Online Detection System and Detection Method for the Content of Non-Methane Total Hydrocarbons in Ambient Air

Abstract

The present invention relates to an on-line detection system and detection method for the content of non-methane total hydrocarbons in ambient air. Two interfaces of the two-way three-way valve are respectively a sample gas inlet and a carrier gas inlet Ⅳ, and one interface is connected to the V0 interface of the ten-way valve; the quantitative loop is connected between the V9 interface and the V2 interface of the ten-way valve, the methane pre-column is connected between the V8 interface and the V4 interface of the ten-way valve, the methane main column is connected to the V9 interface of the ten-way valve and is connected to the FID detector, the V3 interface of the ten-way valve is the carrier gas inlet Ⅱ, the V6 interface of the ten-way valve is the carrier gas inlet Ⅲ, and the V7 interface of the ten-way valve is the vent port Ⅱ; the cold trap tube is connected between the A3 interface and the A6 interface of the six-way valve, the total hydrocarbon special column is connected to the A5 interface of the six-way valve and is connected to the FID detector through a gas resistance, the A4 interface of the six-way valve is the carrier gas inlet Ⅰ; the sampling pump is connected to the A2 interface of the six-way valve, and the outlet is the vent port Ⅰ.

Description

Technical Field

[0001] The present invention relates to the technical field of environmental detection equipment, and particularly relates to an on-line detection system and method for the content of non-methane total hydrocarbons in ambient air. Background Art

[0002] Existing methods for measuring non-methane total hydrocarbons in air mostly include the methane total hydrocarbon subtraction method, the chromatographic column backflush separation method, or the cold trap separation method. All of the above three separation methods have drawbacks: If the methane total hydrocarbon subtraction method is used, when the methane content in the air is much higher than the non-methane total hydrocarbon content, this method will cause the superposition of analysis errors, resulting in a large deviation of the results; If the chromatographic column backflush separation method is used, this method requires that the separation ability of the chromatographic column must be strong enough and the adsorption and desorption time of the heavy components cannot be too long, otherwise it will cause too large an injection bandwidth of non-methane total hydrocarbons, a low peak shape, and a high detection limit; If the cold trap separation method is used, when the air contains components with lower boiling points, it will cause separation errors between methane and non-methane total hydrocarbons, resulting in analysis errors of methane results. Summary of the Invention

[0003] The present invention provides an on-line detection system and method for the content of non-methane total hydrocarbons in ambient air. The cold trap adsorption, high-temperature desorption, and methane chromatographic column separation methods are adopted. The separation of methane and non-methane total hydrocarbons in the air is completed by cold trap adsorption, ensuring a sufficient sampling volume while increasing the measurement sensitivity. The chromatographic principle is used to separate methane, and a pre-column backflush design is included. While ensuring accurate methane analysis, the backflush function increases the service life of the chromatographic column, and increases the stability and reliability of the instrument. The detection gas path of non-methane total hydrocarbons and the detection gas path of methane in the present invention are relatively independent and do not interfere with each other, increasing the adjustability of the entire system and the accuracy of the measurement results.

[0004] The technical solution of the present invention is: An on-line detection system for the content of non-methane total hydrocarbons in ambient air includes an FID detector arranged in an FID temperature control box and a six-way valve, a ten-way valve, a two-way three-way valve, a quantitative ring, a cold trap tube, a total hydrocarbon special column, a methane pre-column, a methane main column, and an air resistance arranged in a main temperature control box; It also includes a mass flowmeter and a sampling pump arranged outside the main temperature control box;

[0005] The lead-out pipe of one of the interfaces of the two-way three-way valve is the sample gas inlet, one interface is the carrier gas inlet IV, and one interface is connected to the V0 interface of the ten-way valve;

[0006] The quantitative loop is connected between the V9 and V2 interfaces of the ten-port valve. The methane pre-column is connected between the V8 and V4 interfaces of the ten-port valve. The methane main column is connected to the outlet pipe of the V5 interface of the ten-port valve and is connected to the FID detector. The outlet pipe of the V3 interface of the ten-port valve is the carrier gas inlet II. The outlet pipe of the V6 interface of the ten-port valve is the carrier gas inlet III. The outlet pipe of the V7 interface of the ten-port valve is the vent II;

[0007] The cold trap tube is connected between the A3 and A6 interfaces of the six-port valve. The total hydrocarbon special column is connected to the outlet pipe of the A5 interface of the six-port valve and is connected to the FID detector through a gas resistance. The outlet pipe of the A4 interface of the six-port valve is the carrier gas inlet I;

[0008] The mass flowmeter is connected to the outlet pipe of the A2 interface of the six-port valve. The sampling pump is connected to the mass flowmeter, and the outlet of the sampling pump is the vent I;

[0009] The cold trap tube includes a cooling device and a flash evaporation device, and the flash evaporation device is arranged inside the cooling device;

[0010] The detection system has five gas paths, namely the sample gas path and four carrier gas paths; when in use, the detection system has four states, namely the injection state, the non-methane total hydrocarbon detection state, the methane detection state, and the purge state. The five gas paths have different connection methods in each state, and the gas path connection in each state is achieved by switching the interfaces of the six-port valve, the ten-port valve, and the three-way valve.

[0011] In the above technical solution, in the injection state, the A2 and A3 interfaces in the six-port valve are connected, the A4 and A5 interfaces are connected, the A1 and A6 interfaces are connected. In the ten-port valve, the V1 and V2 interfaces are connected, the V3 and V4 interfaces are connected, the V5 and V6 interfaces are connected, the V7 and V8 interfaces are connected, and the V9 and V0 interfaces are connected. The two-way three-way valve allows the sample gas to flow in the inlet direction and blocks the carrier gas inlet IV direction;

[0012] The sample gas inlet, the two-way three-way valve, the V0 interface of the ten-port valve, the V9 interface of the ten-port valve, the quantitative loop, the V2 interface of the ten-port valve, the V1 interface of the ten-port valve, the A1 interface of the six-port valve, the A6 interface of the six-port valve, the cold trap tube, the A3 interface of the six-port valve, the A2 interface of the six-port valve, the mass flowmeter, the sampling pump, and the vent I are connected in sequence to form the sample gas path;

