Air separation system and method based on liquid air energy storage

Abstract

The invention discloses an air separation system and method based on liquid air energy storage, and belongs to the technical field of air separation.The air separation system comprises an air pretreatment unit, an air rectification unit and a liquid air energy storage unit, and the air pretreatment unit is connected with the air rectification unit and the liquid air energy storage unit; the output end of the liquid air energy storage unit is connected with the input end of the air pretreatment unit to form an air liquefaction circulation loop, an air power generation circulation loop and an air separation circulation loop; by sharing the air pretreatment unit, the system has a peak regulation operation function, the operation cost is reduced, and meanwhile, the investment cost of the liquid air energy storage system is reduced. Under the condition that the air separation yield is met, peak-valley arbitrage is achieved through liquid air energy storage, the comprehensive electricity utilization cost of air separation equipment is reduced, and the economic benefits of enterprises are improved; the air pretreatment unit is shared by the air liquefaction circulation loop and the air separation circulation loop, so that the investment cost of liquid air energy storage can be remarkably reduced.

Description

Technical Field

[0001] The present invention belongs to the technical field of air separation, and particularly relates to an air separation system and method based on liquid air energy storage. Background Art

[0002] With the gradual reduction of fossil energy, the global energy structure is accelerating its transformation. Clean and sustainable renewable energy sources such as solar energy and wind energy are becoming important alternative options. Data from the International Energy Agency shows that the proportion of existing renewable energy power generation in China has reached 31.2%. However, its inherent intermittent characteristics pose significant challenges to the stable operation of the power grid. The progress of energy storage technology provides an effective solution to this problem.

[0003] As an important technical reserve for large-scale energy storage, liquid air energy storage has attracted more and more experts and scholars due to its advantages such as being not restricted by geographical conditions, having a large energy storage density, and being environmentally friendly. The liquid air energy storage system uses liquid air or nitrogen as the "electricity storage medium" and also includes complex heat storage and cold storage processes. Its basic operating principle is as follows: Excess electricity from the power grid drives the compressor to work, performing the air liquefaction process, storing the electricity in the form of liquid air, and storing the compression heat; when power needs to be supplied to the outside world, the liquid air is pressurized by a cryogenic pump and the low-temperature cold energy is recovered, and then drives the air power expansion machine to do work and generate electricity.

[0004] Air separation technology refers to using relevant equipment and technologies to separate nitrogen, oxygen, and other rare gases in the air to meet the gas requirements of industries such as metallurgy, coal chemical industry, petroleum refining, and aviation. The air separation unit needs to operate continuously, and the electricity consumption in each time period is relatively fixed. Due to the time-of-use electricity price policy for industrial electricity, there is a problem of relatively high operating costs during peak electricity price periods.

[0005] During the operation of the liquid air energy storage system, it is usually necessary to use a molecular sieve purifier to purify the air and remove substances such as water, carbon dioxide, and hydrocarbons in the air. These processes are exactly the same as air separation. Combining the two is expected to enable the air separation system to have the function of peak shaving operation, reduce the operating cost, and at the same time reduce the investment cost of the liquid air energy storage system. Summary of the Invention

[0006] In order to solve the above problems, the present invention provides an air separation system and method based on liquid air energy storage.

[0007] To achieve the above object, the technical solutions adopted by the present invention are as follows: An air separation system based on liquid air energy storage, comprising an air pretreatment unit, an air rectification unit and a liquid air energy storage unit. The air pretreatment unit is respectively connected to the air rectification unit and the liquid air energy storage unit, and the output end of the liquid air energy storage unit is connected to the input end of the air pretreatment unit; The air pretreatment unit is used to purify air. A part of the purified air enters the air rectification unit for distillation to separate liquid air, nitrogen, oxygen, argon and waste nitrogen. Another part of the air enters the liquid air energy storage unit to be cooled into liquid air, which is pressurized, evaporated and heated and then expanded to generate electricity, and the cold energy generated by the vaporization of the liquid air is stored in the cold storage packed bed of the liquid air energy storage unit.

[0008] Further, the first input end of the air pretreatment unit is connected to the output end of the first three-way valve, the second input end of the air pretreatment unit is connected to the second output end of the liquid air energy storage unit, and the third input end of the air pretreatment unit is connected to the first output end of the air rectification unit; the first output end of the air pretreatment unit is connected to the input end of the second three-way valve, the second output end of the air pretreatment unit is connected to the first input end of the liquid air energy storage unit, and the third input end of the air pretreatment unit is connected to the first output end of the air rectification unit; The first input end of the first three-way valve is used to input air, and the second input end of the first three-way valve is connected to the first output end of the liquid air energy storage unit; The first output end of the second three-way valve is connected to the first input end of the third three-way valve, and the second output end of the second three-way valve is connected to the second input end of the liquid air energy storage unit; The first output end of the third three-way valve is connected to the first input end of the air rectification unit, and the second input end of the second three-way valve is connected to the third output end of the liquid air energy storage unit.

[0009] Further, the air pretreatment unit includes: A first compressor, the input end of which is used as the first input end of the air pretreatment unit and is connected to the first output end of the first three-way valve; A first cooler, the first input end of which is connected to the output end of the first compressor; A second compressor, the input end of which is connected to the first output end of the first cooler; A second cooler, the first input end of which is connected to the output end of the second compressor; A third compressor, the input end of which is connected to the first output end of the second cooler; An air cooling tower, the first input end of the air cooling tower is connected to the output end of the third compressor, the second input end of the air cooling tower is connected to the output end of the water pump, and the output end of the air cooling tower is connected to the input end of the first adsorption tower; The first adsorption tower, the output end of the first adsorption tower is used as the first output end of the air pretreatment unit and is connected to the input end of the second three-way valve; A dry air cooling tower, the input end of the dry air cooling tower is connected to the second output end of the ninth three-way valve; A water pump, the input end of the water pump is connected to the output end of the dry air cooling tower; The second adsorption tower, the input end of the second adsorption tower is connected to the first output end of the ninth three-way valve; The ninth three-way valve, the input end of the ninth three-way valve is used as the third input end of the air pretreatment unit and is connected to the first output end of the air rectification unit; The second input end of the first cooler and the second input end of the second cooler are connected in parallel as the second input end of the air pretreatment unit and are connected to the second output end of the liquid air energy storage unit; the second output end of the first cooler and the second output end of the second cooler are connected in parallel as the second output end of the air pretreatment unit and are connected to the first input end of the liquid air energy storage unit.

