Device and method for recovering and liquefying redundant nitrogen emptied by high-purity nitrogen device

Abstract

The invention belongs to the technical field of nitrogen recovery devices, and particularly relates to a recovery and liquefaction device for excess nitrogen emptied by a high-purity nitrogen device, the recovery and liquefaction device comprises a nitrogen compressor, an expansion machine, a main heat exchanger, a gas-liquid separator, a subcooler and a liquid measuring cylinder; a discharging pipeline of the nitrogen compressor is divided into a first pipeline and a second pipeline, the first pipeline penetrates through the main heat exchanger to be connected with the expansion end of the expansion machine and then penetrates through the main heat exchanger, and then the first pipeline is communicated with an emptying pipeline between the fractionating tower and the nitrogen compressor; the second pipeline is connected with the compression end of the expansion machine, then penetrates through the main heat exchanger and then penetrates through the subcooler after passing through the gas-liquid separator; a liquid nitrogen discharging pipeline of the liquid measuring cylinder penetrates through the subcooler, and the liquid measuring cylinder is supplemented with liquid nitrogen prepared by the subcooler. The device is used for solving the technical problem that a matched high-purity nitrogen production device in the current photovoltaic manufacturing process can empty part of nitrogen, and waste is caused.

Description

Technical Field

[0001] The invention belongs to the technical field of nitrogen recovery devices, and in particular relates to a device and method for recovering and liquefying excess nitrogen discharged from a high-purity nitrogen device. Background Art

[0002] Nitrogen is the most commonly used gas in the photovoltaic manufacturing process. Its role is to protect materials from corrosion by oxygen and water vapor in the air. In the silicon wafer manufacturing process, nitrogen is used to protect the wafer surface from oxidation and water vapor erosion, thereby ensuring the quality of wafer production. In addition, nitrogen is also used to accelerate the production and drying process of photovoltaic cells.

[0003] However, the high-purity nitrogen production equipment currently used in the photovoltaic cell industry often uses less product nitrogen due to market raw materials, environmental and other reasons, which will cause 0.85MPa nitrogen with a purity of 99.999% to be vented, resulting in a certain amount of waste and is not conducive to energy conservation and environmental protection. Summary of the invention

[0004] In view of the deficiencies in the prior art, the purpose of the present invention is to provide a device and method for recovering and liquefying excess nitrogen discharged from a high-purity nitrogen device, so as to solve the technical problem that part of the nitrogen will be discharged from the high-purity nitrogen production device in the current photovoltaic manufacturing process, resulting in waste.

[0005] To achieve the above-mentioned purpose, the technical scheme of the present invention is: a recovery and liquefaction device for the excess nitrogen discharged from the high-purity nitrogen device, the recovery and liquefaction device comprising a nitrogen compressor connected to the fractionation tower, an expander, a main heat exchanger, a gas-liquid separator, a subcooler and a liquid measuring cylinder; the discharge pipeline of the nitrogen compressor is divided into a first pipeline and a second pipeline, the first pipeline passes through the main heat exchanger and is connected to the expansion end inlet of the expander, and extends from the expansion end outlet and passes through the main heat exchanger, and the first pipeline after passing through the main heat exchanger is connected to the fractionation tower. The vent pipeline between the distillation tower and the nitrogen compressor is connected; the second pipeline is connected to the compression end inlet of the expander, and extends from the compression end outlet and passes through the main heat exchanger. The second pipeline after passing through the main heat exchanger is connected to the gas-liquid separator, and the second pipeline after passing through the gas-liquid separator passes through the subcooler, and the finished liquid nitrogen is prepared by the subcooler; the liquid nitrogen discharge pipeline at the bottom of the liquid measuring cylinder passes through the subcooler to provide cooling capacity, and the liquid nitrogen in the liquid measuring cylinder is supplemented by the liquid nitrogen prepared by the subcooler.

[0006] Preferably, a mist nitrogen discharge pipeline extends out of the top of the liquid measuring cylinder, and the mist nitrogen discharge pipeline passes through the main heat exchanger and is connected to a finished nitrogen pipeline to provide finished nitrogen for users.

