JPH08299758A - Method for removing nitrogen oxide and device therefor - Google Patents

Abstract

PURPOSE: To provide the method and device for efficiently and economically removing the dil. NOx in the atmosphere by using an adsorbent. CONSTITUTION: A gas 1 in the atmosphere contg. dil. NOx is introduced into an adsorption tower 3 to adsorb the NOx on an adsorbent 4. The adsorbent 4 is then treated with a gas heated by a heater 8 to desorb the adsorbed gas and regenerated, and the desorbed NOx is decomposed in a catalytic device 10 and discharged outside the system. The regenerated adsorbent 4 is cooled by the gas passed through a cooler 9, and the adsorption and desorption are repeated. The adsorbent 4 is regenerated in a heated inert gas also reduced in oxygen concn., and the oxygen concn. in the atmosphere at the end of regeneration and in cooling is decreased to zero or the atmosphere is made slightly reductive.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to nitrogen oxides such as low concentrations of nitric oxide (NO) and nitrogen dioxide (NO ₂ ) mainly contained in ventilation gas from road tunnels and closed parking lots. Hereinafter, a method for adsorbing and removing NO _x ) and an apparatus therefor.

[0002]

2. Description of the Related Art Ventilation equipment in a road tunnel is used to secure a clear visual distance mainly due to soot and carbon monoxide (C).
O), NO _x, etc. are installed for the purpose of reducing the harmful substances to below the allowable value. As the current ventilation method, a method is generally used in which fresh outside air is taken in from outside the tunnel, soot is removed if necessary, and then forced ventilation is performed outside the tunnel.

However, this method only diffuses ventilation gas containing harmful substances into the atmosphere, and does not improve the environment fundamentally. Particularly in urban areas where air pollution due to automobile exhaust gas is becoming serious, a highly polluted area is expanded, which may hinder tunneling and shelter installation in road planning. Therefore, it is desired to develop a new ventilation method that is energy-saving and has no effect on the surrounding environment.

The tunnel ventilation gas is NO at room temperature and has a large capacity.
_{The x} concentration is as low as 10ppm or less, and N depends on the traffic volume.
Because of the peculiarity that the O _x concentration fluctuation is severe, it is not possible to directly apply the NO _x purification method using NH ₃ as a reducing agent, which has already been put to practical use in boiler combustion exhaust gas.

Therefore, various dry methods and wet methods have been proposed as low-concentration NO _x purification methods, but the wet method is difficult to put into practical use because it requires a wastewater treatment apparatus. The following dry methods are available.

(1) After adsorbing NO _{x of the} tunnel ventilation gas to the adsorbent, separating and concentrating from the adsorbent by changing the temperature and pressure, NO _x is harmless without adding a reducing agent in the presence of contact. Catalytic decomposition method that decomposes to nitrogen.

(2) Adsorption method in which NO _{x of} tunnel ventilation gas is adsorbed by an adsorbent, separated and concentrated by changing temperature and pressure, and then NH ₃ is removed as harmless nitrogen as a reducing agent in the presence of a catalyst. . Depending on the adsorbent, if NO ₂ is used, the performance will be high. Therefore, when oxidizing with ozone in advance, propane may be used as the reducing agent instead of NH ₃ .

(3) An electron beam irradiation method in which NH ₃ is added to the tunnel ventilation gas, and at the same time, an electron beam is irradiated to replace NO _x with ammonium nitrate, and is recovered and removed by an electrostatic precipitator.

The present inventor has a strong image of harmful substances in consideration of the fact that the NO _x purification equipment is installed in the city.
The use of NH _3, O ₃ there is a risk of the following pollutants occurs, and consider cleaning method without such a solid by-product generation in the ammonium nitrate was first proposed a scheme (1).

