JPH08257351A - System and process for treating low concentration nox-containing gas - Google Patents

Abstract

PURPOSE: To purify NOx on an adsorbent and make the same harmless without adding a purifying catalyst by providing a dust removing device for removing a dust component in exhaust gas and an adsorption device for adsorbing and removing NOx , feeding a reducing agent at the time of regenerating the adsorption device and reduce, and decomposite desoluted NOx thus adsorbed in the device. CONSTITUTION: Exhaust gas 1 mixed with ozone synthesized by an ozonizer 3 in an oxidization process 2 to oxidize a part or the whole of NO and convert the same into NO2 . Exhaust gas is introduced into an adsorption layer 4 to adsorb and remove NOx and discharged 5 into atmosphere. In the case when a unit with lowered adsorption capability is regenerated on the adsorption layer 4 composed of a plurality of units, nitrogen 6 is introduced into the adsorbent regenerating process by a fan 7, and flowed into an adsorption unit 8 extracted from the adsorption layer 4. Then hydrocarbon 9 is introduced when the oxygen density in the unit 8 is lowered sufficiently, and heated by a heater 10 to reduce and decompose NOx by using hydrocarbon.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for removing nitrogen oxides (NOx) contained in the atmosphere, and particularly to a low concentration of NOx contained in ventilation gases from automobile tunnels, underground roads and indoor automobile parking lots. Concentration NOx that efficiently removes NOx
The present invention relates to a treatment system for contained gas and a treatment method thereof.

[0002]

2. Description of the Related Art Generally, as a method for detoxifying and removing NOx in exhaust gas, a selective catalytic reduction method in which ammonia is added to NOx-containing exhaust gas and decomposed into harmless N ₂ on a catalyst is mainly applied in a thermal power plant. On the other hand, in a gasoline engine vehicle, a method of reducing and decomposing NOx on a three-way catalyst is applied.

Therefore, as a treatment method for dilute NOx in the atmosphere, after preliminarily concentrating NOx with an adsorbent, ammonia is added to a heated high-concentration NOx-containing gas to produce harmless N ₂ by the selective catalytic reduction method. A method of decomposing and releasing (Japanese Patent Publication No. 5-78369) has been proposed.

On the other hand, if the form of NOx is NO ₂ , it is relatively easy to remove NOx with an adsorbent or with an alkali even in the presence of water, so that a low concentration of NOx is obtained.
NO in the contained gas is converted to N by corona discharge or addition of ozone.
A method of oxidizing to O ₂ and absorbing and removing the NO ₂ with an alkaline absorbent, or a method of oxidizing NO to NO ₂ by ozone oxidation,
A method of adsorbing and removing the NO ₂ has been proposed (JP-A-6-99030).

[0005]

DISCLOSURE OF THE INVENTION The present invention solves the above-mentioned drawbacks of the prior art, and has a low concentration of N contained in ventilation gas from an automobile tunnel, an underground road or an indoor automobile parking lot.
This is a method of efficiently removing Ox.

In all of the conventional techniques, the reaction temperature is usually 200.
This is an economical and excellent method for treating high-temperature exhaust gas, which is above ℃, but it is difficult to apply when treating a large amount of gas at room temperature, such as tunnel ventilation gas.
Therefore, as a treatment method for dilute NOx in the atmosphere, after NOx is previously concentrated by an adsorbent, ammonia is added to a heated high-concentration NOx-containing gas and decomposed into harmless N ₂ by a selective catalytic reduction method. In the release method, 90% or more of NOx discharged into the atmosphere is generally NO with poor adsorptivity, and if the process gas contains water, the NO adsorption performance is extremely deteriorated. It is necessary to dehumidify the process gas in advance. Therefore, a dehumidifying agent is required in addition to the NOx adsorbent, which causes a problem of increasing the processing cost.

