JP5692957B2 - Exhaust gas treatment system and exhaust gas treatment method - Google Patents

Description

  The present invention relates to an exhaust gas treatment system and an exhaust gas treatment method for an underground structure in which ventilation is restricted such as an automobile tunnel or an underground parking lot.

  Ventilation is required for structures with limited ventilation, such as automobile tunnels and underground parking lots, in order to suppress contamination of internal air by automobile exhaust gas. For tunnels that are short in length, using natural ventilation may be sufficient to achieve environmental standards for the atmospheric environment in the tunnel. However, in underground structures such as long tunnels and underground parking lots, ventilators are installed and ventilation operations are performed with ventilation fans in order to satisfy the environmental standards for the air environment in automobile tunnels. Ventilation prevents harmful substances contained in automobile exhaust gas from adversely affecting the human body and ensures a good visual environment, enabling users and managers inside underground structures to pass safely and comfortably. It is done for the purpose of securing.

  Various design standards have been established for the above-mentioned harmful substances in tunnels. For example, the design standards for carbon monoxide (CO) and soot are defined by automobile exhaust gas regulations since 1973. . In the present specification, soot is referred to as black smoke from automobile exhaust gas and road and tire dust as substances that hinder the visual field environment.

In addition, as harmful substances that may exist in underground structures such as automobile tunnels, hydrocarbons HC, nitrogen oxides NOx (NO, NO ₂ etc.), in addition to CO and soot, Sulfur oxide SOx and the like are also known. These harmful substances are discharged into the atmosphere from the tunnel exit in a naturally ventilated tunnel, and are discharged into the atmosphere from a ventilation tower in a tunnel with a ventilating station. Environmental standards related to air pollution are also regulated from the viewpoint of health and safety, and suspended particulate matter (hereinafter referred to as SPM) is designated as one that corresponds to the above-mentioned hazardous substances. .

In general ventilation stations of automobile tunnels, the wind speed at the exit of the ventilation tower is set to about 10 m / s, and the exhaust gas containing harmful substances is quickly diffused and diluted toward the sky, causing harmful effects from the ventilation tower. The impact of substances on the surrounding air environment is reduced. However, it is difficult to achieve environmental standards for SPM concentrations and NO ₂ concentrations in urban areas, particularly in large cities. In addition to problems such as SPM concentration, in the vicinity of ventilation towers constructed in the city, forced ventilation is known to cause complex turbulence due to the influence of natural crosswinds, and no treatment is performed from the ventilation tower. It has been pointed out that when exhaust gas is released, the exhaust gas in the tunnel containing harmful substances does not diffuse sufficiently and may affect the surrounding air environment before diffusion dilution.

For this reason, in recent years, it has been considered to install an air purification system such as a dust collection / NOx removal device in a ventilation place such as an automobile tunnel or an underground parking lot installed in a city. When the dust collection / NOx removal device is installed in a ventilation place, the processing gas whose concentrations of SPM and NO ₂ are below the environmental standard is released to the surrounding environment. In the future, when adaptation to regulatory standards for automobile exhaust gas proceeds smoothly, the concentration of harmful substances in the road tunnel will decrease as described above, so as long as the traffic volume is comparable to the current level, It is considered that the amount of ventilation for purification can be reduced, the cost can be reduced and the space can be saved, and the availability of the exhaust gas treatment system in the urban space can be improved.

  Until now, removal of harmful substances contained in exhaust gas emitted from automobiles has been studied. Japanese Unexamined Patent Publication No. 2006-247524 (Patent Document 1) discloses a metal ultrafine particle composite in which metal ultrafine particles are fixed to a porous material without agglomeration. Japanese Patent Application Laid-Open No. 2004-267872 (Patent Document 2) discloses an exhaust gas purification method in which CO is burned by supplying exhaust gas having a CO concentration of 1% or more to a catalyst supporting a single noble metal containing ceria. Yes.

  Japanese Patent Laid-Open No. 2004-209356 (Patent Document 3) discloses at least one selected from Ti, Al, Si, W, and Zr in order to efficiently remove harmful substances such as CO and NOx contained in exhaust gas. An exhaust gas treatment catalyst and an exhaust gas treatment method in which at least one noble metal element selected from the group consisting of Pt, Pd, Rh, Ru, Ir, and Au is supported on a metal oxide containing any of the above metals are disclosed. .

Furthermore, the removal of harmful substances in automobile tunnels in urban spaces is disclosed in Japanese Patent Application Laid-Open No. 2005-270802 (Patent Document 4). Patent document 4 discloses a structure having an air purification system and an air purification system that realizes air purification without using a ventilation shaft.
On the other hand, CO removal by catalytic oxidation has also been studied. For example, in Japanese Patent Application Laid-Open No. 2006-122850 (Patent Document 5), a discharge reaction is performed to generate a catalytically reactive species, and nitrogen oxide and monoxide A gas purification system for removing carbon is disclosed.

