Municipal pipe network steam invasion simulation device and application thereof

Abstract

The invention discloses a device for simulating steam invasion of a municipal pipe network and application of the device. The device comprises a trap pipeline simulation unit, an indoor space simulation unit and a concentration monitoring device, the trap pipeline simulation unit controls the flow of gas entering a pipeline space through an air compressor and a flowmeter so as to simulate different mass transfer environments, and the water seal condition in a U-shaped pipe of a trap can be controlled through the height change of the liquid level in the U-shaped pipe. The indoor space simulation unit simulates the ventilation condition of the indoor environment through the combined action of a mass flow meter and an air pump, and the concentration monitoring device achieves the function of regularly monitoring the indoor space pollutant concentration through the periodic sampling mode of an automatic sampler. The device provided by the invention can verify the accuracy of the municipal pipe network steam invasion numerical model, and changes the mass transfer condition to optimize the model.

Description

Technical Field

[0001] The present invention belongs to the field of environmental risk assessment, and relates to a device for simulating vapor intrusion in a municipal pipe network and its application. Background Art

[0002] Vapor intrusion (VI) is a newly discovered way in recent years that volatile organic compounds (VOCs) enter indoor air and cause pollution. It refers to the process that when there is a soil pollution source underground in a building, due to the high volatility of VOCs pollutants themselves, these pollutants can directly volatilize from the underground pollution source, enter the indoor in gaseous form through the soil vadose zone or other channels and accumulate indoors, thus affecting the health of residents. Nielsen et al. (Nielsen K B, Hvidberg B. (2017) Remediation techniques for mitigating vapor intrusion from sewer systems to indoor air. Remediation Journal, 27(3):67 - 73.) once thought that about 20% - 30% of vapor intrusion cases were caused by the unreasonable transport process of pollutants in the drain pipe. And because the drainage pipe network is usually directly connected to the indoor toilet, it is more likely to cause the situation that pollutants enter the indoor without attenuation, causing more serious pollution and harm to the indoor air than the soil vapor intrusion process. Therefore, the risk assessment method for the priority path has become a research hotspot in recent years.

[0003] Currently, common risk assessment models for vapor intrusion in contaminated sites, such as the J&E model, the AAM model, and the Biovapor model, etc., are all based on traditional soil vapor intrusion and do not consider the situation of the existence of priority paths in the site. As a result, the risk assessment results of some VOCs - contaminated sites with priority path scenarios such as abandoned municipal pipelines are too conservative, unable to reflect the actual site risk situation. This may lead to the neglect of the site pollution risk, unable to correctly solve the environmental problems of the contaminated site, and is also not conducive to the healthy development of the contaminated site remediation industry.

[0004] In the current risk assessment systems for vapor intrusion sites at home and abroad, although virtual simulation software such as Fluent and COMSOL Multiphysics can be used to calculate the mass transfer of pollutants in pipe networks, the usability of these simulations in actual situations remains to be verified. The methods for verifying virtual simulation results usually include actual site investigations and physical experiment verifications. Conducting actual site investigations to verify gaseous pollutants in pipe networks is costly and greatly affected by the spatio-temporal volatility of gaseous pollutants in the pipe network, and it cannot be well used to verify the feasibility of simulation results. Therefore, there is an urgent need to construct an experimental device that can be used to simulate the scenario of municipal pipe networks as the priority path for vapor intrusion to verify the feasibility of software calculation results. Summary of the Invention

[0005] The object of the present invention is to provide a device for simulating vapor intrusion in municipal pipe networks and its application. The structure of the device is reasonably arranged, and it can accurately simulate the migration process of gaseous volatile organic pollutants volatilized from the municipal pipe network, transferred through the water seal, and finally entering the indoor space.

