A multi-energy complementary plateau salt lake lithium extraction system and method

Abstract

A kind of multi-energy complementary plateau salt lake lithium extraction system and method, belong to salt lake brine lithium extraction and multi-energy complementary technical field.The system does not need external power or fossil fuel heat energy in salt difference energy power generation unit, utilizes solar light heat to drive salt difference energy power generation at the same time to concentrate salt lake brine, saves the cost of salt lake brine evaporation concentration.Using the low-grade heat carried by photovoltaic photothermal component to preheat salt lake brine, saves its evaporation energy consumption;With hot water generated by solar flat plate collector as heat source for salt lake lithium extraction evaporation concentration and evaporation crystallization, low cost reduces the period of salt lake brine natural evaporation, improves the efficiency of continuous production of salt lake lithium extraction.Using photovoltaic power generation and salt difference energy power generation to heat water tank, hot water provides driving heat energy for salt lake lithium extraction system, stores electric energy into hot water heat energy, realizes the complement of low-grade hot water and high-grade electric energy, and realizes continuous production of salt lake lithium extraction when the temperature of solar flat plate collector hot water is insufficient in early morning and evening.

Description

Technical Field

[0001] This invention relates to a multi-energy complementary lithium extraction system and method for high-altitude salt lakes, belonging to the technical fields of lithium extraction from salt lake brine and multi-energy complementarity. Background Technology

[0002] Lithium-ion batteries possess technological advantages such as high energy density, long lifespan, and low self-discharge rate, and are widely used in high-tech fields such as electric vehicles, electronic devices, and aerospace, becoming a crucial driver of the energy revolution. my country's lithium resources mainly consist of salt lakes and ores, with salt lake lithium deposits accounting for approximately 85% of total reserves. The high-temperature decomposition process for lithium extraction from ores consumes significant amounts of energy and generates substantial solid waste, causing severe environmental pollution. Lithium in salt lake brines is found in simpler forms, facilitating enrichment and concentration. Salt lake lithium extraction processes are shorter, require less equipment investment, and are environmentally friendly, offering significant advantages. my country's salt lake brines are primarily located on the Qinghai-Tibet Plateau at altitudes above 4000 meters. These brines are characterized by low lithium content and a high magnesium-to-lithium ratio. High-altitude areas lack electricity and fossil fuels, and the salt lake water is cold and ecologically fragile. Therefore, energy-efficient and environmentally friendly high-altitude salt lake lithium extraction technology is of great significance for the development of my country's salt lake lithium resources.

[0003] The insufficient supply of electricity and fossil fuels on the Qinghai-Tibet Plateau makes adsorption and electrochemical methods for lithium extraction from salt lakes costly. The high magnesium-to-lithium ratio in the Qinghai-Tibet Plateau's salt lakes makes it difficult to obtain high-purity lithium carbonate through evaporation-crystallization and precipitation methods, while extraction methods using chemical reagents are unsuitable for the fragile ecosystem of the Qinghai-Tibet Plateau. The Qinghai-Tibet Plateau possesses abundant renewable energy sources such as solar energy and salinity gradient energy. Integrating these renewable energy sources into a multi-energy complementary system to provide heat and electricity for lithium extraction from the brine of the plateau's salt lakes would help reduce dependence on fossil fuels and grid power. Therefore, utilizing multi-energy complementarity for lithium extraction from salt lakes is a suitable technology for the natural environment of the Qinghai-Tibet Plateau.

[0004] Chinese patent CN117575104A discloses a multi-energy complementary low-carbon heating system, device, and method for lithium extraction from salt lakes. The multi-energy complementarity includes a gas-fired boiler, an air-source heat pump, and a water-source heat pump, providing heat to the salt lake lithium extraction system through the addition of high-quality electricity. However, the low ambient temperature at high altitudes on the Qinghai-Tibet Plateau makes air-source heat pumps too inefficient for heating. Furthermore, the lack of electricity consumed by heat pumps and gas consumed by boilers in the plateau salt lake region makes this system unsuitable for lithium extraction from Qinghai-Tibet Plateau salt lakes.

[0005] Chinese patent CN219058781U discloses a combined device for lithium extraction from lithium-containing brine in salt lakes, which can effectively overcome the single-function limitation of solar ponds in salt lake brine and shorten the lithium extraction cycle. Chinese patent CN116177574A discloses a highly efficient and environmentally friendly method and device for lithium extraction from salt lakes, coupling MVR (Mechanical Vapor Reduction) process with three-stage concentration, two-stage nanofiltration, and two-stage lithium precipitation. However, these methods require a large amount of high-grade electricity, resulting in high energy costs and making them unsuitable for the actual conditions of the Qinghai-Tibet Plateau, where electricity and fossil fuels are scarce.

[0006] Chinese patent CN115925199A discloses a lithium extraction recycling system from salt lakes, employing a multi-stage process combining ultrafiltration, inclined plate sedimentation tanks, ion exchange, nanofiltration, reverse osmosis, and bipolar membranes to achieve the reuse of tailings and concentrates from each stage. Chinese patent CN112661321B discloses a membrane separation-based lithium extraction system and method from salt lakes, achieving efficient separation of multiple components in salt lake brine. Both of these lithium extraction methods rely on reverse osmosis membrane technology and chemical methods, requiring the consumption of electricity and chemical reagents. However, power supply is difficult to guarantee in high-altitude areas, and chemical reagents can pollute the ecologically fragile plateau.

[0007] The multi-energy complementary lithium extraction technology from salt lakes has the following problems: (1) Existing methods for lithium extraction from salt lakes require the consumption of fossil fuels and electricity to generate heat for the evaporation and concentration of brine in salt lakes. Fossil fuels and electricity are scarce on the Qinghai-Tibet Plateau, resulting in high costs for lithium extraction from salt lakes. The air source and water source heat pumps in the existing multi-energy complementary heating methods for lithium extraction from salt lakes are not suitable for the low-temperature environment of the high-altitude Qinghai-Tibet Plateau. The steam quality provided by the gas boiler is too high, exceeding the heat source parameter requirements for the evaporation of brine in salt lakes.

