A device for producing liquid air by nitrogen compression-expansion cycle refrigeration

Abstract

The utility model belongs to air liquefaction technical field relates to a kind of nitrogen compression expansion cycle refrigeration production liquid air's device, and the device includes raw material air compression system, air precooling system, air drying purification system, air circulation pressurization system, nitrogen circulation pressurization system, expansion refrigeration system, heat exchange cold box and liquid air storage tank.The utility model realizes the efficient production of liquid air by multistage compression, cooling, drying, purification, pressurization and expansion refrigeration etc.Step, by introducing nitrogen compression expansion refrigeration cycle, optimization energy utilization, recovery low-temperature air cold quantity, save compression work and power consumption, significantly reduce production cost.The utility model is applicable to energy storage, metal smelting and precision manufacturing etc.Field.

Description

Technical Field

[0001] This utility model belongs to the field of air liquefaction technology and relates to a device for producing liquid air by nitrogen compression and expansion cycle refrigeration. Background Technology

[0002] Liquid air is the liquid form of air, often abbreviated as liquid air. As a multi-component mixture, its boiling point differences lead to unstable purity. In the traditional field of air separation (air separation), liquid air is usually only used as an intermediate product in the process and has not been widely applied. However, with the rapid development of new energy production capacity in my country, especially the in-depth research and exploration of liquid air energy storage and compressed air energy storage technologies, liquid air is gradually becoming an ideal energy storage carrier due to its low temperature (approximately -196℃), huge vaporization expansion coefficient (volume expansion of approximately 700 times), and increasingly mature transportation and storage technologies. Liquid air energy storage systems can store electrical energy by liquefying air and release energy by vaporization during peak demand, achieving grid peak shaving and smooth integration of renewable energy, which is of great significance for energy transition.

[0003] The inherent oxygen content of liquid air has led to its increasing applications in metal smelting and oxygen-enriched combustion. For example, in steel production, liquid air can provide high-purity oxygen, improving combustion efficiency and reducing carbon emissions; in the chemical industry, it can be used for oxidation reactions to increase yield. Furthermore, the drying and cleaning properties of liquid air are increasing its applications in precision manufacturing, cleanrooms, and semiconductor production, such as as a cooling medium or inert gas source. The endothermic potential released during liquid air vaporization and the mechanical work generated by expansion represent enormous energy potential. Coupling the utilization of liquid air with air separation units not only allows for the recovery of the liquid air's cooling capacity to replace part of the expansion refrigeration, thus saving the compression work of the expanded air used for refrigeration but not participating in distillation; simultaneously, the introduction of liquid air also increases the amount of feed air required for separation, saving some electricity used for feed air compression. This coupling method can significantly reduce overall energy consumption and improve system efficiency.

[0004] Despite the promising prospects of liquid air, existing liquid air production technologies still face numerous challenges. First, traditional air liquefaction methods largely rely on Claude or Linde cycles, which have limited refrigeration efficiency, especially during large-scale production, resulting in high energy consumption. Second, existing refrigeration cycles typically do not adequately consider the subcooling of liquid air, leading to easy vaporization loss during storage and transportation, affecting stability. Third, existing systems suffer from poor energy matching during heat exchange and expansion processes, resulting in large temperature differences in heat exchangers and wasted cooling capacity. Furthermore, nitrogen, a major component of air, is underutilized in refrigeration cycles, requiring continuous nitrogen replenishment in many methods, increasing operating costs. Utility Model Content

[0005] In view of this, the purpose of this utility model is to solve the above problems and provide a device for producing liquid air by nitrogen compression and expansion cycle refrigeration.