[0006] The technical solution for achieving the object of the present invention is as follows:

[0007] The device for simulating vapor intrusion in municipal pipe networks includes a water seal pipe simulation unit, an indoor space simulation unit, and a concentration monitoring device; the water seal pipe simulation unit consists of a water seal 11, a pollution source sampling bottle 12, a differential pressure sensor 13, a flowmeter 14, and an air compressor 15. Among them, the pollution source sampling bottle 12 is placed at the bottom of the pipe section, and the lower end of the water seal 11 is sequentially connected to the differential pressure sensor 13, the flowmeter 14, and the air compressor 15; the indoor space simulation unit consists of a simulated indoor space 5, a mass flowmeter sensor 3, a mass flowmeter display controller 4, a pressure reducing valve 2, an air bottle 1, a tail gas absorption device 9, and an air extraction pump 10. The bottom end of the simulated indoor space is sequentially connected to the mass flowmeter sensor 3, the pressure reducing valve 2, and the air bottle 1. The mass flowmeter display controller 4 is connected to the mass flowmeter sensor 3. The top end of the simulated indoor space 5 is sequentially connected to a gas automatic sampler 6, an air extraction pump 10, and a tail gas absorption device 9; the concentration monitoring device consists of a gas automatic sampler 6, a gas chromatograph 7, a pressure reducing valve 2, and a gas chromatograph carrier gas cylinder 8. The gas automatic sampler 6 is sequentially connected to the gas chromatograph 7, the pressure reducing valve 2, and the gas chromatograph carrier gas cylinder 8; sampling points C1, C2, C3, and C4 are respectively arranged at the upper end of the pollution source sampling bottle 12, the bottom of the inverted U-shaped pipe section of the water seal 11, the outlet of the U-shaped pipe section of the water seal 11, and the bottom of the simulated indoor space 5.

[0008] Further, the pollution source is a liquid organic pollutant.

[0009] Further, the simulated indoor space 5 is composed of PVC pipe sections, and two semi-circular baffles are bonded in the middle of the pipe sections.

[0010] Furthermore, an inspection hole is installed at the bottom of the U-shaped pipe section of the trap 11.

[0011] Based on the above-described method for verifying the mass transfer model of pollutants entering the indoor environment from the municipal pipe network using the simulated municipal pipe network vapor intrusion device, the method specifically includes the following steps:

[0012] Step 1, set the mass transfer and water seal conditions of the model to be verified: If it is necessary to verify the diffusion mass transfer conditions, a certain volume of distilled water is injected from the C3 sampling port into the trap to control the water seal conditions. If it is necessary to verify the convective mass transfer conditions, turn on the air compressor and adjust the flow rate of the flowmeter to a constant value, and control the mass transfer conditions required by the model according to the type of the model to be verified;

[0013] Step 2, measure the change of the pollutant decay coefficient in the simulated indoor space over time: Set the sampling time, equilibration time, injection time, injection volume, and analysis period of the gas automatic sampler. Sample cyclically every analysis period. The gas automatic sampler injects samples into the gas chromatograph in a passive injection manner. At this time, the concentration monitored by the gas chromatograph is the pollutant concentration in the simulated indoor space;

[0014] Step 3, sample at the sampling points in the pipe space: After the gas automatic sampler has completed all sampling, use a syringe to sample the pollutant concentration in the pipe space at the C1, C2, C3, and C4 sampling points respectively, and dilute them for later measurement;

[0015] Step 4, measure the change of the pollutant decay coefficient in the pipe space with distance: Remove the gas automatic sampler from the device, and set the sampling time, equilibration time, injection time, injection volume, and analysis period of the gas automatic sampler the same as in Step 2. Change the injection method to active injection. Connect the diluted samples taken from C4, C3, C2, and C1 in Step 3 to the gas automatic sampler respectively, and use the same gas chromatographic conditions as in Step 2 to measure the pollutant concentration at each sampling point;

[0016] Step 5, draw the calibration curve: Prepare pollutant standard gas samples with different concentrations, measure them using the gas chromatographic conditions in Step 2, and draw the standard curve;

[0017] Step 6, sample analysis: According to the measurement results in Step 2, plot a graph with time as the abscissa and the pollutant decay coefficient as the ordinate to obtain the change curve of the pollutant decay coefficient in the simulated indoor space over time;

[0018] Step 7, sample analysis: According to the measurement results in Step 4, plot a graph with the distance from the sampling point to the pollution source as the abscissa and the pollutant decay coefficient as the ordinate to obtain the change curve of the pollutant decay coefficient in the pipe space with distance.

[0019] Further, in step 1, the model to be verified is a convection-diffusion mass transfer model.

[0020] Further, in step 2, the pollutant is a chlorinated organic pollutant. In a specific embodiment of the present invention, tetrachloroethylene (PCE) is taken as an example.