[0008] (2) Due to the limitations of the geographical conditions of the Qinghai-Tibet Plateau and the characteristics of salt lakes, the existing methods for lithium extraction from salt lakes have technical problems such as low efficiency of natural evaporation crystallization and precipitation methods, easy damage to the ecological environment by extraction methods, and high heat consumption and cost of adsorption methods.

[0009] (3) The abundant solar and salinity gradient energy resources of the Qinghai-Tibet Plateau have not been effectively applied to the multi-energy complementary system. Based on the principle of using energy according to quality, the thermal and electrical energy provided by the multi-energy complementary system cannot be effectively coupled with the heat source quality required for the evaporation and concentration of salt lake brine. Summary of the Invention

[0010] To overcome the shortcomings of existing technologies, this invention proposes a multi-energy complementary lithium extraction system and method for high-altitude salt lakes. Targeting the unique solar resources and climate of the Qinghai-Tibet Plateau, a multi-energy complementary system consisting of salinity gradient energy, solar photovoltaic, and solar thermal energy is coupled with the lithium extraction method for salt lakes. This achieves both the use of low-quality hot water generated by solar thermal energy for the evaporation and concentration of brine in the salt lake, and the addition of new green electricity generated by solar photovoltaic and solar thermal-driven salinity gradient energy, enabling low-cost, continuous lithium extraction from high-altitude salt lakes.

[0011] The present invention adopts the following technical solution: a multi-energy complementary high-altitude salt lake lithium extraction system, which includes a salinity gradient power generation unit, a photovoltaic and photothermal unit, an evaporation and concentration unit, an adsorption lithium extraction unit, a nanofiltration membrane separation unit, a multi-effect evaporation and crystallization unit, and a lithium carbonate precipitation unit; The salinity gradient power generation unit includes a brine pump, a forward osmosis membrane module, a draw liquid pump, a turbine generator set, and an NH4HCO3 draw liquid regenerator. Pipelines connected to the feed liquid inlet of the forward osmosis membrane module via the brine pump are connected to the feed liquid side inlet. The feed liquid side outlet pipe splits into two branches at the feed liquid branch point of the forward osmosis membrane module, connecting to the photovoltaic thermal unit and the evaporation and concentration unit respectively. Pipelines connected to the draw liquid inlet of the forward osmosis membrane module via the draw liquid pump are connected to the draw liquid side outlet of the forward osmosis membrane module via pipelines. The draw liquid side outlet is connected to the turbine generator set and the inlet of the NH4HCO3 draw liquid regenerator via pipelines. The outlet of the NH4HCO3 draw liquid regenerator is connected back to the draw liquid pump inlet. The NH4HCO3 draw liquid regenerator heat exchanger is connected to a hot water storage tank via inlet and outlet pipelines. The photovoltaic-thermal unit includes a photovoltaic-thermal module, a salt lake brine preheater, a solar flat plate collector, and a hot water storage tank; the photovoltaic-thermal module is electrically connected to a salt lake brine pump, a draw-out pump, and a nanofiltration membrane booster pump. The photovoltaic thermal module and the brine preheater form a thermal circulation loop. Part of the brine from the brine at the feed liquid branch of the forward osmosis membrane module flows through the brine preheater and then enters the evaporation and concentration unit. The electricity generated by the photovoltaic thermal module is connected to the electric heater embedded in the hot water storage tank through a cable. The hot water outlet of the solar flat plate collector is connected to the cold water inlet of the solar flat plate collector. The evaporation and concentration unit includes a plate evaporator, a plate condenser, and a freshwater tank. The plate evaporator is located below the plate condenser, and the plate condenser and the hot water storage tank form a thermal circulation loop. The low-temperature brine, which has been preheated by the brine preheater, and another low-temperature brine at the feed liquid branch point of the forward osmosis membrane module converge and enter the brine inlet of the plate condenser. The heated brine enters the plate evaporator through a pipe. The secondary steam generated by evaporation in the plate evaporator enters the plate condenser. The brine, which has been heated, evaporated, and concentrated, is connected to the adsorption and lithium extraction unit through the concentrated brine outlet of the plate evaporator. The adsorption lithium extraction unit includes an adsorption tower, an outlet check valve, and an inlet check valve; the nanofiltration membrane separation unit includes a nanofiltration membrane booster pump and a nanofiltration membrane module; the outlet check valve in the adsorption lithium extraction unit is connected to the inlet of the nanofiltration membrane module via a pipeline through the nanofiltration membrane booster pump, and then connected to the multi-effect evaporation crystallization unit from the outlet of the nanofiltration membrane module. The multi-effect evaporation crystallization unit includes a multi-effect evaporator and a condenser; the multi-effect evaporator and the hot water storage tank form a thermal circulation loop; the lithium solution inlet of the condenser is connected to the multi-effect evaporator via a pipeline; the final secondary steam generated by evaporation in the multi-effect evaporator enters the condenser; the lithium solution after heating, evaporation and concentration is connected to the lithium carbonate precipitation unit via the concentrated lithium solution outlet of the multi-effect evaporator.

[0012] Furthermore, the thermal circulation loop formed by the photovoltaic thermal module and the salt lake brine preheater is as follows: the outlet of the photovoltaic thermal module is connected to the hot water side inlet of the salt lake brine preheater, and the hot water side outlet of the salt lake brine preheater is connected to the photovoltaic thermal module via the photovoltaic thermal module inlet.

[0013] Furthermore, the heat circulation loop formed by the plate condenser and the hot water storage tank is as follows: the first hot water outlet of the hot water storage tank is connected to the hot water inlet of the plate evaporator, and the hot water outlet of the plate evaporator is connected to the first hot water return outlet of the hot water storage tank.

