Closed circuit gas mixture flux measurement system

Abstract

The application discloses a closed-circuit mixed gas flux measuring system, and relates to the technical field of flux measurement.The gas path structure of a gas analyzer in the measuring system is designed by connecting a gas cell with a gas suction pump.A set of TDLAS sensors is arranged at the light transmission path of each gas cell, and the specifications of the light transmission paths of the gas cells and the sets of TDLAS sensors are matched and designed according to the characteristics of various to-be-measured gases.In the gas suction process of the gas suction pump, the measuring host can calculate the concentration measurement results of various to-be-measured gases by using the data of the sets of TDLAS sensors and compensating the transmission time delay of the three-dimensional ultrasonic wind, thereby avoiding the cross interference of different gases and basically realizing the synchronous measurement of various to-be-measured gases within an error range, so that the flux measurement accuracy, reliability and efficiency are improved, and the flux can be measured all day round and in all weathers.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of flux measurement, and in particular to a closed-circuit mixed gas flux measurement system. BACKGROUND

[0002] Accurate estimation of greenhouse gas emissions is crucial for studying global material circulation and climate change. In order to achieve "quantifiable, executable and assessable" of greenhouse gas emissions and absorption, the micrometeorological method for determining flux mainly includes aerodynamic method, heat balance method and eddy correlation method (EC), etc. At present, the eddy correlation method is the mainstream internationally.

[0003] The eddy correlation method is realized based on a flux observation system composed of a three-dimensional ultrasonic anemometer and a gas analyzer, and can serve as a bridge between remote sensing (global or regional scale) and leaf scale greenhouse gas observation, verify the accuracy of remote sensing greenhouse gas observation, and provide high-frequency, continuous and non-interfering measurement data of material exchange and energy cycle at the regional scale (10 2 m~10 3 m) of the underlying surface.

[0004] The gas analyzer in the mainstream flux observation system is realized by using an NDIR (Non-Dispersive InfraRed) sensor, which has the advantages of high sensitivity, high accuracy and fast gas analysis, etc. In application, a dual-wavelength infrared light measurement technology is often used: a wide-frequency infrared light source (i.e. containing all the absorption wavelengths of the target gas) is used to modulate the infrared light into two beams, i.e. a measurement beam with a measurement wavelength (the wavelength at which the gas has the strongest absorption) and a reference beam with a reference wavelength (the wavelength at which the gas has no absorption ability), and the infrared detector can calculate the real concentration of the target gas by comparing the difference between the reference signal and the measurement signal.

[0005] The most common application of the flux observation system is to measure the gas concentrations of CO2 and H2O, so the existing gas analyzer is also equipped with a motor to rotate the filter to select the spectrum, so as to realize the concentration measurement of different target gases. However, the NDIR technology uses a wide-wavelength light source, which has cross interference in different gas measurement, and the use of a motor to switch the spectrum selection also has the problems of limited service life of moving parts and high power consumption. The highest measurement frequency is also limited by the motor speed, resulting in unsatisfactory mixed system flux measurement effect. SUMMARY

[0006] In view of the above problems and technical needs, the present application provides a closed-circuit mixed gas flux measurement system, and the technical scheme of the present application is as follows:

[0007] The gas analyzer in the closed-circuit mixed gas flux measurement system comprises N gas cells, N groups of TDLAS sensors, and an air extraction pump. Each gas cell is connected in series through a respective light transmission gas inlet and a light transmission gas outlet. The light transmission gas inlet of the first gas cell is connected to the gas inlet of the gas analyzer and obtains the mixed gas to be measured. The light transmission gas outlet of the last gas cell is connected to the air extraction pump. The specifications of the light transmission gas of the i-th gas cell in series match the i-th gas to be measured in the mixed gas to be measured. The integer parameter N is greater than or equal to 2, and the integer parameter 1 is less than or equal to i and less than or equal to N.

[0008] The laser and the receiver in any i-th group of TDLAS sensors are oppositely arranged at both ends of the light transmission gas path of the i-th gas cell. The laser emission path of the laser is along the gas transmission direction inside the gas cell. The i-th group of TDLAS sensors matches the i-th gas to be measured in the mixed gas to be measured. The wavelength of the laser in the i-th group of TDLAS sensors reaches the upper limit intensity threshold for the absorption intensity of the i-th gas to be measured and is lower than the lower limit intensity threshold for the absorption intensity of other gases to be measured.

[0009] The measurement host in the closed-circuit mixed gas flux measurement system is connected to the N groups of TDLAS sensors. During the air extraction process of the air extraction pump, the measurement host detects the original concentration data of the i-th gas to be measured in the mixed gas to be measured based on the TDLAS technology by using any i-th group of TDLAS sensors. The measurement host obtains the basic time delay of the i-th gas to be measured by dividing the pipe volume from the gas inlet of the i-th gas cell to the gas inlet of the gas analyzer by the gas flow rate of the mixed gas to be measured. The measurement host obtains the concentration measurement result of the i-th gas to be measured by performing transmission time delay compensation on the original concentration data of the i-th gas to be measured according to the transmission time delay of the i-th gas to be measured.

