Carbon dioxide mixed flow cooling and density difference separation device applied to power generation circulation cold end
By using a device for mixing and condensing carbon dioxide and cooling working fluids and separating them by density difference, the problem of cooling difficulties at the cold end of a supercritical carbon dioxide Brayton cycle under extreme low temperature environments has been solved. This achieves efficient cooling and liquefaction, reduces compressor load, improves cycle efficiency, and is suitable for cold end heat exchange and liquefaction under extreme environments.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2026-02-06
- Publication Date
- 2026-04-10
AI Technical Summary
Supercritical carbon dioxide Brayton cycle cold end is difficult to cool in extreme low temperature environments, heat transfer matching is difficult, compressor load is high, it is difficult to achieve efficient cooling and liquefaction, and conventional cooling media are limited by freezing point, resulting in poor system availability and poor adaptability.
A device for mixing and condensing carbon dioxide and cooling working fluids and separating them by density difference is adopted. CO2 liquefaction is achieved under the same pressure conditions through direct contact heat exchange, and the working fluid is separated by density difference, which reduces compression power consumption and improves cycle efficiency.
It achieves efficient cooling and liquefaction in extreme low-temperature environments, reduces compressor load, and improves cycle efficiency. It is suitable for cold-end heat exchange and liquefaction in extreme environments and is suitable for platform applications with limited space and weight.
Smart Images
Figure CN121829032A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of thermodynamic engineering technology, specifically a carbon dioxide mixed flow condensation and density difference separation device applied to the heat release process at the cold end of a power cycle. Background Technology
[0002] Supercritical carbon dioxide (S-CO2) Brayton cycle power generation is considered a promising power generation cycle in the field of thermal power generation due to its flexibility and high efficiency.
[0003] Supercritical carbon dioxide (S-CO2) cycle utilizes supercritical CO2 as the working medium. The S-CO2 cycle using S-CO2 as the working fluid has significant advantages in terms of size and efficiency, such as: (1) low CO2 critical parameters (304.13K / 7.377MPa), making it easy to reach the supercritical state. (2) under medium and high temperature conditions (main gas temperature >550℃) o (C) The S-CO2 cycle efficiency is higher than that of the steam Rankine cycle. (3) The reaction rate with metals is lower than that of steam, which can further increase the main gas temperature at the turbine inlet and improve the cycle efficiency. (4) The S-CO2 cycle system is compact and highly flexible, and is suitable for peak shaving and variable load operation.
[0004] The rapid change in the physical properties of CO2 near the critical point makes heat transfer matching difficult during the cooling process, resulting in a large average temperature difference during cooling. Furthermore, under near-critical compression conditions, the compressor is highly sensitive to inlet parameters, and small deviations at the cold end can be amplified into significant compression work penalties and efficiency reductions.
[0005] In practical engineering applications, the cold-end performance of supercritical carbon dioxide (S-CO2) Brayton cycles is limited by the temperature conditions of the external heat source and the design of the heat exchanger. For ground-based installations, the minimum permissible temperature difference between the cooling medium (e.g., circulating cooling water or air) and the heat exchanger determines the feasibility of cooling S-CO2 to near or below the critical temperature, especially in areas with high ambient temperatures or water resource constraints, where achieving ideal low-temperature heat unloading is difficult. Meanwhile, near-critical compression strategies, by utilizing the rapid change in carbon dioxide density near the critical point, can significantly reduce the theoretical power consumption compared to isothermal or isentropic compression of pure gaseous states. However, this process does not cross the phase transition to become true liquid-phase compression: the working fluid still exhibits low density and high specific volume in the compression stage, resulting in higher volumetric flow rates and mechanical loads on the compressor, and presenting engineering challenges in compression efficiency, leakage, and multi-stage compression configurations. In contrast, liquid-phase compression performed by a pump results in significantly lower compression work per unit mass due to the high fluid density, low specific volume, and compression process approaching the isothermal / isobaric movement of incompressible fluids. Therefore, although near-critical compression is one of the effective ways to reduce compression energy consumption, liquid (or pump-driven) compression still has a clear energy consumption advantage in achieving lower cold end temperatures or lower overall compression work.