[0013] The carrier gas inlet I, the A4 interface of the six-port valve, the A5 interface of the six-port valve, the total hydrocarbon special column, the gas resistance, and the FID detector are connected in sequence to form the first carrier gas path;

[0014] The carrier gas inlet II, the V3 interface of the ten-port valve, the V4 interface of the ten-port valve, the methane pre-column, the V8 interface of the ten-port valve, the V7 interface of the ten-port valve, and the vent II are connected in sequence to form the second carrier gas path;

[0015] The carrier gas inlet Ⅲ, the V6 interface of the ten-way valve, the V5 interface of the ten-way valve, the methane main column, and the FID detector are connected in sequence to form the third carrier gas path;

[0016] In the above technical solution, in the non-methane total hydrocarbon detection state, the A1 and A2 interfaces in the six-way valve 1 are connected, the A3 and A4 interfaces are connected, and the A5 and A6 interfaces are connected. The connections of the interfaces in the ten-way valve 2 are the same as those in the injection state. The sample gas inlet direction of the two-way three-way valve is in circulation, and the carrier gas inlet Ⅳ direction is blocked;

[0017] The sample gas inlet, the two-way three-way valve, the V0 interface of the ten-way valve, the V9 interface of the ten-way valve, the quantitative loop, the V2 interface of the ten-way valve, the V1 interface of the ten-way valve, the A1 interface of the six-way valve, the A2 interface of the six-way valve, the mass flowmeter, the sampling pump, and the vent port Ⅰ are connected in sequence to form the sample gas path;

[0018] The carrier gas inlet Ⅰ, the A4 interface of the six-way valve, the A3 interface of the six-way valve, the cold trap tube, the A6 interface of the six-way valve, the A5 interface of the six-way valve, the total hydrocarbon special column, the gas resistance, and the FID detector are connected in sequence to form the first carrier gas path;

[0019] The carrier gas inlet Ⅱ, the V3 interface of the ten-way valve, the V4 interface of the ten-way valve, the methane pre-column, the V8 interface of the ten-way valve, the V7 interface of the ten-way valve, and the vent port Ⅱ are connected in sequence to form the second carrier gas path;

[0020] The carrier gas inlet Ⅲ, the V6 interface of the ten-way valve, the V5 interface of the ten-way valve, the methane main column, and the FID detector are connected in sequence to form the third carrier gas path;

[0021] In the above technical solution, in the methane detection state, the connections of the interfaces in the six-way valve are the same as those in the injection state. The V0 and V1 interfaces in the ten-way valve are connected, the V2 and V3 interfaces are connected, the V4 and V5 interfaces are connected, the V6 and V7 interfaces are connected, and the V8 and V9 interfaces are connected; the sample gas inlet direction of the two-way three-way valve is blocked, and the carrier gas inlet Ⅳ direction is in circulation;

[0022] The carrier gas inlet Ⅰ, the A4 interface of the six-way valve, the A3 interface of the six-way valve, the cold trap tube, the A6 interface of the six-way valve, the A5 interface of the six-way valve, the total hydrocarbon special column, the gas resistance, and the FID detector are connected in sequence to form the first carrier gas path;

[0023] The carrier gas inlet Ⅱ, the V3 interface of the ten-way valve, the V2 interface of the ten-way valve, the quantitative loop, the V9 interface of the ten-way valve, the V8 interface of the ten-way valve, the methane pre-column, the V4 interface of the ten-way valve, the V5 interface of the ten-way valve, the methane main column, and the FID detector are connected in sequence to form the second carrier gas path;

[0024] The carrier gas inlet Ⅲ, the V6 interface of the ten-way valve, the V7 interface of the ten-way valve, and the vent port Ⅱ are connected in sequence to form the third carrier gas path;

[0025] The carrier gas inlet Ⅳ, the two-way three-way valve, the V0 interface of the ten-way valve, the V1 interface of the ten-way valve, the A1 interface of the six-way valve, the A2 interface of the six-way valve, the mass flow meter, the sampling pump, and the vent port Ⅰ are connected in sequence to form the fourth carrier gas path.

[0026] In the above technical solution, in the purging state, the connections of the interfaces of the six-way valve and the ten-way valve are the same as those in the sampling state. The sample gas inlet direction of the two-way three-way valve is blocked, and the carrier gas inlet Ⅳ direction is in circulation;

[0027] The carrier gas inlet Ⅰ, the A4 interface of the six-way valve, the A5 interface of the six-way valve, the special column for total hydrocarbons, the gas resistance, and the FID detector are connected in sequence to form the sample gas path connection;

[0028] The carrier gas inlet Ⅱ, the V3 interface of the ten-way valve, the V4 interface of the ten-way valve, the methane pre-column, the V8 interface of the ten-way valve, the V7 interface of the ten-way valve, and the vent port Ⅱ are connected in sequence to form the second carrier gas path;

[0029] The carrier gas inlet Ⅲ, the V6 interface of the ten-way valve, the V5 interface of the ten-way valve, the methane main column, and the FID detector are connected in sequence to form the third carrier gas path;

[0030] The carrier gas inlet Ⅳ, the two-way three-way valve, the V0 interface of the ten-way valve, the V9 interface of the ten-way valve, the quantitative loop, the V2 interface of the ten-way valve, the V1 interface of the ten-way valve, the A1 interface of the six-way valve, the A6 interface of the six-way valve, the cold trap tube, the A3 interface of the six-way valve, the A2 interface of the six-way valve, the mass flow meter, the sampling pump, and the vent port Ⅰ are connected in sequence to form the fourth carrier gas path.

