JP2002028452A - Method and device for treating nitrogen oxides - Google Patents

Abstract

PROBLEM TO BE SOLVED: To efficiently remove NOX by suppressing the effect of the humidity fluctuation of a gas to be treated (polluted air) and so forth. SOLUTION: Plural removal modules 2 each consisting of a sheet with TiO2 as the main component and lamp modules 3 to irradiate each removal module with ultraviolet light are arranged along the passage for the gas to be treated in a housing 1, and a monitor 4 is provided to measure the NOX composition of the gas to be treated at the outlet side of each of the removal modules irradiated with the light. In this case, the removal modules on the upstream side are used as an irradiation zone and the removal modules on the downstream side as a non-irradiation zone with a position close to 0.5 in 0.3 to 0.8 ratio of NO2/NOX as the boundary, and the lighting of the lamp is controlled in a state where the removal modules are irradiated with the light.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention is, for example, nitrogen oxides are air pollutants from the ventilation air of an automobile road tunnel (NO _X: nitrogen monoxide NO, collectively nitrogen dioxide NO ₂₎ nitrogen oxides to remove And a processing apparatus.

[0002]

Air pollution caused by NO _X in the Background of the Invention metropolis is still a serious problem. Cause is mainly automobile of air pollution due to the NO _X, in particular, is said to be in the exhaust gas from diesel vehicles, NO _X concentration of the atmosphere around the road intersection in the urban areas is 0.2~0.3ppm, also automobile 1-2 ppm of NO _{X in} ventilation gas for road tunnels
And is a major source of pollution to the surrounding environment. Therefore, apart from the NO _X reduction measures automobile engine, various studies with respect to removal techniques of the NO _X as the Clean Air measures have also been made in the environment side.

[0003] Further, the result of the exhaust gas of an automobile was investigated composition of the NO _X in the tunnel ventilation gas as a source of contamination,
The ratio of NO and NO ₂ is about 9: 1 and NO is the majority, in the removal of NO _X from the atmosphere from this point of view, can be mass processed the the main component NO remain cold technology Is required.

On the other hand, the aforementioned NO_XProcess contaminated air containing
Recently, photocatalytic acid
Chemical removal methods are attracting attention. This treatment method is a photocatalyst
Mainly as TiO₂400 nm on the photocatalyst sheet using
Illuminated by sunlight or photochemical lamps containing the following ultraviolet light
OH radical (OH *) generated on the surface of the photocatalyst,
Superoxide anion (O₂ ^-NO)_X
To nitrate ion (NO₃ ^-) To TiO₂On the surface
That is what we are trying to capture. NO at this time is NO
 → NO₂→ NO₃ ^-Oxidized in two stages
It is. Note that NO₃ ^-With TiO2 trapped on the surface₂Is
The photocatalytic activity decreases as the trapping amount increases,
For example, TiO due to rainfall, shower, etc.₂Wash with water
As a result, the NO trapped on the surface₃ ^-Shifts to washing water
As a result, the photocatalytic activity is restored.

Further, as the processing method of the processed gas inventors have containing NO _X, if the sheet as a main component the same TiO ₂ as the previous SL photocatalyst flow NO _X without light irradiation as an adsorbent, A phenomenon in which NO and NO ₂ are simultaneously adsorbed and removed by an equal amount (hereinafter referred to as “equimolar adsorption”) has been found. NO in (contaminated air) N
Oxidized to O ₂ to adjust the concentration balance between NO and NO ₂ ,
In the post-processing, NO and NO ₂ are adsorbed on the sheet-shaped adsorbent using the same material as the photocatalyst in an equimolar amount to form NO _X.
And a treatment method in which the first half region of the adsorbent laid along the ventilation path of the gas to be treated is used as a light irradiation zone, where UV light having a wavelength of 400 nm or less is irradiated, and NO is determined as NO. oxidized to _2, the second half (not irradiated with ultraviolet light) unirradiated zone region in nO and nO ₂ processing method equimolar by combining a light irradiation zone and non-irradiated zones to adsorb JP 11-9957 an Proposed in the gazette. According to this processing method, it is not necessary to irradiate the non-irradiation zone with light, and it is not necessary to input light energy, and contaminated air can be processed at low running cost.

[0006]

By the way, as in the above proposal, the light irradiation zone in the first half of the sheet mainly composed of TiO ₂ or the like is irradiated with ultraviolet light, and the gas to be treated (contaminated air: NO _X When the ratio of NO to NO _{2 in the} composition is about 9: 1), the concentration balance of NO and NO ₂ is adjusted,
The processing method in which NO and NO ₂ are removed in an equimolar amount in the latter half of the non-irradiation zone has the following problems to be solved.

