Method and device for separating oxygen and nitrogen in liquid air

Abstract

The invention relates to the technical field of liquid air energy storage, and particularly discloses a method and a device for separating oxygen and nitrogen in liquid air. The device comprises a liquid air storage tank, a liquid pump, a rectifying tower, a subcooler, a main heat exchanger, a liquid nitrogen storage tank, a liquid oxygen storage tank and a nitrogen circulating compressor. The rectifying tower realizes oxygen-nitrogen separation through structured packing and a condensation evaporator, liquid air is used as a raw material, pressurized through a liquid pump and then fed into the rectifying tower for rectification, and nitrogen and liquid oxygen products are obtained. The nitrogen is recycled through reheating, compression and heat exchange so as to condense and evaporate liquid oxygen to generate liquid nitrogen. Part of the liquid nitrogen is stored after throttling, and part of the liquid nitrogen serves as reflux liquid to continue to participate in rectification. External cooling capacity supplement is not needed, thermodynamic characteristics of liquid air are fully utilized, oxygen and nitrogen separation energy consumption is reduced, the process is simplified, the number of devices is reduced, investment and maintenance cost is reduced, and resource waste is avoided. The device is especially suitable for application scenarios with liquid nitrogen requirements far higher than liquid oxygen.

Description

Technical Field

[0001] The invention belongs to the technical field of liquid air energy storage and relates to a method and device for separating oxygen and nitrogen from liquid air. Background Art

[0002] Liquid air energy storage technology is an emerging energy storage technology. Its basic principle is to cool air to an extremely low temperature through an air liquefaction device to turn it into liquid form for storage and use. This technology has broad application prospects and is a new technology that can solve the problem of energy storage and conversion for us.

[0003] At present, liquid air energy storage is mainly used for power generation and cold storage, but there is no corresponding example of directly using it to separate and obtain low-temperature oxygen and nitrogen liquid products, and this field is still blank; the efficiency of liquid air power generation and cold storage for the reuse of liquid air is relatively low, and the potential of liquid air itself has not been fully developed. If the liquid air converted from liquid air energy storage technology is directly separated, its own thermodynamic properties will be fully utilized and the efficiency will be higher. Compared with traditional full liquid air separation, the production and operation costs will be greatly reduced.

[0004] Overall, the technology of separating oxygen and nitrogen from liquid air has broad application prospects and is expected to provide us with a better option for solving the problems of energy storage and conversion. Summary of the invention

[0005] In view of this, the object of the present invention is to solve the above-mentioned problem and provide a method and device for separating oxygen and nitrogen in liquid air.

[0006] In order to achieve the above object, the present invention provides the following technical solutions:

[0007] A liquid air oxygen and nitrogen separation device, comprising a liquid air storage tank, a liquid pump, a distillation tower, a subcooler, a main heat exchanger, a liquid nitrogen storage tank, a liquid oxygen storage tank, and a nitrogen circulation compressor;

[0008] The distillation tower comprises a tower body, a structured packing arranged in the tower body, and a condenser evaporator integrated in the lower part of the tower body; the tower body is provided with five inlets and outlets, namely, a liquid nitrogen inlet, a liquid air inlet, a liquid oxygen outlet, an oxygen outlet, and a nitrogen outlet; the subcooler is provided with two groups of inlets and outlets, namely, a first inlet of the subcooler, a first outlet of the subcooler, a second inlet of the subcooler, and a second outlet of the subcooler; the main heat exchanger is provided with three groups of inlets and outlets, namely, a first inlet of the main heat exchanger, a first outlet of the main heat exchanger, a second inlet of the main heat exchanger, a second outlet of the main heat exchanger, a third inlet of the main heat exchanger, and a third outlet of the main heat exchanger;

[0009] The liquid air storage tank is connected to the liquid air inlet via a liquid pump, the nitrogen outlet is connected to the first inlet of the subcooler, and the first outlet of the subcooler is connected to the first inlet of the main heat exchanger; the first outlet of the main heat exchanger is connected to the inlet of the nitrogen circulation compressor, the outlet of the nitrogen circulation compressor is connected to the third inlet of the main heat exchanger, the third outlet of the main heat exchanger is connected to the inlet of the condenser evaporator, the outlet of the condenser evaporator is connected to the second inlet of the subcooler, and the second outlet of the subcooler is divided into two paths, one path is connected to the nitrogen inlet via a first throttle valve, and the other path is connected to the liquid nitrogen storage tank via a second throttle valve; the oxygen outlet is connected to the second inlet of the main heat exchanger, and the second outlet of the main heat exchanger is connected to a low-pressure oxygen pipeline network or to the atmosphere for venting; the liquid oxygen outlet is connected to the liquid oxygen storage tank.

