Seawater desalination closed cycle device and system

Abstract

This application relates to the field of seawater desalination technology, disclosing a closed-loop seawater desalination device and system. The seawater circulation unit stores seawater containing inorganic salts and can heat the seawater to a preset temperature for membrane distillation. The membrane distillation unit desalinates the heated seawater supplied by the seawater circulation unit, generating desalinated steam. A two-stage condensation assembly in the purge gas circulation unit performs multi-stage cooling of the desalinated steam and produces condensate for recovery. A positive pressure purge assembly collects the dry, cold gas discharged from the two-stage condensation assembly and pumps it back to the membrane distillation unit for recycling. A thermal circulation unit is located between the seawater circulation unit and the two-stage condensation assembly. The thermal circulation unit supplies the circulating working fluid from the two-stage condensation assembly to the seawater circulation unit for thermal recycling and cools the recycled working fluid after thermal recycling for further recycling. Compared with existing technologies, this invention can save approximately 20% of energy consumption and reduce seawater desalination costs by approximately 25%.

Description

Technical Field

[0001] This application belongs to the field of seawater desalination technology, specifically relating to a closed-loop seawater desalination device and system. Background Technology

[0002] With the rapid growth of the global population and the continuous development of industry, the shortage of freshwater resources has become a global problem that urgently needs to be solved. Seawater desalination is an effective way to solve the freshwater crisis.

[0003] Currently, the cost of seawater desalination is between 5 and 8 yuan per ton, which is still relatively high compared to the price of tap water. The cost of seawater desalination is composed of various factors, mainly including equipment and material investment, energy consumption, pipeline laying, and pretreatment. Energy consumption accounts for more than 60% of the cost. For example, in a seawater desalination project with a capacity of 10,000 tons or more, the amount of electricity consumed by the distillation method would be a very considerable figure. Currently, seawater desalination mainly utilizes the reverse osmosis method. Reverse osmosis membranes are expensive and easily fouled during use, generally requiring replacement every 3-5 years.

[0004] Among various seawater desalination technologies, membrane distillation technology utilizes the vapor pressure difference across a membrane as the driving force for mass transfer and uses heat to drive water vapor through a porous hydrophobic membrane material for desalination. It has significant advantages in treating high-concentration, highly polluted brine and utilizing low-grade heat such as industrial waste heat, as well as solar and geothermal energy. However, existing membrane seawater desalination technologies suffer from high costs and high energy consumption, which urgently need to be addressed. Summary of the Invention

[0005] The purpose of this application is to provide a closed-loop desalination device and system to reduce the energy consumption cost of desalination.

[0006] To achieve the above objectives, this application provides a closed-loop seawater desalination device, comprising:

[0007] The seawater circulation unit stores seawater containing inorganic salts and can heat the seawater to a preset membrane distillation temperature.

[0008] A membrane distillation unit is used to desalinate the heated seawater supplied by the seawater circulation unit and generate desalinated water vapor.

[0009] The purge gas circulation unit and the seawater circulation unit are located on both sides of the membrane distillation unit. The purge gas circulation unit includes a two-stage condensation assembly and a positive pressure purge assembly. The two-stage condensation assembly is used to perform multi-stage cooling of the demineralized water vapor and produce condensate for recovery. The positive pressure purge assembly is used to collect the dry and cold gas discharged from the two-stage condensation assembly and pump it to the membrane distillation unit for recycling.

[0010] A thermal circulation unit is located between the seawater circulation unit and the two-stage condensation assembly. The thermal circulation unit is used to transport the circulating working fluid of the two-stage condensation assembly to the seawater circulation unit for thermal circulation and to cool and recycle the circulating working fluid after thermal circulation.

[0011] In some embodiments, the seawater circulation unit includes a storage tank, a medium-temperature heater, and a high-temperature heater connected sequentially by pipelines. A booster pump is also provided on the pipeline between the storage tank and the medium-temperature heater to pressurize the seawater in the pipeline. The storage tank stores seawater containing inorganic salts. The medium-temperature heater is used to heat the seawater discharged from the storage tank to a first preset temperature. The high-temperature heater is disposed in the membrane distillation unit and is used to heat the seawater with the first preset temperature to a membrane distillation preset temperature, wherein the membrane distillation preset temperature is greater than the first preset temperature.

