JPS63267423A - Decomposition method for nitrogen oxide in gas mixture containing nitrogen oxide - Google Patents

Abstract

PURPOSE:To convert NOX into harmless gas efficiently by irradiating gas containing at least NOX with laser beam. CONSTITUTION:Exhaust gas containing NOX exhausted out of a combustion furnace is guided into a laser beam irradiating device 2 and NOX is decomposed into N2 and O2. At that time, the wave length of the laser beam is 110-400nm, and eximer laser is mainly used. Even if N2O is contained in the exhaust gas, N2O can be decomposed, and SOX can also be decomposed into S and O2 by irradiating laser beams of 222, 282 and 308nm. The exhaust gas after decomposition is exhausted out of a stack 4 through a fan 3.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for treating gas mixtures such as exhaust gases containing nitrogen oxides.

[Conventional technology and problems]

Conventionally, legal and other regulatory measures have been taken to prevent the release of exhaust gas from various industries and automobiles into the atmosphere from the perspective of pollution prevention. As a causative agent of photochemical smog, its emission is strictly restricted. Many methods have been proposed to treat nitrogen oxides (NOx) and sulfur oxides ('E30x) in exhaust gas, which are subject to emission regulations, but there are many practical issues. be.

For example, as conventional exhaust gas denitrification techniques, a reduction method by adding ammonia, a reduction method using a catalyst, a radiation irradiation method, etc. have been proposed.

These conventional methods each have the following problems.

■ Reduction method by adding ammonia: The denitrification effect rate is low.

■ Reduction method using a catalyst: Catalytic performance decreases when used continuously. Since metals and precious metals are used as catalysts, it is necessary to reconsider from the viewpoint of resource conservation. Susceptible to dust and acidic substances.

■ Radiation irradiation method: Since secondary products such as ammonium sulfate and ammonium nitrate are produced, separate treatment of by-products is required.

Furthermore, since all of these methods involve the addition of ammonia, ammonia that is not consumed in the denitrification reaction is discharged as leak ammonia, resulting in secondary pollution. Furthermore, it is necessary to reconsider the use of ammonia from the perspective of resource conservation.

Furthermore, Japanese Patent Laid-Open No. 51-98670 discloses that exhaust gas containing nitrogen and nitrogen oxides (N0x) is activated by microwaves, millimeter waves, or lasers, and the activated nitrogen is used to convert N0xt-N2. Although a method for converting it to O or 01 is described, the publication only specifically describes a method of applying microwaves and does not specifically describe a laser.

[Structure of the invention]

The present invention relates to a method for treating a gas mixture containing nitrogen oxides, and is a method for decomposing nitrogen oxides in a gas mixture, the method comprising irradiating the gas mixture with a laser beam. , treatment of exhaust gas from various combustion equipment,
It can be applied to the treatment of ammonia and nitric acid industrial exhaust gas, the treatment of automobile exhaust gas, and the purification of air in homes, offices, hospitals, etc.

As an embodiment of the method of the present invention, FIG. 1 shows a conceptual diagram when the method is applied to the treatment of NOx in flue gas generated from a petroleum-based fuel combustion furnace.

Average 550 ppm NOx emitted from combustion furnace 1
The exhaust gas containing (No and No snow, mainly No) is introduced into the laser beam irradiator 2 and decomposed into NOx I/iNs and 02, and the NOx decomposed exhaust gas is sent from the chimney 4 by the suction fan 3. The emitted @laser source irradiator 2 is a reactor in which NOx is decomposed by laser light irradiation, which is a feature of the present invention.

A specific example of the laser beam irradiator 2 is shown in FIG.

The laser beam irradiator 2 uses a laser beam oscillation tube 5 and laser beam irradiation to determine the wavelength of the laser beam from the laser beam oscillation f5, which is composed of a reactor 6 in which NOx decomposition is performed, depending on the wavelength of the laser beam to be processed. It is sufficient if the wavelength is absorbed by the substance (110 to 400 nm, preferably 160 to 550 nm).

