Geothermal brine lithium extraction system and method based on cascade waste heat utilization

Abstract

The present application belongs to the technical field of geothermal resource comprehensive utilization and geothermal brine lithium extraction, and discloses a geothermal brine lithium extraction system and method based on cascade waste heat utilization, which comprises a geothermal brine extraction unit; the geothermal brine extraction unit is used for extracting and conveying liquid-phase geothermal brine to a thermal energy cascade utilization subsystem; the thermal energy cascade utilization subsystem is used for cascade thermal utilization of the liquid-phase geothermal brine; a brine temperature regulation unit is used for temperature regulation of the geothermal brine after waste heat recovery; a lithium extraction subsystem is used for lithium selective extraction treatment to obtain lithium salt and lithium-lean tail liquid; a tail liquid regulation and reinjection unit is used for temperature, water quality or pressure regulation of the lithium-lean tail liquid, and the lithium-lean tail liquid is conveyed into a target reinjection well after meeting the reinjection requirements; the present application can fully recover and utilize geothermal brine low-temperature waste heat, accurately match the heat demand of the lithium extraction process, stabilize the optimal lithium extraction working temperature range, and greatly improve the comprehensive development and utilization rate of geothermal thermal energy and lithium resources and the development economic benefits.

Description

Technical Field

[0001] This invention belongs to the field of geothermal resource comprehensive utilization and geothermal brine lithium extraction technology, and specifically relates to a geothermal brine lithium extraction system and method based on cascade waste heat utilization. Background Technology

[0002] Geothermal resources, as a stable and continuously functioning clean and renewable energy source, have become one of the key resources for development and utilization in the new energy system. Among them, medium- and high-temperature geothermal resources are characterized by high thermal energy quality and wide applicability. The geothermal fluids obtained from their extraction can be widely used in geothermal power generation, district heating, industrial heating and other fields. High-mineralized geothermal brine not only contains exploitable geothermal energy, but is also rich in a variety of high-value-added rare metal elements such as lithium, potassium, boron, rubidium and cesium, and has the dual resource attributes of thermal energy development and mineral resource recovery.

[0003] In existing geothermal development projects, geothermal fluids are typically extracted through drilling, and their high-temperature heat energy is prioritized for power generation, achieving the initial utilization of geothermal energy. The geothermal tailwater after power generation is then further treated and reinjected. However, the tailwater generated after the geothermal fluids are used for power generation still possesses medium-low temperature waste heat of 100-180℃, which is a low-grade heat energy that can be reused. However, current technologies often simply treat this part of the tailwater and directly reinject it into the formation, which not only causes a large amount of waste heat resources to be wasted, but also discards valuable metal resources such as lithium remaining in the tailwater, greatly reducing the overall development benefits of geothermal brine.

[0004] Furthermore, the mainstream processes for lithium extraction from geothermal brine at present mainly include adsorption, ion sieving, membrane separation, and electrochemical methods, all of which are highly temperature-sensitive. Among them, adsorption is the most widely used in the field of lithium extraction from geothermal brine due to its strong adaptability and controllable cost. The reaction efficiency and adsorption effect of this process are highly dependent on the ambient temperature: too low a temperature will significantly reduce the lithium-ion diffusion rate and weaken the adsorption kinetics; too high a temperature will damage the microstructure of the adsorption material, reduce the material's adsorption selectivity for lithium ions, and shorten the material's cycle life. Each lithium extraction process has its corresponding optimal temperature. The existing development system cannot achieve precise temperature matching within the working range of geothermal energy utilization, brine lithium extraction, and tailings reinjection. More importantly, the existing technology sets geothermal energy utilization, brine lithium extraction, and tailings reinjection as independent process units. The operating logic of each process unit is isolated and the parameters are incompatible. The brine temperature after front-end thermal energy utilization cannot meet the operating conditions of the back-end lithium extraction process. Moreover, the dynamic fluctuations in geothermal output flow and heat exchange system load will directly cause instability in the inlet water temperature of the lithium extraction unit, ultimately leading to fluctuations in lithium extraction efficiency and low lithium resource recovery rate, which seriously restricts the stable industrial application of geothermal brine lithium extraction technology.

[0005] To address the technical problems of traditional processes, such as waste heat, poor temperature zone matching, and insufficient coordination among multiple processes, the industry has gradually developed integrated development technologies for multiple processes. These technologies aim to achieve the synergistic and comprehensive development of geothermal fluid pressure energy, thermal energy, and lithium mineral resources. Currently, a typical existing integrated solution is exemplified by the Chinese patent application "An Integrated System and Method for Power Generation and Lithium Extraction from Produced Fluid in Medium-High Temperature and High Pressure Water Gas Reservoirs" (Publication No.: CN121875681A). This application discloses an integrated processing flow that includes gas-liquid separation, differential pressure power generation, ORC power generation, lithium extraction from power generation tailwater, and tailwater reinjection. This integrated solution achieves the simultaneous development of multi-dimensional geothermal fluid resources by integrating pressure energy power generation, waste heat resource utilization, lithium resource extraction, and closed-loop tailwater reinjection. It effectively improves the problems of single function and low resource utilization in traditional processes and is currently the mainstream optimized technology solution in the field of comprehensive geothermal brine development.

[0006] While the existing integrated solutions described above improve the comprehensive utilization rate of geothermal brine resources to some extent, they still suffer from several drawbacks in practical engineering applications. These include insufficient heat distribution in the geothermal brine before it enters the lithium extraction unit, inadequate matching between the waste heat in the low-temperature section and the preheating of the liquid used in the lithium extraction process, and difficulty in maintaining stable control of the lithium extraction inlet temperature. Consequently, they cannot simultaneously achieve efficient utilization of waste heat and stable high lithium resource utilization. Specifically, firstly, the existing integrated solutions are primarily designed for gas-liquid mixtures produced from gas reservoirs, with the core objective of developing the pressure energy, thermal energy, and lithium resources within the mixture. They are not specifically optimized for the physical properties and development requirements of pure geothermal brine, and therefore cannot be adapted to the refined development scenarios of single geothermal brine. Secondly, the existing integrated solutions have not yet established a complete system. The existing thermal energy cascade distribution system cannot classify and precisely allocate the waste heat from geothermal brine, making it difficult to direct the low-temperature waste heat to the core heat-using processes of lithium extraction. It cannot provide a stable heat source for key process steps such as brine preheating, desorption reaction, material washing, precipitation reaction, and lithium-rich liquid concentration, and the potential utilization value of low-temperature waste heat has not been fully explored. In addition, the existing integrated solution lacks a targeted brine temperature control mechanism for lithium extraction, which cannot offset the temperature disturbances caused by fluctuations in geothermal extraction conditions and changes in front-end heat exchange load. As a result, the lithium extraction unit is in a fluctuating temperature environment for a long time, making it difficult to maintain the optimal lithium extraction temperature range. This leads to problems such as unstable lithium extraction efficiency, accelerated wear of adsorption materials, and difficulty in improving lithium resource recovery rate. Summary of the Invention

[0007] To address the technical problems existing in the prior art, this invention provides a geothermal brine lithium extraction system and method based on cascaded waste heat utilization. This solves the problems that existing integrated solutions still have in practical engineering applications, such as insufficient cascaded heat distribution of geothermal brine before entering the lithium extraction unit, insufficient matching between low-temperature waste heat and preheating of the lithium extraction process liquid, and difficulty in stabilizing the lithium extraction inlet temperature. As a result, they cannot simultaneously achieve efficient utilization of waste heat and stable high lithium resource utilization.

[0008] To achieve the above objectives, the technical solution adopted by the present invention is as follows: This invention provides a geothermal brine lithium extraction system based on cascade waste heat utilization, including a geothermal brine extraction unit, a thermal energy cascade utilization subsystem, a brine temperature control unit, a lithium extraction subsystem, and a tail liquid regulation and reinjection unit. The geothermal brine extraction unit is used to connect to the liquid phase geothermal brine extraction pipeline of the target extraction well to extract and transport liquid phase geothermal brine to the thermal energy cascade utilization subsystem. The thermal energy cascade utilization subsystem is used to perform cascade thermal utilization of liquid phase geothermal brine and output geothermal brine after waste heat recovery; among them, the low-temperature heat recovered during the cascade thermal utilization process is used for preheating of the liquid used in the lithium extraction process in the lithium extraction subsystem. The brine temperature control unit is used to regulate the temperature of the geothermal brine after waste heat recovery and output geothermal brine that meets the target temperature range for lithium extraction inlet. The lithium extraction subsystem is used to selectively extract lithium from geothermal brine that meets the target temperature range for lithium extraction inlet, in order to obtain lithium salts and lithium-poor tailings. The tail fluid conditioning and reinjection unit is used to regulate the temperature, water quality, or pressure of the lithium-poor tail fluid to meet the reinjection requirements before delivering it to the target reinjection well.