[0006] To achieve the above objectives, this utility model provides the following technical solution: An apparatus for producing liquid air by nitrogen compression-expansion cycle refrigeration includes a raw material air compression system, an air precooling system, an air drying and purification system, an air circulation booster system, a nitrogen circulation booster system, an expansion refrigeration system, a heat exchange cold box, and a liquid air storage tank. The raw material air compression system includes a feed air compressor and an air cooler; the air precooling system includes a refrigerated dryer; the air drying and purification system includes two adsorption dryers, one of which is in operation and the other is undergoing desorption and regeneration; the air circulation and pressurization system includes an air circulation pressurizer and a pressurized air cooler; the nitrogen circulation and pressurization system includes a nitrogen circulation pressurizer and a pressurized nitrogen cooler. The expansion and refrigeration system includes a hot-end turboexpander, a hot-end pressurizer, a cold-end turboexpander, a cold-end pressurizer, a nitrogen turboexpander, and a nitrogen pressurizer. The hot-end turboexpander has two sets of inlets and outlets: a hot-end pressurizer air inlet and outlet, and a hot-end expansion air inlet and outlet. The cold-end turboexpander has two sets of inlets and outlets: a cold-end pressurizer air inlet and outlet, and a cold-end expander air inlet and outlet. The nitrogen turboexpander has two sets of inlets and outlets: a nitrogen pressurizer inlet and outlet, and a nitrogen expander inlet and outlet. The heat exchange cold box includes a hot-end heat exchanger, a cold-end heat exchanger, and a subcooler. The hot-end heat exchanger has five sets of inlets and outlets: a first inlet and a first outlet, a second inlet and a second outlet, a third inlet and a third outlet, a fourth inlet and a fourth outlet, and a fifth inlet and a fifth outlet. The cold-end heat exchanger has four sets of inlets and outlets: a first inlet and a first outlet, a second inlet and a second outlet, a third inlet and a third outlet, and a fourth inlet and a fourth outlet. The subcooler has two sets of inlets and outlets: a first subcooling inlet and a first subcooling outlet, and a second subcooling inlet and a second subcooling outlet. The raw material air compression system, refrigerated dryer, and adsorption dryer are connected in series, and the outlet of the adsorption dryer is divided into two paths: One path is connected to the desorption gas inlet of another adsorption dryer to provide desorption gas for the regeneration of the adsorption dryer. Finally, the desorption gas is discharged into the atmosphere from the desorption gas outlet of the adsorption dryer. The other outlet of the adsorption dryer is connected to the inlet of the air circulation booster system. The outlet of the air circulation booster system is divided into two paths: one path is connected to the first inlet of the hot-end heat exchange, the first outlet of the hot-end heat exchange is connected to the inlet of the hot-end expansion air, and the outlet of the hot-end expansion air is connected to the fourth inlet of the hot-end heat exchange; the medium-pressure air from the fourth outlet of the hot-end heat exchange merges with the air from the outlet of the adsorption dryer and returns to the inlet of the air circulation booster system; the other path of the air circulation booster system outlet is connected to the air inlet of the hot-end booster compressor, the air from the hot-end booster compressor outlet is cooled by the hot-end booster cooler and then connected to the air inlet of the cold-end booster compressor, and the air from the cold-end booster compressor outlet is cooled by the cold-end booster cooler and then connected to the second inlet of the hot-end heat exchange, the second outlet of the hot-end heat exchange is further divided into two paths: One path connects to the air inlet of the cold-end expander, and the air outlet of the cold-end expander is connected to the third inlet of the cold-end heat exchange. The third outlet of the cold-end heat exchange merges with the air outlet of the hot-end expansion and connects to the fourth inlet of the hot-end heat exchange. The other path connects to the first inlet of the cold-end heat exchange. The high-pressure liquid air from the first outlet of the cold-end heat exchange is cooled and depressurized by the throttle valve V1, and then the medium-pressure liquid air is connected to the first subcooled inlet. The medium-pressure liquid air from the first subcooled outlet is throttled and depressurized again by the throttle valve V2 and then connected to the inlet of the liquid air storage tank. The liquid air enters the storage tank for storage.

[0007] Furthermore, the throttling valve V1 between the first outlet of the cold end heat exchange and the first inlet of the subcooling is a high-pressure liquid throttling valve.

[0008] Furthermore, the liquid air storage tank is an atmospheric pressure cryogenic liquid storage tank.

[0009] Furthermore, the air drying and purification system also includes an automatic control system, which is connected to the two adsorption dryers and switches the working status of the two adsorption dryers through an automatic valve.

[0010] Furthermore, the hot-end heat exchanger, cold-end heat exchanger, and subcooler all adopt aluminum alloy plate-fin heat exchangers and are arranged in three series within the heat exchange cold box.

