Two-stage compression liquid gas energy storage system for offshore wind turbine

Abstract

The application discloses a two-stage compression liquid gas energy storage system of offshore wind turbine, which comprises offshore wind turbine, motor, air compressor, first clutch, generator, second clutch, first steam turbine and second steam turbine which are connected in sequence, and storage tank, second regenerator, expansion turbine, first regenerator and combustor which are connected in sequence, wherein the combustor is connected with the first steam turbine, and the second steam turbine is connected with condenser and steam generator in sequence to form a loop. The application can significantly increase the power generation, and when the low-temperature liquid air is used to produce new air, the energy storage efficiency of the system is also significantly improved compared with the traditional compressed air energy storage system.

Description

Technical Field

[0001] This invention relates to a technology in the field of offshore wind power, specifically to a two-stage compressed liquid gas energy storage system for offshore wind turbines. Background Technology

[0002] The main drawbacks of wind energy are its intermittency and the fact that its availability often doesn't align with electricity demand. Energy storage systems can provide stable and predictable power by storing excess energy and releasing it when demand exceeds supply. Compressed air energy storage uses compressed air to store energy for later use. Excess energy generated by wind renewable energy can be stored using this technology. Traditional compressed air energy storage systems can effectively store unused energy, but large-scale applications suffer from significant heat loss because compressed air generates heat, resulting in energy loss. Furthermore, traditional compressed air energy storage systems require large storage chambers (deep underground caves, etc.), are greatly limited by geographical location, and have low energy density. Summary of the Invention

[0003] This invention addresses the shortcomings of existing single-stage compression technology, which directly compresses air to 4MPa and sends it to the regenerator, resulting in low compression efficiency and incompatibility with existing power plant systems. It proposes a two-stage compressed liquid gas energy storage system for offshore wind turbines, which can significantly increase power generation. When the cryogenic liquid air is used to produce fresh air, the energy storage efficiency of this system is also significantly higher than that of traditional compressed air energy storage systems.

[0004] This invention is achieved through the following technical solution:

[0005] This invention relates to a two-stage compressed liquid gas energy storage system for offshore wind turbines, comprising: an offshore wind turbine, a motor, an air compressor, a first clutch, a generator, a second clutch, a first steam turbine, and a second steam turbine connected in sequence, and a storage tank, a second regenerator, an expansion turbine, a first regenerator, and a burner connected in sequence, wherein: the burner is connected to the first steam turbine, and the second steam turbine is connected in sequence to a condenser and a steam generator to form a loop.

[0006] The first and second regenerators are further connected via a cryogenic air compressor.

[0007] The storage tank is further connected to the second regenerator via an expansion valve.

[0008] The air compressor and the first regenerator are further connected by a throttle valve.

[0009] The regenerator is composed of several regular hexagonal steel tube units, with no gap between adjacent regular hexagonal steel tube units, thereby significantly reducing the volume of the entire cold storage regenerator.

[0010] This invention relates to an energy storage method based on the above system, wherein compressed air is cooled to near the liquefaction temperature by a cold storage regenerator, and after being throttled to the ambient pressure, part of the air is liquefied through the throttling effect and stored in a storage tank in liquid form. The remaining air returns to the cold storage regenerator to release its cold energy and is then discharged into the outside atmosphere. At the same time, a blower stabilizes the pressure in the cold storage regenerator.

[0011] The stored liquid air is pressurized by a cryogenic pump and then released into the cold storage regenerator before entering the combustion chamber to release energy. Technical effect

[0012] This invention employs a two-stage process flow. The air pressure fed into and returned from the regenerator is adjusted to meet the conditions of existing combined cycle gas turbines and steam turbines. Existing compressors compress air to 1.3 MPa, cool it to near its liquefaction temperature in the primary regenerator, and then pressurize it to above supercritical pressure by a cryogenic compressor. Compared to existing technologies, the power required to produce liquid air in this invention decreases as the inlet temperature decreases. At atmospheric pressure, the density of liquid air is approximately 10.6 times that of compressed air at 70 bar at room temperature. If compressed air is stored at constant pressure, the volume of a liquid air storage tank is only 0.009 times that of an 80 bar compressed air storage tank for the same mass of air. Furthermore, traditional compressed air energy storage systems leave residual compressed air in the storage tank after energy release, while liquid air has a constant density. Therefore, liquid air requires a smaller storage tank compared to compressed air. Overall, this invention has a higher energy density. Attached Figure Description

[0013] Figure 1 This is a structural diagram of the present invention;

[0014] Figure 2 This is a partial horizontal cross-sectional view of the regenerator.