[0010] Further, the air rectification unit includes: A fourth three-way valve, the input end of the fourth three-way valve is used as the input end of the air rectification unit and is connected to the output end of the third three-way valve, the first output end of the fourth three-way valve is connected to the input end of the fourth compressor, and the second output end of the fourth three-way valve is connected to the second input end of the main heat exchanger; The fourth compressor, the output end of the fourth compressor is connected to the first input end of the main heat exchanger; The main heat exchanger, the first output end of the main heat exchanger is connected to the input end of the expansion turbine, the second output end of the main heat exchanger is connected to the input end of the first stop valve, the third output end of the main heat exchanger is connected to the first input end of the sixth three-way valve, the fourth output end of the main heat exchanger is connected to the user, the fifth output end of the main heat exchanger is connected to the user, the sixth output end of the main heat exchanger is connected to the user, the seventh output end of the main heat exchanger is used as the output end of the air rectification unit and is connected to the input end of the ninth three-way valve, the third input end of the main heat exchanger is connected to the output end of the liquid oxygen pump, the fourth input end of the main heat exchanger is connected to the third output end of the subcooler, the fifth input end of the main heat exchanger is connected to the second output end of the argon rectification unit, and the sixth input end of the main heat exchanger is connected to the fourth output end of the subcooler; An expansion turbine, the output end of which is connected to the first input end of the fifth three-way valve; A first gas-liquid separator, the first output end of which is connected to the second input end of the fifth three-way valve, the second output end of which is connected to the second input end of the lower column of the rectification column, and the input end of which is connected to the output end of the first stop valve; The lower column of the rectification column, the first output end of which is connected to the first input end of the subcooler, the second output end of which is connected to the input end of the main condenser-evaporator, the first input end of which is connected to the output end of the sixth three-way valve, and the third input end of which is connected to the first output end of the seventh three-way valve; The upper column of the rectification column, the first output end of which is connected to the input end of the liquid oxygen pump, the second output end of which is connected to the third input end of the subcooler, the third output end of which is connected to the input end of the argon rectification unit, the fourth output end of which is connected to the fourth input end of the subcooler, the first input end of which is connected to the output end of the second stop valve, the second input end of which is connected to the output end of the third stop valve, and the third input end of which is connected to the first output end of the argon rectification unit; The main condenser-evaporator, the output end of which is connected to the input end of the seventh three-way valve; The subcooler, the second input end of which is connected to the second output end of the seventh three-way valve; The fifth three-way valve, the output end of which is connected to the second input end of the sixth three-way valve; The second stop valve, the input end of which is connected to the second output end of the subcooler; The sixth three-way valve, the input end of which is connected to the first output end of the subcooler.

[0011] The present invention also provides an air separation method based on liquid air energy storage, which is realized by using the above-mentioned air separation system based on liquid air energy storage. Nitrogen, oxygen, argon and waste nitrogen are separated from air through an air separation circulation loop. The pure air extracted is compressed, cooled and then expanded and depressurized to obtain liquid air by using an air liquefaction circulation loop. The liquid air is transmitted to an air power generation circulation loop, and the air compression heat generated during the compression process is stored in the hot water tank of the liquid air energy storage unit. The air liquefaction circulation loop and the air separation circulation loop share an air pretreatment unit. The received liquid air is pressurized, evaporated and vaporized, and heated in an air power generation cycle loop, and then expanded for power generation. The cold energy generated during the vaporization process of the liquid air is stored in the cold storage packed bed of the liquid air energy storage unit.

[0012] Further, the air separation cycle loop is as follows: After the air is compressed by the first compressor, the second compressor and the third compressor and cooled by the first cooler and the second cooler, it enters the air cooling tower for cooling, and then enters the first adsorption tower to remove components such as water, carbon dioxide, and alkanes in the air; The purified air is divided into two parts. One part of the air enters the main heat exchanger after passing through the second three-way valve and the third three-way valve, is cooled by the refluxing waste nitrogen, nitrogen, and oxygen, and then enters the lower column of the rectification tower to participate in rectification; the other part enters the main heat exchanger after being compressed by the fourth compressor, is preliminarily cooled by the refluxing waste nitrogen, nitrogen, and oxygen, and is then divided into two parts. One part passes through the expansion turbine to reduce pressure and temperature, and then enters the lower column of the rectification tower to participate in rectification. The other part is further cooled and throttled to reduce pressure, and then enters the first gas-liquid separator to separate gaseous air and liquid air, which respectively enter the lower column of the rectification tower to participate in rectification. The air entering the lower column of the rectification tower is preliminarily separated, and oxygen-rich liquid air is obtained at the bottom of the lower column of the rectification tower, and high-purity nitrogen is obtained at the top of the lower column of the rectification tower; the liquid air drawn from the bottom of the lower column of the rectification tower is subcooled by the subcooler and then enters the upper column of the rectification tower, while most of the nitrogen at the top of the lower column of the rectification tower enters the main condenser-evaporator, is cooled by the liquid oxygen to become liquid nitrogen, and a part of the liquid nitrogen is used as the reflux liquid of the lower column of the rectification tower, and the other part of the liquid nitrogen is subcooled by the subcooler and then enters the upper column of the rectification tower to participate in rectification; Various materials enter the upper column of the rectification tower for further separation. High-purity nitrogen can be obtained at the top of the upper column of the rectification tower, waste nitrogen is drawn from the upper middle part, crude argon is drawn from the middle part, and high-purity liquid oxygen is obtained at the bottom; nitrogen and oxygen are reheated by the subcooler and the main heat exchanger and supplied to users; the waste nitrogen is reheated and divided into two parts, one part is used as the regeneration gas of the second adsorption tower, and the other part is supplied to the dry air cooling tower; the crude argon is purified by the argon rectification unit and reheated by the main heat exchanger and then supplied to users; The air liquefaction cycle loop is as follows: Part of the air from the first adsorption tower is extracted from the second three-way valve, compressed by the fifth compressor and the sixth compressor and cooled by the third cooler and the fourth cooler, then enters the cold box heat exchanger, is cooled to a low temperature by the low-temperature fluid at the outlet of the cold storage packed bed and the gaseous low-temperature air refluxed from the second gas-liquid separator, and then enters the fourth stop valve to expand and reduce pressure. Part of the air is liquefied, and the liquid air is separated by the second gas-liquid separator and stored in the liquid air storage tank; The air power generation cycle loop is as follows: The liquid air output from the liquid air storage tank is pressurized to a high pressure by a cryogenic pump and then enters an evaporator to undergo a liquid-vapor phase change process. The cold energy is recovered and stored in a cold storage packed bed through a cryogenic fluid. The high-pressure air at the outlet of the evaporator is expanded and generated electricity through a first heater, a first expansion generator, a second heater, and a second expansion generator, and then is divided into two parts. One part flows back to a third three-way valve; the other part is expanded and generated electricity through a third heater, a third expansion generator, a fourth heater, and a fourth expansion generator, and the expanded air flows to a first three-way valve.

