A device and method for monitoring the in-situ pressure profile of dissolved methane in a water body

Abstract

The application discloses a device and method for monitoring the in-situ pressure-maintained profile of dissolved methane in water bodies. The device is provided with a multi-channel water inlet and replacement assembly, a pressure-maintained flow detection assembly, a pressure stabilizing cavity and a sensor assembly in a diving monitoring cabin. After being coarsely filtered, finely filtered and channel gated, water samples enter a rapid replacement branch or a detection branch. A controller executes switching pump speed and back pressure preset, constant pressure handover, effective value determination and blockage recovery according to environmental water pressure, cumulative flow, equivalent dead volume, methane response change rate and pressure stability, thereby reducing cross-water layer residues, switching pressure underflow and dissolved methane precipitation, and realizing in-situ pressure-maintained profile monitoring of dissolved methane in water bodies.

Description

Technical Field

[0001] This invention relates to the field of water environment monitoring and in-situ detection of dissolved gases, and particularly to a device and method for in-situ pressure-maintaining profile monitoring of dissolved methane in water. Background Technology

[0002] High-value dissolved methane layers with small vertical scales are often found at the tail end of river-type reservoirs, in river-lake confluence areas, and in stratified water bodies. It is difficult to obtain high-resolution concentration profiles continuously through fixed-depth monitoring or manual stratified sampling.

[0003] Existing methods often involve extracting methane through aeration, headspace displacement, or gas-liquid equilibrium before measurement. The measurement results are easily affected by equilibrium time, temperature, and gas-liquid volume ratio.

[0004] Another method involves first depressurizing the water sample, then detecting gaseous methane through gas-liquid separation or membrane separation. This process alters the original pressure of the water sample and the gas-liquid distribution state, which may affect the characterization of liquid phase concentration.

[0005] Existing pressure-holding sampling structures are mostly used to maintain pressure after the sampling chamber is sealed or recovered, but they do not address the issue of instantaneous pressure connection when switching between rapid replacement branches and detection branches in continuous flow detection.

[0006] During flow monitoring, pump pulsation, valve switching, and changes in pipeline resistance can cause localized pressure drops and methane evolution. Relying solely on feedback regulation after switching is insufficient to promptly suppress the pressure surge at the moment of switching.

[0007] When measuring different water layers sequentially, residual water samples in the pipeline and testing chamber will exhibit a cross-layer memory effect. Fixed flushing times are difficult to adapt to changes in pipeline volume, flow rate, and degree of blockage.

[0008] Fixed depth measurement intervals may miss thin-layer peak values, and blockage of the inlet can interrupt continuous monitoring.

[0009] Therefore, it is necessary to establish a pressure benchmark that varies with water depth and to incorporate constant pressure switching, actual displacement degree, stability determination, and anomaly recovery into the same monitoring process. Summary of the Invention

[0010] To address the issue that water sample decompression, gas-liquid distribution changes, layer replacement residues, and instantaneous pressure drop during switching can affect dissolved methane measurements in existing technologies, this invention aims to establish a pressure benchmark that varies with water depth and incorporate filtration selection, rapid replacement, constant pressure handover, determination of actual replacement degree, and anomaly recovery into the same in-situ monitoring process.

[0011] The technical solution adopted in this invention is: an in-situ pressure-holding profile monitoring device for dissolved methane in water, comprising a submersible monitoring chamber, a water inlet and displacement assembly, a pressure-holding flow detection assembly, a sensor assembly, and a data acquisition and control unit;

[0012] The water inlet and replacement assembly includes multiple water inlet branches, a channel selection valve group, a manifold, a flow sensor, a reversible variable speed water inlet pump, a flow path switching valve, and a rapid replacement branch; each water inlet branch is equipped with a coarse filter and a fine filter assembly, and is connected to the manifold through the channel selection valve group;

[0013] The pressure-holding flow detection assembly includes a pressure-stabilizing chamber, a flow detection chamber, a methane sensor, a pressure sensor, an electrically controlled back pressure valve, a bubble detector, a safety relief valve, a bypass valve, and a calibration interface; the pressure-stabilizing chamber includes a flexible diaphragm, a sample side chamber, a reference side chamber, an environmental connection port, and a pre-tightening mechanism;

[0014] The reference side cavity is connected to the ambient water at the depth of the diving monitoring chamber via an environmental communication port. The data acquisition and control unit receives ambient water pressure, depth, temperature, pH, conductivity, turbidity, attitude, pressure, flow rate, methane and bubble detection signals, and controls the water inlet pump, valve group and safety components.

