Salinity power-turbine coupled energy recovery device for seawater desalination and working method

Abstract

The application belongs to the technical field of seawater resource utilization, and discloses a salt-difference energy-turbine coupled energy recovery device and working method for seawater desalination. The device structure is divided into a first chamber, a second chamber, a third chamber, a fourth chamber and a fifth chamber, and comprises a first chamber water inlet, a first chamber water outlet, a first chamber water inlet bearing, a first chamber impeller, a first chamber solid bearing, a second chamber impeller, a second chamber water inlet, a second chamber hollow bearing, a third chamber impeller, a third chamber water outlet, a third chamber solid bearing, a fourth chamber impeller, a fourth chamber water outlet bearing, a fourth chamber water inlet, a fourth chamber water outlet, a fifth chamber raw seawater water inlet, a fifth chamber forward osmosis membrane assembly and a fifth chamber water outlet. The technical scheme can realize step-by-step energy utilization of the concentrated brine discharged by the reverse osmosis system, improve the salt-difference energy utilization efficiency, and reduce the comprehensive energy consumption of the reverse osmosis seawater desalination system.

Description

Technical Field

[0001] This invention belongs to the field of seawater resource utilization technology, specifically relating to a salinity gradient energy-turbine coupled energy recovery device and its working method for seawater desalination. Background Technology

[0002] Reverse osmosis (RO) technology, as the most mature and widely used membrane separation technology for seawater desalination, operates on the principle of applying a working pressure of 4.0-8.5 MPa to the raw seawater using a high-pressure pump. This forces water molecules to overcome the osmotic pressure difference and pass through a semi-permeable membrane, thus achieving effective separation of fresh water and concentrated brine. During operation, this technology generates high-pressure concentrated brine. The Energy Recovery Device (ERD), a key energy-saving component of the reverse osmosis system, primarily recovers residual pressure energy from the concentrated brine through positive displacement or centrifugal operation. This can reduce system energy consumption by 40%-50%, lowering energy consumption per ton of water to 2.0-4.5 kWh / m³.

[0003] In the field of renewable energy, salinity gradient energy (SGE), a renewable energy source based on the chemical potential difference of solutions, has a theoretical energy density of up to 0.8 kWh / m³. Among these, pressure-delayed osmosis (PRO) technology is the most promising method for utilizing SGE. It converts salinity gradient energy into hydraulic energy by driving water molecule migration through the osmotic pressure difference between solutions of different salinities (such as seawater and river water) on both sides of a semi-permeable membrane. Studies have shown that in a typical seawater-river water system, the theoretical power density of PRO technology can reach 5-10 W / m². However, the energy recovery devices in existing seawater desalination reverse osmosis systems can only recover the residual pressure energy in concentrated brine, failing to utilize the salinity gradient energy between concentrated brine and low-salinity water, resulting in significant energy waste.

[0004] Patent application CN118183941A discloses a "dual-engine" seawater desalination brine treatment system based on PRO+PRMD. It utilizes pressure-delayed osmosis (PDOS) and pressure-delayed membrane distillation (PDDM) technologies to construct a "dual-engine" power drive system powered by salinity gradient energy and temperature gradient energy. This system transfers the salinity gradient energy and temperature gradient energy contained in the brine to ambient temperature and pressure seawater in the form of mechanical energy, thereby reducing salinity and increasing flow rate, achieving energy and resource utilization of high-salt, high-temperature brine. Patent application CN106379961A discloses a multi-stage reverse osmosis seawater desalination coupled with salinity gradient energy power generation system, including multi-stage reverse osmosis units, raw seawater pipelines, forward osmosis units, energy recovery units, turbines, generators, and discharge pipelines. The original seawater pipeline is divided into two paths: one path enters a multi-stage reverse osmosis unit for desalination, and the other path enters a forward osmosis unit. The osmotic pressure between the forward osmosis unit and the high-concentration wastewater from the multi-stage reverse osmosis unit forces some of the freshwater in the seawater through a semi-permeable membrane to mix with the wastewater, driving a turbine to generate electricity. The remaining seawater is pressurized by an energy recovery unit and then introduced into the multi-stage reverse osmosis unit. This technical solution features low investment cost, stable operation, and high practicality, which is conducive to the practical application of salinity gradient energy generation. Furthermore, this invention further leverages the advantages of the multi-stage reverse osmosis unit—high water production and high recovery rate—while reducing the environmental impact of its wastewater discharge.

[0005] In addition, existing technologies utilize energy recovery devices and salinity gradient power generation to achieve energy savings in the entire system, such as... Figure 1 As shown, the process involves pressurizing seawater, desalinating it through a reverse osmosis membrane, separating it into freshwater and high-pressure concentrated brine, recovering energy from the high-pressure concentrated brine using a first energy recovery device, then discharging it as low-pressure concentrated brine. A second energy recovery device then pressurizes the low-pressure concentrated brine to generate pressurized concentrated brine, which is then fed to a forward osmosis membrane. The pressurized concentrated brine is further pressurized by the forward osmosis membrane and then sent to a turbine generator to generate electricity. Using SGE (Sequencing-Generated Geological Optimization) power generation technology to reduce seawater desalination energy consumption involves a long process, a complex system, and low energy conversion efficiency.

