JPH10314545A - Gas purifying apparatus and gas purifying method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To optionally control NOx removal efficiency, which has not been attained by a NOx -removing method using an adsorbent, by detecting NOx concentration by a sensor installed in an apparatus inlet and adjusting either the supply amount of an absorption liquid necessary for absorbing NOx or the circulation flow rate of the absorption liquid. SOLUTION: A waste gas 1 is sent to a NOx oxidizing means 5 by a blower 2 and a part of or all of NOx in the gas is oxidized to NO2 . Then, after dust removal from the resultant waste gas by a dust removing means 6, the resultant waste gas is sent to an absorption part 7 and in the part, NOx in the gas is absorbed in an absorption liquid. The absorption liquid is led to a spray 8 by a circulation pump 11 from an absorption liquid pool 9 and sprayed to the absorption part 7. At that time, the NOx concentration in the purified gas 14 is detected by a sensor 15 and based on the detection result, a new absorption liquid is supplied from an absorption liquid adding means 10 to retain the absorption performance. Moreover, the absorption liquid by which NO2 is absorbed is led to a reducing means comprising a culture part 18 and a circulation pump 20 to reduce NO2 to nitrogen by using denitrification microroganisms.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gas purifying apparatus and a gas purifying method for removing dust and low-concentration NOx generated by driving an automobile or the like from the atmosphere.

[0002]

2. Description of the Related Art As traffic increases, automobile tunnels,
It is an urgent task to treat soot and NOx in gas at places where traffic is particularly heavy, such as at intersections, indoor parking lots, and highways, that is, places where the concentration of exhaust gas from automobiles is high. 2. Description of the Related Art Conventionally, in automobile tunnels, a method of exhausting gas inside the tunnel to the outside of the tunnel using a blower, or providing an electric dust remover as an incidental facility, and removing dust using the electric dust remover has been often used. However, the demand for the prevention of environmental pollution has been increasing year by year, and low-concentration NOx
Measures are also being taken against An example of a denitration technique for preventing such a low concentration of NOx is disclosed in Japanese Patent Application Laid-Open No. 5-192.
535 and JP-A-4-250822. Both of those described in these publications contain N as an adsorbent.
After adsorbing Ox, the adsorbed NOx is desorbed and reduced to nitrogen and water using a reducing agent to purify the gas. Here, the adsorbent is divided into a plurality of modules, most of the modules function as modules for adsorbing NOx on the adsorbent, and some modules adsorb when the amount of adsorbed NOX reaches a predetermined value. It functions as a module that desorbs NOX, concentrates NOX to a high concentration, and reduces this high concentration of NOX to nitrogen and water by selective catalytic reduction using a reduction catalyst. The module being adsorbed is the adsorbent NOx
When the adsorption amount reaches a predetermined value, the module is switched to the reduction module, while the module that has completed the reduction is switched to the adsorption module. And in each module, NOx
Adsorption and reduction are alternately performed, whereby NOx adsorption and regeneration by the adsorbent are continuously performed.

[0003]

In the above-mentioned conventional method, continuous adsorption and reduction can be performed. However, a large amount of energy is required for desorbing the adsorbent, and it is necessary to reduce the energy.
For this reason, various devices have been proposed which realize reduction of energy consumption without using an adsorbent. In these outlines, the initial cost of the adsorbent or the running cost of a heat source required for regeneration of the adsorbent is eliminated by utilizing the nitrogen fixing action or the denitrifying action of living organisms.

Further, in the conventional method using an adsorbent, in order to obtain a target NOx removal rate usually, the NOx
The gas must remain in the adsorbent for a time commensurate with the removal rate. In order to obtain this residence time, the volume of the adsorbent must be increased. Moreover, it is necessary to cope with a fluctuating NOx concentration, and a large adsorbent volume is required in consideration of the maximum concentration. In addition, since the adsorbent continues to be adsorbed by the adsorption specifications specific to the adsorbent until the adsorption of NOx reaches a saturated state, it has been difficult to arbitrarily set the NOx removal rate.

[0005] It is an object of the present invention to arbitrarily control the NOx removal rate, which is difficult with the conventional method using an adsorbent, and to optimally control the gas purifier based on the set removal rate. . Further, it is another object of the present invention to provide a gas purification device in which running costs are reduced.