[0012] In some embodiments, the seawater circulation unit further includes a replenishment water circuit and a wastewater discharge circuit respectively located at the side and bottom of the storage tank. The replenishment water circuit is equipped with a first heat exchanger, and the pipeline connecting the replenishment water circuit and the wastewater discharge circuit is equipped with a second heat exchanger. Low-concentration, low-temperature seawater is heated by passing through the first heat exchanger and the second heat exchanger and then replenished into the storage tank along the replenishment water circuit. The wastewater discharge circuit is used to receive high-concentration seawater discharged from the storage tank and discharge it to the salt field after cooling by the second heat exchanger.

[0013] In some embodiments, the membrane distillation unit includes a distillation body and a distillation membrane. The distillation membrane is used to divide the distillation body into a first cavity and a second cavity. The high-temperature heater is disposed in the first cavity, and a heating and humidifying device is disposed in the second cavity. The distillation membrane is used to perform membrane distillation on seawater heated by the high-temperature heater to form demineralized water vapor. The heating and humidifying device is used to absorb the high-temperature demineralized water vapor from the inlet dry and cold air to heat and humidify it into humid gas and deliver it to the two-stage condensation assembly.

[0014] In some embodiments, the two-stage condensation assembly includes a medium-temperature condenser and a low-temperature condenser connected by pipes. The inlet end of the medium-temperature condenser is connected to the outlet end of the second cavity. The outlet end of the medium-temperature condenser discharges condensate through a first condensate discharge pipe. The medium-temperature air discharged from the medium-temperature condenser enters the low-temperature condenser for low-temperature condensation. The outlet end of the low-temperature condenser discharges condensate through a second condensate discharge pipe. A circulation pipe is also connected between the medium-temperature condenser and the low-temperature condenser, allowing the dry, cold gas discharged from the low-temperature condenser to enter the medium-temperature condenser for recycling.

[0015] In some embodiments, the positive pressure purging assembly includes a purging pipeline and a fan disposed on the purging pipeline. The purging pipeline is connected between the intermediate temperature condenser and the second cavity. The fan is used to circulate a portion of the dry, cold gas discharged from the intermediate temperature condenser into the second cavity through the purging pipeline. Another portion of the dry, cold gas discharged from the intermediate temperature condenser enters the low temperature condenser through the pipeline.

[0016] In some embodiments, a recovery tank is also provided on the purge pipeline between the blower and the distillation body. The recovery tank is connected to the first condensate discharge pipeline and is used to recover the condensate formed in the purge pipeline.

[0017] In some embodiments, the thermal cycling unit includes:

[0018] The compressor has its inlet end connected to the circulation outlet of the low-temperature condenser. The superheated working fluid discharged from the outlet end of the compressor passes through the high-temperature heater and the medium-temperature heater in sequence via the first hot circulation pipeline for pre-cooling.

[0019] The subcooling component is used to subcool the pre-cooled circulating working fluid.

[0020] The throttling valve assembly throttles the circulating working fluid after it has been subcooled and returns it to the circulation inlet of the cryogenic condenser.

[0021] In some embodiments, the subcooling assembly includes components connected via a conduit along the transport direction of the circulating working fluid:

[0022] The first heat exchanger uses seawater to cool the circulating working fluid that flows out after being cooled by the medium-temperature heater.

[0023] The secondary subcooler is used to collect the condensate discharged from the first condensate discharge pipe and the second condensate discharge pipe, and to perform secondary cooling on the circulating working fluid after the first cooling through the condensate.

[0024] The three-stage subcooler cools the circulating working fluid a third time after the second cooling.

[0025] In some embodiments, the closed-loop desalination device further includes a recovery tank connected to the outlet of the secondary subcooler and used to collect condensate discharged from the secondary subcooler after subcooling.

[0026] In some embodiments, the three-stage subcooler includes an inlet end, an outlet end, a first circulation end, and a second circulation end. The inlet end is connected to the second-stage subcooler, and the outlet end is connected to the low-temperature condenser. A first electromagnetic throttling valve is also provided on the connecting pipe between the two. The first circulation end is connected to the compressor, and a second electromagnetic throttling valve is provided on the connecting pipe between the second circulation end and the outlet end. The first electromagnetic throttling valve is used to significantly reduce the pressure and temperature of the circulating working fluid to achieve heat absorption by the evaporator. The second electromagnetic throttling valve is used to slightly throttle and reduce the temperature of the circulating working fluid after three cooling cycles to achieve the function of gas replenishment and enthalpy increase.

[0027] In some embodiments, the circulating working fluid is a non-azeotropic mixture, or supercritical carbon dioxide can be used to reduce the irreversibility of heat transfer by utilizing the temperature slip phenomenon during the cooling process of the circulating working fluid.