[0009] Furthermore, the thermal energy cascade utilization subsystem includes a primary thermal utilization unit, a secondary thermal utilization unit, and a tertiary thermal utilization unit arranged sequentially along the flow direction of the liquid phase geothermal brine; The primary heat utilization unit is used to recover the high-temperature section of heat in the liquid phase geothermal brine through geothermal power generation or high-temperature heat exchange to form medium-temperature geothermal brine. The secondary heat utilization unit is used to recover and utilize the medium-temperature heat in the medium-temperature geothermal brine through one or more forms such as district heating, domestic heat or industrial heat, to form low-temperature geothermal brine. The three-stage heat utilization unit is used to recover the low-temperature section of heat in the low-temperature geothermal brine through indirect heat exchange, forming geothermal brine with waste heat recovery.

[0010] Furthermore, the brine temperature control unit includes a temperature control module and a temperature sensor; The inlet of the temperature control module is connected to the outlet of the three-stage heat utilization unit, and the outlet of the temperature control module is connected to the inlet of the lithium extraction subsystem; the temperature sensor is located at the outlet of the temperature control module. The temperature control module is used to regulate the temperature of the geothermal brine after waste heat recovery through one or more of the following methods: bypass mixing, heat exchange, and flow regulation. A temperature sensor is used to collect the brine temperature at the outlet of the temperature control module.

[0011] Furthermore, the temperature control equipment includes a bypass mixing branch, a cooler, and a flow control valve; Among them, the bypass mixing branch is used to mix the high-temperature brine of the preset bypass with the geothermal brine after waste heat recovery, and use the mixed geothermal brine as the geothermal brine that meets the target temperature range of lithium extraction inlet. The cooler is used to cool the geothermal brine after waste heat recovery to form geothermal brine that meets the target temperature range for lithium extraction inlet. The flow regulating valve is used to regulate the flow rate of the geothermal brine after waste heat recovery, and to use the geothermal brine with the regulated flow rate as the geothermal brine that meets the target temperature range for lithium extraction inlet.

[0012] Furthermore, the three-stage heat utilization unit operates in conjunction with the brine temperature control unit; Among them, when the brine temperature at the outlet of the temperature control module is higher than the preset target temperature range, the heat exchange capacity of the three-stage heat utilization unit is increased, or the temperature control module is used to reduce the temperature of the geothermal brine after waste heat recovery. When the brine temperature at the outlet of the temperature control module is lower than the preset target temperature range, the heat exchange capacity of the three-stage heat utilization unit is reduced, or the temperature control module is used to increase the temperature of the geothermal brine after waste heat recovery.

[0013] Furthermore, it also includes a control unit; the input terminal of the control unit is connected to the output terminal of the temperature sensor, and the output terminal of the control unit is connected to both the three-stage heat utilization unit and the temperature control module. The control unit is used to generate and send control commands to the three-stage heat utilization unit and the temperature control module based on the brine temperature at the outlet of the temperature control module. The control commands are used to control the three-stage heat utilization unit to adjust the heat exchange capacity or to control the operating mode of the temperature control module.

[0014] Furthermore, the liquid used in the lithium extraction process includes one or more of the following: desorption liquid, washing liquid, precipitation reaction water, and feed to the concentration unit.

[0015] Furthermore, the lithium extraction subsystem includes a pretreatment unit, a lithium selective extraction unit, a desorption / elution unit, a lithium-rich solution purification and concentration unit, and a lithium salt preparation unit connected in sequence.

[0016] Furthermore, the lithium selective extraction unit performs lithium selective extraction processing through one or more of the following methods: adsorption lithium extraction, ion exchange lithium extraction, membrane separation lithium extraction, and electrochemical lithium intercalation / deintercalation.

[0017] This invention also provides a method for lithium extraction from geothermal brine based on cascade waste heat utilization. The method utilizes the aforementioned geothermal brine lithium extraction system based on cascade waste heat utilization, and includes: Using the geothermal brine extraction unit, liquid geothermal brine is extracted from the liquid phase geothermal brine extraction pipeline of the target extraction well and transported to the thermal energy cascade utilization subsystem. The thermal energy cascade utilization subsystem is used to perform cascade thermal utilization of liquid phase geothermal brine and output geothermal brine after waste heat recovery; among them, the low-temperature heat recovered during the cascade thermal utilization process is used for preheating of the liquid used in the lithium extraction process in the lithium extraction subsystem. Using a brine temperature control unit, the temperature of the geothermal brine after waste heat recovery is regulated, and the output geothermal brine meets the target temperature range for lithium extraction inlet. Using a lithium extraction subsystem, selective lithium extraction is performed on geothermal brine that meets the target temperature range for lithium extraction inlet to obtain lithium salts and lithium-poor tailings. The tail fluid regulation and reinjection unit is used to regulate the temperature, water quality or pressure of the lithium-poor tail fluid to meet the reinjection requirements before it is transported to the target reinjection well.

[0018] Compared with the prior art, the beneficial effects of the present invention are as follows: The geothermal brine lithium extraction system based on cascaded waste heat utilization provided by this invention can fully recover and utilize the low-temperature waste heat of geothermal brine and accurately match the heat demand of the lithium extraction process, stabilizing the optimal operating temperature range for lithium extraction. While adapting to the refined development scenarios of pure geothermal brine, it significantly improves the comprehensive development and utilization rate of geothermal energy and lithium resources, as well as the economic benefits of development, and enables an environmentally friendly development model of closed-loop reinjection of tail liquid. Specifically, through a cascaded heat utilization subsystem, the geothermal brine undergoes graded heat recovery, allowing the high-temperature waste heat to be used for power generation or heating, while the low-temperature heat is selectively recovered and matched to the preheating supply and demand of the lithium extraction process liquid in the lithium extraction subsystem. This effectively solves the grade mismatch problem between low-temperature waste heat and the heat demand of the lithium extraction process, avoiding the waste of high-temperature waste heat. Furthermore, brine temperature control is introduced... As a temperature buffer between the end of heat utilization and the lithium extraction inlet, the unit can adjust the brine temperature in real time to ensure that the fluid entering the lithium extraction subsystem remains stable within the optimal operating temperature range corresponding to the lithium extraction process. This overcomes the defects of traditional integrated solutions, such as adsorption efficiency decay and shortened material lifespan caused by temperature drift. In addition, the tail liquid regulation and reinjection unit performs comprehensive adjustments to the temperature, water quality, and pressure of the lean liquid after lithium extraction, enabling safe reinjection without disrupting the formation's thermal and chemical balance. This forms a closed-loop, collaborative operation mechanism covering the entire process from extraction, thermal energy cascade distribution, lithium extraction temperature control to reinjection. This allows the thermal energy grade in the geothermal brine and lithium resource extraction to achieve quality matching and synchronous optimization within the same process chain, thereby improving the utilization rate of low-temperature waste heat and the stable recovery rate of lithium resources without significantly increasing external energy consumption. Attached Figure Description

[0019] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0020] Figure 1 A schematic diagram of the structure of the geothermal brine lithium extraction system based on cascade waste heat utilization provided in Example 1; Figure 2 This is a flowchart illustrating the principle of the coordinated operation of the three-stage heat utilization unit and the brine temperature control unit in Example 1.

[0021] The system comprises: 1. Geothermal brine extraction unit; 2. Thermal energy cascade utilization subsystem; 21. Primary thermal utilization unit; 22. Secondary thermal utilization unit; 23. Tertiary thermal utilization unit; 3. Brine temperature regulation unit; 4. Pretreatment unit; 5. Lithium selective extraction unit; 6. Desorption / elution unit; 7. Lithium-rich liquid purification and concentration unit; 8. Lithium salt preparation unit; 9. Tailings liquid regulation and reinjection unit; 100. Target extraction well; 200. Target reinjection well; 21. Primary thermal utilization unit; 22. Secondary thermal utilization unit; 23. Tertiary thermal utilization unit. Detailed Implementation

[0022] To make the technical problems, technical solutions, and beneficial effects solved by this application clearer, the technical solutions in the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are within the scope of protection of this application.

[0023] This invention provides a geothermal brine lithium extraction system based on cascaded waste heat utilization to solve the problems of insufficient heat distribution in geothermal brine before entering the lithium extraction unit, insufficient matching between low-temperature waste heat and preheating of the lithium extraction process liquid, and difficulty in stable control of the lithium extraction inlet temperature in existing integrated solutions. It takes the main process of liquid phase geothermal brine as the processing object and sets up a thermal energy cascaded utilization subsystem 2 between the geothermal brine extraction unit 1 and the lithium extraction subsystem. The key points are the cascaded utilization of heat before entering the lithium extraction subsystem, the preheating of the lithium extraction process liquid, and the control of the lithium extraction inlet temperature.

