JPH0616818B2 - Exhaust gas purification method and device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention relates to nitrogen oxides such as low concentration nitric oxide (NO) and nitrogen dioxide (NO ₂ ) such as ventilation gas from a road tunnel. The present invention relates to a method and an apparatus for purifying exhaust gas containing (NOx).

[Conventional technology]

Ventilation equipment in road tunnels is provided mainly for the purpose of removing visibility obstacles caused by soot dust or maintaining the concentration of harmful substances below a permissible concentration, ensuring the safety of tunnel users and reducing discomfort. As a ventilation method generally used at present, a method of diluting contaminated air by sending fresh outside air into the tunnel or ventilating contaminated air outside the tunnel is used.

On the other hand, in recent road tunnels, there are cases where long tunnels are planned, such as construction of roads with an extension of more than 10 km. In the ventilation equipment for such a long tunnel, it is necessary to construct a ventilation shaft for exchanging air in the middle part of the tunnel, which results in a large construction cost for the ventilation equipment and a large operating cost.

On the other hand, in the conventional ventilation method, the air polluted to a high concentration inside the tunnel is continuously discharged from the well or the ventilation port in a concentrated manner, which causes a problem of pollution of the surrounding atmospheric environment. Therefore, it is desired to develop a new ventilation method that can save energy and reduce the degree of pollution to the surrounding environment. As a method of solving these problems, a method of adsorbing and removing nitrogen oxides in the air discharged from the tunnel with activated carbon has been studied, but in the case of the current activated carbon, the adsorbed amount is not sufficient, It has not been put to practical use because it has a problem in terms of economic efficiency, including recycling costs.

Conventionally, JP-A-49-129671 discloses that NOx is mixed with a gas containing ozone and the mixed gas is passed through an activated carbon layer.
A NOx removing device for removing NOx is disclosed.

JP-A-49-129695 discloses that NO is converted to NO by an MnO ₂ -based catalyst.
_A method of removing NO is disclosed, in which after being oxidized to ₂ , NO is adsorbed and removed by an adsorbent.

JP-A 1-155933 discloses a method of treating ventilation gas from a road tunnel with a zeolite-based adsorbent to remove NOx by adsorption, and then regenerating the adsorbent with NH ₃ -containing high temperature air. There is.

Moreover, in JP-A-1-155934, after treating ventilation gas from a road tunnel with a silica gel-based dehumidifying agent, NOx is adsorbed and removed with a zeolite-based adsorbent, and this treated ventilation gas is passed through the dehumidifying agent. However, a method of heating and regenerating is disclosed.

[Problems to be Solved by the Invention]

As mentioned above, the ventilation gas in the tunnel is currently released into the atmosphere without any treatment. As a purification method,
The adsorption removal method using activated carbon was investigated, but NOx of activated carbon
The amount of adsorption is insufficient and it has not been put to practical use.

The NOx in the tunnel exhaust gas is mainly nitric oxide (NO), and this NO is not adsorbed on the activated carbon or the like as it is, nor is it adsorbed on the alkali adsorbent.

Currently, as described above, mainly, a technology of oxidizing NO to NO ₂ and then adsorbing it to activated carbon or zeolite is being studied, but in the case of activated carbon, there is no NO ₂ adsorption amount that is sufficiently large. However, it is difficult to put it into practical use from the economical aspect. Further, in the case of zeolite, since the adsorption performance of NO ₂ is extremely lowered when there is moisture, it is necessary to dehumidify the treated gas in advance, and a large amount of gas (300 to 40
0Nm ³ / sec) is not practical.

The present invention focuses on the fact that if NO is oxidized to N ₂ O ₅ , it is very easily adsorbed or absorbed, and NO is oxidized by ozone to be converted to N ₂ O ₅ to be absorbed. is there.

