Method for rapidly detecting methane content in combustible ice

Abstract

The application discloses a method for rapidly detecting the content of methane in combustible ice, and comprises the following steps: using a combustible ice vacuum decomposition device to perform vacuum decomposition on a combustible ice sample, so that the combustible ice sample is completely decomposed to obtain combustible ice decomposition gas; using a microscopic confocal laser Raman spectrometer to test the combustible ice decomposition gas; according to the obtained Raman spectrum, analyzing the corresponding methane spectrum peak area; and according to the external standard method, calculating the content of methane. The combustible ice is placed in vacuum for decomposition to obtain pure combustible ice decomposition gas; a vacuum pump is used to extract the decomposition device to a vacuum state; a constant temperature bath with controllable temperature is used to control the decomposition temperature; the phase equilibrium relationship of the combustible ice is used to collect the decomposition gas; a transparent gas bag is used to fill the decomposition gas; the Raman spectrometer is used to test the decomposition gas; the Raman spectrum of the sample is subjected to baseline correction, curve smoothing and other treatments to obtain the Raman characteristic peak area; and the external standard method is used to realize the rapid detection of the content of methane in the combustible ice.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of combustible ice component content detection, and particularly relates to a method for rapidly detecting methane content in combustible ice. BACKGROUND

[0002] Combustible ice, also known as natural gas hydrate, is an ice-like crystalline substance formed by natural gas and water under high pressure and low temperature conditions. Combustible ice is distributed in deep sea or land permafrost, and only a small amount of carbon dioxide and water is generated after combustion, which is much less polluting than coal, oil and other fossil fuels. The reserves are huge, and the carbon equivalent is twice the total reserves of coal, oil and natural gas in the world, so it is internationally recognized as a replacement energy for fossil fuels such as oil. Because combustible ice has a special cage structure and strong gas storage capacity, it is a high-energy-density solid material, so it has broad prospects in the field of solid storage and transportation of natural gas.

[0003] In terms of detection technology, research teams at home and abroad have also done a lot of exploratory work. X-ray diffractometer, laser Raman spectrometer, nuclear magnetic resonance spectrometer, differential scanning calorimeter, scanning electron microscope, gas chromatograph, X-CT scanning system, isotope ratio instrument and other equipment are used to study the physical and chemical properties of combustible ice.

[0004] Combustible ice stably exists in a special temperature and pressure environment, and will decompose into water and gas molecules once it is separated from the appropriate temperature and pressure conditions. The chemical composition of combustible ice gas is related to the source of the gas, the hydrate formation process, the hydrate decomposition process, instrument analysis, data processing and other aspects, and is not a simple analysis and testing of the sample to be tested. At present, the gas composition analysis of combustible ice can only rely on gas chromatography, which requires carrier gas and multiple chromatographic columns for separation and detection, and generally takes tens of minutes. SUMMARY

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

[0006] To achieve the above-mentioned purpose, the technical solution of the present application is:

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

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

[0009] A microscopic confocal laser Raman spectrometer is used to test the combustible ice decomposition gas, analyze the corresponding methane spectrum peak area according to the obtained Raman spectrum, and calculate the methane content according to the external standard method.

[0010] Optionally, the combustible ice vacuum decomposition device comprises a vacuum pump, an ultralow-temperature bath, a decomposition tank and a vacuum buffer tank.

[0011] The decomposition tank is arranged in the ultralow-temperature bath; the vacuum pump is provided with two, one vacuum pump is connected with the decomposition tank and provided with a first air extraction valve in the connected pipeline; one vacuum pump is connected with the vacuum buffer tank and provided with a second air extraction valve in the connected pipeline; the vacuum buffer tank is further connected with the decomposition tank and provided with an air release valve in the connected pipeline.

[0012] Optionally, the decomposition tank is provided with a pressure sensor and a temperature sensor.

[0013] Optionally, the combustible ice vacuum decomposition device comprises:

[0014] The air release valve and the first and second air extraction valves are closed, and after the temperature sensor reading is stable at the first target temperature value for three minutes, the decomposition tank cover is opened, the combustible ice sample in the liquid nitrogen is transferred to the decomposition tank, and the temperature sensor reading of the decomposition tank is stable at the first target temperature value again.