In addition, the present inventor has proposed a nitrogen oxide removing device for purifying exhaust gas in an automobile tunnel. Nitrogen oxide can be stably removed from the automobile tunnel, and ventilation is provided. It has been found that the NOx concentration at the tower outlet can be reduced (Patent Document 6).
JP 2006-247524 A JP 2004-267872 A JP 2004-209356 A JP 2005-270802 A JP 2006-122850 A Japanese Patent No. 3946158

  On the other hand, if the amount of harmful substances contained in exhaust gas decreases as a result of automobile exhaust gas countermeasures, the ventilation volume in the ventilator can be reduced. As a result, it is expected to improve the applicability of the air purification system in urban areas. However, various problems also occur when the ventilation volume is simply reduced.

FIG. 12 shows the concentration of harmful substances inside the automobile tunnel when the ventilation volume of the ventilator is lowered, in the case of ventilation only, and in the case of using a typical air purification system having SPM removal and NOx removal functions in combination. The result of simulating is shown. As shown in FIG. 12, even in the case of only ventilation, the CO concentration at the present time generally achieves environmental standards. However, it can be seen that the NO ₂ concentration and the SPM concentration cannot achieve the environmental standard value or less by ventilation alone. On the other hand, when the long-term regulatory standards for harmful substances are achieved, SPM and CO can be set to environmental standards of 0.1 ppm and 10 ppm or less even when the ventilation rate is reduced to ½. However, it is shown that NO ₂ cannot satisfy the environmental standard value = 0.06 ppm by ventilation alone even when the long-term regulatory standard value is achieved. In addition, in FIG. 12, the hazardous | toxic substance density | concentration which exceeds an environmental standard is shown by hatching.

Furthermore, when the ventilation volume is reduced to 1/3 and 1/4, the environmental standard for CO as well as NO ₂ and SPM will be exceeded. In addition, even if the environmental standards in the automobile tunnel are achieved, simply reducing the ventilation volume in the ventilation station will reduce the flow velocity at the tunnel exit and the ventilation tower outlet, resulting in insufficient diffusion and ventilation. There is also the possibility of causing problems such as an increase in the concentration of harmful substances near the exit.

  On the other hand, when using the NOx purification system, as shown in FIG. 12, even if the ventilation rate is reduced to ¼ of the current ventilation rate, it has a performance that sufficiently satisfies the environmental standards. However, it was found that when the ventilation volume was reduced to ¼, the CO concentration exceeded the environmental standard as shown in FIG. Therefore, in order to reduce the ventilation amount of the air purification system, it is necessary to remove CO as well.

  Further, if the reduction of the ventilation amount is restricted, the environmental standard for CO can be satisfied without removing CO. However, the traffic volume of automobiles, etc. is likely to fluctuate depending on the automobile penetration rate, road environment, traffic conditions, and economic circumstances, and the CO concentration is left unattended just because the CO concentration is below the environmental standard. In some cases, due to the relationship between the increase in traffic volume and the degree of achievement of long-term regulatory standards, the environmental standards for CO may not be satisfied sooner or later. Moreover, since the amount of ventilation reduction is limited, downsizing, space saving, and cost reduction of the air purification system are also limited, leading to the spread of the air purification system.

As described above, although Patent Documents 1 to 5 are known, it is necessary to treat high concentrations of NOx and CO at high temperatures. Therefore, in order to further spread the air purification system, it was necessary to efficiently remove low concentrations of NOx and CO from the exhaust gas. Further, with the addition of the CO removal device, it has been necessary to remove CO from the exhaust gas without increasing NO ₂ which is a regulated substance. Furthermore, low-concentration NOx and CO, which are subject to regulation, contained in the exhaust gas from the underground structure, are used in a temperature / humidity / pressure environment (−20 ° C. to 40 ° C., 10 to 100%) in an underground structure such as an automobile tunnel. RH and 101.325 kPa), while providing sufficient NOx removal and CO removal capability, it is sufficient in the presence of soot that can be a catalyst poison such as heavy metal elements in addition to harmful substances accompanying combustion of internal combustion engines, and for a long time There was a need to provide a stable CO removal capability.

  Furthermore, it has been necessary to reduce the ventilation volume to such an extent that the advantages of downsizing, cost reduction, and space saving can be provided, and to further spread the air purification system.

  In other words, the present invention has been made in view of the above-mentioned problems of the prior art. In the present invention, the ventilation volume is reduced to the extent that it exceeds the cost of adding a CO removal device, thereby reducing the size and space. It is another object of the present invention to provide an exhaust gas processing system and an exhaust gas processing method that can reduce costs.

The present invention also provides an exhaust gas treatment system and an exhaust gas that can stably remove CO over a long period of time without obstructing the NO ₂ removal capability, which is the strictest environmental standard, by adding a CO removal device. An object is to provide a gas treatment method.

  Furthermore, the present invention provides an exhaust gas treatment system and an exhaust gas that can add CO removal capacity in response to the amount of CO to be removed while minimizing degradation of SPM and NOx purification capacity. An object is to provide a processing method.