[0028] Furthermore, a second aspect of this application provides a closed-loop desalination system, including an electronic control device and a closed-loop desalination device as described above.

[0029] Through the above technical solution, the seawater to be desalinated stored in the seawater circulation unit is heated and then enters the membrane distillation unit for membrane distillation to obtain demineralized steam. The demineralized steam enters the two-stage condenser of the purge gas circulation unit for condensation to form condensate for recovery. The positive pressure purge unit pumps the dry, cold gas discharged from the two-stage condenser to the membrane distillation unit for recycling, thereby absorbing the ineffective heat load in the two-stage condenser and improving the seawater desalination efficiency of membrane distillation. In addition, this application sets up a thermal circulation unit, which is used to transport the circulating working fluid of the two-stage condenser to the seawater circulation unit for thermal recycling and to cool and recycle the circulating working fluid after thermal recycling, thereby reducing the energy consumption of the entire device and lowering the cost of seawater desalination.

[0030] Other features and advantages of the embodiments of this application will be described in detail in the following detailed description section. Attached Figure Description

[0031] The accompanying drawings are provided to further illustrate the embodiments of this application and form part of the specification. They are used together with the following detailed description to explain the embodiments of this application, but do not constitute a limitation on the embodiments of this application. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without any inventive effort. In the drawings:

[0032] Figure 1 This is a schematic diagram of the closed-loop desalination device of this application.

[0033] Explanation of reference numerals in the attached figures

[0034] 11. Storage tank; 42. Recovery tank; 12. Medium-temperature heater; L1. Make-up water circuit; 13. High-temperature heater; L2. Wastewater circuit; 14. First heat exchanger; L3. First condensate discharge pipeline; 15. Second heat exchanger; L4. Second condensate discharge pipeline; 16. Booster pump; L5. Circulation pipeline; 21. Distillation body; L6. Purge pipeline; 22. Distillation membrane; 51. Compressor; 23. Heating and humidifying unit; 52. Secondary subcooler; 31. Medium-temperature condenser; 53. Tertiary subcooler; 32. Low-temperature condenser; 54. First electromagnetic throttle valve; 41. Fan; 55. Second electromagnetic throttle valve. Detailed Implementation

[0035] The specific embodiments of this application will be described in detail below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are for illustration and explanation only and are not intended to limit this application.

[0036] The following description, with reference to the accompanying drawings, describes a closed-loop desalination device according to this application.

[0037] like Figure 1 As shown, this application provides a closed-loop seawater desalination device, including a seawater circulation unit, a membrane distillation unit, a purge gas circulation unit, and a thermal circulation unit. The seawater circulation unit stores seawater containing inorganic salts and can heat the seawater to a preset temperature for membrane distillation. The membrane distillation unit desalinates the heated seawater supplied by the seawater circulation unit and generates desalinated steam. The purge gas circulation unit and the seawater circulation unit are located on opposite sides of the membrane distillation unit. The purge gas circulation unit includes a two-stage condensation assembly and a positive pressure purge assembly. The two-stage condensation assembly is used to perform multi-stage cooling of the desalinated steam and produce condensate for recovery. The positive pressure purge assembly is used to collect the dry, cold gas discharged from the two-stage condensation assembly and pump it to the membrane distillation unit for recycling. The thermal circulation unit is located between the seawater circulation unit and the two-stage condensation assembly. The thermal circulation unit is used to supply the circulating working fluid from the two-stage condensation assembly to the seawater circulation unit for thermal recycling and to cool and recycle the circulating working fluid after thermal recycling. The seawater circulation unit is formed as follows: Figure 1 The purple loop shown has a thermal cycle unit that forms as follows: Figure 1 The green circulation loop shown has a portion of the purge air circulation unit forming as follows: Figure 1 The red pipe shown.

[0038] In this embodiment, the seawater to be desalinated stored in the seawater circulation unit is heated and then enters the membrane distillation unit for membrane distillation to obtain desalinated steam. The desalinated steam enters the two-stage condenser assembly of the purge gas circulation unit for condensation to form condensate for recovery. The positive pressure purge assembly pumps the dry, cold gas discharged from the two-stage condenser assembly to the membrane distillation unit for recycling, thereby absorbing the ineffective heat load in the two-stage condenser assembly and improving the seawater desalination efficiency of membrane distillation. In addition, by setting up a thermal circulation unit, the energy of the circulating working fluid in the two-stage condenser assembly can be recycled, thereby reducing the energy consumption of the entire device and lowering the cost of seawater desalination.

