Method for rapidly detecting methane content in combustible ice

Abstract

The invention discloses a method for rapidly detecting the content of methane in combustible ice, which comprises the following steps: carrying out vacuum decomposition on a combustible ice sample by adopting a combustible ice vacuum decomposition device to completely decompose the ice sample to obtain combustible ice decomposed gas; and testing the combustible ice decomposed gas by using a microscopic confocal laser Raman spectrometer, analyzing the corresponding methane spectrum peak area according to the obtained Raman spectrogram, and calculating the methane content according to an external standard method. The combustible ice is placed in vacuum to be decomposed to obtain pure combustible ice decomposition gas, the decomposition device is pumped to be in a vacuum state through the vacuum pump, meanwhile, the temperature-controllable constant-temperature bath is used for controlling the decomposition temperature, the decomposition gas is collected through the phase equilibrium relation of the combustible ice, and the combustible ice decomposition gas is obtained. The method comprises the following steps: filling decomposition gas through a transparent gas bag, testing the decomposition gas by using a Raman spectrometer, carrying out baseline correction, curve smoothing and the like on a Raman spectrogram of a sample to obtain a Raman characteristic peak area, and rapidly detecting the content of methane in combustible ice by adopting an external standard method.

Description

Technical Field

[0001] The present invention relates to the field of combustible ice component content detection, and in particular to a method for rapidly detecting methane content in combustible ice. Background Art

[0002] Methane hydrate is a natural gas hydrate, which is an ice-like crystalline substance formed by natural gas and water under high pressure and low temperature conditions. Methane hydrate is distributed in deep sea or terrestrial permafrost. After burning, it only produces a small amount of carbon dioxide and water, which is far less polluting than coal, oil, etc., and its reserves are huge. Its carbon equivalent is equivalent to twice the total known reserves of coal, oil and natural gas in the world. Therefore, it is internationally recognized as a replacement energy for fossil fuels such as oil. Since methane hydrate has a special cage structure and strong gas storage capacity, it is a solid material with high energy density, so it has broad prospects in the field of solid storage and transportation of natural gas.

[0003] In terms of detection technology, domestic and foreign research teams have also done a lot of exploratory work, using X-ray diffractometers, laser Raman spectrometers, nuclear magnetic resonance spectrometers, differential scanning calorimeters, scanning electron microscopes, gas chromatographs, X-CT scanning systems, isotope ratio meters and other equipment to study the physical and chemical properties of methane hydrate.

[0004] Methane hydrate exists stably in a special temperature and pressure environment. Once it is out of the appropriate temperature and pressure conditions, it will decompose into water and gas molecules. The chemical composition of methane hydrate gas is related to various links such as gas source, hydrate formation process, hydrate decomposition process, instrument analysis, data processing, etc. It is not a simple analysis and test of the sample to be tested. At present, the gas composition analysis of methane hydrate can only rely on gas chromatography, which requires carrier gas and multiple chromatographic columns for separation and detection, and generally takes more than ten minutes to dozens of minutes. Summary of the invention

[0005] The purpose of the present invention is to solve the problem of detecting the methane content in combustible ice and provide a method for quickly detecting the methane content in combustible ice.

[0006] To achieve the above object, the technical solution of the present invention is:

[0007] A method for quickly detecting methane content in combustible ice, comprising:

[0008] A combustible ice vacuum decomposition device is used to vacuum decompose the combustible ice sample to completely decompose the combustible ice sample to obtain combustible ice decomposition gas;

[0009] The decomposition gas of methane hydrate was tested using a microscopic confocal laser Raman spectrometer. Based on the obtained Raman spectrum, the corresponding methane spectrum peak area was analyzed and the methane content was calculated using the external standard method.

[0010] Optionally, the combustible ice vacuum decomposition device includes a vacuum pump, an ultra-low temperature bath, a decomposition tank and a vacuum buffer tank;

[0011] The decomposition tank is arranged in the ultra-low temperature bath; the vacuum pumps are provided with two, one vacuum pump is connected to the decomposition tank, and a first air extraction valve is arranged in the connected pipeline; the other vacuum pump is connected to the vacuum buffer tank, and a second air extraction valve is arranged in the connected pipeline; the vacuum buffer tank is also connected to the decomposition tank, and an air release valve is arranged in the connected pipeline.

