Device and method for real-time non-destructive calculation of equivalent specific heat of hydrate dissociation process

Abstract

The present application belongs to the technical field of natural gas hydrate exploitation, and discloses a device and method for real-time nondestructive calculation of equivalent specific heat in hydrate decomposition process. The device comprises a visual flat reaction kettle, a nondestructive high-precision phase state identification system, a gas and liquid inlet and exhaust system, and a computer acquisition system. The principle of the present application is that: through the method of providing uniform heat source by heat conduction outside the reaction kettle, hydrate decomposition is promoted, and internal heat convection can be ignored. Real-time volume fraction of each component is obtained by the nondestructive high-precision phase state identification system, Newton interpolation calculation is used for the volume fraction, latent heat of phase transition of hydrate deposit at adjacent temperature is calculated, and equivalent specific heat of hydrate deposit is obtained. The present application realizes real-time nondestructive calculation of equivalent specific heat field in hydrate decomposition process. The method is environmentally friendly and economical, and the device is clear and visual, which provides technical support for the research on latent heat of phase transition and equivalent specific heat in the process of hydrate exploitation.

Description

Technical Field

[0001] This invention belongs to the field of natural gas hydrate extraction technology, specifically a device and method for real-time non-destructive calculation of the equivalent specific heat of hydrate decomposition process. Background Technology

[0002] Natural gas hydrates are non-stoichiometric cage-like crystalline mixtures composed of water molecules and small-molecule gases such as methane. They are characterized by wide distribution, large reserves, and high energy density, and have the potential to become a substitute for conventional fossil fuels; under standard conditions, 1m³ 3 The natural gas hydrate can release approximately 164 m³ 3 Natural gas and 0.8m 3 Water has an energy density 2 to 5 times that of conventional natural gas and 10 times that of coal. Large quantities of natural gas hydrates are buried in the permafrost of the South my country Sea and the Qinghai-Tibet Plateau. Based on their resource type, occurrence, and geological conditions, preliminary estimates suggest that my country's offshore natural gas hydrate resources amount to approximately 80 billion tons of oil equivalent. Commercial exploitation and large-scale utilization of these resources, increasing their share in my country's energy consumption, would be of great significance for environmental protection and sustainable development.

[0003] Currently, hydrate extraction faces challenges such as low gas production efficiency, sand production, wellhead sinking, methane leakage, secondary hydrate formation, and icing. To address these issues, experimental and numerical simulation studies of the hydrate extraction process are essential. Traditional heat transfer studies primarily consider the influence of material heat capacity and thermal conductivity. However, hydrate research reveals phase changes during extraction, such as secondary hydrate formation and ice formation, which significantly impact gas production efficiency. Studying heat transfer involving phase changes is a major challenge in hydrate development. Secondary hydrate formation and ice formation result in changes in latent heat of phase change, which severely affects the temperature field. Furthermore, heat measurement and calculation are difficult in experiments; considering only external heat sources as the sole influence on hydrate decomposition will affect the accuracy of temperature field predictions. However, latent heat of phase change and specific heat can be equivalently represented by a single parameter—equivalent specific heat. Equivalent specific heat, as a crucial parameter for heat research during hydrate decomposition, is significant for numerical simulation and the description and calculation of latent heat of phase change during field extraction.

[0004] For the reasons mentioned above, the existing research on phase change heat transfer in hydrate mining is mainly lacking in the following aspects: (1) a device for real-time non-destructive calculation of the equivalent specific heat of hydrate decomposition process; and (2) an experimental method for studying the changes in equivalent specific heat during hydrate mining. Therefore, providing a technical method that can overcome these shortcomings and achieve real-time non-destructive calculation of the equivalent specific heat of hydrate decomposition process is a technical problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0005] The purpose of this invention is to provide an apparatus and method for real-time non-destructive calculation of the equivalent specific heat of hydrate decomposition process, so as to solve the problems existing in the prior art.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] A device for real-time non-destructive calculation of the equivalent specific heat of hydrate decomposition process includes a visual flat reaction vessel, a non-destructive high-precision phase identification system, an air-inlet and liquid-outlet and exhaust-liquid-drainage system, and a computer;

[0008] The visible flat reactor is shaped like a flat cuboid, with the ratio of its second longest side to its shortest side greater than 20, thus it can be considered a two-dimensional plane. A viewing window is located on the front of the reactor, made of pressure-resistant materials such as sapphire. The rest of the reactor is made of pressure-resistant stainless steel. The reactor contains several detachable simulated porous media cylinders. The reactor is placed in a constant temperature chamber and connected to an air / liquid inlet and an exhaust / discharge system.