[0039] This device innovatively integrates and couples a seawater circulation unit, a membrane distillation unit, a purge gas circulation unit, and a thermal circulation unit. It combines the advantages of multiple technologies, including supplemental heating membrane distillation, positive pressure purge and negative pressure condensation purging, and three-stage non-azeotropic mixed working fluid subcooling. The thermal circulation unit efficiently recovers ineffective heat load, increases seawater temperature, and enhances the vaporization rate of water molecules on the surface of the distillation membrane 22. Thermally driven water vapor passes through the porous hydrophobic membrane material for desalination, achieving efficient and low-energy-consumption seawater production. This invention can be widely applied in the field of seawater desalination. Compared with existing membrane seawater desalination technologies, it can save approximately 20% of energy consumption and reduce seawater desalination costs by approximately 25%, demonstrating broad prospects for widespread application.

[0040] In some embodiments, the seawater circulation unit includes a storage tank 11, a medium-temperature heater 12, and a high-temperature heater 13 connected in sequence by pipes. The storage tank 11 stores seawater containing inorganic salts. The medium-temperature heater 12 is used to heat the seawater discharged from the storage tank 11 to a first preset temperature. The high-temperature heater 13 is disposed in the membrane distillation unit and is used to heat the seawater with the first preset temperature to the membrane distillation preset temperature, wherein the membrane distillation preset temperature is greater than the first preset temperature.

[0041] In this embodiment, to improve the operating efficiency of the membrane distillation unit, the heat exchanger used to heat the seawater transported from the storage tank 11 is divided into a high-temperature section and a medium-temperature section. The medium-temperature section is a medium-temperature heater 12, and the high-temperature section is a high-temperature supplementary heater 13 located within the membrane distillation unit. The medium-temperature heater 12 is located on the pipeline between the storage tank 11 and the membrane distillation unit. The medium-temperature heater 12 is used to heat the seawater to a first preset temperature. Then, the high-temperature supplementary heater 13 continuously supplements the seawater at the first preset temperature within the membrane distillation unit, thereby continuously replenishing the heat energy consumed by the vaporization of water molecules on the membrane surface, maintaining a higher transport driving force on the membrane surface, ensuring uniform and efficient mass transfer across the entire distillation membrane 22 surface, and improving the utilization rate of the distillation membrane 22.

[0042] Furthermore, a booster pump 16 is installed on the pipeline between the storage tank 11 and the intermediate temperature heater 12. The booster pump 16 is used to pressurize the seawater in the pipeline. By installing the booster pump 16, one end of which is connected to the top of the storage tank 11, and the pipeline extending below the liquid surface of the storage tank 11, the seawater transported from the storage tank 11 is raised to a certain pressure by the booster pump 16 and then enters the intermediate temperature heater 12 for heating, so as to ensure the smooth operation of the entire seawater transport.

[0043] In order to make full use of the low-temperature cold source of seawater replenishment and the waste heat of sewage seawater, the seawater circulation unit also includes a replenishment water circuit L1 and a sewage discharge circuit L2 respectively located at the side and bottom of the storage tank 11. The replenishment water circuit L1 is equipped with a first heat exchanger 14, and the pipeline connecting the replenishment water circuit L1 and the sewage discharge circuit L2 is equipped with a second heat exchanger 15. The low-concentration low-temperature seawater is heated by the first heat exchanger 14 and the second heat exchanger 15 and then replenished into the storage tank 11 along the replenishment water circuit L1. The sewage discharge circuit L2 is used to receive the high-concentration seawater discharged from the storage tank 11 and discharge it to the salt field after cooling by the second heat exchanger 15.

[0044] The first heat exchanger 14 can increase the temperature of the incoming low-concentration, low-temperature seawater, reducing energy consumption, and also lower the temperature of the non-azeotropic refrigerant mixture after the condenser in the thermal cycle unit, increasing the refrigerant's subcooling. The second heat exchanger 15 can effectively recover the waste heat from the discharged high-concentration seawater to heat the seawater in the replenishment water loop L1. This allows for cooling the discharged high-concentration seawater while simultaneously warming the incoming low-temperature, low-concentration seawater, thereby reducing system heat loss.

[0045] In some embodiments, the membrane distillation unit includes a distillation body 21 and a distillation membrane 22. The distillation membrane 22 is used to divide the distillation body 21 into a first chamber and a second chamber. A high-temperature heater 13 is disposed in the first chamber, and a heating and humidifying device 23 is disposed in the second chamber. The distillation membrane 22 is used to perform membrane distillation on seawater heated by the high-temperature heater 13 to form demineralized water vapor. The heating and humidifying device is used to absorb the high-temperature demineralized water vapor with inlet dry and cold air, heat and humidify it into humid gas, and deliver it to the two-stage condensation assembly.