[0015] The data acquisition and control unit is electrically connected to the environmental water pressure sensor, pressure sensor, reversible variable speed inlet pump, flow path switching valve and electrically controlled back pressure valve.

[0016] Furthermore, the pre-tightening mechanism applies a pre-tightening force toward the sample side cavity to the flexible diaphragm, causing the sample side cavity to form a positive pressure bias relative to the reference side cavity; the pre-tightening mechanism includes a pressure-bearing guide plate, a pre-tightening spring, a spring seat, and at least two stroke limiting posts, and the periphery of the flexible diaphragm is sealed and clamped by a diaphragm pressure ring.

[0017] Furthermore, the flow cross-sectional area of ​​the rapid replacement branch is larger than the flow cross-sectional area of ​​the pressure stabilizing chamber inlet; the data acquisition and control unit is configured to control the reversible variable speed water pump to operate at a first flow rate when the flow path switching valve is connected to the rapid replacement branch; and to control the reversible variable speed water pump to operate at a second flow rate less than the first flow rate when the flow path switching valve is connected to the pressure holding flow detection component.

[0018] Furthermore, the data acquisition and control unit is configured to store the equivalent dead volumes of the common water path upstream of the flow path switching valve and the internal flow path of the pressure holding flow detection component, and to determine the degree of displacement of the common water path and the degree of displacement of the internal flow path of the pressure holding flow detection component based on the cumulative flow of the flow sensor; when both the degree of displacement of the common water path and the degree of displacement of the internal flow path of the pressure holding flow detection component reach a preset threshold, and when the methane response change rate is not greater than a preset threshold and the pressure fluctuation detected by the pressure sensor is not greater than a preset threshold within a preset sliding time window, the valid measurement value of the current depth is saved.

[0019] Furthermore, the sensor assembly also includes a depth sensor and an attitude sensor; the data acquisition and control unit determines the actual measurement depth based on the environmental water pressure conversion value or the output of the depth sensor, and adjusts the depth measurement interval based on the methane concentration gradient between two adjacent valid measurement values.

[0020] Furthermore, the data acquisition and control unit is configured to, when the pump speed of the reversible variable speed inlet pump reaches the set value and the measured flow rate is continuously lower than the corresponding reference flow rate, control the flow path switching valve to connect the rapid replacement branch and cause the reversible variable speed inlet pump to perform reverse pulse flushing; at least one of the multiple inlet branches is a backup inlet branch, and the flow rate is switched to the backup inlet branch when the flow rate does not recover after flushing.

[0021] Furthermore, the pressure holding and flow detection component also includes a bubble detector, a safety relief valve, a bypass valve, and a calibration interface, which are used for bubble identification, overpressure protection, venting and maintenance, and sensor calibration, respectively.

[0022] The second technical solution adopted in this invention is: an in-situ pressure-maintaining method for dissolving methane in water, which includes the following steps:

[0023] S1: Perform equipment self-test and read ambient water pressure in Pa;

[0024] S2: Deploy the diving monitoring chamber to the target depth and wait for stabilization;

[0025] S3: Open the selected inlet branch and connect the quick replacement branch to replace the public waterway with the first flow rate;

[0026] S4: Reduce the pump speed of the reversible variable speed inlet pump and preset the opening of the electronically controlled back pressure valve, connect the pressure holding flow detection component, and adjust the pump speed to the second flow rate.

[0027] S5: Adjust the reversible variable speed inlet pump and the electronically controlled back pressure valve to maintain the pressure Pt in the pressure holding flow detection component during the measurement stage within the range of ambient water pressure Pa plus positive pressure bias, and replace the internal flow path of the pressure holding flow detection component.

[0028] S6: When the displacement volume of the common water channel and the internal flow channel of the pressure holding flow detection component both reach the preset threshold, and the methane response change rate and pressure fluctuation meet the stability conditions within the set time window, save the valid measurement value of the current depth.

[0029] S7: Determine the next target depth and repeat S2~S6.

[0030] Furthermore, the degree of displacement of the internal flow path of the pressure-holding flow detection component is determined based on the equivalent dead volume of the pressure-stabilizing chamber, the flow detection chamber and its connecting pipeline; the methane response change rate and pressure fluctuation are calculated within a preset sliding time window.