[0006] As supercritical carbon dioxide power cycles expand into mobile, modular, and multi-scenario energy systems, their cold end is increasingly addressing engineering needs in extreme conditions and special environments, beyond conventional power plants and industrial waste heat recovery. Examples include polar research and cold-region resource development, operational platforms in frozen oceans and high-latitude seas, ship and icebreaker power, distributed energy stations in cold regions, emergency power supplies for high-altitude stations / remote areas, and integrated energy systems coupled with cryogenic industrial processes (such as LNG cold energy cascade utilization, cryogenic energy storage, and cryogenic separation devices). In these scenarios, ambient temperatures are consistently low or even frigid, leading to icing and frosting on the cold source side, freezing and blockage of heat exchanger channels, and reduced system availability. Simultaneously, the freezing point of conventional cooling media limits the usable heat transfer temperature difference and adjustment range at the cold end, resulting in difficulties in startup, poor adaptability to varying operating conditions, and sensitivity to compressor inlet parameter fluctuations. In engineering, antifreeze agents or blended working fluids are often added to lower the freezing point. However, existing cold-end heat exchangers are mostly indirect, which are limited by terminal temperature difference, fouling thermal resistance, and heat transfer matching. This makes it difficult to fully utilize the cooling capacity of extreme low-temperature environments to achieve deep cooling and stable liquefaction of high-pressure CO2. Compression often still needs to occur near the critical state or through a two-phase unstable region, resulting in large volumetric flow rates, high power consumption, and small control margins in the compression section. If direct contact cooling / condensation combined with density difference separation to obtain stable liquid CO2 can be introduced while maintaining pressure safety and a low freezing point, gas-liquid phase change can be achieved at even lower temperature levels. This would further increase the proportion of liquid-phase pumped compression, significantly reduce compression power consumption, and improve cycle net efficiency and system power density. Simultaneously, direct contact heat exchange has advantages such as high heat transfer coefficient, compact equipment, and strong adaptability to low-temperature cold sources, making it particularly suitable for mobile platforms and cold-region equipment with significant space, weight, and reliability constraints. Therefore, there is still significant engineering demand and room for improvement in efficient cold-end heat exchange and liquefaction technology for extreme low-temperature environments. Summary of the Invention
[0007] To address the problems existing in the background technology, the present invention provides a carbon dioxide mixed-flow condensation and density difference separation device applied to the cold end of a power generation cycle. The technical solution includes: a carbon dioxide working fluid circuit, a cooling working fluid circuit, and a mixed working fluid circuit. The mixed working fluid circuit mixes and exchanges heat between the high-temperature and high-pressure gaseous CO2 input from the carbon dioxide working fluid circuit and the cooling working fluid at the cooling temperature in the cooling working fluid circuit. Then, by utilizing the density difference between the working fluids in the mixed working fluid circuit, the liquefied carbon dioxide and the cooling working fluid are separated in a separation tank.
[0008] In cryogenic mixing, the pressure range is below the critical pressure of CO2, and CO2 and the cooling medium are at the same pressure; the temperature of the cooling medium is lower than the saturation temperature of CO2 at the pressure before mixing.
[0009] The temperature of the cooling medium after mixing with CO2 is below the critical temperature of CO2, thus achieving liquefaction.
[0010] In the carbon dioxide working fluid circuit, the inlet of the carbon dioxide working fluid circuit, the first temperature and pressure sensor, the first carbon dioxide pressurizing pump valve, the carbon dioxide pressurizing pump, the second carbon dioxide pressurizing pump valve, the external power circulation system, the second gas phase check valve, the first gas phase check valve, and the outlet of the carbon dioxide working fluid circuit are connected in sequence through a carbon dioxide pipeline.
[0011] A carbon dioxide mass flow meter is installed on the carbon dioxide pipeline.
[0012] The carbon dioxide working fluid circuit also includes: a carbon dioxide storage cylinder and a high-pressure carbon dioxide cylinder with an electric heating wire wound around it. The high-pressure carbon dioxide cylinder with the electric heating wire wound around it is connected to the pipeline before the carbon dioxide mass flow meter through a check valve at the cylinder outlet. The outlet of the second gas phase check valve is connected to the carbon dioxide storage cylinder through a pressure reducing valve of the storage cylinder.
[0013] In the cooling working fluid circuit, the inlet of the cooling working fluid circuit, the second temperature and pressure sensor, the hot side of the high-pressure conventional heat exchanger, the valve of the third liquid pressurizing pump, the second liquid pressurizing pump, the valve of the fourth liquid pressurizing pump, the liquid phase check valve, and the outlet of the cooling working fluid circuit are connected in sequence through the cooling working fluid pipeline.
[0014] A liquid mass flow meter is installed on the cooling working fluid pipeline.
[0015] A branch of the outlet of the third liquid pressurizing pump valve is introduced into the cooling medium storage tank via a pressure reducing valve. The outlet of the cooling medium storage tank is introduced into the pipeline before the liquid mass flow meter via the first liquid pressurizing pump valve, the first liquid pressurizing pump, and the second liquid pressurizing pump valve. The cold side inlet and cold side outlet of the high-pressure conventional heat exchanger are connected to the outlet and inlet of the external cold source, respectively.
[0016] The mixing working fluid loop includes: a three-way pipe, a static mixer, a third temperature and pressure sensor, and a separator; wherein the first port of the three-way pipe is connected to the inlet of the separator via the static mixer and the third temperature and pressure sensor in sequence; the second port of the three-way pipe is connected to the outlet of the cooling working fluid loop, and the third port of the three-way pipe is connected to the outlet of the carbon dioxide working fluid loop; the cooling working fluid outlet at the bottom of the separator is connected to the inlet of the cooling working fluid loop via a lower back pressure valve, and the working fluid outlet at the top of the separator is connected to the inlet of the carbon dioxide working fluid loop via an upper back pressure valve;
[0017] The temperature on the cooling medium side before mixing in the static mixer is higher than the freezing point of the cooling medium.
