Solar-thermal coupling supercritical water desalination device and process

Abstract

This invention discloses a solar-thermal coupled supercritical water desalination seawater desalination device and process, belonging to the field of seawater desalination and new energy coupling utilization technology. The device includes a feeding unit, a solar-thermal unit, a supercritical water desalination unit, a product water collection unit, and a steam treatment unit. The process employs a high-pressure feeding-countercurrent preheating-solar supercritical heating-gravity water-salt separation-product water cooling-solid salt flash evaporation recovery flow. Through temperature and pressure coordinated control to adapt to varying solar operating conditions, stable operation under high temperature and high pressure is achieved. This invention achieves a solar heating ratio of ≥80%, a water recovery rate of ≥90%, a salt recovery rate of ≥90%, a product water salinity of ≤500mg / L, no concentrated brine discharge, corrosion resistance and anti-clogging properties, and can treat real seawater. It is suitable for coastal areas, islands, ships, and other scenarios, providing a complete technical solution for zero-carbon seawater desalination.

Description

Technical Field

[0001] This invention belongs to the field of seawater desalination and new energy coupling utilization technology, specifically relating to a solar thermal coupled supercritical water desalination seawater desalination device and process. Background Technology

[0002] With population growth and accelerated industrialization, freshwater scarcity has become a core bottleneck restricting sustainable development, forcing seawater desalination technology to rapidly evolve towards large-scale and high-efficiency production. Currently, mature technologies such as reverse osmosis (RO), multi-stage flash distillation (MSF), and multi-effect distillation (MED), while widely used, suffer from the following problems: First, low resource utilization; traditional processes typically achieve water recovery rates of only 40%-50%, meaning more than half of the water resources are wasted. Second, high ecological and environmental costs; direct discharge of high-salinity, high-temperature brine into the ocean without proper treatment significantly alters local salinity and dissolved oxygen levels, posing a serious threat to marine biodiversity. Third, challenges to operational stability and economic viability; membrane modules are highly susceptible to inorganic scaling and biofouling in high-salinity environments, leading to frequent chemical cleaning and maintenance shutdowns, increasing costs. Fourth, it has high energy consumption and relies on fossil fuels. In terms of energy consumption, reverse osmosis requires extremely high driving pressure, while thermal processes require a large amount of latent heat, resulting in high energy consumption per unit of water produced and a very high proportion of energy in operating costs. In addition, existing systems generally lack clean energy alternatives and are deeply dependent on fossil fuels, making it difficult to meet the future development needs of green and low-carbon development.

[0003] Supercritical water desalination (SCWD) utilizes the characteristic that the solubility of inorganic salts in water decreases sharply under supercritical conditions (temperature >374℃, pressure >22.1MPa) to achieve efficient phase separation of water and salt, with a water recovery rate of over 95% and no concentrated brine discharge. However, existing SCWD devices mostly use electric heating or fossil fuel heating, resulting in high operating costs and large carbon emissions, which restricts industrial application. Secondly, inorganic salts have very low solubility in supercritical water, easily precipitating and adhering to the inner wall surface, which deteriorates heat transfer, increases pressure drop, and in severe cases, causes pipeline blockage and affects continuous operation of the equipment. Finally, supercritical conditions place extremely stringent requirements on equipment materials; acidic substances and inorganic ions in the supercritical water environment can exacerbate equipment corrosion, affecting equipment reliability and service life. Summary of the Invention

[0004] Based on the above-mentioned technical problems, this invention proposes a solar thermal coupled supercritical water desalination seawater desalination device and process.

[0005] A solar thermal coupled supercritical water desalination seawater desalination device includes a feeding unit, a solar thermal unit, a supercritical water desalination unit, and a product water collection unit. The supercritical water desalination unit includes a countercurrent heat exchanger. The top outlet of the countercurrent heat exchanger is connected to the bottom inlet of the electric supplementary heater through a first conveying pipe. A heat transfer oil heat exchanger is installed on the outer wall of the electric supplementary heater. The top outlet of the electric supplementary heater is connected to the top inlet of the gravity separator through a second conveying pipe. The upper outlet of the gravity separator is connected to the upper inlet of the countercurrent heat exchanger through a third conveying pipe. The bottom outlet of the gravity separator is connected to the top inlet of the capillary trickle tube via a first flash valve. The bottom outlet of the capillary trickle tube is connected to the top inlet of the first-stage salt collector. The bottom outlet of the first-stage salt collector is connected to the top inlet of the second-stage salt collector via a second flash valve. The upper outlet of the first-stage salt collector is connected to the upper inlet of the cyclone separator. The feeding unit is connected to the bottom inlet of the counter-current heat exchanger; The solar thermal unit is connected to the heat transfer oil heat exchanger; The product water collection unit is connected to the lower outlet of the counter-current heat exchanger.

[0006] Preferably, the bottom of the secondary salt collector is provided with a bottom temperature shut-off valve.