[0014] Furthermore, the freshwater outlet of the NH4HCO3 extractant regenerator, the plate condenser condensate outlet of the plate condenser, and the condenser condensate outlet of the condenser are connected to the inlet of the freshwater tank, and the freshwater tank outlet is connected to the inlet of the middle section of the adsorption tower.

[0015] Furthermore, the concentrated brine outlet of the plate evaporator is connected to the inlet of the liquid inlet check valve at the top of the adsorption tower via a pipeline, the adsorbent is attached to the packed bed inside the adsorption tower, and the liquid outlet check valve is connected to the bottom of the adsorption tower.

[0016] Furthermore, the outlet of the nanofiltration membrane module is also connected to the nanofiltration external drainage tank.

[0017] Furthermore, the heat circulation loop formed by the multi-effect evaporator and the hot water storage tank is as follows: the second hot water outlet of the hot water storage tank and the second hot water return port of the hot water storage tank are respectively connected to the hot water inlet and the hot water outlet of the multi-effect evaporator through pipes.

[0018] A working method for a multi-energy complementary lithium extraction system from high-altitude salt lakes includes the following steps: (a) In the salinity gradient power generation unit, low-concentration brine from the salt lake is pumped into the feed liquid side of the forward osmosis membrane module via a brine pump, while concentrated NH4HCO3 draw solution is pumped into the draw solution side of the forward osmosis membrane module via a draw solution pump. Driven by the osmotic pressure difference across the forward osmosis membrane, water molecules flow from the feed liquid side through the forward osmosis membrane to the draw solution side, concentrating the brine and diluting the concentrated NH4HCO3 draw solution. After dilution, the NH4HCO3 draw solution enters the turbine generator set to output electrical energy. The NH4HCO3 draw solution flowing out of the turbine generator set is then processed by the NH4HCO3 draw solution pump. The 4HCO3 draw liquid regenerator heat exchanger absorbs heat from the hot water in the hot water storage tank and decomposes it into NH3 and CO2 gases. The decomposed gases are absorbed by the fresh water and regenerated into concentrated NH4HCO3 draw liquid. The concentrated NH4HCO3 draw liquid is reused after being pumped by the draw liquid pump. The fresh water generated in the forward osmosis process enters the fresh water tank through the NH4HCO3 draw liquid regenerator. The concentrated brine is split into two streams at the feed liquid bifurcation point of the forward osmosis membrane module. One stream is heated in the brine preheater and then merged with the other brine stream before entering the evaporation and concentration unit for further concentration. (b) In the photovoltaic-thermal unit, the photovoltaic-thermal module absorbs solar energy to generate electricity for the pump power consumption of the lithium extraction system in the salt lake and to heat the hot water in the hot water storage tank. The 35-40°C hot water generated by the photovoltaic-thermal module absorbs solar energy serves as the heat source for the salt lake brine preheater to preheat the brine. The solar flat plate collector absorbs solar energy and then heats the hot water in the hot water storage tank. The electric heater generated by the turbine generator set and the photovoltaic-thermal module in the salinity gradient power generation unit heats the hot water in the hot water storage tank to 75-80°C. (c) Hot water in the hot water storage tank serves as the heat source for the evaporation and concentration unit. After releasing sensible heat in the plate evaporator, the temperature of the 75-80℃ hot water drops to 53-55℃. It then returns to the hot water storage tank for heating and continuous circulation. The brine absorbs the sensible heat released by the hot water and partially evaporates. The lithium ion concentration in the brine is further concentrated and then enters the adsorption lithium extraction unit. The secondary steam generated by evaporation is condensed into fresh water in the plate condenser and then flows into the fresh water tank. The low-temperature brine in the plate condenser absorbs the latent heat of vaporization released by the secondary steam and then heats up to 40-45℃ before entering the plate evaporator for evaporation and concentration. (d) In the adsorption lithium extraction unit, the hot brine from the salt lake, which has been further concentrated in the plate evaporator, enters the adsorption tower through the inlet check valve at the top. The adsorbent in the adsorption tower selectively adsorbs magnesium ions and lithium ions at 50°C. After the adsorbent is saturated, the adsorption process is completed. Fresh water from the fresh water tank enters from the middle section of the adsorption tower and washes the saturated adsorbent. A lithium-containing solution is obtained at the outlet check valve at the bottom of the adsorption tower, thus completing the desorption process. (e) In the nanofiltration membrane separation unit, the lithium-containing solution is pressurized by the nanofiltration membrane booster pump and magnesium ions are separated in the nanofiltration membrane module. The lithium-containing solution after magnesium ions are removed is used as the feed liquid for the multi-effect evaporation crystallization unit for evaporation, and the concentrated magnesium solution enters the nanofiltration external drainage tank. (f) In the multi-effect evaporation crystallization unit, the hot water in the hot water storage tank serves as the heat source for the multi-effect evaporator. The lithium-containing solution is heated, evaporated, and concentrated into a concentrated lithium solution before entering the lithium carbonate precipitation unit. The secondary steam generated by evaporation is condensed in the condenser. The condensate generated in the multi-effect evaporation crystallization unit is collected in the fresh water tank through the condensate outlet of the condenser. (g) Add sodium carbonate precipitant to the lithium carbonate precipitation unit, and obtain battery-grade lithium carbonate after precipitation reaction of concentrated lithium solution.

[0019] Furthermore, the low-concentration brine has a lithium ion mass fraction of 0.02%; the concentrated extract is a solution with an NH4HCO3 mass fraction of 20%; and the diluted extract is a solution with an NH4HCO3 mass fraction of 12%.

[0020] Furthermore, after the brine is further concentrated in the plate evaporator, the lithium ion concentration in the brine is 1.0-1.2%; the lithium ion concentration in the lithium-containing solution discharged from the bottom of the adsorption tower is 1.5-2.0%; and the lithium ion concentration in the concentrated lithium solution after heating and evaporation in the multi-effect evaporation crystallization unit is 3.0-3.5%.