[0021] Further, in step 2, the sampling time of the gas auto-sampler is 0.1 min, the equilibration time is 0.05 min, the injection time is 0.5 min, the injection volume is 1 mL, the analysis period is 25 min, the number of sampling times per experimental cycle is 60 times, and every 25 min, the gas auto-sampler injects samples into the gas chromatograph in a passive injection manner. At this time, the concentration monitored by the gas chromatograph is the PCE concentration in the simulated indoor space. The gas chromatograph conditions are as follows: (1) The inlet temperature is 100 °C, the injection method is split injection, and the split ratio is 10:1; (2) The temperature programming of the column oven is: the initial temperature is 45 °C and is held for 3 min, then it is heated to 150 °C at a rate of 20 °C / min and held for 0 min, with a total time of 8.25 min; (3) Gas flow rate: The carrier gas is high-purity nitrogen, the total flow rate is 40 mL / min, the column flow rate is 1.00 mL / min, and the purge flow rate is 0.5 mL / min; the hydrogen flow rate is 30 mL / min, and the air flow rate is 300 mL / min; (4) The detector temperature is 250 °C; (5) The chromatographic column is a DB-5MS column with an inner diameter of 0.25 mm, a film thickness of 0.1 μm, and a length of 30 m.

[0022] Further, in step 3, the specific methods of sampling and dilution are as follows: Use a syringe to draw V1, V2, V3, and V4 volumes of pollutant gas from sampling points C1, C2, C3, and C4 and introduce them into a 500 mL Tedler sampling bag, and then introduce (500 - V1), (500 - V2), (500 - V3), and (500 - V4) volumes of clean air respectively. After shaking well and standing for 15 min, gases with dilution factors of (V1 / 500), (V2 / 500), (V3 / 500), and (V4 / 500) compared to the original pollutant gas are obtained.

[0023] Further, in step 4, the number of cycles is 4 times.

[0024] Further, in step 5, PCE standard gas samples with mass concentrations of 0, 5000, 10000, 25000, 50000, and 100000 μg / m 3 are prepared.

[0025] Compared with the prior art, the present invention has the following advantages:

[0026] The present invention designs a device for simulating pipeline vapor intrusion, including a trap pipeline simulation unit, an indoor space simulation unit, and a concentration monitoring device, which can perform better physical simulation on the process of pollutants entering the indoor space from the municipal pipe network, and can control various different mass transfer conditions and water seal conditions for pollutants to enter the room from the trap, so as to verify the applicability and accuracy of the mass transfer model under different conditions in describing the process of vapor intrusion in the municipal pipe network. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 FIG. is a schematic structural diagram of the device for simulating vapor intrusion in the municipal pipe network of the present invention, where 1 is an air bottle, 2 is a pressure reducing valve, 3 is a mass flowmeter sensor, 4 is a mass flowmeter display controller, 5 is a simulated indoor space, 6 is a gas automatic sampler, 7 is a gas chromatograph, 8 is a gas chromatograph carrier gas cylinder, 9 is a tail gas absorption device, 10 is a suction pump, 11 is a trap, 12 is a pollution source injection bottle, 13 is a differential pressure sensor, 14 is a flowmeter, and 15 is an air compressor. C1, C2, C3, and C4 are sampling points located at the upper end of the pollution source injection bottle, the bottom of the inverted U-shaped pipe section of the trap, the outlet of the U-shaped pipe section of the trap, and the bottom of the simulated indoor space, respectively;

[0028] Figure 2 FIG. shows the variation of the pollutant attenuation coefficient in the indoor space simulation part obtained from the experiment and model calculation in Example 1 with time, where A, B, C, and D respectively represent the situation where diffusion is the main mass transfer effect (Q = 0) and there is no water seal in the trap (h = 0), the situation where diffusion is the main mass transfer effect (Q = 0) and there is a half water seal in the trap (h = 2.5 cm), the situation where convection is the main mass transfer effect (Q = 100 mL / min) and there is no water seal in the trap (h = 0), and the situation where convection is the main mass transfer effect (Q = 100 mL / min) and there is a half water seal in the trap (h = 2.5 cm);