[0012] Optionally, a pressure sensor and a temperature sensor are provided in the decomposition tank.

[0013] Optionally, the step of using a combustible ice vacuum decomposition device to vacuum decompose the combustible ice sample includes:

[0014] Close the vent valve and the first and second exhaust valves, and wait for the temperature sensor to stabilize at the first target temperature for three minutes. Then, open the lid of the decomposition tank, transfer the combustible ice sample in liquid nitrogen to the decomposition tank, and wait for the temperature sensor of the decomposition tank to stabilize at the first target temperature again.

[0015] Open the vent valve and the first and second exhaust valves, start the two vacuum pumps to evacuate until the pressure sensor reading of the decomposition tank is stable, and the pressure sensor should be no greater than the pressure threshold; close the first and second exhaust valves and the two vacuum pumps, and check the air tightness of the entire combustible ice vacuum decomposition device through the changes in the sensor readings;

[0016] After the entire methane hydrate vacuum decomposition device passes the air tightness test, close the vent valve, set the bath temperature to the second target temperature value and stabilize it for a period of time. When the pressure sensor reading no longer increases, the methane hydrate sample is completely decomposed;

[0017] The decomposition gas is collected into a transparent gas bag that has been evacuated in advance by connecting the sampling port to a suitable interface.

[0018] Optionally, the calculating of the methane content according to the external standard method comprises:

[0019] Measure the Raman peak area of ​​methane in the combustible ice decomposition gas sample to be tested and the Raman peak area of ​​methane in the standard gas, and the molar fraction of methane in the sample to be tested y i Calculate according to the following formula:

[0020] y i =y0(A i / A0)…………………………………………(1)

[0021] in:

[0022] y0 represents the mole fraction of methane in the standard gas, in %;

[0023] A i Represents the Raman peak area of ​​methane in the sample to be tested;

[0024] A0 represents the Raman peak area of ​​methane in the standard gas, where A i The units of both are the same as A0.

[0025] Optionally, the Raman peak area of ​​methane in the standard gas is obtained by:

[0026] Pure methane gas and nitrogen were mixed to prepare methane mixed gases of different concentrations, and the mixed gases were filled into transparent gas bags. The mixed gases of different concentrations were tested using a microscopic confocal laser Raman spectrometer. Based on the obtained Raman spectra, the corresponding methane spectrum peak area was analyzed to serve as the Raman peak area of ​​methane in the standard gas.

[0027] Optionally, the method of testing the combustible ice decomposition gas using a microscopic confocal laser Raman spectrometer and analyzing the corresponding methane spectrum peak area according to the obtained Raman spectrum includes:

[0028] Turn on the microscope confocal laser Raman spectrometer and laser to check whether the optical path is normal. Select the laser wavelength and grating, and after the laser power emitted by the laser is stable, use a single crystal silicon wafer to calibrate the Raman shift spectrum;

[0029] Place the sample transparent air bag on the sample stage and adjust the microscope focus under visible light conditions to focus the light source inside the air bag;

[0030] Set the test parameters, and start the test after the instrument is stable, obtain the Raman spectrum of the sample, and perform corresponding data processing on the spectrum;

[0031] The Raman spectrum of the sample was baseline corrected and the curve was smoothed. The obtained Raman spectrum was curve fitted using the Lorentz-Gaussian linear function to obtain the Raman shift peak position and peak area of ​​the methane molecule.

[0032] Optionally, the first target temperature value is -50°C.

[0033] Optionally, the pressure threshold is 0.1Pa.

[0034] Optionally, the second target temperature value is 20°C.

