JP2008249455A - NOx GAS GENERATION DEVICE - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To acquire pseudo NOx including atmosphere with a simple constitution wherein a dilution channel or an ozone generator is not used. <P>SOLUTION: High-purity air dilution NO<SB>2</SB>gas having a low concentration is generated by gas preparation device 10 for calibration using a permeation tube method, and divided into two passages by a branch part 21, and one portion is introduced into a mixing tank 23 as it is through a flowmeter 22, and the other portion is allowed to pass a reaction tube 26 filled with a NO<SB>2</SB>reduction catalyst 25. NO<SB>2</SB>is converted into NO with high efficiency, and the high-purity air dilution NO gas is introduced into the mixing tank 23 via a flowmeter 27. NO and NO<SB>2</SB>which are the same dilution gases are mixed in the mixing tank 23, and supplied to a system to be measured through a flowmeter 28 as the pseudo NOx including atmosphere. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a NOx gas generator for supplying a standard gas necessary for calibration of a nitrogen oxide concentration measuring device, for example.

Nitrogen oxide (NOx) is one of the air pollutants generated by combustion in incinerators of factories and combustion in automobile engines. Among them, particularly toxic nitrogen dioxide (NO ₂ ) is an atmospheric environmental standard. In addition, NOx emissions in automobile exhaust gas are regulated. NOx is a general term for oxides of nitrogen, and is nitric oxide (NO), nitrogen dioxide (NO ₂ ), dinitrogen monoxide (N ₂ O), dinitrogen trioxide (N ₂ O ₃ ), and dinitrogen pentoxide. (N ₂ O ₅ ) and the like are included, but the air pollutants are mainly NO and NO _2, and a nitrogen oxide concentration measuring device for measuring the concentration of these two substances contained in the air and exhaust gas (NOx meter) has been commercially available (see, for example, Non-Patent Document 1).

When performing device calibration such as zero / span calibration or creating a calibration curve in the NOx meter as described above, it is necessary to prepare a standard gas that contains NO / NO ₂ in multiple concentrations. There is. When measuring NOx in the atmosphere with a NOx meter, the standard gas is pseudo-NOx in which high-purity air (generally referred to as air or Air) composed of N ₂ and O ₂ is added with a predetermined concentration of NO and NO _2. Contained atmosphere. Therefore, here, a case where a pseudo NOx-containing atmosphere is supplied is considered.

The equilibrium of the following equation (1) is established between NO and NO ₂ in the atmosphere, and all of these gases exist in the atmosphere at a concentration of several tens to several hundreds ppb.
NO + (1/2) O ₂ ＮＯ NO ₂ (1)
Since there is an equilibrium as described above, it is necessary to set the dilution gas to nitrogen N ₂ in order to fill the gas cylinder with NO gas. On the other hand, to fill the gas cylinder with NO ₂ gas, the dilution gas is made to be high-purity air. There is a need. Also, it is difficult to adjust the concentration of NO and NO ₂ filled in the gas cylinder to a low concentration of the ppb order, and even if it can be adjusted, it becomes very expensive. It is.

Therefore, in order to prepare the pseudo NOx-containing atmosphere using the above-described two types of gas cylinders of NO and NO ₂ , first, a dilution channel is provided either before or after the NO gas and NO ₂ gas mixing channel. It is necessary to dilute these concentrations to the ppb order, which is the atmospheric level. In addition, since NO is supplied from an N ₂ dilution cylinder not containing O ₂ , it is appropriate to consider the mixing ratio of NO / NO ₂ gas especially for the gas equivalent to the atmosphere, that is, high purity air dilution gas. It is necessary to add an amount of O ₂ . In this method, especially when the mixing ratio of NO and NO ₂ is changed, the amount of O ₂ to be mixed is changed, and further, the entire flow rate needs to be adjusted. Become. From the above, it takes a lot of time and effort to prepare a pseudo-NOx-containing atmosphere using two types of gas cylinders of NO and NO ₂ , resulting in a large cost.

