JP4355789B2 - Discharge generator - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a discharge generator used to easily and efficiently decompose harmful substances contained in exhaust gas and waste water.
[0002]
[Prior art]
In order to decompose exhaust gases emitted from thermal power plants, factories, diesel vehicles, etc., various harmful substances contained in waste water, or kill microorganisms, a dry decomposition method using discharge has been put into practical use. . In order to efficiently decompose harmful substances by electric discharge, it is important to create a so-called non-equilibrium plasma state in which only the electron temperature is high and the molecular temperature is low. Since it is difficult to constantly maintain a non-equilibrium plasma state, a method of repeatedly applying a high voltage pulse that causes an abrupt electric field change in the nanosecond region has been studied, and its effectiveness has already been recognized.
[0003]
In the case of a conventional pulse voltage generator, one high voltage pulse is applied to the discharge electrode by taking out the energy accumulated in the device within a short time by one switching operation. Therefore, in order to increase the discharge generation period, it is essential to improve the switching frequency. In order to improve the switching frequency, a method of repeating an on / off operation at a high speed by rotating a switch connected to a motor at a high speed has been often used. Recently, a method of dramatically increasing the switching frequency by applying a high-voltage semiconductor switch using a high-speed thyristor element has been developed and has been put to practical use (for example, see Non-Patent Document 1).
[0004]
[Non-Patent Document 1]
Yasui, “Exhaust gas treatment technology by pulse corona discharge”, The Institute of Electrical Engineers of Japan, Vol. 119-A, no. 5, pp. 274-277 (1999)
[0005]
[Problems to be solved by the invention]
Although the switching frequency is increased by using the semiconductor switch, since the maintenance and management at the site where the apparatus is used becomes difficult, the versatility of the apparatus becomes poor . The problem to be solved by the present inventor is that it is possible to generate a pulse voltage with a simple structure, generate a strong discharge, and generate a discharge that is easy to maintain and versatile. Is to develop equipment.
[0006]
[Means for Solving the Problems]
In order to solve the above-mentioned problems, the present invention provides a discharge generator configured as described in (1) to (4) below.
(1) A discharge generator that generates pulse discharge using the principle that when two conductors constituting a line are short-circuited on one side of a charged transmission line, the direction of the electric field between the conductors on the other side is reversed. .
(2) A discharge generator characterized in that a coaxial cable is used for the transmission line according to (1).
(3) The discharge generator according to (1) or (2), wherein the impedance of the short circuit portion is smaller than the characteristic impedance of the transmission line.
(4) A discharge electrode is connected to the other end (non-short-circuited side ) of the transmission line, and the chemical reaction or shape of the substance present in the space where the discharge spreads due to the discharge that develops from the discharge electrode The discharge generator according to any one of (1) to (3), which is used for the purpose of promoting change.
(5) A discharge electrode is connected to the other end of the transmission line (the side that is not the short-circuited portion), and for the purpose of killing microorganisms existing in the region where the discharge spreads by the discharge that develops from the discharge electrode The discharge generator according to any one of (1) to (3), which is used.
[0007]
DETAILED DESCRIPTION OF THE INVENTION
An embodiment according to the present invention will be described in detail with reference to the drawings. FIG. 1 shows the configuration of a pulse discharge generator , and also shows the configuration of an optical system for examining the repetition state of discharge. In FIG. 1, as one embodiment of the discharge generator, a transmission line 111, a short-circuit switch 112, a DC power supply 113, a high resistance 114 (50 MΩ), a discharge electrode 115, a short-circuit prevention insulating plate 116, a glass discharge tube 117. A voltage waveform observation probe 118 was used. The discharge observation optical system 121 shown in FIG. 1 is arranged to confirm the effectiveness of the discharge generator according to the present invention. Therefore, the types of these optical systems, their relative arrangement, etc. are not indispensable constituent requirements in the present invention.
[0008]
The transmission line 111 is charged by the DC power supply 113, and the voltage between the conductors of the line rises. From this state, the pulse voltage waveform measured by the voltage probe 118 immediately after the shorting switch 112 is turned on is shown in FIG. The charging voltage at this time was -20 kV. A short circuit was made at time 0 nanoseconds in the graph of FIG. 2, and then the first reversal of the open-circuit voltage occurred 170 nanoseconds thereafter, and the reversal was repeated at a period of 350 nanoseconds. The rise time at the first inversion was 20 nanoseconds. In addition, although the rise time tends to be delayed with the increase in the number of repetitions, it has been found that a pulse voltage having sufficient speed to cause non-equilibrium plasma is repeatedly applied.
[0009]
In this embodiment, a coaxial cable (maximum outer diameter 22 mm, length 35 m) having a characteristic impedance of 52 Ω is used as the transmission line, but a strip line made of a parallel plate can also be used.
[0010]
The short-circuit switch 112 in this embodiment is mainly composed of a cylindrical metal container and a sphere-to-sphere gap housed therein. The distance between the gaps was variable, and after charging, the distance between the gaps was shortened to cause a spark discharge to cause a short circuit. As a power source for charging, a DC power source may be used as in the present embodiment, but not limited to this, for example, a sine wave AC power source may be used. When applying an AC voltage, adjust the distance between the gaps and the time constant of the charging circuit so that a short circuit occurs at each phase where the sine wave voltage reaches near the maximum value of both positive and negative values. Switching was performed with a period equal to the frequency of. An exhaust valve 120 is mounted in the metal container so that the atmosphere inside the metal container can be adjusted, and stable switching characteristics can be obtained by sealing a gas such as dry air or sulfur hexafluoride. It was. In addition, as a method of short-circuiting the charged transmission line, a method of repeating charging and short-circuiting while an electrode attached to the rotating machine repeats circular motion is also possible.
