JP6611316B2 - Nitrogen oxide concentration measuring device - Google Patents

Description

  The present invention relates to a nitrogen oxide concentration measuring apparatus.

  Non-Patent Document 1 below describes dilution of sample gas (nitrogen oxide-containing gas) such as nitrogen oxide for the purpose of protecting the sensor and continuing measurement when measuring high-concentration component gas in combustion exhaust gas. Is described. Non-Patent Document 2 below describes that a high-temperature sample gas is diluted with a dilution gas in order to dry it. Further, Non-Patent Document 3 below describes a calibration gas adjustment device that obtains a low-concentration adjustment gas (calibration gas) by diluting a component gas with a dilution gas.

Product explanation homepage of the handy type flue gas meter testo340 (http://www.testo.jp/products/01/testo340.html) JIS B 7982 Annex 5 (normative) “About sample gas dilution of automatic measuring instrument for nitrogen oxides in exhaust gas” Japan Environmental Technology Association "Environmental Atmospheric Continuous Monitoring Practice Manual (Third Edition)"

  By the way, when measuring the concentration by diluting the sample gas (nitrogen oxide-containing gas), the sample gas flow rate and the dilution gas flow rate are set to a desired flow rate and mixed, and the adjustment gas obtained by the mixing is mixed. The concentration is measured with a sensor. A value obtained by multiplying the concentration (actual measurement value) of the adjustment gas by a dilution factor acquired in advance is used as a final concentration measurement value. In this case, the dilution factor is not a direct value obtained at the time of measurement of the sample gas (nitrogen oxide-containing gas), but is an indirect value acquired in advance, which may cause an error.

  This invention is made | formed in view of the situation mentioned above, and it aims at confirming a dilution ratio in parallel, when diluting nitrogen oxide containing gas and measuring a nitrogen oxide density | concentration.

  In order to achieve the above object, in the present invention, as a first solving means, a nitrogen oxide concentration measuring apparatus for measuring a nitrogen oxide concentration by diluting a nitrogen oxide-containing gas with a predetermined dilution gas, An inert gas is taken in as the dilution gas, a flow rate adjusting means for adjusting the flow rate of the inert gas and the flow rate of the nitrogen oxide-containing gas separately taken to a desired flow rate, and the flow rate adjusted by the flow rate adjusting means, A gas mixing means for generating a regulated gas by mixing a nitrogen oxide-containing gas and the dilution gas, a nitrogen oxide concentration detecting means for detecting the nitrogen oxide concentration of the regulated gas, and detecting the oxygen concentration of the regulated gas Oxygen concentration detection means, oxygen concentration detection value in the oxygen concentration detection means, known oxygen concentration of the nitrogen oxide-containing gas, and nitrogen acid in the nitrogen oxide concentration detection means Based on the object density detection value, wherein and a calculation means for calculating a dilution ratio with the nitrogen oxides concentration of the nitrogen oxide-containing gas in the nitrogen oxide-containing gas with inert gas, to adopt a means of.

  In the present invention, as the second solving means, in the first solving means, the flow rate adjusting means includes a first capillary through which the nitrogen oxide-containing gas flows and a second capillary through which the inert gas flows. A means of providing a capillary tube is adopted.

  In the present invention, as the third solving means, in the first or second solving means, a means is adopted in which the flow rate adjusting means includes a thermostatic bath.

  In the present invention, as a fourth solution means, in any one of the first to third solution means, a selection means for sequentially selecting the adjustment gas or the inert gas and supplying it to the oxygen concentration detection means is provided. , Is adopted.

  In the present invention, as the fifth solving means, in the fourth solving means, the selecting means includes the nitrogen oxide-containing gas before being diluted with the dilution gas in addition to the adjustment gas or the inert gas. Are sequentially selected and supplied to the oxygen concentration detecting means.

  In the present invention, as sixth solving means, in any one of the first to fifth solving means, a reducing means for reducing nitrogen dioxide contained in the nitrogen oxide-containing gas to nitrogen monoxide, and the reducing means A detour route for detouring and a second selection unit for alternatively selecting the return unit or the detour route is employed.

  In the present invention, as a seventh solving means, in the first to sixth solving means, a means is adopted in which the inert gas is nitrogen.

According to the present invention, an inert gas containing no oxygen is used as the dilution gas, and the oxygen concentration of the adjustment gas is adjusted by the oxygen concentration detection means in parallel with the nitrogen oxide concentration of the adjustment gas by the nitrogen oxide concentration detection means. Therefore, the dilution rate is calculated based on the known oxygen concentration in the nitrogen oxide-containing gas and the oxygen concentration in the adjustment gas.
Therefore, according to the present invention, when diluting the nitrogen oxide-containing gas with an inert gas and measuring the concentration of the nitrogen oxide concentration, it is possible to obtain the dilution ratio of the nitrogen oxide-containing gas in parallel. Therefore, it is possible to measure the nitrogen oxide concentration while confirming the dilution rate in parallel.

It is a systematic diagram which shows the apparatus structure of the nitrogen oxide concentration measuring apparatus which concerns on one Embodiment of this invention. It is a characteristic view which shows the relationship between the oxygen concentration of the sample gas (adjustment gas) after dilution, and dilution magnification in one Embodiment of this invention. It is a systematic diagram which shows the apparatus structure of the nitrogen oxide concentration measuring apparatus which concerns on the modification of one Embodiment of this invention.

Hereinafter, a nitrogen oxide concentration measuring apparatus (hereinafter simply referred to as a measuring apparatus) according to an embodiment of the present invention will be described with reference to the drawings.
This measuring device is a device that measures the concentration of nitrogen oxides (NO _x ) by diluting a sample gas (raw gas), which is a nitrogen oxide-containing gas, with a predetermined dilution gas, and is diluted as shown in FIG. A part A1 and a measurement part A2 are provided. In addition, this measuring device particularly contains oxygen (O ₂ ) in the same degree (about 21%) as the atmosphere (air), for example, nitrogen oxide containing nitrogen as a carrier gas of nitrogen oxide (NO _x ). Gas is to be measured.