[0015] The air release valve and the first and second air extraction valves are opened, and the two vacuum pumps are started to extract vacuum until the pressure sensor reading of the decomposition tank is stable, and the pressure sensor should be not more than the pressure threshold value; the first and second air extraction valves and the two vacuum pumps are closed, and the air tightness of the entire combustible ice vacuum decomposition device is checked through the sensor reading change;

[0016] After the air tightness test of the entire combustible ice vacuum decomposition device is passed, the air release valve is closed, the bath temperature is set to the second target temperature value and stabilized for a period of time, and when the pressure sensor reading no longer increases, the combustible ice sample is completely decomposed;

[0017] The decomposition gas is collected into a pre-vacuumized transparent gas bag through the sampling port and a suitable interface.

[0018] Optionally, the methane content is calculated according to the external standard method, comprising:

[0019] The Raman peak area of methane in the combustible ice decomposition gas sample to be measured and the Raman peak area of methane in the standard gas are measured, and the mole fraction y of methane in the sample to be measured i According to the following formula:

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

[0021] Wherein:

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

[0023] A i The Raman peak area represents the methane content in the sample being tested.

[0024] A0 represents the Raman peak area of ​​methane in standard gas, where A i Both A0 and A0 use the same unit.

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

[0026] Methane mixtures of different concentrations were prepared by mixing pure methane gas and nitrogen gas. The mixtures were filled into transparent gas bags, and the mixtures of different concentrations were tested using a microconfocal laser Raman spectrometer. Based on the obtained Raman spectra, the corresponding methane peak areas were analyzed to serve as the Raman peak areas of methane in the standard gas.

[0027] Optionally, the step of using a microconfocal laser Raman spectrometer to test the decomposition gas of combustible ice, and analyzing the corresponding methane peak area based on the obtained Raman spectrum, includes:

[0028] Turn on the microconfocal laser Raman spectrometer and laser, and check if the optical path is normal. Select the laser wavelength and grating, and after the laser power emitted by the laser stabilizes, perform Raman shift spectroscopy calibration using a single-crystal silicon wafer;

[0029] Place the transparent gas bag of the sample on the sample stage, and adjust the microscopic focus under visible light conditions to focus the light source inside the gas bag.

[0030] Set the test parameters, and once the instrument is stable, you can start the test to obtain the Raman spectrum of the sample and perform corresponding data processing on the spectrum.

[0031] Baseline correction and curve smoothing were performed on the Raman spectra of the samples. The obtained Raman spectra were then curve-fitted using the Lorentz-Gaussian line shape function to obtain the Raman shift peak position and peak area of ​​methane molecules.

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

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

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

[0035] Compared with the prior art, the advantages of this invention are as follows:

[0036] The present application obtains pure combustible ice decomposition gas by decomposing combustible ice in vacuum, uses a vacuum pump to extract the decomposition device to a vacuum state, uses a constant temperature bath with controllable temperature to control the decomposition temperature, collects the decomposition gas by using the phase equilibrium relationship of combustible ice, fills the decomposition gas through a transparent gas bag, and tests the decomposition gas by using a Raman spectrometer, processes the Raman spectrum of the sample by baseline correction and curve smoothing to obtain the methane Raman characteristic peak area, and realizes rapid detection of the methane content in combustible ice by using an external standard method. BRIEF DESCRIPTION OF DRAWINGS

[0037] Figure 1 The flowchart of the method for rapidly detecting the methane content in combustible ice provided by the embodiment of the present application is shown in the figure.

[0038] Figure 2 The composition schematic diagram of the combustible ice vacuum decomposition device is shown in the figure.

[0039] Figure 3 The typical Raman spectrum of methane is shown in the figure.

[0040] In the figure, 1 is a decomposition tank, 2 is a vacuum buffer tank, 21 is a sampling port, 3 is a vacuum pump, 4 is a pressure sensor, 5 is a temperature sensor, 6 is a first air extraction valve, 7 is a gas exhaust valve, 81 is an ultralow temperature bath, and 9 is a second air extraction valve. DETAILED DESCRIPTION

[0041] Embodiment:

[0042] The technical solutions of the present application will be further described in combination with the drawings and embodiments.

[0043] Referring to Figure 1 The method for rapidly detecting the methane content in combustible ice provided by the embodiment mainly includes the following steps:

[0044] The combustible ice sample is vacuum decomposed by using the combustible ice vacuum decomposition device, so that the combustible ice sample is completely decomposed, and combustible ice decomposition gas is obtained.

[0045] In this step, the combustible ice sample is vacuum decomposed by using the combustible ice vacuum decomposition device, so that pure combustible ice decomposition gas is obtained, thereby ensuring the accuracy of subsequent detection.

[0046] The combustible ice decomposition gas is tested by using a microscopic confocal laser Raman spectrometer, the corresponding methane spectrum peak area is analyzed according to the obtained Raman spectrum, and the methane content is calculated according to an external standard method.