  In order to solve the above problems, the present invention provides an exhaust gas treatment system and an exhaust gas purification method capable of removing SPM, NOx, and CO efficiently and stably. An exhaust gas treatment system according to the present invention includes an electrostatic precipitator that uses an electrostatic precipitator process that removes SPM, a NOx remover that removes nitrogen oxides, and a CO remover that removes carbon monoxide. Are connected in series from the upstream side to the downstream side along the flow direction of the exhaust gas.

The electrostatic precipitator uses corona discharge to remove SPM between the electrode plates, further generates ozone, and oxidizes nitrogen monoxide (NO) in the exhaust gas to nitrogen dioxide (NO ₂ ). NOx removal device, preferably a NOx originally contained in the NO ₂ and the exhaust gas is oxidized from NO are removed by adsorption using a carbonaceous adsorbent, and supplies the gas to be treated to the CO removal device . The CO removal apparatus includes a catalyst that oxidizes CO to CO ₂ , and removes CO contained in the gas to be treated by low-temperature oxidation to CO ₂ in a temperature, humidity, and pressure environment in the automobile tunnel.

In the exhaust gas treatment system and the exhaust gas purification method of the present invention, the ozone generated by the electrostatic precipitator is efficiently used for NO oxidation to increase the total nitrogen oxide removal efficiency and remain in the treated gas. By removing the CO to be removed by the CO removing device, it is possible to efficiently use ozone. Furthermore, the addition of a CO removal device can sufficiently reduce the ventilation amount, and NO remaining in the gas to be treated without being absorbed and completely absorbed by the CO ₂ can be reduced by CO. It is possible to oxidize CO without oxidizing it to NO ₂ or the like in the removal device, and efficiently remove nitrogen oxides having the strictest environmental standards, while satisfying environmental standards for both SPM and CO. Enables gas purification treatment.

Hereinafter, although this invention is demonstrated with embodiment, this invention is not limited to embodiment mentioned later. FIG. 1 is an embodiment of an exhaust gas treatment system 100 of the present embodiment. The exhaust gas treatment system 100 is arranged such that the exhaust gas of the automobile is introduced from an underground structure in which ventilation is restricted, such as an automobile tunnel and an underground parking lot, and the automobile passes. In the embodiment shown in FIG. 1, the exhaust gas processing system 100 is installed adjacent to the natural tunnel side of the tunnel shield 142 adjacent to the automobile tunnel, and exhaust gas is introduced from the direction of the arrow A, Purified gas is discharged in the direction of arrow C. Exhaust gas introduced in the direction of the arrow line A, particularly exhaust gas from an automobile tunnel, contains NO of about 5 ppm, NO ₂ of about several ppm, and CO of about several tens of ppm.

  The exhaust gas treatment system 100 of this embodiment includes an electrostatic precipitator 126, a NOx removal device 130, and a CO removal device 134, which are disposed from the upstream side in the exhaust gas inflow direction in order to treat the exhaust gas. It is out. The electric dust collector 126, the NOx removal device 130, and the CO removal device 134 constitute the air purification module 120 of this embodiment. In the embodiment shown in FIG. 1, the air purification module 120 is adjacent to the tunnel shield 142. It arrange | positions in the machine room 110 arrange | positioned at the natural mountain side. An inlet duct 122 and an inlet fan 124 are arranged on the upstream side of the electric dust collector 126, and the inlet duct 122 and the inlet fan 124 are configured so that the exhaust gas from the tunnel is indicated by an arrow A, as shown by an arrow A. It is introduced into the exhaust gas treatment system 100.

  The exhaust gas introduced into the exhaust gas treatment system 100 flows sequentially through the electrostatic precipitator 126 and the NOx removal device 130 in the exhaust gas flow direction. The exhaust gas after passing through the electric dust collector 126 and the NOx removing device 130 is referred to as a gas to be treated for CO removal, as indicated by an arrow B. The gas to be treated passes through the CO removal device 134 and is removed from the CO, and then passes through the outlet duct 136 and the outlet fan 138. As shown in the arrow C, the gas to be treated is externally supplied as purified gas from the ventilation tower 140. Released into the atmosphere.

  The purification process of the exhaust gas treatment system 100 will be described. The exhaust gas is introduced into the electric dust collector 126 from the inlet duct 122, and first, SPM is removed. The electrostatic precipitator 126 includes a plurality of counter electrode plates, a high voltage is applied between the counter electrode plates, and corona discharge is generated between the electrode plates. It is preferable to generate the corona discharge under a negative bias in terms of suppressing generation of harmful substances accompanying the corona discharge. In the corona discharge, the SPM in the exhaust gas is charged and electrostatically removed by an electrode plate or a filter to which a bias is applied. In the present embodiment, the SPM removal capability can be adjusted as appropriate by the voltage of the corona conduction, and the SPM removal rate is preferably about 90%. The SPM removal rate can be obtained as SPR = (inlet SPM concentration−outlet SPM concentration) / inlet SPM concentration × 100. The exhaust gas from which PM has been removed then flows into the NOx removal device.