[0009] The air intake and liquid intake, as well as the exhaust and liquid discharge system, mainly consists of an air intake pipe, a liquid intake pipe, an exhaust pipe, a liquid discharge pipe, a pump, a vacuum pump, a booster pump, valves, and a back pressure valve. The air intake pipe, liquid intake pipe, exhaust pipe, and liquid discharge pipe serve as channels for fluid flow between the various devices. The pump is used to transport the fluid. The vacuum pump is used to evacuate the visible flat reactor before the reaction. The booster pump is used to pressurize the fluid, control the natural gas entering the visible flat reactor, and reach the specified pressure. The valves are used to control the fluid flow. The back pressure valve discharges waste gas and waste liquid under safe pressure.

[0010] The specific connection method of the gas inlet / liquid inlet and gas outlet / liquid outlet systems is as follows: the inlet pipe of the storage tank is connected to the visible flat reactor, on which the storage tank valve, pump, and reactor inlet valve are installed in sequence; the inlet pipe of the carbon dioxide cylinder is connected to the visible flat reactor, on which the carbon dioxide cylinder pressure reducing valve, booster pump, and reactor inlet valve are installed in sequence; the visible flat reactor is also equipped with a vacuum pump valve, reactor exhaust valve, and reactor drain valve, and a vacuum pump is connected to the vacuum pump valve; the visible flat reactor is connected to a computer through a non-destructive high-precision phase state recognition system.

[0011] The non-destructive high-precision phase recognition system mainly consists of multiple high-speed cameras. The high-speed cameras take pictures through the viewing window of the visible flat reactor. The high-speed cameras accurately capture a unit area. The high-speed cameras upload the captured images to the computer in real time. The high-speed cameras are arranged alternately. The captured unit area is regarded as the known unit area, and the uncaptured unit area data is regarded as the unknown unit area.

[0012] The computer receives photos uploaded in real time by the non-destructive high-precision phase recognition system and analyzes the phase distribution in the unit region using an image segmentation method based on grayscale values. The computer interpolates data from known unit regions to obtain phase data for unknown unit regions. Based on the analyzed phase distribution, the computer calculates the equivalent average specific heat field within the visible flat reactor in real time and displays it on the computer monitor. The equivalent average specific heat field is determined by...

[0013]

[0014] Perform the calculation, where C E Equivalent volumetric specific heat of sediments (kJ / (m³)) 3 ·K), The equivalent average volumetric specific heat of sediments is kJ / (m³). 3 ·K), T a and T b The temperatures of the system at different times are represented by T. a For the previous moment, T b For the next time step, ρ h The density of the hydrate is kg / m³ 3 n h L is the volume fraction of hydrate. h The latent heat of hydrates is expressed in kJ / kg. The latent heat is released during hydrate formation (represented by a negative value) and absorbed during hydrate decomposition (represented by a positive value). ρ i The density of ice is kg / m³ 3 n i L represents the volume fraction of ice. i The latent heat of ice is given by ρ (kJ / kg). Water releases latent heat when it freezes into ice (latent heat is negative), while ice absorbs latent heat when it melts into water (latent heat is positive). α The density of the substance in the αth term (kg / m³) 3 n α c is the volume fraction of the α-th substance. α Let α be the specific heat of mass of the substance in the αth term, kJ / (kg·K), where α = s, w, g, h, and i, representing sediment particles, water, gas, hydrates, and ice, respectively.

[0015] A method for real-time non-destructive calculation of the equivalent specific heat of a hydrate decomposition process includes the following steps:

[0016] (1) Before the experiment begins, open the vacuum pump valve and use the vacuum pump to evacuate the visible flat reactor. Open the reactor inlet valve and the carbon dioxide cylinder pressure reducing valve. Use the booster pump to control the carbon dioxide to enter the visible flat reactor. Open the storage tank valve and the reactor inlet valve. Use the pump to control the water to enter the visible flat reactor. Control the constant temperature chamber to adjust the temperature of the visible flat reactor to below the equilibrium temperature in order to form hydrates. After the experiment is completed, discharge the waste gas and waste liquid through the reactor exhaust valve and the reactor drain valve under safe pressure.