[0007] Preferably, the outer walls of the countercurrent heat exchanger, the electric supplementary heater, the gravity separator, and the secondary salt collector are respectively provided with a first supplementary heating unit, a second supplementary heating unit, a third supplementary heating unit, and a fourth supplementary heating unit.

[0008] Preferably, the solar thermal unit includes a trough-type concentrating collector; The top heat transfer medium outlet of the trough-type concentrating solar collector is connected to the top of the low-temperature molten salt storage tank via the fourth and sixth conveying pipes, and to the top of the high-temperature molten salt storage tank via the fourth and seventh conveying pipes. It is also connected to the upper heat transfer medium inlet of the heat transfer oil heat exchanger via the fourth conveying pipe. The top of the low-temperature molten salt storage tank is connected to the upper heat transfer medium inlet of the heat transfer oil heat exchanger via the sixth and fourth conveying pipes, and the top of the high-temperature molten salt storage tank is connected to the upper heat transfer medium inlet of the heat transfer oil heat exchanger via the seventh and fourth conveying pipes. The lower heat transfer medium outlet of the heat transfer oil heat exchanger is connected to the bottom heat transfer medium inlet of the heat transfer oil tank through the tenth conveying pipe, and the top heat transfer medium outlet of the heat transfer oil tank is connected to the bottom heat transfer medium inlet of the trough concentrating solar collector through the twelfth conveying pipe. The low-temperature molten salt storage tank and the high-temperature molten salt storage tank are respectively equipped with a first heat exchanger and a second heat exchanger.

[0009] Preferably, a heat transfer medium circulation pump is installed at the position of the twelfth delivery pipeline near the top of the heat transfer oil tank.

[0010] Preferably, a first electric heater and a second electric heater are respectively provided on the lower inner sidewall of the low-temperature molten salt storage tank and the high-temperature molten salt storage tank.

[0011] Preferably, the feeding unit includes a brine tank and a deionized water tank. The lower outlet ends of both tanks are connected to the input end of a first three-way switching valve. The output end of the first three-way switching valve is connected in series with a feed pump and a damper. The damper is connected to the bottom inlet of the countercurrent heat exchanger.

[0012] Preferably, the product water collection unit includes a first cooler, the top inlet of which is connected to the lower outlet of a countercurrent heat exchanger, and the bottom outlet of the first cooler is connected in series with a first automatic regulating valve and a first conductivity meter, and finally connected to the feed inlet at the top of the product water tank.

[0013] Preferably, a solar thermal coupled supercritical water desalination seawater desalination device further includes a steam treatment unit; The steam treatment unit includes a first steam treatment unit and a second steam treatment unit; the first steam treatment unit includes a second cooler, the upper inlet of the second cooler is connected to the top outlet of the cyclone separator, and the bottom outlet of the second cooler is connected to the feed inlet at the top of the first condensate tank by a second automatic regulating valve and a second conductivity meter connected in series. The second steam treatment unit includes a third cooler, the top inlet of which is connected to the top outlet of the secondary salt collector, and the bottom outlet of which is connected to the top inlet of the second condensate tank.

[0014] A solar-thermal coupled supercritical water desalination process for seawater, employing the aforementioned apparatus, includes the following steps: (1) Switch the first three-way switching valve to the deionized water tank, start the feed pump, and allow deionized water to flow through; at the same time, heat the electric heating heater and gravity separator through the second and third heating units respectively to maintain the system in a stable state. (2) After the steady state is established, the first three-way switching valve is switched to the brine tank. The seawater in the brine tank is pressurized to 22.1-30 MPa by the feed pump, and then enters the countercurrent heat exchanger and is preheated to 30-280°C through the first heat replenishment unit. (3) After the seawater is preheated, it enters the electric heating heater and is heated to 290-400℃ by the heat transfer oil heat exchanger through the solar thermal unit, entering the supercritical state, and then enters the gravity separator to achieve water-salt separation. (4) After water-salt separation, the low-salt flow at the top of the gravity separator releases heat through the countercurrent heat exchanger, cools down through the first cooler, and depressurizes through the first automatic regulating valve before entering the product water tank. (5) When the concentrated salt flow at the bottom of the gravity separator reaches the set trigger value, stop the seawater feeding; (6) Open the bottom temperature shut-off valve. The concentrated salt flow at the bottom of the gravity separator passes through the first flash valve and the capillary drain pipe in sequence and enters the first-stage salt collector to complete the first-stage flash evaporation. The resulting solid salt is retained in the first-stage salt collector. (7) A portion of the steam and entrained fine salt generated by the first-stage flash evaporation enters the cyclone separator to separate and recover the solid salt. The water vapor generated at the top of the cyclone separator is condensed and recovered by the first water vapor treatment unit. The other portion enters the second-stage salt collector through the second flash valve to complete the second-stage flash evaporation. The water vapor generated at the top of the second-stage salt collector is condensed and recovered by the second water vapor treatment unit.