However, the oxidation reaction of NO to N ₂ O ₅ has a low reaction rate, it is necessary to take the contact time of NO and ozone for several tens of seconds, and in the case of the treatment of tunnel exhaust gas, there is a restriction on the space of the treatment device.
It is necessary to shorten the reaction time. Therefore, as a result of investigating a catalyst that promotes the oxidation of NO to N ₂ O ₅ , it was found that manganese oxide-based catalyst, nickel oxide-based catalyst, and activated carbon (especially coconut husk activated carbon) are promising.

FIG. 4 shows the effect of catalyst time on the oxidation of NO to N ₂ O ₅ without catalyst. Supply gas NO concentration is 4.4pp
m, the supply gas amount is 5 / min, the O ₃ / NO molar ratio is 4.7, 8.
The experiment was conducted for the cases of 1 and 10.6.
It can be seen from FIG. 4 that it takes about 20 seconds to set the conversion rate of NO to N ₂ O ₅ to 80%.

It should be noted that the above publication does not disclose or suggest any method of removing NOx after oxidizing it to N ₂ O ₅ .

The present invention has been made in view of the above points, NO, NO is mixed with exhaust gas containing NOx such as NO ₂ , NOx by manganese oxide-based catalyst, nickel oxide-based catalyst, activated carbon and the like.
It is an object of the present invention to provide a method and an apparatus for highly efficiently absorbing and removing nitrogen after being oxidized to N ₂ O ₅ .

[Means and Actions for Solving the Problems]

In order to achieve the above object, the exhaust gas purification method according to claim 1 mixes ozone with exhaust gas containing nitrogen oxides (NOx) such as nitric oxide (NO) and nitrogen dioxide (NO ₂ ), By passing the gas through a catalyst layer containing a catalyst substance selected from the group consisting of manganese dioxide, nickel oxide, silicon dioxide, titanium dioxide, copper oxide and activated carbon as a main component,
Nitrogen oxide (NOx) is oxidized to dinitrogen pentoxide (N ₂ O ₅ ) and at the same time unreacted ozone is decomposed.
The catalyst layer is characterized by absorbing and removing N ₂ O ₅ and NOx.

The above-mentioned catalyst substance has an effect of promoting the oxidation of NO to N ₂ O ₅ , N ₂ O ₅ and
It has the effect of absorbing NOx such as NO ₂ and the effect of decomposing unreacted ozone.

The method according to claim 2 is applied to nitric oxide (NO) and nitrogen dioxide (NO ₂ ).
Ozone is mixed with exhaust gas containing nitrogen oxides (NOx), etc.,
Nitrogen oxides (NOx) are obtained by passing this mixed gas through a catalyst layer whose main component is a catalyst substance selected from the group consisting of manganese dioxide, nickel oxide, silicon dioxide, titanium dioxide, copper oxide, and activated carbon. It is characterized by oxidizing undiluted ozone at the same time as oxidizing to dinitrogen pentoxide (N ₂ O ₅ ), and then absorbing and removing N ₂ O ₅ and NOx in this mixed gas with an alkali absorbent.

A method of oxidizing NO to N ₂ O ₅ by the catalyst layer and then absorbing and removing with an alkali absorbent (solid) such as limestone may be used. However, as a result of the experiment, it was revealed that the catalyst itself was absorbed when it was oxidized to N ₂ O ₅ . This is probably because the coexisting water changes to nitrous acid or nitric acid.

The method of claim 3 is characterized in that an alkaline absorbent such as limestone, quick lime or dolomite is mixed with the catalyst substance and used.

The method of claim 4 is characterized in that a mixture of a manganese dioxide-based catalyst or a nickel oxide-based catalyst and activated carbon is used as the catalyst substance.

The method of claim 5 is characterized in that a mixture of a manganese dioxide-based catalyst or a nickel oxide-based catalyst, activated carbon and an alkali absorbent is used as the catalyst substance.

In the above method, the exhaust gas is mixed with ozone, and the mixed gas is passed through the manganese dioxide catalyst layer, the nickel oxide catalyst layer or the activated carbon layer to obtain
Most of NOx is oxidized to N ₂ O ₅ . The exhaust gas subjected to the oxidation treatment is absorbed (adsorbed) by the catalyst or activated carbon, or is absorbed and removed by an alkaline absorbent such as limestone.

