JPH0741142B2 - Method for removing low-concentration nitrogen oxides in road tunnel ventilation gas - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION This invention, low concentrations of nitric oxide contained in the ventilation gas from road tunnels (NO), for adsorbing and removing nitrogen dioxide (NO ₂₎ nitrogen oxides etc. (NOx) It concerns the removal method. The low concentration referred to here is a range of 50 ppm or less. In the case of exhaust gas treatment in a normal thermal power plant, the NOx concentration contained in the exhaust gas is several hundred ppm, and this is reduced to several + ppm by the ammonia reduction method (SCR method) using a denitration catalyst. On the other hand, the method of the present invention is applicable to the case where the NOx concentration is further reduced below the concentration level of NOx contained in the SCR process gas .

[0002]

2. Description of the Related Art Ventilation equipment in road tunnels is mainly intended to remove visibility obstacles caused by soot dust or to maintain the concentration of harmful substances below a permissible concentration to ensure the safety of tunnel users and reduce discomfort. It is provided. 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 a recent road tunnel, the total length is 10 km.
There are cases where a long tunnel is planned, such as one that exceeds the limit. In such a long ventilation equipment for a 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 an adsorbent has been studied. As the main adsorbent,
There are activated carbon and zeolite.

For example, in Japanese Unexamined Patent Publication No. 54-161582, carbon containing NOx is impregnated with one or more of alkali metal nitrates, nitrites, carbonates, and hydroxides. A method for removing NOx in a gas by contacting it with a substance as a main component is described. Further, Japanese Patent Laid-Open No. 1-155934 describes a method of absorbing and removing NOx by absorbing moisture in a road tunnel ventilation gas with a silica gel dehumidifying agent and then dry-treating with a zeolite adsorbent. ing. In addition, Japanese Examined Japanese Patent Publication Sho 63-22181
Japanese Patent Laid-Open Publication No. 2005-242242 discloses a method of adsorbing and removing NOx by contacting an adsorbent obtained by heating and dehydrating tuff containing mordenite and / or clinoptilolite without drying an O ₂ -containing gas containing NOx without drying. Is listed. Furthermore, “Catalyst” Vol. 31 No. 8th 586
On the page, α-Fe ₂ O ₃ highly dispersed ACF (activated carbon fiber)
However, there is a description that NO can be adsorbed like vapor.

[0004]

When activated carbon is used,
It has the ability to adsorb nitrogen dioxide (NO ₂ ), but once it has been adsorbed, when it is desorbed and regenerated with heated air, it is oxidized by oxygen in the air to become carbon dioxide gas and consumed ( However, since there is a risk of fire when regenerating at high temperatures of several hundreds of degrees or more, there is a drawback that it must be taken out of the system and regenerated, which is practical for denitration of tunnel ventilation gas. Not.
Further, in order to reduce the power consumption required for the treatment, it is necessary to reduce the pressure loss in the adsorbent layer as much as possible. Therefore, a honeycomb type is desirable as the shape of the adsorbent,
In the case of activated carbon, it is said that honeycomb forming is relatively difficult. Further, when zeolite is used, the zeolite is affected by moisture coexisting in the treatment gas, and has a low NOx adsorption capacity in the normal humidity range of the tunnel ventilation gas, and the moisture in the treatment gas must be dehumidified in advance. However, it is not practical in the case where the relative humidity is relatively high and the amount of treated gas is large, as in the case of tunnel exhaust gas. In addition, when using tuff containing mordenite or / and clinoptilolite, it is a natural product and thus the performance as an adsorbent varies, and it is difficult to form it into a pipe type, a honeycomb type or the like. There is. Further, the adsorbent described in the above-mentioned document “Catalyst” is an adsorbent in which α-Fe ₂ O ₃ is dispersed in fibrous activated carbon, and it is difficult to regenerate with high temperature air like the above-mentioned activated carbon. have.