Further, if the form of NOx is NO ₂ ,
Even in the presence of water, it is relatively easy to remove NOx with an adsorbent or with an alkali.
A method of oxidizing NO in the x-containing gas to NO ₂ by corona discharge or addition of ozone, and absorbing and removing the NO ₂ with an alkaline absorbent, or oxidizing NO to NO ₂ by ozone oxidation,
Although there are methods of adsorbing and removing the NO ₂ , there is a problem that these methods consume a large amount of electric power as energy for oxidizing NO to NO ₂ . In any case, when the method for removing low-concentration NOx by the adsorbent is saturated with the NOx adsorption capacity by the adsorbent and the predetermined NOx removal efficiency is not exhibited, it is necessary to regenerate the adsorbent. Usually, this regeneration is performed by heating the adsorbent while flowing a regeneration gas. Therefore, regeneration of the adsorbent requires a large amount of energy for heating, which is not economical. The regenerated gas that has passed through the adsorbent contains a high concentration of NOx, and if necessary, the temperature is raised to a predetermined temperature to add a reducing agent, and decomposed into harmless N ₂ on the denitration catalyst. It will be released, and in the case of NO ₂ , it will be absorbed by an alkaline solution. Therefore, a new denitration catalyst tower may be needed. Usually, ammonia and hydrocarbons have been proposed as reducing agents for this denitration reaction.

[0008]

The above problems can be achieved by the following means. The treatment system and the treatment method for efficiently removing low-concentration NOx according to the present invention are characterized in that the adsorbent is regenerated by circulating a gas containing a reducing agent. Usually, the NOx removed by the adsorbent is desorbed as a concentrated gas by heating and regenerating the adsorbent, and is reductively decomposed into N ₂ in the reductive decomposition step. In the reductive decomposition step, a method of adding a reducing agent to a concentrated NOx-containing gas and then decomposing it on a catalyst, a method of absorbing it in an alkaline compound or a solution, and then performing a reduction treatment have been proposed.
These reduction decomposition steps can be omitted or simplified by applying the method of the present invention.

Further, in the exhaust gas treatment system containing a low concentration of NOx according to the present invention, NOx is adsorbed and removed by the adsorber, and the adsorbed NOx is converted into nitrogen in the adsorber simultaneously with desorption when the adsorber is regenerated. It is characterized by reductive decomposition. In order to further improve the performance of the adsorption device, an NO oxidation device is installed upstream of the adsorption device,
Part or all of the above may be oxidized to NO ₂ . Further, when the exhaust gas contains a large amount of dust components, a dust removing device may be provided upstream of the adsorption device. NOx of this system
In order to further improve the removal performance, NO is placed downstream of the adsorption device.
An x reduction decomposition device may be provided.

The low-concentration NOx treatment method of the present invention can be roughly classified into two types depending on the reducing agent species used. One method is to use urea or a decomposition product of urea as a reducing agent, and the other method is to use hydrocarbons or alcohols.

According to a detailed study by the present inventors, it was found that when the regeneration gas contains a compound that acts as a reducing agent for NOx, the adsorption agent is promptly regenerated. Moreover, in normal regeneration, the gas released from the adsorbent at the time of regeneration contains a high concentration of NOx, but in the method of the present invention, most of NOx is regenerated by the reducing agent which is also a desorption accelerator. It is characterized by being reduced and removed.

The adsorbent used in the present invention is characterized in that, in addition to its ability to adsorb NOx, it has a function of promoting the reaction between urea, a decomposition product of urea, hydrocarbons, or alcohols and NOx during desorption. For example, alumina, silica, titania, silica-alumina, zeolite, activated carbon, etc. N
Various substances having an Ox adsorbing ability to which various substances having a reaction promoting action between a reducing agent and NOx are added are used. Typical examples of these include Pt, Rh, when urea or a decomposition product of urea is used as the reducing agent.
Noble metals such as Ru, V, Mo, W, Cr, Mn, Fe,
Base metals such as Co, Ni and Ce can be given. When hydrocarbon or alcohol is used as the reducing agent, precious metals such as Pt, Rh, Pd, Ru, Au and Ag, C
Examples include base metals such as o, Ni, Fe, Cu, Mn, and Ga.

It is also a preferable method to add various alkalis, alkaline earths and rare earths in order to improve the NOx adsorption capacity. For example, Li, Na, K, M
g, Ca, Sr, Ba, La, Ce and the like.

Further, it is preferable to contain a catalyst component having NO oxidation performance, since NO can be converted to NO ₂ which is more easily adsorbed and adsorbed, and the adsorption capacity is improved. Usually, noble metals, Co, Mn, etc. are preferable. In addition, perovskite compounds have NOx adsorbing ability and are often active in the reaction of NOx with hydrocarbons or alcohols, and are therefore preferable adsorbent candidates.

