JPH11128673A - Apparatus for purifying gas - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the amt. of an absorbent used by providing a two-stage structure to an absorption part in an apparatus for purifying exhaust gas in an automobile tunnel and introducing an absorbing soln. having deteriorated absorbing performance in the post-stage absorption part into the fore-stage absorption part. SOLUTION: Exhaust gas 1 contg. dust and NOx is introduced into a gas inlet 3 by a blower 2 and the NOx in the gas is oxidized to NO2 by a method such as the addition of ozone by an NOx oxidizing means 5. The NO2 -contg. gas and the dust are sent to a fore-stage absorption part 29 through a dust removing means 6 and the absorption of excess ozone and the preabsorption of the NO2 are carried out. The absorption of the remaining NO2 in the gas is then carried out in the post-stage absorption part 7. An absorbing soln. having deteriorated absorbing performance in the post-stage absorption part 7 is introduced into the fore-stage absorption part 29, the excess ozone is absorbed in the soln. and a fresh absorbing soln. is supplied to the post-stage absorption part 7. The leak of ozone into the post-stage absorption part 7 is suppressed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to an automobile tunnel,
The present invention relates to a gas purification device mainly used for removing NOx and dust in a gas at a place where dust and gas containing low concentration NOx are concentrated at an intersection, an indoor parking lot, a highway, and the like.

[0002]

2. Description of the Related Art In recent years, with the increase in traffic, in places such as automobile tunnels, intersections, indoor parking lots, and highways where traffic is particularly frequent, that is, places where the concentration of exhaust gas from automobiles is high, gas emissions are low. The treatment of dust and NOx is problematic.

Conventionally, in an automobile tunnel or the like, a method has been adopted in which gas inside the tunnel is discharged to the outside of the tunnel by using a blower, or dust is removed by using an electric dust remover as auxiliary equipment.

[0004] However, with increasing awareness of environmental issues, there is a need for countermeasures against low-concentration NOx in automobile tunnels and the like. Known examples of the low-density denitration technology include JP-A-5-192535 and JP-A-4-192535.
-250822. Both known systems are systems in which gas is purified by adsorbing NOx on an adsorbent, desorbing the adsorbed NOx, and reducing it to nitrogen and water with a reducing agent.

In these systems, a plurality of adsorbents are modularized, and most of the modules contain NO as adsorbent.
Some of the modules desorb the adsorbed NOx when the adsorbed amount of NOx increases to a predetermined value to form highly concentrated NOx, and the high-concentration NOx Is reduced to nitrogen and water by selective catalytic reduction using a reduction catalyst.

[0006] The module performing adsorption is the adsorbent N
When the Ox adsorption amount reaches a predetermined value, the module is switched to a module that performs reduction, and the module that has completed the reduction is switched to a module that performs adsorption.
Reproduction can be performed continuously.

[0007]

In the conventional method, the energy required for desorbing the adsorbent is very large, and a large volume of the adsorbent is required to obtain the performance, and the size of the apparatus is very large. And so on. In order to solve these problems, Japanese Patent Application Laid-Open No. Hei 9-136015 was filed. This is because the initial cost of the adsorbent etc. is eliminated by utilizing the nitrogen fixing action or denitrification action of living organisms, or the energy and cost of the whole system is eliminated by eliminating energy such as a heat source required for regeneration of the adsorbent. This is intended to reduce. Further, in the conventional method using the above-mentioned adsorbent, in order to obtain the target NOx removal performance, the volume of the adsorbent is required to meet the NOx removal performance.

Therefore, in order to cope with the fluctuating NOx concentration, it is necessary to consider a very large adsorbent volume. In the above-mentioned patent, the performance can be controlled by the addition amount of the absorbent by using the absorbent, so that the size of the apparatus can be reduced.

[0009] However, in the method using an absorbent, there is a problem in reducing the amount of the absorbent used because the amount of the used absorbent affects the running cost.

[0010] An object of the present invention is to provide a gas purifying apparatus capable of reducing the use amount of the absorbent, which is a problem described above.

