JP2007333405A - Nox measuring instrument and nox measurement method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an inexpensive NOx measuring instrument that is easy to maintain, and accurately detecting the concentration of nitrogen oxide in a gas to be detected, by excluding, especially the effect of ammonia or urea, even if a low-cost zirconia NOx sensor is used, and to provide an NOx measuring method. <P>SOLUTION: The NOx measuring instrument is adapted to a denitration apparatus, which is constituted so as to reduce nitrogen oxide in an exhaust gas G by injecting ammonia or nitrogen into an exhaust gas G and passing this exhaust gas G through a denitration catalyst, to detect the concentration of nitrogen oxide remaining in the exhaust gas G discharged from the denitration apparatus and equipped with a cooler 7 for cooling the exhaust gas G into condensed moisture in the exhaust gas G and the zirconia NOx sensor 11 for supplying the exhaust gas G, after the condensed moisture has been removed by the cooler 7, to detect the concentration of nitrogen oxide in the exhaust gas G. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a NOx measuring device and a NOx measuring method for detecting nitrogen oxides (NOx). In particular, it is used with a denitration device that reduces nitrogen oxides using ammonia or urea water as a reducing agent, and the concentration of nitrogen oxides remaining in the exhaust gas from the denitration device is adjusted to the ammonia or urea injected as the reducing agent. The present invention relates to a NOx measuring device and a NOx measuring method for detecting with a zirconia type NOx sensor without being affected.

  Conventionally, there are an atmospheric pressure type chemiluminescent type and a zirconia type as NOx sensors.

  However, the chemiluminescent NOx sensor has a complicated measurement principle and apparatus, requires one million yen, and is expensive. Moreover, it is inconvenient because the calibration work using the calibration gas needs to be performed frequently. On the other hand, although the zirconia-type NOx sensor is inexpensive, there is a problem that ammonia is erroneously measured as nitrogen oxide by the measurement principle. Therefore, it is difficult to accurately measure the concentration of nitrogen oxides remaining in the exhaust gas from the denitration device, particularly when used with a denitration device that reduces nitrogen oxides using ammonia or urea water as a reducing agent. there were.

  The problem to be solved by the present invention is to provide a NOx measuring device and a NOx measuring method which are inexpensive, easy to maintain and accurately detect nitrogen oxides. In particular, an object of the present invention is to provide a NOx measuring device and a NOx measuring method capable of accurately detecting the nitrogen oxide concentration in a detection gas by removing the influence of ammonia and urea even if a zirconia type NOx sensor is used.

  The present invention has been made to solve the above-mentioned problems, and the invention according to claim 1 uses a NOx sensor for detecting a nitrogen oxide concentration that is affected by ammonia or urea, but in a detection gas. Is a device that detects the concentration of nitrogen oxides in the detection gas while removing the influence of ammonia or urea contained in the gas, and condenses and removes moisture from the detection gas, and the detection gas after the moisture removal is The NOx measuring device is characterized in that it is supplied to a NOx sensor to detect a nitrogen oxide concentration.

  According to the first aspect of the present invention, by condensing moisture in the detection gas, ammonia or urea in the detection gas can be dissolved in the condensed water. And after removing such condensed water, the exact concentration measurement which excluded the influence of ammonia or urea is attained by detecting a nitrogen oxide density | concentration with a NOx sensor.

  The invention according to claim 2 is applied to a denitration apparatus that reduces nitrogen oxides in exhaust gas with a denitration catalyst while injecting ammonia or urea water into the exhaust gas as a reducing agent, and is discharged from the denitration apparatus. A device for detecting the concentration of nitrogen oxides remaining in the exhaust gas, a cooler that condenses moisture in the exhaust gas by cooling the exhaust gas, and an exhaust gas from which moisture condensed by the cooler has been removed. A NOx measuring device comprising a zirconia-type NOx sensor that is supplied and detects the concentration of nitrogen oxides in the exhaust gas.

  According to the invention of claim 2, by condensing moisture in the exhaust gas, ammonia or urea in the exhaust gas can be dissolved in the condensed water. And after removing such condensed water, even if it is a zirconia type NOx sensor, accurate concentration measurement which excluded the influence of ammonia or urea is possible by detecting nitrogen oxide concentration with a NOx sensor. Become. Therefore, even when used with a denitration device that reduces nitrogen oxides using ammonia or urea water as a reducing agent, the concentration of nitrogen oxides remaining in the exhaust gas from the denitration device can be accurately measured.

