Ocean salinity gradient energy utilization system and method based on retired offshore wind turbine single pile foundation

Abstract

The invention discloses an ocean salinity gradient energy utilization system and method based on a retired offshore wind turbine single pile foundation, and belongs to the technical field of ocean renewable energy sources. The system comprises a basic support module, a salinity gradient energy conversion module, an energy management module and a system control module, the basic support module is used for supporting normal operation of each system and providing a maintenance platform; the salinity difference energy conversion module is used for converting osmotic pressure of fresh water and saline water into mechanical energy; the energy management module is used for converting mechanical energy into electric energy and transmitting the electric energy to a power grid; and the system control module is used for monitoring and controlling the salinity gradient energy conversion module and the energy management module. Compared with an existing method, the cost of an independent supporting structure is saved by 50% or above, and the payback period is shortened to 10-20 years from 20 years or above. Meanwhile, a power transmission line and an operation and maintenance platform can be shared by a previous wind power plant, and the grid connection and operation and maintenance cost is reduced.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of marine renewable energy, and particularly relates to a marine salinity gradient energy utilization system and method based on a retired offshore wind turbine single pile foundation. BACKGROUND

[0002] With the rapid growth of global offshore wind power installed capacity (cumulative installed capacity over 300 GW by 2025), a large number of early offshore wind turbines will enter the retirement period. Taking a single pile foundation as an example, its service life is usually 25 years, but the designed service life is often 50 years. If it is directly removed after retirement, the following problems will be caused: (1) Environmental burden: the offshore wind turbine single pile foundation (diameter 4-10m, length 50-110m) is composed of high-strength steel or concrete, and the removal process may damage the marine ecology; (2) Economic waste: the offshore wind turbine single pile foundation has high manufacturing cost (single cost about 10-40 million yuan), and direct waste leads to resource waste; (3) Space occupation: the retired offshore wind turbine single pile foundation occupies the sea for a long time, affecting the channel planning and new project construction.

[0003] Therefore, how to functionally transform the retired single pile foundation and give it secondary utilization value has become a research hotspot in the global marine engineering field.

[0004] Salinity gradient energy (SGE) is the osmotic energy generated by the salinity difference between seawater and freshwater, with a theoretical reserve of 2.6TW. However, there are still some problems in the existing technology, which makes the economic cost higher than the benefit and cannot be applied on a large scale. For example, the independent salinity gradient energy power generation system needs to build new infrastructure (such as a permeable membrane assembly and a pressure exchanger), which has high initial investment and construction cost. In addition, the existing device is difficult to adapt to complex marine environments (such as tidal fluctuations and biological attachment), and considering the influence of complex marine environment will further increase the cost of the marine salinity gradient energy utilization system. SUMMARY

[0005] To solve the above problems, the application provides a marine salinity gradient energy utilization system and method based on a retired offshore wind turbine single pile foundation, which further obtains marine salinity gradient energy power generation benefits without increasing marine space occupation, realizes good reuse of retired single pile foundation resources, and to a great extent protects the marine environment, realizes the double value improvement of "retired resources + clean energy".

[0006] To solve the above technical problems, the application provides a marine salinity gradient energy utilization system based on a retired offshore wind turbine single pile foundation, which comprises a foundation support module, a salinity gradient energy conversion module, an energy management module and a system control module. The foundation support module is used to support the normal operation of each system and provide a maintenance platform; The salt differential energy conversion module is used to convert the osmotic pressure of fresh water and salt water into mechanical energy; The energy management module is used to convert the mechanical energy into electrical energy and transmit it to the power grid; The system control module is used to monitor and control the salt differential energy conversion module and the energy management module.

[0007] As a preferred, the foundation support module comprises a decommissioned offshore wind power single pile foundation, the single pile foundation body fixed to the seabed, the single pile foundation body top is sleeved with an auxiliary structure, the single pile foundation body top is provided with a hatch cover matched with the caliber of the single pile foundation, the hatch cover surface is provided with a loading hatch, the single pile foundation body is provided with a support steel beam, the support steel beam lower part is provided with a corbel at the connection with the single pile foundation body, the support steel beam and the hatch cover are provided with a working ladder, the single pile foundation body upper part is provided with a communication hole and a fresh water delivery unit, the single pile foundation body lower part is provided with a submarine cable hole and a seawater delivery unit.

