JP2003080025A - Reduction apparatus and denitrification apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To decrease the use quantity of a reduction gas in a reducing reaction in a denitrification step. SOLUTION: When a treating gas containing nitrogen oxide flows from the upstream side A of a denitrification apparatus 106 to be supplied to the denitrifrication apparatus 106, corona discharge is produced by AC voltage applied between an electrode 35 and a wire like electrode 24 to form a non- equilibrium plasma atmosphere. NO in the treating gas is oxidized in the atmosphere to be changed to NO2 . The NO2 is adsorbed by an alkali adsorbing material 64 made of Ba(OH)2 coming out from holes 35a provided on the electrode 35 to be turned to Ba(NO3 )2 to and stored. Because DC voltage is also applied to the electrode 35 and the wire like electrode 24 from a DC power source 213, NO3 <-> in the alkali adsorbing material 64 moves toward a positive electrode (the electrode 35) to be decomposed into N2 and O2 .

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a technique for removing nitrogen oxides in exhaust gas, and more particularly to a reducing device and a denitration device capable of reducing the amount of reducing gas used in the reduction reaction in the denitration process.

[0002]

2. Description of the Related Art Since nitrogen oxides contained in exhaust gas from internal combustion engines and boilers cause acid rain and photochemical smog, it is desired to reduce the amount of nitrogen oxides in the atmosphere. On the other hand, a small amount of nitrogen oxide remains in the tunnel for automobiles, and when the convection of air disappears at an intersection with a lot of traffic, the nitrogen oxide may stay. In recent years, in order to reduce the concentration of nitrogen oxides in the atmosphere as much as possible, there is a growing demand for a denitration technique that can easily remove nitrogen oxides in the atmosphere even in such a place.

A well-known denitration method is a three-way catalyst method for purifying exhaust gas from gasoline engines such as automobiles. However, since this method requires a temperature of about 300 ° C., it is necessary to raise the temperature of the processing gas when this method is applied to a room temperature gas, which requires a large amount of energy. Furthermore, this method cannot be applied in the coexistence of oxygen. Moreover, it is not suitable for use in denitration in a tunnel or the like. Therefore, as a measure to reduce the generation of nitrogen oxides even in the coexistence of oxygen, for example, a so-called selective process of performing reduction treatment of nitrogen oxides by passing catalyst feed after supplying ammonia as a reducing agent into the target gas There is known an exhaust gas purification method that removes nitric oxide and suppresses the generation of nitrogen oxides by a catalytic reduction method.

[0004]

However, even in this selective catalytic reduction method, it is necessary that the gas temperature is 300 ° C. or higher. Furthermore, in this method, since ammonia, which is a poisonous substance, is used as a reducing agent, there is a problem in applying it to a closed space such as a tunnel or an intersection with a lot of traffic. When treating low-concentration nitrogen oxides at room temperature, the denitration method is effective, in which the nitrogen oxides are oxidized by pulse discharge or electron beam irradiation and the nitrogen oxides are recovered by increasing the oxidation number. Is. But,
Since these methods have low energy efficiency, there is a problem that the oxidation treatment requires a long time to obtain a sufficient denitration effect and the treatment efficiency is low. Further, in the reduction step after the oxidation recovery, it is necessary to flow the HC gas as the reducing gas while discharging, which is troublesome and expensive. Therefore, the present invention has been made in view of the above,
The present invention relates to a reducing device and a denitration device that can reduce the amount of reducing gas used in the reduction reaction in the denitration process.

[0005]

In order to achieve the above-mentioned object, a reducing apparatus according to a first aspect applies a DC voltage to a chemical adsorbent that adsorbs a processing gas obtained by oxidizing nitrogen oxides. Then, the electrons of nitrate ions present in the chemical adsorbent are applied to the positive electrode of the DC voltage applying electrode to reduce the nitrate ions.

This reducing device reduces the nitrate ions adsorbed on the chemical adsorbent on the electrodes to which a DC voltage is applied.
For this reason, reducing gas, discharge, heat treatment using a catalyst, etc. are not required, so that nitrate ions can be easily reduced. Therefore, when this reducing device is used for the reduction treatment of the denitration device, a reducing gas supply system and the like are not required, and the denitration device can be constructed compactly. Further, since no reducing gas is required, the running cost can be reduced accordingly. This reducing device can be applied to denitration of exhaust gas from internal combustion engines such as gasoline engines, diesel engines or gas turbine engines, exhaust gas from incinerators and boilers, and denitration of atmosphere in tunnels and at intersections with high traffic volumes. .

The chemical adsorbent has alkalinity such as alkali metal such as Li, Na and K, hydroxide of alkaline earth metal such as Mg and Ca, and alkali metal and has a neutralization reaction with nitrate ion. It means an adsorbent that exhibits an adsorption ability via Since the chemical adsorbent adsorbs NO ₂ etc. by the neutralization reaction,
Since the adsorption amount per unit volume can be increased, the device size can be reduced. Therefore, it is effective when the installation space is limited.

