JP2001113118A - Electrical discharge gas treating method and device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce power consumption in the technology for treating the gas to be treated by using pulse corona discharge. SOLUTION: In this electric discharge gas treating method, the gas 12 to be treated is treated by introducing the gas 12 into the discharge space 8 of a discharge treating part 2 having a coaxial cylindrical external electrode (non- corona electrode) 4 and an internal electrode (corona electrode) 6 and repeatedly applying pulse voltage Vp from a pulse power source 14 between both electrodes 4 and 6 to generate pulse corona discharge 10 in the gas 12 at the inside of the discharge space 8. At that time, the electric energy density introduced into the gas 12 to be treated at the discharge space 8 per 1 pulse of the pulse voltage Vp is kept in 10-150 J/Nm3, preferably 10-50 J/Nm3.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a process for treating a gas to be treated by pulse corona discharge to decompose and remove harmful substances such as NOx, SOx, hydrogen sulfide and ammonia contained in the gas to be treated and odorous substances. The present invention relates to a discharge gas treatment method and apparatus for performing ozone generation or ozone, and more specifically, to means for reducing power consumption.

[0002]

2. Description of the Related Art A technique for decomposing and removing harmful substances and odorous substances in a gas to be treated by generating a pulse corona discharge in the gas to be treated has already been proposed (for example,
See JP-A-62-289249).

FIG. 3 shows an example of such an apparatus. In this discharge gas processing apparatus, a linear internal electrode 6 is coaxially arranged within a cylindrical external electrode 4, and a gas to be processed 12 is introduced into a discharge space 8 formed between the electrodes 4, 6. a discharge treatment unit 2 that is, the pulse power source for generating a pulsed corona discharge 10 in the gas to be treated 12 of the repeating pulse voltage V _P in applied to the discharge space 8 between the electrodes 4, 6 of the discharge section 2 14 is provided. In this example, the cylindrical external electrode 4 is a non-corona electrode, the linear internal electrode 6 is a corona electrode, and these coaxially face each other. The pulse corona discharge 10 extends from the side of the internal electrode 6 which is thin and has high electric field strength to the external electrode 4 on the outside.

[0004] pulse voltage V _P is a short pulse of the pulse width, for example, about 10Ns～1myuesu, and the distance mean electric field strength is e.g. 8d~30d [kV in the discharge space 8
/ Cm] (where d is the relative density of the gas at the temperature and pressure of the gas to be treated when the density of the gas at 0 ° C. and 1 atm is 1). This pulse voltage _VP is normally a positive pulse, but may be a negative pulse.

[0005] Note that the distance mean electric field strength in this specification refers to a field strength divided by the spatial distance from the (inner electrode 6 in this example) the peak value of the pulse voltage V _P corona electrode.

The above-mentioned harmful substances and odorous substances in the gas to be treated 12 are decomposed by high-speed electrons and radicals generated in the pulse corona discharge 10 to make them harmless.
Processing such as removal is performed. When the gas to be treated 12 is air, ozone, which is a kind of radical, can be generated.

[0007] Depending on the type of harmful substances or odorous substances, the combined use of the above-described discharge treatment section 2 and the catalyst section provided downstream thereof can further enhance the decomposition and removal performance. Is already known (see, for example, JP-A-3-16616).

[0008]

One of the factors hindering the spread of the technique for treating the gas to be treated 12 by using the pulse corona discharge as described above is that the power consumption is large. No specific proposal for reducing power consumption has been made in the art.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to reduce the power consumption in a technique for treating a gas to be treated using the above-described pulse corona discharge.

[0010]

According to the present invention, there is provided a method for treating a discharge gas, wherein the density of electric energy supplied to the gas to be treated in the discharge space per one pulse of the pulse voltage is 10 to 150 J / Nm ³ . It is characterized by doing.

[0011] In the discharge gas processing apparatus according to the present invention, the electric energy density injected into the gas to be processed in the discharge space per one pulse of the pulse voltage is 10 to 150 J.
/ Nm ³ , wherein the volume of the discharge space and the electric energy applied per pulse of the pulse voltage to the discharge space are set.

