Nitrogen oxide analysis device and method

Abstract

The invention relates to a spectrum technology, and particularly provides a nitrogen oxide analysis device and a nitrogen oxide analysis method. The flow cell is provided with a main flow channel along the axial direction, an inlet is arranged close to the first end of the flow cell, and an outlet is arranged close to the second end; the first end, the inlet, the outlet and the second end are sequentially arranged in the axial direction of the flow cell; the first flow channel and the second flow channel are arranged in the body of the flow cell, and gas sequentially passes through the inlet, the first flow channel and the second flow channel, enters the main flow channel and flows in the direction from the first end to the second end; the third flow channel and the fourth flow channel are arranged in the body of the flow cell, and gas in the second end sequentially passes through the third flow channel, the fourth flow channel and the outlet; the flow direction of gas in the third flow channel and the flow direction of gas in the second flow channel are the same and are opposite to the flow direction in the main flow channel. The method has the advantages of accurate measurement result and the like.

Description

TECHNICAL FIELD

[0001] The present application relates to spectroscopy, in particular to a nitrogen oxide analysis device and method. BACKGROUND

[0002] Currently, the measurement methods of NOx can be divided into two technical paths according to the detection principle. The first path is based on the direct detection of NO2 and the conversion of NO to NO2, which includes the Saltzman method, the Luminox method, the TDLAS method, the DOAS method, the CRDS method, and the LIF method. The second path is based on the direct detection of NO and the conversion of NO2 to NO, which includes the Mo-catalytic conversion-chemiluminescence method and the Photolysis-Chemiluminescence method (P-CL).

[0003] Among the above two monitoring methods, the Mo-catalytic conversion-chemiluminescence method is the standard method for automatic determination of nitrogen oxides in the environment air in China. The principle is that at 300-350℃, NO2 is converted to NO by a hot substrate such as molybdenum catalyst, and then detected by chemiluminescence method to obtain the concentration of NOx. However, this method has a cross-interference problem in practical application, that is, other nitrogen-containing compounds (such as HNO3, N2O, etc.) will also be converted to NO, resulting in overestimation of the actual concentration of NOx.

[0004] The principle of the Photolysis-Chemiluminescence method (P-CL) is that NO2 will photolyze to NO and O atoms under the irradiation of light at a specific wavelength, and then the photolyzed product NO is detected by chemiluminescence method to obtain the concentration of NOx. This method can effectively avoid cross-interference by selecting a light source at a specific wavelength, thereby improving the accuracy of measuring the concentration of NOx.

[0005] The photolysis device is the core component of the nitrogen oxide analyzer based on the photolysis conversion-chemiluminescence method. Many scholars have conducted related research on the design and implementation of this device.

[0006] US11435291 and CN109310979B both disclose a photolysis converter for converting reactant molecules in a fluid sample to product molecules by electromagnetic radiation. The converter includes a reaction chamber, an electromagnetic radiation source, an inflow conduit, and an outflow conduit. At least one of the conduits extends into the reaction chamber. The conduit extending into the reaction chamber can cause the airflow inside the reaction chamber to flow in an orderly manner, which reduces the possibility of recombination reactions between photolyzed products and improves the conversion efficiency. The disadvantage of this method is that: 1. Extending the inflow or outflow pipes into the reaction chamber increases the complexity and manufacturing cost of the photolysis device.

[0007] 2. The flow guiding structure inside the reaction chamber can obstruct electromagnetic radiation and airflow, thus affecting the photolysis conversion efficiency. This scheme must use a pipe extending into the reaction chamber as the air inlet; otherwise, turbulence will form at the air inlet, further affecting the photolysis conversion efficiency.

[0008] like Figure 1 In the fluid simulation results shown, the asymmetric design results in a significantly longer airflow streamline below than above, which leads to an uneven distribution of the residence time of gas molecules in the reaction chamber, thus affecting the conversion efficiency.

[0009] 3. Pipes used as flow guiding structures are usually made of glass. Glass is fragile and requires high precision during installation and handling.

[0010] Chinese patent CN102445415B discloses a nitrogen dioxide photolysis device. This nitrogen dioxide photolysis device includes a light source system, a gas path system, and a heat dissipation system. Photolysis of nitrogen dioxide is achieved by arranging the light source system opposite to each other on the upper and lower sides of the quartz gas path system, supplemented by a heat dissipation system for the light source. The axial direction of the quartz tube used in the gas path system is the same as the airflow direction, resulting in orderly internal airflow. The shortcomings of this solution are: 1. The device requires multiple LEDs to be arranged along the axial direction, which results in a complex heat dissipation system, large size, and high cost.

[0011] 2. The gas system uses quartz tubes, which are relatively fragile and require high precision during installation and handling. Summary of the Invention

[0012] To address the shortcomings of the existing technical solutions, the present invention provides a nitrogen oxide analysis device.

