A liquid air energy storage system based on frequent start-stop

Abstract

The present application relates to a liquid air energy storage system based on frequent start-stop, comprising an air purification unit, an air pressurization unit matched with a cold source, a heat exchange unit, a circulating cold preservation unit, an air liquefaction storage unit and a power generation unit coupled with a heat source. The air pressurization unit matched with the cold source comprises an air compressor and a first heat exchanger communicated with the compressor inlet. The heat exchange unit matched with the cold source mainly comprises a cold box heat exchanger. The circulating cold preservation unit mainly comprises a cold storage device. The air liquefaction storage unit comprises a throttle valve and a liquid air storage tank. The power generation unit coupled with the heat source comprises a cryogenic pump, an expander and a second heat exchanger communicated with the expander inlet. The system contains four working substances, namely the cold source, air, nitrogen and the heat source. Through the above equipment and the circulating work of the working substances, the continuous operation of the liquid air energy storage system can be realized, the practical problems such as long pre-cooling time and large cold source consumption can be solved, and the liquid air energy storage project can be promoted.

Description

Technical Field

[0001] This invention relates to a liquid air energy storage system based on frequent start-stop cycles, belonging to the field of liquid air energy storage. Background Technology

[0002] Large-scale energy storage technology is an important means to improve the peak-shaving capacity of the power grid. Cryogenic liquefied air storage utilizes inexpensive off-peak electricity to absorb air from the environment, cool it until it becomes liquid, and then store it in storage tanks at a low temperature of -196°C. During peak electricity demand, the liquid air is released from the tanks, pressurized and heated, and used to drive a steam turbine to generate electricity, thus realizing peak-shaving utilization of off-peak electricity.

[0003] Existing energy storage systems consist of energy storage units and power generation units. During periods of low electricity demand, the energy storage unit uses the cold energy from a cold source to pressurize and cool purified air into liquid air, which is then stored in a liquid air storage tank. The equipment involved includes compressors, heat exchangers, cold boxes, throttle valves, separators, and liquid air storage tanks, etc., storing surplus electricity through efficient utilization of the cold energy from the cold source. During periods of high electricity demand, the power generation unit uses liquid air to expand and generate electricity. The equipment involved includes cryogenic pumps, expanders, heat exchangers, etc., thereby achieving integration with grid peak shaving.

[0004] Existing energy storage systems have the following problems: the cold box cannot operate continuously, and there is a need for reheating during the discharge phase and re-precooling during the energy storage phase. For conditions that require frequent start-stop operation, there are problems such as long precooling time and large cold source consumption, which cannot meet the requirements. Summary of the Invention

[0005] To address the aforementioned problems, the purpose of this invention is to provide a liquid air energy storage system based on frequent start-stop cycles, including a liquid air energy storage system with the participation of a cold source. This solution enables continuous operation of the liquid air energy storage system, thereby solving the problem of reheating during the discharge phase and re-precooling during the energy storage phase when the cold box cannot operate continuously. The implementation of this solution can save a significant amount of operating costs such as manpower and materials, while improving the safety and reliability of the system and increasing the feasibility of its engineering implementation.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] This invention provides a liquid air energy storage system based on frequent start-stop cycles, comprising:

[0008] Cold source piping, air piping, and heat source piping;

[0009] The system comprises an air purification unit, an air pressurization unit, a heat exchange unit, a liquefaction storage unit, a cryogenic pump, and a power generation unit. The air pressurization unit is coupled to a cold source, and the power generation unit is coupled to a heat source. The air pipeline sequentially connects the air purification unit, air pressurization unit, heat exchange unit, liquefaction storage unit, cryogenic pump, and power generation unit. The cold source pipeline is connected to the heat exchange unit, through which the cold source enters the heat exchange unit to exchange heat with the air. The air after heat exchange condenses into liquid air and enters the liquid storage unit for storage. The heat source pipeline is connected to the power generation unit, through which the heat source enters the power generation unit to exchange heat with the liquid air. The liquid air after heat exchange releases energy to generate electricity.

[0010] A circulating cold insulation unit includes a cold storage device and a cold insulation circulation pipeline. The cold storage device and the heat exchange unit form a closed loop through the cold insulation circulation pipeline. A cold insulation medium circulates within the circulating cold insulation unit.