In the present method, at least a part of NO in the low concentration NOx-containing gas is oxidized to NO ₂ by corona discharge or addition of ozone, and then the generated NOx.
The method of bringing the (NO + NO ₂ ) -containing gas into contact with the adsorbent is also an effective method because the NOx adsorption / removal effect is enhanced.
The adsorbed NOx is not limited to NO and may be in the form of NO ₂ .

When the adsorbent is regenerated with a gas containing a reducing agent, a preheated regeneration gas is circulated in order to promote the desorption of NOx and the reaction of NOx with hydrocarbons or alcohols efficiently. The adsorbent is 2
The temperature is preferably raised to a temperature of 00 to 500 ° C. Of course, the adsorbent may be directly heated by other means such as an electric heater. It is also a preferable method to circulate the regeneration gas in a closed system containing an adsorbent to sufficiently reduce and purify NOx adsorbed on the adsorbent. in this case,
It is also possible to add a reducing agent appropriately.

The urea used as the reducing agent of the present invention may be spray-mixed into the regeneration gas as a solid, or may be supplied in the form of an aqueous solution. Alternatively, a urea decomposing device may be provided in advance and a gas generated by hydrolyzing urea may be appropriately supplied. Of the decomposition products of urea, amines such as ammonia and isocyanic acid can be used as a reducing agent for NOx. As the decomposition device, for example, a device that supplies urea in the heating system in the presence of steam, or a device that supplies urea on the heated urea decomposition catalyst in the presence of steam can be used.

The hydrocarbon used in the reducing agent of the present invention may be a simple substance such as methane, ethane, propane, butane, ethylene or propylene, or a mixture such as LPG. Of course, higher hydrocarbons having more carbon atoms may be used, and of course, a mixture of gasoline, kerosene, etc. may be used. As alcohols, methyl alcohol, ethyl alcohol, propyl alcohol and the like can be used, and the type is not particularly limited.

These hydrocarbons or alcohols are
In the case of gas, it may be supplied as it is into the regeneration gas. In the case of a liquid or a solid, depending on its properties, it can be directly sprayed into the regeneration gas or can be supplied after being dissolved in an appropriate solvent.

In the low concentration NOx removal method of the present invention,
When the adsorbent is regenerated by circulating a gas containing hydrocarbons or alcohols, the regeneration efficiency may be further improved by lowering the oxygen concentration in the gas. For example, when NOx is adsorbed and removed by an adsorbent containing a noble metal such as Pt, Rh, Pd, Ru and a nitrogen gas containing a hydrocarbon is circulated during regeneration, the NOx reduction reaction is caused by oxygen adsorbed on the surface of the noble metal. May be inhibited and the reaction efficiency may be reduced. However, when the oxygen concentration in the gas is lowered, the inhibition by oxygen is reduced, so that NOx can be reduced more efficiently and the adsorbent can be regenerated.

For example, generally, in the case of an adsorbent containing a noble metal, NOx can be most efficiently reduced with hydrocarbons when the oxygen concentration in the flowing gas at the time of regeneration treatment is 0.5% or less. Even when the oxygen concentration in the flowing gas is 0.5% or more, the lower the oxygen concentration, the more efficiently NOx
Can be reduced.

In some cases, NOx can be efficiently reduced by reducing the oxygen concentration in the flowing gas other than the adsorbent containing a noble metal.

There are various methods for reducing the oxygen concentration in the flowing gas when the adsorbent is regenerated. For example, a method of burning a hydrocarbon or the like to reduce the oxygen concentration, a method of using an adsorbent such as the PSA method, or a tank of an inert gas such as nitrogen gas or carbon dioxide gas is provided so There is a method of mixing and circulating.

The compound used as the reducing agent in the method of the present invention not only promotes the reductive decomposition of NOx on the adsorbent, but also promotes the desorption of NOx. Therefore, it becomes possible to regenerate the adsorbent at a lower temperature by using the compound as an NOx desorption accelerator from the adsorbent. In this case, a part of NOx may be desorbed from the adsorbent without being reduced, and it is necessary to provide a NOx reduction step in the downstream, but the reduction step can be performed as compared with the case where no desorption accelerator is used. It is possible to simplify.

[0025]

In the method according to the present invention, since the NOx adsorbent is regenerated with the gas containing the reducing agent at the time of regeneration, the regeneration is facilitated. Unlike the case of using a regenerating gas that does not contain these components, N is maintained even in a relatively low temperature range of 50 to 200 ° C.
Ox release occurs. This is because the adsorbent is added with a component having a catalytic action that promotes the reaction between NOx and the reducing agent, so that the adsorbed NOx is not simply desorbed, but above a certain temperature above the adsorbent. Then, it is considered that the compound is decomposed into N ₂ by the reaction with a reducing agent such as hydrocarbon or alcohol, and is easily desorbed.