[0021] The above technical solution is characterized by: adopting a photovoltaic-thermal driven salinity gradient power generation system, which enables the initial concentration of salt lake brine and the output of green electricity without the need for external power; utilizing the low-grade heat generated by photovoltaic-thermal components to preheat the high-altitude, low-temperature salt lake brine, saving the heat consumption of salt lake brine evaporation and concentration; using hot water generated by solar flat plate collectors to replace steam as the heat source for the evaporation crystallization unit and the evaporation concentration unit, reducing the cycle of the natural evaporation crystallization process of salt lake brine and lowering the heat consumption cost of lithium solution concentration; and using the hot water obtained by photovoltaic power heating as the heat energy of the salt lake lithium extraction system, achieving complementarity between low-grade hot water and high-grade electricity under different light intensity levels in the morning and evening.

[0022] The beneficial effects of this invention are: (1) A multi-energy complementary salt lake lithium extraction system and method suitable for the Qinghai-Tibet Plateau were designed. The multi-energy complementary salt gradient energy power generation system does not require externally supplied electrical energy or fossil fuel thermal energy. It uses solar photothermal to drive salt gradient energy power generation while simultaneously performing preliminary concentration of salt lake brine. The preliminary concentration of forward osmosis salt lake brine reduces the cost of salt lake brine evaporation and concentration.

[0023] (2) In view of the low temperature characteristics of high-altitude salt lake brine, the low-grade heat of 35-40℃ carried away by photovoltaic thermal modules is used to preheat the salt lake brine, realizing the efficient utilization of low-grade heat and saving the heat consumption of salt lake brine evaporation; compared with the natural evaporation cycle of salt lake brine, the hot water generated by the solar flat plate collector is used as the heat source for the evaporation and concentration of lithium extraction from salt lake, which can shorten the concentration time of salt lake brine at low cost and improve the efficiency of continuous production of lithium extraction from salt lake; the hot water generated by the solar flat plate collector replaces the high-temperature steam as the heat source for the evaporation and crystallization of lithium extraction from salt lake. Low-grade hot water can be used to drive low-temperature evaporation and crystallization for lithium extraction from salt lakes. Solar flat-plate collectors that generate hot water can replace solar trough collectors that generate high-temperature steam, significantly reducing the investment cost of heat collection in the lithium extraction system. Photovoltaic power generation and salinity gradient power generation are used to heat the hot water in the storage tank. The hot water provides heat energy for the lithium extraction system, and the electrical energy is stored as heat energy for the hot water. This achieves complementarity between low-grade hot water and high-grade electrical energy, and also enables continuous production of the lithium extraction system in the salt lake when the hot water temperature of the solar flat-plate collectors is insufficient in the morning and evening. Attached Figure Description

[0024] Figure 1 This is a diagram of a multi-energy complementary lithium extraction system from a high-altitude salt lake.

[0025] In the diagram: 1. Salinity gradient power generation unit; 2. Salt lake brine pump; 3. Forward osmosis membrane module; 3a. Forward osmosis membrane module feed solution bifurcation port; 4. Draw liquid pump; 5. Turbine generator set; 6. NH4HCO3 draw liquid regenerator; 6a. NH4HCO3 draw liquid regenerator heat exchanger; 7. Photovoltaic thermal unit; 8. Photovoltaic thermal module; 8a. Photovoltaic thermal module outlet; 8b. Photovoltaic thermal module inlet; 9. Salt lake brine preheater; 9a. Salt lake... 9b. Hot water inlet of brine preheater; 10. Hot water outlet of brine preheater; 10a. Solar flat plate collector; 10b. Hot water outlet of solar flat plate collector; 11. Cold water inlet of solar flat plate collector; 11. Hot water storage tank; 11a. Plate heat exchanger embedded in hot water storage tank; 11b. Electric heater; 11c. First hot water outlet of hot water storage tank; 11d. First hot water return outlet of hot water storage tank; 11e. Second hot water outlet of hot water storage tank; 11f. 11. Hot water return inlet of hot water storage tank; 12. Evaporation and concentration unit; 13. Plate evaporator; 13a. Hot water inlet of plate evaporator; 13b. Hot water outlet of plate evaporator; 13c. Concentrated brine outlet of plate evaporator; 14. Plate condenser; 14a. Salt lake brine inlet of plate condenser; 14b. Condensate outlet of plate condenser; 15. Fresh water tank; 16. Adsorption and lithium extraction unit; 17. Adsorption tower; 18. One-way valve for liquid outlet; 19. Liquid inlet. 20. One-way valve; 21. Nanofiltration membrane separation unit; 22. Nanofiltration membrane booster pump; 23. Nanofiltration membrane module; 24. Nanofiltration external drain tank; 25. Multi-effect evaporation crystallization unit; 26. Multi-effect evaporator; 27. Multi-effect evaporator hot water inlet; 28. Multi-effect evaporator hot water outlet; 29. ​​Multi-effect evaporator concentrated lithium solution outlet; 20. Condenser; 21. Condenser lithium solution inlet; 22. Condenser condensate outlet; 23. Lithium carbonate precipitation unit. Detailed Implementation