That is, under pressure using a zeolite-based adsorbent
NO_xSelectively adsorb gas and desorb the adsorbed gas under reduced pressure.
PSA (pressure swing adsorption) method that is set to separate
NO _xNO after separating and concentrating_xDecomposition catalyst to nitrogen and oxygen
It is a decomposition method, but NO _xConcentration several thousand times (about 1%
NO if not concentrated)_xDecomposition catalyst has predetermined decomposition performance
NO because it does not express_xThe volume occupied by the separation / concentration unit
It is inferior in terms of equipment cost and required power.

Therefore, the method (2) in which the same adsorbent as in the case (1) is used and it is converted into nitrogen by a catalytic action by addition of a reducing gas was proposed. Here, as the reducing gas, N which has a strong image as a harmful substance should it leak out.
Instead of H ₃ , propane, a household fuel, was selected.

However, this method is affected by the saturated water content (about 2.6%) contained in the treated gas, and even if the hydrophobic zeolite adsorbent is used, N by repeated adsorption and desorption is used.
A reduction in O _x adsorption capacity was observed. Therefore, it is necessary to take measures to reduce the water content of the processing gas to zero or increase the adsorbent capacity, and it must be said that the effect of improving the NO _x separation / concentration section is small.

[0013] Further, as a result of selecting an adsorbent having a small decrease in NO _x adsorption capacity even after repeated adsorption and desorption in the presence of water and studying adsorption and desorption conditions, it was found that activated carbon was used as the adsorbent.
Adsorption and desorption by the TSA (Temperature Swing Adsorption) method, which utilizes the fact that the adsorption capacity for O _x gas varies depending on the temperature,
It was concluded that a process using nitrogen, which is harmless as a catalyst with H ₃ as a reducing agent, is also promising.

However, ordinary activated carbon has a slow adsorption rate,
In addition, due to the influence of NO partial pressure, in order to achieve the specified adsorption performance,
In terms of practical application, the process gas flow rate must be 0.1 m / sec or less, and if the activated carbon is heated and regenerated in the air, there is a risk of ignition. There was a problem.

Next, as an adsorbent for efficiently adsorbing NO, a noble metal adsorbent such as Pt-Al ₂ O ₃ is well known. However, it has been found that when the noble metal-based adsorbent is repeatedly adsorbed and desorbed by NO _{x in the} presence of oxygen, the NO _x adsorption capacity is rapidly reduced.

The tunnel ventilation gas contains oxygen in the atmosphere, and if the TSA method is used for adsorption and desorption under the same conditions, the noble metal-based adsorbent and the activated carbon adsorbent have the respective problems described above. However, it cannot be said to be practical for practical use as a process of adsorbing and removing NO without converting ozone to NO ₂ by adding ozone or the like from outside the system.

The tunnel ventilation gas contains soot and dust, and soot and dust removing equipment such as an electric dust collector has already been installed. When the load voltage is increased with an electric dust collector, NO changes to N
Become converted to O _2, since conversion with increasing load voltage increases or utilizing this phenomenon, or to convert NO to NO _x by adding ozone from the outside of the system, with respect to NO ₂ By applying an adsorbent that selectively adsorbs,
The present inventors have already proposed a method for efficiently removing dilute NO _x in tunnel ventilation gas and an adsorbent therefor.

[0018]

As described above, the method of removing the lean NO _x in the tunnel ventilation gas without adding NO or the like from the outside of the system and converting NO into NO ₂ is available.
It is attractive because there is no fear of the next pollutant generation, but it can be said that a method for practically efficient and economical removal has not yet been found. NO _x desorption with an activated carbon adsorbent is usually performed if the atmospheric oxygen content is reduced to several percent or less.
Under the conditions of around ℃, the adsorbent is stable without sudden oxidation.

Further, the present inventors have conducted various experiments in order to elucidate the cause of the decrease in capacity of the noble metal-based adsorbent, and the surface of the adsorbent after NO _x desorption in the presence of oxygen has oxygen at the noble metal active sites. Since it is strongly adsorbed, it has been clarified that the adsorbent after regeneration is deteriorated by not adsorbing NO _x , oxygen adsorption does not occur under the condition of zero oxygen, and adsorption O _{2 under the} condition of reducing gas such as hydrogen. Has been clarified regarding the prevention of deterioration and recovery measures, such as the fact that deterioration is quickly recovered by reduction to H ₂ O.