[0031] An on-line detection method for the content of non-methane total hydrocarbons in ambient air includes four stages, namely the sampling stage, the stage of detecting non-methane total hydrocarbons, the stage of detecting methane, and the purging stage, and is carried out according to the following steps: Turn on the power of the detection system, set the temperature of the cold trap tube to -100°C to -150°C, the temperature of the main temperature control box to 80 - 140°C, and the temperature of the FID temperature control box to 160 - 200°C;

[0032] Step 1, Sampling Stage: After the temperatures of the cold trap tube, the main temperature control box, and the FID temperature control box reach the set values, turn on the sampling pump and switch the six-way valve, ten-way valve, and two-way three-way valve to the sampling state. The fourth carrier gas does not flow, and the sample gas and the other three carrier gases flow in the gas path during the sampling state. The sample gas is inhaled from the sample gas inlet through the mass flowmeter and the sampling pump. After passing through the two-way three-way valve, the sample gas passes through the V0 interface and V9 interface of the ten-way valve in sequence. When passing through the quantitative loop, the sample gas fills the quantitative loop. The remaining gas then passes through the V2 interface, V1 interface of the ten-way valve, the A1 interface, and A6 interface of the six-way valve and enters the cold trap tube. The non-methane hydrocarbons in the sample gas are fully absorbed by the cold trap tube, and the excess gas passes through the A3 interface and A2 interface of the six-way valve and is finally discharged through the vent port I. Start timing from 0 seconds and maintain for 150 - 200 seconds;

[0033] Step 2, Non-Methane Total Hydrocarbon Detection Stage: After the cold trap tube completes the absorption of non-methane total hydrocarbons, stop the sampling pump and switch the six-way valve to the non-methane total hydrocarbon detection state. The fourth carrier gas still does not flow, and the sample gas and the other three carrier gases flow in the gas path during the non-methane total hydrocarbon detection state. At the same time, the flash evaporation device of the cold trap tube starts to work. The ten-way valve and the two-way three-way valve remain in the sampling state. The first carrier gas is injected from the A4 interface of the six-way valve, passes through the A3 interface of the six-way valve, and blows the non-methane total hydrocarbon gas flashed out from the cold trap tube into the total hydrocarbon special column, and then enters the FID detector. The non-methane total hydrocarbon, abbreviated as NMHC, peaks, and the content of non-methane total hydrocarbons is detected. Maintain for 30 - 45 seconds;

[0034] Step 3, Methane Detection Stage: After the non-methane total hydrocarbon detection is completed, switch the ten-way valve and the two-way three-way valve to the methane detection state, stop sampling, and the four carrier gases flow in the gas path during the methane detection state. The second carrier gas is injected from the V3 interface of the ten-way valve, passes through the V3 interface of the ten-way valve, and blows the sample gas in the quantitative loop through the V9 interface and V8 interface of the ten-way valve into the methane pre-column in sequence to filter out the heavy components in the sample gas. The light-component sample gas then passes through the V4 and V5 interfaces of the ten-way valve and is blown into the methane main column, and finally enters the FID detector. Methane peaks, and the methane content is detected. Maintain for 30 - 45 seconds;

[0035] Step 4, Purge Stage: After the methane detection is completed, that is, after the detection is completed, switch the six-way valve, ten-way valve, and two-way three-way valve to the purge state, stop sampling, and the four carrier gases flow in the gas path during the purge state. The fourth carrier gas purges the quantitative loop and the cold trap tube, the second carrier gas purges the methane pre-column, the third carrier gas purges the methane main column, and the first carrier gas purges the total hydrocarbon special column to make the entire system clean. Maintain for 250 - 300 seconds;

[0036] Step Five, Temperature Control: If the temperature of the cold trap tube is higher than the set temperature, start the refrigeration device; when the set temperature is reached, go to Step One to continue the next round of detection, realizing on-line detection.

[0037] In the above technical solution, the cooling temperature of the cold trap tube is -130 °C, the heating rate during flash evaporation is 100 °C / second, the temperature rises to 280 - 300 °C, the temperature of the main temperature control box is 120 °C, and the temperature of the FID temperature control box is 180 °C.

[0038] Advantages of the present invention: According to the characteristics that the cold trap can be quickly cooled and quickly heated, the present invention first uses the cold trap to adsorb non-methane hydrocarbons in the environment at low temperature, then vaporizes them at high temperature by flash evaporation, and separates methane with a chromatographic column. The separation of methane and non-methane total hydrocarbons in the air is completed by the adsorption of the cold trap, ensuring a sufficient sampling volume while increasing the measurement sensitivity. Chromatographic principle is used to separate methane, and there is a design of pre-column backflushing. While ensuring the accuracy of methane analysis, the backflushing function increases the service life of the chromatographic column and improves the stability and reliability of the instrument; the detection gas path for non-methane total hydrocarbons and the detection gas path for methane of the present invention are relatively independent and do not interfere with each other, increasing the adjustability of the whole system and the accuracy of the measurement results. Through a six-way valve, a ten-way valve and a two-position three-way valve, the gas path is reasonably designed, and through an automatic control device, the gas path is automatically switched in different detection states to realize on-line continuous automatic monitoring of non-methane total hydrocarbons in the environment. Description of the Drawings

[0039] Figure 1 is a schematic structural diagram of the present invention in the sample injection state;

[0040] Figure 2 is a schematic structural diagram of the present invention when detecting non-methane total hydrocarbons;

[0041] Figure 3 is a schematic structural diagram of the present invention when detecting methane;

[0042] Figure 4 is a schematic structural diagram of the present invention in the purge state;

[0043] Figure 5 is a schematic structural diagram of the cold trap of the present invention. Detailed Embodiments

[0044] As Figure 1 shown, for the on-line detection system of the non-methane total hydrocarbon content in ambient air, a six-way valve 1, a ten-way valve 2, a two-position three-way valve 3, a quantitative loop 5, a cold trap tube 6, a total hydrocarbon special column 7, a methane pre-column 8, a methane main column 9 and a gas resistance 10 are connected and installed in a main temperature control box 14; an FID detector 11 is installed in an FID temperature control box 15. The six-way valve 1 is a Canadian AFP six-way valve, and the ten-way valve 2 is a Canadian AFP ten-way valve;

[0045] The six-way valve 1, ten-way valve 2, two-position three-way valve 3, quantitative loop 5, cold trap tube 6, total hydrocarbon special column 7, methane pre-column 8, methane main column 9, gas restrictor 10, mass flowmeter 16 and sampling pump 17 are connected as follows:

[0046] At the V0 interface of the ten-way valve 2, the two-position three-way valve 3 is connected through a gas pipe. At the V9 interface and V2 interface of the ten-way valve 2, the quantitative loop 5 is connected through a gas pipe. Between the V8 interface and V4 interface of the ten-way valve 2, the methane pre-column 8 is connected through a gas pipe. At the V5 interface of the ten-way valve 2, the methane main column 9 is connected through a gas pipe. The methane main column 9 is connected to the inlet gas pipe of the FID detector 11 through a gas pipe;

