Pretreatment system suitable for measuring mole fraction of carbon dioxide in water body by water-gas balance method and automatic measurement method

Abstract

The invention discloses a pretreatment system and an automatic measuring method suitable for measuring the mole fraction of carbon dioxide in a water body through a water-gas balance method, and relates to the field of gas analysis and measurement, the pretreatment system comprises an automatic condensation water removal system, a gas valve automatic switching system, a control system and PC end upper computer software; the automatic condensation water removal system adopts a semiconductor condenser and a Nafion drying pipe to remove water; the gas valve automatic switching system automatically switches standard gas and balance gas through a valve; the control system is connected with the gas valve automatic switching system and PC end upper computer software, monitors and adjusts the gas flow rate in real time, and ensures that the gas flow rate is within a preset range; the upper computer software of the PC end integrates data processing and visualization functions, and automatic control and real-time data recording and analysis of the whole system are achieved. The system is reasonable and simple in structure, easy to carry and install, easy and convenient to use, stable in operation and capable of visually displaying the change trend of the CO2 mole fraction in a research area in real time.

Description

Technical Field

[0001] The present invention relates to the field of gas analysis and measurement, and in particular to a pre-processing system and an automatic measurement method suitable for determining the molar fraction of carbon dioxide in water using a "water-gas balance method". Background Art

[0002] Sea-air CO2 exchange is a key process in the ocean carbon cycle. The accuracy of seawater CO2 partial pressure measurement is the key to accurately estimate the source and sink of ocean CO2, and is also a prerequisite for predicting future climate change through atmospheric climate models. The CO2 partial pressure of water bodies such as estuaries and lakes is also an important parameter for clarifying their biogeochemical processes and mechanisms. There are two ways to measure the CO2 partial pressure of water bodies: one is to observe with an in-situ CO2 sensor mounted on a buoy; the other is to observe continuously online on a ship or at a fixed point.

[0003] The core issue of determining the CO2 partial pressure of water is to accurately determine the CO2 mole fraction of the water body, and then calculate the CO2 partial pressure by combining the atmospheric pressure and the saturated water vapor pressure. The continuous flow water-gas balance method is a classic method commonly used for continuous online observation of CO2 partial pressure of seawater on board or at fixed points in international marine surveys. The workflow is: the surface seawater is continuously extracted by a water pump, and the seawater is transported to the water-gas balance in the laboratory through a high-density water pipe. The nozzle breaks the incoming water sample into fine water droplets under a certain water pressure, and quickly reaches CO2 partial pressure equilibrium with the air in the balance chamber. The balanced air is sucked out by a small air pump, and the moisture is completely removed through the drying system (spiral tube ice water cold trap + Mg(ClO4)2 drying tube), and sent to a non-dispersive infrared CO2 detector or other CO2 measuring instrument to measure the CO2 mole fraction in dry air and record it in real time. At the same time, the CO2 measurement system and CO2 standard gas are switched regularly to calibrate the CO2 detector.

[0004] At present, the equipment for shipboard measurement of CO2 partial pressure can be divided into two categories: automatic system and manual system. Automatic systems (such as the US GO-8050 and Apollo AS-P3-850) are expensive and suitable for fixed installation on scientific research ships, but not suitable for use in estuaries, nearshore environments, etc. The main problems of manual systems are as follows: (1) High workload: During the sample measurement process, it is necessary to regularly replace ice and Mg(ClO4)2 desiccant in the drying tube, and to manually calibrate and calibrate the CO2 detector regularly. (2) Poor stability: It is highly dependent on the operator's experience and operating ability, which is mainly reflected in the fact that the gas flow rate sent to the CO2 detector has a great influence on the instrument's CO2 mole fraction response value; when manually calibrating, the gas flow rate sent to the CO2 detector is completely controlled by experience, resulting in low accuracy when correcting the CO2 mole fraction. (3) Poor integration: When the system is manually built, the construction process is cumbersome and slow due to the large number of accessories and complex circuits. When collecting data, it can only obtain the data of the CO2 detector but cannot draw a graph in real time. It is not intuitive enough and cannot distinguish whether the gas being measured is the standard gas or the balanced sample gas (hereinafter referred to as "balanced gas"), nor can it reflect the fault conditions of the system gas circuit.

[0005] Therefore, establishing a pretreatment system suitable for the "water-gas balance method" to determine the CO2 mole fraction in water bodies, modularizing, integrating and automating the bulk system, will help to better play the important role of the "water-gas balance method" in CO2 monitoring and scientific research activities in oceans, estuaries, lakes and other water bodies. Summary of the invention

[0006] The purpose of the present invention is to solve the above-mentioned problems of the existing ship-borne manual measurement system of CO2 partial pressure in water bodies in the prior art, such as high work intensity and poor integration, and to provide a pre-treatment system and automatic measurement method suitable for the "water-gas balance method" to measure the mole fraction of carbon dioxide in water bodies; with automatic control as the core, a drying system composed of semiconductor refrigeration technology and the drying characteristics of Nafion drying tubes and a gas valve automatic switching system are adopted, and data communication technology and data acquisition technology are combined. The system has a reasonable and simple structure, is easy to carry and install, is easy to use, has stable operation, and can intuitively and real-timely display the changing trend of the CO2 mole fraction in the study area.