[0013] The objective of this invention is achieved through the following technical solution: A nitrogen oxide analysis apparatus includes a first light source for exciting the photolysis reaction of nitrogen dioxide; the analysis apparatus further includes: A flow cell has a main channel along its axial direction, an inlet located adjacent to a first end of the flow cell, and an outlet located adjacent to a second end; the first end, the inlet, the outlet, and the second end are arranged sequentially along the axial direction of the flow cell. The first flow channel and the second flow channel are disposed in the body of the flow pool. Gas enters the main flow channel through the inlet, the first flow channel and the second flow channel in sequence, and flows in the direction from the first end to the second end. A third flow channel and a fourth flow channel are arranged in the body of the flow cell, and the gas in the second end sequentially passes through the third flow channel, the fourth flow channel and the outlet; the flow direction of the gas in the third flow channel and the second flow channel is the same and opposite to the flow direction in the main flow channel.

[0014] The application also aims to provide a nitrogen oxide analysis method. The nitrogen oxide analysis method based on the analysis device of the application is as follows: The gas sequentially passes through the inlet, the first flow channel and the second flow channel, and enters the main flow channel; The light emitted by the first light source enters the main flow channel, and the nitrogen dioxide in the gas undergoes a photolysis reaction to generate nitric oxide; The generated nitric oxide sequentially passes through the third flow channel and the fourth flow channel and is sent to the downstream analysis.

[0015] Compared with the prior art, the application has the beneficial effects that: The application guides the internal airflow to realize orderly flow by designing the flow guide channel in the body of the flow cell, without the need for additional flow guide structure, thereby significantly improving the conversion efficiency of the photolysis reaction; The external structure is omitted, the device structure is simplified, the manufacturing cost is reduced, and the radiation and airflow are prevented from being hindered, so that the radiation field distribution and airflow in the reaction cavity are more uniform, and the efficient conversion is further ensured; The flow cell made of metal material has higher mechanical strength than the flow cell made of glass material, and the risk of damage is greatly reduced. BRIEF DESCRIPTION OF DRAWINGS

[0016] The disclosure of the application will become more apparent with reference to the accompanying drawings. It is easy for those skilled in the art to understand that these drawings are only used to illustrate the technical solutions of the application, and are not intended to limit the protection scope of the application. In the drawings: Figure 1 is a fluid simulation schematic diagram in the prior art; Figure 2 is a structural schematic diagram of the analysis device according to the application; Figure 3 is a fluid simulation schematic diagram of the analysis device according to embodiment 2 of the application; Figure 4 is a schematic diagram of the relationship between conversion efficiency and residence time; Figure 5 is a fluid simulation schematic diagram of the analysis device according to embodiment 3 of the application.

[0017] In the drawings, 11 - first light source, 12 - second light source, 21 - heat sink, 31 - first annular seal, 32 - second annular seal, 41 - flow cell, 42 - first flow channel, 43 - second flow channel, 44 - main flow channel, 45 - third flow channel, 46 - fourth flow channel, 47 - first end, 48 - second end, 49 - end portion. DETAILED DESCRIPTION

[0018] Figures 2-5 The alternative embodiments of the present application described in the following description and illustrated in the accompanying drawings are presented by way of example only. The entire disclosure of the applications listed in Table I is hereby incorporated by reference herein. Numerous specific details of the present application are described for the purpose of providing a thorough understanding of the application. Persons skilled in the relevant art will recognize, however, that the application can be practiced without one or more of the specific details. In other instances, well-known structures and components are not described in order to avoid obscuring aspects of the application. Persons skilled in the art will appreciate that the features described with respect to one embodiment can be combined in various ways with features described with respect to other embodiments. Thus, the present application is not to be limited to the specific embodiments described and shown in order to teach any and all combinations.

[0019] Example 1

[0020] The nitrogen oxide analysis device of the present embodiment comprises a conversion unit and an analysis unit, as shown in Figure 2 The conversion unit comprises: The light emitted by the first light source 11 irradiates the gas, so that the nitrogen dioxide in the gas undergoes a photolysis reaction to generate nitric oxide.

[0021] The flow cell 41 has a main flow channel 44 along its axial direction, and an inlet is arranged adjacent to the first end 47 of the flow cell 41, and an outlet is arranged adjacent to the second end 48; in the axial direction of the flow cell 41, the first end 47, the inlet, the outlet and the second end 48 are arranged in sequence.

[0022] The first flow channel 42 and the second flow channel 43 are arranged in the body of the flow cell 41, and the gas sequentially passes through the inlet, the first flow channel 42 and the second flow channel 43, enters the main flow channel 44, and flows in the direction from the first end 47 to the second end 48.