[0035] Compared with the prior art, the present invention has the following beneficial effects:

[0036] The present invention decomposes combustible ice in a vacuum to obtain pure combustible ice decomposition gas, uses a vacuum pump to draw a decomposition device into a vacuum state, uses a temperature-controllable constant temperature bath to control the decomposition temperature, collects the decomposition gas by using the phase equilibrium relationship of combustible ice, fills the decomposition gas with a transparent air bag and tests the decomposition gas by using a Raman spectrometer, performs baseline correction and curve smoothing on the Raman spectrum of the sample to obtain the methane Raman characteristic peak area, and uses an external standard method to realize rapid detection of the methane content in the combustible ice. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 A flow chart of a method for rapidly detecting methane content in combustible ice provided by an embodiment of the present invention;

[0038] Figure 2 This is a schematic diagram of the composition of the combustible ice vacuum decomposition device;

[0039] Figure 3 This is a typical Raman spectrum of methane;

[0040] In the figure: 1-decomposition tank, 2-vacuum buffer tank, 21-sampling port, 3-vacuum pump, 4-pressure sensor, 5-temperature sensor, 6-first air extraction valve, 7-air release valve, 81-ultra-low temperature bath; 9-second air extraction valve. DETAILED DESCRIPTION

[0041] Example:

[0042] The technical solution of the present invention is further described below in conjunction with the accompanying drawings and embodiments.

[0043] See also Figure 1 As shown, the method for quickly detecting the methane content in combustible ice provided in this embodiment mainly includes the following steps:

[0044] A combustible ice vacuum decomposition device is used to vacuum decompose the combustible ice sample to completely decompose the combustible ice sample to obtain combustible ice decomposition gas;

[0045] In this step, a combustible ice vacuum decomposition device is used to vacuum decompose the combustible ice sample, and pure combustible ice decomposition gas can be obtained to ensure the accuracy of subsequent detection.

[0046] The decomposition gas of methane hydrate was tested using a microscopic confocal laser Raman spectrometer. Based on the obtained Raman spectrum, the corresponding methane spectrum peak area was analyzed and the methane content was calculated using the external standard method.

[0047] In this step, a microscopic confocal laser Raman spectrometer is used to test the decomposition gas of combustible ice. According to the obtained Raman spectrum, the corresponding methane spectrum peak area is analyzed, and the methane content is calculated according to the external standard method, thereby eliminating the need for carrier gas and multiple chromatographic columns for separation and detection. This method is simple, fast, and accurate, and can serve as a beneficial supplement to gas chromatography to enrich the detection methods for analyzing the content of combustible ice components.

[0048] In a specific embodiment, the combustible ice vacuum decomposition device includes a vacuum pump 3, an ultra-low temperature bath 81, a decomposition tank 1, and a vacuum buffer tank 2; the decomposition tank 1 is arranged in the ultra-low temperature bath 81; the vacuum pump 3 is provided with two, one vacuum pump 3 is connected to the decomposition tank 1, and a first air extraction valve 6 is arranged in the connected pipeline; the other vacuum pump 3 is connected to the vacuum buffer tank 2, and a second air extraction valve 9 is arranged in the connected pipeline, and the vacuum buffer tank 2 is provided with a sampling port 21; the vacuum buffer tank 2 is also connected to the decomposition tank 1, and a venting valve 7 is arranged in the connected pipeline. A pressure sensor 4 and a temperature sensor 5 are arranged in the decomposition tank 1.

[0049] By utilizing Figure 2 The combustible ice vacuum decomposition device shown can realize vacuum decomposition of combustible ice samples, which specifically includes the following steps:

[0050] Close the vent valve and the first and second exhaust valves, immerse the decomposition tank in an ultra-low temperature bath filled with ethylene glycol, and after the temperature sensor reading stabilizes at -50°C for three minutes, open the decomposition tank lid and quickly transfer the combustible ice sample in liquid nitrogen to the decomposition tank until the temperature sensor reading of the decomposition tank stabilizes at -50°C again.

[0051] Open the vent valve and the exhaust valve, start the two vacuum pumps to evacuate the air until the pressure sensor reading of the decomposition tank is stable. The pressure sensor should be no greater than 0.1Pa. Close the two exhaust valves and the vacuum pump, and check the air tightness of the entire methane hydrate vacuum decomposition device by the changes in the reading of the decomposition tank pressure sensor.

[0052] After the entire methane hydrate vacuum decomposition device passes the air tightness test, close the air release valve, set the bath temperature to 20°C and stabilize it for a period of time, and when the pressure sensor reading no longer increases, the methane hydrate sample is completely decomposed.