The electric energy density is obtained by converting the electric energy (unit: joule J) applied to the discharge space per one pulse of the pulse voltage to the gas volume (unit: reduced volume Nm ³ ) exposed to the discharge. Because it depends on pressure and temperature, the value is expressed in cubic meters based on the gas volume at 0 ° C. and 1 atmosphere.) The gas volume exposed to the discharge has a distance average electric field strength of 8 d [kV /
cm] (d: relative gas density when the density of the gas to be treated at 0 ° C. and 1 atm is 1) is the gas volume in the discharge space.

The present inventors have conducted test and research to achieve the above object. As a result, the electric energy density supplied to the gas in the discharge space per pulse is set within the above range, so that the discharge space in the discharge space is reduced. It has been found that the generation efficiency of radicals effective for the treatment of the gas to be treated by the method is improved. By improving the radical generation efficiency, the gas to be processed can be efficiently processed, so that power consumption can be reduced.

In particular, the electric energy density is set to 10 to 5
When the content is in the range of 0 J / Nm ³ , the radical generation efficiency is significantly improved.

[0015]

FIG. 1 is a schematic diagram showing an example of a discharge gas processing apparatus for performing a discharge gas processing method according to the present invention. This device has basically the same configuration as the conventional device shown in FIG. Therefore, the same or corresponding parts as those in the conventional example shown in FIG.
Hereinafter, differences from the conventional example will be mainly described.

In the apparatus having the configuration shown in FIG. 1, the volume M (unit liter L) of the discharge space 8 of the discharge processing section 2 is three types of 1.4L, 2.8L, and 4.7L, and the pulse power source 1
1 to 4 of the pulse voltage V _P to be applied to the discharge section 2
The energy per pulse E (unit J) is 100 mJ,
300 mJ, 3 kinds of 600 mJ, the pulse voltage V _P of the repetition rate f (pulse number pps per second) 10
4 of pps, 20pps, 100pps, 200pps
Electric energy density ε (unit: J / N) injected into the gas to be treated 12 in the discharge space 8 per pulse.
FIG. 2 shows an example of the result of experimentally measuring the relationship between m ³ ) and the ozone generation efficiency η, which is an index of radical generation efficiency.

Ozone is a typical radical generated by electric discharge, and is useful as an index of radical generation because it is easy to measure. In the above experiment, the internal electrode 6 (corona electrode) and the external electrode 4 (non-corona electrode) of the discharge processing unit 2 were used.
Since the distance average electric field strength exceeds 8 d [kV / cm] over the entire area of the coaxial cylinder space sandwiched between the discharge space 8 and the discharge space 8. Generally, the gas to be treated 12 is mainly composed of air.
In the above experiment, the temperature of the gas to be treated 12 was 25 ° C. and the pressure was 1
Atm air is used.

The air as the gas to be treated 12 flows through the discharge space.
In the range of seconds to 1 second, On the other hand, since the discharge time per pulse of the pulse voltage V _P is less than 100ns, epsilon
= 1000 E / M (strictly speaking, ε = 1092 E / M due to temperature conversion of gas volume). The ozone generation efficiency η indicates how many g of ozone is generated per electric energy input to the gas. According to a custom, the number of ozone g generated per 1 Wh (= 3600 J) of electric energy is calculated. I took it.

As apparent from FIG. 2, the electric energy density ε per pulse is 10 to 150 J / Nm ^3.
It has been found that setting the ratio within the range improves the ozone generation efficiency η, which is an index of the radical generation efficiency. In particular, the electric energy density ε is set to 10 to 50 J /
By setting the value within the range of Nm ³ , the ozone generation efficiency η is significantly improved.

Incidentally, although there is no prior art focusing on the electric energy density ε as described above, a known literature (eg, Electronology A, Vol. 117, No. 9, 1997, pp. 956-961 or Journal of the Electrostatics Society of Japan) , 12, 4 (198
8) The electric energy density ε based on the electric energy and the discharge space volume described in 277-283)
Is about 250 to 400 J / Nm ³ .

If the radical generation efficiency is improved, a predetermined amount of radicals required for treating a predetermined amount of harmful substances and malodorous substances can be supplied with less power consumption. That is, power consumption can be reduced.

[0022] For example, ε = 200J / Nm ³ when the reference, ε = 150J / Nm ³ to about 15%, ε = 50J /
About 30% ^{Nm 3, ε = 20J / Nm} 3 in the can to reduce power consumption of about 50 percent.

Although the reason why the electric energy density ε is related to the radical generation efficiency is not clear, it is supposed as follows.