[0010] Preferably, the distillation tower is a structured packing reboiler absorption tower.

[0011] Preferably, the liquid oxygen storage tank and the liquid nitrogen storage tank are both normal pressure low-temperature liquid storage tanks.

[0012] Preferably, the liquid-air storage tank is a normal-pressure low-temperature liquid storage tank.

[0013] Preferably, the liquid pump is a centrifugal cryogenic liquid pump.

[0014] Preferably, the condenser-evaporator is a fully immersed liquid oxygen plate-fin condenser-evaporator.

[0015] Preferably, the nitrogen circulation compressor is a centrifugal nitrogen circulation compressor.

[0016] Preferably, the main heat exchanger and the subcooler are both plate-fin heat exchangers.

[0017] A method for separating oxygen and nitrogen from liquid air, using the above-mentioned device for separating oxygen and nitrogen from liquid air, taking liquid air obtained by storing liquid air in a liquid air storage tank as a raw material, and sending it to the middle of a distillation tower as a stripping section reflux liquid to participate in distillation after being pressurized by a liquid pump; obtaining nitrogen at the top of the distillation tower, and sending it to a nitrogen circulation compressor for pressurization after being reheated to room temperature through a subcooler and a main heat exchanger, and then entering the main heat exchanger again for heat exchange and cooling, and then returning to the condenser evaporator at the bottom of the distillation tower to exchange heat with the liquid oxygen at the bottom of the distillation tower, the nitrogen partially evaporates the liquid oxygen, and the nitrogen itself is condensed into liquid nitrogen, the liquid nitrogen enters the subcooler for supercooling, a part of the supercooled liquid nitrogen is throttled and sent to a liquid nitrogen storage tank, and the other part is throttled and sent to the top of the distillation tower as a distillation section reflux liquid to continue to participate in distillation; a part of the liquid oxygen at the bottom of the distillation tower is evaporated by the nitrogen as the rising steam of the distillation tower to participate in distillation, and the other part is sent to the liquid oxygen storage tank as a product.

[0018] The beneficial effects of the present invention are:

[0019] 1. The present invention uses liquid air as raw material to directly separate oxygen and nitrogen to obtain liquid oxygen and liquid nitrogen products, which is different from the traditional full liquid air separation using air as raw material. When oxygen and nitrogen are separated by liquid air, the thermodynamic properties of liquid air itself are fully utilized. The whole process does not require the supplement of external cooling capacity, and there is no cycle refrigeration for pressurization and expansion, which reduces the energy consumption of oxygen and nitrogen separation and improves the economic benefits of oxygen and nitrogen separation.

[0020] 2. The nitrogen obtained in the distillation process of the present invention is recycled, so that the entire device does not consume additional nitrogen in the remaining stages except for the additional nitrogen consumption during the startup process, and only the nitrogen produced by itself is recycled for use by the device.

[0021] 3. The present invention uses liquid air as raw material, omits the pre-cooling system and purification system, has no top condenser evaporator, has a short oxygen and nitrogen separation process, requires less equipment, reduces equipment failure points, increases equipment operation reliability, saves overall investment and equipment maintenance costs. At the same time, there is no exhaust gas, sewage and dust emission during the production process.

[0022] 4. The present invention is particularly suitable for scenarios where the demand ratio of liquid nitrogen to liquid oxygen is more than 2.5 times. It can separate the liquid air obtained from liquid air energy storage into the required oxygen and nitrogen products while avoiding the waste of a large amount of nitrogen and the consumption of energy.