[0015] In the diagram: 1. Offshore wind turbine; 2. Motor; 3. Air compressor; 4. Clutch; 5. Generator; 6. Clutch; 7. Steam turbine; 8. Steam generator; 9. Steam turbine; 10. Pump; 11. Condenser; 12. Burner; 13. Regenerator; 14. Blower; 15. Cryogenic air compressor; 16. Expansion turbine; 17. Regenerator; 18. Pump; 19. Expansion valve; 20. Storage tank; 21. Throttling valve; 22. Throttling valve. Detailed Implementation

[0016] like Figure 1As shown, this embodiment relates to a two-stage compressed liquid gas energy storage system for offshore wind turbines, comprising: an offshore wind turbine 1, a motor 2, an air compressor 3, a first clutch 4, a generator 5, a second clutch 6, a first steam turbine 7, and a second steam turbine 9 connected in sequence; and a storage tank 20, a pump 18, a second regenerator 17, an expansion turbine 16, a first regenerator 13, and a burner 12 connected in sequence, wherein: the burner 12 is connected to the first steam turbine 7, and the second steam turbine 9 is connected in sequence to a condenser 11 and a steam generator 8 to form a loop.

[0017] The first regenerator 13 and the second regenerator 17 are further connected by a cryogenic air compressor 15.

[0018] The storage tank 20 is further connected to the second regenerator 17 via an expansion valve 19.

[0019] The air compressor 3 and the first regenerator 13 are further connected by a throttle valve 21.

[0020] like Figure 2 As shown, the regenerator is composed of several regular hexagonal steel pipe units with no gap between adjacent steel pipe units, thereby significantly reducing the volume of the entire cold storage regenerator; the steel pipe units are filled with heat storage medium, and compressed air effectively exchanges heat by directly contacting the medium.

[0021] The heat storage medium may be, but is not limited to, granular pebbles.

[0022] Since the density of liquid air is approximately 10.6 times that of compressed air at 70 bar at room temperature, the energy storage volume in this embodiment, including the regenerator, is approximately 1 / 20 of that of a traditional compressed air energy storage system.

[0023] This embodiment relates to an energy storage method for the above-mentioned device, including: 1) normal operation mode, 2) energy storage mode and 3) energy recovery mode.

[0024] The normal operating mode refers to the following: generator 5 is connected to compressor 3 and gas turbine 7 respectively, compressed air is delivered to gas turbine 7, the motor of compressor 3 drives generator 5 to generate electricity; the motor of gas turbine 7 drives generator 5 to generate electricity.

[0025] The energy storage mode described refers to the following: At night or on holidays, generator 5 is configured via the first clutch 4 to operate at constant power only with the offshore wind turbine connected to compressor 3. Excess electricity generated is used to compress air at night, which is then cooled to near its liquefaction temperature by regenerators 13 and 17. The cooled compressed air expands to atmospheric pressure, and most of it liquefies under the Joule-Thomson effect. The liquefied air is stored at atmospheric pressure in storage tank 20. The gaseous portion of the expanded air is returned to regenerators 13 and 17. After the cold energy is stored in regenerators 13 and 17, the air is released into the environment. A blower is installed downstream of regenerator 13 to compensate for the pressure drop in regenerator 13.