[0015] The beneficial technical effects of the present invention are as follows: This invention provides a solar-thermal coupled supercritical water desalination seawater desalination device and process, achieving efficient integration of high-temperature solar thermal energy with a supercritical water desalination system. It operates stably under real seawater conditions, achieving high water recovery rate, zero concentrated brine discharge, and a high proportion of solar energy for heating. Specifically: (1) Zero-carbon heating: Solar heating accounts for ≥80%, significantly reducing fossil energy consumption and carbon emissions.

[0016] (2) High recovery rate: The main process water recovery rate is ≥90%, the salt recovery rate is ≥90%, the salinity of the product water is ≤500mg / L, and there is no concentrated brine discharge.

[0017] (3) Stable and controllable: Temperature and pressure coordinated control adapts to solar variable operating conditions, and the system can run continuously and stably for more than 72 hours.

[0018] (4) Corrosion resistance and anti-clogging: The use of corrosion-resistant alloys and optimized flow channel structure significantly improves the life and reliability of the device.

[0019] (5) Applicable to real seawater: It can directly treat real seawater and solve the problems of scaling and salt entrainment in multi-salt systems. Attached Figure Description

[0020] Figure 1 This is a PID piping and instrumentation flow diagram of the solar thermal coupling supercritical water desalination seawater desalination device of the present invention. Figure 2 This is a PID piping instrumentation flow diagram for the solar thermal unit of this invention; Figure 3 This is a PID piping and instrumentation flow diagram for the supercritical water desalination unit of this invention.

[0021] In the diagram: 1-Brine tank, 2-Deionized water tank, 3-First three-way switching valve, 4-Feed pump, 5-Damper, 6-Countercurrent heat exchanger, 7-Heat transfer oil heat exchanger, 8-Electric supplementary heater, 9-Gravity separator, 10-First flash valve, 11-Second flash valve, 12-Capillary drain pipe, 13-Flow controller, 14-Nitrogen tank, 15-First cooler, 16-Second cooler, 17-Third cooler, 18-First automatic regulating valve, 19-Second automatic regulating valve, 20-First conductivity meter, 21-Product water tank, 22-First-stage salt collector, 23-Second-stage salt collector, 24-Cyclone separator, 25-Second conductivity meter, 26-First condensate tank, 27-Second condensate tank, 28-Trough concentrating solar collector, 29-Heat transfer oil... Medium circulation pump, 30-heat transfer oil tank, 31-first heat exchanger, 32-second heat exchanger, 33-low temperature molten salt storage tank, 34-high temperature molten salt storage tank, 35-bottom temperature shut-off valve, 36-second three-way switching valve, 37-third three-way switching valve, 38-fourth three-way switching valve, 39-fifth three-way switching valve, 40-sixth three-way switching valve, 41-seventh three-way switching valve, 42-first conveying pipeline, 43-second conveying pipeline, 44-third conveying pipeline, 45-fourth conveying pipeline, 46-fifth conveying pipeline, 47-sixth conveying pipeline, 48-seventh conveying pipeline, 49-eighth conveying pipeline, 50-ninth conveying pipeline, 51-tenth conveying pipeline, 52-eleventh conveying pipeline, 53-twelfth conveying pipeline.

[0022] 601-First heating unit, 801-Second heating unit, 901-Third heating unit, 2301-Fourth heating unit, 2302-Stirring mechanism, 3101-First electric heater, 3201-Second electric heater. Detailed Implementation

[0023] like Figure 1 As shown, a solar thermal coupled supercritical water desalination seawater desalination device includes a feeding unit, a solar thermal unit, a supercritical water desalination unit, a product water collection unit, and a steam treatment unit.

[0024] like Figure 3As shown, the supercritical water desalination unit includes a countercurrent heat exchanger 6. The top outlet of the countercurrent heat exchanger 6 is connected to the bottom inlet of the electric supplementary heater 8 via a first conveying pipe 42. A heat transfer oil heat exchanger 7 is installed on one side of the electric supplementary heater 8. The top outlet of the electric supplementary heater 8 is connected to the top inlet of the gravity separator 9 via a second conveying pipe 43. The bottom inlet of the countercurrent heat exchanger 6 is connected to the feeding unit. Seawater is sequentially fed into the countercurrent heat exchanger 6, the electric supplementary heater 8, and the gravity separator 9 by the feeding unit. The seawater in the gravity separator 9 is in a supercritical state and water-salt separation is achieved. The generated high-temperature supercritical water enters the upper inlet of the countercurrent heat exchanger 6 through the upper outlet of the gravity separator 9, and exchanges heat with the seawater in the countercurrent heat exchanger 6 to recover waste heat and reduce energy consumption. Therefore, the upper outlet of the gravity separator 9 is connected to the upper inlet of the countercurrent heat exchanger 6 via a third conveying pipe 44.

