Device and method of gas hydrate pressure maintaining replacement for in-situ Raman analysis

Abstract

The invention discloses a gas hydrate pressure maintaining replacement device and method for in-situ Raman analysis. Comprehensive experiments such as the formation/decomposition/displacement of high-pressure gas hydrates can be realized, and in-situ Raman characterization can be performed. Including reaction kettle system with temperature control unit, pressure control gas supply system, pressure holding system, replacement gas system, sample pre-cooling system, vacuum system and data acquisition and processing system. The device can solve the problem that the Raman peak position of the 512 cage is covered by the Raman peak position of the gas when the high-pressure gas hydrate is characterized in situ in the reaction kettle, at the same time, it solves the problems of sampling difficulties in ex-situ Raman characterization and experimental errors caused by sample transfer.

Claims

1. A gas hydrate pressure-maintaining replacement device for in-situ Raman analysis, wherein the device includes a Raman spectrometer, a reaction kettle system, a sample pre-cooling system, a pressure-controlled gas supply system, a pressure-maintaining system, a vacuum system and a data acquisition and processing system; wherein a reactor system is placed on a XY operating table of the Raman spectrometer; the reaction kettle system includes a visual hydrate reaction kettle, a temperature sensor, and a liquid nitrogen temperature control component; a window is provided on the top surface of the visual hydrate reaction kettle, and a liquid nitrogen inlet/outlet is provided on the side of the visual hydrate reaction kettle for temperature control; the temperature sensor is set on a sample table in the visual hydrate reaction kettle, the visual hydrate reaction kettle is covered with a plastic insulation shell; a casing is equipped with a liquid nitrogen purge pipe to maintain an overall low temperature state of the visual hydrate reaction kettle and prevent frosting in the window from hindering measurement; the pressure-controlled gas supply system includes a pressure regulating valve A and a replaced gas cylinder connected by a pipeline to provide stable replaced gas to generate initial hydrate; the pressure-maintaining system includes a pressure regulating valve B and an isotope gas cylinder connected through a pipeline, the pressure regulating valve B is used to adjust the pressure of the pipeline, and isotope gas is used to maintain the pressure after exhausting the displaced gas; the sample pre-cooling system includes a water bath and an attached temperature control unit; an entrance of the sample pre-cooling system is connected to the pressure-maintaining system and the pressure-controlled gas supply system, wherein the pressure-maintaining system and the pressure-controlled gas supply system are parallel, which is to pre-cool gas provided in the pressure-control gas supply system or the pressure-maintaining system; an outlet of the sample pre-cooling system is connected to the reactor system, and sends the gas after pre-cooling to a reactor; a displacement gas system includes a plunger pump, an anti-corrosion pressure regulating valve and a CO.sub.2 gas cylinder connected in sequence by a pipeline; the plunger pump is used to accurately adjust the pressure in a CO.sub.2 pipeline, and the anti-corrosion pressure regulating valve and CO.sub.2 gas cylinder are used to provide a replacement gas CO.sub.2; the vacuum system includes a vacuum pump connected to a pipeline by a pipe joint, which is used to evacuate the visual hydrate reaction kettle before a reaction, to eliminate the influence of impurity gases in the visual hydrate reaction kettle, and to quickly exhaust after the reaction; the data acquisition and processing system is used to collect the temperature from the temperature sensor and the data of the Raman spectrum of the sample for analysis.