  The exhaust gas from which the SPM has been removed is humidified by the humidifier 128 and then subjected to NOx removal processing by the NOx removal device 130. The humidifier 128 humidifies the exhaust gas so that the humidity is 60% or more, more preferably 80% or more, in order to stabilize the NO removal capability of the NOx removal device 130 in particular. The NOx removal device 130 includes multiple NOx removal stages, and each NOx removal stage includes a NOx removal agent holding unit 132. Exhaust gas is introduced into each NOx removal stage in parallel or in series, and NOx removal by the NOx removal agent is performed.

In this embodiment, examples of the NOx removing agent include carbon-based adsorbents such as coconut shell activated carbon, pitch-based activated carbon, PAN-based activated carbon, carbon fiber, charcoal, fullerene, and carbon nanotube. Examples of inorganic materials include activated clay, alumina, zeolite, silica, magnesia, titania and the like. Among them, a carbon adsorbent having a large specific surface area such as activated carbon can be cited as a particularly preferable solid adsorbent. In particular, activated carbon is excellent in NO ₂ removal ability, is inexpensive, and can regenerate the adsorption ability. Thus, it is a preferable NOx remover in that NO can be removed.

  In particular, in the present embodiment, as described in Patent Document 5, for example, the NOx removing agent is configured to use activated carbon and to periodically regenerate the adsorption ability of the activated carbon with the regenerant. Is preferred. The regenerant is not particularly limited, but an aqueous solution containing a basic substance or a reducing substance is preferably used.

  Examples of basic substances include alkali metal hydroxides, alkaline earth hydroxides, alkali metal carbonates, alkaline earth metal carbonates, etc., and efficiently remove nitrogen oxides adsorbed by solid adsorbents. In view of the above, alkali metal hydroxides and alkaline earth hydroxides, which are strongly basic substances, are particularly preferably used.

  Examples of the alkali metal hydroxide include lithium hydroxide, sodium hydroxide, potassium hydroxide and the like. Examples of the alkaline earth hydroxide include calcium hydroxide and magnesium hydroxide. Examples of the alkali metal carbonate include lithium carbonate, sodium carbonate, and potassium carbonate. Examples of the alkaline earth metal carbonate include calcium carbonate and magnesium carbonate.

  Further, the reducing substance is not particularly limited, and examples thereof include sulfites, thiosulfates, hydrides, hydrogen sulfide, aldehydes, etc. From the viewpoint of reducing nitrogen oxides to nitrogen gas at room temperature, sulfurous acid. It is preferable to use a salt.

  Examples of the sulfite include lithium sulfite, sodium sulfite, potassium sulfite, calcium sulfite, magnesium sulfite, iron sulfite, and copper sulfite. Examples of the thiosulfate include lithium thiosulfate, sodium thiosulfate, potassium thiosulfate, calcium thiosulfate, and magnesium thiosulfate. Examples of the hydride include sodium borohydride and lithium aluminum hydride. Examples of aldehydes include formaldehyde and acetaldehyde.

  The NOx removal capacity by the NOx removal device can be given by NR = (inlet NOx concentration−outlet NOx concentration) / inlet NOx concentration × 100 using measured values of the inlet NOx concentration and the outlet NOx concentration. The NOx removal apparatus of this embodiment has a NOx removal capability of about 80%, and NO2 has a removal capability of about 98% to about 99%. It is preferable in that it can be adapted over a wide range and maintenance costs can be optimized.

The gas to be processed after NOx is processed by the NOx removing device 130 is introduced into the CO removing device 134. The CO removing device 134 is configured to contain a CO removing agent in a housing, and reduces the CO concentration by oxidizing the remaining CO in the gas to be processed into CO ₂ using catalytic oxidation. Yes. Examples of the CO oxidation catalyst include a metal oxide, a material in which a noble metal catalyst is supported on the metal oxide, and the like. For example, MnO ₂ , anatase TiO ₂ , Al ₂ O ₃ , Au / TiO ₂ , Cu / MnOx, Pd / Al ₂ O ₃ , Pt / Al ₂ O _{3 and the} like can be mentioned.

  The CO removal device 134 is preferably operable in an environment in an automobile tunnel from the viewpoint of installation space, running cost, maintainability, and safety. The operating conditions are about −20 ° C. to about 40 ° C., about 10 to 100 It is preferable that the temperature and humidity are% RH and normal pressure (101.325 kPa).

The shape of the CO removing agent may be any shape such as a porous powder, a honeycomb, or a porous plate having a plurality of openings, depending on the configuration of the CO removing device 134. When using the CO adsorbent as a powder, the particle diameter of the CO adsorbent is preferably 1 mm to 10 mm from the viewpoint of conductance. From the viewpoint of the CO adsorption processing capability, the particle diameter is about 1 mm to 6 mm. It is most preferable in terms of improving the powder operability and CO adsorption capacity by making the particle diameter in the range of 1 mm to 2 mm. Further, when a noble metal element having catalytic activity is supported on the porous powder, a colloid or sol containing the noble metal element is applied to the porous powder such as TiO ₂ and Al ₂ O ₃ with a silane coupling agent, By attaching using a suitable coupling agent such as a titanium coupling agent, it is possible to impart an appropriate CO removal capability.