[0046] In this embodiment, during device operation, water molecules in the high-temperature seawater on the high-temperature heater 13 side are transferred to the second chamber via the distillation membrane 22. The driving force is that the water vapor pressure on the surface of the distillation membrane 22 is higher than the water vapor partial pressure in the second chamber. The pressure difference drives the water in the seawater to continuously migrate into the second chamber, thus achieving seawater desalination. Meanwhile, the heating and humidifying unit 23 in the second chamber heats the desalinated water vapor in the second chamber and forms a humid gas that is then transported to the medium-temperature condenser 31 for condensation.

[0047] In some embodiments, the two-stage condensation assembly includes a medium-temperature condenser 31 and a low-temperature condenser 32 connected by pipes. The inlet end of the medium-temperature condenser 31 is connected to the outlet end of the second chamber. The outlet end of the medium-temperature condenser 31 discharges condensate through a first condensate discharge pipe, and the outlet end of the low-temperature condenser 32 discharges condensate through a second condensate discharge pipe. A circulation pipe L5 is also connected between the medium-temperature condenser 31 and the low-temperature condenser 32, so that the dry and cold gas discharged from the low-temperature condenser 32 can enter the medium-temperature condenser 31 for recycling.

[0048] In this embodiment, the hot, humid gas discharged from the outlet of the second chamber after membrane distillation can enter the medium-temperature condenser 31 through the inlet of the medium-temperature condenser 31 for condensation. A portion forms condensate, which is discharged and recycled through the first condensate discharge pipe. The remaining portion forms dry, cold gas, which enters the low-temperature condenser 32 for further low-temperature condensation. After condensation in the low-temperature condenser 32, condensate is formed and discharged and recycled through the second condensate discharge pipe. The remaining dry, cold gas returns to the medium-temperature condenser 31 for recycling, thereby reducing energy loss. The circulating medium in the entire purge gas circulation unit can be air, nitrogen, etc.

[0049] In some embodiments, the positive pressure purging assembly includes a purging pipe L6 and a fan 41 mounted on the purging pipe L6, which is connected between the intermediate-temperature condenser 31 and the second chamber. To improve the water vapor absorption efficiency of the purging gas circulation unit, a positive pressure purging and negative pressure condensation method is adopted. Compared with the prior art where the fan 41 is placed before the condenser, in this embodiment, by adjusting the position of the fan 41 from before the condenser to after the condenser, the fan 41 can receive dry and cold gas discharged from the condenser. In this way, the inlet working fluid of the fan 41 is changed from high-temperature and high-humidity gas to dry and cold gas, which can reduce the power consumption of the fan 41, improve the operational reliability of the fan 41, and further reduce the humidity of the dry and cold gas. Furthermore, the negative pressure condensation scheme of this application adopts a two-stage series condenser: a medium-temperature condenser and a low-temperature condenser. The medium-temperature condenser receives the hot and humid gas discharged from the membrane distillation unit and performs medium-temperature condensation. The blower 41 is used to circulate the dry and cold gas discharged from the medium-temperature condenser 31 into the second chamber through the purge pipe L6 to absorb water vapor on the surface of the distillation membrane 22. Another part of the dry and cold gas discharged from the medium-temperature condenser enters the low-temperature condenser through the pipeline for further low-temperature condensation, thereby efficiently recovering the moisture in the high-temperature and high-humidity purge gas and improving the seawater desalination efficiency.

[0050] When dry, cold gas is purged and recovered in the purge line L6, some water vapor in the dry, cold gas condenses into condensate due to the increased pressure. Therefore, a recovery tank 42 is also provided in the purge line L6 between the blower 41 and the distillation body 21. The recovery tank 42 is connected to the first condensate discharge line. The recovery tank 42 is used to recover the condensate formed in the purge line L6, improving the safe and reliable operation of the blower 41. On the other hand, in order to realize the recovery of condensate on the purge line L6, the outlet of the recovery tank 42 is connected to the first condensate discharge line, so that the condensate on the purge line L6 can be collected in the first condensate discharge line for discharge and recovery.

[0051] In some embodiments, the thermal circulation unit includes a compressor 51, a subcooling assembly, and a throttling valve assembly; the inlet end of the compressor 51 is connected to the circulation outlet of the low-temperature condenser 32, and the superheated working fluid discharged from the outlet end of the compressor 51 is pre-cooled by passing through the high-temperature heater 13 and the medium-temperature heater 12 in sequence through the first thermal circulation pipeline; the subcooling assembly is used to subcool the pre-cooled circulating working fluid; the throttling valve assembly throttles the subcooled circulating working fluid and returns it to the circulation inlet of the low-temperature condenser 32.