[0026] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0027] Figure 1A diagram of a multi-energy complementary lithium extraction system from a high-altitude salt lake is shown. The system includes a salinity gradient power generation unit 1, a photovoltaic and photothermal unit 7, an evaporation and concentration unit 12, an adsorption lithium extraction unit 16, a nanofiltration membrane separation unit 20, a multi-effect evaporation and crystallization unit 23, and a lithium carbonate precipitation unit 26. The salinity gradient power generation unit 1 includes a salt lake brine pump 2, a forward osmosis membrane module 3, a draw liquid pump 4, a turbine generator set 5, and an NH4HCO3 draw liquid regenerator 6. Salt lake brine enters the feed liquid side inlet of forward osmosis membrane module 3 via a pipeline and brine pump 2. After preliminary concentration, the brine flows out from the feed liquid side outlet of forward osmosis membrane module 3 and splits into two paths at feed liquid bifurcation point 3a, connecting to photovoltaic thermal unit 7 and evaporation concentration unit 12 respectively. NH4HCO3 draw liquid enters the draw liquid side inlet of forward osmosis membrane module 3 via a pipeline and draw liquid pump 4. The diluted NH4HCO3 draw liquid exits from the draw liquid side outlet of forward osmosis membrane module 3 and connects to turbine generator set 5 via a pipeline. The diluted NH4HCO3 draw liquid, after generating electricity using salinity gradient energy, connects to NH4HCO3 draw liquid regenerator 6 via a pipeline. The concentrated and regenerated NH4HCO3 draw liquid enters the inlet of draw liquid pump 4 via a pipeline. The freshwater produced in NH4HCO3 draw liquid regenerator 6 enters the freshwater tank 15 via a pipeline. The NH4HCO3 draw liquid regenerator heat exchanger 6a is connected to the hot water storage tank 11 via inlet and outlet pipelines.

[0028] The photovoltaic-thermal unit 7 includes a photovoltaic-thermal module 8, a brine preheater 9, a solar flat-plate collector 10, and a hot water storage tank 11. The electricity generated by the photovoltaic-thermal module 8 is connected via cables to the brine pump 2, the extraction liquid pump 4, and the nanofiltration membrane booster pump 21. The photovoltaic-thermal module outlet 8a is connected to the hot water inlet 9a of the brine preheater. The hot water outlet 9b of the brine preheater is connected to the photovoltaic-thermal module 8 via the photovoltaic-thermal module inlet 8b. A portion of the brine flowing through the feed liquid bifurcation port 3a of the forward osmosis membrane module passes through the brine preheater 9 and enters the evaporation and concentration unit 12. The electricity generated by the photovoltaic-thermal module 8 is connected via cables to the electric heater 11b embedded in the hot water storage tank. The hot water outlet 10a of the solar flat-plate collector is connected via a pipe through the hot water side of the plate heat exchanger 11a embedded in the hot water storage tank to the cold water inlet 10b of the solar flat-plate collector.

[0029] The evaporation and concentration unit 12 includes a plate evaporator 13, a plate condenser 14, and a freshwater tank 15. The plate evaporator 13 is located below the plate condenser 14. The first hot water outlet 11c of the hot water storage tank is connected to the hot water inlet 13a of the plate evaporator, and the hot water outlet 13b of the plate evaporator is connected to the first hot water return outlet 11d of the hot water storage tank. The low-temperature brine, preheated by the brine preheater 9, and another low-temperature brine from the feed liquid bifurcation port 3a of the forward osmosis membrane module converge and enter the brine inlet 14a of the plate condenser. The heated brine enters the plate evaporator 13 through a pipe. The secondary steam formed by evaporation in the plate evaporator 13 enters the plate condenser 14. The condensate outlet 14b of the plate condenser is connected to the inlet of the freshwater tank 15. The concentrated brine after heating and evaporation is connected to the adsorption lithium extraction unit 16 through the concentrated brine outlet 13c of the plate evaporator.

[0030] The adsorption lithium extraction unit 16 includes an adsorption tower 17, an outlet check valve 18, and an inlet check valve 19. The concentrated brine outlet 13c of the plate evaporator is connected to the inlet of the inlet check valve 19 at the top of the adsorption tower 17 via a pipeline. The adsorption tower 17 is filled with a bed of adsorbent. The bottom of the adsorption tower 17 is connected to the outlet check valve 18, and the outlet of the freshwater tank 15 is connected to the inlet of the middle section of the adsorption tower 17.

[0031] The nanofiltration membrane separation unit 20 includes a nanofiltration membrane booster pump 21 and a nanofiltration membrane module 22. The liquid outlet check valve 18 in the adsorption lithium extraction unit 16 is connected to the inlet of the nanofiltration membrane module 22 via a pipeline through the nanofiltration membrane booster pump 21, and then connected to the multi-effect evaporation crystallization unit 23 and the nanofiltration external drainage tank 22a via the outlet of the nanofiltration membrane module 22.

[0032] The multi-effect evaporation crystallization unit 23 includes a multi-effect evaporator 24 and a condenser 25. The second hot water outlet 11e and the second hot water return outlet 11f of the hot water storage tank 11 are connected to the hot water inlet 24a and the hot water outlet 24b of the multi-effect evaporator respectively via pipes. The lithium solution inlet 25a of the condenser is connected to the multi-effect evaporator 24 via a pipe. The final secondary steam generated by evaporation in the multi-effect evaporator 24 enters the condenser 25. The condensate outlet 25b of the condenser is connected to the inlet of the fresh water tank 15. The lithium solution concentrated by heating and evaporation is connected to the lithium carbonate precipitation unit 26 via the concentrated lithium solution outlet 24c of the multi-effect evaporator.

[0033] The system's processing method employs the following steps: (a) In the salinity gradient power generation unit 1, brine with a lithium ion concentration of 0.02% is pumped into the feed liquid side of the forward osmosis membrane module 3 via brine pump 2, and concentrated draw liquid with an NH4HCO3 concentration of 20% is pumped into the draw liquid side of the forward osmosis membrane module 3 via draw liquid pump 4. Driven by the osmotic pressure difference between the solutions on both sides of the forward osmosis membrane, water molecules flow from the brine feed liquid side to the NH4HCO3 draw liquid side through the forward osmosis membrane. The brine is concentrated to 0.03%, and the NH4HCO3 solution is diluted to 12%. The NH4HCO3 draw liquid, which has increased in volume after dilution, enters the turbine generator set 5 to output electrical energy, and flows out from the turbine generator set 5. The NH4HCO3 draw solution absorbs heat from the hot water in the hot water storage tank 11 through the NH4HCO3 draw solution regenerator heat exchanger 6a and decomposes into NH3 and CO2 gases. The decomposed gases are absorbed by the fresh water and regenerated into 20% concentrated NH4HCO3 draw solution. The concentrated NH4HCO3 draw solution is reused after passing through the draw solution pump 4. The fresh water generated in the forward osmosis process enters the fresh water tank 15 through the NH4HCO3 draw solution regenerator 6. The concentrated brine is divided into two streams at the feed solution bifurcation port 3a of the forward osmosis membrane module. One stream is heated in the brine preheater 9 and then merged with the other stream of brine before entering the evaporation concentration unit 12 for further concentration.