The type of laser light and the medium gas may be selected as long as they emit laser light of the above-mentioned wavelengths, and can be appropriately selected and used depending on the field of application, the substance to be treated, the coexisting substances, etc. Usually, the laser source is an excimer laser, and the medium gas is ArF.
%ArC1%KrC4XeC1%XeF or XeBr
etc., and these can be used singly or in combination of type 1 or more.0 The laser beam irradiation method may be any method as long as it irradiates the exhaust gas uniformly and effectively. Applicable.

Usually, it is preferable to irradiate the exhaust gas in a countercurrent direction to the flow of the exhaust gas as shown in Fig. 2. Also, it is preferable to provide a stirring mechanism such as a stirring blade inside the reactor 6 or to stir the exhaust gas by using a swirling flow so that the exhaust gas is uniformly distributed. Irradiation is effective.

Further, the laser beam irradiation can be carried out with or without focusing as appropriate.

In FIG. 2, 7 indicates the flow of exhaust gas, 7-fold indicates the gas flow at the inlet, 7-fold indicates the gas flow at the outlet, and 8 indicates the laser beam irradiation window.

In this method, the temperature effect on NOx decomposition is small. Therefore, special temperature control is usually not necessary. In this illustrated example, the outlet exhaust gas of the combustion furnace 1 (temperature 500-
350℃ exhaust gas) is that'! It is also introduced into the laser beam irradiator 2, and is carried out without any special temperature control.

Normally, when treating combustion gas, the temperature of the reactor 6 is higher than the temperature at which adhesion and condensation of acid mist in the exhaust gas to the reactor can be ignored, and generally higher than the acid dew point (for example, 120°C or higher). It is preferable to do it with

In the above explanation, we talked about the decomposition treatment of NOx in exhaust gas, but if there is any N20 (nitrous oxide) in the exhaust gas, N20 can also be treated in the same way.0 NOx (No + NO2) and Neo If the decomposition treatment is performed simultaneously, irradiation can be performed with a laser having a wavelength that is absorbed by both NOx and Neo, for example, 160 to 210 nm, or with a laser having a wavelength that is characteristic of both NOx and Neo, such as 222 nm (NO3C
).

This can be effectively carried out by irradiating simultaneously or alternately with respective lasers having a wavelength of 193 nm (N20).

Regarding the decomposition treatment of N and O in a mixed gas, there is another invention by the present inventor (Japanese Patent Application No. 61-255790).

In the above explanation, NO.
Although the description has been made for the case where there are many NO geese, the same process is applied when there are many NO geese. Also, if the exhaust gas is designated as Box, 80x can be treated in the same way. These treatments can be carried out efficiently by appropriately selecting the wavelength of the laser beam, as shown in Table 1 below.

Table 1 shows examples of laser light wavelengths and medium gases suitable for the substance to be treated. Among these wavelengths, the wavelength of 222 nm is
It is preferable because it is absorbed by all of No, NO2, and 130x.

Table 1 SOx treatment is performed by irradiating the SOx listed in Table 1 with a laser beam having an absorption wavelength.
ox is decomposed into S and S and 0 snow.

8 (sulfur), which is a decomposition product of SOx, can be captured by installing a well-known dust collection and collection device such as an electrostatic precipitator or a back filter behind the laser beam irradiator (2 in Figure 1). The recovered S can be appropriately purified by well-known methods and effectively utilized as a resource.

A method for simultaneously treating NOx and Sox is to irradiate with a laser at a wavelength that is absorbed by both NOx and BOX, for example 222 nm, or to irradiate with a laser at a wavelength that is absorbed by both NOx and F30x, for example 222 nm (NOx, 28 nm).
This can be effectively carried out by irradiating simultaneously or alternately with lasers having respective wavelengths of 2 nm (Box).

Again, NO! Only the processing may be performed using this method (laser irradiation method), and the SOx processing may be performed using a known processing method. B
Well-known treatment methods for ox include the ammonia-ammonium sulfate method, the ammonia-gypsum method, the lime-gypsum method, the sulfite-gypsum method, and the activated carbon-adsorption method.

The SOx treatment method has fewer practical issues and problems than the NOx treatment method, and although it has some drawbacks, it has been put into practical use, and there are many devices currently in operation.

Therefore, we decided to treat SOx using a well-known treatment method.
If only the treatment of NOx, which has many problems, is performed by this method, it may be practically advantageous depending on the field of application, location conditions, etc.

