Method for rapid preparation of gas hydrates in an endogenic force field reactor

Abstract

The application discloses a method for rapidly preparing gas hydrate in an endogenous force field reactor. The method comprises the following steps: introducing an aqueous solution containing a surfactant into the reactor to form a circulating water flow, controlling the temperature to be 2-10 DEG C and the pressure to be 2-9 MPa, utilizing the planar secondary flow centrifugal force generated by the internal spiral groove structure in the reaction section to strengthen the heat and mass transfer among the gas-liquid-solid three phases, promoting the generation of hydrate and the separation of multiple phases, adjusting the residence time through an internal circulator to make the hydrate enriched in the upper part of the reactor, discharging the slurry, and separating the gas hydrate product. The application can efficiently and stably prepare high-gas-storage hydrate by strengthening the heat and mass transfer and promoting the phase separation, and is suitable for the storage and transportation of natural gas, coal-bed gas, biogas and other various gases.

Description

Technical Field

[0001] This invention relates to a method for the rapid preparation of gas hydrates using an endogenous force field reactor, belonging to the field of renewable energy. Background Technology

[0002] Energy is the material foundation of national economic development, the "lifeblood" of socio-economic progress. There is a close link between energy and socio-economic development. With my country's increasingly rapid development, the energy gap has become a significant constraint on growth. In recent years, my country's energy demand has grown exponentially, making it the world's second-largest energy consumer. Although my country possesses relatively abundant fossil fuels and renewable energy sources, the supply still cannot meet the massive demand. At the same time, my country faces serious energy waste, low energy efficiency, and an irrational industrial structure. While my country's coal resources can maintain self-sufficiency for a considerable period, most of its oil and natural gas needs to be imported to meet current and long-term needs. my country's national conditions constrain its energy structure, and the future development of my country's energy sector will face enormous challenges.

[0003] Natural gas (including coalbed methane and shale gas) is an important chemical raw material and clean energy source. In my country's current energy structure, natural gas accounts for approximately 4% of total energy consumption, while in other countries the proportion reaches 20%. Driven primarily by the "coal-to-gas" policy, China's natural gas consumption has continued to grow rapidly. Data shows that in 2018, China's natural gas consumption reached 276.6 billion cubic meters, with an annual increase of over 39 billion cubic meters, representing a growth rate of 16.6%, accounting for nearly 8% of total primary energy consumption. It is projected that domestic natural gas consumption will exceed 300 billion cubic meters in 2019, a year-on-year increase of 11.3%. my country's conventional natural gas reserves are insufficient, while coalbed methane is the largest and most realistic clean energy source besides conventional natural gas, serving as the most important supplement to conventional natural gas and the most realistic strategic replacement energy source. The development of coalbed methane can not only reduce coal mine gas accidents but also reduce the greenhouse effect caused by methane emissions, while simultaneously addressing energy shortages and optimizing my country's energy structure.

[0004] In order to better address the comprehensive utilization of natural gas (including coalbed methane, shale gas, etc.), biogas, and landfill gas, and to achieve safe, convenient, and reliable storage and transportation of these gases to meet the needs of industries and fields such as industry, civil use, power generation, and vehicles, this invention aims to provide a novel method for preparing gas hydrates for gas storage and transportation. Summary of the Invention

[0005] The purpose of this invention is to provide a method for rapidly preparing gas hydrates using an endogenous force field reactor. The reactor used in this invention employs an internal spiral groove structure, which generates planar secondary flow within the tube. This structure enhances heat transfer and, due to the density difference between the gas, liquid, and solid components, promotes the separation of the gas-water-hydrate system under the influence of the endogenous force field within the spiral groove tube. This causes denser substances such as water to adhere to the tube wall, while less dense substances such as hydrates and gases accumulate towards the center of the tube. This process promotes heat and mass transfer as well as the separation of the multiphase system, ultimately enabling the efficient and stable production of gas hydrates using the method of this invention.