[0034] (b) In the photovoltaic-thermal unit 7, the photovoltaic-thermal module 8 absorbs solar energy to generate electricity for the pump power consumption of the lithium extraction system in the salt lake and to heat the hot water in the hot water storage tank 11. The 35-40°C hot water generated by the photovoltaic-thermal module 8 absorbs solar energy serves as the heat source for the salt lake brine preheater 9, preheating the salt lake brine at a design temperature of 4°C to 10°C. The solar flat plate collector 10 absorbs solar energy and then heats the hot water in the hot water storage tank 11. The electric heater 11b produced by the turbine generator set 5 and the photovoltaic-thermal module 8 in the salinity gradient power generation unit 1 heats the hot water in the hot water storage tank 11 to 75-80°C.

[0035] (c) The hot water in the hot water storage tank 11 serves as the heat source for the evaporation and concentration unit 12. The 75-80℃ hot water releases sensible heat in the plate evaporator 13 and then the temperature drops to 53-55℃. It then returns to the hot water storage tank 11 to be heated and then continuously circulates. The brine absorbs the sensible heat released by the hot water and partially evaporates. The lithium ion concentration of the brine is concentrated to 1.0-1.2% and then enters the adsorption lithium extraction unit 16. The secondary steam generated by evaporation is condensed into fresh water in the plate condenser 14 and then flows into the fresh water tank 15. The low-temperature brine in the plate condenser 14 absorbs the latent heat of vaporization released by the condensation of the secondary steam and then heats up to 40-45℃ before entering the plate evaporator 13 for evaporation and concentration.

[0036] (d) In the adsorption lithium extraction unit 16, the 52-55℃ hot brine from the plate evaporator 13, after further concentration, enters the adsorption tower 17 through the top liquid inlet check valve 19. The adsorbent in the adsorption tower 17 selectively adsorbs magnesium ions and lithium ions at 50℃. After the adsorbent is saturated, the adsorption process is completed. Fresh water from the fresh water tank 15 enters from the middle section of the adsorption tower 17 and washes the saturated adsorbent. A lithium-containing solution with a lithium ion concentration of 1.5-2.0% is obtained at the bottom liquid outlet check valve 18 of the adsorption tower 17, completing the desorption process.

[0037] (e) In the nanofiltration membrane separation unit 20, the lithium-containing solution is pressurized by the nanofiltration membrane booster pump 21 and magnesium ions are separated in the nanofiltration membrane module 22. The lithium-containing solution after magnesium ions are removed is used as the feed liquid of the multi-effect evaporation crystallization unit 23 for evaporation, and the concentrated magnesium solution enters the nanofiltration external drainage tank 22a.

[0038] (f) In the multi-effect evaporation crystallization unit 23, the hot water in the hot water storage tank 11 serves as the heat source for the multi-effect evaporator 24. The lithium-containing solution is heated and evaporated to concentrate it into a concentrated lithium solution with a lithium ion concentration of 3.0-3.5%, and then enters the lithium carbonate precipitation unit 26. The secondary steam generated by evaporation is condensed in the condenser. The condensate generated in the multi-effect evaporation crystallization unit 23 is collected in the fresh water tank 15 through the condenser condensate outlet 25b.

[0039] (g) Add sodium carbonate precipitant to lithium carbonate precipitation unit 26, and obtain battery-grade lithium carbonate after precipitation reaction of concentrated lithium solution.

[0040] Using the above technical solutions, a multi-energy complementary lithium extraction system and method suitable for the Qinghai-Tibet Plateau was developed. This system couples a multi-energy complementary system consisting of salinity gradient power generation, solar photovoltaic, and solar thermal power generation with the lithium extraction method. The salinity gradient power generation system requires no externally supplied electricity or fossil fuels, utilizing solar thermal power to drive salinity gradient power generation while simultaneously performing preliminary concentration of the brine. The low-grade heat (35-40℃) carried away by the photovoltaic and solar thermal modules is used to preheat the brine, achieving efficient utilization of this low-grade heat. Compared to the natural evaporation cycle of the brine, the hot water generated by the solar flat-plate collector is used for lithium extraction evaporation and concentration. The heat source can shorten the concentration time of brine in salt lakes at low cost and improve the efficiency of continuous lithium extraction from salt lakes; the use of solar flat plate collectors that generate hot water to replace solar trough collectors that generate high-temperature steam allows hot water to replace high-temperature steam as the heat source for evaporation and crystallization of lithium in salt lakes, which can significantly reduce the investment cost and energy consumption cost of the heat collection system for lithium extraction from salt lakes; photovoltaic power generation and salinity gradient power generation are used to heat the hot water in the storage tank, and the electrical energy is stored as the heat energy of the hot water, which not only achieves the complementarity of low-grade hot water and high-grade electrical energy, but also enables continuous production of the lithium extraction system from salt lakes when the hot water temperature of the solar flat plate collectors is insufficient in the morning and evening.