In the present method, the desorbed NOx is converted to N _{2 on the} spot.
It is reduced and decomposed into and is hardly contained in exhaust gas. Therefore, when the normal NOx adsorbent is regenerated, the high concentration N desorbed.
An Ox aftertreatment device is required, but is not needed in the method according to the invention.

[0027]

【Example】

(Embodiment 1) An example of the NOx removal system according to the present invention will be described with reference to the overall flow of FIG. The exhaust gas 1 containing a low concentration of NOx is mixed with ozone synthesized by the ozonizer 3 in the oxidation step 2, and some or all of the NO is converted into N 2.
Oxidized to O ₂ . The gas flowing out of the oxidation step 2 is introduced into the adsorption layer 4, NOx is adsorbed and removed, and then released from the ventilation tower 5 into the atmosphere.

The adsorption layer 4 is composed of a plurality of units,
A unit in which a large amount of NOx is adsorbed and the adsorption capacity is lowered is extracted and a regeneration process described later is performed.

Nitrogen 6 is introduced into the adsorbent regeneration process by the fan 7, and the adsorbent unit 8 extracted from the adsorption layer 4 is circulated. When the oxygen concentration inside the unit 8 is sufficiently lowered, the hydrocarbon 9 is introduced into the nitrogen stream, and heated by the heating device 10 to about 200 ° C. and circulated. On the unit 8, NOx is reductively decomposed into N ₂ by hydrocarbons. The decomposed gas is again introduced upstream of the adsorption layer 4. If unreacted NOx and hydrocarbons remain in the decomposed gas, the adsorption layer 4
After being adsorbed, the air is released from the ventilation tower 5 into the atmosphere. The unit 8 that has completed the regeneration process is incorporated into the adsorption layer 4 again.

With this system, it is possible to efficiently adsorb and remove low-concentration NOx, and also quickly reduce NOx adsorbed by the adsorbent to render it harmless.

(Embodiment 2) An example of the NOx removal system according to the present invention will be described with reference to the overall flow of FIG. The exhaust gas 1 containing a low concentration of NOx is introduced into the adsorption layer 4, where NOx is adsorbed and removed, and then released from the ventilation tower 5 to the atmosphere. The adsorption layer 4 is composed of a plurality of units, and a unit whose NOx is adsorbed in a large amount and whose adsorbability is lowered is extracted and subjected to a regeneration process described later.

Nitrogen 6 is introduced into the unit 8 by the fan 7 and further upstream of the adsorption layer 4. When the oxygen concentration inside the unit 8 is sufficiently reduced, the flow path switching valves 11 and 12 are switched so that the gas flowing out from the adsorbent unit 8 circulates and flows into the adsorbent unit 8 again. Heating device 1
A gas heated to about 200 ° C. at 0 is circulated through a fan 7 to heat 8 to a temperature required for NOx reduction decomposition.
At the same time, hydrocarbon 9 is introduced into the circulation system, and NOx desorbed from 8 is reduced and decomposed into N ₂ simultaneously with desorption. NOx that has been sufficiently reduced and purified and regeneration is completed is again in the adsorption layer 4
Built in.

By this method, low-concentration NOx can be efficiently adsorbed and removed, and NOx can be purified on the adsorbent by subjecting the adsorbent after the NOx adsorption to a heating regeneration treatment by a circulation system.

Example 3 A nitrogen oxide adsorbent used in the present invention was prepared as follows.

Yttrium oxide 23 g, barium oxide 3
1 g and 16 g of copper oxide were kneaded with a raikai machine for 1 hour.
The kneaded product was dried at 150 ° C. for 2 hours and then pre-baked at 500 ° C. for 2 hours. The obtained oxide was sufficiently crushed in a mortar and then calcined at 870 ° C. for 4 hours. Next, the obtained powder was pressed into a disk shape having a diameter of 45 mm, which was crushed to be granulated to have a particle size of 0.5 to 1 mm. This compound had a composition of YBaCuO _7-x , and as a result of X-ray diffraction measurement, it was found to be a complex oxide having a perovskite type crystal structure.