[0031] Furthermore, the data acquisition and control unit is configured to adjust the next target depth based on the methane concentration gradient between the actual measurement depths of two adjacent valid measurement values; when the measured flow rate is continuously lower than the reference flow rate, the valid value determination is paused and a reverse pulse flush is performed; if the flow rate still does not recover, the backup inlet branch is switched.

[0032] The present invention has at least the following beneficial effects: reducing the risk of particulate matter entering the detection branch through coarse filtration and fine filtration; shortening the layer replacement residue through the division of labor between the manifold, the rapid replacement branch and the detection branch; following the environmental pressure and absorbing pump pulsation through the pressure stabilizing chamber and the pre-tightening mechanism; and improving operational safety and data verifiability through bubble detection, pressure relief, bypass and calibration interfaces.

[0033] 1. Through the coordinated adjustment of the ambient water pressure sensor, pressure sensor, reversible variable speed inlet pump and electronically controlled back pressure valve, the pressure inside the pressure-holding flow detection component follows the ambient water pressure and maintains a positive pressure bias, reducing the precipitation of dissolved methane due to pressure fluctuations.

[0034] 2. The flexible diaphragm in the pressure stabilizing chamber forms a positive pressure bias with the pre-tightening mechanism and can compensate for instantaneous volume changes, buffering the pressure surge during sudden flow changes or valve switching.

[0035] 3. The flow path switching valve switches between the rapid replacement branch and the pressure holding flow detection component. In conjunction with reducing the pump speed and setting the back pressure valve opening before switching, constant pressure handover is achieved, reducing the pressure drop at the moment of switching.

[0036] 4. The rapid replacement branch has a large flow cross-sectional area. It first replaces the public water channel with a large flow rate and then replaces the internal flow channel of the pressure-holding flow detection component, reducing the residual and memory effect across the water layer.

[0037] 5. The data acquisition and control unit determines the degree of displacement in the two stages based on the cumulative flow and equivalent dead volume, and combines the methane response change rate and pressure fluctuation to jointly determine the effective measurement endpoint, avoiding insufficient displacement and invalid waiting.

[0038] 6. Adjust the depth measurement interval according to the methane concentration gradient between adjacent effective measurement depths, and increase the number of measurement points in areas with larger gradients to improve the capture capability in high-value areas of thin layers.

[0039] 7. The reversible variable speed inlet pump performs reverse pulse flushing when inlet blockage is detected, and can switch to a backup inlet branch when flushing is ineffective, thereby improving the reliability of continuous monitoring. Attached Figure Description

[0040] The accompanying drawings, which are included to provide a further understanding of this application and form part of this application, illustrate exemplary embodiments and are used to explain this application, but do not constitute an undue limitation of this application. In the drawings:

[0041] Figure 1 This is a schematic diagram of the overall structure of the monitoring device of the present invention, showing the surface float, anchoring assembly, winch lifting assembly, underwater monitoring cabin, and power supply and communication assembly.

[0042] Figure 2 This is a schematic diagram of the internal structure and component layout of the diving monitoring cabin, showing the inlet filtration, channel selection, confluence, rapid replacement, flow detection, and safety maintenance components.

[0043] Figure 3 This is a longitudinal sectional view of the pressure stabilizing chamber, showing the flexible diaphragm, sample side chamber, reference side chamber, environmental connection port, throttling filter, and pre-tightening mechanism.

[0044] Figure 4 This is an exploded structural diagram of the flexible diaphragm, diaphragm pressure ring, pressure-bearing guide plate, stroke limit post, preload spring, and spring seat in the pressure stabilizing chamber.

[0045] Figure 5 This is a schematic diagram of the water circuit connection for multi-channel water inlet, rapid replacement, and pressure holding testing, showing the filter selection accessories, manifold, testing branch, pressure relief bypass, and calibration interface.