  According to a third aspect of the present invention, the cooler is configured such that a coiled pipe through which exhaust gas is passed is air-cooled or water-cooled, and the exhaust gas from the coiled pipe is supplied into a hollow tank. The exhaust gas from which condensed water is separated in a tank is supplied from the hollow tank to the NOx sensor via a metering pump.

  According to the third aspect of the present invention, the moisture from the exhaust gas can be condensed smoothly and easily by passing the exhaust gas through the coiled pipe that is air-cooled or water-cooled. Then, after discarding the condensed water in the hollow tank, the exhaust gas is supplied to the NOx sensor via the metering pump, thereby enabling more accurate concentration measurement.

  According to a fourth aspect of the present invention, water is stored in the hollow tank, and exhaust gas is ejected from the upper surface of the hollow tank toward the NOx sensor while water is ejected into the surface of the stored water or into the water. The NOx measuring device according to claim 3, wherein the NOx measuring device is provided.

  According to the fourth aspect of the present invention, it is possible to more reliably dissolve ammonia or urea in the exhaust gas into the water by ejecting the exhaust gas into the water surface or into the water.

  According to a fifth aspect of the present invention, in the NOx measuring device according to the third or fourth aspect, the hollow tank includes a cooling fin and is capable of draining a predetermined amount or more of condensed water. is there.

  According to invention of Claim 5, exhaust gas and condensed water can be aimed at by a cooling fin. Further, when a predetermined amount or more of water accumulates in the hollow tank, it can be automatically discharged.

  The invention according to claim 6 is a NOx measurement characterized by detecting the concentration of nitrogen oxide in the detection gas from which ammonia or urea contained in the detection gas has been dissolved in water and then the water has been removed. Is the method.

  According to the invention described in claim 6, after the ammonia or urea in the detection gas is dissolved in water and removed, the nitrogen oxide concentration is detected, thereby accurately measuring the concentration without the influence of ammonia or urea. Is possible.

  Furthermore, the invention described in claim 7 is a denitration apparatus that reduces nitrogen oxides in exhaust gas with a denitration catalyst while injecting ammonia or urea water into the exhaust gas as a reducing agent. A method for detecting the concentration of nitrogen oxides remaining in exhaust gas, wherein the concentration of moisture in the exhaust gas is attempted by cooling the exhaust gas, and then the concentration of nitrogen oxide in the exhaust gas from which the condensed water has been removed is measured as a zirconia NOx sensor. It is a NOx measuring method characterized by detecting by.

  According to the invention described in claim 7, by condensing moisture in the exhaust gas, ammonia or urea in the exhaust gas can be dissolved in the condensed water. And after removing such condensed water, even if it is a zirconia type NOx sensor, accurate concentration measurement which excluded the influence of ammonia or urea is possible by detecting nitrogen oxide concentration with a NOx sensor. Become. Therefore, even when used with a denitration device that reduces nitrogen oxides using ammonia or urea water as a reducing agent, the concentration of nitrogen oxides remaining in the exhaust gas from the denitration device can be accurately measured.

  According to the NOx measuring device and the NOx measuring method of the present invention, it is possible to detect nitrogen oxides at low cost, with easy maintenance, and accurately. In particular, even if a zirconia-type NOx sensor is used, it is possible to provide a NOx measurement device and a NOx measurement method that can accurately detect the nitrogen oxide concentration in the detection gas by eliminating the influence of ammonia and urea.

  Next, embodiments of the NOx measuring device and the NOx measuring method according to the present invention will be described. Although this measuring device and measuring method uses an inexpensive NOx sensor that is susceptible to the effects of ammonia and urea, it eliminates the effects of ammonia and urea contained in the detection gas and is originally included in the detection gas. The concentration of nitrogen oxides can be measured accurately. The present invention is characterized in that moisture is condensed and removed from the detection gas, and the detection gas after the moisture is removed is supplied to the NOx sensor to detect the nitrogen oxide concentration. As described above, when the moisture in the detection gas is condensed, ammonia and urea in the detection gas dissolve in the condensed water. When the condensed water is separated and removed from the exhaust gas, ammonia and urea are removed from the exhaust gas. Therefore, the exhaust gas from which ammonia and urea are removed is sent to the NOx sensor to detect the NOx value. This makes it possible to accurately measure the NOx concentration without the influence of ammonia or urea.