The granular YBaCuO _7-x was impregnated with a predetermined amount of dinitrodiamineplatinic acid aqueous solution. 150 this
After being dried at ℃ for 2 hours, it was baked at 500 ℃ for 2 hours to obtain an adsorbent 1. As a result of chemical analysis, platinum (Pt) is YBaC
The supported amount was 0.1% by weight based on uO _7-x .

Example 4 The NOx adsorption performance of the adsorbent 1 was measured. 4 ml of adsorbent 1 with an inner diameter of 20 mm and a length of 8
It was filled in the center of a quartz glass cylindrical tube of 00 mm and treated with an NO-containing gas under the conditions shown in Table 1. The temperature of the adsorbent was measured by inserting a thermocouple. In addition, NOx (NO and NO ₂ ) in the inlet and outlet gas of the quartz glass cylindrical tube
The concentration was continuously measured by a chemiluminescence type nitrogen oxide analyzer.

[0038]

[Table 1]

The NOx removal rate was calculated according to the following equation.

[0040]

[Equation 1]

Here, NOx is the total concentration of NO and NO ₂ (p
pm).

Table 2 shows the NOx adsorption removal rate of the adsorbent 1 set to each temperature after 15 hours of gas flow. It was found that the adsorbent 1 has a high NOx adsorption performance in the temperature range near room temperature.

[0043]

[Table 2]

(Example 5) Using the adsorbent 1, the NOx-containing gas was circulated at 25 ° C for 15 hours in the same manner as in Example 4 to perform the adsorption treatment, and then the regeneration treatment was performed by the following method.

A quartz glass cylindrical tube filled with the adsorbent 1 after the NOx adsorption treatment was filled with nitrogen gas containing propylene shown in Table 3, and the gas flowing out from one end of the cylindrical tube was circulated using a circulation pump. It was returned to the other end and circulated. The cylindrical tube was heated to 200 ° C. and regenerated for 30 minutes.

After the regeneration treatment, the gas in the cylindrical tube was sampled to obtain N
As a result of measuring the Ox concentration, it was 0.1 ppm or less. In addition, the adsorbent 1 after the regeneration treatment was heated to 700 ° C. in a nitrogen stream, but no desorption of NOx from the adsorbent was observed. From these results, it was found that most of the NOx adsorbed on the adsorbent 1 by the above regeneration treatment was desorbed and decomposed into nitrogen.

[0047]

[Table 3]

Example 6 Using the adsorbent 1, the NOx-containing gas was circulated at 25 ° C. for 15 hours in the same manner as in Example 4 to carry out the adsorption treatment, and then the regeneration treatment was carried out by the following method.

A quartz glass cylindrical tube filled with the adsorbent 1 was filled with nitrogen containing no reducing agent as shown in Table 4, and a gas discharged from one end of the cylindrical tube was supplied to the other end by using a circulation pump. It was returned and circulated. At the same time, the cylindrical tube
It was heated up to and regenerated for 30 minutes.

After the regeneration treatment, the gas in the cylindrical tube is sampled and N
As a result of measuring the Ox concentration, it was about 13 ppm. As a result, it was found that some or all of NOx is desorbed from the adsorbent 1 without being sufficiently reduced unless hydrocarbon oxygen is contained in the regeneration treatment gas.

[0051]

[Table 4]

Example 7 The NOx adsorbent used in the present invention was prepared as follows.

[0053] and sieved commercial particulate γ-Al ₂ O ₃ by crushing in a mortar into particles having a particle size of 0.5 to 1 mm. This was impregnated with a predetermined amount of dinitrodiamineplatinic acid aqueous solution and dried at 150 ° C. for 2 hours. Further, it was calcined at 500 ° C. for 2 hours to obtain an adsorbent 2. As a result of chemical analysis, platinum (Pt) was supported in an amount of 0.1% by weight based on Al ₂ O ₃ .

Example 8 An adsorbent 3 was obtained in the same manner as in Example 7 except that the aqueous solution of cobalt nitrate was used instead of the aqueous solution of dinitrodiamineplatinic acid in Example 7. The amount and concentration of the cobalt nitrate aqueous solution were adjusted so that the cobalt contained in the adsorbent 3 was 10% by weight.

