection electrodes 4 are hollow columnar circular pipes having a circular cross section, and are arranged at predetermined intervals in the x direction (gas flow G direction) perpendicular to the longitudinal direction of the z direction. It is A plurality of rows of dust collecting electrodes 4 arranged in the x direction are provided in parallel at predetermined intervals in the z direction and the y direction perpendicular to the x direction. A discharge electrode 5 is arranged in the xz plane between each row of dust collection electrodes 4 . In FIG. 1, the position of the mounting frame 5c of the discharge electrode 5 is shown. As can be seen from FIG. 1, the discharge electrode 5 extends from the central position CL between the dust collection electrodes 4 arranged in the y direction orthogonal to the direction of the gas flow G toward one of the dust collection electrodes 4 (the right side in the y direction in FIG. 1). are offset.

The dust collection electrode 4 is grounded. The discharge electrode 5 is connected to a power supply having a negative polarity (not shown). The power supply connected to the discharge electrode 5 may have positive polarity.

As shown in FIG. 2, the discharge electrode 5 includes a main body portion 5b fixed to a mounting frame 5c, and a plurality of spine-like protrusions (corona discharge portions) 5a protruding from the main body portion 5b. . The protruding portion 5a is provided so as to protrude toward only one dust collecting electrode 4 side. The protrusions 5a are arranged so as to be positioned between the dust collection electrodes 4 in the x direction, which is the gas flow G direction. A corona discharge is generated at the protrusion 5a, and an ion wind is generated from the tip of the protrusion 5a toward the opposing dust collection electrode 4 side.

As shown in FIG. 2, the center C1 of the body portion 5b of the discharge electrode 5 is offset from the central position CL between the dust collection electrodes 4. As shown in FIG. Specifically, the center C1 of the body portion 5b of the discharge electrode 5 is in a direction away from the dust collection electrode 4 (hereinafter, this dust collection electrode 4 is referred to as the “discharge side dust collection electrode 4a”) facing the protrusion 5a. Also, the dust collecting electrode 4 on the opposite side of the protrusion 5a (hereinafter, this dust collecting electrode 4 is referred to as the "opposite dust collecting electrode 4b") is shifted from the central position CL. Therefore, the distance D1 in the y-direction between the center C1 of the body portion 5b and the arrangement position passing through the center C2 of the discharge side dust collection electrode 4a is the center C1 of the body portion 5b and the center of the opposite side dust collection electrode 4b. greater than the distance D2 in the y-direction between the array position through C3 (D1>D2). Since the discharge electrodes 5 and the dust collection electrodes 4 are alternately arranged in the y direction, the projection 5a side of one dust collection electrode 4 becomes the discharge side dust collection electrode 4a, and the opposite side of the projection 5a becomes the discharge side dust collection electrode 4a. It becomes the dust collecting electrode 4b on the opposite side.

The distance D1 is the distance between the center C1 of the body portion 5b of the discharge electrode 5 and the arrangement position passing through the center C2 of the discharge side dust collection electrode 4a. That is, D1 is the distance between the center C1 of the body portion 5b of the discharge electrode 5 and the arrangement position (center axis line) of the discharge side dust collection electrodes 4a in the direction (y direction) perpendicular to the arrangement direction of the discharge side dust collection electrodes 4a. is the distance between

The distance D2 is the distance between the center C1 of the body portion 5b of the discharge electrode 5 and the arrangement position passing through the center C3 of the opposite dust collection electrode 4b. That is, D2 is the distance between the center C1 of the body portion 5b of the discharge electrode 5 and the arrangement position (center axis line) of the opposite dust collection electrodes 4b in the direction (y direction) perpendicular to the arrangement direction of the opposite dust collection electrodes 4b. is the distance between

For example, when the distance from the center of the body portion 5b of the discharge electrode 5 to the tip of the discharge portion, that is, Dd/2+Lb (see FIG. 4B) is less than 30 mm, preferably about 20 mm, the tip of the protrusion 5a is located at the center. It is arranged so as to be positioned closer to the dust collecting electrode 4b on the opposite side than the position CL.

As described above, by orienting the projection 5a in one direction and arranging it between the dust collection electrodes 4 in the x direction, the ion wind from the projection 5a to the discharge-side dust collection electrode 4a is directed in substantially the same direction. , to avoid the interference of the ionic wind.

FIG. 3 shows a front view of FIG. 1 viewed from the gas flow G direction. As shown in the figure, the protrusions 5a are provided at predetermined intervals in the height direction.