That is, it has been reported that ozone, which is a typical radical, has a reaction of inactivating ozone (decomposing ozone) by electrons (for example, Electrodynamics A, Vol. 116, No. 2). No. 1996, pp. 121-
127). When the electric energy density ε is increased, the electron density during pulse discharge increases. Electrons are indispensable for the generation of oxygen atom radicals, which are precursors to ozone generation (this is thought to be generated by the dissociation of oxygen molecules by electrons), but when the electron density becomes excessive, ozone is deactivated. It is considered that the contribution of the reaction to be performed is large, and the ozone generation efficiency is reduced.

For example, such a reaction mechanism is not clear for radicals other than ozone such as a hydroxyl radical, but it is considered that, like ozone, deactivation by excess electrons may affect the reaction.

Next, Table 1 shows an example of the result of measuring the relationship between the electric energy density ε and the performance of removing harmful substances and odorous substances. This pulse voltage V _P discharge treatment unit 2 (applied thereto as shown in FIG. 1, the pulse width 40n
s, a peak value of 40 kV) and a catalyst (ozone decomposition catalyst) in combination with a gas to be treated 12 containing 10 ppm of hydrogen sulfide, and a removal rate of the hydrogen sulfide (= concentration after treatment / inlet) Concentration).
In this experiment, a product (i.e., average power consumption) of the repetition rate f of the electric energy density ε and the pulse voltage V _P was constant.

[0027]

[Table 1]

As can be seen from this table, by setting the electric energy density ε to 66 J / Nm ³ , the performance of removing hydrogen sulfide is greatly improved. This is in good agreement with the result of FIG. Compiling the results of Table 1 and FIG. 2, the electric energy density ε is 10 to 150 J / Nm ^3.
It can be seen that the performance of removing harmful substances and offensive odors is improved by setting the content to 10 to 50 J / Nm ³ , and the performance is significantly improved by setting the content to 10 to 50 J / Nm ³ .

In practice, it is preferable to continuously process the gas to be treated 12. In this case, the gas to be treated 12 is allowed to continuously flow through the discharge space 8,
The discharge time during which electric energy is applied by the pulse corona discharge 10 is a time region of at most about 1 μs per pulse, while the time for the gas to be processed 12 to pass through the discharge space 8 is practically 10 ms to 1 s. Time domain. That is, the gas may be treated as substantially stationary during the discharge time of one pulse, and the electric energy density ε
Is calculated by dividing the electric energy supplied to the discharge space 8 per pulse by the volume of the discharge space,
It is sufficient to apply a correction coefficient determined by the temperature and pressure. That is,
Temperature T (unit ° C), pressure P (unit at) of the gas to be treated 12
m), the volume M of the discharge space 8 (unit L), and the electric energy E input to the discharge space 8 per pulse.
(Unit joule J) and the electric energy density ε
(Unit J / Nm ³ ) can be expressed by the following equation.

[0030]

Ε = 1000 × {(273 + T) / 273} ×
{E / (M × P)}

When the target gas 12 is continuously processed,
Radicals are continuously supplied into the gas to be processed 12 by the pulse corona discharge 10 in the discharge processing unit 2. In that case, depending on the substance to be treated concentration in the processed gas 12 may be set and repetition rate f of the electric energy density ε and the pulse voltage V _P.

For example, the repetition rate f (unit: pps) is set as follows. Since the residence time of the gas to be treated 12 of the discharge treatment unit 2 is normally is often set to be about 100Ms～1s, when the electric energy density 100 J / Nm ^3, thrown into 1 Nm ³ per subject gas 12 The total electric energy density α (unit: J / Nm ³ ) is given by the following equation.

[0033]

Α = (10-100) × f [J / Nm ³ ]

As a general idea, it is a standard to set the amount of radicals necessary for 1 mol of the substance to be treated to 1 mol, that is, to be chemically equivalent. The concentration of the substance to be treated is 100 ppm
In this case, the necessary radical concentration is about 100 ppm in terms of ozone. As can be seen from FIG. 2, when the electric energy density ε is 100 J / Nm ³ or less, the ozone generation efficiency η> 0.06 g / Wh = 16.7 μg / J. Assuming that the gas to be treated 12 is mainly air, 10
Since the ozone concentration of 0 ppm corresponds to 0.21 g / Nm ³ , α = (0.21 mg / Nm ³ ) / (16.7 μg
^{/ J) = 12600J / Nm 3} . Therefore, if the electric energy density ε is set to 100 J / Nm ³ , f can be about 126 to 1260 pps from Equation 2.