In FIG 1, the elements that are not on essential importance in describing the present invention, for example, various on-off valve and filter, also for the part or the like relating to the calibration of the NO _X detector 30 and O ₂ detectors 31 Omitted.

The sample gas (original gas) is a measurement target gas in the present embodiment, and as described above, nitrogen oxidation using air (atmosphere) as a carrier gas and containing a relatively high concentration of nitrogen oxides (NO _x ). It is a substance-containing gas. The nitrogen oxide (NO _x ) contained in the sample gas (raw gas) is nitrogen monoxide (NO) and / or nitrogen dioxide (NO ₂ ). Such sample gas (raw gas) is supplied to the dilution unit A1 from an external sample gas supply source (not shown).

The dilution unit A1 is a functional component that dilutes the sample gas (original gas) with a predetermined dilution gas nitrogen gas (N ₂ ). The sample gas (raw gas) is a nitrogen oxide-containing gas containing a high concentration of nitrogen oxide (NO _x ) that exceeds the concentration measurement range of the measurement unit A2, and therefore, the measurement unit A2 performs nitrogen oxide (NOx). The concentration of _X ) cannot be measured directly. Under such circumstances, the measuring apparatus according to the present embodiment includes a diluting unit A1 as a preprocessing unit of the measuring unit A2.

The dilution gas is applicable as long as it does not contain oxygen (O ₂ ), but an inert gas is preferable in terms of chemical stability with respect to the sample gas (raw gas), and the inert gas is also applicable. Among these, the cheapest nitrogen (N ₂ ) is preferable. Also in this embodiment, this nitrogen (N ₂ ) is adopted as a dilution gas. Such a dilution gas (nitrogen (N ₂ )) is supplied to the dilution unit A1 from an external dilution gas supply source (not shown).

  As shown in FIG. 1, the diluting part A1 includes a pre-converter 1, a first dehumidifier 2, a first SP pump 3, a first drain pot 4, a first capillary 5 (first capillary), a first 1 flow meter 6, second capillary 7, third capillary 8 (second capillary tube), second flow meter 9, thermostat 10, gas mixer 11, suction pump 12, and third flow meter 13.

The pre-converter 1 is a first reduction unit that reduces (chemically reduces) most of nitrogen dioxide (NO ₂ ) contained in the sample gas (raw gas) to nitrogen monoxide (NO). When the sample gas (raw gas) contains nitric oxide (NO) and nitrogen dioxide (NO ₂ ), the sample gas that has passed through the pre-converter 1 is essentially nitrogen monoxide (NO) contained in the sample gas (raw gas). ) And nitrogen monoxide (NO) newly generated from nitrogen dioxide (NO ₂ ) by the reduction treatment by the pre-converter 1.

Such a pre-converter 1 is necessary for the principle of detection of nitrogen oxides in the measurement unit A2, that is, the measurement unit A2 can detect only nitrogen monoxide (NO) and cannot detect nitrogen dioxide (NO ₂ ). It is provided based on circumstances. Therefore, for example, when the sample gas (raw gas) contains only nitrogen monoxide (NO) as nitrogen oxide, the pre-converter 1 can be omitted.

  The first dehumidifier 2 is a device that removes moisture contained in the sample gas reduced by the pre-converter 1. The first dehumidifier 2 supplies the sample gas from which moisture has been removed to the first SP pump 3, while supplying moisture separated from the sample gas to the first drain pot 4. The first SP pump 3 is a pump that operates under the control of the control calculation unit 36, and discharges the sample gas supplied from the first dehumidifier 2 toward the first capillary 5 and the first flow meter 6. The first drain pot 4 is a container that stores a certain amount of the water supplied from the first dehumidifier 2 and discharges it to the outside.

  The first capillary 5 is a capillary tube having a predetermined pipe diameter (flow path diameter) through which the sample gas supplied from the first SP pump 3 flows, and adjusts the flow rate of the sample gas to a desired first flow rate R1 (desired flow rate). The first flow meter 6 is an overflow type float gas flow meter connected to the discharge port of the first SP pump 3, that is, the inlet of the first capillary 5, and the discharge port of the first SP pump 3, that is, the first capillary 5. Set the inlet pressure to atmospheric pressure.

The second capillary 7 is a capillary tube having a predetermined pipe diameter (flow path diameter) through which nitrogen (N ₂ ) supplied from the outside flows, and the third capillary 7 is adjusted by adjusting the flow rate of nitrogen (N ₂ ) to the second flow rate R 2. 8 and the second flow meter 9. The third capillary 8 is a capillary of a predetermined pipe diameter nitrogen of the second flow rate R2 supplied from the second capillary 7 _{(N 2)} flows (Nagarero径), nitrogen _{(N 2)} a third flow rate R3 ( To the desired flow rate). That is, nitrogen (N2) supplied from the outside is throttled to the second flow rate R2 by the second capillary 7 and further throttled to the third flow rate R3 smaller than the second flow rate R2 by the third capillary 8.

  The second flow meter 9 is an overflow type flow type gas flow meter connected to the outlet of the second capillary 7, that is, the inlet of the third capillary 8. Set the pressure to atmospheric pressure.

The thermostatic chamber 10 is a temperature adjusting device that houses the first capillary 5 and the third capillary 8 and maintains the environmental temperature of the first capillary 5 and the third capillary 8 at a preset temperature. Here, the first capillary 5, the third capillary 8, and the thermostatic chamber 10 take in nitrogen (N ₂ ) as a diluent gas, and set the flow rate of the nitrogen (N ₂ ) and the flow rate of the sample gas taken in separately as desired flow rates. The flow rate adjusting means for adjusting the flow rate respectively.