On the other hand, in order to generate a standard gas containing NO / NO ₂ , a NOx gas generator as shown in FIG. 3 is conventionally known. This NOx gas generator is defined in JIS B7982. In this NOx gas generator, the standard gas supply source 50 delivers a relatively high concentration of N ₂ diluted NO gas, and the dilution gas supply source 52 delivers high purity air. High-purity air is sent to the ozone generator 55 via the flow rate controller 53, where ozone O ₃ having strong oxidizing power is generated from oxygen O ₂ . The ozone 0 ₃ and the flow controller 51 N ₂ dilution NO gas flow rate is adjusted by being introduced into the reactor 56 are mixed, the reactor 56 a portion of NO is oxidized by ozone and NO ₂ is generated To do. In the diluter 57, high-purity air whose flow rate is adjusted by the flow rate controller 54 is mixed with gas containing NO and NO ₂ , diluted, and supplied to the system to be measured.

However, even in such a NOx gas generator, the composition ratio of N ₂ and O ₂ closer to field conditions 8: Because not assumed to obtain air dilution considerable NOx gas is 2, in order that additional O ₂ Need to be added. Moreover, since ozone O ₃ is used to generate NO ₂ , it is necessary to prepare an ozone generator or the like separately. Therefore, even if the NOx gas generator shown in FIG. 3 is used, it is inevitable that the configuration is complicated for the preparation of the pseudo-NOx-containing atmosphere.

Furthermore, the calibration gas used for calibrating and evaluating the apparatus is preferably closer to field conditions, and in the atmosphere containing pseudo-NOx for atmospheric NOx meter evaluation, the gas should be a humidified gas instead of a dry gas. Is desired. However, since NO ₂ is water-soluble, it is difficult to humidify the atmosphere containing pseudo NOx by bubbling or the like. Further, even when trying to mix a humidified gas with the dried NOx-containing gas, it is difficult to humidify such that the humidity is kept constant because the saturated vapor pressure fluctuates.

"Portable gas analyzer for source monitoring", [online], Shimadzu Corporation, [Search on March 5, 2007], Internet <URL: http://www.shimadzu.co.jp/products/enviro /jnoa7000.html>

  The present invention has been made to solve the above-mentioned problems. The first object of the present invention is to provide a simple configuration, that is, to meet field conditions without using complicated dilution system channels and mixing system channels. An object of the present invention is to provide a NOx gas generator capable of generating a standard gas containing NOx gas.

  The second object of the present invention is to generate a humidified high-purity air diluted standard gas containing NOx gas without using a simple configuration, that is, a complicated dilution system flow path or a mixing system flow path. An object of the present invention is to provide a NOx gas generation device capable of

The present invention was made in order to solve the above problems, the concentration each a NOx gas generator for supplying NOx gas containing NO and NO ₂ is known,
a) NO ₂ gas supply means for supplying NO ₂ gas at a specified concentration;
and NO gas supply means to deliver NO gas generated by converting the NO ₂ to NO by reducing handling NO ₂ gas supplied from b) the NO ₂ gas supply means,
c) mixing the NO ₂ from the gas supply means and NO ₂ gas supplied to said a NO gas supplied from the NO gas supply means on the respective flow rate adjustment, sending the NO / NO ₂ mixture gas as NOx gas First mixing means for feeding;
It is characterized by having.

One aspect of the present invention, the NO ₂ gas supply means may be configured as is to deliver NO ₂ gas diluted with pure air. Here, preferably, the concentration of NO ₂ is several tens to several hundreds ppb of the atmospheric NOx level.

In order to stably supply such a relatively low-concentration high-purity air-diluted NO ₂ gas, the NO ₂ gas supply means holds a porous tube filled with NO ₂ in a liquid state in a constant temperature atmosphere. In this state, it is preferable to use a permeation tube method capable of generating high-purity air-diluted NO ₂ gas having an arbitrary concentration by circulating high-purity air at a constant flow rate around the tube.

In the NOx gas generator according to the present invention, the NO ₂ gas supply means generates, for example, a relatively low-concentration high-purity air-diluted NO ₂ gas as described above. One system is left as it is, and the other system is passed through a NO ₂ gas supply means that is a NO ₂ → NO conversion system in which a catalyst having a conversion efficiency of nearly 100%, such as phosphoric acid-supported activated carbon, is arranged in the heating furnace. Is reduced to NO to produce highly pure air diluted NO. Then, the above two systems of gas, that is, high purity air diluted NO ₂ gas and high purity air diluted NO gas are introduced into the first mixing means and adjusted to a predetermined flow rate and mixed to be diluted with high purity air. NO / NO ₂ mixed gas is obtained. Note that the first mixing means may include a flow rate controller and a mixing tank provided in each flow path.