The main reaction in the oxidation catalyst layer is as follows.

NO + O ₃ = NO ₂ + O ₂ NO ₂ + O ₃ = NO ₃ + O ₂ NO ₃ + NO ₂ → N ₂ O _{5 In} addition, the reaction when limestone is used as the alkaline agent is
The formula is as follows.

CaCO ₃ + N ₂ O ₅ → Ca (NO ₃ ) ₂ + CO ₂ The method of claim 6 has an O ₃ / NOx molar ratio of 0.5 to 10.
It is characterized by adjusting to the range of.

When the O ₃ / NOx molar ratio is less than 0.5, the production of N ₂ O ₅ is significantly reduced, and when it exceeds 10,
If the electric power required to generate O ₃ increases and it becomes economically disadvantageous, unreacted ozone increases at that time, which may cause secondary pollution.

The method of claim 7 is characterized in that the catalyst layer is heated to 40 to 80 ° C.

When the temperature of the catalyst layer is 40 ° C or higher, the processing gas must be heated, but there is an advantage that the oxidation reaction rate of NO to N ₂ O ₅ is significantly increased, and when it exceeds 80 ° C, The cost required for heating the processing gas increases too much, and when activated carbon is used, oxidation of activated carbon by ozone is promoted, resulting in significant disappearance of activated carbon.

The exhaust gas purifying apparatus according to claim 8, as shown in FIG. 1, was filled with a catalyst for absorbing N ₂ O ₅ by oxidizing NO in the exhaust gas, the NOx such as NO ₂ to N ₂ O ₅ It is characterized by including a catalyst filling portion 1 and an ozonizer 2 connected to the upstream side of the catalyst filling portion 1. 4 is an exhaust fan, and 5 is a ventilation tower.

According to the apparatus of claim 9, as shown in FIG.
O, NOx and N ₂ O ₅ oxide and N ₂ O ₅ catalyst, the alkaline agent filling section 1 filled with a catalyst and an alkaline agent for absorbing such NO ₂
a and an ozonizer 2 connected to the upstream side of the catalyst / alkali agent filled portion 1a.

The apparatus of claim 10 is, as shown in FIG.
NO, NOx in such NO ₂ and catalyst packed portion 1 catalyst was packed to absorb N ₂ O ₅ oxidized to N ₂ O _5, and ozonizer 2 connected to the upstream side of the catalyst packed section 1, It is characterized by including an alkaline agent filling portion 3 connected to the downstream side of the catalyst filling portion 1.

The catalyst filling unit 1, the catalyst / alkali agent filling unit 1a, and the alkali agent filling unit 3 may be either a fixed bed or a moving bed.

〔Example〕

 Hereinafter, examples and comparative examples of the present invention will be described.

Example 1 A cylindrical catalyst packed bed having an inner diameter of 150 mm was packed with a manganese dioxide-based catalyst having an average particle size of 5 mm, and a treated gas obtained by mixing 25.9 ppm of ozone with exhaust gas containing 4.3 ppm of NO and 0.9 ppm of NO ₂ was passed through. The continuous purification treatment was carried out under the following treatment conditions. As a result, 90% of the steady state after continuous operation for about 60 hours
The NOx removal rate was obtained. The gas composition at the layer inlet and outlet was as follows.

(1) Treatment conditions Treatment gas amount 600 / min O ₃ / NO = 5 NOx oxidation catalyst …… Manganese dioxide catalyst Air velocity (SV) of catalyst layer 50,000h ^-1 (room temperature) (2) Supply gas composition NO 4.3ppm NO ₂ 0.9ppm O ₃ 25.9ppm Air balance (3) Catalyst layer outlet gas composition NO 0.2ppm NO ₂ 0.3ppm N ₂ O ₅ 0.0ppm O ₃ 0.0ppm Example 2 Average particle size in cylindrical catalyst packed bed with inner diameter of 150mm A treatment gas in which a manganese dioxide-based catalyst having a diameter of 5 mm and a limestone having an average particle diameter of 5 mm are mixed and filled at a weight ratio of 5: 1, and exhaust gas containing 7.0 ppm of NO and 1.5 ppm of NO ₅ is mixed with 42.0 ppm of ozone. The continuous purification treatment was carried out under the following treatment conditions. As a result, in the steady state after about 60 hours of continuous operation, 92%
The NOx removal rate of was obtained. The gas composition at the layer inlet and outlet was as follows.