[0053] Connect the sampling port to a suitable interface and collect the decomposition gas into a transparent air bag that has been evacuated in advance. The inflation pressure of the air bag should not be too small and should not exceed 6000Pa. Visual observation should show that the air bag is fully inflated and is not very tight when pressed with fingers.

[0054] Thus, pure combustible ice decomposition gas can be obtained quickly and efficiently through the above-mentioned operation steps.

[0055] In a specific embodiment, the method of testing the decomposition gas of combustible ice using a microscopic confocal laser Raman spectrometer, analyzing the corresponding methane spectrum peak area according to the obtained Raman spectrum, and calculating the methane content according to the external standard method includes:

[0056] Turn on the microscope confocal laser Raman spectrometer and laser to check whether the optical path is normal. Select the laser wavelength and grating, and after the laser power emitted by the laser is stable, use a single crystal silicon wafer to calibrate the Raman shift spectrum.

[0057] Place the prepared sample air bag on the sample stage and adjust the microscope focus under visible light conditions to focus the light source inside the air bag.

[0058] Set the test parameters such as scanning wave number range, laser power, exposure time and integration times. After the instrument is stable, you can start the test, obtain the Raman spectrum of the sample, and perform corresponding data processing on the spectrum.

[0059] Typical Raman spectra of methane from the decomposition of combustible ice are shown in Figure 2 The Raman spectrum of the sample was subjected to baseline correction, curve smoothing and other processing, and the obtained Raman spectrum was curve fitted using the Lorentz-Gaussian linear function to obtain the Raman shift peak position and peak area of ​​the methane molecule.

[0060] Measure the peak area of ​​methane in the sample to be tested and the peak area of ​​methane in the standard gas, and the molar fraction of methane in the sample to be tested y i Calculate according to the following formula:

[0061] y i =y0(A i / A0)…………………………………………(1)

[0062] in:

[0063] y0 represents the mole fraction of methane in the standard gas, in %;

[0064] A i Represents the Raman peak area of ​​methane in the sample to be tested;

[0065] A0 represents the Raman peak area of ​​methane in the standard gas, where A i The units of both are the same as A0.

[0066] The Raman peak area of ​​methane in the standard gas is obtained by the following method:

[0067] Pure methane gas and high-purity nitrogen are mixed to prepare methane mixed gases of different concentrations, and the mixed gases are filled into transparent gas bags. Microscopic confocal laser Raman spectrometer is used to test the mixed gases of different concentrations. Based on the obtained Raman spectrum, the corresponding methane spectrum peak area is analyzed as the Raman peak area of ​​methane in the standard gas. Finally, the Raman peak area is used to make a standard curve for methane concentration.

[0068] In summary, the present invention decomposes combustible ice in a vacuum to obtain pure combustible ice decomposition gas, uses a vacuum pump to draw the decomposition device to a vacuum state, and uses a temperature-controllable constant temperature bath to control the decomposition temperature, collects the decomposition gas by using the phase equilibrium relationship of combustible ice, fills the decomposition gas with a transparent air bag and tests the decomposition gas with a Raman spectrometer, performs baseline correction and curve smoothing on the Raman spectrum of the sample to obtain the Raman characteristic peak area, and uses an external standard method to achieve rapid detection of the methane content in combustible ice.

[0069] The above embodiments are only for illustrating the technical concept and features of the present invention, and their purpose is to enable ordinary technicians in the field to understand the content of the present invention and implement it accordingly, and they cannot be used to limit the protection scope of the present invention. Any equivalent changes or modifications made based on the essence of the content of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for rapidly detecting the methane content in combustible ice, characterized in that: include: A combustible ice vacuum decomposition device is used to vacuum decompose the combustible ice sample to completely decompose the combustible ice sample to obtain combustible ice decomposition gas; The decomposition gas of methane hydrate was tested using a microscopic confocal laser Raman spectrometer. Based on the obtained Raman spectrum, the corresponding methane spectrum peak area was analyzed and the methane content was calculated using the external standard method.

2. The method for rapidly detecting methane content in combustible ice according to claim 1, characterized in that: The combustible ice vacuum decomposition device comprises a vacuum pump, an ultra-low temperature bath, a decomposition tank and a vacuum buffer tank; The decomposition tank is arranged in the ultra-low temperature bath; the vacuum pumps are provided with two, one vacuum pump is connected to the decomposition tank, and a first air extraction valve is arranged in the connected pipeline; the other vacuum pump is connected to the vacuum buffer tank, and a second air extraction valve is arranged in the connected pipeline; the vacuum buffer tank is also connected to the decomposition tank, and an air release valve is arranged in the connected pipeline.