[0007] Preferably, the liquid nitrogen discharge pipeline at the bottom of the liquid measuring cylinder passes through the supercooler and is connected to the mist nitrogen discharge pipeline at the top of the liquid measuring cylinder.

[0008] Preferably, the expander includes a high-temperature expander and a low-temperature expander, the second discharge pipe is connected to the compression ends of the high-temperature expander and the low-temperature expander in sequence, and a cooler is provided on the second pipeline behind the high-temperature expander and the low-temperature expander; the first pipeline is connected to the expansion end of the high-temperature expander after passing through the main heat exchanger.

[0009] Preferably, a second pipeline branch is provided on the portion of the second pipeline passing through the main heat exchanger, and the second pipeline branch is connected to the expansion end of the low-temperature expander and then merged with the second pipeline.

[0010] A method for recovering and liquefying excess nitrogen vented from a high-purity nitrogen device comprises the following steps: S1: The excess nitrogen discharged from the fractionation tower of the high-purity nitrogen device is passed into the nitrogen compressor through a pipeline. The nitrogen pressurized by the nitrogen compressor is separated into two streams, namely the raw gas and the cold gas. The cold gas passes through the main heat exchanger and then enters the expander to expand and reduce its own temperature. The cooled cold gas passes through the main heat exchanger again to provide coldness, and then the cold gas flows back to the pipeline between the fractionation tower and the nitrogen compressor; S2: The raw gas in S1 is re-pressurized and passes through the main heat exchanger, where it is cooled and liquefied through heat exchange to form mist nitrogen; S3: The mist nitrogen in S2 is separated by a gas-liquid separation device, where the mist nitrogen stops flowing, the nitrogen still in gaseous state is separated, and the remaining forms suspended liquid nitrogen; S4: The suspended liquid nitrogen in S3 is liquefied after liquid nitrogen heat exchange to generate finished liquid nitrogen, which is stored in a storage tank or enters a liquid nitrogen backup system; S5: The liquid nitrogen used for heat exchange with suspended liquid nitrogen in S4 is heated to generate nitrogen gas. The liquid nitrogen used for heat exchange with suspended liquid nitrogen is provided by a stream separated from the finished liquid nitrogen.

[0011] Preferably, the nitrogen gas generated in S5 flows through the main heat exchanger to be heated to a suitable temperature to form finished nitrogen gas, which is then used by users.

[0012] Preferably, the pressurization of the raw gas in S2 is completed in two steps, namely, primary pressurization and secondary pressurization, to ensure that the required pressure value is reached.

[0013] Preferably, the driving force required for the first-stage pressurization is provided by a process of expansion and cooling of cold gas.

[0014] Preferably, the raw gas stream is separated into a single stream after passing through the main heat exchanger, which is expanded and cooled and provides driving force for the secondary pressurization.

[0015] The beneficial effects of the technical solution of the present invention are: The nitrogen discharged from the fractionation tower of the air separation device of the present invention is pressurized by a nitrogen compressor and then separated into two streams. The first stream flows through a main heat exchanger through a first pipeline and then enters an expander for expansion and cooling. After expansion and cooling, it flows through the main heat exchanger again to provide cooling capacity and then flows back to the nitrogen compressor; the second stream enters the expander through a second pipeline for pressurization, flows through the main heat exchanger after pressurization, exchanges heat with the nitrogen in the first pipeline for cooling and forms mist nitrogen, and the mist nitrogen enters a gas-liquid separator through a second pipeline for gas-liquid separation, and the separated nitrogen flows through the main heat exchanger again to provide cooling capacity, thereby realizing cooling capacity recovery, and the separated suspended liquid nitrogen passes through a subcooler for liquefaction to generate finished liquid nitrogen; the liquid nitrogen in the subcooler that provides cooling capacity for the suspended liquid nitrogen is provided by a liquid measuring cylinder, and the liquid nitrogen in the liquid measuring cylinder is supplemented by the finished liquid nitrogen generated after passing through the subcooler. Based on this, the entire recovery and liquefaction device is reasonably designed, and the exhaust nitrogen is divided into two streams, one of which is used for expansion and cooling to provide cold capacity, and the other is used as the raw material for recovery and liquefaction. The nitrogen that provides cold capacity eventually flows back to the front of the exhaust nitrogen split to form a circulation loop. The nitrogen that serves as the raw material is cooled and atomized, and then passes through the gas-liquid separator to separate another nitrogen stream. The nitrogen stream passes through the gas-liquid separator again to provide cold capacity and then flows back to the venting pipeline to form a second circulation loop, which increases the recovery rate of the released nitrogen; and, the nitrogen that serves as the raw material is finally liquefied through the cooler and then separated into another stream, which flows back to the supercooler to provide cold capacity for the final liquefaction of the raw nitrogen in the supercooler. It does not require the input of additional cold capacity materials, and ensures the recovery efficiency of the exhaust nitrogen. In addition, the exhaust nitrogen itself is used to provide cold capacity, which reduces additional investment and is more energy-saving and efficient. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 A schematic diagram of the process flow of an embodiment of a device for recovering and liquefying excess nitrogen vented from a high-purity nitrogen device.