[0011] Furthermore, the air pressurization unit includes a first heat exchanger and an air compressor, which are connected in sequence through the air pipeline. The cold source pipeline is connected in sequence to the heat exchange unit and the first heat exchanger, and the cold source flows through the heat exchange unit and the first heat exchanger to exchange heat with the air.

[0012] Furthermore, the power generation unit includes a second heat exchanger and an expander, which are connected in sequence through the air pipeline. The heat source enters the second heat exchanger through the heat source pipeline to exchange heat with the liquid air.

[0013] Furthermore, the cold insulation medium is nitrogen gas, which enters the heat exchange unit from the cold storage unit through the cold insulation circulation pipeline for heat exchange or cold insulation, and then flows back into the cold storage unit.

[0014] Furthermore, the circulating cold insulation unit is configured to have unidirectional or bidirectional flow. In the bidirectional flow, the nitrogen gas flows in the same direction as air in the heat exchange unit during the energy storage stage, and flows in the opposite direction to the energy storage stage during the energy release stage. In the unidirectional flow, the nitrogen gas flows in the same direction as air.

[0015] Furthermore, the air booster unit comprises multiple sets, which are connected in series via the air pipeline.

[0016] Furthermore, the heat exchange unit and the circulating cold insulation unit include multiple sets, each set of heat exchange units corresponds to a set of circulating cold insulation units, and the multiple sets of heat exchange units are connected in series through the air pipeline.

[0017] Furthermore, the power generation unit comprises multiple sets, which are connected in series via the air duct.

[0018] Furthermore, the number of the power generation units is the same as the number of the air booster units.

[0019] Furthermore, the liquefied storage unit includes a throttle valve and a liquid air storage tank, which are connected in sequence.

[0020] The present invention has the following advantages due to the adoption of the above technical solutions:

[0021] The liquid air energy storage system based on frequent start-stop operation in this invention includes a cold-insulating circulation pipeline. During the energy storage phase, the cold-insulating medium and high-pressure air enter the heat exchange unit together to exchange heat with the cold source in the heat exchange unit. The cold-insulating medium and air jointly absorb the cold energy from the cold source and store the cold energy in the cold storage device in the circulating cold-insulating unit. During the energy release phase, the flow rate of the cold-insulating medium is adjusted according to the reheating situation of the heat exchange unit, and the cold energy stored in the cold storage device is exchanged to the heat exchange unit, realizing the cold-insulating circulation. Therefore, for operating conditions that require frequent start-stop operation, there is no need for reheating during the discharge phase and re-precooling during the energy storage phase, which reduces the cold source consumption, reduces the precooling time, and improves the energy storage efficiency. Attached Figure Description

[0022] Various other advantages and benefits will become apparent to those skilled in the art upon reading the following detailed description of preferred embodiments. The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. Throughout the drawings, the same reference numerals denote the same parts.

[0023] In the attached diagram:

[0024] Figure 1 This is a schematic diagram of an embodiment of a liquid air energy storage system based on frequent start-stop cycles;

[0025] The markings in the attached diagram are as follows:

[0026] 1-Air purification unit, 2-First heat exchanger, 3-Air compressor, 4-Heat exchange unit, 5-Energy storage device, 6-Throttle valve, 7-Liquid air storage tank, 8-Cryogenic pump, 9-Second heat exchanger, 10-Expander, 11-Circulating cold insulation unit, 100-Cold source pipeline, 200-Heat source pipeline, 300-Air pipeline, 400-Cold insulation circulation pipeline. Detailed Implementation

[0027] Exemplary embodiments of the invention will now be described in more detail with reference to the accompanying drawings. While exemplary embodiments of the invention are shown in the drawings, it should be understood that the invention can be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided to enable a more thorough understanding of the invention and to fully convey the scope of the invention to those skilled in the art.

[0028] This invention provides a liquid air energy storage system based on frequent start-stop operation, including an air purification unit, an air pressurization unit working with a cold source, a heat exchange unit working with a cold source, a circulating cold preservation unit, an air liquefaction storage unit, and a power generation unit coupled with a heat source. The air pressurization unit working with the cold source includes an air compressor and a first heat exchanger connected to the compressor inlet. The heat exchange unit mainly consists of a cold box heat exchanger. The circulating cold preservation unit mainly consists of a cold storage device. The air liquefaction storage unit includes a throttling valve and a liquid air storage tank. The power generation unit coupled with the heat source includes a cryogenic pump, an expander, and a second heat exchanger connected to the expander inlet. This system contains four working fluids: a cold source, air, nitrogen, and a heat source. Through the cyclical operation of the above equipment and working fluids, continuous operation of the liquid air energy storage system can be achieved, solving practical problems such as long pre-cooling time and large cold source consumption, and promoting the implementation of liquid air energy storage projects.