[0023] Other advantages, objectives and features of the present invention will be described in the following description to some extent, and to some extent, will be obvious to those skilled in the art based on the following examination and study, or can be taught from the practice of the present invention. The objectives and other advantages of the present invention can be realized and obtained through the following description. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to make the purpose, technical solutions and advantages of the present invention more clear, the present invention will be described in detail below in conjunction with the accompanying drawings, wherein:

[0025] Figure 1 It is a schematic diagram of the liquid air oxygen and nitrogen separation device of the present invention.

[0026] Figure numerals: 1-distillation tower; 2-subcooler; 3-main heat exchanger; 4-liquid air storage tank; 5-liquid pump; 6-nitrogen circulation compressor; 7-liquid oxygen storage tank; 8-liquid nitrogen storage tank; 11-liquid nitrogen inlet; 12-liquid air inlet; 13-condenser evaporator inlet; 14-liquid oxygen outlet; 15-condenser evaporator outlet; 16-oxygen outlet; 17-nitrogen outlet; 21-first inlet of subcooler; 22-first outlet of subcooler; 23-second inlet of subcooler; 24-second outlet of subcooler; 31-first inlet of main heat exchange; 32-second inlet of main heat exchange; 33-third outlet of main heat exchange; 34-first outlet of main heat exchange; 35-second outlet of main heat exchange; 36-third inlet of main heat exchange. DETAILED DESCRIPTION

[0027] The following describes the embodiments of the present invention by specific examples, and those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that the illustrations provided in the following embodiments only illustrate the basic concept of the present invention in a schematic manner, and the following embodiments and features in the embodiments can be combined with each other without conflict.

[0028] Among them, the drawings are only used for illustrative explanations, and they only represent schematic diagrams rather than actual pictures, and should not be understood as limitations on the present invention. In order to better illustrate the embodiments of the present invention, some parts of the drawings may be omitted, enlarged or reduced, and do not represent the size of actual products. For those skilled in the art, it is understandable that some well-known structures and their descriptions in the drawings may be omitted.

[0029] The same or similar numbers in the drawings of the embodiments of the present invention correspond to the same or similar parts; in the description of the present invention, it should be understood that if the terms "upper", "lower", "left", "right", "front", "rear", etc. indicate the orientation or position relationship, they are based on the orientation or position relationship shown in the drawings, which is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operate in a specific orientation. Therefore, the terms describing the position relationship in the drawings are only used for illustrative purposes and cannot be understood as limiting the present invention. For ordinary technicians in this field, the specific meanings of the above terms can be understood according to specific circumstances.

[0030] See also Figure 1 , which is a liquid air oxygen and nitrogen separation device, comprising a liquid air storage tank 4, a liquid pump 5, a distillation tower 1, a subcooler 2, a main heat exchanger 3, a liquid nitrogen storage tank 8, a liquid oxygen storage tank 7, and a nitrogen circulation compressor 6;

[0031] The distillation tower 1 includes a tower body, a structured packing arranged in the tower body, and a condenser evaporator integrated in the lower part of the tower body; the tower body is provided with five inlets and outlets, namely a liquid nitrogen inlet 11, a liquid air inlet 12, a liquid oxygen outlet 14, an oxygen outlet 16, and a nitrogen outlet 17; the subcooler 2 is provided with two groups of inlets and outlets, namely a first inlet 21 of the subcooler, a first outlet 22 of the subcooler, a second inlet 23 of the subcooler, and a second outlet 24 of the subcooler; the main heat exchanger 3 is provided with three groups of inlets and outlets, namely a first inlet 31 of the main heat exchange, a first outlet 34 of the main heat exchange, a second inlet 32 ​​of the main heat exchange, a second outlet 35 of the main heat exchange, a third inlet 36 of the main heat exchange, and a third outlet 33 of the main heat exchange;

[0032] The liquid air storage tank 4 is connected to the liquid air inlet 12 via the liquid pump 5, the nitrogen outlet 17 is connected to the first inlet 21 of the subcooler, and the first outlet 22 of the subcooler is connected to the first inlet 31 of the main heat exchange; the first outlet 34 of the main heat exchange is connected to the inlet of the nitrogen circulation compressor 6, the outlet of the nitrogen circulation compressor 6 is connected to the third inlet 36 of the main heat exchange, the third outlet 33 of the main heat exchange is connected to the inlet 13 of the condenser evaporator, the outlet 15 of the condenser evaporator is connected to the second inlet 23 of the subcooler, and the second outlet 24 of the subcooler is divided into two paths, one path is connected to the nitrogen inlet via the first throttle valve V1, and the other path is connected to the liquid nitrogen storage tank 8 via the second throttle valve V2; the oxygen outlet 16 is connected to the second inlet 32 ​​of the main heat exchange, and the second outlet 35 of the main heat exchange is connected to the low-pressure oxygen pipeline network or connected to the atmosphere for venting; the liquid oxygen outlet 14 is connected to the liquid oxygen storage tank 7.