According to a second aspect of the present invention, in the reducing device, a physical adsorbent adsorbs nitrate ions, a DC voltage is applied to the physical adsorbent, and electrons of the nitrate ions are applied to the positive electrode of the DC voltage application electrode. It is characterized by reducing the nitrate ion. This reducing device reduces nitrate ions by adsorbing nitrate ions on the physical adsorbent and then applying a DC voltage. For this reason, reducing gas, discharge, heat treatment using a catalyst, etc. are not required, so that nitrate ions can be easily reduced. Further, since no reducing gas is required, the running cost can be reduced accordingly.

Here, the physical adsorbents are Al ₂ O ₃ and TiO _2.
2 , an amphoteric oxide, etc. and an adsorbent that exhibits an adsorption capacity through physical interaction with zeolite, gamma-alumina, molecular sieve, activated carbon and the like. The physical adsorbent is
Since NO ₂ or the like is adsorbed on the surface by a physical interaction, the movement of nitrate ions in the electrode reaction becomes easier as compared with a chemical adsorbent. Therefore, the nitrate ion can be reduced with less energy as compared with the chemical adsorbent, which is preferable when the reducing device is used in a place where sufficient energy cannot be supplied for the electrode reaction. Hereinafter, unless otherwise specified, the adsorbent is the chemical adsorbent of claim 1 or claim 2
The physical adsorbent of is shown.

Further, the reducing apparatus according to a third aspect is characterized in that, in the reducing apparatus, at least the positive electrode of the electrodes is Fe. Therefore, the change in the oxidation number of Fe can also be used for the reduction of nitrate ions, so that the reduction proceeds faster. Therefore, if this reducing device is used in a denitration device, the denitration rate can be increased. Further, since inexpensive Fe is used, the manufacturing cost can be suppressed.

Further, in the reducing device according to claim 4, in the reducing device, the reducing agent is flown through the chemical adsorbent or the physical adsorbent when the DC voltage is applied, and the discharging is performed by the discharging means. It is characterized by reducing nitrate ions and nitrogen oxides. This reduction device
When reducing only by applying a DC voltage is not sufficient, a reducing gas is also used. For this reason, nitrate ions and NO ₂ can be reduced more completely, so that the denitration efficiency can be increased and cleaner air can be obtained.

The denitration apparatus according to a fifth aspect of the present invention comprises a discharge means for oxidizing the processing gas containing nitrogen oxides.
A chemical adsorbent or a physical adsorbent that adsorbs nitrogen oxides contained in the processing gas after the oxidation treatment in the form of nitrate ions, and a DC voltage application for applying a DC voltage to the chemical adsorbent or the physical adsorbent. Means for applying the electrons of nitrate ions adsorbed on the chemical adsorbent or the physical adsorbent to the positive electrode of the DC voltage applying electrode to reduce the nitrate ions.

In this denitrification device, the discharge oxidization process and the reduction by applying the DC voltage can be simultaneously and continuously performed, so that the denitration rate can be increased. In addition, since reducing gas is not required, running cost can be kept low, and replenishment of reducing gas is not required, so maintenance and inspection work can be reduced accordingly. Further, since a reducing gas pipe or the like is not required, the denitration device can be made compact and reliability can be improved.

A denitration apparatus according to a sixth aspect of the present invention is characterized in that, in the denitration apparatus, the processing gas is further oxidized by the discharge means with a photocatalyst interposed. Therefore, the efficiency of the oxidation treatment of NO contained in the process gas can be increased, and the denitration efficiency can be increased accordingly. Further, it is preferable to interpose the photocatalyst in the chemical adsorbent, because the NO ₂ adsorption efficiency can be increased, and the denitration efficiency can be increased accordingly.

Further, in the denitration apparatus according to the seventh aspect, the light irradiation means for oxidizing the treatment gas containing nitrogen oxides through the photocatalyst, and the nitrogen oxidation contained in the treatment gas after the oxidation treatment. A chemical adsorbent or a physical adsorbent for adsorbing a substance in the form of nitrate ion, and a direct current voltage applying means for applying a direct current voltage to the chemical adsorbent or the physical adsorbent, It is characterized in that the nitrate ion electrons adsorbed on are given to the positive electrode of the DC voltage applying electrode to reduce the nitrate ion.