  The CO removing agent can also be used as a honeycomb shape or a porous plate. When using a CO remover as a porous plate, mix a suitable binder and form a metal oxide as a honeycomb or porous plate using powder metallurgy, and support the noble metal catalyst on the honeycomb or porous plate. This makes it possible to use the CO removing agent as a molded body.

  Further, in another embodiment of the exhaust gas treatment system 100, a CO sensor and a NOx sensor can be provided. The exhaust gas treatment system 100 can be configured such that when the CO concentration detected by the CO sensor exceeds the environmental standard, the CO removal device is activated so that the CO concentration falls below the environmental standard value. Further, when the CO concentration is lower than the environmental standard value, the CO removing device 134 is stopped, and the environmental standard of each harmful substance is achieved while reducing the running cost. In the case of this embodiment, the CO concentration is set by monitoring the CO concentration while lowering the ventilation amount according to the traffic volume and the environment in the underground structure, regardless of the revision of the set value of the long-term regulation standard. The CO removal device 134 can be activated at the stage when it is determined that the air circulation based on the ventilation amount cannot be used.

  In this case, the CO removal device 134 is not started as long as the CO concentration is low, but the ventilation amount of the exhaust gas treatment system 100 as a whole can be set low, so that the running cost such as the scale of the blower system and the electricity bill is reduced, and the CO It is possible to respond flexibly to changes in the environment of valuation structures such as traffic and changes in environmental standards without changing the configuration of the exhaust gas treatment device 100, even in response to an increase in the level of regulations and stricter long-term regulatory standards. An exhaust gas treatment system can be provided.

  FIG. 2 is an embodiment showing the configuration of the CO removing agent 200. In the embodiment of FIG. 2, the CO removal agent 200 is configured as a perforated plate. The CO removing agent 200 of the CO removing device 134 shown in FIG. 2 is configured to include a plurality of perforated plates 202 and 204 carrying a CO removing agent. The perforated plate 202 is formed as so-called ceramics obtained by sintering glass, clay, porcelain clay, metal oxide powder or the like. The catalytic metal element may be supported on the CO removing agent 200 by coating using a sol-gel method. When the porous plate 202 has a small space in the plate, the porous plate 202, A catalytic metal element can be supported on the perforated plate itself such as 204.

  In addition, a plurality of openings 206 are formed in the perforated plate 202, and the contact area with respect to the entire CO removing agent 200 is improved while improving the conductance of the entire CO removing apparatus with respect to the gas to be processed flowing from the direction of the arrow D. Secured.

  FIG. 3 shows a configuration of the CO removing agent 300 of another embodiment of the CO removing apparatus 134 of the present embodiment. In the CO removing agent 300 shown in FIG. 3, the metal oxide powder is sintered as a honeycomb. In the honeycomb, a honeycomb wall 304 and a honeycomb passage 302 formed inside the honeycomb wall 304 are formed. The gas to be treated flows into the honeycomb from the direction of the arrow E, CO is removed, and the gas to be treated is discharged outside the exhaust gas treatment system 100 as a purified gas. A honeycomb can be formed by sintering a metal oxide powder carrying a catalytic metal element, or by firing a porous metal oxide into a honeycomb and then carrying a catalytic metal. Can be formed.

  The arrangement of the CO removing agent in the CO removing device is determined according to the shape of the CO removing agent such as the CO removing agent 200 and the CO removing agent 300 shown in FIGS. The exhaust gas processing capacity, cost, and maintainability can be selected as appropriate. Regardless of the shape of the CO removing agent, the CO removing device 134 can have any shape as long as it can remove about 70% to about 100% of CO contained in the gas to be treated.

The exhaust gas processing system 100 according to the present embodiment controls exhaust gas discharged from an environment where ventilation is restricted, such as an automobile tunnel, by using an inlet fan 124 and an outlet fan 138, thereby processing the exhaust gas. Adjust ability. The exhaust gas treatment capability of the exhaust gas treatment system 100, when expressed using the space velocity SV, space velocity, 1000～200000H ^-1, more preferably be set to be 3000～100000H ^-1 . Further, in the present embodiment, when the ventilation amount is decreased, the space velocity can be set to be preferably about 3000 to 30000 h ⁻¹ by decreasing the ventilation amount. Even if the ventilation amount is reduced to this level, as shown in FIG. 12, it is possible to sufficiently satisfy the environmental standards for SPM and NO ₂ . In addition, by reducing the ventilation volume to the above-mentioned space velocity, it is possible to simultaneously achieve low cost, low running cost, and space saving, and the cost of adding a CO removal device required to meet environmental standards. Can be sufficiently offset, and more flexible exhaust gas purification capability can be provided.