[0017] (2) Adjust the constant temperature chamber to raise the temperature of the visible flat reactor to above the phase equilibrium temperature, thereby promoting the decomposition reaction of hydrates in the visible flat reactor;

[0018] (3) When the hydrate begins to decompose, the non-destructive high-precision phase identification system captures the situation inside the visible flat reactor in real time through the visual window and uploads the image to the computer for image recognition. The computer uses grayscale images to identify the phases and calculates the volume fraction of sediment particles, water, gas, hydrate, and ice in each known unit area. The volume fraction of each phase in the unknown unit area that has not been collected is obtained by using the volume fraction values ​​of each phase in the adjacent known unit areas. The volume fraction of each phase is obtained by linear interpolation. In some preferred embodiments, the volume fraction of each phase in the unknown unit area that has not been collected can be obtained by using the volume fraction of each phase in all adjacent known unit areas through Largrange, Newton, Hermite, and cubic spline interpolation, etc., to obtain a higher accuracy volume fraction of each phase in the unknown unit area that has not been collected. Thus, the volume fraction of each phase in the entire area is obtained.

[0019] (4) Using the formula

[0020] The equivalent average specific heat of each unit is calculated in real time, and the equivalent specific heat field of the entire region is obtained and displayed on the computer screen.

[0021] (5) After the hydrate has decomposed, the gas and liquid are discharged under safe pressure through the exhaust valve and the liquid discharge valve of the reactor.

[0022] The present invention discloses a method for real-time non-destructive calculation of the equivalent specific heat of hydrate decomposition process. The principle is as follows: a constant temperature chamber uniformly supplies heat to the reaction vessel through heat conduction, promoting hydrate decomposition; internal thermal convection is negligible. A non-destructive, high-precision phase identification system is used to obtain the real-time volume fractions of each component in known unit regions. For the volume fractions of unknown unit regions not collected, interpolation calculations are used to obtain the volume fractions. Based on this, the equivalent specific heat of hydrate deposits in all units is calculated. This method achieves real-time non-destructive calculation of the equivalent specific heat field during hydrate decomposition.

[0023] The beneficial effects of this invention are as follows: This invention proposes a device and method for real-time non-destructive calculation of the equivalent specific heat of hydrate decomposition processes. It comprehensively considers the influence of latent heat of phase change and specific heat of matter on the equivalent specific heat, providing technical support for the calculation of the equivalent specific heat of real hydrate sediment systems. This method is environmentally friendly and economical, and the device is clearly visible, enabling real-time non-destructive calculation of the equivalent specific heat field during hydrate decomposition. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the device structure for real-time non-destructive calculation of the equivalent specific heat of the hydrate decomposition process according to the present invention.

[0025] Figure 2 This is a schematic diagram showing the arrangement of known and unknown unit regions acquired by the non-destructive high-precision phase recognition system involved in this invention.

[0026] In the diagram: 1. Storage tank; 2. Pump; 3. Vacuum pump; 4. Visual flat reactor; 5. Transparent viewing window; 6. Detachable cylinder; 7. Booster pump; 8. Natural gas cylinder; 9. Constant temperature chamber; 10. Non-destructive high-precision phase identification system; 11. Computer; 12-1 Storage tank valve; 12-2 Reactor inlet valve; 12-3 Vacuum pump valve; 12-4 Reactor exhaust valve; 12-5 Reactor gas inlet valve; 12-6 Natural gas cylinder pressure reducing valve; 12-7 Reactor drain valve; 13. Known unit region; 14. Unknown unit region. Detailed Implementation

[0027] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings.

[0028] Reference Figure 1 The present invention provides a device for real-time non-destructive calculation of the equivalent specific heat of hydrate decomposition process. The device includes a visual flat reaction vessel 4, a non-destructive high-precision phase identification system 10, an air inlet and liquid inlet and an exhaust and liquid outlet system, and a computer acquisition system 11.