[0017] in, Figure 1 In the figure, 1- venting pipeline, 2- nitrogen compressor, 3- first pipeline, 4- second pipeline, 5- first cooler, 6- high temperature expander, 7- second cooler, 8- low temperature expander, 9- second pipeline branch, 10- main heat exchanger, 11- subcooler, 12- liquid measuring cylinder, 13- liquid nitrogen discharge pipeline, 14- mist nitrogen discharge pipeline, 15- gas-liquid separator, 16- reflux pipeline. DETAILED DESCRIPTION

[0018] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments, and do not limit the scope of the present invention.

[0019] In the description of the present invention, it should be noted that the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc., indicating the orientation or positional relationship, are based on the orientation or positional relationship shown in the drawings, and are 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 operated in a specific orientation, and therefore cannot be understood as limiting the present invention. In addition, the terms "first", "second", and "third" are used for descriptive purposes only, and cannot be understood as indicating or implying relative importance.

[0020] In the description of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0021] The specific embodiments are as follows: Embodiment 1, as Figure 1 As shown, a recovery and liquefaction device for excess nitrogen vented from a high-purity nitrogen device is used to recover nitrogen vented from a distillation tower of an air separation device and prepare liquid nitrogen or nitrogen gas that meets user needs.

[0022] The recovery liquefaction device includes a nitrogen compressor 2, an expander, a main heat exchanger 10, a gas-liquid separator 15, a subcooler 11 and a liquid measuring cylinder 12. The distillation tower is connected to the nitrogen compressor 2 through a venting pipeline 1, and the nitrogen to be vented from the distillation tower is discharged into the nitrogen compressor 2 through the venting pipeline 1 for pressurization. The discharge pipeline of the nitrogen compressor 2 is divided into two routes, namely the first pipeline 3 and the second pipeline 4; based on this, the nitrogen pressurized by the nitrogen compressor 2 is divided into two streams, the nitrogen flowing through the first pipeline 3 is called cold gas, and the nitrogen flowing through the second pipeline 4 is called raw gas.

[0023] After passing through the main heat exchanger 10, the first pipeline 3 is connected to the expansion end inlet of the expander, and then extends from the expansion end outlet and passes through the main heat exchanger 10 again. After passing through the main heat exchanger 10 again, the first pipeline 3 is reconnected to the venting pipeline 1 to complete a circulation loop. Among them, after the cold gas in the first pipeline 3 expands and cools down, it provides cold energy when passing through the main heat exchanger 10 again with the first pipeline 3, exchanges heat with the raw gas in the second pipeline 4, and the cold gas is heated and flows back to the venting pipeline 1 with the first pipeline 3.