[0046] Explanation of reference numerals in the attached figures

[0047] 100-Surface float; 101-Central through opening; 200-Mooring assembly; 201-Mooring connection point; 301-Winder; 302-Carrying cable; 303-Guide component; 400-Diving monitoring chamber; 500-Inlet and displacement assembly; 501-Inlet branch; 502-Channel selection valve assembly; 503-Manifold; 504-Flow sensor; 505-Reversible variable speed inlet pump; 506-Coarse filter; 507-Fine filter assembly; 508-Flow path switching valve; 509-Quick displacement branch; 601-Flow detection chamber; 602-Methane sensor; 603-Pressure sensor; 604-Electrically controlled back pressure valve; 605-Bubble detector; 606- Safety relief valve; 607-Bypass valve; 608-Calibration interface; 609a-Quick replacement drain; 609b-Detection drain; 610-Pressure stabilizing chamber; 611-Flexible diaphragm; 612-Sample side chamber; 613-Reference side chamber; 614-Environmental connection port; 615-Pre-tightening spring; 616-Sample inlet; 617-Sample outlet; 618-Throttle filter element; 619-Diaphragm pressure ring; 620-Pressure-bearing guide plate; 621-Stroke limit post; 622-Spring seat; 802-Controller; 900-Power supply and communication components; 901-Battery; 902-Solar power supply module; 903-Wireless communication module; 904-Solar panel mounting bracket. Detailed Implementation

[0048] The invention will now be further described with reference to the accompanying drawings.

[0049] Please see Figure 1 This embodiment provides an in-situ pressure-holding profile monitoring device for dissolved methane in water. The surface float 100 is a circular annular float with a central through-hole 101. A winch 301 and a guide 303 are located near the opening, and a support cable 302 passes through the opening and connects to the diving monitoring chamber 400. The mooring assembly 200 includes a mooring cable and an anchor. The upper end of the mooring cable is connected to a mooring connection point 201 circumferentially arranged on the surface float 100, and the lower end is connected to the anchor, used to limit the horizontal drift of the surface float 100 and maintain a stable monitoring position. A power supply and communication assembly 900 is installed on the float and includes a battery 901, a solar power module 902, a wireless communication module 903, and a solar panel mounting bracket 904. The diving monitoring chamber 400 houses a water inlet and displacement assembly 500, a pressure-holding flow detection assembly, a sensor assembly, and a data acquisition and control unit.

[0050] like Figure 2 As shown, the diving monitoring chamber 400 adopts a pressure-resistant shell. Multiple water inlet branches 501 are introduced from the side of the chamber. Each water inlet branch 501 is sequentially equipped with a coarse filter 506, a fine filter assembly 507, and a channel selection valve group 502, and then merges into a manifold 503. The outlet of the reversible variable speed water pump 505 is connected to a flow path switching valve 508, which connects to the quick replacement branch 509 and the detection branch respectively; the quick replacement drain port 609a and the detection drain port 609b are respectively connected to the corresponding drain branches.

[0051] The channel selection valve assembly 502 is used to select the target inlet branch 501. The coarse filter 506 intercepts larger particles, and the fine filter assembly 507 further reduces the risk of suspended particles entering the pump and detection chamber. At least one inlet branch 501 serves as a backup branch. The flow sensor 504 is located between the manifold 503 and the reversible variable speed inlet pump 505 to measure the actual flow rate and cumulative volume.

[0052] like Figure 3 As shown, the pressure stabilizing chamber 610 consists of a pressure-resistant shell, a flexible diaphragm 611, a sample side chamber 612, and a reference side chamber 613. The flexible diaphragm 611 is sealed and clamped by a diaphragm clamping ring 619; the sample inlet 616 and the sample outlet 617 are connected to the sample side chamber 612, and the reference side chamber 613 is connected to the external water body through the environmental communication port 614.

[0053] The environmental connection port 614 is equipped with a throttling filter 618 to block suspended particles and transmit environmental pressure.

[0054] The pressure-bearing guide plate 620 is attached to the reference side of the flexible diaphragm 611 and slides in cooperation with two or more stroke limiting posts 621; the limiting structure is used to limit the working stroke of the diaphragm.

[0055] The preload spring 615 is positioned between the pressure-bearing guide plate 620 and the spring seat 622. The initial positive pressure bias approximately satisfies ΔP0=F0 / A, where F0 is the preload force and A is the effective pressure-bearing area of ​​the diaphragm.

[0056] From the perspective of fluid continuity and hydraulic compliance, sudden changes in flow rate will alter the instantaneous volume requirement of the sample side cavity 612. The flexible diaphragm 611 absorbs or releases volume ΔV through displacement, thereby buffering pressure changes. Its dynamic response is mainly determined by the water circuit resistance Rh and the equivalent volume compliance Cv of the pressure stabilizing cavity. The time constant can be characterized as τ≈RhCv.