[0029] The visible flat reactor 4 is shaped like a flat cuboid, with the ratio of its second longest side to its shortest side being greater than 20, thus it can be considered a two-dimensional plane. A viewing window 5 is opened on the front side of the visible flat reactor 4. The viewing window 5 is made of visible pressure-resistant materials such as sapphire. The material of the parts other than the viewing window 5 is pressure-resistant stainless steel. The visible flat reactor 4 contains several detachable simulated porous media cylinders 6. The visible flat reactor 4 is placed in a constant temperature chamber 9. The constant temperature chamber 9 can control the temperature of the visible flat reactor 4 to change slowly or remain constant. The visible flat reactor 4 is connected to the air inlet and liquid inlet and the exhaust and liquid outlet systems.

[0030] The air intake and liquid intake, and exhaust and drainage system consists of an air intake pipe, a liquid intake pipe, an exhaust pipe, a drainage pipe, a pump 2, a vacuum pump 3, a booster pump 7, valves 12-1, 12-2, 12-3, 12-5, 12-6, and back pressure valves 12-4 and 12-7. The air intake pipe, liquid intake pipe, exhaust pipe, and drainage pipe serve as channels for fluid flow between the various devices. Pump 2 is used to transport the fluid. Vacuum pump 3 is used to evacuate the reactor before the reaction. Booster pump 7 is used to pressurize the fluid. Booster pump 7 can control the entry of natural gas into the visible flat reactor and reach the specified pressure. The function of valves 12-1, 12-2, 12-3, 12-5, and 12-6 is to control the fluid flow. Back pressure valves 12-4 and 12-7 can discharge waste gas and waste liquid under safe pressure after the experiment is completed.

[0031] The non-destructive high-precision phase recognition system 10 consists of multiple experimental high-speed cameras. These cameras capture images through the viewing window 5 of the visual flat reactor 4. Each camera precisely captures a unit area. The non-destructive high-precision phase recognition system 10 uploads the captured images to the computer acquisition system 11 in real time. The non-destructive high-precision phase recognition system 10 is arranged in an alternating pattern. The unit area captured by the non-destructive high-precision phase recognition system 10 is designated as the known unit area 13, and the uncaptured unit area data is designated as the unknown unit area 14. This allows for obtaining more accurate and detailed data with fewer cameras. The known area 13 and the unknown area 14 are arranged alternately, as shown below. Figure 2 ;

[0032] The computer acquisition system 11 receives photos uploaded in real time by the non-destructive high-precision phase recognition system 10, and analyzes the phase distribution in the unit region using an image segmentation method based on grayscale values. The computer acquisition system 11 interpolates the data of the known unit region 13 to obtain the phase data of the unknown unit region 14. Based on the analyzed phase distribution, the computer acquisition system 11 calculates the equivalent average specific heat field within the visible flat reactor 4 in real time and displays it on the computer monitor. The equivalent average specific heat field is determined by...

[0033]

[0034] Perform the calculation, where C E Equivalent volumetric specific heat of sediments (kJ / (m³)) 3 ·K), The equivalent average volumetric specific heat of sediments is kJ / (m³). 3 ·K), T a and T b The temperatures of the system at different times are represented by T. a For the previous moment, T b For the next time step, ρh The density of the hydrate is kg / m³ 3 n h L is the volume fraction of hydrate. h The latent heat of hydrates is expressed in kJ / kg. The latent heat is released during hydrate formation (represented by a negative value) and absorbed during hydrate decomposition (represented by a positive value). ρ i The density of ice is kg / m³ 3 n i L represents the volume fraction of ice. i The latent heat of ice is given by ρ (kJ / kg). Water releases latent heat when it freezes into ice (latent heat is negative), while ice absorbs latent heat when it melts into water (latent heat is positive). α The density of the substance in the αth term (kg / m³) 3 n α c is the volume fraction of the α-th substance. α Let α be the specific heat of mass of the substance in the αth term, kJ / (kg·K), where α = s, w, g, h, and i, representing sediment particles, water, gas, hydrates, and ice, respectively.

