JPS6146178B2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention is capable of quickly and effectively treating solid particles, particularly solid particles with extremely high electrical resistance, such as fly ash and plastic powder produced by the combustion of low-sulfur coal, without being affected by the interfering effects of reverse corona. The present invention relates to a novel particle charging device for applying a charge to enable effective electrostatic treatment and dust collection of particles.

To provide electric charge to solid particles industrially, usually a corona discharge needle-like or linear electrode 1 as shown in FIG. Generally, a method is used in which a DC corona discharge 4 is performed using a charging device, and the collision and adhesion of ions 5 generated by this corona discharge to solid particles 6 in a corona space 8 is utilized. Case (1) The charged particles 7 are driven by the Coulomb force in the direction from the corona discharge electrode 1 toward the counter electrode 2, and particles with a large amount of charge adhere to the counter electrode 9 and reach the target work area 1.
(2) The counter electrode 9 is covered with a fine particle layer with high electrical resistance, and charges are accumulated by the ions flying onto it. However, the electric potential on the fine particle layer rises, causing dielectric breakdown, and ions of opposite polarity are released from this into the charged space 8, causing a so-called reverse corona phenomenon that neutralizes and reduces the electric charge of the fine particles, resulting in a large amount of damage. There were major drawbacks such as a decrease in charging performance.

In order to overcome this first drawback, the present inventor developed another invention, "Particle Charging Device" (Patent Application No. 50087, 1972).
For example, as shown in FIG. 2, alternating electrodes 11 and 12 are provided which are insulated from each other and arranged parallel to each other with a certain distance apart, and small holes or slits 13 and 14 are provided in each of the alternating electrodes. Insulated from the alternating electrode, a third electrode 1 for discharge is placed in the center of each electrode.
5 and 16 are provided, and an alternating main voltage is applied between the alternating electrodes 11 and 12, for example, via the secondary winding terminals 18 and 19 of the transformer 17, to form an alternating main electric field in the charged space 20 between the two electrodes. , and further the third electrode for discharge 1
For example, as shown in the figure, rectifiers 21 and 2 are connected to 5 and 16.
2, coupled with resistors 23, 24 and capacitors 25, 26, and secondary winding terminals 27, 28 of the transformer 17;
By supplying a pulsating current voltage having the same polarity and the same frequency as the alternating main voltage through the alternating current main voltage, in the example shown in the figure, when the alternating electrode 11 reaches a sufficiently high voltage of negative polarity, the voltage between the alternating electrode 11 and the third electrode 15 increases. Then, a spark discharge is repeatedly generated (at this time, no discharge is generated between 12 and 16 due to the action of the rectifier 22), and the generated negative ions are released into the charged space 20 from the left to the right. The solid particles are charged by impact, and then when the polarity of the main voltage is reversed and the electrode 12 reaches a sufficiently high voltage of negative polarity, the above operation is reversed and the negative ions are introduced into the charged space 20 from the right to the left. When the particles are emitted in the same direction, the fine particles are charged with an impact charge, thus constantly giving the particles a strong negative charge in this example, and alternating the Coulomb force acting on the particles to prevent the particles from adhering to the electrode. proposed a method.

However, the present invention provides alternating electrodes 11, 1 of fine particles.
Although the loss due to adhesion to 2 can be significantly reduced, it is impossible to completely prevent it, and as time passes, the surfaces of 11 and 12 will eventually become covered with a layer of high-resistance fine particles, and the opposing discharge third It was not possible to prevent the above-mentioned reverse corona damage from occurring due to the accumulation of ions flying from the electrodes.

Similarly, for the purpose of preventing adhesion loss of particles, the inventor of the present invention used corona electrodes as the third discharge electrodes 15 and 16 in another invention, "High Performance Particle Charging Device" (Japanese Unexamined Patent Publication No. 50-52673). gaps 13, 14 between this and the alternating electrodes 11, 12
is increased, and when the respective alternating electrodes 11 and 12 alternately reach a sufficiently high voltage of negative polarity of the alternating main voltage, a voltage of the same frequency with the latter being negative is applied between these and the third electrode for corona discharge. A pulsating current voltage is applied in synchronization with the alternating voltage, and a corona discharge, in this case a negative corona discharge, is generated alternately from the third electrode for corona discharge, and the resulting negative ions are released and supplied into the charged space 20. proposed a method of charging particles by making them bounce back and forth from side to side.

However, in this case as well, it was unavoidable that particles with high electrical resistance adhered to the surfaces of the alternating electrodes 11 and 12, and the occurrence of the reverse corona phenomenon was unavoidable.