[0025] The bottom concentrated brine outlet of gravity separator 9 is connected to the top of capillary drain pipe 12 through the first flash valve 10. The bottom of capillary drain pipe 12 is connected to the top inlet of primary salt collector 22. The bottom outlet of primary salt collector 22 is connected to the top inlet of secondary salt collector 23 through the second flash valve 11. The high-concentration brine at the bottom of gravity separator 9 enters the primary salt collector 22 via the first flash valve 10 and capillary drain pipe 12. During this process, primary flash evaporation is completed through the first flash valve 10, and the main solid salts preferentially settle or remain in the primary salt collector 22. The steam and entrained fine salt generated in the primary salt collector 22 enter the cyclone separator 24 and the secondary salt collector 23 from the top and bottom, respectively. The component entering the cyclone separator 24 is mainly water vapor with a small portion of entrained fine salt, while the main component entering the secondary salt collector 23 is slurry with entrained fine salt and a small amount of water vapor. In addition, the material flowing out of the liquid phase outlet at the bottom of the primary salt collector 22 undergoes secondary flash evaporation through the second flash valve 11 before entering the secondary salt collector 23. The bottom of the secondary salt collector 23 is equipped with a bottom temperature shut-off valve 35. This valve is a high-temperature shut-off valve that is only opened when the stock level and thermal condition are confirmed to be acceptable and the downstream is receptive. Once the termination criteria are met or the operating conditions exceed the limits, it is immediately closed.

[0026] The side walls of the aforementioned countercurrent heat exchanger 6, electric supplementary heater 8, gravity separator 9, and secondary salt collector 23 are respectively provided with a first supplementary heating unit 601, a second supplementary heating unit 801, a third supplementary heating unit 901, and a fourth supplementary heating unit 2301. The addition of supplementary heating units is mainly to cope with the intermittency of solar energy, maintain the supercritical state, and balance the heat distribution of the system. All of the above supplementary heating units adopt electric heating for supplementary heating.

[0027] To meet the fluidity requirements of the high-concentration salt slurry in the secondary salt collector 23, a stirring mechanism 2302 is installed inside the secondary salt collector 23. The stirring mechanism 2302 includes a rotating shaft, which is arranged vertically. The top of the rotating shaft is connected to a motor, and the bottom of the rotating shaft is equipped with stirring blades. In addition, the salt collector is designed with an open top structure to ensure operational safety and air pressure stability.

[0028] like Figure 2 As shown, the solar thermal unit includes a trough-type concentrating collector 28. The top heat transfer oil outlet of the trough-type concentrating collector 28 is connected to the top of the low-temperature molten salt storage tank 33 via a fourth conveying pipe 45 and a sixth conveying pipe 47, and is connected to the top of the high-temperature molten salt storage tank 34 via a fourth conveying pipe 45 and a seventh conveying pipe 48. It is also connected to the upper heat transfer oil inlet of the heat transfer oil heat exchanger 7 via a fourth conveying pipe 45. The top of the low-temperature molten salt storage tank 33 is connected to the upper heat transfer oil inlet of the heat transfer oil heat exchanger 7 via a sixth conveying pipe 47 and a fourth conveying pipe 45. The hot oil inlet is connected to the top of the high-temperature molten salt storage tank 34 via the seventh conveying pipe 48 and the fourth conveying pipe 45, which are connected to the upper heat transfer oil inlet of the heat transfer oil heat exchanger 7. The lower heat transfer oil outlet of the heat transfer oil heat exchanger 7 is connected to the bottom heat transfer oil inlet of the heat transfer oil tank 30 via the tenth conveying pipe 51. The top heat transfer oil outlet of the heat transfer oil tank 30 is connected to the bottom heat transfer oil inlet of the trough-type concentrating solar collector 28 via the twelfth conveying pipe 53. A heat transfer medium circulation pump 29 is installed near the top of the heat transfer oil tank 30 on the twelfth conveying pipe 53. The first supplementary heat exchanger 31 and the second supplementary heat exchanger 32 are respectively installed in the center of the interior of the low-temperature molten salt storage tank 33 and the high-temperature molten salt storage tank 34.

[0029] At the intersections of the fourth conveying pipe 45 with the fifth, sixth, seventh, and eighth conveying pipes 46, 47, 48, and 49, respectively, a second three-way switching valve 36, a third three-way switching valve 37, a fourth three-way switching valve 38, and a fifth three-way switching valve 39 are respectively installed; at the intersections of the tenth conveying pipe 51 with the ninth and eleventh conveying pipes 50 and 52, respectively, a sixth three-way switching valve 40 and a seventh three-way switching valve 41 are respectively installed. Therefore, the top of the heat transfer oil tank 30 is also connected to the second three-way switching valve 36 via the fifth conveying pipe 46, the bottom of the low-temperature molten salt storage tank 33 is connected to the seventh three-way switching valve 41 via the eleventh conveying pipe 52, the bottom of the high-temperature molten salt storage tank 34 is connected to the sixth three-way switching valve 40 via the ninth conveying pipe 50, and the ninth conveying pipe 50 is connected to the fifth three-way switching valve 39 via the eighth conveying pipe 49.