[0011]

According to the gas purifying apparatus of the present invention, the absorption section in the absorption process has a two-stage structure including a front stage and a rear stage. In the subsequent absorption unit with fresh absorption liquid, so that the exhaust NO ₂ concentration after absorption below a predetermined value NO
Perform the absorption of ₂ . The absorption performance decreases over time, and when the predetermined performance cannot be obtained, it is necessary to replace the absorption solution with fresh one. However, the absorption solution having deteriorated absorption performance is led to the absorption section in the preceding stage. The absorption liquid led to the previous stage is NO ₂ or N ₂
The ability to absorb O and NO _{2 up} to a predetermined performance is lost, but the ability to absorb ozone remains.

Therefore, it is possible to absorb the excess ozone generated in the oxidation process in the former absorption part and reduce the ozone leak to the latter absorption part. Can be suppressed from deteriorating. At the same time, NO
₂ or NO, NO ₂ pre-absorption. Absorption performance of NO ₂ at the absorption portion of the front is lower than the absorption unit in the subsequent stage, this preabsorbed, NO ₂ is led to the subsequent absorber or NO, concentrations load NO ₂ is reduced.

[0013] By these absorption operations in the former absorption section, it is possible to extend the life of the absorbent in the latter absorption section, reduce the amount of absorbent used, and reduce the running cost. it can.

[0014]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram of a gas purification device that best illustrates the present invention. Exhaust gas 1 is a gas containing dust and NOx, and is led to the device from a gas inlet 3 by a blower 2. Exhaust gas 1 is partially or entirely oxidized to NO ₂ by NOx oxidizing means 5. The NOx oxidizing means 5 is usually performed by using a method of adding ozone. This enables efficient oxidation. As another means, oxidation by electric discharge may be used.
The oxidized NO ₂ -containing gas and dust are removed by the dust removing means 6 in the gas. As the dust removing means 6, a wet or dry type electric dust collector is used. Alternatively, a means using a filter may be used.

The gas after dust removal is guided to an absorption process, which has a two-stage structure including an absorption section 29 in the front stage and an absorption section 7 in the rear stage. The gas from which dust has been removed is first sent to the absorption section 29 in the preceding stage. The absorption section 29 in the former stage absorbs the excess ozone contained in the fed gas and which has become excessive in the oxidizing means 5. At the same time, preliminary absorption of NO _{2 in} the gas is performed. In the latter absorption section 7, ozone absorption and NO ₂ absorption in the former absorption section 29 are performed.
After the preliminary absorption of NO, the NO ₂ contained in the gas is absorbed.

The absorption performance of the absorption section 7 in the latter stage decreases with time, and when the predetermined performance cannot be obtained, it is necessary to replace the absorption solution with a fresh one. It leads to the absorption section 29 in the preceding stage. The absorbing liquid guided to the absorption section 29 in the preceding stage does not have the ability to absorb NO ₂ , or NO, NO ₂ to a predetermined performance, but has the ability to absorb ozone. Therefore, the excess ozone generated in the oxidation process 5 can be absorbed by the absorption section 29 in the former stage, and ozone leak to the absorption section 7 in the subsequent stage can be reduced.

When ozone leaks into the absorption section 7 at the subsequent stage,
The absorption liquid in the absorption section 7 at the subsequent stage absorbs the ozone and leads to deterioration of the absorption liquid, and as a result, the life of the absorption liquid is shortened.
Therefore, the ozone is absorbed by the former absorption unit 2, so that the deterioration of the absorption liquid in the latter absorption unit 7 can be suppressed.

At the same time, N
Preliminary absorption of O ₂ , or NO, NO ₂ is performed. The absorption performance of NO ₂ in the absorption section 29 in the former stage is the same as that in the absorption section 7 in the latter stage.
Lesser, NO ₂ is led to the subsequent absorption unit 7, or NO,, concentration loading of NO ₂ is reduced by the preliminary absorption. The lower the concentration of NO ₂ guided to the latter stage, the longer the life of the absorbent in the latter absorbent section 7, so that the lifetime of the absorbent in the later absorbent section 7 can be extended.
As a result, the amount of the absorbent used is reduced.

The absorption method in the first absorption section 29 and the second absorption section 7 is performed by bringing the gas containing NO ₂ introduced into the absorption section into gas-liquid contact with the absorption liquid. The properties of the absorbing solution may be neutral or alkaline such as caustic soda and sodium sulfite. Usually, for such an absorbing solution, N rather than NO
O ₂ is easier to absorb. Therefore, the above-described oxidation of NOx to NO ₂ by the NOx oxidizing means 5 is an operation performed to enhance absorption performance.