The gas mixer 11 stirs and mixes the sample gas whose flow rate has been adjusted by the first capillary 5 and nitrogen (N ₂ ) whose flow rate has been adjusted by the third capillary 8 to generate a regulated gas. In FIG. 1, the outlet of the first capillary 5 and the outlet of the third capillary 8 are connected by a trifurcated pipe and then connected to the inlet of the gas mixer 11. The adjustment gas is generated by the pipe and the gas mixer 11. Such a gas mixer 11, more precisely, a three-pronged pipe and the gas mixer 11 is a gas mixing means in the present embodiment. By providing the two inlets to the gas mixer 11, the sample gas and nitrogen (N ₂₎ to the gas mixer 11 and may also be supplied individually and directly.

Here, the mixing ratio of the sample gas and nitrogen (N ₂ ) in such a gas mixing means is theoretically determined by the first flow rate R1 of the first capillary 5 and the third flow rate R3 of the third capillary 8. The Such a mixing ratio is an amount corresponding to the dilution ratio of the sample gas with nitrogen (N ₂ ).

The suction pump 12 is a pump that operates under the control of the control calculation unit 36, and sucks the adjustment gas generated by the gas mixer 11. More precisely, the sample gas is sucked from the first capillary 5 to the gas mixer 11 and nitrogen (N ₂ ) is sucked from the third capillary 8 to the gas mixer 11 by the suction force exerted by the suction pump 12. The adjustment gas is generated in the gas mixer 11. The suction pump 12 supplies the adjustment gas sucked from the gas mixer 11 to the third flow meter 13 and the inlet of the measurement unit A2.

  The third flow meter 13 is an overflow type float gas flow meter connected to the discharge port of the suction pump 12, that is, the inlet of the measuring unit A2. The third flow meter 13 sets the pressure at the discharge port of the suction pump 12 and the inlet of the measurement unit A2 to atmospheric pressure.

On the other hand, the measurement unit A2 calculates the dilution rate KR of the sample gas in the dilution unit A1 based on the adjustment gas generated in the dilution unit A1 and the dilution gas (nitrogen (N ₂ )) separately supplied via the dilution unit A1. This is a functional component that calculates and measures the nitrogen oxide concentration of the sample gas based on the dilution factor KR and the nitrogen oxide concentration of the adjustment gas separately detected. Since the nitrogen oxide (NO _x ) in the adjustment gas is pretreated by the dilution unit A1 so as to be within the concentration measurement range of the measurement unit A2, the measurement unit A2 stabilizes the nitrogen oxide concentration of the adjustment gas. Can be measured accurately and accurately.

As shown in FIG. 1, the measuring unit A2 includes the second SP pump 14, the second dehumidifier 15, the fourth flow meter 16, the second drain pot 17, the third drain pot 18, the fourth capillary 19, and the main Converter 20 (reduction means), detour path 21, first three-way valve 22 (second selection means), second three-way valve 23, first activated carbon tank 24, fifth capillary 25, third three-way valve 26 (selection means) , Fifth flow meter 27, ozone generator 28, sixth capillary 29, NO _X detector 30 (nitrogen oxide concentration detecting means), O ₂ detector 31 (oxygen concentration detecting means), seventh capillary 32, ozone decomposition The apparatus 33, the 2nd activated carbon tank 34, the pressure reduction pump 35, the control calculating part 36 (calculation means), and the display part 37 are provided.

  The second SP pump 14 is a pump that operates under the control of the control calculation unit 36, and takes in the adjustment gas discharged from the suction pump 12 of the dilution unit A1 into the measurement unit A2. The second dehumidifier 15 is a device that removes the moisture of the adjustment gas supplied from the second SP pump 14 and the moisture of the air separately taken from the atmosphere. The second dehumidifier 15 supplies the adjusted gas from which moisture has been removed to the fourth flow meter 16, while supplying moisture separated from the adjusted gas to the second drain pot 17. The second dehumidifier 15 supplies air (dry air) from which moisture has been removed to the ozone generator 28, and supplies moisture separated from the air to the third drain pot 18.

  The fourth flow meter 16 measures the flow rate of the adjustment gas supplied from the second dehumidifier 15 and supplies it to the fourth capillary 19 and the first activated carbon tank 24. The second drain pot 17 is a container that stores a certain amount of water (water separated from the adjustment gas) supplied from the second dehumidifier 15 and discharges it to the outside. The third drain pot 18 is a container that stores a certain amount of water (water separated from air) supplied from the second dehumidifier 15 and discharges it to the outside.

The fourth capillary 19 is a capillary tube having a predetermined pipe diameter (flow path diameter) through which the adjustment gas supplied from the fourth flow meter 16 flows, and adjusts the flow rate of the adjustment gas to the fourth flow rate R4 to bypass the main converter 20 and the bypass. Supply to path 21. The main converter 20 is a second reduction unit that reduces nitrogen dioxide (NO ₂ ) in the sample gas that has not been reduced by the pre-converter 1. The main converter 20 converts all nitrogen dioxide (NO ₂ ) contained in the sample gas into nitrogen monoxide (NO) and supplies it to the first three-way valve 22.

  The bypass path 21 is a pipe provided to bypass the main converter 20 and supplies the adjustment gas to the first three-way valve 22 without passing through the main converter 20. The first three-way valve 22 is an electromagnetic valve that operates under the control of the control calculation unit 36 and selectively selects the adjustment gas supplied from the main converter 20 or the adjustment gas supplied from the bypass path 21. Supply to the second three-way valve 23.

