Liquid air energy storage system coupled with air separation device

Abstract

The invention relates to the technical field of energy storage, and provides a liquid air energy storage system coupled with an air separation device, which comprises an air compression system, an expansion power generation system, a cold box cold storage system and a liquid air storage tank. The air compression system and the expansion power generation system are both connected with the cold box cold storage system and the liquid air storage tank. The cold box cold storage system is coupled with the air separation device; in the energy storage stage, extra liquid nitrogen produced by the air separation device is used for cooling and liquefying the high-pressure air passing through the cold box, and the liquid nitrogen is gasified and stored in a medium-pressure nitrogen tank; and in the energy release stage, the nitrogen stored in the medium-pressure nitrogen tank reheats the liquid air passing through the cold box, and the nitrogen is cooled and liquefied by the liquid air for use. The cold box cold storage system is coupled with the air separation device to replace an original cold storage unit of the liquid air energy storage system to achieve the energy storage and release process, a cold storage medium does not need to be arranged for the liquid air energy storage system, the purchase cost of the cold storage medium is reduced, and safe operation of the liquid air energy storage system is facilitated.

Description

Technical Field

[0001] The present invention relates to the field of energy storage technology, and in particular to a liquid air energy storage system coupled with an air separation device. Background Art

[0002] Liquid air energy storage is a clean, low-carbon, safe and long-life large-scale long-term energy storage technology. It can compress air into high-pressure air during low-power consumption periods, cool and liquefy it through a cold box, and then convert it into liquid air for normal pressure storage through expansion throttling. During the air compression stage, high-pressure water is used to cool the high-temperature air between stages, and the generated high-temperature hot water is stored in a storage tank. During peak power consumption periods, liquid air is pressurized and sent to the cold box through a low-temperature centrifugal pump to provide cold capacity for the cold storage medium to prepare for cooling the air in the next energy storage stage. In this process, the liquid air is reheated and vaporized, and after being heated by the high-temperature hot water stored in the compression stage, it enters the expansion unit to expand and generate electricity. The high-temperature hot water heats the air and then cools it down. The cooled hot water is then converted into normal-temperature water through heat exchange in the air cooler. The normal-temperature water is stored for interstage air cooling in the next energy storage stage compression stage. In traditional solutions, the cold energy required for the energy storage stage comes from the reheating and vaporization process of liquid air in the energy release stage, and a cold storage medium is required to transfer the cold energy of the energy release stage to the energy storage stage across time scales.

[0003] The air separation unit is an energy-intensive production unit that mainly consumes electricity to produce large-scale industrial gases such as oxygen and nitrogen. The traditional cryogenic air separation system needs to provide cooling for the air separation system in the form of high-pressure expansion, which consumes a lot of electricity in the process. At present, the demand for use of air separation units in major industries such as metallurgy and chemical industry has declined, that is, the demand for industrial gas on the user side is intermittent and cyclical. Since the air separation system needs to operate continuously, it is difficult to quickly adjust and respond to meet user needs in real time. When the air separation system is in a low-load state, the efficiency is low, and the operating cost of the air separation system increases.

[0004] At present, the cold storage medium used in the liquid air energy storage system coupled with the air separation device includes liquid cold storage medium and solid cold storage medium. The liquid cold storage medium has the characteristics of combustion and explosion, which is not conducive to the safe operation of the energy storage system; while the solid cold storage medium is used in large quantities, which is not conducive to the expansion of the energy storage system. It is difficult for the air separation device to quickly adjust the operation process according to the user's usage needs, resulting in an increase in the operating cost of the air separation system. For this reason, the present invention provides a liquid air energy storage system coupled with the air separation device. Summary of the invention

[0005] The present invention provides a liquid air energy storage system coupled with an air separation device to solve the above technical defects in the prior art. The cold box cold storage system is coupled with the air separation device to replace the original cold storage unit of the liquid air energy storage system to realize the energy storage and energy release process. There is no need to set a liquid phase cold storage medium or a solid phase cold storage medium for the liquid air energy storage system, which can reduce the procurement cost of the cold storage medium, which is not only conducive to the safe operation of the liquid air energy storage system, but also conducive to the expansion of application scenarios of the liquid air energy storage system coupled with the air separation device. At the same time, it can ensure the smooth operation of the air separation device and reduce the operating cost of the air separation system.

[0006] The present invention provides a liquid air energy storage system coupled with an air separation device, comprising a liquid air storage tank, an air compression system, an expansion power generation system and a cold box cold storage system.

[0007] The air compression system is connected to the inlet of the cold box cold storage system, and is used to compress the air to high pressure and store the heat generated during the compression process in the form of hot water in the hot water tank; The expansion power generation system is connected to the outlet of the cold box cold storage system, and is used to heat the reheated liquid air with the hot water stored in the hot water tank to perform expansion power generation; The cold box cold storage system is coupled to the air separation unit, and the cold box cold storage system includes a medium-pressure nitrogen tank. In the energy storage stage, the high-pressure air passing through the cold box is cooled and liquefied by the additional liquid nitrogen produced by the air separation unit, and the liquid nitrogen in the air separation unit is gasified to be stored in the medium-pressure nitrogen tank; in the energy release stage, the nitrogen stored in the medium-pressure nitrogen tank is reheated by the liquid air of the cold box, and the nitrogen is liquefied for use.