[0008] As a preferred, the salt differential energy conversion module comprises a osmotic pressure generating device arranged at the lower part of the support steel beam, the osmotic pressure generating device comprises a fresh water chamber and a seawater chamber, the fresh water chamber is connected with the fresh water delivery unit, the seawater chamber is connected with the seawater delivery unit, the seawater chamber is connected with the water storage tank through a potential pressure conversion pipe, the osmotic pressure generating device bottom is provided with a tank partition plate, the fresh water chamber and the seawater chamber are provided with a permeable membrane assembly, the support steel beam upper part is provided with a generator connected with the fresh water chamber, the seawater chamber is provided with a sensor.

[0009] As a preferred, the fresh water enters the fresh water chamber through the fresh water delivery unit, the seawater enters the seawater chamber through the seawater delivery unit, the permeable membrane assembly can only allow water molecules to pass, so as to generate an osmotic pressure difference between the fresh water chamber and the seawater chamber, so that the water molecules in the fresh water chamber will continuously enter the seawater chamber, the seawater chamber is connected with the potential pressure conversion pipe; so that the water body continuously climbs above the sea surface through the potential pressure conversion pipe and enters the water storage tank, and the osmotic pressure is converted into mechanical energy.

[0010] As a preferred, the osmotic pressure generating device is connected with the support steel beam through a connecting member, and the tank partition plate is located below the fresh water chamber and the seawater chamber, so as to separate the osmotic pressure generating device into an empty cabin.

[0011] As a preferred, the energy management module comprises a submarine cable connected with the generator, the generator is connected with the water storage tank through a connecting pipe, the water in the water storage tank enters the turbine chamber of the generator through the connecting pipe, the mechanical energy is converted into electrical energy, and then transmitted to the power grid end through the submarine cable.

[0012] As preferred, the integrated monitoring control device of the control system module monitors and controls the salinity difference energy conversion module and the energy management module through sensors, and controls the salinity difference energy conversion module and the energy management module through control rules, and the sensors are arranged inside the single-pile foundation body.

[0013] As preferred, the control rules comprise: Sensors and valves are arranged in the seawater conveying unit, the sensors are used to monitor the salinity in the seawater chamber, when the salinity in the seawater chamber is lower than a set threshold, the valves are opened to make the seawater naturally replace, after the osmotic pressure difference salinity requirement is met, the valves are closed, so that the seawater can only climb up by the potential pressure conversion pipe; A pressure monitoring sensor is arranged at the bottom of the water storage tank, when the water pressure at the bottom of the water storage tank exceeds a preset limit value, an electric signal is sent to close the valve of the seawater conveying unit; An electrically controlled valve is arranged in the connecting pipe, when the power grid transmits a 'no power generation' signal to the control system, the control system will control the valve in the connecting pipe to be closed.

[0014] The design method of the ocean salinity difference energy utilization system based on the retired offshore wind turbine single-pile foundation is suitable for the system as described above, and comprises the following steps: S1, safety performance inspection and evaluation of the retired wind turbine single-pile foundation, to determine whether there is potential risk, if the risk is controllable, S2 is executed; S2, according to the size data of the retired wind turbine foundation, the salinity difference energy utilization system is designed, the system power generation installed power and the annual average power generation during operation are calculated, the system cost and the recovery period are calculated, and the economic feasibility of the project is evaluated; S3, if the project economy meets the requirements, the system device is manufactured and shipped to the predetermined wind turbine foundation for installation.

[0015] Compared with the prior art, the beneficial effects of the present application are: 1. The present application realizes the reuse of the foundation and the power transmission channel, and significantly reduces the cost The internal cavity or peripheral space of the single-pile foundation (diameter 6-10m) can install the salinity difference energy module (such as the microbial desalination unit), which saves the cost of independent supporting structure by more than 50%, shortens the investment recovery period from >20 years to 10-20 years. At the same time, the previous wind farm can share the power transmission line and operation and maintenance platform, reducing the grid connection and operation and maintenance cost.

[0016] 2. The present application efficiently couples resources The single-pile foundation constructed in the early stage is mostly located in the estuary and offshore area, and the salinity gradient of seawater changes greatly, and there is rich salinity difference energy resources. The present application arranges the fresh water conveying unit inlet near the sea surface and the seawater conveying unit inlet near the seabed, which can adjust the salinity gradient difference to a better level and improve the power generation income.