[0052] In this embodiment, since the temperature of the circulating working fluid discharged from the outlet of compressor 51 is very high, in order to fully utilize this heat energy, the outlet of compressor 51 is connected to the high-temperature heater 13 and the medium-temperature heater 12 through the first thermal circulation pipeline. This allows the heat energy of compressor 51 to be utilized sequentially by the high-temperature heater 13 and the medium-temperature heater 12, thus gradually reducing the temperature of the circulating working fluid after passing through these components, achieving pre-cooling. After pre-cooling, the circulating working fluid undergoes subcooling via a subcooling assembly and finally throttling via a throttling valve assembly to complete the entire thermal cycle. Through the thermal cycle process of the thermal circulation unit, the heat energy of the circulating working fluid can be supplied to the high-temperature heater 13 and the medium-temperature heater 12, and cooled by the replenished cold seawater of the first heat exchanger 14 and the recovered condensate of the secondary subcooler 52. This ensures full utilization of energy within the entire device, reducing energy consumption and the overall cost of seawater desalination.

[0053] In some embodiments, the subcooling assembly includes a first heat exchanger 14, a second-stage subcooler 52, and a third-stage subcooler 53 connected by pipes along the flow direction of the circulating working fluid. The first heat exchanger 14 performs primary cooling of the circulating working fluid flowing out from the intermediate-temperature heater 12 by seawater makeup. The second-stage subcooler 52 collects condensate discharged from the first and second condensate discharge pipes and performs secondary cooling of the circulating working fluid after primary cooling using the condensate. The third-stage subcooler 53 performs tertiary cooling of the circulating working fluid after secondary cooling. The three-stage subcooling device can significantly improve the subcooling degree of the non-azeotropic refrigerant mixture and increase the enthalpy difference between the inlet and outlet of the evaporator.

[0054] Furthermore, the closed-loop desalination unit also includes a recovery tank connected to the outlet of the secondary subcooler 52 and used to collect the condensate discharged from the secondary subcooler 52 after subcooling. The condensate collected in the coils of the medium-temperature condenser and the low-temperature condenser is collected and then sent to the secondary subcooler 52 to perform secondary subcooling of the circulating working fluid, thereby increasing the cooling capacity of the heat pump system. It is then sent to the recovery tank for pure water recovery, completing the freshwater collection process.

[0055] In some embodiments, the three-stage subcooler 53 includes an inlet end, an outlet end, a first circulation end, and a second circulation end. The inlet end is connected to the second-stage subcooler 52, and the outlet end is connected to the low-temperature condenser. A first electromagnetic throttling valve 54 is also provided on the connecting pipe between the two. The first circulation end is connected to the compressor 51, and a second electromagnetic throttling valve 55 is provided on the connecting pipe between the second circulation end and the outlet end. The first electromagnetic throttling valve 54 is used to significantly reduce the pressure and temperature of the circulating working fluid to achieve heat absorption by the evaporator. The second electromagnetic throttling valve 55 is used to slightly throttle and cool the circulating working fluid that has undergone three cooling cycles to achieve the function of gas replenishment and enthalpy increase.

[0056] The first electromagnetic throttling valve 54 and the second electromagnetic throttling valve are both common throttling valves in existing heat pump circulation systems, which can achieve the effects of pressure reduction and temperature reduction of the circulating working fluid. During operation, the high-pressure liquid circulating working fluid experiences a sudden pressure drop (approaching an isenthalpic process) after passing through the small orifice or narrow channel of the electromagnetic throttling valve, and some of the liquid flashes into vapor, resulting in a decrease in temperature. Furthermore, the flow rate of the circulating working fluid can be adjusted according to system requirements to ensure full utilization of the evaporator and prevent liquid slugging in the compressor 51. Before the two electromagnetic throttling valves apply throttling, the circulating working fluid needs to undergo three stages of subcooling to ensure sufficient subcooling (typically ≥5°C) of the liquid circulating working fluid, preventing excessive flashing gas from causing a decrease in flow rate.

[0057] In some implementations, the circulating working fluid is a non-azeotropic mixture, such as R245fa / R152a, R134a / R245fa, etc. Supercritical carbon dioxide can also be used. The temperature glide phenomenon during the cooling process of the circulating working fluid is used to reduce the irreversibility of heat transfer.