[0008] According to the liquid air energy storage system coupled to an air separation unit provided by the present invention, the cold box cold storage system comprises a first cold box heat exchanger and a second cold box heat exchanger; The first cold box heat exchanger is connected to the outlet of the liquid nitrogen storage tank of the air separation unit and the inlet of the medium-pressure nitrogen tank, and the high-pressure air at the outlet of the air compression system is cooled and liquefied through the first cold box heat exchanger; The second cold box heat exchanger is connected to the outlet of the medium-pressure nitrogen tank and the liquid nitrogen transportation equipment, and the nitrogen stored in the medium-pressure nitrogen tank will be reheated by the liquid air of the second cold box heat exchanger.

[0009] According to the liquid air energy storage system coupled to the air separation unit provided by the present invention, the first cold box heat exchanger is also connected to the backflow air outlet of the liquid-to-air-liquid separator, so as to reverse the air separated by the liquid-to-air-liquid separator to the first cold box heat exchanger, so as to supplement the cooling capacity of the first cold box heat exchanger.

[0010] According to the liquid air energy storage system of the coupled air separation device provided by the present invention, the liquid air cooled by the first cold box heat exchanger is expanded by the liquid expander and throttled by the low-temperature throttle valve, and enters the liquid-air-liquid separator in the form of gas-liquid two-phase flow, and the gaseous air separated by the liquid-air-liquid separator flows back to the first cold box heat exchanger, and the liquid air separated by the liquid-air-liquid separator is stored in the liquid-air storage tank.

[0011] According to the liquid air energy storage system coupled with an air separation unit provided by the present invention, the cold box cold storage system further includes a nitrogen compressor, a nitrogen throttle valve and a liquid nitrogen pump; The liquid nitrogen pump is connected to the pipeline between the liquid nitrogen storage tank and the first cold box heat exchanger, and is used to pressurize the liquid nitrogen in the liquid nitrogen storage tank and send it into the first cold box heat exchanger; The nitrogen compressor is connected to the pipeline between the medium-pressure nitrogen tank and the second cold box heat exchanger, and is used for secondary pressurizing the nitrogen discharged from the medium-pressure nitrogen tank; The nitrogen throttle valve is connected to the pipeline between the second cold box heat exchanger and the liquid nitrogen transportation equipment, and is used to throttle the high-pressure liquid nitrogen liquefied by the second cold box heat exchanger to a low pressure.

[0012] According to the liquid air energy storage system coupled with an air separation unit provided by the present invention, the cold box cold storage system further comprises a liquid nitrogen gas-liquid separator, the liquid nitrogen gas-liquid separator is arranged on the pipeline between the nitrogen throttle valve and the liquid nitrogen transportation equipment, and the liquid outlet of the liquid nitrogen gas-liquid separator is respectively connected to the liquid nitrogen storage tank or the liquid nitrogen transportation equipment; The reflux gas outlet of the liquid nitrogen gas-liquid separator is connected to the second cold box heat exchanger, and is used to reflux the nitrogen separated by the liquid nitrogen gas-liquid separator to the second cold box heat exchanger, so as to supplement the cooling capacity of the second cold box heat exchanger.

[0013] The liquid air energy storage system coupled with an air separation device provided by the present invention further comprises an air cooler, a cold water tank, a cold water pump and a hot water pump, wherein the hot water tank, the hot water pump, the air cooler, the cold water tank and the cold water pump constitute a heat storage unit; The heat generated by the air compression system during the air compression process is taken away by the high-pressure cold water discharged by the cold water pump to form high-pressure and high-temperature hot water which is stored in the hot water tank; The liquid air that has been restored to room temperature enters the expansion power generation system, is heated by the high-pressure hot water stored in the hot water tank, and expands to output shaft work to drive the generator to generate electricity and transmit it to the power grid.

[0014] According to the liquid air energy storage system coupled with an air separation device provided by the present invention, the air compression system includes an air filter, a molecular sieve purifier and a multi-stage air compressor unit; The multi-stage air compressor unit comprises a multi-stage air compressor and inter-stage coolers corresponding to the number of the air compressors, wherein the inter-stage coolers are connected to the outlet ends of the corresponding air compressors; The inlet end of the molecular sieve purifier is connected to the outlet end of the interstage cooler, and the outlet end of the molecular sieve purifier is connected to the inlet end of the lower-stage air compressor.

[0015] According to the liquid air energy storage system coupled to an air separation unit provided by the present invention, the expansion power generation system includes a plurality of groups of air expanders and heaters corresponding to the number of the air expanders; the first-stage heater is connected to the cold box cold storage system.