[0006] The gas hydrate involved in this invention is a non-stoichiometric cage-like ice-like crystal formed by water molecules and small gas molecules such as CH4, C2H6, CO2, and H2S under specific temperature and pressure conditions. Water molecules form the crystal framework through hydrogen bonds, and the pores within the framework are filled with methane, light hydrocarbons, or non-light hydrocarbon molecules. Studies have found that natural gas hydrates have a considerable gas storage rate; typically, 1 m³ / s² = 1000 m³ / s². 3 Hydrates can be stored at approximately 150-180 m³. 3 Natural gas. Different forms of gas hydrates can be stored at -25 to -10°C and normal pressure. After gasification, they can be utilized efficiently, enabling the safe storage and transportation of gases such as natural gas, coalbed methane, landfill gas, and biogas, and significantly reducing storage and transportation costs.

[0007] The present invention provides a method for rapid preparation of gas hydrates using an endogenous force field reactor, comprising the following steps: An aqueous solution containing surfactant is introduced into the reactor to form a circulating water flow; The temperature inside the reactor is controlled at 2-10℃ by a refrigeration unit; Gas is introduced into the reactor to maintain a pressure of 2-9 MPa; Within the reaction section of the reactor, the planar secondary flow centrifugal force generated by the internal spiral groove structure enhances the heat and mass transfer between the gas-liquid-solid three phases, promoting the formation of hydrates and multiphase separation. The hydrate residence time is adjusted by an internal recirculator to achieve hydrate enrichment in the upper part of the reactor; The enriched hydrate slurry is discharged and subjected to gas-liquid-solid separation to obtain the gas hydrate product.

[0008] Preferably, the reactor is an internal spiral groove reactor, and its reaction section is provided with a spiral inner groove tube, which is used to generate secondary flow when the fluid flows, enhance heat transfer and form an endogenous force field, and promote the accumulation of hydrates towards the center of the tube.

[0009] Preferably, the shell side of the reactor adopts a falling film heat transfer method, which works in conjunction with the spiral inner groove tube to enhance heat transfer and form cold trap conditions.

[0010] In this invention, the gas includes one or more of methane, coalbed methane, shale gas, biogas, and landfill gas.

[0011] The method of the present invention also includes adjusting the connection mode of the two reactors through a process change control unit to achieve parallel or countercurrent operation to adapt to different gas concentrations.

[0012] Preferably, for high-concentration methane gas, co-current operation is used; for medium- and low-concentration methane gas, multi-stage counter-current operation is used. The concentration of the high-concentration methane gas is ≥90%.

[0013] The present invention also provides a system for implementing the method, comprising: At least one internal spiral tank reactor, the reaction section of which is equipped with an internal spiral tank tube; The cooling unit is used to provide cooling to the reactor; A gas compressor is used to supply gas to the reactor; Transfer pumps are used to transfer aqueous solutions; Process change control unit, used to control the connections and processes between reactors; Separator, used to separate hydrate slurry; The central control system is used to monitor and control process parameters.

[0014] The internal spiral channel reactor includes a lower airflow distributor, a middle reaction tube and shell side, and an upper internal circulator and multiphase separation zone. Specifically, the lower part of the internal spiral groove reactor is provided with an air inlet and a water inlet. The air inlet is connected to a compressor, and the water inlet is connected to a delivery pump. The upper part of the inner spiral groove reactor is provided with an air outlet, and the air outlet pipeline is equipped with a heat exchanger and a throttling valve; The inner spiral trough reactor is equipped with product discharge ports at both the upper and lower parts, which are connected to the intermediate storage tank; the upper section of the reactor is a multiphase separation zone, which is equipped with an internal circulator to achieve multiphase separation. The middle section of the internal spiral tank reactor is the reaction section, which consists of a reaction tube array and a shell side. The reaction liquid flows in the tube array and undergoes a hydration reaction. The shell side is filled with ethylene glycol refrigerant, which flows from top to bottom.

[0015] The refrigeration unit is connected to the reactor, intermediate storage tank, water tank and cold storage unit through multiple circuits respectively; Specifically, the refrigeration unit has five circuits: one circuit is connected to the inner spiral groove reactor, one circuit is connected to another inner spiral groove reactor, one circuit is connected to the intermediate storage tank, one circuit is connected to the water tank, and one circuit is connected to the cold storage unit.

[0016] The system is also equipped with anomaly alarm and safety protection devices to ensure stable system operation.