[0018] The cooling medium circuit is activated during startup to ensure sufficient liquid level is established in the separator, a stable cold source is established through a high-pressure conventional heat exchanger and an external cold source, the system back pressure is increased to the target pressure, and the separator temperature is controlled at 3-6 degrees Celsius below the CO2 saturation temperature at the corresponding pressure. o After setting condition C, CO2 working fluid is introduced, with an initial CO2 flow rate of 10% to 20% of the design value. After monitoring that the separation interface is stable and the light phase density meets the liquid phase criterion, the flow rates of both CO2 and the cooling working fluid are increased simultaneously.
[0019] The carbon dioxide working fluid loop is first recovered after shutdown. After the CO2 side pressure drops to a safe value and the relevant valves are closed, the flow rate of the cooling working fluid is gradually reduced. The cooling working fluid is reduced from high pressure to normal pressure and returned to the cooling working fluid storage tank through the pressure reducing valve. Finally, the second liquid pressurization pump is stopped and all valves are closed to achieve safe shutdown of the device and recovery of the working fluid.
[0020] In case of an emergency, the carbon dioxide working fluid circuit is first recovered by using the pressure reducing valve of the gas cylinder to introduce CO2 into the carbon dioxide storage cylinder in stages; after the pressure and temperature drop to a safe range, the working fluid on the cooling working fluid side is slowly depressurized back to the cooling working fluid storage tank through the pressure reducing valve.
[0021] The cooling medium is: pure water, alcohol-containing water, or water containing inorganic salts;
[0022] The proportion of alcohol-containing water is 10%-60%, and the proportion of inorganic salt-containing water is 20%-30%.
[0023] The beneficial effects of this invention are as follows:
[0024] 1. Significantly reduces power consumption during cold-end compression of the power cycle and improves cycle efficiency.
[0025] This invention addresses the problems of "difficulty in reducing cooling temperature and high compression power consumption" at the cold end of traditional semi-closed supercritical carbon dioxide power cycles. It enhances heat transfer through direct contact mixed-flow condensation under the same pressure conditions, making it easier for CO2 to be cooled below the corresponding pressure saturation temperature and form a stable liquid phase. This allows liquid-phase pumping to replace or significantly reduce the proportion of near-critical / gas-phase compression, ultimately resulting in lower compression power per unit mass, higher net output power, and higher cycle efficiency at the system level. Simultaneously, it can be used for research and engineering applications in cold-end heat exchange, phase change, and separation processes, providing an effective technical means for cold-end optimization.
[0026] 2. It is suitable for extreme low temperature environments and has universal cold source interfaces, with strong system integration and operation support capabilities.
[0027] The present invention allows for the use of blended working fluids to lower the freezing point, enabling the device to stably establish a cold source and reduce the risk of freezing / blockage in scenarios such as polar regions, frozen oceans, high-latitude sea areas, ships / icebreakers, and energy stations in cold regions. Simultaneously, the cooling working fluid side indirectly exchanges heat with an external cold source via a conventional heat exchanger. This external cold source can be seawater cooling, district cooling, natural cold sources, cryogenic refrigerant systems, or even cryogenic industrial waste cooling, achieving "standardization of the cold-end device and universalization of the cold source interface." Furthermore, the cooling working fluid loop and the external cold source form a two-stage cold source cycle, allowing for the recycling of cooling capacity within the system and reducing dependence on external cooling conditions, thereby improving overall energy efficiency and engineering economy.
[0028] 3. The system is more compact and has a higher power density, making it suitable for platform applications with limited space and weight.
[0029] Compared to traditional solutions that rely on large indirect heat exchangers for deep cooling, this invention uses direct contact heat exchange to enhance the heat transfer process and liquid phase pumping to achieve pressure recovery. This can reduce the heat exchange area and compressor volume requirements while meeting the same cooling and compression targets, thereby improving the overall compactness and power density of the device. It is particularly suitable for scenarios that are sensitive to volume, weight and layout space, such as ships, icebreakers, offshore platforms and containerized modular energy systems. Attached Figure Description
[0030] Figure 1 This is a schematic diagram of an embodiment of a carbon dioxide mixed-flow condensation and density difference separation device applied to the cold end of a power generation cycle according to the present invention.
