JPS647829B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a novel electrostatic precipitator in which a charging section and a dust collecting section are separated. In conventional gas parallel electrostatic precipitators, the charging section and the dust collection section were not separated. In the dust collection mechanism, a charged part and a dust collection part coexisted together. The principle of an electric precipitator is to charge the dust and make the ionized dust adsorbed to the dust collector plate using Coulomb force. Conventional dust collectors have a structure in which a large number of thin parallel discharge wires are suspended, and a wide dust collection electrode plate is provided between them. The dust collecting electrode plate is grounded, and a high voltage is applied between the discharge wire and the dust collecting electrode plate. Corona discharge occurs because the electric field near the discharge line is large. The dust is thereby ionized.
The ionized dust is attracted to and adheres to the collecting electrode plate of opposite polarity. In this way, the discharge wire has two functions: a corona discharge function to ionize the dust, and a function to create an electric field that pushes the ionized dust to the dust collecting electrode plate. At first glance, this configuration of the Kottrell type dust collector seems to be rational. However, it is not always satisfactory in the following points. In order to saturately charge the dust, the amount of corona discharge from the discharge wire must be increased. For this reason, the discharge wire is made thinner. Furthermore, irregularly shaped protrusions are often provided. In this way, the electric field strength near the discharge line is increased. In order to effectively collect ionized dust onto the dust collector plate, it is necessary to increase the voltage between the two electrodes. In fact, it has been found that the dust collection function, that is, the movement speed of dust, is proportional to the square of the electric field. This point will be briefly explained. Consider a model in which a homogeneous object of dielectric constant ε and radius α is placed in an electric field E ₀ . This is regarded as a positively charged sphere and a negatively charged sphere with radius α whose center positions are shifted by δ. If the charge density of the charge sphere is ρ, the polarization density I is given by P=δρ (1). Since it is a sphere, the anti-electric field E' is determined by E'=-4/3πP (2). The electric flux density D is D=εE =E+4πP (3) where the total electric field E is E=E ₀ +E' (4). Solve these to find P. The charge q of the ionized sphere can be approximated as the polarization P multiplied by the cross-sectional area, so it is given by q=3(ε-1)E ₀ α ² /4(ε+2) (5). The frictional force of a ball in the air is approximated by Stokes' formula, and since this balances the force due to the electric field, it is multiplied by qE=6πμαv (6). μ is the viscosity coefficient. Then, the moving speed v of the dust is given by v=(ε-1)E ₀ ² α/8(ε+2)πμ (7). In other words, it is proportional to the square of the electric field. The best way to increase collection efficiency is to increase the voltage. However, this is not possible in order to sustain corona discharge near the discharge line. The electric field strength is high near the discharge line and low near the dust collector plate. An unequal electric field is created between the two poles. When the voltage between the electrodes is increased to increase the dust collection ability, a transition occurs from corona discharge to arc discharge near the discharge line. In the arc discharge region, dust is not ionized. A spatial short circuit phenomenon occurs. For this reason, the voltage between the two poles cannot be increased beyond a certain level. The ionized dust is carried along with the gas stream flowing parallel to the collecting electrode plates. During this time, the dust is drawn toward the dust collector plate by Coulomb force. If the gas flow velocity is low, the dust collecting electrode plate may be short. However, this limits processing power. In order to achieve complete dust collection when the gas flow rate is high, the dust collection chamber must be long and the distance between the electrode plates must be narrowed. There is a limit to narrowing the distance between the electrode plates, so