[0047] Between the A3 interface and A6 interface of the six-way valve 1, the cold trap tube 6 is connected through a gas pipe. At the A5 interface of the six-way valve 1, the total hydrocarbon special column 7 is connected through a gas pipe. Downstream of the total hydrocarbon special column 7, the gas restrictor 10 is connected through a gas pipe. The gas restrictor 10 is connected to the inlet gas pipe of the FID detector 11 through a gas pipe;

[0048] The connected six-way valve 1 and ten-way valve 2 are installed in the main temperature control box 14. The A1 interface of the six-way valve 1 and the V1 interface of the ten-way valve 2 are connected through a gas pipe;

[0049] The A2 interface of the six-way valve 1, the V3 interface of the ten-way valve 2, the V6 interface of the ten-way valve 2, the A4 interface of the six-way valve 1, the V7 interface of the ten-way valve 2 and the two interfaces of the two-position three-way valve 3 are respectively led out of the main temperature control box 14 through gas pipes;

[0050] The mass flowmeter 16 is connected to the outlet pipe of the A2 interface of the six-way valve 1. The sampling pump 17 is connected downstream of the mass flowmeter 16. The outlet of the sampling pump 17 is the vent port I 12-1; The outlet pipe of the V7 interface of the ten-way valve 2 is the vent port II 12-2;

[0051] The outlet pipe of one interface of the two-position three-way valve 3 is the sample gas inlet 4, and the outlet pipe of the other interface is the carrier gas inlet IV 13-4. The outlet pipe of the A4 interface of the six-way valve 1 is the carrier gas inlet I 13-1. The outlet pipe of the V3 interface of the ten-way valve 2 is the carrier gas inlet II 13-2. The outlet pipe of the V6 interface of the ten-way valve 2 is the carrier gas inlet III 13-3;

[0052] As Figure 5As shown in the figure, the cold trap tube 6 includes a cooling device 6-1 and a flash evaporation device 6-2. The flash evaporation device 6-2 is installed inside the cooling device 6-1. The cooling device 6-1 cools the temperature of the cold trap tube 6 to -100°C to -150°C, ensuring maximum adsorption and collection of non-methane hydrocarbons in the sample gas. The flash evaporation device 6-2 raises the temperature of the cold trap tube 6 to 280 - 300°C at a speed of 100°C per second, ensuring instantaneous vaporization of the non-methane hydrocarbons adsorbed by the cold trap tube 6 for detection by the downstream FID detector.

[0053] The detection system has five gas paths, namely the sample gas path and four carrier gas paths. When in use, the detection system has four states, namely the injection state, the non-methane total hydrocarbon detection state, the methane detection state, and the purge state. The five gas paths have different flow directions in each state. The on and off of the six-way valve 1 and the ten-way valve 2 drivers are used to control the flow direction of the internal passages in the valves, and the switching of the interfaces of the three-way valve 3 is combined to achieve the gas path connection in each state. The gas path formed by the six-way valve 1 controls the gas path during the detection of non-methane total hydrocarbons, and the gas path formed by the ten-way valve 2 controls the gas path during the detection of methane. The two-position three-way valve 3 controls the entry of the sample gas and the fourth carrier gas.

[0054] As Figure 1 shown, in the injection state, the A2 and A3 interfaces in the six-way valve 1 are connected, the A4 and A5 interfaces are connected, and the A1 and A6 interfaces are connected. In the ten-way valve 2, the V1 and V2 interfaces are connected, the V3 and V4 interfaces are connected, the V5 and V6 interfaces are connected, the V7 and V8 interfaces are connected, and the V9 and V0 interfaces are connected. The two-position three-way valve 3 allows the sample gas to flow in the direction of the inlet 4 and blocks the carrier gas inlet in the direction of Ⅳ13-4.

[0055] The sample gas inlet 4, the two-position three-way valve 3, the V0 interface of the ten-way valve 2, the V9 interface of the ten-way valve 2, the quantitative loop 5, the V2 interface of the ten-way valve 2, the V1 interface of the ten-way valve 2, the A1 interface of the six-way valve 1, the A6 interface of the six-way valve 1, the cold trap tube 6, the A3 interface of the six-way valve 1, the A2 interface of the six-way valve 1, the mass flow meter 16, the sampling pump 17, and the vent port Ⅰ12-1 are connected in sequence to form the sample gas path.

[0056] The carrier gas inlet Ⅰ13-1, the A4 interface of the six-way valve 1, the A5 interface of the six-way valve 1, the total hydrocarbon special column 7, the gas resistance 10, and the FID detector 11 are connected in sequence to form the first carrier gas path.

[0057] The carrier gas inlet Ⅱ13-2, the V3 interface of the ten-way valve 2, the V4 interface of the ten-way valve 2, the methane pre-column 8, the V8 interface of the ten-way valve 2, the V7 interface of the ten-way valve 2, and the vent port Ⅱ12-2 are connected in sequence to form the second carrier gas path.

[0058] The carrier gas inlet III 13-3, the V6 interface of the ten-way valve 2, the V5 interface of the ten-way valve 2, the methane main column 9, and the FID detector 11 are connected in sequence to form the third carrier gas path;

[0059] As Figure 2 shown, in the non-methane total hydrocarbon detection state, the A1 and A2 interfaces in the six-way valve 1 are connected, the A3 and A4 interfaces are connected, and the A5 and A6 interfaces are connected. The connections of each interface in the ten-way valve 2 are the same as those in the injection state. The two-way three-way valve 3 allows the sample gas to flow in the direction of the inlet 4, and the carrier gas inlet IV 13-4 is blocked;

[0060] The sample gas inlet 4, the two-way three-way valve 3, the V0 interface of the ten-way valve 2, the V9 interface of the ten-way valve 2, the quantitative loop 5, the V2 interface of the ten-way valve 2, the V1 interface of the ten-way valve 2, the A1 interface of the six-way valve 1, the A2 interface of the six-way valve 1, the mass flowmeter 16, the sampling pump 17, and the vent port I 12-1 are connected in sequence to form the sample gas path;