[0013] Furthermore, during the low electricity consumption period, the air pretreatment unit increases the air flow rate. Under the condition of ensuring the output of the air rectification unit, the excess air is extracted after the first adsorption tower and used for the air liquefaction cycle.

[0014] Furthermore, during the high electricity consumption period, the air after two-stage expansion and power generation by the first expansion generator and the second expansion generator can all flow back to the rear end of the first adsorption tower. Under the condition of ensuring the air separation output, the air volume of the air pretreatment unit is reduced, thereby reducing the high-peak electricity consumption; Or, the air after two-stage expansion and power generation by the first expansion generator and the second expansion generator continues to expand and generate electricity to atmospheric pressure, and then flows back to the inlet of the air pretreatment unit, reducing the intake of ambient air and the air treatment volume of the first adsorption tower.

[0015] Compared with the prior art, the technical progress achieved by the present invention is as follows: By sharing the air pretreatment unit, the system of the present invention has the function of peak shaving operation, reduces the operation cost, and at the same time reduces the investment cost of the liquid air energy storage system. During the low electricity consumption period, the air pretreatment unit increases the air flow rate. Under the condition of ensuring the output of the air rectification unit, the excess air is extracted after the adsorption tower and used for the air liquefaction cycle; during the high electricity consumption period, the air after two-stage expansion and power generation can all flow back to the rear end of the adsorption tower. Under the condition of ensuring the air separation output, the air volume of the air pretreatment unit can be reduced, reducing the high-peak electricity consumption; it can also continue to expand and generate electricity to atmospheric pressure and then flow back to the first three-way valve, reducing the intake of ambient air, reducing the air treatment volume of the adsorption tower, and reducing the energy consumption of desorption. The present invention can achieve peak-valley arbitrage through liquid air energy storage under the condition of meeting the air separation output, reduce the comprehensive electricity consumption cost of the air separation equipment, and improve the economic benefits of the enterprise; by sharing the air pretreatment unit between the air liquefaction cycle loop and the air separation cycle loop, the investment cost of liquid air energy storage can be significantly reduced. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The drawings are used to provide a further understanding of the present invention and constitute a part of the specification. They are used to explain the present invention together with the embodiments of the present invention and do not constitute a limitation to the present invention.

[0017] Figure 1 The structural schematic diagram of an air separation system based on liquid air energy storage provided by an embodiment of the present invention; In the figure: 100, the first three-way valve; 300, the second three-way valve; 400, the third three-way valve; 200, the air pretreatment unit, 201, the first compressor, 202, the first cooler, 203, the second compressor, 204, the second cooler, 205, the third compressor, 206, the air cooling tower, 207, the first adsorption tower, 208, the dry air cooling tower, 209, the water pump, 210, the second adsorption tower, 211, the ninth three-way valve; 500, the air rectification unit, 501, the fourth compressor, 502, the main heat exchanger, 503, the expansion turbine, 504, the first gas-liquid separator, 505-1, the lower column of the rectification tower, 505-2, the upper column of the rectification tower, 506, the main condenser-evaporator, 507, the subcooler, 508, the argon rectification unit, 509, the liquid oxygen pump, 510, the fourth three-way valve, 511, the first stop valve, 512, the fifth three-way valve, 513, the sixth three-way valve, 514, the seventh three-way valve, 515, the second stop valve, 516, the third stop valve; 600, the energy storage unit, 601, the fifth compressor, 602, the third cooler, 603, the sixth compressor, 604, the fourth cooler, 605, the cold box heat exchanger, 606, the fourth stop valve, 607, the second gas-liquid separator, 608, the liquid air storage tank, 609, the cryogenic liquid pump, 610, the evaporator, 611, the cold storage packed bed, 612, the first heater, 613, the first expansion generator, 614, the second heater, 615, the second expansion generator, 616, the third heater, 617, the third expansion generator, 618, the fourth heater, 619, the fourth expansion generator, 620, the hot water tank, 621, the normal temperature water tank, 622, the eighth three-way valve, 623, the first circulation fan, 624, the second circulation fan, 625, the thirteenth three-way valve. Specific embodiments

[0018] The following specific embodiments can be combined with each other, and the same or similar concepts or processes may not be repeated in some embodiments. The embodiments of the present invention will be described below with reference to the accompanying drawings.

