Monitoring equipment for monitoring gas emission of discharged water flow of hydropower station and use method of monitoring equipment

Abstract

The invention discloses monitoring equipment for monitoring gas emission of discharged water flow of a hydropower station and a use method thereof, and relates to the field of hydropower station greenhouse gas emission monitoring, the monitoring equipment comprises two spectrometers and two heat insulation shells, and further comprises a data memory, a data transmitter, an open box and a closed box; the two spectrometers are arranged in the open box and the closed box respectively, and hygrometers used for monitoring the internal environment humidity of the open box and the closed box are arranged in the open box and the closed box; according to the monitoring equipment for monitoring the gas emission of the discharged water flow of the hydropower station and the use method of the monitoring equipment, when greenhouse gas is measured by utilizing a CRDS technology, the ring-down time of three different laser signals under the same environment humidity is compared and measured; the measurement result of the ring-down process of the target gas in the open box is corrected and compensated by using the ring-down signal result of the optical cavity in the closed box, so that the influence of water vapor on the measurement result of the concentration of the greenhouse gas can be eliminated or reduced, and the measurement precision is remarkably improved.

Description

Technical Field

[0001] The invention relates to a greenhouse gas emission monitoring technology for a hydropower station, and in particular to a monitoring device for monitoring the gas emission of a downstream water flow of a hydropower station and a use method thereof. Background Art

[0002] Greenhouse gas emissions from reservoir-power station systems are an important part of global greenhouse gas emissions. Strengthening greenhouse gas monitoring at hydropower stations is conducive to strengthening the understanding of the mechanisms, laws and emissions of greenhouse gas emissions from various reservoirs and hydropower stations throughout their life cycle. The current mainstream greenhouse gas monitoring technology uses spectroscopy technology to achieve non-contact quantitative inversion of greenhouse gas concentrations at different times, spaces and distances. During the operation of hydropower stations, the discharge of water will generate a large amount of water flow and accompanying water vapor, which often carry greenhouse gases such as carbon dioxide (CO 2 ), methane (CH 4 ) and nitrous oxide (N 2 O), etc. At present, there is a lack of research on greenhouse gas emissions from water under discharge conditions. Most of them regard the reservoir as a whole and estimate the greenhouse gas emissions through upstream and downstream control sections. There is a lack of monitoring methods for greenhouse gases released during the discharge process of water bodies.

[0003] In order to accurately monitor the emission of greenhouse gases released during the discharge of water bodies, high-precision and high-sensitivity monitoring equipment is required. Traditional greenhouse gas monitoring methods mainly rely on optical absorption spectroscopy technology, such as tunable diode laser absorption spectroscopy (TDLAS) and cavity ring-down spectroscopy (CRDS). However, since water vapor absorbs part of the laser energy, the existing monitoring technology is often difficult to accurately measure the concentration of greenhouse gases when faced with water vapor interference in the discharge flow of hydropower stations, resulting in a certain deviation between the measurement results and the actual values. Summary of the invention

[0004] The purpose of the present invention is to provide a monitoring device for monitoring gas emissions from downstream water flows of a hydropower station and a method of using the same, so as to solve the technical problems in the prior art of lacking means for monitoring greenhouse gases released during the downstream water flow, and generating a large amount of water vapor during the water flow discharge process. The presence of water vapor will affect the accuracy of the measurement of greenhouse gas emission concentration, resulting in a certain deviation between the measurement result and the actual value.

[0005] In order to achieve the above-mentioned object, the present invention provides the following technical solutions: a monitoring device for monitoring gas emissions from downstream water flow of a hydropower station, comprising two spectrometers and two heat-insulating housings, the spectrometers comprising a laser, a mode field matching optical system, a chamber, two reflectors, a photodetector, a constant temperature heater and a ring-down signal acquisition card;

[0006] Two reflectors are respectively arranged on both sides of the inner cavity of the chamber, and an optical cavity is formed between the two reflectors. The optical cavity is a ring-down cavity. The laser is used to generate a pulsed laser beam and couple the generated pulsed laser beam into the optical cavity. The mode field matching optical system is used to perform mode matching on the pulsed laser beam generated by the laser.