[0011] In this invention, the cold source in the subcooler comes from a nitrogen compression-expansion refrigeration cycle: Pressurized nitrogen flows out from the outlet of the nitrogen circulation booster system and enters the inlet of the nitrogen booster compressor. After being cooled by the nitrogen booster cooler, the pressurized nitrogen enters the third inlet of the hot-end heat exchanger. After heat exchange and cooling in the hot-end heat exchanger, it is led out from the third outlet of the hot-end heat exchanger and enters the second inlet of the cold-end heat exchanger. After further cooling in the cold-end heat exchanger, the nitrogen flows out from the second outlet of the cold-end heat exchanger and enters the inlet of the nitrogen expander. After being cooled by expansion cooling, the low-pressure nitrogen enters the second subcooling inlet. After being reheated by heat exchange in the subcooler, the low-pressure nitrogen flows out from the second subcooling outlet and enters the fourth cold-end heat exchange inlet. After further recovering the cold energy of the low-temperature nitrogen by the cold-end heat exchanger, it is drawn out from the fourth cold-end heat exchange outlet and enters the fifth hot-end heat exchange inlet. Finally, the low-pressure nitrogen is reheated to room temperature in the hot-end heat exchanger and then drawn out from the fifth hot-end heat exchange outlet and returned to the nitrogen circulation pressurization system inlet. In this process, the nitrogen forms a closed loop.

[0012] The beneficial effects of this utility model are as follows: This invention significantly improves the efficiency of liquid air production through a combination of multi-stage compression, expansion refrigeration, and a high-efficiency heat exchanger. Specific advantages are as follows: 1. This invention employs a pressurized turboexpander (three units: hot-end, cold-end, and nitrogen-filled) to extract cooling capacity, effectively matching the pressurization and expansion rates to improve expansion-refrigeration efficiency. Traditional methods often use a single expander, resulting in uneven cooling distribution. This invention utilizes three expanders working in tandem: the hot-end expander handles the mid-temperature range, the cold-end expander focuses on the low-temperature range, and the nitrogen expander is dedicated to subcooling, ensuring balanced cooling capacity across all sections, reducing heat exchanger temperature differences, and minimizing heat loss.

[0013] 2. The heat exchange section is divided into three parts (hot-end heat exchanger, cold-end heat exchanger, and subcooler), arranged in series within the cold box, optimizing energy utilization efficiency during the air liquefaction process. The hot-end heat exchanger handles ambient temperature reheating and initial cooling, the cold-end heat exchanger achieves liquefaction, and the subcooler uses low-temperature nitrogen to subcool the liquid air, increasing the degree of subcooling and significantly reducing storage vaporization losses. This not only increases liquid air production but also reduces unit energy consumption, saving electricity costs compared to traditional methods.

[0014] 3. The nitrogen compression-expansion refrigeration cycle introduced in this invention is a closed-loop cycle. Except for a small amount of nitrogen supplementation during the start-up phase, there is no additional consumption during normal operation, reducing resource waste. This cycle utilizes the high specific heat capacity and expansion potential of nitrogen to provide an independent cold source, performing targeted subcooling of the liquid-air flow path, thus solving the problem of insufficient cooling capacity in traditional air circulation. Simultaneously, the series connection of the high-pressure liquid throttling valve V1 and the medium-pressure liquid throttling valve V2 achieves a gradual pressure reduction from high pressure to atmospheric pressure, preventing flash evaporation losses and improving product stability.

[0015] Other advantages, objectives, and features of this invention will be set forth in part in the description which follows, and in part will be apparent to those skilled in the art from the following examination and study, or may be learned from practice of this invention. The objectives and other advantages of this invention can be realized and obtained through the following description. Attached Figure Description

[0016] To make the objectives, technical solutions, and advantages of this utility model clearer, the preferred embodiments of this utility model will be described in detail below with reference to the accompanying drawings, wherein: Figure 1 This is a schematic diagram of the device for producing liquid air by nitrogen compression and expansion cycle refrigeration in this utility model.