[0024] The second pipeline 4 is connected to the compression end inlet of the expander, and then extends from the compression end outlet and passes through the main heat exchanger 10. After passing through the main heat exchanger 10, the second pipeline 4 is connected to the gas-liquid separator 15. After passing through the gas-liquid separator 15, the second pipeline 4 passes through the subcooler 11. After passing through the subcooler 11, the second pipeline 4 is connected to the storage tank or the liquid nitrogen backup system. A reflux pipeline 16 extends from the top of the gas-liquid separator 15, and the reflux pipeline 16 extends into the main heat exchanger 10 and is connected to the first pipeline 3 that passes through the main heat exchanger 10 for the second time, and finally communicates with the venting pipeline 1. The setting of the gas-liquid separator 15 can not only maintain the pressure stability of the entire system, but also realize the recovery of cold, making the entire recovery device more energy-efficient. The raw gas in the second pipeline 4 is pressurized for the second time, and then passes through the main heat exchanger 10 with the second pipeline 4. In the main heat exchanger 10, the raw gas exchanges heat with the cooling gas after expansion and cooling in the first pipeline 3, and the raw gas is cooled to form mist nitrogen; the mist nitrogen enters the gas-liquid separator 15 through the second pipeline 4, and the raw gas stops flowing in the gas-liquid separator 15, wherein the light gaseous part rises and is separated, passes through the main heat exchanger 10 through the reflux pipeline 16 to provide cooling capacity, realizes cooling capacity recovery, and then flows back to the venting pipeline 1 to form a circulation loop; the heavy liquid part in the gas-liquid separator 15 forms suspended liquid nitrogen, passes through the subcooler 11 with the second pipeline 4, and performs heat exchange again in the subcooler 11 to realize liquefaction, thereby generating finished liquid nitrogen that meets the needs of users, and the finished liquid nitrogen flows into the storage tank for storage, or is introduced into the liquid nitrogen backup system for use by users.

[0025] In the subcooler 11, the suspended liquid nitrogen in the second pipeline 4 exchanges heat with the liquid nitrogen passing through the subcooler 11, so that the suspended liquid nitrogen flows through the subcooler 11 and liquefies to generate finished liquid nitrogen that meets the needs of the user. The liquid nitrogen flowing through the subcooler 11 to provide cooling is provided by the liquid measuring cylinder 12, and the liquid nitrogen discharge pipeline 13 extending from the bottom of the liquid measuring cylinder 12 passes through the subcooler 11; and, after passing through the subcooler 11, the second pipeline 4 is not connected to the storage tank or the liquid nitrogen standby system, and another path is separated to communicate with the liquid measuring cylinder 12, which is used to replenish the liquid measuring cylinder with liquid nitrogen.

[0026] In this embodiment, the nitrogen compressor 2, the expander, the main heat exchanger 10, the gas-liquid separator 15, the subcooler 11 and the liquid measuring cylinder 12 are all prior art and are therefore not described in detail. More specifically, the nitrogen compressor 2 is a nitrogen compressor used to pressurize the vented nitrogen. A single-axis multi-stage type or a double-axis four-stage type can be selected according to actual use requirements; the expander adopts a turbine expander, which is mainly composed of three parts: the expander flow part, the booster part and the body; the expansion end expands and cools the gas, and the energy released in the process is transferred to the compression end, where the gas is pressurized; the gas-liquid separator 15 is used to separate nitrogen from liquid nitrogen. A liquid nitrogen gas-liquid separator can be used to separate liquid nitrogen and nitrogen in the pipeline by gravity sedimentation. Nitrogen is heavier than nitrogen gas, so it gathers at the bottom of the container. Nitrogen gas itself is lighter, so it mainly gathers at the top of the container and is discharged through the top pipe. The purified liquid nitrogen at the bottom is discharged through the bottom pipe. The subcooler 11 is used to further cool the saturated liquid to form stable liquid nitrogen. The structural type of the subcooler includes a sleeve type, a spray type or a plate exchanger, which can be selected according to the use requirements. The liquid measuring cylinder 12 is used to store liquid nitrogen, and its liquid nitrogen flows through the subcooler 11 to provide cooling capacity. The liquid nitrogen in the liquid measuring cylinder 12 can be supplemented by recycled finished liquid nitrogen.

[0027] Furthermore, a mist nitrogen discharge pipeline 14 extends out from the top of the liquid measuring cylinder 12, and the mist nitrogen discharge pipeline 14 passes through the main heat exchanger 10 and then enters the gas supply pipeline of the nitrogen user; wherein, the mist nitrogen atomized in the liquid measuring cylinder 12 passes through the main heat exchanger 10 through the mist nitrogen discharge pipeline 14, and is subjected to heat exchange and temperature increase in the main heat exchanger 10 to produce finished nitrogen at a temperature required by the user, which is provided to the nitrogen user.