The inventors of the present invention have found that activated alumina is suitable for a ventilation gas having a relatively high humidity as a result of searching for an adsorbent having a NOx adsorption capacity without dehumidification. Furthermore, as a result of extensive studies on a method of increasing the adsorption capacity of NOx, by incorporating oxides of alkali elements such as sodium and potassium and / or oxides of alkaline earth elements such as magnesium and calcium into activated alumina, It was found that the adsorption capacity increased significantly. In particular, it was found that the content ratio is 0.3 to 40% by weight, preferably 0.5 to 20% by weight. If the content is less than 0.3% by weight, the effect is small, and if the content exceeds 40% by weight, durability in repeated adsorption / regeneration is reduced, which is not practical. Furthermore, 0.3 to 10% by weight of the above NOx adsorbent,
Nitric oxide (NO) generated on the surface of the adsorbent, preferably by including 0.5 to 5% by weight of iron oxide, copper oxide, cobalt oxide, nickel oxide or manganese oxide.
It was found that the amount of NOx can be reduced and a higher NOx removal rate can be obtained. If the content is less than 0.3% by weight, the effect is small, and if the content exceeds 10% by weight, the surface area of the adsorbent is reduced, and the NOx adsorption capacity is reduced.

Further, when the adsorbent continues to adsorb nitrogen oxides, the adsorbed amount increases and gradually approaches the saturated adsorbed amount, and the NOx concentration at the adsorbent packed bed outlet increases from a certain point of time. In this case, stop the adsorption once, 150-600 ℃
It has been found that heating air in the range of, preferably heating air in the range of 200 to 500 ° C. can be regenerated and returned to the initial performance by passing the adsorbent packed bed to desorb the adsorbed NOx. Further, most of NOx in the tunnel ventilation gas (about 80 to 90%) is nitric oxide (NO), but when treating such a gas, nitric oxide and equimolar ozone (O ₃ ) are used in advance. By a method such as mixing
It was found that if nitric oxide (NO) is oxidized to nitrogen dioxide (NO ₂ ), it can be easily adsorbed and removed. The present invention is
The present invention has been made in view of the above points based on the above findings, and an object thereof is to provide a method for removing low-concentration NOx using a NOx removing agent having a high NOx adsorption capacity without dehumidifying the processing gas. It is a thing.

[0007]

Means and Actions for Solving the Problems In order to achieve the above object , a low concentration in a ventilation gas for a road tunnel of the present invention is provided.
The method of removing nitrogen oxides is to use monoxide in road tunnel ventilation gas containing low concentrations of nitrogen oxides of 50ppm or less.
After oxidizing nitrogen to nitrogen dioxide, the gas is contacted with an activated alumina-based adsorbent containing an oxide of at least one element selected from the group consisting of sodium, potassium, magnesium and calcium (dry type). process) is not nitrogen dioxide <br/> adsorbed removed, 150 a sorbent that has adsorbed nitrogen dioxide
It is characterized in that it is treated with hot air at 600 ° C. and regenerated. If the ratio of the oxide of at least one element selected from sodium, potassium, magnesium, and calcium contained in the activated alumina-based adsorbent is too large, the strength of the adsorbent and the durability during repeated use of adsorption and regeneration deteriorate. If it is too small, the NOx adsorption capacity will decrease. Therefore, sodium, potassium, magnesium,
As an oxide of at least one element selected from calcium, 0.3 to 40% by weight, preferably 0.5 to 2
The range is 0% by weight.

In some cases, the oxide of at least one element selected from sodium, potassium, magnesium, and calcium is included together with 0.3 to 10% by weight of iron oxide. This is intended to suppress the generation of nitric oxide, and if the iron oxide is too much, the specific surface area of the activated alumina-based adsorbent will be reduced, and if it is too little, the effect will be reduced. Therefore, 0.3 to 1 as iron oxide
It is 0% by weight, preferably 0.5 to 5% by weight. That is, an oxide of at least one element selected from the group consisting of sodium, potassium, magnesium, and calcium, and an oxide of at least one element selected from the group consisting of iron, copper, cobalt, nickel, and manganese.
It is desirable to use an activated alumina-based adsorbent containing 3-10% by weight.