[0007] The chamber is provided with an air inlet and an air outlet, both of which are connected to the optical cavity, a constant temperature heater is used to keep the temperature in the optical cavity constant, two insulating shells respectively wrap the two spectrometers and isolate the two spectrometers from the external environment, and also includes: a data storage device, a data transmitter, an open box and a closed box;

[0008] Two spectrometers are respectively arranged inside the open box and the closed box. The open box and the closed box are both provided with hygrometers for monitoring the humidity of the environment inside the open box and the closed box. The closed box is also provided with a humidifier for replenishing water vapor into the closed box.

[0009] The photoelectric detector is used to detect the light intensity signal in the optical cavity and record the laser attenuation process in the optical cavity into the ring-down signal acquisition card. The data storage device is used to store the measurement data recorded by the ring-down signal acquisition card. The data transmitter is used to send the measurement data stored in the data storage device to the external terminal in real time.

[0010] Furthermore, the laser can inject three different wavelengths of laser light into the optical cavity, corresponding to CO 2 , CH 4 and N 2 O has a strong absorption band.

[0011] Furthermore, the mode field matching optical system can complete the matching of the laser mode of the laser and the ring-down cavity mode before the laser light emitted by the laser enters the ring-down cavity.

[0012] Furthermore, the reflectivity of the reflector is greater than 99.99%.

[0013] Furthermore, the humidifier can add water vapor to the interior of the closed box according to the humidity data monitored by the two hygrometers and keep the humidity inside the closed box consistent with the humidity inside the open box.

[0014] The method for using the monitoring device for monitoring the gas emission of the downstream water flow of a hydropower station is applicable to the monitoring device for monitoring the gas emission of the downstream water flow of a hydropower station as described above, and comprises the following steps:

[0015] S1. Inject the target gas to be detected into the open box. After the target gas fills the chamber in the open box, three different wavelengths of laser are injected into the optical cavity in sequence through the laser in the open box, corresponding to CO 2 , CH 4 and N2 Strong absorption band of O;

[0016] S2. Measure and record the decay time of the light intensity signal at this time, calculate the decay time of the pulse laser signal under three different wavelengths, and open the CO 2 , CH 4 and N 2 The decay time of O is denoted as τ 1 , τ 2 , τ 3 ;

[0017] S3, detecting the ambient humidity in the open box and the closed box respectively by using the hygrometers in the open box and the closed box, and adjusting the water vapor concentration in the closed box by using the humidifier in the closed box until the ambient humidity in the closed box is consistent with that in the open box;

[0018] S4, when the water vapor concentration in the closed box and the open box is the same, the same pulse laser as in step S1 is injected into the chamber in the closed box through the laser in the closed box, and the ring-down time of the light intensity signal at this time is measured and recorded, and the ring-down time of the pulse laser signal under three different wavelengths is calculated. 2 , CH 4 and N 2 The ring-down time of O is denoted as τ' 1 , τ′ 2 , τ′ 3 ;

[0019] S5. Using CO in a closed box 2 , CH 4 and N 2 The decay time of O is proportional to the CO 2 , CH 4 and N 2 The ring-down time of O is corrected and compensated, and the CO content in the target gas is calculated according to the formula: Δτ=τ'-τ 2 , CH 4 and N 2 The actual ring-down time Δτ of O 1 , Δτ 2 and Δτ 3 ;

[0020] S6. According to the CO in the target gas 2 , CH 4 and N 2 The actual ring-down time of O is calculated by combining the Lambert-Beer law with the following formula to calculate the gas concentration:

[0021]

[0022] Where C is the target gas concentration, α is the absorption coefficient of the target gas, σ is the absorption cross-sectional area of ​​the target gas, c is the speed of light in a vacuum, τ is the light intensity decay time when the target gas fills the cavity, and τ 0 is the cavity ring-down time in vacuum state. According to the calculation results, CO 2 , CH 4 and N 2 The concentration of O is denoted as C 1 , C 2 and C 3 ;