[0057] like Figure 4 As shown, the flexible diaphragm 611, diaphragm pressure ring 619, pressure-bearing guide plate 620, stroke limit post 621, preload spring 615 and spring seat 622 are assembled along the axial direction of the pressure stabilizing chamber 610, respectively undertaking the functions of sealing, load transmission and stroke limitation.

[0058] In one exemplary embodiment, the effective volume of the sample side cavity 612 is 60 mL, and the effective pressure-bearing area of ​​the diaphragm is 40-80 cm². 2 The allowable stroke is 2~8mm, and the positive pressure offset is 5~30kPa. Specific parameters can be determined based on the target water depth, pump pulsation, pipeline resistance, and the sensor's allowable pressure.

[0059] like Figure 5 As shown, the target inlet branch 501 is connected to the flow sensor 504 and the reversible variable speed inlet pump 505 via a coarse filter 506, a fine filter assembly 507, a channel selection valve assembly 502, and a manifold 503. Each inlet branch 501 is equipped with independent filtration and selection accessories, and the controller 802 only opens the channel selection valve assembly 502 of the target branch at a time.

[0060] The reversible variable speed inlet pump 505 is located upstream of the flow path switching valve 508. It can be a pressure-resistant gear pump, plunger pump or diaphragm pump, and has the ability to deliver in the forward direction and run in the reverse pulse direction. The flow path switching valve 508 is used to switch between the rapid replacement branch 509 and the detection branch.

[0061] When the rapid replacement branch 509 is connected, the water sample is discharged from the rapid replacement drain 609a without passing through the methane sensor 602; its flow cross-sectional area is larger than that of the detection branch to reduce the resistance of high-flow replacement.

[0062] When the detection branch is connected, the water sample flows sequentially through the pressure stabilizing chamber 610, the flow detection chamber 601, the pressure sensor 603, the electrically controlled back pressure valve 604, and the detection drain outlet 609b. The flow detection chamber 601 is made of a material with low methane adsorption and low gas permeability, and the bubble detector 605 is installed inside the flow detection chamber 601 or near its outlet.

[0063] The methane sensor 602 is installed in the flow detection chamber 601. It can be an optical, electrochemical or other liquid phase in-situ sensor suitable for the target pressure range, and the dissolved methane concentration can be calculated based on the concentration, temperature and pressure calibration parameters.

[0064] Pressure sensor 603 measures the pressure of the detection branch, while the ambient water pressure sensor is located on the outside of the diving monitoring chamber 400 to provide a reference for pressure control.

[0065] The controller 802 sets the target pressure based on the ambient water pressure and adjusts the speed of the inlet pump 505 and the opening of the electrically controlled back pressure valve 604 according to the pressure deviation of the detected branch; the pressure stabilizing chamber 610 undertakes short-term pressure buffering.

[0066] When the bubble detector 605 detects a bubble, it pauses the determination of the effective value and increases the branch pressure by adjusting the pump speed and the back pressure valve. The safety relief valve 606 is used for overpressure protection, the bypass valve 607 is used for venting and maintenance or bypass circulation, and the calibration interface 608 is used for sensor calibration and zero-point check. All of the above components are connected to the controller 802.

[0067] Upon reaching the new water layer, the flow path switching valve 508 first connects the rapid replacement branch 509, and the inlet pump 505 operates at the first flow rate, and calculates the rapid replacement volume V1 based on the cumulative flow rate.

[0068] The volume from the inlet branch 501 to the flow path switching valve 508 is recorded as the first equivalent dead volume Vd1; the volume of the pressure stabilizing chamber 610, the flow detection chamber 601, and the detection branch is recorded as the second equivalent dead volume Vd2. The rapid replacement ends after the volume reaches 2.5~4.0Vd1, and the degree of replacement is determined based on Vd2 after the detection branch is connected.

[0069] After rapid replacement, before connecting the detection branch, the controller 802 reduces the inlet pump 505 to the transfer flow rate and presets the opening of the electrically controlled back pressure valve 604. After connection, the pump speed is adjusted to the second flow rate. For example, the pump speed adjustment time is 2~10s, the first flow rate is 200~800mL / min, and the second flow rate is 30~100mL / min.

[0070] During constant pressure handover, Pt should not be lower than Pa + ΔPmin. If the pressure is lower than this value and remains below the set time, controller 802 will return to the quick replacement branch 509 and re-execute the handover.