FIG. 4A shows the positional relationship between the dust collection electrode 4 and the discharge electrode 5 when viewed from above.
The interval between the dust collection electrodes 4 arranged in the x direction, which is the direction of the gas flow G, is Pc, and the interval between the discharge electrodes 5 arranged in the x direction is Pd. The interval between the dust collection electrodes 4 arranged in the y direction is 2D. The diameter of the dust collection electrode 4 is set to Dc.

In the present embodiment, the offset position of the discharge electrode 5, that is, the position where the center of the body portion 5b of the discharge electrode 5 is displaced in the y direction from the central position CL, the ratio of the distance D1 and the distance D2 is 1.1≦D1/ It is desirable to set in the range of D2≦2.0. It is even better if the lower limit of D1/D2 is 1.2.

The distance between the tip of the protrusion 5a of the discharge electrode 5 and the side surface of the nearest discharge side dust collection electrode 4a is L1. The distance from the side surface is L2.
A curve drawn between the discharge electrode 5 and the dust collection electrode 4 shown in FIG. 4A is an electric line of force.

FIG. 4B shows an enlarged cross section at a height position corresponding to the protrusion 5a of the discharge electrode 5. As shown in FIG. As shown in the figure, the body portion 5b of the discharge electrode 5 has a circular cross section with a diameter of Dd. The protrusion length of the protrusion 5a protruding from the main body 5b is Lb.

Using the specifications shown in FIGS. 4A and 4B, L1 and L2 can be expressed as follows.
L1=((D1-Dd/2-Lb) ² +(Pd/2) ² ) ^0.5 -Dc/2
L2=(D2 ² +(Pd/2) ² ) ^0.5 -Dc/2-Dd/2
An offset amount Le by which the center of the body portion 5b of the discharge electrode 5 is displaced from the central position CL in the y direction is expressed by the following equation.
Le = (D1-D2)/2
Although FIGS. 4A and 4B show an example of a cross section at the position of the thorn-like protrusion 5a, the portion occupied by the protrusion 5a is actually a part of the discharge electrode 5, and two adjacent electrodes are shown. The portion between the two protrusions 5a occupies most of the discharge electrode 5. As shown in FIG. Therefore, L1 and L2 may be evaluated ignoring the length Lb of the protrusion 5a.

2D, which is the distance between the dust collecting electrodes 4 arranged in the y direction, is, for example, 300 mm or more and 500 mm or less for general industrial use. However, other dimensions may be used for other applications.

Next, the effect of offsetting the discharge electrode 5 will be described with reference to FIGS. 5A to 6B.

5A and 5B show the electric field intensity distribution in the case of no offset with the offset amount Le=0, that is, in the case where the body portion 5b of the discharge electrode 5 is provided on the central position CL. As shown in FIG. 5A, as the corona current flows between the projecting portion 5a and the discharge-side dust collection electrode 4a, the electric field strength E1max near the discharge-side dust collection electrode 4a changes with the negative ions present in the space. It rises due to the space charge of dust. The spark discharge limit electric field strength (Ecr) near the discharge side dust collecting electrode 4a is the maximum applicable maximum electric field strength condition (E1max≦Ecr).

On the other hand, as shown in FIG. 5B, between the opposite side of the protrusion 5a and the opposite dust collection electrode 4b, there is no lifting due to the space charge as shown in FIG. E2max is smaller than E1max.
The areas A1 and A2 obtained by integrating the electric field intensity with respect to the distances L1 and L2 correspond to the applied voltage Vo, respectively, and therefore have the same value.

6A and 6B correspond to this embodiment and show the electric field intensity distribution between the discharge electrode 5 and the dust collection electrode 4 when the discharge electrode 5 is offset from the central position CL. 6A corresponds to FIG. 5A, and FIG. 6B corresponds to FIG. 5B.

As shown in FIGS. 6A and 6B, the electric field intensity between the protrusion 5a and the discharge-side dust collection electrode 4a is L1>L2 or D1>D2 due to the offset. The electric field strength E1max in the vicinity of 4a is lower than that in FIG. 5A if the voltage Vo is the same as in the case of no offset, and E1ave. (=Vo/L1) is also smaller. On the other hand, the offset makes L2 smaller than in the case of FIG. 5B, and the average electric field intensity E2ave.