In this denitration apparatus, since NO in the processing gas is oxidized by light irradiation with a photocatalyst interposed, a power source for oxidation treatment and a power source for reduction treatment are separately prepared. For this reason, the NO oxidation condition and the nitrate ion reduction condition can be set separately, so that denitration can be performed under optimum conditions against environmental changes such as temperature and humidity. Therefore, stable denitration performance can be obtained regardless of the environment. In addition, it is preferable to use an excimer lamp as the light irradiating means, since the oxidation efficiency can be increased.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described below in detail with reference to the drawings. The present invention is not limited to this embodiment. In addition, constituent elements in the following embodiments include those that can be easily assumed by those skilled in the art or those that are substantially the same.

(Embodiment 1) FIG. 1 is a flowchart showing a denitration procedure according to the present invention. First, NO contained in the processing gas is changed to NO ₂ by an oxidation process (step S101). Next, NO ₂ contained in the gas to be treated is adsorbed on the alkali adsorbent (step S102). Then, oxygen is extracted from the adsorbed NO ₂ by a reduction process, NO ₂ is changed to N ₂ (step S103), and this denitration process is completed (step S).
104). Next, regarding denitration according to the first embodiment,
The oxidizing hand treatment and the reducing treatment will be separately described.

(Oxidation treatment) FIG. 2 is a sectional view showing an oxidation device according to the first embodiment of the present invention. Note that FIG.
2B is a sectional view taken along line XX of FIG. This oxidizer uses a semiconductor-based photocatalyst such as TiO _{2 to} generate NO
It is characterized in that it accelerates the oxidative reaction that changes carbon dioxide to NO ₂ . The oxidation device 100 includes a linear electrode 20 near the center of the tubular body 10, and an electrode 30 is provided on the outer periphery of the tubular body 10. A dielectric 40 is formed on the inner wall surface of the tubular body 10, and TiO ₂ as a photocatalyst 50 is carried thereon by a method such as baking. Here, since TiO ₂ is a photocatalyst, the action as a catalyst decreases unless energy is given by light or discharge. Therefore, it is desirable that TiO ₂ be carried on the dielectric 40 as finely and uniformly as possible. The tubular body portion 10 is made of quartz glass, and the linear electrode 20 is made of, for example, a piano wire.

The linear electrode 20 is connected to a power source 200, from which a voltage of about -10 kV is applied in pulses. Then, a corona discharge is caused between the body 30 and the electrode 30 provided on the outer periphery of the body 10 to generate non-equilibrium plasma. In addition to the above corona discharge, an ozonizer discharge,
Discharging means capable of generating non-equilibrium plasma can be used, such as creeping discharge, streamer discharge or glow discharge. Further, in addition to the discharge, the electron gun is used to inject electrons to generate oxidative radicals.
O may be oxidized.

By the non-equilibrium plasma generated by the corona discharge or the like, NO contained in the gas to be treated introduced into the body 10 is oxidized and converted into NO ₂ .
NO ₂ oxidized by the oxidizer 100 is Ba (N
In the form of O ₃ ) ₂ , it is adsorbed by an alkali adsorbent (not shown) such as Ba (OH) ₂ which is an adsorbent, and reduced by the reducing means. When a chemical adsorbent is used, NO _{2 and the} like are adsorbed by a neutralization reaction, so that the adsorption amount per unit volume can be increased. In the present invention, Li, Na,
Alkali metal-based adsorbents such as K and Cs, Be, Mg and C
Alkaline earth metal adsorbents such as a can also be used. Particularly in the present invention, alkali metal hydroxides such as Ba (OH) ₂ and KOH as well as BaOH and K _{2 are used.}
Alkali metal-based oxides such as O are more preferable because they have excellent adsorption ability for nitrogen oxides such as NO ₂ .

In the following description, the case of using an alkaline adsorbent which is a chemical adsorbent will be described as an example.
Instead of the chemical adsorbent, amphoteric oxides such as Al ₂ O ₃ and TiO ₂ and physical adsorbents such as zeolite, gamma alumina, molecular sieves and activated carbon may be used. Since the physical adsorbent adsorbs NO _{2 and the} like on the surface by physical interaction, the movement of nitrate ions in the electrode reaction becomes easier as compared with the chemical adsorbent. Therefore, the nitrate ions can be reduced with less energy as compared with the chemical adsorbent. Since the physical adsorbent can increase the adsorption amount only by increasing the surface area, it is desirable to increase the surface area by making the physical adsorbent into as small particles as possible in order to increase the adsorption amount. .

Here, the effect of the catalyst will be described. FIG. 3 is an explanatory diagram showing the relationship between input energy and oxidation efficiency when TiO ₂ is used and when it is not used. As shown in the figure, the oxidizer 100 according to the present invention.
(See FIG. 2), TiO ₂ which is a semiconductor photocatalyst
Promotes an oxidation reaction, so that NO can be extremely efficiently oxidized with the same input energy. The catalyst that can be used in the present invention is not limited to TiO ₂ . For example, G
aP, ZrO ₂ , Si, CdS, KTaO ₃ , CdSe,
SrTiO ₃ , Nb ₂ O ₅ , ZnO, Fe ₂ O ₃ , WO ₃ , S
A catalyst such as nO ₂ can be used. Even if these catalysts are not used, NO is oxidized only by corona discharge
It can also be changed to O ₂ . In this case, although the oxidation efficiency is inferior, it is not necessary to provide the catalyst on the inner wall surface of the tubular body 10 by a method such as baking, so that the manufacturing cost can be reduced.