[0010] Further technical solutions are as follows.

[0011] The original concentration data of the i-th gas to be measured after the transmission time delay compensation is performed thereon is corrected for delay error based on the wind measurement data obtained by the three-dimensional ultrasonic wind sensor in the closed-circuit mixed gas flux measurement system every average time length T, to obtain the concentration measurement result of the i-th gas to be measured that is matched in synchronization with the wind measurement data.

[0012] Further technical solutions are as follows.

[0013] A vertical wind speed time sequence is extracted from the wind measurement data obtained by the three-dimensional ultrasonic wind sensor within the last average time length T at any correction time t. The vertical wind speed time sequence comprises M vertical wind speed data arranged in time sequence.

[0014] Extracting a plurality of different raw concentration time sequences of the i-th to-be-detected gas respectively from the detected M raw concentration data of the i-th to-be-detected gas at different delay offsets of the current correction time t, the j-th delay offset τ j The j-th raw concentration time sequence extracted below comprises: the raw concentration data after the last raw concentration data obtained at the correction time t is offset by the j-th delay offset τ j j data points and the continuous M-1 raw concentration data before the same; wherein, the delay offset τ j is less than 0, indicating that it is offset in the direction of the previous correction time, and the delay offset τ j is greater than 0, indicating that it is offset in the direction of the next correction time; the integer parameter 1≤j≤J, and the integer parameter J≥2;

[0015] Calculate the covariance between the j-th raw concentration time sequence and the vertical wind speed time sequence, and determine the delay offset corresponding to the raw concentration time sequence with the maximum covariance between the vertical wind speed time sequence as the target delay offset;

[0016] After completing the delay error correction of the raw concentration data of the i-th to-be-detected gas after completing the transmission time delay compensation according to the target delay offset, the concentration measurement result of the i-th to-be-detected gas synchronized with the wind measurement data is obtained.

[0017] A further technical solution is that the delay error correction of the raw concentration data of the i-th to-be-detected gas after completing the transmission time delay compensation based on the wind measurement data further comprises:

[0018] At any correction time t, according to the wind measurement data obtained by the three-dimensional ultrasonic wind sensor in the previous average time T, and combining the layout structure of the three-dimensional ultrasonic wind sensor and the gas analyzer in the closed-loop mixed gas flux measurement system, the theoretical offset τ δ of the correction time t is determined; wherein, the theoretical offset τ δ is an integer parameter;

[0019] According to the theoretical offset τ δ of the correction time t, τ j ∈[τ δ -τ max , τ δ +τ max ], extract J=2τ max +1 raw concentration time sequences, wherein, the positive integer τ max represents the maximum delay offset.

[0020] A further technical solution is to determine the theoretical offset τ of the correction time t δ Comprise:

[0021] According to the layout structure of the three-dimensional ultrasonic wind sensor and the gas analyzer, the distance between the probe position of the three-dimensional ultrasonic wind sensor and the gas inlet of the gas analyzer is determined.

[0022] According to the wind direction and wind speed in the wind data obtained by the three-dimensional ultrasonic wind sensor in the last average time T of the correction time t, the stable wind speed in the direction from the probe position of the three-dimensional ultrasonic wind sensor to the gas inlet of the gas analyzer at the correction time t is determined.

[0023] According to the distance between the probe position of the three-dimensional ultrasonic wind sensor and the gas inlet of the gas analyzer and the stable wind speed in the direction from the probe position of the three-dimensional ultrasonic wind sensor to the gas inlet of the gas analyzer at the correction time t, the theoretical offset τ of the correction time t is determined δ ; wherein, the greater the distance between the probe position of the three-dimensional ultrasonic wind sensor and the gas inlet of the gas analyzer, the smaller the wind speed in the direction from the probe position of the three-dimensional ultrasonic wind sensor to the gas inlet of the gas analyzer, and the greater the theoretical offset τ δ .

[0024] A further technical solution is that the flow rate of the air pump is not less than L max *F, wherein L max is the maximum gas path capacity of all N gas pools, and F is the frequency of the gas signal of the closed-circuit mixed gas flux measurement system.

[0025] A further technical solution is that the specification of the light-transmitting gas path of each gas pool includes the aperture and the optical path of the light-transmitting gas path, the optical path of the light-transmitting gas path of the i-th gas pool matches the gas absorption characteristics of the i-th gas to be measured, and the apertures of the light-transmitting gas paths of the N gas pools are all equal and match the maximum light spot of the laser in all N groups of TDLAS sensors.

[0026] A further technical solution is that each gas pool is further provided with a curved temperature guide path before the light-transmitting gas path inlet, and the temperature guide path is made of heat-conducting material, and the mixed gas to be measured enters the light-transmitting gas path after heat transfer through the temperature guide path.

[0027] A further technical solution is that a temperature sensor and a gas pressure sensor are arranged at the light-transmitting gas path inlet of each gas pool, and the measurement host in the closed-circuit mixed gas flux measurement system is further connected with each temperature sensor and gas pressure sensor.