[0006] Based on the above technical background, developing a short-process, high-efficiency energy recovery device that can simultaneously recover residual pressure energy and salinity gradient energy from concentrated brine has important theoretical value and engineering significance for the seawater desalination industry. Summary of the Invention

[0007] This invention addresses the problem of the lack of efficient and rapid utilization of salinity gradient energy in existing seawater desalination technologies by proposing a short-process, high-efficiency salinity gradient energy-turbine coupled energy recovery device and its working method for seawater desalination.

[0008] A salinity gradient energy-turbine coupled energy recovery device for seawater desalination, the structure of which is divided into a first chamber, a second chamber, a third chamber, a fourth chamber, and a fifth chamber; The first chamber, the second chamber, the third chamber, the fourth chamber, and the fifth chamber adopt an upper and lower split chamber structure, and the upper and lower chambers are connected by a flange mechanical seal. The first chamber, the second chamber, the third chamber, and the fourth chamber are arranged axially along the central axis, and the fifth chamber is located outside the third and fourth chambers. The first chamber, the second chamber, the third chamber, and the fourth chamber are connected by a central shaft and a mechanical seal structure to achieve coaxial rotation and fluid isolation. The first chamber contains a first chamber inlet, a first chamber outlet, a first chamber inlet bearing, a first chamber impeller, and a first chamber solid bearing. The first chamber inlet bearing is equipped with a mechanical seal to ensure that the fluid in the first chamber will not leak. The second chamber contains a second chamber impeller, a second chamber inlet, and a second chamber hollow bearing; The third chamber contains a third chamber impeller, a third chamber outlet, and a third chamber solid bearing; The fourth chamber contains a fourth chamber impeller, a fourth chamber outlet bearing, a fourth chamber inlet, and a fourth chamber outlet. A mechanical seal is installed on the fourth chamber outlet bearing to ensure that the fluid in the fourth chamber does not leak. The fifth chamber is located outside the third and fourth chambers, forming an independent membrane separation unit. Inside, there is the original seawater inlet of the fifth chamber, the forward osmosis membrane module of the fifth chamber, and the outlet of the fifth chamber. The fifth chamber's raw seawater inlet is connected to the pretreated raw seawater; The fifth chamber forward osmosis membrane module is the core functional component, and it is installed using hollow fiber, spiral wound, or tubular separation membranes. The key flow channel structure of the fifth chamber forward osmosis membrane module adopts a dual independent flow channel design with a raw seawater side flow channel and a draw liquid side flow channel. The raw seawater side flow channel and the draw liquid side flow channel are strictly isolated by a high-performance forward osmosis membrane. This membrane only allows water molecules to selectively permeate and blocks the migration of salt ions. The raw seawater side flow channel connects the raw seawater inlet and outlet of the fifth chamber, allowing the flow of low-osmotic-pressure raw seawater. The draw liquid side flow channel connects the outlet of the third chamber and the inlet of the fourth chamber, and is used to transport the draw liquid, i.e., the low-pressure concentrated seawater from the third chamber. The outlet of the fifth chamber is used to discharge the medium-salinity seawater produced during the forward osmosis process, i.e., the concentrated original seawater; The first chamber solid bearing connects the first chamber impeller and the second chamber impeller by an interference fit, and the shaft is sealed by a sealing ring to prevent fluid leakage between the chambers. The hollow bearing in the second chamber has a guide groove on its inner wall, which allows the concentrated seawater after the second chamber is depressurized to enter the impeller in the third chamber through the hollow internal flow channel of the shaft. The shaft is sealed with a sealing ring to prevent fluid leakage between the chambers. The impeller in the second chamber and the impeller in the third chamber are connected by threads on the shaft. The solid bearing in the third chamber connects the impeller of the third chamber and the impeller of the fourth chamber through an interference fit, and the shaft prevents fluid leakage between the chambers through a sealing ring. The fifth chamber is connected to the third chamber in a copy forest manner through the outlet of the third chamber. The outlet of the third chamber has a one-way valve that only allows water to flow from the third chamber to the fifth chamber. The fifth chamber is connected to the fourth chamber via the inlet of the fourth chamber in a copy forest configuration.

[0009] An overrunning clutch is installed at the connection between the solid bearing in the third chamber and the impeller in the third chamber.