As a result, the dust collection chamber becomes longer. This makes it an extremely large-scale device. Let me give you a concrete example. In general, industrial gas parallel electrostatic precipitators have a gas velocity of 1 m/sec or less, a gas residence time of 4 to 10 seconds (depending on the length of the precipitator), and a distance between poles of 0.1 to 0.125 m. It is a large-scale device that depends on the amount of gas to be processed and the efficiency of dust collection. There are also two-stage dust collectors in which the charging section and the dust collecting section are separate. In the charged part, corona discharge is caused by thin metal wires at both poles. In the dust collecting section, parallel positive and negative electrode plates are provided alternately. While passing through the parallel electrode plates, the ionized dust is attracted to the electrode plates and adheres to the dust collection electrode plate. In such a two-stage precipitator, since the corona discharge voltage and the dust collection voltage are independent, the dust collection voltage can be increased as desired. The electrode plates in the dust collecting section are parallel, which has many advantages, such as uniform electrical lifting. However, since parallel plates are used and a voltage is applied between them, the distance between the plates cannot be kept below a certain level. The minimum is 0.08m. As expected, the dust collection chamber will be longer. In the end, it becomes large. Furthermore, power must be supplied to the dust collection chamber, making the configuration more complex than the Kottorel type. The present invention was made for the purpose of significantly reducing the size of a conventional electrostatic precipitator without sacrificing the dust collection efficiency of the device. Despite being miniaturized, the processing capacity and dust collection efficiency are comparable to conventional ones, so the economic effect is great. EMBODIMENT OF THE INVENTION Hereinafter, the structure, operation, and effect of the present invention will be explained in detail with reference to drawings showing examples. FIG. 1 is a longitudinal sectional view of an electrostatic precipitator according to an embodiment of the present invention. 1 is the dust collector jacket. 2 is a charged part of dust. Here, the dust is subjected to only ionization, becomes completely saturated and ionized. The charging section 2 includes a discharge wire 20 and a ground electrode 21. Both are wire rods and do not use plate materials. Figure 2 is a cross-sectional view of the main part, Figure 3 is an enlarged side view of the charging section 2, Figure 4 is an enlarged front view of the discharge line, and Figure 5 is an enlarged front view of the discharge line.
The figure is an enlarged side view of the discharge line. The discharge wire 20 is made by pressing a round wire at a plurality of locations, and a protrusion 23 is formed laterally at the pressed location 22. A large number of discharge wires 20, 20, . The opposite pole side round wire ground pole 21, 21, ... is also pole frame 2
5, many are strung up and down. The charging section 2 is constructed by disposing these pole frames 24 and 25 alternately in parallel. The purpose of providing the protrusion 23 on the discharge line 20 is to locally strengthen the electric field here. Reliable corona discharge is performed at the protrusion 23. There is no movement of the discharge position. Therefore, stable electron emission into space is performed. The spatial electron density and spatial ion density for ionization in the space through which the gas passes are kept constant. Dust is reliably ionized. Regarding the examples, the performance of each discharge wire shape is listed below. When the parameters are: charging section length 1m, moving layer thickness 0.2m x 2-layer gas velocity 1m/sec, inlet dust amount 1.295g/ ^m3 , (a) when a 4φ round wire is used as the discharge wire, and (b) )
When a 4φ round wire with protrusions was used as the discharge wire, the amount of dust at the outlet and the efficiency were as follows. Exit dust amount (g/m ³ ) Efficiency (%) (a) 0.059 95.46 (b) 0.015 98.82 Despite the extremely short charging section and overall small size, all show good results. In particular, round wire with protrusions is better. The reason is thought to be as follows. In the case of a simple round discharge wire, the formation of charge is nearly uniform, so the corona discharge voltage range is narrow. However, in the case of a discharge wire with protrusions, the magnitude of the electric charge near the discharge wire is uneven, and there are many variations in strength.
Therefore, the discharge wire with projections has a wider corona discharge region in terms of voltage. Even if there is vibration or fluctuation in the applied voltage, the corona discharge position will not shift. A stable fixed position discharge is generated at the protrusion. As a result, the spatial electron (ion) density becomes stable, and the ionization ability of the dust increases. The pole frames 24 and 25 are arranged alternately to constitute the charging section 2. The charging section 2 is operated by a suspension device 4.