[0028] The raw concentration data of the i-th to-be-measured gas detected by the measurement host comprises: detecting the raw concentration data of the i-th to-be-measured gas based on the TDLAS technology by using any i-th group of TDLAS sensors in combination with the temperature data collected by the temperature sensor at the gas inlet of the light transmission gas path of the i-th gas cell and the gas pressure data collected by the gas pressure sensor.

[0029] Further, a particulate filter is arranged at the gas inlet of the gas analyzer, and an air filter is arranged between the gas outlet of the light transmission gas path of the last gas cell and the air pump.

[0030] The beneficial technical effects of the present application are as follows:

[0031] The present application discloses a closed-circuit mixed gas flux measurement system. The gas path structure of the gas analyzer in the closed-circuit mixed gas flux measurement system is designed by connecting gas cells in series and combining an air pump. The specifications of the light transmission gas paths of the gas cells and the groups of TDLAS sensors are designed according to the characteristics of various to-be-measured gases. By using multiple groups of TDLAS sensors, the synchronous measurement of multiple to-be-measured gases can be realized based on the TDLAS technology. By performing transmission time delay compensation on the raw concentration data of each to-be-measured gas, the transmission time delay introduced by the connected gas cells can be compensated. Due to the characteristics of the TDLAS measurement technology, the cross interference of different gases is avoided, thereby improving the flux measurement accuracy, reliability and efficiency. In addition, the gas analyzer uses an air pump to obtain sample gas, which avoids exposing the analyzer to air, avoids pollution of the optical lens, reduces the maintenance frequency, avoids the influence of precipitation and snow, and can realize all-weather flux measurement.

[0032] The present application also corrects the measurement results of the TDLAS sensors based on the wind measurement data of the three-dimensional ultrasonic wind sensor of the closed-circuit mixed gas flux measurement system, which further improves the accuracy of the concentration measurement results without the need for additional correction devices. BRIEF DESCRIPTION OF DRAWINGS

[0033] Figure 1 FIG. 1 is a system structure block diagram of a closed-circuit mixed gas flux measurement system according to an embodiment of the present application.

[0034] Figure 2 FIG. 2 is a schematic diagram of the series connection structure of two gas cells in an embodiment of the present application.

[0035] Figure 3 FIG. 3 is a structural schematic diagram of a gas analyzer in another embodiment of the present application.

[0036] Figure 4is a flow chart of a method for obtaining a concentration measurement result of the ith to-be-measured gas in an embodiment of the present application.

[0037] Figure 5 is a schematic diagram of a raw concentration time sequence obtained at different delay offsets in an example of the present application. DETAILED DESCRIPTION

[0038] The specific embodiments of the present application are further described below with reference to the accompanying drawings.

[0039] The present application discloses a closed-circuit mixed gas flux measurement system, please refer to Figure 1 The closed-circuit mixed gas flux measurement system includes a gas analyzer, a three-dimensional ultrasonic wind sensor, and a measurement host. The present application optimizes the traditional NDIR-based gas analyzer. The gas analyzer in the present application includes N gas cells, N sets of TDLAS sensors, and a gas suction pump. The integer parameter N≥2, and the value of N is determined according to the number of to-be-measured gases to be measured. For example, the closed-circuit mixed gas flux measurement system is used to measure the flux of carbon dioxide and water vapor in air, and N=2 is taken. When more to-be-measured gases need to be measured simultaneously, the number of gas cells and TDLAS sensors is increased accordingly.

[0040] Each gas cell includes a light transmission gas path inside. The direction of gas transmission inside each gas cell along the light transmission gas path from the gas inlet to the gas outlet is the gas transmission direction inside the gas cell.

[0041] Each gas cell is connected in series through its own light transmission gas path inlet and light transmission gas path outlet. The light transmission gas path inlet of the first gas cell is connected to the gas inlet of the gas analyzer and obtains the to-be-measured mixed gas. The light transmission gas path outlet of the last gas cell is connected to the gas suction pump. During the gas suction process of the gas suction pump, the to-be-measured mixed gas enters the gas analyzer from the gas inlet of the entire gas analyzer and is transmitted through the light transmission gas paths of each gas cell in turn. The light transmission gas path is formed inside the gas cell. In actual application, the gas cell and the TDLAS sensor are packaged in a shell, thereby forming a closed-circuit structure, avoiding the influence of precipitation, snowfall, and other environmental factors on the light path measurement process, and effectively reducing the maintenance frequency. Please refer to Figure 1 and Figure 2 Taking the series connection structure of the gas cell 1 and the gas cell 2 as an example, the dashed portion inside the gas cell 1 is the light transmission gas path 11 of the gas cell 1, and the dashed portion inside the gas cell 2 is the light transmission gas path 21 of the gas cell 2. The gas outlet of the light transmission gas path 21 of the gas cell 2 is connected to the gas suction pump 3. The gas transmission directions inside the two gas cells are shown by arrows.