(1) Treatment conditions Treatment gas amount 600 / min O ₃ /NO=4.0 NOx Oxidation catalyst …… Manganese dioxide catalyst Alkaline …… Limestone Catalyst / Alkali mixed layer air velocity (SV) 50,000h ^-1 (normal temperature) (2) ) Supply gas composition NO 7.0ppm NO ₂ 1.5ppm O ₃ 42.0ppm Air balance (3) Catalyst / limestone layer outlet gas composition NO 0.1ppm NO ₂ 0.6ppm N ₂ O ₅ 0.0ppm O ₃ 0.1ppm Example 3 of 150mm inner diameter Cylindrical catalyst packed bed was packed with coconut shell activated carbon with an average particle size of 3 mm, and exhaust gas containing NO of 4.5 ppm and NO ₂ of 0.6 ppm was mixed with ozone at 13.1 ppm and passed under the following processing conditions. Purified. As a result, NOx removal rate of 82% was obtained in steady state after continuous operation for about 60 hours. The gas composition at the layer inlet and outlet was as follows.

(1) Treatment conditions Treatment gas amount 600 / min O ₃ /NO=2.5 NOx Oxidation catalyst ...... Coconut husk activated carbon Air velocity in catalyst layer (SV) 80,000h ^-1 (room temperature) (2) Supply gas composition NO 4.5ppm NO ₂ 0.6ppm O ₃ 13.1ppm Air balance (3) Activated carbon layer outlet gas composition NO 0.1ppm NO ₂ 0.8ppm N ₂ O ₅ 0.0ppm O ₃ 0.0ppm Example 4 Average particle size in cylindrical catalyst packed bed with inner diameter of 150mm 5 mm coconut shell activated carbon and coal stone with an average particle size of 5 mm were mixed and filled at a weight ratio of 4: 1 to produce a treated gas in which exhaust gas containing 9.0 ppm of NO and 1.5 ppm of NO ₂ was mixed with ozone of 31.4 ppm. Throughout, continuous purification treatment was carried out under the following treatment conditions. As a result, NOx removal rate of 92% was obtained in the steady state after continuous operation for about 60 hours. The gas composition at the layer inlet and outlet was as follows.

(1) Treatment conditions Treatment gas amount 600 / min O ₃ /NO=3.0 NOx oxidation catalyst …… coconut husk activated carbon alkali ・ ・ ・ Limestone space velocity (SV) 70,000h ^-1 (normal temperature) (2) Supply Gas composition NO 9.0ppm NO ₂ 1.5ppm O ₃ 31.4ppm Air balance (3) Activated carbon / limestone layer outlet gas composition NO 0.3ppm NO ₂ 0.5ppm N ₂ O ₅ 0.0ppm O ₃ 0.0ppm Example 5 Cylindrical type with inner diameter of 150mm The catalyst packed bed is filled with a nickel oxide-based catalyst having an average particle size of 4 mm, and another cylindrical catalyst packed layer having an inner diameter of 150 mm is filled with limestone having an average particle size of 5 mm, and these packed layers are connected in series, A treatment gas in which 57.4 ppm of ozone was mixed with exhaust gas containing 6.1 ppm of NO and 1.1 ppm of NO ₂ was passed through to carry out continuous purification treatment under the following treatment conditions. As a result, a NOx removal rate of 79% was obtained in a steady state after continuous operation for about 60 hours. The gas composition at the layer inlet and outlet was as follows.

