JP7713620B2 - Electrostatic Precipitator - Google Patents

Description

The present invention relates to an electrostatic precipitator that charges particles suspended in the air and collects them using electrostatic force.

Conventionally, this type of electrostatic precipitator applies a high DC voltage to the discharge electrode of the charging section to generate a positive or negative corona, charging the dust passing through the charging section with a positive or negative charge. A widely known technology is to collect this charged dust on the surface of the dust collecting electrode plate by electrostatic force using a high electric field in the dust collecting section, which has a charging electrode plate to which a high DC voltage is applied and a dust collecting electrode plate connected to ground (Patent Documents 1 and 2).

The electrostatic precipitators used to remove dust in road tunnels are large because they process large volumes of air.

The principle of electrostatic precipitator, which is a known technology, will be described with reference to Figs. 7 and 8. As shown in Fig. 7, the dust collection unit of the electrostatic precipitator is composed of a charging section 101 and a dust collection section 102. The direction of airflow is from the charging section 101 to the dust collection section 102 (from the lower left to the upper right in Fig. 7). As shown in Fig. 8, DC high voltages of -10 kV and -7.2 kV are supplied to the charging section 101 and the dust collection section 102 from DC power sources 107 and 108, respectively. The charging section 101 is composed of a discharge electrode plate 103 having spikes for discharge and a ground electrode plate 104. A DC high voltage of -10 kV is applied to the discharge electrode plate 103, and a negative corona discharge is generated in the space between the discharge electrode plate 103 and the ground electrode plate 104. The negative ions generated by this negative corona give a negative charge to the dust (not shown) in the space, and the dust becomes negatively charged. The charged dust particles are collected on the dust collection plate 106 by Coulomb force due to the electric field formed between the charged electrode plate 105 and the dust collection plate 106 in the downstream dust collection section 102 (dust collection principle). For simplicity, only two plates of each are drawn, but in reality, each charged section is made up of several tens of plates.

In the dust collection section 102 of such an electric dust collector, in order to secure a large dust collection area, the charged electrode plate 105 and the dust collection electrode plate 106 are arranged alternately and parallel to the wind direction, with the charged electrode plate 105 and the dust collection electrode plate 106 being of approximately the same size and shape. Then, as described above, an electric field is formed between the charged electrode plate 105 and the dust collection electrode plate 106, and in the case of FIG. 6 (negative charge), negatively charged particles adhere to the dust collection electrode plate 106 and are collected. In this way, dust is removed by particles adhering to the surface of the dust collection electrode plate 106, so the larger the area of the dust collection electrode plate 106, the higher the dust collection efficiency. In other words, in order to secure dust collection efficiency, as the area of the electrode plate increases, the entire electric dust collector becomes larger and heavier.

JP 2014-087734 A JP 2015-33696 A

However, the installation space for electrostatic precipitators is limited, and they need to be as small and lightweight as possible for ease of transportation, on-site construction, and maintenance. Therefore, reducing weight while maintaining dust collection efficiency was one of the challenges facing electrostatic precipitators.

In order to achieve this object, the electric dust collector according to the present invention has a charging section in which charged electrode plates and grounding electrode plates are alternately arranged, and a dust collecting section in which charged electrode plates and dust collecting electrode plates are arranged in parallel and alternately, and no multiple openings are provided in a region of the charging electrode plate on the inlet side along the ventilation direction, which is 1/2 of the total length of the charging electrode plate, and multiple openings are provided in a region of the charging electrode plate on the outlet side of the inlet 1/2 of the total length of the charging electrode plate along the ventilation direction . This achieves the intended object.

According to the present invention, the weight of the electric dust collector can be reduced by providing multiple openings on the outflow side of the charged electrode plate. In addition, an uneven electric field is formed near the edge of the openings in the charged electrode plate, and particles are attracted to the end of the openings where the electric field lines are concentrated, and are attached and collected. As a result, the weight of the electric dust collector can be reduced without reducing the dust collection efficiency.