[0023] S7, measuring the initial concentration C" of the target gas in the atmospheric environment before the water body starts to discharge and the target gas concentration C' after the water body starts to discharge. The difference ΔC between the target gas concentration C' after the water body starts to discharge and the target gas concentration C" in the atmospheric environment before the water body starts to discharge is the greenhouse gas concentration released during the water body discharge process;

[0024] S8. Record the time t from the beginning of water discharge to the beginning of measurement by the monitoring equipment, and calculate the total flow Q in the time period t based on the flow rate q of the water body discharged at the site per unit time. 0 , Q 0 =qt, calculate the total water flow Q within the measurement range of the monitoring equipment:

[0025]

[0026] Among them, L is the length of the ring-down cavity, and W is the width of the downstream water flow cross section;

[0027] According to the formula:

[0028]

[0029] Calculate the CO per unit flow rate during the water discharge process 2 , CH 4 and N 2 Emission concentration of O 1 、n 2 、n 3 .

[0030] Furthermore, corresponding to CO 2 , CH 4 and N 2 The pulsed laser wavelengths of the strong absorption bands of O are 14.7 μm, 1.65 μm and 3.94 μm respectively.

[0031] Furthermore, the photodetector detects the decay of the outgoing light intensity to the incident light intensity. -1 The time elapsed is the decay time.

[0032] Furthermore, the step S1 and the step S4 measure and record the decay time of the light intensity signal at this time, and calculate the decay time of the pulse laser signals of three different wavelengths, which both include the following steps:

[0033] The light intensity signal in the cavity is detected by the photodetector, and the attenuation process of the laser in the optical cavity is recorded to the ring-down signal acquisition card. After the data storage acquires and records the ring-down signal data collected by the ring-down signal acquisition card, the data transmitter sends the cavity ring-down signal data to the terminal. The photodetector detects that the energy of the outgoing light intensity is attenuated to the energy of the incident light intensity. -1 The time elapsed is the decay time, and the decay time is calculated.

[0034] Furthermore, τ 0 Calculated by the following formula:

[0035]

[0036] Wherein, L is the optical cavity length, R is the cavity mirror reflectivity, d is the target gas distribution length, and when the target gas fills the cavity, d=L.

[0037] Compared with the prior art, the monitoring device for monitoring gas emissions from the downstream water flow of a hydropower station and the method for using the same provide a monitoring device for monitoring gas emissions from the downstream water flow of a hydropower station. When measuring greenhouse gases using the CRDS technology, the ring-down time of three different laser signals under the same ambient humidity is compared and measured, and the ring-down signal result of the optical cavity in the closed box is used to correct and compensate the measurement result of the ring-down process of the target gas in the open box, thereby eliminating or reducing the influence of water vapor on the measurement result of the greenhouse gas concentration, and significantly improving the measurement accuracy.

[0038] By improving the accuracy and efficiency of measuring greenhouse gas emission concentrations when water is discharged from hydropower stations, it can promote the construction of a greenhouse gas monitoring technology system for reservoir-power station systems and provide basic data support for subsequent carbon emission research;

[0039] It can realize real-time monitoring of greenhouse gas concentrations in a certain area when water is discharged from a hydropower station, eliminate or reduce the impact of a large amount of water vapor generated when water is discharged on the detection results, and help to objectively and scientifically understand the greenhouse gas emission mechanism, law and emission amount of reservoirs and hydropower stations throughout their life cycle, and build a low-carbon green hydropower industry. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in the present invention. For ordinary technicians in this field, other drawings can also be obtained based on these drawings.

[0041] Figure 1 A schematic diagram of the structure of a monitoring device for monitoring gas emissions from downstream water flow of a hydropower station provided in an embodiment of the present invention.

[0042] Description of reference numerals:

[0043] 1. Humidity meter; 2. Humidifier; 3. Laser; 4. Mode field matching optical system; 5. Air inlet; 6. Chamber; 7. Reflector; 8. Air outlet; 9. Photodetector; 10. Constant temperature heater; 11. Insulating shell; 12. Ring-down signal acquisition card; 13. Data storage device; 14. Data transmitter; 15. Open box; 16. Closed box. DETAILED DESCRIPTION

[0044] In order to enable those skilled in the art to better understand the technical solution of the present invention, the present invention will be further described in detail below with reference to the accompanying drawings.