  Further, in a boiler or the like, nitrogen and oxygen in the air react to generate NOx by burning at a high temperature and high pressure, and therefore a denitration device is additionally provided to remove this NOx. This denitration apparatus injects ammonia or urea water into the exhaust gas as a reducing agent, passes the exhaust gas injected with the reducing agent through the denitration catalyst, and reduces and removes NOx in the exhaust gas. However, when ammonia or urea water is used as a reducing agent as in this denitration apparatus, it is easily affected by ammonia or urea. For example, when the residual NOx concentration contained in the exhaust gas from the denitration apparatus is examined using an inexpensive zirconia type NOx sensor, the NOx sensor makes an erroneous measurement. Therefore, the present invention can be applied to the above-described denitration apparatus to eliminate the influence of ammonia and urea water injected into the exhaust gas as a reducing agent, and to accurately measure only NOx originally contained in the exhaust gas. It is a thing.

  The denitration device is provided, for example, in a path of exhaust gas from combustion equipment provided in a generator, and a reducing agent injector for injecting a nitrogen oxide reducing agent into the exhaust gas, and the reducing agent is injected by the reducing agent injector. And a denitration reactor loaded with a denitration catalyst for reducing nitrogen oxides in the exhaust gas. Then, a reducing agent is injected from the injector into the exhaust gas discharged from the combustion equipment, and this reducing agent reacts with NOx in the exhaust gas in the denitration reactor, and NOx is decomposed into nitrogen and water and rendered harmless. The As the denitration catalyst loaded in the denitration reactor, for example, a vanadium or tungsten catalyst is preferably used. This denitration catalyst can promote the reaction between the reducing agent and NOx in the exhaust gas. As the reducing agent injector, for example, a stroke type pump is used, and a nozzle is attached to the discharge side tip of the pump, and the reducing agent is injected into the exhaust gas from the nozzle.

  The measuring device used in the above denitration apparatus is a cooler that cools the exhaust gas and condenses the moisture contained therein, a hollow tank and a metering pump provided downstream thereof, and nitrogen oxidation in the exhaust gas that has passed through these And a NOx sensor for measuring the concentration of the substance. At this time, a zirconia type made of zirconia ceramic is used as the NOx sensor.

  In the measurement device, a part of the exhaust gas that has passed through the denitration device is taken in by driving the metering pump, sent to the cooler, cooled when passing through this, and moisture (water vapor) contained in the exhaust gas is condensed. Is done. At this time, since ammonia and urea water used as the reducing agent are water-soluble, they are dissolved in the water condensed by cooling with the cooler. And it is sent to the hollow tank from the said cooler, and gas-liquid separation is carried out here, The condensed water in which the liquid, ie, ammonia, and urea dissolved, is stored in the said tank. On the other hand, the exhaust gas from which the gas, that is, the condensed water including ammonia and urea water has been removed, is sent from the hollow tank to the NOx sensor via the metering pump. The concentration is measured.

  As the cooler, an air-cooled or water-cooled coiled pipe is used. By passing the exhaust gas through the pipe, the moisture contained in the exhaust gas is condensed smoothly and easily. And after separating condensed water in the said hollow tank, it sends to the said zirconia-type NOx sensor through a metering pump, and the exact density | concentration measurement of the nitrogen oxide which remains in waste gas is performed.

  The hollow tank is preferably provided with a number of cooling fins on the outer peripheral wall. If it does in this way, the exhaust gas and condensed water which are sent to the said tank by the cooling fin will be cooled, and ammonia and urea injected as a reducing agent will be removed more reliably, and accurate NOx measurement can be performed. Further, it is preferable that an overflow pipe is attached to the hollow tank, and when a predetermined amount or more of condensed water is accumulated in the tank, this is discharged to the outside.

  Furthermore, water is stored in the hollow tank, and the tip of coiled pipe cooling provided as the cooler on the water surface or in the water is faced, and the end of the pipe leading to the NOx sensor is connected to the stored water. It is preferable that the exhaust gas from the pipe is blown into the stored water and brought into contact with the NOx sensor after being positioned above the water surface. In this way, it is possible to reliably dissolve ammonia or urea in the exhaust gas into water.

