JPH0788327A - Nox purging device - Google Patents

Abstract

PURPOSE:To efficiently remove NOx from an automobile tunnel exhaust gas, etc., contg. reducing suspended matter by providing an oxidation part for oxidizing nitrogen monoxide to nitrogen dioxide and dry absorbent beds for absorbing the nitrogen dioxide and furnishing a second oxidation part between the beds. CONSTITUTION:An oxidation part 12 to bring about an oxidation reaction by an electrical discharge, etc., using an electrode plate and dry absorbent beds 13 independent of each other to adsorb or absorb nitrogen dioxide are provided to an main body 10. An ozonizer 15 is furnished between the beds 13, and ozone is supplied to a second oxidation part 17 through an ozone feed pipe 16 to oxidize NO to NO2. The second oxidation part is provided between the absorbent beds to purge the NOx with high efficiency.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to nitrogen oxides (NO _x ).
Purification device. More specifically, especially for the purpose of removing nitrogen oxides in exhaust gas emitted from automobiles,
The present invention relates to a purification device used for purification of exhaust gas from an automobile road tunnel, an intersection, particularly a highly sealed parking lot, and purification of air introduced into a building near the intersection.

[0002]

2. Description of the Related Art In recent years, NO _x emitted from automobiles is
From where it leads to the deterioration of the local environment and the destruction of the global environment,
Development of technology for preventing or purifying such generation is ongoing. However, especially as the automobile society develops, NO _X generated from a vehicle is difficult to purify because it mixes with the atmosphere immediately after generation and has a low concentration and a large air volume. However, especially in a motor vehicle road tunnels, for stagnant exhaust gas to a certain enclosed space harmful gas concentrations, including NO _X from the outer tunnel rises. In such a tunnel, but the concentration of the internal noxious gases are ventilated so as not to exceed the reference value, typically several tens of times or more of the NO _X in the air is discharged from the exhaust port. Recently, automobile tunnels using underground urban is planned, also the exhaust location tunnel air is originally poor place environment, is concerned worsen further environmental purification device of the NO _X is sought Has been done. Conventionally, a denitration device as disclosed in Japanese Patent Laid-Open No. 1-224031 has been generally used as this type of purification device. The configuration will be described below with reference to FIG. 7. As shown in FIG. 7, the tunnel exhaust gas 11 drawn in by the fan 14
Of NO and NO ₂ which are the main components of NO _X contained in NO, NO is oxidized to NO ₂ by the oxidizing unit 12. And NO ₂ obtained by the oxidation, is absorbed by the dry absorbent filter 18 also originally both present are the NO _2.

[0003]

In the case of purifying an actual automobile tunnel exhaust gas by the denitration device shown in the conventional example, the exhaust gas contains nitric oxide (N).
O) is present at a concentration more than several times that of nitrogen dioxide (NO ₂ ), but NO itself is a gas that is much less likely to be adsorbed than NO ₂ , and therefore a discharge phenomenon or ozone is introduced.
The step of oxidizing the carbon dioxide to NO ₂ is provided before the dry adsorbent. However, in an actual automobile tunnel exhaust gas, there is simultaneously a reducing suspended substance mainly containing carbon, which is mainly contained in diesel engine exhaust gas, and this adheres to the surface of the dry absorbent. A remarkable phenomenon is that NO ₂ is reduced to NO before being absorbed. That is, in the process of oxidizing NO to NO ₂ , NO _x in the exhaust gas
All even be converted to NO _2, NO ₂ for reducing suspended solids adhering to the dry absorbent layer is again converted into NO, will be discharged without being purified. In reality, it is difficult to obtain a NO _x purification rate of 50% or more due to the reducing suspended solids. Although expected improvement of some of the NO _X purification performance by raising the oxidation capacity, the excess in this case oxidation process ozone will be generated, when this is discharged, the secondary pollution due to new environmental destruction The problem arises. Therefore, a first object of the present invention is to provide a nitrogen oxide purification device having high NO _x purification efficiency. A second object of the present invention is to provide a nitrogen oxide purifying device without secondary pollution.