[0030] The aforementioned trough-type concentrating solar collector 28 absorbs solar radiation and transfers heat to the internal heat transfer medium, raising its temperature. Part of the heated heat transfer medium enters the first supplementary heat exchanger 31 and the second supplementary heat exchanger 32, storing the heat in the molten salt in the low-temperature molten salt tank 33 and the high-temperature molten salt tank 34, respectively. The other part directly enters the heat transfer oil heat exchanger 7 to release heat. The molten salt in the low-temperature molten salt tank 33 and the high-temperature molten salt tank 34 can be mutually adjusted via a transfer pump between them. When solar energy is insufficient or fluctuates, the molten salt in the molten salt tanks participates in heating, transferring heat to the heat transfer oil medium in the first and second supplementary heat exchangers 31 and 32, raising its temperature, and further entering the heat transfer oil heat exchanger 7 to release heat. The low-temperature heat transfer oil flowing out of the lower heat transfer oil outlet of the heat transfer oil heat exchanger 7 returns to the heat transfer oil tank 30 and is pumped to the trough-type concentrating solar collector 28 by the heat transfer medium circulation pump 29 to continue absorbing solar radiation.

[0031] In the above system, the parabolic trough concentrator 28 is the main heating source, while the molten salt storage tank, as an energy storage unit, only participates in heating when solar energy is insufficient or fluctuates. When the parabolic trough concentrator 28 is the main heating source, the passage of the second three-way switching valve 36 to the heat transfer oil tank 30 is closed, the three-way switching valves 37 and 38 are fully open, the passage of the fifth three-way switching valve 39 connecting to the eighth conveying pipeline 49 is closed, the passage of the sixth three-way switching valve 40 to the high-temperature molten salt storage tank 34 is closed, and the seventh three-way switching valve... The passage from the switching valve 41 to the low-temperature molten salt storage tank 33 is closed, and the other open pipes form a closed loop. Part of the heat transfer oil heated by solar radiation is transported to the molten salt storage tank for heat storage through the fourth conveying pipe 45, the sixth conveying pipe 47 and the seventh conveying pipe 48, while the other part is directly introduced into the heat transfer oil heat exchanger 7 through the fourth conveying pipe 45 to release heat. The low-temperature heat transfer oil flowing out from the heat transfer oil outlet at the bottom of the heat transfer oil heat exchanger 7 returns to the trough concentrator 28 to continue absorbing solar radiation. When solar energy is insufficient or fluctuates, the molten salt storage tank participates in heating. At this time, only the three-way valve of the second three-way switching valve 36 is completely closed, and the channel of the third three-way switching valve 37 leading to the second three-way switching valve 36 is closed. The opening and closing states of other valves remain unchanged. At this time, the molten salt in the molten salt storage tank participates in heating, transferring heat to the heat transfer oil in the first supplementary heat exchanger 31 and the second supplementary heat exchanger 32. After the oil is heated, the high-temperature heat transfer oil is transported to the heat transfer oil heat exchanger 7 through the sixth conveying pipe 47, the seventh conveying pipe 48 and the fourth conveying pipe 45 to release heat.

[0032] The lower sidewalls of the aforementioned low-temperature molten salt storage tank 33 and high-temperature molten salt storage tank 34 are respectively equipped with a first electric heater 3101 and a second electric heater 3201; this device is used to provide auxiliary heating for the molten salt in the tank when solar energy is absent or irradiation is insufficient, to maintain the molten salt temperature within the safe operating range, and to ensure the continuity and stability of the system operation.

[0033] The feeding unit includes a brine tank 1 and a deionized water tank 2. The outlets of both tanks are connected to the input of a first three-way switching valve 3, allowing the system to flexibly switch the feed source according to process requirements. The outlet of the first three-way switching valve 3 is connected in series with a feed pump 4 and a damper 5, and finally connected to the bottom inlet of a counter-current heat exchanger 6, forming a stable and controllable upstream feed channel. The core function of the damper 5 is to suppress pressure pulsations generated during fluid flow and stabilize the system pressure and flow rate.

[0034] The product water collection unit includes a first cooler 15. The top inlet of the first cooler 15 is connected to the lower outlet of the counter-current heat exchanger 6. The bottom outlet of the first cooler 15 is connected to the feed port at the top of the product water tank 21 via a first automatic regulating valve 18 and a first conductivity meter 20 connected in series.

[0035] The steam treatment unit comprises two parts. One part treats the steam generated at the top of the secondary salt collector 23. This part includes a third cooler 17, the top inlet of which is connected to the steam outlet at the top of the secondary salt collector 23, and the bottom outlet of which is connected to the top inlet of the second condensate tank 27. The other part treats the steam generated at the top of the cyclone separator 24. This part includes a second cooler 16, the upper inlet of which is connected to the steam outlet at the top of the cyclone separator 24, and the bottom outlet of which is connected to the feed inlet at the top of the first condensate tank 26 via a second automatic regulating valve 19 and a second conductivity meter 25 connected in series.