[0033] As a preferred choice, in this embodiment, the distillation tower 1 is a structured packing reboiling absorption tower. The liquid oxygen storage tank 7 and the liquid nitrogen storage tank 8 are both atmospheric low-temperature liquid storage tanks. The liquid air storage tank 4 is an atmospheric low-temperature liquid storage tank. The liquid pump 5 is a centrifugal low-temperature liquid pump 5. The condenser evaporator is a fully immersed liquid oxygen plate-fin condenser evaporator. The nitrogen circulation compressor 6 is a centrifugal nitrogen circulation compressor 6. The main heat exchanger 3 and the subcooler 2 are both plate-fin heat exchangers.

[0034] A method for separating oxygen and nitrogen from liquid air, using the above-mentioned device for separating oxygen and nitrogen from liquid air, taking the liquid air obtained by storing liquid air in the liquid air storage tank as a raw material, and sending it to the middle of the distillation tower 1 as the reflux liquid of the stripping section to participate in distillation after being pressurized by a liquid pump 5; obtaining nitrogen at the top of the distillation tower 1, and reheating it to room temperature through a subcooler 2 and a main heat exchanger 3, and then sending it to a nitrogen circulation compressor 6 for pressurization, and then entering the main heat exchanger 3 again for heat exchange and cooling, and then returning to the condensation vapor at the bottom of the distillation tower 1 In the evaporator, heat is exchanged with the liquid oxygen at the bottom of the distillation tower 1, and the nitrogen partially evaporates the liquid oxygen. At the same time, the nitrogen itself is condensed into liquid nitrogen. The liquid nitrogen enters the subcooler 2 for supercooling. Part of the supercooled liquid nitrogen is throttled and sent to the liquid nitrogen storage tank 8, and the other part is throttled and sent to the top of the distillation tower 1 as the reflux liquid of the distillation section to continue to participate in the distillation; part of the liquid oxygen at the bottom of the distillation tower 1 is evaporated by the nitrogen and participates in the distillation as the rising steam of the distillation tower 1, and the other part is sent to the liquid oxygen storage tank 7 as a product.

[0035] Among them, liquid air is pressurized by a liquid pump and sent to the distillation tower, with a connection pressure of about 0.4MPa and an interface diameter of DN80. Nitrogen is pressurized by a nitrogen circulation compressor and sent to the main heat exchanger, with a connection point pressure of about 0.55MPa and an interface diameter of DN250. Oxygen is drawn from the main heat exchanger and sent to the low-pressure oxygen network or vented, with a connection point pressure of about 135kPa and an interface diameter of DN65. Liquid oxygen is taken out from the bottom of the distillation tower and sent to the liquid oxygen storage tank, with a connection point pressure of about 145kPa and an interface diameter of DN40. Liquid nitrogen is taken out from the subcooler and sent to the liquid nitrogen storage tank, with a connection point pressure of about 0.3MPa and an interface diameter of DN65.

[0036] Raw materials used in the present invention: Liquid air: 7500Nm 3 / h (converted to gas), 0.4MPa. The obtained product: liquid nitrogen: 5600Nm 3 / h (converted to gas); liquid oxygen: 1500Nm 3 / h (converted to gas); oxygen: 73Nm 3 / h, 135kPa.

[0037] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the purpose and scope of the technical solution, which should be included in the scope of the claims of the present invention.

