JP3982044B2 - Ozone generation method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an ozone generation method in a pulse streamer corona discharge type ozone generator used for sterilization, oxidation, decolorization, deodorization and the like of a substance such as a liquid, and more specifically, a transient glow following a streamer discharge. The present invention relates to a method for suppressing discharge and increasing ozone generation efficiency.
[0002]
[Prior art]
In the pulse streamer corona discharge type ozone generator, a source gas containing oxygen is introduced into an ozone generator equipped with opposed electrodes that can generate a significantly unequal electric field, and a high-voltage pulse that rises rapidly between the opposed electrodes. By applying a voltage, streamer discharge (specifically, streamer corona discharge; the same applies hereinafter) is generated in the source gas containing oxygen, and ozone is generated from oxygen atom radicals generated in the discharge plasma by this streamer discharge. The
[0003]
An example of such an ozone generator is shown in FIG. This ozone generator has a coaxial cylindrical discharge tubular ozone generator 2 in which a wire electrode 6 is arranged on the central axis of the cylindrical electrode 4, and a raw material gas containing oxygen from one end side of the ozone generator 2. 14 is supplied from the source gas source 12 and a pulse voltage V _P is applied from the pulse power source 18 between the inner and outer electrodes 4, 6. Thereby, the streamer discharge 10 advances from the wire electrode 6 toward the cylindrical electrode 4 to generate discharge plasma, thereby generating ozone, and the ozone-containing gas 16 is taken out from the other end side of the ozone generator 2.
[0004]
An example of an ozone generator based on the same principle is disclosed in Japanese Patent Publication No. 3-64443.
[0005]
In this type of ozone generator, generally, the higher the converted electric field strength E / N (E is the electric field and N is the gas particle density) in the discharge plasma, the more suitable for ozone generation. When a pulse voltage V _P rising at a high speed is applied, a strong streamer discharge is formed between the electrodes 4 and 6. In the streamer discharge, the space charge density is unevenly distributed, and an extremely strong converted electric field is locally formed by the space electric field due to the space charge, which propagates between the electrodes 4 and 6. The feature of the pulse streamer corona discharge type ozone generator is that ozone can be generated with high efficiency by using the streamer discharge having a remarkably strong converted electric field strength.
[0006]
[Problems to be solved by the invention]
Since streamer discharge occurs in the portion of the steep voltage change at the ozone generator of the pulse streamer corona discharge method, generally, streamer discharge is formed only to the rising portion of the applied pulse voltage V _P. Its duration is at most several tens of ns. When the pulse width of the applied pulse voltage V _P is longer than the duration of the streamer discharge, transient glow discharge is formed so as to follow the streamer discharge. Since the significant unequal electric field generated between the electrodes 4 and 6 by the pulse voltage V _P applied between the counter electrodes 4 and 6 is alleviated by the rearrangement of the space charge by the preceding streamer discharge, conversion in the transient glow discharge plasma The electric field strength E / N is low. For this reason, the ozone generation efficiency in the transient glow discharge is lower than that in the streamer discharge, and the ozone generation efficiency decreases if the transient glow discharge cannot be sufficiently suppressed.
[0007]
In the conventional ozone generator, the gas pressure (absolute pressure; hereinafter the same) of the raw material gas 14 introduced between the electrodes 4 and 6 of the ozone generator 2 is approximately 1 atmosphere (atmospheric pressure). The pulse width of the observed discharge current I _P is as short as about 150 ns, which is much longer than the streamer duration (several tens of ns). That is, in the past, power input due to transient glow discharge could not be suppressed, and therefore ozone generation efficiency was not good.