[0024] To achieve the above objectives, the geothermal brine lithium extraction system based on cascade waste heat utilization described in this invention includes a geothermal brine extraction unit 1, a thermal energy cascade utilization subsystem 2, a brine temperature control unit 3, a lithium extraction subsystem, and a tailings regulation and reinjection unit 9. The geothermal brine extraction unit is connected to the liquid-phase geothermal brine extraction pipeline of the target extraction well 100 to extract and transport the liquid-phase geothermal brine to the thermal energy cascade utilization subsystem 2. The thermal energy cascade utilization subsystem 2 is used to perform cascade heat utilization on the liquid-phase geothermal brine, outputting geothermal brine after waste heat recovery. The low-temperature heat recovered during the cascade heat utilization process is used for preheating the lithium extraction process fluid in the lithium extraction subsystem; the brine temperature control unit 3 is used to regulate the temperature of the geothermal brine after waste heat recovery, and output geothermal brine that meets the target temperature range for lithium extraction inlet; the lithium extraction subsystem is used to selectively extract lithium from the geothermal brine that meets the target temperature range for lithium extraction inlet, and obtain lithium salt and lithium-lean tailings; the tailings regulation and reinjection unit 9 is used to regulate the temperature, water quality or pressure of the lithium-lean tailings, and after meeting the reinjection requirements, it is transported to the target reinjection well 200.

[0025] In the above embodiments, a complete system architecture is formed by setting up a geothermal brine extraction unit 1, a thermal energy cascade utilization subsystem 2, a brine temperature control unit 3, a lithium extraction subsystem, and a tail liquid regulation and reinjection unit 9. This achieves full-process integration from geothermal brine extraction to thermal energy cascade utilization, lithium extraction, and tail liquid reinjection. Without limiting the core lithium extraction method, it has good compatibility with one or more of the following processes: adsorption lithium extraction, ion exchange lithium extraction, membrane separation lithium extraction, and electrochemical lithium intercalation / deintercalation. This facilitates engineering transformation and promotion, providing an efficient, stable, and economical technical solution for the comprehensive utilization of geothermal brine resources.

[0026] In this invention, a cascaded thermal energy utilization subsystem 1 is used to utilize the liquid geothermal brine in stages, recovering heat from the high-temperature, medium-temperature, and low-temperature stages respectively. This avoids the downgrading of high-grade thermal energy and the direct waste of low-grade thermal energy, significantly improving the overall thermal energy utilization efficiency of the geothermal brine. Specifically, by using the low-temperature heat recovered during the cascaded thermal utilization process to preheat the lithium extraction process liquids in the lithium extraction subsystem, the waste heat from the low-temperature stage can be directed to preheat the lithium extraction process liquids such as desorption liquid, washing liquid, precipitation reaction water, and feed to the concentration unit. This effectively reduces the external heating requirements of the lithium extraction process, thereby reducing external energy consumption and operating costs.

[0027] Secondly, the temperature of the geothermal brine after waste heat recovery is regulated by the brine temperature control unit 3, and the output geothermal brine meets the target temperature range of the lithium extraction inlet. This ensures that the temperature of the geothermal brine entering the lithium extraction subsystem can be stably maintained within a suitable operating temperature range, avoiding the impact of temperature fluctuations caused by changes in extraction conditions and heat exchange load on the lithium extraction effect. This is beneficial to ensuring the adsorption kinetics performance, material structure stability and cycle life of the lithium selective extraction unit, and improving the stability of lithium extraction operation and the lithium resource recovery rate.

[0028] Furthermore, by adjusting the temperature, water quality, or pressure of the lithium-poor tail fluid through the tail fluid regulation and reinjection unit 9, it is transported to the target reinjection well 200, thereby achieving qualified reinjection of the tail fluid, reducing the potential environmental impact of brine discharge, and helping to maintain geothermal reservoir pressure and ensure the long-term stable development of geothermal resources; this is the system described in this invention.

[0029] The following specific embodiments further explain the geothermal brine lithium extraction system based on cascade waste heat utilization provided by the present invention: Example 1 As attached Figure 1 As shown, this embodiment 1 provides a geothermal brine lithium extraction system based on cascade waste heat utilization, including a geothermal brine extraction unit 1, a thermal energy cascade utilization subsystem 2, a brine temperature control unit 3, a lithium extraction subsystem, and a tail liquid regulation and reinjection unit 9 connected in sequence.

[0030] In this embodiment 1, the geothermal brine extraction unit 1 is used to connect to the liquid phase geothermal brine extraction pipeline of the target extraction well 100 to extract and transport liquid phase geothermal brine to the thermal energy cascade utilization subsystem 2.

[0031] Explanatoryly, by setting up a geothermal brine production unit 1, connecting the inlet of the geothermal brine production unit 1 to the liquid phase geothermal brine production pipeline of the target production well 100, and connecting the outlet of the geothermal brine production unit 1 to the inlet of the thermal energy cascade utilization subsystem 2, the safe and stable transportation of liquid phase geothermal brine from the geothermal reservoir to the thermal energy cascade utilization subsystem 2 is realized; wherein, the target production well 100 refers to a drilling engineering structure that penetrates the geothermal reservoir and is able to export geothermal fluids to the surface, and its liquid phase geothermal brine production pipeline is connected to the inlet end of the geothermal brine production unit.

[0032] For example, the geothermal brine extraction unit 1 includes an extraction pipeline, a booster pump set, and a flow regulating valve; optionally, the geothermal brine extraction unit 1 can be configured with booster pump sets of different head and temperature resistance levels according to the wellhead pressure and temperature conditions of the target extraction well 100, to ensure that the liquid phase geothermal brine can overcome the friction resistance along the pipeline and be smoothly transported to the subsequent processing unit; after the geothermal brine extraction unit 1 is connected to the liquid phase geothermal brine extraction pipeline of the target extraction well 100, the extracted geothermal brine enters the ground through the extraction pipeline. The hot brine extraction unit 1 then transports the brine to the thermal energy cascade utilization subsystem 2. It should be noted that, since geothermal brine usually has high mineralization and temperature, the pipelines and equipment in the geothermal brine extraction unit 1 must have good corrosion resistance and high temperature resistance to ensure long-term stable operation of the system. Optionally, the geothermal brine extraction unit 1 can also be equipped with pressure monitoring and flow regulation functions to adjust the extraction flow rate in real time according to the load demand of the thermal energy cascade utilization subsystem 2.

[0033] In this embodiment 1, the thermal energy cascade utilization subsystem 2 is used to perform cascade thermal utilization of liquid phase geothermal brine and output geothermal brine after waste heat recovery; wherein, the low-temperature heat recovered during the cascade thermal utilization process is used for preheating of the liquid used in the lithium extraction process in the lithium extraction subsystem.

[0034] Explained, by setting up a thermal energy cascade utilization subsystem 2, connecting the inlet of the thermal energy cascade utilization subsystem 2 to the inlet of the geothermal brine extraction well 1, and connecting the outlet of the thermal energy utilization subsystem 2 to the inlet of the brine temperature control unit 3, heat is recovered from the extracted liquid geothermal brine according to its temperature grade from high to low, forming a cascade thermal utilization system from high temperature to low temperature, thereby maximizing the comprehensive utilization rate of geothermal brine thermal energy. After the thermal energy cascade utilization subsystem 2 performs cascade thermal utilization on the liquid geothermal brine, it outputs geothermal brine with waste heat recovery to the brine temperature control unit 3. It should be noted that the geothermal brine with waste heat recovery refers to the geothermal brine that has completed heat recovery in the high temperature, medium temperature and low temperature sections and is about to enter the brine temperature control unit 3 for temperature regulation.

[0035] Specifically, in the cascaded thermal utilization process, the recovered low-temperature heat is used to preheat the lithium extraction process fluid in the lithium extraction subsystem. This process fluid includes one or more of the following: desorption solution, washing solution, precipitation reaction water, and feed to the concentration unit. Explaining this, by directing the use of low-temperature heat for preheating the lithium extraction process fluid, the temperatures of desorption, elution, precipitation reactions, and concentration processes in the lithium extraction process can be increased, reducing dependence on external steam, electric heating, or other heat sources. Secondly, based on the heat released by geothermal brine during the cascaded thermal utilization process... The quantity can achieve a reasonable match between the heat energy grade and user needs; for example, the high-temperature heat can be used for geothermal power generation, the medium-temperature heat can be used for district heating or industrial heating, and the low-temperature heat is used for preheating the liquid used in the lithium extraction process; for illustration, the temperature of the geothermal brine is significantly reduced after the cascade heat utilization, but it still carries a certain amount of low-grade heat energy. If it is directly discharged or reinjected, it will cause heat waste. In this embodiment 1, the low-grade heat energy is recovered through a three-stage heat utilization unit and used for preheating the liquid used in the lithium extraction process, realizing the targeted utilization of waste heat.