[0016] The liquid air energy storage system coupled with the air separation unit provided by the present invention is achieved by coupling the cold box cold storage system with the air separation unit; in the energy storage stage, the high-pressure air passing through the cold box is cooled and liquefied by the additional liquid nitrogen produced by the air separation unit, and the liquid nitrogen is gasified and stored in a medium-pressure nitrogen tank; in the energy release stage, the nitrogen stored in the medium-pressure nitrogen tank of the cold box cold storage system rewarms the liquid air passing through the cold box into high-pressure gaseous air, and the nitrogen is cooled and liquefied by the liquid air for use. In this arrangement, the cold box cold storage system is coupled with the air separation unit to replace the original cold storage unit of the liquid air energy storage system to realize the energy storage and energy release process, and there is no need to set up an additional liquid phase cold storage medium or solid phase cold storage medium for the liquid air energy storage system, which can reduce the procurement and storage costs of the cold storage medium, which is not only beneficial to the safe operation of the liquid air energy storage system, but also beneficial to the expansion of the application scenarios of the liquid air energy storage system. At the same time, the smooth operation of the air separation unit can be guaranteed and the operating cost of the air separation system can be reduced.

[0017] In other words, the embodiment of the present invention can simultaneously solve the problem of using the cold storage medium in the liquid air energy storage system by coupling the liquid nitrogen storage tank of the air separation unit to the cold box cold storage system in the liquid air energy storage system, and can also solve the problem that it is difficult for the air separation unit to quickly adjust the operation process according to the user's usage requirements, resulting in an increase in the operating cost of the air separation system. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In order to more clearly illustrate the technical solutions in the present invention or the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0019] Figure 1 It is a system block diagram of a liquid air energy storage system coupled to an air separation device provided in an embodiment of the present invention.

[0020] Figure 2It is a system block diagram of a cold box cold storage system in a liquid air energy storage system coupled to an air separation device provided in an embodiment of the present invention.

[0021] Figure 3 It is a system block diagram of another embodiment of a cold box cold storage system in a liquid air energy storage system coupled to an air separation device provided in an embodiment of the present invention.

[0022] Reference numerals: 100. Air compression system; 1. Air filter; 2. First-stage air compressor; 3. First-stage interstage cooler; 4. Molecular sieve purifier; 5. Second-stage air compressor; 6. Second-stage interstage cooler; 7. Third-stage air compressor; 8. Third-stage interstage cooler; 9. Cold box; 10. Liquid expander; 11. Low-temperature throttle valve; 12. Liquid-air liquid separator; 13. Liquid-air storage tank; 14. Liquid-air pump; 200, expansion power generation system; 15, primary heater; 16, primary air expander; 17, secondary heater; 18, secondary air expander; 19, tertiary heater; 20, tertiary air expander; 21, tertiary heater; 22, tertiary air expander; 23, hot water tank; 24, hot water pump; 25, cold water pump; 26, cold water tank; 27, air cooler; 28. First cold box heat exchanger; 29. ​​Liquid nitrogen pump; 30. Medium-pressure nitrogen tank; 31. Nitrogen compressor; 32. Second cold box heat exchanger; 33. Liquid nitrogen throttle valve; 34. Liquid nitrogen gas-liquid separator. DETAILED DESCRIPTION

[0023] In order to make the purpose, technical solution and advantages of the present invention clearer, the technical solution of the present invention will be clearly and completely described below in conjunction with the drawings of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0024] In the description of the embodiments of the present application, it should be noted that, unless otherwise clearly specified and limited, the terms "connected" and "connection" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be directly connected or indirectly connected through an intermediate medium. For ordinary technicians in this field, the specific meanings of the above terms in the embodiments of the present application can be understood according to specific circumstances.

[0025] In the embodiments of the present application, unless otherwise clearly specified and limited, a first feature being "above" or "below" a second feature may mean that the first and second features are in direct contact, or the first and second features are in indirect contact through an intermediate medium. Moreover, a first feature being "above", "above" or "above" a second feature may mean that the first feature is directly above or obliquely above the second feature, or simply means that the first feature is higher in level than the second feature. A first feature being "below", "below" or "below" a second feature may mean that the first feature is directly below or obliquely below the second feature, or simply means that the first feature is lower in level than the second feature.

[0026] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the embodiments of the present application. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine the different embodiments or examples described in this specification and the features of the different embodiments or examples, without contradiction.

[0027] Air separation refers to the use of related equipment and technology to separate nitrogen, oxygen and other rare gases from the air to meet the needs of various gases in industries such as metallurgy, coal chemical industry, petroleum refining, and aviation. Traditional cryogenic air separation systems need to provide cooling capacity for the air separation system in the form of high-pressure expansion. A large amount of electricity is consumed in this process. At present, major industries such as metallurgy and chemical industry that use air separation units are generally facing production cuts and shutdowns, which means that the demand for industrial gas on the user side is intermittent and cyclical. Since the air separation system needs to operate continuously, it is difficult to quickly adjust and respond to meet real-time needs, resulting in a "supply and demand contradiction" during the operation of the air separation system. When the air separation system is in a low-load state, the efficiency is low, and the operating cost of the air separation system increases.