The above-mentioned adsorbent that adsorbs NOx is
Adsorbed NOx is desorbed using high-temperature air (hot air), and the desorbed high-concentration NOx is reduced to nitrogen and oxygen by a catalytic reduction method using ammonia to render it harmless. At this time, if the temperature of the high temperature air used for regeneration is too low, regeneration is insufficient, and if it is too high, it is economically disadvantageous. Therefore, the temperature range of the high temperature air for regeneration is 150 to 600 ° C, preferably 200 to 500 ° C. In addition, it is preferable to use a honeycomb-shaped adsorbent in order to reduce the pressure loss in the packed bed of the adsorbent as much as possible and to prevent clogging due to dust in the processing gas. The shape of the honeycomb is, for example, 40 × 4 with a 200 mm opening.
A cell having 0 cells and a length of about 1 m is suitable. Also road tons
Most of the nitrogen oxides in the flannel ventilation gas are nitric oxide
Therefore , since nitrogen dioxide has a larger adsorption rate and adsorption capacity than nitrogen monoxide and is easier to adsorb and remove, nitric oxide in ventilation gas is oxidized to nitrogen dioxide, and then dry treated with an adsorbent to perform nitrogen oxidation. It is configured to adsorb and remove an object . The method of the present invention, the concentration of nitrogen oxides in road tunnels ventilation gas to be processed is to Target the low concentration of nitrogen oxides under 50Pp m or less. In the removal of nitrogen oxides having a higher concentration than this, the reduction treatment with ammonia gas using a catalyst is more economically advantageous. Thus, "low-concentration nitrogen oxides" in the method of the present invention, the "50Pp m nitrogen oxides follows" referred to the finger.

[0010]

EXAMPLES Hereinafter, examples and test examples of the present invention will be described. Test Example 1 The NO ₂ adsorption capacities of various adsorbents were measured and compared. That is, activated carbon that is a general-purpose adsorbent, hydrophobic zeolite,
Using four adsorbent activated alumina及beauty 3 wt% Na ₂ O-containing activated alumina, was subjected to cleaning test of air containing 5ppm of NO _2. Specifically, each of these four kinds of adsorbents was filled in a cylindrical container having an inner diameter of 22 mm and a height of 220 mm, NO ₂ -containing air was sent from the lower part of the container, and purified air was extracted from the upper part of the container. . The test conditions were as follows. Adsorbent: Activated alumina containing 3 wt% Na ₂ O 1-2 mm spherical 72 ml Activated alumina 1-2 mm spherical 72 ml Hydrophobic zeolite 0.5 mm φ × 4 mm cylindrical 72 ml Activated carbon 1-2 mm spherical 72 ml Processing gas: NO ₂ 5 ppm-Air 12 l / Min Relative humidity 60% (25 ° C) SV (space velocity): 10,000 h ^-1 adsorbent layer temperature: 40 ° C The test results are shown in FIG. 1. As can be seen from FIG. 1, NO ₂
The adsorption performance of O is as follows: activated alumina containing Na ₂ O> activated carbon>
Activated alumina> hydrophobic zeolite order, Na ₂
The O-containing activated alumina was the best.

Test Example 2 The effect of including MgO in the activated alumina adsorbent was tested. That is, as an adsorption remover, MgO was added to activated alumina and similar alumina at 3 wt% and 9 w
An adsorption test of NO ₂ was conducted using the one containing t%. The test conditions were as follows. Adsorbent: 3 wt% MgO-containing activated alumina 1-2 mm spherical 72 ml 9 wt% MgO-containing activated alumina 1-2 mm spherical 72 ml Activated alumina 1-2 mm spherical 72 ml Processing gas: NO ₂ 5 ppm-Air 12 l / min Relative humidity 60% (25% C) SV (space velocity): 10,000 h ⁻¹ adsorbent layer temperature: 40 ° C. The test results are shown in FIG. 2. As can be seen from FIG. 2, NO ₂
The higher the MgO content, the better the adsorption performance of.