[0047] In this step, the combustible ice decomposition gas is tested by using a confocal laser Raman spectrometer, 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, so that the separation detection is carried out without carrier gas and multiple chromatographic columns, the method is simple, fast and accurate, can be used as a beneficial supplement to gas chromatography, and enriches the detection means of combustible ice component content analysis.

[0048] In a specific embodiment, the combustible ice vacuum decomposition device comprises a vacuum pump 3, an ultralow-temperature bath 81, a decomposition tank 1, and a vacuum buffer tank 2; the decomposition tank 1 is arranged in the ultralow-temperature bath 81; the vacuum pump 3 is provided with two, one vacuum pump 3 is connected with the decomposition tank 1, and a first air extraction valve 6 is arranged in the connected pipeline; one vacuum pump 3 is connected with 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 with the decomposition tank 1, and a gas release valve 7 is arranged in the connected pipeline. The pressure sensor 4 and the temperature sensor 5 are arranged in the decomposition tank 1.

[0049] By using Figure 2 The combustible ice vacuum decomposition device shown in the figure can realize vacuum decomposition of the combustible ice sample, and specifically comprises the following steps:

[0050] Close the gas release valve and the first and second air extraction valves, immerse the decomposition tank in the ultralow-temperature bath containing ethylene glycol, wait for the temperature sensor to show that the number is stable at-50℃ for three minutes, open the decomposition tank cover, quickly transfer the combustible ice sample in liquid nitrogen to the decomposition tank, and wait for the temperature sensor of the decomposition tank to show that the number is stable at-50℃ again.

[0051] Open the gas release valve and the air extraction valve, start the two vacuum pumps to extract vacuum until the pressure sensor of the decomposition tank shows that the number is stable, and the pressure sensor should be not more than 0.1Pa; close the two air extraction valves and the vacuum pump, and check the air tightness of the entire combustible ice vacuum decomposition device through the change of the pressure sensor of the decomposition tank.

[0052] After the air tightness test of the entire combustible ice vacuum decomposition device is passed, close the gas release valve, set the bath temperature to 20℃ and stabilize for a period of time, and when the pressure sensor shows that the number is no longer increased, the combustible ice sample is completely decomposed.

[0053] Connect the sampling port with a suitable interface, collect the decomposition gas into a transparent gas bag which has been pre-vacuumized, the inflation pressure of the gas bag should not be too small, nor exceed 6000Pa; directly observe that the gas bag is fully inflated, and it is appropriate that the gas bag is not very tight when pressed by fingers.

[0054] In this way, the pure combustible ice decomposition gas can be quickly and efficiently obtained through the above operation steps.

[0055] In a specific embodiment, the combustible ice decomposition gas is tested by using a confocal laser Raman spectrometer, according to the obtained Raman spectrum, the corresponding methane spectrum peak area is analyzed, and the methane content is calculated according to an external standard method, comprising:

[0056] Turn on the confocal laser Raman spectrometer and the laser, and 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 gas bag on the sample stage, and adjust the microfocus under visible light conditions so that the light source is focused inside the gas bag.

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

[0059] The typical Raman spectrum of methane in combustible ice decomposition gas is shown in Figure 2 The Raman spectrum of the sample is processed by baseline correction and curve smoothing, and the Raman spectrum obtained is curve-fitted by using a Lorentz-Gaussian linear function to obtain the Raman shift peak position and peak area of methane molecules.

[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 mole fraction y i According to the following formula:

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

[0062] Wherein:

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

[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, wherein A i and A0 have the same unit.

[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 gas are mixed to prepare methane mixed gas with different concentrations, the mixed gas is filled into a transparent gas bag, and different concentrations of the mixed gas are tested by using a confocal laser Raman spectrometer; according to the obtained Raman spectrum, the corresponding methane spectrum peak area is analyzed to serve as the Raman peak area of methane in the standard gas; finally, the Raman peak area is used to draw a standard curve of the methane concentration.

[0068] As can be seen, the combustible ice is placed in a vacuum for decomposition to obtain pure combustible ice decomposition gas, the decomposition device is extracted to a vacuum state by using a vacuum pump, a constant-temperature bath with controllable temperature is used to control the decomposition temperature, the decomposition gas is collected by using the phase equilibrium relationship of the combustible ice, the decomposition gas is filled into a transparent gas bag and tested by using a Raman spectrometer, the Raman spectrum of the sample is processed by baseline correction and curve smoothing to obtain the Raman characteristic peak area, and the external standard method is used to realize rapid detection of the methane content in the combustible ice.

