Non-methane total hydrocarbon detection device and method

Abstract

The invention provides a non-methane total hydrocarbon detection device and a non-methane total hydrocarbon detection method. The non-methane total hydrocarbon detection device comprises a catalysis unit and an FID (Flame Ionization Detector), the switching module is used for enabling the outlet to selectively communicate with the first inlet or the second inlet; a sample gas is divided into a first flow path, a second flow path and a third flow path after passing through the first branch; the second branch is arranged on the second flow path and divides the second flow path into a flow path communicated with the first inlet and a flow path communicated with the fourth branch; the third branch is arranged on the first flow path and is used for dividing the first flow path into a flow path communicated with the second inlet and a flow path communicated with the fourth branch; the pressure sensor and the FID detector are respectively communicated with the fourth branch; the catalytic unit is arranged in the second flow path or a flow path between the fourth branch and the FID detector; the gas passing through the flow adjusting unit carries the sample gas in the third flow path and flows to the downstream; the controller adjusts the flow adjusting unit according to the output of the pressure sensor. The method has the advantages of accurate detection and the like.

Description

Technical Field

[0001] This invention relates to gas detection, and more particularly to a device and method for detecting non-methane total hydrocarbons. Background Technology

[0002] With rapid industrialization, VOC emissions have increased significantly, and environmental monitoring is paying increasing attention to VOC emissions. Since methane is harmless to the human body, VOC emissions are mainly monitored by measuring the content of non-methane total hydrocarbons (NMHC).

[0003] Currently, some regions are experiencing a complex pollution pattern characterized by regional haze, ozone, and acid rain, with non-methane hydrocarbons (NMH) being a significant contributing factor. Most NMH have distinctive odors that can cause various adverse reactions in the human body, including eye and respiratory irritation, skin allergies, headaches, sore throats, and fatigue. They are also toxic, irritating, teratogenic, and carcinogenic, with benzene, toluene, and formaldehyde being particularly harmful to human health.

[0004] Non-methane hydrocarbons react with nitrogen oxides under ultraviolet light to form ozone, a representative pollutant of photochemical smog. Non-methane hydrocarbons are a significant contributor to rising atmospheric ozone concentrations, leading to regional photochemical smog, acid rain, and haze. Non-methane hydrocarbons also participate in the formation of secondary aerosols in the atmosphere. These secondary aerosols are mostly fine particles that are difficult to settle and can remain in the atmosphere for extended periods. They have a strong light-scattering effect, significantly reducing atmospheric visibility.

[0005] There are many methods for monitoring NMHC in ambient air and industrial exhaust gases, the main ones being: 1. Chromatography, specifically, involves separating multiple components of a sample one by one and measuring their respective contents. Chromatography has a complex structure, slow response speed, and requires multi-port valves to control sample injection, resulting in high costs.

[0006] 2. Catalytic oxidation method: This method can remove organic matter other than methane and then directly measure the methane content, and then use the difference method to directly obtain the result.

[0007] like Figure 1 As shown, in commonly used non-methane total hydrocarbon detection devices, the catalytic unit 41 is installed in the methane flow path 11. A first solenoid valve 21 controls whether the methane flow path 11 is connected to the FID detector 31, and a second solenoid valve 22 controls whether the total hydrocarbon flow path 12 is connected to the FID detector 31. The drawback of this scheme is: 1. The solenoid valve is located upstream of the FID detector. The high temperature of the solenoid valve's sealing ring causes the release of volatile organic compounds, which interferes with the detection results and leads to inaccurate measurements. 2. The solenoid valve has a dead volume, and there is residual sample gas in the first half of the switching cycle when the first solenoid valve and the second solenoid valve switch, resulting in inaccurate measurement. 3. The sampling flow rate is small, the gas replacement volume is large during switching, the sampling and replacement time is long, and the response is relatively slow. Summary of the Invention

[0008] To address the shortcomings of the existing technical solutions, the present invention provides a non-methane total hydrocarbon detection device.