As a method of gas-liquid contact, sprays 31 and 8 are used.
Or a filling method using a filler such as Raschig ring or saddle, a wet wall method, or a method combining these absorption methods. Absorbing liquids in the first-stage absorbing section 29 and the second-stage absorbing section 7 are stored in absorbing liquid reservoirs 32 and 9, respectively.
At 1, it is guided to the sprays 31 and 8 and injected inside. The absorbing liquid is again stored in the absorbing liquid reservoirs 32 and 9 while performing the absorption reaction. This operation is performed continuously or intermittently by the circulation pumps 30 and 11, and the absorption reaction is always maintained.

The absorption liquid in the absorption section 7 at the subsequent stage continues to be absorbed and the performance deteriorates with time. When the absorption liquid has deteriorated to a predetermined absorption performance, the absorption liquid in the absorption liquid reservoir 9 is guided to the absorption liquid reservoir 32 in the absorption section 29 in the preceding stage, and at the same time, the absorption liquid existing in the absorption liquid reservoir 32 is stored in the water storage tank 16. Be guided. Further, the absorbing liquid reservoir 9 is replenished with a new absorbing liquid by the absorbing liquid adding means 10, and the absorption is performed again. The gas from which dust, NO, and NO ₂ have been removed is discharged to the atmosphere as a purified gas 14 from a gas outlet 13 after removing mist contained in the gas by a mist eliminator 12.

The absorption liquid guided to the water storage tank 16 is
Sent to In the culturing section 18, denitrifying bacteria or fine underwater photosynthetic organisms are cultured. When the denitrifying bacteria are cultured in the culturing unit 18, the denitrifying bacteria adhere to the carrier 17 such as activated carbon or ceramic and increase the culture density, thereby improving the processing performance. If the performance is sufficient even if the carrier is not attached, the carrier 17 may be omitted.

Substances necessary for growing denitrifying bacteria are replenished by the nutrient addition means 19 as needed. The denitrifying bacteria consume nitrate ions in the absorbing solution by the denitrification reaction and release N ₂ . The liquid is repeatedly circulated by the circulating pump 20 until the concentration of nitrate ions reaches a predetermined value, thereby performing denitrification. The denitrifying bacteria that have multiplied or have become obsolete are separated by the solid-liquid separation means 21 into individual denitrifying bacteria and a solution.

When a fine underwater photosynthetic organism is cultured in the culture tank 18, the fine underwater photosynthetic organism performs photosynthesis using a nitrate ion in a solution as a necessary nitrogen source. As a light source required for photosynthesis, an artificial light source such as a fluorescent lamp or sunlight is used. Substances required for the growth of photosynthesis of fine underwater photosynthetic organisms are replenished by the nutrient addition means 19 as needed. Fine water photosynthetic organisms consume nitrate ions by photosynthesis and release O ₂ to immobilize the nitrate ions. Further, fine underwater photosynthetic organisms that have undergone cell division by photosynthesis and become surplus as a result of proliferation, or obsolete fine underwater photosynthetic organisms are separated into fine underwater photosynthetic organisms and solution components by the solid-liquid separation means 21.

Denitrifying bacteria or fine underwater photosynthetic organisms
The collecting means 22 turns into a collected matter 23 and a drainage 24, the collected matter 23 is collected, and the drainage 24 is discharged. Part or all of the solution separated by the solid-liquid separation means 21 is stored in a water storage tank 26 by a pump 25. The liquid stored in the water storage tank 26 is processed by a circulating liquid regenerating means 27 for unnecessary ions and the like.

For the treatment of the unnecessary ions, selective separation of the ions by electrodialysis may be used, or a means for producing a salt by adding a chemical and performing the treatment may be used. The unnecessary ions or salts selectively separated by the above-described method are recovered by the recovery unit 28. The liquid from which the unnecessary ions have been removed is sent to the absorbing liquid reservoir 9 and reused. By performing the recirculation of the utility, the amount of water required in the absorbing section 7 can be reduced, and the running cost can be reduced.