[0010] The working method of the above-mentioned salinity gradient energy-turbine coupling energy recovery device is shown in the figure. The raw seawater, after passing through the security filter and high-pressure pump, enters the inlet of the first chamber. The outlet of the first chamber is connected to the inlet of the reverse osmosis membrane module. The pressurized seawater comes out from the outlet of the first chamber and enters the reverse osmosis membrane module. The outlet of the high-pressure concentrated seawater of the reverse osmosis membrane module is connected to the inlet of the second chamber. The outlets of the fifth chamber and the fourth chamber are used to discharge the brine and brine of the salinity gradient energy-turbine coupling energy recovery device, respectively. The raw seawater inlet of the fifth chamber is connected to the inlet of the raw seawater branch pipeline after being filtered by the security filter. The inlet of the extraction liquid is connected to the outlet of the third chamber, and the outlet of the extraction liquid is connected to the inlet of the fourth chamber. High-precision pressure sensors are installed at the water inlets of the second and fourth chambers. The pipe connected to the outlet of the fourth chamber is equipped with an electromagnetic flow control valve; The specific working method of the salinity gradient energy-turbine coupled energy recovery device is as follows: The raw seawater, pressurized by a high-pressure pump, enters the salinity gradient energy-turbine coupling energy recovery device through the inlet of the first chamber. After passing through the bearing at the inlet of the first chamber and the internal flow channel of the impeller in the first chamber, it enters the reverse osmosis membrane module through the outlet of the first chamber. After being filtered by the reverse osmosis membrane module, the high-pressure concentrated seawater enters the second chamber through the inlet of the second chamber. The high pressure drives the impeller to rotate, converting the residual pressure energy of the high-pressure concentrated seawater into the mechanical energy of the impeller rotation in the second chamber. The impeller in the second chamber drives the impeller in the first chamber to rotate through the solid shaft in the first chamber, causing the impeller in the first chamber to pressurize the raw seawater entering the first chamber, thus completing the first energy conversion process of the high-pressure concentrated seawater. The depressurized concentrated seawater in the second chamber enters the impeller in the third chamber through the flow channel inside the hollow shaft of the second chamber. It then enters the fifth chamber through the outlet of the third chamber through the flow channel arranged inside the impeller of the third chamber. The pretreated raw seawater enters the raw water side of the forward osmosis membrane module in the fifth chamber through the raw seawater inlet of the fifth chamber. The depressurized low-pressure concentrated seawater enters the absorbent side of the forward osmosis membrane module in the fifth chamber through the outlet of the third chamber. In the forward osmosis membrane module, because the osmotic pressure of the low-pressure concentrated seawater is greater than that of the raw seawater, water molecules in the raw seawater migrate to the low-pressure concentrated seawater side, resulting in an increase in pressure on the low-pressure concentrated seawater side. This pressurizes the low-pressure concentrated seawater to medium-pressure seawater. Under the action of salinity gradient energy, the raw seawater forms medium-salinity seawater. With the action of the one-way valve at the outlet of the third chamber, the medium-pressure seawater enters the fourth chamber through the inlet of the fourth chamber. The medium-salinity seawater in the fifth chamber is discharged from the outlet of the fifth chamber. Thus, the salinity gradient energy conversion is completed in the fifth chamber, converting the salinity gradient energy of the low-pressure concentrated seawater into the hydraulic energy of the medium-pressure seawater. Medium-pressure seawater carrying hydraulic energy enters the fourth chamber through the inlet, driving the impeller in the fourth chamber to rotate. The impeller in the fourth chamber drives the impeller in the first chamber to rotate through the solid shaft in the third chamber, the hollow shaft in the second chamber, and the solid shaft in the first chamber, thus pressurizing the original seawater entering the first chamber a second time. This completes the second energy conversion of the low-pressure concentrated seawater. The medium-pressure seawater, after being depressurized, flows through the impeller in the fourth chamber and the bearing at the outlet of the fourth chamber, and is discharged through the outlet of the fourth chamber. This completes the recovery and utilization of the residual pressure energy and salinity gradient energy of the high-pressure concentrated seawater.

[0011] Working principle of the fifth chamber forward osmosis membrane module: In this technical solution, the draw liquid refers to the low-pressure concentrated seawater flowing out of the third chamber after being depressurized by primary residual pressure recovery. This concentrated seawater originates from the reverse osmosis seawater desalination process, and its salinity (or solute concentration) is much higher than that of the original seawater entering the fifth chamber, thus possessing extremely high osmotic pressure.

[0012] The flow process of raw seawater and draw solution: Pretreated raw seawater (low osmotic pressure) enters the raw seawater side channel of the fifth chamber forward osmosis membrane module through the raw seawater inlet of the fifth chamber. The depressurized low-pressure concentrated seawater (as the high osmotic pressure draw solution) enters the draw solution side channel of the fifth chamber forward osmosis membrane module through the outlet of the third chamber (where a one-way valve ensures unidirectional flow).

[0013] Salinity gradient energy-driven forward osmosis: Due to the osmotic pressure difference across the forward osmosis membrane (the osmotic pressure on the draw solution side is greater than that on the source seawater side), water molecules spontaneously and selectively migrate from the low-osmotic-pressure source seawater side to the high-osmotic-pressure draw solution (concentrated seawater) side through the forward osmosis membrane, according to the principle of osmosis. This process is spontaneous and does not require additional hydraulic pressure; its driving force comes entirely from the salinity difference (i.e., salinity gradient energy) between the concentrated seawater (draw solution) and the source seawater.

[0014] Energy conversion and changes in solution state: Raw seawater side: As water molecules migrate out, the raw seawater is concentrated, the salinity increases, forming mesosalinous seawater, which is eventually discharged through the outlet of the fifth chamber.

[0015] On the draw liquid side: As water molecules continuously migrate in, the originally low-pressure concentrated seawater is diluted, and its volume increases. Because this process occurs within a relatively closed flow channel (and subsequently connects to a fourth chamber), the dilution effect causes a significant increase in the pressure of the solution on the draw liquid side. Therefore, the salinity gradient energy (osmotic pressure difference) is directly converted into the hydraulic energy of the medium-pressure seawater in this process. This diluted and pressurized medium-pressure seawater (i.e., the original draw liquid) flows out from the draw liquid side flow channel.