  Hereinafter, specific examples of the NOx measuring apparatus and measuring method according to the present invention will be described with reference to the drawings. FIG. 1 is a piping block diagram of a denitration apparatus equipped with a measuring apparatus according to the present invention. In the embodiment of this figure, a denitration reaction in which a generator 1 provided with a combustion device as a NOx emission source and a flue 2 extending from the generator 1 is connected and, for example, a vanadium-based denitration catalyst is loaded therein. The spray nozzle 41 which inject | pours the urea water and ammonia (reducing agent) which reduce | restore NOx contained in the waste gas 3 which is arrange | positioned in the downstream of the generator 1 in the flue 2 and the flue 2, and passes the inside of the flue 2. And a control means 5 for controlling the amount of reducing agent R injected by the reducing agent injector 4 based on the amount of power generated by the generator 1 and the denitration reactor 3. And a NOx measuring device 6 for measuring nitrogen oxides (NOx) contained in the exhaust gas discharged to the atmosphere.

  The control means 5 detects the signal from the output unit 12 of the generator 1 and controls the injection amount from the injector 41 based on the injection amount of a function map that is predetermined according to the power generation amount of the generator 1.

  FIG. 2 is a flowchart showing an outline of the measuring device 6. In FIG. 2, a cooler 7 is connected to the flue 2 on the outlet side of the denitration reactor 3 via a first pipe P 1, and a hollow tank 8 is connected to the downstream side, and in the middle of the outlet side of the tank 8. A metering pump 9 is connected via a second pipe P2 in which a check valve V and a flow meter M are interposed, and a zirconia type NOx connected to the NOx detector 10 via a third pipe P3 on the outlet side thereof. A sensor 11 is provided.

  In the embodiment of FIG. 2, an air-cooled coiled pipe 71 is used as the cooler 7, and the inlet side of the cooler 7 is vertically connected to the first pipe P <b> 1 connected to the flue 2, and the outlet side thereof is Each is connected to an inlet pipe 82 attached through. In addition, an outlet pipe 83 that protrudes upward and is connected to the second pipe P <b> 2 is attached to the lid plate 81. Further, a large number of cooling fins 84 are formed on the outer wall of the tank 8, and the exhaust gas sent from the inlet pipe 82 into the tank 8 and the condensed water by the cooler 7 are cooled by the fins 84.

  In the embodiment of FIG. 2, water W is loaded into the tank 8, the tip of the inlet pipe 82 of the tank 8 is inserted into this water, and the exhaust gas G and the condensed water cooled by the cooler 7 are introduced into the inlet pipe 82. It is made to squirt into the water and bubbling.

  An overflow pipe 85 is attached to the bottom wall of the tank 8, and when condensed water of a predetermined amount or more is accumulated in the tank 8, it is automatically discharged to the outside through the overflow pipe 85.

  In the above NOx measuring device 6, a part of the exhaust gas G denitrated by the denitration reactor 3 and discharged to the atmosphere through the flue 2 is taken into the cooler 7 from the first pipe P <b> 1 by driving the metering pump 9. Then, when passing through the coiled pipe 71, it is cooled by air, and moisture (water vapor) contained in the exhaust gas G is condensed. At this time, since ammonia and urea water used as a reducing agent for denitration in the denitration reactor 3 are water-soluble, they are dissolved in the water condensed by cooling in the cooler 7. Then, it is sent from the cooler 7 through the inlet pipe 82 to the tank 8 where it is gas-liquid separated, and the water in which ammonia or urea water is dissolved is mixed and stored in the water W loaded in the tank 8. . On the other hand, the exhaust gas G from which the water containing ammonia and urea water has been removed is sent from the tank 8 to the zirconia type NOx sensor 11 through the metering pump 9, and the denitration reaction is performed by the detector 10 based on the detected value by the NOx sensor 11. The NOx concentration remaining in the exhaust gas G from the vessel 3 is measured.

  At this time, since the water W is loaded into the tank 8 and the tip of the inlet pipe 82 of the tank 8 is inserted into the water, the exhaust gas and the condensed water cooled by the cooler 7 are discharged from the inlet pipe 82. It is jetted into the water and bubbled. For this reason, the ammonia and urea water in the exhaust gas can be more reliably dissolved in the water W, that is, the ammonia and urea water can be more reliably separated from the exhaust gas. In addition, a large number of cooling fins 84 are formed on the outer wall of the tank 8, and the exhaust gas and the condensed water from the cooler 7 are cooled by the fins 84, so that ammonia and urea water injected as a reducing agent can be more reliably removed. Thus, the measurement of NOx by the zirconia NOx sensor 11 is performed more accurately.

