CN115090216A - A Visualized Low-Temperature High-Pressure Reactor for Monitoring the Multiphysics Response of Gas Hydrate Phase Change Process - Google Patents

Abstract

The invention provides a visual low-temperature high-pressure reaction kettle for monitoring multi-physical field response in a gas hydrate phase change process. The reaction kettle is of a special-shaped fan-shaped structure, the temperature and pressure sensors are distributed in the radial direction of the bottom surface and the back surface of the kettle in an equidifferent manner, the positions close to the circle center are distributed more densely, and the temperature field and the pressure field of a severe phase change region of the gas hydrate are accurately monitored. The high-pressure air bags are arranged on the upper cover and the side surface to apply overlying pressure and confining pressure on the stratum, so that a real pressure environment is simulated. And a full-visual large window is adopted on the front surface of the kettle, and the spatial and temporal evolution of a flow field, a saturation field and a strain field in the phase change process of the gas hydrate is analyzed by a PIV (particle image velocimetry) and DIC (digital information computer) method. Compared with the traditional cylindrical reaction kettle, the structural design of the sector and the modeling of the numerical geometric model have natural accurate matching, and transient, multi-point and nondestructive thermal-flow-force-based multi-physical-field monitoring of the whole phase change process of the gas hydrate is realized by more reasonable sensor arrangement and visual window monitoring.

Description

A visualization of low temperature and high temperature for monitoring the multiphysics response of gas hydrate phase transition processes pressure reactor

technical field

The invention belongs to the technical field of research on basic physical properties of gas hydrate, and relates to a visualized low-temperature high-pressure reaction kettle with multi-physical field response in a gas hydrate phase transition process.

Background technique

Gas hydrate is a crystalline compound formed by gas and water at low temperature and high pressure. Natural gas hydrate in frozen soil and deep-sea sediments is a kind of clean energy with huge reserves. Its safe and efficient development is a solution. An important way of energy shortage; carbon dioxide hydrate, as a technical application of carbon sequestration, is of great significance for carbon emission reduction. The gas hydrate phase transition process involves heat-fluid-mechanical-chemical multi-physics coupling. Accurate and real-time monitoring of the multi-physics of the phase transition process is the premise for the realization of gas hydrate development and technical application.

Laboratory-scale studies can reveal the multi-physics control mechanisms of heat, flow, force, and chemical processes for the formation and decomposition of gas hydrates. But Rossi,F.,M.Filipponi,and B.Castellani,Investigation on a novel reactor for gas hydrate production The reactor cavity used for research is mostly cylindrical, and the production wells are arranged in the center of the circle to simulate gas injection and production. . On the one hand, this kind of reactor has a simple structure and is easy to manufacture, but for multi-physics monitoring, it can only monitor pressure and temperature by arranging pressure sensors and temperature sensors at the cylinder surface and end cap, and then according to the gas state equation. The evolution of the saturation of each phase at different positions cannot be obtained by calculating the variation of the saturation of hydrate, gas and water with time in the entire reactor. Similarly, for the monitoring of the force field, the external loading device is generally used to calculate the overall force change of the sample, and the spatial change cannot be obtained. Although the method of optical fiber implantation monitoring can solve this problem, the pre-buried optical fiber itself in the sample cannot be obtained. The properties of the sample will be affected, and the results obtained by this invasive measurement method are less reliable. In order to solve the defect of not being able to monitor the evolution of the physical field inside the sample, Wang, Z., et al., Study on the growth habit of methane hydrate at pore scale by visualization experiment, opened a transparent window on the wall of the reactor [2] or Almenningen, S. ., et al., Visualization of hydrate formation during CO2 storage in water-saturatedsandstone using MRI [3] to compare the evolution of hydrate spatial distribution by collecting images during gas hydrate phase transitions, but still lacks the understanding of the force field. Monitoring; Wu, P., et al., Pore-Scale 3D Morphological Modeling and Physical Characterization of Hydrate-Bearing Sediment Based on ComputedTomography CT (electron computed tomography) triaxial reactor can realize the force of gas hydrate phase transition process However, it is expensive, and the quality of scanning imaging is limited by the time-consuming scanning, so it is difficult to capture the instantaneous changes in the formation and decomposition of gas hydrates. On the other hand, the traditional cylindrical reactor has poor accuracy in the docking of physical experiments and numerical experiments, which makes it difficult to verify the results of numerical models by physical experiments.