[0058] Furthermore, this application also proposes a closed-loop seawater desalination system, including an electronic control device and a closed-loop seawater desalination device as described above. The electronic control device can be a power supply device and provides power to the closed-loop seawater desalination device to ensure its normal operation. Moreover, since this system employs all embodiments of the aforementioned closed-loop seawater desalination device, it possesses all the beneficial effects of the aforementioned closed-loop seawater desalination device, which will not be elaborated upon here.

[0059] In the description of this application, it should be understood that the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this application, "multiple" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0060] In this application, unless otherwise expressly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection, an electrical connection, or a connection that allows communication between components; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components, unless otherwise expressly limited. Those skilled in the art can understand the specific meaning of the above terms in this application based on the specific circumstances.

[0061] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0062] Although embodiments of this application have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting this application. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of this application.

Claims

1. A closed-loop seawater desalination device, characterized in that, It includes an integrated and coupled seawater circulation unit, membrane distillation unit, purge gas circulation unit, and thermal circulation unit; among which, The seawater circulation unit stores seawater containing inorganic salts and can perform secondary heating of the seawater to the membrane distillation preset temperature. The seawater circulation unit includes a storage tank (11), a medium-temperature heater (12), and a high-temperature heater (13) connected in sequence by pipes. The storage tank (11) stores seawater containing inorganic salts. The medium-temperature heater (12) is located on the pipeline between the storage tank (11) and the membrane distillation unit and is used to heat the seawater discharged from the storage tank (11) to a first preset temperature. The high-temperature heater (13) is installed in the membrane distillation unit and is used to heat the seawater with the first preset temperature to the membrane distillation preset temperature. The membrane distillation preset temperature is greater than the first preset temperature. The membrane distillation unit is used to desalinate the heated seawater supplied by the seawater circulation unit and generate desalinated water vapor. The membrane distillation unit includes a distillation body (21) and a distillation membrane (22). The purge gas circulation unit and the seawater circulation unit are located on both sides of the membrane distillation unit. The purge gas circulation unit includes a two-stage condensation assembly and a positive pressure purge assembly. The two-stage condensation assembly is used to cool the demineralized water vapor in two stages and generate condensate for recovery. The positive pressure purge assembly is used to collect the dry and cold gas discharged from the two-stage condensation assembly, compress and pressurize it, and then send it to the membrane distillation unit. The thermal circulation unit is a circulation loop located between the seawater circulation unit and the two-stage condensation assembly. The thermal circulation unit uses a subcooling assembly to recover the ineffective heat load contained in the circulating working fluid of the two-stage condensation assembly, utilizes the seawater circulation unit for a two-stage heating process, and cools and recycles the circulating working fluid in the thermal circulation unit to recover the ineffective heat load and increase the vaporization rate of water molecules on the surface of the distillation membrane (22).

2. The closed-loop seawater desalination device according to claim 1, characterized in that, A booster pump (16) is also provided on the pipeline between the storage tank (11) and the medium-temperature heater (12). The booster pump (16) is used to pressurize the seawater in the pipeline. One end of the booster pump (16) is connected to the top of the storage tank (11), and the pipeline extends below the liquid surface of the storage tank (11) so that the seawater transported in the storage tank (11) is raised to a certain pressure by the booster pump (16) and then enters the medium-temperature heater (12) for heating.

3. The closed-loop seawater desalination device according to claim 1, characterized in that, The seawater circulation unit also includes a replenishment water circuit (L1) and a wastewater circuit (L2) respectively located at the side and bottom of the storage tank (11). The replenishment water circuit (L1) is provided with a first heat exchanger (14), and the pipeline connecting the replenishment water circuit (L1) and the wastewater circuit (L2) is provided with a second heat exchanger (15). Low-concentration low-temperature seawater is heated by passing through the first heat exchanger (14) and the second heat exchanger (15) and then replenished into the storage tank (11) along the replenishment water circuit (L1). The first heat exchanger (14) is used to increase the water temperature of the replenished low-concentration low-temperature seawater and reduce the temperature of the non-azeotropic mixed refrigerant after the condenser in the heat circulation unit. The wastewater circuit (L2) is used to receive the high-concentration seawater discharged from the storage tank (11) and discharge it to the salt field after being cooled by the second heat exchanger (15). The second heat exchanger (15) is used to recover the waste heat of the discharged high-concentration seawater to heat the seawater in the replenishment water circuit (L1).

