JP6179934B2 - Method and apparatus for detecting NOx gas in ozone-containing gas - Google Patents

Description

  The present invention relates to a method and apparatus for detecting and measuring a NOx component in a gas to be measured containing ozone as a component.

As a method for measuring the concentration of nitrogen oxides in the atmosphere, the chemiluminescence method and the spectrophotometric method are described in JIS "Automatic nitrogen oxide measuring instrument in the atmosphere".
The chemiluminescence method is a method in which ozone gas is added and reacted, and the luminescence intensity due to the chemical reaction is measured. When nitric oxide reacts with ozone to form nitrogen dioxide, some excited nitrogen dioxide emits light and returns to the ground state. In this method, the concentration of nitric oxide is estimated by measuring the intensity of light. The measurement of nitrogen dioxide concentration is obtained by once decomposing nitrogen dioxide into nitric oxide and then measuring the emission intensity by the ozone-mixed emission method. With the above method, the total concentration of nitrogen oxides (nitrogen monoxide + nitrogen dioxide) in the sample atmosphere can be measured.

Meanwhile, absorptiometry prepares a liquid to absorb nitrogen monoxide and nitrogen dioxide, to absorb nitrogen monoxide and nitrogen dioxide by preferably under a gas to be measured in the absorbing solution. Since the absorbance of the absorbing solution changes due to gas absorption, nitrogen oxides in the sample atmosphere are estimated by measuring the absorbance.

JIS B 7953 "Automatic measuring instrument for nitrogen oxides in the atmosphere"

  However, when ozone gas is previously contained in the gas to be measured, the chemiluminescence method cannot be used for NOx detection. This is because the nitric oxide component is previously oxidized by the ozone component, and no new light emission occurs even when ozone gas is newly added for chemiluminescence measurement.

  Moreover, when the ozone partial pressure management in the gas to be measured is an important application and it is desired to measure the NOx concentration in-line, the measuring method of adding or decomposing ozone gas cannot be applied because the ozone partial pressure is changed. Especially when the ozone concentration is higher than 20 vol%, the decomposition of some ozone may cause a chain decomposition reaction of the total amount of ozone, so the heat source and the light absorbed by ozone are used for measurement. Use should be avoided.

  In the absorptiometric method, since the gas to be measured is circulated in the absorption liquid, the vapor of the absorption liquid is mixed into the gas to be measured. For this reason, it is difficult to perform in-line measurement in the middle of the piping of the gas to be measured. When the gas to be measured has a negative pressure, the evaporation of the absorbing liquid is promoted and piping contamination becomes a problem.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a method and an apparatus for measuring NOx concentration even if ozone gas is contained in the gas to be measured in advance.

As a method for detecting NOx gas contained in the gas of the present invention,
At least one component selected from N ₂ O, NO, NO ₂ , N ₂ O ₄ , N ₂ O ₅ , NO ₃ , and HNO ₃ and ozone are disposed in the gas flow path portion in which the NOx adsorbing portion to which NOx adheres is disposed. by supplying a gas to be measured which contains the NOx adsorbed to the NOx adsorption unit (5),
The NOx adsorbing part is irradiated with incident light of 360 nm to 410 nm, which is a wavelength range not absorbed by ozone, from the light irradiating part,
The material substrate of the portion exposed to the incident light and the gas to be measured of the NOx adsorption portion is formed of silica gel or quartz or glass having a porous surface,
The light detection unit detects at least one of transmitted light that has passed through the NOx adsorption unit, reflected light that has been reflected from the NOx adsorption unit, and generated light that has been generated at the NOx adsorption unit,
The light intensity obtained by the light detection unit is analyzed and recorded by the data recording / analysis unit.

In this case, if the light irradiated from the light irradiation unit is light within a predetermined wavelength range (360 nm to 410 nm), it is either a single wavelength, a plurality of wavelengths, or a wavelength having a predetermined width. Can also be used.

Furthermore , it is desirable that the gas to be measured has an ozone concentration of 0.1 vol% or more and less than 100 vol%, and the ozone concentration is higher than the NOx concentration.

In addition, as an apparatus for carrying out the above method,
The NOx gas detection device internally contains a gas to be measured containing ozone and at least one component selected from N ₂ O, NO, NO ₂ , N ₂ O ₄ , N ₂ O ₅ , NO ₃ , and HNO _3. A gas flow path section to be filled with,
A NOx adsorbing section having a NOx adsorbing material for adhering NOx disposed in a part of the gas flow path section;
A light irradiation unit that irradiates incident light of 360 nm to 410 nm, which is a wavelength region that is not absorbed by ozone, into the NOx adsorption unit;
At least one of the transmitted light that has passed through the NOx adsorption portion of the incident light irradiated from the light irradiation portion, the reflected light that has been reflected by the NOx adsorption portion, and the generated light that has been generated at the NOx adsorption portion by the incident light. A light detection unit to detect;
A data recording analysis unit that records and analyzes the light intensity obtained from the light detection unit,
The material substrate of the NOx adsorbing portion exposed to the incident light from the light irradiating portion and the gas to be measured is formed of silica gel or quartz or glass having a porous surface.