In general, E1max is operated at a spark discharge limit electric field strength Ecr or less, but since the distance on the projection side becomes longer by offsetting, in order to make the electric field strength the same as the initial E1max compared to the case without offset , the applied linear pressure Vn itself can be increased (Vn>Vo), so that the maximum electric field strength E2max on the opposite side of the projection can be further increased. In this way, by increasing the applied voltage along with the offset, the electric field strength E1max is maintained at the same level as before the offset, and E2max is increased to the same level as E1max. It is possible to increase the electric field strength of the effective field and increase the collection efficiency by the Coulomb force. By offsetting, the distance on the corona discharge side becomes longer, and the movement distance of the dust moving between them becomes longer. The decrease in the average electric field strength in the middle does not negatively affect the performance, and the electric field strength E2max in the vicinity of the dust collecting electrode 4b on the opposite side of the dust that has entered the dust collecting electrode 4b on the opposite side of the dust collecting electrode 4a on the discharge side is reduced. It is possible to improve the performance by increasing the number.

The offset amount Le is preferably adjusted so that the electric field intensity E1max of the discharge side dust collection electrode 4a and the electric field intensity E2max of the opposite side dust collection electrode 4b are equal. The example of the electric field intensity shown in FIGS. 5A to 6B is an example in which the pipe-shaped dust collection electrodes 4 are arranged with an interval, and is described based on the shortest distance at L1 and L2. As an example of the electrode of the dust collection electrode 4, there is also a mesh electrode, etc. Therefore, in order to define the offset amount below, the arrangement position passing through the centers C2 and C3 of the dust collection electrode 4 and the center C1 of the discharge electrode 5 They are collectively represented by D1 and D2, which are distances. In this case, even if it is a pipe-shaped electrode, even if it is evaluated by D1 and D2 instead of L1 and L2, it can be regarded as almost equivalent within a practical range, so there is no problem.

The range in which both electric field intensities are equal is, for example, 1.5 ≤ D1/D2 ≤ 1.8. However, the optimum range of D1/D2 varies depending on the operating conditions of the electrostatic precipitator 1 and the conditions of the dust collection electrode 4 or the discharge electrode 5 .

The lower limit of the ratio D1/D2 of the distances D1 and D2 is, for example, 1.1, and more preferably 1.2. As shown in FIG. 10, it has been found that the flow velocity of the gas flow G changes the relationship between the offset amount and the dust collection performance. When the gas flow G is relatively fast, dust collection performance improves when D1/D2 is 1.1 or more. When the gas flow G is relatively slow, the dust collection performance is improved when D1/D2 is 1.2 or more, and within this range, when the gas flow G is relatively fast, the dust collection performance is reliably improved. .

Under conditions where the flow velocity of the gas flow G is high, the effect of the Coulomb force is greater, so the dust collection performance is improved even with a relatively small offset amount (for example, 1.1 ≤ D1/D2) due to the increase in the electric field strength. do. On the other hand, under conditions where the flow velocity is slow, the effect of the ion wind is large, so a larger offset amount (for example, 1.2 ≤ D1/D2) is required in order to improve the dust collection performance by increasing the electric field strength. Become. If 1.2 ≤ D1/D2, the dust collection performance can be improved regardless of the flow velocity of the gas flow G.

If the offset amount is excessive, the electric field strength E2max > E1max in the vicinity of the dust collection pole on the opposite side, and the limit electric field strength of the spark discharge on the opposite side of the corona discharge becomes a restriction condition for operation, and the performance on the corona discharge side is exhibited. I don't like it because I can't do it. Therefore, it is desirable that the maximum offset amount be set within a range in which E2max does not greatly exceed E1max.

FIG. 11 shows the corona discharge side (the side having the protrusion 5a on the main body 5b of the discharge electrode 5, i.e., the side having the protrusion 5a on the main body 5b of the discharge electrode 5, that is, the thorns on the discharge wire) when D1/D2 is changed in the electrostatic precipitator 1 for general industrial use. side) and the electric field strength near the discharge side dust collection electrode 4a, and the opposite side dust collection electrode on the electric field side (the side without the projection 5a on the main body 5b of the discharge electrode 5, that is, the side without thorns) An example of analyzing and comparing the electric field intensity in the vicinity of 4b is shown. Both the current and the voltage as operating conditions of the electrostatic precipitator 1 were increased. In FIG. 11, the current voltage increases from the left graph to the right graph.

In any case, when D1/D2=1, the discharge side dust collection electrode 4a on the side with the thorns is closer to the thorn length, and the space charge due to the corona current raises the electric field. is added, the electric field intensity is higher on the discharge side dust collection electrode 4a on the side with the thorns. Then, as the current increases, the effect of the rising becomes greater, and the value of the electric field strength becomes higher.

On the other hand, in any of the graphs of FIG. 11, as D1/D2 increases, the electric field strength of the opposite dust collecting electrode 4b on the side without thorns shows a unique tendency to increase. Ideally, the point where the electric field intensity on the side with thorns and the side without thorns is the same is considered to be the most balanced electric field intensity distribution. However, in actual operation, various conditions are combined, and the optimal conditions fluctuate. For this reason, even in the test results regarding the improvement of dust collection performance when D1/D2 is changed in FIG. 10, the optimum point of dust collection performance also has some variation.