[0016] Transport and utilization of medium-pressure seawater: The medium-pressure seawater, carrying the hydraulic energy converted from the salinity gradient, flows out from the liquid side of the forward osmosis membrane module and enters the fourth chamber through the inlet of the fourth chamber, driving the impeller of the fourth chamber to rotate, thereby realizing the mechanical energy recovery of the salinity gradient (i.e., the second energy conversion).

[0017] During operation, the external control PLC compares the pressure sensor values ​​at the inlets of the second and fourth chambers and automatically adjusts the opening of the electromagnetic flow control valve on the connecting pipe to the outlet of the fourth chamber. This ensures that the medium-pressure seawater flow rate matches the impeller speed, preventing overload or energy waste. When the salinity gradient energy boost in the fifth chamber is insufficient, the overrunning clutch automatically disconnects the transmission connection between the impellers of the third and fourth chambers, preventing the fourth chamber impeller from obstructing the rotation of the third chamber impeller and ensuring priority for residual pressure energy recovery. When the salinity gradient energy boost reaches the target, the overrunning clutch re-engages, achieving dual-energy coupling drive.

[0018] In the above-mentioned salinity gradient energy-turbine coupled energy recovery device, seawater is first pressurized. The pressurized seawater is then desalinated through a reverse osmosis membrane module to generate fresh water and high-pressure concentrated seawater. The high-pressure concentrated seawater first completes the first-stage residual pressure energy recovery in the salinity gradient energy-turbine coupled energy recovery device, converting it into low-pressure concentrated seawater. Under the action of the forward osmosis separation membrane, the low-pressure concentrated seawater and the original seawater undergo osmotic pressure transfer to form medium-pressure seawater. The medium-pressure seawater directly drives the impeller to rotate, completing the second-stage salinity gradient energy recovery. The seawater that has recovered the residual pressure energy and salinity gradient energy is then discharged. The entire process is streamlined, the system is simpler and more efficient, and the conversion efficiency is higher because the salinity gradient energy is directly converted into mechanical energy.

[0019] This technical solution proposes a salinity gradient energy-turbine coupled energy recovery device and its operating method. It utilizes the salinity difference between raw seawater and concentrated seawater to recover and utilize the salinity gradient energy of low-pressure concentrated seawater, coupled with a hydraulic turbine-type residual pressure energy recovery technology, achieving a gradient recovery of concentrated seawater energy. This technical solution not only enables the cascaded energy utilization of concentrated brine discharged from reverse osmosis systems but also improves the efficiency of salinity gradient energy utilization. The application of this dual energy recovery technology is expected to further reduce the overall energy consumption of reverse osmosis seawater desalination systems. This technical solution has significant strategic importance in promoting the development of seawater desalination technology towards greater efficiency and environmental friendliness, and in achieving the sustainable use of water resources. Attached Figure Description

[0020] The accompanying drawings, as part of this invention, are provided to further illustrate the invention. The illustrative embodiments and descriptions of the invention are used to explain the invention, but do not constitute an undue limitation thereof. Clearly, the drawings described below are merely some embodiments, and those skilled in the art can obtain other drawings based on these drawings without any creative effort.

[0021] Figure 1 This is a roadmap for existing seawater desalination salinity gradient power generation technology; Figure 2 This is a process flow diagram of the salt gradient energy-turbine coupling energy recovery device of the present invention; Figure 3 This is a cross-sectional view of the salt gradient energy-turbine coupling energy recovery device of the present invention. Figure 4 This is a rotor structure diagram of the salt gradient energy-turbine coupling energy recovery device of the present invention; Figure 5 This is an external view of the salt gradient energy-turbine coupling energy recovery device of the present invention. Figure 6 This is a comparison table of experimental data from embodiments of the present invention.

[0022] In the picture: 1. First chamber, wherein: 1-1 is the inlet of the first chamber, 1-2 is the outlet of the first chamber, 1-3 is the inlet bearing of the first chamber, 1-4 is the impeller of the first chamber, and 1-5 is the solid bearing of the first chamber; 2. Second chamber, wherein: 2-1 is the impeller of the second chamber, 2-2 is the water inlet of the second chamber, and 2-3 is the hollow bearing of the second chamber; 3. The third chamber, wherein: 3-1 is the impeller of the third chamber, 3-2 is the outlet of the third chamber, and 3-3 is the solid bearing of the third chamber; 4. Fourth chamber, wherein: 4-1 is the impeller of the fourth chamber, 4-2 is the bearing of the outlet of the fourth chamber, 4-3 is the inlet of the fourth chamber, and 4-4 is the outlet of the fourth chamber; 5. Fifth chamber, of which: 5-1 is the original seawater inlet of the fifth chamber, 5-2 is the forward osmosis membrane module of the fifth chamber, and 5-3 is the outlet of the fifth chamber.

[0023] It should be noted that these accompanying drawings and textual descriptions are not intended to limit the scope of the invention in any way, but rather to illustrate the concept of the invention to those skilled in the art by referring to specific embodiments. Detailed Implementation

[0024] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments will be clearly and completely described below with reference to the accompanying drawings. The following embodiments are used to illustrate the present invention, but are not intended to limit the scope of the present invention.