[0036] In one possible implementation, the thermal energy cascade utilization subsystem 2 includes a primary thermal utilization unit 21, a secondary thermal utilization unit 22, and a tertiary thermal utilization unit 23 arranged sequentially along the flow direction of the liquid phase geothermal brine; wherein, the inlet of the primary thermal utilization unit 21 is connected to the outlet of the geothermal brine extraction unit 1, the outlet of the primary thermal utilization unit 21 is connected to the inlet of the secondary thermal utilization unit 22, the outlet of the secondary thermal utilization unit 22 is connected to the inlet of the tertiary thermal utilization unit 23, and the outlet of the tertiary thermal utilization unit 23 is connected to the inlet of the brine temperature control unit 3.

[0037] The primary heat utilization unit 21 is used to recover heat from the high-temperature section of the liquid-phase geothermal brine through geothermal power generation or high-temperature heat exchange to form medium-temperature geothermal brine. Specifically, the primary heat utilization unit 23 includes one or more of a geothermal power generation device, a high-temperature heat exchanger, or a high-temperature heating heat exchanger. Explanatoryly, the primary heat utilization unit 23 is located at the front end of the thermal energy cascade utilization subsystem 2 to prioritize the utilization of the highest-grade heat from the high-temperature section of the liquid-phase geothermal brine. When the geothermal brine temperature is high, the high-grade heat energy is first converted into electrical energy output through the geothermal power generation device, or the heat is transferred to other high-temperature heat users through the high-temperature heat exchanger. For example, the primary heat utilization unit 21 can adopt an organic Rankine cycle power generation device or a flash evaporation power generation device. After the heat recovery by the primary heat utilization unit 21, the geothermal brine temperature is reduced from the initial extraction temperature to a medium-temperature level, forming medium-temperature geothermal brine.

[0038] The secondary heat utilization unit 22 is used to recover and utilize the medium-temperature heat in the medium-temperature geothermal brine through one or more forms of district heating, domestic heat, or industrial heat to form low-temperature geothermal brine. Specifically, the secondary heat utilization unit 22 is connected to one or more heat exchange systems, including district heating systems, domestic hot water systems, industrial hot water systems, and drying systems. Explanatoryly, the secondary heat utilization unit 22 is located after the primary heat utilization unit 21 to recover the medium-temperature heat in the medium-temperature geothermal brine after the primary heat utilization unit 21. The heat grade of the medium-temperature heat is lower than that of the high-temperature heat. Although the medium-temperature geothermal brine has a high utilization value, it is suitable for district heating, domestic hot water preparation, industrial heat use, or material drying. After heat recovery through the secondary heat utilization unit 22, the temperature of the medium-temperature geothermal brine is further reduced to form low-temperature geothermal brine. By setting up the secondary heat utilization unit 22, the geothermal brine completes the effective recovery of heat in the medium-temperature section before entering the lithium extraction subsystem, avoiding heat loss caused by simple cooling. Explainingly, by setting up the secondary heat utilization unit 22, the cascade matching and differentiated utilization of geothermal brine heat can be achieved, significantly improving the comprehensive development benefits of geothermal resources.

[0039] The tertiary heat utilization unit 23 is used to recover the low-temperature heat in the low-temperature geothermal brine through indirect heat exchange, forming geothermal brine with waste heat recovery. Specifically, the tertiary heat utilization unit 23 includes a lithium extraction process liquid preheating module. The lithium extraction process liquid preheating module is used to recover the low-temperature heat in the low-temperature geothermal brine through indirect heat exchange, and to indirectly preheat one or more of the desorption liquid, washing liquid, precipitation reaction water, and lithium-rich liquid concentration feed. Explanatoryly, the tertiary heat utilization unit 23 is set after the secondary heat utilization unit 22 and before the brine temperature control unit 3, and is used to recover the low-temperature heat still contained in the low-temperature geothermal brine after the secondary heat utilization unit 22. Among them, the heat grade of the low-temperature heat is low, and it is difficult to use it directly for conventional heat utilization methods such as power generation or heating, but it is a suitable matching solution for preheating the lithium extraction process liquid.

[0040] It should be noted that the lithium extraction process liquid preheating module transfers heat from the low-temperature geothermal brine to the lithium extraction process liquid through indirect heat exchange, achieving targeted utilization of heat in the low-temperature section. For example, the lithium extraction process liquid preheating module can be connected to one or more of the following heat exchangers: desorption liquid preheating heat exchanger, washing liquid preheating heat exchanger, precipitation reaction water preheating heat exchanger, or lithium-rich liquid concentration feed preheating heat exchanger. The above heat exchangers can be arranged in parallel or in series, and can be equipped with regulating valves to adjust the preheating heat of different process liquids according to the operating status of the lithium extraction process. Explained, through the three-stage heat utilization unit 23, the recovery of heat in the low-temperature section enables the geothermal brine to complete the main heat recovery before entering the lithium extraction subsystem, while providing preheating guarantee for the subsequent lithium extraction process and reducing the consumption of external heat sources.

[0041] In this embodiment 1, the brine temperature control unit 3 is used to regulate the temperature of the geothermal brine after waste heat recovery and output geothermal brine that meets the target temperature range for lithium extraction inlet.

[0042] Explained, by setting up a brine temperature control unit 3, connecting the inlet of the brine temperature control unit 3 to the outlet of the three-stage heat utilization unit 23, and connecting the outlet of the brine temperature control unit 3 to the inlet of the lithium extraction subsystem, the temperature of the geothermal brine after the cascade heat utilization is precisely adjusted to a suitable operating temperature range for the subsequent lithium extraction process. The target temperature range for the lithium extraction inlet is determined based on the suitable operating temperature of the adsorption material, ion exchange material, membrane module, or electrochemical lithium extraction unit. Different lithium extraction methods have different temperature adaptability ranges; during engineering implementation, the target temperature range is determined based on the temperature resistance performance of the adsorption material, membrane module, ion exchange material, or electrochemical unit. After adjusting the geothermal brine to a suitable target temperature range for lithium extraction, the brine temperature control unit outputs geothermal brine that meets the target temperature range for the lithium extraction inlet. Based on the brine temperature control unit's regulation of the geothermal brine temperature, the temperature of the geothermal brine entering the lithium extraction subsystem can be stably maintained within the target temperature range, avoiding the impact of temperature fluctuations on the lithium extraction effect. When the geothermal brine temperature before entering the lithium extraction subsystem is higher than the target temperature range, the brine temperature can be reduced by increasing cooling or increasing preheating heat extraction. When the geothermal brine temperature before entering the lithium extraction subsystem is lower than the target temperature range, the brine temperature can be increased by reducing preheating heat extraction or by bypassing mixing. Preferably, the brine temperature control unit 3 and the three-stage heat utilization unit 23 operate in conjunction, achieving precise temperature control through coordinated regulation.

[0043] In one possible implementation, the brine temperature control unit 3 includes a temperature control module and a temperature sensor; wherein, the inlet of the temperature control module is connected to the outlet of the three-stage heat utilization unit, and the outlet of the temperature control module is connected to the inlet of the lithium extraction subsystem; the temperature control module is used to regulate the temperature of the geothermal brine after waste heat recovery through one or more of the following methods: bypass mixing, heat exchange, and flow regulation; the temperature sensor is set at the outlet of the temperature control module to collect the brine temperature at the outlet of the temperature control module.

[0044] Explained, the temperature control module, as the execution component of the brine temperature control unit 3, receives geothermal brine after waste heat recovery from the outlet of the tertiary heat utilization unit 23 at its inlet end, and delivers temperature-controlled geothermal brine to the lithium extraction subsystem at its outlet end; the temperature control module can adopt one or more combinations of bypass mixing branch, cooler, and flow regulating valve; based on the multiple temperature control methods of the temperature control module, it can flexibly meet the temperature control needs under different working conditions; for example, when it is necessary to raise the temperature, the bypass mixing branch can be opened to mix some of the higher temperature brine with the lower temperature brine, and when it is necessary to lower the temperature, the cooler can be started for forced cooling.

[0045] Secondly, the temperature sensor is located at the outlet of the temperature control module, enabling real-time monitoring of the geothermal brine temperature about to enter the lithium extraction subsystem, providing feedback signals for the closed-loop control of the temperature control module. The temperature sensor can be a thermocouple, resistance temperature detector (RTD), or infrared thermometer. Based on the temperature data collected by the temperature sensor, real-time monitoring and automatic adjustment of the operating status of the temperature control module can be achieved. In addition, placing the temperature sensor at the outlet of the temperature control module can eliminate measurement errors caused by uneven temperature distribution within the temperature control module.

[0046] In one possible implementation, the temperature control device includes a bypass mixing branch, a cooler, and a flow control valve.