It hangs down from box 5. Moving dust collection layers 7 and 8 separated by perforated plates 6
is provided following the charging section 2. One of the features of the present invention is that the moving dust collection layers 7 and 8 are provided. This is not a type of conventional two-stage dust collector in which the electrode plates are placed opposite each other and voltage is applied. This is a dust collection layer in which a porous plate 6 is filled with a conductive material such as small iron balls. It does not have high voltage plates, but instead consists of a small diameter filling of grounded conductive material. The perforated plate 6 has a large number of openings to allow gas to pass therethrough but not conductive material. In this example, an oval opening of 5 x 30 mm is used.
It is set so that the aperture ratio is 60%. In this embodiment, the conductive material filled in the perforated plate 6 is a small iron ball having a diameter of 6 to 10 mm. The small iron ball is
The moving dust collection layers 7 and 9, which are divided into two, are filled from bottom to top. The perforated plate 6 and the small iron ball are grounded. The ionized dust passing through the charging section 2 passes through the perforated plate 6 and enters the moving dust collection layers 7 and 9. In the case of a conventional gas parallel type electrostatic precipitator, the gas flow passes between the dust collection plates as a parallel laminar flow, so the probability of collision with the dust collection plates is low. However, in the case of the present invention, since the gas passes through a narrow gap in the conductive material, there is a high probability that the gas will collide with the material. The dust collection function of the present invention is completely different from that of conventional dust collection. There are three dust collecting functions of the present invention. The ionized dust that has entered the moving dust collection layer moves through the gaps between the small iron balls and collides with the small iron balls. Because the gap is narrow, the probability of collision is high. (1) Separation of dust due to collision Dust collides with the iron ball and detaches from it, but sometimes it does not detach and remains attached to it. Since the gas flow becomes turbulent in the dust collection layer, there are many stagnation points where the flow velocity is particularly slow. The dust attached to the stagnation point remains attached. (2) Dust collection effect by Coulomb force Since the dust is ionized, it is attracted to the small iron ball of opposite polarity by Coulomb force. Conventionally, it was necessary to apply a high voltage to the dust collection layer to accelerate ions in order to improve the dust collection function. Conventional electrode plates were separated by 100 to 125 mm, so high voltage was essential. However, in the case of the present invention, the gap between the iron balls is significantly narrower. The width is 2 mm to 3 mm at most. It is about 1/50 of the conventional one. Therefore, the influence of Coulomb force is large, and ionized dust is attracted very effectively. Eliminates the need for anti-polarity accelerating electrodes and high voltage. (3) Overeffect due to packing This refers to the effect of the moving dust collection layer acting as a filter. Large-diameter foreign objects in the dust cannot pass through the moving dust collection layer that forms the packed bed, and remain in the dust collection layer. (1) and (3) are physical effects, and (2) is electrical effects. (2) is common to conventional precipitators, but is superior because it does not require an accelerating electrode. (1) and (2) are considered to be proportional to the effective surface area. In the present invention, the effective surface area of the dust collecting section is significantly larger than that of conventional dust collectors. Comparing the dust collection layer with the same volume, the dust collection layer of the present invention has approximately
Has 12 times more effective surface area. Conversely, this means that the dust collection section of the present invention can be made more compact. Even if the size of the dust collecting section is made smaller, the same dust collection efficiency as the conventional one can be achieved. The openings in the perforated plate 6 can have any shape and distribution as long as they allow gas to pass through but not small iron balls. It is convenient to make it an ellipse that is vertically elongated, as shown in FIG. Dust collects in the openings and blocks them, so you have to clean them from time to time. If the opening is long vertically, the iron ball will wipe the opening as it descends and is ejected. The opening is therefore automatically cleaned by the iron ball. The small iron balls move from top to bottom in the moving dust collection layer and take turns. The small iron balls that have collected dust and become dirty are subjected to vibrations by vibrators 10 and 11, and are moved to a small iron ball discharge device 12 and a small iron ball jamming prevention device 13.