[0006]

According to a first aspect of the present invention, there is provided a gas purifying apparatus for purifying a gas containing at least dust and low-concentration NOx. an oxidation means for oxidizing at least a part NO _2, and dust removing means for removing dust in the gas, and absorbing means for absorbing a gas containing NO ₂ oxidized neutral or alkaline absorbing solution, a NO ₂ It has a reducing means for reducing nitrate ions generated by ionizing the absorbed liquid to nitrogen using denitrifying bacteria, and a collecting means for collecting grown denitrifying bacteria, and measures the NOx concentration of the inflowing gas. Measuring means, a means for calculating a replenishing amount of the absorbing solution necessary for the NOx removal amount based on the measured value of the measuring means, and a replenishing means for replenishing the absorbing means with the absorbing solution based on the calculated value. Provided

A second aspect of the present invention for achieving the above object is a gas purifying apparatus for purifying a gas containing at least dust and low-concentration NOx, wherein at least a part of NOx in the gas is converted to NO ₂ Oxidizing means for oxidizing gas, dust removing means for removing dust in the gas, absorbing means for absorbing a gas containing oxidized NO ₂ into a neutral or alkaline absorbing solution, and an absorbing solution absorbing NO ₂ is ionized. A biological immobilization means for immobilizing the collected nitrate ions in the body of a fine underwater photosynthetic organism, and a recovery means for recovering the propagated fine underwater photosynthetic organism, and measuring the NOx concentration of the gas flowing into the body. Means, a means for calculating a replenishing amount of the absorbing solution necessary for the NOx removal amount based on the measured value, and a replenishing means for replenishing the absorbing solution based on the calculated value.

A third aspect of the present invention for achieving the above object is a gas purification method for purifying a gas containing at least dust and low concentration NOx, wherein at least a part of NOx in the gas is reduced to NO ₂ An oxidation process for oxidizing to gas, a dust removal process for removing dust in the gas, and the oxidized N
An absorption process of absorbing a gas containing O ₂ into a neutral or alkaline absorbing solution, and a process of reducing nitrate ions generated by ionizing the absorbing solution that has absorbed NO ₂ to nitrogen using denitrifying bacteria, A recovery process for recovering the denitrifying bacteria that have grown, calculating a replenishment amount of the absorbing solution necessary for the NOx removal amount based on the measured NOx concentration value of the inflowing gas, and replenishing the solution during the absorption process.

A fourth aspect of the present invention for achieving the above object is a gas purification method for purifying a gas containing at least dust and a low concentration of NOx, wherein at least a part of NOx in the gas is reduced to NO _2. Oxidation process to oxidize, dust removal process to remove dust in gas, and oxidized NO ₂
An absorption process in which a gas containing nitrogen is absorbed into a neutral or alkaline absorbing solution, a biological immobilizing process in which an absorbing solution that absorbs NO ₂ immobilizes ionized nitrate ions in the body of a fine underwater photosynthetic organism, and proliferation. A recovery process for recovering fine underwater photosynthetic organisms, calculating the replenishment amount of the absorption solution necessary for the NOx removal amount based on the measured NOx concentration value of the inflowing gas, and replenishing the absorption solution during the absorption process Is what you do.

A fifth aspect of the present invention for achieving the above object is a gas purification method for purifying a gas containing at least dust and a low concentration of NOx, wherein at least a part of NOx in the gas is reduced to NO _2. An oxidation process for oxidizing to gas, a dust removal process for removing dust in the gas, and the oxidized N
An absorption process of absorbing a gas containing O ₂ into a neutral or alkaline absorbing solution, and a process of reducing nitrate ions generated by ionizing the absorbing solution that has absorbed NO ₂ to nitrogen using denitrifying bacteria, A recovery process for recovering the denitrifying bacteria that have grown, calculating the circulating flow rate of the absorbent necessary for the NOx removal amount based on the measured NOx concentration of the inflowing gas, and circulating the absorbent based on the calculated value. It is to let.

A sixth aspect of the present invention for achieving the above object is a gas purification method for purifying a gas containing at least dust and low-concentration NOx, wherein at least a part of NOx in the gas is reduced to NO _2. Oxidation process to oxidize, dust removal process to remove dust in gas, and oxidized NO ₂
An absorption process in which a gas containing nitrogen is absorbed into a neutral or alkaline absorbing solution, a biological immobilizing process in which an absorbing solution that absorbs NO ₂ immobilizes ionized nitrate ions in the body of a fine underwater photosynthetic organism, and proliferation. A recovery process for recovering fine underwater photosynthetic organisms, calculating a circulating flow rate of the absorbing solution necessary for the NOx removal amount based on the measured NOx concentration value of the inflowing gas, and calculating the absorbing solution based on the calculated value. Is circulated.