  FIG. 3 is a graph showing the amount of change in the NOx value with respect to the amount of reducing agent injected, with the vertical axis representing the NOx indication value (ppm) and the horizontal axis representing the number of pump strokes (spm). In the graph, A1 is a measured value obtained by measuring the NOx concentration contained in the exhaust gas after passing through the denitration reactor by the measuring device 6 in FIG. 2, and B1 is a commercially available high-precision NOx concentration detecting device (Horiba Co., Ltd.). It is the line | wire which each represented the measured value which measured the NOx density | concentration in waste gas using MEXA made from a factory, and an engine exhaust gas measuring apparatus). This line B1 is obtained by measuring the exhaust gas G collected from the first pipe P1 at the S position upstream of the cooler 7.

  As apparent from the respective lines A1 and B1 in FIG. 3, the use of the measuring device of this embodiment makes it possible to detect the NOx concentration with almost the same accuracy as when an expensive high-precision NOx concentration detecting device is used. . In particular, the lines A1 and B1 show almost no difference in the region where the number of pump strokes exceeds 150, that is, in the region where the NOx instruction value is small, and the measurement device of this embodiment uses a high-precision NOx concentration detection device. It can be understood that the NOx concentration can be detected with the same high accuracy as the case.

  FIG. 4 shows another embodiment of the measuring apparatus according to the present invention. In the embodiment shown in this figure, without filling the tank 8 with water W, the inside of the tank 8 is made empty, and the exhaust gas G that has passed through the coiled pipe 71 is ejected into the empty tank 8. Gas-liquid separation is performed without bubbling, and the water in which the separated ammonia and urea water are dissolved is stored in the tank 8. Further, the exhaust gas G from which water containing ammonia and urea water has been removed is sent from the tank 8 to the zirconia-type NOx sensor 11 through the metering pump 9 in the same manner as described above, and based on the detection value by the NOx sensor 11, the detector 10. Thus, the NOx concentration remaining in the exhaust gas G from the denitration reactor 3 is measured.

  FIG. 5 is a graph showing the amount of change in the NOx value with respect to the amount of reducing agent injected, with the vertical axis representing the NOx indication value (ppm) and the horizontal axis representing the pump stroke number (spm), as in FIG. In the graph, A2 is a measurement value obtained by measuring the NOx concentration contained in the exhaust gas after passing through the denitration reactor by the measurement device 6 of FIG. 4, and B2 is a commercially available high-precision NOx concentration detection device (Horiba Co., Ltd.). It is the line | wire which each represented the measured value which measured the NOx density | concentration in waste gas using MEXA made from a factory, and an engine exhaust gas measuring apparatus). This line B2 is obtained by measuring the exhaust gas G collected from the first pipe P1 at the S position upstream of the cooler 7.

  As apparent from the respective lines A2 and B2 in FIG. 5, the use of the measurement apparatus of the second embodiment makes it possible to detect the NOx concentration with almost the same accuracy as when an expensive high-precision NOx concentration detection device is used. it can. In particular, the lines A2 and B2 show almost no difference in the area where the number of pump strokes exceeds 150, that is, in the area where the NOx instruction value is small, with the same high accuracy as when using a high-precision NOx concentration detection device. It can be understood that the NOx concentration can be detected.

  FIG. 6 shows still another embodiment of the measuring apparatus 6 according to the present invention. In the embodiment of this figure, unlike the above embodiments, a water-cooled type is used as the cooler 7. The cooler 7 is loaded with water W in the tank 8, installed with the water-cooled tank 72 partially buried in the water W, and cools the outer wall of the water-cooled tank 72 with the water W. The fourth pipe P4 extending from the flue 2 is exposed at the upper part of the water cooling tank 72, and the fifth pipe P5 extending from the upper part of the water cooling tank 72 to the NOx sensor 11 is extended.

  In the measuring apparatus 6 described above, a water-cooled tank 72 in which a part of the exhaust gas G denitrated in the denitration reactor 3 and discharged to the atmosphere through the flue 2 is cooled by the water W in the tank 8 from the fourth pipe P4. The water contained in the exhaust gas G is condensed here, and ammonia or urea water used as a reducing agent is dissolved in the condensed water W1, and the condensed water W1 is separated from the exhaust gas G in the water-cooled tank 7. And stored in the water-cooled tank 7. On the other hand, the exhaust gas G from which the condensed water W1 has been removed is sent from the upper part of the water-cooled tank 72 to the zirconia-type NOx sensor 11 through the fifth pipe 5 and denitrated by the detector 10 based on the detected value by the NOx sensor 11. The concentration of NOx remaining in the exhaust gas G from the reactor 3 is measured.