[0061] The carrier gas inlet I 13-1, the A4 interface of the six-way valve 1, the A3 interface of the six-way valve 1, the cold trap tube 6, the A6 interface of the six-way valve 1, the A5 interface of the six-way valve 1, the total hydrocarbon special column 7, the gas resistance 10, and the FID detector 11 are connected in sequence to form the first carrier gas path;

[0062] The carrier gas inlet II 13-2, the V3 interface of the ten-way valve 2, the V4 interface of the ten-way valve 2, the methane pre-column 8, the V8 interface of the ten-way valve 2, the V7 interface of the ten-way valve 2, and the vent port II 12-2 are connected in sequence to form the second carrier gas path;

[0063] The carrier gas inlet III 13-3, the V6 interface of the ten-way valve 2, the V5 interface of the ten-way valve 2, the methane main column 9, and the FID detector 11 are connected in sequence to form the third carrier gas path;

[0064] As Figure 3 shown, in the methane detection state, the connections of each interface in the six-way valve 1 are the same as those in the injection state. The V0 and V1 interfaces in the ten-way valve 2 are connected, the V2 and V3 interfaces are connected, the V4 and V5 interfaces are connected, the V6 and V7 interfaces are connected, and the V8 and V9 interfaces are connected. The two-way three-way valve 3 blocks the sample gas inlet 4, and the carrier gas inlet IV 13-4 allows the gas to flow;

[0065] The carrier gas inlet I 13-1, the A4 interface of the six-way valve 1, the A3 interface of the six-way valve 1, the cold trap tube 6, the A6 interface of the six-way valve 1, the A5 interface of the six-way valve 1, the total hydrocarbon special column 7, the gas resistance 10, and the FID detector 11 are connected in sequence to form the first carrier gas path;

[0066] The carrier gas inlet II 13-2, the V3 interface of the ten-way valve 2, the V2 interface of the ten-way valve 2, the quantitative loop 5, the V9 interface of the ten-way valve 2, the V8 interface of the ten-way valve 2, the methane pre-column 8, the V4 interface of the ten-way valve 2, the V5 interface of the ten-way valve 2, the methane main column 9, and the FID detector 11 are connected in sequence to form the second carrier gas path;

[0067] The carrier gas inlet III 13-3, the V6 interface of the ten-way valve 2, the V7 interface of the ten-way valve 2, and the vent II 12-2 are connected in sequence to form the third carrier gas path;

[0068] The carrier gas inlet IV 13-4, the two-way three-way valve 3, the V0 interface of the ten-way valve 2, the V1 interface of the ten-way valve 2, the A1 interface of the six-way valve 1, the A2 interface of the six-way valve 1, the mass flowmeter 16, the sampling pump 17, and the vent I 12-1 are connected in sequence to form the fourth carrier gas path.

[0069] As Figure 4 shown, in the purge state, the connections of each interface of the six-way valve 1 and the ten-way valve 2 are the same as those in the injection state. The sample gas inlet 4 direction of the two-way three-way valve 3 is blocked, and the carrier gas inlet IV 13-4 direction is in circulation;

[0070] The carrier gas inlet I 13-1, the A4 interface of the six-way valve 1, the A5 interface of the six-way valve 1, the total hydrocarbon special column 7, the gas resistance 10, and the FID detector 11 are connected in sequence to form the sample gas path connection;

[0071] The carrier gas inlet II 13-2, the V3 interface of the ten-way valve 2, the V4 interface of the ten-way valve 2, the methane pre-column 8, the V8 interface of the ten-way valve 2, the V7 interface of the ten-way valve 2, and the vent II 12-2 are connected in sequence to form the second carrier gas path;

[0072] The carrier gas inlet III 13-3, the V6 interface of the ten-way valve 2, the V5 interface of the ten-way valve 2, the methane main column 9, and the FID detector 11 are connected in sequence to form the third carrier gas path;

[0073] The carrier gas inlet IV 13-4, the two-way three-way valve 3, the V0 interface of the ten-way valve 2, the V9 interface of the ten-way valve 2, the quantitative loop 5, the V2 interface of the ten-way valve 2, the V1 interface of the ten-way valve 2, the A1 interface of the six-way valve 1, the A6 interface of the six-way valve 1, the cold trap tube 6, the A3 interface of the six-way valve 1, the A2 interface of the six-way valve 1, the mass flowmeter 16, the sampling pump 17, and the vent I 12-1 are connected in sequence to form the fourth carrier gas path.

[0074] An on-line detection method for the content of non-methane total hydrocarbons in ambient air. First, the carrier gas source is connected to the four carrier gas inlets after passing through the electronic pressure controller, and then the detection system is connected to the central control system. Turn on the power of the detection system, set the temperature of the cold trap tube 6 to -130 °C, the temperature of the main temperature control box 14 to 120 °C, and the temperature of the FID temperature control box 15 to 180 °C;

[0075] Corresponding to the four states of the detection system, the detection method includes four stages, namely the sample injection stage, the non-methane total hydrocarbon detection stage, the methane detection stage, and the purging stage. The entire detection process is controlled by the central control system and is carried out according to the following steps:

[0076] Step 1, sample injection stage: When the central control system detects that the temperatures of the cold trap tube 6, the main temperature control box 14, and the FID temperature control box 15 reach the set values, the sampling pump 17 is automatically turned on. The six-way valve 1, the ten-way valve 2, and the two-way three-way valve 3 are switched to the sample injection state. The fourth carrier gas does not flow. The sample gas and the other three carrier gases flow in the gas path in the sample injection state. The sample gas is sucked from the sample gas inlet through the mass flow meter 16 and the sampling pump 17. The sample gas passes through the two-way three-way valve 3, successively through the V0 interface of the ten-way valve 2, the V9 interface of the ten-way valve 2. When passing through the quantitative loop 5, the sample gas fills the quantitative loop 5. The remaining gas then successively passes through the V2 interface of the ten-way valve 2, the V1 interface of the ten-way valve 2, the A1 interface of the six-way valve 1, and the A6 interface of the six-way valve 1 and enters the cold trap tube 6. The non-methane hydrocarbons in the sample gas are fully absorbed by the cold trap tube 6. The excess gas passes through the A3 interface and the A2 interface of the six-way valve 1, and finally is discharged through the vent port Ⅰ12-1. Timing starts from 0 seconds and lasts for 185 seconds;