In the method of the present invention and the device of the present invention to which the method is applied,
  Since ozone is included as a component in the gas to be measured, NOx is oxidized by ozone and adheres to the NOx adsorption portion placed in the flow path.
When this deposit is irradiated with light to measure the absorption / reflection / emission characteristics of the deposit and measure the amount of NOx, light of wavelength 360 nm to 410 nm is not absorbed by ozone, so the ozone content in the measurement gas NOx concentration can be measured without being affected by pressure, and since ozone gas is difficult to decompose, NOx measurement is also possible for gases containing high-concentration ozone gas that has a high self-degradability such as ozone concentration exceeding 20 vol%. Can be applied.

Further, by using silica gel or quartz or glass having a porous surface for the material substrate of the NOx adsorbing portion, NOx that has been oxidized by ozone adheres compared to the case of using a material substrate having a smooth surface. Since the possible area can be increased, the NOx detection signal can be increased.

Furthermore, since the silica gel, quartz, and glass that are the base materials of the material transmit light having a wavelength of 360 nm to 410 nm, the irradiation light reaches the inside of the porous portion of the base material of the NOx adsorption portion, and the NOx detection signal is increased. be able to.

Ozone gas having an ozone concentration of about 1 to 5 vol% is frequently used because it can be easily generated by an industrial silent discharge type ozonizer. However, NOx measurement can also be applied to a gas containing ozone gas having a general concentration. Further, NOx measurement can be applied to a gas containing a high concentration ozone gas having a high self-decomposition property such as an ozone concentration exceeding 20 vol%.
Further, when the ozone concentration is higher than the NOx concentration, NOx oxidation proceeds and the final oxidation state is stably obtained, which is advantageous for the application of the present invention. Therefore, the present invention includes 0.1 vol% or more ozone gas. It can be suitably used for gas.

It is a figure showing typically one embodiment of the NOx gas detection device concerning the present invention. It is a figure which shows typically another embodiment of the NOx gas detection apparatus which concerns on this invention. It is a figure which shows typically different embodiment of the NOx gas detection apparatus which concerns on this invention. It is an example of a measurement of NOx detection in the NOx gas detection device according to the present invention. It is a figure which shows typically further another embodiment of the NOx gas detection apparatus which concerns on this invention.

The apparatus for detecting NOx gas contained in the gas of the present invention,
The gas that contains ozone as a component is the gas to be measured,
The gas to be measured contains at least one component of N ₂ O, NO, NO ₂ , N ₂ O ₄ , N ₂ O ₅ , NO ₃ , HNO ₃ ,
This gas to be measured is circulated through the gas flow path.
At this time, the NOx adsorbing part provided in a part of the gas flow path part is exposed to the gas to be measured, and oxides of NOx due to ozone adhere thereto.

The NOx adsorbing part is irradiated with light in the wavelength range of 360 nm to 410 nm from the light irradiation part.
The intensity of the irradiation light transmitted through the NOx adsorption unit is captured by the light detection unit. The data recording / analyzing unit records and analyzes the light intensity.

When silica gel is used as the NOx adsorbent, the oxidation of NOx under the flow of ozone progresses due to ozone, and changes in the order NO → NO ₂ → NO ₃ → HNO ₃ and is adsorbed on the silica gel surface.
When irradiated with ultraviolet rays, the NOx absorbs the ultraviolet rays and is reduced. Therefore, the larger the amount of NOx adhering to the silica gel surface, the better the ultraviolet rays are absorbed. Therefore, the amount of NOx can be measured by observing the change in transmitted light intensity of ultraviolet rays.

  In addition to the transmitted light intensity, light reflected by the NOx adsorption unit or light generated by the NOx adsorption unit can also be used.

As the incident light, not only single-wavelength light but also light in which a plurality of different wavelengths are mixed within the range of 360 nm to 410 nm can be used. Further , light having a wavelength continuously or discretely spread within a range of 360 nm to 410 nm can also be used.

  Since light having a wavelength of 360 nm to 410 nm is not absorbed by ozone gas, there is an advantage that ozone in the gas to be measured is not decomposed by light. There is also an advantage that the transmitted light intensity is not affected by the partial pressure of ozone gas in the gas.

  By using silica gel or quartz or glass having a porous surface for the material substrate of the NOx adsorption part, the area on which NOx oxidized by ozone can adhere can be increased compared to the case of using a smooth material substrate. The NOx detection signal can be increased.