[0008]
Although the transient glow discharge can be suppressed if the pulse width of the applied pulse voltage V _P can be suppressed to about the duration of the streamer discharge or less, it is not possible to reduce the pulse width of the applied pulse voltage V _P to about several tens of ns or less in a practical device. Have difficulty. This is because the ozone generator 2 can be regarded as a parallel circuit of CR in terms of an equivalent circuit (C is a capacitance between the electrodes 4 and 6, R is a resistance due to discharge), and C and R are considerably large. The time constant is considerably large, and such a CR parallel circuit is connected in parallel to the pulse power supply 18. Therefore, no matter how short the pulse voltage V _P is applied from the pulse power supply 18, this CR parallel circuit is applied. This is because it is difficult to shorten the pulse width below the time determined by the time constant of the parallel circuit. Further, even if a resistor is connected in parallel between the electrodes 4 and 6 to try to forcibly reduce the combined resistance value of the entire circuit, power loss is generated by the resistor, and thus the ozone generation efficiency cannot be increased. .
[0009]
Therefore, the present invention mainly provides an ozone generation method capable of suppressing the transient glow discharge following the streamer discharge and improving the ozone generation efficiency without shortening the pulse width of the applied pulse voltage. Objective.
[0010]
[Means for Solving the Problems]
The ozone generation method of the present invention is characterized in that the raw material gas pressure between the electrodes of the ozone generator is set to 2 atm or more in absolute pressure when ozone is generated.
[0011]
The inventors have achieved a streamer discharge without increasing the pulse width of the applied pulse voltage by increasing the pressure of the raw material gas between the electrodes of the ozone generator, specifically by increasing the pressure to 2 atmospheres or more. It was experimentally found that the subsequent transient glow discharge can be suppressed. By this method, the ozone generation efficiency can be improved.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
In the ozone generator having the configuration shown in FIG. 1, a coaxial cylindrical discharge tubular ozone generator 2 comprising a cylindrical electrode 4 having a diameter (inner diameter) of 40 mm and a length of 1 m and a wire electrode 6 having a diameter of 0.4 mm is used. A pulse voltage V _P having a pulse width of about 150 ns as shown in FIG. 2A was applied from the pulse power source 18 to the ozone generator 2. The polarity of the pulse voltage V _P may be positive or negative, but is usually a positive pulse voltage at which the wire electrode 6 is positive. The observed waveform of the discharge current I _P in the ozone generator 2 in this case, that is, when the gas pressure of the source gas 14 between the electrodes 4 and 6 is changed from 1.2 atmospheres to 2.5 atmospheres is shown in FIG. 2B. Show. As described above, the streamer discharge region is at most several tens of ns (shown by about 50 ns in FIG. 2B), and the subsequent region is a transient glow discharge region.
[0013]
As can be seen from FIG. 2B, although the current component due to the streamer discharge generated at the rising portion of the pulse voltage V _P is hardly changed even when the raw material gas pressure is changed, the current component due to the transient glow discharge following the streamer discharge is the raw material gas. Suppressed with increasing pressure. In particular, it can be seen that the transient glow discharge current component is effectively suppressed by setting the source gas pressure to 2 atmospheres or more.
[0014]
FIG. 3 shows an actual measurement example of ozone generation efficiency when the raw material gas pressure between the electrodes 4 and 6 is increased as described above. The used raw material gas is dry air having a dew point of -60 degrees or less. The pulse widths of the ozone generator 2 and the applied pulse voltage V _P used are the same as in the example of FIG. The reason why a plurality of data points exist at the same source gas pressure is that measurement is performed by changing parameters such as the source gas flow rate.
[0015]
As can be seen from FIG. 3, when the raw material gas pressure is 1.2 to 1.7 atmospheres, a large amount of input power is required to increase the ozone concentration in the ozone-containing gas 16 output from the ozone generator 2. However, when the raw material gas pressure is 2 atm or higher, the ozone concentration in the ozone-containing gas 16 can be increased without increasing the input power. That is, it can be seen that by setting the raw material gas pressure to 2 atmospheres or more, the transient glow discharge is suppressed and the ozone generation efficiency is improved. As a result, ozone can be produced at a lower cost than in the past.
[0016]
It can be seen from FIG. 2B that the higher the raw material gas pressure between the electrodes 4 and 6, the more effectively the transient glow discharge following the streamer discharge can be suppressed. Since approval by the gas control law is required, from the viewpoint of making this approval unnecessary, the raw material gas pressure between the electrodes 4 and 6 is preferably 2 atm or more and less than 3 atm.