[0029] Figure 3 FIG. shows the variation of the pollutant attenuation coefficient in the trap pipeline simulation part obtained from the experiment and simulation calculation in Example 1 with distance, where A, B, C, and D respectively represent the situation where diffusion is the main mass transfer effect (Q = 0) and there is no water seal in the trap (h = 0), the situation where diffusion is the main mass transfer effect (Q = 0) and there is a half water seal in the trap (h = 2.5 cm), the situation where convection is the main mass transfer effect (Q = 100 mL / min) and there is no water seal in the trap (h = 0), and the situation where convection is the main mass transfer effect (Q = 100 mL / min) and there is a half water seal in the trap (h = 2.5 cm). DETAILED DESCRIPTION OF THE INVENTION

[0030] To make the object, technical solutions and advantages of the present invention clearer, the present invention will be described in detail below with reference to specific embodiments and drawings.

[0031] Figure 1 FIG. is a schematic structural diagram of a simulated municipal pipe network vapor intrusion device of the present invention, including a water seal pipe simulation unit, an indoor space simulation unit and a concentration monitoring device; the water seal pipe simulation unit is composed of a water seal 11, a pollution source sampling bottle 12, a differential pressure sensor 13, a flow meter 14 and an air compressor 15, wherein the pollution source sampling bottle 12 is placed at the bottom of the pipe section, and the lower end of the water seal 11 is sequentially connected to the differential pressure sensor 13, the flow meter 14 and the air compressor 15; the indoor space simulation unit is composed of a simulated indoor space 5, a mass flow meter sensor 3, a mass flow meter display and control instrument 4, a pressure reducing valve 2, an air cylinder 1, a tail gas absorption device 9 and an air extraction pump 10. The bottom end of the simulated indoor space is sequentially connected to the mass flow meter sensor 3, the pressure reducing valve 2 and the air cylinder 1. The mass flow meter display and control instrument 4 is connected to the mass flow meter sensor 3. The top end of the simulated indoor space 5 is sequentially connected to a gas automatic sampler 6, an air extraction pump 10 and a tail gas absorption device 9; the concentration monitoring device is composed of a gas automatic sampler 6, a gas chromatograph 7, a pressure reducing valve 2 and a gas chromatograph carrier gas cylinder 8. The gas automatic sampler 6 is sequentially connected to the gas chromatograph 7, the pressure reducing valve 2 and the gas chromatograph carrier gas cylinder 8; sampling points C1, C2, C3 and C4 are respectively arranged at the upper end of the pollution source sampling bottle 12, the bottom of the inverted U-shaped pipe section of the water seal 11, the outlet of the U-shaped pipe section of the water seal 11 and the bottom of the simulated indoor space.

[0032] In the present invention, the water seal pipe simulation unit is used to simulate the mass transfer of pollutants through the water seal. The pollutant gas in the pollution source sampling bottle placed at the bottom of the pipe section can pass through specific mass transfer and finally enter the indoor space simulation part through the water seal. An air compressor and a flow meter are connected to the lower end of the water seal pipe. When considering the convective mass transfer effect, the air compressor can be used to ventilate the pipe section, and the flow meter can be used to control the air flow entering the pipe section. The differential pressure sensor can read the pressure difference in the pipe section under different mass transfer conditions.

[0033] In order to verify the distribution of pollutants in the water seal pipe with distance, sampling points C1, C2, C3 and C4 are respectively arranged at the upper end of the pollution source sampling bottle, the bottom of the inverted U-shaped pipe section of the water seal, the outlet of the U-shaped pipe section of the water seal and the bottom of the simulated indoor space. Among them, C1 is the pollution source monitoring point, and the concentration at this point directly represents the concentration of the pollution source entering the pipe section. According to the actual situation, a water seal is arranged at a certain distance from the bottom of the pipe section. An inspection hole is installed at the bottom of the U-shaped pipe section of the water seal. Opening the inspection hole can drain all the water seals in the water seal. The effective water seal height of the water seal is equal to the diameter of the water seal pipe section.

[0034] The indoor space simulation unit is used to simulate the distribution of pollutants in the indoor space. Clean air is pumped into the indoor space by a suction pump, and a mass flowmeter is connected between the air bottle and the simulated indoor space to control the constant rate of air flowing into the indoor space, thereby simulating the ventilation process of the indoor space. The simulated indoor space is composed of a section of PVC pipe, and two semi-circular baffles are bonded in the middle of the pipe section to ensure that the clean air and pollutant gas in the indoor space reach a fully mixed state.