Further, in the graph on the right side of FIG. 11, that is, in the operation with increased current and voltage, in the region where D1/D2 with a particularly large offset amount is large, the spark discharge electric field intensity ( Although this varies greatly depending on the gas composition and operating temperature conditions, it is usually set to 8 kV/cm to 12 kV/cm). , unfavorable.
More specifically, it is desirable that D1/D2≦2.0.

When D1/D2 exceeds 2.0, the electric field intensity on the side of the dust collection electrode 4b on the opposite side reaches or reaches the region where spark discharge occurs under normal operating conditions of the electrostatic precipitator 1. get close to Therefore, the stable operation becomes difficult due to the restriction of the operating conditions of the electrostatic precipitator 1 . Therefore, it is desirable that the upper limit of D1/D2 is 2.0.

Next, operation|movement of the electrostatic precipitator 1 of this embodiment is demonstrated.
In the electrostatic precipitator 1, a negative voltage is applied from a power source to the discharge electrode 5, thereby generating corona discharge at the tip of the protrusion 5a. Dust contained in the gas flow G is charged by corona discharge. According to the collection principle of a conventional electrostatic precipitator, charged dust is attracted to the grounded dust collection electrode 4 by the Coulomb force and collected on the dust collection electrode 4. is greatly affected by the ionic wind.

When corona discharge occurs, negative ions are generated near the protrusion 5a, and the negative ions move toward the dust collecting electrode 4 by an electric field, generating an ion wind. Therefore, the Coulomb force acts on the dust, and at the same time, the ion wind flowing toward the dust collection electrode 4 acts to move the dust contained in the gas flow G to the vicinity of the discharge side dust collection electrode 4a. In the region near the discharge-side dust collecting electrode 4a, the electric field strength rises to increase the Coulomb force and effectively collect the dust. In addition, by arranging the dust collection electrodes 4 in the form of circular pipes at intervals in the x direction, which is the direction of the predetermined gas flow G, the ion wind flowing from the protrusion 5a toward the discharge-side dust collection electrode 4a is reduced. The part is allowed to come out to the back side of the dust collecting electrode 4. As a result, it is possible to suppress the flow in which the ion wind is reversed by the dust collection electrode 4 and separated, so that the collection efficiency is improved.

Part of the ion wind containing dust and flowing toward the dust collecting electrode 4 passes through between the dust collecting electrodes 4 . Since the ionic winds are directed in one direction, they do not interfere with each other.

On the other hand, between the projecting portion 5a and the opposite dust collecting electrode 4b on the opposite side, as described with reference to FIG. 6B, by offsetting the discharge electrode 5 from the central position CL, field strength E2max can be increased compared to no offset. As a result, dust is effectively collected by the Coulomb force even at the dust collection electrode 4b on the opposite side of the protrusion 5a. That is, it is possible to efficiently collect uncollected dust that has flowed into the opposite dust collection electrode 4b, which is the rear surface of the dust collection electrode 4, due to the ion wind.

The dust collected by the dust collecting electrode 4 is separated and collected by hammering. Alternatively, a method of moving the dust collecting electrode to scrape off the dust with a brush, or a wet cleaning method may be employed.

According to this embodiment, the following effects are obtained.
Since the center of the body portion 5b of the discharge electrode 5 is located in a direction away from the discharge side dust collection electrode 4a than the central position CL between the discharge side dust collection electrode 4a and the opposite side dust collection electrode 4b, the discharge electrode The body portion 5b of 5 and the dust collecting electrode 4b on the opposite side come close to each other. As a result, the electric field strength between the body portion 5b of the discharge electrode 5 and the opposite dust collection electrode 4b can be increased, and the dust collection efficiency by the Coulomb force can be enhanced in the opposite dust collection electrode 4b as well.

In the above-described embodiment, the discharge electrode 5 has a structure in which the protrusion 5a is provided on the main body 5b having a circular cross section. It is good also as a structure which provided the projection part 5a in the square bar 5b' which was formed. Alternatively, as shown in FIG. 7B, it may be formed by punching out a flat plate so that the projecting portion 5a and the main body portion 5b'' are integrally formed.

Further, as shown in FIGS. 8A and 8B, instead of the dust collecting electrode 4 as a circular pipe, a flat dust collecting electrode 4' such as a punching metal having a large number of holes formed in a flat plate may be used. Alternatively, as shown in FIGS. 9A and 9B, a folded plate-like dust collection electrode 4'' may be formed by alternately and regularly folding a flat plate such as punching metal with a large number of holes formed in the direction of the gas flow G. In this case, the projecting portion 5a of the discharge electrode 5 is offset according to the unevenness of the opposing bent plate.