The pulse power source 14, to generate at a repetition rate f number 1000pps pulse voltage V _P of the short pulse high voltage as described above can relatively easily form in the current technology. If the residence time of the gas to be treated 12 in the discharge treatment unit 2 is appropriately selected, it is possible to cope with the repetition rate f of several thousand pps or less even when the concentration of the substance to be treated is 1000 ppm or more.

As an example, the flow rate of the gas to be treated 12 is 10
Consider a case where a discharge treatment is performed when 0 Nm ³ / min and the concentration of the substance to be treated are 10 ppm. Assuming that the gas residence time in the discharge processing unit 2 is 0.1 sec, the required discharge space volume M is about 170 L. In this case, if the coaxial cylindrical discharge processing unit 2 as shown in FIG. 1 is used, for example, the inner diameter (more specifically, the inner diameter of the external electrode 4) is 80 mm,
What is necessary is just to connect 40 discharge processing units 2 having a length of 0.85 m in parallel.

The electric energy density ε is, for example, 50 J
When / Nm ^3, the electrical energy E per pulse of the pulse voltage V _P required the discharge unit 2 is about 8.5
It becomes J. Assuming that the transmission loss of the electric energy E from the pulse power supply 14 to the discharge processing unit 2 is about 15%, it is sufficient that the pulse power supply 14 can store 10 J of electric energy E per pulse. Since the discharge unit 2 having an inner diameter of 80mm usually a pulse voltage V _P of about 60kV can applied, the energy E in the discharge from the capacitor
Given the pulse power supply 14 supplies a pulsed voltage V _P of the capacitance of the capacitor may be about 6 nf.

When the electric energy density ε = 50 J / Nm ³ , the ozone generation efficiency η = 0.07 g / Wh = 1 from FIG.
Since the required radical concentration is 10 ppm = 0.021 g / Nm ^{3 in} terms of ozone, the required total electric energy density α is 1082 J / Nm ^{3 because} it is 9.4 μg / J. Since the gas residence time in the discharge processing unit 2 is 0.1 s,
The required repetition rate f is 216 pps.

The electric energy density ε is proportional to the electric energy E input to the discharge space 8 per pulse divided by the discharge space volume M as given by the following equation (1). Therefore, in order to make the electric energy density ε within the above range, the electric energy E may be adjusted by the electric energy E,
The adjustment may be made by the discharge space volume M, or both may be adjusted.

In practice, the electric energy E is
It is not simply determined by the electric energy stored in the pulse power supply 14. Transmission efficiency of the electrical energy from the pulse power source 14 to the gas to be treated 12 in the discharge space 8, an average electric field duration of the pulse voltage V _P, at an applied voltage peak value determined, the repetition rate of the pulse voltage V _P, the treated This is because it depends complicatedly on conditions such as the pressure of the gas 12 and the residence time of the gas 12 to be discharged in the discharge space.

As can be seen from FIG. 2, the electric energy E usually tends to be excessive, so the conditions are selected so as to suppress this. In particular, in order to increase the efficiency of electric energy transfer from the pulse power source 14 into the gas 12 to be treated in the discharge space 8 and improve the energy efficiency of the entire apparatus, the above conditions are set so that the discharge duration is narrowed. It is preferable to select one. Specifically, it will be described below.

For example, when the distance average electric field strength is 8 d
18 d [kV / cm] (d: 0 ° C. and 1 atm.
(Relative density when the density is set to 1).
Choosing a value as low as possible will shorten the discharge duration
Is done. Also, the pulse voltage V _P200ns or less
Lower, more preferably 100 ns or less,
Time is reduced. Also, the pulse voltage V_PRepeat
As the rate becomes higher than 100 pps, the discharge duration
Is known to be narrowed. Also, the gas to be treated
The discharge duration is narrowed by setting the pressure of No. 12 to 2 atmospheres or more.
It can also be reduced. Any one or more of the above
The electrical energy that is likely to be excessive in the combination of
E and the electric energy density ε within the above range.
Can be selected.