[0045] Embodiment 1:

[0046] See also Figure 1 , monitoring equipment for monitoring gas emissions from downstream water flows of a hydropower station, two spectrometers and two thermally insulated housings 11, the spectrometers comprising a laser 3, a mode field matching optical system 4, a chamber 6, two reflectors 7, a photodetector 9, a constant temperature heater 10 and a ring-down signal acquisition card 12;

[0047] Two reflectors 7 are respectively arranged on both sides of the inner cavity of the chamber 6. The reflectivity of the reflectors 7 is greater than 99.99%. An optical cavity is formed between the two reflectors 7. The optical cavity is a ring-down cavity. The high-reflectivity reflectors 7 can form a ring-down optical path of multiple reflections of the laser in the chamber 6. The absorption optical path of the laser is extended, thereby improving the accuracy of the monitoring data.

[0048] Laser 3 is used to generate a pulsed laser beam and couple the generated pulsed laser beam into the optical cavity. Laser 3 can inject three different wavelengths of laser light into the optical cavity, corresponding to CO 2 , CH 4 and N 2 The strong absorption bands of O are pulsed lasers at 14.7 μm, 1.65 μm, and 3.94 μm, respectively;

[0049] The mode field matching optical system 4 is used to perform mode matching on the pulsed laser beam generated by the laser 3. The mode field matching optical system 4 can complete the matching of the laser mode of the laser 3 with the mode of the ring-down cavity before the laser emitted by the laser 3 enters the ring-down cavity, that is, the mode of the laser beam generated by the laser 3 is matched with the mode of the optical cavity to ensure that the laser beam can be efficiently reflected and amplified in the optical cavity. The pulsed laser beam generated by the laser 3 can be transformed and adjusted (such as the focusing position, focal length and other parameters of the laser beam) through a series of optical elements (such as lenses, diffraction gratings, etc.) to match its mode with the mode of the optical cavity.

[0050] The chamber 6 is provided with an air inlet 5 and an air outlet 8, both of which are connected to the optical cavity. The constant temperature heater 10 is used to keep the temperature in the optical cavity constant. The absorption cross section of the gas is determined by the temperature and the laser wavelength. During the monitoring process, the temperature change in the optical cavity will affect the laser spectrum. The constant temperature heater 10 is used to keep the temperature in the optical cavity constant, and two insulating shells 11 are used to respectively wrap the two spectrometers and isolate the two spectrometers from the external environment to reduce the influence of temperature on the spectrum output by the laser. The chamber 6 also includes: a data storage 13, a data transmitter 14, an open box 15 and a closed box 16;

[0051] The two spectrometers are respectively arranged inside the open box 15 and the closed box 16. The open box 15 can be set as a box with an open top or an opening on one side, so as to fill the target gas to be detected into the open box 15.

[0052] The open box 15 and the closed box 16 are both provided with a hygrometer 1 for monitoring the humidity of the environment inside the open box 15 and the closed box 16. The closed box 16 is also provided with a humidifier 2 for replenishing water vapor into the closed box 16. The humidifier 2 can replenish water vapor into the closed box 16 according to the humidity data monitored by the two hygrometers 1 and keep the humidity inside the closed box 16 consistent with the humidity inside the open box 15. The humidifier 2 can be an ultrasonic humidifier, which uses high-frequency vibration to spray water mist to adjust the humidity in the closed box 16 to be consistent with the humidity in the open box 15.

[0053] The photodetector 9 is used to detect the light intensity signal in the optical cavity and record the laser attenuation process in the optical cavity into the ring-down signal acquisition card 12. The ring-down signal acquisition card 12 can be a data acquisition card of Advantech PCI-1710U / PCI-1712.