3. The method for rapidly detecting methane content in combustible ice according to claim 1, characterized in that: A pressure sensor and a temperature sensor are arranged in the decomposition tank.

4. The method for rapidly detecting methane content in combustible ice according to claim 1, characterized in that: The method of using the combustible ice vacuum decomposition device to vacuum decompose the combustible ice sample comprises: Close the vent valve and the first and second exhaust valves, and wait for the temperature sensor to stabilize at the first target temperature value for three minutes, then open the lid of the decomposition tank, transfer the combustible ice sample in liquid nitrogen to the decomposition tank, and wait for the temperature sensor of the decomposition tank to stabilize at the first target temperature value again; Open the vent valve and the first and second exhaust valves, start the two vacuum pumps to evacuate until the pressure sensor reading of the decomposition tank is stable, and the pressure sensor should be no greater than the pressure threshold; close the first and second exhaust valves and the two vacuum pumps, and check the air tightness of the entire combustible ice vacuum decomposition device through the changes in the sensor readings; After the entire methane hydrate vacuum decomposition device passes the air tightness test, close the vent valve, set the bath temperature to the second target temperature value and stabilize it for a period of time. When the pressure sensor reading no longer increases, the methane hydrate sample is completely decomposed; The decomposition gas is collected into a transparent gas bag that has been evacuated in advance by connecting the sampling port to a suitable interface.

5. The method for rapidly detecting methane content in combustible ice according to claim 1, characterized in that: The method of calculating the methane content according to the external standard method comprises: Measure the Raman peak area of ​​methane in the combustible ice decomposition gas sample to be tested and the Raman peak area of ​​methane in the standard gas, and the molar fraction of methane in the sample to be tested y i Calculate according to the following formula: and i =y0(A i / A0)……………………………………(1) in: y0 represents the mole fraction of methane in the standard gas, in %; A i Represents the Raman peak area of ​​methane in the sample to be tested; A0 represents the Raman peak area of ​​methane in the standard gas, where A i The units of both are the same as A0.

6. The method for rapidly detecting the methane content in combustible ice according to claim 5, characterized in that: The Raman peak area of ​​methane in the standard gas is obtained by the following method: Pure methane gas and nitrogen were mixed to prepare methane mixed gases of different concentrations, and the mixed gases were filled into transparent gas bags. The mixed gases of different concentrations were tested using a microscopic confocal laser Raman spectrometer. Based on the obtained Raman spectra, the corresponding spectral peak areas were analyzed to serve as the Raman peak area of ​​methane in the standard gas.

7. The method for rapidly detecting methane content in combustible ice according to claim 1, characterized in that: The method of using a microscopic confocal laser Raman spectrometer to test the combustible ice decomposition gas and analyzing the corresponding methane spectrum peak area according to the obtained Raman spectrum includes: Turn on the microscope confocal laser Raman spectrometer and laser to check whether the optical path is normal. Select the laser wavelength and grating, and after the laser power emitted by the laser is stable, use a single crystal silicon wafer to calibrate the Raman shift spectrum; Place the sample transparent air bag on the sample stage and adjust the microscope focus under visible light conditions to focus the light source inside the air bag; Set the test parameters, and start the test after the instrument is stable, obtain the Raman spectrum of the sample, and perform corresponding data processing on the spectrum; The Raman spectrum of the sample was baseline corrected and the curve was smoothed. The obtained Raman spectrum was curve fitted using the Lorentz-Gaussian linear function to obtain the Raman shift peak position and peak area of ​​the methane molecule.

8. The method for rapidly detecting the methane content in combustible ice according to claim 4, characterized in that: The first target temperature value is -50°C.

9. The method for rapidly detecting the methane content in combustible ice according to claim 4, characterized in that: The pressure threshold is 0.1Pa.

10. The method for rapidly detecting the methane content in combustible ice according to claim 4, characterized in that: The second target temperature value is 20°C.

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