[0077] Step 2, non-methane total hydrocarbon detection stage: When the central control system detects that the cold trap tube 6 has completed the absorption of non-methane total hydrocarbons, the sampling pump stops working and automatically switches the six-way valve 1 to the non-methane total hydrocarbon detection state. The fourth carrier gas still does not flow. The sample gas and the other three carrier gases flow in the gas path in the non-methane total hydrocarbon detection state. At the same time, the flash evaporation device 6-2 of the cold trap tube 6 starts to work, with a heating rate of 100 °C per second, and the temperature rapidly rises to 300-350 °C. The ten-way valve 2 and the two-way three-way valve 3 remain in the sample injection state. The first carrier gas is injected from the A4 interface of the six-way valve 1, passes through the A3 interface of the six-way valve 1, and blows the non-methane total hydrocarbon gas flashed out from the cold trap tube 6 into the total hydrocarbon special column 7, and then enters the FID detector 11. The non-methane total hydrocarbon, abbreviated as NMHC, peaks, and the content of non-methane total hydrocarbons is detected. This state is maintained for 95 seconds, and the total duration reaches 280 seconds;

[0078] Step 3, Methane Detection Stage: When the central control system detects that the non-methane total hydrocarbon detection is completed, it automatically switches the ten-way valve 2 and the two-way three-way valve 3 to the methane detection state, stops sample injection, and the four-way carrier gas flows in the gas path in the methane detection state. The second-way carrier gas is injected from the V3 interface of the ten-way valve 2. Through the V3 interface of the ten-way valve 2, the sample gas in the quantitative loop 5 is blown into the methane pre-column 8 successively through the V9 and V8 interfaces of the ten-way valve 2 to filter out the heavy components in the sample gas. The light-component sample gas is then blown into the methane main column 9 successively through the V4 and V5 interfaces of the ten-way valve 2, and finally enters the FID detector 11. Methane peaks, and the methane content is detected and maintained for 35 seconds, with the total duration reaching 315 seconds;

[0079] Step 4, Purge Stage: When the central control system detects that the methane detection is completed, that is, after the detection is completed, it automatically switches the six-way valve 1, the ten-way valve 2, and the two-way three-way valve 3 to the purge state, stops sample injection, and the four-way carrier gas flows in the gas path in the purge state. During this period, the fourth-way carrier gas purges the quantitative loop 5 and the cold trap tube 6, the second-way carrier gas purges the methane pre-column 8, the third-way carrier gas purges the methane main column 9, and the first-way carrier gas purges the total hydrocarbon special column 7, making the entire system clean again, maintaining for 285 seconds, and the total duration reaches 600 seconds;

[0080] Step 5, On-line Continuous Detection: The central control system always detects whether the temperature of the cold trap tube 6 reaches the set temperature: If it is higher than the set temperature, the refrigeration device 6-2 is started; when it reaches the set temperature, that is, -130 °C, it goes to Step 1 to continue the next round of detection and complete the on-line detection.

[0081] Table 1 records the detection results in Binhai New Area, Tianjin in January 2022. The table shows the test results of continuous sample injection 6 times within 80 minutes, achieving the goal of on-line detection of the non-methane total hydrocarbon content in ambient air.

[0082] Table 1: Record Statistics of Atmospheric Detection Results in Binhai New Area, Tianjin in January 2022

[0083]

[0084] It can be seen from Table 1 that the present invention has carried out 6 detections within 80 minutes. The repeatability error of the non-methane total hydrocarbon concentration is 0.079%, and the repeatability error of the methane concentration is 0.128%, which is much smaller than the standard requirement of ±2%, meeting the requirements of on-line monitoring.

Claims

1. An on-line detection system for the content of non-methane total hydrocarbons in ambient air, comprising an FID detector (11) arranged in an FID temperature control box (15), a six-way valve (1), a ten-way valve (2), a two-position three-way valve (3), a quantitative loop (5), a cold trap tube (6), a total hydrocarbon special column (7), a methane pre-column (8), a methane main column (9), an air resistance (10) arranged in a main temperature control box (14), and a sampling pump (17) arranged outside the main temperature control box (14), characterized in that: It also includes a mass flowmeter (16); The cold trap tube (6) is connected between the A3 interface and the A6 interface of the six-way valve (1). The total hydrocarbon special column (7) is connected to the lead-out pipe of the A5 interface of the six-way valve (1), and is connected to the FID detector (11) through a gas resistance (10). The lead-out pipe of the A4 interface of the six-way valve (1) is the carrier gas inlet I (13-1); The mass flowmeter (16) is connected to the lead-out pipe of the A2 interface of the six-way valve (1). The sampling pump (17) is connected to the mass flowmeter (16), and the outlet of the sampling pump (17) is the vent port I (12-1); The lead-out pipe of one of the interfaces of the two-way three-way valve (3) is the sample gas inlet (4), one interface is the carrier gas inlet IV (13-4), and one interface is connected to the V0 interface of the ten-way valve (2); The quantitative loop (5) is connected between the V9 interface and the V2 interface of the ten-way valve (2). The methane pre-column (8) is connected between the V8 interface and the V4 interface of the ten-way valve (2). The methane main column (9) is connected to the lead-out pipe of the V5 interface of the ten-way valve (2) and is connected to the FID detector (11). The lead-out pipe of the V3 interface of the ten-way valve (2) is the carrier gas inlet II (13-2), the lead-out pipe of the V6 interface of the ten-way valve (2) is the carrier gas inlet III (13-3), and the lead-out pipe of the V7 interface of the ten-way valve (2) is the vent port II (12-2); The cold trap tube (6) includes a cooling device (6-1) and a flash evaporation device (6-2), and the flash evaporation device (6-2) is arranged inside the cooling device (6-1); The detection system has five gas paths, namely a sample gas path and four carrier gas paths; when in use, the detection system has four states, namely the injection state, the non-methane total hydrocarbon detection state, the methane detection state, and the purge state. The five gas paths have different connection methods in each state, and the gas path connection in each state is realized through the switching of the interfaces of the six-way valve (1), the ten-way valve (2), and the three-way valve (3); In the non-methane total hydrocarbon detection state, the A1 and A2 interfaces in the six-way valve (1) are connected, the A3 and A4 interfaces are connected, and the A5 and A6 interfaces are connected. In the ten-way valve (2), the V1 and V2 interfaces are connected, the V3 and V4 interfaces are connected, the V5 and V6 interfaces are connected, the V7 and V8 interfaces are connected, and the V9 and V0 interfaces are connected. The sample gas inlet (4) of the two-way three-way valve (3) is in the flowing direction, and the carrier gas inlet IV (13-4) is in the cut-off direction; The sample gas inlet (4), the two-way three-way valve (3), the V0 interface of the ten-way valve (2), the V9 interface of the ten-way valve (2), the quantitative loop (5), the V2 interface of the ten-way valve (2), the V1 interface of the ten-way valve (2), the A1 interface of the six-way valve (1), the A2 interface of the six-way valve (1), the mass flowmeter (16), the sampling pump (17), and the vent port I (12-1) are connected in sequence to form the sample gas path; The carrier gas inlet Ⅰ (13-1), the A4 interface of the six-way valve (1), the A3 interface of the six-way valve (1), the cold trap tube (6), the A6 interface of the six-way valve (1), the A5 interface of the six-way valve (1), the total hydrocarbon special column (7), the gas resistance (10), and the FID detector (11) are connected in sequence to form the first carrier gas path; The carrier gas inlet Ⅱ (13-2), the V3 interface of the ten-way valve (2), the V4 interface of the ten-way valve (2), the methane pre-column (8), the V8 interface of the ten-way valve (2), the V7 interface of the ten-way valve (2), and the vent Ⅱ (12-2) are connected in sequence to form the second carrier gas path; The carrier gas inlet Ⅲ (13-3), the V6 interface of the ten-way valve (2), the V5 interface of the ten-way valve (2), the methane main column (9), and the FID detector (11) are connected in sequence to form the third carrier gas path.