[0017] 3, the construction installation of the scheme is convenient Each module of the salt difference energy utilization system can be modularly designed and prefabricated on land, and can be quickly hoisted and constructed after being shipped to the wind turbine foundation by a ship. BRIEF DESCRIPTION OF DRAWINGS

[0018] Figure 1 It is a whole three-dimensional schematic view of the marine temperature difference energy utilization system based on the retired single pile foundation of the application; Figure 2 It is a front view of the system of the application; Figure 3 It is a side view of the system of the application; Figure 4 It is a top view of the system of the application; Figure 5 It is a schematic view of the internal structure of the system of the application; Figure 6 It is a control logic diagram of the system control module receiving the "no power generation" signal of the power grid of the application; Figure 7 It is a control logic diagram of the system control module receiving the "power generation" signal of the power grid of the application; In the figure: 1 is a single pile foundation body, 2 is an auxiliary structure, 3 is a cabin top cover, 4 is an inspection and transportation cabin door, 5 is a working ladder, 6 is a fresh water conveying unit, 7 is a sea water conveying unit, 8 is a submarine cable, 9 is a submarine cable hole, 10 is an osmotic pressure generating device, 11 is a generator, 12 is a water storage cabin, 13 is a potential pressure conversion pipe, 14 is a connecting pipe, 15 is an osmotic membrane assembly, 16 is a cabin partition plate, 17 is a corbel, 18 is a supporting steel beam, 19 is a platform plate, 20 is a communication hole, 21 is a connecting member, and 22 is an integrated monitoring and control device. DETAILED DESCRIPTION

[0019] Example 1: as shown in Figure 1 - Figure 7 The marine salt difference energy utilization system based on the retired offshore wind turbine single pile foundation includes: a foundation support module, a salt difference energy conversion module, an energy management module and a system control module; the foundation support module is used for supporting the normal operation of each system and providing a maintenance platform; the salt difference energy conversion module is used for converting the osmotic pressure of fresh water and salt water into mechanical energy; the energy management module is used for converting the mechanical energy into electric energy and conveying it to the power grid; and the system control module is used for monitoring and controlling the salt difference energy conversion module and the energy management module.

[0020] The foundation support module comprises a retired offshore wind power single pile foundation, the offshore wind power single pile foundation comprises a single pile foundation body 1 fixed to a seabed, an auxiliary structure 2 sleeved at the top of the single pile foundation body 1, a hatch cover 3 matched with the caliber of the single pile foundation arranged at the top of the single pile foundation body 1, a hatch door 4 arranged on the surface of the hatch cover 3, a support steel beam 18 arranged in the single pile foundation body 1, a corbel 17 arranged at the connecting position between the lower part of the support steel beam 18 and the single pile foundation body 1, a working ladder 5 arranged between the support steel beam 18 and the hatch cover 3, a communication hole 20 and a fresh water delivery unit 6 arranged at the upper part of the single pile foundation body 1, and a submarine cable hole 9 and a sea water delivery unit 7 arranged at the lower part of the single pile foundation body 1.

[0021] Specifically, the foundation support module is modified from the retired offshore wind power single pile foundation and is mainly used for supporting the normal operation and maintenance of each system, comprising the single pile foundation body 1, the auxiliary structure 2, the hatch cover 3, the hatch door 4, the working ladder 5, the corbel 17, the support steel beam 18 and the platform plate 19.

[0022] The lower part of the single pile foundation body structure is inserted into the seabed above the mud surface to keep stable, the upper part of the single pile foundation body structure is provided with the hatch cover 3 by using the original flange after the fan tower is removed, and the submarine cable hole 9 and the communication hole 20 are arranged on the single pile foundation body structure. The submarine cable hole is used for submarine cable crossing, and the communication hole is used for water intercommunication between the inside and outside of the single pile foundation. The fresh water delivery unit 6 and the sea water delivery unit 7 pass through the single pile foundation body to the outside.