[0007] In order to achieve the above object, the present invention adopts the following technical scheme:

[0008] A pre-treatment system suitable for determining the CO2 mole fraction of water by the "water-gas balance method", including an automatic condensation and water removal system, a gas valve automatic switching system, a control system and a PC-side host computer software. The pre-treatment system needs to be used in conjunction with a water-gas balance and a CO2 detector. During the sampling process, the CO2 detector is calibrated with CO2 standard gas at regular intervals ( Figure 1). The gas flow path of the balance gas sampling passes through the water-gas balancer, automatic condensation and water removal system, the air pump of the control system, the gas valve automatic switching system, and the CO2 detector in turn. The control system sends the balance gas to the CO2 detector for detection. The balance gas after detection returns to the flow meter of the control system to detect the gas flow, and finally returns to the water-gas balancer to form a loop. The gas valve automatic switching system is connected to the control system through a data line, and the control system and the CO2 detector are connected to the computer with the software installed through a data line. The control system and the CO2 detector upload the detected sensor parameters to the software, and the software performs corresponding actions on the gas valve automatic switching system and the associated equipment of the control system through the self-programming function. At the same time, the acquired CO2 mole fraction and other data are stored and output in real time, and the graph is drawn according to the balance gas CO2 mole fraction.

[0009] The automatic condensation and dehumidification system is a condensation and dehumidification box, with an air inlet and an air outlet on the top of the box and a liquid discharge port on the side. The system includes: (1) a pre-dehumidification unit, which is used to extract the balance gas from the water-gas balancer and condense and dehumidify the balance gas entering the pre-dehumidification unit; (2) a condensation water removal unit, which is used to discharge the waste water condensed by the pre-dehumidification unit out of the box at a fixed time; (3) a fine dehumidification unit, which is used to further dry the balance gas flowing out of the pre-dehumidification unit. The balance gas flows from the gas outlet of the water-gas balancer, the pre-dehumidification unit, and the fine dehumidification unit in sequence.

[0010] The pre-dehumidification unit comprises an aluminum alloy block, an electronic refrigeration sheet, a thermal insulation layer, a heat sink, a fan, a temperature probe, a relay and a temperature controller.

[0011] The core component of the pre-dehumidification unit is an aluminum alloy block.

[0012] The aluminum alloy block has two U-shaped bending flow paths, wherein the gas inlet is the gas inlet of one of the U-shaped paths, and the gas outlet is the gas outlet of the other U-shaped path, which are connected to the air inlet of the fine dehumidification unit.

[0013] The two U-shaped bending flow paths of the aluminum alloy block are connected to each other through an air pipeline.

[0014] The side of the aluminum alloy block has two holes corresponding to two U-shaped flow paths respectively.

[0015] The aluminum alloy block has two grooves, and the shapes of the grooves match the electronic refrigeration plate.

[0016] The outer surface of the aluminum alloy block is covered with a heat-insulating layer. Preferably, polyurethane is used as the heat-insulating material of the heat-insulating layer. The heat-insulating layer avoids the hot surface of the electronic refrigeration plate.

[0017] The bottom of the aluminum alloy block is provided with two drain ports which are connected to the condensed water removal unit.

[0018] The cold surface of the electronic refrigeration sheet is in contact with the outer wall of the aluminum alloy block and is evenly distributed and is located directly above the two U-shaped bending areas.

[0019] The heat sink is in contact with the hot surface of the electronic refrigeration sheet.

[0020] The fan is attached to the heat sink and is used to cool the heat sink.

[0021] The temperature probe is installed in a hole on one side of the aluminum alloy block, and the hole on the other side is blocked with a plug to prevent the balance gas in the aluminum alloy block from exchanging with the outside.

[0022] The temperature probe is connected to the temperature controller, and the temperature controller, the electronic refrigeration sheet and the relay are connected. The temperature controller controls whether the electronic refrigeration sheet works or not according to the temperature detected by the temperature sensor. A lower temperature limit is preset in the temperature controller. When the temperature detected by the temperature probe is higher than the lower temperature limit, the relay connects the electronic refrigeration sheet circuit and the electronic refrigeration sheet works; when the temperature detected by the temperature probe is lower than the lower temperature limit, the relay disconnects the electronic refrigeration sheet circuit and the electronic refrigeration sheet stops working.

[0023] The condensed water removal unit comprises two peristaltic pumps and a single and double countdown cycle controller.

[0024] One end of the two peristaltic pumps is respectively connected to the two drainage ports at the bottom of the aluminum alloy block, and the other end is connected to the drainage port on the side of the condensation and water removal box.

[0025] The single and double countdown cycle controller is connected to two peristaltic pumps, and the operator presets the on and off time of the controller, thereby controlling the working time and interval of the peristaltic pump to drain condensed water.

[0026] The fine dehumidification unit comprises a Nafion drying tube, an air pump, a molecular sieve drying box, a filter membrane and a needle valve.

