JP4568054B2 - Catalyst unit and analyzer using the same - Google Patents

Description

  The present invention relates to a heating means, a catalyst unit, and an analyzer using the same, and, for example, a heating means, a catalyst unit, and an analyzer using the same when high-speed processing is required as in an ammonia analyzer in automobile exhaust gas. About.

Conventionally, as a method for measuring ammonia (NH ₃ ), a stationary emission source NH ₃ analyzer configured as shown in FIG. 7 is known (see, for example, Patent Document 1). A sampling probe unit 51 composed of two sampling probe lines of NH ₃ system and nitrogen oxide (NOx) system, an analysis unit 52 equipped with an analyzer for measuring the nitrogen monoxide (NO) concentration of each system, and and a calculation unit 53 for calculating the NH ₃ concentration than NO concentration obtained from the two analyzers. One of the sampling probe lines (NH ₃ system) is provided with an oxidized or reduced catalyst C. An ammonia oxidation catalyst is used for the oxidized form, and an ammonia reduction catalyst is used for the reduced form.

The measurement principle of the oxidized form is to measure NH ₃ concentration by oxidizing NH ₃ based NH ₃ to equimolar NO by the action of an oxidation catalyst and detecting the concentration of this NO. In general, NOx is also present in the exhaust gas, so nitrogen dioxide (NO ₂ ) in the exhaust gas is reduced to NO by the NO ₂ -NO converter upstream of the detector. Only the NOx concentration is detected in the NOx system flow path, and the total concentration of NH ₃ and NOx is detected in the NH ₃ system flow path. Therefore, the difference between the detection values of the detectors of the two flow paths is the NH ₃ concentration. It becomes. The measurement principle of the reduced form, of NH ₃ NH ₃ system to perform the reaction with equimolar NOx by the action of the reduction catalyst, by detecting a NOx concentration deficient by the reaction, and measures the NH ₃ concentration . In this case, the NO ₃ concentration decreased by the NH ₃ concentration is detected in the NH ₃ system flow path, and the difference between the detected values of both flow paths becomes the NH ₃ concentration.

On the other hand, as an automobile exhaust gas analyzer for mobile emission sources, it is hardly contained in exhaust gas in normal operation, and NH ₃ instability, NH ₃ adsorptive strength and Since there is no measurement means that can respond to a sudden change in the measurement components in the exhaust gas, there has been no practical use.
JP 2000-9603 A

However, along with the recent importance of environmental analysis and various improvements of automobiles or engines, an automobile exhaust gas NH ₃ analyzer that can continuously measure in response to a sudden change in measurement components in exhaust gas as a measuring means. The request for is getting stronger.

Specifically, in a gasoline engine, several tens to several thousand ppm of NH ₃ may be generated by a reducing atmosphere, which is called a lean burn or a rich spike, under a reducing atmosphere. In diesel engines, urea addition has recently attracted attention as an exhaust gas treatment. In other words, a selective reduction catalyst (SCR) is promising as a NOx reduction measure for large diesel vehicles. This is a nitrogen (N ₂ ) that is harmless on the catalyst with NOx discharged from the engine using urea aqueous solution as a reducing agent. In this case, several tens to several hundred ppm of NH ₃ may be generated. Measuring the generated NH ₃ accurately and with good responsiveness is a problem of the analyzer.

In particular, when the generated NH ₃ is converted by oxidation treatment or reduction treatment, response delay and efficiency reduction (loss during processing) due to the instability of NH ₃ and the strength of adsorption are as described above. The impact cannot be ignored. In other words, the function and characteristics of the oxidation treatment means or the reduction treatment means are a major factor for such problems, and improvement is an urgent problem.

Further, not only NH ₃ measurement, but also heating means or catalyst units used in various analyzers, along with a demand for responsiveness and high efficiency, downsizing has been a major issue from the past.

  SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide an analysis apparatus that can respond to such a request and can quickly follow component fluctuations in a sample. It is another object of the present invention to provide a heating means or a catalyst unit that is an essential component of such an analyzer and that can be easily exchanged with little pressure loss, is compact, and functions quickly.

  As a result of extensive research, the present inventor has found that the above object can be achieved by the heating means, catalyst unit, and analyzer using the same, and has completed the present invention.