[0031] Among them, 1-high-pressure carbon dioxide cylinder, 2-check valve at cylinder outlet, 3-carbon dioxide mass flow meter, 4-first gas phase check valve, 5-first temperature and pressure sensor, 6-first carbon dioxide pressurization pump valve, 7-carbon dioxide pressurization pump, 8-second carbon dioxide pressurization pump valve, 9-second gas phase check valve, 10-gas cylinder pressure reducing valve, 11-carbon dioxide storage cylinder, 12-cooling working fluid storage tank, 13-first liquid pressurization pump valve, 14-first liquid pressurization pump. 15-Second liquid pressurization pump valve, 16-Liquid mass flow meter, 17-Liquid phase check valve, 18-External cold source, 19-High-pressure conventional heat exchanger, 20-Third liquid pressurization pump valve, 21-Second liquid pressurization pump, 22-Fourth liquid pressurization pump valve, 23-Pressure reducing valve, 24-Second temperature and pressure sensor, 25-T-way pipe, 26-Static mixer, 27-Third temperature and pressure sensor, 28-Back pressure valve, 29-Separation tank, 30-External power circulation system. Detailed Implementation
[0032] The present invention will be further described in detail below with reference to the accompanying drawings.
[0033] like Figure 1The embodiment of the present invention shown includes: a carbon dioxide working fluid circuit 100, a cooling working fluid circuit 200, and a mixing working fluid circuit 300. The mixing working fluid circuit 300 mixes and exchanges the high-temperature, high-pressure gaseous CO2 input from the carbon dioxide working fluid circuit 100 with the cooling working fluid in the cooling working fluid circuit 200 at the same pressure and cooling temperature. This direct contact heat exchange cools the CO2 to below its saturation temperature at a set pressure, thus liquefying the carbon dioxide. Then, utilizing the density difference between the working fluids in the mixing working fluid circuit, the liquefied carbon dioxide and the cooling working fluid are separated in a separation tank. After separation, they return to their respective circuits, and the CO2 and cooling working fluid are separated in their respective circuits. The self-circulation is completed by compensating for pressure and temperature through a series of devices in the loop to return to the state before mixing. Specifically, in the mixing working fluid loop 300, the temperature of the cooling working fluid is lower than the saturation temperature of CO2 under the pressure before mixing. CO2 and the cooling working fluid undergo direct contact heat exchange under isobaric conditions. The volume fraction of CO2:cooling working fluid is controlled by a mass flow meter to be 3:7, the characteristic L / D ratio of the mixing section is (about 10 to 19), and the arrangement of check valves and buffer cavities are used to ensure continuous interface renewal and full gas-liquid contact. Thus, under the critical pressure of CO2, the inlet temperature is controlled at the saturation temperature of the pressure, and CO2 is cooled to below the saturation temperature of CO2 to complete liquefaction.
[0034] The carbon dioxide working fluid circuit 100 includes: a high-pressure carbon dioxide cylinder 1, a check valve 2 at the cylinder outlet, a carbon dioxide mass flow meter 3, a first gas phase check valve 4, a first temperature and pressure sensor 5, a first carbon dioxide pressurizing pump valve 6, a carbon dioxide pressurizing pump 7, a second carbon dioxide pressurizing pump valve 8, an external power circulation system 30, a second gas phase check valve 9, a carbon dioxide storage cylinder 11, and a storage cylinder pressure reducing valve 12. The working fluid in the carbon dioxide circuit 100 is carbon dioxide. The inlet of the carbon dioxide working fluid circuit 100, the first temperature and pressure sensor 5, the first carbon dioxide pressurizing pump valve 6, the carbon dioxide pressurizing pump 7 (specifically a plunger pump), the second carbon dioxide pressurizing pump valve 8, the second gas phase check valve 9, the carbon dioxide mass flow meter 3, the first gas phase check valve 4, and the outlet of the carbon dioxide working fluid circuit 100 are connected in sequence through a carbon dioxide pipeline. The carbon dioxide mass flow meter 3 is installed at the location on the carbon dioxide pipeline where data needs to be collected.
[0035] A high-pressure carbon dioxide cylinder 1 with an electric heating wire is connected to the pipeline before the carbon dioxide mass flow meter 3 through a check valve 2 at the cylinder outlet.
[0036] The carbon dioxide working fluid circuit 100 also includes a gas cylinder pressure reducing valve 10 and a carbon dioxide gas cylinder 121. The outlet of the second gas phase check valve 9 is connected to the carbon dioxide gas cylinder 11 via the gas cylinder pressure reducing valve 10.
[0037] The cooling medium circuit 200 includes: a cooling medium storage tank 12, a first liquid pressurization pump valve 13, a first liquid pressurization pump 14, a second liquid pressurization pump valve 15, a liquid mass flow meter 16, a liquid phase check valve 17, an external cold source 18, a high-pressure conventional heat exchanger 19, a third liquid pressurization pump valve 20, a second liquid pressurization pump 21, a fourth liquid pressurization pump valve 22, and a pressure reducing valve 23. The inlet of the cooling medium circuit 200, the second temperature and pressure sensor 24, the hot side of the high-pressure conventional heat exchanger 19, the third liquid pressurization pump valve 20, the second liquid pressurization pump 21, the fourth liquid pressurization pump valve 22, the liquid mass flow meter 16, the liquid phase check valve 17, and the outlet of the cooling medium circuit 200 are sequentially connected via cooling medium pipelines. The liquid mass flow meter 16 is installed at the location on the cooling medium pipeline where data needs to be collected.