[0026] The energy recovery mode refers to the following: when peak power demand increases, generator 5 is configured to connect only to gas turbine 7 via second clutch 6. Liquid air stored in storage tank 20 is pumped to high pressure and heated by pump 18, simultaneously providing cooling to the regenerator. The operating conditions of burner 12, gas turbine 7, and steam turbine 9 are the same as in normal operating mode. The power required for the operation of liquid-gas pump 18 is approximately 4% of the power consumed by the air compressor in normal operating mode, equivalent to 51% to 62% of the gas turbine's power generation. Therefore, this operating mode generates approximately twice the power of the normal operating mode.

[0027] like Figure 1 As shown, if air is compressed to 4 MPa and fed into the regenerator, it would be difficult to integrate this system into an existing power plant, as the output pressure of a typical compressor in a power plant is less than 1.5 MPa. Furthermore, compressing air to supercritical pressure without intercooling requires a large amount of compression power. Since the compressor outlet temperature increases with pressure, high-temperature resistant materials are needed to withstand the higher temperatures. The air pressures fed into and returned from the regenerator are adjusted to meet the conditions of existing gas turbine and steam turbine combined cycle systems. The existing compressor 3 compresses air to 1.3 MPa, cools it to near its liquefaction temperature in the primary regenerator 13, and then pressurizes it above supercritical pressure by the cryogenic compressor 15. The power required to produce liquid air is reduced because the power required to compress the gas decreases with decreasing inlet temperature. The compressed air expands to atmospheric pressure after being cooled by the second regenerator 17. The liquefied air is stored in the storage tank 20, and the cryogenic gaseous air is returned to regenerators 17 and 13.

[0028] When liquid air is pumped to pressures above supercritical pressure, the pressure exceeds the burner's operating pressure. Therefore, an expansion turbine 16 is installed between regenerators 17 and 13 to recover energy and reduce pressure. In energy recovery mode, the expansion turbine 16 increases power generation. During the two-stage process, the air temperature rises, requiring more cooling due to the operation of the cryogenic compressor 15. The expansion turbine 16 lowers the air temperature, and the resulting cryogenic air compensates for the insufficient cooling.

[0029] By pumping liquid air to a position higher than the output pressure of the cryogenic compressor 15, the power recovery rate of the expansion turbine 16 can be improved and the air temperature can be reduced, thereby promoting the recovery of cold energy in the regenerator.

[0030] Through practical experiments, this system utilizes off-peak electricity from offshore wind turbines to produce liquid air at night, and during the day, the stored liquid air is pumped to high pressure and fed into the combustor of the gas turbine. When the cooling capacity of the liquid air is reused to produce new liquid air, the energy storage efficiency is more than doubled. When the temperature of the expansion valve is below 102K, MATLAB simulations show that the energy storage efficiency of this system can exceed that of a typical pumped-storage hydroelectric power station.

[0031] In this embodiment, the energy storage efficiency reaches 74%, and the compressor power decreases as the output pressure drops from 4.0 MPa to 1.25 MPa. Furthermore, the power recovery rate increases with the addition of the expansion turbine 16. The advantage of this two-stage process is that, due to the reduction of the compressor's compression ratio to 31% of the basic system, the compressor outlet temperature drops significantly from 860 K to 618 K. Therefore, the materials for the compressor or regenerator can be easily selected.

[0032] This two-stage process can be easily integrated with existing gas turbine and steam turbine combined systems. If the supercritical air temperature at the inlet of expansion valve 19 is below 102K, the energy storage efficiency will exceed 74%. A typical pumped-storage hydropower station has an energy storage efficiency of 70%, and the system in this embodiment can exceed the energy storage efficiency of a typical pumped-storage hydropower station by 4%.

[0033] This embodiment generates more than twice the power of a conventional gas turbine system. The system produces liquid air at night using off-peak electricity from offshore wind turbines, and during the day, the stored liquid air is pumped to high pressure and fed into the gas turbine's burner. When the cold energy of the liquid air is reused to produce new liquid air, the energy storage efficiency is more than doubled. When the temperature of expansion valve 19 is below 102K and 23K higher than the temperature of the stored liquid air, MATLAB simulations show that the system's energy storage efficiency exceeds that of a typical pumped-storage hydroelectric power station.