  FIG. 7 is a graph showing the amount of change in the NOx value with respect to the amount of reducing agent injected with the NOx instruction value (ppm) on the vertical axis and the number of pump strokes (spm) on the horizontal axis, as in FIG. In the graph, A3 is a measured value obtained by measuring the NOx concentration contained in the exhaust gas after passing through the denitration reactor by the measuring device 6 in FIG. 6, and B3 is a commercially available high-precision NOx concentration detecting device (Horiba Co., Ltd.). It is the line | wire which each represented the measured value which measured the NOx density | concentration in waste gas using MEXA made from a factory, and an engine exhaust gas measuring apparatus). This line B3 is obtained by connecting a commercially available concentration detection device D at the same position as the NOx sensor 11 in the fifth pipe P5 and measuring the exhaust gas G collected from the fifth pipe P5.

  As apparent from the respective lines A3 and B3 in FIG. 7, the use of the measurement apparatus of the third embodiment makes it possible to detect the NOx concentration with almost the same accuracy as when an expensive high-precision NOx concentration detection device is used. it can. In particular, the lines A1 and B1 show almost no difference in the region where the number of pump strokes exceeds 150, that is, in the region where the NOx instruction value is small. In the measurement device of this third embodiment, the high-precision NOx concentration detection device It can be understood that the NOx concentration can be detected with the same high accuracy as when D is used.

It is a piping block diagram of the denitration apparatus equipped with the measuring apparatus concerning this invention. It is a flowchart which shows the outline of the measuring apparatus. It is a graph which shows the variation | change_quantity of NOx with respect to the injection amount of the reducing agent by the measuring device. It is a flowchart which shows another Example of the measuring apparatus concerning this invention. It is a graph which shows the variation | change_quantity of NOx with respect to the injection amount of the reducing agent by the measuring device. It is a flowchart which shows another Example of the measuring apparatus concerning this invention. It is a graph which shows the variation | change_quantity of NOx with respect to the injection amount of the reducing agent by the measuring device.

Explanation of symbols

7 Cooler
71 Coiled piping 8 Hollow tank 84 Fin 9 Metering pump 10 NOx sensor (Zirconia type NOx sensor)
G exhaust gas W water W1 condensed water

Claims (7)

A device that detects the concentration of nitrogen oxides in a detection gas while removing the influence of ammonia or urea contained in the detection gas using a NOx sensor that is affected by ammonia or urea but detects the concentration of nitrogen oxides Because
A NOx measuring device characterized by condensing and removing moisture from a detection gas and supplying the detection gas after the moisture removal to the NOx sensor to detect a nitrogen oxide concentration. Nitrogen oxide remaining in exhaust gas discharged from this denitration device, applied to denitration device that reduces nitrogen oxide in exhaust gas with denitration catalyst while injecting ammonia or urea water as reducing agent into exhaust gas A device for detecting the concentration of
A cooler that condenses moisture in the exhaust gas by cooling the exhaust gas;
A NOx measuring device comprising: a zirconia-type NOx sensor that is supplied with exhaust gas from which moisture condensed by the cooler is removed and detects a nitrogen oxide concentration in the exhaust gas. The cooler is configured such that a coiled pipe through which exhaust gas is passed is air-cooled or water-cooled,
The exhaust gas from the coiled pipe is supplied into the hollow tank,
The exhaust gas from which condensed water is separated in the hollow tank is supplied from the hollow tank to the NOx sensor via a metering pump. The water is stored in the hollow tank, and the exhaust gas is discharged from the upper part of the hollow tank toward the NOx sensor while the exhaust gas is jetted into the surface of the stored water or into the water. 3. The NOx measuring device according to 3. The NOx measurement device according to claim 3 or 4, wherein the hollow tank includes a cooling fin and can drain a predetermined amount or more of condensed water. A method for measuring NOx, comprising dissolving ammonia or urea contained in a detection gas into water and then detecting a nitrogen oxide concentration in the detection gas from which the water has been removed. Detects the concentration of nitrogen oxides remaining in the exhaust gas after passing through the denitration catalyst in a denitration device that injects ammonia or urea water into the exhaust gas as a reducing agent and reduces the nitrogen oxides in the exhaust gas with a denitration catalyst. A way to
A NOx measurement method comprising: condensing moisture in exhaust gas by cooling the exhaust gas, and then detecting a nitrogen oxide concentration in the exhaust gas from which the condensed water has been removed with a zirconia NOx sensor.

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