[0035] The concentration monitoring device is used to monitor the concentration of pollutant gas in the simulated indoor space. The gas automatic sampler is an important part connecting the indoor space simulation part and the concentration monitoring device. When the automatic sampler is set in the "non-sampling" state, the automatic sampler only acts as a gas path, and the indoor space gas directly enters the tail gas treatment device for treatment after passing through the automatic sampler. When the automatic sampler is set in the "sampling" state, the rotation of the six-way valve is controlled to make the indoor space gas enter the gas chromatography for measurement and then discharge the excess gas.

[0036] Since chlorinated organic pollutants are difficult to be biodegraded, the mass transfer in the pipe network usually includes two mass transfer mechanisms: diffusion and convection. Therefore, the convection-diffusion mass transfer model is most commonly used. To describe the mass transfer process of chlorinated organic pollutants in the pipe network. When there is no gas flow or the gas flow velocity is very small in the pipe, the mass transfer of pollutants in the pipe is mainly dominated by diffusion mass transfer. When there is a certain flow rate of gas in the pipe, the diffusion mass transfer of pollutants in the pipe can be almost ignored, and the mass transfer in the pipe is mainly convection mass transfer. The theoretical mass transfer calculation results of the convection-diffusion mass transfer model can be directly obtained using virtual simulation software, and the feasibility of the theoretical calculation mass transfer results can be better verified through the device of the present invention.

[0037] This embodiment mainly verifies the feasibility of using the convection-diffusion mass transfer model to describe the mass transfer process of tetrachloroethylene (PCE) under two water seal conditions in the trap pipe section. The model calculation results are obtained using COMSOL Multiphysics simulation software.

[0038] In this embodiment, the main body of the trap pipeline simulation unit is a PVC trap pipe section with a total length of 100 cm and a diameter of 5 cm. 4 mL of 99.8% pure PCE solvent is placed in a 5 mL pollution source sampling bottle and placed at the bottom of the pipe section as a constant pollution source. An air compressor and a flowmeter are connected to the lower end of the pipeline. When considering the air convection phenomenon in the trap, the air compressor is used to ventilate the pipe section, and the flowmeter is used to control the air flow entering the pipe section. Sampling points are set at four locations: the upper end of the pollution source, the bottom of the inverted U-shaped pipe section of the trap, the outlet of the U-shaped pipe section of the trap, and the bottom of the indoor space, which are C1, C2, C3, and C4 in sequence. Among them, C1 is the pollution source monitoring point, and the concentration at this point directly represents the concentration of the pollution source entering the pipe section. A trap is set at a certain distance from the bottom of the pipe section. An inspection hole is installed at the bottom of the U-shaped pipe section of the trap, and the effective water seal height of the trap is equal to the diameter of the trap pipe section, which is 5 cm in this embodiment.

[0039] In this embodiment, the indoor space simulation unit is composed of a simulated indoor space, a mass flowmeter sensor, a mass flowmeter digital display, a pressure reducing valve, a gas cylinder, and a vacuum pump. The volume of the entire simulated indoor space is 1520 cm 3 . The lower end of the simulated indoor space is connected to the mass flowmeter to ensure that clean air enters the indoor space at a constant flow rate, simulating the natural ventilation process of the indoor space in reality. The clean air is pumped through the mass flowmeter, the simulated indoor space, the gas auto-sampler, and the gas chromatograph in sequence by the vacuum pump. The flow rate of the mass flowmeter is set to be constant at 100 mL / min, that is, the air changes about 4 times within 1 hour. The gas auto-sampler is set in the passive sampling mode. When the gas auto-sampler does not inject gas into the gas chromatograph, the gas finally enters the tail gas absorption device.

[0040] The concentration monitoring device includes a gas chromatograph, a gas auto-sampler, a pressure reducing valve, and a gas chromatograph carrier gas cylinder.

[0041] During the operation of the device, ensure that the indoor air exchange conditions and the air flow rate flowing into the trap part are stable and do not change randomly.