4. The closed-loop seawater desalination device according to claim 3, characterized in that, The distillation membrane (22) is used to divide the distillation body (21) into a first cavity and a second cavity. The high-temperature heater (13) is located in the first cavity, and the second cavity is equipped with a heating and humidifying device (23). The distillation membrane (22) is used to perform membrane distillation on the seawater heated by the high-temperature heater (13) to form demineralized water vapor. The heating and humidifying device (23) is used to absorb the high-temperature demineralized water vapor from the inlet dry and cold air to achieve heating and humidification into humid gas and deliver it to the two-stage condensation assembly.

5. The closed-loop seawater desalination device according to claim 4, characterized in that, The two-stage condensation assembly includes a medium-temperature condenser (31) and a low-temperature condenser (32) connected in series by pipes. The inlet end of the medium-temperature condenser (31) is connected to the outlet end of the second cavity. The outlet end of the medium-temperature condenser (31) discharges condensate through a first condensate discharge pipe. The medium-temperature air discharged from the medium-temperature condenser (31) enters the low-temperature condenser (32) for low-temperature condensation. The outlet end of the low-temperature condenser (32) discharges condensate through a second condensate discharge pipe. A circulation pipe (L5) is also connected between the medium-temperature condenser (31) and the low-temperature condenser (32). The dry and cold gas discharged from the low-temperature condenser (32) can enter the medium-temperature condenser (31) for recycling.

6. The closed-loop seawater desalination device according to claim 5, characterized in that, The positive pressure purging assembly includes a purging pipe (L6) and a fan (41) installed on the purging pipe (L6). The purging pipe (L6) is connected between the medium-temperature condenser (31) and the second cavity. The fan (41) is used to circulate a portion of the dry and cold gas discharged from the medium-temperature condenser (31) into the second cavity through the purging pipe (L6). Another portion of the dry and cold gas discharged from the medium-temperature condenser enters the low-temperature condenser through a pipe.

7. The closed-loop seawater desalination device according to claim 6, characterized in that, A recovery tank (42) is also provided on the purge pipeline (L6) between the blower (41) and the distillation body (21). The recovery tank (42) is connected to the first condensate discharge pipeline. The recovery tank (42) is used to recover the condensate formed in the purge pipeline (L6).

8. The closed-loop seawater desalination device according to claim 7, characterized in that, The thermal cycling unit includes: The compressor (51) is connected to the circulation outlet of the low-temperature condenser (32) at its inlet end. The superheated working fluid discharged from the outlet end of the compressor (51) is pre-cooled by passing through the high-temperature heater (13) and the medium-temperature heater (12) in sequence through the first hot circulation pipeline. The subcooling component is used to subcool the pre-cooled circulating working fluid. The throttling valve assembly throttles the circulating working fluid after it has been subcooled and returns it to the circulation inlet of the cryogenic condenser (32).

9. The closed-loop seawater desalination device according to claim 8, characterized in that, The subcooling assembly includes components connected via pipes along the transport direction of the circulating working fluid: The first heat exchanger (14) cools the circulating working fluid that flows out after being cooled from the medium-temperature heater (12) by replenishing it with seawater; The secondary subcooler (52) is used to collect the condensate discharged from the first condensate discharge pipe and the second condensate discharge pipe, and to perform secondary cooling on the circulating working fluid after the first cooling through the condensate. The three-stage subcooler (53) cools the circulating working fluid a third time after the second cooling.

10. The closed-loop seawater desalination device according to claim 9, characterized in that, The closed-loop desalination device also includes a recovery tank, which is connected to the outlet end of the secondary subcooler (52) and is used to collect the condensate discharged from the secondary subcooler (52) after subcooling.

11. The closed-loop seawater desalination device according to claim 9, characterized in that, The three-stage subcooler (53) includes an inlet end, an outlet end, a first circulation end, and a second circulation end. The inlet end is connected to the second-stage subcooler (52), and the outlet end is connected to the low-temperature condenser. A first electromagnetic throttling valve (54) is also provided on the connecting pipe between the two. The first circulation end is connected to the compressor (51), and a second electromagnetic throttling valve (55) is provided on the connecting pipe between the second circulation end and the outlet end. The first electromagnetic throttling valve (54) and the second electromagnetic throttling valve work together to throttle the circulating working fluid that has undergone three cooling cycles.

12. The closed-loop seawater desalination device according to any one of claims 1 to 11, characterized in that, The circulating working fluid is a non-azeotropic mixture.

13. A closed-loop seawater desalination system, characterized in that, It includes an electronic control device and a closed-loop desalination device according to any one of claims 1 to 12.

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