[0017] Figure reference numerals: 1-Raw air compression system; 2-Refrigerated dryer; 3-Adsorption dryer; 4-Air circulation booster system; 5-Hot end booster turbine expander; 6-Hot end booster cooler; 7-Cold end booster turbine expander; 8-Cold end booster cooler; 9-Hot end heat exchanger; 10-Cold end heat exchanger; 11-Subcooler; 12-Nitrogen circulation booster system; 13-Nitrogen booster turbine expander; 14-Nitrogen booster cooler; 15-Liquid air storage tank; 1-1, Raw air compression system inlet; 1-2, Raw air compression system outlet; 21-Refrigerated dryer inlet; 22-Refrigerated dryer outlet; 31-Adsorption dryer air inlet; 32-Adsorption dryer air inlet; Attached are the air outlets for the dryer; 33-Adsorption dryer desorbed gas inlet; 34-Adsorption dryer desorbed gas outlet; 41-Air circulation booster system inlet; 42-Air circulation booster system outlet; 51-Hot-end booster compressor air inlet; 52-Hot-end booster compressor air outlet; 53-Hot-end expansion air inlet; 54-Hot-end expansion air outlet; 61-Hot-end cooling air inlet; 62-Hot-end cooling air outlet; 63-Cooling water inlet; 64-Cooling water outlet; 71-Cold-end booster compressor air inlet; 72-Cold-end booster compressor air outlet; 73-Cold-end expander air inlet; 74-Cold-end expander air outlet; 81-Cold-end cooling air outlet. 82 - Cold end cooling air outlet; 83 - Cooling water inlet; 84 - Cooling water outlet; 91 - First inlet for hot end heat exchange; 92 - Second inlet for hot end heat exchange; 93 - Third inlet for hot end heat exchange; 94 - Fourth outlet for hot end heat exchange; 95 - Fifth outlet for hot end heat exchange; 96 - First outlet for hot end heat exchange; 97 - Second outlet for hot end heat exchange; 98 - Third outlet for hot end heat exchange; 99 - Fourth inlet for hot end heat exchange; 90 - Fifth inlet for hot end heat exchange; 101 - First inlet for cold end heat exchange; 102 - Second inlet for cold end heat exchange; 103 - Third outlet for cold end heat exchange; 104 - Fourth outlet for cold end heat exchange; 105 - First outlet for cold end heat exchange. 106 - Second outlet of cold end heat exchange; 107 - Third inlet of cold end heat exchange; 108 - Fourth inlet of cold end heat exchange; 111 - First inlet of subcooling; 112 - Second outlet of subcooling; 113 - First outlet of subcooling; 114 - Second inlet of subcooling; 121 - Inlet of nitrogen circulation booster system; 122 - Outlet of nitrogen circulation booster system; 131 - Inlet of nitrogen booster; 132 - Outlet of nitrogen booster; 133 - Inlet of nitrogen expander; 134 - Outlet of nitrogen expander; 141 - Inlet of nitrogen booster cooling; 142 - Outlet of nitrogen booster cooling; 143 - Inlet of cooling water; 144 - Outlet of cooling water; 151 - Inlet of liquid air storage tank. Detailed Implementation

[0018] The following specific examples illustrate the implementation of this utility model. Those skilled in the art can easily understand other advantages and effects of this utility model from the content disclosed in this specification. This utility model can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of this utility model. It should be noted that the illustrations provided in the following embodiments are only schematic representations of the basic concept of this utility model. Unless otherwise specified, the following embodiments and features can be combined with each other.

[0019] The accompanying drawings are for illustrative purposes only and are schematic diagrams, not actual pictures. They should not be construed as limiting the present invention. To better illustrate the embodiments of the present invention, some parts in the drawings may be omitted, enlarged, or reduced, and do not represent the actual product dimensions. It is understandable to those skilled in the art that some well-known structures and their descriptions may be omitted in the drawings.

[0020] In the accompanying drawings of this utility model, the same or similar reference numerals correspond to the same or similar components. In the description of this utility model, it should be understood that if terms such as "upper," "lower," "left," "right," "front," and "rear" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, they are only for the convenience of describing this utility model and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, the terms used to describe positional relationships in the drawings are only for illustrative purposes and should not be construed as limiting this utility model. For those skilled in the art, the specific meaning of the above terms can be understood according to the specific circumstances.