To sum up, it is difficult for the current reactor to monitor the thermal-fluid-mechanical-chemical physical fields and the spatial and temporal changes of each phase in the gas hydrate phase transition process in real time, and it is in the black box stage. The invention provides a visualized low-temperature high-pressure reactor capable of monitoring the heat-flow-mechanical-chemical multi-physical field coupling response of the gas hydrate formation and decomposition process.

SUMMARY OF THE INVENTION

The invention provides a visualized low-temperature and high-pressure reaction kettle for multi-physical field response of gas hydrate phase transition process, which can reveal the gas hydrate generation and decomposition mechanism under laboratory conditions, improve the visualization research of multi-physical field response process, and accurately connect physical experiments. Modeling with numerical experiments provides a laboratory basis for establishing multiscale gas hydrates.

The technical scheme of the present invention is as follows:

A visualized low-temperature and high-pressure reactor for monitoring the multi-physical field response of gas hydrate phase transition process, including a visualized low-temperature and high-pressure reactor body, a confining pressure loading system, a temperature and pressure monitoring system in the reactor, and a displacement and strain monitoring system;

The main body of the visualized low-temperature autoclave is mainly used for the preparation of hydrate-containing sediment samples and the phase transition experiment of gas hydrate. It is made by cutting a cylinder in the direction of the original cylinder, and the ratio of the radius to the height of the original cylinder is greater than 2; the front and back of the sector are rectangular, and the upper cover and bottom are fan-shaped; except the front viewing window is made of sapphire, the rest of the Made of stainless steel; 5 holes are arranged on the bottom surface, of which 1 is the waste liquid discharge port, 4 are multi-point thermal resistance interfaces, and the 4 thermal resistance interface openings are located on the bisector of the fan shape, radially outward, The spacing is distributed by equal difference; 3 holes are arranged on the upper cover surface, of which 2 are located on the bisector of the angle, which are the gas/liquid inlet and outlet and the reserved port, which are as close as possible to the upper cover on the basis of satisfying the safety check. The center and circumference of the surface, the middle one is the air intake and exhaust interface; 15 holes are arranged at the back for external pressure sensors, and the 15 holes are arranged in 3 rows in the axial direction and 5 columns in the radial direction, with the axial direction up and so on. The spacing is distributed, the spacing distance is one-fourth of the inner height of the reactor, and the radius is radially outward from the center of the circle, and the spacing is equally distributed, which is the same as the opening tolerance of the thermal resistance interface;

The confining pressure loading system includes airbags and external pressure supply equipment; the airbags are located on the inner side of the upper cover of the reactor and the inner side of the arc side, which are used for load application, simulating the pressure and confining pressure of the underground overlying layer; the external pressure supply equipment passes through the high-pressure hose Connect the air bag to control the gas pressure in the air bag.

The temperature and pressure monitoring system in the kettle is mainly composed of a temperature sensor and a pressure sensor; the temperature sensor adopts a multi-point thermal resistance (each with 3 temperature measurement points), and the temperature measurement points are distributed at equal intervals (the interval distance is four of the highest in the reaction kettle. one part).

The displacement and strain monitoring system is mainly composed of laser displacement sensor, PIV and DIC monitoring modules; among them, the laser displacement sensor is located on the inner side of the upper cover of the reactor, between the airbag and the sediment, to observe the sediment settlement and expansion; PIV and DIC monitoring The module is composed of a camera and an image processing system. The camera takes pictures through the front view window, and uses PIV and DIC technology to process the collected images to obtain the flow field, displacement field and strain field of the whole process.