[0011]
The discharge electrode 115 connected to the central conductor of the coaxial cable preferably has a projection like a needle electrode, and a comb electrode, a sword electrode, a line electrode, a saw electrode, or the like can also be used. The streamer discharge extending from the needle electrode extends toward the lower electrode opposite to the needle electrode. At this time, if there is a flash between the electrodes, no positive reflection occurs. Has been inserted. Further, in this embodiment, a potential adjustment switch 119 is attached to the lower electrode side. By switching the switch, the potential of the lower electrode can be made equal to either the ground potential or the output voltage of the DC power supply 113. When the lower electrode is grounded, the time change of the interelectrode voltage becomes equal to the waveform of FIG. 2, so that positive and negative pulse voltages are alternately applied. The advantage of grounding the lower voltage is that the corona discharge caused by the DC electric field formed between the electrodes during charging charges the dust, harmful gas or microorganisms in the gas, and the insulating plate by the electrostatic force acting on them. It is a point that can be captured on. At the moment when the voltage is reversed, these ionic substances act as so-called hetero space charges, and thus act to increase the electric field strength in the discharge space. Due to this space charge effect, it is possible to obtain a stronger discharge than when a single pulse voltage having the same peak value is applied. In addition, since the discharge that has reached the surface of the insulating plate progresses along the region where the ionized harmful substance is deposited, it also has an effect that the harmful substance captured during charging is efficiently exposed to the discharge. On the other hand, if the potential of the lower electrode is made equal to the charging voltage, the potential difference between the needle electrode and the lower electrode during cable charging is eliminated, but the peak value of the voltage pulse applied between the electrodes immediately after the short circuit is the charging voltage. In this case, too, a strong discharge can be obtained.
[0012]
In this example, a polytetrafluoroethylene plate was used as the insulating plate. However, it is known that it is preferable to use an inorganic insulating material with little insulation deterioration in order to extend the life of the device. A molded product made of a metal oxide such as titanium may be used. Further, a substance having a photocatalytic effect such as platinum may be supported on these insulating plates.
[0013]
FIG. 3 is a result of observing an initial emission image of discharge in air using the optical system shown in FIG. When the voltage is reversed from -15 kV to 15 kV, the discharge extending between the electrodes of 3 cm is photographed for 50 nanoseconds from the start of the reversal, as shown in FIG. 3A, with the tip of the needle electrode approaching the insulating plate. When the voltage is reversed from -15 kV to 15 kV, the surface discharge spreading on the insulating plate is photographed for 30 nanoseconds from the start of the reversal, as shown in FIG. In either case, the discharge extends over a wide range in a few tens of nanoseconds.
[0014]
When the switch is short-circuited under the state of being charged at −20 kV, the result of observing the repeated light emission of the discharge extending through the space having a gap length of 3 cm with a photomultiplier tube is shown in FIG. FIG. 4B shows the result of observation of repeated light emission of creeping discharge spreading from the tip of the needle electrode on the insulating plate with a photomultiplier tube when the switch is short-circuited in a state charged at 25 kV. In each graph, light emission occurs when the optical signal waveform shows a negative voltage. As can be seen in FIG. 4B, it was confirmed that the discharge repeatedly occurred in one switching. The light emission period is 350 nanoseconds, which is equal to the time required for the traveling wave to reciprocate in the coaxial cable. This result proves that the potential of the discharge electrode is reversed every time the traveling wave reciprocates because negative reflection occurs in the short-circuit portion and positive reflection occurs on the discharge electrode side. . In order to increase the number of repetitions, the ratio of the energy consumed by one discharge to the charging energy may be reduced. Specifically, measures such as increasing the cable length, arranging the cables in parallel, and increasing the charging voltage can be taken.
[0015]
【The invention's effect】
As described above, according to the present invention, it is possible to generate a strong discharge by increasing the electric field strength in the discharge space between the electrodes from the electric field strength due to the charging voltage .
[Brief description of the drawings]
FIG. 1 is a configuration diagram showing a discharge generator.
FIG. 2 is a graph showing that positive and negative pulse voltages are alternately applied by one switching.
FIG. 3 is a photograph showing that streamer discharge extends from the discharge electrode.
FIG. 4 is a graph of an optical signal indicating that discharge is repeatedly generated.
[Explanation of symbols]
111 Transmission Line 112 Short-Circuit Switch 113 DC Power Supply 114 Resistor 115 Discharge Electrode 116 Insulating Plate 117 Discharge Tube 118 Voltage Probe 119 Potential Adjustment Switch 120 Exhaust Valve 121 Discharge Observation Optical System

Claims (2)

Transmission line, DC power source for charging the transmission line, short-circuit switch for short-circuiting two conductors constituting the transmission line on one side, discharge electrode connected to each conductor on the other side, and this And an insulating material connected between the conductors on the other end side, the conductors are short-circuited on one side by a short-circuit switch, and the direction of the electric field between the conductors on the other side is reversed . A discharge generator that generates pulse discharge by making the electric field strength of the discharge space from the electrode to the opposite electrode stronger than the electric field strength by the charging voltage. The discharge generator according to claim 1, wherein a coaxial cable is used for the transmission line, and an insulating material is inserted between the electrode for electric discharge and the electrode facing the electrode .

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