[0012]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic view of one embodiment of the gas purification device of the present invention. The exhaust gas 1 is a gas containing dust and NOx, and is led by a blower 2 from a gas inlet 3 to a gas purification device. Exhaust gas 1 introduced into the purification device has NOx oxidizing means 5 in which part or all of NOx in the gas is NO ₂
Is oxidized. The oxidation method in the NOx oxidation means 5 is as follows.
Ozone may be added, or oxidation by electric discharge may be used. The dust containing gas containing the oxidized NO ₂ gas and the dust is removed by the dust removing means 6.
This dust removing means 6 can be a wet or dry type electric dust collector,
Alternatively, filter means may be used.

The gas from which dust has been removed is sent to the absorbing section 7. The absorption unit 7 converts NO ₂ in the fed gas into NO ₂
When NO is contained, NO and NO ₂ are absorbed in the absorbing solution. The gas sent into the absorbing section 7 and the absorbing liquid are brought into gas-liquid contact to cause an absorbing reaction. As the absorbing solution, any of a neutral solution and an alkaline solution such as caustic soda and sodium sulfite can be used. Usually, NO ₂ is more easily absorbed by such an absorbent than NO. Accordingly, the NOx oxidizing means 5 described above
Oxidation to NO ₂ is an operation performed to enhance the absorption performance.
In the case of possible remains absorbed without oxidizing enough NO to _2, NOx oxidation means 5 may be omitted. As an absorption method, an absorption method using the spray 8 is used. However, a filling method filled with Raschig rings or the like, a wet wall method, or a method combining these absorption methods may be used. The absorbing liquid is stored in the absorbing liquid reservoir 9, guided to the spray 8 by the circulation pump 11, and injected into the absorbing section 7. The absorbing liquid is again stored in the absorbing liquid reservoir 9 while performing an absorbing reaction. This operation is continuously performed by the circulation pump 11, and the absorption reaction is always maintained. As the absorption liquid continues to absorb, its performance deteriorates. In order to prevent the deterioration of the absorbing performance, the absorbing liquid adding means 10 replenishes a new absorbing liquid and maintains the absorbing performance. The replenisher is continuously replenished to maintain a constant performance. Dust and N
The gas from which O and NO ₂ have been removed is the mist eliminator 1
After the mist contained in the gas is removed in 2, the gas is released from the gas outlet 13 to the atmosphere as a purified gas 14.

The amount of the nitrate ions accumulated in the absorbing solution or the amount of specific ions in the absorbing solution accumulated by adding the absorbing solution reaches a specified value. Then, the liquid is sent to the water storage tank 16 after removing impurities such as dust in the liquid by a filtering means such as a filter.
Alternatively, a small amount of the absorbing liquid may be continuously sent to the water storage tank 16. The absorption liquid guided to the water storage tank 16 is sent to the culture unit 18. In the culturing section 18, denitrifying bacteria or fine underwater photosynthetic organisms are cultured.

When the denitrifying bacteria are cultured in the culturing section 18, the denitrifying bacteria are adhered to the carrier 17 such as activated carbon or ceramic to increase the culture density, thereby improving the processing performance. If the performance is sufficient without attaching the carrier, the carrier 17 may be omitted. The substances necessary for the growth of the denitrifying bacteria are supplied by the nutrient addition means 19 as necessary. The denitrifying bacteria consume nitrate ions in the absorbing solution by the denitrification reaction and release N2. The circulation pump 20 circulates the liquid until the concentration of the nitrate ions reaches a predetermined value, and denitrification is repeatedly performed. The denitrifying bacterium proliferates in small amounts during repeated denitrification. The excess denitrifying bacteria or abolished denitrifying bacteria as a result of the multiplication 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 nitrate ions in the solution as a necessary nitrogen source. An artificial light source such as a fluorescent lamp or sunlight is used as a light source required for photosynthesis. This light may be irradiated from the inside of the culture unit 18 or from the outside. The substances necessary for the growth of photosynthesis of fine underwater photosynthetic organisms are the nutrient addition means 19
Replenish as needed. Fine underwater photosynthetic organisms consume nitrate ions by photosynthesis, release O _2, and immobilize the nitrate ions. In addition, fine underwater photosynthetic organisms or obsolete fine underwater photosynthetic organisms that have become excessive as a result of cell division and proliferation due to photosynthesis are separated into fine underwater photosynthetic organisms and a solution component by solid-liquid separation means 21.

