Nitrogen oxide analysis device and method

Abstract

The present application relates to spectral technology, and specifically provides a nitrogen oxide analysis device and method, the analysis device comprising a first light source; further comprising: a flow cell having a main flow channel along its axial direction, an inlet being arranged adjacent to a first end of the flow cell, and an outlet being arranged adjacent to a second end; the first end, the inlet, the outlet and the second end are sequentially arranged in the axial direction of the flow cell; a first flow channel and a second flow channel are arranged in the body of the flow cell, and the 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; a third flow channel and a fourth flow channel are arranged in the body of the flow cell, and the gas sequentially passes through the third flow channel, the fourth flow channel and the outlet in the second end; the flow directions of the gas in the third flow channel and the second flow channel are the same and opposite to the flow direction in the main flow channel. The present application has the advantages of accurate measurement results.

Description

Technical Field

[0001] This invention relates to spectroscopic techniques, and more particularly to apparatus and methods for analyzing nitrogen oxides. Background Technology

[0002] Currently, NOx measurement methods can be divided into two technical paths based on their detection principles. The first category is based on direct NO2 detection and NO-to-NO2 conversion techniques, including naphthylethylenediamine hydrochloride spectrophotometry (Saltzman method), luminol chemiluminescence (Luminox), tunable diode laser absorption spectroscopy (TDLAS), differential absorption spectroscopy (DOAS), cavity ring-down spectroscopy (CRDS), and laser-induced fluorescence (LIF). The second category is based on direct NO detection and NO2-to-NO conversion techniques, including molybdenum catalytic conversion-chemiluminescence and photolysis-chemiluminescence (P-CL).

[0003] Among the two monitoring methods mentioned above, the molybdenum catalytic conversion-chemiluminescence method is the standard method for the automatic determination of nitrogen oxides in ambient air in my country. The principle is that at 300-350℃, NO2 is converted to NO through catalysis by a thermal matrix such as molybdenum oxide, and then the NOx concentration is determined using chemiluminescence. However, this method suffers from cross-interference in practical applications; other nitrogen-containing compounds (such as HNO3 and N2O) can also be converted to NO, leading to an overestimation of the actual NOx concentration.

[0004] The principle of photocatalytic conversion-chemiluminescence (P-CL) is that NO2 is photocatalytically broken down into NO and O atoms under light irradiation in a specific wavelength range. The NO photocatalytic product is then detected using chemiluminescence to determine the NOx concentration. This method can effectively avoid cross-interference by selecting a light source in a specific wavelength range, thereby improving the accuracy of NOx concentration measurements.

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

[0006] Both US Patent 11435291 and Chinese Patent CN109310979B disclose a photolysis converter for converting reactant molecules in a fluid sample into product molecules using electromagnetic radiation. The converter includes a reaction chamber, an electromagnetic radiation source, an inlet pipe, and an outlet pipe. At least one of the pipes extends into the reaction chamber. This extension into the reaction chamber allows for orderly airflow within the chamber, reducing the likelihood of recombination reactions between the photolysis products and improving conversion efficiency. However, this method has the following drawbacks:

[0007] 1. Extending the inflow or outflow pipes into the reaction chamber increases the complexity and manufacturing cost of the photolysis device.

[0008] 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, the airflow at the inlet will form turbulence, which will further affect the photolysis conversion efficiency.

[0009] 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.

[0010] 3. Pipes used as flow guiding structures are usually made of glass. Glass is fragile and requires high precision during installation and handling.

[0011] 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:

[0012] 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.

[0013] 2. The gas system uses quartz tubes, which are relatively fragile and require high precision during installation and handling. Summary of the Invention

[0014] To address the shortcomings of the existing technical solutions, the present invention provides a nitrogen oxide analysis device.

[0015] The objective of this invention is achieved through the following technical solution:

[0016] A nitrogen oxide analysis apparatus includes a first light source for exciting the photolysis reaction of nitrogen dioxide; the analysis apparatus further includes:

[0017] 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.

[0018] 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.

[0019] 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.

[0020] Another objective of this invention is to provide a method for analyzing nitrogen oxides, which is achieved through the following technical solution:

[0021] The nitrogen oxide analysis method based on the analytical apparatus of the present invention is as follows:

[0022] The gas passes sequentially through the inlet, the first flow channel, and the second flow channel before entering the main flow channel;

[0023] 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;

[0024] The generated nitric oxide is sequentially sent downstream for analysis through the third and fourth flow channels.

[0025] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0026] This invention, by designing a flow channel on the body of the flow cell, can guide the internal airflow to achieve orderly flow without the need for additional flow guiding structures, thus significantly improving the conversion efficiency of the photolysis reaction;

[0027] By eliminating the external structure, the device structure is simplified, manufacturing costs are reduced, and obstruction to radiation and airflow is avoided, ensuring a more uniform distribution of the radiation field and airflow within the reaction chamber, thus further guaranteeing efficient conversion.