2. The on-line detection system for the content of non-methane total hydrocarbons in ambient air according to claim 1, wherein: In the injection state, the A2 and A3 interfaces in the six-way valve (1) are connected, the A4 and A5 interfaces are connected, the A1 and A6 interfaces are connected, the V1 and V2 interfaces in the ten-way valve (2) are connected, the V3 and V4 interfaces are connected, the V5 and V6 interfaces are connected, the V7 and V8 interfaces are connected, the V9 and V0 interfaces are connected, the sample gas inlet (4) of the two-way three-way valve (3) flows in the forward direction, and the carrier gas inlet Ⅳ (13-4) is blocked; The sample gas inlet (4), the two-way three-way valve (3), the V0 interface of the ten-way valve (2), the V9 interface of the ten-way valve (2), the quantitative ring (5), the V2 interface of the ten-way valve (2), the V1 interface of the ten-way valve (2), the A1 interface of the six-way valve (1), the A6 interface of the six-way valve (1), the cold trap tube (6), the A3 interface of the six-way valve (1), the A2 interface of the six-way valve (1), the mass flowmeter (16), the sampling pump (17), and the vent Ⅰ (12-1) are connected in sequence to form the sample gas path; The carrier gas inlet Ⅰ (13-1), the A4 interface of the six-way valve (1), the A5 interface of the six-way valve (1), the total hydrocarbon special column (7), the gas resistance (10), and the FID detector (11) are connected in sequence to form the first carrier gas path; The carrier gas inlet Ⅱ (13-2), the V3 interface of the ten-way valve (2), the V4 interface of the ten-way valve (2), the methane pre-column (8), the V8 interface of the ten-way valve (2), the V7 interface of the ten-way valve (2), and the vent Ⅱ (12-2) are connected in sequence to form the second carrier gas path; The carrier gas inlet Ⅲ (13-3), the V6 interface of the ten-way valve (2), the V5 interface of the ten-way valve (2), the methane main column (9), and the FID detector (11) are connected in sequence to form the third carrier gas path.

3. The on-line detection system for the content of non-methane total hydrocarbons in ambient air according to claim 1, characterized in that: In the methane detection state, the A2 and A3 interfaces in the six-way valve (1) are connected, the A4 and A5 interfaces are connected, the A1 and A6 interfaces are connected, the V0 and V1 interfaces in the ten-way valve (2) are connected, the V2 and V3 interfaces are connected, the V4 and V5 interfaces are connected, the V6 and V7 interfaces are connected, the V8 and V9 interfaces are connected; the sample gas inlet (4) of the two-way three-way valve (3) is blocked, and the carrier gas inlet Ⅳ (13-4) flows in the forward direction; The carrier gas inlet Ⅰ (13-1), the A4 interface of the six-way valve (1), the A3 interface of the six-way valve (1), the cold trap tube (6), the A6 interface of the six-way valve (1), the A5 interface of the six-way valve (1), the special column for total hydrocarbons (7), the gas resistance (10), and the FID detector (11) are connected in sequence to form the first carrier gas path; The carrier gas inlet Ⅱ (13-2), the V3 interface of the ten-way valve (2), the V2 interface of the ten-way valve (2), the sampling loop (5), the V9 interface of the ten-way valve (2), the V8 interface of the ten-way valve (2), the methane pre-column (8), the V4 interface of the ten-way valve (2), the V5 interface of the ten-way valve (2), the methane main column (9), and the FID detector (11) are connected in sequence to form the second carrier gas path; The carrier gas inlet Ⅲ (13-3), the V6 interface of the ten-way valve (2), the V7 interface of the ten-way valve (2), and the vent Ⅱ (12-2) are connected in sequence to form the third carrier gas path; The carrier gas inlet Ⅳ (13-4), the two-way three-way valve (3), the V0 interface of the ten-way valve (2), the V1 interface of the ten-way valve (2), the A1 interface of the six-way valve (1), the A2 interface of the six-way valve (1), the mass flow meter (16), the sampling pump (17), and the vent Ⅰ (12-1) are connected in sequence to form the fourth carrier gas path.