The object of the present invention is to fundamentally improve all of the above-mentioned drawbacks and to provide an extremely high-performance particle charging device that can effectively impart a charge to fine particles having extremely high electrical resistance.

The present invention aims to (1) reduce the adhesion loss of charged fine particles to the electrode by increasing the frequency of the alternating main electric field by at least 50%;
(2) In addition to the condition (1), the generation of reverse corona can be significantly suppressed by raising the electric field to a temperature higher than Hertz. By using a planar plasma ion source for ion supply, the charge accumulated on the electrode-attached fine particle layer is effectively neutralized and eliminated by ions of different polarity from the plasma ion source.

Regarding (1), since the vibration amplitude of charged particles decreases as the frequency increases in an alternating electric field, it is necessary to increase the frequency of the alternating main electric field in order to prevent particles from colliding and adhering to the electrode. 50
This is based on experimental results that show that the effect only appears when the temperature is selected to be above Hertz. Regarding (2), there are two conditions for preventing reverse corona: first, the temporal increase in the particle layer surface potential on the corona discharge electrode during the half cycle of plasma generation and pause, before reaching its dielectric breakdown value, It is necessary to reverse the polarity of the voltage and stop the ions from flying in, and for this purpose, it is impossible if the period of the alternating main voltage is too long, and in practice it is necessary to satisfy the condition (1).Secondly, During operation of the ion source, it is necessary to form a plasma containing abundant positive and negative ions, and for this purpose, an alternating voltage (its frequency must be at least twice that of the alternating mains voltage)
It is essential to generate an alternating current corona discharge, and only then can a plasma ion source containing abundant positive and negative ions be formed, effectively neutralizing and eliminating the accumulated surface charge, and completely preventing reverse corona. This is based on the experimental results.

In other words, the particle charging device according to the present invention includes a plurality of corona discharge electrodes for performing high-frequency corona discharge parallel to and close to each other on both sides of a pair of parallel surfaces sandwiching a charging space for charging fine particles. are arranged adjacently and insulated from each other to form a pair of planar plasma generating sections, and the pair of planar plasma generating sections are mutually insulated and supported, and one of the corona discharge electrodes belonging to each It has an output frequency of at least 50 Hz to apply an alternating main voltage between the pair of planar plasma generating parts by connecting them as one, and to form an alternating main electric field in the charged space sandwiched between them. Only when an alternating current main power source is provided, and these plasma generating parts alternately assume a specific polarity of the alternating main voltage, the frequency of the alternating main voltage is changed between adjacent corona discharge electrodes belonging to it. The present invention is characterized in that a separate high-frequency AC power source is provided for applying a high-frequency voltage having a frequency at least twice or more to generate a high-frequency corona discharge between the corona discharge electrodes.

In this case, the output frequency of the AC main power source must be selected to be at least 50 Hz as described above, but in order to more fully demonstrate the effect of preventing fine particles from adhering to the electrodes, it is necessary to select a frequency of 100 to 500 Hz. It is desirable to select between As mentioned above, the output frequency of the high-frequency AC power supply must be selected to be at least twice that of the AC main power supply, but in order to achieve the highest ion supply capacity and reverse corona prevention effect, it is necessary to select a frequency of 1 kHz. It is desirable to select a range of 10 kilohertz or higher.

The shape of the corona discharge electrode can be round wire, square wire, strip, barbed strip, barbed rod, etc.
Any suitable shape can be used, but a square edge shape or a knife edge shape with sharp edges facing each other so that both adjacent discharge electrodes face each other and generate an alternating current corona discharge are always preferred. It is necessary to have a corona discharge generation edge such as a shape, or a corona discharge generation protrusion row that is sharp toward the other side. Therefore, among the plurality of corona discharge electrode arrays, the edges on both sides of the electrodes other than the outermost two must each have a shape capable of generating corona discharge as described above. However, it is necessary for the outermost two wires to have a structure in which there is no corona discharge generating portion on their respective outward edges. The reason for this is that a large concentration of the main electric field occurs at these edges, so if these have sharp corona-generating parts, even during the half-cycle of the alternating main voltage when no high-frequency alternating voltage is applied to the electrode array. This is because a corona discharge occurs due to the concentration of the main electric field, and ions of different polarity are released into the charged space, resulting in a significant decrease in charging efficiency.

As a result of the above-mentioned features, the particle charging device according to the present invention has the following advantages: (1) The loss of fine particles adhering to the corona discharge electrode is greatly suppressed, and almost all the particles are discharged into the working area after being charged, reducing the loss. disappears,
(2) Even if particles with extremely high electrical resistance adhere to the surface of the corona discharge electrode in a layered manner, a large amount of positive and negative ions will be induced between adjacent corona discharge electrodes every half cycle of the alternating main voltage. Since ions of different polarity from the plasma generated by the high-frequency corona discharge containing the particles effectively neutralize and eliminate the charges accumulated on the particle layer, the generation of reverse corona is completely prevented, which is an excellent effect.