[0029] like Figure 1 As shown, an embodiment of the present invention provides a liquid air energy storage system based on frequent start-stop operation, including a cold source pipeline 100, an air pipeline 300, a heat source pipeline 200, an air purification unit 1, an air pressurization unit, a heat exchange unit 4, a liquefaction storage unit, a cryogenic pump 8, a power generation unit, and a circulating cold insulation unit 11. The air pressurization unit is coupled to the cold source, and the power generation unit is coupled to the heat source. The air pipeline 300 sequentially connects the air purification unit 1, the air pressurization unit, the heat exchange unit, the liquefaction storage unit, the cryogenic pump 8, and the power generation unit. The cold source pipeline 100 is connected to the heat exchange unit 4. The cold source enters the heat exchange unit 4 through the cold source pipeline 100 to exchange heat with the air. The air after heat exchange condenses into liquid air and enters the liquid storage unit for storage. The heat exchange unit 4 mainly consists of a cold box heat exchanger. The heat source pipeline 200 is connected to the power generation unit. The heat source enters the power generation unit through the heat source pipeline 200 and exchanges heat with the liquid air. The liquid air releases energy to generate electricity after heat exchange. The circulating cold insulation unit 11 includes a cold storage device 5 and a cold insulation circulation pipeline 400. The cold storage device 5 and the heat exchange unit 4 form a closed loop through the cold insulation circulation pipeline 400. The circulating cold insulation unit 11 circulates a cold insulation medium. The working fluids involved in the system are air, a cold source, nitrogen, and a heat source.

[0030] During the energy storage phase, air enters the system through purification unit 1, is pressurized to over 3 MPa by air pressurization unit, and then enters heat exchange unit 4 to exchange heat with the cold source, lowering the temperature to approximately -180°C. After being throttled and depressurized by liquefaction storage unit, it becomes atmospheric pressure liquid air and is stored in liquid air storage tank 7. The cold source enters the system through heat exchange unit 4, exchanges heat with high-pressure air, and then heats up, achieving efficient utilization of cold energy. During the energy storage phase, the insulation medium and high-pressure air enter heat exchange unit 4 together to exchange heat with the cold source within heat exchange unit 4. The insulation medium and air jointly absorb the cold energy from the cold source and store it in the cold storage device 5 in the circulating insulation unit 11. During the energy storage phase, the power generation unit is in a shut-off state, and the working fluid heat source does not enter the system.

[0031] During the energy release phase, liquid air is pumped out by cryogenic pump 8, increasing its pressure to over 10 MPa, and enters the power generation unit to expand and perform work, outputting electrical energy. The heat source enters the system from the power generation unit and exchanges heat with the high-pressure liquid air, thereby improving the working efficiency of the power generation unit. Since no other media pollute the process, it can be directly discharged into the sea without causing environmental pollution. The flow rate of the cold insulation medium is adjusted according to the rewarming status of the heat exchange unit 4, exchanging the cold energy stored in the cold storage device 5 to the heat exchange, realizing the cold insulation cycle. During the energy release phase, the air purification unit 1 and the air pressurization unit are in the off state, and the working fluid air and cold source do not enter the system.

[0032] The liquid air energy storage system based on frequent start-stop operation in this invention includes a cold-insulating circulation pipeline. During the energy storage phase, the cold-insulating medium and high-pressure air enter the heat exchange unit 4 together to exchange heat with the cold source in the heat exchange unit 4. The cold-insulating medium and air jointly absorb the cold energy from the cold source and store the cold energy in the cold storage device 5 in the circulating cold-insulating unit 11. During the energy release phase, the flow rate of the cold-insulating medium is adjusted according to the reheating situation of the heat exchange unit 4, and the cold energy stored in the cold storage device 5 is exchanged to the heat exchange unit 4, realizing the cold-insulating circulation. Therefore, for operating conditions that require frequent start-stop operation, there is no need for reheating during the discharge phase and re-precooling during the energy storage phase, which reduces the cold source consumption, reduces the precooling time, and improves the energy storage efficiency.