4. The on-line detection system for the content of non-methane total hydrocarbons in ambient air according to claim 1, wherein: In the purge state, the A2 and A3 interfaces in the six-way valve (1) are connected, the A4 and A5 interfaces are connected, the A1 and A6 interfaces are connected, the V1 and V2 interfaces in the ten-way valve (2) are connected, the V3 and V4 interfaces are connected, the V5 and V6 interfaces are connected, the V7 and V8 interfaces are connected, the V9 and V0 interfaces are connected, the sample gas inlet (4) direction of the two-way three-way valve (3) is blocked, and the carrier gas inlet Ⅳ (13-4) direction is in circulation; The carrier gas inlet Ⅰ (13-1), the A4 interface of the six-way valve (1), the A5 interface of the six-way valve (1), the special column for total hydrocarbons (7), the gas resistance (10), and the FID detector (11) are connected in sequence to form the sample gas path connection; The carrier gas inlet Ⅱ (13-2), the V3 interface of the ten-way valve (2), the V4 interface of the ten-way valve (2), the methane pre-column (8), the V8 interface of the ten-way valve (2), the V7 interface of the ten-way valve (2), and the vent Ⅱ (12-2) are connected in sequence to form the second carrier gas path; The carrier gas inlet Ⅲ (13-3), the V6 interface of the ten-way valve (2), the V5 interface of the ten-way valve (2), the methane main column (9), and the FID detector (11) are connected in sequence to form the third carrier gas path; The carrier gas inlet Ⅳ (13-4), the two-way three-way valve (3), the V0 interface of the ten-way valve (2), the V9 interface of the ten-way valve (2), the sampling loop (5), the V2 interface of the ten-way valve (2), the V1 interface of the ten-way valve (2), the A1 interface of the six-way valve (1), the A6 interface of the six-way valve (1), the cold trap tube (6), the A3 interface of the six-way valve (1), the A2 interface of the six-way valve (1), the mass flow meter (16), the sampling pump (17), and the vent Ⅰ (12-1) are connected in sequence to form the fourth carrier gas path.

5. A method for using an on-line detection system for the content of total non-methane hydrocarbons in ambient air as described in claim 1, characterized in that: It includes four stages, namely the sample injection stage, the non-methane total hydrocarbon detection stage, the methane detection stage, and the purging stage, and is carried out according to the following steps: Turn on the power of the detection system, set the temperature of the cold trap tube (6) to -100°C to -150°C, the temperature of the main temperature control box (14) to 80 - 140°C, and the temperature of the FID temperature control box (15) to 160 - 200°C; Step 1, sample injection stage: When the temperatures of the cold trap tube (6), the main temperature control box (14), and the FID temperature control box (15) reach the set values, turn on the sampling pump, and switch the six-way valve (1), the ten-way valve (2), and the two-way three-way valve (3) to the sample injection state. The fourth carrier gas does not flow. The sample gas and the other three carrier gases flow in the gas path in the sample injection state. The sample gas is inhaled from the sample gas inlet (4) through the mass flowmeter (16) and the sampling pump (17). After passing through the two-way three-way valve (3), the sample gas passes through the V0 interface of the ten-way valve (2), the V9 interface of the ten-way valve (2) in sequence. When passing through the quantitative loop (5), the sample gas fills the quantitative loop (5). The remaining gas then passes through the V2 interface of the ten-way valve (2), the V1 interface of the ten-way valve (2), the A1 interface of the six-way valve (1), and the A6 interface of the six-way valve (1) and enters the cold trap tube (6). The non-methane hydrocarbons in the sample gas are fully absorbed by the cold trap tube (6). The excess gas passes through the A3 interface and the A2 interface of the six-way valve (1), and finally is discharged through the vent port I (12-1). Start timing from 0 seconds and maintain for 150 - 200 seconds; Step 2, non-methane total hydrocarbon detection stage: When the cold trap tube (6) finishes absorbing the non-methane total hydrocarbons, the sampling pump (17) stops working, and the six-way valve (1) is switched to the non-methane total hydrocarbon detection state. The fourth carrier gas still does not flow. The sample gas and the other three carrier gases flow in the gas path in the non-methane total hydrocarbon detection state. At the same time, the flash evaporation device (6-2) of the cold trap tube (6) starts to work. The ten-way valve (2) and the two-way three-way valve (3) are still in the sample injection state. The first carrier gas is injected from the A4 interface of the six-way valve (1), passes through the A3 interface of the six-way valve (1), and blows the non-methane total hydrocarbon gas flashed out from the cold trap tube (6) into the total hydrocarbon special column (7), and then enters the FID detector (11). The non-methane total hydrocarbon, abbreviated as NMHC, peaks, and the content of the non-methane total hydrocarbon is detected. Maintain this state for 90 - 100 seconds; Step 3, methane detection stage: When the non-methane total hydrocarbon detection is completed, switch the ten-way valve (2) and the two-way three-way valve (3) to the methane detection state, stop sample injection, and the four carrier gases flow in the gas path in the methane detection state. The second carrier gas is injected from the V3 interface of the ten-way valve (2), passes through the V3 interface of the ten-way valve (2), and blows the sample gas in the quantitative loop (5) into the methane pre-column (8) through the V9 interface and the V8 interface of the ten-way valve (2) in sequence to filter out the heavy components in the sample gas. The light-component sample gas then passes through the V4 and V5 interfaces of the ten-way valve (2) and is blown into the methane main column (9), and finally enters the FID detector (11). Methane peaks, and the methane content is detected. Maintain for 30 - 45 seconds; Step 4, purging stage: After the methane detection is completed, that is, after the detection is completed, switch the six-way valve (1), ten-way valve (2) and two-way three-way valve (3) to the purging state, stop the sample injection, and the four-way carrier gas flows in the gas path in the purging state. The fourth-way carrier gas purges the quantitative loop (5) and the cold trap tube (6), the second-way carrier gas purges the methane pre-column (8), the third-way carrier gas purges the methane main column (9), and the first-way carrier gas purges the total hydrocarbon special column (7) to make the whole system clean again and maintain for 250 - 300 seconds; Step 5, temperature control: If the temperature of the cold trap tube (6) is higher than the set temperature, start the refrigeration device; when the set temperature is reached, go to Step 1 to continue the next round of detection to achieve on-line detection.

6. The on-line detection method for the content of non-methane total hydrocarbons in ambient air according to claim 2, wherein: The cooling temperature of the cold trap tube (6) is -130 °C, the heating rate during flash evaporation is 100 °C / second, the temperature rises to 280 - 300 °C, the temperature of the main temperature control box (14) is 120 °C, and the temperature of the FID temperature control box (15) is 180 °C.

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