[0004]

The first technical means of the present invention for achieving the above first object is an oxidizing part for oxidizing NO to NO ₂ , and a dry absorbent for adsorbing or absorbing NO _2. In a purification device having layers, the dry absorbent layer is divided into at least two independent layers and NO is placed between the layers.
_{The second step} is to add a second oxidation part that oxidizes to 2. A second technical means of the present invention for achieving the above-mentioned second object is to provide a carbonaceous substance for purifying ozone, an oxide of Mn, an oxide of Cu, and Fe downstream of the second oxidation part. A layer containing at least one of the above oxides. This ozone purifying substance may be added to the layer of the dry absorbent, or an independent filter layer may be provided.

[0005]

According to the above-mentioned technical means, even if NO ₂ is reduced to NO due to the reducing suspended solids adhering to the dry absorbent layer, the NO ₂ is re-generated by the second oxidizing section provided by the present invention.
It can be absorbed and purified by the dry absorbent layer that has been oxidized to ₂ and is not affected by the reducing suspended solids in the next layer. Also,
Excess ozone generated by the oxidation part is caused by the action of the carbonaceous substance, Mn oxide, Cu oxide or Fe oxide mixed in this dry absorbent, or the action of another filter layer containing these substances. Purified.

[0006]

EXAMPLES Examples of the present invention will be described below, but the present invention is not limited to these examples. [Embodiment 1] FIG. 1 shows an embodiment of the purifying apparatus of the present invention. Reference numeral 10 is a purifying apparatus main body, and the gas to be purified containing NO _X and reducing suspended solids passes through the main body 10 as indicated by an arrow indicated by 11. Reference numeral 12 denotes an oxidizer, which uses a method of causing an oxidation reaction by discharge using an electrode plate or supplying ozone to oxidize. Reference numeral 13 is a dry absorbent layer, and shows an example in which two independent layers are provided. Reference numeral 14 denotes a fan for driving the gas to be purified, which is installed on the outlet side of the main body here, but may be installed on the inlet side of the apparatus main body between the dry absorbent layers or between the oxidizing section and the dry absorbent layer. . Reference numeral 15 is an ozone generator, which supplies ozone to the second oxide 17 between the layers of the dry absorbent layer by an ozone supply pipe 16 to supply NO to NO.
Oxidize to O ₂ . In the purifying device having the above structure, the oxidizing unit controls the oxidizing ability so that 95% of NO can be converted into NO ₂ . On the other hand, the dry absorbent consists of activated carbon or manganese dioxide and gypsum of cement material and has a particle size of about 10 mm.
The granules having the composition shown in Table 1 in which caustic potash is supported are used, and the upstream layer is 10 liters and the downstream layer is 20 liters. In addition, since ozone is supplied to the second oxidation unit 17 so that the remaining amount of unoxidized NO is 0.2 ppm or less, the excess ozone concentration in that portion is about 0.5 ppm.

[0007]

[Table 1]

Thus, the purified gas containing NO of _2.5 ppm, NO ₂ of 0.5 ppm, and reducing suspended solids of 0.2 mg / m ³ is supplied to the purifying device at a rate of 100 m ³ / h to remove NO _x . The purification rate was investigated. The result is shown in FIG. Fig. 2 shows the NO _x purification rate over time, where a is the composition A dry absorbent and b is the composition B.
It shows the characteristics when using the dry absorbent of. Also,
Figure 3 shows the ozone concentration in the exhaust gas.
No ozone was observed when (a) was used, whereas a slight amount of ozone was emitted when (b) was used. However, all of them have a very low concentration of ozone, and there is no danger of secondary pollution.

[Comparative Example 1] FIGS. 2c and 2d are compositions evaluated using the compositions A and B as absorbents under substantially the same conditions as above, but the ozone supply between the layers of the dry absorbent layer is shown. The evaluation results in the state where it is not shown are shown. This test condition is similar to the condition shown in the conventional example, and the performance of the present invention is greatly reduced regardless of which dry absorbent is used.