[0021] Example 1 Please see Figure 1 The device is a nitrogen compression and expansion cycle refrigeration device for producing liquid air, including a raw material air compression system, an air precooling system, an air drying and purification system, an air circulation and pressurization system 4, a nitrogen circulation and pressurization system 12, an expansion refrigeration system, a heat exchange cold box and a liquid air storage tank 15. The raw material air compression system 1 includes a feed air compressor and an air cooler; the air precooling system includes a refrigerated dryer 2; the air drying and purification system includes two adsorption dryers 3, which operate in a switching mode, with one working while the other performs desorption and regeneration; the air circulation booster system 4 includes an air circulation booster and a booster air cooler; the nitrogen circulation booster system 12 includes a nitrogen circulation booster and a booster nitrogen cooler. The expansion refrigeration system includes a hot-end booster turbine expander 5, a hot-end booster cooler 6, a cold-end booster turbine expander 7, a cold-end booster cooler 8, a nitrogen booster turbine expander 13, and a nitrogen booster cooler 14. The hot-end booster turbine expander has two sets of inlets and outlets: a hot-end booster air inlet 51 and a hot-end booster air outlet 52, and a hot-end expansion air inlet 53 and a hot-end expansion air outlet 54. The cold-end booster turbine expander also has two sets of inlets and outlets: a cold-end booster air inlet 53 and a cold-end expansion air outlet 54. The cold-end turbocharger has an air inlet 71 and an air outlet 72; the cold-end expander has an air inlet 73 and an air outlet 74; the nitrogen turbocharger expander has two sets of inlets and outlets: a nitrogen turbocharger inlet 131 and a nitrogen turbocharger outlet 132, and a nitrogen expander inlet 133 and a nitrogen expander outlet 134; the hot-end turbocharger cooler 6 has two sets of inlets and outlets: a hot-end cooling air inlet 61 and a hot-end cooling air outlet 62, and a cooling water inlet 63 and a cooling water outlet 64. The cold-end turbocharger cooler 8 has two sets of inlets and outlets: a cold-end cooling air inlet 81 and a cold-end cooling air outlet 82, and a cooling water inlet 83 and a cooling water outlet 84. The nitrogen turbocharger cooler 14 has two sets of inlets and outlets: a nitrogen turbocharger cooling inlet 141 and a nitrogen turbocharger cooling outlet 142, and a cooling water inlet 143 and a cooling water outlet 144.

[0022] The heat exchange cold box includes a hot-end heat exchanger 9, a cold-end heat exchanger 10, and a subcooler 11. The hot-end heat exchanger has five sets of inlets and outlets: a first inlet 91 and a first outlet 96, a second inlet 92 and a second outlet 97, a third inlet 93 and a third outlet 98, a fourth inlet 99 and a fourth outlet 94, and a fifth inlet 90 and a fifth outlet 95. The cold-end heat exchanger is equipped with… There are four sets of inlets and outlets: the first inlet 101 and the first outlet 105 for cold end heat exchange, the second inlet 102 and the second outlet 106 for cold end heat exchange, the third inlet 107 and the third outlet 103 for cold end heat exchange, and the fourth inlet 108 and the fourth outlet 104 for cold end heat exchange; the subcooler has two sets of inlets and outlets: the first subcooling inlet 111 and the first subcooling outlet 113, and the second subcooling inlet 114 and the second subcooling outlet 112. The raw material air compression system 1, the refrigerated dryer 2, and the adsorption dryer are connected in series 3. The air outlet 32 ​​of the adsorption dryer is divided into two paths: One path is connected to the desorption gas inlet 33 of another adsorption dryer to provide desorption gas for the regeneration of the adsorption dryer. Finally, the desorption gas is discharged into the atmosphere from the desorption gas outlet 34 of the adsorption dryer.

[0023] Another path from the outlet of the adsorption dryer is connected to the inlet 41 of the air circulation booster system. The outlet 42 of the air circulation booster system is divided into two paths: one path is connected to the first inlet 91 of the hot end heat exchange, the first outlet 96 of the hot end heat exchange is connected to the inlet 53 of the hot end expansion air, and the outlet 54 of the hot end expansion air is connected to the fourth inlet 99 of the hot end heat exchange; the medium-pressure air from the fourth outlet 94 of the hot end heat exchange merges with the air from the air outlet 32 ​​of the adsorption dryer and returns to the inlet 41 of the air circulation booster system; the other path from the outlet 42 of the air circulation booster system is connected to the air inlet 51 of the hot end booster compressor, the air from the outlet 52 of the hot end booster compressor is cooled by the hot end booster cooler 6 and then connected to the air inlet 71 of the cold end booster compressor, the air from the outlet 72 of the cold end booster compressor is cooled by the cold end booster cooler 8 and then connected to the second inlet 92 of the hot end heat exchange, and the second outlet 97 of the hot end heat exchange is further divided into two paths: One path connects to the cold-end expander air inlet 73, and the cold-end expander air outlet 74 connects to the cold-end heat exchange third inlet 107. The cold-end heat exchange third outlet 103 merges with the hot-end expansion air outlet 54 and connects to the hot-end heat exchange fourth inlet 99. The other path connects to the cold-end heat exchange first inlet 101. The high-pressure liquid air from the cold-end heat exchange first outlet 105 is cooled and depressurized by the throttle valve V1, and then connected to the subcooled first inlet 111. The medium-pressure liquid air from the subcooled first outlet 113 is throttled and depressurized again by the throttle valve V2 and then connected to the liquid air storage tank inlet 151. The liquid air enters the storage tank 15 for storage.