The present invention is a catalyst unit including a heating unit having a tubular body forming a flow path therein, and an inner portion of the heating unit in the tubular body protrudes inward from an inner peripheral surface of the tubular body, In addition, a plurality of protrusions or step portions functioning as a tubular throttle along the inner peripheral surface are provided, and a catalyst is installed on the downstream side.

  In general, when heating a gas flow close to a laminar flow, a boundary layer is formed in the vicinity of the contact surface with the heating body parallel to the gas flow, and the temperature of the gas body within that rapidly increases, but the outside of the boundary layer It is difficult to raise the temperature of the gas body. In order to solve such problems, the present inventor has formed a turbulent flow by providing a projection or a step in the flow path after forming a gas flow close to a laminar flow, and at the same time, forms a turbulent flow and a gas existing in the boundary layer. In a flow path (parallel flat part) parallel to the gas flow provided at the rear stage of the projection, the gas that has moved to the boundary layer is rapidly heated in a short period of time. It was devised that the overall temperature could be raised. In addition, when the flow rate is large, a rapid heating effect suitable for the gas condition can be obtained by providing a plurality of protrusions or stepped portions.

  That is, the present invention utilizes the gas agitation / mixing effect by the installation of the protrusion or step and the formation of a stable gas flow in the parallel flat part, while the heat flow replacement / thermal diffusion effect in the former and the latter By making effective use of the smooth heat transfer effect, rapid heating means in a short flow path is made possible. Therefore, the heating unit as a whole can be made compact, and the superiority is high particularly when the temperature difference from the introduced gas is large.

The present invention is the above catalyst unit, said heating means, and performs the connection with an external channel by inserting another tubular body having substantially the same outer diameter as the inner diameter of the tubular body.

  While heating a gas at a predetermined flow rate requires securing a predetermined heating volume, it is preferable to transfer the gas quickly after heating. In the present invention, two tubular bodies with different diameters are fitted, a heating volume is secured by using the inside of the large-diameter tubular body as a heating portion, and after heating, the tube diameter is reduced to increase the flow rate, thereby improving the efficiency. A good heating unit can be configured. In addition, since the tube end surfaces inside the two fitted tubular bodies form a step portion, by using this step portion for fixing a member such as a catalyst, an unnecessary member is not used and pressure loss is achieved. The member can be heated without the occurrence of the above. In particular, in the formation of a heating unit or a catalyst unit in a high-speed response type analyzer that is one of the objects to be applied to the present invention, such a function is very effective because it aims at high-speed heating.

The present invention provides a top Kisawa medium unit, the flow path front and rear of the protrusion or the step portion, the parallel flat portions constituting the inner surface area of channel center line parallel and flat predetermined length is formed The catalyst is installed in the parallel flat part on the downstream side .

  As described above, the heating unit according to the present invention enables heating in a very short time and has a protrusion or / and a step in the flow path. Therefore, in order to make more effective use of such a function as a catalyst unit, it is preferable that the catalyst itself inserted therein does not cause an increase in pressure loss and does not use a filter or a holding member for fixing it. In the present invention, from this point of view, by inserting a mesh-shaped catalyst as a fixing means by using a protrusion or a step, the catalyst can be exchanged easily with excellent response speed and no substance adsorption in the gas. Thus, a compact catalyst unit can be configured.

The present invention is an analysis apparatus using the above Kisawa medium unit branches a sampled channel into a plurality, characterized by arranging the front Kisawa medium unit to the at least one channel.

  As described above, the heating unit or the catalyst unit according to the present invention has a very excellent function in response and maintenance. Therefore, if such a function is applied to an analyzer that requires a high-speed response, a very excellent analyzer can be configured. In particular, when the sample collection flow path is branched into a plurality of samples, a predetermined process is performed on one sample, and a comparative measurement with an unprocessed sample is performed, the difference in response between the flow paths is extremely small. Real-time measurement is possible. Even if a slight response deviation occurs, it is possible to measure with high accuracy by correcting individual response characteristics.

The present invention is the above analyzer, wherein the catalyst is a platinum-based catalyst and / or a nickel-based catalyst , and oxidizes ammonia in a sample.