The second three-way valve 23 is an electromagnetic valve that operates under the control of the control calculation unit 36, and is a flow path for supplying the adjustment gas (measurement target gas) supplied from the first three-way valve 22 to the NO _X detector 30. Alternatively, a flow path that bypasses the NO _X detector 30 is sequentially selected. The second three-way valve 23 is provided for causing the detected nitrogen oxide in the measurement target gas in a so-called flow chopping scheme concentration (NO _X) in the NO _X detector 30, a first period T1 which is set in advance in intermittently supplying the measurement target gas in the NO _X detector 30 by selecting the measurement object gas flow passage and the bypass flow path alternately.

The first activated carbon tank 24 is a gas type that becomes a disturbance component of the O ₂ detector 31 from the adjustment gas supplied from the fourth flow meter 16, that is, a nitrogen oxide (NO _X ) or O ₂ detector that exhibits strong positive magnetism. The mist that damages the gas 31 is removed, and the adjustment gas (the gas mainly composed of oxygen (O ₂ ) and nitrogen (N ₂ )) from which the gas species and the like as disturbance components are removed is supplied to the third three-way valve 26. Supply. The fifth capillary 25 is a capillary tube having a predetermined pipe diameter (flow path diameter) through which nitrogen (N ₂ ) supplied from the outside flows, and the third three-way is adjusted by adjusting the flow rate of nitrogen (N ₂ ) to the fifth flow rate R 5. Supply to valve 26.

The third three-way valve 26 is an electromagnetic valve that operates under the control of the control calculation unit 36, and is used as the adjustment gas (oxygen measurement gas) supplied from the first activated carbon tank 24 or the reference gas from the fifth capillary 25. The supplied nitrogen (N ₂ ) is sequentially selected and supplied to the O ₂ detector 31. The third three-way valve 26 is used to cause the O ₂ detector 31 to detect the concentration of oxygen (O ₂ ) in the oxygen measurement gas and the reference gas by a so-called flow chopping method, and is set in advance. By alternately selecting the oxygen measurement gas and the reference gas in the second period T2, the oxygen measurement gas and the reference gas are intermittently supplied to the O ₂ detector 31.

The fifth flow meter 27 is an overflow type float gas flow meter connected to the outlet of the fifth capillary 25, that is, one inlet of the third three-way valve 26. The fifth flow meter 27 sets the pressure at the outlet of the fifth capillary 25 and one inlet of the third three-way valve 26 to atmospheric pressure. The ozone generator 28 converts oxygen (O ₂ ) in the dry air supplied from the second dehumidifier 15 into ozone (O ₃ ). The sixth capillary 29 is a capillary tube having a predetermined pipe diameter (flow path diameter) through which dry air containing ozone (O ₃ ) supplied from the ozone generator 28 circulates, and adjusts the flow rate of the dry air to the sixth flow rate R6. And supplied to the NO _X detector 30.

The NO _X detector 30 determines the nitrogen oxide concentration in the adjustment gas (measurement target gas) supplied from the second three-way valve 23 based on the chemiluminescence method as a first NO _X concentration detection value (nitrogen oxide concentration detection value). and detects as to detect the concentration of nitrogen oxides when bypass the measurement target gas as a 2NO _X concentration detection value. That is, the NO _X detector 30 generates a mixed gas in which dry air containing ozone (O ₃ ) supplied from the sixth capillary 29 is mixed with the measurement target gas (regulated gas), and the mixed gas in the mixed gas The chemiluminescence intensity generated by the chemical reaction between nitric oxide (NO) and ozone (O ₃ ) is output as the first NO _X concentration detection value. Such NO _X detector 30 outputs to the control arithmetic unit 36 the the first 1NO _X concentration detected value and the 2NO _X concentration detected value as a density detection value related to the nitrogen oxide (NO _X).

Here, the chemiluminescence method is a concentration measurement method using a chemical reaction between nitric oxide (NO) and ozone (O ₃ ) as described above, and in principle, only the concentration of nitric oxide (NO) is used. It can be detected and the concentration of nitrogen dioxide (NO ₂ ) cannot be detected. Under such circumstances, the measurement apparatus according to the present embodiment includes the pre-converter 1 and the main converter 20 to reduce nitrogen dioxide (NO ₂ ) in the sample gas or the adjustment gas to nitrogen monoxide (NO). doing.

The O ₂ detector 31 detects the concentration of the adjustment gas (oxygen measurement gas) or the reference gas (nitrogen (N ₂ )) supplied from the third three-way valve 26 based on the magnetic force method. That is, the O ₂ detector 31 is formed by the oxygen (O ₂ ) having a strong magnetic susceptibility acting on _two glass spheres that are suspended at a certain distance and in which nitrogen is enclosed. The concentration of the adjustment gas (oxygen measurement gas) or the reference gas (nitrogen (N ₂ )) is detected by utilizing the phenomenon that the distance of the gas changes.

Such _{O 2} detector 31, adjusts gas oxygen in (oxygen measurement gas) _{(O 2)} concentration of oxygen _{(O 2} in (first oxygen concentration detection value) and the reference gas (nitrogen _(N 2)) ) (Second oxygen concentration detection value) is output to the control calculation unit 36. The seventh capillary 32 is a capillary tube having a predetermined tube diameter (channel diameter) through which the adjustment gas (oxygen measurement gas) or the reference gas (nitrogen (N ₂ )) discharged from the O ₂ detector 31 flows. The flow rates of the adjustment gas (oxygen measurement gas) and the reference gas are adjusted to the seventh flow rate R7.

The ozonolysis device 33 is for decomposing and detoxifying residual ozone (O ₃ ) in the mixed gas of the measurement target gas and the dry air discharged from the NO _X detector 30. The ozonolysis device 33 supplies a mixed gas obtained by decomposing residual ozone (O ₃ ) to the second activated carbon tank 34. The second activated carbon tank 34 removes residual nitric oxide (NO) from the mixed gas supplied from the ozonolysis device 33. The decompression pump 35 is a pump that operates under the control of the control calculation unit 36, and decompresses the mixed gas supplied from the second activated carbon tank 34 and releases it to the atmosphere.