[0024] To ensure the subcooling of the liquid air product in the liquid air storage tank 15, this invention introduces a nitrogen compression-expansion refrigeration cycle to subcool the liquid air flow path. This cycle is a closed loop, and the specific flow path is as follows: The pressurized nitrogen flows out from the outlet 122 of the nitrogen circulation pressurization system and connects to the inlet 131 of the nitrogen booster. After being cooled by the nitrogen booster cooler 14, the nitrogen at the outlet 132 of the nitrogen booster connects to the third inlet 93 of the hot end heat exchange. The third outlet 98 of the hot end heat exchange connects to the second inlet 102 of the cold end heat exchange. The second outlet 106 of the cold end heat exchange connects to the inlet 133 of the nitrogen expander. The low-pressure nitrogen, after being cooled by expansion and cooling, connects to the second subcooling inlet 114. After being heated by the subcooler 11, the low-pressure nitrogen flows out from the second subcooling outlet 112 and enters the fourth inlet 108 of the cold end heat exchange. After further recovering the cold energy of the low-temperature nitrogen through the cold end heat exchanger, it enters the fifth inlet 90 of the hot end heat exchange from the fourth outlet 104 of the cold end heat exchange. Finally, the low-pressure nitrogen is reheated to room temperature and returns to the inlet 121 of the nitrogen circulation pressurization system from the fifth outlet 95 of the hot end heat exchange. In this process, the nitrogen forms a closed loop.

[0025] The nitrogen compression-expansion refrigeration cycle is a closed-loop cycle. Except for the initial stage where nitrogen needs to be supplied, no additional nitrogen is consumed during normal operation. The air drying and purification system consists of two adsorption dryers 3. An automatic control system controls the automatic valve to switch between the two adsorption dryers, ensuring that one adsorption dryer is working while the other is desorption and regeneration. A high-pressure liquid throttling valve V1 is used to throttle, cool, and depressurize the liquid air between the first cold-end heat exchange outlet 105 and the first subcooling inlet 111. The hot-end heat exchanger 9, the cold-end heat exchanger 10, and the subcooler 11 all adopt aluminum alloy plate-fin heat exchangers and are arranged in three series in the heat exchange cold box.

[0026] The liquid air production process using the apparatus described in this embodiment is as follows: Air enters through the raw material air compression system inlet 1-1 of the raw material air compression system 1, and isothermally compressed to obtain medium-pressure air. This medium-pressure air then enters the refrigerated dryer 2 through the raw material air compression system outlet 1-2 and the refrigerated dryer inlet 21 for pre-cooling. It then enters the adsorption dryer 3 through the adsorption dryer outlet 22 and the adsorption dryer air inlet 31 to remove moisture, carbon dioxide, and other impurities. The dry and clean medium-pressure air exiting the adsorption dryer outlet 32 ​​is divided into two paths: One path provides desorption gas to another adsorption dryer in the regeneration process, and finally the desorption gas is discharged into the atmosphere from the adsorption dryer desorption gas outlet 34.