FIG. 4 is a front view showing an arrangement example of the oxidation device 100. In the above description, a single oxidizer 10 is used.
Although the case where the gas to be processed passes through the inside of 0, in the actual denitration apparatus, as shown in FIGS. 4 (a) and 4 (b), a plurality of oxidizing apparatuses 100 or 101 are bundled and used for oxidation. It is desirable to do. This way,
Since the area in which the processing gas comes into contact with TiO ₂ as the catalyst can be increased, a large amount of processing gas can be efficiently processed. When used in combination with an oxidizer, the cross section of the oxidizer 100 has a rectangular cross section as shown in FIG. 4B rather than a circular cross section perpendicular to the axial direction as shown in FIG. It is preferable to use the oxidizer 101 described above because the ineffective area 150 can be reduced.

(Modification 1) FIG. 5 is a cross-sectional view perpendicular to the axial direction showing a first modification of the oxidizing device according to the first embodiment. The tubular body 1 that constitutes the oxidizer 102
The inner surface of No. 1 is coated with the alkali adsorbent 60, and the photocatalyst 5
It is characterized in that it coexists with TiO ₂ which is 1. In this way, the NO ₂ after simultaneous oxidation and the oxidation of NO can adsorb to the alkaline sorbent 60, the adsorption of NO oxidation and NO ₂ can be realized by one device, it can be simplified device configuration Becomes Furthermore, when the alkali adsorbent 60 and TiO ₂ are allowed to coexist, the alkali adsorbent 60 is absorbed by the TiO ₂ .
The chemical reaction of is promoted to improve the adsorption efficiency. As a result, the amount of nitrogen oxides that are not adsorbed and flow out of the oxidation device 102 can be reduced, so that the amount of nitrogen oxides that can be treated in the next reduction step also increases, and the denitration efficiency can be increased correspondingly, which is preferable.

(Modification 2) FIG. 6 is a sectional view perpendicular to the axial direction showing a second modification of the oxidizing apparatus according to the first embodiment. The oxidizing device 103 is characterized in that TiO ₂ which is a photocatalyst is used more efficiently by a light irradiation means such as an excimer lamp or a laser, instead of discharging by a line electrode. As described above, this oxidizer has a cylindrical body 10 having TiO ₂ on its inner wall surface.
(See FIG. 2) can be used. Further, as described in the first modification, the alkali adsorbent 60 and the T that is the photocatalyst 51 are used.
It is also possible to coexist with iO ₂ (see FIG. 5).

An excimer lamp 70 connected to a power source 201 is provided inside the tubular body 12, and a Ti, which is a photocatalyst 52 provided on the inner wall surface of the tubular body 12, is provided.
Irradiated with O ₂ . Generally, TiO ₂ is excited by irradiation with light having an energy potential of 3.2 eV or more, and forms a hole. The electrons of the molecule that comes into contact with the surface of the photocatalyst are taken into this hole, thereby promoting the oxidation of the molecule. Since the excimer lamp 70 has a very high hole forming efficiency, it can sufficiently excite TiO ₂ to further promote the oxidation of NO. Even if laser light is irradiated instead of the excimer lamp 70, TiO ₂ can be sufficiently excited to accelerate the oxidation of NO.

(Reduction Processing) Next, the reduction processing will be described. FIG. 7: is explanatory drawing which shows the reduction | restoration apparatus which concerns on Embodiment 1 of this invention. The reducing device 104 exposes an alkaline adsorbent that adsorbs nitrogen oxides to a discharge field to release NO ₂ which is a nitrogen oxide into a gas phase, and then reduces it in a reducing gas atmosphere to reduce N or CO _2. It is what In the oxidation procedure described above, the alkaline adsorbent 61 has sufficiently adsorbed nitrogen oxides. Therefore, the alkaline adsorbent 61 is connected to the power source 202 and a voltage is applied to cause a discharge between the electrodes 32 and 21. At the same time, HC (hydrocarbon) gas is supplied to the alkali adsorbent 61 as a reducing gas to reduce the nitrogen oxides in the reducing gas atmosphere.