[0017] The reactor used in this invention employs an internal spiral groove structure. This structure generates planar secondary flow centrifugal force, creating strong disturbances and enhancing the disturbance at the wall boundary. Due to the effect of the planar secondary flow centrifugal force, the synergy between the velocity and temperature fields is enhanced, thereby strengthening heat transfer. Simultaneously, the spiral flow of the fluid increases the turbulence within the tube, further enhancing heat transfer. Due to the density difference between the gas, liquid, and solid phases, under the influence of the generated spiral flow and centrifugal force, the already formed hydrates accumulate at the center of the tube, while the denser aqueous phase moves towards the wall, accelerating the renewal of the reaction surface medium. Furthermore, the hydrates no longer remain at the heat exchange surface of the tube wall, promoting heat exchange surface renewal. The tiny bubbles are almost unaffected by the endogenous force field, which promotes the separation of the multiphase system. The method of this invention can efficiently and stably prepare gas hydrates, and the water / slurry mixture can be separated using a separator.

[0018] The method of the present invention has the following advantages: 1) The reactor innovatively adopts an internal spiral groove structure, which can generate an endogenous force environment, accelerate the renewal of the reaction surface medium, promote heat and mass transfer, promote the separation of multiphase systems, and increase the gas hydrate storage capacity.

[0019] 2) The heat exchange method innovatively adopts shell-side falling film heat exchange, and the heat transfer is enhanced by secondary flow generated by the fluid in the spiral inner groove tube, creating cold trap conditions conducive to hydrate formation. Within the scope of the investigation, the heat transfer performance of falling film heat exchange is more than 5 times that of traditional shell-and-tube heat transfer.

[0020] 3) The process change control unit enables the adjustment of residence time in multiphase systems and multi-stage forward / reverse circulation operation, which improves the stability and applicability of the equipment. Attached Figure Description

[0021] Figure 1 This is a physical diagram of a natural gas hydrate generation and storage process system.

[0022] Figure 2 This is a schematic diagram of the internal structure of the internal spiral groove reactor unit.

[0023] Figure 3 A comparison of the heat transfer performance of falling film heat exchangers and shell-and-tube heat exchangers.

[0024] Figure 4 This is a simulation diagram of multiphase flow transport. Detailed Implementation

[0025] Unless otherwise specified, the experimental methods used in the following examples are conventional methods.

[0026] Unless otherwise specified, all materials and reagents used in the following examples are commercially available.

[0027] The apparatus used in the method of this invention, such as Figure 1 As shown, it includes a process change control unit, an internal spiral tank reactor, inlet valves, throttle valves, discharge valves, transfer pumps, a refrigeration unit, an intermediate storage tank, a cold storage unit, an additive tank, a water storage tank, a separator, a central control system, and a compressor. Specifically, A schematic diagram of the internal spiral groove reactor structure is shown below. Figure 2 As shown, a loop is formed by connecting the two ends of the process change control unit; The internal spiral reactor consists of three parts: a gas flow distributor is installed in the lower section of the reactor; an inlet pipe connected to the compressor and a water inlet pipe connected to the delivery pump are located in the lower part of the reactor; the refrigerant outlet and refrigerant inlet of the reactor are connected to both ends of the refrigeration unit to form a loop; the middle section of the reactor is the reaction section formed by the reaction tubes and the shell side. Gas and water flow in the reaction tubes and undergo a hydration reaction, while the shell side provides cooling to remove the heat of reaction in the reaction tubes; the upper section of the reactor is a multiphase separation zone, equipped with an internal circulator to achieve multiphase separation. The refrigeration unit has five loops: one connected to the inner spiral groove reactor, one connected to another inner spiral groove reactor, one connected to the intermediate storage tank, one connected to the water tank 11, and one connected to the cold storage unit. The internal spiral tank reactor forms a water circulation loop via a discharge valve, intermediate storage tank, separator, water tank, and high-pressure delivery pump; the additive storage tank is connected to the water tank.

[0028] Example 1: Preparation of natural gas hydrates using high-concentration coalbed methane In this embodiment, coalbed methane with a methane volume fraction of approximately 97% is used as the feed gas.

[0029] System preparation: Check the status of all valves in the unit. Add sufficient water to the water tank and add 0.05 wt% sodium dodecyl sulfate (SDS) as a surfactant to form a reaction mixture. Turn on the refrigeration unit to cool the reaction mixture in the water tank and intermediate storage tank to 6.5°C.

[0030] Establish circulation: Start the transfer pump to pump the cooled reaction mixture into the No. 1 inner spiral tank reactor. When the liquid level in the reactor exceeds the top of the inner circulator, open the discharge valve of the bypass pipeline, adjust the valve opening and the pump flow rate to form a stable external circulation of the reaction mixture through the intermediate storage tank, the separator (without activating the separation function at this time), and the water tank.