[0047] A bypass mixing branch is used to mix the high-temperature brine from the preset bypass with the geothermal brine after waste heat recovery, and the mixed geothermal brine is used as the geothermal brine that meets the target temperature range for lithium extraction. Specifically, one end of the bypass mixing branch is connected to the pipeline before the third-stage heat utilization unit 23, and the other end is connected to the outlet of the temperature control module, with a regulating valve in the middle. Explanatoryly, when the temperature of the geothermal brine after the third-stage heat utilization unit 23 is too low, the bypass mixing branch can be opened to introduce some higher-temperature geothermal brine that has not passed through the third-stage heat utilization unit 23 or has less heat extraction, to mix with the low-temperature geothermal brine after waste heat recovery, thereby increasing the temperature of the mixed geothermal brine. Based on the setting of the bypass mixing branch, temperature regulation can be achieved without external heating, and it has the advantages of fast response and low energy consumption. For example, the regulating valve on the bypass mixing branch can automatically adjust its opening degree according to the feedback signal of the temperature sensor to control the mixing ratio of the high-temperature brine, thereby achieving precise temperature control.

[0048] A cooler is used to cool the geothermal brine after waste heat recovery, forming geothermal brine that meets the target temperature range for lithium extraction inlet. Specifically, the cooler is installed on the internal piping of the temperature control module for forced cooling of the geothermal brine. Explanatoryly, when the temperature of the geothermal brine after passing through the three-stage heat utilization unit 23 is still higher than the target temperature range for lithium extraction inlet, the cooler needs to be activated for cooling. The cooler can be an air cooler, a water-cooled heat exchanger, or an evaporative cooler. Based on the cooler, the geothermal brine can be effectively cooled under high-temperature conditions, ensuring that the brine temperature entering the lithium extraction subsystem does not exceed the upper limit. For example, the cooling medium flow rate of the cooler can be adjusted according to the feedback signal from the temperature sensor to achieve energy-saving operation.

[0049] A flow control valve is used to regulate the flow rate of geothermal brine after waste heat recovery, and to ensure that the regulated geothermal brine meets the target temperature range for lithium extraction. Specifically, the flow control valve is installed on the outlet pipe of the temperature control module. Explain that the flow control valve indirectly affects the residence time and heat exchange effect of the geothermal brine in the temperature control module by adjusting the flow rate of the geothermal brine entering the lithium extraction subsystem, thereby assisting in achieving the temperature control target. Based on the flow control valve, the flow rate of the temperature control module is regulated, improving the flexibility and response speed of temperature control. Optionally, the flow control valve can work in conjunction with the regulating valve of the bypass mixing branch and the medium flow control valve of the cooler to jointly complete the temperature control task.

[0050] In one possible implementation, the three-stage heat utilization unit 23 operates in conjunction with the brine temperature control unit; wherein the process of this linkage operation is as follows: (1) When the brine temperature at the outlet of the temperature control module is higher than the preset target temperature range, the heat exchange capacity of the three-stage heat utilization unit is increased, or the temperature of the geothermal brine after waste heat recovery is reduced by using the temperature control module.

[0051] Specifically, when the temperature sensor detects that the brine temperature at the outlet of the temperature control module is higher than the target temperature range, the heat extraction of the lithium extraction process liquid preheating module in the three-stage heat utilization unit 23 is increased, allowing more low-temperature heat to be transferred to the lithium extraction process liquid. Explained, by increasing the heat exchange of the three-stage heat utilization unit 23, the temperature of the geothermal brine entering the brine temperature control unit can be reduced, alleviating the cooling load on the temperature control module from the source. Alternatively, the geothermal brine can be forcibly cooled using a cooler in the temperature control module. Based on the linkage control strategy of increasing preheating heat extraction or auxiliary cooling, the three-stage heat utilization unit 23 and the temperature control module work collaboratively, improving the efficiency and stability of temperature control. Simultaneously, it ensures the heat demand for preheating the lithium extraction process liquid, increasing waste heat recovery while achieving the cooling objective, resulting in energy savings.

[0052] (2) When the temperature of the brine at the outlet of the temperature control module is lower than the preset target temperature range, reduce the heat exchange of the three-stage heat utilization unit, or use the temperature control module to increase the temperature of the geothermal brine after waste heat recovery.

[0053] Specifically, when the temperature sensor detects that the brine temperature at the outlet of the temperature control module is lower than the target temperature range, the heat output of the preheating module for the lithium extraction process liquid in the third-stage heat utilization unit 23 is reduced, so that less heat is transferred from the geothermal brine side to the lithium extraction process liquid. Explained, by reducing the heat exchange of the third-stage heat utilization unit 23, the temperature of the geothermal brine entering the brine temperature control unit 3 can be increased, reducing the heating load of the temperature control module from the source. Alternatively, a portion of the higher-temperature geothermal brine can be introduced into the bypass mixing branch in the temperature control module to mix with the low-temperature geothermal brine after waste heat recovery, thereby increasing the temperature of the mixed geothermal brine. Based on the linkage control strategy of reducing preheating heat output or assisting in bypass mixing, coordinated heating control under low-temperature conditions is achieved, ensuring that the brine temperature entering the lithium extraction subsystem is not lower than the lower limit. Among these measures, by prioritizing the reduction of heat consumption from the preheating of the lithium extraction process liquid, the reasonable distribution of waste heat is ensured while achieving the heating objective.

[0054] In one possible implementation, the system further includes a control unit. The input of the control unit is connected to the output of the temperature sensor, and the output of the control unit is connected to both the three-stage heat utilization unit 23 and the temperature control module. Specifically, the control unit is communicatively connected to the three-stage heat utilization unit, the brine temperature control unit, the temperature sensor, and the regulating valve.

[0055] Explained, the control unit, as the core of the system control, receives temperature signals collected by temperature sensors, performs internal logic judgment and calculation, and then sends control commands to the three-stage heat utilization unit 23 and the temperature control module. The control unit can be implemented in the form of a programmable logic controller, a distributed control system, or an industrial computer. Based on the setting of the control unit, the automation and intelligence of temperature control are realized. The control unit is used to generate and send control commands to the three-stage heat utilization unit and the temperature control module according to the brine temperature at the outlet of the temperature control module. Among them, the control commands are used to control the three-stage heat utilization unit to adjust the heat exchange capacity, or to control the operating mode of the temperature control module.

[0056] Optionally, the control commands include adjusting the heat output of the preheating branch of the lithium extraction process liquid in the three-stage heat utilization unit 23, adjusting the mixing ratio of the bypass mixing branch, adjusting the cooling medium flow rate of the cooler, and adjusting the opening of the flow regulating valve. Explanatoryly, the control unit has a preset target temperature range for the lithium extraction inlet. The control unit compares the actual temperature collected by the temperature sensor with the preset target temperature range and generates corresponding control commands based on the comparison results. For example, when the actual temperature is higher than the upper limit of the target temperature range, the control unit generates control commands to increase the preheating heat output and increase the cooling medium flow rate; when the actual temperature is lower than the lower limit of the target temperature range, the control unit generates control commands to reduce the preheating heat output and increase the bypass mixing ratio. Based on the closed-loop control of the control unit, the brine temperature at the outlet of the temperature control module can always be kept stable within the target temperature range. Preferably, the control unit can also be used to collect one or more parameters among the following: geothermal brine extraction temperature, brine temperature after each stage of heat utilization, preheating temperature of the lithium extraction process liquid, lithium-rich liquid concentration, tailings water quality, and reinjection pressure, to achieve comprehensive monitoring and integrated management of the system.

[0057] As attached Figure 2 As shown, attached Figure 2 The diagram below illustrates the principle of the coordinated operation of the three-stage heat utilization unit and the brine temperature control unit; see the attached diagram. Figure 2 As can be seen from this, the principle of the linkage operation between the three-stage heat utilization unit and the brine temperature control unit is as follows: First, the temperature T of the geothermal brine before entering the lithium extraction subsystem is collected; specifically, the temperature of the brine at the outlet of the temperature control module is collected using a temperature sensor as the temperature T of the geothermal brine before entering the lithium extraction subsystem.

[0058] Next, the target temperature range T at the lithium extraction inlet is read. min -T max Determine whether the geothermal brine temperature T before entering the lithium extraction subsystem is higher than the upper limit T of the target temperature range for the lithium extraction inlet. max When the temperature T of the geothermal brine before entering the lithium extraction subsystem is higher than the upper limit T of the target temperature range for the lithium extraction inlet. max At the same time, the heat output of the third-stage heat utilization unit 23 is increased to increase the heat output of one or more of the feed preheating branches for desorption liquid, washing liquid, precipitation reaction water or lithium-rich liquid concentration.

[0059] Next, monitor the geothermal brine temperature T before it enters the lithium extraction subsystem; if the geothermal brine temperature T before entering the lithium extraction subsystem is still higher than the upper limit T of the target temperature range for the lithium extraction inlet... max If the temperature is high, the cooler will be activated or the flow rate of the cooling medium will be increased, and the temperature will be returned to the monitoring station.