[0023] In embodiment 2, the salt difference energy conversion module comprises a osmotic pressure generating device 10 arranged at the lower part of the support steel beam 18, the osmotic pressure generating device 10 comprises a fresh water chamber and a sea water chamber, the fresh water chamber is connected with the fresh water delivery unit 6, the sea water chamber is connected with the sea water delivery unit 7, the sea water chamber is connected with the water storage tank 12 through a potential pressure conversion pipe 13, the osmotic pressure generating device 10 is provided with a cabin partition plate 16 at the bottom, the fresh water chamber and the sea water chamber are provided with an osmotic membrane assembly 15, the upper part of the support steel beam 18 is provided with a generator 11 connected with the fresh water chamber, and the sea water chamber is provided with a sensor. The osmotic pressure generating device 10 is connected with the support steel beam 18 through a connecting member 21, and the cabin partition plate 16 is located below the fresh water chamber and the sea water chamber, so as to separate the osmotic pressure generating device 10 into an empty cabin room.

[0024] The fresh water enters the fresh water chamber through the fresh water delivery unit 6, the sea water enters the sea water chamber through the sea water delivery unit 7, the osmotic membrane assembly 15 can only allow water molecules to pass, so as to generate an osmotic pressure difference between the fresh water chamber and the sea water chamber, so that the water molecules in the fresh water chamber will continuously enter the sea water chamber, the sea water chamber is connected with the potential pressure conversion pipe 13; so that the water body continuously climbs to above the sea surface through the potential pressure conversion pipe 13 and enters the water storage tank 12, and the osmotic pressure is converted into mechanical energy.

[0025] The salt difference energy conversion module is mainly used for converting the osmotic pressure of fresh water and salt water into mechanical energy. It mainly comprises an osmotic pressure generating device 10, a potential pressure conversion pipe 13 and a water storage cabin 12. The osmotic pressure generating device 10 comprises a fresh water conveying unit 6, a sea water conveying unit 7, a permeation membrane assembly 15 and a cabin partition plate 16. Fresh water enters a fresh water chamber through the fresh water conveying unit 6, and sea water enters a sea water chamber through the sea water conveying unit 7. The permeation membrane assembly 15 can only allow water molecules to pass through, so as to generate an osmotic pressure difference between the fresh water chamber and the sea water chamber, so that water molecules in the fresh water chamber will continuously enter the sea water chamber. The sea water chamber is connected with the potential pressure conversion pipe 13. Water bodies continuously climb to above the sea surface through the potential pressure conversion pipe 13 and enter the water storage cabin 12, so as to convert the osmotic pressure into mechanical energy.

[0026] In the embodiment 3, the energy management module comprises a submarine cable 8 connected with a generator 11. The generator 11 is connected with the water storage cabin 12 through a connecting pipe 14. Water in the water storage cabin 12 enters a turbine chamber of the generator 11 through the connecting pipe 14, so as to convert the mechanical energy into electric energy, which is then transmitted to a power grid end through the submarine cable 8.

[0027] The energy management module is mainly used for converting mechanical energy into electric energy and transmitting the electric energy to a power grid. It mainly comprises a submarine cable 8, a generator 11 and a connecting pipe 14. Water bodies enter a turbine chamber of the generator 11 through the connecting pipe from the water storage cabin 12, so as to convert the mechanical energy into electric energy, which is then transmitted to the power grid end through the submarine cable 8.

[0028] The integrated monitoring and control device 22 of the control system module monitors and controls the salt difference energy conversion module and the energy management module through sensors. The integrated monitoring and control device 22 controls the salt difference energy conversion module and the energy management module through control rules. The sensors are arranged inside the single-pile foundation main body 1.

[0029] The control rules comprise: A sensor and a valve are arranged in the sea water conveying unit. The sensor is used for monitoring the salinity of the sea water chamber. When the salinity in the sea water chamber is lower than a set threshold value, the valve is opened to make the sea water naturally replace, and after the salinity requirement of the osmotic pressure difference is met, the valve is closed, so that the sea water can only climb through the potential pressure conversion pipe 13. A pressure monitoring sensor is arranged at the bottom of the water storage cabin 12. When the water pressure at the bottom of the water storage cabin 12 exceeds a preset limit value, an electric signal is sent to close the valve of the sea water conveying unit. An electrically controlled valve is arranged in the connecting pipe 14. When the power grid transmits a “no power generation” signal to the control system, the control system will control the valve in the connecting pipe to be closed.