[0031] Start the reaction: Turn on the refrigeration unit to supply an ethylene glycol aqueous solution at 2°C to the shell side of the reactor, using a liquid film heat exchange method, such as... Figure 3 As shown, compared to shell-and-tube type, it has a higher heat transfer coefficient and better heat exchange performance, creating a "cold trap" for the reaction tube side.

[0032] Inlet reaction: After the temperature inside the reaction tube stabilizes at approximately 6.5℃, turn on the gas compressor and inlet valve to pressurize the coalbed methane to 7.5 MPa and then introduce it into the gas distributor at the bottom of the reactor. The gas flow rate is controlled at 80 Nm³. 3 / h. The airflow distributor disperses the gas into a large number of microbubbles, which come into countercurrent contact with the cold water flowing down in the "cold trap".

[0033] Process control: At this point, within the tube side of the internal spiral reactor, the fluid will generate strong planar secondary flow and centrifugal force (i.e., an endogenous force field). Under the influence of this force field: Enhanced mass and heat transfer: The bubbles and water are violently disturbed, the interface is renewed quickly, and the heat generated by the reaction is efficiently removed.

[0034] Promoting phase separation: The generated hydrate crystals (solid phase) and unreacted microbubbles (gas phase) aggregate towards the center of the tube under centrifugal force, while the denser aqueous phase (liquid phase) is pushed towards the tube wall, such as... Figure 4 As shown. This prevents hydrates from adhering to the heat exchange wall surface, thus maintaining high heat transfer efficiency and reaction surface area.

[0035] Product Separation and Collection: The hydrate-enriched slurry rises to the multiphase separation zone at the top of the reactor under buoyancy. After further concentration by the internal circulator, it is discharged from the upper product outlet. The discharged slurry is depressurized and then enters a separator for solid-liquid separation, yielding dry, blocky natural gas hydrate product. Measurements show that the gas storage capacity (V / V) of this hydrate reaches 170 (i.e., 1 cubic meter of hydrate contains 170 cubic meters of natural gas under standard conditions).

[0036] Material circulation: The cold water discharged from the separator (temperature of about 4-5℃) is returned to the water tank. After being replenished with fresh water and additives, it is circulated back to the reactor by the transfer pump, realizing the recovery and utilization of cold energy and materials.

[0037] Example 2: Comparison under different pressure conditions This embodiment aims to illustrate the effect of reaction pressure on the hydrate formation rate and gas storage capacity, and to verify the pressure stability control of the system.

[0038] The operation steps are basically the same as in Example 1, only the core operation parameters are changed: The system reaction pressure was increased and stabilized at 9.0 MPa.

[0039] The initial temperature of the reaction mixture is precisely controlled at 5.0℃ by a refrigeration unit.

[0040] The feed gas remains coalbed methane with a concentration of 97%.

[0041] At higher pressures and slightly lower temperatures, the thermodynamic driving force for hydrate formation is greater. The reaction rate is further accelerated by the enhanced effect of the endogenous force field reactor. The final hydrate product gas storage capacity (V / V) reaches 115.36. This embodiment demonstrates that the process change and pressure stabilization unit can effectively maintain stable system operation at higher pressures and shows that product performance can be improved by optimizing process parameters.

[0042] Example 3: Treatment of low-to-medium concentration landfill gas This embodiment illustrates the flexibility of the process conversion control unit of the present invention, which is used to process gases with low methane concentration and complex composition.

[0043] The feed gas is landfill gas with a methane volume fraction of approximately 45%, and the remaining main components are CO2 and N2.

[0044] A two-stage countercurrent production process is adopted. Reactor No. 1 and reactor No. 2 are connected in series through a process change control unit.

[0045] The feed gas first enters reactor No. 2 (stage 1) at an operating pressure of 7.5 MPa and an initial reaction liquid temperature of 5.0 °C. Here, most of the methane and some of the CO2 are captured and formed into hydrates.

[0046] The unreacted gas discharged from the top of reactor 2 (at which point the methane concentration has decreased) enters reactor 1 (second stage) and undergoes a deep reaction under the same conditions.