Test Example 3 An adsorption test of NO ₂ was carried out on a honeycomb-type activated alumina containing iron oxide and Na ₂ O. That is, as an adsorption removal agent, a honeycomb activated alumina, the N _{a 2} O 3
An adsorption test of NO ₂ was conducted using a honeycomb-type activated alumina containing 1 wt% and ₂ wt% of Fe ₂ O ₃ .
The test conditions were as follows. Adsorbent: Honeycomb type activated alumina Na ₂ O ₃ wt% and Fe ₂ O ₃ 2 wt% containing honeycomb type active Arna Honeycomb adsorbent shape: 20 mm square × 1800 mm L 16 cells (4 cells × 4 cells) Processing gas: NO ₂ 5 ppm-Air 48 l / min Relative humidity 70% (25 ° C.) SV (space velocity): 4,000 h ⁻¹ adsorbent layer temperature: 30 ° C. The test results are shown in FIG. 3. As can be seen from FIG. 3, NO ₂
The honeycomb type activated alumina containing Na ₂ O and Fe ₂ O ₃ was excellent in the adsorption performance.

Test Example 4 A NO ₂ adsorption / regeneration repeating test was carried out using MgO-containing activated alumina. That is, as the adsorption remover, Mg
A repeated adsorption / regeneration test of NO ₂ was performed using a honeycomb-type activated alumina containing 4 wt% of O and 1 wt% of Fe ₂ O ₃ . The test conditions were as follows. Adsorbent: 4 wt% of MgO and 1 wt% of Fe ₂ O ₃ Honeycomb type activated alumina Honeycomb adsorbent shape: 20 mm square × 1800 mm L 16 cells (4 cells × 4 cells) Processing gas: NO ₂ 5 ppm-Air 48 l / min Relative Humidity 70% (25 ° C.) SV (space velocity): 4,000 h ⁻¹ adsorbent layer temperature: 30 ° C. The test results are shown in FIG. 4. As can be seen from FIG. 4, 5 pp
Even if mNO ₂ adsorption and 450 ° C. hot air regeneration treatment were repeated, no change in NO ₂ adsorption performance was observed, indicating that this honeycomb adsorbent can be repeatedly used. Note that MgO
It was confirmed that an adsorbent using Na ₂ O, CaO, or K ₂ O instead of the above can also be repeatedly used in the same manner.

Example 1 An adsorption test of NO was carried out on activated alumina containing Na ₂ O. That is, as an adsorption removal agent, the Na ₂ O 7 wt
% And Fe ₂ O ₃ 3 wt% were used to conduct an adsorption test of NO using honeycomb-type activated alumina. The test conditions were as follows. Adsorbent: Na ₂ O ₇ wt% and Fe ₂ O ₃ 3 wt% contained honeycomb type activated alumina Honeycomb adsorbent shape: 20 mm square × 1800 mm L 16 cells (4 cells × 4 cells) Processing gas: NO 5 ppm-O ₃ 5 ppm-Air 48 l / min relative humidity 55% (25 ° C.) SV (space velocity): 4,000 h ⁻¹ adsorbent layer temperature: 25 ° C. The test results are shown in FIG. N for gas containing 5ppm NO
O and equimolar ozone (O ₃ ) were mixed to oxidize NO to NO ₂ , and then the adsorbent was used for adsorption treatment. As a result, as can be seen from FIG. 5, it was possible to remove by adsorption in the same manner as the treatment with 5 ppm NO ₂ . In addition, no change in NO ₂ adsorption performance was observed even after repeated adsorption and 450 ° C. hot air regeneration treatment, indicating that the adsorbent of the present invention can be repeatedly used. In addition, instead of Na ₂ O, MgO, CaO,
It was confirmed that the adsorbent using K ₂ O could be used repeatedly as well.