The structure of the discharge processing section 2 may be other than the coaxial cylindrical shape shown in FIG. In short, it is only necessary that the corona electrode and the non-corona electrode are opposed to each other and that a pulse corona discharge occurs in the gas to be treated. For example, the external electrode 4 (non-corona electrode) of the discharge processing unit 2 may have a cylindrical shape other than a cylindrical shape, for example, a square cylindrical shape. A tubular shape can be rephrased as a tubular shape. Further, a plurality of linear internal electrodes 6 (corona electrodes) may be arranged in the external electrode 4 along the external electrode 4. The linear shape can be rephrased as a thin rod shape. With such an external electrode 4 and an internal electrode 6,
By generating an uneven electric field between the electrodes 4 and 6, the pulse corona discharge 10 can be generated.

Further, a catalyst section for decomposing the substance to be treated in the gas to be treated 12 which has passed through the discharge processing section 2 may be provided on the downstream side of the discharge processing section 2 as described above. If this is the case, the performance of removing the substance to be treated is further improved. The catalyst is
For example, it is an ozone decomposition catalyst, a photocatalyst, or the like.

A pre-processing section for pre-processing (for example, dust removal, temperature and humidity adjustment) the processing target gas 12 and a blower for supplying the processing target gas 12 upstream of the discharge processing section 2 as described above. May be provided.

[0046]

As described above, according to the present invention, the electric energy density injected into the gas in the discharge space per one pulse of the pulse voltage is set within the above range,
Since the generation efficiency of radicals effective for processing the gas to be treated in the discharge space is improved and the gas to be treated can be efficiently treated, power consumption can be reduced.

In particular, when the electric energy density is 10 to 1
By setting the content within the range of 50 J / Nm ³ , the radical generation efficiency is remarkably improved, and the effect of reducing the power consumption is further remarkable.

[Brief description of the drawings]

FIG. 1 is a schematic view showing an example of a discharge gas processing apparatus for performing a discharge gas processing method according to the present invention.

FIG. 2 is a diagram showing an example of a measurement result of a relationship between an electric energy density injected into a gas in a discharge space per pulse and an ozone generation efficiency.

FIG. 3 is a schematic view showing an example of a conventional discharge gas processing apparatus.

[Explanation of symbols]

 2 Discharge processing part 4 External electrode (non-corona electrode) 6 Internal electrode (Corona electrode) 8 Discharge space 10 Pulse corona discharge 12 Gas to be treated 14 Pulse power supply

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Hitoshi Shibano 47-47 Umezu Takaune-cho, Ukyo-ku, Kyoto-shi, Kyoto, Japan (72) Inventor Yu Kawakita 47-47 Umezu Takaune-cho, Ukyo-ku, Kyoto, Kyoto Nissin Electric Incorporated (72) Inventor Shigeru Kato 47, Umezu Takaune-cho, Ukyo-ku, Kyoto, Japan F-term in Nissin Electric Co., Ltd.

Claims (4)

[Claims] 1. A gas to be treated is introduced into a discharge space formed between a corona electrode and a non-corona electrode facing each other, and a pulse voltage is repeatedly applied between the two electrodes to form a gas to be treated in the discharge space. In the method of treating a gas to be treated by generating a pulse corona discharge in a gas, the electric energy density supplied to the gas to be treated in the discharge space per one pulse of the pulse voltage is set to 10 to 150 J / Nm ^3. A discharge gas treatment method. 2. An electric energy density of 10 to 50 J
Discharge gas processing method according to claim 1 wherein the / Nm ^3. 3. A discharge processing section having a corona electrode and a non-corona electrode opposed to each other and in which a gas to be processed is introduced into a discharge space formed between the electrodes, and between the two electrodes of the discharge processing section. A pulse power supply for generating a pulse corona discharge in the gas to be treated in the discharge space by repeatedly applying a pulse voltage to the gas to be treated in the discharge space per one pulse of the pulse voltage. So that the electrical energy density to be obtained is 10 to 150 J / Nm ³ ,
A discharge gas treatment apparatus, wherein a volume of the discharge space and electric energy applied per pulse of the pulse voltage to the discharge space are set. 4. An electric energy density of 10 to 50 J
4. The discharge gas processing apparatus according to claim 3, wherein the volume of the discharge space and the electric energy applied per pulse of the pulse voltage to the discharge space are set so as to be / Nm ³ .