[0019] Such as Figure 1As shown in the figure, an air separation system based on liquid air energy storage provided by an embodiment of the present invention includes an air pretreatment unit 200, an air rectification unit 500, and a liquid air energy storage unit 600. The air pretreatment unit 200 is respectively connected to the air rectification unit 500 and the liquid air energy storage unit 600, and the output end of the liquid air energy storage unit 600 is connected to the input end of the air pretreatment unit 200; The air pretreatment unit 200 is used to purify air. A part of the purified air enters the air rectification unit 500 for distillation to separate liquid air, nitrogen, oxygen, argon, and waste nitrogen. Another part of the air enters the liquid air energy storage unit 600 to be cooled into liquid air, which is pressurized, evaporated and vaporized, and heated to expand and generate electricity after that. And the cold energy generated by the vaporization of the liquid air is stored in the cold storage packed bed 611 of the liquid air energy storage unit 600.

[0020] The above three units are interconnected to form an air liquefaction circulation loop, an air power generation circulation loop, and an air separation circulation loop. The air separation circulation loop is used to separate air to generate nitrogen, oxygen, argon, and waste nitrogen.

[0021] The air liquefaction circulation loop is used to compress and cool the extracted pure air and then expand and depressurize it to obtain liquid air. The liquid air is transported to the air power generation circulation loop, and the air compression heat generated during the compression process is stored in the hot water tank 620.

[0022] The air power generation circulation loop expands and generates electricity after pressurizing, evaporating and vaporizing, and further heating the received liquid air. And the cold energy generated during the vaporization process of the liquid air is stored in the cold storage packed bed 611.

[0023] Specifically, the air separation circulation loop includes: a first three-way valve 100, an air pretreatment unit 200, a second three-way valve 300, a third three-way valve 400, and an air rectification unit 500; The first input end of the first three-way valve 100 is used to input ambient air. The second input end of the first three-way valve 100 is connected to the first output end of the liquid air energy storage unit 600, and the first output end of the first three-way valve 100 is connected to the first input end of the air pretreatment unit 200; The first output end of the air pretreatment unit 200 is connected to the input end of the second three-way valve 300. The second output end of the air pretreatment unit 200 is connected to the first input end of the liquid air energy storage unit 600. The second input end of the air pretreatment unit 200 is connected to the second output end of the liquid air energy storage unit 600. The third input end of the air pretreatment unit 200 is connected to the first output end of the air rectification unit 500; The first output end of the second three-way valve 300 is connected to the first input end of the third three-way valve 400, and the second output end of the second three-way valve 300 is connected to the second input end of the liquid air energy storage unit 600; The first output end of the third three-way valve 400 is connected to the first input end of the air rectification unit 500, and the second input end of the second three-way valve 300 is connected to the third output end of the liquid air energy storage unit 600.

[0024] Specifically, the air pretreatment unit 200 includes: A first compressor 201, the input end of the first compressor 201 is used as the first input end of the air pretreatment unit 200 and is connected to the first output end of the first three-way valve 100; A first cooler 202, the first input end of the first cooler 202 is connected to the output end of the first compressor 201; A second compressor 203, the input end of the second compressor 203 is connected to the first output end of the first cooler 202; A second cooler 204, the first input end of the second cooler 204 is connected to the output end of the second compressor 203; A third compressor 205, the input end of the third compressor 205 is connected to the first output end of the second cooler 204; An air cooling tower 206, the first input end of the air cooling tower 206 is connected to the output end of the third compressor 205, the second input end of the air cooling tower 206 is connected to the output end of the water pump 209, and the output end of the air cooling tower 206 is connected to the input end of the first adsorption tower 207; A first adsorption tower 207, the output end of the first adsorption tower 207 is used as the first output end of the air pretreatment unit 200 and is connected to the input end of the second three-way valve 300; A dry air cooling tower 208, the input end of the dry air cooling tower 208 is connected to the second output end of the ninth three-way valve 211; A water pump 209, the input end of the water pump 209 is connected to the output end of the dry air cooling tower 208; A second adsorption tower 210, the input end of the second adsorption tower 210 is connected to the first output end of the ninth three-way valve 211; A ninth three-way valve 211, the input end of the ninth three-way valve 211 is used as the third input end of the air pretreatment unit 200 and is connected to the first output end of the air rectification unit 500; The second input end of the first cooler 202 and the second input end of the second cooler 204 are connected in parallel as the second input end of the air pretreatment unit 200 to the second output end of the liquid air energy storage unit 600; the second output end of the first cooler 202 and the second output end of the second cooler 204 are connected in parallel as the second output end of the air pretreatment unit 200 to the first input end of the liquid air energy storage unit 600.

