JPH01153504A - Method for initiating corona discharge reaction - Google Patents

Abstract

PURPOSE:To contrive an increase in formed concentration of ozone, etc., and power efficiency by applying a rectangular wave voltage in which at least one of leading and trailing edges satisfies specific conditions and simultaneously generating a sufficient electric field across electrodes to form corona discharge. CONSTITUTION:A plate electrode 24 is placed in the longitudinal direction of a flow passage 23 and a knife edge-like electrode 25 is provided opposite the plate electrode 24. Both electrodes 24 and 25 are connected with a high- voltage power source 26 including a pulse generating circuit. A rectangular wave voltage in which at least one of leading and trailing edges satisfies conditions of 1-0.125kV/ns and simultaneously generates a sufficient electric field to form corona discharge is applied across the electrodes for corona discharge. Thereby corona discharge is realized over a required length along the flow passage 23 and formed concentration of ozone, etc., and power efficiency can be increased.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method for generating a corona discharge reaction using a corona discharge, which has a very high energy conversion efficiency from electrical energy to chemical reaction energy.

[Prior Art] Some ozone generators that generate ozone from pure oxygen gas or oxygen-containing gas (for example, air) utilize silent discharge.

It is the 14th ozone generator that uses silent discharge.
There is one shown in the figure.

An outer pipe 2 is placed inside a grounded container l, and an inner pipe 3 is attached to the outer pipe 2.
is inserted with an appropriate gap, the gap 4 formed by the outer tube 2 and the inner tube 3 is made airtight, and the gap 4 is communicated with an inlet tube 5 for dry air or oxygen and an outlet tube 6. An electrode 7 which also serves as a cooling water supply pipe is inserted into the inner pipe 3.

Cooling water 9 is supplied to the container 1 from the cooling water port 8, and the container 1 is filled with the cooling water and discharged from the cooling water outlet 10 with the outer tube 2 immersed therein. Further, cooling water 9 is supplied into the inner tube 3 through the electrode 7, so that the electrode 7 is immersed in the cooling water 9, and is discharged through the discharge port 11. 12 indicates an AC high voltage source.

With a high AC voltage applied between the electrode 7 and the container I, air or the like 13 is introduced through the inlet pipe 5 and then passed through the gap 4 into the discharge pipe 6.
Make it flow more. Silent discharge occurs between the outer tube 2 and the inner tube 3, and the oxygen flowing through the gap 4 causes a chemical reaction to generate ozone.

[Problems to be Solved by the Invention] The silent discharge described above occurs in a pulsed manner due to the charge adsorption and release action of the dielectric material (in the above example, the outer tube and the inner tube) sandwiched between the electrodes. is used. Therefore, the pulse current waveform depends not only on the shape and size of the electrode and dielectric, but also on the
It varies greatly depending on the processing accuracy. Moreover, fundamentally the pulse current waveform is not actively controlled but is determined passively by the dielectric. Therefore, the first
In contrast to the voltage waveform shown in Figure 5 (E), the current waveform is extremely irregular as shown in Figure 15 (8), and conversion from electrical energy to chemical reaction energy through discharge energy is not performed efficiently, and almost no discharge energy is used. It is converted into thermal energy and generates a large amount of heat, the power efficiency for ozone generation is low at approximately 90 g'/kwh, and running costs are high, such as requiring a large amount of cooling water.

Furthermore, the processing accuracy and assembly accuracy are required to be on the order of 1 dust, making the device extremely expensive.

Therefore, some attempts are made to utilize corona discharge, which has a high relative energy conversion efficiency, for silent discharge.

Generally, corona discharge is generated by using at least one of the electrodes as a protrusion and applying an extremely short pulse voltage to the electrode side. In order to make the corona discharge strong and stable, the shorter the time width of the extremely short pulse, the better. ), and the pulse generation power supply for this purpose is extremely expensive.

In view of the above circumstances, the present invention aims to generate corona discharge at a lower cost.

[Means for Solving the Problems] The present invention provides a method for producing a corona discharge reaction in which corona discharge is caused in a reaction gas flow to produce ozone, etc. It is characterized in that at least one side satisfies the conditions of I KV/ns to 0.125 KV/ns, and a rectangular wave voltage is applied that generates an electric field sufficient to generate corona discharge.

[Function] In corona discharge, ozone etc. are generated by the rising and falling parts of the applied voltage, and the generation is controlled by the rising speed,
The higher the falling speed, the more efficient it is, I KV/ns ~ 0
．． Appropriate efficiency can be obtained by satisfying the condition of 125 KV/ns.

[Example] An embodiment of the present invention will be described below with reference to the drawings.