[0030] The control system module is mainly used for monitoring and controlling the salt gradient energy conversion module and the energy management module. It is connected to the salt gradient energy conversion module and the energy management module by an integrated monitoring and control device 22 through electrical signals. The main sensors and on-off valves are set as follows: (1) a sensor and a valve are arranged in the seawater conveying unit. The sensor is used to monitor the salinity in the seawater chamber. When the salinity in the seawater chamber is lower than the threshold value (Csea water=5 g / L), the valve will be opened to allow natural replacement of seawater, and when the osmotic pressure difference salinity (Csea water≥35 g / L) is met, the valve will be closed, so that seawater can only be lifted by the pressure conversion pipe. (2) A pressure monitoring sensor is arranged at the bottom of the water storage tank. When the water pressure at the bottom of the water storage tank exceeds the limit value, a signal will be sent to close the seawater conveying unit valve. (3) An electrically controlled valve is arranged in the connecting pipe. When the power grid transmits a "no power generation" signal to the control system, the control system will control the valve in the connecting pipe to be closed.

[0031] The control flow is shown in Figure 6 and 7 .

[0032] As shown in Figure Six , the whole process can be divided into the following steps: power grid state triggering, valve control, pressure monitoring and feedback, pressure judgment and decision execution. Specifically: The control flow starts from the condition of "no power generation of the power grid". This signal is transmitted to the control system module.

[0033] After receiving the signal, the control system module performs two operations: controls the "seawater conveying valve" (whether to open it will be determined later based on pressure judgment), and ensures that the "connecting pipe valve" remains closed.

[0034] The water storage tank pressure sensor monitors the pressure in real time and feeds back the data to the control system module.

[0035] Based on the feedback data, the control system judges whether the "pressure exceeds the limit value".

[0036] If it does not exceed the limit: send the instruction "open" the seawater conveying valve to allow seawater to enter. If it exceeds the limit: maintain the valve closed state to prevent high pressure from causing risks.

[0037] The whole process described above is controlled through a closed loop to ensure that the system dynamically adjusts the valve state according to the water storage tank pressure when the power grid does not generate power, ensuring safe operation.

[0038] The specific process of the flow chart as shown in Figure 7 is as follows: the process starts from the power grid to provide initial power (electrical signal) for the system, which is directly connected to the control system module.

[0039] The control system module receives real-time data from the seawater chamber salinity sensor and simultaneously opens the seawater conveying valve and the connecting pipe valve. After the valve is opened, if the salinity is up to standard: execute the "close" operation. The salinity up to standard refers to the salinity of the seawater chamber ≥ 35g / L, and the closing operation after reaching the standard is to close the valve at the seawater conveying unit; If the salinity is not up to standard: execute the "open" operation. If the salinity is not up to standard, open the valve of the seawater conveying unit to allow the seawater in the seawater chamber to be naturally replaced.

[0040] The design method of the ocean salinity difference energy utilization system based on the retired offshore wind turbine single pile foundation is applicable to the system as described above, and includes the following steps: S1, safety performance inspection and evaluation of the retired wind turbine single pile foundation, to determine whether there is potential risk, if the risk is controllable, then execute S2; S2, design the salinity difference energy utilization system according to the size data of the retired wind turbine foundation, calculate the system installed power and annual average power generation during operation, and calculate the system cost and payback period to evaluate the economic feasibility of the project; S3, if the economic efficiency of the project meets the requirements, then manufacture the system device and transport it to the predetermined wind turbine foundation for installation.

[0041] Specifically, S1, safety performance evaluation of the retired wind turbine single pile foundation. Perform performance inspection and evaluation of the structural bearing capacity, corrosion resistance, etc. of the retired wind turbine single pile foundation to determine whether there is potential risk. Safety performance evaluation of the retired wind turbine single pile foundation is an important link to ensure that it does not pose potential risks to the environment and personnel after retirement. Safety performance evaluation can be performed from the following aspects: Structural integrity evaluation, including material detection: detect the strength of concrete and the degree of reinforcement corrosion to ensure that the material performance meets the requirements. Defect detection: use ultrasonic waves and other methods to detect whether the pile body has cracks, cavities and other defects.

[0042] Bearing capacity evaluation, including static load test: evaluate the vertical compression and uplift bearing capacity of the pile foundation through static load test. Soil property analysis: analyze the performance changes of the soil around the pile to evaluate its influence on the bearing capacity of the pile foundation.