Example 9 Commercially available Al ₂ O ₃ / SiO ₂
A ZSM-5 zeolite powder having a ratio of about 30 was kneaded with a predetermined amount of an aqueous copper nitrate solution in a mortar, dried at 150 ° C. for 2 hours and then calcined at 500 ° C. for 2 hours to obtain an adsorbent 4. The amount and concentration of the copper nitrate aqueous solution is such that the copper contained in the adsorbent 4 is 1
It was adjusted to be 0% by weight.

(Example 10) Regarding the adsorbents 2 to 4, 2
Table 5 shows the results of an NO adsorption experiment carried out for 15 hours at 5 ° C. under the same conditions as in Example 4. It was found that all the adsorbents had high adsorption ability.

[0057]

[Table 5]

(Example 11) With respect to the adsorbents 2 to 4 which were subjected to the NOx adsorption treatment in Example 10, an adsorbent regeneration experiment was conducted under the same conditions as in Example 5 except that ethylene was used instead of propylene. It was Table 6 shows the results of measuring the NOx concentration by collecting the gas in the cylindrical tube made of quartz glass after the regeneration treatment. It was found that all the adsorbents were simultaneously decomposed and converted into nitrogen when the adsorbed NOx was desorbed.

[0059]

[Table 6]

(Example 12) As to the adsorbents 2 to 4 which were subjected to the NOx adsorption treatment in Example 10, ethyl alcohol was used in place of propylene, and air was used in place of nitrogen, and the same operation as in Example 5 was performed. An adsorbent regeneration experiment was conducted under the conditions. Table 7 shows the results of measuring the NOx concentration by collecting the gas in the cylindrical tube made of quartz glass after the regeneration treatment. It was found that all the adsorbents were simultaneously decomposed and converted into nitrogen when the adsorbed NOx was desorbed.

[0061]

[Table 7]

(Example 13) Regarding the adsorbent 1, 25 ° C
Table 8 shows the result of carrying out the NO adsorption experiment for a predetermined time under the same conditions as in Example 4 except that NO ₂ was used instead of NO. It was found that the adsorbent 1 had a high NO ₂ adsorption capacity.

[0063]

[Table 8]

(Example 14) With respect to the adsorbent 1 which was subjected to the NO ₂ adsorption treatment at 25 ° C for 15 hours in Example 13, a regeneration experiment was conducted under the same conditions as in Example 5. After the regeneration treatment, the gas in the quartz glass cylindrical tube was sampled and the NOx concentration was measured. As a result, it was about 0.2 ppm. Further, the temperature of the adsorbent 1 after the regeneration treatment was raised to 700 ° C. in a nitrogen stream, but NOx
Was not desorbed from the adsorbent. This result adsorbent NO ₂ is adsorbed also can be reproduced treated by the method of the present invention, it was found that the NO ₂ can be reduced and purified on the adsorbent as well as NO.

Example 15 A regeneration experiment was conducted using the adsorbent 4 having NO adsorbed in Example 10.

Gas having the composition shown in Table 9 was filled in a quartz glass cylindrical tube filled with the adsorbent 4 after the adsorption treatment, and the gas flowing out from one end of the cylindrical tube was returned to the other end using a circulation pump. Circulated. Heat cylindrical tube to 200 ° C for 30
It was regenerated for a minute.

The urea used as the reducing agent was stored as an aqueous solution, and a predetermined amount was dropped into a quartz glass tube for urea decomposition heated to 400 ° C. to hydrolyze, and then mixed with other gas components.

After the regeneration treatment, the gas in the cylindrical tube was sampled and N
As a result of measuring the Ox concentration, it was 0.1 ppm or less. From this result, it was found that NO can be reduced and purified on the adsorbent by using urea as the reducing agent.

[0069]

[Table 9]

[0070]

According to the present invention, since it is not necessary to provide a catalyst layer other than an adsorbent when purifying low-concentration NOx, it is possible to perform compact and efficient purifying treatment, especially for automobile tunnels and It is suitable for exhaust gas denitration in underground parking lots.

[Brief description of drawings]

FIG. 1 is a conceptual diagram of an apparatus used for processing a low concentration NOx-containing gas according to the present invention.

FIG. 2 is a conceptual diagram of an apparatus used for processing a low concentration NOx-containing gas according to the present invention.