[0034] This embodiment employs methods such as depressurization to liquefy the air. The liquefaction coefficient (the proportion of liquefied air to the air entering the liquefaction device) is crucial in this system because air is the working fluid; unliquefied air will dissipate some of the compressed work. Therefore, the liquefaction coefficient should be maximized. The performance of the cold storage regenerator significantly impacts the liquefaction coefficient; it needs to effectively recover the cold energy of the liquid air and effectively cool the compressed air. Traditional cold storage regenerators are generally large, resulting in a situation where the liquefaction tank is reduced in size, but the regenerator itself increases in size. This negatively impacts the economics and engineering cost of the energy storage system. The cold storage regenerator in this embodiment overcomes a bottleneck in liquid air energy storage technology.

[0035] The above-described specific implementations can be partially adjusted by those skilled in the art in different ways without departing from the principles and purpose of the present invention. The scope of protection of the present invention is defined by the claims and is not limited to the above-described specific implementations. All implementation schemes within the scope of the claims are bound by the present invention.

Claims

1. An application of a two-stage compressed liquid gas energy storage system based on an offshore wind turbine, characterized in that, The two-stage compressed liquid gas energy storage system includes: an offshore wind turbine, a motor, an air compressor, a first clutch, a generator, a second clutch, a first steam turbine, and a second steam turbine connected in sequence, as well as a storage tank, a second regenerator, an expansion turbine, a first regenerator, and a burner connected in sequence, wherein: the burner is connected to the first steam turbine, and the second steam turbine is connected in sequence to a condenser and a steam generator to form a loop; The first regenerator and the second regenerator are further connected by a cryogenic air compressor. The storage tank and the second regenerator are also connected via an expansion valve; The air compressor and the first regenerator are also connected via a throttle valve; The regenerator is composed of several regular hexagonal steel tube units with no gap between adjacent regular hexagonal steel tube units, thereby significantly reducing the volume of the entire cold storage regenerator; the steel tube units are filled with heat storage medium, and compressed air effectively exchanges heat by directly contacting the medium; the heat storage medium is granular pebbles. The applications mentioned refer to energy storage methods including: 1) normal operation mode, 2) energy storage mode and 3) energy recovery mode; The normal operating mode refers to the following: the generator is connected to both the compressor and the gas turbine; compressed air is delivered to the gas turbine; the compressor motor drives the generator to generate electricity; and the gas turbine motor drives the generator to generate electricity. The energy storage mode refers to the following: at night or on holidays, the generator is set to be connected only to the compressor via the first clutch. The excess electricity generated by the offshore wind turbine, which operates at a constant power, is used to compress air at night. The compressed air is then cooled to near the liquefaction temperature by the regenerator. The cooled compressed air expands to atmospheric pressure and most of it liquefies under the Joule-Thomson effect. The liquefied air is stored in the air tank at atmospheric pressure. The gaseous part of the expanded air is sent back to the regenerator. After the cold energy is stored in the regenerator, the air is released into the environment. A blower is installed downstream of the regenerator to compensate for the pressure drop in the regenerator. The energy recovery mode refers to the following: when peak power demand increases, the generator is set to connect only to the gas turbine via the second clutch, the liquid air stored in the gas tank is pumped to high pressure and heated, and at the same time provides cooling to the regenerator. The operating conditions of the burner, gas turbine and steam turbine are the same as in the normal operating mode. An expansion turbine is provided between the first and second regenerators to recover energy and reduce pressure. In energy recovery mode, the expansion turbine can increase power generation. During the two-stage process, the air temperature rises. Due to the operation of the cryogenic compressor, more cooling is required. The expansion turbine lowers the air temperature, and the generated cryogenic air makes up for the lack of cooling. By pumping liquid air to a position higher than the output pressure of the cryogenic compressor, the power recovery rate of the expansion turbine can be improved and the air temperature can be reduced, thereby promoting the recovery of cooling capacity by the regenerator.

Images