[0020] The present invention will promptly restore the deterioration of the adsorbent, a dilute NO _x in the atmosphere by repeating adsorption and desorption of NO _x, efficiently providing a method and apparatus for economically removed Is an issue.

[0021]

Means for Solving the Problems The present invention for solving the above problems, the gas in the ambient atmosphere containing dilute NO _x adsorbs primarily NO _x was dry treated with an adsorbent, then The adsorbent is treated with a heating gas to desorb and regenerate the adsorbed gas, the desorbed NO _x is decomposed with a denitration catalyst and discharged to the outside of the system, and the regenerated adsorbent is cooled to perform the adsorption / desorption. A repeated NO _x removal method is adopted.

In the NO _x removal method according to the present invention,
The regeneration of the adsorbent described above is performed in an inert heating gas atmosphere in which the oxygen concentration is reduced, and the oxygen concentration in the atmosphere at the end of regeneration and at the time of cooling is set to almost zero or a slight reducing atmosphere. In the NO _x removal method according to the present invention, it is preferable to use an adsorbent such as an activated carbon adsorbent or a noble metal-based adsorbent that efficiently absorbs nitric oxide.

Further, in the NO _x removal method according to the present invention, in order to reduce the oxygen concentration in the system before the adsorbent regeneration step is completed, and to make a slight reducing atmosphere, if necessary, as described below. Diluting and desorbing by supplying seal nitrogen C
Oxygen concentration reducing effects such as oxygen consumption due to O, C ₃ H ₈ combustion can be utilized.

(1) Diluting effect by supply of seal nitrogen: Through the regeneration process, seal nitrogen for sealing the inside of the apparatus from the atmosphere is supplied to the inlet / outlet of the absorption tower. Oxygen in the system is replaced with nitrogen and the concentration is gradually reduced, and is discharged out of the system through an exhaust gas purifier described later. The larger the nitrogen supply amount, the greater the reduction in oxygen concentration due to dilution. However, considering the decrease in oxygen concentration after (2), the nitrogen supply amount remains at the amount required to seal the inside of the device from the atmosphere. .

(2) Diluting effect of desorbed water: NO _x at the stage of heating at about 100 to 120 ° C. at the beginning of the regeneration process.
The water adsorbed on the adsorbent is desorbed. The desorbed water is discharged out of the system through the exhaust gas purifier while diluting oxygen in the system. The oxygen concentration in the system is drastically reduced in combination with the dilution effect of the seal nitrogen supply.

(3) Desorption of CO, C ₃ H ₈ Oxygen consumption by combustion: The NO _x adsorbent also adsorbs the lean NO _x containing gas to be treated, for example, CO and C ₃ H ₈ in the tunnel ventilation gas. Due to the combustion catalytic action of the adsorbent, these adsorbed CO and the like react with O _{2 at} around 200 ° C. to change into CO ₂ and H ₂ O, which lowers the oxygen concentration.

Regarding the oxygen concentration at the end of this step, since the next denitration reaction is carried out in the presence of oxygen, it is necessary to leave about 1% to 2% of oxygen or desorption CO, If the O ₂ concentration is too low due to C ₃ H ₈ combustion, the oxygen concentration can be adjusted by changing the temporary seal gas to air. In addition, the heat generated by combustion can be effectively used as a part of the energy required for the regeneration process.

(4) Reduction of oxygen concentration during NO _x decomposition: C
Since NO _x begins to be desorbed almost at the same time as the combustion of O and C ₃ H _{8 on} the adsorbent, a NO _x reducing agent such as NH ₃ or aqueous urea is supplied to decompose NO _x on the denitration catalyst. Also in this case, a slight decrease in oxygen concentration occurs due to oxygen consumption due to the denitration reaction and evaporation of water due to the supply of urea water.