[0015]

Since the present invention is constructed as described above, it has the following effects. (1) Occupy most of nitrogen oxides in tunnel ventilation gas
Oxidize nitric oxide to nitrogen dioxide that is easy to remove by adsorption
After processing, this nitrogen dioxide is adsorbed and removed, so low concentration
Even nitrogen oxides of a certain degree can be removed efficiently. ( 2 ) In the method of the present invention, an activated alumina-based adsorbent containing an oxide of at least one element selected from the group consisting of sodium, potassium, magnesium and calcium is used. And, the adsorption capacity of nitrogen oxide is large even in the case of high-humidity process gas. ( 3 ) Since the method of the present invention uses the adsorbent shown in ( 2 ), there is no fear of exhaustion or fire due to oxidation even in regeneration with heated air as in the case of the activated carbon adsorbent.
Excellent in durability after long-term adsorption and regeneration. ( 4 ) Since the method of the present invention uses the adsorbent shown in ( 2 ), it has an advantage that the honeycomb molding can be relatively easily performed, and in this case, the pressure loss of the adsorbent layer can be reduced .

[Brief description of drawings]

FIG. 1 is a graph showing the test results in Test Example 1, showing a comparison of NOx adsorption capacities of various adsorbents.

FIG. 2 shows the test results in Test Example 2, where Mg
It is a graph which shows the effect of O addition.

FIG. 3 is a graph showing the test results in Test Example 3 and showing a comparison of NO adsorption by honeycomb-type activated alumina.

FIG. 4 is a graph showing the test results in Test Example 4, showing the adsorption / regeneration repeating characteristics.

FIG. 5 shows the test results in Example 1 , NO
Is a graph showing the effect of treatment (O ₃ oxide-adsorption).

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical display location B01J 20/08 C 7202-4G 20/34 F 7202-4G H 7202-4G B01D 53/34 ZAB ( 72) Inventor Yoshinori Matsuo 3-1-1 Higashikawasaki-cho, Chuo-ku, Kobe-shi, Hyogo Kawasaki Heavy Industries, Ltd. Kobe factory (56) Reference JP-A-49-63685 (JP, A) JP-A-63-264136 (JP, A) Japanese Patent Publication 6-16818 (JP, B2)

Claims (4)

[Claims] The method according to claim 1] 50ppm or less of nitric oxide of a road tunnel ventilation gas containing a low concentration of nitrogen oxides dioxide
After oxidizing to nitrogen, this gas is contacted with an activated alumina-based adsorbent containing an oxide of at least one element selected from the group consisting of sodium, potassium, magnesium and calcium to adsorb and remove nitrogen dioxide, Road tunnel ventilation gas characterized by treating an adsorbent having adsorbed nitrogen with high temperature air of 150 to 600 ° C. to regenerate it.
Method for removing low-concentration nitrogen oxides in medium. 2. The ratio of the oxide of at least one element selected from the group consisting of sodium, potassium, magnesium and calcium contained in the activated alumina adsorbent is
Low in the road tunnel ventilation gas according to claim 1, characterized in that an adsorbent in the range of 0.3-40% by weight is used.
Method for removing concentrated nitrogen oxides. 3. Sodium, potassium, magnesium,
An activity containing 0.3 to 10% by weight of an oxide of at least one element selected from the group consisting of iron, copper, cobalt, nickel and manganese, together with an oxide of at least one element selected from the group consisting of calcium. The road torus according to claim 1 or 2, wherein an alumina-based adsorbent is used .
A method for removing low-concentration nitrogen oxides in ventilation gas . 4. A honeycomb type adsorbent is used.
Road ton of claim 1, 2 or 3, wherein the that
Method for removing low-concentration nitrogen oxides from flannel ventilation gas .