FIG. 1 is a diagram showing a dust collecting section of an electric dust collector according to an embodiment of the present invention. FIG. 2A is an overall view of a charged electrode plate of a dust collecting section of an electric dust collector according to an embodiment of the present invention, and FIG. 2B is an enlarged view of an opening portion thereof. System diagram of an electric dust collector according to an embodiment of the present invention FIG. 1 is a diagram of a positive electric field analysis system simulating the dust collection section of a conventional electric dust collector (a) and the dust collection section of an electric dust collector according to an embodiment of the present invention (b). FIG. 1 is a diagram showing the results of calculations of a positive electric field analysis simulating the dust collection section of a conventional electric dust collector (a) and the dust collection section of an electric dust collector according to an embodiment of the present invention (b). FIG. 1 is a diagram showing a re-entrainment suppression process in the dust collecting section of the electric dust collector according to the first embodiment of the present invention. Diagram of a conventional electrostatic precipitator System diagram of a conventional electrostatic precipitator Observation diagram of dust adhesion on the electrode plate surface in the dust collection section of a conventional electrostatic precipitator

The electrostatic precipitator according to the present invention has a charging section in which charged electrode plates and grounding electrode plates are arranged alternately, and a dust collecting section in which charged electrode plates and dust collecting electrode plates are arranged in parallel and alternately. The charged electrode plates have multiple openings on the outflow side.

This reduces the weight of each dust collecting electrode plate, and also reduces the weight of the entire electrostatic precipitator. Furthermore, by providing holes in the charged electrode plate, an uneven electric field is formed near the edge of the hole. In an uneven electric field region, electric field lines concentrate, and in combination with the gradient force, dust can be collected with a greater force than in a uniform electric field. This is why a lot of dust gathers at the outlet end of the dust collecting section. By providing a large number of holes, it is possible to create a large number of these uneven electric field regions, which leads to improved dust collection capacity.

On the other hand, when dust accumulates in this unequal electric field region and exceeds a limit, it eventually peels off and scatters again. Conventionally, it was thought that when dust accumulated in the unequal electric field region at the outlet end of the dust collection section exceeds a limit, it will eventually peel off and scatter again. Conventionally, technologies have been disclosed for recapturing re-scattered dust by changing the positions of the outlet end of the charged electrode plate and the dust collection electrode plate, or by providing a new electrode plate for preventing re-scattering (Patent Documents 1 and 2). In the dust collection section of the dust collector of the present invention, the unequal electric field region can be increased, so the dust collection capacity is increased in the unequal electric field region and the dust collection efficiency is maintained. In addition, the re-scattered particles are charged to the same polarity as the electrode by induction charging and are re-scattered, and can be re-collected by the dust collection electrode plate downwind from the point of scattering. This also contributes to improving the dust collection efficiency.

(Embodiment 1)
As shown in FIG. 1, the electric dust collector according to the present invention includes a charging section 1 and a dust collecting section 2.
The charging section 1 and the dust collecting section 2 are arranged in this order from the inlet side along the direction of airflow. The charging section 1 has a plurality of charging electrodes 3 and a plurality of grounding electrode plates 4, and the charging electrodes 3 and the grounding electrode plates 4 are arranged alternately. The dust collecting section 2 has a plurality of charging electrode plates 5 and a plurality of dust collecting electrode plates 7, and the charging electrode plates 5 and the dust collecting electrode plates 7 are arranged parallel to each other and alternately.

As shown in FIG. 2, a plurality of openings 6 are provided in the area of 1/2 of the outflow side of the charged electrode plate 5. In this embodiment, the charged electrode plate 5 has a length and width of approximately 700×900 mm, and round holes with a diameter of 5 mm are arranged in a 60° staggered pattern at intervals of 8 mm on the charged electrode plate 5. The number of openings 6 is approximately 2100. The shape of the openings 6 is not limited to this embodiment, and they may be elongated round holes or rectangular holes, and there is no difference in their action and effect as long as an uneven electric field can be formed. The diameter, interval, and pattern are also not limited to this embodiment, and an uneven electric field can be formed as long as the diameter of the openings 6 is approximately 2 mm or more. The same applies to the ratio of the openings 6 provided in the charged electrode plate 5. In the pattern of this embodiment, the porosity is approximately 13% in the area where the openings 6 are provided, so if the openings 6 are provided in 1/2 of the entire charged electrode plate 5 (when the openings 6 are provided only on the downstream side), the mass of the charged electrode plate 5 can be reduced by 6.5% per sheet compared to a flat plate without the openings 6. If 50 charged electrode plates 5 are used per electrostatic precipitator, each plate with the above area weighs approximately 2.0 kg, resulting in a weight reduction of approximately 6.5 kg per electrostatic precipitator.