[0043] Environmental impact evaluation, including corrosion evaluation: evaluate the influence of seawater corrosion on the materials of the pile foundation. Geological condition evaluation: analyze the influence of geological changes on the stability of the pile foundation, such as earthquakes, seabed changes, etc.

[0044] Fatigue performance evaluation, including long-term load analysis: evaluate the influence of long-term repeated loads on the cumulative deformation and lateral stiffness of the pile foundation. Fatigue life evaluation: evaluate the remaining life of the pile foundation according to its fatigue damage.

[0045] S2, design of the salinity difference energy utilization system. Design the salinity difference energy utilization system according to the size data of the retired wind turbine foundation, and calculate the system installed power and annual average power generation during operation.

[0046] The calculation method of power generation installed capacity is as follows: Theoretical osmotic pressure calculation: ; Δp: osmotic pressure difference (unit: Pa), representing the theoretical maximum osmotic pressure difference between seawater and freshwater, is the core driving force for water flow through the permeable membrane. R: gas constant, with a value of 8.314 mol·K, representing the macroscopic thermodynamic properties of ion diffusion in the permeation process. T: absolute temperature (unit: K), taking seawater environment temperature 20℃ (corresponding to T=293K), temperature rise will increase the ion migration rate. Csea water, Cfresh water: salt concentration (unit: g / L), one percent of salt concentration corresponds to 10 g / L.

[0047] Membrane flux calculation: ; J: membrane flux (unit: L / (m2·h)), representing the volume of freshwater passing through the membrane per unit area per unit time, directly affecting the power generation. α: membrane water permeability coefficient (unit: L / (m2·h·Pa)), reflecting the permeability of the membrane to water, taking 1.0 L / (m2·h·Pa). : non-ideal membrane influence coefficient, considering the coefficient of deviation from ideal membrane conditions, taking 0.9. Δploss: flow channel pressure loss (unit: Pa), caused by fluid friction and turbulence, which can be 5% of Δp.

[0048] System efficiency comprehensive formula: ; ηsystem: total system efficiency (dimensionless), reflecting the overall conversion ability from salinity energy to electrical energy. ηmembrane: current laboratory efficiency 38.5%, considering commercialization taking 25%. ηgenerator: turbine mechanical efficiency, adopting biomimetic spiral flow channel design to reduce turbulence loss, taking 80%. ηpotential pressure conversion: potential pressure conversion device efficiency, taking 60%.

[0049] Power generation power calculation: ; P: power generation power (unit: kW), directly determines the economic efficiency of the device. ρ: seawater density (unit: kg / m 3 ), taking 1025 kg / m 3 (20℃ seawater), salinity increase will slightly increase ρ. g: acceleration of gravity (unit: m / s 2 ), taking 9.8 m / s 2 , as a constant. H: equivalent water head (unit: m), converting osmotic pressure difference Δp into static water head, H=Δp / (ρg), such as Δp=10 kPa≈1 m water column.

[0050] ηsystem=25% x 80% x 60% = 12%.

[0051] S3, system cost and payback period calculation, evaluate the economic feasibility of the project.

[0052] The additional cost of the salt difference energy utilization system is mainly the salt difference energy conversion module, the generator, the system control module and the operation and maintenance cost. The income is the electricity generation cost, and the electricity generation after deducting the self-use electricity (about 2%) is all put on the network.

[0053] The annual average power generation capacity calculation formula is: ; E: annual average power (unit: Kw·h); t: time, 365 days a year, a total of 8760h; : self-use electricity ratio coefficient, take 2%; ηeffective: system annual effective utilization coefficient considering the influence of extreme weather, take 0.85.

[0054] S4, if the economic efficiency of the project meets the requirements, the salt difference energy utilization system device based on the retired single pile foundation can be manufactured at the shore port, and shipped to the predetermined wind turbine foundation for installation.

[0055] S5, system later operation and maintenance. The operation and maintenance of the salt difference energy utilization system can be carried out regularly by using small wind turbine operation and maintenance ships, and the remaining wind turbine foundation auxiliary structure can well meet the needs of the personnel and equipment to board.