[0042] The N groups of TDLAS sensors are respectively arranged at the N gas cells, and any ith group of TDLAS sensors is arranged at an ith gas cell in turn in series. The laser and the receiver in the ith group of TDLAS sensors are respectively arranged at two ends of a light transmission gas path of the ith gas cell, and the laser emission path of the laser is along the gas transmission direction inside the gas cell. Figure 1 In the embodiment, the laser 12 and the receiver 13 in the first group of TDLAS sensors are arranged at two ends of the light transmission gas path 11 of the gas cell 1, and the laser 22 and the receiver 23 in the second group of TDLAS sensors are arranged at two ends of the light transmission gas path 21 of the gas cell 2. The integer parameter is 1≤i≤N.

[0043] When the fluxes of the N kinds of to-be-measured gases in the to-be-measured mixed gas need to be measured, the structures of the light transmission gas paths of the gas cells and the TDLAS sensors arranged at the gas cells need to be designed according to the types of the to-be-measured gases, including:

[0044] (1) The specification of the light transmission gas path of the ith gas cell in series is matched with the ith to-be-measured gas in the to-be-measured mixed gas. It needs to be noted that the ith to-be-measured gas in the present application is used to represent any to-be-measured gas in the to-be-measured mixed gas, and this representation does not mean that the to-be-measured gases in the to-be-measured mixed gas need to be arranged in a specific order. In fact, since the to-be-measured mixed gas is transmitted through the gas cells in turn, the serial order of the gas cells can be set at will, as long as the gas cells are matched with the to-be-measured gases one by one.

[0045] In an embodiment, the light transmission gas path of each gas cell adopts a cylindrical structure, and the specification of the light transmission gas path of each gas cell includes an aperture along the radial direction of the cylindrical structure and an optical path along the length direction of the cylindrical structure. Since the laser emission path of the laser is along the gas transmission direction inside the gas cell and is received by the receiver after passing through the light transmission gas path, the optical path of the light transmission gas path of the ith gas cell is matched with the gas absorption characteristic of the ith to-be-measured gas. The gas absorption characteristic of the ith to-be-measured gas is the spectral absorption peak of the ith to-be-measured gas, and the detection range of the absorption intensity and the gas concentration. The optical path of the light transmission gas path of the ith gas cell is determined by the Lambert-Beer law. For example, in the embodiment, Figure 2 In the embodiment, the gas cell 1 corresponds to water vapor, and the optical path L1 of the light transmission gas path of the gas cell 1 is matched with the gas absorption characteristic of the water vapor. The gas cell 2 corresponds to carbon dioxide, and the optical path L2 of the light transmission gas path of the gas cell 2 is matched with the gas absorption characteristic of the carbon dioxide. Since the gas absorption characteristics of different to-be-measured gases are different, the optical paths of the light transmission gas paths of different gas cells can be different.

[0046] In order to ensure the stability of the transmission of the mixed gas to be measured in each cell and the same flow rate of the gas in each cell, the apertures of the light transmission paths of the N cells are equal. The aperture of the light transmission path of each cell needs to be determined according to the spot size of the laser at the cell, and thus the aperture matching the largest spot of the lasers in all the N groups of TDLAS sensors is selected as the aperture of the light transmission path of each cell. Generally, the aperture of the light transmission path of each cell is slightly larger than the largest spot of all the N lasers. When the light emitted by the lasers is not parallel, the spot of the laser in the i-th group of TDLAS sensors is related to the optical path of the light transmission path of the i-th cell, and the spot size can also be adjusted by an optical lens.

[0047] (2) The i-th group of TDLAS sensors matches the i-th gas to be measured in the mixed gas to be measured, the mixed gas to be measured is transmitted through each cell in turn, and the i-th group of TDLAS sensors is used to measure the i-th gas to be measured. Therefore, the wavelength of the laser in the i-th group of TDLAS sensors reaches the upper limit intensity threshold for the absorption intensity of the i-th gas to be measured and is lower than the lower limit intensity threshold for the absorption intensity of other gases to be measured. That is, the laser in the i-th group of TDLAS sensors selects a wavelength with strong absorption for the i-th gas to be measured and negligible absorption for the other N-1 gases to be measured. The absorption intensity for various gases can be determined by referring to the absorption peaks of various gases in the HITRAN database.

[0048] The measurement host in the closed-circuit mixed gas flux measurement system is connected to the N groups of TDLAS sensors in the gas analyzer. During the pumping process of the air pump, the mixed gas to be measured is transmitted through the light transmission path of each cell in turn. In the light transmission path of any i-th cell, the laser of the i-th group of TDLAS sensors emits a laser with a wavelength matching the i-th gas to be measured and is received by the corresponding receiver. The original concentration data of the i-th gas to be measured can be measured by using the TDLAS technology. Since the TDLAS measurement technology using a narrow-linewidth laser source avoids cross interference of different gases to be measured, the original concentration data of various gases to be measured can be obtained by using each group of TDLAS sensors during the process of the mixed gas to be measured being transmitted through each cell. Within the error range, it can be considered that the synchronous measurement of multiple gases to be measured is achieved, without the need to switch the filter for measurement as in NDIR, and thus the measurement efficiency is also higher. The measurement results of the original concentration data of the gas to be measured by using the signal of each group of TDLAS sensors can refer to the existing single-gas flux measurement method, which will not be described here.