[0028] In the current liquid air energy storage system, the cold box cold storage system is usually provided with cold energy by liquid cold storage medium and solid cold storage medium. When using liquid cold storage medium to provide cold energy, it is often necessary to arrange two or more cold storage units in the cold box, and recover or transfer the cold energy of liquid air in sections. The liquid cold storage medium used on the deep cooling side is generally a natural hydrocarbon, which has the characteristics of being flammable and explosive, and is not conducive to the safe operation of the energy storage system. When using solid cold storage medium to provide cold energy, solid particles such as basalt and glass are generally used as cold storage medium. The air liquefaction or gasification process directly contacts the cold medium for heat exchange or transfers cold energy in the form of indirect heat exchange with intermediate gas. Although this method can avoid the use of liquid cold storage medium, it is conducive to the safe operation of the energy storage system. However, the particles of the solid cold storage medium have a small specific heat and there is an axial heat conduction problem. After multiple energy storage or energy release processes, the development of the thermocline layer will destroy the cold storage temperature gradient. In addition, the cold box cold storage unit occupies a large area and has a high maintenance cost. To this end, the present invention provides a liquid air energy storage system coupled with an air separation device.

[0029] Figure 1 It is a system block diagram of a liquid air energy storage system coupled with an air separation device provided in an embodiment of the present invention. Figure 2 It is a system block diagram of a cold box cold storage system in a liquid air energy storage system coupled to an air separation unit provided in an embodiment of the present invention.

[0030] See also Figure 1 and Figure 2 An embodiment of the present invention provides a liquid air energy storage system coupled to an air separation device, wherein the liquid air energy storage system coupled to the air separation device includes a liquid air storage tank 13, an air compression system 100, an expansion power generation system 200, and a cold box cold storage system.

[0031] The air compression system 100 uses cheap electricity during off-peak hours to compress air to high pressure through a compressor unit. High-pressure water is used for inter-stage cooling of the compressor unit, and the heat generated by the air compression is stored in the hot water tank 23 in the form of hot water.

[0032] Among them, the air compression system 100 includes an air filter 1, a molecular sieve purifier 4 and a multi-stage air compressor group; along the flow path of the air, the air filter 1, the molecular sieve purifier 4 and the multi-stage air compressor group are arranged in sequence, and the molecular sieve purifier 4 is located between two adjacent stages of air compressors.

[0033] The air filter 1 is used to filter the air entering the air compression system 100 to remove impurities such as dust in the ambient air.

[0034] The molecular sieve purifier 4 is used to remove moisture, CO2 and other hydrocarbons from the air. During the air compression process of the liquid air energy storage system coupled with the air separation unit, the molecular sieve purifier 4 is required to remove moisture, CO2 and other hydrocarbons from the air to prevent them from solidifying in the low temperature environment of the cold box 9 and blocking the heat exchange channel of the cold box 9.

[0035] The multi-stage air compressor unit includes a multi-stage air compressor and an interstage cooler arranged between the air compressors, and the interstage cooler is connected to the outlet end of the corresponding air compressor; the inlet end of the molecular sieve purifier 4 is connected to the outlet end of the interstage cooler, and the outlet end of the molecular sieve purifier 4 is connected to the inlet end of the lower-stage air compressor.

[0036] For example, a three-stage air compressor unit is used in the embodiment of the present invention, that is, the air compression system 100 includes a primary air compressor 2, a secondary air compressor 5 and a tertiary air compressor 7. Accordingly, a primary interstage cooler 3 is connected between the primary air compressor 2 and the secondary air compressor 5, a secondary interstage cooler 6 is connected between the secondary air compressor 5 and the tertiary air compressor 7, and a tertiary interstage cooler 8 is connected between the tertiary air compressor 7 and the cold box 9. Of course, the embodiment of the present invention can also be provided with a four-stage air compressor unit or more according to the use requirements.

[0037] The expansion power generation system 200 is connected to the outlet of the cold box cold storage system, and is used to heat the reheated liquid air with hot water stored in the hot water tank 23 to perform expansion power generation. That is, the expansion power generation system 200 pressurizes the liquid air and sends it to the cold box cold storage system through the liquid air pump 14, reheats the liquid air that has passed through the cold box 9 into high-pressure gaseous air, and enters the expander for expansion power generation after being heated by the high-temperature hot water stored in the compression stage. The high-temperature hot water heats the air and then cools it down. The cooled hot water then changes to normal-temperature water after heat exchange in the air cooler. The normal-temperature water is stored for cooling the high-temperature compressed air.

[0038] The expansion power generation system 200 includes a plurality of air expanders and heaters located between the air expanders; the first-stage heater is connected to the cold box cold storage system.

[0039] For example, a four-stage air expander is used in the embodiment of the present invention, that is, the expansion power generation system 200 includes a primary air expander 16, a secondary air expander 18, a tertiary air expander 20 and a quaternary air expander 22. Accordingly, a primary heater 15 is connected between the cold box 9 and the primary air expander 16, a secondary heater 17 is connected between the primary air expander 16 and the secondary air expander 18, a tertiary heater 19 is connected between the secondary air expander 18 and the tertiary air expander 20, and a quaternary heater 21 is connected between the tertiary air expander 20 and the quaternary air expander 22. Of course, the embodiment of the present invention can also be provided with five or more stages of air expanders according to the use requirements.