[0038] A branch line from the outlet of the third liquid pressurizing pump valve 20 is introduced into the cooling medium storage tank 12 via the pressure reducing valve 23. The outlet of the cooling medium storage tank 12 is introduced into the pipeline before the liquid mass flow meter 16 via the first liquid pressurizing pump valve 13, the first liquid pressurizing pump 14 (specifically a plunger pump), and the second liquid pressurizing pump valve 15. The cold side inlet and cold side outlet of the high-pressure conventional heat exchanger 19 are connected to the outlet and inlet of the external cold source 18, respectively.
[0039] The mixing working fluid loop 300 includes: a three-way pipe 25, a static mixer 26, a third temperature and pressure sensor 27, and a separator 29; wherein the first port of the three-way pipe 25 is connected to the static mixer 26 and the third temperature and pressure sensor 27 in sequence, and to the inlet of the separator 29; the second port of the three-way pipe 25 is connected to the outlet of the cooling working fluid loop 200, and the third port of the three-way pipe 25 is connected to the outlet of the carbon dioxide working fluid loop 100; the cooling working fluid outlet at the bottom of the separator 29 is connected to the inlet of the cooling working fluid loop 200 via a lower back pressure valve 28, and the working fluid outlet at the top of the separator 29 is connected to the inlet of the carbon dioxide working fluid loop 100 via an upper back pressure valve 28;
[0040] Before mixing, CO2 and cooling working fluid are pretreated at the same pressure and temperature to ensure that the two working fluids enter the mixing section within a controlled window of the same pressure.
[0041] Subsequently, isobaric direct contact condensation of high-pressure gaseous CO2 and high-pressure low-temperature liquid cooling medium is achieved in a static mixer, cooling CO2 to below the saturation temperature at the corresponding pressure to complete liquefaction;
[0042] After heat exchange, the mixed working fluid enters the inlet of the separator from the outlet of the static mixer. Once in the separator, under the influence of gravity and the density difference between the carbon dioxide and cooling working fluids, stratification occurs, maintaining a small pressure-temperature difference window before and after separation. The carbon dioxide working fluid, being the lighter phase, flows out from the upper outlet of the separator, while the cooling working fluid (water), being the heavier phase, flows out from the lower outlet. The upper outlet of the separator is connected to valve 1 of the carbon dioxide plunger pump in the carbon dioxide pressurization pump circuit, and the lower outlet is connected to the inlet section of the high-pressure conventional heat exchanger in the cooling working fluid circuit, enabling continuous circulation. The external power circulation system 30 is a closed / semi-closed power circulation interface, used to allow the working fluid pressurized by the carbon dioxide pressurization pump 7 to enter the external power circulation system 30, where it undergoes heating (vaporization / temperature rise) and expansion, subsequently returning to the carbon dioxide pipeline as a gaseous working fluid via the second gas phase check valve 9.
[0043] Before mixing in the static mixer, the temperature of the cooling medium on the working fluid side is generally above zero degrees Celsius. Other substances can be added to the cooling medium circuit 200 to lower the freezing point, such as ethylene glycol, to achieve a lower cooling effect. Therefore, in this embodiment, the cooling medium in the cooling medium circuit 200 provides three options: pure water, alcohol-containing water, and water containing inorganic salts. The temperature of the cooling medium on the working fluid side before mixing in the static mixer 26 is higher than the freezing point of the cooling medium. When the cooling medium is pure water, the freezing point is freezing. In the closed-loop liquid circulation, other substances (such as ethylene glycol) can be added to lower the freezing point, allowing the cooling medium to participate in mixing and condensation at a lower temperature, achieving a better cooling effect. Therefore, the options of using alcohol-containing water and water containing inorganic salts as cooling medium can provide a lower freezing point, with the alcohol-containing water blending ratio being 10%-60% and the inorganic salt-containing water blending ratio being 20%-30%.
[0044] In this embodiment, the external power circulation system 30 can be specifically implemented through combustion heating, indirect heat exchange heating, and turbine work, etc.
[0045] The workflow of this embodiment is as follows:
[0046] Step 1, Start-up phase: The carbon dioxide working medium is stored in a high-pressure carbon dioxide cylinder 1 with an electric heating wire wrapped around it, and the cooling working medium is stored in a cooling working medium storage tank 12.
[0047] The device of this invention employs a startup strategy of "cooling the working fluid circuit first, then starting CO2." During startup, the cooling working fluid circuit is first activated, and the liquid pressurization pump is started at a low flow rate. This allows the separator to establish a sufficient liquid level and establishes a stable cold source through a high-pressure conventional heat exchanger and an external cold source, while simultaneously raising the system back pressure to the target pressure. The separator temperature is then controlled to be 3-6 degrees below the CO2 saturation temperature at the corresponding pressure. oAfter reaching the range of C, CO2 working fluid is gradually introduced, with the initial CO2 flow rate being 10% to 20% of the design value. After monitoring that the separation interface is stable and the light phase density meets the liquid phase criterion, the flow rates of CO2 and cooling working fluid are gradually increased simultaneously until the design conditions are reached.