[0025] Example: Figures 3-5 As shown, a salinity gradient energy-turbine coupled energy recovery device for seawater desalination has a structure consisting of a first chamber 1, a second chamber 2, a third chamber 3, a fourth chamber 4, and a fifth chamber 5. The first chamber 1, the second chamber 2, the third chamber 3, the fourth chamber 4, and the fifth chamber 5 adopt an upper and lower split chamber structure, and the upper and lower chambers are connected by a flange mechanical seal. The first chamber 1, the second chamber 2, the third chamber 3, and the fourth chamber 4 are arranged axially along the central axis, and the fifth chamber 5 is located outside the third chamber 3 and the fourth chamber 4. The chambers 1, 2, 3, and 4 are connected by a central shaft and a mechanical seal structure to achieve coaxial rotation and fluid isolation. The first chamber 1 contains a first chamber inlet 1-1, a first chamber outlet 1-2, a first chamber inlet bearing 1-3, a first chamber impeller 1-4, and a first chamber solid bearing 1-5. The first chamber inlet bearing 1-3 is equipped with a mechanical seal to ensure that the fluid in the first chamber 1 will not leak. The second chamber 2 contains a second chamber impeller 2-1, a second chamber inlet 2-2, and a second chamber hollow bearing 2-3; The third chamber 3 contains a third chamber impeller 3-1, a third chamber outlet 3-2, and a third chamber solid bearing 3-3; The fourth chamber 4 contains a fourth chamber impeller 4-1, a fourth chamber outlet bearing 4-2, a fourth chamber inlet 4-3, and a fourth chamber outlet 4-4. A mechanical seal is installed on the fourth chamber outlet bearing 4-2 to ensure that the fluid in the fourth chamber 4 will not leak. The fifth chamber 5 is located outside the third chamber 3 and the fourth chamber 4, forming an independent membrane separation unit. Inside it are the original seawater inlet 5-1, the forward osmosis membrane module 5-2, and the outlet 5-3. The fifth chamber's original seawater inlet 5-1 connects to the pretreated original seawater; The fifth chamber forward osmosis membrane module 5-2 is the core functional component, installed using hollow fiber, spiral wound, or tubular separation membranes. The key flow channel structure of the fifth chamber forward osmosis membrane module 5-2 adopts a dual independent flow channel design: a raw seawater side flow channel and a draw solution side flow channel. These two flow channels are strictly isolated by a high-performance forward osmosis membrane that allows only selective permeation of water molecules while blocking salt ion migration. The raw seawater side flow channel connects the raw seawater inlet 5-1 and the outlet 5-3 of the fifth chamber, allowing the flow of low-osmotic-pressure raw seawater. The draw solution side flow channel connects the outlet 3-2 of the third chamber and the inlet 4-3 of the fourth chamber, used to transport the draw solution, i.e., the low-pressure concentrated seawater from the third chamber 3. The outlet 5-3 of the fifth chamber is used to discharge the medium-salinity seawater produced during the forward osmosis process, i.e., the concentrated original seawater; The first chamber solid bearing 1-5 connects the first chamber impeller 1-4 and the second chamber impeller 2-1 by an interference fit, and the shaft is sealed by a sealing ring to prevent fluid leakage between the chambers. The hollow bearing 2-3 in the second chamber has a guide groove on its inner wall, which allows the concentrated seawater after the second chamber 2 is depressurized to enter the impeller 3-1 in the third chamber through the hollow internal flow channel of the shaft. The shaft prevents fluid leakage between the chambers through a sealing ring. The impeller 2-1 in the second chamber and the impeller 3-1 in the third chamber are connected by a thread on the shaft. The solid bearing 3-3 of the third chamber connects the impeller 3-1 of the third chamber and the impeller 4-1 of the fourth chamber through an interference fit. The shaft is sealed with a sealing ring to prevent fluid leakage between the chambers. The fifth chamber 5 is connected to the third chamber 3 in a copy forest manner through the outlet 3-2 of the third chamber. The outlet 3-2 of the third chamber has a one-way valve, which only allows water to flow from the third chamber 3 to the fifth chamber 5. The fifth chamber 5 is connected to the fourth chamber 4 in a copy forest manner through the inlet 4-3 of the fourth chamber.

[0026] An overrunning clutch is provided at the connection between the solid bearing 3-3 in the third chamber and the impeller 3-1 in the third chamber.