[0040] The cold box 9 includes a shell and a cold box cold storage system arranged in the shell. The cold box cold storage system is coupled to the air separation unit. The cold box cold storage system includes a medium-pressure nitrogen tank 30. In the energy storage stage, the high-pressure air passing through the cold box 9 is cooled and liquefied by the additional liquid nitrogen produced by the air separation unit, and the liquid nitrogen in the air separation unit is gasified to be stored in the medium-pressure nitrogen tank 30; in the energy release stage, the nitrogen stored in the medium-pressure nitrogen tank 30 is reheated by the liquid air of the cold box 9, and at the same time, the nitrogen stored in the medium-pressure nitrogen tank 30 is liquefied for use.

[0041] The coupling between the cold box cold storage system and the air separation unit can be understood as the cold box cold storage system and the air separation unit being matched or connected, so that there is a connection between the cold storage system and the air separation unit. The air separation unit is a full liquid air separation unit.

[0042] It can be understood that the liquid air energy storage system coupled with the air separation unit provided in the embodiment of the present invention couples the cold box cold storage system with the air separation unit. In the energy release stage, the high-pressure air passing through the cold box 9 is cooled to a low-temperature liquefied state by using the additional liquid nitrogen produced by the air separation unit, and the liquid nitrogen in the air separation unit is gasified to be stored in the medium-pressure nitrogen tank 30; in the energy release stage, the cold box cold storage system rewarms the liquid air passing through the cold box 9 into high-pressure gaseous air, and at the same time, the nitrogen stored in the medium-pressure nitrogen tank 30 is liquefied for use. In this way, the cold box cold storage system is coupled with the air separation unit to replace the original cold storage unit of the liquid air energy storage system to realize the energy storage and energy release process. There is no need to set a liquid phase cold storage medium or a solid phase cold storage medium for the liquid air energy storage system, which can reduce the procurement cost of the cold storage medium, which is not only conducive to the safe operation of the liquid air energy storage system, but also can ensure the smooth operation of the air separation unit and reduce the operating cost of the air separation system.

[0043] In other words, the embodiment of the present invention can simultaneously solve the problem of using the cold storage medium in the liquid air energy storage system by coupling the liquid nitrogen storage tank of the air separation unit to the cold box cold storage system in the liquid air energy storage system, and can also solve the problem that it is difficult for the air separation unit to quickly adjust the operation process according to the user's usage requirements, resulting in an increase in the operating cost of the air separation system.

[0044] Due to the loss in the energy transmission process and the quality damage during the heat transfer process, the current air separation unit operates smoothly for 24 hours, but the downstream user demand is intermittent. Therefore, in order to ensure the smooth operation of the air separation unit and realize the storage of cold storage working fluid, the air separation unit is coupled with the cold storage system of the present invention, which can ensure the smooth operation of the air separation unit and reduce the operating cost of the air separation system.

[0045] Continue reading Figure 2 In some embodiments of the present invention, the cold box cold storage system includes a first cold box heat exchanger 28 and a second cold box heat exchanger 32. The first cold box heat exchanger 28 is connected to the outlet of the liquid nitrogen storage tank of the air separation unit and the inlet of the medium-pressure nitrogen tank 30. The high-pressure air at the outlet of the air compression system 100 is cooled and liquefied through the first cold box heat exchanger 28. The second cold box heat exchanger 32 is connected to the outlet of the medium-pressure nitrogen tank 30 and the liquid nitrogen transportation equipment. The nitrogen stored in the medium-pressure nitrogen tank 30 will be reheated by the liquid air of the second cold box heat exchanger 32.

[0046] When it is necessary to cool the high-pressure air passing through the cold box 9 into liquid air, liquid nitrogen is pressurized from the liquid nitrogen storage tank of the air separation unit into the first cold box heat exchanger 28 to cool the high-pressure air to low temperature and liquefy it. At the same time, the liquid nitrogen is vaporized and warmed to room temperature and stored in the medium-pressure nitrogen tank 30. This process is equivalent to the cold release stage of the liquid nitrogen cold storage system.

[0047] When it is necessary to reheat the liquid air passing through the cold box 9 into high-pressure gaseous air, the nitrogen stored in the medium-pressure nitrogen tank 30 is pressurized and enters the second cold box heat exchanger 32 to absorb the cold of the liquid air and liquefy, and then throttles to medium pressure and transports to the liquid nitrogen transportation equipment, which can be a tank truck storage tank. This process is equivalent to the cold storage stage of the liquid nitrogen cold storage system.

[0048] Continue reading Figure 1 In some embodiments of the present invention, the first cold box heat exchanger 28 is also connected to the reverse flow air outlet of the liquid-to-air-liquid separator 12, so as to reverse the air separated by the liquid-to-air-liquid separator 12 to the first cold box heat exchanger 28, so as to supplement the cooling capacity of the first cold box heat exchanger 28.

[0049] The liquid air cooled by the cold box 9 is expanded by the liquid expander 10 and throttled by the low-temperature throttle valve 11, and enters the liquid-air-liquid separator 12 in the form of gas-liquid two-phase flow. The gaseous air separated by the liquid-air-liquid separator 12 flows back to the first cold box heat exchanger 28 to supplement the cooling capacity for the air liquefaction process. The liquid air separated by the liquid-air-liquid separator 12 enters the liquid-air storage tank 13 for storage, completing the energy storage process of the liquid air energy storage system coupled to the air separation device. The first cold box heat exchanger 28 is also connected to the outside air, and is used to discharge the gas of the first cold box heat exchanger 28 to the ambient air.