[0036] To ensure stable operation of the entire system under high temperature and high pressure, temperature and pressure coordinated control components are installed as needed in the feeding unit, supercritical water desalination unit, product water collection unit, and steam treatment unit. These components mainly include a temperature controller, a pressure controller, a pressure transmitter, and a temperature sensor. The temperature controller and pressure controller respectively monitor and regulate temperature and pressure in real time, while the pressure transmitter and temperature sensor respectively monitor pressure and temperature in real time, achieving temperature fluctuations ≤ ±5℃ and pressure fluctuations ≤ ±0.5MPa. The temperature and pressure coordinated control is adaptable to solar-powered variable operating conditions, allowing the system to operate continuously and stably for over 72 hours.

[0037] As a further design of the present invention, a nitrogen supply device is connected to the upper gas inlet of the primary salt collector 22. The device includes a nitrogen tank 14, and the outlet end of the nitrogen tank 14 is connected to the upper gas inlet of the primary salt collector 22 through a flow controller 13.

[0038] Furthermore, weighing devices can be installed at the bottom of the brine tank 1, deionized water tank 2, product water tank 21, and first condensate tank 26 respectively for weighing the materials in the tanks.

[0039] This invention also provides a solar-thermal coupled supercritical water desalination process for seawater, employing the apparatus described above, and comprising the following steps: 1. Pre-run checks (1) Inspect all joints, seals, thermocouples, pressure transmitters, weighing modules, valve actions and data acquisition systems to confirm that there are no leaks, no looseness and no obvious zero drift; (2) Turn on the heating section of gravity separator 9, the heating section of capillary flow tube 12, the heat preservation heating section of primary salt collector 22 and cyclone separator 24, and check whether the temperature rise of each section is normal. (3) Confirm that the cooling water, nitrogen, pressure relief system, emergency shutdown circuit and safety interlocks are all ready; (4) Zero the weighing devices of deionized water tank 2, brine tank 1, product water tank 21 and first condensate tank 26 and start recording the mass continuously; (5) If nitrogen replacement is required, turn on the nitrogen supply device, first complete the inerting of the rear section of the device and the collection space, and then proceed to the deionized water circulation step.

[0040] 2. Deionized water infusion, temperature and pressure increase, and steady-state establishment. (1) Switch the first three-way switching valve 3 to the deionized water tank 2, start the feed pump 4 at a low flow rate, and gradually increase the system pressure to 30%, 60% and 100% of the target pressure; (2) Simultaneously increase the temperature of the electric heating heater 8 and the gravity separator 9 so that the separator inlet reaches the set temperature, and confirm that the temperature of the top cooling section of the separator and the temperature before the first automatic regulating valve 18 are within the allowable range. (3) Maintain the target temperature and pressure under deionized water conditions as the blank breakthrough and steady-state establishment stage; (4) Only when the fluctuation of the critical temperature point does not exceed ±1℃ and the fluctuation of the critical pressure point does not exceed ±2bar and is maintained continuously for 30min, can the steady state be established and the salt cutting stage be entered. (5) Record the flow rate, weight, heat loss and online conductivity data under blank operating conditions as the baseline for subsequent salt operating conditions comparison.

[0041] 3. Salt-cutting operation and continuous top water production (1) Switch the first three-way switching valve 3 to the brine tank 1, and keep the main process pressure, separation temperature and top cooling pressure reduction boundary unchanged; (2) The low-salt stream at the top of the gravity separator 9 continues to release heat through the countercurrent heat exchanger 6, cool down through the first cooler 15, and reduce pressure through the first automatic regulating valve 18 before entering the product water tank 21. (3) Record the conductivity, key temperature and pressure and mass of each collection tank at the top inlet of product water tank 21 online continuously; take samples at predetermined frequencies for offline ion chromatography analysis; (4) Continuously observe the pressure difference before and after the countercurrent heat exchanger 6, the pressure difference before and after the bottom flash section of the gravity separator 9, and the mass change of each tank to confirm that there is no continuously increasing pressure drop or abnormal weight loss; (5) Nitrogen scavenging is not enabled by default in this stage so as to establish a baseline operating condition without scavenging.