[0054] The data storage 13 is used to store the measurement data recorded by the ring-down signal acquisition card 12. The data storage 13 can be a DRAM, SRAM, Flash memory, etc., to ensure that the data will not be lost in the event of a power outage. The data storage 13 is provided with a high-speed data interface, such as SATA, PCIe or USB 3.0 / 3.1, etc., to ensure that the data can be efficiently transferred from the ring-down signal acquisition card 12 to the data storage 13;

[0055] The data transmitter 14 is used to send the measurement data stored in the data storage 13 to the external terminal (computer) in real time. The data transmitter 14 can adopt the XTR105UA / XTR106U series current transmitter;

[0056] In this embodiment, a corresponding control unit can also be set for use. The control unit can select any controller to be connected to the electrical parts in this application, so as to control the opening and closing operation of each electrical part. This part is the prior art. Here, a single-chip microcomputer can be provided as a control unit for display. The single-chip microcomputer in this embodiment is a typical embedded microcontroller (Microcontroller Unit), which is composed of an arithmetic unit, a controller, a memory, an input and output device, etc., which is equivalent to a microcomputer. Compared with the general-purpose microprocessor used in personal computers, it emphasizes self-supply (no external hardware) and cost saving. Its biggest advantage is that it is small in size and can be placed inside the instrument, but it has a small storage capacity, a simple input and output interface, and low functional consumption.

[0057] Since a large amount of water vapor is generated during the water body discharge process, when using CRDS technology to measure greenhouse gases, water vapor will absorb part of the laser energy, shortening the decay time of the target gas. The measurement results of the target gas concentration are affected by water vapor, resulting in a certain deviation between the measurement results and the actual values.

[0058] To this end, the present application sets two spectrometers, and sets the two spectrometers in an open box 15 and a closed box 16 respectively, fills the open box 15 with target gas, and the spectrometer in the open box 15 measures the target gas containing water vapor. The target gas enters the chamber 6 from the air inlet 5, and the laser 3 in the open box 15 injects 14.7 micron, 1.65 micron, and 3.94 micron pulse lasers into the ring-down cavity of the spectrometer in sequence, corresponding to CO 2 , CH 4 and N 2 O has a strong absorption band. After mode field matching, the pulse laser enters the optical ring-down cavity. The high-reflectivity mirrors 7 on both sides of the cavity 6 reflect the laser back and forth to form a ring-down optical path. When the photodetector 9 detects that the energy of the outgoing light intensity decays to e-1 of the energy of the incident light intensity, the time experienced is the ring-down time.

[0059] After the ring-down signal is collected, the data storage device 13 records the relevant data and transmits the ring-down signal to the external terminal through the data transmitter 14. The target gas CO measured on one side of the open box 15 2 , CH 4 and N 2 The decay time of O;

[0060] The closed box 16 simulates the same environmental humidity (same water vapor concentration) as the target gas and measures the ring-down time of three different laser signals. The optical cavity ring-down signal result in the closed box 16 can be used to correct and compensate the measurement result of the target gas ring-down process in the open box 15, thereby eliminating the influence of water vapor on the measurement result of greenhouse gas concentration when the water body of the hydropower station is discharged, making the measurement result more accurate.

[0061] Embodiment 2:

[0062] See also Figure 1 , also provides a method for using a monitoring device for monitoring gas emissions from a downstream water flow of a hydropower station, which is applicable to the above-mentioned monitoring device for monitoring gas emissions from a downstream water flow of a hydropower station, and includes the following steps:

[0063] S1, inject the target gas to be detected into the open box 15, and after the target gas fills the chamber 6 in the open box 15, inject three different wavelengths of laser light into the optical cavity in sequence through the laser 3 in the open box 15, corresponding to CO 2 , CH 4 and N 2 The strong absorption band of O, the pulse laser wavelengths are 14.7 μm, 1.65 μm and 3.94 μm;

[0064] S2, measure and record the decay time of the light intensity signal at this time, and detect the time when the outgoing light intensity energy decays to the incident light intensity energy according to the photoelectric detector. -1 The time elapsed is the ring-down time τ. The ring-down time of three different wavelengths of pulsed laser signals is calculated. The light intensity signal in the optical cavity is detected by the photodetector 9, and the attenuation process of the laser in the optical cavity is recorded to the ring-down signal acquisition card 12. The data storage 13 obtains and records the ring-down signal data collected by the ring-down signal acquisition card 12. The data transmitter 14 sends the optical cavity ring-down signal data to the terminal. The ring-down time is calculated. The CO in the open box 15 is 2 , CH 4 and N 2 The decay time of O is denoted as τ 1 , τ 2 , τ 3 ;