[0028] Flow cells made of metal have higher mechanical strength than those made of glass, significantly reducing the risk of breakage. Attached Figure Description

[0029] The disclosure of this invention will become more readily understood with reference to the accompanying drawings. It will be readily understood by those skilled in the art that these drawings are merely illustrative of the technical solutions of this invention and are not intended to limit the scope of protection of this invention. In the drawings:

[0030] Figure 1 This is a schematic diagram of fluid simulation in existing technology;

[0031] Figure 2This is a schematic diagram of the structure of the analytical device according to the present invention;

[0032] Figure 3 This is a schematic diagram of fluid simulation of the analysis device according to Embodiment 2 of the present invention;

[0033] Figure 4 This is a diagram illustrating the relationship between conversion efficiency and dwell time;

[0034] Figure 5 This is a schematic diagram of fluid simulation of the analysis device according to Embodiment 3 of the present invention.

[0035] In the attached diagram, 11-first light source, 12-second light source, 21-heat sink, 31-first annular seal, 32-second annular seal, 41-flow pool, 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. Detailed Implementation

[0036] Figures 2-5 The following description illustrates optional embodiments of the invention to teach those skilled in the art how to implement and reproduce the invention. Some conventional aspects have been simplified or omitted to explain the technical solutions of the invention. Those skilled in the art should understand that variations or substitutions derived from these embodiments will be within the scope of the invention. Those skilled in the art should understand that the following features can be combined in various ways to form multiple variations of the invention. Therefore, the invention is not limited to the following optional embodiments, but is defined only by the claims and their equivalents.

[0037] Example 1

[0038] The nitrogen oxide analysis device of this invention includes a conversion unit and an analysis unit, such as... Figure 2 As shown, the conversion unit includes:

[0039] The light emitted by the first light source 11 irradiates the gas, causing the nitrogen dioxide in the gas to undergo a photolysis reaction to generate nitric oxide.

[0040] The flow cell 41 has a main channel 44 along its axial direction, with an inlet located adjacent to the first end 47 of the flow cell 41 and an outlet located adjacent to the second end 48; the first end 47, the inlet, the outlet, and the second end 48 are arranged sequentially along the axial direction of the flow cell 41.

[0041] The first flow channel 42 and the second flow channel 43 are disposed in the body of the flow pool 41. The gas passes through the inlet, the first flow channel 42 and the second flow channel 43 in sequence, enters the main flow channel 44, and flows in the direction from the first end 47 to the second end 48.

[0042] The third flow channel 45 and the fourth flow channel 46 are disposed within the body of the flow pool 41. Gas in the second end 48 passes through the third flow channel 45, the fourth flow channel 46 and the outlet in sequence. The gas flows in the same direction in the third flow channel 45 and the second flow channel 43, and in the opposite direction to the main flow channel 44.

[0043] To prevent turbulence, the gas flows in the same direction in the first channel 42 and the fourth channel 46, and the distance between the second channel 43 and the third channel 45 is greater than the diameter of the main channel 44.

[0044] A first annular seal 31 is provided between the first light source 11 and the first end 47. Gas enters the area enclosed by the first annular seal 31 from the second flow channel 43, and then enters the main flow channel 44.

[0045] A second annular seal 32 is provided between the second light source 12 and the second end 48. Gas flowing out of the main channel 44 enters the area enclosed by the second annular seal 32 and then enters the third channel 45.

[0046] To further improve conversion efficiency, the light source is an LED with a center wavelength of 395nm.

[0047] For ease of manufacturing, the first flow channel 42 and the fourth flow channel 46 are further arranged radially along the flow pool 41.

[0048] The nitrogen oxide analysis method based on the analytical apparatus of this embodiment is as follows:

[0049] The gas passes through the inlet, the first flow channel 42, and the second flow channel 43 in sequence, and enters the main flow channel 44.

[0050] The light emitted by the first light source 11 enters the main channel 44, and the nitrogen dioxide in the gas undergoes a photolysis reaction to generate nitric oxide.

[0051] The generated nitric oxide is sequentially sent downstream for analysis through the third flow channel 45 and the fourth flow channel 46.

[0052] The conversion efficiency CE of nitrogen dioxide in the flow cell 41 satisfies:

[0053] CE=Aexp(-k2t res )[1-exp(-k1t res )]+C,t res =V / Q;

[0054] V is the volume of the flow cell, Q is the gas flow rate, and A, k1, and k2 are coefficients.

[0055] Example 2

[0056] Application examples of the nitrogen oxide analysis apparatus and method according to Embodiment 1 of the present invention.

[0057] In this application example, such as Figure 2 As shown, the flow cell 41 is made of metal and is cylindrical, with a cylindrical main channel 44 inside. The inner wall of the flow cell 41 adjacent to the main channel 44 is polished.

[0058] The first light source 11 and the second light source 12 are narrowband LEDs with a center wavelength of 395nm and adjustable power from 10W to 100W.