That is, NO and N
In order to adsorb O ₂ efficiently, the NO _X composition of the gas to be treated flowing on the inlet side (= light irradiation zone outlet side) in the non-irradiation zone should be NO: NO ₂ ≒ 1: 1. Is desirable.

However, it is known that the oxidizing ability of TiO ₂ as a photocatalyst in the light irradiation zone is not constant, but varies depending on the relative humidity of the gas to be treated. For this purpose, the ratio of the light irradiation zone to the entire sheet area at the beginning is determined by the light irradiation zone exit (= non-irradiation zone entrance).
Even if the NO _X composition is set so that NO: NO ₂ ≒ 1: 1, if the humidity of the gas to be processed fluctuates due to weather conditions or the like, the NO _X composition of the gas to be processed that moves to the non-irradiation zone NO _X in the non-irradiation zone
It is difficult to make equimolar adsorption with high efficiency.

Therefore, in order to put the above-mentioned treatment method into practical use for purification of contaminated air, even if the oxidation ability of the light irradiation zone of the TiO ₂ sheet fluctuates due to the change in the humidity of the gas to be treated, it is necessary to use this method. The NO _X composition of the gas to be treated passing through the light irradiation zone and moving to the downstream non-irradiation zone is NO:
The challenge is to adjust the concentration balance so that NO ₂ ≒ 1: 1.

The present invention has been made in view of the above-mentioned point, and a light irradiation zone and a non-irradiation zone are set on a sheet containing TiO ₂ as a main component, and NO _X
The processing method of purifying by removing the processing method of the nitrogen oxides with improved so without being influenced by the ambient conditions, in a non-irradiation zone can be performed efficiently NO _X removal, such as changes in humidity of the process gases, and An object of the present invention is to provide a processing device.

[0011]

In order to achieve the above object, according to the present invention, Ti along the air guide path of the gas to be treated is provided.
A sheet containing O ₂ as a main component is laid, and the first half region is irradiated with ultraviolet light having a wavelength of 400 nm or less as a light irradiation zone to oxidize and capture NO _X in a gas to be processed flowing through the region by photocatalysis, In a nitrogen oxide treatment method in which NO and NO ₂ are adsorbed in the same moles without light irradiation in the latter half region as a non-irradiation zone, the ratio of the light irradiation zone to the non-irradiation zone of the sheet is made variable. In the above, NO _X is processed by setting the ratio of NO _X and NO ₂ (NO ₂ / NO _X ) measured at the exit end of the region of the light irradiation zone to be 0.3 to 0.8. (Claim 1).

Further, the processing apparatus of the present invention for carrying out the above-mentioned method comprises a plurality of removal modules mainly composed of TiO ₂ and a removal module of each stage having a wavelength of 400 nm along the air guide path of the gas to be treated. Along with arranging a lamp module for irradiating the following ultraviolet light, a monitor for measuring the NO _X composition of the gas to be treated at the exit side of each of the elimination modules irradiated with light is provided.
The ratio of NO _X and NO ₂ detected by the monitor (NO ₂ /
NO _X) is the boundary of a point close to 0.5 in the range of 0.3 to 0.8, the upstream side irradiation zone removal module, in accordance with this removal module downstream as a non-irradiation zone lamp The lighting control of the module is configured (claim 2).

As described above, the oxidation of NO by the photocatalyst containing TiO ₂ as a main component is carried out in the following manner: NO → NO ₂ → NO ₃ ⁻
It consists of two stages. Both of these two-stage reactions involve irradiation of ultraviolet light, and the reaction proceeds by active oxygen species generated by light irradiation. However, the first reaction, NO → NO ₂
The reaction is very fast, whereas the reaction of NO ₂ → NO ₃ ⁻ is slow. The reason may be that active oxygen species involved in the reaction of NO → NO ₂ and active oxygen species involved in the reaction of NO ₂ → NO ₃ ⁻ are different. For this, when single processing only the photocatalytic action by irradiation of ultraviolet light to the sheet throughout a portion of the NO ₂ is NO 3 ^_- TiO ₂ without being oxidized to
It may leave the surface and be released directly into the gas phase. This phenomenon is particularly susceptible to the influence of the relative humidity of the gas to be treated. If the relative humidity is high, the rate at which NO is oxidized to NO ₂ without oxidizing to NO ₃ ⁻ is released into the gas phase when NO is oxidized. Become.