[0049] In order to reduce the influence of temperature on the flux measurement, in one embodiment, as shown in FIG. 6, a temperature sensor is arranged in the light transmission path of each cell, and the temperature sensor is connected to the measurement host. The measurement host can obtain the temperature of each cell in real time, and the measurement host can compensate the measured data according to the temperature of each cell. Figure 3As shown, each gas cell is further provided with a curved temperature guide gas path before the gas inlet of the light transmission gas path, and the temperature guide gas path is made of heat conductive material. The measured mixed gas enters the light transmission gas path after heat transfer through the temperature guide gas path. The aperture of the temperature guide gas path can be consistent with or inconsistent with the light transmission gas path. The length of the temperature guide gas path is designed according to the actual heat transfer effect to ensure that the gas temperature is consistent with the gas cell temperature. In actual application, the entire gas cell is generally made of metal material, which has the characteristics of heat conduction, corrosion resistance and non-absorption. Figure 3 In the embodiment, the temperature guide gas path 14 is arranged before the gas inlet of the light transmission gas path 11 of the gas cell 1, and the temperature guide gas path 24 is arranged before the gas inlet of the light transmission gas path 21 of the gas cell 2. In addition, as shown in Figure 3 The temperature sensor and the gas pressure sensor are arranged at the gas inlet of the light transmission gas path of each gas cell, and the measurement host in the closed-loop mixed gas flux measurement system is further connected with the temperature sensor and the gas pressure sensor. When the measurement host detects the original concentration data of the ith kind of gas to be measured based on the TDLAS technology by using the ith group of TDLAS sensors, the temperature data collected by the temperature sensor at the gas inlet of the light transmission gas path of the ith gas cell and the gas pressure data collected by the gas pressure sensor are applied in the TDLAS algorithm. The specific content of the TDLAS algorithm is not described herein.

[0050] In the above measurement process, the gas update rate in the gas cell and the gas analyzer measurement rate determine the highest measurement rate of the entire closed-loop mixed gas flux measurement system. The gas cells are in series, so the update rate of the gas in the largest gas cell determines the update rate of the gas in the entire gas analyzer. Therefore, in an embodiment, the flow rate of the air pump is not less than L max *F, wherein L max is the light transmission gas path capacity of the largest gas cell among the N gas cells, and F is the frequency of the gas signal of the closed-loop mixed gas flux measurement system.

[0051] As introduced above, the air pump is used to draw the mixed gas to be measured into the gas analyzer, and the closed-loop structure is adopted, which can effectively avoid the exposure of the gas analyzer to the air, avoid the pollution of the optical lens, and is conducive to reducing the maintenance frequency. In order to further reduce the pollution of the optical lens, as shown in Figure 3 The gas inlet of the gas analyzer is provided with a particulate filter 4, and the air filter 5 is arranged between the light transmission gas path outlet of the last gas cell and the air pump.

[0052] However, due to this closed-loop structure, even if the gas exchange rate is increased by increasing the flow rate of the pump, there will still be an unavoidable time delay in the transmission of the gas mixture to be measured to the light-transmitting gas path of each gas cell. Therefore, the original concentration data of the i-th gas to be measured obtained directly based on TDLAS technology is not directly used as the concentration measurement result. Instead, the basic time delay of the i-th gas to be measured is obtained by dividing the pipeline volume from the inlet of the light-transmitting gas path of the i-th gas cell to the inlet of the gas analyzer by the gas flow rate of the gas mixture to be measured. After the gas cell structure design is determined, the pipeline volume from the inlet of the light-transmitting gas path of the i-th gas cell to the inlet of the gas analyzer is known, and the gas flow rate during the pumping process is also known. The base time delay of the i-th gas to be measured is the time delay of the gas mixture being measured from the inlet of the gas analyzer to the inlet of the light-transmitting gas path of the i-th gas cell, and it is also the time delay of the existence of the original concentration data of the i-th gas to be measured. Then, the original concentration data of the i-th gas to be measured is compensated for the transmission time delay according to the transmission time delay of the i-th gas to be measured to obtain the concentration measurement result of the i-th gas to be measured, thereby making up for the transmission time delay introduced by the series gas cells.

[0053] For closed-loop mixed gas flux measurement systems, the obtained concentration measurement results need to be used in conjunction with wind measurement data. However, in reality, due to the physical separation between the gas analyzer's inlet and the probe of the three-dimensional ultrasonic wind sensor, it is still difficult to guarantee the synchronization of the original concentration data after compensation for transmission delay based on the transmission delay within the gas pool with the wind measurement data. Therefore, in one embodiment, after obtaining the original concentration data of the i-th analyte gas after transmission delay compensation using any i-th group of TDLAS sensors based on TDLAS technology, it is not directly used as the final concentration measurement result. Instead, every average time interval T, the original concentration data of the i-th analyte gas after transmission delay compensation is corrected for delay error based on the wind measurement data obtained from the three-dimensional ultrasonic wind sensor in the closed-loop mixed gas flux measurement system, to obtain a concentration measurement result of the i-th analyte gas that is synchronized with the wind measurement data. Because the 3D ultrasonic wind sensor uses an open-circuit structure, its wind measurement data can be considered to have no time delay. Furthermore, the wind measurement data is consistent with the changes in the concentration measurement results of the gas being measured. Therefore, this embodiment uses the wind measurement data as a benchmark to correct the delay error in the original concentration data to offset the time delay introduced by the closed-circuit structure. Since the 3D ultrasonic wind sensor is an inherent component of the closed-circuit mixed gas flux measurement system, this approach requires no additional hardware. The average duration T can be customized, taking into account the stability of the ambient wind; for example, the average duration T can be set to half an hour.