[0023] The third flow channel 45 and the fourth flow channel 46 are arranged in the body of the flow cell 41, and the gas sequentially passes through the third flow channel 45, the fourth flow channel 46 and the outlet in the second end 48; the flow direction of the gas in the third flow channel 45 and the second flow channel 43 is the same, and opposite to the flow direction in the main flow channel 44.

[0024] In order to prevent turbulence, further, the flow direction of the gas in the first flow channel 42 and the fourth flow channel 46 is the same, and the distance between the second flow channel 43 and the third flow channel 45 is greater than the diameter of the main flow channel 44.

[0025] A first annular seal 31 is provided between the first light source 11 and the first end 47, and gas from the second flow channel 43 enters the area surrounded by the first annular seal 31 and then enters the main flow channel 44.

[0026] A second annular seal 32 is provided between the second light source 12 and the second end 48, and gas from the main flow channel 44 enters the area surrounded by the second annular seal 32 and then enters the third flow channel 45.

[0027] In order to improve the conversion efficiency, further, the light source is an LED with a central wavelength of 395 nm.

[0028] In order to facilitate manufacturing, further, the first flow channel 42 and the fourth flow channel 46 are arranged along the radial direction of the flow cell 41.

[0029] Based on the nitrogen oxide analysis method of the analysis device of the embodiment, the analysis method is as follows: The gas sequentially passes through the inlet, the first flow channel 42 and the second flow channel 43, and then enters the main flow channel 44.

[0030] The light emitted by the first light source 11 enters the main flow channel 44, and the nitrogen dioxide in the gas undergoes photolysis to generate nitric oxide.

[0031] The generated nitric oxide sequentially passes through the third flow channel 45 and the fourth flow channel 46 and is sent to the downstream analysis.

[0032] The conversion efficiency CE of the nitrogen dioxide in the flow cell 41 satisfies: CE=Aexp(-k2t res )[1-exp(-k1t res )]+C, t res =V / Q; V is the volume of the flow cell, Q is the gas flow rate, and A, k1 and k2 are coefficients.

[0033] Embodiment 2

[0034] Application example of the nitrogen oxide analysis device and method according to Embodiment 1 of the application.

[0035] In this application example, as shown in Figure 2 The flow cell 41 is made of metal and is in a cylindrical shape, and the inside is a cylindrical main flow channel 44. The inner wall of the flow cell 41 adjacent to the main flow channel 44 is polished.

[0036] The first light source 11 and the second light source 12 are narrow-band LEDs with a central wavelength of 395 nm, and the power is adjustable from 10 W to 100 W.

[0037] Under the irradiation of the light emitted by the light source, the photolysis reaction formula of NO2 is as follows: NO2 + hv → NO + O.

[0038] In order to maintain high conversion efficiency while avoiding cross-interference of other nitrogen-containing compounds such as HONO, NO3, BrONO2, etc., each flow channel is designed as follows: The first flow channel 42 and the fourth flow channel 46 are arranged along the radial direction of the flow cell 41 in a cylindrical shape, and the central axes of the two flow channels are perpendicular to the central axis of the flow cell 41 and coplanar. The second flow channel 43 and the third flow channel 45 are both annular grooves. The end portion 49 of the cylindrical body between the annular groove and the main flow channel 44 is located to the right of the first end 47 and to the left of the second end 48, i.e., at both ends of the main flow channel 44. Along the central axis direction of the flow cell 41, the first end 47, the end portion 49, the inlet, the outlet, the end portion 49, and the second end 48 are sequentially arranged. In the radial direction of the flow cell 41, the inlet, the first flow channel 42, the second flow channel 43, the main flow channel 44, the third flow channel 45, the fourth flow channel 46, and the outlet are sequentially arranged.

[0039] The tooth-shaped heat sink 21, the first light source 11, the first annular sealing member 31, the flow cell 41 body, the second annular sealing member 32, the second light source 12, and the tooth-shaped heat sink 21 are sequentially arranged, so that the main flow channel 44 is only in communication with the opening and the outlet.

[0040] The conversion efficiency CE of nitrogen dioxide in the flow cell 41 satisfies: CE = Aexp(-k2t res )[1-exp(-k1t res )]+C, t res =V / Q; V is the volume of the flow cell, Q is the gas flow rate, A, k1, and k2 are coefficients. Based on the measured residence time-conversion efficiency data in FIG. 4, the aforementioned CE formula is globally optimized and fitted using the Differential Evolution algorithm (Differential Evolution), and the optimal fitting degree R2≈0.9464 is obtained. Accordingly, the model parameters of this embodiment are determined as follows: A≈11.1585, k1≈1.2079, k2≈0.1761, C≈89.0019.