Denitrifying bacteria or fine underwater photosynthetic organisms
The collecting means 22 separates the collected matter 23 and the 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. Water storage tank 26
Unnecessary ions and the like are processed in the circulating liquid regenerating means 27 of the solution stored in the circulating fluid. For the treatment of this unnecessary ion,
A method of selectively separating unnecessary ions by electrodialysis or a method of adding a chemical to generate a salt is used. Unnecessary ions or salts selectively separated by using these methods are collected by the collecting means 28.
Will be collected. The solution from which the unnecessary ions have been removed is sent to the absorbing solution reservoir 9 and reused. By circulating this utility, the amount of water required in the absorbing section 7 can be reduced, and the running cost can be reduced.

FIG. 2 shows an example of the change with time of the NOx concentration in the tunnel. Usually, vehicle traffic is very low during the early morning and late night hours. Therefore, the amount of exhaust gas is small and the concentration of the processed NOx is also small. Thus, depending on the time zone, etc., N
Since the concentration of Ox is changing, an optimal operation corresponding to the change in this concentration is desired.

In the present embodiment, a sensor 4 is provided at the gas inlet 3 to sense the NOx concentration at the inlet. Based on the obtained sensing data, a target replenishing amount of the absorbing solution necessary for removing NOx is calculated, and the absorbing solution adding means 10 continuously replenishes the absorbing solution. Then, the target NOx removal rate corresponding to the actual NOx concentration is always maintained. As a result, it is possible to optimally replenish the absorbent, thereby reducing running costs. In this embodiment, it is also possible to set an arbitrary NOx removal rate by adjusting the replenishing amount of the absorbing solution.

As another method, a sensor 4 is provided at the gas inlet 3 to sense the NOx concentration at the inlet. Based on the obtained sensing data, the circulating flow rate of the absorbing liquid required for removing NOx is calculated, and the required amount is circulated. Therefore, the required NOx removal rate corresponding to the NOx concentration can always be maintained. As a result, the absorbent can be optimally replenished, and the running cost is reduced. Further, an arbitrary NOx removal rate can be set by adjusting the circulation amount of the absorbing liquid.

As still another method, the sensor 4 attached to the gas inlet 3 and the sensor 1 attached to the gas outlet 13
5 is used to sense the NOx concentration at the inlet and the outlet of the apparatus, and feedback control is performed on the replenishing amount of the absorbent or the circulating flow of the absorbent. As a result, the set NOx removal amount is corrected, and a more accurate NOx removal rate can be obtained.

[0022]

According to the gas purifying apparatus of the present invention, NOx
The replenishing amount of the absorbing solution or the circulating flow rate of the absorbing solution necessary for absorbing the water is adjusted by sensing the NOx concentration with a sensor provided at the entrance of the apparatus. Therefore, it is possible to arbitrarily control the NOx removal rate which cannot be achieved by the conventional NOx removal method using the adsorbent. As a result, it is possible to operate the system optimally according to the NOx concentration and to reduce the running cost.

[Brief description of the drawings]

FIG. 1 is a schematic view of one embodiment of a gas purification device of the present invention.

FIG. 2 is a diagram illustrating an example of a time change of a NOx concentration in a tunnel.

[Explanation of symbols]

1 ... exhaust gas, 2 ... blower, 3 ... gas inlet, 4 ...
... Sensor, 5 ... NOx oxidation means, 6 ... Dust removal means,
7: Absorber, 8: Spray, 9: Absorber reservoir, 1
0: Absorbing liquid adding means, 11: Circulating pump, 12:
Mist eliminator, 13 ... gas outlet, 14 ... purified gas, 15 ... sensor, 16 ... water tank, 17 ... carrier, 18 ... culture unit, 19 ... nutrient addition means, 20 ...
... circulation pump, 21 ... solid-liquid separation means, 22 ... collection means, 23 ... collection, 24 ... drainage, 25 ... pump,
26 ... water storage tank, 27 ... circulating liquid regeneration means, 28 ... collection means.