NO ₂ , which is a nitrogen oxide desorbed from the alkaline adsorbent by the discharge, is released into the reducing gas atmosphere. Here, since NO ₂ is itself an oxidant,
Since other substances are oxidized, NO ₂ forms an atmosphere in which NO ₂ easily acts as an oxidant due to discharge, and oxidizes HC gas which is a reducing gas. By this reaction, N in the nitrogen oxide becomes N ₂ , and O combines with C and H of the reducing gas to become CO ₂ and H ₂ O. In this way, the reduction of nitrogen oxides is completed. Note that NO is converted to NO ₂ by the oxidation procedure.
The reason why it is not directly reduced is that the NO ₂ concentration is low, so the denitration efficiency becomes extremely poor. Therefore, the nitrogen oxide NO ₂ is adsorbed onto the alkali adsorbent 61 until it is saturated, thereby increasing the concentration of nitrogen oxide released into the reducing gas atmosphere.

In this reduction treatment, the nitrogen oxides adsorbed on the alkali adsorbent are reduced by discharging in a reducing gas atmosphere, but the nitrogen oxides can be similarly removed by heating with a catalyst having a reducing function. Can be reduced. However, a catalyst having a reducing function is often a noble metal, which increases the cost of the apparatus, which is not preferable. Therefore, in such a case, it is preferable to use the above-described reduction treatment by electric discharge.

(Second Embodiment) FIG. 8 is an explanatory view showing a denitration device according to a second embodiment of the present invention. This denitration device is characterized by a reduction treatment, and is characterized in that a direct current is applied to the alkali adsorbent to decompose the nitrogen oxides adsorbed by the alkali adsorbent into N ₂ and O ₂ . Figure 8
In the alkaline adsorbent 62 composed of Ba (OH) ₂ shown in (a), nitrogen oxides are adsorbed to the saturated state by the oxidation treatment in the previous stage. Any oxidation treatment described in the first embodiment may be applied to this oxidation treatment.

The alkali adsorbent 62 includes electrodes 33 and 3
4 is attached. The electrodes 33 and 34 are connected to a DC power supply 210, and a DC voltage is applied to the alkali adsorbent 62. Further, the electrode 34 attached to the surface where the alkali adsorbent 62 contacts the processing gas containing nitrogen oxide is provided with a plurality of holes 34a. Then, the processing gas passes through the holes 34a and comes into contact with the alkali adsorbent 62, and in the oxidation treatment, the holes 3
NO ₂ is adsorbed by the alkali adsorbent 62 from 4a.

Nitrogen oxides are absorbed in the form of Ba (NO ₃ ) _{2 in} the alkaline adsorbent 62, but when a direct current voltage is applied to the alkaline adsorbent 62, the electrode 34 which is the positive electrode.
NO ₃ ⁻ which is a nitrate ion moves to the side. Then, in the process of passing the electrons to the electrode 34, which is the positive electrode, the following electrode reaction is performed and NO ₃ ⁻ is directly reduced.

2NO ₃ ⁻ → N ₂ + 3O ₂ + 2e ^{− In} this reduction treatment, the nitrogen oxides adsorbed on the alkali adsorbent 62 can be directly reduced without returning them to the gas phase, so that the reduction treatment can be performed easily. You can speed up the time. Further, since no reducing gas is required, the cost is reduced accordingly, and the gas supply system is also unnecessary, so that the apparatus is simplified. Here, the types of electrodes used for this reduction treatment will be described. Of the electrodes used for this reduction treatment, it is desirable to use Fe for at least the positive electrode. Since the oxidation number of Fe changes when it is given an electron, it can receive more electrons at the positive electrode and accelerate the reduction of NO ₃ ⁻ . In this example, NO ₃ ⁻ stored in the alkaline adsorbent is reduced at the positive electrode, but instead of the chemical adsorbent, Al ₂ O ₃ or TiO ₂ or the like, or a physical adsorbent such as activated carbon or molecular sieve is used. May be used to adsorb NO ₂ on this surface and then reduced by the electrode reaction.

If this reduction process (hereinafter referred to as DC reduction process) is not sufficient, as shown in FIG. 8B, the AC power source 203 for discharging and the DC power source for DC reduction process are used. 211 may be connected in series so that the linear electrode 22 is discharged and at the same time the electrode 34 is subjected to direct current reduction treatment. Then, at the time of discharging, a reducing gas such as HC gas is caused to flow to simultaneously perform the reducing process described in the first embodiment. By doing so, most of the nitrogen oxides that could not be reduced by the direct current reduction treatment can be reduced. In addition,
According to this reduction method, the nitrogen oxide is also reduced by the direct current reduction, so that a small amount of reducing gas can be used.