Moreover, since the wood charge base silica, quartz, glass that transmits light with a wavelength of 360 nm~410 nm, for irradiating light to the interior of the porous in the base material of the NOx adsorption unit arrives, to increase the NOx detection signal be able to.

  It is desirable that the NOx adsorbing material has a property of selectively adsorbing NOx over ozone.

  The pore diameter of the porous material is preferably in the range of 1.5 nm or more and 30 nm or less in average value, median value, or mode value.

  The depth of the hole is desirably 5 times or more the diameter of the hole.

  Further, as a characteristic of the material of the NOx adsorbing portion, it is desirable that the saturated adsorption amount of NOx that has been oxidized by ozone is larger than the saturated adsorption amount of ozone gas.

  A NOx gas detection device according to the present invention will be described.

As shown in FIG. 1, the NOx gas detection device (1) includes a gas flow path portion (2) that circulates and fills the gas to be measured, and a part of the gas flow path portion (2) includes A quartz window (3) is provided, and a light irradiation section (4) for irradiating light with a wavelength of 380 nm is disposed outside the quartz window (3).
And the inside of the gas flow path part (2) corresponding to the formation part of the said quartz window (3) accommodates the NOx adsorption material made from a silica gel, and it is set as the NOx adsorption part (5).
The NOx adsorption part (5) is irradiated with incident light (Li) having a wavelength of 380 nm from the light irradiation part (4).

The transmitted light (Lt) that has passed through the NOx adsorbent (silica gel) of the NOx adsorbing section (5) is captured by the light detecting section (6) using a photodiode.
The signal intensity of the transmitted light (Lt) is recorded in time series by the data recording analysis unit (7).

  The silica gel as the NOx adsorbent may be granular or powder. These silica gels may be coated on a substrate such as quartz that transmits ultraviolet light. Instead of silica gel, a substrate obtained by chemically treating the surface of a glass substrate to be porous may be used. If the surface of the glass substrate is increased with a material to which NOx adheres and ultraviolet light is transmitted, it can be used.

  FIG. 2 is an apparatus in which a mechanism for removing fluctuations in incident light intensity is added to the apparatus of FIG. Incident light intensity fluctuates due to deterioration of the light source over time or ambient temperature fluctuations. Part of the incident light is reflected and split by the half mirror (8), and the split incident light (Ld) detects the intensity of the incident light by the incident light detector (9) using a photodiode. The signal of the transmitted light intensity from the light detection unit (6) is normalized by the signal from the incident light detection unit (9), so that fluctuations in the incident light intensity can be removed. This processing is performed by the data recording analysis unit (7). By removing the fluctuation of the incident light intensity, the transmittance can be obtained instead of the transmitted light intensity, and a slight change of the transmittance due to NOx adhesion can be detected.

FIG. 3 shows an example of an apparatus for obtaining the transmittance even when only one photodetecting section (6) is used. Incident light (Li) passes through the NOx adsorbent (silica gel) and becomes transmitted light (Lt), while incident light (Ld) partially split by the half mirror (8) is the gas flow path ( The light directly enters the light detection section (6) through the back surface of 2) . The incident light (Li) and the split incident light (Ld) are switched to the chopper from (10). In the data recording analysis unit (7), first, the rotation of the chopper (10) and the signal from the light detection unit (6) are processed synchronously to determine the intensity of the incident light (Ld) and the transmitted light (Lt) respectively. Then, the intensity of the transmitted light (Lt) can be normalized by the intensity of the incident light (Ld) thus dispersed, and finally the transmittance of the silica gel can be obtained.

  In this example, an example of an apparatus for light transmitted through silica gel as an adsorbent is shown, but reflected light (Lr) from the surface of silica gel can also be used. In this case as well, the reflectance changes as NOx adheres, as with the transmittance. Therefore, if the change rate is measured, it can be used for NOx detection.

  When NOx emits light by ultraviolet rays, the emission intensity of the generated light (Lg) can be used. In that case, since the emission wavelength is in the visible region, it is necessary to correct the amount of absorption by the measurement gas.

FIG. 4 shows an example in which NOx gas is detected from the transmitted light intensity (Tr) with respect to the incident light intensity (Io) using the apparatus shown in FIG.
In the figure, from 0 to 280 minutes, oxygen gas or an ozone-containing gas of 95% by volume of oxygen and 5% by volume of ozone was flowed, and the transmission intensity of silica gel placed therein was measured. Between 280 and 530 minutes, an ozone-containing gas of 95 vol% oxygen-5 vol% ozone mixed with 100 ppm NO gas was allowed to flow down. At this time, the transmittance (Tr / Io) attenuated by 3.8% with the passage of time under the flow of NOx. On the silica gel surface, the adsorption process of N ₂ O _{5 and} the reduction process by ultraviolet rays (N ₂ O ₅ → NO ₃ → NO ₂ ) proceed in equilibrium. However, it is considered that it takes time for the amount of adsorbed NOx to reach saturation because the diffusion of HNO ₃ into the inside due to capillary condensation proceeds gradually.