[0027] The balance gas inlet end of the Nafion drying tube is connected to the gas outlet end of the pre-dehumidification unit. The balance gas outlet end of the Nafion drying tube is connected to the balance gas inlet end of the gas valve automatic switching system.

[0028] The outer tube of the Nafion drying tube is a drying air tube, which is sequentially connected to the air pump, the molecular sieve drying box, the filter membrane and the needle valve.

[0029] The air pump provides power for the gas flow of the drying tube.

[0030] The molecular sieve drying box is filled with molecular sieves for absorbing moisture in the air pipe.

[0031] The filter membrane is used to prevent large particles from entering the drying tube.

[0032] The needle valve is used to control the gas flow rate in the drying tube.

[0033] Preferably, the filter membrane is a polytetrafluoroethylene hydrophobic membrane with a pore size of 0.1 μm.

[0034] Preferably, the gas flow rate in the Nafion drying tube is 200 mL min -1 .

[0035] Preferably, the molecular sieve is a 13* type molecular sieve with a pore size of 10A.

[0036] The gas valve automatic switching system is a gas valve automatic switching device box, a gas inlet and a gas outlet are arranged on the top of the box, and the system comprises a gas automatic switching valve, a connecting bolt and a needle valve.

[0037] The gas automatic switching valve is an eight-way valve automatic switching device, and the eight-way valve has 7 inlets for the gas to be tested and 1 outlet. The inlet for the gas to be tested is used to connect the CO2 standard gas and the balance gas, and the outlet is connected to the control system.

[0038] The top of the gas valve automatic switching device box is provided with 8 through holes corresponding to the gas ports on the eight-way valve, and connecting bolts are installed in the holes.

[0039] The outer side of the connecting bolt box is used for connecting the gas pipeline, and the inner side is used for connecting the gas automatic switching valve.

[0040] The needle valve is installed between the connecting bolts on the inner side of the top of the gas valve automatic switching device box and the gas automatic switching valve, and is used for fine-tuning the gas flow rate in the pipeline.

[0041] The gas valve automatic switching system is connected to the control system via a data line.

[0042] The control system is installed in the box and is used to receive program instructions from the PC-side host computer software, so that the gas automatic switching valve executes the corresponding instructions. At the same time, the gas flow rate in the system gas circuit is detected and displayed in real time. In particular, when the system is detecting the balance gas, the gas flow rate in the pipeline is automatically adjusted by adjusting the duty cycle of the air pump. The control system includes: an air pump, a flow meter, a detection unit, an execution unit and a control unit.

[0043] The top of the control system box body has four through holes, in which connecting bolts are arranged, two of which are used for air inlet and air outlet of the air pump, and the other two are used for air inlet and air outlet of the flow meter.

[0044] The control system box body has two through holes on its side, in which data connection ports are arranged.

[0045] The air pump is used to provide pneumatic power for the entire system when the control module control system measures the balance gas, that is, to extract the balance gas, pass it through the automatic condensation and water removal system, the gas valve automatic switching system, the control system, enter the CO2 detector for detection, and then pass through the flow meter and finally return to the water-gas balancer.

[0046] The air pump has an air inlet end connected to the air outlet end of the automatic condensation and water removal system through connecting bolts, and the air outlet end is connected to the balance gas inlet of the gas valve automatic switching system.

[0047] The air pump has a power line connected to a circuit board of a control system control unit;

[0048] The detection unit is used to receive the gas flow rate signal of the flow meter and transmit it to the PC host software.

[0049] The flow meter measures the gas flow rate in the system and transmits the signal to the detection unit.

[0050] The flow meter has an air inlet end connected to the air outlet end of the CO2 detector through a connecting bolt, and the air outlet end is connected to the water-gas balancer circuit.

[0051] The flow meter has a power line connected to a circuit board of a control system detection unit;

[0052] The execution unit is used to receive the sample test program instructions set by the operator in the PC host computer software, and transmit the instructions to the gas automatic switching valve and the control unit.

[0053] The control unit is used to receive instructions from the execution unit to control the switching time and duration of the gas automatic switching valve, and at the same time adjust the switch and duty cycle of the air pump to keep the gas flow rate within a preset value range.

[0054] The control system and CO2 detector are connected to a computer with software installed via a data cable. The main function of the PC host software is to read the data of the control system and CO2 detector. The user presets the sample program instruction control system in the software to complete the action, and the sample program sets the sample quantity, duration, time interval and number of samples of CO2 standard gas and balance gas. When measuring CO2 standard gas, the air pump in the control system stops working, the software reads the data of the CO2 detector, records the sample type STDn (STDn represents standard gas) and outputs the data; when measuring sample gas, the air pump of the control system is turned on and the air pump is automatically controlled. When the gas flow rate is greater than the set value, the air pump duty cycle is reduced, and when the gas flow rate is less than the set value, the air pump duty cycle is increased. The software reads the data of the CO2 detector, records the sample type EQU (EQU represents balance gas) and outputs the data. In real time, the software stores and outputs the acquired CO2 mole fraction and other data, and draws a graph based on the CO2 mole fraction of the balance gas.