Although the current problems in the analysis of NH ₃ are as described above, in the analyzer using the heating means or the catalyst unit in the present invention, improvement of response speed and prevention of adsorption of NH ₃ are the biggest problems among them. Can exhibit excellent functions. Specifically, NH _{3 in} a sample is oxidized using a catalyst unit according to the present invention in which a sampling channel is branched into a plurality of channels and a platinum-based catalyst and / or a nickel-based catalyst is arranged in one channel. Accordingly, less adsorption of NH _3, can quickly NH ₃ → NOx conversion, by performing the NOx comparative measurements with the untreated sample, it is possible to construct a superior NH ₃ analyzer very response speed. In particular, since NH ₃ → NOx conversion requires a high temperature condition of 800 ° C. or higher, the catalyst unit according to the present invention is very useful, and there is almost no pressure loss in the flow path, and the other in the sample. Since there is no adsorption / loss of these components, it is excellent in that there is almost no difference in response with the untreated flow path.

As described above, according to the present invention, it is possible to provide a heating means or a catalyst unit, which has been difficult in the past, can be easily replaced with little pressure loss, is compact, and functions quickly. Further, by utilizing such a heating means or catalyst unit in an analyzer, it is possible to quickly follow fluctuations in the components in the sample, and one sample flow path is branched into a plurality of flow paths, and one of the heating means or the catalyst is provided. Even in the case where the unit is provided, it is possible to provide an analyzer with little difference in response between the flow paths. In particular, a very useful device can be provided in a field that has not been put into practical use in terms of responsiveness and the like, such as an NH ₃ analyzer in automobile exhaust gas.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1A illustrates the basic configuration of the heating means according to the present invention. A tubular body 2 that forms a flow path is disposed inside the heating unit 1, and protrusions 3 (specifically represented by 3 a, 3 b, and 3 c) are formed at a plurality of portions of the tubular body 2, Parallel flat portions 4 (specifically, 4a, 4b, 4c, and 4d, respectively) are formed on the front and rear portions of the protrusion 3 in the flow path.

  As a method for forming the protrusion 3, for example, as shown in FIG. 1A, the protrusions 3 a, 3 b, and 3 c are formed by providing a restriction on the portions A, B, and C of the tubular body 2. It is possible. In the case where the tubular body 2 is provided with a diaphragm to form the protrusion 3, the protrusion 3 having a relatively smooth shape can be obtained. Moreover, the method of forming the protrusion part 3 is not limited to this, A various method can be used. For example, as illustrated in FIG. 1B, it is possible to insert a tubular body 2 a having a different diameter into the tubular body 2. In this case, the cross-sectional shape of the tubular body 2a can be arbitrarily set, and various shapes such as a case where a corner portion is provided (a step portion is formed) can be obtained.

  In FIG. 1B, a tubular body 5 having an outer diameter substantially the same as the inner diameter of the tubular body 2 is inserted for connection to the external flow path. The end 5a of the tubular body 5 performs the same function as the protrusion 3c in FIG. 1A, and an efficient heating unit can be configured by increasing the flow rate of the heated gas body.

  Here, the tube diameter of the tubular body 2 can be arbitrarily set depending on the use flow rate or the size of the heating means, but in the case of a gas flow rate of about 1 L / min, the inner diameter is about about 4 to 8 mm. It is said.

  The inventor presumes the phenomenon in the protrusion at this time and the accompanying temperature change due to the position in the flow channel as shown in FIG. 2A based on the experimental results and knowledge. Hereinafter, the state of the gas body inside the flow path will be described in two layers or three layers.

(1) Considering the state of the gas body inside the channel divided into two layers (boundary layer and central layer),
(1-1) Initially, a gas flow close to a laminar flow is formed in the flow path in the parallel flat portion 4a. At this time, the flow close to the tube wall forms a boundary layer, and as shown in FIG. 2 (B), the heat transfer effect is relatively high and the temperature rises in a short time. The temperature rises due to heat transfer from the gas.
(1-2) Next, in the protrusion 3a, a turbulent flow is formed, and the gas in the boundary layer and the gas in the central layer are mixed and moved. At this time, part of the gas in the boundary layer moves to the central layer while maintaining a high temperature while lowering the temperature somewhat, and part of the gas in the central layer is received from the gas in the boundary layer. Move to the boundary layer while increasing the amount of heat. Therefore, the gas temperature in the boundary layer once decreases as indicated by a solid line A, and the gas temperature in the central layer rapidly increases as indicated by a solid line B.
(1-3) In the parallel flat portion 4b provided at the rear stage of the protruding portion 3a, the gas moved to the boundary layer is rapidly heated and the gas temperature in the central layer is gradually increased as in (1-1). To do.
(1-4) After the protrusion 3b, the temperature of the entire gas flow can be increased in a short time by repeating (1-2) and (1-3).