[0071] After the detection branch is connected, the pressure stabilizing chamber 610 compensates for the instantaneous volume change, and the controller 802 adjusts the pump speed and the opening of the back pressure valve according to e(t)=Pt-(Pa+ΔP).

[0072] After the replacement of the detection branch reaches the preset level, the controller 802 judges the methane response change rate and pressure fluctuation within the set time window; when both meet the stability conditions, the valid measurement value is saved.

[0073] In one exemplary embodiment, a 60-second sliding time window is used, with the relative change rate of methane response not exceeding 2% / min and the pressure range not exceeding 2 kPa; after maintaining both conditions continuously for 30 seconds, the average or median of the time window is saved.

[0074] The data acquisition and control unit includes a controller 802, a storage module, and a communication module. It receives signals from ambient water pressure, depth, flow rate, detection branch pressure, methane, and auxiliary sensors, and controls the winch, channel selection valve group 502, flow path switching valve 508, inlet pump, electrically controlled back pressure valve 604, safety pressure relief valve 606, and bypass valve 607.

[0075] The actual measured depth is determined by the converted value of the ambient water pressure or the output of the depth sensor, and is verified using the cable length and attitude information.

[0076] A monitoring cycle includes equipment self-inspection, lowering, depth stabilization, rapid replacement, constant pressure handover, pressure holding test, valid value storage, determination of the next depth measurement, and equipment recovery.

[0077] After completing adjacent depth measurements, the controller 802 calculates the methane concentration gradient G = |C2 - C1| / |z2 - z1|; when G is greater than the first threshold, the measurement points are densified, and when it is continuously lower than the second threshold, the subsequent interval is increased.

[0078] New measuring points can be selected by prioritizing the midpoint of adjacent depths; when the distance between new measuring points and existing measuring points is less than the minimum allowable interval of the equipment, no additional points will be added.

[0079] When the measured flow rate is consistently lower than the reference flow rate corresponding to the current pump speed, or when the pump speed is increased but the flow rate does not recover, the inlet branch 501 is determined to be blocked.

[0080] After blockage, connect the quick-displacement branch 509, and run the inlet pump 505 in reverse for 0.5~2 seconds, repeating 3~10 times. Displace again after the flow rate is restored; if it is not restored, switch to the backup branch.

[0081] In one exemplary embodiment, the diving monitoring chamber 400 is suitable for water depths of 0-30m, with an inlet pipe inner diameter of 2-4mm, and effective volumes of the sample side chamber 612 and the flow detection chamber 601 of approximately 60mL and 80mL, respectively; the positive pressure bias can be set to 15kPa, the minimum positive pressure margin is 5kPa, the first and second flow rates are 400mL / min and 60mL / min, respectively, and the pump speed ramp time is 5s. Those skilled in the art can adjust the above parameters according to actual application scenarios.

[0082] Before monitoring, fill the sample water path with bubble-free water, check the assembly and sealing status of the coarse filter 506, fine filter assembly 507, various valves, and pressure stabilizing chamber 610, and verify the environmental water pressure sensor, detection branch pressure sensor 603, and methane sensor 602 through calibration interface 608.

[0083] During monitoring, after the diving monitoring chamber 400 reaches the target depth, it sequentially performs rapid replacement, back pressure preset, flow path switching, and pump speed ramp adjustment; if the pressure is too low, it is re-handed over; if the pressure is too high, the back pressure valve opening is increased or the pressure is released by the safety relief valve 606.

[0084] After the current depth measurement is completed, the next target depth is determined based on the concentration gradient; during the ascent and descent process, the detection branch is shut down or a low-flow bypass circulation is maintained.

[0085] Temperature, pH, conductivity, and turbidity can be recorded synchronously with methane measurements; data is stored in the storage module when communication is interrupted and retransmitted after communication is restored.

[0086] The flexible diaphragm 611 can be replaced with a flat diaphragm, a rolling diaphragm, or a corrugated metal diaphragm, and the preload spring 615 can be replaced with a disc spring assembly, as long as fluid isolation, preload, and stroke limitation can be achieved.

[0087] The form of each component can be adjusted as needed. Constant pressure handover still includes pump speed and back pressure pre-adjustment before switching and detection flow adjustment after switching.