[0048] The process of starting the cooling medium circuit is as follows: the cooling medium in the cooling medium storage tank 12 enters the first liquid pressurization pump 14 through the first liquid pressurization pump valve 13 for primary pressurization, raising the pressure of the cooling medium to the same pressure level as the carbon dioxide working medium at the first gas phase check valve 4 in the carbon dioxide circuit; the pressurized cooling medium flows into the liquid mass flow meter 16 through the second liquid pressurization pump valve 15, and the liquid mass flow meter 16 monitors the cooling medium flow in real time, and then enters the mixed working medium circuit 300 through the liquid phase check valve 17, where it acts as a cooling medium for direct contact heat exchange with carbon dioxide;
[0049] The process of introducing CO2 working fluid is as follows: The electric heating wire in the high-pressure carbon dioxide cylinder 1 is energized to heat the cylinder, causing the carbon dioxide inside to heat up and pressurize, pushing it out through the check valve 2 at the cylinder outlet. The opening degree of the check valve 2 at the cylinder outlet is used to regulate the carbon dioxide flow rate during the start-up phase, and the flow rate data is monitored in real time by the carbon dioxide mass flow meter 3. When the flow rate monitored by the carbon dioxide mass flow meter 3 and the inlet pressure of the first gas phase check valve 4 reach the preset value, the first gas phase check valve 4 opens, and the carbon dioxide working fluid flows into the mixing working fluid circuit 300 through the carbon dioxide mass flow meter 3. It then enters the static mixer 26 through the three-way pipe 25 and directly contacts the high-pressure, low-temperature cooling working fluid for heat exchange, completing cooling and liquefaction in the mixing working fluid circuit 300.
[0050] Step 2, Entering a stable cycle: When the carbon dioxide mass and pressure in the loop are stable, and the reading of the carbon dioxide mass flow meter 3 reaches the set value and remains stable for a period of time, turn off the electric heating of the high-pressure carbon dioxide cylinder 1 with the electric heating wire wrapped around it and close the check valve 2 at the cylinder outlet. After that, the carbon dioxide is completely supplied by the internal circulation of the loop, realizing the transition from "cylinder supply + loop circulation" to "pure closed loop circulation".
[0051] Simultaneously, when the pressure, flow rate, and liquid level in the separator 29 within the cooling medium side circuit reach a preset stable range, and the flow rate monitored by the liquid mass flow meter 16 remains stable for a period of time, the first liquid pressurizing pump 14 and the second liquid pressurizing pump valve 15 are closed. The cooling medium storage tank 12 no longer continuously supplies material, and is only opened when replenishment is needed, thus achieving a switch from "cooling medium storage tank supplying medium + high-pressure circulation" to "pure high-pressure closed-loop circulation". After the test is completed, the liquid phase check valve 17 is closed, and the pressure reducing valve 23 is opened, allowing the cooling medium that has passed through the fourth liquid pressurizing pump valve 22 to be depressurized and flow back to the cooling medium storage tank 12, thereby completing the safe recovery of the cooling medium.
[0052] During stable cyclic operation, the separator 29 maintains the rated working pressure and maintains the outlet pressure through the upper back pressure valve 28 and the lower back pressure valve 28 to ensure that the pressure after separation is slightly greater than that before separation, so as to suppress the liquid CO2 to drop pressure and return to vapor along the flow path and avoid phase interface disturbance.
[0053] Meanwhile, a first temperature and pressure sensor 5 and a second temperature and pressure sensor 24 are arranged at the top and bottom of the separator 29 shell, and a third temperature and pressure sensor 27 is also set after the static mixer 26 to detect the pressure difference through measurement data.
[0054] Step 3, Continuous Operation: After cooling and separation, the liquid carbon dioxide working fluid separate tank 29 flows out from the upper outlet and enters the carbon dioxide pressurizing pump 7 through the first carbon dioxide pressurizing pump valve 6 for liquid phase pressurization, restoring the pressure to the level before entering the mixed working fluid circuit to compensate for the pressure loss during the cooling and separation process; after compression, the liquid carbon dioxide working fluid flows out through the second carbon dioxide pressurizing pump valve 8 and enters the external power circulation system 30. After a series of heating and expansion processes, the working fluid becomes gaseous again and returns to the inlet of the first gaseous check valve 4 through the second gas phase check valve 9, where it merges with the carbon dioxide working fluid supplied by the gas cylinder during the start-up phase to form a continuous operation path;
[0055] At the same time, the heated high-pressure cooling medium undergoes indirect heat exchange with the low-temperature cooling medium in the cold source circuit in a conventional heat exchanger, cooling the cooling medium to the temperature level before it enters the mixed working medium circuit.