[0065] S3, respectively detecting the ambient humidity in the open box 15 and the closed box 16 by means of the hygrometer 1 in the open box 15 and the closed box 16, and adjusting the water vapor concentration in the closed box 16 by means of the humidifier 2 in the closed box 16 until the ambient humidity in the closed box 16 is consistent with that in the open box 15;

[0066] S4, when the water vapor concentration in the closed box 16 and the open box 15 are the same, the same pulse laser as in step S1 is injected into the chamber 6 in the closed box 16 through the laser 3 in the closed box 16, and the ring-down time of the light intensity signal at this time is measured and recorded as in step S2, and the ring-down time of the pulse laser signal under three different wavelengths is calculated. 2 , CH 4 and N 2 The ring-down time of O is denoted as τ' 1 , τ' 2 , τ' 3 ;

[0067] S5, using the CO in the closed box 16 2 , CH 4 and N 2 The ring-down time of O is proportional to the CO 2 , CH 4 and N 2 The ring-down time of O is corrected and compensated, and the CO content in the target gas is calculated according to the formula: Δτ=τ'-τ 2 , CH 4 and N 2 The actual ring-down time Δτ of O 1 , Δτ 2 and Δτ 3 ;

[0068] S6. According to the CO in the target gas 2 , CH 4 and N 2 The actual ring-down time of O is calculated by combining the Lambert-Beer law with the following formula to calculate the gas concentration:

[0069]

[0070] Where C is the target gas concentration, α is the absorption coefficient of the target gas, σ is the absorption cross-sectional area of ​​the target gas determined according to a specific temperature and a certain wavelength, c is the speed of light in a vacuum, τ is the light intensity decay time when the target gas fills the cavity (optical cavity), τ 0 is the cavity (optical cavity) ring-down time in vacuum state. According to the calculation results, CO 2 , CH 4 and N 2 The concentration of O is denoted as C1 , C 2 and C 3 ;

[0071] Among them, τ 0 It can be calculated by the following formula:

[0072]

[0073] Wherein, L is the optical cavity length, R is the cavity mirror reflectivity (reflectivity of the reflector 7), d is the target gas distribution length, when the target gas fills the chamber 6, d = L;

[0074] S7, measuring the initial concentration C" of the target gas in the atmospheric environment before the water body starts to discharge and the target gas concentration C' after the water body starts to discharge. The difference ΔC between the target gas concentration C' after the water body starts to discharge and the target gas concentration C" in the atmospheric environment before the water body starts to discharge is the greenhouse gas concentration released during the water body discharge process;

[0075] S8. Record the time t from the beginning of water discharge to the beginning of measurement by the monitoring equipment, and calculate the total flow Q in the time period t based on the flow rate q of the water body discharged at the site per unit time. 0 , Q 0 =qt, calculate the total water flow Q within the measurement range of the monitoring equipment:

[0076]

[0077] Among them, L is the length of the ring-down cavity, and W is the width of the downstream water flow cross section;

[0078] According to the formula:

[0079]

[0080] Calculate the CO per unit flow rate during the water discharge process 2 , CH 4 and N 2 Emission concentration of O 1 、n 2 、n 3 ;

[0081]

[0082] Through the above-mentioned monitoring equipment and method, this application can effectively improve the accuracy and efficiency of measuring greenhouse gas emission concentration when water flows downstream from hydropower stations, promote the construction of a greenhouse gas monitoring technology system for reservoir-power station systems, and provide basic data support for subsequent carbon emission research;

[0083] When using CRDS technology to measure greenhouse gases, the ring-down time of three different laser signals under the same ambient humidity is compared and measured, and the measurement results of the target gas ring-down process in the open box 15 are corrected and compensated using the optical cavity ring-down signal results in the closed box 16. This can effectively eliminate the influence of water vapor on the measurement results of greenhouse gas concentrations and significantly improve the measurement accuracy.