[0088] The present invention also provides a method for in-situ pressure maintenance of dissolved methane in water, which is used in the above-mentioned device for in-situ pressure maintenance of dissolved methane in water. The method includes the following steps:

[0089] S1: Perform equipment self-test and read ambient water pressure in Pa;

[0090] S2: Deploy the diving monitoring chamber to the target depth and wait for stabilization;

[0091] S3: Open the selected inlet branch and connect the quick replacement branch to replace the public waterway with the first flow rate;

[0092] S4: Reduce the pump speed of the reversible variable speed inlet pump and preset the opening of the electronically controlled back pressure valve, connect the pressure holding flow detection component, and adjust the pump speed to the second flow rate.

[0093] S5: Adjust the reversible variable speed inlet pump and the electronically controlled back pressure valve to maintain the pressure Pt in the pressure holding flow detection component during the measurement stage within the range of ambient water pressure Pa plus positive pressure bias, and replace the internal flow path of the pressure holding flow detection component.

[0094] S6: When the displacement volume of the common water channel and the internal flow channel of the pressure holding flow detection component both reach the preset threshold, and the methane response change rate and pressure fluctuation meet the stability conditions within the set time window, save the valid measurement value of the current depth.

[0095] S7: Determine the next target depth and repeat S2~S6.

[0096] The degree of displacement of the internal flow path of the pressure-holding flow detection component is determined based on the equivalent dead volume of the pressure-stabilizing chamber, the flow detection chamber and its connecting pipeline; the methane response change rate and pressure fluctuation are calculated within a preset sliding time window.

[0097] The data acquisition and control unit is configured to adjust the next target depth based on the methane concentration gradient between the actual measurement depths of two adjacent valid measurement values; when the measured flow rate is continuously lower than the reference flow rate, the valid value determination is paused and a reverse pulse flush is performed; if the flow rate still does not recover, the backup inlet branch is switched.

[0098] The above description merely illustrates preferred embodiments of the present invention and is quite specific and detailed; however, it should not be construed as limiting the scope of the invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the inventive concept, and these all fall within the scope of protection of the present invention. Therefore, the scope of protection of this invention should be determined by the appended claims.

Claims

1. A device for in-situ pressure-holding profile monitoring of dissolved methane in water, comprising a submersible monitoring chamber, a water inlet and displacement assembly, a pressure-holding flow detection assembly, a sensor assembly, and a data acquisition and control unit, characterized in that: The water inlet and replacement assembly includes multiple water inlet branches, a channel selection valve group, a manifold, a flow sensor, a reversible variable speed water inlet pump, a flow path switching valve, and a rapid replacement branch; each water inlet branch is equipped with a coarse filter and a fine filter assembly along the water sample flow direction, and is connected to the manifold via the channel selection valve group; the flow path switching valve is used to selectively connect the rapid replacement branch or the inlet of the pressure holding flow detection assembly; The pressure-holding flow detection assembly includes a pressure-stabilizing chamber, a flow detection chamber, a pressure sensor, and an electrically controlled back pressure valve along the water sample flow direction. A methane sensor is installed in the flow detection chamber. The pressure-stabilizing chamber includes a flexible diaphragm, a sample side chamber, a reference side chamber, an environmental connection port, and a pre-tightening mechanism. The flexible diaphragm separates the sample side chamber from the reference side chamber. The reference side chamber is connected to the ambient water at the depth of the diving monitoring chamber via the environmental connection port. The sensor assembly includes an environmental water pressure sensor, and includes one or more of a depth sensor, a temperature sensor, a pH sensor, a conductivity sensor, a turbidity sensor, and an attitude sensor; The data acquisition and control unit is connected to the environmental water pressure sensor, pressure sensor, flow sensor and methane sensor respectively, and is also connected to the reversible variable speed inlet pump, flow path switching valve and electrically controlled back pressure valve for control.

2. The in-situ pressure-maintaining device for dissolving methane in water as described in claim 1, characterized in that, The pre-tightening mechanism applies a pre-tightening force to the flexible diaphragm toward the sample side cavity, causing the sample side cavity to form a positive pressure bias relative to the reference side cavity; the pre-tightening mechanism includes a pressure-bearing guide plate, a pre-tightening spring, a spring seat, and at least two stroke limiting posts, and the periphery of the flexible diaphragm is sealed and clamped by a diaphragm pressure ring.