(4) Oxygen consumption due to addition of reducing gas: The residual oxygen at the end of denitration is a low concentration of about 1%,
The time until the completion of the regeneration process is relatively short, and it is effective to add a reducing gas such as CH ₄ or C ₃ H ₈ and burn at the same time as diluting by supplying the seal nitrogen to completely eliminate the residual oxygen.

The reducing gas is used in a relatively small amount and there is no particular problem. If a slight excess is added, a reducing atmosphere can be obtained. Moreover, especially as a CH ₄ raw material, city gas is often practical.

By utilizing the effect of reducing the oxygen concentration as described above, the oxygen concentration in the system can be made almost zero, and a slight reducing atmosphere can be created if necessary.

The present invention also provides a NO _x removal device for carrying out the above-mentioned NO _x removal method. The apparatus includes a dust collector, and _the NO _x adsorption agent adsorption tower filled, the NO _x removing unit and a processing gas suction fan.

The NO _x removing device according to the present invention, in addition to the NO _x removing section described above, includes a heater, a NO _x decomposition catalyst device, a cooler, a circulating gas blower, and a gas outside the system while equalizing pressure. An exhaust gas purifier for discharging the gas, and a regeneration section that is connected to the adsorption tower via a seal gas valve and forms a gas circulation path passing through the adsorption tower.

[0034]

In the NO _x removal method of the present invention, the adsorbent adsorbs the lean NO _x in the gas, desorbs the desorbed NO _x , and decomposes the desorbed NO _x with the denitration catalyst. The desorption step of desorbing from the adsorbent is performed under zero oxygen conditions and, if necessary, under a slight reducing gas condition.

This prevents the oxidation of adsorbed NO _x ,
When oxidized, the NO
_This facilitates desorption of _x and complete regeneration of the NO _x adsorbent at relatively low temperatures. Thus the suction, by repeating the desorption reaction, air can efficiently purify over a long period of time containing dilute NO _x.

The following experiment was conducted to examine the effect of the desorption process in the NO _x removal method according to the present invention described above.

(Experimental example) A Pt-Al ₂ O ₃ adsorbent was prototyped, and the adsorption and desorption test conditions were set as shown in Table 1 below to evaluate the influence of the desorption conditions on the adsorption / desorption repetition performance.

In this adsorbent, γ-Al ₂ O ₃ was impregnated with an aqueous solution of chloroplatinic oxide to support 2 wt% of Pt.
A powder obtained by drying at 110 ° C. and firing at 500 ° C. for 5 hours was coated with a cordierite honeycomb substrate of 400 cells / inch ² at 200 g / 1 by a wash coating method.

Using the results of the second adsorption test after one adsorption and desorption test as data, the breakthrough time (time to reach C / C ₀ 0.2) and the NO adsorption capacity were determined. The desorption conditions were air (relative humidity 60% (25 ° C.)) at 400 ° C. for 60 minutes, and then treatment was performed with the gases from to in Table 1 to examine the influence on the adsorption performance.

[0040]

[Table 1]

The test results are shown in Table 2, and the breakthrough curve and desorption curve under each desorption condition are shown in FIG. In Table 2, the breakthrough time when C / C ₀ = 0.2 is not reached in the adsorption time of 120 minutes is described as 120 minutes or more, and the NO _x adsorption capacity is the adsorption amount up to the adsorption time of 120 minutes.

[0042]

[Table 2]

From the results shown in Table 1 and FIG. 1, after regeneration with air, treatment with inert gas and nitrogen (), reducing gas hydrogen (), and C ₃ H ₈ () was performed to obtain the following NO: It was found that the NO adsorbed amount of the adsorbent in the adsorption step is increased, which makes it possible to improve the performance of the adsorbent, that is, reduce the amount of the adsorbent used.

Next, the NO _x removal apparatus according to the present invention is
The NO _x removing unit and the regenerating unit having the above-described configuration are provided, and in this regenerating unit, the adsorbent is regenerated in the atmosphere in which the oxygen concentration in the system is reduced by utilizing the oxygen concentration reducing effect described above. The above-described NO _x removal method of the present invention can be effectively implemented.