[0042] 4. Bottom flash evaporation and optional scavenging operation (1) When the amount of concentrated brine in the gravity separator 9 reaches the set trigger value based on mass balance or volume estimation, this trigger value refers to the sudden increase in pressure in the gravity separator 9, when the brine feed is stopped and the relevant hot section temperature is maintained. (2) Confirm that the primary salt collector 22, cyclone separator 24, secondary salt collector 23, first cooler 15, second cooler 16 and third cooler 17 are in an acceptable state (meaning that the equipment has the conditions for safe and stable operation); if nitrogen scavenging is required for this test, the scavenging flow rate should be set in advance and its entry point should be confirmed to be located in the gas phase section downstream of the first flash valve 10. (3) Open the bottom temperature shut-off valve 35 according to the preset operation mode, so that the concentrated brine enters the primary salt collector 22 through the capillary drain tube 12. The concentrated brine completes the primary flash evaporation in this process, and the main solid salts preferentially settle or remain in the primary salt collector 22; (4) Steam and entrained fine salt continue to enter the cyclone separator 24 and the secondary salt collector 23. During the process of steam and entrained fine salt entering the secondary salt collector 23, the secondary flash evaporation is completed through the second flash valve 11. After the steam is condensed in the corresponding cooler, it enters the condensate tank. (5) If nitrogen scavenging is used, it shall only be turned on during the first-stage flash evaporation and for a short time thereafter, and the flow rate shall be kept stable. The main process pressure control, condenser load or second automatic regulating valve 19 shall not be significantly unstable. (6) When the separator pressure drops to the first-stage flash set low pressure, or the bottom discharge flow rate decreases significantly and reaches the end criterion, close the bottom temperature shut-off valve 35, stop the scavenging and complete the bottom recovery of this round.

[0043] 5. Rinsing, shutdown, and sampling (1) After the bottom two-stage flash evaporation is completed, switch back to deionized water as required by the scheme to rinse the countercurrent heat exchanger 6, gravity separator 9 and bottom flash evaporation section; (2) Under the premise of ensuring that the pressure relief path is clear and each collection unit is stable, slowly reduce the pressure and cool down the system; (3) When nitrogen purging is required, it should only be turned on briefly during the shutdown phase, and the downstream condensation or collection path should be kept clear. (4) After being kept at room temperature and pressure, the primary salt collector 22, cyclone separator 24 and secondary salt collector 23 are removed to collect solid salt, residual liquid and condensate respectively, and then proceed to subsequent drying, weighing and composition analysis.

[0044] The entire process described above is maintained by a temperature and pressure co-control device to keep the system temperature and pressure stable.

[0045] Example 1 The device has a feed flow rate of 8 kg / h, a solar collector temperature of 393℃, a system pressure of 25 MPa, and a separation temperature of 380℃. Product water salinity: 420 mg / L; Water recovery rate: 92%; Solar heating accounted for 85%; Continuous and stable operation: 72 hours; Salt recovery rate: 92%; The device showed no blockages or obvious corrosion.

[0046] Example 2 The device has a feed flow rate of 10 kg / h, a solar collector temperature of 393℃, a system pressure of 28 MPa, and a separation temperature of 390℃. Product water salinity: 480 mg / L; Water recovery rate: 91%; Solar heating accounted for 82%; Continuous and stable operation: 72 hours; Salt recovery rate: 93%; The device showed no blockages or obvious corrosion.

[0047] For any parts not mentioned in the above embodiments, existing technologies can be adopted or referenced.

[0048] Of course, the above description is not intended to limit the present invention, and the present invention is not limited to the above embodiments. Any changes, modifications, additions or substitutions made by those skilled in the art within the scope of the present invention should be protected by the present invention.

Claims

1. A solar-thermal coupled supercritical water desalination seawater desalination device, characterized in that, It includes a feeding unit, a solar thermal unit, a supercritical water desalination unit, and a product water collection unit; The supercritical water desalination unit includes a countercurrent heat exchanger. The top outlet of the countercurrent heat exchanger is connected to the bottom inlet of the electric supplementary heater through a first conveying pipe. A heat transfer oil heat exchanger is installed on the outer wall of the electric supplementary heater. The top outlet of the electric supplementary heater is connected to the top inlet of the gravity separator through a second conveying pipe. The upper outlet of the gravity separator is connected to the upper inlet of the countercurrent heat exchanger through a third conveying pipe. The bottom outlet of the gravity separator is connected to the top inlet of the capillary trickle tube via a first flash valve. The bottom outlet of the capillary trickle tube is connected to the top inlet of the first-stage salt collector. The bottom outlet of the first-stage salt collector is connected to the top inlet of the second-stage salt collector via a second flash valve. The upper outlet of the first-stage salt collector is connected to the upper inlet of the cyclone separator. The feeding unit is connected to the bottom inlet of the counter-current heat exchanger; The solar thermal unit is connected to the heat transfer oil heat exchanger; The product water collection unit is connected to the lower outlet of the counter-current heat exchanger.

2. The solar thermal coupled supercritical water desalination seawater desalination device according to claim 1, characterized in that, The bottom of the secondary salt collector is equipped with a bottom temperature shut-off valve.

3. The solar thermal coupled supercritical water desalination seawater desalination device according to claim 1, characterized in that, The outer walls of the countercurrent heat exchanger, the electric supplementary heater, the gravity separator, and the secondary salt collector are respectively provided with a first supplementary heating unit, a second supplementary heating unit, a third supplementary heating unit, and a fourth supplementary heating unit.