[0027]

According to the gas purifying apparatus of the present invention, the absorption section in the absorption process has a two-stage structure including a front stage and a rear stage. In the absorption section at the later stage, fresh absorption liquid is used, and the discharged NO ₂ after absorption is used.
NO ₂ is absorbed so that the concentration becomes equal to or lower than a predetermined value.
The absorption performance decreases over time, and when the predetermined performance cannot be obtained, it is necessary to replace the absorption solution with fresh one. However, the absorption solution having deteriorated absorption performance is led to the absorption section in the preceding stage. The absorption liquid guided to the previous stage has no ability to absorb NO ₂ , or NO, NO ₂ to a predetermined performance, but has an ability to absorb ozone. Therefore, it is possible to absorb the excess ozone generated in the oxidation process in the former absorption part and reduce the ozone leak to the latter absorption part, thereby reducing the deterioration of the absorbing liquid due to the ozone in the latter absorption part. It is possible to suppress.

In addition, at the same time, NO
₂ or NO, NO ₂ pre-absorption. Absorption performance of NO ₂ at the absorption portion of the front is lower than the absorption unit in the subsequent stage, this preabsorbed, NO ₂ is led to the subsequent absorber or NO, concentrations load NO ₂ is reduced.

By the absorption operation in the former absorption section, it is possible to extend the life of the absorbent in the latter absorption section, reduce the amount of the absorbent used, and reduce the running cost. it can.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a gas purification device according to an embodiment of the present invention.

[Explanation of symbols]

1: Exhaust gas, 2: Blower, 3: Gas inlet, 5: NOx
Oxidizing means, 6: dust removing means, 7: post-stage absorbing section, 8, 31
... spray, 9, 32 ... absorption liquid reservoir, 10 ... absorption liquid addition means, 11, 20, 30 ... circulation pump, 12 ... mist eliminator, 13 ... gas outlet, 14 ... purification gas, 16,
26 ... water tank, 17 ... carrier, 18 ... culture section, 19 ... nutrient addition means, 21 ... solid-liquid separation means, 22, 28 ... collection means, 23 ... collection, 24 ... drainage, 25 ... pump, 27 …
Circulating fluid regenerating means, 29 ... absorption section at the preceding stage.

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification symbol FI B01D 53/34 130Z (72) Inventor Masaru Namba 7-1-1, Omikamachi, Hitachi City, Ibaraki Prefecture Within Hitachi Research Laboratory, Hitachi, Ltd. (72) Inventor Jyuta Yukitake 7-1-1, Omika-cho, Hitachi City, Ibaraki Prefecture Inside the Hitachi Research Laboratory, Hitachi, Ltd. (72) Inventor Takeyoshi Yokosuka 7-1-1, Omika-cho, Hitachi City, Ibaraki Prefecture Hitachi, Ltd., Hitachi Laboratory

Claims (1)

[Claims] An object of the present invention is to purify a dust and a gas containing a low concentration of NOx, wherein an oxidation process of oxidizing a part or all of the NOx in the gas to NO ₂ by ozone oxidation is provided. The dedusting process for removing, the absorbing process for absorbing oxidized NO ₂ or NO, NO ₂ into a neutral or alkaline absorbing solution, and the absorbing solution for absorbing NO ₂ or NO, NO ₂ are subjected to denitrifying bacteria. Introduced into the cultured part, which has been cultured, NO ₂ in the solution has a process of converting the ionized nitrate ions to nitrogen by the denitrifying action of denitrifying bacteria, and by performing a series of these processes, In a gas purification device that purifies air,
The absorption part in the absorption process has a two-stage structure consisting of a first stage and a second stage. Fresh absorption liquid is used in the second stage, and the absorption solution that has deteriorated to the specified performance after use in the second stage is used in the first stage. The excess ozone generated in the oxidation process is absorbed by the former absorption part, eliminating ozone leakage to the latter absorption part, preventing the absorption liquid in the latter absorption part from deteriorating by the ozone and simultaneously absorbing the former ozone. NO ₂ or N
O, A preliminary absorption of NO _2, NO ₂ is led to the subsequent absorber or NO,, subjected to reduction in the load of the concentration of NO _2, by operating at the absorption portion of these front, in the rear stage of the absorber A gas purifier characterized by extending the life of an absorbent and reducing the amount of an absorbent used.