[0055] Accordingly, the present invention provides a method for automatically measuring the CO2 mole fraction on board a ship, the method comprising the following steps:

[0056] 1) The CO2 gas balanced by the water-gas balance is driven by the control system air pump at a rate of 80 mL min -1 ~ 120mL min -1 The gas enters the automatic condensation and dehydration system at a flow rate of 10000 m / s. After being cooled in the pre-dehumidification unit of the automatic condensation and dehydration system, most of the water is removed. Then, the gas continues to be dehydrated by the fine dehumidification unit of the automatic condensation and dehydration system. After being basically dried, it is sent to the gas valve automatic switching system.

[0057] 2) The gas valve automatic switching system automatically switches the CO2 standard gas and balance gas at different durations and time intervals under the control of the preset sampling program of the PC host software, and sends the gas to the CO2 detector to detect its molar fraction;

[0058] 3) The PC host software controls the pipeline flow rate when measuring the balance gas. According to the type of sample gas, duration and time interval set by the program, the data of the CO2 detector is read, and the output CO2 mole fraction, H2O mole fraction, detector working temperature, working pressure and gas flow rate in the pipeline measured by the flowmeter are recorded in real time. And the balance gas CO2 mole fraction is plotted online in real time;

[0059] 4) The balance gas detected by the CO2 detector is sent back to the flow meter of the control system to detect the system gas flow, and then returns to the water-gas balancer to form a closed loop.

[0060] Compared with the prior art, the technical solution of the present invention has the following beneficial effects:

[0061] The present invention can efficiently remove moisture from the balance gas, and cooperates with the gas automatic switching valve and the air pump to realize the automation of the "water-gas balance method" to measure the CO2 mole fraction of water. The system has a compact layout, simple equipment, and stable operation; the modular design makes it easy to operate, and it can be easily moved in blocks and combined for application; the precise control of the gas flow rate in the system can eliminate the operational errors introduced by the experimenter's uneven flow rate control; reduce the use of CO2 standard gas, and at the same time improve the accuracy of gas sample analysis. BRIEF DESCRIPTION OF THE DRAWINGS

[0062] Figure 1 Schematic diagram of the gas flow path of the present invention, wherein the dotted line is the gas line and the solid line is the data line;

[0063] Figure 2 It is a schematic diagram of the overall structure of the present invention;

[0064] Figure 3 This is a schematic diagram of the structure of the automatic condensation and water removal system;

[0065] Figure 4 It is a structural schematic diagram of a pre-dehumidification unit in an automatic condensation and water removal system;

[0066] Figure 5 This is a schematic diagram of the structure of the gas valve automatic switching system;

[0067] Figure 6 It is the structural diagram of the control system;

[0068] Figure 7 This is the workflow diagram of the PC host software;

[0069] Figure 8 (a) and (b) are the results of the H2O mole fraction of the CO2 detector during the spring and summer cruises in the Pearl River Estuary in 2023, respectively. The horizontal dashed line in (b) indicates that the H2O mole fraction was between -0.4 and 0.2 mmol mol during the cruise. -1 between;

[0070] Fig. 9 Figures (a) and (b) in the middle are the calibration results of the CO2 detector for 396 ppm CO2 standard gas during the spring and summer voyages in the Pearl River Estuary in 2023, respectively. The black circle in Figure (a) indicates that the calibration point is an erroneous result that deviates from the change trend, and the dotted line in Figure (b) indicates the changing trend of the calibration of 396 ppm CO2 standard gas during the summer voyage. DETAILED DESCRIPTION

[0071] In order to make the technical problems, technical solutions and beneficial effects to be solved by the present invention clearer and more understandable, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments.

[0072] like Figure 2 As shown, the pretreatment system of the present invention needs to be used in conjunction with a water-gas balancer 1, a CO2 detector 5 and a CO2 standard gas 7, and includes an automatic condensation and water removal system 2, a gas valve automatic switching system 3, a control system 4 and a PC-side host computer software 6.

[0073] The water-gas balancer 1 used in this embodiment is a packing tower filled with plastic balls, with an inner diameter of 9 cm, a packing height of 20 cm, a headspace (balance chamber) of 100 ml, a nozzle and an air outlet at the top, and a gas reflux port at the bottom. When in use, the nozzle breaks the incoming water sample into small water droplets under a certain water pressure, and quickly reaches equilibrium with the air in the balance chamber.

[0074] The balanced air in the water-gas balancer 1 is pumped by the air pump of the control system 4 at a rate of 80 mL min -1 ~120 mL min -1 The flow rate is sucked out through the gas pipeline, passes through the automatic condensation and water removal system 2, the air pump of the control system 4, the gas valve automatic switching system 3, the CO2 detector 5, the flow meter of the control system 4, and then returns to the water-gas balancer 1 to form a loop. The CO2 standard gas 7 is connected to the gas valve automatic switching system 3 through the pressure reducing valve 8 and the gas pipeline.

[0075] The gas valve automatic switching system 3 is connected to the control system 4 through a data line, and the control system 4 and the CO2 detector 5 are connected to the computer installed with the PC-side host computer software 5 through a data line. The control system 4 and the CO2 detector 5 send the acquired flow meter data and CO2 mole fraction data to the PC-side host computer software 6 and record and output, and the PC-side host computer software 6 draws a graph based on the real-time CO2 mole fraction data. At the same time, the control system 4 receives the instructions issued by the PC-side host computer software 6, and controls the associated devices to perform corresponding actions according to the instructions.