Between 530 and 800 minutes, the permeation intensity began to return by flowing an oxygen gas or an ozone-containing gas of 95% by volume of oxygen and 5% by volume of ozone. This is because the adsorbed NOx is reduced by ultraviolet rays and desorbed as a gas from the silica gel surface. The time constant for desorption from the surface is 0.5 hour. The time-consuming process is a process in which HNO ₃ confined in the capillaries and confined inside diffuses to the surface, and the time constant was 19 hours.

The apparatus shown in FIG. 5 uses the differential light absorption method to determine the transmittance of silica gel. The emitted light (Li) from the light irradiator (4) passes through the NOx adsorbent (silica gel), and a part of the transmitted light (Lt) is reflected and spectrumd by the half mirror (8). (Ld) detects the intensity of transmitted light spectrally separated by the spectroscopic detection unit (12) using a photodiode through the 370 nm interference filter (11). On the other hand, the transmitted light (Lt) transmitted through the half mirror (8) reaches the light detection unit (6) through the 400 nm interference filter (13), and is transmitted from the spectral detection unit (12) and the light detection unit (6). The transmitted light intensity signal is sent to the data recording / analyzing unit (7), and the light absorption of NOx has a wavelength dependency (for example, the absorption coefficient at 400 nm is larger than the absorption coefficient at 360 nm for NO ₂ ). Then, the transmitted light intensity is measured by the data recording analysis unit (7), and the NOx concentration is obtained from the difference between the signal intensities.

  The present invention can be applied to all facilities using ozone gas generated by discharge.

  2 ... Gas channel part, 4 ... Light irradiation part, 5 ... NOx adsorption part, 6 ... Light detection part, 7 ... Data recording analysis part, Lt ... NOx adsorption part transmitted light, Lr ... NOx adsorption part reflected light, Lg ... NOx adsorption part generated light.

Claims (4)

A method for detecting NOx gas contained in a gas, comprising:
At least selected from N ₂ O, NO, NO ₂ , N ₂ O ₄ , N ₂ O ₅ , NO ₃ , and HNO ₃ in the gas flow path part (2) in which the NOx adsorbing part (5) to which NOx adheres is arranged. Supplying a gas to be measured containing one component and ozone, and adsorbing NOx to the NOx adsorbing section (5);
The NOx adsorbing part (5) is irradiated with incident light (Li) having a wavelength range of 360 nm to 410 nm which is not absorbed by ozone from the light irradiating part (4).
The material substrate of the portion exposed to the incident light (Li) and the gas to be measured of the NOx adsorption portion (5) is formed of silica gel or quartz or glass having a porous surface,
At least one of transmitted light (Lt) transmitted through the NOx adsorbing part (5), reflected light (Lr) reflected from the NOx adsorbing part (5), and generated light (Lg) generated at the NOx adsorbing part (5) The light is detected by the light detector (6),
A method for detecting NOx gas in an ozone-containing gas, characterized in that the light intensity obtained by the light detection unit (6) is analyzed and recorded by a data recording analysis unit (7). The method for detecting NOx gas in ozone-containing gas according to claim 1, wherein the ozone concentration in the gas to be measured is an ozone concentration of 0.1 vol% or more and less than 100 vol%, and the ozone concentration is larger than the NOx concentration. . An apparatus for detecting NOx gas contained in a gas,
This NOx gas detector is composed of ozone and N ₂ O, NO, NO ₂ , N ₂ O ₄ , N ₂ O ₅ , NO ₃ , HNO ₃ A gas flow path section (2) for filling the gas to be measured containing at least one component selected from
A NOx adsorbing section (5) having a NOx adsorbing material for adhering NOx disposed in a part of the gas flow path section (2);
A light irradiating unit (4) for irradiating the NOx adsorbing unit (5) with incident light (Li) having a wavelength range of 360 nm to 410 nm which is not absorbed by ozone;
The incident light (Li) irradiated from this light irradiation part (4) is transmitted through the NOx adsorption part (Lt), the reflected light reflected from the NOx adsorption part (Lr), incident light (Li) A light detection unit (6) for detecting at least one of generated light (Lg) generated in the NOx adsorption unit by light (Li);
A data recording analysis section (7) for recording and analyzing the light intensity obtained from the light detection section (6),
The material base material in the NOx adsorption part exposed to incident light (Li) from the light irradiation part and the gas to be measured is formed of silica gel or quartz or glass having a porous surface. A NOx gas detector in ozone-containing gas. 4. The NOx in the ozone-containing gas according to claim 3, wherein the ozone concentration in the gas to be measured is 0.1 vol% or more and less than 100 vol%, and the ozone concentration is higher than the NOx concentration. Gas detection device.

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