4. The solar thermal coupled supercritical water desalination seawater desalination device according to claim 1, characterized in that, The solar thermal unit includes a parabolic trough concentrator. The top heat transfer medium outlet of the trough-type concentrating solar collector is connected to the top of the low-temperature molten salt storage tank via the fourth and sixth conveying pipes, and to the top of the high-temperature molten salt storage tank via the fourth and seventh conveying pipes. It is also connected to the upper heat transfer medium inlet of the heat transfer oil heat exchanger via the fourth conveying pipe. The top of the low-temperature molten salt storage tank is connected to the upper heat transfer medium inlet of the heat transfer oil heat exchanger via the sixth and fourth conveying pipes, and the top of the high-temperature molten salt storage tank is connected to the upper heat transfer medium inlet of the heat transfer oil heat exchanger via the seventh and fourth conveying pipes. The lower heat transfer medium outlet of the heat transfer oil heat exchanger is connected to the bottom heat transfer medium inlet of the heat transfer oil tank through the tenth conveying pipe, and the top heat transfer medium outlet of the heat transfer oil tank is connected to the bottom heat transfer medium inlet of the trough concentrating solar collector through the twelfth conveying pipe. The low-temperature molten salt storage tank and the high-temperature molten salt storage tank are respectively equipped with a first heat exchanger and a second heat exchanger.

5. A solar thermal coupled supercritical water desalination seawater desalination device according to claim 4, characterized in that, A heat transfer medium circulation pump is installed near the top of the heat transfer oil tank in the twelfth delivery pipeline.

6. A solar thermal coupled supercritical water desalination seawater desalination device according to claim 4, characterized in that, The lower inner wall of the low-temperature molten salt storage tank and the high-temperature molten salt storage tank are respectively equipped with a first electric heater and a second electric heater.

7. A solar thermal coupled supercritical water desalination seawater desalination device according to claim 1, characterized in that, The feeding unit includes a brine tank and a deionized water tank. The lower outlet of both tanks is connected to the input of a first three-way switching valve. The output of the first three-way switching valve is connected in series with a feed pump and a damper. The damper is connected to the bottom inlet of the countercurrent heat exchanger.

8. A solar thermal coupled supercritical water desalination seawater desalination device according to claim 1, characterized in that, The product water collection unit includes a first cooler, the top inlet of which is connected to the lower outlet of a counter-current heat exchanger, and the bottom outlet of which is connected in series with a first automatic regulating valve and a first conductivity meter, and finally connected to the feed inlet at the top of the product water tank.

9. A solar thermal coupled supercritical water desalination seawater desalination device according to claim 1, characterized in that, It also includes a steam treatment unit; The steam treatment unit includes a first steam treatment unit and a second steam treatment unit; the first steam treatment unit includes a second cooler, the upper inlet of the second cooler is connected to the top outlet of the cyclone separator, and the bottom outlet of the second cooler is connected to the feed inlet at the top of the first condensate tank by a second automatic regulating valve and a second conductivity meter connected in series. The second steam treatment unit includes a third cooler, the top inlet of which is connected to the top outlet of the secondary salt collector, and the bottom outlet of which is connected to the top inlet of the second condensate tank.

10. A solar-thermal coupled supercritical water desalination process for seawater, employing the apparatus described in any one of claims 1-9, characterized in that, Includes the following steps: (1) Switch the first three-way switching valve to the deionized water tank, start the feed pump, and allow deionized water to flow through; at the same time, heat the electric heating heater and gravity separator through the second and third heating units respectively to maintain the system in a stable state. (2) After the steady state is established, the first three-way switching valve is switched to the brine tank. The seawater in the brine tank is pressurized to 22.1-30 MPa by the feed pump, and then enters the countercurrent heat exchanger and is preheated to 30-280°C through the first heat replenishment unit. (3) After the seawater is preheated, it enters the electric heating heater and is heated to 290-400℃ by the heat transfer oil heat exchanger through the solar thermal unit, entering the supercritical state, and then enters the gravity separator to achieve water-salt separation. (4) After water-salt separation, the low-salt flow at the top of the gravity separator releases heat through the countercurrent heat exchanger, cools down through the first cooler, and depressurizes through the first automatic regulating valve before entering the product water tank. (5) When the concentrated salt flow at the bottom of the gravity separator reaches the set trigger value, stop the seawater feeding; (6) Open the bottom temperature shut-off valve. The concentrated salt flow at the bottom of the gravity separator passes through the first flash valve and the capillary drain pipe in sequence and enters the first-stage salt collector to complete the first-stage flash evaporation. The resulting solid salt is retained in the first-stage salt collector. (7) A portion of the steam and entrained fine salt generated by the first-stage flash evaporation enters the cyclone separator to separate and recover the solid salt. The water vapor generated at the top of the cyclone separator is condensed and recovered by the first water vapor treatment unit. The other portion enters the second-stage salt collector through the second flash valve to complete the second-stage flash evaporation. The water vapor generated at the top of the second-stage salt collector is condensed and recovered by the second water vapor treatment unit.

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