As a result of studying the mechanism of ozone generation by corona discharge, the present inventors found that ozone is generated not by the width of the ultrashort pulse but by the rise and fall speeds of the rectangular wave voltage. Ta.

That is, the causal relationship between the rising speed and falling speed of the rectangular wave voltage and ozone generation was investigated using the ozone generator shown in FIG.

In the figure, 14 is a high voltage DC power supply, 15 is an ozone reactor, and a resistor 16, 17 is connected in series and a resistor 18 is connected in parallel to the circuit connecting the high voltage DC power supply 14 and the reactor 15. A switch 19 is provided between the high voltage DC power supply 14 and a switch 20 between the resistor 18 and the resistor 18, respectively.

In the above circuit, switches 19 and 20 are turned 0N-o alternately.
pp, the voltage applied to the reactor 15 that generates corona discharge becomes a rectangular wave (in the following experiments, the frequency of this square wave is 50 Hz, and the width of the rectangular wave is from several FF1S to several tens of IO).
S level). Specifically, the switches 19 and 20 are low-crisp gap-type switches.

The waveform of the rectangular wave generated in the circuit shown in FIG.
As shown in Figure (E), the rectangular wave width is 20fflS. The ozone production concentration at this time was 4QOppm. Next, when the circuit in Figure 1 is removed from the resistor 17.18, the waveform has a slow rise speed as shown in Figure 2 (B), and the ozone concentration at this time was 200 ppm. . Furthermore, when the circuit shown in Fig. 1 is removed from the resistor 16.17, the waveform has a slow rise speed as shown in Fig. 2 (C), and the ozone production concentration at this time is 200 pp.
Furthermore, when the resistor 18.18 is removed from the circuit in Figure 1, the waveform is slow in both the rising speed and the falling speed, as shown in Figure 2 (CD). Almost no ozone formation was observed.

Therefore, it has been confirmed that ozone generation is caused by the rising speed and falling speed of the waveform, and it has also been found that ozone is not generated when a voltage is constantly applied. Further, the contribution of the rising portion and the falling portion to ozone generation is approximately the same.

Next, an experiment was conducted using the circuit shown in FIG. 3 to determine the causal relationship between the rising speed, falling speed, and ozone production rate (power efficiency) of the applied voltage.

Switches 19 and 20 are connected in series to the high voltage DC power supply 14, and the reactor 15 and the resistor 21 are connected in parallel,
The switches 19 and 20 are connected to the high voltage DC power supply 14 via a capacitor 22.

When switches 19 and 20 are alternately connected and disconnected, the applied voltage waveform shown in FIG. 4 is obtained. Here, the switches 19 and 20 are the rotary spark gear type switches described above.

In this circuit, the rising speed is determined by the performance of the switch 20, and the falling speed is determined by the time constant determined by the capacitor 22 and the resistor 21.

As mentioned above, the degree of contribution to ozone generation in the rising and falling parts of the applied voltage is the same, so in the following experiments, the rising was sufficiently slowed down and only the rising part was investigated. The results are shown in the table below.

As a result of the above experiment, the rise time is 50KV, 150ns to 50KV.
It can be seen that a rise of 50 KV/1.5 .mu.s or less is not suitable as a condition for ozone generation.

Although not specifically shown, the same data can be obtained even if the pulse width itself is changed, so it was found that the pulse width has little to do with ozone generation.

In addition, factors for ozone generation include rise and fall speeds, electric field strength, and gap length between electrodes.

As the voltage is increased, corona discharge shifts to arc discharge, but for ozone production, the electric field strength just before the shift to arc discharge is good for both ozone concentration and amount of ozone production.
Its limiting electric field strength is 15KV/cm when positive voltage is applied.
It is about 30 KV/effl when a negative voltage is applied.

The relationship between the electric field strength and the amount of ozone produced was determined at an applied voltage of 50 KV.
(50 Hz) constant and the corona discharge electrode gap varied. The results are shown in FIG. In FIG. 5, ozone production decreases with increasing gap length, ie decreasing electric field strength. Therefore, considering the economic effect, the electric field strength is 5
~30KV/cm is suitable.

Next, regarding the gap length, set the electric field strength to 8KV/c+I
The relationship between the gap length and the discharge current (Figure 6), the relationship between the gap length and the amount of ozone generated (Figure 7), and the relationship between the gap length and power efficiency (Figure 8) were investigated assuming that l was constant.

From FIGS. 6 to 8, when the electric field strength is constant, the longer the gap length, the better the amount of ozone produced and the power efficiency, and the appropriate gap length is about 1 to 20 cm.