3. The in-situ pressure-maintaining device for dissolving methane in water as described in claim 1, characterized in that, The flow cross-sectional area of ​​the rapid replacement branch is larger than the flow cross-sectional area of ​​the pressure stabilizing chamber inlet; the data acquisition and control unit is configured to control the reversible variable speed water pump to operate at a first flow rate when the flow path switching valve is connected to the rapid replacement branch; and to control the reversible variable speed water pump to operate at a second flow rate less than the first flow rate when the flow path switching valve is connected to the pressure holding flow detection component.

4. The in-situ pressure-maintaining device for dissolving methane in water as described in claim 1, characterized in that, The data acquisition and control unit is configured to store the equivalent dead volumes of the common water path upstream of the flow path switching valve and the internal flow path of the pressure holding flow detection component, and to determine the degree of displacement of the common water path and the degree of displacement of the internal flow path of the pressure holding flow detection component based on the cumulative flow of the flow sensor. When both the degree of displacement of the common water path and the degree of displacement of the internal flow path of the pressure holding flow detection component reach a preset threshold, and the methane response change rate is not greater than the preset threshold and the pressure fluctuation detected by the pressure sensor is not greater than the preset threshold within a preset sliding time window, the valid measurement value of the current depth is saved.

5. The in-situ pressure-maintaining device for dissolving methane in water as described in claim 1, characterized in that, The sensor assembly also includes a depth sensor and an attitude sensor; the data acquisition and control unit determines the actual measurement depth based on the environmental water pressure conversion value or the output of the depth sensor, and adjusts the depth measurement interval based on the methane concentration gradient between two adjacent valid measurement values.

6. The in-situ pressure-maintaining device for dissolving methane in water as described in claim 1, characterized in that, The data acquisition and control unit is configured to, when the pump speed of the reversible variable speed inlet pump reaches the set value and the measured flow rate is continuously lower than the corresponding reference flow rate, control the flow path switching valve to connect the rapid replacement branch and cause the reversible variable speed inlet pump to perform reverse pulse flushing; at least one of the multiple inlet branches is a backup inlet branch, and the flow rate is switched to the backup inlet branch when the flow rate does not recover after flushing.

7. The in-situ pressure-maintaining device for dissolving methane in water as described in claim 1, characterized in that, The pressure holding and flow detection component also includes a bubble detector, a safety relief valve, a bypass valve, and a calibration interface, which are used for bubble identification, overpressure protection, venting and maintenance, and sensor calibration, respectively.

8. A method for in-situ pressure-maintaining profile monitoring of dissolved methane in water, based on the apparatus of any one of claims 1 to 7, characterized in that, Includes the following steps: S1: Perform equipment self-test and read ambient water pressure in Pa; S2: Deploy the diving monitoring chamber to the target depth and wait for stabilization; S3: Open the selected inlet branch and connect the quick replacement branch to replace the public waterway with the first flow rate; S4: Reduce the pump speed of the reversible variable speed inlet pump and preset the opening of the electronically controlled back pressure valve, connect the pressure holding flow detection component, and adjust the pump speed to the second flow rate. S5: Adjust the reversible variable speed inlet pump and the electronically controlled back pressure valve to maintain the pressure Pt in the pressure holding flow detection component during the measurement stage within the range of ambient water pressure Pa plus positive pressure bias, and replace the internal flow path of the pressure holding flow detection component. S6: When the displacement volume of the common water channel and the internal flow channel of the pressure holding flow detection component both reach the preset threshold, and the methane response change rate and pressure fluctuation meet the stability conditions within the set time window, save the valid measurement value of the current depth. S7: Determine the next target depth and repeat S2~S6.

9. The method for in-situ pressure maintenance of dissolved methane in water as described in claim 8, characterized in that, The degree of displacement of the internal flow path of the pressure holding and flow detection component is determined based on the equivalent dead volume of the pressure stabilizing chamber, the flow detection chamber and its connecting pipeline; the methane response change rate and pressure fluctuation are calculated within a preset sliding time window.

10. The method for in-situ pressure maintenance of dissolved methane in water as described in claim 8, characterized in that, The data acquisition and control unit is configured to adjust the next target depth based on the methane concentration gradient between the actual measurement depths of two adjacent valid measurement values; when the measured flow rate is continuously lower than the reference flow rate, the valid value determination is paused and a reverse pulse flush is performed; if the flow rate still does not recover, the backup inlet branch is switched.

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