(1) Treatment conditions Treatment gas amount 600 / min O ₃ /NO=8.0 NOx oxidation catalyst …… Nickel oxide / diatomaceous earth carrier catalyst Space velocity (SV) of catalyst layer 80,000h ^-1 (normal temperature) Alkaline …… Limestone Air velocity (SV) 200,000h ^-1 (room temperature) (2) Supply gas composition NO 6.1ppm NO ₂ 1.1ppm O ₃ 57.4ppm Air balance (3) Catalyst layer outlet gas composition NO 0.2ppm NO ₂ 1.8ppm N ₂ O ₅ 1.9ppm O ₃ 0.4ppm (4) Limestone layer outlet gas composition NO 0.1ppm NO ₂ 1.4ppm N ₂ O ₅ 0.0ppm O ₃ 0.1ppm Example 6 Oxidation with an average particle diameter of 5mm in a cylindrical catalyst packed bed with an inner diameter of 150mm A nickel-based catalyst and limestone having an average particle size of 5 mm were used in a weight ratio of 4:
1 was mixed and filled, and a treatment gas in which 60.0 ppm of ozone was mixed with exhaust gas containing 7.0 ppm of NO and 1.4 ppm of NO ₂ was passed through to carry out continuous purification treatment under the following treatment conditions. As a result, about
72% NOx in steady state after 60 hours of continuous operation
A removal rate was obtained. The gas composition at the layer inlet and outlet was as follows.

(1) Treatment conditions Treatment gas amount 600 / min O ₃ /NOx=7.0 NOx oxidation catalyst …… Nickel oxide / diatomaceous earth carrier catalyst Alkaline ・ ・ ・ Limestone catalyst / space velocity of mixed layer (SV) 80,000h ^-1 (normal temperature) (2) Supply gas composition NO 7.0ppm NO ₂ 1.4ppm O ₃ 60.0ppm Air balance (3) Catalyst / alkali agent layer outlet gas composition NO 0.3ppm NO ₂ 2.1ppm N ₂ O ₅ 0.0ppm O ₃ 0.2ppm Comparative Example 1 A cylindrical packed bed with an inner diameter of 150 mm was filled with limestone with an average particle size of 5 mm, and exhaust gas containing NO 4.4 ppm and NO ₂ 0.5 ppm was mixed with ozone at 20.2 ppm to pass through the processing gas and continuously purify under the following processing conditions. The treatment was carried out. As a result, only about 25% NOx removal rate was obtained in the steady state after continuous operation for about 60 hours. The gas composition at the layer inlet and outlet was as follows.

(1) Treatment conditions NOx Oxidation catalyst …… No catalyst Alkali ・ ・ ・ Limestone O ₃ / NO = 5 Treatment gas amount 600 / min Air velocity in alkali layer (SV) 50,000h ^-1 (room temperature) (2) Supply gas composition NO 4.4ppm NO ₂ 0.5ppm O ₃ 20.2ppm Air balance (3) Limestone layer outlet gas composition NO 0.5ppm NO ₂ 3.3ppm N ₂ O ₅ 0.0ppm O ₃ 16.2ppm [Effect of the invention] The present invention is configured as described above Therefore, the following effects are achieved.

(1) Since NO and NO ₂ are oxidized to N ₂ O _5, they can be adsorbed / removed or absorbed / removed extremely easily.

(1) manganese dioxide, nickel oxide, silicon dioxide,
Catalytic substances such as titanium dioxide, copper oxide, activated carbon are NO _{2 of} NO.
Since it has the effect of promoting oxidation to O ₅ , the effect of absorbing NO x such as N ₂ O ₅ and NO ₂ , and the effect of decomposing unreacted ozone, it can be purified very efficiently.

(3) A more efficient purification treatment can be achieved by mixing the above-mentioned catalyst substance with an alkaline agent or providing an alkaline agent-filled layer downstream of the catalytic layer. Therefore, a large amount of NOx can be removed with a small amount of scavenger,
It can be greatly improved in terms of economy.