[0035] The principle of this invention for real-time non-destructive calculation of the equivalent specific heat of hydrate decomposition process is as follows: A constant temperature chamber 9 uniformly supplies heat to the reaction vessel 4 via heat conduction, promoting hydrate decomposition; internal heat convection is negligible. A non-destructive high-precision phase identification system 10 obtains the real-time volume fractions of each component in the known unit region 13. For the volume fractions of the unknown unit region 14 (not collected), interpolation is used to calculate the volume fractions. Thus, the equivalent specific heat of the hydrate deposits in all units is calculated. This method achieves real-time non-destructive calculation of the equivalent specific heat field during hydrate decomposition.

[0036] A method for real-time non-destructive calculation of the equivalent specific heat of a hydrate decomposition process includes the following steps:

[0037] (1) After all the devices are connected, the visible flat reactor 4 is evacuated to a vacuum, natural gas is injected into the visible flat reactor 4 to reach the predetermined pressure condition, and then water is injected into the visible flat reactor 4. The natural gas hydrate is generated in the visible flat reactor 4 by adjusting the constant temperature box 9.

[0038] (2) Adjust the constant temperature box 9 to raise the system temperature above the phase equilibrium temperature, thereby promoting the decomposition reaction of hydrates in the visible flat reactor 4.

[0039] (3) When the hydrate begins to decompose, the non-destructive high-precision phase identification system 10 takes real-time pictures of the situation inside the reactor 4 through the viewing window 5 and uploads the pictures to the computer acquisition system 11 for image recognition. The computer acquisition system 11 uses grayscale images to identify phases and calculates the volume fraction of sediment particles, water, gas, hydrates and ice in each known unit region 13. The volume fraction of each phase in the uncollected unknown unit region 14 is obtained by using the volume fraction of each phase in the adjacent left and right known unit regions 13. The volume fraction of each phase is obtained by linear interpolation. In some preferred embodiments, the volume fraction of each phase in the uncollected unknown unit region 14 can be obtained by using all the adjacent collected known unit regions 13 through Largrange, Newton, Hermite and cubic spline interpolation, etc., to obtain the volume fraction of each phase in the entire region.

[0040] (4) Using the formula

[0041] The equivalent average specific heat of each unit is calculated in real time, and the equivalent specific heat field of the entire region is obtained and displayed on the computer screen.

[0042] (5) After the hydrate has decomposed, the gas and liquid are discharged under safe pressure through the reactor exhaust valve 12-4 and the reactor liquid discharge valve 12-7.

Claims

1. A device for real-time, non-destructive calculation of the equivalent specific heat of a hydrate decomposition process, characterized in that, The device for real-time non-destructive calculation of the equivalent specific heat of the hydrate decomposition process includes a visual flat reactor, a non-destructive high-precision phase identification system, an air-inlet and liquid-outlet and exhaust-drainage system, and a computer. The visible flat reactor is a flat cuboid with a length ratio of its second longest side to its shortest side greater than 20, and can be considered as a two-dimensional plane. A viewing window is opened on the front side of the visible flat reactor, and several detachable simulated porous media cylinders are installed inside the visible flat reactor. The visible flat reactor is placed in a constant temperature chamber and is connected to the air inlet and liquid inlet and air outlet and liquid outlet systems. The air intake and liquid intake and exhaust / discharge system mainly consists of an air intake pipe, a liquid intake pipe, an exhaust pipe, a discharge pipe, a pump, a vacuum pump, a booster pump, valves, and a back pressure valve. The air intake pipe, liquid intake pipe, exhaust pipe, and discharge pipe serve as channels for fluid flow between the various devices. The pump is used to transport the fluid. The vacuum pump is used to evacuate the visible flat reactor before the reaction. The booster pump is used to pressurize the fluid, control the natural gas to enter the visible flat reactor and reach the specified pressure. The valves are used to control the fluid flow. The back pressure valve discharges waste gas and waste liquid under safe pressure. The non-destructive high-precision phase recognition system mainly consists of multiple high-speed cameras. The high-speed cameras take pictures through the viewing window of the visible flat reactor. The high-speed cameras accurately capture a unit area. The high-speed cameras upload the captured images to the computer in real time. The high-speed cameras are arranged alternately. The captured unit area is regarded as the known unit area, and the uncaptured unit area data is regarded as the unknown unit area. The computer receives photos uploaded in real time by the non-destructive high-precision phase recognition system and analyzes the phase distribution in the unit region using an image segmentation method based on grayscale values. The computer interpolates data from known unit regions to obtain phase data for unknown unit regions. Based on the analyzed phase distribution, the computer calculates the equivalent average specific heat field within the visible flat reactor in real time and displays it on the computer monitor. The equivalent average specific heat field is composed of: ； Perform the calculation, where Equivalent volumetric specific heat of sediments (kJ / (m³)) 3 ·K), The equivalent average volumetric specific heat of sediments is kJ / (m³). 3 ·K), and The temperatures of the system at different times are respectively. For the previous moment, For the next moment, The density of the hydrate is kg / m³ 3 , This represents the volume fraction of the hydrate. The latent heat of hydrate is kJ / kg; the latent heat is released during the formation of hydrate, and the latent heat is a negative value; the latent heat is absorbed during the decomposition of hydrate, and the latent heat is a positive value. The density of ice is kg / m³ 3 , This represents the volume fraction of ice. The latent heat of ice is kJ / kg; water releases latent heat when it freezes into ice, and the latent heat is a negative value; ice absorbs latent heat when it melts into water, and the latent heat is a positive value. The density of the α-th substance (kg / m³) 3 , Let α be the volume fraction of the substance. α is the specific heat of mass of the substance in the αth term, kJ / (kg·K); α = s, w, g, h, i, representing sediment particles, water, gas, hydrates, and ice, respectively.