In this respect, according to the processing method of the present invention, the ratio of NO _X to NO ₂ (N
A point where O ₂ / NO _X ) is 0.3 to 0.8 is detected by the monitor, and the light irradiation zone is set on the upstream side and the non-irradiation zone is set on the downstream side from this point.
The NO _X composition of the gas to be processed which passes through the light irradiation zone and flows into the non-irradiation zone is always NO: NO ₂ ≒ 1: 1 irrespective of the ambient conditions of humidity. As a result, NO and NO ₂ are efficiently and equimolarly adsorbed in the non-irradiation zone, and NO _X can be efficiently removed totally by the combination of the non-irradiation zone and the light irradiation zone.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below based on illustrated embodiments.

[0016] Figure 1 is a block diagram of the NO _X processor, reference numeral 1 is an housing of the processing apparatus connected to the air passage of the gas to be treated (contaminated air) (e.g. ventilating air passage of an automobile road tunnels) Inside, along the air duct
A plurality of stages constituted by a sheet-like material to the O ₂ as a main component (# 1, # 2, # 3, .., # n) removal of the module 2
And a lamp module 3 for irradiating ultraviolet light having a wavelength of 400 nm or less toward the removal module 2 at each stage, and a composition of nitrogen oxide is provided between the removal modules 2 at each stage. , Gas sampling port 4a drawn from monitor (nitrogen oxide concentration meter) 4 for measuring concentration
Is open.

Here, the removal module 2 at each stage is made of, for example, TiO ₂ and polytetrafluoroethylene (PTFE).
And a sheet made by mixing and rolling the above powders and pasting them on both sides of a substrate such as a plastic plate. The lamp module 3 has a configuration in which, for example, one or several photochemical lamps (center wavelength: 352 nm) 3a are incorporated and ultraviolet light is emitted toward the removal module 2 adjacent to the upstream side.

[0018] In the processing apparatus having the above-described structure, NO is removed from contaminated air.
_{In order} to remove and purify _X , the lamps of the lamp modules 3 arranged in the upstream side of the plurality of removal modules 2 (# 1 to #n) basically arranged in the front and rear stages and the lamp modules 3 corresponding to the individual stages are basically used. 3a is turned on to irradiate the removal module 2 with ultraviolet light, and the removal module 2 having received the light irradiation functions as a photocatalyst (light irradiation zone). Further, the lamp module 3 at the subsequent stage arranged on the downstream side does not turn on the lamp 3a,
The corresponding removal module 2 is used as an equimolar adsorbent (non-irradiation zone).

On the other hand, the gas to be treated is passed through
O In the operating state _{in which X} processing is performed, leading to treated gas taken through the gas sampling port 4a which arranged on the downstream side of each removed module 2 undergoing light irradiation on the monitor 4, wherein the removal of each stage NO _X composition of the gas to be treated flowing through the module 2 to measure the concentration, based on the measurement data in the monitor 4, and the lights controlling the lamp 3a of the lamp module 3 of each stage in the below-described conditions The ratio between the light irradiation zone and the non-irradiation zone is set appropriately according to the state at that time.

Here, an experimental example performed to verify the processing method of the present invention will be described. In this experimental apparatus, TiO ₂ (70% by weight) and PTF were used as removal modules.
E powder (30% by weight). Samples prepared by rolling and forming into sheets and pasting on both sides of a 30 × 60 cm PVC plate were prepared as test samples, and 25 of them were arranged at regular intervals along the air guide passage. In addition, one 20 w photochemical lamp was used as a lamp module, and this was disposed between the above-described removal modules. On the other hand, polluted air collected from the inside of a motorway tunnel was used as the gas to be treated. Then, the gas to be treated flows while the lamp of the lamp module is turned on. In this state, gas is collected from the outlet side of the removal module at each stage by the monitor (nitrogen oxide concentration meter) shown in FIG. _X composition and concentration were measured.

[0021] Figure 2 is a distribution diagram of the NO _X composition along the removal modules in each stage based on data measured by the experiments, NO when the vertical axis is taken as 1 the concentration of NO _X device inlet , The ratio of NO ₂ , and the horizontal axis is the number of stages (1 to 16) of the removal module performing light irradiation, and each characteristic line shown in the figure was measured at the exit side for each removal module of each stage. It represents the composition ratio of NO _X , NO, and NO ₂ .