The control calculation unit 36 samples the sample in the dilution unit A1 based on the first oxygen concentration detection value input from the O ₂ detector 31 every moment and the known oxygen concentration (raw gas oxygen concentration) in the sample gas (raw gas). by sequentially calculating a dilution ratio KR of the gas, also multiplying the dilution factor KR to the 1NO _X concentration detected value inputted every moment from the NO _X detector 30, before being diluted with a dilution unit A1 The nitrogen oxide (NO _x ) concentration (measurement target concentration D) in the sample gas is sequentially calculated. In addition, the control calculation unit 36 converts the dilution factor KR and the measurement target concentration D, which are sequentially calculated in time series, into measurement image data and outputs the measurement image data to the display unit 37.

  Further, the control calculation unit 36 controls the entire operation of the measuring device, and the first SP pump 3, the suction pump 12, the second SP pump 14, the decompression pump 35, and the first to third three-way valves 22, 23, 26. To control the operation. The display unit 37 displays the measurement image data input from the control calculation unit 36 as a two-dimensional image.

  Next, the operation of the measuring apparatus configured as described above will be described in detail with reference to FIG.

In the dilution unit A1, when the first SP pump 3 starts operating under the control of the control calculation unit 36, the sample gas is taken into the pre-converter 1 from an external sample gas supply source (not shown), and is contained in the sample gas. Most of the nitrogen dioxide (NO ₂ ) is reduced to nitric oxide (NO). Then, the sample gas that has been subjected to such a reduction process has its moisture removed by the first dehumidifier 2 and flows into the first SP pump 3.

Even if the sample gas flowing into the first SP pump 3 in this way contains nitrogen dioxide (NO ₂ ), which is a kind of nitrogen oxide (NO _X ), most of it is converted into nitric oxide (NO). Since it is reduced, the content of nitrogen dioxide (NO ₂ ) is significantly lower than the sample gas (raw gas) taken from the sample gas supply source.

In the dilution unit A1, the suction pump 12 starts operating simultaneously with the first SP pump 3 under the control of the control calculation unit 36. As a result, the sample gas discharged from the first SP pump 3 flows into the first capillary 5 and the flow rate is adjusted to the first flow rate R1. When the suction pump 12 starts operating, nitrogen (N ₂ ) flows from the external dilution gas supply source (not shown) into the third capillary 8 and the flow rate is adjusted to the third flow rate R3.

The sample gas whose flow rate is adjusted to the first flow rate R1 by the first capillary 5 is diluted by being mixed with nitrogen (N ₂ ) whose flow rate is adjusted to the third flow rate R3 by the third capillary 8, but the nitrogen gas is diluted. The dilution rate of the sample gas by (N ₂ ) depends exclusively on the first flow rate R 1 of the first capillary 5 and the third flow rate R 3 of the third capillary 8.

  Here, for example, when the dilution rate of the sample gas is set to 10 times, the third flow rate R3 is set to 9 times the first flow rate R1. That is, a capillary having a flow rate nine times that of the first capillary 5 is selected as the third capillary 8. However, the first flow rate R1 and the third flow rate R3 can vary depending on the environmental temperature of the first capillary 5 and the third capillary 8.

  For this reason, in the present embodiment, the first capillary 5 and the third capillary 8 are accommodated in the thermostat 10 to maintain the environmental temperature at a constant temperature. The constant temperature bath 10 maintains the environmental temperature of the first capillary 5 and the third capillary 8 at, for example, 45 ° (constant), thereby minimizing fluctuations in the first flow rate R1 and the third flow rate R3. Minimize sample gas dilution factor fluctuations.

In the present embodiment, the first flow meter 6 is connected to the inlet of the first capillary 5, and the second flow meter 9 is connected to the inlet of the third capillary 8, so that the first capillary 5 is connected to the inlet of the first capillary 5. The pressure of the sample gas and the pressure of nitrogen (N ₂ ) at the inlet of the third capillary 8 are made constant at atmospheric pressure. This also minimizes fluctuations in the first flow rate R1 and the third flow rate R3, and thus minimizes fluctuations in the dilution rate of the sample gas.

The sample gas diluted at a desired dilution ratio with nitrogen (N ₂ ) in this way is agitated by the gas mixer 11 so as to be mixed with nitrogen (N 2) without any bias and from the suction pump 12. It is discharged to the measurement unit A2. Further, since the third flow meter 13 is connected to the discharge port of the suction pump 12, the discharge pressure is made constant at atmospheric pressure.

  The operation of the dilution unit A1 has been described above. The adjustment gas discharged from the suction pump 12 is taken into the measurement unit A2 by the second SP pump 14 of the measurement unit A2. That is, the adjusted gas is supplied to the second dehumidifier 15 by the operation of the second SP pump 14 under the control of the control calculation unit 36, moisture is removed, and the flow rate is measured by the fourth flow meter 16. Later, it is supplied to the fourth capillary 19.

The adjustment gas is adjusted to the fourth flow rate R4 in the fourth capillary 19 and then supplied to the input of the main converter 20 and one end of the bypass path 21. The adjustment gas supplied to the main converter 20 is supplied to the first three-way valve 22 after the nitrogen dioxide (NO ₂ ) in the adjustment gas is reduced in the main converter 20. On the other hand, the adjustment gas supplied to one end of the bypass path 21 is supplied to the first three-way valve 22 without any processing.