[0059] Under the illumination of the light emitted from the light source, the photolysis reaction of NO2 is as follows:

[0060] NO2 + hv → NO + O.

[0061] To maintain high conversion efficiency while minimizing cross-interference from other nitrogen-containing compounds such as HONO, NO3, and BRONO2, the flow channels are designed as follows:

[0062] The first flow channel 42 and the fourth flow channel 46 are arranged radially along the flow pool 41 and are cylindrical. The central axes of these two flow channels are perpendicular to the central axis of the flow pool 41 and are coplanar. The second flow channel 43 and the third flow channel 45 are both annular grooves. The end 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 of the flow pool 41, the first end 47, the end 49, the inlet, the outlet, the end 49, and the second end 48 are arranged sequentially. In the radial direction of the flow pool 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 arranged sequentially.

[0063] The toothed radiator 21, the first light source 11, the first annular seal 31, the main body of the flow pool 41, the second annular seal 32, the second light source 12 and the toothed radiator 21 are arranged in sequence so that the main flow channel 44 is only connected to the opening and the outlet.

[0064] The conversion efficiency CE of nitrogen dioxide in the flow cell 41 satisfies:

[0065] CE=Aexp(-k2t res )[1-exp(-k1t res )]+C,t res =V / Q;

[0066] V is the volume of the flow cell, Q is the gas flow rate, and A, k1, and k2 are coefficients. Based on the measured residence time-conversion efficiency data in Figure 4, the Differential Evolution algorithm was used to globally optimize and fit the aforementioned CE formula, obtaining a goodness-of-fit R²≈ 0.9464. Based on this, the model parameters for this embodiment were determined as follows: A≈11.1585, k1≈1.2079, k2≈0.1761, C≈89.0019.

[0067] like Figure 4 As shown, the conversion efficiency CE increases with residence time t res The increase is due to the increase in the duration of the stay, but excessively long stay times t res This will increase the recombination reactions between photolysis products, thus leading to a decrease in conversion efficiency. With a fixed volume V of the flow cell 41 (i.e., the volume of the photolysis reaction chamber), the residence time t can be adjusted by adjusting the inlet / outlet gas flow rate Q. res This 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.

[0068] In this embodiment, the dwell time t res The conversion efficiency reaches over 96% within the range of 1.4s to 1.8s.

[0069] 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.

[0070] The nitrogen oxide analysis method based on the analytical apparatus of this embodiment is as follows:

[0071] 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).

[0072] 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.

[0073] 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.

[0074] Example 3

[0075] 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:

[0076] 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 method based on a nitrogen oxide analysis device, wherein the analysis device includes a first light source for exciting the photolysis reaction of nitrogen dioxide; the analysis device 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, inlet, outlet, and second end are sequentially arranged along the axial direction of the flow cell; the flow cell is cylindrical in shape, with a cylindrical main channel inside. The first flow channel and the second flow channel are disposed within the body of the flow pool. 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. A first annular seal is disposed 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. 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. 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. The first and fourth flow channels are arranged radially along the flow pool and are cylindrical. The central axes of the first and fourth flow channels are perpendicular to the central axis of the flow pool and are coplanar. The gas flows in the same direction in the first and fourth flow channels. Both the second and third flow channels are annular grooves. The first end of the cylindrical body between the second flow channel and the main flow channel is located to the right of the first end, and the second end of the cylindrical body between the third flow channel and the main flow channel is located to the left of the second end. Along the central axis of the flow pool, the first end, the first end, the inlet, the outlet, the second end, and the second end are arranged in sequence. In the radial direction of the flow pool, the inlet, the first flow channel, the second flow channel, the main flow channel, the third flow channel, the fourth flow channel, and the outlet are arranged in sequence. The analytical method is as follows: The gas passes through the inlet and the first flow channel in sequence, and then enters the second flow channel surrounding the main flow channel. The gas flows in reverse in the second flow channel, from the second end to the first end. Then it enters the area enclosed by the first annular seal and the area between the first end and the first end. Finally, it enters the main flow channel and flows in the forward direction, from the first end to the second end. The reverse light emitted by the first and second light sources enters the main channel, and the nitrogen dioxide in the gas undergoes a photolysis reaction to generate nitric oxide. The generated nitric oxide enters the area enclosed by the second annular seal and the area between the second end and the second end, then flows in reverse into the third flow channel surrounding the main flow channel, and finally exits from the fourth flow channel and the outlet, and is sent downstream for analysis. 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; Conversion efficiency CE as a function of residence time t res The increase is due to the increase in the excessively long dwell time t res This will increase the recombination reaction between photolysis products, thus leading to a decrease in conversion efficiency; with a fixed volume V, the residence time t can be adjusted by adjusting the inlet / outlet flow rate. res This optimizes conversion efficiency; conversely, given a fixed intake / exhaust flow rate, the residence time t can be adjusted by adjusting the volume V. res This optimizes conversion efficiency.

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