[0056] Meanwhile, the mixed working fluid flows into the static mixer 26 via the three-way pipe 25, where it merges with the working fluid from the carbon dioxide loop and the cooling working fluid loop. In the static mixer 27, the high-pressure gaseous CO2 and the high-pressure low-temperature liquid cooling working fluid undergo direct contact heat exchange, reducing the temperature of the carbon dioxide to below the saturation temperature of the pressure at which it is located, thus completing liquefaction. After cooling, the liquid mixture of carbon dioxide and cooling working fluid enters the separator 29. The stratification between the working fluids is observed through a visualization window. Due to the density difference, carbon dioxide is the light phase and flows out from the upper outlet of the separator 29, while water (or water or other mixtures) in the cooling working fluid is the heavy phase and flows out from the lower outlet of the separator 29.
[0057] During continuous operation, the system is monitored by the first temperature and pressure sensor 5, the second temperature and pressure sensor 24, the static mixer 26, the carbon dioxide mass flow meter 3, and the liquid mass flow meter 16 to ensure that the low-temperature and high-pressure liquid cooling medium is used as the cooling medium in the mixing section, so as to achieve direct contact heat exchange with the CO2 side under the same pressure but different temperature conditions.
[0058] Step 4: After the test, the shutdown process should be executed in the reverse logic of startup, and the system should be connected to the existing recirculation path, adopting the reverse sequence of startup, and implementing a strategy of "reducing CO2 first, then reducing water":
[0059] First, the working medium in the carbon dioxide working medium loop 100 is recovered, and the CO2 flow rate is gradually reduced to zero. The gas source heating and CO2 inlet valve are closed, while the cooling working medium side is kept circulating and cooled to ensure that the separator is still in a liquid-sealed and cooled state.
[0060] Subsequently, the remaining CO2 in the circuit is controlled and recovered to the carbon dioxide storage cylinder via the pressure reducing valve of the gas cylinder downstream of the pipeline electric heater. The first gas phase check valve 4 is closed, and the gas cylinder pressure reducing valve 10 is opened, so that the carbon dioxide working medium, after being depressurized by the second gas phase check valve 9, enters the carbon dioxide storage cylinder 11 after being depressurized by the gas cylinder pressure reducing valve 10, thus achieving safe recovery of the carbon dioxide working medium.
[0061] After the CO2 side pressure drops to a safe level and the relevant valves are closed, the flow rate of the cooling medium is gradually reduced. The cooling medium is then reduced from high pressure to atmospheric pressure and returned to the cooling medium storage tank through the pressure reducing valve. Finally, the liquid pump is stopped and all valves are closed to achieve safe shutdown of the unit and recovery of the working medium.
[0062] In case of an emergency during any of steps 1-4, immediately shut off the CO2 inlet, stop the gas source heating, and maintain circulation and cooling on the cooling working fluid side to preserve the liquid seal and temperature control of the separator and mixing section. Simultaneously, lock the system back pressure via the back pressure valve to prevent large-scale backflow due to a sudden pressure drop. Then, following the principle of prioritizing CO2 recovery, use the gas cylinder pressure reducing valve to gradually introduce CO2 from the circuit into the carbon dioxide storage cylinder. Once the pressure and temperature drop to a safe range, slowly depressurize the cooling working fluid back to the cooling working fluid storage tank via the pressure reducing valve, and finally stop the pump and close all valves. This emergency shutdown strategy can maintain controllable pressure-temperature window in the separation section under abnormal operating conditions, ensuring the safety of the experimental equipment and personnel.
Claims
1. A carbon dioxide mixed-flow condensation and density difference separation device applied to the cold end of a power cycle, characterized in that, include: The system includes a carbon dioxide working fluid circuit (100), a cooling working fluid circuit (200), and a mixed working fluid circuit (300). The mixed working fluid circuit (300) mixes and exchanges heat between the high-temperature, high-pressure gaseous CO2 input from the carbon dioxide working fluid circuit (100) and the cooling working fluid at the cooling temperature in the cooling working fluid circuit (200). Then, by utilizing the density difference between the working fluids in the mixed working fluid circuit, the liquefied carbon dioxide and the cooling working fluid are separated in a separation tank. In cryogenic mixing, the pressure range is below the critical pressure of CO2, and CO2 and the cooling medium are at the same pressure. The temperature of the cooling medium is lower than the saturation temperature of CO2 under the pressure before mixing.
2. The carbon dioxide mixed-flow condensation and density difference separation device applied to the cold end of a power cycle according to claim 1, characterized in that, The temperature of the cooling medium after mixing with CO2 is below the critical temperature of CO2, thus achieving liquefaction.
3. A carbon dioxide mixed-flow condensation and density difference separation device applied to the cold end of a power cycle according to claim 1 or 2, characterized in that, In the carbon dioxide working fluid circuit (100), the inlet of the carbon dioxide working fluid circuit (100), the first temperature and pressure sensor (5), the first carbon dioxide pressurizing pump valve (6), the carbon dioxide pressurizing pump (7), the second carbon dioxide pressurizing pump valve (8), the external power circulation system (30), the second gas phase check valve (9), the first gas phase check valve (4) and the outlet of the carbon dioxide working fluid circuit (100) are connected in sequence through a carbon dioxide pipeline; The carbon dioxide pipeline is equipped with a carbon dioxide mass flow meter (3).