As shown in FIG. 3, the charging unit 1 includes a plurality of charging electrodes 3, a plurality of grounding electrode plates 4, and a charging unit DC power supply 8. A high voltage is applied to the charging electrodes 3 by the charging unit DC power supply 8. When a high voltage is applied to the charging electrodes 3, a corona discharge occurs between the grounding electrode plates, which are grounded, and the dust flowing in from the inflow side is charged. Note that in this embodiment, the charging electrodes 3 are described as being so-called thorn electrodes, which are flat plates with a plurality of thorns, but the charging electrodes 3 may be needle electrodes, wire electrodes, or other electrodes that can discharge the incoming particles.

A high voltage is applied to the charging electrode plate 5 by the dust collection section DC power supply 9. In the inlet half of the dust collection section 2, i.e., the area where the charging electrode plate 5 does not have the openings 6, a uniform electric field area is formed between the charging electrode plate 5 and the dust collection electrode plate 7, so that the particles charged in the charging section 1 are subjected to Coulomb force and are collected by the dust collection electrode plate 7.

On the other hand, in the area on the outflow side of the dust collector 2, i.e., the area where the openings 6 are provided in the charged electrode plate 5, the electric field lines are concentrated near the edges of the openings 6, creating an area of non-uniform electric field with a higher electric field strength than the uniform electric field created by the flat plate (Figure 3). Since a gradient force is at work in the non-uniform electric field area, dust is attracted by an even stronger force in the vicinity of this area.

A positive electric field analysis was performed using a conventional dust collection section 102 model (Fig. 4(a)) in which a flat charged electrode plate 105 and a dust collection electrode plate 106 are arranged in parallel, and a dust collection section 2 model (Fig. 4(b)) in which a charged electrode plate 5 with an opening 6 and a dust collection electrode plate 7 according to the present embodiment are arranged in parallel, and the electric field strengths of each were compared.

As shown in FIG. 4(a), the conventional dust collection section 102 model has one charged electrode plate 105 sandwiched between two dust collection electrode plates 106.

As shown in FIG. 4(b), the dust collecting section 2 model of this embodiment has an opening 6 in the charged electrode plate 5 of the same external shape as the conventional dust collecting section 102 model. The conventional dust collecting section 102 and the dust collecting section 2 of this embodiment are both set to 200 mm in the ventilation direction. Although the shape is finite in FIG. 4, the calculation is performed on the assumption that the shape continues periodically to infinity in the vertical direction (periodic boundary condition). The length in the ventilation direction is set to a length at which the tendency of the electric field intensity can be seen in the central part. The inter-electrode distance between the dust collecting electrode plate 106 and the charged electrode plate 105, and between the dust collecting electrode plate 7 and the charged electrode plate 5 is 9 mm. Considering that a voltage of −7.2 kV is applied to the charged electrode plate 105 and the charged electrode plate 5 by the dust collecting section DC power supply 9, the voltage boundary conditions are set to −7.2 kV for the charged electrode plate and 0 kV for the dust collecting electrode plate.

The analysis results are shown in Figure 5. Figure 5 is a cross-sectional view of the dust collecting unit 102 and dust collecting unit 2, respectively, viewed vertically from above, with the electric field strength indicated by the color intensity. As shown in Figure 5(a), in the dust collecting unit 102 of the conventional model, it can be seen that the electric field strength is uniform in the space between the plates. On the other hand, as shown in Figure 5(b), in the dust collecting unit 2 of this embodiment, it can be seen that a non-uniform electric field is formed near the edge of the aperture 6 of the charged electrode plate 5, and a stronger electric field region exists near the edge of the aperture 6 than in the uniform electric field. In this region, the electric field strength is about 9.0 x ¹⁰⁵ [V/m].

Figure 6 is a horizontal cross-sectional view of the dust collection section 2 in this embodiment, passing through the center of the opening 6 in the charging electrode plate 5. Using Figure 6, the dust collection action of the charging electrode plate 5 and the dust collection electrode plate 7 in this embodiment will be explained.

As described above, a stronger non-uniform electric field is formed near the edge of the opening 6 compared to the conventional method. The non-uniform electric field, combined with the gradient force, attracts dust with a greater force. Figure 6 shows how dust is collected intensively by the non-uniform electric field in this area. In the inlet 1/2 area of the dust collection section 2, 1) dust that is not sufficiently charged, 2) dust that was once collected in the inlet 1/2 area of the dust collection section 2 and has been re-scattered, and 3) dust that escapes due to the fluid resistance of the turbulent flow reach the outlet 1/2 area of the dust collection section 2 without being collected. In the outlet 1/2 area of the dust collection section 2, as described above, the inflowing dust can be collected by the non-uniform electric field created by the opening 6.