FIG. 8C is a partial cross-sectional view showing the reducing device according to the second embodiment installed in an actual desulfurization device.
The reducing device 105 includes two tubular members 14 having different diameters.
And 15 are arranged concentrically, and an alkali adsorbent 63 is provided in the gap between them. Then, the processing gas containing nitrogen oxides passes through the inside of the tubular member 14 provided inside. Here, as shown in the figure, since the cylindrical member 14 is provided with a plurality of holes 14a, the nitrogen oxides in the processing gas are adsorbed by the alkali adsorbent 63 through the holes 14a. Further, the tubular members 14 and 15 together form an electrode and are connected to the DC power supply 212. Then, when a DC voltage is applied, NO ₃ ⁻ passes electrons to the tubular member 14, and N ₂ gas or O ₂ flows through the hole 14a. To discharge at the same time, the tubular member 14
It suffices to provide the linear electrode 23 in the inside of and to discharge between the tubular member 14 and the linear electrode 23.

(Modification) FIG. 9 is an explanatory view showing a denitration device according to a modification of the second embodiment. This denitration device 10
6 oxidizes NO in the processing gas to NO ₂ , and
It is characterized in that a direct current voltage is applied to the alkaline adsorbent to directly reduce NO ₃ ⁻ . For the alkali adsorbent 64, the electrode
And a plurality of holes 35 a are provided in the electrode 35. Then, NO ₂ is passed through this hole 35a.
Are adsorbed on the alkali adsorbent 64.

Similarly, the electrode 35 is provided with TiO ₂ 53, which is a semiconductor photocatalyst, by baking or the like. The TiO ₂ 53 plays a role of promoting the oxidation when NO in the processing gas is oxidized. Also, Ti
When a semiconductor photocatalyst such as O ₂ 53 coexists with the alkali adsorbent 64, the adsorption efficiency of NO ₂ which is a nitrogen oxide becomes high. Therefore, the alkali adsorbent 64 also has TiO ₂ 53
Is desirable to be dispersed.

The electrode 35 and the linear electrode 24 are connected to a DC power supply 213 and an AC power supply 214 which are connected in series. Now, when the processing gas containing nitrogen oxides flows from the upstream side A of the denitration device 106 and is supplied to this denitration device 106, corona discharge is generated by the AC voltage applied between the electrode 35 and the linear electrode 24. Then, a non-equilibrium plasma atmosphere is formed. In this atmosphere, N in the processing gas
O is oxidized and changed to NO ₂ .

Here, since TiO ₂ 53, which is a semiconductor photocatalyst, is provided on the electrode 35, the N 3
O 2 oxidation reaction is promoted and NO ₂ is rapidly generated in a large amount. This NO ₂ is adsorbed by the alkali adsorbent 64 made of Ba (OH) ₂ through the hole 35a provided in the electrode 35 and stored as Ba (NO ₃ ) ₂ . Since TiO ₂ 53 coexists with the alkali adsorbent 64, NO ₂ is quickly adsorbed by the alkali adsorbent 64.

The DC power source 2 is used for the electrode 35 and the linear electrode 24.
Since a DC voltage is also applied from 13, the NO ₃ ⁻ in the alkaline adsorbent 64 is positive (electrode 3
5) direction, where electrons are given to the electrode 35 and N
O ₃ ⁻ is decomposed into N ₂ and O ₂ . As described above, since the denitration device 106 can continuously advance the oxidation / reduction reaction, the denitration process can be performed quickly. Moreover, since no reducing gas is required, the denitration cost is low, and replenishment of reducing gas is not required, so that maintenance and inspection are not troublesome. Therefore, it is suitable as a denitration device for a facility such as a denitration device used for a tunnel or the like, in which it is desired to reduce maintenance and inspection work as much as possible.

The process gas containing nitrogen oxide is oxidized.
Instead of the linear electrode 24, excimer
A pump (not shown) may be used. Excimer lamp T
iO ₂When irradiated to semiconductor photocatalysts such as
Since it is possible to oxidize, the denitration treatment speed is improved, which is preferable.
It should be noted that, along with NO oxidation processing, NO₃ ^-The reduction process of
Good or use until the alkali adsorbent 64 reaches saturation
After that, you may reduce by applying a DC voltage in another facility.
If you do this, you will not be able to secure enough power for the return.
Even in the case, denitration treatment can be performed.

(Embodiment 3) FIG. 10 is an explanatory view showing a denitration apparatus according to Embodiment 3 of the present invention. The oxidation device and the reduction device described in the first and second embodiments are applied to this denitration device. FIG. 10A shows a circular honeycomb denitration unit 180 formed by combining a plurality of the oxidation devices 100 (see FIG. 2) described in the first embodiment (only three are described, the rest are omitted). There is. About 1/4 of this denitration unit is designed to prevent the invasion of the processing gas by the lid 181 for the reduction process.