[0054] The method of correcting the raw concentration data of various to-be-detected gases is the same, and the method of correcting the raw concentration data of the i-th to-be-detected gas based on the wind data includes the following steps, please refer to the flowchart shown in Figure 4

[0055] Step 1, at any correction time t, obtain the wind data obtained by the three-dimensional ultrasonic wind sensor in the last average time T, that is, the time period between the last correction time and the current correction time t. The obtained wind data includes the wind speed and wind direction of M wind time points. Since the wind measurement frequency of the three-dimensional ultrasonic wind sensor is known, the number of wind time points included in each average time T is also fixed and known, such as commonly taking the average time T as half an hour, and according to the common wind measurement frequency of the three-dimensional ultrasonic wind sensor, the three-dimensional ultrasonic wind sensor can obtain 18000 wind data of wind time points in an average time T.

[0056] Step 2, extract the vertical wind speed time sequence from the wind data obtained by the three-dimensional ultrasonic wind sensor in the last average time T at any correction time t. After obtaining the wind speed and wind direction of each wind time point, the vertical wind speed data of each wind time point can be calculated, so as to extract the vertical wind speed time sequence including M vertical wind speed data arranged in time sequence.

[0057] Step 3, extract the M raw concentration data of the i-th to-be-detected gas detected at different delay offsets of the current correction time t to form a plurality of different raw concentration time sequences.

[0058] The j-th raw concentration time sequence obtained at the j-th delay offset τ j of the current correction time t includes: the raw concentration data after the latest raw concentration data obtained at the correction time t is offset by τ j data points and the continuous M-1 raw concentration data before it, that is, each raw concentration time sequence extracted also includes M raw concentration data arranged in time sequence.

[0059] Wherein, the delay offset τ j is less than 0, indicating that it is offset to the direction of the last correction time, and the delay offset τ j is greater than 0, indicating that it is offset to the direction of the next correction time.

[0060] For example, in an example, based on the discrete point diagram of the i-th raw concentration data arranged in time sequence shown in Figure 5 In this example, the 10 raw concentration data arranged in time sequence in the black dashed line box are the delay offset τ j ​The original concentration time series extracted under = 0, and the 10 original concentration data arranged in time sequence in the green dashed box is the delay offset τ j The original concentration time series extracted under = 0, and the 10 original concentration data arranged in time sequence in the green dashed box is the delay offset τ j The original concentration time series extracted under = 0, and the 10 original concentration data arranged in time sequence in the green dashed box is the delay offset τ Figure 5 For the convenience of illustration, M = 10 is taken as an example, but in fact, as described above, the value of M is large.

[0061] Through the above method, J different original concentration time series can be extracted, and the integer parameter J ≥ 2, the above integer parameter 1 ≤ j ≤ J, and the value of J can be set by the user.

[0062] Step 4, calculate the covariance between the jth original concentration time series and the vertical wind speed time series, and determine the delay offset corresponding to the original concentration time series with the maximum covariance between the J original concentration time series and the vertical wind speed time series as the target delay offset. The original concentration time series with the maximum covariance between the vertical wind speed time series is the original concentration time series with the highest consistency with the change of the vertical wind speed time series.

[0063] Step 5, according to the target delay offset, the original concentration data after the time delay compensation of the i-th kind of gas to be tested is time-shifted to complete the delay error correction, that is, the original concentration data after shifting τ j data points of the original concentration data detected at the correction time t is the actual original concentration data corresponding to the correction time t, thereby obtaining the concentration measurement result of the i-th kind of gas matched with the wind data.

[0064] In another embodiment, in order to improve the correction efficiency, at any correction time t, first, according to the wind data obtained by the three-dimensional ultrasonic wind sensor in the last average time T, combined with the layout structure of the three-dimensional ultrasonic wind sensor and the gas analyzer in the closed loop mixed gas flux measurement system, the theoretical offset τ δ of the correction time t is determined. δ Then, according to the theoretical offset τ δ of the correction time t, the target delay offset should be around the current theoretical offset τ j . δ Within the range of τ max - τ δ + τ max , extract J = 2 τ max + 1 original concentration time series, wherein the positive integer τ maxThe maximum delay offset can be set by the user. Since the gas in the gas cell is quickly updated, the time delay introduced by the closed loop structure will not be too large, so the positive integer τ max Generally, 5-10 is acceptable.