[0025] Specifically, the air rectification unit 500 includes: A fourth three-way valve 510, the input end of the fourth three-way valve 510 is used as the input end of the air rectification unit 500 and is connected to the output end of the third three-way valve 400, the first output end of the fourth three-way valve 510 is connected to the input end of the fourth compressor 501, and the second output end of the fourth three-way valve 510 is connected to the second input end of the main heat exchanger 502; A fourth compressor 501, the output end of the fourth compressor 501 is connected to the first input end of the main heat exchanger 502; A main heat exchanger 502, the first output end of the main heat exchanger 502 is connected to the input end of the expansion turbine 503, the second output end of the main heat exchanger 502 is connected to the input end of the first stop valve 511, the third output end of the main heat exchanger 502 is connected to the first input end of the sixth three-way valve 513, the fourth output end of the main heat exchanger 502 is connected to a user, the fifth output end of the main heat exchanger 502 is connected to a user, the sixth output end of the main heat exchanger 502 is connected to a user, the seventh output end of the main heat exchanger 502 is used as the output end of the air rectification unit 500 and is connected to the input end of the ninth three-way valve 211, the third input end of the main heat exchanger 502 is connected to the output end of the liquid oxygen pump 509, the fourth input end of the main heat exchanger 502 is connected to the third output end of the subcooler 507, the fifth input end of the main heat exchanger 502 is connected to the second output end of the argon rectification unit 508, and the sixth input end of the main heat exchanger 502 is connected to the fourth output end of the subcooler 507; An expansion turbine 503, the output end of the expansion turbine 503 is connected to the first input end of the fifth three-way valve 512; A first gas-liquid separator 504, the first output end of the first gas-liquid separator 504 is connected to the second input end of the fifth three-way valve 512, the second output end of the first gas-liquid separator 504 is connected to the second input end of the lower column 515-1 of the rectification column, and the input end of the first gas-liquid separator 504 is connected to the output end of the first stop valve 511; The lower column 505-1 of the rectification column, the first output end of the lower column 505-1 of the rectification column is connected to the first input end of the subcooler 507, the second output end of the lower column 505-1 of the rectification column is connected to the input end of the main condenser-evaporator 506, the first input end of the lower column 505-1 of the rectification column is connected to the output end of the sixth three-way valve 513, and the third input end of the lower column 505-1 of the rectification column is connected to the first output end of the seventh three-way valve 514; The upper column 505-2 of the rectification column, the first output end of the upper column 505-2 of the rectification column is connected to the input end of the liquid oxygen pump 509, the second output end of the upper column 505-2 of the rectification column is connected to the third input end of the subcooler 507, the third output end of the upper column 505-2 of the rectification column is connected to the input end of the argon rectification unit 508, the fourth output end of the upper column 505-2 of the rectification column is connected to the fourth input end of the subcooler 507, the first input end of the upper column 505-2 of the rectification column is connected to the output end of the second stop valve 515, the second input end of the upper column 505-2 of the rectification column is connected to the output end of the third stop valve 516, and the third input end of the upper column 505-2 of the rectification column is connected to the first output end of the argon rectification unit 508; The main condenser-evaporator 506, the output end of the main condenser-evaporator 506 is connected to the input end of the seventh three-way valve 514; The subcooler 507, the second input end of the subcooler 507 is connected to the second output end of the seventh three-way valve 514; The fifth three-way valve 512, the output end of the fifth three-way valve 512 is connected to the second input end of the sixth three-way valve 513; The second stop valve 515, the input end of the second stop valve 515 is connected to the second output end of the subcooler 507; The sixth three-way valve 513, the input end of the sixth three-way valve 513 is connected to the first output end of the subcooler 507.

[0026] The present invention also provides an air separation method based on liquid air energy storage, which is realized by using the above air separation system based on liquid air energy storage. The air pretreatment unit 200, the air rectification unit 500, and the liquid air energy storage unit 600 are interconnected to form an air separation circulation loop, an air liquefaction circulation loop, and an air power generation circulation loop; The air separation circulation loop separates air to produce nitrogen, oxygen, argon, and waste nitrogen; The extracted pure air is compressed and cooled by the air liquefaction circulation loop and then expanded and depressurized to obtain liquid air. The liquid air is transmitted to the air power generation circulation loop, and the air compression heat generated during the compression process is stored in the hot water tank 620 of the liquid air energy storage unit 600; The air liquefaction cycle circuit and the air separation cycle circuit share an air pretreatment unit; The received liquid air is pressurized, evaporated and vaporized, and heated in the air power generation cycle circuit, and then expanded for power generation. The cold energy generated during the vaporization process of the liquid air is stored in the cold storage packed bed 611 of the liquid air energy storage unit 600.

[0027] Among them, the air separation cycle circuit is as follows: Ambient air is compressed by the first compressor 201, the second compressor 203 and the third compressor 205, and cooled by the first cooler 202 and the second cooler 204, and then enters the air cooling tower 206 for cooling, and then enters the first adsorption tower 207 to remove components such as water, carbon dioxide, and alkanes in the air.

[0028] The purified air is divided into two parts. One part of the air enters the main heat exchanger 502 after passing through the second three-way valve 300 and the third three-way valve 400, is cooled by the refluxing waste nitrogen, nitrogen, and oxygen, and then enters the lower column 505-1 of the rectification column to participate in rectification; the other part is compressed by the fourth compressor 501 and then enters the main heat exchanger 502. After being preliminarily cooled by the refluxing waste nitrogen, nitrogen, and oxygen, it is divided into two parts. One part passes through the expansion turbine 503 to reduce pressure and temperature, and then enters the lower column 505-1 of the rectification column to participate in rectification. The other part is further cooled and throttled to reduce pressure, and then enters the first gas-liquid separator 504 to separate gaseous air and liquid air, and respectively enter the lower column 505-1 of the rectification column to participate in rectification. The air entering the lower column 505-1 of the rectification column is preliminarily separated, and oxygen-rich liquid air is obtained at the bottom of the lower column 505-1 of the rectification column, and high-purity nitrogen is obtained at the top of the lower column 505-1 of the rectification column. The liquid air drawn from the bottom of the lower column 505-1 of the rectification column is subcooled by the subcooler 507 and then enters the upper column 505-2 of the rectification column, while most of the nitrogen at the top of the lower column 505-1 of the rectification column enters the main condenser-evaporator 506 and is cooled by liquid oxygen to become liquid nitrogen. One part of the liquid nitrogen is used as the reflux liquid of the lower column 505-1 of the rectification column, and the other part of the liquid nitrogen is subcooled by the subcooler 507 and then enters the upper column 505-2 of the rectification column to participate in rectification.

[0029] Various materials enter the upper column 505-2 of the rectification column for further separation. High-purity nitrogen can be obtained at the top of the upper column 505-2 of the rectification column, waste nitrogen is drawn from the upper middle part, crude argon is drawn from the middle part, and high-purity liquid oxygen is obtained at the bottom; nitrogen and oxygen are reheated by the subcooler 507 and the main heat exchanger 502 and then supplied to users; the waste nitrogen is divided into two parts after reheating. One part is used as the regeneration gas of the second adsorption tower 210, and the other part is supplied to the dry air cooling tower 208; the crude argon is purified by the argon rectification unit 508 and reheated by the main heat exchanger 502 and then supplied to users; The air liquefaction cycle circuit is as follows: Part of the air from the first adsorption tower 207 is extracted from the second three-way valve 300, compressed by the fifth compressor 601 and the sixth compressor 603, and cooled by the third cooler 602 and the fourth cooler 604, then enters the cold box heat exchanger 605, and is cooled to a low temperature by the low-temperature fluid at the outlet of the cold storage packed bed 611 and the gaseous low-temperature air refluxed from the second gas-liquid separator 607. Then it enters the fourth stop valve 606 for expansion and pressure reduction, and part of the air is liquefied. The liquid air is separated by the second gas-liquid separator 607 and stored in the liquid air storage tank 608.