  If there is no protrusion, as shown in FIG. 2 (B), the temperature of the boundary layer gas is increased by a temperature gradient as shown by a broken line A ′, and the temperature of the gas at the center layer is increased by a temperature gradient as shown by a broken line B ′. On the other hand, in the present invention, the boundary layer gas repeats a temperature increase in a meandering manner as indicated by the solid line A and the central layer gas by the solid line B. At this time, since the temperature rise gradient of the gas in the boundary layer in the parallel flat portion immediately after that increases due to the presence of the protrusion 3, the average temperature of the entire gas flow at the outlet of the heating means is compared with the case where there is no protrusion. As a result, the heating channel can be significantly increased or the length of the heating channel can be significantly shortened.

(2) Considering the state of the gas body inside the flow path divided into three layers (boundary layer, intermediate layer, central layer),
(2-1) In the state in the flow path in the parallel flat part 4a, a gas flow close to a laminar flow is formed. At this time, as shown in FIG. 2B, the gas in the boundary layer has a relatively high heat transfer effect and causes a temperature rise in a short time, and is in the middle (intermediate layer) between the channel center layer and the boundary layer. The gas dissipates heat to the center layer while causing a temperature rise due to heat received from the gas in the boundary layer, and the temperature of the gas in the center layer is raised only by heat received from the intermediate layer.
(2-2) In the protrusion 3a, a turbulent flow is formed, and gases in the boundary layer, the intermediate layer, and the central layer are mixed and moved with each other. At this time, part of the gas in the boundary layer moves to the intermediate layer and the central layer while maintaining a high temperature while lowering the temperature somewhat. Part of the gas in the intermediate layer moves to the boundary layer while increasing the amount of heat received from the gas in the boundary layer, and at the same time, part of the gas moves to the central layer while lowering the temperature somewhat. Part of the gas in the central layer moves to the boundary layer or intermediate layer while increasing the amount of heat received from the gas in the boundary layer or intermediate layer.
Therefore, the gas temperature in the boundary layer once decreases as indicated by the solid line A, and the gas temperature in the intermediate portion or the central portion rapidly increases as indicated by the solid line B.
(2-3) In the parallel flat portion 4b provided at the rear stage of the protruding portion 3a, the gas that has moved to the boundary layer is rapidly heated, and the gas temperatures at the intermediate portion and the central portion, as in (2-1). Also rises gradually.
(2-4) After the protrusion 3b, the temperature of the entire gas flow can be increased in a short time by repeating (2-2) and (2-3).

  The relationship between the position in the flow path and the temperature of each layer at this time is shown in FIG. 2 (the solid layer A shows the gas temperature in the boundary layer, and the average gas temperature in the middle and the center as shown by the solid line B. The curve is almost the same as in B), and the presence of the protrusion 3 makes it possible to significantly increase the average temperature of the entire gas flow at the outlet of the heating means, or to greatly shorten the length of the heating channel.

  As shown in FIGS. 3A and 3B, the above contents can be verified by actually measured data on the temperature distribution in the pipe radial direction at the in-pipe position 4c in FIG. 2A. A temperature difference of about 140 ° C. is generated in the central portion of the overheating means set at 900 ° C., as shown by a solid line C in a state where one protrusion 3 is provided and a broken line C ′ in a state without the protrusion 3. .

  Next, a catalyst unit configured by applying the heating means will be described. FIG. 4A illustrates the case where the catalyst 6 is disposed at the position of the parallel flat portion 4b between the protrusions 3b and 3c of the heating means. It becomes possible to make the catalyst 6 function under the condition that the protrusions 3a and 3b are sequentially heated and sufficiently heated to a predetermined temperature.

  The catalyst 6 can be selected in any shape / composition according to use and installed in the catalyst unit. However, the shape of the catalyst 6 is fixed by the protrusions 3b and 3c as shown in FIG. In some cases, a mesh catalyst is preferred. Since the pressure loss due to the catalyst 6 does not increase and can be fixed without using a filter or a holding member, loss due to adsorption or response delay can be prevented. Further, the catalyst 6 is excellent in that it can be easily attached and detached and can be easily replaced.