[0065] Since the probe position of the three-dimensional ultrasonic wind sensor and the gas inlet of the gas analyzer are not at the same position, there is an inherent error due to physical separation of the input between the probe position of the three-dimensional ultrasonic wind sensor and the gas inlet of the gas analyzer, which will have a time delay. In addition, under the condition of fixed structural design, when the environmental wind is different, the time delay between the probe position of the three-dimensional ultrasonic wind sensor and the gas inlet of the gas analyzer is also different, so the theoretical offset τ δ needs to be dynamically adjusted according to the wind data, including:

[0066] At any correction time t, according to the wind data obtained by the three-dimensional ultrasonic wind sensor in the last average time T, and combining the layout structure of the three-dimensional ultrasonic wind sensor and the gas analyzer in the closed loop mixed gas flux measurement system, the theoretical offset τ δ at the correction time t is determined. Including: according to the layout structure of the three-dimensional ultrasonic wind sensor and the gas analyzer, the distance between the probe position of the three-dimensional ultrasonic wind sensor and the gas inlet of the gas analyzer is determined, and according to the wind direction and wind speed in the wind data obtained by the three-dimensional ultrasonic wind sensor in the last average time T at the correction time t, the stable wind speed in the direction from the probe position of the three-dimensional ultrasonic wind sensor to the gas inlet of the gas analyzer at the correction time t is determined. The wind data actually obtained by the three-dimensional ultrasonic wind sensor is dynamic discrete data, and the stable wind speed at the correction time t can be calculated using the existing method.

[0067] Then, according to the distance between the probe position of the three-dimensional ultrasonic wind sensor and the gas inlet of the gas analyzer and the stable wind speed in the direction from the probe position of the three-dimensional ultrasonic wind sensor to the gas inlet of the gas analyzer at the correction time t, the theoretical offset τ δ at the correction time t is determined. The layout structure of the three-dimensional ultrasonic wind sensor and the gas analyzer is fixed, that is, the distance between the probe position of the three-dimensional ultrasonic wind sensor and the gas inlet of the gas analyzer is determined, but the wind data changes dynamically. When the distance and the wind speed are used to determine the theoretical offset τ δ , the greater the distance between the probe position of the three-dimensional ultrasonic wind sensor and the gas inlet of the gas analyzer, the smaller the wind speed in the direction from the probe position of the three-dimensional ultrasonic wind sensor to the gas inlet of the gas analyzer, and the greater the theoretical offset τ δ . The specific numerical setting method can be customized.

[0068] The above merely describes the preferred embodiments of the present application, and the present application is not limited to the above embodiments. It can be understood that other improvements and changes directly derived or thought by those skilled in the art without departing from the spirit and concept of the present application shall be considered to be included in the protection scope of the present application.

Claims

1. A closed-loop mixed gas flux measurement system, characterized in that, The gas analyzer in the closed-loop mixed gas flux measurement system includes N gas cells, N sets of TDLAS sensors, and a pump. Each gas cell is connected in series through its own light-transmitting gas path inlet and outlet. The light-transmitting gas path inlet of the first gas cell is connected to the inlet of the gas analyzer to acquire the mixed gas to be measured, and the light-transmitting gas path outlet of the last gas cell is connected to the pump. The specifications of the light-transmitting gas path of the i-th gas cell connected in series are matched with the i-th gas to be measured in the mixed gas. Wherein, the integer parameter N≥2, and the integer parameter 1≤i≤N. In any i-th group of TDLAS sensors, the laser and receiver are respectively positioned facing each other at both ends of the light-transmitting gas path of the i-th gas cell, and the laser emission path of the laser is along the gas transmission direction inside the gas cell; the i-th group of TDLAS sensors is matched with the i-th gas to be measured in the gas mixture to be measured, and the wavelength of the laser in the i-th group of TDLAS sensors has an absorption intensity of the i-th gas to be measured that reaches the upper limit intensity threshold and an absorption intensity of the other gases to be measured that is lower than the lower limit intensity threshold; The measurement host in the closed-loop mixed gas flux measurement system is connected to N sets of TDLAS sensors. During the gas extraction process of the pump, the measurement host uses any i-th set of TDLAS sensors to detect the original concentration data of the i-th gas in the mixed gas to be measured based on TDLAS technology. The volume of the pipeline from the inlet of the light-transmitting gas path of the i-th gas cell to the inlet of the gas analyzer is divided by the gas flow rate of the mixed gas to be measured to obtain the basic time delay of the i-th gas. The original concentration data of the i-th gas is then compensated for the transmission time delay of the i-th gas to obtain the concentration measurement result of the i-th gas.

2. The closed-loop mixed gas flux measurement system according to claim 1, characterized in that, Obtaining the concentration measurement result of the i-th gas to be tested also includes: Every average time interval T, based on the wind measurement data obtained from the three-dimensional ultrasonic wind sensor in the closed-loop mixed gas flux measurement system, the original concentration data of the i-th gas to be measured after transmission delay compensation is corrected for delay error, so as to obtain the concentration measurement result of the i-th gas to be measured that is synchronously matched with the wind measurement data.