According to the NOx gas generator according to the present invention, since NO and NO ₂ are both diluted with the same diluent gas, for example, high-purity air, dilution is performed by appropriately adjusting the flow rates in the two channels. It is possible to adjust the composition ratio of NO / NO ₂ without causing fluctuations in gas components. Therefore, the apparatus can be calibrated and performance can be evaluated under conditions closer to the field conditions. Further, for example, when generating pseudo-NOx-containing air, it is not necessary to add O ₂ in order to adjust the air composition to N ₂ : O ₂ = 8: 2, and ozone is not generated because ozone O ₃ is not used. A device or the like is not necessary, and the configuration of the apparatus can be simplified, so that an inexpensive apparatus can be provided.

Moreover, if the permeation tube method is used for supplying NO ₂ gas, it is possible to stably generate NO ₂ at a low concentration of ppb level from the beginning, so a dilution system flow path to ppb level is provided. There is no need, and the configuration is further simplified.

  In the NOx gas generator according to the present invention, the humidified air supply means for sending the humidified high purity air, and the humidified high purity air supplied by the humidified air supply means are generated by the first mixing means. And a second mixing means for mixing with the purity air diluted NOx gas. Here, the form of the humidified air supply means is not particularly limited as long as it can impart humidity to the high-purity air.

According to this configuration, the pseudo-NOx-containing atmosphere can be humidified without causing fluctuations in the components of high-purity air and fluctuations in NO / NO ₂ concentration. In addition, since it is not necessary to pass NO ₂ -containing gas through water for humidification, it is not necessary to consider the loss due to dissolution of NO ₂ in water, so that a humidified pseudo-NOx-containing atmosphere can be obtained stably. .

  In addition, a cooling means for cooling the humidified high-purity air diluted NOx gas generated by the second mixing means is provided, and a portion of the water vapor is condensed and liquefied by cooling by the cooling means to have a predetermined saturated water vapor pressure. Purified diluted NOx gas may be obtained.

  That is, for example, high-purity air for humidification is first sufficiently saturated with a humidified air supply means using bubbling at a moderately high temperature T1, and then mixed with a non-humidified pseudo-NOx-containing atmosphere. Saturated humidified NOx-containing atmosphere. Then, this is passed through a cooling means such as an electronic cooler set so that the amount of water vapor contained at the temperature T2 is equal to or lower than the dew point, thereby obtaining a humidified pseudo-NOx-containing atmosphere having a saturated water vapor pressure.

  As a result, it becomes possible to stably obtain a pseudo-NOx-containing atmosphere having an arbitrary humidity, and the apparatus can be calibrated and performance evaluation can be performed under conditions closer to the field conditions.

[First embodiment]
Hereinafter, a NOx gas generator according to an embodiment (first embodiment) of the present invention will be described with reference to FIG. FIG. 1 is a schematic block diagram of the NOx gas generator of the first embodiment.

In the configuration of the first embodiment, the calibration gas preparation apparatus 10 using the permeation tube method is used as the NO ₂ supply means in the present invention. As the calibration gas preparation device 10, for example, a permeator sold by Gastec Co., Ltd. can be used (“calibration gas preparation device”, [online], Gastech Co., Ltd., March 2007). 5 days search], Internet <URL: http://www.gastec.co.jp/products/frame.php?place=seihin/c4.htm>). The permeator has a tube called a permeation tube 16 in which a high-quality liquefied gas is sealed in a porous fluororesin tube of a certain quality, and when this is maintained at a constant temperature, it permeates and diffuses through the tube tube wall. This utilizes the property that the amount of diffusion gas becomes constant per unit time. If the permeation tube 16 is kept at a constant temperature and a dilution gas is allowed to flow around the tube 16 in a constant amount, a calibration gas having a constant concentration can be obtained continuously.

Specifically, high-purity air is supplied as a dilution gas from a high-purity air (Air) supply source 20 to the calibration gas preparation device 10, and the pressure control system 13 and the needle valve 12 incorporated in the device 10. And the supply amount of high purity air is adjusted with high accuracy by the flow rate adjusting device 11 including the flow meter 14. A constant concentration of NO ₂ is generated by keeping the permeation tube 16 at a constant temperature in a constant temperature bath 15 in the apparatus 10. Since the generated NO ₂ is diluted with the supplied high-purity air, the concentration of the high-purity air diluted NO ₂ delivered from the device 10 is adjusted by adjusting the supply amount of the high-purity air by the flow rate adjusting device 11. be able to. For example, by using a permeator of Gastec Co., Ltd .: PD-1B and a permeation tube for NO ₂ generation: P-9-1, high-purity air diluted NO ₂ gas having a concentration of 0.05 to 3.99 ppm. Can be obtained.