In this figure, the N of contaminated air at the inlet end
The composition of O _X is, NO is about 85 percent, although NO ₂ is approximately 15% NO X by the photocatalytic action of removing modules light irradiation as traveling wind guide path in the _apparatus, NO concentration rapidly decreases are doing. On the other hand, although the concentration of NO ₂ slightly decreases in the process of passing through the first several stages, in the subsequent stages, the concentration starts to increase and then gradually decreases. The reason why the concentration of NO ₂ is increased in the middle of the path, as described before, NO ₂ as compared with the reaction of NO → NO ₂
→ NO ₃ ^- the reaction speed is slow, NO _2, which was converted from NO
Is oxidized to NO ₃ ^- and is desorbed and released into the gas phase before being adsorbed on the surface of the removal module.

In the case shown in FIG. 2, NO: NO _{2 is provided at} the outlet side of the seventh removal module counted from the inlet.
Is about 1: 1. Therefore, from this point as a starting point, the first to seventh steps arranged on the upstream side are set as light irradiation zones, the lamps of the lamp modules corresponding to the removal modules arranged in this range are turned on, and the eighth and subsequent steps are set as non-irradiation zones. If the lamps of the lamp modules are turned off, the composition of the gas to be treated that passes through the light irradiation zone and shifts to the subsequent non-irradiation zone becomes NO: NO ₂ ≒ 1: 1. In the removal module,
NO and NO ₂ are efficiently adsorbed on an equimolar basis.

Next, the following experiment was conducted in order to verify the effect on the NO _X removal rate of the non-irradiation zone when the ratio of NO to NO _{2 in} the gas to be treated was variously changed. In this experiment, TiO ₂ was used as an equimolar adsorbent material as described above.
(70% by weight) and PTFE powder (30% by weight)
Rolled to obtain a 5 × 30 cm sheet as a test sample,
As the gas to be treated, a simulated gas prepared by diluting a standard gas with various ratios of NO and NO ₂ with purified air and adjusting to 3 ppm was used. Then, the simulation gas was flowed from the entrance without performing light irradiation, and the equimolar adsorption effect was examined.

FIG. 3 is a characteristic diagram obtained from this experiment, in which NO ₂ / NO _{X at the} inlet is 0.5 to 0.6, that is, N
O: NO ₂ is 1: 1 to 1: A 1.5 NO _X removal rate is the maximum (about _{70%), NO 2 / NO} X 0.3
It can be seen that even in the range of ０．８0.8, the removal rate is slightly reduced and the removal rate is maintained at a relatively high level (50%).

Further, the present inventors conducted the following experiment in order to examine the influence of the relative humidity of the gas to be treated flowing in the light irradiation zone on the oxidizing ability of the removal module functioning as a photocatalyst. In this experiment, as in the previous experiment, T
A mixture of iO ₂ (70% by weight) and PTFE powder (30% by weight) was rolled to obtain a 5 × 30 cm sheet as a test sample, and a standard gas containing only NO as a gas to be treated was reduced to 3 ppm with purified air. The adjusted simulated pollutant gas was used. And, as an ultraviolet light source, the UV intensity is 1.1 to 1.5 w / c.
irradiating the sheet with a ramp of m ^2, conversion of NO under conditions variously changed the humidity of the gas to be treated, and NO _X
Was measured at the outlet side.

FIG. 4 is a characteristic diagram obtained from this experiment. As shown, the NO conversion rate is hardly affected by the relative humidity of the gas to be treated, but the NO _X removal rate is greatly affected by the humidity. We understand that we receive. The NO conversion rate (%) and the NO _X removal rate (%) are defined as follows.

NO conversion rate = [(inlet NO concentration / outlet NO concentration)
Concentration) / Inlet NO concentration] × 100 NO _X removal rate = [(Inlet NO _X concentration / Outlet NO _X concentration)
Since the / inlet NO _X concentration] × 100 This experiment is the inlet gas by diluting the standard gas of NO, NO is as NO _X at the inlet. The NO conversion rate is the rate at which NO supplied from the inlet has undergone some action by reaction with the photocatalyst, and the action is that NO is oxidized into NO ₂ and released into the gas or NO
₂ NO 3 ^_- is oxidized to adsorb on the sheet surface of the TiO _2, it is either trapped. In contrast, N
O _X removal rate NO is NO 3 photocatalytically ^_- represents the percentage captured on the surface of the TiO ₂ sheets progressed oxidized to.

FIG. 4 shows that NO → NO
₂ → NO ₃ ^- of in a two-step reaction, the first half of the NO → NO
Reaction ₂ is hardly affected by humidity, but NO ₂ → NO
_{3 ^-} of the reaction is that the humidity has a great influence. When this is applied to the NO _X ratio distribution diagram shown in FIG. 2, when the relative humidity of the gas to be treated is high, the NO decreasing tendency does not change, but the NO ₂ concentration is closer to the inlet than in FIG. Ascending from the number of stages.