[Second Embodiment] FIG. 4 shows a second embodiment of the present invention. Similar to the first embodiment, but here layer 1
A honeycomb structure made of porous alumina is used as the dry absorbent of No. 3, and an independent filter 18 is installed for ozone purification. For this filter, 5 liters of a granulated product having a composition shown in Table 2 and having a particle size of about 10 mm, which is obtained by curing activated carbon or various oxide powders with gypsum as a cement material, is used.

[0011]

[Table 2]

FIG. 5 shows the result of the NO _x purification test conducted on the apparatus of this embodiment under the same conditions as in the first embodiment.
Since an almost identical purification rate curve was drawn regardless of the composition of the ozone purification filter, the one (e) using the composition E ozone purification filter is shown as a representative. FIG. 6 shows the ozone emission concentration. The ozone emission concentration varied depending on the ozone purification filter. e, f, g, and h represent the emission concentrations of ozone when the ozone purification filters of compositions E, F, G, and H are used.

[Comparative Example 2] In FIG. 5, i is evaluated under almost the same conditions as above, but shows an evaluation result in a state where ozone is not supplied between the layers of the dry absorbent layer. This test condition is similar to the condition shown in the conventional example. Even if this porous alumina honeycomb structure is used as a dry absorbent, the NO _x purification rate is greatly reduced due to the influence of the reducing suspended solids. . [Comparative Example 3] j of FIG. 6 shows a change with time of the discharged ozone concentration of the evaluation conducted without installing the ozone purification filter.
As is clear from this result, a very dangerous amount of ozone is emitted.

[0014]

As described above, by providing the second oxidation portion between the layers of the dry absorbent layer of the present invention, NO _{x can be produced at a} high rate from a gas containing a reducing floating substance such as automobile exhaust gas.
Can be purified. In addition, by providing a layer containing any one of a carbon-based substance, Mn oxide, Fe oxide, and Cu oxide downstream of the second oxide, ozone generated
It is possible to obtain a NO _x purifying device which is free of secondary pollution.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing the configuration of a nitrogen oxide purifying apparatus according to a first embodiment of the present invention.

FIG. 2 is a diagram showing a NO _x purification rate by the nitrogen oxide purification device of the first embodiment of the present invention in comparison with a conventional example.

FIG. 3 is a diagram similarly showing an ozone emission concentration.

FIG. 4 is a schematic diagram showing the configuration of a nitrogen oxide purifying apparatus according to a second embodiment of the present invention.

FIG. 5 is a diagram showing the NO _x purification rate by the nitrogen oxide purification device of the second embodiment of the present invention in comparison with the conventional example.

FIG. 6 is a diagram similarly showing ozone emission concentration.

FIG. 7 is a schematic diagram showing a configuration of a conventional denitration device.

[Explanation of symbols]

 10 Purification Device Main Body 11 Exhaust Gas Flow 12 Oxidation Part 13 Dry Absorbent Layer 14 Fan 15 Ozone Generator 16 Ozone Supply Pipe 17 Second Oxidation Part 18 Ozone Purification Filter

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Claims (2)

[Claims] 1. An apparatus for purifying nitrogen oxides in a gas containing nitrogen oxides and reducing suspended solids, comprising an oxidation unit for oxidizing at least nitric oxide to nitrogen dioxide and adsorbing or absorbing nitrogen dioxide. A nitrogen oxide purifying apparatus comprising: at least two independent dry absorbent layers; and a second oxidation unit that oxidizes nitric oxide into nitrogen dioxide between the dry absorbent layers. 2. A carbonaceous substance for purifying ozone, an oxide of Mn, an oxide of Cu, and F are provided downstream of the second oxide.
The nitrogen oxide purification apparatus according to claim 1, further comprising a layer containing at least one of the oxides of e.