[0060] The geothermal brine temperature T before entering the lithium extraction subsystem should not exceed the upper limit of the target temperature range for the lithium extraction inlet. max Then, continue to determine whether the geothermal brine temperature T before entering the lithium extraction subsystem is lower than the lower limit T of the target temperature range for the lithium extraction inlet. min .

[0061] When the temperature T of the geothermal brine before entering the lithium extraction subsystem is lower than the lower limit of the target temperature range for the lithium extraction inlet, min At that time, the heat taken by the third-stage heat utilization unit 23 is reduced to reduce the heat taken by the preheating branch of the lithium extraction process liquid, and the bypass mixing branch is opened to mix some of the higher temperature geothermal brine with the low temperature geothermal brine after waste heat recovery, and then return to the temperature detection.

[0062] When the geothermal brine temperature T before entering the lithium extraction subsystem is within the target temperature range T at the lithium extraction inlet. min -T max Within the specified range, maintain the current heat extraction, bypass mixing ratio, and cooling medium flow rate to allow geothermal brine to enter the lithium extraction subsystem.

[0063] In this embodiment 1, the lithium extraction subsystem is used to selectively extract lithium from geothermal brine that meets the target temperature range for lithium extraction inlet, in order to obtain lithium salt and lithium-poor tailings.

[0064] Explained, by setting up a lithium extraction subsystem, connecting the inlet of the lithium extraction subsystem to the outlet of the brine temperature control unit 3, and connecting the outlet of the lithium extraction subsystem to the inlet of the tail liquid regulation and reinjection unit 9, selective lithium extraction is achieved from geothermal brine that meets the target temperature range for lithium extraction. The lithium extraction subsystem selectively recovers lithium resources from the geothermal brine and converts them into high-value-added lithium salt products. Specifically, the lithium extraction subsystem achieves efficient enrichment and productization of lithium ions from low-concentration geothermal brine through pretreatment, selective lithium extraction, desorption / elution, lithium-rich liquid purification and concentration, and lithium salt preparation. Optionally, the lithium selective extraction process employs one or more of the following methods: adsorption lithium extraction, ion exchange lithium extraction, membrane separation lithium extraction, and electrochemical lithium intercalation / deintercalation. Explained, since geothermal brine contains not only lithium ions but also various associated ions such as sodium, potassium, calcium, and magnesium, the lithium selective extraction process requires the use of materials or membrane modules with lithium ion sieving capabilities to selectively capture lithium ions in the complex ion system. After the lithium selective extraction process, lithium salts and lithium-poor tailings are obtained. Lithium salts include lithium carbonate, lithium hydroxide, or other lithium salt products. Lithium-poor tailings refer to brine with a significantly reduced lithium ion concentration after lithium selective extraction.

[0065] In one possible implementation, the lithium extraction process liquid includes one or more of the following: desorption liquid, washing liquid, precipitation reaction water, and concentrate unit feed. Specifically, the desorption liquid is the liquid used in the desorption / elution unit to transfer lithium ions from the lithium-rich phase or lithium-loaded material to the liquid phase, typically a dilute acid solution or salt solution; the washing liquid is the liquid used between the lithium selective extraction unit and the desorption / elution unit to clean the lithium-loaded material to remove associated impurities; the precipitation reaction water is the water used in the lithium salt preparation unit to prepare the precipitant solution or adjust the concentration of the reaction system; and the concentrate unit feed refers to the lithium-rich liquid material that enters the lithium-rich liquid purification and concentration unit for concentration treatment.

[0066] It should be noted that the temperature of the lithium extraction process solution is usually lower than the optimal temperature required by the process before entering its respective process stage. Through the preheating treatment of the three-stage heat utilization unit 23, its temperature can be raised to a suitable range, thereby improving the desorption efficiency, washing effect, precipitation reaction rate and concentration efficiency. For example, the desorption solution can be accelerated after preheating, and the precipitation reaction water can be improved after preheating, which is conducive to obtaining lithium salt products with uniform particle size and high purity.

[0067] In one possible implementation, the lithium extraction subsystem includes a pretreatment unit 4, a lithium selective extraction unit 5, a desorption / elution unit 6, a lithium-rich liquid purification and concentration unit 7, and a lithium salt preparation unit 8 connected in sequence; wherein, the inlet of the pretreatment unit 4 is connected to the outlet of the brine temperature regulation unit 3, the tail liquid outlet of the lithium selective extraction unit 5 is connected to the inlet of the tail liquid regulation and reinjection unit 9, and the product outlet of the lithium selective extraction unit 5 is connected to the inlet of the desorption / elution unit 6.

[0068] Specifically, pretreatment unit 4 is used to remove one or more impurities, such as suspended solids, silicon, iron, manganese, calcium, and magnesium, from the geothermal brine to reduce the adverse effects of impurities on the subsequent lithium selective extraction unit. Pretreatment unit 4 includes one or more modules of filtration, sedimentation, silicon removal, iron and manganese removal, softening, and precision filtration. The pretreatment process includes one or more methods of reagent precipitation, oxidation, flocculation, filtration, ion exchange, and membrane filtration. Explanation: Geothermal brine dissolves a large number of mineral ions and gases under high temperature and pressure, which are prone to scaling and precipitation when temperature and pressure change. By setting up pretreatment unit 4, these impurities that may affect the lithium extraction effect can be removed before lithium selective extraction.

[0069] The lithium selective extraction unit 5 is used to selectively extract lithium from pretreated geothermal brine to obtain a lithium-rich phase or lithium-loaded material and a lithium-poor tail liquid. Optionally, the lithium selective extraction unit 5 recovers lithium ions through one or more of the following methods: adsorption, ion exchange, membrane separation, and electrochemical lithium extraction. Explanation: When geothermal brine passes through the lithium selective extraction unit 5, lithium ions are selectively enriched in the adsorbent, ion exchange material, membrane separation enrichment side, or electrochemical carrier, thereby obtaining a lithium-rich phase or lithium-loaded material.

[0070] The desorption / elution unit 6 is used to transfer lithium ions from the lithium-rich phase or lithium-carrying material to the liquid phase through a desorption liquid or an eluent to obtain a lithium-rich liquid. Explanatoryly, desorption / elution refers to the step of releasing lithium ions from the solid support back into the liquid phase. Preheating the desorption liquid or eluent can improve the desorption or elution efficiency and shorten the processing time.

[0071] The lithium-rich liquid purification and concentration unit 7 is used to remove associated impurities in the lithium-rich liquid and increase the lithium ion concentration to obtain a concentrated lithium-rich liquid; explanatoryly, through purification and concentration treatment, the lithium ion concentration can be increased from a low lithium-rich liquid level to a concentration level that meets the requirements for lithium salt preparation.

[0072] The lithium salt preparation unit 8 is used to prepare lithium carbonate by adding a carbonate precipitant, or to prepare lithium hydroxide by one or more steps of causticization, conversion, concentration and crystallization; explanatoryly, the water or precipitant solution used for precipitation reaction can be preheated in a three-stage heat utilization unit to improve the temperature conditions of precipitation reaction; wherein, the lithium salt product obtained is output after solid-liquid separation, washing and drying.

[0073] In one possible implementation, the lithium selective extraction unit 5 performs lithium selective extraction through one or more of the following methods: adsorption lithium extraction, ion exchange lithium extraction, membrane separation lithium extraction, and electrochemical lithium intercalation / deintercalation. It should be noted that in specific practical applications, the appropriate lithium extraction method can be flexibly selected according to different geothermal brine water quality conditions, lithium extraction scale, and economic requirements, which has good applicability and scalability.

[0074] Specifically, adsorption-based lithium extraction uses manganese-based, titanium-based, or aluminum-based adsorbents to selectively adsorb lithium ions from geothermal brine. After adsorption saturation, the lithium ions are desorbed from the adsorbent using a desorption solution. For example, manganese-based adsorbents have excellent selective recognition capabilities for lithium ions and can preferentially adsorb lithium ions in geothermal brine with a high magnesium-to-lithium ratio. Ion exchange-based lithium extraction utilizes lithium-ion exchange resins or lithium-ion sieve materials to exchange lithium ions from the geothermal brine onto the resin or material through an ion exchange reaction, followed by the removal of the lithium ions using a regeneration solution. Membrane separation-based lithium extraction uses nanofiltration membranes, electrodialysis membranes, or ion-imprinted membranes with lithium-ion selective permeability to separate lithium ions from other ions under applied pressure or an electric field. Electrochemical lithium intercalation / deintercalation utilizes the reversible intercalation and deintercalation characteristics of electrode materials during charging and discharging to extract lithium ions from geothermal brine through electrochemical methods.

[0075] In this embodiment 1, the tail fluid regulation and reinjection unit 9 is used to regulate the temperature, water quality or pressure of the lithium-poor tail fluid, and after meeting the reinjection requirements, it is transported to the target reinjection well 200.