The high-purity air diluted NO ₂ sent out from the calibration gas preparation device 10 is branched into two flow paths by the branching section 21, and one of the flow paths passes through a flow meter 22 with a first needle valve for flow rate adjustment. And introduced into the NOx mixing tank 23. Another flow path of the high-purity air-diluted NO ₂ is a reaction filled with a NO ₂ reduction catalyst 25 such as phosphoric acid-carrying activated carbon, which is installed in a heating furnace 24 whose temperature is adjusted to about 200 ° C. Introduced into the tube 26. This reaction tube 26 converts NO ₂ into NO by a reduction reaction, and corresponds to the NO gas supply means in the present invention. Here, high-purity air diluted NO is secondarily generated and introduced into the NOx mixing tank 23 via the flow meter 27 with a second needle valve. Accordingly, the flow meter 22 with the first needle valve, the flow meter 27 with the second needle valve, and the NOx mixing tank 23 correspond to the first mixing means in the present invention.

When phosphoric acid-supporting activated carbon is used as the NO ₂ reduction catalyst 25, it is usually possible to convert NO _{2 at} a concentration of 10 ppm into NO with a high efficiency of 95% or more. Since O ₂ in the atmosphere is in the order of% and O ₂ generated when NO ₂ is converted to NO is in the ppb order, the amount of O _{2 that} increases due to the reduction reaction is substantially ignored. Can do.

When the calibration gas preparation apparatus 10 generates NO ₂ with a specified concentration, it is necessary to flow high-purity air with a specified flow rate around the permeation tube 16 as a diluent gas. Therefore, the amount of high-purity air-diluted NO ₂ gas supplied from the calibration gas preparation device 10 may exceed the processing capacity of the NO ₂ reduction catalyst 25 and may become excessive. The flow rate of the high-purity air diluted NO ₂ may be bypassed and exhausted by the flow meter 30 with a needle valve, so that the amount of gas supplied to the downstream, that is, the branch portion 21 may be limited.

High-purity air dilution NO ₂ supplied from the calibration gas preparation device 10 via the flow meter 22 with the first needle valve, and high-purity air dilution NO supplied via the reaction tube 26 and the flow meter 27 with the second needle valve Are mixed in the NOx mixing tank 23 to become a high purity air diluted NO / NO ₂ mixed gas. This is a pseudo-NOx-containing atmosphere that is close to an actual atmospheric component, and the composition ratio between NO ₂ and NO contained therein is adjusted by the flow rates of the first and second flow meters 22 and 27 with a needle valve. The mixed gas prepared here is supplied to a system under measurement, for example, a NOx meter to be calibrated, through a flow meter 28 with a third needle valve for flow rate control. In addition, a part of the NO / NO ₂ mixed gas is bypassed and exhausted by a flow meter 29 with a fourth needle valve for adjusting the excess gas flow, which is arranged as necessary, so that the amount of gas supplied to the system to be measured Can also be restricted.

As described above, in the NOx gas generator of this embodiment, the high-purity air-diluted NO ₂ gas generated primarily and the high-purity air-diluted NO gas generated secondarily based on this are mixed. By doing so, a high-purity air NO / NO ₂ mixed gas can be obtained. In particular, a pseudo NOx-containing atmosphere can be obtained by setting the concentration of NO and NO ₂ to high purity air dilution of several tens to several hundreds ppb.

In the above embodiment, a permeator is used as the calibration gas preparation device 10, but the present invention is not limited to this, and a combination of a general high-purity air diluted NO ₂ cylinder and a dilution system flow path may be used. .

[Second Embodiment]
Next, a NOx gas generator as another embodiment (second embodiment) of the present invention will be described with reference to FIG. The first embodiment supplies dry pseudo-NOx-containing air, but the second embodiment supplies humidified pseudo-NOx-containing air. In FIG. 2, the same components as those shown in FIG.