3. The closed-loop mixed gas flux measurement system according to claim 2, characterized in that, The delay error correction for the original concentration data of the i-th gas under test after transmission delay compensation based on wind measurement data includes: At any calibration time t, a vertical wind speed time series is extracted from the wind measurement data obtained by the three-dimensional ultrasonic wind sensor within the previous average duration T. The vertical wind speed time series includes M vertical wind speed data arranged in chronological order. At different delay offsets at the current correction time t, multiple different raw concentration time series are formed by extracting M raw concentration data of the i-th analyte gas. At the j-th delay offset τ at the current correction time t... j The j-th raw concentration time series obtained by extraction includes: the most recent raw concentration data obtained at correction time t, offset by the j-th delay offset τ. j The original concentration data after each data point and the preceding M-1 consecutive original concentration data points; where the delay offset τ j A value less than 0 indicates a directional shift to the previous correction time, with a delay shift τ. j A value greater than 0 indicates a directional shift towards the next correction time; integer parameters 1 ≤ j ≤ J, and integer parameters J ≥ 2; Calculate the covariance between the j-th original concentration time series and the vertical wind speed time series, and determine the delay offset corresponding to the original concentration time series with the largest covariance with the vertical wind speed time series among the J original concentration time series as the target delay offset; After time offsetting the original concentration data of the i-th gas to be tested after transmission delay compensation according to the target delay offset, and completing the delay error correction, the concentration measurement result of the i-th gas to be tested is obtained and synchronized with the wind measurement data.

4. The closed-loop mixed gas flux measurement system according to claim 3, characterized in that, The delay error correction for the original concentration data of the i-th gas under test after transmission delay compensation based on wind measurement data also includes: At any calibration time t, based on the wind measurement data obtained by the three-dimensional ultrasonic wind sensor within the previous average time period T, and combined with the layout structure of the three-dimensional ultrasonic wind sensor and gas analyzer in the closed-loop mixed gas flux measurement system, the theoretical offset τ at calibration time t is determined. δ Among them, the theoretical offset τ δ The parameter is an integer. Based on the theoretical offset τ at correction time t δ In τ j ∈[τ δ -τ max , τ δ +τ max Extract J = 2τ within the range max +1 original concentration time series, where the positive integer τ max This indicates the maximum delay offset.

5. The closed-loop mixed gas flux measurement system according to claim 4, characterized in that, Determine the theoretical offset τ at correction time t δ include: Based on the layout of the three-dimensional ultrasonic wind sensor and the gas analyzer, the distance between the probe position of the three-dimensional ultrasonic wind sensor and the air inlet of the gas analyzer is determined. Based on the wind direction and wind speed in the wind measurement data obtained by the three-dimensional ultrasonic wind sensor within the previous average time T before the calibration time t, determine the stable wind speed at the calibration time t from the probe position of the three-dimensional ultrasonic wind sensor to the air inlet of the gas analyzer. Based on the distance between the probe position of the three-dimensional ultrasonic wind sensor and the air inlet of the gas analyzer, and the stable wind speed at calibration time t along the direction from the probe position of the three-dimensional ultrasonic wind sensor to the air inlet of the gas analyzer, the theoretical offset τ at calibration time t is determined. δ The greater the distance between the probe position of the three-dimensional ultrasonic wind sensor and the air inlet of the gas analyzer, the smaller the wind speed in the direction from the probe position of the three-dimensional ultrasonic wind sensor to the air inlet of the gas analyzer, and the greater the theoretical offset τ. δ The larger.

6. The closed-loop mixed gas flux measurement system according to claim 1, characterized in that, The flow rate of the air pump is not less than L. max *F, where L max It is the light-transmitting gas path capacity of the largest gas cell among all N gas cells, and F is the frequency of the gas signal of the closed-loop mixed gas flux measurement system.

7. The closed-loop mixed gas flux measurement system according to claim 1, characterized in that, The specifications of the optical path of each gas cell include the aperture and optical path length. The optical path length of the optical path of the i-th gas cell is matched with the gas absorption characteristics of the i-th gas to be measured. The apertures of the optical paths of the N gas cells are all equal and are matched with the maximum spot size of the laser in all N groups of TDLAS sensors.

8. The closed-loop mixed gas flux measurement system according to claim 1, characterized in that, Each gas chamber is equipped with a curved temperature-conducting gas path before the light-conducting gas path inlet. The temperature-conducting gas path is made of thermally conductive material. After the mixed gas to be measured passes through the temperature-conducting gas path, it undergoes heat transfer before entering the light-conducting gas path.

9. The closed-loop mixed gas flux measurement system according to claim 1, characterized in that, Temperature and pressure sensors are also arranged at the air inlet of each gas cell through the light-transmitting gas path. The measurement host in the closed-loop mixed gas flux measurement system is also connected to each temperature and pressure sensor. The measurement host detects the original concentration data of the i-th gas to be tested by: using any i-th group of TDLAS sensors based on TDLAS technology, combined with the temperature data collected by the temperature sensor at the air inlet of the i-th gas pool and the air pressure data collected by the air pressure sensor, to detect the original concentration data of the i-th gas to be tested.

10. The closed-loop mixed gas flux measurement system according to claim 1, characterized in that, A particulate filter is installed at the air inlet of the gas analyzer, and an air filter is installed between the air outlet of the last gas cell and the air pump.

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