[0042] In this embodiment, in order to verify the feasibility of the convection-diffusion model calculated by the numerical simulation software, the experimental results of this device are compared and verified with the theoretical calculation results. Specifically, it includes:

[0043] Step 1: Open the inspection hole in the trap, drain all the liquid in it, then close the inspection hole, turn on the air compressor and the vacuum pump, and purge the entire system for 12 hours to ensure that there is no residual pollutant gas in the system.

[0044] Step 2: Use a syringe to extract a certain volume of distilled water and inject it into the trap from the C3 sampling port to control the water seal height in the trap.

[0045] Step 3: Turn on the air compressor and use a flow meter to control the gas flow into the pipeline. Turn on the suction pump and control the mass flow meter to a flow rate of 100 mL / min.

[0046] Step 4: Set the conditions of the gas auto-sampler as follows: sampling time is 0.1 min, equilibration time is 0.05 min, injection time is 0.5 min, injection volume is 1 mL, analysis cycle is 25 min, and the number of sampling times per experimental cycle is 60 times. Then, every 25 min, the gas auto-sampler will inject samples into the gas chromatograph in a passive injection manner. At this time, the concentration monitored by the gas chromatograph is the PCE concentration in the indoor space. The gas chromatograph conditions are as follows: (1) The injection port temperature is 100 °C, the injection method is split injection, and the split ratio is 10:1; (2) The temperature programming of the column oven is: the initial temperature is 45 °C and is held for 3 min, then it is heated to 150 °C at a rate of 20 °C / min and held for 0 min, with a total time of 8.25 min; (3) Gas flow rate: The carrier gas is high-purity nitrogen, the total flow rate is 40 mL / min, the column flow rate is 1.00 mL / min, and the purge flow rate is 0.5 mL / min; the hydrogen flow rate is 30 mL / min, and the air flow rate is 300 mL / min; (4) The detector temperature is 250 °C; (5) The chromatographic column is a DB-5MS column with an inner diameter of 0.25 mm, a film thickness of 0.1 μm, and a length of 30 m.

[0047] Step 5: After all 60 samplings of the gas auto-sampler are completed, sample the pollutant concentration in the pipeline space. The specific sampling method is as follows: Use a 50 mL syringe to extract 25 mL, 25 mL, 50 mL, and 50 mL volumes of pollutant gas from sampling points C1, C2, C3, and C4 respectively and introduce them into a 500 mL Tedler sampling bag. Then introduce 475 mL, 475 mL, 450 mL, and 450 mL of clean air respectively. After shaking well and standing for 15 min, gas bag samples with dilution factors of 1 / 20, 1 / 20, 1 / 10, and 1 / 10 compared to the original pollutant gas are obtained for testing.

[0048] Step 6: Remove the gas auto-sampler from the device and change the conditions of the gas auto-sampler: sampling time is 0.1 min, equilibration time is 0.05 min, injection time is 0.5 min, injection volume is 1 mL, analysis cycle is 25 min, the number of sampling times per cycle is 4 times, and the injection method is changed to active injection. Connect the gas bag samples collected at C4, C3, C2, and C1 to the gas auto-sampler in turn. The gas chromatograph conditions are the same as those in sampling step 4, and measure the concentrations at each sampling point.

[0049] Step 7: Prepare solutions with mass concentrations of 0, 5000, 10000, 25000, 50000, 100000 μg / m 3The PCE standard gas sample was measured under the gas chromatography conditions in Step 4, and a standard curve was plotted.

[0050] Step 8: Based on the measurement results of the indoor concentration, plot a graph with time as the abscissa and the PCE decay coefficient as the ordinate to obtain the variation of the PCE decay coefficient with time in the simulated indoor space, and compare it with the software calculation results.

[0051] Step 10: Based on the measurement results of the pipeline space, plot a graph with the distance from the sampling point to the pollution source as the abscissa and the PCE decay coefficient as the ordinate to obtain the variation of the PCE decay coefficient with distance in the pipeline space, and compare it with the software calculation results.

[0052] Step 11: Change the water seal height and the flow rate of the pollutant entering the pipeline space and repeat the above steps. Each experiment is repeated three times.