[0041] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments, or make equivalent substitutions for some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A multi-energy complementary lithium extraction system from high-altitude salt lakes, characterized in that: It includes a salinity gradient power generation unit (1), a photovoltaic and photothermal unit (7), an evaporation and concentration unit (12), an adsorption lithium extraction unit (16), a nanofiltration membrane separation unit (20), a multi-effect evaporation and crystallization unit (23), and a lithium carbonate precipitation unit (26). The salinity gradient power generation unit (1) includes a brine pump (2), a forward osmosis membrane module (3), a draw liquid pump (4), a turbine generator set (5), and an NH4HCO3 draw liquid regenerator (6). The pipeline is connected to the feed liquid side inlet of the forward osmosis membrane module (3) after passing through the brine pump (2). The feed liquid side outlet pipeline is split into two paths at the feed liquid bifurcation point (3a) of the forward osmosis membrane module, which are respectively connected to the photovoltaic thermal unit (7) and the evaporation and concentration unit (12). The pipeline is connected to the draw liquid side inlet of the forward osmosis membrane module (3) after passing through the draw liquid pump (4). The draw liquid side outlet is connected to the turbine generator set (5) and the inlet of the NH4HCO3 draw liquid regenerator (6) through the pipeline. The outlet of the NH4HCO3 draw liquid regenerator (6) is connected to the inlet of the draw liquid pump (4). The NH4HCO3 draw liquid regenerator heat exchanger (6a) is connected to the hot water storage tank (11) through the inlet and outlet pipelines. The photovoltaic thermal unit (7) includes a photovoltaic thermal module (8), a salt lake brine preheater (9), a solar flat plate collector (10), and a hot water storage tank (11); the photovoltaic thermal module (8) is electrically connected to the salt lake brine pump (2), the extractor pump (4), and the nanofiltration membrane booster pump (21); The photovoltaic thermal module (8) and the salt lake brine preheater (9) form a thermal circulation loop. Part of the salt lake brine that flows through the feed liquid branch port (3a) of the forward osmosis membrane module flows through the salt lake brine preheater (9) and then enters the evaporation and concentration unit (12). The electrical energy generated by the photovoltaic thermal module (8) is connected to the electric heater (11b) embedded in the hot water storage tank through a cable. The hot water outlet (10a) of the solar flat plate collector is connected to the cold water inlet (10b) of the solar flat plate collector through a pipe via the hot water side of the plate heat exchanger (11a) embedded in the hot water storage tank. The evaporation and concentration unit (12) includes a plate evaporator (13), a plate condenser (14), and a freshwater tank (15). The plate evaporator (13) is located below the plate condenser (14), and the plate evaporator (13) and the hot water storage tank (11) form a heat circulation loop. The low-temperature brine that has been preheated by the brine preheater (9) and another low-temperature brine that has been fed into the plate condenser brine inlet (14a) after being combined with the feed liquid bifurcation port (3a) of the forward osmosis membrane module, are heated and enter the plate condenser brine inlet (14a). The heated brine enters the plate evaporator (13) through a pipe. The secondary steam formed by evaporation in the plate evaporator (13) enters the plate condenser (14). The brine that has been heated, evaporated, and concentrated is connected to the adsorption lithium extraction unit (16) through the concentrated brine outlet (13c) of the plate evaporator. The adsorption lithium extraction unit (16) includes an adsorption tower (17), an outlet check valve (18), and an inlet check valve (19). The nanofiltration membrane separation unit (20) includes a nanofiltration membrane booster pump (21) and a nanofiltration membrane module (22); the liquid outlet check valve (18) in the adsorption lithium extraction unit (16) is connected to the inlet of the nanofiltration membrane module (22) via a pipeline through the nanofiltration membrane booster pump (21), and then connected to the multi-effect evaporation crystallization unit (23) through the outlet of the nanofiltration membrane module (22). The multi-effect evaporation crystallization unit (23) includes a multi-effect evaporator (24) and a condenser (25); the multi-effect evaporator (24) and the hot water storage tank (11) form a heat circulation loop; the lithium solution inlet (25a) of the condenser is connected to the multi-effect evaporator (24) through a pipe, the final secondary steam generated by evaporation in the multi-effect evaporator (24) enters the condenser (25), and the lithium solution after heating and evaporation concentration is connected to the lithium carbonate precipitation unit (26) through the concentrated lithium solution outlet (24c) of the multi-effect evaporator.

2. The multi-energy complementary lithium extraction system for high-altitude salt lakes according to claim 1, characterized in that: The heat circulation loop formed by the photovoltaic thermal module (8) and the salt lake brine preheater (9) is as follows: the outlet (8a) of the photovoltaic thermal module is connected to the hot water side inlet (9a) of the salt lake brine preheater, and the hot water side outlet (9b) of the salt lake brine preheater is connected to the photovoltaic thermal module (8) via the photovoltaic thermal module inlet (8b).

3. The multi-energy complementary lithium extraction system from high-altitude salt lakes according to claim 2, characterized in that: The heat circulation loop formed by the plate evaporator (13) and the hot water storage tank (11) is as follows: the first hot water outlet (11c) of the hot water storage tank is connected to the hot water inlet (13a) of the plate evaporator, and the hot water outlet (13b) of the plate evaporator is connected to the first hot water return outlet (11d) of the hot water storage tank.

4. The multi-energy complementary lithium extraction system from high-altitude salt lakes according to claim 3, characterized in that: The freshwater outlet of the NH4HCO3 extract regenerator (6), the plate condenser condensate outlet (14b) of the plate condenser (14), and the condenser condensate outlet (25b) of the condenser (25) are connected to the inlet of the freshwater tank (15), and the outlet of the freshwater tank (15) is connected to the middle section inlet of the adsorption tower (17).

5. The multi-energy complementary lithium extraction system from high-altitude salt lakes according to claim 4, characterized in that: The concentrated brine outlet (13c) of the plate evaporator is connected to the inlet of the liquid inlet check valve (19) at the top of the adsorption tower (17) through a pipeline. The adsorption tower (17) is filled with adsorbent and the bottom of the adsorption tower (17) is connected to the liquid outlet check valve (18).

6. The multi-energy complementary lithium extraction system from high-altitude salt lakes according to claim 5, characterized in that: The outlet of the nanofiltration membrane module (22) is also connected to the nanofiltration external drainage tank (22a).