[0027] The working method of the above-mentioned salinity gradient energy-turbine coupled energy recovery device, and its process route in seawater desalination are as follows: Figure 2As shown, the raw seawater, after passing through the security filter and high-pressure pump, enters the inlet 1-1 of the first chamber. The outlet 1-2 of the first chamber is connected to the inlet of the reverse osmosis membrane module. The pressurized seawater exits from the outlet 1-2 of the first chamber and enters the reverse osmosis membrane module. The outlet of the high-pressure concentrated seawater of the reverse osmosis membrane module is connected to the inlet 2-2 of the second chamber. The outlet 5-3 of the fifth chamber and the outlet 4-4 of the fourth chamber are used to discharge brine 1 and brine 2 from the salinity gradient energy-turbine coupling energy recovery device, respectively. The raw seawater inlet 5-1 of the fifth chamber is connected to the inlet of the raw seawater branch pipeline after filtration by the security filter. The inlet of the extractant is connected to the outlet 3-2 of the third chamber, and the outlet of the extractant is connected to the inlet 4-3 of the fourth chamber. High-precision pressure sensors are installed at the water inlet 2-2 of the second chamber and the water inlet 4-3 of the fourth chamber. An electromagnetic flow control valve is installed on the pipe connected to the outlet 4-4 of the fourth chamber. The specific working method of the salinity gradient energy-turbine coupled energy recovery device is as follows: The raw seawater, pressurized by a high-pressure pump, enters the salinity gradient energy-turbine coupling energy recovery device through the inlet 1-1 of the first chamber. After passing through the bearing 1-3 of the inlet of the first chamber and the internal flow channel of the impeller 1-4 of the first chamber, it enters the reverse osmosis membrane module through the outlet 1-2 of the first chamber. After being filtered by the reverse osmosis membrane module, the high-pressure concentrated seawater enters the second chamber 2 through the inlet 2-2 of the second chamber. The high pressure drives the impeller to rotate, converting the residual pressure energy of the high-pressure concentrated seawater into the mechanical energy of the impeller 2-1 of the second chamber. The impeller 2-1 of the second chamber drives the impeller 1-4 of the first chamber to rotate through the solid shaft 1-5 of the first chamber, causing the impeller 1-4 of the first chamber to pressurize the raw seawater entering the first chamber 1, thus completing the first energy conversion process of the high-pressure concentrated seawater. The concentrated seawater, depressurized in the second chamber 2, enters the impeller 3-1 in the third chamber through the flow channel within the hollow shaft 2-3 of the second chamber. It then flows through the flow channel within the impeller 3-1 and through the outlet 3-2 of the third chamber into the fifth chamber 5. The pretreated raw seawater enters the raw water side of the forward osmosis membrane module 5-2 in the fifth chamber through the raw seawater inlet 5-1. The depressurized, low-pressure concentrated seawater enters the extractor side of the forward osmosis membrane module 5-2 in the fifth chamber through the outlet 3-2 of the third chamber. Within the forward osmosis membrane module, due to the low-pressure concentrated seawater… When the osmotic pressure is greater than that of the original seawater, water molecules in the original seawater migrate to the low-pressure concentrated seawater side, resulting in an increase in pressure on the low-pressure concentrated seawater side. This pressurizes the low-pressure concentrated seawater into medium-pressure seawater. Under the action of salinity gradient energy, the original seawater forms medium-salinity seawater. With the action of the one-way valve at the outlet 3-2 of the third chamber, the medium-pressure seawater enters the fourth chamber 4 from the inlet 4-3 of the fourth chamber. The medium-salinity seawater in the fifth chamber 5 is discharged from the outlet 5-3 of the fifth chamber. Thus, the salinity gradient energy conversion is completed in the fifth chamber, converting the salinity gradient energy of the low-pressure concentrated seawater into the hydraulic energy of the medium-pressure seawater. Medium-pressure seawater carrying hydraulic energy enters the fourth chamber 4 through the inlet 4-3, driving the impeller 4-1 of the fourth chamber to rotate. The impeller 4-1 of the fourth chamber drives the impeller 1-4 of the first chamber to rotate through the solid shaft 3-3 of the third chamber, the hollow shaft 2-3 of the second chamber, and the solid shaft 1-5 of the first chamber, thus giving the original seawater entering the first chamber 1 a second pressurization, thereby completing the second energy conversion of the low-pressure concentrated seawater. The medium-pressure seawater after depressurization flows through the interior of the impeller 4-1 of the fourth chamber and the bearing 4-2 of the outlet of the fourth chamber, and flows out through the outlet 4-4 of the fourth chamber for discharge. This completes the recovery and utilization of the residual pressure energy and salinity gradient energy of the high-pressure concentrated seawater.

[0028] Working principle of the fifth chamber forward osmosis membrane module 5-2: In this embodiment, the draw liquid refers to the low-pressure concentrated seawater flowing out of the third chamber 3 after being depressurized by primary residual pressure recovery. This concentrated seawater originates from the reverse osmosis seawater desalination process, and its salinity (or solute concentration) is much higher than that of the original seawater entering the fifth chamber 5, thus having extremely high osmotic pressure.

[0029] The flow process of raw seawater and draw solution: Pretreated raw seawater (low osmotic pressure) enters the raw seawater side channel of the fifth chamber forward osmosis membrane module 5-2 through the raw seawater inlet 5-1 of the fifth chamber. The depressurized low-pressure concentrated seawater (as the high osmotic pressure draw solution) enters the draw solution side channel of the fifth chamber forward osmosis membrane module 5-2 through the outlet 3-2 of the third chamber (with a one-way valve inside to ensure unidirectional flow).

[0030] Salinity gradient energy-driven forward osmosis: Due to the osmotic pressure difference across the forward osmosis membrane (the osmotic pressure on the draw solution side is greater than that on the source seawater side), water molecules spontaneously and selectively migrate from the low-osmotic-pressure source seawater side to the high-osmotic-pressure draw solution (concentrated seawater) side through the forward osmosis membrane, according to the principle of osmosis. This process is spontaneous and does not require additional hydraulic pressure; its driving force comes entirely from the salinity difference (i.e., salinity gradient energy) between the concentrated seawater (draw solution) and the source seawater.

[0031] Energy conversion and changes in solution state: Raw seawater side: As water molecules migrate out, the raw seawater is concentrated, the salinity increases, forming mesosalinous seawater, which is eventually discharged through the outlet 5-3 of the fifth chamber.