The high-purity air diluted NO / NO ₂ mixed gas prepared by mixing in the NOx mixing tank 23 as described above is introduced into the humidification mixing tank 33 via the flow meter 28 with a third needle valve for flow rate control. Is done.

The flow path for supplying the high-purity air for humidification to the humidification mixing tank 33 includes a humidifier 31 held at a temperature T1 (for example, 40 ° C. (H ₂ O: 70000 ppm)) and a sixth needle for flow rate adjustment. A flow meter 32 with a valve is provided. The form of the humidifier 31 is not particularly limited as long as it can give humidity to the gas passing therethrough, such as one that performs bubbling in water or one that is via a humidifying tube having semipermeable membrane properties. The high-purity air humidified by the humidifier 31 is adjusted in flow rate by a flow meter 32 with a sixth needle valve, introduced into the humidification mixing tank 33, and mixed with the dry pseudo NOx-containing air described above.

However, since the humidified pseudo-NOx-containing air obtained in the humidification mixing tank 33 is a mixed gas of humidified high-purity air having a relative humidity of 90% or more and pseudo-NOx-containing air having a relative humidity of 10% or less, the humidity is Indefinite. Therefore, in order to obtain a saturated water vapor pressure gas at an arbitrary temperature, the humidified pseudo-NOx-containing air generated in the humidification mixing tank 33 is introduced into the electronic cooler 34, and a temperature T2 (eg, 2 ° C. (H ₂ O: 7000 ppm)) forcibly cooled. Thus, a part of the excess water vapor is condensed and liquefied and removed from the gas, so that a desired humidified saturated / pseudo NOx-containing atmosphere can be obtained and sent to the system to be measured.

  As described above, in the NOx gas generator of the second embodiment, a humidified pseudo-NOx-containing atmosphere can be obtained.

  It should be noted that any of the above embodiments is an embodiment of the present invention, and it is obvious that modifications, additions, and changes as appropriate within the scope of the present invention are included in the scope of the claims of the present application.

The schematic block block diagram of the NOx gas generator which is one Example of this invention. The schematic block block diagram of the NOx gas generator which is another Example of this invention. The schematic block block diagram of the conventional NOx gas generator.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Calibration gas preparation apparatus 11 ... Flow rate adjustment apparatus 12 ... Needle valve 13 ... Pressure regulation system 14 ... Flow meter 15 ... Constant temperature bath 16 ... Permeation tube 21 ... Branch part 22, 27, 28, 29, 30, 32 ... flow with needle valve meter 23 ... NOx mixing tank 24 ... heating furnace 25 ... NO ₂ reduction catalyst 26 ... reaction tube 31 ... humidifier 33 ... humidifying mixing tank 34 ... electronic cooler

Claims (5)

Each A NOx gas generator for supplying NOx gas containing NO and NO ₂ is known concentration,
a) NO ₂ gas supply means for supplying NO ₂ gas at a specified concentration;
and NO gas supply means to deliver NO gas generated by converting the NO ₂ to NO by reducing handling NO ₂ gas supplied from b) the NO ₂ gas supply means,
c) mixing the NO ₂ from the gas supply means and NO ₂ gas supplied to said a NO gas supplied from the NO gas supply means on the respective flow rate adjustment, sending the NO / NO ₂ mixture gas as NOx gas First mixing means for feeding;
A NOx gas generator characterized by comprising: The NO ₂ gas supply means, NOx gas generator according to claim 1, characterized in that to deliver the NO ₂ gas diluted with pure air. The NO ₂ gas supply means maintains a porous tube filled with NO ₂ that is in a liquid state in a constant temperature atmosphere, and allows high-purity air at a constant flow rate to flow around the tube to have an arbitrary concentration. _2. The NOx gas generator according to claim 1, wherein a permeation tube method capable of generating high-purity air-diluted NO2 gas is used.   Humidified air supply means for delivering humidified high-purity air, and second mixing for mixing the humidified high-purity air supplied by the humidified air supply means with the high-purity air-diluted NOx gas generated by the first mixing means The NOx gas generator according to claim 2, further comprising means.   Humidity and high purity having a predetermined saturated water vapor pressure, comprising cooling means for cooling the humidified high purity air diluted NOx gas generated by the second mixing means, and condensing and liquefying part of the water vapor by cooling by the cooling means 5. The NOx gas generator according to claim 4, wherein diluted NOx gas is obtained.

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