[0050] Continue reading Figure 2 In some embodiments of the present invention, the cold box cold storage system also includes a nitrogen compressor 31, a nitrogen throttle valve 33 and a liquid nitrogen pump 29.

[0051] The liquid nitrogen pump 29 is connected to the pipeline between the liquid nitrogen storage tank and the first cold box heat exchanger 28 , and is used to pressurize the liquid nitrogen in the liquid nitrogen storage tank and send it to the first cold box heat exchanger 28 .

[0052] The nitrogen compressor 31 is connected to the pipeline between the medium-pressure nitrogen tank 30 and the second cold box heat exchanger 32 and is used for secondary pressurizing the nitrogen in the medium-pressure nitrogen tank 30 .

[0053] The nitrogen throttle valve 33 is connected to the pipeline between the second cold box heat exchanger 32 and the liquid nitrogen transportation equipment, and is used to throttle the high-pressure liquid nitrogen liquefied by the second cold box heat exchanger 32 to a low pressure.

[0054] Figure 3 It is a system block diagram of another embodiment of a cold box cold storage system in a liquid air energy storage system coupled to an air separation device provided in an embodiment of the present invention.

[0055] See also Figure 3 In some embodiments of the present invention, the cold storage system further includes a liquid nitrogen gas-liquid separator 34, which is arranged on the pipeline between the nitrogen throttle valve 33 and the liquid nitrogen transportation equipment, and the reflux port of the liquid nitrogen gas-liquid separator 34 is connected to the second cold box heat exchanger 32, and the liquid outlet of the liquid nitrogen gas-liquid separator 34 is respectively connected to the liquid nitrogen storage tank and the liquid nitrogen transportation equipment.

[0056] The liquid nitrogen cooled by the second cold box heat exchanger 32 has a lower pressure after being throttled by the liquid nitrogen throttle valve 33, and the nitrogen separated by the liquid nitrogen gas-liquid separator 34 flows back to the second cold box heat exchanger 32 to supplement the cooling capacity of the second cold box heat exchanger 32 to improve the liquefaction rate of the nitrogen. The liquid nitrogen separated by the liquid nitrogen gas-liquid separator 34 enters the liquid nitrogen storage tank and the liquid nitrogen transportation equipment.

[0057] The cold box cold storage system provided in the embodiment of the present invention is basically the same as the above-mentioned embodiment, mainly in that the pressure of liquid nitrogen is lower after throttling by the liquid nitrogen throttling valve 33, and the gas-liquid mixture produced by throttling is separated into gas and liquid by the liquid nitrogen gas-liquid separator 34, and the separated nitrogen flows back to the second cold box heat exchanger 32 to supplement the cold capacity of the second cold box heat exchanger 32, so as to improve the liquefaction rate of nitrogen and make the liquid nitrogen cold energy quality higher, and the separated liquid nitrogen can be directly returned to the liquid nitrogen storage tank or enter the tank truck storage tank.

[0058] For air separation units that require higher quality of liquid nitrogen cold energy or have lower pressure in tank trucks for transporting liquid nitrogen, it is necessary to reduce the pressure after the throttle valve to produce atmospheric pressure liquid nitrogen. Since the cold energy quality of liquid air is lower than that of atmospheric pressure liquid nitrogen, the nitrogen is not enough to be completely liquefied. The nitrogen after the throttle valve is in a gas-liquid two-phase state. Adding a gas-liquid separation process can achieve gas-liquid separation.

[0059] Continue reading Figure 1 In some embodiments of the present invention, the liquid air energy storage system coupled with the air separation unit further includes an air cooler 27, a cold water tank 26, a cold water pump 25 and a hot water pump 24, and the hot water tank 23, the hot water pump 24, the air cooler 27, the cold water tank 26 and the cold water pump 25 constitute a heat storage unit.

[0060] The heat generated by the air compression system 100 during the air compression process is taken away by the high-pressure cold water discharged by the cold water pump 25 to form high-pressure and high-temperature hot water which is stored in the hot water tank 23; The liquid air that has been restored to room temperature enters the expansion power generation system 200, is heated by the high-pressure hot water stored in the hot water tank 23, and expands to output shaft work to the outside, driving the generator to generate electricity and transmit it to the power grid.

[0061] It should be noted that the first cold box heat exchanger 28 and the second cold box heat exchanger 32 can be one or a combination of shell and tube structure, plate-fin structure, coiled tube structure, etc.

[0062] The medium-pressure nitrogen tank 30 may be in the form of a mother-and-child tank, a spherical tank, etc. The pressure of the nitrogen stored in the medium-pressure nitrogen tank 30 may be 0.6-3.0 MPa.

[0063] See also Figure 1 and Figure 2 The operation process of the liquid air energy storage system coupled with the air separation device provided by the present invention is as follows: In the energy storage stage of the liquid air energy storage system coupled with the air separation unit, the external ambient air passes through the air filter 1 to remove dust and impurities, and then enters the multi-stage air compressor unit to be compressed to high pressure. The heat generated by the air compression system 100 during the air compression process is taken away by the high-pressure cold water discharged by the cold water pump 25, forming high-pressure and high-temperature hot water stored in the hot water tank 23, that is, recovering the compression heat.