[0032] On the draw liquid side: As water molecules continuously migrate in, the originally low-pressure concentrated seawater is diluted, and its volume increases. Because this process occurs within a relatively closed flow channel (and subsequently connects to the fourth chamber 4), the dilution effect causes a significant increase in the pressure of the solution on the draw liquid side. Therefore, the salinity gradient energy (osmotic pressure difference) is directly converted into the hydraulic energy of the medium-pressure seawater in this process. This diluted and pressurized medium-pressure seawater (i.e., the original draw liquid) flows out from the draw liquid side flow channel.

[0033] Transport and utilization of medium-pressure seawater: The medium-pressure seawater, carrying the hydraulic energy converted from the salinity gradient, flows out from the liquid side of the forward osmosis membrane module and enters the fourth chamber 4 through the inlet 4-4 of the fourth chamber, driving the impeller of the fourth chamber 4 to rotate, thereby realizing the mechanical energy recovery of the salinity gradient (i.e., the second energy conversion).

[0034] During operation, the external control PLC compares the pressure sensor values ​​at the inlet 2-2 of the second chamber and the inlet 4-3 of the fourth chamber, automatically adjusting the opening of the electromagnetic flow control valve connected to the outlet 4-4 of the fourth chamber to ensure that the medium-pressure seawater flow rate matches the impeller speed, avoiding overload or energy waste. When the salinity difference energy boost in the fifth chamber is insufficient, the overrunning clutch automatically disconnects the transmission connection between the impeller 3-1 of the third chamber and the impeller 4-1 of the fourth chamber, preventing the impeller 4-1 of the fourth chamber from obstructing the rotation of the impeller of the third chamber and ensuring that residual pressure energy recovery is prioritized. When the salinity difference energy boost reaches the target, the overrunning clutch re-engages, achieving dual-energy coupling drive.

[0035] In the above-mentioned salinity gradient energy-turbine coupled energy recovery device, seawater is first pressurized. The pressurized seawater is then desalinated through a reverse osmosis membrane module to generate fresh water and high-pressure concentrated seawater. The high-pressure concentrated seawater first completes the first-stage residual pressure energy recovery in the salinity gradient energy-turbine coupled energy recovery device, converting it into low-pressure concentrated seawater. Under the action of the forward osmosis separation membrane, the low-pressure concentrated seawater and the original seawater undergo osmotic pressure transfer to form medium-pressure seawater. The medium-pressure seawater directly drives the impeller to rotate, completing the second-stage salinity gradient energy recovery. The seawater that has recovered the residual pressure energy and salinity gradient energy is then discharged. The entire process is streamlined, the system is simpler and more efficient, and the conversion efficiency is higher because the salinity gradient energy is directly converted into mechanical energy.

[0036] The experimental data comparison table of the embodiments of the present invention is as follows: Figure 6 As shown, the three schemes are compared under the same influent conditions: Option 1: Use only a high-pressure pump; Option 2: Use a high-pressure pump and a turbine-type energy recovery device; Option 3: Use a high-pressure pump coupled with a salinity gradient energy-turbine energy recovery device; As can be seen, the energy consumption and energy consumption per ton of water for the three high-pressure system schemes are as follows: Option 1 has an energy consumption of 316.7 kW and an energy consumption of 4.59 kWh per ton of water. Option 2 has an energy consumption of 187 kW and an energy consumption of 2.71 kWh per ton of water. Option 3 has an energy consumption of 163.4 kW and an energy consumption of 2.37 kWh per ton of water. As can be seen from the total energy consumption or energy consumption per ton of water, Scheme 3 reduces energy consumption by 48% compared to Scheme 1 and by 12.6% compared to Scheme 2. This embodiment not only enables cascaded energy utilization of concentrated brine discharged from the reverse osmosis system but also improves salinity gradient energy utilization efficiency by 15%-20%. The application of this dual energy recovery technology is expected to further reduce the overall energy consumption of the reverse osmosis seawater desalination system by 10%-15%.

[0037] In this embodiment, the salinity gradient energy-turbine coupled energy recovery device utilizes the salinity difference between raw seawater and concentrated seawater to recover and utilize the salinity gradient energy of low-pressure concentrated seawater. Coupled with a hydraulic turbine-type residual pressure energy recovery technology, it achieves gradient recovery of concentrated seawater energy, realizing a dual energy-saving effect. This promotes the development of seawater desalination technology towards greater efficiency and environmental friendliness, and is of significant strategic importance for achieving sustainable water resource utilization.

[0038] Numerous specific details are set forth in the specification provided herein. However, it will be understood that embodiments of the invention may be practiced without these specific details. In some instances, well-known methods, structures, and techniques have not been shown in detail so as not to obscure the understanding of this specification.