2. A method for using the gas hydrate pressure-maintaining replacement device for in-situ Raman analysis of claim 1, wherein the method includes the following steps: Step 1: deionized water is added to the visual hydrate reaction kettle, and the temperature sensor and liquid nitrogen temperature control component are used to reduce the temperature of the visual hydrate reaction kettle to below 0° C. to freeze the deionized water; a vacuum pump and valve is turned on after the temperature is stable, and the vacuum pump and valve are closed after evacuating the reactor; Step 2: a needle valve is closed that is located at a connection between the sample pre-cooling system and the reactor; a knob of the replaced gas cylinder is unscrewed that is located in the pressure-controlled gas supply system, and the pressure regulating valve A adjusts the gas pressure in the pipeline to a target pressure, and let it stand until a digital pressure gauge shows that the pressure is stable; at this time, the pre-cooling of the replaced gas is completed; the needle valve of a precooling device is opened to send the replaced gas into the visual hydrate reaction kettle, at the same time a reaction temperature is raising to a desired temperature; Step 3: determine a hydrate formation by Raman spectroscopy; when the formation of methane hydrate is complete, that is, the cage occupancy rate is more than 90%, the temperature of the visual hydrate reaction kettle is reduced to below −80° C. through the liquid nitrogen temperature control component; the vacuum pump is turned on to draw vacuum after the temperature is stable, and then the vacuum pump and a needle valve of the pressure-controlled gas supply system and the sample pre-cooling system are closing after vacuuming; a needle valve of the pressure-maintaining system is opened and a knob of the isotope gas cylinder is unscrewed, then the pressure in a gas pipeline is adjusted to the target pressure; the isotope gas in the sample pre-cooling system is pre-cooled; the needle valve of the sample pre-cooling system is opened to pass the pre-cooled isotope gas into the reactor to maintain the pressure; Step 4: a gas end valve of a pressure holding system is closed and the CO.sub.2 gas cylinder of a replacement gas system is opened; the anti-corrosion pressure regulating valve is adjusted to the required pressure, and a plunger pump valve is opened; so that CO.sub.2 gas could be pre-cooled through the sample pre-cooling system; Step 5: the needle valve of the sample pre-cooling system is opened to pass the pre-cooled CO.sub.2 gas into the reactor, after the ventilation is completed, the temperature is raised to a replacement temperature; Step 6: in steps 1 to 5, the temperature parameters in the reactor are collected by the temperature sensor, and spectral data is collected by Raman spectroscopy at regular intervals to monitor the hydrate formation and filling rate changes in the reactor in real time.

3. The method according to claim 2, wherein the replaced gas is one or a mixture of two or more of methane, ethane, and propane.

Description

BRIEF DESCRIPTION

(1) FIG. 1: a schematic diagram of an experimental apparatus of the present invention suitable for in-situ Raman characterization of gas hydrate replacement.

(2) In the figure: 1 Computer; 2 Raman spectrometer; 3 Visualized hydrate reactor; 4 Pre-cooled spiral pipe; 5 Vacuum pump; 6 Digital display pressure gauge; 7 pressure regulating valve A; 8 replaced gas cylinder; 9 pressure regulating valve B; 10 Isotope gas cylinder; 11 plunger pump; 12 Anti-corrosion pressure regulating valve C; 13 Replacement gas cylinder.

(3) FIG. 2: the in-situ Raman experimental data of deuterated methane gas to maintain methane hydrate.