In the exhaust gas treatment system 100 of the present embodiment, it is preferable that the electrostatic precipitator 126, the NOx removing device 130, and the CO removing device 134 are arranged in series along the flow direction of the exhaust gas. The reason for this is that the NOx removal device 130 of this embodiment uses ozone generated by corona discharge of the electrostatic precipitator 126 to oxidize NO in the exhaust gas to NO ₂ and improve the NOx removal capability. Is. On the other hand, if the electrostatic precipitator 126 generates a large amount of ozone by corona discharge, it causes environmental pollution. Therefore, ozone is stoichiometrically equivalent to NO or not used for oxidation of NO. It is necessary to set the concentration so that the ozone is adsorbed by activated carbon or the like and is not discharged to the outside of the exhaust gas treatment system 100.

On the other hand, many metal oxides also function as an ozone decomposition catalyst. For this reason, when the CO removal device 134 is installed immediately downstream of the electrostatic precipitator 126, the ozone generated by the electrostatic precipitator 126 is reduced. In addition to the oxidation reaction of NO, it is consumed by a decomposition reaction. As a result, the NO conversion efficiency of NO present in the exhaust gas to NO _{2 that} is highly adsorbed by activated carbon or the like is lowered, and the NO ₂ removal ability with the strictest environmental standards is adversely affected.

For this reason, in this embodiment, the NOx removal device 130 is disposed immediately downstream of the electrostatic precipitator 126, thereby ensuring high efficiency of NOx removal efficiency. On the other hand, the gas to be processed from which NOx has been removed flows into the CO removing device 134. At this stage, the gas to be treated is removed for both SPM and NOx, and as harmful components, CO and NOx that could not be removed exist. The CO removal device 134 is preferably operated under normal temperature and humidity and normal pressure from the viewpoints of maintainability, running cost, and installation properties in automobile tunnels, underground parking lots, and the like. Further, under the temperature and humidity environment in the automobile tunnel, even if NO remains in the gas to be treated, the low temperature oxidation reaction of NO is sufficiently low. For this reason, the efficiency with which NO is oxidized to NO ₂ in the CO removal apparatus is remarkably low, and NO ₂ generation is negligible. Further, increased as the oxidation catalyst, for example, by the use of TiO ₂ having photocatalytic activity, to decompose the entire NOx present in the gas to be treated, adding CO removing device NO ₂ concentration, the NO ₂ concentration It can be set as the structure which is not made to do.

On the other hand, for CO, a catalytic oxidation reaction occurs efficiently even in a normal temperature and normal humidity and normal pressure environment, so the CO removal device 134 substantially removes CO and does not cause an increase in NO _2. Furthermore, it becomes possible to generate purified gas. In addition, since the gas to be treated after passing through the phase of the NOx removing agent such as activated carbon is introduced into the CO removing device 134, components that may become catalyst poisons such as oil mist and SOx are sufficiently removed. In addition, the long-term operability of the CO removal device 134 can also be improved.

  FIG. 4 shows an underground structure 400 that uses the exhaust gas treatment system of the present embodiment. The underground structure 400 includes an automobile tunnel 410 and an exhaust gas treatment system. The exhaust gas treatment system includes an electric dust collector 430, a NOx removal device 440, and a CO removal device 450. The entire exhaust gas treatment system is a machine room 420 installed on the natural mountain side of the automobile tunnel 410. Is housed in.

  The automobile tunnel 410 is constructed as a shield tunnel or the like, and the automobile 470 travels inside the tunnel. Inside the automobile tunnel 410 is an exhaust gas 480 containing SPM, NOx, CO, etc. as combustion products of the engine of the automobile 470.

  The exhaust gas treatment system shown in FIG. 4 sucks the exhaust gas 480 from the inside of the automobile tunnel 410 while adjusting the flow rate with the inlet fan and the outlet fan. The sucked exhaust gas sequentially passes through the electrostatic precipitator 430, the NOx removing device 440, and the CO removing device 450, and harmful substances are removed by each device, and the purified gas passes through the ventilation tower 460 to the surface GL. Purified gas 490 is released to the outside atmosphere where the building constructed above exists. The exhaust gas treatment device of the embodiment shown in FIG. 4 achieves environmental standards for SPM, NOx, and CO even at the present stage when the automobile 470 has not cleared the long-term regulatory standards.

  The exhaust gas treatment system shown in FIG. 4 has an exhaust gas treatment margin because the ventilation amount is greatly reduced, and the running cost, installation space, equipment cost is reduced and CO removal is just enough to exceed the cost of adding the CO removal equipment. And an advantage that the exhaust gas treatment system can be widely used can be provided.

  FIG. 5 shows an underground structure 500 of the second embodiment. In the underground structure 500, a machine room 550 is installed on the ground side of the shield of the automobile tunnel 510 constructed in the basement below the surface GL. The exhaust gas removal system is arranged inside the machine room 550, and an electric dust collector 520, a NOx removal device 530, and a CO removal device 540 are sequentially installed from the upstream side to the downstream side of the exhaust gas flow path. Yes. In the embodiment shown in FIG. 5, the exhaust gas treatment system sucks the exhaust gas 570 discharged from the automobile 560 from the inside of the automobile tunnel, and circulates the treated purified gas 580 into the automobile tunnel 510.