[0076] Explanatoryly, the inlet of the tailings conditioning and reinjection unit 9 is connected to the tailings outlet of the lithium selective extraction unit 5 to regulate the temperature, water quality, or pressure of the lithium-poor tailings, so that the lithium-poor tailings generated during the lithium extraction process are treated to meet the reinjection standards, and then safely reinjected into the target reinjection well. Optionally, the tailings conditioning and reinjection unit 9 can regulate one or more of the following parameters of the tailings: temperature, suspended solids content, pH value, salinity, scaling tendency, and pressure, to meet the reinjection requirements. The target reinjection well 200 is a drilling engineering structure used to reinject the treated tailings into the geothermal reservoir. It should be noted that by reinjecting the tailings liquid, the potential impact of brine discharge on surface water and soil environment can be reduced, the pressure of geothermal reservoir can be maintained, and the long-term stable development of geothermal resources can be facilitated. Preferably, the tailings liquid regulation and reinjection unit 9 includes a buffer tank, a booster pump set, a precision filter, a pH adjustment device, and necessary online monitoring instruments. For example, when the temperature of the lithium-lean tailings liquid is too high, a cooling device can be set to lower the temperature; when the lithium-lean tailings liquid contains trace suspended matter, it can be filtered by a precision filter; when the reinjection pressure is insufficient, the pressure can be increased by a booster pump set.

[0077] Operating principle explanation: The geothermal brine lithium extraction system based on cascaded waste heat utilization described in Embodiment 1 integrates the entire process of geothermal brine extraction, cascaded utilization of thermal energy, temperature control, selective lithium extraction, and tail liquid reinjection. In the entire process, the geothermal brine first enters through the geothermal brine extraction unit 1, then sequentially undergoes multi-stage thermal utilization by the cascaded utilization subsystem 2, temperature regulation by the brine temperature control unit 3, selective lithium extraction by the lithium extraction subsystem, and reinjection treatment by the tail liquid regulation and reinjection unit 9. Together, these processes constitute an efficient, stable, and economical geothermal brine lithium extraction technology. Specifically, by setting up the cascaded utilization subsystem 2 to utilize heat before lithium extraction, the downgrading of high-grade heat energy and the direct waste of low-grade heat energy are avoided. By directing the heat from the low-temperature section for preheating the lithium extraction process liquid, effective recycling of waste heat within the system is achieved. Through precise temperature regulation by the brine temperature control unit 3, the lithium extraction subsystem is ensured to always operate within a suitable temperature range.

[0078] Specifically, the system operation process is as follows: During system operation, liquid geothermal brine enters geothermal brine extraction unit 1 from target extraction well 100, and then enters primary heat utilization unit 21 of thermal energy cascade utilization subsystem 2 for primary heat utilization. Primary heat utilization unit 21 employs one or more of the following: geothermal power generation device, high-temperature plate heat exchanger, shell-and-tube heat exchanger, or high-temperature heating heat exchanger, for geothermal power generation, high-temperature heat exchange, or high-temperature heating. This stage prioritizes the utilization of heat from the high-temperature section of the brine.

[0079] After primary heat utilization, the geothermal brine enters the secondary heat utilization unit 22 for secondary heat utilization. The secondary heat utilization unit 22 is connected to one or more heat exchangers in the district heating system, domestic hot water system, industrial hot water system, and drying system to utilize the heat in the medium temperature range. This allows the geothermal brine to complete the main heat recovery before entering the lithium extraction subsystem, avoiding heat loss caused by simple cooling.

[0080] After secondary heat utilization, the geothermal brine enters the tertiary heat utilization unit 23 for tertiary heat utilization. The tertiary heat utilization unit 23 includes a lithium extraction process liquid preheating module for indirect heat exchange with the lithium extraction process liquid. In the tertiary heat utilization unit 23, the geothermal brine releases residual heat from the low-temperature section to preheat the lithium extraction process liquid. After completing this indirect heat exchange preheating, the geothermal brine then enters the brine temperature control unit 3.

[0081] After completing the three-stage thermal utilization, the geothermal brine enters the brine temperature control unit 3. The brine temperature control unit 3 is used to adjust the brine temperature to a suitable range for pretreatment and lithium selective extraction. The temperature-controlled geothermal brine enters the pretreatment unit 4 to reduce the impact of one or more impurities among suspended solids, silicon, iron, manganese, calcium, and magnesium on the subsequent lithium extraction unit. The pretreated geothermal brine enters the lithium selective extraction unit 5. When the geothermal brine passes through the lithium selective extraction unit 5, lithium ions are selectively enriched in the adsorbent, ion exchange material, membrane separation enrichment side, or electrochemical carrier, thereby obtaining a lithium-rich phase or lithium-loaded material. The lithium-poor tail liquid is discharged from the lithium selective extraction unit 5.

[0082] The lithium-rich phase or lithium-loaded material enters the desorption / elution unit 6; in the desorption / elution unit 6, the desorption liquid or eluent transfers lithium ions from the lithium-rich phase or lithium-loaded material to the liquid phase to obtain a lithium-rich solution; wherein, the desorption liquid or eluent can be preheated in the three-stage heat utilization unit 23 to improve the desorption or elution efficiency and shorten the processing time; the obtained lithium-rich solution enters the lithium-rich solution purification and concentration unit 7 to remove associated impurities and increase the lithium concentration; the lithium-rich solution concentration feed can also be preheated in the three-stage heat utilization unit 23 to reduce the external heat supply requirements of the concentration stage.

[0083] The purified and concentrated lithium-rich solution enters the lithium salt preparation unit 8; wherein, the lithium salt preparation unit 8 prepares lithium carbonate by adding a carbonate precipitant, or prepares lithium hydroxide through one or more steps of causticization, conversion, concentration and crystallization; the water or precipitant solution used for precipitation reaction can be preheated in the tertiary heat utilization unit 23 to improve the temperature conditions of the precipitation reaction. The obtained lithium salt product is output after solid-liquid separation, washing and drying.

[0084] The lithium-poor tailings discharged from the lithium selective extraction unit 5 enter the tailings regulation and reinjection unit 9; wherein, the tailings regulation and reinjection unit 9 regulates one or more of the following: temperature, suspended solids content, pH, mineralization, scaling tendency, and pressure of the tailings, so that it meets the reinjection requirements before entering the target reinjection well 200; through tailings reinjection, brine discharge can be reduced, geothermal reservoir pressure can be maintained, and it is conducive to the long-term stable development of geothermal resources.

[0085] Example 2 This embodiment 2 provides a method for lithium extraction from geothermal brine based on cascade waste heat utilization. Utilizing the geothermal brine lithium extraction system based on cascade waste heat utilization described in embodiment 1, the method includes: Using the geothermal brine extraction unit, liquid geothermal brine is extracted and transported from the liquid phase geothermal brine extraction pipeline of the target extraction well 100 to the thermal energy cascade utilization subsystem 2. The thermal energy cascade utilization subsystem 2 performs cascade thermal utilization of the liquid phase geothermal brine, outputting geothermal brine after waste heat recovery. The low-temperature heat recovered during the cascade thermal utilization process is used to preheat the lithium extraction process fluid in the lithium extraction subsystem. Using the brine temperature control unit 3, the temperature of the geothermal brine after waste heat recovery is adjusted to output geothermal brine that meets the target temperature range for lithium extraction inlet. Using the lithium extraction subsystem, the geothermal brine meeting the target temperature range for lithium extraction inlet undergoes selective lithium extraction treatment to obtain lithium salt and lithium-lean tailings. Using the tailings regulation and reinjection unit 9, the temperature, water quality, or pressure of the lithium-lean tailings are regulated to meet reinjection requirements before being transported to the target reinjection well 200.

[0086] It should be noted that all relevant content of each step involved in the embodiment of the geothermal brine lithium extraction system based on cascade waste heat utilization described in Embodiment 1 above can be referenced to the corresponding step description of the geothermal brine lithium extraction method based on cascade waste heat utilization in this Embodiment 2, and will not be repeated here.

[0087] The geothermal brine lithium extraction system based on cascaded waste heat utilization described in this invention, by setting up a thermal energy cascade utilization subsystem 2 between the geothermal brine extraction unit 1 and the lithium extraction subsystem, can recover all the waste heat of the geothermal brine in stages according to high temperature, medium temperature and low temperature, which can significantly improve the overall thermal energy utilization rate of the geothermal brine and avoid the waste of geothermal energy caused by direct reinjection of high temperature tailwater; wherein, through the three-stage thermal utilization unit 23, the recovered low temperature waste heat is directed to preheat the lithium extraction process liquids such as desorption liquid, washing liquid, precipitation reaction water and concentration unit feed, which can replace the external electric heating and steam heating equipment of traditional processes, significantly reduce the external heat source consumption of the entire lithium extraction process, and reduce production energy consumption and operating costs.