[0056] The salt difference energy generation device is integrated into the retired single pile foundation of the offshore wind power, which has the following core advantages: (1) realize the reuse of foundation and power transmission channel, and significantly reduce the cost The internal cavity or peripheral space of the single pile foundation (diameter 6-10m) can install the salt difference energy module (such as microbial desalination unit), which can save more than 50% of the cost of independent supporting structure, shorten the investment payback period from >20 years to 10-20 years. At the same time, the transmission line and operation and maintenance platform of the previous wind farm can be shared, reducing the grid connection and operation and maintenance cost.

[0057] (2) efficient coupling of resources The single pile foundation constructed in the early stage is mostly located in the estuary and offshore area, and the salinity gradient of seawater changes greatly, which has rich salt difference energy resources. The inlet of the fresh water delivery unit is arranged near the sea surface, and the inlet of the seawater delivery unit is arranged near the seabed, which can adjust the salinity gradient difference to a better level and improve the power generation income.

[0058] (3) convenient construction and installation The modules of the salt difference energy utilization system can be designed in a modular way and prefabricated on land, and then quickly hoisted and installed after being shipped to the wind turbine foundation by ship.

[0059] Example 4: Modification of a certain retired wind farm in the East China Sea Single pile parameters: diameter 6 m, pile length 80 m, service life after retirement 23 years.

[0060] Salt difference energy conversion module configuration: Permeable membrane area A membrane = 200 m 2 Seawater salinity C seawater = 35 g / L, considering the continuous decrease of seawater chamber salinity, take 20 g / L for calculation, fresh water salinity C freshwater = 3 g / L Osmotic pressure difference Δp = 8.314 × 293 × ln(35 / 3) = 4621.4 Pa Membrane flux J = 1.0 × 0.9 × (1-5%) × 4621.4 = 3951.3 L / (m2·h); Generator power P = 12% × 4621.4 × 40 × 3951.3 ≈ 24 kW Annual average power generation E = 24 × 24 × 365 × 0.85 × (1-2%) = 17.51 million kW·h Annual income Q = 17.51 × 0.5 = 70,000 yuan Initial investment cost: salt difference energy conversion module 500,000 yuan, generator 250,000 yuan, system control module 50,000 yuan, total 800,000 yuan; Annual operation and maintenance cost 10,000 yuan / year, considering 23 years of operation period, total investment is 103 million yuan; Simple rate of return is 7 / 103 × 100% = 6.8%; Static investment recovery period is 14.71 years If the supporting structure and power transmission channel of the salt difference energy generation system are constructed separately, the investment cost increases about 1 million yuan (50%), the total cost is 2 million yuan, and the investment recovery period is 28.6 years. Therefore, the modification of the retired single pile foundation for salt difference energy utilization system has great significance for the early commercialization of salt difference energy development.

Claims

1. A marine salinity gradient energy utilization system based on the monopile foundation of a decommissioned offshore wind turbine, comprising a foundation support module, a salinity gradient energy conversion module, an energy management module, and a system control module; The basic support module is used to support the normal operation of each system and provide a maintenance platform; The salinity gradient energy conversion module is used to convert the osmotic pressure of fresh water and salt water into mechanical energy; The energy management module is used to convert mechanical energy into electrical energy and transmit it to the power grid; The system control module is used for monitoring and controlling the salinity gradient energy conversion module and the energy management module.

2. The marine salinity gradient energy utilization system based on a decommissioned offshore wind turbine monopile foundation as described in claim 1, characterized in that, The basic support module includes a decommissioned offshore wind turbine monopile foundation. The offshore wind turbine monopile foundation includes a monopile foundation body (1) fixed to the seabed. An auxiliary structure (2) is fitted on the top of the monopile foundation body (1). A hatch cover (3) matching the diameter of the monopile foundation is provided on the top of the monopile foundation body (1). An inspection and transportation hatch (4) is provided on the surface of the hatch cover (3). A supporting steel beam (18) is provided inside the monopile foundation body (1). A corbel (17) is provided at the connection between the lower part of the supporting steel beam (18) and the monopile foundation body (1). A working ladder (5) is provided between the supporting steel beam (18) and the hatch cover (3). A connecting hole (20) and a freshwater transportation unit (6) are provided on the upper part of the monopile foundation body (1). A submarine cable hole (9) and a seawater transportation unit (7) are provided on the lower part of the monopile foundation body (1).