and then reaches the vibrating sieve device 14. As the dust gradually moves through the vibrating sieving device 14, it is sieved off and removed to the outside by the dust conveyor 15. The cleaned iron balls enter the bucket conveyor 16 from the vibrating sieve device 14. The bucket conveyor 16 lifts up the iron balls and returns them to the iron ball feeder 8. The iron ball discharge device 12 has, for example, a rotating rotor structure. When subjected to slight vibrations by the vibrators 10 and 11, the iron ball is ready to be ejected whenever the ejection port is opened. However, since the space between the discharge device 12 and the wall is narrow, the small iron balls form a bridge and discharge is stopped. In this state, the iron ball discharge device 1
When the second rotor starts rotating, the bridge collapses and the small iron balls are ejected downward little by little. Instead of the vibrating sieve device 14, a suitable classifier can also be used. It is also possible to use a wind sorter, cyclone, etc. Although a single moving dust collection layer may be used, the dust collection efficiency is even higher when there are two layers. This is because two layers can suitably prevent re-scattering. Since dust accumulates in the moving dust collecting layer, it must be discharged together with the small iron balls out of the moving dust collecting layer by the above-mentioned mechanism. When the small iron balls are ejected, they collide with each other and rub against each other on the surface, and the dust that has adhered to it is scraped off and rises again. This dust is carried by the gas flow and re-dispersed. Since the small iron balls must be ejected, re-scattering itself cannot be prevented. However, if there are two moving dust collection layers and one of them is always in a stationary state, a significant drop in dust collection efficiency can be avoided. Give an example. Charged part length 1m Length of moving dust collection layer 0.2m x 2nd stage inlet dust amount 1.488g/m ³ When gas velocity is 1m/sec, 1st stage moving dust collection layer 7 is stationary, exit dust amount when in flowing state (g/m ³ ) and efficiency (%) were as follows. 1st stage moving dust collection layer (a) Stationary 0.023g/m ³ 98.47% (b) Movement (discharge) 0.101g/m ³ 93.18% , nearly 7% of the dust remains. However, the second stage moving dust collection layer 9 can absorb almost all of this dust. In fact, when the inlet dust amount of the second stage moving dust collection layer is 0.101g/m ³ , the outlet dust amount (g/m ³ ) and efficiency (%) are as follows: Second stage moving dust collection layer (a) Stationary 0.011g/m ³ 88.63% (b) Movement 0.017g/m ³ 83.34%. For the entire device, even in the worst case, the amount of dust at the inlet is 1.488g/ ^m3 , the amount of dust at the outlet is 0.017g/ ^m3 , and the efficiency is 98.86%. Therefore, while the first moving dust collecting layer is discharging small iron balls, the second moving dust collecting layer is made to stand still. Even if the dust is scattered again in the first stage, it will be collected in the second stage. When discharging small iron balls from the second stage moving dust collection layer, the first stage moving dust collection layer is kept stationary. The amount of dust at the exit of the first stage dust collection layer is small. Even when the dust is re-scattered in the second moving dust collection layer, the original amount of dust is very small, so there is no problem in practical use. In the embodiment, the first and second moving dust collection layers are operated according to the operation cycle diagram shown in FIG. In the figure, the shaded area indicates the moving time, and the blank area indicates the stationary time. It alternates between moving and stationary states every 20 minutes. Describe the effect. The dust-laden gas enters the charging section 2 of the electrostatic precipitator. Here, a part of the dust descends due to its own weight as the flow velocity decreases, and is discharged to the outside via the dust hopper 17, dust screw conveyor 18, and dust discharge rotary valve 19. The remaining dust is ionized by electric lift between the discharge wire 20 and the earth electrode 21. The ionized dust flows through the perforated openings 2 of the perforated plate 6.