[0053] Figure 2 shows the variation of the pollutant decay coefficient with time in the indoor space under different water seals and convection intensities verified by using the device of the present invention. A, B, C, and D respectively represent the case where diffusion is the main mass transfer effect (Q = 0) and there is no water seal in the trap (h = 0), the case where diffusion is the main mass transfer effect (Q = 0) and there is half water seal in the trap (h = 2.5 cm), the case where convection is the main mass transfer effect (Q = 100 mL / min) and there is no water seal in the trap (h = 0), and the case where convection is the main mass transfer effect (Q = 100 mL / min) and there is half water seal in the trap (h = 2.5 cm). The dotted lines in the figure represent the theoretically predicted variation values of the decay coefficient. It is found that the experimental results in these four cases are in agreement with the theoretical calculation results, and it can be considered that the convection-diffusion model can be used to describe the vapor intrusion process in the municipal pipe network.

[0054] Figure 3 shows the variation of the pollutant decay coefficient with distance in the pipeline space under different water seals and mass transfer conditions verified by using the device of the present invention. A, B, C, and D respectively represent the case where diffusion is the main mass transfer effect (Q = 0) and there is no water seal in the trap (h = 0), the case where diffusion is the main mass transfer effect (Q = 0) and there is half water seal in the trap (h = 2.5 cm), the case where convection is the main mass transfer effect (Q = 100 mL / min) and there is no water seal in the trap (h = 0), and the case where convection is the main mass transfer effect (Q = 100 mL / min) and there is half water seal in the trap (h = 2.5 cm). The dotted lines in the figure represent the theoretically predicted variation values of the decay coefficient. It is found that the experimental results in these four cases are in agreement with the theoretical calculation results, and it can be considered that the convection-diffusion model can be used to calculate the flux variation of pollutants in the pipe network.

Claims

1. Simulated municipal pipe network steam intrusion device, characterized in that, It includes a trap pipeline simulation unit, an indoor space simulation unit and a concentration monitoring device; the trap pipeline simulation unit consists of a trap (11), a pollution source sampling bottle (12), a differential pressure sensor (13), a flowmeter (14) and an air compressor (15), wherein the pollution source sampling bottle (12) is placed at the bottom of the pipe section, and the lower end of the trap (11) is sequentially connected to the differential pressure sensor (13), the flowmeter (14) and the air compressor (15); the indoor space simulation unit consists of a simulated indoor space (5), a mass flowmeter sensor (3), a mass flowmeter display and controller (4), a pressure reducing valve (2), an air cylinder (1), a tail gas absorption device (9) and an air extraction pump (10), the bottom end of the simulated indoor space is sequentially connected to the mass flowmeter sensor (3), the pressure reducing valve (2) and the air cylinder (1), the mass flowmeter display and controller (4) is connected to the mass flowmeter sensor (3), and the top end of the simulated indoor space (5) is sequentially connected to a gas automatic sampler (6), the air extraction pump (10) and the tail gas absorption device (9); the concentration monitoring device consists of a gas automatic sampler (6), a gas chromatograph (7), a pressure reducing valve (2) and a gas chromatograph carrier gas cylinder (8), and the gas automatic sampler (6) is sequentially connected to the gas chromatograph (7), the pressure reducing valve (2) and the gas chromatograph carrier gas cylinder (8); sampling points C1, C2, C3 and C4 are respectively arranged at the upper end of the pollution source sampling bottle (12), the bottom of the inverted U-shaped pipe section of the trap (11), the outlet of the U-shaped pipe section of the trap (11) and the bottom of the simulated indoor space (5).

2. The simulated municipal pipe network vapor intrusion device according to claim 1, wherein The pollution source is a liquid organic pollutant.

3. The vapor intrusion device for simulating a municipal pipe network according to claim 1, wherein The simulated indoor space (5) is composed of PVC pipe sections, and two semi-circular baffles are bonded in the middle of the pipe sections.

4. The simulated municipal pipe network vapor intrusion device according to claim 1, wherein An inspection hole is installed at the bottom of the U-shaped pipe section of the trap (11).