Claims

1. A device for separating oxygen and nitrogen from liquid air, characterized in that: Including liquid air storage tank, liquid pump, distillation tower, subcooler, main heat exchanger, liquid nitrogen storage tank, liquid oxygen storage tank, nitrogen circulation compressor; The distillation tower comprises a tower body, a structured packing arranged in the tower body, and a condenser evaporator integrated in the lower part of the tower body; the tower body is provided with five inlets and outlets, namely, a liquid nitrogen inlet, a liquid air inlet, a liquid oxygen outlet, an oxygen outlet, and a nitrogen outlet; the subcooler is provided with two groups of inlets and outlets, namely, a first inlet of the subcooler, a first outlet of the subcooler, a second inlet of the subcooler, and a second outlet of the subcooler; the main heat exchanger is provided with three groups of inlets and outlets, namely, a first inlet of the main heat exchanger, a first outlet of the main heat exchanger, a second inlet of the main heat exchanger, a second outlet of the main heat exchanger, a third inlet of the main heat exchanger, and a third outlet of the main heat exchanger; The liquid air storage tank is connected to the liquid air inlet via a liquid pump, the nitrogen outlet is connected to the first inlet of the subcooler, and the first outlet of the subcooler is connected to the first inlet of the main heat exchanger; the first outlet of the main heat exchanger is connected to the inlet of the nitrogen circulation compressor, the outlet of the nitrogen circulation compressor is connected to the third inlet of the main heat exchanger, the third outlet of the main heat exchanger is connected to the inlet of the condenser evaporator, the outlet of the condenser evaporator is connected to the second inlet of the subcooler, and the second outlet of the subcooler is divided into two paths, one path is connected to the nitrogen inlet via a first throttle valve, and the other path is connected to the liquid nitrogen storage tank via a second throttle valve; the oxygen outlet is connected to the second inlet of the main heat exchanger, and the second outlet of the main heat exchanger is connected to a low-pressure oxygen pipeline network or to the atmosphere for venting; the liquid oxygen outlet is connected to the liquid oxygen storage tank.

2. The device for separating oxygen and nitrogen from liquid air according to claim 1, characterized in that: The distillation tower is a structured packing reboiling absorption tower.

3. The device for separating oxygen and nitrogen from liquid air according to claim 1, characterized in that: The liquid oxygen storage tank and the liquid nitrogen storage tank are both normal pressure low temperature liquid storage tanks.

4. The device for separating oxygen and nitrogen from liquid air according to claim 1, characterized in that: The liquid-air storage tank is a normal-pressure low-temperature liquid storage tank.

5. The device for separating oxygen and nitrogen from liquid air according to claim 1, characterized in that: The liquid pump is a centrifugal cryogenic liquid pump.

6. The device for separating oxygen and nitrogen from liquid air according to claim 1, characterized in that: The condenser evaporator is a fully immersed liquid oxygen plate-fin condenser evaporator.

7. The device for separating oxygen and nitrogen from liquid air according to claim 1, characterized in that: The nitrogen circulation compressor is a centrifugal nitrogen circulation compressor.

8. The device for separating oxygen and nitrogen from liquid air according to claim 1, characterized in that: The main heat exchanger and the subcooler are both plate-fin heat exchangers.

9. A method for separating oxygen and nitrogen in liquid air, characterized in that: The liquid air oxygen-nitrogen separation device as claimed in any one of claims 1 to 8 is used, and the liquid air obtained by storing liquid air in the liquid air storage tank is used as a raw material, and is sent to the middle of the distillation tower as the reflux liquid of the stripping section to participate in the distillation after being pressurized by a liquid pump; nitrogen is obtained at the top of the distillation tower and is reheated to room temperature through a subcooler and a main heat exchanger and then sent to a nitrogen circulation compressor for pressurization, and then enters the main heat exchanger again for heat exchange and cooling, and then returns to the condenser evaporator at the bottom of the distillation tower to exchange heat with the liquid oxygen at the bottom of the distillation tower, the nitrogen partially evaporates the liquid oxygen, and the nitrogen itself is condensed into liquid nitrogen, the liquid nitrogen enters the subcooler for supercooling, a part of the supercooled liquid nitrogen is throttled and sent to the liquid nitrogen storage tank, and the other part is throttled and sent to the top of the distillation tower as the reflux liquid of the distillation section to continue to participate in the distillation; a part of the liquid oxygen at the bottom of the distillation tower is evaporated by the nitrogen as the rising steam of the distillation tower to participate in the distillation, and the other part is sent to the liquid oxygen storage tank as a product.

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