[0033] The air pressurization unit includes a first heat exchanger 2 and an air compressor 3, which are connected sequentially via an air pipeline 300. A cold source pipeline 100 connects sequentially to the heat exchange unit 4 and the first heat exchanger 2. The cold source flows through the heat exchange unit 4 and the first heat exchanger 2 to exchange heat with the air. The cold source enters the system through the cold box heat exchanger 4, exchanges heat with high-pressure air and circulating nitrogen, and then enters the first heat exchanger 2 at the inlet of the air compressor 3 to exchange heat with purified air, thereby improving the efficiency of the air compressor 3.

[0034] The power generation unit includes a second heat exchanger 9 and an expander 10, which are sequentially connected via an air pipe 300. A heat source enters the second heat exchanger 9 through the heat source pipe 200 to exchange heat with liquid air. The heat source enters the system through the inlet heat exchanger 9 of the expander 10, where it exchanges heat with high-pressure liquid air, thereby improving the operating efficiency of the expander 10. Since no other media contaminate the process, the heat source can be directly discharged into the sea without causing environmental pollution.

[0035] The preferred cold-insulating medium is nitrogen. The nitrogen enters the heat exchange unit 4 from the cold storage accumulator 5 through the cold-insulating circulation pipeline 400 for heat exchange or cold insulation, and then flows back to the cold storage accumulator 5.

[0036] Furthermore, the circulating cold insulation unit 11 is configured to have unidirectional or bidirectional flow. The bidirectional flow means that during the energy storage stage, the flow direction of nitrogen in the heat exchange unit 4 is the same as that of air, and during the energy release stage, the flow direction of nitrogen is opposite to that of the energy storage stage. The unidirectional flow means that the flow direction of nitrogen is the same as that of air.

[0037] When unidirectional flow is set, the flow direction of nitrogen in the cold box heat exchanger 4 is the same as that of high-pressure air; when bidirectional flow is set, the flow direction of nitrogen in the cold box heat exchanger 4 during the energy storage stage is the same as that of high-pressure air, while the flow direction of nitrogen is reversed during the energy release stage to improve the cold preservation efficiency.

[0038] The air booster unit may include multiple sets, which are connected in series through the air pipeline, preferably no more than four sets.

[0039] The heat exchange unit 4 and the circulating cold insulation unit 11 may include multiple groups, with each group of heat exchange units corresponding to a group of circulating cold insulation units 11. The multiple groups of heat exchange units are connected in series through the air pipeline, preferably no more than 3 groups.

[0040] The power generation unit comprises multiple sets, which are connected in series via the air duct 300, preferably no more than four sets.

[0041] Preferably, the number of the power generation units is the same as the number of the air booster units.

[0042] The working principle of the liquid air energy storage system based on frequent start-stop operation includes:

[0043] During the energy storage phase, air enters the system through purification unit 1, exchanges heat with the cold source through the first heat exchanger 2, and then enters the air compressor 3. After compression, the pressure increases to over 3 MPa, and then enters the cold box heat exchanger 4, where it exchanges heat with the cold source and nitrogen, reducing the temperature to approximately -180°C. After being throttled and depressurized by the throttling valve 6, it becomes atmospheric pressure liquid air and is stored in the liquid air storage tank 7. The cold source enters the system through the cold box heat exchanger 4, exchanges heat with the high-pressure air and circulating nitrogen, and then enters the first heat exchanger 2 at the compressor inlet, where it exchanges heat with the purified air, thereby improving the efficiency of the air compressor 3. After passing through 2, the cold source is heated, achieving efficient utilization of cold energy. Nitrogen and air jointly absorb the cold energy from the cold source and store it in the cold storage device 5 in the nitrogen circulation unit. During the energy storage phase, the cryogenic pump 8, the expander inlet heat exchanger 9, and the expander 10 are in a shut-off state, and the working fluid heat source does not enter the system.

[0044] During the energy release phase, liquid air is pumped out by cryogenic pump 8, increasing its pressure to over 10 MPa, and enters the second heat exchanger 9 to exchange heat with the heat source and increase its temperature. Then it enters the expander 10 to expand and do work, outputting electrical energy. The heat source enters the system through the expander inlet heat exchanger 9 and exchanges heat with the high-pressure liquid air, thereby improving the working efficiency of the expander 10. Since there is no pollution from other media during the process, it can be directly discharged into the sea without causing environmental pollution. The nitrogen flow rate is adjusted according to the retemperature of the cold box heat exchanger 4, exchanging the cold energy stored in the cold storage device 5 into 4 to achieve the cold preservation cycle of 4. During the energy release phase, the air purification unit 1, the compressor inlet heat exchanger 2, and the air compressor 3 are in the off state, and the working fluid air and cold source do not enter the system.