[0030] The air power generation cycle loop is as follows: The liquid air output from the liquid air storage tank 608 is pressurized to a high pressure by the cryogenic pump 609, and then enters the evaporator 610 to undergo a liquid-vapor phase change process. The cold energy is recovered through the low-temperature fluid and stored in the cold storage packed bed 611. The high-pressure air at the outlet of the evaporator 610 is divided into two parts after expanding and generating electricity through the first heater 612, the first expansion generator 613, the second heater 614, and the second expansion generator 615. One part flows back to the third three-way valve 400; the other part expands and generates electricity through the third heater 616, the third expansion generator 617, the fourth heater 618, and the fourth expansion generator 619, and the expanded air flows to the first three-way valve 100.

[0031] Among them, the air liquefaction cycle loop and the air separation cycle loop share the air pretreatment unit.

[0032] In this embodiment, during the low electricity consumption period, the air pretreatment unit increases the air flow rate. While ensuring the output of the air rectification unit, the excess air is extracted after the adsorption tower and used for the air liquefaction cycle.

[0033] During the high electricity consumption period, the air after two-stage expansion and power generation by the first expansion generator 613 and the second expansion generator 615 can all flow back to the rear end of the adsorption tower. While ensuring the output of the air separation unit, the air volume of the air pretreatment unit can be reduced, thereby reducing the high peak electricity consumption; the air after two-stage expansion and power generation can also continue to expand and generate electricity to atmospheric pressure, and then flow back to the inlet of the air pretreatment unit, reducing the intake of ambient air, reducing the air treatment volume of the adsorption tower, and reducing the energy consumption of desorption.

[0034] To further illustrate the embodiments of the present invention, for Figure 1A simulation calculation was carried out on an air separation system based on liquid air energy storage. Taking the investigated 50MW liquid air energy storage system as an example, two types of liquid air energy storage systems, traditional and existing, were studied and compared. The round-trip efficiency of the system is 50%, the initial investment is 400 million yuan, the electricity price during peak hours is 0.9 yuan / kWh, and the electricity price during off-peak hours is 0.3 yuan / kWh. By sharing the air pretreatment unit, the initial investment of the existing liquid air energy storage system is reduced by 20%, and the investment payback period is reduced by 20.08%. The specific data is shown in the following table:

[0035] In summary, the present invention has the following beneficial effects: 1. In the present invention, the air liquefaction cycle and the air separation cycle share the air pretreatment unit. During off-peak electricity hours, the air pretreatment unit increases the air flow rate. Under the condition of ensuring the output of the air rectification unit, the excess air is extracted after the adsorption tower and used for the air liquefaction cycle, significantly reducing the investment cost of liquid air energy storage.

[0036] 2. When the present invention is adopted during peak electricity hours, the air after two-stage expansion power generation can all flow back to the rear end of the adsorption tower. Under the condition of ensuring the air separation output, the air volume of the air pretreatment unit can be reduced, thereby reducing the peak electricity consumption and operating cost of the air separation system.

[0037] 3. When the present invention is adopted during peak electricity hours, the normal-pressure pure air after expansion power generation flows back to the inlet of the air pretreatment unit, reducing the intake of ambient air, reducing the air treatment volume of the adsorption tower, and reducing the energy consumption of desorption.

[0038] 4. The present invention has the advantages of flexible operation and high energy efficiency. It can realize peak-valley arbitrage through liquid air energy storage under the condition of meeting the air separation output, reducing the comprehensive electricity consumption cost of the air separation equipment and improving the economic benefits of the enterprise.

[0039] Finally, it should be noted that the above are only the preferred embodiments of the present invention and are not used to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements for some of the technical features. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the scope of protection of the claims of the present invention.

Claims

1. An air separation system based on liquid air energy storage, characterized in that: It includes an air pretreatment unit (200), an air rectification unit (500) and a liquid air energy storage unit (600). The air pretreatment unit (200) is respectively connected to the air rectification unit (500) and the liquid air energy storage unit (600), and the output end of the liquid air energy storage unit (600) is connected to the input end of the air pretreatment unit (200). The air pretreatment unit (200) is used to purify air. A part of the purified air enters the air rectification unit (500) for distillation to separate liquid air, nitrogen, oxygen, argon and waste nitrogen. Another part of the air enters the liquid air energy storage unit (600) to be cooled into liquid air, which is pressurized, evaporated and vaporized, and heated to expand and generate electricity. The cold energy generated by the vaporization of the liquid air is stored in the cold storage packed bed (611) of the liquid air energy storage unit (600).

2. The air separation system based on liquid air energy storage according to claim 1, wherein: The first input end of the air pretreatment unit (200) is connected to the output end of the first three-way valve (100), the second input end of the air pretreatment unit (200) is connected to the second output end of the liquid air energy storage unit (600), and the third input end of the air pretreatment unit (200) is connected to the first output end of the air rectification unit (500). The first output end of the air pretreatment unit (200) is connected to the input end of the second three-way valve (300), the second output end of the air pretreatment unit (200) is connected to the first input end of the liquid air energy storage unit (600), and the third input end of the air pretreatment unit (200) is connected to the first output end of the air rectification unit (500). The first input end of the first three-way valve (100) is used to input air, and the second input end of the first three-way valve (100) is connected to the first output end of the liquid air energy storage unit (600). The first output end of the second three-way valve (300) is connected to the first input end of the third three-way valve (400), and the second output end of the second three-way valve (300) is connected to the second input end of the liquid air energy storage unit (600). The first output end of the third three-way valve (400) is connected to the first input end of the air rectification unit (500), and the second input end of the second three-way valve (300) is connected to the third output end of the liquid air energy storage unit (600).