[0076] like Figure 3 As shown, the automatic condensation and dehumidification system includes a pre-dehumidification unit 9, a condensation water removal unit 10 and a fine dehumidification unit 11. The various components of the system are fixed on a rectangular aluminum alloy box. The upper part of the box corresponds to the inlet and outlet of the balancing gas, and there are two drain ports 15 on the side, corresponding to two peristaltic pumps 16 respectively.

[0077] The pre-dehumidification unit 9 is used to condense and remove water from the gas with 100% humidity sucked out from the water-gas balancer. In the pre-dehumidification unit 9, most of the water-gas in the gas will be condensed to form water droplets. Every 20 minutes, the condensation water removal unit 10 will discharge the gas from the box through the drain port 15. The fine dehumidification unit 11 is used to further dry the gas flowing out of the pre-dehumidification unit 9. After drying, the water content in the balance gas can be maintained at 1 mmol mol -1The following has no significant effect on the CO2 mole fraction results of the CO2 detector.

[0078] The pre-dehumidification unit 9 includes a semiconductor condenser 17 , a relay 18 , a temperature probe 19 and a temperature controller 20 .

[0079] Two electronic refrigeration sheets 21 are installed in the semiconductor condenser 17 .

[0080] The electronic refrigeration sheet 21 is connected to the relay 18, and the relay 18 and the temperature probe 19 are respectively connected to the temperature controller 20. The pre-dehumidification unit 9 controls the temperature of the semiconductor condenser 17 to be constant at 4°C.

[0081] The semiconductor condenser 17 has two U-shaped bend flow paths 22 and 23 inside and four air holes on the top. The gas inlet of the semiconductor condenser 17 is the gas inlet 12 of the U-shaped path 22. The U-shaped paths 22 and 23 are interconnected through the air holes 13. The gas outlet 14 is the gas outlet of the U-shaped path 23 and is connected to the air inlet 26 of the fine dehumidification unit.

[0082] A temperature probe 19 is installed on one side of the semiconductor condenser 17, that is, one side of the U-shaped flow path 22, and the temperature probe 19 is connected to a temperature controller 20. The U-shaped flow path 23 on the other side is blocked with a plug 24 to prevent the gas in the condenser from exchanging with the outside.

[0083] The condensed water removal unit 10 includes a peristaltic pump 16 and an odd / even countdown cycle controller 25 .

[0084] The peristaltic pump 16 is correspondingly connected to the drain port 15 at the bottom of the pre-dehumidification unit 9 to discharge the liquid in the drain port 15 .

[0085] The single / double countdown cycle controller 25 is connected to the peristaltic pump 16. The operator presets the duration of its on and off, thereby controlling the working duration and interval of the peristaltic pump 16 to discharge condensed water.

[0086] Preferably, the peristaltic pump is set to work once every 20 minutes, and each working time is 1 minute.

[0087] The fine dehumidification unit 11 includes a Nafion drying tube 27 , an air pump 28 , a molecular sieve drying box 29 , a filter membrane 30 and a needle valve 31 .

[0088] The inner tube of the Nafion drying tube is a sample balance gas pipe, the sample gas inlet end 26 is connected to the gas outlet 14 of the pre-dehumidification unit 9, and the sample gas outlet end 33 is connected to the gas valve automatic switching system balance gas inlet end.

[0089] The outer tube of the Nafion drying tube is a drying gas tube, and the mark 32 is the flow path of the drying gas of the outer tube of the Nafion drying tube. The drying gas tube is connected to the air pump 28, the molecular sieve drying box 29, the filter membrane 30 and the needle valve 31 in sequence.

[0090] The air pump 28 provides power for the gas flow rate of the drying air pipe. Preferably, the maximum gas flow rate that the air pump can provide is 1 L min -1 .

[0091] The molecular sieve drying box 29 is filled with molecular sieves to absorb moisture in the dry air pipe. Preferably, the molecular sieve drying box is columnar, with a diameter of 4 cm and a length of 35 cm, and cotton is filled at the upper and lower ends of the drying box. Preferably, the molecular sieve is a 13* type molecular sieve with a pore size of 10A. Preferably, the molecular sieve in the molecular sieve drying box is replaced every 5 days to ensure the water removal efficiency of the system.

[0092] The filter membrane 30 is used to prevent particles from entering the drying tube. Preferably, the filter membrane is a 0.1 μm polytetrafluoroethylene hydrophobic membrane.

[0093] The needle valve 31 is used to control the gas flow rate in the drying gas pipe. Preferably, the gas flow rate in the drying gas pipe is 200 mL min -1 .

[0094] like Figure 4 As shown, the structure of the semiconductor condenser is described in detail.

[0095] The semiconductor condenser includes an aluminum alloy block 34 , an electronic refrigeration plate 21 , a condensed water drain port 15 , a heat sink 35 , a fan 36 , and a thermal insulation layer 37 .