[Explanation of symbols]

1 ... Exhaust gas containing low concentration NOx, 2 ... Oxidation step, 3
… Ozonizer, 4… Adsorption layer, 5… Ventilation tower, 6… Nitrogen, 7
... Fan, 8 ... Adsorbent unit extracted from adsorption layer 4, 9 ... Hydrocarbon, 10 ... Heating device, 11, 12 ... Flow path switching valve.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hisao Yamashita 7-1, 1-1 Omika-cho, Hitachi-shi, Ibaraki Hitachi Ltd. Hitachi Research Laboratory (72) Inventor Shigeru Shodohata 7-chome, Omika-cho, Hitachi, Ibaraki No. 1 Hitachi Ltd. Hitachi Research Laboratory

Claims (12)

[Claims] 1. A dust removing device for removing dust components in exhaust gas, an adsorbing device for adsorbing and removing NOx, a reducing agent is supplied when the adsorbing device is regenerated, and the adsorbing device is provided when desorbing the collected NOx. A system for treating a low-concentration NOx-containing gas, comprising a control device for reducing and decomposing it into nitrogen inside. 2. After removing dust components in exhaust gas by a dust remover, a NO oxidizing device oxidizes a part or all of NO in exhaust gas to NO ₂ , and an adsorbing device removes NOx by adsorption, and the adsorbing device When regenerating, the reducing agent is supplied to collect the collected N
A treatment system for a low-concentration NOx-containing gas, wherein Ox is reductively decomposed into nitrogen in the adsorption device during desorption. 3. After removing dust components in the exhaust gas by a dust remover, a NO oxidizing device oxidizes a part or all of NO in the exhaust gas into NO ₂ , and an adsorbing device adsorbs and removes NOx. At the time of regeneration of NOx, a gas containing a reducing agent is supplied to desorb the collected NOx, and a part of the NOx is reduced and decomposed into nitrogen in the adsorption device and then introduced into the NOx reduction device.
A treatment system for a low-concentration NOx-containing gas, characterized in that the reduction device purifies the rest of the desorbed NOx by reduction. 4. A system for adsorbing and removing NOx by bringing a low-concentration NOx-containing gas into contact with the adsorbent, and providing a device for reducing the oxygen concentration in the gas flowing through the adsorbent when the adsorbent is regenerated. The treatment system for a low-concentration NOx-containing gas according to claim 1, wherein the oxygen concentration is reduced and a gas containing a hydrocarbon or alcohol is circulated to reduce NOx on the adsorbent into N ₂ . 5. The low-concentration NOx-containing gas treatment system according to claim 4, wherein an inert gas containing hydrocarbons or alcohols is circulated during regeneration of the adsorbent to reduce NOx to N ₂ on the adsorbent. A treatment system for a low-concentration NOx-containing gas, which is characterized by decomposing. 6. A method of adsorbing and removing NOx by bringing a low-concentration NOx-containing gas into contact with the adsorbent, wherein a gas containing a reducing agent is passed during regeneration of the adsorbent, and N 2 is adsorbed on the adsorbent.
Low concentration NO characterized by reducing and decomposing Ox into N _2.
Treatment method of x-containing gas. 7. The method for treating a low-concentration NOx-containing gas according to claim 6, wherein the reducing agent is a hydrocarbon or an alcohol. 8. The method for treating a low-concentration NOx-containing gas according to claim 6, wherein the reducing agent is urea or a decomposition product of urea. 9. The method for treating a low concentration NOx-containing gas according to claim 6, wherein the temperature of the adsorbent packed bed at the time of adsorbent regeneration is adjusted to 100 ° C. to 500 ° C. to perform regeneration. A method for treating a gas containing NOx at a concentration. 10. The low-concentration NOx-containing gas treatment method according to claim 6, wherein the adsorbent has a catalytic action on the reaction between the NOx and the reducing agent.
Treatment method of contained gas. 11. A method for adsorbing and removing NOx by bringing a low-concentration NOx-containing gas into contact with the adsorbent, and flowing a gas containing a reducing agent during regeneration of the adsorbent so that a part of the NOx is removed on the adsorbent. ₂ and decomposed into N in the wake of the adsorbent.
Low concentration NO characterized by having an Ox reduction decomposition step
Treatment method of x-containing gas. 12. A method for adsorbing and removing NOx by bringing a low-concentration NOx-containing gas into contact with the adsorbent, wherein a gas containing a compound that promotes desorption of NOx is circulated during regeneration of the adsorbent, and NOx is adsorbed from the adsorbent. A method for treating a low-concentration NOx-containing gas, characterized in that after desorption, NOx is reduced and decomposed into N ₂ in a NOx reduction-decomposition step provided in the downstream.