3. The air separation system based on liquid air energy storage according to claim 2, wherein: The air pretreatment unit (200) includes: A first compressor (201), the input end of the first compressor (201) is used as the first input end of the air pretreatment unit (200) and is connected to the first output end of the first three-way valve (100). A first cooler (202), the first input end of the first cooler (202) is connected to the output end of the first compressor (201). A second compressor (203), the input end of the second compressor (203) is connected to the first output end of the first cooler (202). A second cooler (204), the first input end of the second cooler (204) is connected to the output end of the second compressor (203). The third compressor (205), the input end of the third compressor (205) is connected to the first output end of the second cooler (204); The air cooling tower (206), the first input end of the air cooling tower (206) is connected to the output end of the third compressor (205), the second input end of the air cooling tower (206) is connected to the output end of the water pump (209), and the output end of the air cooling tower (206) is connected to the input end of the first adsorption tower (207); The first adsorption tower (207), the output end of the first adsorption tower (207) serves as the first output end of the air pretreatment unit (200) and is connected to the input end of the second three-way valve (300); The dry air cooling tower (208), the input end of the dry air cooling tower (208) is connected to the second output end of the ninth three-way valve (211); The water pump (209), the input end of the water pump (209) is connected to the output end of the dry air cooling tower (208); The second adsorption tower (210), the input end of the second adsorption tower (210) is connected to the first output end of the ninth three-way valve (211); The ninth three-way valve (211), the input end of the ninth three-way valve (211) serves as the third input end of the air pretreatment unit (200) and is connected to the first output end of the air rectification unit (500); The second input ends of the first cooler (202) and the second cooler (204) are connected in parallel and serve as the second input end of the air pretreatment unit (200) and are connected to the second output end of the liquid air energy storage unit (600); the second output ends of the first cooler (202) and the second cooler (204) are connected in parallel and serve as the second output end of the air pretreatment unit (200) and are connected to the first input end of the liquid air energy storage unit (600).

4. The air separation system based on liquid air energy storage according to claim 3, characterized in that: The air rectification unit (500) includes: The fourth three-way valve (510), the input end of the fourth three-way valve (510) serves as the input end of the air rectification unit (500) and is connected to the output end of the third three-way valve (400), the first output end of the fourth three-way valve (510) is connected to the input end of the fourth compressor (501), and the second output end of the fourth three-way valve (510) is connected to the second input end of the main heat exchanger (502); The fourth compressor (501), the output end of the fourth compressor (501) is connected to the first input end of the main heat exchanger (502); Main heat exchanger (502), the first output end of the main heat exchanger (502) is connected to the input end of the expansion turbine (503), the second output end of the main heat exchanger (502) is connected to the input end of the first stop valve (511), the third output end of the main heat exchanger (502) is connected to the first input end of the sixth three-way valve (513), the fourth output end of the main heat exchanger (502) is connected to a user, the fifth output end of the main heat exchanger (502) is connected to a user, the sixth output end of the main heat exchanger (502) is connected to a user, the seventh output end of the main heat exchanger (502) serves as the output end of the air rectification unit (500) and is connected to the input end of the ninth three-way valve (211), the third input end of the main heat exchanger (502) is connected to the output end of the liquid oxygen pump (509), the fourth input end of the main heat exchanger (502) is connected to the third output end of the subcooler (507), the fifth input end of the main heat exchanger (502) is connected to the second output end of the argon rectification unit (508), the sixth input end of the main heat exchanger (502) is connected to the fourth output end of the subcooler (507); Expansion turbine (503), the output end of the expansion turbine (503) is connected to the first input end of the fifth three-way valve (512); First gas-liquid separator (504), the first output end of the first gas-liquid separator (504) is connected to the second input end of the fifth three-way valve (512), the second output end of the first gas-liquid separator (504) is connected to the second input end of the lower column of the rectification column (515-1), the input end of the first gas-liquid separator (504) is connected to the output end of the first stop valve (511); Lower column of the rectification column (505-1), the first output end of the lower column of the rectification column (505-1) is connected to the first input end of the subcooler (507), the second output end of the lower column of the rectification column (505-1) is connected to the input end of the main condenser-evaporator (506), the first input end of the lower column of the rectification column (505-1) is connected to the output end of the sixth three-way valve (513), the third input end of the lower column of the rectification column (505-1) is connected to the first output end of the seventh three-way valve (514); The upper column of the rectification column (505-2), the first output end of the upper column of the rectification column (505-2) is connected to the input end of the liquid oxygen pump (509), the second output end of the upper column of the rectification column (505-2) is connected to the third input end of the subcooler (507), the third output end of the upper column of the rectification column (505-2) is connected to the input end of the argon rectification unit (508), the fourth output end of the upper column of the rectification column (505-2) is connected to the fourth input end of the subcooler (507), the first input end of the upper column of the rectification column (505-2) is connected to the output end of the second stop valve (515), the second input end of the upper column of the rectification column (505-2) is connected to the output end of the third stop valve (516), and the third input end of the upper column of the rectification column (505-2) is connected to the first output end of the argon rectification unit (508); The main condenser-evaporator (506), the output end of the main condenser-evaporator (506) is connected to the input end of the seventh three-way valve (514); The subcooler (507), the second input end of the subcooler (507) is connected to the second output end of the seventh three-way valve (514); The fifth three-way valve (512), the output end of the fifth three-way valve (512) is connected to the second input end of the sixth three-way valve (513); The second stop valve (515), the input end of the second stop valve (515) is connected to the second output end of the subcooler (507); The sixth three-way valve (513), the input end of the sixth three-way valve (513) is connected to the first output end of the subcooler (507).