3. The marine salinity gradient energy utilization system based on a decommissioned offshore wind turbine monopile foundation as described in claim 1, characterized in that, The salinity gradient energy conversion module includes an osmotic pressure generating device (10) located at the bottom of the supporting steel beam (18). The osmotic pressure generating device (10) includes a freshwater chamber and a seawater chamber. The freshwater chamber is connected to a freshwater delivery unit (6), and the seawater chamber is connected to a seawater delivery unit (7). The seawater chamber is connected to a water storage tank (12) through a potential pressure conversion pipe (13). The bottom of the osmotic pressure generating device (10) is provided with a bulkhead (16), a permeable membrane assembly (15) is provided between the fresh water chamber and the seawater chamber, a generator (11) connected to the fresh water chamber is provided on the upper part of the supporting steel beam (18), and a sensor is provided in the seawater chamber.

4. The marine salinity gradient energy utilization system based on a decommissioned offshore wind turbine monopile foundation as described in claim 3, characterized in that, Fresh water enters the fresh water chamber through the fresh water transport unit (6), and seawater enters the seawater chamber through the seawater transport unit (7). The permeation membrane assembly (15) only allows water molecules to pass through, thereby generating an osmotic pressure difference between the fresh water chamber and the seawater chamber, so that water molecules in the fresh water chamber will continuously enter the seawater chamber. The seawater chamber is connected to the potential pressure conversion pipe (13), so that the water body continuously rises above the sea surface through the potential pressure conversion pipe (13) and enters the water storage tank (12), converting the osmotic pressure into mechanical energy.

5. The marine salinity gradient energy utilization system based on a decommissioned offshore wind turbine monopile foundation as described in claim 3, characterized in that, The osmotic pressure generating device (10) is connected to the supporting steel beam (18) via a connecting member (21). The bulkhead (16) is located below the freshwater chamber and the seawater chamber, separating the osmotic pressure generating device (10) into an empty chamber.

6. The marine salinity gradient energy utilization system and method based on a decommissioned offshore wind turbine monopile foundation as described in claim 1, characterized in that, The energy management module includes a submarine cable (8) connected to the generator (11). The generator (11) is connected to the water tank (12) through a connecting pipe (14). Water in the water tank (12) enters the turbine chamber of the generator (11) through the connecting pipe (14), converting mechanical energy into electrical energy, which is then transmitted to the power grid by the submarine cable (8).

7. The marine salinity gradient energy utilization system and method based on a decommissioned offshore wind turbine monopile foundation as described in claim 1, characterized in that, The integrated monitoring and control device (22) of the control system module monitors and controls the salinity gradient energy conversion module and the energy management module through sensors. The integrated monitoring and control device (22) controls the salinity gradient energy conversion module and the energy management module through control rules. The sensors are installed inside the main body (1) of the single pile foundation.

8. The marine salinity gradient energy utilization system and method based on a decommissioned offshore wind turbine monopile foundation as described in claim 7, characterized in that, The control rules include: Sensors and valves are installed in the seawater transport unit. The sensors are used to monitor the salinity of the seawater chamber. When the salinity of the seawater chamber is lower than the set threshold, the valve is opened to allow the seawater to be naturally replaced. After the salinity requirement of osmotic pressure difference is met, the valve is closed so that the seawater can only rise through the potential pressure conversion pipe (13). The bottom of the water storage tank (12) is equipped with a pressure monitoring sensor. When the water pressure at the bottom of the water storage tank (12) exceeds the preset limit, an electrical signal will be sent to close the valve of the seawater delivery unit. An electrically controlled valve is installed in the connecting pipe (14). When the power grid transmits a "no power generation" signal to the control system, the control system will control the valve in the connecting pipe to close.

9. A design method for a marine salinity gradient energy utilization system based on a decommissioned offshore wind turbine monopile foundation, applicable to the system described in any one of claims 1-8, characterized in that, Includes the following steps: S1. Safety performance inspection and assessment of the single pile foundation of the decommissioned wind turbine to determine whether there are potential risks. If the risks are controllable, proceed to S2. S2. Design a salinity gradient energy utilization system based on the foundation size data of the decommissioned wind turbines, calculate the system's installed power generation capacity and average annual power generation during the operation period, and calculate the system cost and payback period to assess the economic feasibility of the project. S3. If the project's economics meet the requirements, the system equipment will be manufactured and transported by ship to the designated wind turbine foundation for installation.

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