[0064] The purified air enters the first-stage air compressor 2 for pressurization and temperature increase, and enters the molecular sieve purifier 4 for purification after being cooled by the first-stage interstage cooler 3. The purified air enters the second-stage air compressor 5 for pressurization and temperature increase, and enters the final-stage air compressor, i.e., the third-stage air compressor 7 for pressurization and temperature increase, and enters the cold box 9 after being cooled by the third-stage interstage cooler 8. The high-pressure air is cooled to low-temperature liquefaction through the cold box 9, i.e., the cold box cold storage system uses the additional liquid nitrogen produced by the air separation unit to cool and liquefy the high-pressure air passing through the cold box 9, and gasifies the liquid nitrogen in the air separation unit to be stored in the medium-pressure nitrogen tank 30. The low-temperature liquefied air is expanded by the liquid expander 10 and throttled by the low-temperature throttle valve 11, and enters the liquid-air-liquid separator 12 in the form of gas-liquid two-phase flow, wherein the gaseous air separated by the liquid-air-liquid separator 12 flows back to the first cold box heat exchanger 28 to supplement the cooling capacity for the air liquefaction process; the liquid air separated by the liquid-air-liquid separator 12 enters the liquid-air storage tank 13 for storage, completing the energy storage process of the liquid air energy storage system coupled to the air separation unit.

[0065] In this process, the electricity source for air compressors at each stage is renewable energy electricity or grid off-peak electricity. That is, when the liquid air energy storage system coupled with the air separation unit is located near a new energy power station, it can be directly connected to the grid from the new energy power station, with lower electricity costs.

[0066] In the energy release stage of the liquid air energy storage system coupled with the air separation unit, the liquid air in the liquid air storage tank 13 is increased to high pressure by the liquid air pump 14, and is vaporized and superheated to room temperature by absorbing heat through the cold box 9, that is, the nitrogen stored in the medium-pressure nitrogen tank 30 will be reheated by the liquid air in the cold box 9, and at the same time, the nitrogen stored in the medium-pressure nitrogen tank 30 is liquefied for use. Normal temperature air enters the air expansion unit and is heated to high temperature by the high-pressure hot water stored in the hot water tank 23. The air expands and outputs shaft work to the outside, driving the generator to generate electricity and transmit it to the power grid, completing the energy release process of the liquid air energy storage system coupled with the air separation unit.

[0067] During the energy storage and release stages of the liquid air energy storage system coupled to the air separation unit, the air separation unit can complete the storage and external transportation of liquid nitrogen. During the storage and external transportation of liquid nitrogen, it can provide cold storage for the liquid air energy storage system coupled to the air separation unit, so that the liquid air energy storage system coupled to the air separation unit no longer needs to be equipped with liquid or solid cold storage media, which greatly reduces the procurement cost of cold storage media and improves the safety of the liquid air energy storage system coupled to the air separation unit.

[0068] In this process, since the quality of liquid air cooling energy is lower than that of liquid nitrogen cooling energy at normal pressure, the quality of liquid nitrogen cooling energy delivered by the air separation unit is lower than the initial state and the temperature is higher.

[0069] The present invention provides a liquid air energy storage system coupled to an air separation unit, in which a cold storage system is coupled to a liquid nitrogen storage tank of the air separation unit, and liquid nitrogen is used to replace the original cold storage medium liquefied air of the liquid air energy storage system coupled to the air separation unit. The air separation unit stores nitrogen in a medium-pressure form, which can reduce the amount of electricity consumed in the secondary compression process of nitrogen, thereby reducing the operating cost of the air separation unit. The extra liquid nitrogen generated by the all-liquid air separation unit due to the "supply and demand contradiction" is used as a refrigerant to liquefy the air; and the cold capacity of the liquid air is used to liquefy the generated nitrogen. The supply of liquid gas to the air separation unit is guaranteed, and at the same time, the liquid air expands to do work, which can supply electricity to the air compressor unit and the booster unit of the air separation unit during peak electricity consumption.

[0070] In the embodiment of the present invention, the liquid air energy storage system coupled to the air separation unit is only coupled to the on-site liquid nitrogen storage tank and does not affect the operation process of the original air separation unit. Therefore, the present invention can be applied to the equipment of the existing air separation unit for flexible transformation, and can expand the promotion scenarios of the liquid air energy storage system coupled to the air separation unit, and improve the economy of the liquid air energy storage system coupled to the air separation unit.