A visualized low-temperature autoclave for monitoring the multiphysics response of gas hydrate phase transition process can be applied to the following scenarios:

(1) For thermal field monitoring, use thermal resistance to monitor the temperature field response of the phase transition process;

(2) For flow field monitoring, use pressure sensor and particle velocimetry (PIV) to monitor the flow field response of the phase change process;

(3) For force field monitoring, high-pressure airbags are used to apply confining pressure and overlying pressure, and laser displacement sensors and digital image correlation (DIC) methods are used to monitor the stress and strain field responses of the phase transition process;

(4) For chemical field monitoring, a high-definition camera was used to monitor the spatiotemporal distribution response of gas hydrates during the phase transition process through window imaging.

The effect and benefit of the present invention is to realize the thermal-fluid-mechanical-chemical multi-physics monitoring of the gas hydrate phase transition process. A special-shaped low-temperature high-pressure reaction kettle is proposed. The fan-shaped reaction kettle has holes on the upper cover, the bottom surface and the back. The opening positions are arranged according to the following principles: the openings on the upper cover and the bottom surface are located on the corner bisector of the sector, and the openings for the gas/liquid inlet and outlet and the reserved openings are as close as possible to the center of the circle and the edge of the circumference; the openings for the bottom surface of the external temperature sensor The openings are distributed along the radius from the center of the circle to the outside, and the hole spacing is equally distributed (tolerance is greater than 0). tolerance). This arrangement principle is more in line with the characteristics of decreasing temperature and pressure gradient change from near field (circle center) to far field (circumferential edge) during gas hydrate phase transition process, and the monitoring of temperature and pressure physical field in the autoclave is more accurate. The pressure airbags on the inner side of the upper cover of the reactor and the inner side of the arc can simulate the overburden pressure and confining pressure conditions of gas hydrate deposits, and accurately simulate the real pressure environment of the seabed. The front of the reactor adopts a large sapphire window and a high-definition camera to realize the visual monitoring of the phase transition process of gas hydrate in the sediment. PIV (particle image velocimetry) and DIC (digital image correlation method) are used to coordinate the gap between the reactor airbag and the sediment. The laser displacement sensor can realize transient, multi-point and non-destructive dynamic monitoring of the whole process flow field, displacement field and stress field. Compared with the traditional cylindrical reactor, the structural design of the special-shaped reactor sector and the modeling of the computer numerical geometric model have natural matching characteristics, and the verification of the physical model is more accurate.

Description of drawings

Figure 1 is a visualization of the structure of a low temperature and high pressure reactor for the multiphysics response of a gas hydrate phase transition process.

Figure 2 is a basic view of a low temperature autoclave to visualize the multiphysics response of a gas hydrate phase transition process.

Figure 3 is an application example of a low-temperature autoclave visualization of the multiphysics response of a gas hydrate phase transition process.

Figure 4 is an example of the geometric model and meshing of a low-temperature autoclave in a numerical simulation software to visualize the multiphysics response of a gas hydrate phase transition process.

In Figure 1: 1 air inlet and exhaust port; 2 reactor gas-liquid inlet and outlet; 3 wells; 4-1-4 multi-point thermal resistance; 5 pressure sensor interface array; 6-1-4 multi-point thermal resistance interface 7 reactor bottom surface; 8 sapphire visual window; 9 waste liquid outlet; 10 air bag; 11 reserved port; 12 reactor cover.