The structure and features of the particle charging device according to the present invention will be explained in more detail below with reference to examples and drawings.

FIG. 3 is a block diagram of an embodiment of the present invention. In the figure, reference numerals 29 and 30 are a pair of parallel planar plasma generating sections that are insulated and parallel to each other and facing each other with the charging space 20 in between. Two sets of strip-shaped corona discharge electrodes 31, 32, 33 and 34, 3 are insulated and arranged close to each other, parallel to each other and at equal intervals.
5, 36, 37, 38 and 39, 40. Among these, 31, 32, 33 are connected to a common conductor 41, an AC power supply 43 with a frequency of 10 kHz that operates intermittently through a protective resistor 42, and a step-up/insulation transformer 4.
One high-frequency high-voltage power supply for corona generation consisting of 4
5 is connected to one output terminal 46 of 5. Also 3
4 and 35 are connected to the other output terminal 49 of the power source 45 via a common conducting wire 47 and a protective resistor 48. Next, 36, 37, and 38 are connected to a common conductor 50, an AC power supply 52 with a frequency of 10 kHz, which operates intermittently through a protective resistor 51, and a step-up/isolation transformer 53.
It is connected to one output terminal 55 of the other high-frequency, high-voltage power source 54 for generating corona. Further, 39 and 40 are connected to the other output terminal 58 of the power source 54 via a common conducting wire 56 and a protective resistor 57. These strip-shaped corona discharge electrodes are sharp on both sides and form a corona generation part, but the electrodes 31, 33 and 36, 3 at the extreme end
Cylindrical non-corona electrodes 59, 60, 61, and 62 are added to the outside of 8 and in contact with these.
Reference numeral 63 is an AC high-voltage power source for forming a main electric field with a frequency of 500 Hz for forming an alternating main electric field in the charged space 20 between the pair of planar plasma generating parts 29 and 30, which is connected to an AC power source 64 and a step-up transformer 65. The output terminals 66 and 67 are connected to the terminals 42 and 51, respectively. As a result, an alternating main voltage is applied between the planar plasma generating parts 29 and 30, and an alternating main electric field alternating at a frequency of 500 hertz is formed in the charging space 20. Furthermore, now output terminal 6
Only when the signals 6 and 67 alternately assume a specific polarity, in this example negative polarity, the signal is alternately transmitted to the conductors 68 and 6.
9 to the alternating current power supplies 43 and 52, and each alternating current power supply 43 and 52 operates alternately during a half cycle of the main voltage to generate an alternating voltage with a frequency of 10 kilohertz. Therefore, in the half period in which the planar plasma generating section 29 has a negative polarity with respect to the polarity 30, two adjacent sets of strip-shaped corona discharge electrodes 31, 32, 33 and 3 constituting the plasma generating section 29
Between 4 and 35, the AC high voltage power supply 45 for generating the corona
A high frequency alternating current high voltage with a frequency of 10 kilohertz is applied from to form.
During the period of this main voltage half cycle, the main electric field in the space 20 is in the direction from right to left, so only negative ions are drawn out from the plasma to the right, and the charged space 20 moves to the right. The particles 71 introduced into the plasma generator 20 from above collide with them from the left and are absorbed by the discharge electrode group 36-40 of the plasma generator 30 which is in a resting state. be charged. During this half cycle, the AC power supply 52
Since no operating signal is applied to the AC power source 52 through the conductor 69, the AC power source 52, and thus the corona generation AC high voltage power source 54, are inactive, and the planar plasma generating section 30, which is in the positive polarity, is not operated. No high-frequency AC high voltage was applied between the adjacent strip-shaped corona discharge electrodes 36, 37, 38 and 39, 40, and no high-frequency corona discharge occurred between the two sets of discharge electrodes. Therefore, no plasma is generated in the planar plasma generating section 30. As a result, positive polarity ions are emitted from here into the charged space 20 and do not neutralize and reduce the negative charges imparted to the fine particles 71.