By the way, even in such a high humidity situation,
As described above, from the measurement data on the monitor 4 in FIG. 1, in the removal module lined up in the region of the light irradiation zone,
When the ratio of NO _X to NO ₂ (NO ₂ / NO _X ) is 0.3 to
After confirming the number of stages closest to 0.5 in the range of 0.8,
A light irradiation zone is set on the upstream side (entrance side) of the removal module corresponding to the number of stages, and the lamp 3a of the lamp module 3 in this area is turned on to irradiate the removal module 2 with ultraviolet light. The lamps of the lamp modules 3 arranged in this area are turned off on the downstream side (exit side) as a non-irradiation zone. As a result, the ratio of the light irradiation zone in which the removal module 2 is used as a photocatalyst and the non-irradiation zone in which the removal module 2 is used as an equimolar adsorbent is changed from the initial setting. The NO _X composition of the gas to be treated that moves to the zone is NO: N
O ₂ ≒ 1: 1. As a result, in the removal module 2 arranged in the non-irradiation zone, NO and NO ₂ are efficiently adsorbed in an equimolar manner, and as a result, NO _X of the contaminated air is efficiently removed in the processing apparatus, and NO is removed. It can be sent out as clean air containing almost no _X.

[0031]

As described above, according to the nitrogen oxide treatment method and apparatus of the present invention, a sheet mainly composed of TiO ₂ is combined with an ultraviolet light source, and the sheet is irradiated with a light irradiation zone in the first half. And the non-irradiation zone in the latter half, and the NO (contaminated air)
_In the cleaning apparatus in which _X is removed, the ratio between the light irradiation zone and the non-irradiation zone of the sheet is made variable, and the NO _X and NO _X measured in the area of the light irradiation zone at the exit end thereof. ₂ (NO ₂ / NO _X ) is 0.3-
Preferably by that so as to process the NO _X was set to be 0.5 in the range of 0.8, etc. NO _X composition, oxidative capacity of the TiO ₂ with changes in the relative humidity of the gas to be treated NO _X NO and N in the non-irradiation zone
O ₂ to thereby efficiently equimolar adsorption.

[Brief description of the drawings]

FIG. 1 is a sectional view of a configuration of a nitrogen oxide processing apparatus according to an embodiment of the present invention.

FIG. 2 shows the number of removal module stages and the NO _X corresponding to each stage when the removal module is irradiated with light in the configuration of FIG.
Diagram showing change in composition ratio

FIG. 3 is a diagram showing the relationship between the NO ₂ / NO _X ratio of the gas to be treated and the NO _X removal rate for a non-irradiated removal module;

FIG. 4 is a diagram showing the relationship between the relative humidity of a gas to be treated with respect to a light irradiation removal module and the oxidizing ability of a photocatalyst;

[Explanation of symbols]

 2 Removal module 3 Lamp module 3a Lamp 4 Monitor (nitrogen oxide concentration meter) 4a Gas sampling port

Claims (2)

[Claims] 1. A sheet mainly composed of TiO ₂ is laid along an air guide path of a gas to be treated, and the first half of the sheet is irradiated with ultraviolet light having a wavelength of 400 nm or less as a light irradiation zone to flow through the sheet. the NO _X in the gas captured by oxidized by photocatalytic action, the processing method of the nitrogen oxides to adsorb the NO and NO ₂ in equal molar without photoirradiation half region as a non-irradiation zone, the seat The ratio of the NO _X to NO ₂ (NO ₂ / NO _X ) measured at the exit end of the region of the light irradiation zone after the ratio of the light irradiation zone to the non-irradiation zone is made variable is 0.3 to 0. 8. A method for treating nitrogen oxides, wherein NO _X is treated at a setting of 0.8. 2. An apparatus for treating nitrogen oxides for use in carrying out the treatment method according to claim 1, comprising a multi-stage removal module mainly composed of TiO ₂ along an air guide path of a gas to be treated. and with arranging the lamp module for irradiating the following ultraviolet light wavelengths 400nm to remove modules in each stage, a monitor for measuring at the outlet side of the removal modules in each stage were light irradiated with NO _X composition of the gas to be treated, removed NO _X detected by the monitor while the module was irradiated with light
And the boundary of the point close to 0.5 within the range of the ratio of _{NO 2 (NO 2 / NO X} ) is 0.3 to 0.8, the removal module of the upstream light irradiation zone, the removal module downstream An apparatus for treating nitrogen oxides in the atmosphere, characterized in that the lighting of a lamp module is controlled in accordance with the non-irradiation zone.