[0027] The other path merges with the medium-pressure air returning from the fourth outlet 94 of the hot end heat exchange and enters the air circulation and pressurization system 4 for further pressurization. The high-pressure air obtained by isothermal compression in the air circulation and pressurization system 4 is then divided into two paths again: The air enters the first inlet 91 of the hot end heat exchanger, is cooled in the hot end heat exchanger, and is then drawn out from the first outlet 96 of the hot end heat exchanger. It then enters the hot end expansion air inlet 53, expands and cools, and is drawn out from the hot end expansion air outlet 54. It returns to the fourth inlet 99 of the hot end heat exchanger, is reheated to room temperature by the hot end heat exchanger, and is drawn out from the fourth outlet 94 of the hot end heat exchanger. It then merges with the air from the air outlet 32 ​​of the adsorption dryer and returns to the air circulation pressurization system inlet 41. Another path from the air circulation booster system outlet 42 enters the hot-end booster air inlet 51. The boosted air is cooled by the hot-end booster cooler 6 and then enters the cold-end booster air inlet 71. After being boosted again, it exits from the cold-end booster air outlet 72, is cooled by the cold-end booster cooler 8, and then enters the hot-end heat exchanger second inlet 92. The air, further cooled in the hot-end heat exchanger, exits from the hot-end heat exchanger second outlet 97, and is then split into two paths once more. The air enters the cold-end expander air inlet 73, and the medium-pressure air obtained after expansion and cooling is drawn out from the cold-end expander air outlet 74. The drawn-out medium-pressure air returns to the cold-end heat exchange third inlet 107, and after heat exchange in the cold-end heat exchanger, it is drawn out from the cold-end heat exchange third outlet 103, and merges with the air from the hot-end expansion air outlet 54 and is connected to the hot-end heat exchange fourth inlet 99. Another path enters the first inlet 101 of the cold end heat exchange. After being cooled by the heat exchange, the air becomes high-pressure liquid air and is led out from the first outlet 105 of the cold end heat exchange. After being cooled and depressurized by the throttling valve V1, the medium-pressure liquid air enters the first subcooling inlet 111. After being subcooled in the subcooler, the liquid air is throttled and depressurized again by the throttling valve V2 and then sent to the liquid air storage tank 15 for storage as a liquid air product.

[0028] The cold source in the subcooler 11 comes from the nitrogen compression-expansion refrigeration cycle introduced in this invention, and the specific flow path is as follows: Pressurized nitrogen flows out from outlet 122 of the nitrogen circulation booster system and enters inlet 131 of the nitrogen booster. After being cooled by nitrogen booster cooler 14, the pressurized nitrogen enters the third inlet 93 of the hot end heat exchanger. After being cooled by heat exchange in the hot end heat exchanger, it is led out from the third outlet 98 of the hot end heat exchanger and enters the second inlet 102 of the cold end heat exchanger. After being further cooled by the cold end heat exchanger, the nitrogen flows out from the second outlet 106 of the cold end heat exchanger and enters inlet 133 of the nitrogen expander. After being cooled by expansion and cooling, the low-pressure nitrogen enters... The low-pressure nitrogen gas, after being reheated by the heat exchanger 11, flows out from the second subcooling outlet 112 and enters the fourth cold-end heat exchange inlet 108. After the cold-end heat exchanger further recovers the cold energy of the low-temperature nitrogen gas, it is drawn out from the fourth cold-end heat exchange outlet 104 and enters the fifth hot-end heat exchange inlet 90. The low-pressure nitrogen gas is finally reheated to room temperature in the hot-end heat exchanger and then drawn out from the fifth hot-end heat exchange outlet 95 and returned to the nitrogen gas circulation pressurization system inlet 121. The nitrogen gas forms a closed loop in this process.

[0029] In this embodiment, the high-pressure air obtained by the air circulation booster system is 2.8~3.2MPa(A), and then boosted to 5.6~6.0MPa(A) by the hot end booster and cold end booster. The nitrogen pressure obtained by the nitrogen circulation pressurization system is 0.9~1.3MPa(A), and then pressurized to 1.2~1.6MPa(A) by the nitrogen expansion pressurizer. The circulating booster compressor uses variable frequency start-up to reduce the impact of startup on the power grid; Liquid air production facilities operate during periods of low electricity prices and shut down during periods of high electricity prices.

[0030] The raw material air used in this embodiment is 5700 Nm³. 3 / h, 0.098MPa (A). Product liquid air obtained: 4200 Nm³3 / h (converted to gaseous state).

[0031] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of this utility model and are not intended to limit it. Although this utility model has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solution of this utility model without departing from the spirit and scope of this technical solution, and all such modifications or substitutions should be covered within the scope of the claims of this utility model.