5. A method for verifying a mass transfer model describing the entry of pollutants from a municipal pipe network into a room using the simulated municipal pipe network vapor intrusion device according to any one of claims 1 to 4, characterized in that, Specifically, it includes the following steps: Step 1, set the mass transfer and water seal conditions of the model to be verified: if it is necessary to verify the diffusion mass transfer conditions, a certain volume of distilled water is injected into the trap from the C3 sampling port to control the water seal conditions; if it is necessary to verify the convective mass transfer conditions, turn on the air compressor and adjust the flow rate of the flowmeter to a constant value, and correspondingly control the mass transfer conditions required by the model according to the type of the model to be verified. Step 2, measure the change of the pollutant attenuation coefficient in the simulated indoor space with time: set the sampling time, equilibrium time, injection time, injection volume and analysis period of the gas automatic sampler, and sample cyclically every analysis period. The gas automatic sampler injects samples into the gas chromatograph in a passive injection manner, and the concentration monitored by the gas chromatograph at this time is the pollutant concentration in the simulated indoor space. Step 3, sample at the pipeline space sampling points: after all the samplings of the gas automatic sampler are completed, use a syringe to sample the pollutant concentration in the pipeline space from the sampling points C1, C2, C3 and C4 respectively, and dilute it for later measurement. Step 4. Measure the change of the pollutant attenuation coefficient in the pipeline space with distance: Remove the gas auto-sampler from the device, and set the sampling time, equilibrium time, injection time, injection volume, and analysis period of the gas auto-sampler the same as those in Step 2. Change the injection mode to active injection. Connect the diluted samples taken from C4, C3, C2, and C1 in Step 3 to the gas auto-sampler respectively, and measure the pollutant concentrations at each sampling point under the same gas chromatography conditions as in Step 2. Step 5. Draw a calibration curve: Prepare pollutant standard gas samples with different concentrations, measure them under the gas chromatography conditions in Step 2, and draw a standard curve. Step 6. Sample analysis: According to the measurement results in Step 2, plot a graph with time as the abscissa and the pollutant attenuation coefficient as the ordinate to obtain the change curve of the pollutant attenuation coefficient with time in the simulated indoor space. Step 7. Sample analysis: According to the measurement results in Step 4, plot a graph with the distance from the sampling point to the pollution source as the abscissa and the pollutant attenuation coefficient as the ordinate to obtain the change curve of the pollutant attenuation coefficient with distance in the pipeline space.

6. The method according to claim 5, characterized in that, In Step 1, the model to be verified is the convection-diffusion mass transfer model; in Step 2, the pollutant is a chlorinated organic pollutant.

7. The method according to claim 5, wherein In Step 2, the pollutant is tetrachloroethylene.

8. The method according to claim 5, wherein In Step 2, the sampling time of the gas auto-sampler is 0.1 min, the equilibrium time is 0.05 min, the injection time is 0.5 min, the injection volume is 1 mL, the analysis period is 25 min, the number of sampling times per experimental cycle is 60 times, and the gas auto-sampler injects samples into the gas chromatography in a passive injection manner every 25 min. At this time, the concentration monitored by the gas chromatography is the PCE concentration in the simulated indoor space. The gas chromatography conditions are as follows: (1) The injection port temperature is 100 °C, the injection mode is split injection, and the split ratio is 10:1; (2) The temperature programming of the column oven is: the initial temperature is 45 °C and is held for 3 min, then it is raised to 150 °C at a rate of 20 °C / min and held for 0 min, and the total time is 8.25 min; (3) Gas flow rate: The carrier gas is high-purity nitrogen, the total flow rate is 40 mL / min, the column flow rate is 1.00 mL / min, and the purge flow rate is 0.5 mL / min; the hydrogen flow rate is 30 mL / min, and the air flow rate is 300 mL / min; (4) The detector temperature is 250 °C; (5) The chromatographic column is a DB-5MS column with an inner diameter of 0.25 mm, a film thickness of 0.1 μm, and a length of 30 m.

9. The method according to claim 5, wherein In Step 3, the specific methods of sampling and dilution are as follows: Use a syringe to extract pollutant gases with volumes of V1, V2, V3, and V4 from the sampling points C1, C2, C3, and C4 respectively and introduce them into a 500 mL Tedler sampling bag, and then introduce clean air with volumes of (500 - V1), (500 - V2), (500 - V3), and (500 - V4) respectively. After shaking well and standing for 15 min, gases with dilution multiples of (V1 / 500), (V2 / 500), (V3 / 500), and (V4 / 500) compared with the original pollutant gas are obtained.

10. The method according to claim 5, characterized in that, In Step 4, the number of cycles is 4; in Step 5, PCE standard gas samples with mass concentrations of 0, 5000, 10000, 25000, 50000, and 100000 μg / m 3 are prepared.

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