[0045]

Embodiments of the NO _x removal method according to the present invention and one embodiment of the NO _x removal device according to the present invention will be specifically described below with reference to FIG.

In FIG. 2, reference numeral 3 denotes a NO _x adsorption tower, which introduces a lean NO _x- containing gas 1 to be treated, for example, a tunnel ventilation gas, to a dust remover 2 to remove soot and dust in the treated gas to form a dust 19 system. After taking it out, NO _x adsorbent 4
Is introduced into the NO _x adsorption tower 3 filled with. Where NO _x
Are adsorbed and removed, and become clean gas 6 through the suction fan 5 to be released to the atmosphere.

To continuously purify NO _x , N
The O _x adsorption tower 3 by installing two towers above, while performing _the NO _x adsorption in 1 column, performing desorption of adsorbed NO _x in another column, to continue the operation while switching adsorption and desorption However, in this embodiment, NO _x adsorption is performed in the daytime,
Corresponding to the case where desorption of adsorbed NO _x (hereinafter referred to as a regeneration step) is performed at night, one NO _x adsorption column 3 is switched and used.

The regeneration process is divided into a heating process and a cooling process. In the heating process, the NO _x adsorbent 4 is heated to absorb the adsorbed N 4.
This is a step of desorbing O _x to decompose NO _x concentrated in the desorption gas. The cooling step is a step of cooling the regenerated NO _x adsorbent 4 and preparing for the next NO _x adsorption.

NO_xStop suction and stop the suction fan 5
Then, set the four seal gas valves V1, V2, V3 and V4.
Closed, NO_xBetween the adsorption tower 3 and the atmosphere side (upstream and downstream sides)
Stop gas flow. Then close V7 and V8
Open V5 and V6 together, operate heater 8 and _x
Adsorption tower 3-circulating gas blower 7-heater 8-NO_xDisassembly
A heating circulation path that connects the media devices 10 is formed, and the adsorbent 4
Start heating and enter the regeneration process.

At the beginning of the heating process, the amount of the adsorbent 4 is 100 to 120.
In the vicinity of the temperature, the water adsorbed on the NO _x adsorbent is desorbed. Desorbed water dilutes oxygen in the system,
Clean gas 16 through exhaust gas purifier 11 and cooler 12
Is discharged outside the system.

The seal gas 18 is used to seal the inside of the apparatus from the atmosphere through the regeneration process.
It is supplied through 7. Nitrogen is used as a seal gas to reduce oxygen in the system. Combined with the oxygen diluting effect due to the supply of the seal nitrogen, the oxygen concentration in the system is significantly reduced.

The NO _x adsorbent 4 has a property of adsorbing hydrocarbon gases such as CO and C ₃ H ₈ in the tunnel ventilation gas, and these adsorbed hydrocarbons are produced by the combustion catalytic action of the adsorbent. At around 200 ° C, it reacts with O ₂ and CO ₂ and H
Change to ₂ O. The reaction formulas for CO and C ₃ H ₈ are shown in (1) and (2) of Formula 1.

[0053]

Embedded image

The oxygen concentration at the end of this step is obtained by subtracting the oxygen consumed by the combustion of the hydrocarbon from the oxygen concentration of the hydrocarbon and the oxygen before combustion. Therefore, it is necessary to leave about 1% to 2% of oxygen.

Therefore, the combustion of the desorbed hydrocarbon causes O ₂
If the concentration is too low, the oxygen concentration can be adjusted by temporarily changing the seal gas to air. The heat generated by combustion is represented by H in the equations (1) and (2), but it can be effectively used as a part of the required energy for the regeneration process.

[0056] Since almost simultaneously NO _x and combustion on the adsorbent of the adsorption hydrocarbons begin to desorb, NO _x in the heating circulation path
Since the concentration increases, urea water 14 is supplied as an NO _x reducing agent to the inlet line 13 of the NO _x decomposition catalyst device 10 to decompose NO _x on the denitration catalyst. The generation of NH ₃ and the denitration reaction by hydrolysis of urea water are described in Equation 2 (3),
This is shown in equations (4) and (5).