[0041] As Figure 4 shown, the conversion efficiency CE increases with the increase of the residence time t res , but too long residence time t res will increase the recombination reaction between photolysis products, thereby causing the conversion efficiency to decrease. In the case where the volume of the flow cell 41 (i.e., the volume of the photolysis reaction chamber) V is determined, the residence time t resThis optimizes conversion efficiency; conversely, with a fixed inlet / outlet flow rate Q, the residence time t can be adjusted by changing the volume V of the reaction chamber. res This optimizes conversion efficiency.

[0042] In this embodiment, the dwell time t res The conversion efficiency reaches over 96% within the range of 1.4s to 1.8s.

[0043] like Figure 3 As shown, the airflow in the reaction chamber (mainstream channel 44) is highly ordered, ensuring that the airflow streamlines in the reaction chamber are almost of equal length, which fundamentally guarantees the uniformity of the residence time of gas molecules.

[0044] The nitrogen oxide analysis method based on the analytical apparatus of this embodiment is as follows: The gas passes through the inlet and the first flow channel 42 in sequence, and then enters the second flow channel 43 (around the main flow channel 44). The gas flows in the reverse direction (from the second end 48 to the first end 47) in the second flow channel 43, and then enters the area enclosed by the first annular seal 31, as well as the area between the first end 47 and the end 49. Finally, it enters the main flow channel 44 and flows in the forward direction (from the first end 47 to the second end 48).

[0045] The reverse light emitted by the first light source 11 and the second light source 12 enters the main channel 44, and the nitrogen dioxide in the gas undergoes a photolysis reaction to generate nitric oxide.

[0046] The generated nitric oxide enters the area enclosed by the second annular seal 32 and the area between the second end 48 and the end 49, then flows in reverse into the third flow channel 45 (around the main flow channel 44), and finally exits from the fourth flow channel 46 and the outlet for downstream analysis.

[0047] Example 3

[0048] The application example of the nitrogen oxide analysis apparatus and method according to Embodiment 1 of the present invention differs from that in Embodiment 2 in that: like Figure 5 As shown, the second flow channel 43 and the third flow channel 45 are both cylindrical and parallel to the central axis of the flow pool 41. The distance between the central axes of the two flow channels is greater than the diameter of the main flow channel 44.

Claims

1. A nitrogen oxide analysis apparatus, comprising a first light source, the first light source being used to excite the photolysis reaction of nitrogen dioxide; characterized in that, The analytical apparatus further includes: A flow cell has a main channel along its axial direction, an inlet located adjacent to a first end of the flow cell, and an outlet located adjacent to a second end; the first end, the inlet, the outlet, and the second end are arranged sequentially along the axial direction of the flow cell. The first flow channel and the second flow channel are disposed in the body of the flow pool. Gas enters the main flow channel through the inlet, the first flow channel and the second flow channel in sequence, and flows in the direction from the first end to the second end. The third and fourth flow channels are disposed within the body of the flow pool. Gas in the second end passes through the third and fourth flow channels and the outlet in sequence. The gas flows in the same direction in the third and second flow channels and in the opposite direction to the main flow channel.

2. The analytical apparatus according to claim 1, characterized in that, The gas flows in the same direction in the first and fourth flow channels, and the distance between the second and third flow channels is greater than the diameter of the main flow channel.

3. The analytical apparatus according to claim 2, characterized in that, A first annular seal is provided between the first light source and the first end. Gas enters the area enclosed by the first annular seal from the second flow channel, and then enters the main flow channel.

4. The analytical apparatus according to claim 2, characterized in that, The analytical apparatus further includes: A second light source is provided between the second light source and the second end. Gas flowing out of the main channel enters the area enclosed by the second annular seal and then enters the third channel.

5. The analytical apparatus according to claim 1, 3, or 4, characterized in that, The second and third flow channels are cylindrical or annular grooves.

6. The analytical apparatus according to claim 5, characterized in that, The ends of the cylindrical body between the annular groove and the main channel are located on the right side of the first end and on the left side of the second end.

7. The analytical apparatus according to claim 1, characterized in that, The first and fourth flow channels are arranged radially along the flow pool.

8. A nitrogen oxide analysis method based on the analytical apparatus of claim 1, wherein the analytical method comprises: The gas passes sequentially through the inlet, the first flow channel, and the second flow channel before entering the main flow channel; The light emitted by the first light source enters the main channel, and the nitrogen dioxide in the gas undergoes a photolysis reaction to generate nitric oxide; The generated nitric oxide is sequentially sent downstream for analysis through the third and fourth flow channels.

9. The analytical method according to claim 8, characterized in that, The conversion efficiency CE of nitrogen dioxide in the flow cell satisfies: CE=Aexp(-k2t res )[1-exp(-k1t res )]+C,t res =V / Q; V is the volume of the flow cell, Q is the gas flow rate, and A, k1, and k2 are coefficients.

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