[0084] The above description is only by way of illustration of certain exemplary embodiments of the present invention. It is undoubted that those skilled in the art can modify the described embodiments in various ways without departing from the spirit and scope of the present invention. Therefore, the above drawings and descriptions are illustrative in nature and should not be construed as limiting the scope of protection of the claims of the present invention.

Claims

1. A monitoring device for monitoring gas emissions from downstream water flow of a hydropower station, comprising two spectrometers and two heat-insulating housings (11), wherein the spectrometers comprise a laser (3), a mode field matching optical system (4), a chamber (6), two reflectors (7), a photodetector (9), a constant temperature heater (10) and a ring-down signal acquisition card (12); Two reflectors (7) are respectively arranged on both sides of the inner cavity of the chamber (6); an optical cavity is formed between the two reflectors (7); the optical cavity is a ring-down cavity; the laser (3) is used to generate a pulsed laser beam and couple the generated pulsed laser beam into the optical cavity; and the mode field matching optical system (4) is used to perform mode matching on the pulsed laser beam generated by the laser (3); The chamber (6) is provided with an air inlet (5) and an air outlet (8), both of which are connected to the optical cavity. The constant temperature heater (10) is used to maintain a constant temperature in the optical cavity. Two insulating shells (11) respectively wrap the two spectrometers and isolate the two spectrometers from the external environment. The invention is characterized in that: Also includes: A data storage device (13), a data transmitter (14), an open box (15) and a closed box (16); Two spectrometers are respectively arranged inside the open box (15) and the closed box (16); a hygrometer (1) for monitoring the humidity of the environment inside the open box (15) and the closed box (16) is arranged inside the open box (15) and the closed box (16); a humidifier (2) for replenishing water vapor into the closed box (16) is also arranged inside the closed box (16); The photoelectric detector (9) is used to detect the light intensity signal in the optical cavity and record the laser attenuation process in the optical cavity into a ring-down signal acquisition card (12); the data storage (13) is used to store the measurement data recorded by the ring-down signal acquisition card (12); and the data transmitter (14) is used to send the measurement data stored in the data storage (13) to an external terminal in real time.

2. The monitoring device for monitoring gas emissions from downstream water flow of a hydropower station according to claim 1 is characterized in that: The laser (3) can inject three lasers of different wavelengths into the optical cavity, corresponding to the strong absorption bands of CO2, CH4 and N2O respectively.

3. The monitoring device for monitoring gas emissions from downstream water flow of a hydropower station according to claim 1 is characterized in that: The mode field matching optical system (4) can complete the matching of the laser mode of the laser (3) and the ring-down cavity mode before the laser light emitted by the laser (3) enters the ring-down cavity.

4. The monitoring device for monitoring gas emissions from downstream water flow of a hydropower station according to claim 1, characterized in that: The reflectivity of the reflector (7) is greater than 99.99%.

5. The monitoring device for monitoring gas emissions from downstream water flow of a hydropower station according to claim 1, characterized in that: The humidifier (2) can replenish water vapor into the closed box (16) according to the humidity data monitored by the two hygrometers (1) and keep the humidity inside the closed box (16) consistent with the humidity inside the open box (15).