[0096] There are two grooves on the aluminum alloy block 34, and the grooves match the size and shape of the electronic refrigeration plate 21. The cold surface of the electronic refrigeration plate fits with the aluminum alloy block 34, and the hot surface fits with the heat sink 35. In order to ensure uniform heating, thermal grease is evenly applied to the cold and hot surfaces of the electronic refrigeration plate. One side of the heat sink 35 is connected to the hot surface of the electronic refrigeration plate 21, and the other end is provided with a fan 36, the purpose of which is to take away the heat from the heat sink. One end of the aluminum alloy block 34 is the inlet and outlet of the gas, and the other end is the drain port 15 for condensed water. The outer surface of the aluminum alloy block 34 is provided with a thermal insulation layer 37. Preferably, polyurethane is used as the thermal insulation material of the thermal insulation layer. The thermal insulation layer 37 avoids the hot surface of the electronic refrigeration plate 21.

[0097] like Figure 5 As shown, the gas valve automatic switching system includes a gas automatic switching valve 38, a connecting bolt 39, and a needle valve 40. The gas automatic switching valve 38 and eight connecting bolts 39 evenly distributed throughout the box body are fixed on the rectangular aluminum alloy box body.

[0098] In this embodiment, the gas automatic switching valve 38 is an eight-way valve from VICI. The eight-way valve has eight holes evenly distributed, the seven air inlet holes 41 indicated by dotted lines are the inlets of the gas to be tested, and the air outlet holes 42 indicated by solid lines are the outlets of the gas.

[0099] The eight connecting bolts 39 on the box body of the gas valve automatic switching system are correspondingly connected to the eight holes on the gas automatic switching valve 38 through gas pipelines.

[0100] In this embodiment, seven stainless steel needle valves 40 are installed between the connecting bolts 39 and the air inlet holes 41 corresponding to the seven air inlet holes, and are used to fine-tune the flow rate of the standard gas and the balanced sample gas inlet.

[0101] The gas valve automatic switching system is connected to the control system via an RS232 data line.

[0102] The gas valve automatic switching system can select to connect to up to six bottles of CO2 standard gas with different concentration gradients.

[0103] like Figure 6 As shown, the control system is installed on a rectangular aluminum alloy box body, and includes connecting bolts 43-46, a flow meter 47, a detection unit 48, an execution unit 49, a control unit 50, an air pump 51 and data connection ports 52, 53.

[0104] The top of the control system box body has four through holes, in which connecting bolts 43-46 are arranged.

[0105] The connecting bolt 43 connects the gas outlet of the carbon dioxide detector and the gas inlet of the flow meter 47 .

[0106] The connecting bolt 44 connects the gas outlet of the flow meter 47 and the gas inlet of the water-gas balancer.

[0107] The connecting bolt 45 connects the gas outlet of the automatic condensation and water removal system and the gas inlet of the air pump 51 .

[0108] The connecting bolt 46 connects the gas outlet of the gas pump 51 and the balancing gas inlet of the gas automatic switching valve.

[0109] The control system has two through holes on the side of the box body, in which RS232 data connection ports 52 and 53 are arranged.

[0110] The RS232 data connection port 52 is used for signal connection between the gas automatic switching valve and the execution unit 49 .

[0111] The RS232 data connection port 53 is used for signal connection between the PC host software and the detection unit 48 and the execution unit 49 .

[0112] The flow meter 47 is used to measure the gas flow rate in the system and transmit the signal to the detection unit 48 .

[0113] The detection unit 48 is used to receive the gas flow rate signal from the flow meter 47 and transmit it to the PC host software.

[0114] The execution unit 49 is used to receive the sample testing program set by the operator in the PC host computer software, and transmit the program instructions to the gas valve automatic switching system and the control unit 50.

[0115] The control unit 50 is used to receive the instruction of the execution unit 49 and adjust the switch and duty cycle of the air pump 51. When the system measures the balanced sample gas, the gas flow rate in the control system is 80 mL min -1 ~120 mL min -1 .

[0116] The switch and flow rate of the air pump 51 are controlled by the control unit 50. Preferably, the maximum gas flow rate that the air pump 51 can provide is 1 L min -1

[0117] The PC host software is installed on the computer, and the computer is connected to the control system and the CO2 detector via an RS232 data line. In this embodiment, the CO2 standard gas required for the measurement is 4 concentration gradients, each concentration gradient is measured 8 times, and the balance gas is measured 600 times, and real-time recording is performed in a reciprocating cycle. The 1, 5, 7, 11, and 13 valve positions of the VICI automatic switching valve correspond to the input ports of the balance gas and standard gas 1 to 4, respectively.