[0071] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A liquid air energy storage system coupled with an air separation unit, characterized in that: It includes air compression system, expansion power generation system, cold box cold storage system and liquid air storage tank; The air compression system is connected to the inlet of the cold box cold storage system, and is used to compress the air to high pressure and store the heat generated during the compression process in the form of hot water in the hot water tank; The expansion power generation system is connected to the outlet of the cold box cold storage system, and is used to heat the reheated liquid air with the hot water stored in the hot water tank to perform expansion power generation; The cold box cold storage system is coupled to the air separation unit, and the cold box cold storage system includes a medium-pressure nitrogen tank. In the energy storage stage, the high-pressure air passing through the cold box is cooled and liquefied by the additional liquid nitrogen produced by the air separation unit, and the liquid nitrogen in the air separation unit is gasified to be stored in the medium-pressure nitrogen tank; in the energy release stage, the nitrogen stored in the medium-pressure nitrogen tank is reheated by the liquid air of the cold box, and the nitrogen is liquefied for use.

2. The liquid air energy storage system coupled to an air separation unit according to claim 1, characterized in that: The cold box cold storage system comprises a first cold box heat exchanger and a second cold box heat exchanger; The first cold box heat exchanger is connected to the outlet of the liquid nitrogen storage tank of the air separation unit and the inlet of the medium-pressure nitrogen tank, and the high-pressure air at the outlet of the air compression system is cooled and liquefied through the first cold box heat exchanger; The second cold box heat exchanger is connected to the outlet of the medium-pressure nitrogen tank and the liquid nitrogen transportation equipment, and the nitrogen stored in the medium-pressure nitrogen tank will be reheated by the liquid air of the second cold box heat exchanger.

3. The liquid air energy storage system coupled with an air separation unit according to claim 2, characterized in that: The first cold box heat exchanger is also connected to the reverse flow air outlet of the liquid-to-air-liquid separator, and is used to reverse the air separated by the liquid-to-air-liquid separator to the first cold box heat exchanger, so as to supplement the cooling capacity of the first cold box heat exchanger.

4. The liquid air energy storage system coupled to an air separation unit according to claim 3, characterized in that: The liquid air cooled by the first cold box heat exchanger is expanded by the liquid expander and throttled by the low-temperature throttle valve, and enters the liquid-to-air-liquid separator in the form of gas-liquid two-phase flow. The gaseous air separated by the liquid-to-air-liquid separator flows back to the first cold box heat exchanger, and the liquid air separated by the liquid-to-air-liquid separator is stored in the liquid-to-air storage tank.

5. The liquid air energy storage system coupled with an air separation unit according to claim 2, characterized in that: The cold box cold storage system also includes a nitrogen compressor, a nitrogen throttle valve and a liquid nitrogen pump; The liquid nitrogen pump is connected to the pipeline between the liquid nitrogen storage tank and the first cold box heat exchanger, and is used to pressurize the liquid nitrogen in the liquid nitrogen storage tank and send it into the first cold box heat exchanger; The nitrogen compressor is connected to the pipeline between the medium-pressure nitrogen tank and the second cold box heat exchanger, and is used for secondary pressurizing the nitrogen discharged from the medium-pressure nitrogen tank; The nitrogen throttle valve is connected to the pipeline between the second cold box heat exchanger and the liquid nitrogen transportation equipment, and is used to throttle the high-pressure liquid nitrogen liquefied by the second cold box heat exchanger to a low pressure.

6. The liquid air energy storage system coupled with an air separation unit according to claim 5, characterized in that: The cold box cold storage system also includes a liquid nitrogen gas-liquid separator, which is arranged on the pipeline between the nitrogen throttle valve and the liquid nitrogen transportation equipment, and the liquid outlet of the liquid nitrogen gas-liquid separator is respectively connected to the liquid nitrogen storage tank or the liquid nitrogen transportation equipment; The reflux gas outlet of the liquid nitrogen gas-liquid separator is connected to the second cold box heat exchanger, and is used to reflux the nitrogen separated by the liquid nitrogen gas-liquid separator to the second cold box heat exchanger, so as to supplement the cooling capacity of the second cold box heat exchanger.

7. The liquid air energy storage system coupled to an air separation unit according to any one of claims 1 to 6, characterized in that: It also includes an air cooler, a cold water tank, a cold water pump and a hot water pump, wherein the hot water tank, the hot water pump, the air cooler, the cold water tank and the cold water pump constitute a heat storage unit; The heat generated by the air compression system during the air compression process is taken away by the high-pressure cold water discharged by the cold water pump to form high-pressure and high-temperature hot water which is stored in the hot water tank; The liquid air that has been restored to room temperature enters the expansion power generation system, is heated by the high-pressure hot water stored in the hot water tank, and expands to output shaft work to drive the generator to generate electricity and transmit it to the power grid.

8. The liquid air energy storage system coupled with an air separation unit according to claim 7, characterized in that: The air compression system includes an air filter, a molecular sieve purifier and a multi-stage air compressor unit; The multi-stage air compressor unit comprises a multi-stage air compressor and inter-stage coolers corresponding to the number of the air compressors, wherein the inter-stage coolers are connected to the outlet ends of the corresponding air compressors; The inlet end of the molecular sieve purifier is connected to the outlet end of the interstage cooler, and the outlet end of the molecular sieve purifier is connected to the inlet end of the air compressor of the next stage.

9. The liquid air energy storage system coupled with an air separation unit according to claim 7, characterized in that: The expansion power generation system includes a plurality of groups of air expanders and heaters corresponding to the number of the air expanders; the first-stage heater is connected to the cold box cold storage system.

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