Furthermore, the dust collecting electrode 4 may be a woven wire mesh (for example, a lock crimp woven wire mesh) in which metal wires are crossed in the vertical direction and the horizontal direction. The woven wire mesh has a constant aperture ratio and no edge on the surface, so that the electric field strength in the vicinity of the dust collecting pole 4 can be uniformly increased. The wire mesh is not limited to a woven wire mesh, and may be a welded wire mesh in which wire rods having a circular cross section are arranged in the vertical direction and the horizontal direction and connected.

When the electrostatic precipitator 1 is used as an air purifier for air purification, the particles stay in the apparatus for a short time and the particle concentration is also low. On the other hand, the electrostatic precipitator 1 used in a thermal power plant is large in scale, has a long residence time of particles, and has a high particle concentration, unlike the case of being used for air purification. In the electrostatic precipitator 1 for air purification, when low-concentration particles are allowed to pass through with a short residence time, the particles are transported to the dust collection electrode 4 by the effect of gas circulation generated by the ion wind from the protrusion 5a of the discharge electrode 5. cannot be collected.

Therefore, as shown in FIG. 12, a gas blocking plate 6 should be installed on the upstream side of the gas flow G between the opposite dust collecting electrode 4b and the discharge electrode 5. As shown in FIG. Since the gas flow G is blocked by the gas blocking plate 6, the flow rate of the gas flowing between the dust collection electrode 4b on the opposite side and the discharge electrode 5 is reduced, and the residence time of the particles passing through the dust collection electrode 4 is lengthened. , the collection performance can be enhanced.

1 Electrostatic Precipitator 4 Dust Collection Electrode 4a Discharge Side Dust Collection Electrode 4b Opposite Side Dust Collection Electrode 5 Discharge Electrode 5a Projection (Corona Discharge Part)
5b Main body 5c Mounting frame 6 Gas blocking plate C1 Center CL (of the main body of the discharge electrode) Central position

Claims (5)

a plurality of discharge electrodes each having a body portion and a corona discharge portion for corona discharge projecting from the body portion and arranged along the gas flow direction;
a discharge-side dust collection electrode disposed along the gas flow direction and located on the corona discharge portion side;
an opposite-side dust collection electrode disposed along the gas flow direction and located on the opposite side of the discharge-side dust collection electrode with the discharge electrode interposed therebetween;
with
The plurality of corona discharge units are arranged along the gas flow direction,
two of the corona discharge portions adjacent to each other along the gas flow direction have the same protruding direction;
The corona discharge part protrudes only toward the discharge-side dust collection electrode,
The center of the body portion of the discharge electrode is defined by a first center axis that is an arrangement position passing through the center of the discharge side dust collection electrode and a second center axis that is an arrangement position passing through the center of the opposite side dust collection electrode. is positioned in a direction away from the discharge-side dust collection electrode from the central position between
In the corona discharge portion, a corona discharge is generated on the side of the discharge side dust collection electrode rather than the opposite side dust collection electrode, and an ion wind is generated from the tip of the corona discharge portion toward the discharge side dust collection electrode facing. Electrostatic precipitator . The distance between the center of the body portion of the discharge electrode and the first center axis of the discharge side dust collection electrode is D1, the center of the body portion of the discharge electrode and the second dust collection electrode of the opposite side is D1. When the distance between the central axis is D2,
1.1 ≤ D1/D2 ≤ 2.0
The electrostatic precipitator according to claim 1, wherein the plurality of discharge-side dust-collecting electrodes and the plurality of opposite-side dust-collecting electrodes are arranged along the gas flow direction,
The D1 is the distance between the center of the main body of the discharge electrode and the first central axis of the discharge-side dust collection electrode,
3. The electrostatic precipitator according to claim 2, wherein said D2 is the distance between the center of said discharge electrode main body and said second center axis of said opposite dust collection electrode. 4. Any one of claims 1 to 3, wherein the electric field intensity between the discharge electrode and the discharge-side dust collection electrode and the electric field intensity between the discharge electrode and the opposite-side dust collection electrode are equal to each other. Electrostatic precipitator as described. The tip of the corona discharge portion is positioned closer to the opposite dust collection electrode than the central position between the first center axis of the discharge-side dust collection electrode and the second center axis of the opposite dust collection electrode. 5. An electrostatic precipitator according to any one of claims 1 to 4, wherein the electrostatic precipitator is positioned

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