Here, when the adjustment gas (that is, the sample gas) contains nitrogen dioxide (NO ₂ ), the control calculation unit 36 controls the first three-way valve 22 so as to select the adjustment gas supplied from the main converter 20, On the other hand, when the adjustment gas does not contain nitrogen dioxide (NO ₂ ), that is, when the adjustment gas contains only nitrogen monoxide (NO) as nitrogen oxide (NO _X ), the adjustment gas supplied from the bypass path 21. The first three-way valve 22 is controlled so as to select. However, in any case, the adjustment gas supplied from the first three-way valve 22 to the second three-way valve 23 contains only nitrogen monoxide (NO) as nitrogen oxides (NO _x ). Such adjustment gas (measurement target gas) is alternately selected in the second three-way valve 23 and the flow path bypassing the NO _X detector 30 in the first period T1 and supplied to the NO _X detector 30.

On the other hand, in the measurement unit A2, dry air is generated by removing moisture from the air taken in from the atmosphere by the second dehumidifier 15, and the dry air is supplied to the ozone generator 28. Oxygen (O ₂ ) in the dry air is converted into ozone (O ₃ ) in the ozone generator 28, and the flow rate is adjusted to the sixth flow rate R 6 in the sixth capillary 29 and supplied to the NO _X detector 30. The

In the NO _X detector 30, dry gas containing ozone (O ₃ ) is mixed with the adjustment gas (measurement target gas) that is intermittently input in the first period T 1 to generate a mixed gas, and the adjustment gas ( nitrogen oxides of the measurement target gas) in (NO _X) that concentration and ozone _{(O 3)} nitrogen oxides only in the gas dry air containing nitrogen monoxide (NO) (NO _X) that is nitrogen monoxide (NO ) Are detected alternately. Then, NO _X detector 30, the control arithmetic unit 36, and a second 2NO _X concentration detected value to gas only dry air including first 1NO _X density detection value and the ozone regarding the measurement target gas _{(O 3)} a The signals are alternately output in one cycle T1.

The mixed gas whose nitrogen oxide (NO _X ) concentration has been detected by the NO _X detector 30 is decomposed by residual ozone (O ₃ ) by the ozone decomposer 33, and then the nitrogen oxide ( NO _X) are adsorbed and removed. The mixed gas after passing through the ozonolysis device 33 and the second activated carbon tank 34 sufficiently satisfies the environmental standards for atmospheric release, and is released into the atmosphere after being decompressed by the decompression pump 35. Is done.

On the other hand, a part of the adjustment gas output from the fourth flow meter 16 damages the nitrogen oxide (NO _x ) and the O ₂ detector 31 which are disturbance components of the O ₂ detector 31 in the first activated carbon tank 24. The supplied mist is removed and then supplied to the third three-way valve 26. Separately, nitrogen (N ₂ ) is supplied to the measurement unit A2 from an external dilution gas supply source. This nitrogen (N ₂ ) is a comparison gas (reference gas) when the O ₂ detector 31 detects the concentration of oxygen (O ₂ ) in the adjustment gas (oxygen measurement gas), and the fifth capillary 25, the flow rate is adjusted to the fifth flow rate R5 and then supplied to the third three-way valve 26.

The adjustment gas (oxygen measurement gas) supplied from the first activated carbon tank 24 and the nitrogen (N ₂ ) (reference gas) supplied from the fifth capillary 25 are supplied to the second cycle by the third three-way valve 26. They are alternately selected at T ₂ and supplied to the O ₂ detector 31. That, _{O 2} detector 31, in parallel with the acquisition of the first 1NO _X concentration detected value and the 2NO _X concentration detected value of NO _X detector 30, in the conditioning gas (oxygen measurement gas) in the second period T2 The oxygen concentration and the oxygen concentration in nitrogen (N ₂ ) are detected alternately, and the first oxygen concentration detection value and the second oxygen concentration detection value are alternately output to the control calculation unit 36.

Here, nitrogen (N 2) supplied from the dilution gas supply source does not essentially contain oxygen (O ₂ ). Therefore, when the oxygen concentration in nitrogen (N ₂ ) as the reference gas is detected by the O ₂ detector 31, the concentration detection value is “zero”.

The adjustment gas or nitrogen (N ₂ ) in which the oxygen concentration is detected by the O ₂ detector 31 in this way is adjusted to the seventh flow rate R 7 by the seventh capillary 32 and then reduced by the pressure reducing pump 35. Released into the atmosphere.

On the other hand, the control calculation unit 36 performs the dilution unit A1 based on the first oxygen concentration detection value input from the O ₂ detector 31 and the known oxygen concentration (raw gas oxygen concentration) in the sample gas (raw gas). The dilution factor KR in the dilution of the sample gas with broken nitrogen (N ₂ ) is calculated. That is, air in the atmosphere contains about 21% oxygen, and the oxygen concentration in such an atmosphere can be considered as a known constant value that does not fluctuate. In contrast, the adjustment gas (oxygen measurement gas) input to the O ₂ detector 31 has an oxygen concentration corresponding to the degree of dilution with nitrogen (N ₂ ) performed in the dilution unit A1, that is, the dilution factor KR. Become. Therefore, the control calculation unit 36 dilutes as a ratio between the oxygen concentration (original gas oxygen concentration) of the air that is the carrier gas of the sample gas (raw gas) and the first oxygen concentration detection value input from the O ₂ detector 31. The magnification KR is calculated.

Here, FIG. 2 shows the relationship between the O ₂ concentration (vol% degree) in the sample gas after dilution with nitrogen (N ₂ ) and the dilution factor KR, and the O ₂ concentration (vol. %), That is, a characteristic diagram showing, as a parameter, the O ₂ concentration (vol%) of the sample gas supplied from the external sample gas supply source to the dilution section A1. As shown in this characteristic diagram, the O ₂ concentration (vol% degree) in the diluted sample gas is inversely proportional to the dilution factor KR. That is, the O ₂ concentration (vol% degree) in the diluted sample gas decreases as the dilution factor KR increases.