[0057]

Embedded image

The temperature required for this NO _x desorption varies depending on the type of NO _x adsorbent 4, and is 200 for activated carbon adsorbent.
℃, the noble metal-based adsorbent is about 350 ℃, and at the highest is about 400 ℃, NO _x decomposition catalyst device 1
The temperatures of 0 and the NO _x adsorption tower 3 may be appropriately selected appropriately.

Since denitration can be sufficiently performed in this temperature range, NO _x desorption and denitration are almost completely achieved.
Also here, a slight decrease in oxygen concentration occurs due to oxygen consumption due to the denitration reaction and evaporation of water due to the supply of urea water.

The residual oxygen at the end of denitration is controlled to a low concentration of about 1%, and NO _x in the activated carbon adsorbent is controlled.
In desorption, if the atmospheric oxygen content is reduced to a few percent or less, there is no sudden oxidation and heat generation of the adsorbent under conditions of about 200 ° C. which is usually performed, and the adsorption / desorption repetition performance is stable. Therefore, the desorption may be completed here, and then the cooling process may be performed.

For NO _x desorption with a noble metal-based adsorbent, NO
_In order to prevent the adsorption of oxygen to the noble metal active sites on the adsorbent after desorption of NO _x , which causes a decrease in the _x adsorption capacity, the oxygen concentration was set to almost zero conditions, and if some oxygen adsorption still progressed, a reducing atmosphere was created. None, reduce and remove adsorbed oxygen.

In this method, it is effective to add the reducing gas 15 such as CH ₄ or C ₃ H ₈ and burn at the same time as diluting by supplying the seal nitrogen 18 to completely eliminate the residual oxygen. The amount of reducing gas used is also relatively small, and there is no particular problem. If a slight excess is added, a reducing atmosphere can be obtained. The CH ₄ raw material in this case may be city gas, which is practical.

NO_xWhen desorption is nearing completion, the above heating cycle
NO in the ring route_xIf the concentration drops to a predetermined value, NO_x
The supply of the reducing agent urea water 14 is stopped and the heater 8 is turned on.
Stop, close V5 and V6, and open V7 and V8
When the cooler 9 is activated, NO _xAdsorption tower 3-circulating gas blow
A 7- Forming a cooling circulation path connecting the coolers 9 to circulate
Cooling the path gas, water in the gas is drained 20
Eject, NO_xAfter cooling the adsorption tower 3 to near normal temperature,
NO_xPrepare for the adsorption process.

By using the NO _x removing device shown in FIG.
_{x As the} adsorbent 4, the honeycomb-shaped Pt used in the above experimental example
An NO _x adsorption tower 3 was filled with 30 liters of —Al ₂ O ₃ adsorbent, and 150 m ³ N / h of lean NO _x- containing air having the composition shown in the inlet column of Table 3 was treated, and NO _x removal was performed at 14 times per removal. The adsorption / desorption test was repeated 10 times once a day for 10 hours for regeneration by the TSA (temperature swing adsorption) method.
Table 3 also shows the composition of the outlet gas for each repetition, but there was no change over time, and stable performance was obtained.

[0065]

[Table 3]

The results of the regeneration test were as follows. In Table 4
When desorbing water, CO and C₃H₈NO when burning_xDisassembly time
And CH_FourNO of each process at the time of addition_xAt the adsorption tower outlet
3 shows changes in gas composition with time. Figure 3 shows the desorption process
O₂, N₂, H₂Fig. 4 shows changes in O concentration as NO, CO, C
₃H ₈, NH₃Of CO₂The change in concentration is shown.

As shown in Table 4 and FIG. 3, the O ₂ concentration dropped from 20.8% at the beginning to 8.6% during the desorption of water for 0 to 180 minutes, and the next combustion of CO and C ₃ H ₈ was performed. 180 of the hour
Further decreases until 2.3% between ～240Min, reduced to about 0.5% NO _x decomposition at the end of 420Min, then CH ₄
Zero concentration is achieved by the addition. Table 5 shows the test conditions and results for each process.