2. The apparatus for real-time non-destructive calculation of the equivalent specific heat of hydrate decomposition process according to claim 1, characterized in that, The viewing window is made of sapphire, while the rest of the device is made of pressure-resistant stainless steel.

3. The apparatus for real-time non-destructive calculation of the equivalent specific heat of hydrate decomposition process according to claim 1, characterized in that, The specific connection method of the gas inlet / liquid inlet and gas outlet / liquid outlet systems is as follows: the inlet pipe of the storage tank is connected to the visible flat reactor, on which a storage tank valve, a pump, and a reactor inlet valve are sequentially installed; the inlet pipe of the carbon dioxide cylinder is connected to the visible flat reactor, on which a carbon dioxide cylinder pressure reducing valve, a booster pump, and a reactor gas inlet valve are sequentially installed; the visible flat reactor is also equipped with a vacuum pump valve, a reactor exhaust valve, and a reactor liquid outlet valve, with a vacuum pump connected to the vacuum pump valve; the visible flat reactor is connected to a computer through a non-destructive high-precision phase identification system.

4. A method for real-time non-destructive calculation of the equivalent specific heat of a hydrate decomposition process, based on the apparatus for real-time non-destructive calculation of the equivalent specific heat of a hydrate decomposition process as described in any one of claims 1-3, characterized in that, Includes the following steps: (1) Before the experiment begins, open the vacuum pump valve and use the vacuum pump to evacuate the visible flat reactor. Open the reactor inlet valve and the carbon dioxide cylinder pressure reducing valve. Use the booster pump to control the carbon dioxide to enter the visible flat reactor. Open the storage tank valve and the reactor inlet valve. Use the pump to control the water to enter the visible flat reactor. Control the constant temperature chamber to adjust the temperature of the visible flat reactor to below the equilibrium temperature in order to form hydrates. (2) Adjust the constant temperature chamber to raise the temperature of the visible flat reactor to above the phase equilibrium temperature, thereby promoting the decomposition reaction of hydrates in the visible flat reactor; (3) When the hydrate begins to decompose, the non-destructive high-precision phase identification system takes real-time pictures of the inside of the visual flat reactor through the visual window and uploads the pictures to the computer for image recognition. The computer uses grayscale images to identify the phases and calculates the volume fraction of sediment particles, water, gas, hydrates and ice in each known unit area. The volume fraction of each phase in the unknown unit area that has not been collected is obtained from the volume fraction of each phase in the adjacent known unit areas. The volume fraction of each phase is obtained by linear interpolation. (4) Using the formula The equivalent average specific heat of each unit is calculated in real time, and the equivalent specific heat field of the entire region is obtained and displayed on the computer screen. (5) After the hydrate has decomposed, the gas and liquid are discharged under safe pressure through the exhaust valve and the liquid discharge valve of the reactor.

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