[0045] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A liquid air energy storage system based on frequent start-stop operation, characterized in that, include: Cold source piping, air piping, and heat source piping; The system comprises an air purification unit, an air pressurization unit, a heat exchange unit, a liquefaction storage unit, a cryogenic pump, and a power generation unit. The air pressurization unit is coupled to a cold source, and the power generation unit is coupled to a heat source. The air pipeline sequentially connects the air purification unit, air pressurization unit, heat exchange unit, liquefaction storage unit, cryogenic pump, and power generation unit. The cold source pipeline is connected to the heat exchange unit, through which the cold source enters the heat exchange unit to exchange heat with the air. The air after heat exchange condenses into liquid air and enters the liquefaction storage unit for storage. The heat source pipeline is connected to the power generation unit, through which the heat source enters the power generation unit to exchange heat with the liquid air. The liquid air after heat exchange releases energy to generate electricity. A circulating cold insulation unit includes a cold storage device and a cold insulation circulation pipeline. The cold storage device and the heat exchange unit form a closed loop through the cold insulation circulation pipeline. A cold insulation medium circulates within the circulating cold insulation unit. The cold insulation medium is nitrogen gas. The nitrogen gas enters the heat exchange unit from the cold storage device through the cold insulation circulation pipeline for heat exchange or cold insulation, and then flows back to the cold storage device. The circulating cold insulation unit is configured to have unidirectional or bidirectional flow. In the bidirectional flow, the nitrogen flows in the heat exchange unit in the same direction as the air during the energy storage stage and in the opposite direction to the energy storage stage during the energy release stage. In the unidirectional flow, the nitrogen flows in the same direction as the air. The system comprises four working fluids: a cold source, air, nitrogen, and a heat source. During the energy storage phase, nitrogen and air enter the heat exchange unit together to exchange heat with the cold source within the unit. The nitrogen and air jointly absorb the cold energy from the cold source and store it in the cold storage device. Meanwhile, the power generation unit is in a shut-off state, and the working fluid and heat source do not enter the system. During the energy release phase, the nitrogen flow rate is adjusted according to the retemperature of the heat exchange unit, exchanging the stored cold energy in the cold storage device to the heat exchange unit to achieve a cold-keeping cycle. Meanwhile, the air purification unit and air pressurization unit are in a shut-off state, and the working fluids air and the cold source do not enter the system.

2. The liquid air energy storage system based on frequent start-stop as described in claim 1, characterized in that, The air pressurization unit includes a first heat exchanger and an air compressor. The first heat exchanger and the air compressor are connected in sequence through the air pipeline. The cold source pipeline is connected in sequence to the heat exchange unit and the first heat exchanger. The cold source flows through the heat exchange unit and the first heat exchanger to exchange heat with the air.

3. The liquid air energy storage system based on frequent start-stop as described in claim 1, characterized in that, The power generation unit includes a second heat exchanger and an expander. The second heat exchanger and the expander are connected in sequence through the air pipeline. The heat source enters the second heat exchanger through the heat source pipeline to exchange heat with the liquid air.

4. The liquid air energy storage system based on frequent start-stop as described in claim 2, characterized in that, The air booster unit comprises multiple sets, which are connected in series via the air pipeline.

5. The liquid air energy storage system based on frequent start-stop as described in claim 1, characterized in that, The heat exchange unit and the circulating cold insulation unit include multiple sets, each set of heat exchange units corresponds to a set of circulating cold insulation units, and the multiple sets of heat exchange units are connected in series through the air pipeline.

6. The liquid air energy storage system based on frequent start-stop as described in claim 3, characterized in that, The power generation unit comprises multiple sets, which are connected in series via the air duct.

7. The liquid air energy storage system based on frequent start-stop as described in claim 6, characterized in that, The number of power generation units is the same as the number of air booster units.

8. The liquid air energy storage system based on frequent start-stop as described in claim 6, characterized in that, The liquefied storage unit includes a throttle valve and a liquid air storage tank, which are connected in sequence.

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