Claims (6)

[Claims] 1. A gas purifying apparatus for purifying a gas containing at least dust and low-concentration NOx, comprising:
Oxidizing means for oxidizing at least a portion of the gas to NO ₂ , dust removing means for removing dust in the gas, and oxidized N
Absorbing means for absorbing a gas containing O ₂ into a neutral or alkaline absorbing solution, and reducing means for reducing nitrate ions generated by ionizing the absorbing solution having absorbed NO ₂ to nitrogen using denitrifying bacteria And a collecting unit for collecting the denitrifying bacteria that have multiplied, a measuring unit for measuring the NOx concentration of the gas flowing in, and NO based on the measurement value of the measuring unit.
A gas purifying apparatus comprising: means for calculating a replenishing amount of the absorbing solution required for x removal amount; and replenishing means for replenishing the absorbing means with the absorbing solution based on the calculated value. 2. A gas purifying apparatus for purifying a gas containing at least dust and low-concentration NOx, comprising:
Oxidizing means for oxidizing at least a portion of the gas to NO ₂ , dust removing means for removing dust in the gas, and oxidized N
Absorbing means for absorbing a gas containing O ₂ into a neutral or alkaline absorbing solution, and bioimmobilizing means for immobilizing nitrate ions ionized by the absorbing solution having absorbed NO ₂ in a fine underwater photosynthetic organism. And a collecting means for collecting the propagated fine underwater photosynthetic organisms, measuring means for measuring the NOx concentration of the flowing gas, and replenishment of the absorbing solution necessary for the NOx removal amount based on the measured value. A gas purifying apparatus comprising: means for calculating an amount; and replenishing means for replenishing an absorbing solution based on the calculated value. 3. A gas purification method for purifying a gas containing at least dust and low-concentration NOx, the method comprising:
And oxidation process for oxidizing the NO ₂ at least a part of,
A dust removing process of removing dust in the gas, an absorption process for absorbing the gas containing NO ₂ to the oxidized neutral or alkaline absorbing solution, the absorbing solution having absorbed NO ₂ is produced by ionization A process for reducing nitrate ions to nitrogen using a denitrifying bacterium, and a recovery process for recovering the denitrifying bacterium that has grown, based on the measured value of the NOx concentration of the inflowing gas. A gas purification method comprising calculating a replenishing amount of the absorbing solution and replenishing the absorbing solution during an absorbing process. 4. A gas purification method for purifying a gas containing at least dust and low-concentration NOx, the method comprising:
And oxidation process for oxidizing the NO ₂ at least a part of,
A dust removal process for removing dust in the gas, an absorption process for absorbing the oxidized NO ₂ -containing gas into a neutral or alkaline absorbing solution, and a nitrate-based ion in which the absorbing solution that has absorbed NO ₂ is ionized. And a recovery process for recovering the propagated fine underwater photosynthetic organisms, wherein N is determined based on the NOx concentration measurement value of the flowing gas.
A gas purification method comprising: calculating a replenishment amount of the absorbing solution necessary for an Ox removal amount, and replenishing the absorbing solution during an absorption process. 5. A gas purification method for purifying a gas containing at least dust and low-concentration NOx, the method comprising:
And oxidation process for oxidizing the NO ₂ at least a part of,
A dust removing process of removing dust in the gas, an absorption process for absorbing the gas containing NO ₂ to the oxidized neutral or alkaline absorbing solution, the absorbing solution having absorbed NO ₂ is produced by ionization A process for reducing nitrate ions to nitrogen using a denitrifying bacterium, and a recovery process for recovering the denitrifying bacterium that has grown, based on the measured value of the NOx concentration of the inflowing gas. A gas purification method comprising: calculating a circulation flow rate of the absorbing liquid; and circulating the absorbing liquid based on the calculated value. 6. A gas purification method for purifying a gas containing at least dust and low-concentration NOx, the method comprising:
And oxidation process for oxidizing the NO ₂ at least a part of,
A dust removal process for removing dust in the gas, an absorption process for absorbing the oxidized NO ₂ -containing gas into a neutral or alkaline absorbing solution, and a nitrate-based ion in which the absorbing solution that has absorbed NO ₂ is ionized. And a recovery process for recovering the propagated fine underwater photosynthetic organisms, wherein N is determined based on the NOx concentration measurement value of the flowing gas.
A gas purification method comprising: calculating a circulating flow rate of the absorbing solution necessary for an Ox removal amount; and circulating the absorbing solution based on the calculated value.