[0118] Workflow such as Figure 7 As shown: After starting the PC host software, connect the control system and the CO2 detector. At this time, read the flow meter data and CO2 detector data of the detection unit. Open the self-made program toolbar in the software and enter the sample test program according to the above requirements. The program includes 1 large cycle and 5 small cycles;

[0119] Step 1: Turn off the air pump;

[0120] Step 2: Measure CO2 standard gas 1, and open the gas automatic switching valve to valve position 5. Adjust the gas flow in the pipeline when measuring CO2 standard gas 1 by adjusting the CO2 standard gas 1 pressure reducing valve and needle valve until the flow rate is about 100 mL min -1 ; (The operation of adjusting the standard gas pressure reducing valve and needle valve is only performed when measuring the standard gas for the first time, the same below)

[0121] Step 3: After holding for 60 seconds, take the 10-second average of the CO2 detector as the measurement result of CO2 standard gas 1 and record the data;

[0122] Step 4: Repeat step 3 8 times;

[0123] Step 5: Measure standard gas 2, and open the gas automatic switching valve to valve position 7. Adjust the gas flow in the pipeline when measuring standard gas 2 by adjusting the standard gas 2 pressure reducing valve and needle valve until the flow rate is about 100 mL min -1 ; (The operation of adjusting the pressure reducing valve and needle valve is the same as above)

[0124] Step 6: After holding for 60 seconds, take the 10-second average of the CO2 detector as the standard gas 2 measurement result and record the data;

[0125] Step 7: Repeat step 6 8 times;

[0126] Step 8: Measure standard gas 3, and open the gas automatic switching valve to valve position 11. Adjust the gas flow in the pipeline when measuring standard gas 3 by adjusting the standard gas 3 pressure reducing valve and needle valve until the flow rate is about 100 mL min -1 ; (The operation of adjusting the pressure reducing valve and needle valve is the same as above)

[0127] Step 9: After holding for 60 seconds, take the 10-second average of the CO2 detector as the standard gas 3 measurement result and record the data;

[0128] Step 10: Repeat step 9 8 times;

[0129] Step 11: Measure standard gas 4, and open the gas automatic switching valve to valve position 13. Adjust the gas flow in the pipeline when measuring standard gas 4 by adjusting the standard gas 4 pressure reducing valve and needle valve until the flow rate is about 100 mL min -1 ; (The operation of adjusting the pressure reducing valve and needle valve is the same as above)

[0130] Step 12: After holding for 60 seconds, take the 10-second average of the CO2 detector as the standard gas 4 measurement result and record the data;

[0131] Step 13: Repeat step 12 8 times;

[0132] Step 14: Measure the balanced sample gas, open the gas automatic switching valve to valve position 1, and start the air pump of the control system with a duty cycle of 20%;

[0133] Step 15: The system adjusts the duty cycle of the gas pump according to the measured gas flow rate. If the gas flow rate is greater than the set value, the duty cycle is automatically reduced; if the gas flow rate is less than the set value, the duty cycle is automatically increased until the flow rate is within the set value range of 80~120mL min -1After 60 seconds, take the 10-second average value of the CO2 detector as the balance gas measurement result and record the data;

[0134] Step 16: Repeat step 15 600 times;

[0135] Step 17: Loop back to step 1 and execute repeatedly.

[0136] The software records and lists the current computer time, sample type (standard gas STDn or balanced sample gas EQU), CO2 mole fraction, H2O mole fraction, CO2 detector operating temperature, CO2 detector operating pressure and system gas flow in real time. At the same time, it draws a graph based on the computer time and the measured real-time balanced gas CO2 mole fraction.

[0137] It should be noted that the CO2 detector can not only measure the CO2 mole fraction, but also the H2O mole fraction. The present invention can also detect the effect of the condensation dehydration system through the measured H2O mole fraction.

[0138] Compared with the existing scheme, the present invention provides a pretreatment system and measurement method suitable for determining the CO2 mole fraction of water body by "water-gas balance method". The modular design of the system makes it easy to disassemble and install, simple to operate, and can efficiently remove moisture in the equilibrium sample gas ( Figure 8 ), successfully realized the automatic calibration of CO2 detector, greatly saving labor costs and improving calibration accuracy ( Fig. 9 ). Real-time plotting of the equilibrium gas CO2 mole fraction also makes the data intuitive, facilitating on-site analysis of scientific issues in the research area by operators.

[0139] Experimental verification:

[0140] The CO2 mole fraction in the seawater of the Pearl River Estuary was determined by using the "spiral tube ice water cold trap + Mg(ClO4)2 drying tube" and manually switching the standard gas and sample gas during the spring voyage at the Pearl River Estuary from April to May 2023, while the pretreatment system of the present invention was used during the summer voyage at the Pearl River Estuary in August 2023. The data comparison is shown in Figure 8 and Fig. 9 .

[0141] Figure 8It can be seen that the molar fraction of H2O in the CO2 detector on spring voyages is often much greater than 0. This is because humid ambient air is inhaled when manually changing ice and replacing magnesium perchlorate desiccant. After removing water using the pre-treatment system of the present invention, the molar fraction of H2O in the CO2 detector on summer voyages is between -0.4 and 0.2. The molar fraction of H2O in the CO2 detector on summer voyages is significantly reduced, indicating that the pre-treatment system of the present invention has a significant dewatering effect. However, the spring voyage uses "spiral tube ice water cooling + Mg(ClO4)2 drying tube". During the voyage, it is necessary to manually change ice and replace magnesium perchlorate desiccant regularly, which requires high work intensity, strong dependence on operators, and poor dewatering effect.