[0009] The objective of this invention is achieved through the following technical solution: A non-methane total hydrocarbon detection device, comprising a catalytic unit and an FID detector; the non-methane total hydrocarbon detection device further comprising: A switching module, the switching module being configured to selectively connect its outlet to a first inlet or a second inlet; The first branch, after the sample gas passes through the first branch, is divided into the first flow path, the second flow path and the third flow path; The second branch is disposed on the second flow path and is used to divide the second flow path into a flow path that connects to the first inlet and a flow path that connects to the fourth branch; The third branch is disposed on the first flow path and is used to divide the first flow path into a flow path that connects to the second inlet and a flow path that connects to the fourth branch; The fourth branch and the pressure sensor are respectively connected to the fourth branch; the catalytic unit is disposed in the second flow path, or in the flow path between the fourth branch and the FID detector; The flow adjustment unit allows the gas, carrying the sample gas from the third flow path, to flow downstream. A controller that adjusts the flow adjustment unit based on the output of the pressure sensor.

[0010] The present invention also aims to provide a method for detecting non-methane total hydrocarbons using the non-methane total hydrocarbon detection device of the present invention. This objective is achieved through the following technical solution: According to the non-methane total hydrocarbon detection method of the non-methane total hydrocarbon detection device of the present invention, the non-methane total hydrocarbon detection method is as follows: Total hydrocarbon detection: the switching module switches, and the first inlet is connected to the outlet; after the sample gas passes through the first branch, the flow rates in the first flow path and the second flow path are the same; after the sample gas in the first flow path passes through the third branch, it reaches the fourth branch; part of the sample gas enters the FID detector to obtain the total hydrocarbon content; the other sample gas reaches the second branch; the sample gas in the mixed second flow path passes through the first inlet and the outlet in sequence. Methane detection: the switching module switches, and the second inlet is connected to the outlet; after the sample gas passes through the first branch, the flow rates in the first flow path and the second flow path are the same; after the sample gas in the second flow path passes through the second branch, it reaches the fourth branch; part of the sample gas enters the FID detector to obtain the methane content, and the other sample gas reaches the third branch, mixes with the sample gas in the first flow path, and passes through the second inlet and outlet in sequence. Based on the total hydrocarbon content and methane content, the non-methane total hydrocarbon content in the sample gas is obtained; During the above process, the sample gas flow rate entering the FID detector through the fourth branch is the same; other gases, after passing through the flow adjustment unit, carry the sample gas in the third flow path downstream, and the controller adjusts the flow adjustment unit according to the output value of the pressure sensor.

[0011] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. High detection accuracy; By adjusting the flow path and component settings, when detecting methane or total hydrocarbons, part of the sample gas after upstream diversion enters the single FID detector, and part enters the downstream switching module. That is, the detection does not need to pass through the switching module (such as a three-way solenoid valve) first, so that the detection is not affected by the switching module, such as by the volatiles of the solenoid valve seal ring or the dead volume of the solenoid valve, thereby improving the detection accuracy. By adjusting the driving gas flow rate, the sample gas pressure at the fourth branch was kept stable, further improving the detection accuracy. 2. Large sampling flow rate; When detecting methane (total hydrocarbons), a switching module is used to select the flow path, so that part of the sample gas in the second flow path (first flow path) enters the FID detector, and part of the sample gas enters and mixes with the sample gas in the first flow path (second flow path). Finally, the sample is emptied through the switching module, thereby increasing the sampling flow rate. The sample gas enters the first, second, and third flow paths simultaneously, further increasing the sampling flow rate. Attached Figure Description

[0012] 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: Figure 1 This is a simplified structural diagram of a non-methane total hydrocarbon detection device in the existing technology; Figure 2 This is a simplified structural diagram of a non-methane total hydrocarbon detection device according to an embodiment of the present invention. Detailed Implementation

[0013] Figure 2The 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 for the purpose of teaching 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.

[0014] Example 1.

[0015] The non-methane total hydrocarbon detection device of this invention embodiment, such as Figure 2 As shown, the non-methane total hydrocarbon detection device includes: Catalytic unit 41 and FID detector 31, wherein the catalytic unit 41 is used to catalytically convert non-methane components in the sample gas; Switching module 61, the switching module 61 is used to selectively connect its outlet 64 to the first inlet 62 or the second inlet 63; The first branch 51, after the sample gas passes through the first branch 51, is divided into the first flow path 82, the second flow path 81, and the third flow path 83; The second branch 52 is disposed on the second flow path 81 and is used to divide the second flow path 81 into a flow path that connects to the first inlet 62 and a flow path that connects to the fourth branch 54. The third branch 53 is disposed on the first flow path 82 and is used to divide the first flow path 82 into a flow path that connects to the second inlet 63 and a flow path that connects to the fourth branch 54. The fourth branch 54 and the pressure sensor 91 are connected to the fourth branch 54, and the pressure sensor 91 and the FID detector 31 are respectively connected to the fourth branch 54; the catalytic unit 41 is disposed in the second flow path 81, or in the flow path between the fourth branch 54 and the FID detector 31; The gas passing through the flow adjustment unit 71 carries the sample gas in the third flow path 83 downstream; A controller that adjusts the flow adjustment unit 71 based on the output of the pressure sensor 91.

[0016] To ensure stable combustion, a sixth branch 56 is provided in the flow path between the fourth branch 54 and the FID detector 31. The inlet is connected to the combustion-supporting gas and the fourth branch 54, and the outlet is connected to the FID detector 31, which is connected to air.

[0017] To facilitate compensation of the output value of the pressure sensor 91, the non-methane total hydrocarbon detection device further includes: The fifth branch 55 has an outlet and two inlets, which are respectively connected to the flow adjustment unit 71 and the third flow path 83.

[0018] The non-methane total hydrocarbon detection method of this embodiment of the invention, that is, the working method of the non-methane total hydrocarbon detection device of this embodiment, wherein the non-methane total hydrocarbon detection method is as follows: Total hydrocarbon detection is performed by switching module 61, with the first inlet 62 connected to the outlet 64. After the sample gas passes through the first branch 51, the flow rates in the first flow path 82 and the second flow path 81 are the same. The sample gas in the first flow path 82 passes through the third branch 53 and reaches the fourth branch 54. Part of the sample gas enters the FID detector 31 to obtain the total hydrocarbon content, while the other sample gas reaches the second branch 52. The sample gas in the second flow path 81 is mixed and passes through the first inlet 62 and the outlet 64 in sequence. For methane detection, the switching module 61 switches, and the second inlet 63 is connected to the outlet 64. After the sample gas passes through the first branch 51, the flow rates in the first flow path 82 and the second flow path 81 are the same. The sample gas in the second flow path 81 passes through the second branch 52 and reaches the fourth branch 54. Part of the sample gas enters the FID detector 31 to obtain the methane content, and the other sample gas reaches the third branch 53, mixes with the sample gas in the first flow path 82, and passes through the second inlet 63 and the outlet 64 in sequence. Based on the total hydrocarbon content and methane content, the non-methane total hydrocarbon content in the sample gas is obtained; During the above process, the sample gas flow rate entering the FID detector 31 through the fourth branch 54 is the same; other gases, after passing through the flow adjustment unit 71, carry the sample gas in the third flow path 83 downstream, and the controller adjusts the flow adjustment unit 81 according to the output value of the pressure sensor 91.

[0019] Example 2.

[0020] An application example of the non-methane total hydrocarbon detection device according to Embodiment 1 of the present invention.

[0021] In this application example, such as Figure 2 As shown, the first branch 51 adopts a four-way valve, and the second branch 52 to the sixth branch 56 all adopt three-way valves. Hydrogen is used as a combustion-supporting gas and is connected to the sixth branch 56. The catalytic unit 41 is set in the second flow path 82 and is located between the first branch 51 and the second branch 52. The switching module 61 adopts a three-way solenoid valve, and the flow adjustment unit 71 adopts an EPC.

[0022] The non-methane total hydrocarbon detection method of this embodiment of the invention, that is, the working method of the non-methane total hydrocarbon detection device of this embodiment, wherein the non-methane total hydrocarbon detection method is as follows: For total hydrocarbon detection, the switching module 61 switches, and the first inlet 62 is connected to the outlet 64. After passing through the first branch 51, the sample gas enters the first flow path 82, the second flow path 81 and the third flow path 83 respectively. The flow rate in the first flow path 82 and the second flow path 81 is 100 L / min. The sample gas in the first flow path 82 reaches the fourth branch 54 after passing through the third branch 53. Part of the sample gas enters the FID detector 31 at 20 L / min. Hydrogen and air enter the FID detector 31 to obtain the total hydrocarbon content. The other sample gas reaches the second branch 52 at 80 L / min, mixes with the sample gas in the second flow path 81, and passes through the first inlet 62 and the outlet 64 sequentially at 180 L / min. Methane detection is performed by switching module 61, which connects the second inlet 63 to the outlet 64. After passing through the first branch 51, the sample gas enters the first flow path 82, the second flow path 81, and the third flow path 83 respectively. The flow rates in the first flow path 82 and the second flow path 81 are both 100 L / min. The catalytic unit 41 converts the non-methane in the sample gas in the second flow path 81. After passing through the second branch 52, the sample gas reaches the fourth branch 54. Part of the sample gas, at a flow rate of 20 L / min, enters the FID detector 31 to obtain the methane content. The other sample gas reaches the third branch 53 at a flow rate of 80 L / min, mixes with the sample gas in the first flow path 82, and passes through the second inlet 63 and the outlet 64 sequentially at a flow rate of 180 L / min. Based on the total hydrocarbon content and methane content, the non-methane total hydrocarbon content in the sample gas is obtained; During the above process, other gases reach the fifth branch 55 after passing through the flow adjustment unit 71, carrying the sample gas in the third flow path 83 downstream. The controller adjusts the flow adjustment unit 81 according to the output value of the pressure sensor 91.

Claims

1. A non-methane total hydrocarbon detection device, wherein the non-methane total hydrocarbon detection device comprises a catalytic unit and an FID detector; characterized in that: The non-methane total hydrocarbon detection device also includes: A switching module, the switching module being configured to selectively connect its outlet to a first inlet or a second inlet; The first branch, after the sample gas passes through the first branch, is divided into the first flow path, the second flow path and the third flow path; The second branch is disposed on the second flow path and is used to divide the second flow path into a flow path that connects to the first inlet and a flow path that connects to the fourth branch; The third branch is disposed on the first flow path and is used to divide the first flow path into a flow path that connects to the second inlet and a flow path that connects to the fourth branch; The fourth branch and the pressure sensor are respectively connected to the fourth branch; the catalytic unit is disposed in the second flow path, or in the flow path between the fourth branch and the FID detector; The flow adjustment unit allows the gas, carrying the sample gas from the third flow path, to flow downstream. A controller that adjusts the flow adjustment unit based on the output of the pressure sensor.

2. The non-methane total hydrocarbon detection device according to claim 1, characterized in that: The flow path between the fourth branch and the FID detector is connected to the combustion gas, and the FID detector is connected to the air.

3. The non-methane total hydrocarbon detection device according to claim 1, characterized in that: The non-methane total hydrocarbon detection device also includes: The fifth branch has an outlet and two inlets, the two inlets being connected to the flow adjustment unit and the outlet of the first branch, respectively.

4. The non-methane total hydrocarbon detection device according to claim 1, characterized in that: The flow adjustment unit is an EPC, and the switching module is a three-way solenoid valve.

5. The method for detecting non-methane total hydrocarbons using the non-methane total hydrocarbon detection device according to any one of claims 1-4, wherein the method for detecting non-methane total hydrocarbons is as follows: Total hydrocarbon detection, the switching module switches, and the first inlet is connected to the outlet; After the sample gas passes through the first branch, the flow rates in the first flow path and the second flow path are the same. The sample gas in the first flow path passes through the third branch and reaches the fourth branch. Part of the sample gas enters the FID detector to obtain the total hydrocarbon content, while the other sample gas reaches the second branch. The sample gas in the second flow path is mixed and passes through the first inlet and outlet in sequence. Methane detection, the switching module switches, and the second inlet is connected to the outlet; After the sample gas passes through the first branch, the flow rates in the first and second flow paths are the same. The sample gas in the second flow path passes through the second branch and reaches the fourth branch. Part of the sample gas enters the FID detector to obtain the methane content, while the other sample gas reaches the third branch, mixes with the sample gas in the first flow path, and passes through the second inlet and outlet in sequence. Based on the total hydrocarbon content and methane content, the non-methane total hydrocarbon content in the sample gas is obtained; During the above process, the sample gas flow rate entering the FID detector through the fourth branch is the same; other gases, after passing through the flow adjustment unit, carry the sample gas in the third flow path downstream, and the controller adjusts the flow adjustment unit according to the output value of the pressure sensor.

6. The method for detecting non-methane total hydrocarbons according to claim 5, characterized in that: In total hydrocarbon photodetection and methane detection, the flow rate in the first and second flow paths is 100 L / min, the sample gas flow rate entering the FID detector through the fourth branch is 20 L / min, and the flow rate through the switching module is 180 L / min.

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