Next, the polarity of the main voltage is reversed, and in the half cycle when 29 becomes positive and 30 becomes negative polarity, the above operation is also completely reversed, and this time only the planar plasma generating part 30 with negative polarity is activated. Although a planar plasma 72 is formed and negative ions are emitted leftward into the charged space, the planar plasma generating section 29 suspends the plasma forming operation during this half cycle. Thus, the electric field within the charged space 20 alternates from side to side at a frequency of 500 hertz;
Among them, unipolar ions, in this example only negative polarity ions, always reciprocate from side to side and bombard the fine particles 6 alternately from both sides, rapidly charging them to a theoretically determined saturation charge amount. The sufficiently electrically charged particles 7 fall downward while vibrating at a frequency of 500 hertz and therefore with an extremely small amplitude, and are discharged and supplied to the working area 10 below without colliding with or adhering to the electrodes. In this case, both planar plasma generating parts 2
Over time, fine particles are deposited little by little on the surface of each discharge electrode constituting the discharge electrodes 9 and 30, forming a particle layer.
If the electrical resistance is extremely high, negative ions accumulate on the surface of the particle layer on the discharge electrode of the planar plasma generating section during the rest period, raising the surface potential.
However, since the frequency of the main voltage is sufficiently high at 500 Hz and its period is sufficiently short, the polarity of the main voltage is reversed before the particle layer causes dielectric breakdown, and in the next half cycle, the electrode group generates a high-frequency corona discharge. Since the surface negative charges are completely neutralized by the abundant positive ions supplied from here, no reverse corona is generated, and positive polar ions are released from this to neutralize and reduce the particle charges. There's nothing wrong. Therefore, no matter how high the electrical resistance of the particles is, an extremely high charge is always effectively imparted to them.

The corona discharge electrode used in the present invention is not only a strip-shaped electrode as shown in FIG. 3 or 4a, but also a corona discharge electrode that performs corona discharge at regular intervals on both edges of the strip-shaped electrode as shown in FIG. 4b. A type with a large number of protrusions 73, or a type with both sides covered with an insulating layer 74 so that only the tips of the protrusions 73 are exposed laterally, as shown in FIG.
Any suitable material can be used, such as a rod-like conductor 75 with needle-like corona discharge portions 76 provided at regular intervals on both sides of the rod-like conductor 75, as shown in FIG. 4d.
Further, as the waveform of the main voltage used in the present invention, a sine wave or any other appropriate waveform can be used, but a rectangular wave is particularly preferred since it can improve the charging speed.

An example of the measured value of the particle charge amount by the particle charging device of the present invention is as follows: a value close to the theoretical saturation value was obtained within an extremely short time, demonstrating the excellent charging performance of the present invention. Proven.

Particle diameter 2a = 26 microns Theoretical saturation charge Qmax=0.0124 picocoulomb Actual average charge Q = 0.0120 picocoulomb (Q/Qmax)x100=99% Charging time T = 50 milliseconds

[Brief explanation of the drawing]

Fig. 1 is a block diagram of a conventional particle charging device that uses DC corona discharge, Fig. 2 is a block diagram of a particle charging device that combines an alternating main electric field and spark discharge, which the inventor has already proposed, and Fig. 3 4 is a block diagram of one embodiment of the particle charging device according to the present invention, and FIG. 4 is a diagram showing several configuration examples of corona discharge electrodes constituting a planar plasma generating section. In the figure, 1...acicular corona discharge electrode, 2...
Counter electrode, 3...DC high voltage power supply, 6...Particles,
11, 12... Alternating electrode, 13, 14... Small hole,
15, 16...Spark discharge electrode, 17...Transformer, 2
0... Charge space, 29, 30... Planar plasma generation section, 31-40... Strip-shaped corona discharge electrode, 45, 54... High frequency AC high voltage power supply for plasma generation, 59-62... Cylindrical non-corona electrode, 6
4...AC high voltage main power supply for forming an alternating main electric field, 70,
72...Planar plasma, 73...Protrusion, 74...
...Insulating layer, 75... Rod-shaped conductor, 76... Needle-shaped corona discharge part.

Claims (1)

[Claims] 1. On both sides of a pair of parallel planes sandwiching a charging space for charging microparticles, a plurality of corona discharge electrodes for performing high-frequency corona discharge parallel to each other and close to each other are installed and insulated from each other. A pair of planar plasma generating sections are arranged, and the pair of planar plasma generating sections are supported insulated from each other and connected to any one of the corona discharge electrodes belonging to each. An AC main power source with an output frequency of at least 50 hertz or more is provided to apply an alternating main voltage between the planar plasma generation parts and form an alternating main electric field in the charged space sandwiched between the two. Only when the plasma generating parts alternately assume a specific polarity of the alternating main voltage, the corona discharge electrodes belonging thereto have a frequency that is at least twice the frequency of the alternating main voltage between adjacent ones. A separate high-frequency AC power source whose output frequency is at least twice the output frequency of the AC main power source is provided for applying a high-frequency voltage to generate a high-frequency corona discharge between the corona discharge electrodes. Particle charging device.