[0142] Fig. 9 It can be seen that the results of manual verification in the spring voyage are relatively discrete, and Fig. 9 The three calibration points circled in Figure (a) are obviously deviated from the trend of change. The calibration operation of these points is unqualified and the data cannot be used. After calibration with the pre-treatment system of the present invention, the 396 ppm CO2 standard gas in the summer voyage showed a good calibration result, showing a trend of first decreasing and then increasing ( Fig. 9 (b) in the figure). This is because the system of the present invention monitors the gas flow rate in the pipeline through a flow meter, while the manually calibrated CO2 standard gas can only control the gas flow in the pipeline through the operator's experience, and the gas flow rate is not stable, which affects the CO2 measurement result.

Claims

1. A pre-treatment system suitable for determining the mole fraction of carbon dioxide in water by the "water-gas balance method", characterized in that: Including automatic condensation and water removal system, gas valve automatic switching system, control system and PC-side host computer software; The automatic condensation and water removal system uses a semiconductor condenser and a Nafion drying tube to remove moisture; the gas valve automatic switching system automatically switches the standard gas and the balance gas through the valve; the control system is connected to the gas valve automatic switching system and the PC-side host computer software to monitor and adjust the gas flow rate in real time to ensure that the gas flow rate is within a preset range; the PC-side host computer software integrates data processing and visualization functions to realize automatic control of the entire system and real-time data recording and analysis.

2. A pre-treatment system suitable for determining the mole fraction of carbon dioxide in water by the "water-gas balance method" as claimed in claim 1, characterized in that: The automatic condensation and dehumidification system includes a pre-dehumidification unit, a condensation water removal unit and a fine dehumidification unit; the pre-dehumidification unit is used to condense and dehumidify the balancing gas drawn out from the water-gas balancer and entering the pre-dehumidification unit, and the condensation water removal unit is used to discharge the waste water condensed by the pre-dehumidification unit at a regular interval; the fine dehumidification unit is used to further dry the balancing gas flowing out of the pre-dehumidification unit.

3. A pre-treatment system suitable for determining the mole fraction of carbon dioxide in water by the "water-gas balance method" as claimed in claim 2, characterized in that: The pre-dehumidification unit is provided with the semiconductor condenser.

4. A pre-treatment system suitable for determining the mole fraction of carbon dioxide in water by the "water-gas balance method" as claimed in claim 2, characterized in that: The fine dehumidification unit is provided with the Nafion drying tube.

5. A pre-treatment system suitable for determining the mole fraction of carbon dioxide in water by the "water-gas balance method" as claimed in claim 1, characterized in that: The gas valve automatic switching system is provided with a gas automatic switching valve.

6. A pre-treatment system suitable for determining the mole fraction of carbon dioxide in water by the "water-gas balance method" as claimed in claim 5, characterized in that: The gas automatic switching valve adopts an eight-way valve automatic switching device, and the eight-way valve automatic switching device has 7 gas inlets to be tested and 1 gas outlet.

7. A pre-treatment system suitable for determining the mole fraction of carbon dioxide in water by the "water-gas balance method" as claimed in claim 1, characterized in that: The control system includes an air pump, a flow meter, a detection unit, an execution unit and a control unit; the air pump is used to provide pneumatic force for the entire system when the control system measures the balance gas; the detection unit is used to receive the gas flow rate signal of the flow meter and transmit it to the PC-side host software; the execution unit is used to receive the sample test program instructions in the PC-side host software, and transmit the instructions to the gas automatic switching valve and the control unit; the control unit is used to accept the instructions of the execution unit to realize the control of the switching time and duration of the gas automatic switching valve, and at the same time adjust the switch and duty cycle of the air pump to make the gas flow rate within a preset range.

8. A method for automatically measuring the mole fraction of CO2, characterized in that: The pretreatment system according to claims 1 to 7 is used in conjunction with a water-gas balancer and a CO2 detector, comprising the following steps: 1) The CO2 gas balanced by the water-gas balance is driven by the control system air pump at a rate of 80~120 mL min -1 The gas enters the automatic condensation and dehydration system at a flow rate of 10000 m / s. After cooling in the pre-dehumidification unit of the automatic condensation and dehydration system, most of the water is removed. Then, the gas continues to be dehydrated by the fine dehumidification unit of the automatic condensation and dehydration system, and is sent to the gas valve automatic switching system after drying. 2) The gas valve automatic switching system automatically switches the CO2 standard gas and balance gas at different durations and time intervals under the control of the preset sampling program of the PC host software, and sends the gas to the CO2 detector to detect its molar fraction; 3) The PC host software controls the pipeline flow rate when measuring the balance gas. According to the type of sample gas, duration and time interval set by the program, it reads the data of the CO2 detector, and records the output CO2 mole fraction, H2O mole fraction, detector working temperature, working pressure and gas flow rate in the pipeline measured by the flowmeter in real time, and draws a real-time online graph based on the balance gas CO2 mole fraction; 4) The balance gas detected by the CO2 detector is sent back to the flow meter of the control system to detect the system gas flow, and then returns to the water-gas balancer to form a closed loop.

Images