Therefore, for ozone generation, the applied voltage is I KV/ns ~ 0
．． As the rising and falling conditions of 125 KV/ns, the electric field strength may be selected from 5 to 30 KV/co+s and the gap length between the electrodes from 1 to 20 cm depending on the scale of the device.

Hereinafter, preferred electrode shapes for carrying out the present invention will be described.

In order to generate ozone more effectively, it is preferable to increase the chances of contact between oxygen and corona discharge.

In the case shown in FIG. 9, a flat plate electrode 24 is disposed along the longitudinal direction of the flow path 23, a knife-shaped electrode 25 is provided facing the flat plate electrode 24, and the picture electrodes 24 and 25 are connected to a pulse generating circuit. This electrode is connected to a high-voltage power source 26 containing the channel 23, and a corona discharge can be realized along the flow path 23 over a required length.

In the case shown in FIG. 10, both of the electrodes facing each other are knife-shaped, so that corona discharge is more likely to occur than in the case shown in FIG.

Further, in the case shown in FIG. 11, a net-like electrode 27 is arranged to block the flow path 23, and an electrode 28 with a sharp tip is provided between the image-like electrodes 27 and 27. It is connected to a high voltage power supply 26.

A corona discharge is generated between the electrodes 27 and 28, spreading like a skirt from the electrodes 28 to 27, and reactive gas such as oxygen passes through the corona discharge.

In the system shown in FIG. 12, a channel 23 (which has a rectangular cross section in the figure) is divided into small channels 30 by a partition wall 29, and each small channel 30 has a cross-shaped cross section. An electrode 31 extending along the channel is arranged, and this electrode 31 and the channel wall 32 and the partition wall 2
9 are connected to the high voltage power supply 26.

In this embodiment, a corona discharge is generated from the tip 4 of the electrode 31 toward the joint wall of the small channel 30.

In the case shown in FIG. 13, linear electrodes 33, 34, 35 are arranged concentrically with respect to the channel 23, and the channel wall 32 and the electrode 3 are arranged concentrically with respect to the channel 23.
4 to one pole of the high voltage power supply 26, and the electrode 33°35
Connect the power source to the other wall. Thus, corona discharge is caused between the channel wall 32 and the electrode 33, between the electrodes 33 and 34, and between the electrodes 34 and 35, respectively.

All of the above electrode shapes are intended to cause corona discharge over a wide range inside the flow path.

In addition to ozone, reactants generated by corona discharge include ultrafine diamond particles, silane (SiH4) and methane (C) using a mixed gas of methane (CHa) and hydrogen (H2).
silicon carbide (S i C) with a mixed gas of
Examples include the generation of ultrafine particles.

[Effects of the Invention] As described above, the present invention exhibits an excellent effect in that the concentration of biozone and the like produced and the power efficiency can be dramatically increased compared to conventional methods.

[Brief explanation of the drawing]

Figure 1 is a circuit diagram for investigating the causal relationship between the rise and fall of applied voltage and ozone production, and Figure 2 (A) (B) (C
) (D) is an applied voltage waveform diagram obtained by the circuit or a circuit applying the circuit, Figure 3 is a circuit diagram for investigating the causal relationship between the rise speed and ozone generation, and Figure 4 is the applied voltage by the circuit. Figure 5 is a diagram showing the relationship between the gap length and the amount of ozone produced; Figure 6 is a diagram showing the relationship between the gap length and discharge current when the electric field strength is constant;
Figure 7 is a diagram showing the relationship between the gap length and the amount of ozone produced when the electric field strength is constant, Figure 8 is a diagram showing the relationship between the gap length and power efficiency when the electric field strength is constant, and Figure 8 is a diagram showing the relationship between the gap length and power efficiency when the electric field strength is constant. Figures 9 to 13 are explanatory diagrams showing electrode shapes for effective corona discharge in the flow path, Figure 14 is an explanatory diagram of a conventional ozone generator, and Figure 15 (A) ( B)
FIG. 2 is a diagram showing applied voltage waveforms and current waveforms in the generator. 14 is a high voltage DC power supply, 15 is an ozone reactor, 23 is a flow path, 24.25 is an electrode, 26 is a high voltage power supply, 27°28
．． 33, 34, and 35 indicate electrodes.

Claims (1)

[Claims] 1) In a method of generating a corona discharge reaction in which ozone, etc. is generated by causing a corona discharge in a reaction gas flow, at least one of the rising and falling points between the electrodes causing the corona discharge is 1K.
A method for generating a corona discharge reaction characterized by applying a rectangular wave voltage that satisfies the conditions of V/ns to 0.125 KV/ns and generates an electric field sufficient to generate a corona discharge.