[0039] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-described technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A salinity gradient energy-turbine coupled energy recovery device for seawater desalination, characterized in that, Its structure is divided into a first chamber (1), a second chamber (2), a third chamber (3), a fourth chamber (4), and a fifth chamber (5); The first chamber (1), the second chamber (2), the third chamber (3), the fourth chamber (4), and the fifth chamber (5) adopt an upper and lower split chamber structure, and the upper and lower chambers are connected by a flange mechanical seal; The first chamber (1), the second chamber (2), the third chamber (3), and the fourth chamber (4) are arranged axially along the central axis, and the fifth chamber (5) is located outside the third chamber (3) and the fourth chamber (4); The first chamber (1), the second chamber (2), the third chamber (3), and the fourth chamber (4) are connected by a central shaft and a mechanical seal structure to achieve coaxial rotation and fluid isolation. The first chamber (1) contains a first chamber inlet (1-1), a first chamber outlet (1-2), a first chamber inlet bearing (1-3), a first chamber impeller (1-4), and a first chamber solid bearing (1-5). The first chamber inlet bearing (1-3) is equipped with a mechanical seal. The second chamber (2) contains a second chamber impeller (2-1), a second chamber inlet (2-2), and a second chamber hollow bearing (2-3). The third chamber (3) contains a third chamber impeller (3-1), a third chamber outlet (3-2), and a third chamber solid bearing (3-3). The fourth chamber (4) contains a fourth chamber impeller (4-1), a fourth chamber outlet bearing (4-2), a fourth chamber inlet (4-3), and a fourth chamber outlet (4-4). A mechanical seal is provided on the fourth chamber outlet bearing (4-2). The fifth chamber (5) is located outside the third chamber (3) and the fourth chamber (4), forming an independent membrane separation unit. Inside, there is a fifth chamber seawater inlet (5-1), a fifth chamber forward osmosis membrane module (5-2), and a fifth chamber outlet (5-3). The fifth chamber's raw seawater inlet (5-1) is connected to the pretreated raw seawater; The fifth chamber forward osmosis membrane module (5-2) is installed using hollow fiber, spiral wound, or tubular separation membranes; The key flow channel structure of the fifth chamber forward osmosis membrane module (5-2) adopts a dual independent flow channel design with a raw seawater side flow channel and a draw liquid side flow channel. The two flow channels are strictly isolated by a high-performance forward osmosis membrane. The raw seawater side flow channel connects the raw seawater inlet (5-1) and the outlet (5-3) of the fifth chamber, and the draw liquid side flow channel connects the outlet (3-2) of the third chamber and the inlet (4-3) of the fourth chamber. The outlet (5-3) of the fifth chamber is used to discharge the medium-salinity seawater generated during the forward osmosis process; The first chamber solid bearing (1-5) is connected to the first chamber impeller (1-4) and the second chamber impeller (2-1) by an interference fit, and the shaft is sealed by a sealing ring to prevent fluid leakage between the chambers; The hollow bearing (2-3) of the second chamber is provided with a guide groove on the inner wall of the hollow structure, which allows the concentrated seawater after the pressure is released in the second chamber (2) to enter the impeller (3-1) of the third chamber through the hollow internal flow channel of the shaft. The shaft prevents fluid leakage between the chambers through a sealing ring. The impeller (2-1) of the second chamber and the impeller (3-1) of the third chamber are connected by the thread of the shaft. The solid bearing (3-3) of the third chamber is connected to the impeller (3-1) of the third chamber and the impeller (4-1) of the fourth chamber by an interference fit, and the shaft is sealed by a sealing ring to prevent fluid leakage between the chambers; The fifth chamber (5) is connected to the third chamber (3) in a copy forest manner through the outlet (3-2) of the third chamber. The outlet (3-2) of the third chamber has a one-way valve. The fifth chamber (5) is connected to the fourth chamber (4) in a copy forest manner through the water inlet (4-3) of the fourth chamber; An overrunning clutch is provided at the connection between the solid bearing (3-3) of the third chamber and the impeller (3-1) of the third chamber. When the salt difference energy of the fifth chamber (5) is insufficient, the overrunning clutch automatically disconnects the transmission connection between the impeller (3-1) of the third chamber and the impeller (4-1) of the fourth chamber. When the salt difference energy reaches the standard, the overrunning clutch re-engages.

2. The working method of the salinity gradient energy-turbine coupling energy recovery device for seawater desalination according to claim 1, wherein the raw seawater after passing through the security filter and high pressure pump enters the inlet (1-1) of the first chamber, the outlet (1-2) of the first chamber is connected to the inlet of the reverse osmosis membrane module, the pressurized seawater comes out from the outlet (1-2) of the first chamber and enters the reverse osmosis membrane module, the outlet of the high pressure concentrated seawater of the reverse osmosis membrane module is connected to the inlet (2-2) of the second chamber, the outlet (5-3) of the fifth chamber and the outlet (4-4) of the fourth chamber are respectively used to discharge the brine of the salinity gradient energy-turbine coupling energy recovery device, and the raw seawater inlet (5-1) of the fifth chamber is connected to the inlet of the raw seawater branch pipeline after being filtered by the security filter; The inlet of the extractant is connected to the outlet of the third chamber (3-2), and the outlet of the extractant is connected to the inlet of the fourth chamber (4-3). High-precision pressure sensors are installed at the water inlet (2-2) of the second chamber and the water inlet (4-3) of the fourth chamber. An electromagnetic flow control valve is installed on the pipe connected to the outlet of the fourth chamber (4-4).

3. The operating method of the salinity gradient energy-turbine coupled energy recovery device for seawater desalination according to claim 2, characterized in that, During operation, the external control PLC compares the pressure sensor values ​​of the second chamber inlet (2-2) and the fourth chamber inlet (4-3) to automatically adjust the opening of the electromagnetic flow control valve connected to the fourth chamber outlet (4-4).

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