Now, the processing gas containing nitrogen oxides flows from the upstream side A and flows into the denitration unit 180. Then, electric discharge occurs in the oxidizing device 100 of the denitration unit 180, and NO is oxidized to NO ₂ . This NO ₂ is adsorbed by an alkali adsorbent (not shown) in the oxidizer 100. NO up to the critical amount at which this alkaline adsorbent can be stored
_{When 2} is adsorbed, the denitration unit 180 is rotated to move the oxidizer 100 to the position of the lid 181, and nitrogen oxide is reduced by discharging while flowing a reducing gas from the pipe 182 in this portion. When the reduction is completed, the denitration unit 180 is rotated by ¼ to reduce the next denitration device. If the storage amount of the alkali adsorbent reaches a critical level without providing the lid 181, the denitration unit 180 may be removed together with the reduction treatment at another facility. By doing so, a reducing gas supply system is not required, so that the structure of the apparatus can be simplified and the apparatus can be installed relatively easily even in a place where the installation space is small. Further, since the labor of replenishing the reducing gas is not required, the labor of maintenance and inspection can be reduced.

In the denitration apparatus shown in FIG. 10B, the treatment gas is oxidized by the oxidation unit 192 installed upstream of the reduction unit 190, and the treatment gas after the oxidation treatment is reduced by the reduction unit 190 provided on the downstream side. To do.
The oxidation device 100 (see FIG. 2) used in the oxidation unit 192 is preferably provided with a semiconductor catalyst such as TiO ₂ on its inner surface in order to increase the oxidation efficiency. If the reducing device 105 capable of performing the direct current reduction process described in the second embodiment is used as the reducing unit 190, the oxidizing unit 192
In addition, since the oxidation / reduction treatment can be performed continuously, the treatment time can be shortened. In addition, the reduction unit may be detachable, and when the alkali adsorbent reaches a critical level, it may be removed and subjected to reduction treatment in another treatment facility.

[0046]

As described above, in the reducing device according to the present invention (claim 1), the nitrate ions adsorbed on the chemical adsorbent are reduced by applying a DC voltage. For this reason, a reducing gas, a discharge facility, etc. are not required, and nitrate ions can be easily reduced. Further, since no reducing gas is required, the running cost can be reduced accordingly.

Further, in the reducing device according to the present invention (claim 2), nitrate ions are adsorbed on the physical adsorbent, and the nitrate ions are reduced by applying a DC voltage. For this reason, reducing gas, discharge, etc. are not required, and nitrate ions can be easily reduced. Further, since no reducing gas is required, the running cost can be reduced accordingly.

In the reducing device according to the present invention (claim 3), at least the positive electrode of the electrodes for applying the DC voltage is made of Fe. Therefore, the change in the oxidation number of Fe can also be used for the reduction of nitrate ions, so that the reduction of nitrate ions proceeds more quickly. Therefore, if this reducing device is used in a denitration device, the denitration rate can be increased. Furthermore, since inexpensive Fe is used, the manufacturing cost and running cost of the reduction device can be suppressed.

In the reducing device according to the present invention (claim 4), a reducing gas is also used so as to supplement the case where the reduction by applying the DC voltage is not sufficient. I did it. Therefore, nitrate ions and NO ₂ can be reduced more completely, so that the denitration efficiency can be increased.

Further, in the denitration apparatus according to the present invention (claim 5), since the discharge oxidation treatment and the reduction by applying the DC voltage are continuously performed, the denitration speed can be increased. In addition, since reducing gas is not required, running cost can be kept low, and replenishment of reducing gas is not required, so maintenance and inspection work can be reduced accordingly.

Further, in the denitration apparatus according to the present invention (claim 6), the processing gas is oxidized by the discharging means with the interposition of the photocatalyst. Therefore, the efficiency of the oxidation treatment of NO contained in the process gas can be increased, and the denitration efficiency can be increased accordingly. Further, when the photocatalyst is interposed in the chemical adsorbent, the NO ₂ adsorption efficiency can be increased, and the denitration efficiency can be increased accordingly.

Further, in the denitration apparatus according to the present invention (Claim 7), the photocatalyst is interposed to oxidize the NO in the processing gas by the light irradiation. Can be separated from the power supply. Therefore, NO
The oxidizing conditions and the nitrate ion reducing conditions can be set separately. As a result, denitration can be performed under optimum conditions with respect to environmental changes such as temperature and humidity, so stable denitration performance can be obtained regardless of the environment.

[Brief description of drawings]

FIG. 1 is a flowchart showing a denitration procedure according to the present invention.

FIG. 2 is a sectional view showing an oxidation device according to the first embodiment of the present invention.

FIG. 3 is an explanatory diagram showing the relationship between input energy and oxidation efficiency when TiO ₂ is used and when it is not used.

FIG. 4 is a front view showing an arrangement example of an oxidation device 100.

FIG. 5 is a cross-sectional view perpendicular to the axial direction showing a first modification example of the oxidation device according to the first embodiment.

FIG. 6 is a cross-sectional view perpendicular to the axial direction showing a second modification example of the oxidation device according to the first embodiment.