  FIG. 4B shows a configuration example in which the heating means of FIG. 1B is applied to a catalyst unit. The protrusion 3c and the parallel flat portion 4c are replaced with the tubular body 5, and the catalyst 6 can be fixed by fitting the tubular body 5 after the catalyst 6 is disposed. In addition to the advantage as the heating means, it is excellent in that the tubular body 5 is pulled out or the position thereof is changed so that the flexibility of fixing the catalyst is high or the inserted catalyst can be easily taken out and replaced. Yes.

FIG. 5 illustrates one configuration of an analyzer using the above-described heating means or catalyst unit and using a chemiluminescence analyzer (CLD) as the NO analyzer. Taking the NH ₃ measurement in the sample as an example, the sample introduced from the sample inlet by the sample pump 7 passes through the oxidation catalyst unit 8 and the NO—NO ₂ conversion unit 9 arranged in the collection channel. It is introduced into the NO analyzer 10 and discharged through the ozonolysis unit 11. The NO analysis unit 10 is supplied with ozone (O ₃ ) gas via the ozone generating means 12 based on the oxygen source. When there is not enough oxygen necessary for oxidation in the sample, a predetermined amount of oxygen (air) can be added to replenish the flame retardant in the sample and ensure high oxidation reaction efficiency.

Further, a measurement component is selected by branching the sample flow path immediately before the oxidation catalyst unit 8 and the NO-NO ₂ conversion unit 9 and operating the switching valves 13a and 13b to switch the introduction and path to each unit. be able to. That is, (a) when the sample is introduced into the oxidation catalyst unit 8 and the NO—NO ₂ conversion unit 9, the total nitrogen compound in the sample is measured, and (b) the oxidation catalyst unit 8 is passed and the NO—NO ₂ conversion is performed. When introduced into the unit 9, NOx can be measured, and (c) NO can be measured when both are passed. Therefore, (a)-(b) = NH ₃ and (b)-(c) = NO ₂ can be measured by quickly performing these switching operations.

At this time, the heating means or the catalyst unit according to the present invention can be applied to the oxidation catalyst unit 8, the NO-NO ₂ conversion unit 9, and the ozone decomposition unit 11, which greatly contributes to the downsizing of the entire apparatus. In the oxidation catalyst unit 8, a platinum-based catalyst and / or a nickel-based catalyst is disposed therein, and ammonia in the sample is oxidized at a temperature of about 800 to 900 ° C. Moreover, in the NO-NO ₂ conversion unit 9, a carbon-based catalyst is arranged inside, and NO ₂ in the sample is reduced and converted to NO under conditions of about 150 to 200 ° C. Further, in the ozonolysis unit 11, the exhaust gas is rendered harmless by thermally decomposing O ₃ in the sample under the condition of about 200 to 300 ° C. The heating means or the catalyst unit according to the present invention can be applied to such various temperature conditions, and is particularly superior in that it can cope with high temperature conditions of 800 ° C. or higher under substantially the same conditions.

In the above configuration, a platinum-based catalyst and / or a nickel-based catalyst is exemplified as the NH ₃ oxidation catalyst. However, an oxidation catalyst such as a palladium-based catalyst, copper, or chromium-based catalyst can also be applied. However, a platinum-based catalyst and / or a nickel-based catalyst is preferable in order to form a mesh shape and to set the oxidation efficiency to a predetermined value (for example, a conversion efficiency of 90%) or more.

As described above, in the analyzer according to the present invention, there is little NH ₃ adsorption, rapid NH ₃ → NOx conversion is possible, and NOx comparison measurement with an untreated sample is performed, so that the response speed is extremely excellent. An NH ₃ analyzer can be configured. Moreover, it is possible to perform continuous measurement for NO, NO ₂ and NOx.

Another configuration example of the analyzer according to the present invention is shown in FIG. Taking NH _{3 in a} sample as an example, the sample introduced from the sample inlet by the sample pump 7 is branched into two, (d) one is introduced into the oxidation catalyst unit 8, and (e) the other is left as it is. In the state, they are introduced into the NO analyzers 10a and 10b via the NO-NO ₂ conversion units 9a and 9b, respectively, and discharged through the ozone decomposition units 11a and 11b. At this time, the total nitrogen compound in the sample can be measured in (d), NOx can be measured in (e), and (d) − (e) = NH ₃ can be continuously measured. Further, (f) NO can be measured by operating the switching valve 13b provided by branching the sample flow path immediately before the NO—NO ₂ conversion unit 9b and passing the unit, and (e) − ( f) = NO ₂ can be measured. Further, (g) by operating the switching valve 13a and passing the oxidation catalyst unit 8, a flow path similar to (e) can be formed, and simultaneous measurement of NO and NOx is possible. (E) - it can be measured (f) = NO _2. If there is not enough oxygen necessary for oxidation in the sample, a predetermined amount of oxygen (air) can be added before sample branching to replenish the flame retardant in the sample and ensure high oxidation reaction efficiency. it can.