6. A method for using a monitoring device for monitoring gas emissions from downstream water flow of a hydropower station, characterized in that: The monitoring device for monitoring gas emissions from the downstream water flow of a hydropower station according to any one of claims 1 to 5 above comprises the following steps: S1, injecting the target gas to be detected into the open box (15), and after the target gas fills the chamber (6) in the open box (15), three lasers with different wavelengths corresponding to the strong absorption bands of CO2, CH4 and N2O are injected into the optical cavity in sequence through the laser (3) in the open box (15); S2, measure and record the decay time of the light intensity signal at this time, calculate the decay time under the pulse laser signals of three different wavelengths, and the decay time of CO2, CH4 and N2O in the open box (15) is recorded as τ1, τ2, τ3 respectively; S3, respectively detecting the ambient humidity in the open box (15) and the closed box (16) by means of the hygrometers (1) in the open box (15) and the closed box (16), and adjusting the water vapor concentration in the closed box (16) by means of the humidifier (2) in the closed box (16) until the ambient humidity in the closed box (16) is consistent with that in the open box (15); S4, when the water vapor concentration in the closed box (16) and the open box (15) is the same, the same pulse laser as in step S1 is injected into the chamber (6) in the closed box (16) through the laser (3) in the closed box (16), and the decay time of the light intensity signal at this time is measured and recorded, and the decay time under the pulse laser signal of three different wavelengths is calculated, and the decay time of CO2, CH4 and N2O in the closed box (16) is recorded as τ'1, τ'2, τ'3 respectively; S5. Correct and compensate the CO2, CH4 and N2O ring-down times in the open box (15) using the CO2, CH4 and N2O ring-down times in the closed box (16). According to the formula: Δτ=τ'-τ, calculate the actual ring-down times Δτ1, Δτ2 and Δτ3 of CO2, CH4 and N2O in the target gas. S6. According to the actual decay time of CO2, CH4 and N2O in the target gas, the gas concentration is calculated using the following formula in combination with Lambert-Beer's law: Wherein, C is the concentration of the target gas, α is the absorption coefficient of the target gas, σ is the absorption cross-sectional area of ​​the target gas, c is the speed of light in a vacuum, τ is the light intensity decay time when the target gas fills the cavity, τ0 is the cavity decay time in a vacuum state, and the concentrations of CO2, CH4 and N2O are recorded as C1, C2 and C3 respectively according to the calculation results; S7, measuring the initial concentration C" of the target gas in the atmospheric environment before the water body starts to discharge and the target gas concentration C' after the water body starts to discharge. The difference ΔC between the target gas concentration C' after the water body starts to discharge and the target gas concentration C" in the atmospheric environment before the water body starts to discharge is the greenhouse gas concentration released during the water body discharge process; S8. Record the time t from the beginning of water discharge to the beginning of measurement by the monitoring equipment, and calculate the total flow Q0 within the time period t based on the flow rate q of the water body discharged at the site per unit time, Q0 = qt, and calculate the total water flow Q within the measurement range of the monitoring equipment: Among them, L is the length of the ring-down cavity, and W is the width of the downstream water flow cross section; According to the formula: The emission concentrations n1, n2, and n3 of CO2, CH4, and N2O per unit flow rate during the water discharge process are calculated.

7. The method for using the monitoring device for monitoring gas emissions from downstream water flow of a hydropower station according to claim 6, characterized in that: The pulsed laser wavelengths corresponding to the strong absorption bands of CO2, CH4 and N2O are 14.7 microns, 1.65 microns and 3.94 microns respectively.

8. The method for using the monitoring device for monitoring gas emissions from downstream water flow of a hydropower station according to claim 6, characterized in that: The photoelectric detector (9) detects the energy of the outgoing light intensity attenuated to the energy of the incident light intensity. -1 The time elapsed is the decay time.

9. The method for using the monitoring device for monitoring gas emissions from downstream water flow of a hydropower station according to claim 8, characterized in that: The steps S1 and S4 measure and record the decay time of the light intensity signal at this time, and calculate the decay time of the pulse laser signals of three different wavelengths, which both include the following steps: The light intensity signal in the optical cavity is detected by a photoelectric detector (9), and the attenuation process of the laser in the optical cavity is recorded in a ring-down signal acquisition card (12). After the data storage device (13) acquires and records the ring-down signal data collected by the ring-down signal acquisition card (12), the data transmitter (14) sends the optical cavity ring-down signal data to the terminal. The energy of the outgoing light intensity is detected by the photoelectric detector (9) and decays to the energy of the incident light intensity. -1 The time elapsed is the decay time, and the decay time is calculated.

10. The method for using the monitoring device for monitoring gas emissions from downstream water flow of a hydropower station according to claim 6, characterized in that: τ0 is calculated by the following formula: Wherein, L is the optical cavity length, R is the cavity mirror reflectivity, d is the target gas distribution length, and when the target gas fills the chamber (6), d=L.

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