JPH0651097B2 - Method for decomposing and removing nitrous oxide in gas mixture - Google Patents

Description

FIELD OF THE INVENTION The present invention relates to a method for removing nitrous oxide in a gas mixture. In particular, the present invention relates to various industries and exhaust gas in industry,
For example, exhaust gas from various denitration equipment, exhaust gas from ammonia and nitric acid industry, gas generated from water treatment equipment, especially its denitrification equipment, automobile exhaust gas and nitrogen oxides generated from or leaked from equipment such as medical equipment and cooking equipment. The present invention relates to a method for removing nitrous oxide from exhaust gas containing a trace amount of nitrous oxide, which is suitable for carrying out as a part of the removal treatment of nitrous oxide.

Conventional technology and problems Conventionally, various industries and industries are subject to legal and other restrictions on the emission of exhaust gas into the atmosphere from the viewpoint of pollution prevention. Its emission is severely restricted as the causative agent of smog.

By the way, the nitrogen oxides (NOx) in the exhaust gas that have been conventionally subject to emission regulations are mainly nitric oxide (NO) and nitrogen dioxide (NO ₂ ), and thus the conventional exhaust gas denitration technology is also mainly used. Targeting the removal of nitric oxide and nitrogen dioxide, for example, a reduction method by adding ammonia, a reduction method using a catalyst, a radiation irradiation method and the like have been proposed.

On the other hand, nitrous oxide (N ₂ O) in the exhaust gas is, of course, NO or NO.
_Although it belongs to nitrogen oxides like No. ₂ , there are no legal emission control values up to now, and no official measurement such as Japanese Industrial Standard (JIS) has been established. The reality is that it has been virtually ignored. This is because the concentration of N ₂ O in the atmosphere remained constant compared to NO and NO ₂ concentration, and it was said that it was stable without conversion to other substances, and the physical properties of N ₂ O were sufficient. This is because it was unclear.

However, in the denitration method according to the prior art as described above, NO, depending on the operating conditions of the denitration device used,
It has been recognized that N ₂ O is produced in a relatively high concentration by the reaction of NO ₂ and NH _3, etc., and in recent years, it has become clear that N ₂ O decomposes in the stratosphere to produce NO. _The issue of N ₂ O emissions has been drawing attention, as some have discussed the relationship between ₂ O and the ozone layer. Under these circumstances, various exhaust gases that are sources of N ₂ O in the atmosphere, particularly exhaust gases after NOx removal generated from various NOx removal devices currently used to remove nitrogen oxides in the exhaust gas The need to remove N ₂ O from the.

The above explained mainly the denitration equipment as an example, but as in the well water treatment facility to another, there are N ₂ O in the generation of conventional emission control is not performed facilities, these will similarly N ₂
It is necessary to remove O.

Means for Solving Problems, Actions and Effects The present invention aims to remove nitrous oxide, which is difficult to remove among nitrogen oxides contained in gas mixtures, particularly various exhaust gases. is there.

According to the invention, a gas mixture containing nitrous oxide is
Provided is a method for decomposing and removing nitrous oxide in a gas mixture, which comprises decomposing and detoxifying nitrous oxide by irradiating laser light having a wavelength in the range of 0 to 240 nm.

A specific example in which the method of the present invention is applied to the treatment of N ₂ O produced from a conventional denitration device for heavy oil combustion exhaust gas produced from a heavy oil combustion furnace will be described with reference to FIG.

Average NOx (total of NO and NO ₂ ) concentration from heavy oil combustion furnace 1 2
Exhaust gas discharged at 50 ppm is first denitrified by a normal denitrification device 2 to remove NOx, and then N ₂ O produced here is decomposed by a laser light irradiator 4 to detoxify the detoxified exhaust gas. It is discharged from the chimney 6 via 5.

The denitration by the denitration device 2 is carried out by using a stoichiometric amount of 0.7 to 0.9 equivalent of ammonia (NH ₃ ) 3 with respect to the NOx concentration in the exhaust gas.
Is added.

While the NOx concentration in the exhaust gas stream after the denitrification device 2 is 50 ppm, a portion of the NOx is converted to N ₂ O, N ₂ O Here
The concentration is 45 ppm.

Calculating the denitrification rate here, the denitrification rate when only focusing on the NOx concentration at the inlet and outlet of the conventional denitrification equipment is Becomes Then paying attention to N ₂ O, the N ₂ O concentration in terms of NOx concentration (45ppmN ₂ O corresponds to 90ppmNO), denitration rate when added NOx from N ₂ O as the NOx concentration Becomes

The N ₂ O in the downstream of the denitration device 2 is converted into N by the laser light irradiator 4.
Decomposed into ₂ and O ₂ and rendered harmless.

The laser light irradiator 4 is a reactor in which N ₂ O is decomposed by irradiation with laser light, which is a feature of the present invention.

A specific example of the laser light irradiator 4 will be described with reference to FIG.

The laser light irradiator 4 comprises a laser light oscillating tube 7 and a reactor 8 in which N ₂ O is decomposed by irradiation with laser light.
Laser light from the laser beam oscillation tube 7 is not limited as long as it is absorbed into the N ₂ O decomposing the N ₂ O to N ₂ and O _2.
The wavelength of laser light is 110 to 240 nm, preferably 185
˜240 nm, more preferably 185 to 230 nm.