  In the embodiment shown in FIG. 5, the installation of the ventilation tower 460 shown in FIG. 4 can be made unnecessary, and the effective use of the ground surface GL where the building 590 exists can be achieved without hindering the availability of the ground surface GL. It becomes possible. In addition, it becomes possible to cope with future environmental regulation values and to cope with fluctuations in traffic conditions, and the air environment can be improved more effectively.

  FIG. 6 shows an underground structure 600 of the third embodiment. In the third embodiment, the exhaust gas treatment device is installed in the case of a jet fan for ventilating the automobile tunnel 610 of the underground structure 600. In the jet fan, exhaust gas 660 discharged by the automobile 650 flows in the direction indicated by the arrow. The exhaust gas treatment device removes harmful substances from the upstream side in the exhaust gas suction direction in the order of the electrostatic precipitator 640, the NOx removal device 630, and the CO removal device 620, and the purified gas 670 from which the harmful substances have been removed. Is discharged into the automobile tunnel 610. Also in the embodiment shown in FIG. 6, the installation of the ventilation tower 460 can be eliminated, and the ground surface GL can be effectively used for the building 680. In addition, the installation of machine rooms 420 and 550 is unnecessary, and the amount of ventilation is small. Therefore, a relatively large number of jet fans including an exhaust gas treatment system can be arranged, which is suitable for deep mountain tunnels with long extensions. can do.

  The apparatus configuration of the exhaust gas treatment system of the present invention has been described above. Hereinafter, CO removal by the CO removal apparatus 134 of the present invention will be described with examples. In addition, the following Example is described for the purpose of explanation of the present invention and is not intended to limit the present invention.

1. CO removal apparatus The pilot system 700 of the CO removal apparatus shown in FIG. 7 was created, and the CO removal capability was examined. The pilot system 700 includes a casing 710, an air inlet line 720, and a sample line 730 that supplies a CO / air mixed gas that is a simulation gas of the gas to be processed. A simulation gas for simulating the gas to be treated was introduced into the humidification container 740 disposed in the housing 710 via the sample line 730, and the humidity was adjusted. The casing 710 is configured as a thermostatic bath, and the temperature of the CO removal processing of the pilot system 700 is set to a constant temperature of 25 ° C. that is possible as a temperature environment in the automobile tunnel in the embodiment.

  After the sample gas was discharged from the humidification container 740 filled with water, the flow rate and concentration were adjusted by the air flow from the air line 720 and then introduced into the CO removal tower 750. The CO removal tower 750 was filled with granular CO adsorbent, and caused an oxidation reaction of CO in a humidity environment set for the sample gas that flowed in.

The purified gas from which CO was removed was sucked from the CO removal tower 750 with a suction fan 760 and introduced into the CO / CO ₂ analyzer 770, thereby measuring the CO concentration and the CO ₂ concentration.

2. CO concentration measurement The standard gas having a CO concentration of 50 ppm was used as the CO / air sample gas. Further, as the CO / CO ₂ analyzer 770, a general-purpose infrared analyzer (Horiba, Ltd., model: VIA-510, CO measurement method NDIR method) was used.

3. CO removal agent In the CO removal experiment, a CO removal agent comprising an oxidation catalyst shown in FIG. 8 was used. In FIG. 8, for convenience, a catalyst functioning as a CO removing agent is denoted by a to d, and hereinafter, each CO removing agent is referred to as the catalyst a to the catalyst d. The CO removing agent used is a commercially available oxidation catalyst that oxidizes and removes CO to CO ₂ , and is a catalyst a (Catalyst Type: Type A 1.5 wt% Au / TiO, manufactured by WGC (World Gold Council), UK). ₂ , Lot No. Au / TiO ₂ # 02-7), catalyst b (manufactured by Zude Chemie Catalysts Co., Ltd., product number: N-140), catalyst c (manufactured by N.E. Chemcat Co., Ltd., product number: DASH), catalyst d What was marketed as (Nee Chemcat Co., Ltd., product number: NM-101) was used.

4). CO Removal Experimental Conditions and Results FIG. 9 shows the experimental conditions used for the CO removal experiment. Moreover, the sample gas was circulated about the catalyst a-catalyst using each condition shown in FIG. 9, and the 12-hour initial characteristic of CO removal was evaluated. The result is shown in FIG. Catalyst a showed excellent initial performance under conditions of air in the tunnel, but catalyst b could not be removed at all due to the effect of humidity, and catalyst c and catalyst d were affected by the humidity. In addition, when CO removal performance was measured at 110 degreeC about all the catalysts, CO removal rate was 90% or more about all the catalysts. On the other hand, as shown in FIG. 10, regarding the CO removal performance at room temperature, humidity dependency was observed depending on the type of the catalyst, and the catalyst a showed good characteristics in the normal humidity and high humidity environments.