6 and enters the moving dust collection layers 7 and 9. In the moving dust collection layers 7 and 9, the dust is attracted to, collides with, and adheres to the small iron balls under the three effects described above. The gas that has passed through the moving dust collection layer is sufficiently clean and is therefore discharged from the electrostatic precipitator. The small iron balls in the moving dust collection layers 7 and 9 alternately repeat being stationary and flowing. When moving and discharging, small iron ball discharging device 1
2, the small iron ball jamming prevention device 13, and the vibrator 10 or 11 rotate and vibrate. The dust is separated from the small iron balls by a vibrating sieve device 14 and discharged to the outside by a dust conveyor 15. The cleaned iron balls are lifted upward by the bucket conveyor 16 and returned to the iron ball feeder 8. From here, the small iron balls are again fed to the moving dust collection layers 7, 9. Describe the effects. In the present invention, a charging section and a dust collection section are separated, and the dust collection section is a moving dust collection layer filled with a conductive material. Since the gap between the conductive materials is extremely narrow, dust tends to collide with the conductive materials. Moreover, since it is ionized, it is attracted by Coulomb force. Since the Coulomb force is inversely proportional to the square of the distance, the inherent proximity of the dust and the conductive material has a truly significant effect. Therefore, the moving dust collection layer can be made significantly shorter than the conventional parallel electrode plate dust collection layer. The effect is great because the device can be made smaller. Table 1 shows a comparison of the dimensions of a conventional gas parallel type electrostatic precipitator and an electrostatic precipitator equipped with a moving dust collection layer according to the present invention. The comparison items are the width, height, length (length in the flow line direction of gas), and volume of the dust collection chamber. The amount of decrease is written on the right side. In particular, the length can be reduced and the volume can also be significantly reduced. In this way, it is a useful invention.

[Table] Conditions Processing gas amount = 57000Nm ³ /h Inlet dust amount = 2.5g/m ³ outlet dust amount = 0.05g/m ³ Efficiency = 98%

[Brief explanation of the drawing]

FIG. 1 is a longitudinal sectional view of an electrostatic precipitator according to an embodiment of the present invention. FIG. 2 is a cross-sectional view of the charging section and dust collection section. FIG. 3 is an enlarged side view of the charging section. FIG. 4 is an enlarged front view of the discharge line. FIG. 5 is an enlarged side view of the discharge line. FIG. 6 is a perspective view of the pole frame and perforated plate. Figure 7 is an enlarged view of the perforated plate. FIG. 8 is an operation cycle diagram of the first and second stage moving beds. DESCRIPTION OF SYMBOLS 1... Precipitator jacket, 2... Charge part, 4... Discharge electrode insulating glass, 5... Glass box, 6... Perforated plate, 7... Moving dust collection layer, 8... Small iron ball feeder, 9... Moving dust collection layer, 10... Vibrator, 11... Vibrator, 12... Small iron ball discharge device, 13... Small iron ball biting prevention device, 14
... Vibration sieving device, 15 ... Dust conveyor, 1
6... Bucket conveyor, 17... Dust hopper, 18... Dust screw conveyor, 19...
Dust discharge rotary valve, 20...Discharge wire, 21
...Earth pole, 24, 25...Pole frame.

Claims (1)

[Claims] 1 A charging chamber 2 in which a pole frame 25 on which a discharge wire 20 is stretched and a pole frame 24 on which a ground wire 21 is stretched in parallel in parallel to the gas flow direction is placed in a dust collection chamber made of a perforated plate. A conductive material is filled to form a front moving dust collection layer and a rear moving dust collection layer, and a storage tank is provided in the upper part of the dust collection layer, and a discharge passage is provided in the lower part, and the discharge port is opened above the classification device. An electrostatic precipitator equipped with a moving dust collection layer, characterized in that a conveyor is provided between the classification device and the storage tank to circulate the conductive material.