4. The carbon dioxide mixed-flow condensation and density difference separation device applied to the cold end of a power cycle according to claim 3, characterized in that, The carbon dioxide working fluid circuit (100) also includes: a carbon dioxide storage cylinder (11) and a high-pressure carbon dioxide cylinder (1) with a wound electric heating wire. The high-pressure carbon dioxide cylinder (1) with the wound electric heating wire is connected to the pipeline before the carbon dioxide mass flow meter (3) through the check valve (2) at the cylinder outlet. The outlet of the second gas phase check valve (9) is connected to the carbon dioxide storage cylinder (11) through the storage cylinder pressure reducing valve (10).
5. A carbon dioxide mixed-flow condensation and density difference separation device applied to the cold end of a power cycle according to claim 1 or 2, characterized in that, In the cooling working fluid circuit (200), the inlet of the cooling working fluid circuit (200), the second temperature and pressure sensor (24), the hot side of the high-pressure conventional heat exchanger (19), the third liquid pressurizing pump valve (20), the second liquid pressurizing pump (21), the fourth liquid pressurizing pump valve (22), the liquid phase check valve (17) and the outlet of the cooling working fluid circuit (200) are connected in sequence through the cooling working fluid pipeline; A liquid mass flow meter (16) is installed on the cooling working fluid pipeline.
6. The carbon dioxide mixed-flow condensation and density difference separation device applied to the cold end of a power cycle according to claim 5, characterized in that, The outlet of the third liquid pressurizing pump valve (20) is branched off and fed into the cooling medium storage tank (12) via the pressure reducing valve (23). The outlet of the cooling medium storage tank (12) is fed into the pipeline before the liquid mass flow meter (16) via the first liquid pressurizing pump valve (13), the first liquid pressurizing pump (14), and the second liquid pressurizing pump valve (15). The cold side inlet and cold side outlet of the high-pressure conventional heat exchanger (19) are connected to the outlet and inlet of the external cold source (18), respectively.
7. A carbon dioxide mixed-flow condensation and density difference separation device applied to the cold end of a power cycle according to claim 1 or 2, characterized in that, The mixing working fluid circuit (300) includes: a three-way pipe (25), a static mixer (26), a third temperature and pressure sensor (27), and a separator (29); wherein the first port of the three-way pipe (25) is connected to the static mixer (26) and the third temperature and pressure sensor (27) in sequence, and to the inlet of the separator (29); the second port of the three-way pipe (25) is connected to the outlet of the cooling working fluid circuit (200), and the third port of the three-way pipe (25) is connected to the outlet of the carbon dioxide working fluid circuit (100); the cooling working fluid outlet at the bottom of the separator (29) is connected to the inlet of the cooling working fluid circuit (200) via the lower back pressure valve (28), and the working fluid outlet at the top of the separator (29) is connected to the inlet of the carbon dioxide working fluid circuit (100) via the upper back pressure valve (28); The temperature on the cooling medium side before mixing in the static mixer (26) is higher than the freezing point of the cooling medium.
8. A carbon dioxide mixed-flow condensation and density difference separation device applied to the cold end of a power cycle according to claim 1 or 2, characterized in that, The cooling medium circuit is activated during startup, ensuring that the separator tank reaches a sufficient liquid level, a stable cold source is established through a high-pressure conventional heat exchanger and an external cold source, the system back pressure is increased to the target pressure, and the separator tank temperature is controlled at the CO2 saturation temperature of 5°C at the corresponding pressure. o After the conditions below C are met, CO2 working fluid is introduced, with the initial CO2 flow rate being more than 10% of the design value; after monitoring that the separation interface is stable and the light phase density meets the liquid phase criterion, the flow rates of both CO2 and the cooling working fluid are increased simultaneously. The carbon dioxide working fluid loop (100) is first recovered after shutdown. After the CO2 side pressure drops to a safe value and the relevant valves are closed, the flow rate of the cooling working fluid is gradually reduced. The cooling working fluid is reduced from high pressure to normal pressure and returned to the cooling working fluid storage tank through the pressure reducing valve. Finally, the liquid pump is stopped and all valves are closed to achieve safe shutdown of the device and recovery of the working fluid. In case of emergency, the carbon dioxide working fluid circuit (100) will first recover the CO2 in the circuit by using the pressure reducing valve of the gas storage cylinder to introduce the CO2 in the circuit into the carbon dioxide storage cylinder in stages; after the pressure and temperature drop to a safe range, the working fluid on the cooling working fluid side will be slowly depressurized back to the cooling working fluid storage tank through the pressure reducing valve.
9. A carbon dioxide mixed-flow condensation and density difference separation device applied to the cold end of a power cycle according to claim 7, characterized in that, The cooling medium is: pure water, alcohol-containing water, or water containing inorganic salts; The proportion of alcohol-containing water is 10%-60%, and the proportion of inorganic salt-containing water is 20%-30%.