[Brief description of drawings]

1 to 3 are explanatory views showing an embodiment of the exhaust gas purifying apparatus of the present invention, and FIG. 4 is a contact time in the oxidation of NO to N ₂ O _{5 in} the case of no catalyst, and NO it is a graph showing the relationship between the conversion to N ₂ O _5. 1 ... Catalyst filling section, 1a ... Catalyst / alkali agent filling section,
2 ... Ozonizer, 3 ... Alkaline agent filling part, 4 ...
Ventilator, 5 ... Ventilation tower

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Internal reference number FI Technical display location B01J 20/04 ZAB B 7202-4G 21/18 ZAB 8017-4G 23/34 ZAB A 8017-4G 23 / 74 ZAB 8017-4G 321 A 8017-4G C01B 13/10 ZAB D 9152-4G (72) Inventor Kenro Uejima 3-1-1 Higashikawasakicho, Chuo-ku, Kobe-shi, Hyogo Kawasaki Heavy Industries Ltd.

Claims (10)

[Claims] 1. Ozone is mixed with exhaust gas containing nitrogen oxides (NOx) such as nitric oxide (NO) and nitrogen dioxide (NO ₂ ), and the mixed gas is mixed with manganese dioxide, nickel oxide, silicon dioxide, and dioxide. Nitrogen oxide (NOx) is oxidized to dinitrogen pentoxide (N ₂ O ₅ ) at the same time by passing through a catalyst layer containing a catalyst substance selected from the group consisting of titanium, copper oxide and activated carbon as a main component. A method for purifying exhaust gas, which comprises decomposing reaction ozone and further absorbing and removing N ₂ O ₅ and NOx in the mixed gas by the catalyst layer. 2. Ozone is mixed with exhaust gas containing nitrogen oxides (NOx) such as nitric oxide (NO) and nitrogen dioxide (NO ₂ ), and this mixed gas is mixed with manganese dioxide, nickel oxide, silicon dioxide, and dioxide. Nitrogen oxide (NOx) is oxidized to dinitrogen pentoxide (N ₂ O ₅ ) at the same time by passing through a catalyst layer containing a catalyst substance selected from the group consisting of titanium, copper oxide and activated carbon as a main component. After decomposing reaction ozone, N ₂ O ₅ and NOx in this mixed gas are absorbed and removed by an alkali absorbent, and an exhaust gas purification method is provided. 3. The exhaust gas purification method according to claim 1, wherein an alkaline absorbent such as limestone, quick lime or dolomite is mixed with the catalyst substance. 4. The exhaust gas purification method according to claim 1, wherein a mixture of a manganese dioxide catalyst or a nickel oxide catalyst and activated carbon is used as the catalyst substance. 5. The exhaust gas purification method according to claim 1 or 2, wherein a mixture of a manganese dioxide-based catalyst or a nickel oxide-based catalyst, activated carbon and an alkali absorbent is used as the catalyst substance. 6. The exhaust gas purification method according to claim 1 or 2, wherein the O ₃ / NOx molar ratio is adjusted in the range of 0.5 to 10. 7. The exhaust gas purification method according to claim 1 or 2, wherein the catalyst layer is heated to 40 to 80 ° C. 8. A method for oxidizing NOx such as NO and NO _{2 in} exhaust gas to N ₂ O ₅
Catalyst filling part filled with a catalyst for absorbing N ₂ O ₅ (1)
And an ozonizer (2) connected to the upstream side of the catalyst filling section (1). 9. Oxidizing NOx such as NO and NO _{2 in} exhaust gas to N ₂ O _5.
A catalyst / alkali agent filling part (1a) filled with a catalyst for absorbing N ₂ O ₅ and an alkali agent, and an ozonizer (2) connected to the upstream side of the catalyst / alkali agent filling part (1a). An exhaust gas purification device characterized by including. 10. NO in exhaust gas, the catalyst-filled portion of NOx such as NO ₂ was filled with a catalyst for absorbing N ₂ O ₅ oxidized to N ₂ O ₅ (1), the catalyst packed section (1 ), An ozonizer (2) connected to the upstream side of (1), and an alkali agent charging section (3) connected to the downstream side of the catalyst charging section (1).