5. An air separation method based on liquid air energy storage, characterized in that: It is realized by using the air separation system based on liquid air energy storage as described in claim 4, Air is separated into nitrogen, oxygen, argon and waste nitrogen through the air separation circulation loop; The pure air extracted is compressed, cooled and then expanded and depressurized by the air liquefaction circulation loop to obtain liquid air. The liquid air is transmitted to the air power generation circulation loop, and the air compression heat generated during the compression process is stored in the hot water tank (620) of the liquid air energy storage unit (600); The air liquefaction circulation loop and the air separation circulation loop share the air pretreatment unit; The received liquid air is pressurized, evaporated and vaporized and then heated by the air power generation circulation loop to expand and generate electricity, and the cold energy generated during the vaporization process of the liquid air is stored in the cold storage packed bed (611) of the liquid air energy storage unit (600).

6. The air separation method based on liquid air energy storage according to claim 5, characterized in that: The air separation circulation loop is as follows: After air is compressed by the first compressor (201), the second compressor (203) and the third compressor (205) and cooled by the first cooler (202) and the second cooler (204), it enters the air cooling tower (206) to be cooled and then enters the first adsorption tower (207) to remove water, carbon dioxide and alkane components in the air; The purified air is divided into two parts. One part of the air enters the main heat exchanger (502) after passing through the second three-way valve (300) and the third three-way valve (400), and after being cooled by the counter-flowing waste nitrogen, nitrogen, and oxygen, it enters the lower column (505-1) of the distillation column to participate in rectification; the other part is compressed by the fourth compressor (501) and then enters the main heat exchanger (502). After being preliminarily cooled by the counter-flowing waste nitrogen, nitrogen, and oxygen, it is divided into two parts. One part passes through the expansion turbine (503) to reduce pressure and temperature, and then enters the lower column (505-1) of the distillation column to participate in rectification. The other part, after further cooling and throttling to reduce pressure, enters the first gas-liquid separator (504) to separate gaseous air and liquid air, which respectively enter the lower column (505-1) of the distillation column to participate in rectification. The air entering the lower column (505-1) of the distillation column is preliminarily separated, and oxygen-rich liquid air is obtained at the bottom of the lower column (505-1) of the distillation column, and high-purity nitrogen is obtained at the top of the lower column (505-1) of the distillation column; the liquid air drawn from the bottom of the lower column (505-1) of the distillation column is subcooled by the cooler (507) and then enters the upper column (505-2) of the distillation column, while most of the nitrogen at the top of the lower column (505-1) of the distillation column enters the main condenser-evaporator (506), where it is cooled by liquid oxygen to become liquid nitrogen. One part of the liquid nitrogen is used as the reflux liquid for the lower column (505-1) of the distillation column, and the other part of the liquid nitrogen is subcooled by the cooler (507) and then enters the upper column (505-2) of the distillation column to participate in rectification; The material enters the upper column (505-2) of the distillation column for further separation. High-purity nitrogen is obtained at the top of the upper column (505-2) of the distillation column, waste nitrogen is drawn from the upper middle part, crude argon is drawn from the middle part, and high-purity liquid oxygen is obtained at the bottom; nitrogen and oxygen are reheated by the cooler (507) and the main heat exchanger (502) and then supplied to users; the waste nitrogen is divided into two parts after being reheated. One part is used as the regeneration gas for the second adsorption tower (210), and the other part is supplied to the dry air cooling tower (208); the crude argon is purified by the argon rectification unit (508) and reheated by the main heat exchanger (502) and then supplied to users; The air liquefaction cycle circuit is as follows: Part of the air drawn from the second three-way valve (300) and coming from the first adsorption tower (207) is compressed by the fifth compressor (601) and the sixth compressor (603) and cooled by the third cooler (602) and the fourth cooler (604), and then enters the cold box heat exchanger (605), where it is cooled to a low temperature by the low-temperature fluid at the outlet of the cold storage packed bed (611) and the gaseous low-temperature air refluxed from the second gas-liquid separator (607), and then enters the fourth stop valve (606) to expand and reduce pressure. Part of the air is liquefied, and the liquid air is separated by the second gas-liquid separator (607) and stored in the liquid air storage tank (608); The air power generation cycle circuit is as follows: The liquid air output from the liquid air storage tank (608) is pressurized to a high pressure by a cryogenic pump (609), and then enters an evaporator (610) to undergo a liquid-vapor phase change process. The cold energy is recovered and stored in a cold storage packed bed (611) through a cryogenic fluid. The high-pressure air at the outlet of the evaporator (610) is expanded and generates electricity through a first heater (612), a first expansion generator (613), a second heater (614), and a second expansion generator (615), and then is divided into two parts. One part flows back to a third three-way valve (400); the other part expands and generates electricity through a third heater (616), a third expansion generator (617), a fourth heater (618), and a fourth expansion generator (619), and the expanded air flows towards a first three-way valve (100).

7. The air separation method based on liquid air energy storage according to claim 6, characterized in that: During the low electricity consumption period, the air pretreatment unit (200) increases the air flow rate. Under the condition of ensuring the output of the air rectification unit (500), the excess air is extracted after the first adsorption tower (207) and used for the air liquefaction cycle.

8. The air separation method based on liquid air energy storage according to claim 6, characterized in that: During the high electricity consumption period, the air after two-stage expansion and power generation by the first expansion generator (613) and the second expansion generator (615) all flows back to the rear end of the first adsorption tower (207). Under the condition of ensuring the air separation output, the air volume of the air pretreatment unit (200) is reduced, thereby reducing the high peak electricity consumption.

9. The air separation method based on liquid air energy storage according to claim 6, characterized in that: During the high electricity consumption period, the air after two-stage expansion and power generation by the first expansion generator (613) and the second expansion generator (615) continues to expand and generate electricity to normal pressure, and then flows back to the inlet of the air pretreatment unit (200), reducing the intake of ambient air and reducing the air treatment volume of the first adsorption tower (207).

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