As a basic principle when detecting a physical quantity, the smaller the detected quantity, the lower the ratio of errors contained in the detected quantity, that is, the detection accuracy. In other words, enough first oxygen concentration sensing value in the O ₂ detector 31 is small, the error (dilution magnification error) increases the dilution ratio KR is calculated as described above, the detection range of the O ₂ detector 31 It is necessary to set the target dilution rate in the dilution part A1, that is, the ratio between the first flow rate R1 and the third flow rate R3, considering the balance of the dilution magnification error.

In the case of a sample gas (for example, a nitrogen oxide-containing gas using air as a carrier gas) containing oxygen (O ₂ ) to the same extent (about 21%) as the atmosphere (air) as in this embodiment, dilution is performed. Even if the sample gas (original gas) is diluted to about 20 times in the part A1, the dilution factor KR can be calculated with sufficient accuracy.

In this manner, when calculating the dilution factor KR in the dilution part A1, the control calculation unit 36, originally contained in the sample gas by multiplying the first 1NO _X concentration detected value to the dilution factor KR (crude gas) nitrogen The concentration of oxide (NO _x ) (measurement target concentration D) is calculated. Such dilution factor KR and measurement target concentration D are repeatedly calculated in time series by the control calculation unit 36 and are taken into the measurement image data. That is, the display unit 37, every moment the dilution factor KR and the measurement target density D obtained in real time, also the 1NO _X concentration detected value is the raw data as necessary, the 2NO _X concentration detected value, the first oxygen The concentration detection value and the second oxygen concentration detection value are displayed as time series data.

According to the present embodiment, nitrogen (N ₂ ) that does not contain oxygen is used as the dilution gas, and the sample gas (original gas) is diluted with the nitrogen (N ₂ ). Since the oxygen concentration (first oxygen concentration detection value) is acquired in parallel with the concentration of nitrogen oxide (NO _x ) in the adjustment gas (measurement target concentration D), the sample gas (raw gas) is nitrogen (N ₂ ). The dilution factor KR can be acquired in parallel when the measurement target concentration D is obtained by diluting with (1). Therefore, according to the present embodiment, it is possible to acquire the measurement target concentration D with higher accuracy than before.

  According to the present embodiment, since the first capillary 5 and the third capillary 8 are employed as the flow rate adjusting means, the cost can be reduced as compared with the case where, for example, two mass flow controllers are employed. In addition, since the first capillary 5 and the third capillary 8 are accommodated in the thermostat 10, the first flow rate R1 and the third flow rate R3 can be stabilized. Further, since the third three-way valve 26 is provided as the selection means, an abnormality in the first oxygen concentration detection value can be easily recognized by comparison with the second oxygen concentration detection value.

Further, since the main converter 20 as the reduction means, the bypass path 21 and the first three-way valve 22 as the second selection means are provided, not only the sample gas (raw gas) containing only nitric oxide (NO) but also the dioxide dioxide. The measurement target concentration D can also be obtained for a sample gas (raw gas) containing nitrogen (NO ₂ ). Furthermore, since inexpensive nitrogen (N ₂ ) is used as the diluent gas among the inert gases, the running cost can be reduced.

In addition, this invention is not limited to said each embodiment, For example, the following modifications can be considered.
(1) As described above, a sample gas containing oxygen (O ₂ ) to the same extent (about 21%) as the atmosphere (air) (for example, nitrogen oxide using air as a carrier gas of nitrogen oxide (NO _x )) In the case of the contained gas), the dilution factor KR can be calculated with sufficient accuracy even if the sample gas (original gas) is diluted to about 20 times. However, when the concentration of oxygen (O ₂ ) contained in the nitrogen oxide-containing gas is lowered, the concentration of oxygen (O ₂ ) contained in the adjustment gas is also lowered, so that an oxygen concentration detection error in the O ₂ detector 31 is increased. As a result, the error (dilution factor error) of the dilution factor KR calculated by the control calculation unit 36 increases.

  For such a situation, it is conceivable to devise the device configuration as shown in FIG. That is, this measuring device is obtained by adding a third activated carbon tank 38, a fourth three-way valve 39, and a fifth three-way valve 40 to the measuring device shown in FIG. Prepare.

The first flow meter 6 in the dilution unit A3 supplies the sample gas supplied from the first SP pump 3 to the third activated carbon tank 38 provided in the measurement unit A4. The third activated carbon tank 38 removes nitrogen oxide (NO _X ) that becomes a disturbance component of the O ₂ detector 31 and mist that damages the O ₂ detector 31 from the sample gas supplied from the first flow meter 6. The sample gas (oxygen measurement gas) from which the nitrogen oxide (NO _X ) has been removed is supplied to the fourth three-way valve 39. The fourth three-way valve 39 is provided at the outlet of the third activated carbon tank 38, while the fifth three-way valve 40 is provided at the outlet of the first activated carbon tank 24.

The fourth three-way valve 39 and the fifth three-way valve 40 as described above are controlled by the control calculation unit 36, thereby adjusting gas (oxygen measurement gas) supplied from the first activated carbon tank 24 or the third activated carbon tank 38. The sample gas (oxygen measurement gas) supplied from is alternately output to the third three-way valve 26 at the third period T3. The third three-way valve 26 alternately selects such adjustment gas (oxygen measurement gas) or sample gas (oxygen measurement gas) and nitrogen (N ₂ ) input from the fifth capillary 25 at the second period T2. Thus, the adjustment gas (oxygen measurement gas), the sample gas (oxygen measurement gas), or nitrogen (N ₂ ) (reference gas) is alternately supplied to the O ₂ detector 31.