[0088] Secondly, by linking the three-stage heat utilization unit 23 with the brine temperature control unit 3, and relying on the control unit and temperature sensor to collect the brine temperature at the lithium extraction inlet in real time, the heat exchange load, bypass mixing ratio and cooling medium flow rate can be dynamically adjusted. This can continuously maintain the geothermal brine entering the lithium extraction subsystem within the target temperature range suitable for each lithium extraction process, eliminate the brine temperature disturbance caused by the fluctuation of the geothermal well production conditions, improve the adsorption selectivity, lithium ion enrichment efficiency and cycle life of the lithium selective extraction unit, and ensure the long-term stable and continuous operation of the entire lithium extraction device.

[0089] In this invention, the entire process flow of the system is designed for pure liquid-phase geothermal brine, without the need for gas-liquid separation or differential pressure power generation devices. It can be adapted to geothermal brine resource development scenarios without gas phase production, thus broadening the scope of application for geothermal brine lithium extraction projects. The system is compatible with multiple mainstream lithium extraction processes, including adsorption, ion exchange, membrane separation, and electrochemical lithium intercalation / deintercalation. Existing geothermal brine lithium extraction production lines can be modified simply by adding a cascade heat exchange unit and a linkage temperature control module. The project is easy to implement and has strong adaptability.

[0090] In addition, by treating the lithium-poor tailings after lithium extraction and reinjecting them into the geothermal reservoir through the tailings regulation and reinjection unit, the pressure of the underground geothermal reservoir can be stabilized, the risk of water and soil pollution caused by brine discharge can be reduced, and the closed-loop development of geothermal fluids can be realized, taking into account multiple benefits such as mineral recovery, clean energy utilization and long-term protection of underground reservoirs.

[0091] The above embodiments are merely one of the implementation methods to achieve the technical solution of the present invention. The scope of protection claimed by the present invention is not limited to this embodiment, but also includes variations, substitutions and other implementation methods that are easily conceived by those skilled in the art within the technical scope disclosed in the present invention.

Claims

1. A geothermal brine lithium extraction system based on cascade waste heat utilization, characterized in that, It includes a geothermal brine extraction unit (1), a thermal energy cascade utilization subsystem (2), a brine temperature control unit (3), a lithium extraction subsystem, and a tail liquid regulation and reinjection unit (9). The geothermal brine extraction unit is used to connect to the liquid phase geothermal brine extraction pipeline of the target extraction well (100) to extract and transport liquid phase geothermal brine to the thermal energy cascade utilization subsystem (2). The thermal energy cascade utilization subsystem (2) is used to perform cascade thermal utilization of liquid phase geothermal brine and output geothermal brine after waste heat recovery; wherein, the low-temperature heat recovered during the cascade thermal utilization process is used for preheating of the lithium extraction process liquid in the lithium extraction subsystem. The brine temperature control unit (3) is used to regulate the temperature of the geothermal brine after waste heat recovery and output geothermal brine that meets the target temperature range of the lithium extraction inlet. The lithium extraction subsystem is used to selectively extract lithium from geothermal brine that meets the target temperature range for lithium extraction inlet, in order to obtain lithium salts and lithium-poor tailings. The tail fluid regulation and reinjection unit (9) is used to regulate the temperature, water quality or pressure of the lithium-poor tail fluid, and after meeting the reinjection requirements, it is transported to the target reinjection well (200).

2. The geothermal brine lithium extraction system based on cascade waste heat utilization according to claim 1, characterized in that, The thermal energy cascade utilization subsystem (2) includes a primary thermal utilization unit (21), a secondary thermal utilization unit (22) and a tertiary thermal utilization unit (23) arranged sequentially along the flow direction of the liquid phase geothermal brine. The primary heat utilization unit (21) is used to recover the high-temperature section heat in the liquid phase geothermal brine through geothermal power generation or high-temperature heat exchange to form medium-temperature geothermal brine. The secondary heat utilization unit (22) is used to recover and utilize the heat in the medium-temperature section of the medium-temperature geothermal brine through one or more forms of district heating, domestic heat or industrial heat to form low-temperature geothermal brine. The three-stage heat utilization unit (23) is used to recover the low-temperature section heat in the low-temperature geothermal brine through indirect heat exchange, forming geothermal brine after waste heat recovery.

3. A geothermal brine lithium extraction system based on cascaded heat utilization and cascaded waste heat utilization according to claim 2, characterized in that, The brine temperature control unit (3) includes a temperature control module and a temperature sensor; The inlet of the temperature control module is connected to the outlet of the three-stage heat utilization unit (23), and the outlet of the temperature control module is connected to the inlet of the lithium extraction subsystem; the temperature sensor is set at the outlet of the temperature control module. The temperature control module is used to regulate the temperature of the geothermal brine after waste heat recovery through one or more of the following methods: bypass mixing, heat exchange, and flow regulation. A temperature sensor is used to collect the brine temperature at the outlet of the temperature control module.

4. A geothermal brine lithium extraction system based on cascade waste heat utilization according to claim 3, characterized in that, Temperature control equipment includes a bypass mixing branch, a cooler, and a flow control valve; Among them, the bypass mixing branch is used to mix the high-temperature brine of the preset bypass with the geothermal brine after waste heat recovery, and use the mixed geothermal brine as the geothermal brine that meets the target temperature range of lithium extraction inlet. The cooler is used to cool the geothermal brine after waste heat recovery to form geothermal brine that meets the target temperature range for lithium extraction inlet. The flow regulating valve is used to regulate the flow rate of the geothermal brine after waste heat recovery, and to use the geothermal brine with the regulated flow rate as the geothermal brine that meets the target temperature range for lithium extraction inlet.

5. A geothermal brine lithium extraction system based on cascade waste heat utilization according to claim 3, characterized in that, The three-stage heat utilization unit (23) and the brine temperature control unit (3) operate in conjunction; Among them, when the brine temperature at the outlet of the temperature control module is higher than the preset target temperature range, the heat exchange capacity of the three-stage heat utilization unit (23) is increased, or the temperature of the geothermal brine after waste heat recovery is reduced by the temperature control module. When the brine temperature at the outlet of the temperature control module is lower than the preset target temperature range, the heat exchange capacity of the three-stage heat utilization unit (23) is reduced, or the temperature control module is used to increase the temperature of the geothermal brine after waste heat recovery.

6. A geothermal brine lithium extraction system based on cascade waste heat utilization according to claim 5, characterized in that, It also includes a control unit; the input of the control unit is connected to the output of the temperature sensor, and the output of the control unit is connected to both the three-stage heat utilization unit (23) and the temperature control module. The control unit is used to generate and send control commands to the three-stage heat utilization unit (23) and the temperature control module based on the brine temperature at the outlet of the temperature control module; wherein, the control commands are used to control the three-stage heat utilization unit (23) to adjust the heat exchange capacity, or to control the operating mode of the temperature control module.

7. A geothermal brine lithium extraction system based on cascade waste heat utilization according to claim 1, characterized in that, The solutions used in lithium extraction processes include one or more of the following: desorption solution, washing solution, water for precipitation reaction, and feed to the concentration unit.

8. A geothermal brine lithium extraction system based on cascade waste heat utilization according to claim 1, characterized in that, The lithium extraction subsystem includes a pretreatment unit (4), a lithium selective extraction unit (5), a desorption / elution unit (6), a lithium-rich liquid purification and concentration unit (7), and a lithium salt preparation unit (8) connected in sequence.

9. A geothermal brine lithium extraction system based on cascade waste heat utilization according to claim 1, characterized in that, The lithium selective extraction unit (5) performs lithium selective extraction through one or more of the following methods: adsorption lithium extraction, ion exchange lithium extraction, membrane separation lithium extraction, and electrochemical lithium intercalation / deintercalation.

10. A method for lithium extraction from geothermal brine based on cascade waste heat utilization, characterized in that, The method for extracting lithium from geothermal brine based on cascade waste heat utilization as described in any one of claims 1-9 includes: Using the geothermal brine extraction unit (1), liquid geothermal brine is extracted and transported from the liquid phase geothermal brine extraction pipeline of the target extraction well (100) to the thermal energy cascade utilization subsystem (2). Using the thermal energy cascade utilization subsystem (2), the liquid phase geothermal brine is used for cascade thermal utilization, and the geothermal brine after waste heat recovery is output; wherein, the low-temperature heat recovered during the cascade thermal utilization process is used for preheating of the lithium extraction process liquid in the lithium extraction subsystem. Using the brine temperature control unit (3), the temperature of the geothermal brine after waste heat recovery is adjusted, and the geothermal brine that meets the target temperature range of the lithium extraction inlet is output. Using a lithium extraction subsystem, selective lithium extraction is performed on geothermal brine that meets the target temperature range for lithium extraction inlet to obtain lithium salts and lithium-poor tailings. The tail fluid regulation and reinjection unit (9) is used to regulate the temperature, water quality or pressure of the lithium-poor tail fluid to meet the reinjection requirements and then transport it to the target reinjection well (200).

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