  At this time, the oxidation catalyst unit 8 according to the present invention has a very excellent function such as responsiveness and maintainability. Therefore, the deviation of the response between the flow paths can be extremely reduced, and real-time measurement can be performed. It becomes possible.

As described above, in the analyzer according to the present invention, a sample is collected using the catalyst unit according to the present invention in which the sampling channel is branched into a plurality of channels and the platinum-based catalyst and / or the nickel-based catalyst is arranged in one channel. by oxidation of NH ₃ in less adsorption of NH _3, can quickly NH ₃ → NOx conversion, by performing the NOx comparative measurements with the untreated sample, very responsive excellent NH ₃ analysis A device can be configured. In addition, since there is no pressure loss in the NH ₃ → NOx conversion channel and no adsorption / loss of other components in the sample, there is almost no difference in response with the untreated channel. Further, even when some response deviation occurs, the response characteristics when the same NO gas is introduced into the flow paths (d) to (g), for example, since the individual flow paths have independent response characteristics. This makes it possible to perform highly accurate measurement without being affected by response deviation, such as easy correction based on the above. Furthermore, continuous measurement can be performed for NO, NO ₂ and NOx.

As described above, the present invention can be applied as a very suitable means for quickly measuring NH ₃ and NOx in automobile exhaust gas, and in various exhaust gases including fixed exhaust sources such as various combustion furnaces. It is also applicable to measurement of NH ₃ , NOx or other components, for example, measurement of hydrogen, hydrogen chloride and the like.

Moreover, since it can respond to a wide heating temperature region, it can be applied not only to exhaust gas but also to various processes and research purposes. For example, it can also be applied to the following fields.
(1) Simulated gas generator in catalyst evaluation device as a single heating unit (2) Gas behavior analysis device in the heated state inside the engine

Explanatory drawing which shows the basic composition of the heating means which concerns on this invention. Explanatory drawing which shows roughly the temperature distribution inside the heating means which concerns on this invention. Explanatory drawing which shows the temperature distribution measurement data of the pipe radial direction inside the heating means which concerns on this invention. Explanatory drawing which shows the basic structure of the catalyst unit which concerns on this invention. Explanatory drawing which shows the basic composition of the analyzer concerning the present invention. Explanatory drawing which shows the other structural example of the analyzer which concerns on this invention. Explanatory drawing which shows schematically the structure of the analyzer which concerns on a prior art.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Heating part 2, 5 Tubular body 3 Protrusion part 4 Parallel flat part 6 Catalyst 7 Sample pump 8 Oxidation catalyst unit 9 NO-NO ₂ conversion unit 10 NO analysis part 11 Ozone decomposition unit

Claims (5)

A catalyst unit including a heating means having a tubular body forming a flow path therein,
A plurality of protrusions or step portions protruding inward from the inner peripheral surface of the tubular body and functioning as a tubular throttle along the inner peripheral surface are provided on the inner portion of the heating means in the tubular body. The catalyst unit is characterized in that a catalyst is installed on the downstream side.   2. The catalyst unit according to claim 1, wherein the heating unit inserts another tubular body having an outer diameter substantially the same as the inner diameter of the tubular body to connect to the external flow path. The catalyst unit according to claim 1 or 2,
A parallel flat part constituting the inner surface of a predetermined length region parallel to the flow path center line is formed on the front and rear portions of the flow path of the protrusion or step,
A catalyst unit, wherein a catalyst is installed in the parallel flat portion on the downstream side. An analyzer using the catalyst unit according to any one of claims 1 to 3,
An analyzer characterized by branching a sample collection channel into a plurality of channels and arranging the catalyst unit in at least one of the channels.   The analyzer according to claim 4, wherein the catalyst is a platinum-based catalyst and / or a nickel-based catalyst, and oxidizes ammonia in a sample.

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