That is, in the measuring apparatus of FIG. 3, the O ₂ detector 31 sets each oxygen concentration of the adjusting gas (oxygen measuring gas), nitrogen (N 2) (reference gas) or sample gas (oxygen measuring gas) in a predetermined order. Detect alternately with. As a result, the control calculation unit 36 detects the first oxygen concentration detection value indicating the oxygen concentration of the adjustment gas (oxygen measurement gas) and the second oxygen concentration detection indicating the oxygen concentration of nitrogen (N ₂ ) (reference gas). In addition to the value, a third oxygen concentration detection value indicating the oxygen concentration of the sample gas (oxygen measurement gas) is input. In this measuring apparatus, the third oxygen concentration detection value is displayed on the display unit 37 as time series data in addition to the dilution factor KR.

According to the measurement apparatus according to such a modification, the oxygen concentration is higher than that of the adjustment gas (oxygen measurement gas) used for calculation of the dilution factor KR before being diluted with nitrogen (N ₂ ) (dilution gas). Since the third oxygen concentration detection value indicating the oxygen concentration of the sample gas (oxygen measurement gas) that is higher by the dilution factor KR is displayed as time-series data on the display unit 37, the fluctuation monitoring of the dilution factor KR is better monitored. Is possible. According to this measuring apparatus, even for a sample gas (raw gas) containing, for example, about 10 (vol%) oxygen (O ₂ ), the fluctuation of the dilution factor KR can be accurately monitored.

(2) In each of the above embodiments, the main converter 20 is provided as a reducing means. However, when the sample gas (raw gas) contains only nitrogen monoxide (NO) as nitrogen oxide (NO _X ), the main converter 20 is provided. The bypass 20 and the second three-way valve 23 may be directly connected by omitting the converter 20 (reduction means) and the first three-way valve 22. When the sample gas (raw gas) contains nitrogen dioxide (NO ₂ ), the bypass path 21 and the first three-way valve 22 are omitted, and the outlet of the main converter 20 (reducing means) is connected to the second three-way valve 23. You may connect directly to.

(3) In each of the above embodiments, by providing the third three-way valve 26 as the selection means, the oxygen concentration of nitrogen (N ₂ ) is detected as the reference concentration in addition to the oxygen concentration of the adjustment gas (oxygen measurement gas). However, the third three-way valve 26 (selection means) may be deleted to detect only the oxygen concentration of the adjustment gas (oxygen measurement gas).

A1 dilution part A2 measurement part 1 pre-converter 2 first dehumidifier 3 first SP pump 4 first drain pot 5 first capillary (flow rate adjusting means, first capillary tube)
6 First flow meter 7 Second capillary 8 Third capillary (flow rate adjusting means, second capillary tube)
9 Second flow meter 10 Constant temperature bath 11 Gas mixer (gas mixing means)
Reference Signs List 12 Suction pump 13 Third flow meter 14 Second SP pump 15 Second dehumidifier 16 Fourth flow meter 17 Second drain pot 18 Third drain pot 19 Fourth capillary 20 Main converter (reducing means)
21 detour route 22 first three-way valve (second selection means)
23 second three-way valve 24 first activated carbon tank 25 fifth capillary 26 third three-way valve (selection means)
27 Fifth flow meter 28 Ozone generator 29 Sixth capillary 30 NO _X detector (nitrogen oxide concentration detection means)
31 O ₂ detector (oxygen concentration detection means)
32 7th capillary 33 Ozone decomposer 34 2nd activated carbon tank 35 Depressurization pump 36 Control calculation part (calculation means)
37 Display unit 38 Third activated carbon tank 39 Fourth three-way valve 40 Fifth three-way valve

Claims (6)

A nitrogen oxide concentration measuring device for measuring a nitrogen oxide concentration by diluting a nitrogen oxide-containing gas with a predetermined dilution gas,
A flow rate adjusting means that takes in an inert gas as the dilution gas, and adjusts the flow rate of the inert gas and the flow rate of the nitrogen oxide-containing gas separately taken to a desired flow rate, respectively;
Gas mixing means for generating a regulated gas by mixing the nitrogen oxide-containing gas and the dilution gas whose flow rate has been adjusted by the flow rate adjusting means;
Nitrogen oxide concentration detecting means for detecting the nitrogen oxide concentration of the adjustment gas;
Oxygen concentration detecting means for detecting the oxygen concentration of the adjustment gas;
Based on the oxygen concentration detection value in the oxygen concentration detection means, the known oxygen concentration of the nitrogen oxide-containing gas, and the nitrogen oxide concentration detection value in the nitrogen oxide concentration detection means, the nitrogen oxide by the inert gas A calculation means for calculating a dilution ratio of the contained gas and a nitrogen oxide concentration of the nitrogen oxide-containing gas ;
A nitrogen oxide concentration measuring apparatus comprising: a selecting unit that sequentially selects the adjustment gas or the inert gas and supplies the oxygen gas to the oxygen concentration detecting unit .   2. The nitrogen oxide concentration measuring apparatus according to claim 1, wherein the flow rate adjusting unit includes a first capillary through which the nitrogen oxide-containing gas flows and a second capillary through which the inert gas flows. .   The nitrogen oxide concentration measuring apparatus according to claim 1 or 2, wherein the flow rate adjusting means includes a thermostatic bath. The selection means sequentially selects and supplies the nitrogen oxide-containing gas before being diluted with the dilution gas to the oxygen concentration detection means in addition to the adjustment gas or the inert gas. The nitrogen oxide concentration measuring apparatus according to any one of Items 1 to 3. Reducing means for reducing nitrogen dioxide contained in the nitrogen oxide-containing gas to nitric oxide;
A detour route that detours the return means;
A second selection means for alternatively selecting the return means or the detour path;
The nitrogen oxide concentration measuring device according to any one of claims 1 to 4, further comprising: The nitrogen oxide concentration measuring device according to any one of claims 1 to 5 , wherein the inert gas is nitrogen .

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