In Figure 2: a is a front view; b is a bottom view; c is a rear view; d is a top view

In Figure 3: 13 computer acquisition system; 14 intermediate container; 15 waste gas recovery tank; 16 high precision balance; 17 low temperature water bath; 18 waste liquid recovery container; 19 nitrogen cylinder; 20 gas cylinder for hydrate generation; 21-1 High pressure ISCO pump for intake; 21-2 High pressure ISCO pump for exhaust; 22 Visualized high pressure reactor; 23 Temperature and pressure monitoring system, displacement and strain monitoring system, confining pressure loading system in the kettle; 24-1 Intermediate vessel exhaust port Valve; 24-2 Reactor liquid outlet valve; 24-3 Nitrogen bottle outlet pressure relief valve; 24-4 Gas bottle outlet pressure relief valve for hydrate generation; 24-5 Inlet pipeline valve; 24-6 Reactor Kettle reserved port valve; 24-7 pipeline cut-off valve; 24-8 reactor inlet valve; 24-9 back pressure valve.

Detailed ways

The specific embodiments of the present invention will be described in detail below with reference to the technical solutions and the accompanying drawings.

Figure 3 shows an application example of a low-temperature autoclave for visualizing the multiphysics response of the gas hydrate phase transition process. This example illustrates the specific working process of the reactor in a general gas hydrate phase transition experiment system. The gas hydrate phase transition process includes two parts, namely, the gas hydrate generation process and the decomposition process. The first is the gas hydrate generation process. The quantitative drying sediment and the quantitative deionized water are uniformly mixed and then filled into the reactor. Inside, the reaction kettle was rinsed and dried with deionized water in advance; the upper cover of the reaction kettle was closed, the quick connector of the air inlet was connected, the valve of the air inlet pipeline and the inlet valve of the reaction kettle were opened, and the low pressure nitrogen gas was slowly filled into the reaction kettle by the high pressure pump. , let stand for a period of time to discharge, repeat 3 times to discharge the miscellaneous gas in the reactor; then adjust the pressure reducing valve at the gas cylinder outlet, and slowly fill the high-purity gas used for hydrate generation into the reactor to the set pressure (this value greater than the phase equilibrium pressure), close the inlet valve of the reactor, and let it stand for 24 hours to fully dissolve the gas into the water; at the same time, start the confining pressure loading system, and slowly inject nitrogen into the air bag to the specified pressure; adjust the temperature to the set value, Cool the reaction kettle; start the temperature and pressure monitoring system in the kettle, the displacement and strain monitoring system in the kettle during the cooling process to monitor the temperature, pressure and deformation of the gas hydrate formation process; when the pressure in the reaction kettle no longer drops, it is considered that the hydration Creation ends. For the gas hydrate decomposition process, set the back pressure valve to a set value lower than the equilibrium pressure of the gas hydrate phase, open the outlet valve of the reactor and the exhaust valve of the intermediate container, and the unreacted free gas, decomposed gas, and water are in Driven by the pressure difference, it flows into the intermediate container through the gas production well, and the quality of the intermediate container is weighed in real time; similarly, the high-speed camera monitors the changing signals in the reactor and the images of the decomposition process in real time; the signals are collected and analyzed by the computer in real time; to be decomposed After the end, the sediment was removed from the reactor and rinsed and dried to complete the experiment.

Figure 4 is an example of the geometric model and meshing of a low-temperature autoclave in a numerical simulation software to visualize the multiphysics response of a gas hydrate phase transition process. The connection between numerical simulation and physical (experimental) simulation is the best method to verify the numerical model, which determines the application accuracy of the numerical model in large-scale and large-scale industries. In the finite element numerical simulation, the data of all grid points are calculated to represent the physical quantity changes of the whole area. A high-quality mesh needs to be subdivided at locations where the gradient of physical quantities changes drastically to achieve accurate characterization. If the position where the physical quantity gradient changes drastically in the experimental system (in the reactor) cannot be effectively monitored, the accuracy of the verification of the numerical model cannot be guaranteed. This example presents meshing in a general geometric model to illustrate the effect of the present invention on the placement of opening locations for connecting temperature and pressure sensors. In the process of gas hydrate decomposition, whether it is on the laboratory scale or on the site scale, generally by reducing the bottom hole pressure, the hydrate reaches an unstable state and then decomposes, so the position close to the well is the position where the hydrate decomposes violently. The changes are equally greater. The layout principle of the temperature and pressure sensors in this reaction kettle fully considers this real phenomenon. From the near well to the far well, the sensors are distributed according to the equal difference (tolerance is greater than 0). This reasonable layout method can effectively monitor the near well. Dramatically changing physics at the well. It can be seen from Figure 4 that the grid division on the left side near the center of the circle (the layout position of the well) is more finely divided, and the grid gradually increases from left to right, which is consistent with the layout principle of the temperature and pressure sensor in this direction. It is the same, both realize the detailed monitoring of the position where the physical quantity gradient changes sharply. This application example illustrates the effect of a low temperature and high pressure reactor on the structural design of a visualization of the multiphysics response of the gas hydrate phase transition process.