[0069] The above examples are only used for illustrating the technical concept and characteristics of the present application, and the purpose is to enable those skilled in the art to understand the present application and implement it, and cannot limit the protection scope of the present application. Any equivalent changes or modifications made according to the essence of the present application should be covered within the protection scope of the present application.

Claims

1. A method for rapidly detecting methane content in combustible ice, characterized in that, include: A vacuum decomposition device for combustible ice was used to decompose the combustible ice sample in a vacuum, so as to completely decompose the combustible ice sample and obtain combustible ice decomposition gas. The decomposition gas of combustible ice was tested using a microconfocal laser Raman spectrometer. Based on the obtained Raman spectra, the corresponding methane peak areas were analyzed, and the methane content was calculated using the external standard method. The combustible ice vacuum decomposition device includes a vacuum pump, an ultra-low temperature bath, a decomposition tank, and a vacuum buffer tank. The decomposition tank is located in the cryogenic bath; two vacuum pumps are provided, one of which is connected to the decomposition tank and has a first suction valve in the connecting pipeline; the other vacuum pump is connected to the vacuum buffer tank and has a second suction valve in the connecting pipeline; the vacuum buffer tank is also connected to the decomposition tank and has a venting valve in the connecting pipeline. A pressure sensor and a temperature sensor are installed in the decomposition tank; The method of using a combustible ice vacuum decomposition device to decompose combustible ice samples in a vacuum includes: Close the vent valve and the first and second vent valves. After the temperature sensor reading stabilizes at the first target temperature value for three minutes, open the decomposition tank lid and transfer the combustible ice sample in the liquid nitrogen into the decomposition tank. Wait for the temperature sensor reading in the decomposition tank to stabilize at the first target temperature value again. Open the vent valve and the first and second suction valves, start the two vacuum pumps to evacuate until the pressure sensor reading of the decomposition tank stabilizes and the pressure sensor reading is not greater than the pressure threshold; close the first and second suction valves and the two vacuum pumps, and check the airtightness of the entire combustible ice vacuum decomposition device by the change in the sensor reading. After the air tightness test of the entire combustible ice vacuum decomposition device is passed, 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 combustible ice sample is completely decomposed. The decomposed gas is collected into a pre-vacuumed transparent gas bag by connecting the sampling port to a suitable interface. The calculation of methane content based on the external standard method includes: The Raman peak area of ​​methane in the sample of combustible ice decomposition gas and the Raman peak area of ​​methane in the standard gas were measured, and the mole fraction of methane in the sample was determined. i Calculate using 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 The Raman peak area represents the methane content in the sample being tested. A0 represents the Raman peak area of ​​methane in standard gas, where A i Both A0 and A0 use the same unit.

2. The method for rapid detection of methane content in combustible ice as described in claim 1, characterized in that, The Raman peak area of ​​methane in the standard gas was obtained as follows: Methane mixtures of different concentrations were prepared by mixing pure methane gas and nitrogen gas. The mixtures were filled into transparent gas bags, and the mixtures of different concentrations were tested using a microconfocal laser Raman spectrometer. The corresponding peak areas were analyzed based on the obtained Raman spectra and used as the Raman peak areas of methane in the standard gas.

3. The method for rapid detection of methane content in combustible ice as described in claim 1, characterized in that, The method involves using a microconfocal laser Raman spectrometer to test the decomposition gas of methane hydrate, and analyzing the corresponding methane peak area based on the obtained Raman spectrum, including: Turn on the microconfocal laser Raman spectrometer and laser, check if the optical path is normal, select the laser wavelength and grating, and after the laser power emitted by the laser stabilizes, use a single crystal silicon wafer to perform Raman shift spectrum calibration. Place the transparent gas bag of the sample on the sample stage, and adjust the microscopic focus under visible light conditions to focus the light source inside the gas bag. Set the test parameters, and once the instrument is stable, you can start the test to obtain the Raman spectrum of the sample and perform corresponding data processing on the spectrum. Baseline correction and curve smoothing were performed on the Raman spectra of the samples. The obtained Raman spectra were then curve-fitted using the Lorentz-Gaussian line shape function to obtain the Raman shift peak position and peak area of ​​methane molecules.

4. The method for rapid detection of methane content in combustible ice as described in claim 1, characterized in that, The first target temperature is -50℃.

5. The method for rapid detection of methane content in combustible ice as described in claim 1, characterized in that, The pressure threshold is 0.1 Pa.

6. The method for rapid detection of methane content in combustible ice as described in claim 1, characterized in that, The second target temperature is 20°C.

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