In addition, by providing many openings 6, many unequal electric field regions can be created. This increases the amount of dust that can be collected in the unequal electric field region. On the other hand, the unequal electric field concentrates dust, accumulates it, and then it is re-scattered. When it is re-scattered, it is known that it becomes the same polarity as the electrode plate to which it is attached due to induction charging, and the dust re-scattered from the vicinity of the edge of the opening 6 of the charged electrode plate 5 is negatively charged. This re-scattered dust is re-collected by the dust collecting electrode plate 7 downstream from the re-scattering position, so that it is possible to prevent a decrease in dust collection efficiency due to re-scattering from the unequal electric field region. Therefore, it is preferable that the dust collecting electrode plate 7 is longer in the ventilation direction than the charged electrode plate 5 and is arranged to protrude downstream from the charged electrode plate 5. With this configuration, the dust re-scattered from the outflow side of the charged electrode plate 5 can be collected by the dust collecting electrode plate 7 protruding downstream.

Figure 9 shows the dust collection state of the charged electrode plate 105 and the dust collecting electrode plate 106 in a conventional dust collecting section 102 using flat electrode plates (quoted from Patent Documents 1 and 2 (patent applications by the same applicant as the present application)). Dust also adheres to the charged electrode plate 105 using flat electrode plates, but the degree of adhesion (the adhesion area in the electrode plate area) is 18%, 10%, 6%, and 4% for every 1/4 of the total electrode plate length from the windward side (inlet side). Similarly, the degree of adhesion to the dust collecting electrode plate 106 is 56%, 38%, 23%, and 13% for every 1/4 of the total electrode plate length from the windward side (inlet side).

As described above, it can be seen that the dust collection efficiency of flat electrodes drops significantly downstream (outflow) from 1/2 of the total length. In other words, forming a uniform electric field on the outflow side does not contribute much to the dust collection efficiency, so in this embodiment, openings 6 are provided to form a non-uniform electric field in this downstream 1/2 region. In particular, openings 6 are provided in the charging electrode plate 5, which has the same polarity as the polarity charged in the charging unit 1, to capture dust particles that are re-scattered from the dust collecting electrode plate 7 and dust particles that are not charged in the charging unit 1.

In this way, by providing the openings 6 in the area on the outflow side of the charged electrode plate 5, the weight can be reduced. In addition, the openings 6 form an uneven electric field, which makes it possible to collect dust re-entrained from the inflow side and dust that could not be collected. In addition, by arranging a large number of openings 6 in a certain pattern, a large number of uneven electric field regions are formed, which increases the collection capacity in the uneven electric field regions. Furthermore, there is a re-entrainment prevention process in which dust re-entrained from the uneven electric field region can be re-collected by the dust collecting electrode plate 7 downstream from the re-entrainment position. As a result, the desired problem of reducing weight while maintaining dust collection efficiency is solved.

This technology is particularly useful for large electrostatic precipitators, as it can reduce the weight of the electrodes that are often used in electrostatic precipitators while ensuring dust collection efficiency.

REFERENCE SIGNS LIST 1 Charging section 2 Dust collecting section 3 Charging electrode 4 Ground electrode plate 5 Charging electrode plate 6 Opening 7 Dust collecting electrode plate 8 Charging section DC power supply 9 Dust collecting section DC power supply 101 Charging section 102 Dust collecting section 103 Discharge electrode plate 104 Ground electrode plate 105 Charging electrode plate 106 Dust collecting electrode plate 107 DC power supply 108 DC power supply

Claims (4)

In an electric dust collector having a charging section in which charging electrodes and grounding electrodes are alternately arranged, and a dust collecting section in which charging electrodes and dust collecting electrodes are arranged in parallel and alternately,
Along the air flow direction of the charging electrode plate, a plurality of openings are not provided in a region of 1/2 of the inlet side of the entire length of the charging electrode plate ,
A plurality of openings are provided in an area of the charging electrode plate on the outflow side of the inflow side half area along the air flow direction of the charging electrode plate .
Electrostatic dust collector. 2. An electric dust collector according to claim 1, wherein said openings are provided in a half area of said outlet side of said charging electrode plate. An electric dust collector according to claim 1 or 2, in which the dust collecting electrode plate is longer in the ventilation direction than the charging electrode plate and is arranged to protrude downstream. An electric dust collector according to any one of claims 1 to 3, characterized in that the openings are arranged in a 60° staggered pattern of circular holes with a diameter of 5 mm spaced 8 mm apart.