[0047] The hydrate slurries generated from the two reactors were processed separately and then mixed. Because CO2 in landfill gas can also generate hydrates under different conditions, the final product is a viscous, colloidal mixed hydrate slurry.

[0048] Testing revealed that the average gas storage capacity (V / V) of the mixed hydrate slurry reached 88 (based on total gas). More importantly, through two-stage countercurrent operation, the system's overall methane capture rate was increased by approximately 30% compared to single-stage operation, significantly improving the utilization efficiency of low-grade gases.

[0049] Example 4: Comparative Experiment (Traditional Stirred Tank Reactor) To highlight the advantages of the endogenous force field reactor of this invention, comparative experiments were conducted.

[0050] The internal spiral groove reactor in this invention is replaced with a stirred tank reactor of the same volume with an external cooling jacket.

[0051] The same feed gas (97% coalbed methane), additives, initial temperature (6.5°C), and pressure (7.5 MPa) as in Example 1 were used.

[0052] Start the stirrer to allow the gas and liquid to mix and react fully.

[0053] Experiments have shown that: Heat transfer limitation: Hydrates adhere rapidly to the vessel wall and agitator, forming an insulating layer, which prevents the heat of reaction from being removed in time, causing the temperature inside the vessel to rise and the reaction rate to drop rapidly.

[0054] Separation difficulties: The generated hydrate slurry is uniformly dispersed in the reactor, and solid-liquid separation requires additional settling time or higher energy consumption centrifugation equipment.

[0055] Performance data: In the same time period, the hydrate formation rate per unit volume reactor was only about 35% of that in Example 1, and the gas storage capacity of the final hydrate product was about 145 V / V.

Claims

1. A method for rapid preparation of gas hydrates using an endogenous force field reactor, comprising the following steps: An aqueous solution containing surfactant is introduced into the reactor to form a circulating water flow; The temperature inside the reactor is controlled at 2-10℃ by a refrigeration unit; Gas is introduced into the reactor to maintain a pressure of 2-9 MPa; Within the reaction section of the reactor, the planar secondary flow centrifugal force generated by the internal spiral groove structure enhances the heat and mass transfer between the gas-liquid-solid three phases, promoting the formation of hydrates and multiphase separation. The hydrate residence time is adjusted by an internal recirculator to achieve hydrate enrichment in the upper part of the reactor; The enriched hydrate slurry is discharged and subjected to gas-liquid-solid separation to obtain the gas hydrate product.

2. The method according to claim 1, characterized in that: The reactor is an internal spiral groove reactor, and its reaction section is equipped with a spiral inner groove tube, which is used to generate secondary flow when the fluid flows, enhance heat transfer and form an endogenous force field, and promote the accumulation of hydrates towards the center of the tube.

3. The method according to claim 1 or 2, characterized in that: The reactor shell side employs falling film heat transfer, which, in conjunction with the spiral inner groove tube, enhances heat transfer and creates cold trap conditions.

4. The method according to any one of claims 1-3, characterized in that: The gas includes one or more of methane, coalbed methane, shale gas, biogas, and landfill gas.

5. The method according to any one of claims 1-4, characterized in that: The method also includes adjusting the connection mode of the two reactors through a process change control unit to achieve parallel or countercurrent operation to adapt to different gas concentrations.

6. The method according to claim 5, characterized in that: For high-concentration methane gas, parallel flow operation is used; for medium- and low-concentration methane gas, multi-stage counter-flow operation is used.

7. A system for implementing the method of any one of claims 1-6, comprising: At least one internal spiral tank reactor, the reaction section of which is equipped with a spiral internal tank tube; The cooling unit is used to provide cooling to the reactor; A gas compressor is used to supply gas to the reactor; Transfer pumps are used to transfer aqueous solutions; Process change control unit, used to control the connections and processes between reactors; Separator, used to separate hydrate slurry; The central control system is used to monitor and control process parameters.

8. The system according to claim 7, characterized in that: The internal spiral channel reactor includes a lower airflow distributor, a middle reaction tube and shell side, and an upper internal circulator and multiphase separation zone.

9. The system according to claim 7 or 8, characterized in that: The refrigeration unit is connected to the reactor, intermediate storage tank, water tank and cold storage unit through multiple circuits.

10. The system according to any one of claims 7-9, characterized in that: The system is also equipped with anomaly alarm and safety protection devices to ensure stable system operation.

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