DETAILED DESCRIPTION

Example 1

(4) This embodiment is an experimental device suitable for in-situ Raman characterization of CO.sub.2 displacement high-pressure methane hydrate formation/decomposition/displacement by pressure-holding method. Taking the experiment of replacing methane hydrate with CO.sub.2 as an example, referring to FIG. 1, the experimental process is as follows: The replaced gas cylinder 8 is filled with high-purity methane gas with a purity of 99.99%, the isotope gas cylinder 10 is filled with scientific grade full deuterium methane gas with a purity of 99.98%, and the replacement gas cylinder 13 is filled with 98.99% purity gas; Step 1: Firstly, deionized water is added to the reactor 3. Secondly, the temperature sensor and liquid nitrogen temperature control components are used to reduce the temperature of the reactor 3 to below 0° C. to freeze the deionized water and prevent the water from being drawn out of the reactor 3 due to vacuum. Thirdly, the vacuum pump 5 and the valve are turned on, so that the reaction kettle 3 is evacuated and the vacuum pump 5 and the valve is closed after the sample freezing; Step 2: Firstly, the needle valve is closed which is located at the connection between the sample pre-cooling device 4 and the reaction kettle 3. Secondly, the knob of the methane gas cylinder is unscrewed which located in the pressure-controlled gas supply system and the pressure regulating valve A 7 is adjusted to make the gas pressure in the pipeline the target pressure, and let it stand until the digital pressure gauge 6 shows that the pressure is stable. Now the temperature is adjusted to the target temperature. Thirdly, the needle valve of the sample pre-cooling device 4 is opened to send the pre-cooled methane body to the reaction kettle 3, and at the same time the reaction temperature is raised to the target temperature, you can see that the hydrate quickly forms when it approaches the target temperature; Step 3: Determine the hydrate formation by Raman spectroscopy 2. When the formation of methane hydrate is complete, that is, the cage occupancy rate is more than 90%, the temperature of the reaction kettle 3 is reduced to below −80° C. through the liquid nitrogen temperature control component. The experimental results show that the hydrate decomposition is extremely slow at −80° C., and the hydrate decomposition is less than 0.1% during the replacement for 1 hour. Firstly, the vacuum pump 5 is turned on for vacuuming after the temperature is stable, and the vacuum pump 5 and the needle valves, the pressure-controlled gas supply system and the pre-cooling system 4, are turned off after vacuuming. Secondly, the needle valve of the pressure holding system is opened and the knob of the fully deuterated methane gas cylinder 10 is unscrewed, and the pressure in the gas pipeline is adjusted to the target pressure, so that the fully deuterated methane body is pre-cooled in the pre-cooling system to prevent gas from the decomposes by the heat of gas. Thirdly, the needle valve of the pre-cooling system 4 is opened to pass the pre-cooled fully deuterated methane gas into the reactor 3 to maintain the pressure; Step 4: The gas valve of the pressure-holding system is closed, and the carbon dioxide gas cylinder 13 of the carbon dioxide gas system is opened. The anti-corrosion pressure regulating valve is adjusted to the required pressure. Secondly, the valve of the plunger pump 11 is opened, so that the carbon dioxide gas is pre-cooled through the sample pre-cooling system 4 to prevent the gas from decomposition by the carrying heat of gas; Step 5: The needle valve of the pre-cooling system 4 is opened to allow the pre-cooled carbon dioxide gas to pass into the reactor 3, and after the ventilation is completed, the temperature is raised to the replacement temperature, and the pressure is adjusted to maintain the pressure in the reactor 3 at the target pressure; and Step 6: In steps 1 to 5, the temperature parameters in the reactor 3 are collected by temperature sensors. The spectral data is collected by Raman spectrometer 2 at regular intervals to monitor the hydrate formation and filling rate changes in the reactor 3 in real time.

(5) Deuterated methane gas maintains the in-situ Raman experimental data of methane hydrate, as shown in FIG. 2. The figure shows the Raman spectrum after maintaining the partial pressure of methane hydrate with deuterated methane for 1 h. Among them, the C—H symmetric stretching vibration peak of methane hydrate is 2904 cm.sup.−1, and the gas phase peak of deuterated methane is 2103 cm.sup.−1. The experimental results show that deuterated methane can maintain methane hydrate without decomposition.

Example 2

(6) Taking the experiment of replacing ethane hydrate with CO.sub.2 as an example, referring to FIG. 1, the experimental process is as follows:

(7) The replaced gas cylinder 8 is filled with high-purity ethane gas with a purity of 99.99%, the isotope gas cylinder 10 is filled with scientific grade all-deuterium ethane gas with a purity of 99.98%, and the replacement gas cylinder 13 is filled with a purity of 98.99% CO.sub.2 gas;

(8) Experimental steps 1-6 are the same as in Example 1. Raman peak of C—H of ethane is between 2850-2950 cm.sup.−1, Raman peak of C-D of deuterated ethane is between 2050-2150 cm.sup.−1, similar to methane. Deuterated ethane can maintain the partial pressure of ethane, so in-situ Raman spectroscopy can be performed.

Example 3

(9) This embodiment is a CO.sub.2 displacement gas hydrate generation displacement experiment device suitable for in-situ Raman characterization by pressure-holding method. Taking the experiment of CO.sub.2 replacement of natural gas hydrate as an example, combined with FIG. 1, the experimental process is as follows:

(10) The gas cylinder 8 to be replaced is a mixture of 95% methane and 5% ethane or propane in any ratio. A proportion of mixed gas, the replacement gas cylinder 13 is filled with CO.sub.2 gas with a purity of 98.99%;

(11) Experimental steps 1-6 are the same as in Example 1. The Raman peak of C—H of natural gas is between 2850-2950 cm.sup.−1, and the Raman peak of C-D of deuterated gas is between 2050-2150 cm.sup.−1.

(12) Although the patent technology is described above with reference to the drawings, the patent technology is not limited to the above-mentioned embodiment and the above-mentioned experimental gas. The above usage is only for illustration, not for limitation. Under the inspiration of the present invention, the modifications made without departing from the present invention all fall within the protection of the present invention.