The type of laser and the medium gas may be any one as long as it emits a laser beam having the above wavelength, and the preferable type of laser is an excimer laser and the medium gas is ArF or ArCl.

Laser light with a wavelength smaller than 110 nm or
When laser light having a wavelength larger than 240 nm is used, for example, when an argon laser, a carbon dioxide gas laser, or a YAG laser is used, N ₂ O cannot be decomposed, so that the object of the present invention cannot be achieved. Further, even when an excimer laser is used, if the laser light used has a wavelength outside the range of 110 to 240 nm, N ₂ O cannot be sufficiently decomposed and the object of the present invention cannot be achieved.

The method of irradiating the laser light may be any method as long as it can irradiate the exhaust gas uniformly and effectively, and a known method can be appropriately applied.
Normally, it is preferable to irradiate the exhaust gas flow countercurrently as shown in FIG. 2, and also to provide a stirring mechanism such as a stirring blade in the reactor 8 or to stir the exhaust gas by a swirling flow to laser the laser. It is effective to configure so that the exhaust gas is uniformly irradiated with light.

In FIG. 2, 9 is the flow of exhaust gas, 9 ₁ is the inlet, and 9 ₂
Is an exit, and 10 is a laser beam irradiation window.

In this method, the temperature effect on the N ₂ O decomposition is small, so that special temperature control is usually unnecessary. In this specific example, the exhaust gas at the outlet of the denitration device 2 (exhaust gas at a temperature of 250 to 300 ° C.) is directly introduced into the laser light irradiator 4, and can be implemented without special temperature control.

Usually, the temperature of the reactor 8 in the case of combustion exhaust gas is a temperature at which attachment or condensation of acid mist in exhaust gas to the reactor is negligible or higher, generally an acid dew point or higher (for example, 120 ° C. or higher). ) Is preferable.

The laser beam irradiator 4 of the embodiment shown in FIG. 1 is a case where the laser beam irradiator 4 is separately installed in the downstream of the normal denitration device 2. However, the ordinary denitrification device 2 and the laser beam irradiator 4 are integrated. It goes without saying that you can also do it. Practically, it is preferable to be integrated from the viewpoint of economy (the entire device is downsized).

As is clear from the above description and the examples described below, the following effects (1) to (3) are particularly achieved by the method of the present invention.

N ₂ O in the gas mixture is harmless and stable N ₂ and O ₂
Was disassembled into

N ₂ O was decomposed and the denitration rate was substantially improved. That is, the conventional denitrification rate is a comparison between the NOx concentration at the inlet of the denitrification device and the NOx concentration at the outlet, and the concentration of N ₂ O produced at the outlet is not taken into consideration, but the N ₂ O concentration is taken into consideration (considered as NOx The denitration rate was decreased by the N ₂ O concentration.

Since this method is effective even at about room temperature, it is practically advantageous as compared with the conventional method, for example, the catalytic method, in which high temperature is an essential condition. Specifically, it does not require temperature control such as the conventional denitration method (for example, catalytic method) and is easy to maintain and manage. Sources near room temperature such as water treatment facilities and medical / cooking facilities. It is effective for the treatment of.

Examples Next, the present invention will be further described with reference to Examples.

Laser light irradiation was performed by passing 50 ppm N ₂ O / air balance adjusting gas at 1 / minute to the laser light irradiator shown in FIG. 2, and the N ₂ O concentration at the reactor outlet was measured by gas chromatography. It was measured. The usage conditions are as follows.

Laser: excimer laser, medium gas ArF, 20 W Laser light wavelength: 193 nm Reactor size: 2 Reactor temperature: room temperature Result The N ₂ O concentration at the reactor outlet was 1 ppm or less.

The NOx (NO + NO ₂ ) concentration was measured by the zinc-reduced naphthylethylenediamine method and found to be below the detection limit (5 ppm).

Comparative Example Instead of the laser used in the above example, as a medium gas
Excimer laser using XeF (laser light wavelength 350 nm)
The test was carried out under the same conditions as in the example except that was used.
As a result, the N ₂ O concentration at the obtained reactor outlet was 45 ppm, and only a very small amount could be decomposed.

[Brief description of drawings]

FIG. 1 is a schematic flow sheet of a specific example in which the method of the present invention is applied to the treatment of N ₂ O-containing exhaust gas generated from a conventional denitration device for exhaust gas generated from a heavy oil combustion furnace, and FIG. 2 is the present invention. A laser light irradiator used to carry out the method (first
FIG. 4) shows a specific example. 1 ... Heavy oil combustion furnace, 2 ... Conventional denitration device, 3 ... Ammonia tank, 4 ... Laser light irradiator, 5 ... Juan, 6 ...
… Chimney, 7 …… Laser light irradiator, 8 …… Reactor, 9 ₁ ……
Exhaust gas inlet, 9 ₂ ...... Exhaust gas outlet, 10 ...... Laser light incident window.

Claims (4)

[Claims] 1. A gas mixture containing nitrous oxide containing 110-
A method for decomposing and removing nitrous oxide in a gas mixture, which comprises decomposing and detoxifying nitrous oxide by irradiating laser light having a wavelength in the range of 240 nm. 2. The method according to claim 1, wherein an excimer laser is used as the laser light. 3. The method according to claim 2, wherein the medium gas is ArF and / or ArCl. 4. The method according to any one of claims 1 to 3, wherein the gas mixture to be treated is an exhaust gas containing a trace amount of nitrous oxide.