For catalyst a that gave good results at normal humidity and high humidity, and for catalyst a that had good initial performance, a continuous aeration test for 100 hours was performed under the same conditions as those used for measuring initial characteristics. went. The humidity was RH90% and an acceleration test was performed. The result is shown in FIG. As shown in FIG. 11, the CO removal rate of the catalyst a showed the same CO removal rate as the initial performance up to 100 hours in spite of the accelerated test environment, and a stable CO removal performance was confirmed. Further, since the CO ₂ oxidation rate (5) was equivalent to the CO removal rate (%), it was found that the entire amount of the inlet CO was oxidized to CO ₂ . As a result, it was concluded that the catalyst a can be suitably used as a CO removing agent for a CO removing device under normal temperature / normal humidity and normal temperature / high humidity environments.

  As described above, the exhaust gas removal system of the present invention uses the CO removal device in combination with the electrostatic precipitator, the NOx removal device, and the CO removal device according to the degree of reduction of the ventilation amount. Therefore, it is possible to provide a flexible removal system according to the concentration of harmful substances in response to requests for traffic volume, ventilation volume, maintenance cost, etc. of automobile tunnels.

  As a result, (1) it is possible to provide environmentally friendly road infrastructure development that respects atmospheric environmental standards, (2) the existing tunnel can reduce the ventilation air flow, so the running cost can be reduced, and (3) the new tunnel, Since the ventilation air volume can be reduced from the planning stage, the initial cost of ventilation equipment such as fans can be reduced, or the ventilation air volume can be reduced, so the interval between ventilation stations can be increased. (4) In the new tunnel, the area of the ventilation station can be further reduced, so that the applicability and installation in a limited space in the city can be improved.

In addition, the exhaust gas treatment method of the present invention uses a sequence of SPM removal by an electrostatic precipitator, NOx removal by a NOx removal device containing activated carbon, and CO removal by catalytic oxidation thereafter, so that ozone generated by the electrostatic precipitator can be efficiently removed. NOx removal is performed, and CO is removed by a low-temperature catalytic oxidation reaction at the final stage where SPM, NOx, and other heavy metal components are removed. Efficiency of CO removal while suppressing an increase in NO ₂ The effect that it is possible to maintain the periodic removal over a long period of time is obtained.

1 is a schematic diagram of an exhaust gas treatment system of the present embodiment. The figure which showed the structure of the CO removal agent 200 of the CO removal apparatus 134 of this embodiment. The figure which showed the structure of CO removal agent 300 of other embodiment of CO removal apparatus 134 of this embodiment. The figure which showed the underground structure 400 which uses the exhaust-gas processing system of this embodiment. The figure which showed the underground structure 500 of 2nd Embodiment. The figure which showed the underground structure 600 of 3rd Embodiment. The figure which showed the pilot system of CO removal apparatus. The figure which showed CO removal agent which consists of oxidation catalyst The figure which showed the experimental condition used for CO removal experiment. The figure which showed the evaluation result of the 12-hour initial stage characteristic of CO removal. The figure which showed the evaluation result of the 100-hour acceleration characteristic of CO removal. The figure which showed the result of the simulation of the harmful substance concentration inside the automobile tunnel when the ventilation amount of the ventilation station is lowered.

Explanation of symbols

DESCRIPTION OF SYMBOLS 100 ... Exhaust gas treatment system, 110 ... Machine room, 120 ... Air purification module, 122 ... Inlet duct, 124 ... Inlet fan, 126 ... Electric dust collector, 128 ... Humidifier, 130 ... NOx removal device, 132 ... NOx removal Agent holding part, 134 ... CO removal device, 136 ... Outlet duct, 138 ... Outlet fan, 140 ... Ventilation tower, 142 ... Tunnel shield, 200, 300 ... CO removal agent, 400, 500, 600 ... Underground structure

Claims (3)

An exhaust gas treatment method for an underground structure in which an automobile travels, wherein the exhaust gas treatment method has a low ventilation amount of 3000 to 30000 h ⁻¹ in which CO present in the exhaust gas exceeds an environmental standard value, and the exhaust gas Can handle
NO is generated by removing the suspended particulate matter in the exhaust gas by an electrostatic precipitator operated at a negative bias and at the same time generating ozone for NO oxidation outside the exhaust gas treatment system in the presence of NO. To NO ₂
The NOx removing device is arranged immediately downstream of said electrostatic precipitator, the exhaust of the NO ₂ which NO is produced by oxidation in the gas, a carbon-based gas to be treated by removing the NO ₂ by the adsorbent in the NOx removing device To generate
When the CO concentration detected by the CO sensor exceeds the environmental standard, the CO removal apparatus is started, and the CO removal apparatus generates the CO remaining in the gas to be processed at room temperature using Au / TiO ₂ as a catalyst. An exhaust gas treatment method in which a purified gas is generated by oxidizing under normal humidity and pressure and removing by the CO removal device while preventing an increase in the concentration of NO ₂ .   The exhaust gas treatment method according to claim 1, wherein activated carbon is used as the carbon-based adsorbent, and the activated carbon is regenerated with a regenerant.   The exhaust gas treatment method according to claim 1 or 2, wherein the low-temperature oxidation is performed in a temperature range in the underground structure where the automobile travels.

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