[0017]
Further, since the discharge pressure of the normal source gas source 12 is 7 atm at the maximum, the source gas pressure between the electrodes 4 and 6 is 2 atm or more and 7 atm from the viewpoint of eliminating the need for the special source gas source 12. The following is preferable.
[0018]
The ozone generator 2 may be other than the coaxial cylindrical discharge tube as in the above example. For example, (1) a structure in which a wire electrode is arranged on the central axis of a rectangular tube electrode, (2) a structure in which one or more wire electrodes are arranged between two parallel plate electrodes, etc. In these cases, the same result as above can be obtained.
[0019]
Further, the ozone generator 2 may have a structure in which a plurality of coaxial cylindrical discharge tubes in which the wire electrode 6 is arranged on the central axis of the cylindrical electrode 4 are arranged in the container 8 as in the example shown in FIG. . By doing so, it is possible to process a large amount of the source gas 14 at a time, and the ozone production capacity is improved. Each cylindrical electrode 4 in this case is electrically connected to the container 8 and thus to the pulse power source 18 by the support plate 9. The wire electrodes 6 may be connected in parallel to each other as illustrated, or may be connected in series.
[0020]
In the ozone generator of the pulse streamer corona discharge method, dry air or oxygen gas having a low dew point is usually used as the raw material gas 14 from the viewpoint of ozone generation efficiency. As the supply source of the low dew point dry air and oxygen gas, a membrane type purification apparatus and a liquefaction tank are used for industrial applications, and the discharge pressure of the raw material gas 14 from the supply source is 3 atm or more. Therefore, when the effective pressure loss of the load 22 for supplying the ozone-containing gas 16 (= load pressure loss + load back pressure) is less than 2 atm, the gas of the ozone generator 2 as in the example shown in FIG. A back pressure valve 20 may be provided on the outlet side. By doing so, the raw material gas pressure in the ozone generator 2 can be easily adjusted to 2 atmospheres or more. In general applications, the effective pressure loss of the load is rarely 2 atmospheres or more, but when it is 2 atmospheres or more, the discharge pressure of the source gas source 12 may be increased. In addition, since the pressure loss in the ozone generator 2 is usually about 0.1 atm or less, the source gas source 12 in this case may be set to a discharge pressure that is at least 0.1 atm higher than the effective pressure loss of the load.
[0021]
【The invention's effect】
As described above, according to the present invention, since the raw material gas pressure between the electrodes of the ozone generator is set to 2 atm or more when ozone is generated, it is possible to follow the streamer discharge without reducing the pulse width of the applied pulse voltage. Ozone generation efficiency can be improved by suppressing transient glow discharge. As a result, ozone can be produced at a lower cost than in the past.
[Brief description of the drawings]
FIG. 1 is a schematic view showing an example of an ozone generator.
FIG. 2 is a diagram showing an observation example of a discharge voltage waveform (B) when the pulse voltage waveform (A) and the raw material gas pressure are changed.
FIG. 3 is a diagram showing an actual measurement example of ozone generation efficiency when the raw material gas pressure is changed.
FIG. 4 is a cross-sectional view showing another example of an ozone generator.
FIG. 5 is a diagram showing an example in which a load is connected to an ozone generator.
[Explanation of symbols]
2 Ozone generator 4 Cylindrical electrode 6 Wire electrode 12 Source gas source 14 Source gas 16 Ozone-containing gas 18 Pulse power source

Claims (1)

An ozone generator having opposed electrodes and generating ozone by streamer discharge, a source gas source supplying a source gas containing oxygen to the ozone generator, and a pulse voltage between the electrodes of the ozone generator An ozone generating apparatus comprising a pulse power source to be applied, wherein, when ozone is generated, a raw material gas pressure between electrodes of the ozone generator is set to 2 atm or more in absolute pressure.

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