Claims (1)

1. A visual low-temperature high-pressure reaction kettle for monitoring multi-physical field response in a gas hydrate phase change process is characterized by comprising a visual low-temperature high-pressure reaction kettle main body, a confining pressure loading system, an in-kettle temperature and pressure monitoring system and a displacement and strain monitoring system;

the visualized low-temperature high-pressure reaction kettle main body is mainly used for preparing a hydrate sediment sample and performing a phase change experiment on a gas hydrate, the appearance of the visualized low-temperature high-pressure reaction kettle main body is a sector with a central angle of 30 degrees, namely, the visualized low-temperature high-pressure reaction kettle main body is formed by cutting a cylinder along a direction vertical to a sector with a central angle of 30 degrees, and the radius-height length ratio of an original cylinder is more than 2; the front and the back of the sector are rectangular, the upper cover surface and the bottom surface are sector, and except that the front visible window is made of sapphire, the rest parts are made of stainless steel; 5 holes are distributed on the bottom surface, wherein 1 is a waste liquid discharge port, 4 are multipoint thermal resistance interfaces, and the 4 thermal resistance interface openings are positioned on a fan-shaped angular bisector and distributed outwards along the radial direction at equal intervals; 3 holes are distributed on the upper cover surface, 2 of the holes are positioned on an angular bisector and are respectively an air/liquid inlet/outlet and a reserved opening, the holes are respectively close to the circle center and the circumference of the upper cover surface as much as possible on the basis of meeting safety check, and the middle 1 is an air inlet/outlet interface of the air bag; 15 holes are distributed on the back for externally connecting the pressure sensor, 15 holes are distributed in a mode of 3 rows in the axial direction and 5 columns in the radial direction, the holes are distributed at equal intervals in the axial direction, the interval distance is one fourth of the inner height of the reaction kettle, the holes are distributed along the radial direction from the center of a circle to the outside and at equal intervals, and the hole tolerance of the holes is the same as that of the holes formed on the thermal resistance interface;

the confining pressure loading system comprises an air bag and an external pressure supply device; the air bags are positioned on the inner side of the upper cover surface and the inner side of the arc side surface of the reaction kettle and are used for applying loads to simulate the pressure and confining pressure of the underground upper cover layer; the external pressure supply equipment is connected with the air bag through a high-pressure hose to realize the control of the gas pressure in the air bag;

the temperature and pressure monitoring system in the kettle mainly comprises a temperature sensor and a pressure sensor; wherein the temperature sensor adopts a multipoint thermal resistor, temperature measuring points are distributed at equal intervals, and the interval distance is one fourth of the height in the reaction kettle;

the displacement and strain monitoring system mainly comprises a laser displacement sensor, a PIV and a DIC monitoring module; the laser displacement sensor is positioned on the inner side of the upper cover surface of the reaction kettle, between the air bag and the sediment, and is used for observing the sedimentation and expansion of the sediment; the PIV and DIC monitoring module mainly comprises a camera and an image processing system, wherein the camera shoots pictures through a front visual window, and the PIV and DIC technology is utilized to process the collected images to obtain a flow field, a displacement field and a strain field in the whole process.

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