[0068]

[Table 4]

[0069]

[Table 5]

[0070]

As described above, according to the method for removing NO _x according to the present invention, the diluted NO _x in the air atmosphere, particularly the exhaust gas containing nitric oxide as a main component is treated with the activated carbon adsorbent, the noble metal adsorbent, etc. and the nitric oxide is contacted with efficiently absorbing adsorbent to adsorb and remove nO _x at room temperature, and the adsorbent adsorbs nO _x, regenerated desorbed by heating inert gas containing no oxygen, especially This is a method for removing NO _x , which is characterized in that the oxygen concentration in the system is set to almost zero at the end of the regeneration, and a slight reducing atmosphere is created if necessary.

According to this method, the adsorption / desorption performance does not change with time even after repeated adsorption / desorption in the TSA (temperature swing adsorption) system, and the performance of the adsorbent can be improved. It can be reduced, and more stable long-term use is possible.

Further, according to the NO _x removing apparatus of the present invention having the NO _x removing section and the regenerating section, the NO _x removing method according to the present invention having the above-mentioned effects can be effectively implemented.

[Brief description of drawings]

FIG. 1 is a graph showing a breakthrough curve and a desorption curve showing the results of testing the effect of desorption conditions on adsorption performance.

FIG. 2 is an explanatory diagram showing a configuration example of an apparatus for carrying out the method for removing nitrogen oxides according to the present invention.

FIG. 3 is a graph showing changes in O ₂ , N ₂ , and H ₂ O concentrations during the desorption process.

FIG. 4 NO, CO, C ₃ H ₃ , NH in desorption process
_The graph which shows the density | concentration change of ₃ .

FIG. 5 is a graph showing changes in CO ₂ concentration during the desorption process.

[Explanation of symbols]

1 Dilute NO _x- containing gas 2 Dust remover 3 NO _x adsorption tower 4 NO _x adsorbent 5 Suction fan 6 Clean gas 7 Circulating gas blower 8 Heater 9 Cooler 10 NO _x decomposition catalyst device 11 Exhaust gas cleaner 12 Cooler 13 Inlet line 14 NO _x reducing agent (urea water) 15 reducing gas 16 clean gas 17 seal gas blower 18 seal nitrogen

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁶ Identification number Internal reference number FI Technical display location B01D 53/86 ZAB B01D 53/36 ZAB 53/94 102G B01J 20/08 ZAB (72) Inventor Ueshima Naoyuki 2-1-1, Niihama, Arai-cho, Takasago-shi, Hyogo Mitsubishi Heavy Industries Ltd. Takasago Laboratory

Claims (2)

[Claims] 1. A gas under an atmosphere containing dilute nitrogen oxides is dry-treated with an adsorbent to mainly adsorb nitrogen oxides, and then the adsorbent is treated with a heating gas to obtain an adsorbed gas. Desorption and regeneration, the desorbed nitrogen oxides are decomposed with a denitration catalyst and discharged to the outside of the system, and the regenerated adsorbent is cooled to repeat the adsorption and desorption. A nitrogen oxide characterized in that the adsorbent is regenerated in an inert heating gas atmosphere in which the oxygen concentration is reduced, and the oxygen concentration of the atmosphere at the end of regeneration and at the time of cooling is set to be almost zero or a slight reducing atmosphere. Removal method. 2. A nitrogen oxide removing unit provided with a dust remover, an adsorption tower filled with a nitrogen oxide adsorbent, and a processing gas suction fan, a heater, a nitrogen oxide decomposition catalyst device, and cooling. And a circulating gas blower, and an exhaust gas purifier for discharging gas to the outside of the system while maintaining a uniform pressure, and is connected to the adsorption tower via a seal gas valve to form a gas circulation path through the adsorption tower. A nitrogen oxide removing apparatus for carrying out the removing method according to claim 1, further comprising: