A diversion sampling method

Abstract

This invention relates to the field of environmental monitoring technology, and more particularly to a diversion sampling method. The technical solution of this invention includes: S1, inserting one end of a main sampling tube into the gas flow to be sampled; S2, activating a pump in a flow control assembly to allow the gas to be sampled to enter the main sampling tube; S3, adjusting the flow rates in each sampling branch tube to their corresponding second flow rates, and adjusting the flow rate in the main branch tube to a first flow rate, so that the gas to be sampled passes through the main sampling tube at the sum of the first and second flow rates, and a portion of the gas to be sampled enters the sampling section at the second flow rate, where the second flow rate is the sampling flow rate corresponding to the sampling section; wherein, the first flow rate is much greater than the sum of the second flow rates on all sampling branch tubes, so that the time for the gas to be sampled to pass through the main sampling tube is less than a first preset threshold.

Description

Technical Field

[0001] This invention relates to the field of environmental monitoring technology, and in particular to a diversion sampling method. Background Technology

[0002] Some highly reactive and adsorbent substances are difficult to detect accurately in environmental monitoring. This is largely because they undergo reactions and adsorption during the collection process, making efficient and representative sampling challenging. This situation is particularly severe in stationary source exhaust gases. Stationary source exhaust gases generally have a more complex substrate than ambient air, and different exhaust gases have different substrates; many pollutants have high concentrations, and their impact cannot be ignored; some exhaust gases have high temperatures, even exceeding 200°C, which favors reactions; and some exhaust gases have high moisture content, interfering with monitoring.

[0003] There are actually many highly reactive or highly adsorbent target substances that need to be monitored. For example, ammonia is a target substance required by many emission standards. It is chemically reactive; ammonia in exhaust gas can undergo acid-base reactions with nitrogen oxides and sulfur dioxide, as well as redox reactions with oxides. It also readily adsorbs onto surfaces such as cement, metal, and silica gel. Other substances requiring monitoring include phosgene, ethylene glycol, and ethylene oxide, as required by the "Emission Standard of Pollutants from Petrochemical Industry" (GB 31571-2015). Some substances currently lack relevant analytical methods and standards, making them difficult to monitor; others have technical flaws that hinder accurate monitoring, leading to inadequate control.

[0004] The collection of such substances is currently required by the corresponding analytical method standards. However, these standards do not specifically address the aforementioned characteristics of the target substances. For example, the standard for "Determination of Ammonia in Ambient Air and Exhaust Gas by Nessler's Reagent Spectrophotometric Method" (HJ 533-2009) states: "Industrial exhaust gas sampling: Use a 50ml absorption tube to collect samples at a flow rate of 0.5–1L / min. The sampling time depends on the specific circumstances. If the temperature of the industrial exhaust gas (such as flue gas) is significantly higher than the ambient temperature, the sampling pipeline should be heated to prevent condensation in the sampling pipeline." This only specifies the need for heating, without specifying the heating temperature or the material of the sampling tube. However, because the exhaust pipes of stationary pollution sources have a certain diameter (including wall thickness), the sampling tubes used for collecting exhaust gas have a certain length, generally a minimum of 1.5m and rarely exceeding 5m. For substances with high chemical activity and strong adsorption, losses due to reactions and adsorption already occur during the sample's passage through the sampling tube, and the extent of these losses is difficult to ignore.

[0005] Taking ammonia as an example, some experiments have shown that different materials used for tubing have varying adsorption effects on ammonia. Polytetrafluoroethylene (PTFE) and 316L stainless steel show relatively good results. Using a stainless steel sampling tube, which can be temperature-controlled up to 120℃ and continuously sampled at 0.5 L / min, the recovery rate only gradually increased from over 50% to about 80% after 1 hour, and the subsequent increase became increasingly slow. This not only significantly extended the working time but also greatly affected the accuracy. However, if a higher flow rate is used, the absorption efficiency of the absorbent for ammonia is difficult to guarantee.

[0006] In summary, existing technologies for sampling such substances in exhaust gases have significant reliability issues. Some solutions exist, such as sampling and monitoring methods for condensable particulate matter (CPM) based on the changes in ammonia entering the atmosphere (due to a sharp drop in temperature). However, this sampling method involves complex instruments with large and heavy structures, and cumbersome operation, resulting in a poor on-site sampling experience. Furthermore, due to the complexity of the instruments, their manufacturing costs are high, leading to a correspondingly high price, generally exceeding 400,000 RMB per set.

[0007] In summary, existing technologies have reliability issues in collecting highly active and highly adsorbent target substances from pollutant source gases. Summary of the Invention

[0008] Based on the above analysis, embodiments of the present invention aim to provide a shunting sampling method, including:

[0009] S1. One end of the main sampling tube is inserted into the gas flow to be sampled. One end of the main sampling tube is connected to the main branch tube and at least one sampling branch tube. The main sampling tube is connected to the sampling unit through the sampling branch tube. The main branch tube and each of the sampling units are connected to the flow control assembly. The flow control assembly is used to adjust the flow rate of the gas flowing through the corresponding branch tube.

[0010] S2. Start the pump in the flow control assembly to allow the gas to be sampled to enter the main sampling tube;

[0011] S3. The flow rate in each sampling branch pipe is adjusted to the corresponding second flow rate by the flow control assembly, and the flow rate in the main branch pipe is adjusted to the first flow rate, so that the gas to be sampled passes through the main sampling pipe with the sum of the first flow rate and the second flow rate, and a portion of the gas to be sampled enters the sampling section with the second flow rate, wherein the second flow rate is the sampling flow rate corresponding to the sampling section;

[0012] Wherein, the first flow rate is much greater than the sum of the second flow rates on all sampling branches, so that the time for the gas to be sampled to pass through the main sampling tube is less than a first preset threshold.

[0013] In some embodiments, prior to step S3, the method further includes:

[0014] Simultaneously, the pumps corresponding to the main branch pipe and each sampling branch pipe are turned on, and the flow rate of the main branch pipe is adjusted to 10L / min through the flow control assembly, while the flow rate in each sampling branch pipe is adjusted to 20% of that of the main branch pipe, for a preset time.

[0015] Adjust the flow rate in each sampling branch to the second flow rate corresponding to each sampling section.

[0016] In some embodiments, step S3 includes:

[0017] The flow control assembly first activates the pumps of each sampling branch pipe with the second flow rate corresponding to each sampling branch pipe;

[0018] After a preset time, the corresponding pump in the main branch pipe is activated by the flow control assembly at the first flow rate.

[0019] In some embodiments, the first preset threshold is less than 3 seconds.

[0020] In some embodiments, when performing step S3, the gas flow rate in the main sampling tube is not less than 2 m / s.

[0021] In some embodiments, the flow control assembly includes a multi-channel flow control unit, which is respectively connected to the main branch pipe and each sampling branch pipe, and the flow control unit includes a flow controller and a pump connected in series.

[0022] In some embodiments, the length of the sampling branch pipe is no more than 20 cm.

[0023] In some embodiments, the sampling unit includes one or more of a solution absorption bottle, an adsorption tube, or a gas bag, with each sampling unit corresponding to one sampling branch tube.

[0024] In some embodiments, the method further includes the following steps prior to step S1:

[0025] The main sampling tube and each sampling branch tube are heated and the temperature is controlled to 120℃~220℃.

[0026] This invention, through different flow rate controls on the main branch pipe and the sampling branch pipe, achieves a high gas velocity in the main sampling pipe. This results in a very short gas flow time through the main branch pipe, preventing reactive target substances (such as ammonia) from reacting with other substances. Furthermore, the high-speed "washing" effect significantly reduces the adsorption of highly absorbent target substances (such as ethylene glycol). Under these conditions, the target substances can reach the diversion port "without damage" and then be diverted for collection. This minimizes sampling loss and ensures the representativeness of the collected samples and the accuracy of the monitoring results. Attached Figure Description

[0027] The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. Throughout the drawings, the same reference numerals denote the same parts.

[0028] Figure 1 This is a schematic diagram of the flow sampling method provided by the present invention;

[0029] Figure 2 This is a schematic diagram of the flow splitting method for the sampling method provided by the present invention;

[0030] Figure 3 This is a schematic diagram of the shunt sampling system structure provided by the present invention;

[0031] Figure 4 This is a schematic diagram of the shunt sampling tube structure provided by the present invention;

[0032] Figure 5 A schematic diagram of the arc-shaped bend structure provided by the present invention.

[0033] Figure label:

[0034] 100. Diversion sampling system; 1. Main sampling tube; 2. Main branch tube; 3. Sampling branch tube; 4. Sampling section; 5. Flow control assembly; 6. Flow controller; 7. Pump; 8. Filter adsorption head; 9. Solution absorption bottle; 10. Adsorption tube; 11. Gas bag; 200. Diversion sampling tube; 210. Sampling tube body; 220. Arc-shaped bend; 221. Main body connecting section; 222. Arc-shaped section; 223. Diversion section; 230. Filter cartridge; 240. Sampling nozzle; 241. First straight section; 242. Second straight section; 243. Bending section; 250. Pitot tube; 260. Mounting bracket; 270. Lifting bracket. Detailed Implementation

[0035] The preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings, which constitute a part of the present invention and are used together with the embodiments of the present invention to illustrate the principles of the present invention, but are not intended to limit the scope of the present invention.

[0036] In the description of the embodiments of the present invention, it should be noted that, unless otherwise explicitly specified and limited, the term "connected" should be interpreted broadly. For example, it can refer to a fixed connection, a detachable connection, or an integral connection; it can refer to a mechanical connection or an electrical connection; it can refer to a direct connection or an indirect connection through an intermediate medium. Those skilled in the art can understand the specific meaning of the above terms in the present invention according to the specific circumstances.

[0037] Throughout the text, the terms “top,” “bottom,” “above,” “below,” and “on top” refer to the relative positions of components of the device, such as the relative positions of the top and bottom substrates within the device. It is understood that the device is multifunctional and independent of its spatial orientation.

[0038] The working surface of this invention can typically be a plane or a curved surface, and can be inclined or horizontal. For ease of explanation, the embodiments of this invention are placed on a horizontal surface and used on a horizontal surface, thereby defining "height" and "vertical".

[0039] Example 1

[0040] This embodiment aims to provide a diversion sampling method, such as Figure 1 As shown, it includes:

[0041] S1. The gas to be sampled is introduced into the main sampling pipe. One end of the main sampling pipe is connected to the main branch pipe and at least one diversion sampling branch pipe. The main sampling pipe is connected to the sampling unit through the diversion sampling branch pipe. The main branch pipe and each of the sampling units are connected to the flow control assembly. The flow control assembly is used to adjust the flow rate of the gas flowing through the corresponding branch pipe.

[0042] S2. The flow rate in each shunt sampling branch is adjusted to the second flow rate by the flow control assembly, and the flow rate in the main branch is adjusted to the first flow rate, so that the gas to be sampled passes through the main sampling pipe with the sum of the first flow rate and the second flow rate, and a portion of the gas to be sampled enters the sampling section with the second flow rate, wherein the second flow rate is the sampling standard flow rate of the gas in the corresponding shunt sampling branch.

[0043] Wherein, the first flow rate is much greater than the sum of the second flow rates on all the branch sampling pipes, so that the time for the gas to be sampled to pass through the main sampling pipe is less than a first preset threshold.

[0044] In some embodiments, the flow control assembly includes a multi-channel flow control unit, which is respectively connected to the main branch pipe and each shunt sampling branch pipe. The flow control unit includes a mass flow controller and a pump connected in series.

[0045] Specifically, such as Figure 2 As shown, the number of branching flows can be 1 to n. The flow relationship is: Q0 = Q1 + Q2 + ... + Q n Where Q0 represents the flow rate in the main sampling pipe, Q1 represents the flow rate in the main branch pipe, and Q2~Q nThis indicates the flow rate in other shunt sampling branches. Experimental verification shows that the time for the gas to be sampled to pass through the main sampling tube should not exceed 0.8s, meaning the linear velocity corresponding to Q0 should be greater than 2m / s. The inner diameter of the main sampling tube is generally 1cm, and its length is 1.5m. In this case, Q0 is greater than 9L / min. The corresponding shunt sampling branch pipeline for each shunt (from the shunt inlet to the absorption, adsorption, and gas bag collection points, etc.) should be as short as possible, preferably no more than 20cm, and temperature should be controlled as much as possible to reduce adsorption losses. The corresponding flow rate is the appropriate flow rate for each target analyte. For example, if Q2 is for collecting ammonia using an absorbent liquid, its shunt sampling flow rate should not exceed 0.5L / min. Generally, Q1 is significantly greater than other shunt samples Q2 to Q... n sum.

[0046] Specifically, the flow control for the main branch pipe Q1 should be calculated based on the actual equipment conditions. For example, if particle size is not a concern, at startup, assuming the inner diameter of the main sampling pipe is d (cm) and its length is l (m), and the time for the target object to pass through the main sampling pipe is less than 0.8s, then the flow velocity should be within 1.25l (m / s). Therefore, the total sampling flow rate should be:

[0047]

[0048] If the flow rates of each collected gaseous substance are Q2 to Qn, then the minimum flow rate that the main pipe needs to control is Q1 = Q0 - ∑Q n =5.89d 2 l-∑Q n (L / min).

[0049] As mentioned above, sampling tubes for stationary pollution source exhaust gases typically require at least 1.5m in length. For highly reactive and strongly adsorbed target substances, this length results in negligible losses. For example, the ideal flow rate for ammonia sampling using absorbent is no more than 0.5L / min. After ammonia molecules enter the sampling tube, it takes more than 12 seconds to pass through, providing sufficient time for reaction. In this method, the main sampling tube has a very high flow rate, which prevents the reactive target substance (such as ammonia) from reacting with other substances. Furthermore, strongly adsorbed target substances (such as ethylene glycol) will have reduced adsorption due to the high-speed "washing" effect. The main sampling tube is also heated and temperature-controlled throughout, further reducing the possibility of adsorption. Under these conditions, the target substance can reach the diversion port almost "without loss" and then be sampled. The pipe from the diversion port to the sampling section is as short as possible. Although the flow rate of the diversion sampling branch pipe is lower, its smaller inner diameter (generally less than 6mm) and shorter length (<20cm) allow it to reach the sampling section in only about 1 second for collection, and the flow rate is suitable for the absorption or adsorption of the target substance. The above method is like "instantly teleporting" the exhaust gas in the pipeline of a fixed pollution source to the diversion port, where it is then diverted and collected, minimizing losses and ensuring the representativeness of the collected samples and the accuracy of the monitoring results.

[0050] In some embodiments, when performing step S3, the gas flow rate in the main sampling tube is not less than 2 m / s.

[0051] The flow control assembly in this method incorporates a multi-channel flow controller and pump, featuring integrated control algorithms and logic. However, due to the significant difference in flow velocities between the main branch pipe and the sampling branch pipe, a "backflow" phenomenon can easily occur at the sampling section of the sampling branch pipe. For example, ammonia absorbent may easily overflow towards the branch outlet, leading to monitoring failure. Therefore, the following two methods are used to address this issue:

[0052] In some embodiments, prior to step S2, the method further includes:

[0053] Simultaneously turn on the pumps of the main branch pipe and each sampling branch pipe, and adjust the flow rate of the main branch pipe to 10L / min through the flow control assembly, while adjusting the flow rate in each sampling branch pipe to 20% of that in the main branch pipe, for a preset time.

[0054] Adjust the flow rate in each sampling branch to the second flow rate corresponding to each sampling section.

[0055] That is, all the shunt ports (Q1 to Qn) are opened at the same time, but the initial flow rate of the sampling branch shunt is about 20% of that of the main branch (e.g., Q1 is 10L / min, Q2 is 2L / min). After a few seconds, the sampling branch shunt is reduced to the sampling flow rate (e.g., 0.5L / min). The gas collected in the first few seconds is the original gas in the sampling section, which has little impact on the measurement results.

[0056] In another embodiment, step S2 includes:

[0057] The flow control assembly first activates the pumps of each sampling branch pipe with the second flow rate corresponding to each sampling branch pipe;

[0058] After a preset time, the pump in the main branch pipe is started with a first flow rate via the flow control assembly.

[0059] First, turn on the pump and flow controller corresponding to the small-flow shunt sampling branch pipe and collect data for a few seconds. At this time, the collected data mainly consists of the original gas in the sampling section, which has little impact on the measurement results. Then, turn on the pump and flow controller on the large-flow main branch pipe.

[0060] In some embodiments, the first preset threshold is between 0.5 seconds and 1 second.

[0061] In some embodiments, the length of the main sampling tube is between 1.5m and 5m, and the inner diameter is between 0.5 and 1.5cm.

[0062] In some embodiments, the length of the shunt sampling branch pipe is no more than 20 cm.

[0063] In some embodiments, the sampling unit includes one or more of the following sampling containers (sampling methods): solution absorption bottle, adsorption tube, or gas bag, with each sampling unit corresponding to one of the branch sampling tubes. Specifically, for example, a solution absorption bottle is used to collect ammonia via acid solution absorption-ion chromatography; a solution absorption bottle is used to collect formaldehyde via 2,4-dinitrophenylhydrazine (DNPH) solution derivatization absorption-liquid chromatography; an adsorption tube is used to collect VOCs such as benzene series compounds via solid-phase adsorption-thermal desorption / gas chromatography-mass spectrometry, with the tube filled with solid-phase adsorption material to collect volatile organic compounds (VOCs); a gas bag (3L specification) is used to collect sulfur-containing organic compounds such as methanethiol, employing gas bag sampling-pre-concentration / gas chromatography-mass spectrometry. In some embodiments, the second flow rate corresponds to different sampling units, and the correspondence includes:

[0064] When the sampling unit is the absorption bottle of the absorption liquid, the corresponding second flow rate is less than 1 L / min;

[0065] When the sampling unit is the adsorption tube, the corresponding second flow rate is 50 ml / min;

[0066] When the sampling unit is the air bag, the corresponding second flow rate is less than 1 L / min.

[0067] In some embodiments, the method further includes the following steps prior to step S1:

[0068] The main sampling tube and each shunt sampling branch tube are heated and temperature controlled, with the maximum temperature controlled at 120℃ or 220℃.

[0069] Example 2

[0070] This embodiment aims to provide a diversion sampling system 100, such as Figure 3 As shown, it includes:

[0071] Main sampling tube 1 is used to collect the gas to be sampled from the pollution source;

[0072] Main branch pipe 2 is located at one end of the main sampling pipe 1 and is connected to the main sampling pipe 1;

[0073] At least one shunt sampling branch pipe 3 is located at one end of the main sampling pipe 1 and is connected to the main sampling pipe 1;

[0074] At least one sampling unit 4 is connected to each of the aforementioned shunt sampling branch pipes 3;

[0075] The flow control assembly 5 includes a multi-channel flow control unit, which is respectively connected to the main branch pipe 2 and each diversion sampling branch pipe 3. The flow control assembly 5 is used to control the flow rate in the diversion sampling branch pipe 3 and the main branch pipe 2 respectively, so that the gas flow rate in the diversion sampling branch pipe 3 meets the preset flow rate required by the corresponding sampling unit 4, and so that the time for the gas to be sampled to pass through the main sampling pipe 1 is less than a first preset threshold.

[0076] In this embodiment, the flow control assembly 5 controls the different flow rates of the branch sampling pipe 3 and the main branch pipe 2. The preset flow rate of the branch sampling pipe 3 is relatively small, meeting the sampling requirements of the corresponding sampling unit 4. The main branch pipe 2, on the other hand, controls a larger flow rate, resulting in a higher overall flow rate in the main sampling pipe 1. This allows the gas in the main sampling pipe 1 to pass through quickly, preventing the target analyte from being adsorbed by the main sampling pipe 1 and causing inaccurate detection results. Simultaneously, the small flow rate control of the branch sampling pipe 3 ensures that the target analyte enters at a suitable absorption rate, allowing it to be fully absorbed by the sampling unit 4. This reduces the adsorption effect of the pipe on the target analyte while ensuring the absorption of the target analyte by the sampling unit 4.

[0077] In some embodiments, the length of the main sampling tube 1 is between 1.5m and 5m, and the inner diameter is between 0.5 and 1.5cm. The main sampling tube 1 is heated and temperature controlled. If the entire tube is made of 316L stainless steel with a polished inner surface, the maximum temperature control should be 220℃; if it is lined with polytetrafluoroethylene, the maximum temperature control should be 120℃.

[0078] In some embodiments, the flow control unit includes a mass flow controller 6 and a pump 7 connected in series, with the mass flow controller 6 located close to the sampling unit 4 relative to the pump 7. The flow control assembly 5 integrates multiple flow control units, each with interconnected algorithms and logic. The mass flow controller 6 is a device for accurately measuring and controlling the gas flow rate. Preferably, the mass flow controller 6 employs electronic control and can be an electronic mass flow meter or an electronic pressure flow meter, etc.

[0079] In some embodiments, the flow control unit further includes a filter adsorption head 8, which is disposed on the side of the flow controller 6 near the sampling unit 4. In this embodiment, a filter adsorption material is present at the inlet end of the mass flow controller 6, which can effectively remove moisture and particulate matter.

[0080] In some embodiments, the maximum flow rate of the pump 7 corresponding to the main branch pipe 2 is greater than the maximum flow rate of the pump 7 corresponding to the shunt sampling branch pipe 3. Specifically, the pump 7 on the main branch pipe 2 is a large pump 7, preferably a high-flow pump 7, with a maximum pumping speed of up to 100 L / min; the sampling pump 7 on the shunt sampling branch pipe 3 can be a pump 7 with a smaller maximum flow rate and lower volume and power.

[0081] In some embodiments, the first preset threshold is between 0.5 seconds and 1 second. Preferably, the time for the sample to be collected to pass through the main sampling tube 1 should not exceed 0.8 seconds.

[0082] In some embodiments, the length of the shunt sampling branch pipe 3 is no more than 20 cm. The pipe connecting the shunt sampling branch pipe 3 to the sampling section 4 should be as short as possible. Because the gas flow rate in the shunt sampling branch pipe 3 is small and low, an excessively long shunt sampling branch pipe 3 can easily lead to the adsorption of the target substance.

[0083] In some embodiments, the sampling unit 4 includes one or more of the following sampling containers (sampling methods): solution absorption bottle 9, adsorption tube 10, or gas bag 11. Each sampling unit 4 corresponds to one of the aforementioned diversion sampling branch tubes 3. Specifically, for example, a solution absorption bottle 9 is used to collect ammonia by acid solution absorption-ion chromatography; a solution absorption bottle 9 is used to collect formaldehyde by 2,4-dinitrophenylhydrazine (DNPH) solution derivatization absorption-liquid chromatography; the sampling unit 4 used to collect VOCs such as benzene series compounds by solid phase adsorption-thermal desorption / gas chromatography-mass spectrometry is an adsorption tube 10, which is filled with solid phase adsorption material to collect volatile organic compounds (VOCs); the gas bag 11 (3L specification) is used to collect sulfur-containing organic compounds such as methanethiol by gas bag 11 sampling-pre-concentration / gas chromatography-mass spectrometry. Figure 1 The number of absorption bottles and adsorption tubes 10 connected in series in the diagram is only for illustration purposes. The specific number can be adjusted. For example, three absorption bottles should be connected in series for formaldehyde.

[0084] In addition, the gas flow rate in the shunt sampling branch 3 should be the appropriate flow rate recommended by the standard sampling method for each target object.

[0085] In some embodiments, the main sampling tube 1 is made of stainless steel or an inert alloy, and the inner wall of the main sampling tube 1 is polished.

[0086] In some embodiments, the inner wall of the main sampling tube 1 is provided with a liner, the material of which includes polytetrafluoroethylene or quartz.

[0087] Specifically, the sampling tube must be made of a material with good inertness, meaning it should not react with or promote the adsorption of the target substance, and should also have advantages such as corrosion resistance. It also requires heating throughout the entire process (including the filter head at the inlet end of the sampling tube). All parts of the tubing can be made of 316L stainless steel with electrolytic polishing of the inner wall to reduce adsorption; alternatively, sampling tubes with a polytetrafluoroethylene inner wall and an alloy outer wall can be used, with the inner wall still needing to be as smooth as possible; alternatively, sampling tubes with a quartz inner wall and an alloy outer wall can be used, with the inner wall still needing to be as smooth as possible.

[0088] In this embodiment, the flow control assembly 5 controls the different flow rates of the branch sampling pipe 3 and the main branch pipe 2. The preset flow rate of the branch sampling pipe 3 is relatively small, meeting the sampling requirements of the corresponding sampling unit 4. The main branch pipe 2, on the other hand, controls a larger flow rate, resulting in a higher overall flow rate in the main sampling pipe 1. This allows the gas in the main sampling pipe 1 to pass through quickly, preventing the target analyte from being adsorbed by the main sampling pipe 1 and causing inaccurate detection results. Simultaneously, the small flow rate control of the branch sampling pipe 3 ensures that the target analyte enters at a suitable absorption rate, allowing it to be fully absorbed by the sampling unit 4. This reduces the adsorption effect of the pipe on the target analyte while ensuring the absorption of the target analyte by the sampling unit 4.

[0089] Example 3

[0090] To reduce the adsorption effect on the target object during the sampling process from the structural level of the sampling pipeline, the main sampling pipe 1, main branch pipe 2, and diversion sampling branch pipe 3 in Example 2 can adopt the scheme of this embodiment. This embodiment aims to provide a diversion sampling pipe 200, such as... Figure 4 and Figure 5 As shown, it includes:

[0091] Sampling tube body 210;

[0092] The arc-shaped bend 220 has a main connecting section 221, an arc section 222, and a diversion section 223. The main connecting section 221 is used to coaxially communicate with the sampling tube body 210. The two ends of the arc section 222 are respectively connected to the main connecting section 221 and the diversion section 223.

[0093] The diversion sampling branch pipe 3 is connected to the end of the diversion section 223 away from the arc section 222, and the axis of the diversion sampling branch pipe 3 is coaxial with the axis of the diversion section 223;

[0094] The main branch pipe 2 is located on the side wall of the diversion section 223. The main branch pipe 2 is connected to the diversion section 223, and the axis of the main branch pipe 2 and the axis of the diversion section 223 form an angle.

[0095] This invention employs an arc-shaped bend 220 at the end of the sampling tube, with the arc pointing in the direction of the flow as the branch sampling tube 3 for lower flow rates, and the angled direction as the main branch tube 2 for higher flow rates. This design helps to more uniformly distribute large molecular targets or aerosols. Otherwise, when there are significant flow rate differences, these large molecules or aerosols, due to their higher kinetic energy, preferentially flow in the fluid direction. If the higher flow rate is in the fluid direction, the branch port may not be able to collect the target substance with the corresponding flow rate ratio, resulting in a problem similar to "flow discrimination" in gas chromatography. The solution provided by this invention avoids flow discrimination. Furthermore, the sampling tube in this embodiment uses a branch-shaped arc-shaped bend 220 structure at the rear end, utilizing the guiding effect of the arc structure to reduce the impact and retention of fine particles, thereby improving measurement accuracy.

[0096] In this embodiment, the diversion sampling branch pipe 3 of the small flow diversion port is designed to be vertically downward, and the outlet is directly and seamlessly connected to the inlet of the absorption bottle or adsorption tube 10, so that the condensation of moisture in the waste gas occurs in the air inlet pipe of the absorption bottle, thereby avoiding the measurement result of ammonia due to water vapor condensation.

[0097] Preferably, each part of the pipeline is made of a material with good inertness, meaning it has advantages such as corrosion resistance while not reacting with or promoting the adsorption of the target substance. 316L stainless steel can be used, with the inner wall electropolished to reduce adsorption; alternatively, sampling tubes with a polytetrafluoroethylene inner wall and an alloy outer wall can be used, with the inner wall still needing to be as smooth as possible; or sampling tubes with a quartz inner wall and an alloy outer wall can be used, with the inner wall still needing to be as smooth as possible. 316L stainless steel sampling tubes should ideally have a high controllable temperature range. For example, in ammonia analysis, the maximum temperature control should ideally be up to 220℃. At this temperature, even if ammonium salts are present, they are easily decomposed due to the high temperature. For sampling tubes with a polytetrafluoroethylene coating, the maximum heating temperature should preferably not be lower than 120℃.

[0098] In some embodiments, the two ends of the arc-shaped segment 222 are tangent to the axes of the main connecting segment 221 and the diversion segment 223, respectively. A smooth transition reduces the adsorption or reaction between the target substances in the exhaust gas and the pipe wall, and the tangential transition of the pipe's axes reduces the impact on gas flow rate.

[0099] In some embodiments, the angle between the axis of the main branch pipe 2 and the axis of the branch section 223 is 90 degrees.

[0100] In some embodiments, the angle between the axis of the diversion section 223 and the axis of the main body connecting section 221 is 90 degrees. Generally, the flue is vertical. In this embodiment, the sampling tube body 210 is typically inserted horizontally into the flue, and the end is conveniently connected to the sampling part 4, which is adjusted to have an opening facing downwards via the arc-shaped bend 220.

[0101] In some embodiments, a filter cartridge 230 is further included, disposed at the end of the sampling tube body 210 away from the arc-shaped bend 220. The filter cartridge 230 is used to collect particulate matter. In this embodiment, the front end is equipped with a filter cartridge 230 to collect particulate matter, and the rear end is connected in series with an absorption bottle containing an absorption liquid to collect gaseous matter, thereby achieving simultaneous collection of gaseous and particulate matter.

[0102] Preferably, the filter cartridge 230, the sampling tube body 210, and the arc-shaped bend 220 are all wrapped with heating wires and insulation cotton, providing heat tracing throughout the process, with the heating temperature controlled at 220℃.

[0103] In some embodiments, a sampling nozzle 240 is further included, disposed at one end of the sampling tube body 210 away from the arc-shaped bend 220. The sampling nozzle 240 is connected to the sampling tube body 210. The inlet of the sampling nozzle 240 has a first straight segment 241, the axis of which is parallel to the flow direction of the flue gas to be collected. The end of the sampling nozzle 240 away from the first straight segment 241 has a second straight segment 242, which is coaxially connected to the sampling tube body 210. The sampling nozzle 240 also has a curved segment 243, the two ends of which are tangent to the axes of the first straight segment 241 and the second straight segment 242, respectively.

[0104] In some embodiments, a Pitot tube 250 is also included, which is detachably mounted on the sampling tube body 210 and is used to measure the flow velocity of the flue gas to be collected in real time.

[0105] The detachable Pitot tube 250 design allows the sampling gun to be installed in both horizontal and vertical directions, enabling it to sample in both horizontal and vertical flues.

[0106] In some embodiments, the shunt sampling branch pipe 3 is used to connect to the first pump 7, the first pump 7 being used to make the sampling flow rate in the shunt sampling branch pipe 3 less than 0.5 L / min;

[0107] The main branch pipe 2 is connected to the second pump 7, which is used to match the flow rate at the inlet of the sampling nozzle 240 with the flow rate of the flue gas to be collected, based on the flow velocity of the flue gas to be collected. In this embodiment, a Pitot tube 250 is used to measure the flue gas velocity in real time. By adjusting the sampling pump 7, the sampling flow rate at the sampling nozzle 240 is kept consistent with the flue gas velocity. This allows the exhaust gas to enter the sampling tube in its original state, reducing the adsorption effect caused by changes in flow velocity.

[0108] In some embodiments, the inner walls of the sampling tube body 210, the arc-shaped bend 220, the diversion sampling branch pipe 3, and the main branch pipe 2 are all polished. Preferably, the pipe material is, for example, an electrolytically polished 316L stainless steel tube.

[0109] In some embodiments, the system further includes a mounting bracket 260 for mounting and fixing the sampling tube body 210 and the arc-shaped bend 220; and a lifting bracket 270 connected to the mounting bracket 260, on which a sampling section 4 for placing the target object is mounted. The sampling section 4 may include, for example, an ice bath containing an absorption bottle, and the lifting bracket 270 for holding the ice bath can be adjusted in height to accommodate absorption bottles of different sizes.

[0110] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A diversion sampling method, characterized in that, include: S1. One end of the main sampling tube is inserted into the gas flow to be sampled. One end of the main sampling tube is connected to the main branch tube and at least one sampling branch tube. The main sampling tube is connected to the sampling unit through the sampling branch tube. The main branch tube and each of the sampling units are connected to the flow control assembly. The flow control assembly is used to adjust the flow rate of the gas flowing through the corresponding branch tube. S2. Start the pump in the flow control assembly to allow the gas to be sampled to enter the main sampling tube; S3. The flow rate in each sampling branch pipe is adjusted to the corresponding second flow rate by the flow control assembly, and the flow rate in the main branch pipe is adjusted to the first flow rate, so that the gas to be sampled passes through the main sampling pipe with the sum of the first flow rate and the second flow rate, and a portion of the gas to be sampled enters the sampling section with the second flow rate, wherein the second flow rate is the sampling flow rate corresponding to the sampling section; Wherein, the first flow rate is much greater than the sum of the second flow rates on all sampling branches, so that the time for the gas to be sampled to pass through the main sampling tube is less than a first preset threshold, the first preset threshold being between 0.5 seconds and 1 second.

2. The diversion sampling method according to claim 1, characterized in that: Before step S3, the following is also included: Simultaneously, the pumps corresponding to the main branch pipe and each sampling branch pipe are turned on, and the flow rate of the main branch pipe is adjusted to 10L / min through the flow control assembly, while the flow rate in each sampling branch pipe is adjusted to 20% of that in the main branch pipe, for a preset time. Adjust the flow rate in each sampling branch to the second flow rate corresponding to each sampling section.

3. The diversion sampling method according to claim 1, characterized in that: Step S3 includes: The flow control assembly first activates the pumps of each sampling branch pipe with the second flow rate corresponding to each sampling branch pipe; After a preset time, the corresponding pump in the main branch pipe is activated by the flow control assembly at the first flow rate.

4. The shunting sampling method according to claim 1, characterized in that: When performing step S3, the gas flow rate in the main sampling tube shall not be less than 2 m / s.

5. The diversion sampling method according to claim 1, characterized in that: The flow control assembly includes a multi-channel flow control unit, which is respectively connected to the main branch pipe and each sampling branch pipe. The flow control unit includes a flow controller and a pump connected in series.

6. The diversion sampling method according to claim 1, characterized in that: The length of the sampling branch pipe shall not exceed 20cm.

7. The diversion sampling method according to claim 1, characterized in that: The sampling unit includes one or more of the following: solution absorption bottle, adsorption tube, or gas bag, with each sampling unit corresponding to one sampling branch tube.

8. The diversion sampling method according to claim 1, characterized in that: The steps preceding step S1 also include: The main sampling tube and each sampling branch tube are heated and the temperature is controlled to 120℃~220℃.

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