Claims

1. A device for producing liquid air through nitrogen compression and expansion cycle refrigeration, characterized in that: It includes a raw material air compression system, an air precooling system, an air drying and purification system, an air circulation booster system, a nitrogen circulation booster system, an expansion refrigeration system, a heat exchange cold box, and a liquid air storage tank; The raw material air compression system includes a feed air compressor and an air cooler; the air precooling system includes a refrigerated dryer; the air drying and purification system includes two adsorption dryers, one of which is in operation and the other is undergoing desorption and regeneration; the air circulation and pressurization system includes an air circulation pressurizer and a pressurized air cooler; the nitrogen circulation and pressurization system includes a nitrogen circulation pressurizer and a pressurized nitrogen cooler. The expansion and refrigeration system includes a hot-end turboexpander, a hot-end pressurizer, a cold-end turboexpander, a cold-end pressurizer, a nitrogen turboexpander, and a nitrogen pressurizer. The hot-end turboexpander has two sets of inlets and outlets: a hot-end pressurizer air inlet and outlet, and a hot-end expansion air inlet and outlet. The cold-end turboexpander has two sets of inlets and outlets: a cold-end pressurizer air inlet and outlet, and a cold-end expander air inlet and outlet. The nitrogen turboexpander has two sets of inlets and outlets: a nitrogen pressurizer inlet and outlet, and a nitrogen expander inlet and outlet. The heat exchange cold box includes a hot-end heat exchanger, a cold-end heat exchanger, and a subcooler. The hot-end heat exchanger has five sets of inlets and outlets: a first inlet and a first outlet, a second inlet and a second outlet, a third inlet and a third outlet, a fourth inlet and a fourth outlet, and a fifth inlet and a fifth outlet. The cold-end heat exchanger has four sets of inlets and outlets: a first inlet and a first outlet, a second inlet and a second outlet, a third inlet and a third outlet, and a fourth inlet and a fourth outlet. The subcooler has two sets of inlets and outlets: a first subcooling inlet and a first subcooling outlet, and a second subcooling inlet and a second subcooling outlet. The raw material air compression system, refrigerated dryer, and adsorption dryer are connected in series, and the outlet of the adsorption dryer is divided into two paths: One path is connected to the desorption gas inlet of another adsorption dryer to provide desorption gas for the regeneration of the adsorption dryer. Finally, the desorption gas is discharged into the atmosphere from the desorption gas outlet of the adsorption dryer. The other outlet of the adsorption dryer is connected to the inlet of the air circulation booster system. The outlet of the air circulation booster system is divided into two paths: one path is connected to the first inlet of the hot-end heat exchange, the first outlet of the hot-end heat exchange is connected to the inlet of the hot-end expansion air, and the outlet of the hot-end expansion air is connected to the fourth inlet of the hot-end heat exchange; the medium-pressure air from the fourth outlet of the hot-end heat exchange merges with the air from the outlet of the adsorption dryer and returns to the inlet of the air circulation booster system; the other path of the air circulation booster system outlet is connected to the air inlet of the hot-end booster compressor, the air from the hot-end booster compressor outlet is cooled by the hot-end booster cooler and then connected to the air inlet of the cold-end booster compressor, and the air from the cold-end booster compressor outlet is cooled by the cold-end booster cooler and then connected to the second inlet of the hot-end heat exchange, the second outlet of the hot-end heat exchange is further divided into two paths: One path connects to the air inlet of the cold-end expander, and the air outlet of the cold-end expander is connected to the third inlet of the cold-end heat exchange. The third outlet of the cold-end heat exchange merges with the air outlet of the hot-end expansion and connects to the fourth inlet of the hot-end heat exchange. The other path connects to the first inlet of the cold-end heat exchange. The high-pressure liquid air from the first outlet of the cold-end heat exchange is cooled and depressurized by the throttle valve V1, and then the medium-pressure liquid air is connected to the first subcooled inlet. The medium-pressure liquid air from the first subcooled outlet is throttled and depressurized again by the throttle valve V2 and then connected to the inlet of the liquid air storage tank. The liquid air enters the storage tank for storage.

2. The apparatus for producing liquid air by nitrogen compression and expansion cycle refrigeration according to claim 1, characterized in that: The throttling valve V1 between the first outlet of the cold end heat exchange and the first inlet of the subcooling is a high-pressure liquid throttling valve.

3. The apparatus for producing liquid air by nitrogen compression and expansion cycle refrigeration according to claim 1, characterized in that: The liquid air storage tank is an atmospheric pressure cryogenic liquid storage tank.

4. The apparatus for producing liquid air by nitrogen compression and expansion cycle refrigeration according to claim 1, characterized in that: The air drying and purification system also includes an automatic control system, which is connected to the two adsorption dryers and switches the working status of the two adsorption dryers through an automatic valve.

5. The apparatus for producing liquid air by nitrogen compression and expansion cycle refrigeration according to claim 1, characterized in that: The hot-end heat exchanger, cold-end heat exchanger, and subcooler all use aluminum alloy plate-fin heat exchangers and are arranged in three series within the heat exchange cold box.

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