As mentioned above, NOx and Box can be treated simultaneously.
The choice of whether to use laser irradiation for both the I can do sexual things.

FIG. 3 shows a conceptual diagram of NOx and Box treatment in coal combustion exhaust gas in which Box treatment is performed using the lime-gypsum method.

In FIG. 3, numerals 1 to 4 have the same meaning as the 几 numerals explained in relation to FIG.
In the method shown in Figure 3, the NOx gas introduced into the laser beam irradiator 2 is introduced into the box absorption tower 9 using the lime-5-layer method, and the gas contained in the gas is Box t - After absorption and removal, it is released from the chimney 4 by suction 7 and 5.

Example 1 A laser beam irradiator as shown in FIG.
Air containing xf was introduced at a rate of t-11.7 minutes, laser light was irradiated, and the NOx concentration at the reactor outlet was measured.

Laser: Excimer laser, KrC220W Reactor size: 2 Reactor temperature: Room temperature NOx: No. 400 ppm, No. 3100
Measurement of ppmNOx: Based on the zinc-reduced naphthylethylenediamine method.

The NOx content in the air at the reactor outlet was below 10 ppm.

Example 2 500 ppm0NOx, 5 Q Oppm08Oz
Air having a temperature of t- is introduced into a laser beam irradiator as shown in Fig. 2 at a rate of t-117 minutes, irradiated with laser light, and the NOx and 8026 degrees at the reactor outlet are measured. , KrC120W reactor size: 2 A degree of reactor: room temperature NOx measurement by dizinc reduction naphthyl ethylene diamine method.

Measurement of sol: Use an ultraviolet absorption analyzer.

The NOx content in the air at the reactor outlet was 10 ppm or less, and the 5Ost content was 20 ppm or less.

〔Effect of the invention〕

1. By irradiating a gas mixture containing NOx with a laser th, it can be decomposed into harmless and stable gases such as NOXk, Nz and 0! in the gas mixture (the secondary products to be treated are (not generated).

(2) When N and O were contained in the gas mixture, N and O were also decomposed, and the denitrification rate was substantially improved.

■ If gas mixture 11CBox is included, Box
Since this method is effective at room temperature, maintenance and management are easy as there is no need for temperature control like in conventional denitrification methods (e.g., decomposition methods).・■ Such as water treatment equipment and air purifiers,
Effective against NOx sources near room temperature.

＆ Since it does not require the addition of ammonia, it saves resources and there is no secondary pollution caused by leaked ammonia.
It is a practical way to wear it.

4. Since it is a dry treatment method, secondary treatment such as wastewater treatment is not required, making it a practical method.

& Laser irradiation method 5 NOx, N2O, Box
The treatment method of 04 E30X is a more practical method as a simultaneous denitrification and desulfurization method because it can be treated at the same time. Since the combination can be arbitrarily selected, practical and suitable simultaneous processing of NOx and Box can be performed.

[Brief explanation of drawings]

Fig. 1 is a conceptual diagram when the method of the present invention is applied to the treatment of combustion exhaust gas, Fig. 2 is a conceptual diagram showing an example of a laser beam irradiator used in the present invention, and Fig. 3 is similar to Fig. 1. It is a diagram in which an 80s absorption tower using the lime-gypsum method is incorporated into the shown apparatus.

Claims (1)

[Scope of Claims] 1. A method for decomposing nitrogen oxides in a gas mixture, which comprises irradiating a gas mixture containing nitrogen oxides with a laser beam. 2. The method according to claim 1, wherein the gas mixture to be treated contains sulfur oxides. 3. The method according to claim 1 or 2, wherein the wavelength of the laser beam is 110 to 400 nm, preferably 160 to 350 nm. 4. The method according to claim 5, wherein the type of laser is an excimer laser. 5. Medium gas is ArF, ArCl, KrCl, XeCl
, XeF, and XeBr, or a mixture of two or more thereof. 6. Any one of claims 1 to 5, wherein the treatment of sulfur oxides in the gas mixture to be treated is carried out by a method other than laser beam irradiation, and the treatment of nitrogen oxides is carried out by laser beam irradiation. The method described in 1.