FIG. 7 is an explanatory diagram showing the reduction device according to the first embodiment of the present invention.

FIG. 8 is an explanatory diagram showing a denitration device according to Embodiment 2 of the present invention.

FIG. 9 is an explanatory diagram showing a denitration device according to a modified example of the second embodiment.

FIG. 10 is an explanatory diagram showing a denitration device according to Embodiment 3 of the present invention.

[Explanation of symbols]

10, 11, 12 Body 14 Cylindrical member 14a Holes 20, 21, 22, 23, 24 Linear electrodes 30, 31, 32, 33 Electrode 34 Electrodes 34a, 35a Hole 35 Electrode 40 Dielectric 50 Photocatalyst 51, 52 Photocatalyst 53 TiO ₂ 60, 61, 62, 63, 64 Alkaline adsorbent 70 Excimer lamp 100, 101, 102, 103 Oxidizing device 104, 105 Reduction device 106 Denitration device 150 Ineffective area 180 Denitration unit 181 Lid 182 Piping 190 Reduction unit 192 Oxidation Units 200, 201, 202 Power supplies 203, 214 AC power supplies 210, 211, 213 DC power supplies

Front page continuation (51) Int.Cl. ⁷ Identification code FI theme code (reference) B01J 35/02 F01N 3/08 C F01N 3/08 3/10 A B01D 53/34 129A 53/36 ZABJ 3/10 ( 72) Inventor Yasutoshi Ueda 2-1-1 Shinhama, Arai-cho, Takasago-shi, Hyogo Mitsubishi Heavy Industries Ltd. Takasago Research Institute (72) Inventor Morio Kagami 1-1-1 Wadasaki-cho, Hyogo-ku, Kobe Sanritsu Heavy Industries Co., Ltd. Inside the Kobe Shipyard (72) Akira Mizuno 1-2-4 Kanayama, Naka-ku, Nagoya, Aichi Prefecture (1202, Urban Raffle Kanayama) (72) Katsu Ishibashi 2-chome, Niihama, Niihama, Arai Town, Takasago, Hyogo Prefecture Ryokan Engineering Co., Ltd. F-term (reference) 3G091 AB01 AB09 AB14 BA14 CA18 GB02Y GB03Y GB09Y GB10Y 4D002 AA12 BA04 BA08 CA07 DA11 DA21 DA41 DA45 DA46 EA02 EA07 4D048 AA06 AB01 AB02 BA07X BA41X BB01 CD01 EA01 CA08B CA07A07B08B07B07AA03 BA08B07A08A02 CA08B07A02 EA02Y 4G075 AA22 AA62 BA06 BB04 CA14 EC21 FB0 2

Claims (7)

[Claims] 1. A direct current voltage is applied to a chemical adsorbent that has adsorbed a treatment gas obtained by oxidizing nitrogen oxides, and electrons of nitrate ions present in the chemical adsorbent are applied to the positive electrode of the direct current voltage application electrode. A reducing device characterized by giving the nitrate ion to reduce the nitrate ion. 2. A method of adsorbing nitrate ions on a physical adsorbent, applying a DC voltage to the physical adsorbent, and applying electrons of the nitrate ions to the positive electrode of a DC voltage applying electrode to reduce the nitrate ions. Characterizing reduction device. 3. The reducing apparatus according to claim 1, wherein at least the positive electrode of the electrodes is Fe. 4. A reducing agent is caused to flow through the chemical adsorbent or the physical adsorbent when the DC voltage is applied, and nitrate ions and nitrogen oxides are reduced while discharging by the discharging means. The reduction device according to claim 1. 5. A discharge means for oxidizing a treatment gas containing nitrogen oxides, and a chemical adsorbent or physical adsorption for adsorbing nitrogen oxides contained in the treatment gas after the oxidation treatment in the form of nitrate ions. And a direct current voltage applying means for applying a direct current voltage to the chemical adsorbent or the physical adsorbent, and the electrons of nitrate ions adsorbed on the chemical adsorbent or the physical adsorbent to the positive electrode of the direct current voltage applying electrode. A denitrification device, characterized in that it is applied to reduce the nitrate ions. 6. The denitration device according to claim 5, further comprising oxidizing the processing gas by the discharging means with a photocatalyst interposed. 7. A light irradiation means for oxidizing a treatment gas containing nitrogen oxides through a photocatalyst, and adsorbing nitrogen oxides contained in the treatment gas after the oxidation treatment in the form of nitrate ions. A chemical adsorbent or a physical adsorbent, and a direct current voltage applying means for applying a direct current voltage to the chemical adsorbent or the physical adsorbent, and the electrons of the nitrate ions adsorbed on the chemical adsorbent or the physical adsorbent to the direct current A denitration device characterized by being applied to the positive electrode of a voltage application electrode to reduce the nitrate ions.