7. A multi-energy complementary lithium extraction system for high-altitude salt lakes according to claim 6, characterized in that: The heat circulation loop formed by the multi-effect evaporator (24) and the hot water storage tank (11) is as follows: the second hot water outlet (11e) of the hot water storage tank and the second hot water return port (11f) of the hot water storage tank are respectively connected to the hot water inlet (24a) and the hot water outlet (24b) of the multi-effect evaporator through pipes.

8. The working method of the multi-energy complementary lithium extraction system from plateau salt lakes according to claim 7, characterized in that, Includes the following steps: (a) In the salinity gradient power generation unit (1), low-concentration brine from the salt lake is pumped into the feed liquid side of the forward osmosis membrane module (3) via the brine pump (2), and concentrated NH4HCO3 extract is pumped into the extract liquid side of the forward osmosis membrane module (3) via the extract liquid pump (4). Driven by the osmotic pressure difference of the solutions on both sides of the forward osmosis membrane, water molecules flow from the feed liquid side through the forward osmosis membrane to the extract liquid side, the brine from the salt lake is concentrated, and the concentrated NH4HCO3 extract is diluted; after dilution, the NH4HCO3 extract enters the turbine generator set (5) to output electrical energy, and the NH4HCO3 extract flowing out of the turbine generator set (5) is processed by the NH4HCO3 extract... The heat exchanger (6a) of the 3 draw liquid regenerator absorbs the heat of the hot water in the hot water storage tank (11) and decomposes it into NH3 and CO2 gas. The decomposed gas is absorbed by the fresh water and regenerates concentrated NH4HCO3 draw liquid. The concentrated NH4HCO3 draw liquid is reused after passing through the draw liquid pump (4). The fresh water generated in the forward osmosis process enters the fresh water tank (15) through the NH4HCO3 draw liquid regenerator (6). The concentrated brine is divided into two streams at the feed liquid bifurcation port (3a) of the forward osmosis membrane module. One stream is heated in the brine preheater (9) and then merged with the other brine stream before entering the evaporation concentration unit (12) for further concentration. (b) In the photovoltaic-thermal unit (7), the photovoltaic-thermal module (8) absorbs solar energy to generate electricity for the pump power consumption of the lithium extraction system in the salt lake and to heat the hot water in the hot water storage tank (11). The 35-40℃ hot water generated by the photovoltaic-thermal module (8) absorbs solar energy serves as the heat source for the salt lake brine preheater (9) to preheat the low-temperature salt lake brine. The solar flat plate collector (10) absorbs solar energy and then heats the hot water in the hot water storage tank (11). The electric heater (11b) produced by the turbine generator set (5) and the photovoltaic-thermal module (8) in the salinity gradient power generation unit (1) heats the hot water in the hot water storage tank (11) to 75-80℃. (c) Hot water in the hot water storage tank (11) serves as the heat source for the evaporation and concentration unit (12). After the sensible heat is released in the plate evaporator (13) at 75-80℃, the temperature drops to 53-55℃. Then, it returns to the hot water storage tank (11) to be heated and heated, and then continuously circulates. After absorbing the sensible heat released by the hot water, the brine in the salt lake partially evaporates. After the lithium ion concentration in the brine in the salt lake is further concentrated, it enters the adsorption and lithium extraction unit (16). The secondary steam generated by evaporation is condensed into fresh water in the plate condenser (14) and then flows into the fresh water tank (15). After absorbing the latent heat of vaporization released by the secondary steam in the plate condenser (14), the brine in the low temperature salt lake absorbs the latent heat of vaporization released by the condensation of the secondary steam and is heated to 40-45℃ before entering the plate evaporator (13) for evaporation and concentration. (d) In the adsorption lithium extraction unit (16), the 52-55℃ hot salt lake brine, which has been further concentrated in the plate evaporator (13), enters the adsorption tower (17) through the liquid inlet check valve (19) at the top. The adsorbent in the adsorption tower (17) selectively adsorbs magnesium ions and lithium ions at 50℃. After the adsorbent is saturated, the adsorption process is completed. Fresh water in the fresh water tank (15) enters from the middle section of the adsorption tower (17) and washes the saturated adsorbent. A lithium-containing solution is obtained at the liquid outlet check valve (18) at the bottom of the adsorption tower (17), thus completing the desorption process. (e) In the nanofiltration membrane separation unit (20), the lithium-containing solution is pressurized by the nanofiltration membrane booster pump (21) and magnesium ions are separated in the nanofiltration membrane module (22). The lithium-containing solution after magnesium ions are removed is used as the feed liquid of the multi-effect evaporation crystallization unit (23) for evaporation, and the concentrated magnesium solution enters the nanofiltration external drainage tank (22a). (f) In the multi-effect evaporation crystallization unit (23), the hot water in the hot water storage tank (11) serves as the heat source for the multi-effect evaporator (24). The lithium-containing solution is heated and evaporated to concentrate into a concentrated lithium solution before entering the lithium carbonate precipitation unit (26). The secondary steam generated by evaporation is condensed in the condenser. The condensate generated in the multi-effect evaporation crystallization unit (23) is collected in the fresh water tank (15) through the condenser condensate outlet (25b). (g) Add sodium carbonate precipitant to the lithium carbonate precipitation unit (26), and obtain battery-grade lithium carbonate after precipitation reaction of concentrated lithium solution.

9. The working method of a multi-energy complementary lithium extraction system from a high-altitude salt lake according to claim 8, characterized in that, The low-concentration brine contains 0.02% lithium ions by mass; the concentrated extract is a solution with 20% NH4HCO3 by mass. The diluted extract was a 12% NH4HCO3 solution.

10. The working method of the multi-energy complementary lithium extraction system in a high-altitude salt lake according to claim 9, characterized in that, After further concentration in the plate evaporator (13), the lithium ion concentration in the salt lake brine is 1.0-1.2%; the lithium ion concentration in the lithium-containing solution discharged from the bottom of the adsorption tower (17) is 1.5-2.0%. The lithium ion concentration in the concentrated lithium solution after heating and evaporation in the multi-effect evaporation crystallization unit (23) is 3.0-3.5%.

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