[0028] In this embodiment, the liquid nitrogen discharge pipeline 13 passes through the subcooler 11 and is connected to the mist nitrogen discharge pipeline 14. After passing through the subcooler 11, the liquid nitrogen is heated to form mist nitrogen, which merges with the mist nitrogen of the mist nitrogen discharge pipeline 14 to finally generate finished nitrogen.

[0029] Furthermore, the expander includes a high-temperature expander 6 and a low-temperature expander 8. The raw gas in the second pipeline 4 is pressurized by the high-temperature expander 6 and the low-temperature expander 8 in turn, so as to obtain the raw gas with a qualified pressure value. More specifically, the second pipeline 4 is connected to the compression end of the high-temperature expander 6 and then connected to the first cooler 5. The first cooler 5 preliminarily cools the raw gas after the first-stage pressurization. After the first cooler 5, the second pipeline 4 is connected to the compression end of the low-temperature expander 8 and then connected to the second cooler 7. The second cooler 7 cools the raw gas after the second-stage pressurization. After the second cooler 7, the second pipeline 4 passes through the main heat exchanger 10. The first cooler 5 and the second cooler 7 are arranged to ensure that the raw gas can be cooled to mist nitrogen in the main heat exchanger 10.

[0030] In this embodiment, the first pipeline 3 is connected to the expansion end of the high-temperature expander 6 after passing through the main heat exchanger 10 for the first time. The cold gas in the first pipeline 3 is expanded and cooled here. The energy released during the expansion and cooling process provides power for the compression end of the high-temperature expander 6. Reasonable settings improve the integration and achieve energy-saving effects.

[0031] Furthermore, a second pipeline branch 9 is branched from the second pipeline 4 passing through the main heat exchanger 10, and the second pipeline branch 9 is connected to the expansion end of the cryogenic expander 8, where the raw gas is expanded and cooled again, increasing the liquid nitrogen content of the mist nitrogen entering the gas-liquid separator 15, and the second pipeline branch 9 is connected to the cryogenic expander 8 before entering the gas-liquid separator 15. In addition, the energy released by the raw gas during the expansion and cooling process of the expansion end of the cryogenic expander 8 provides power for the compression end of the cryogenic expander 8, improves the integration of the device, and achieves energy saving.

[0032] Example 2, based on the same inventive concept as the above-mentioned Example 1, the present invention also provides a method for recovering and liquefying excess nitrogen vented from a high-purity nitrogen device, such as Figure 1 As shown, the method comprises the following steps: S1: The excess nitrogen discharged from the distillation tower of the high-purity nitrogen device is passed into the nitrogen compressor 2 through the venting pipeline 1. The nitrogen pressurized by the nitrogen compressor 2 is separated into two streams, one of which flows through the first pipeline 3 as the refrigerant gas, and the other flows through the second pipeline 4 as the raw gas; the refrigerant gas passes through the main heat exchanger 10 for the first time through the first pipeline 3 and enters the expansion end of the high-temperature expander 6 for expansion and cooling (although the temperature of the refrigerant gas is reduced at this point, it is still in a gaseous state), and the cooled refrigerant gas passes through the main heat exchanger 10 for the second time through the first pipeline 3 to provide cooling, and then flows back to the venting pipeline 1 through the first pipeline 3, forming a circulation loop (the vented nitrogen expands to provide cooling, and returns to the venting pipeline 1 after providing cooling, without the need for additional cooling material input); S2: The raw gas in S1 is pressurized again, and this is completed in two steps; first, it passes through the compression end of the high-temperature expander 6 for primary pressurization, and then flows through the first cooler 5 for cooling after the primary pressurization, and then passes through the compression end of the low-temperature expander 8 for secondary pressurization, and then flows through the second cooler 7 for cooling after the secondary pressurization (the two coolers 5 and 7 gradually cool the raw gas), and then passes through the main heat exchanger 10 through the second pipeline 4, and heat is exchanged in the main heat exchanger 10 to cool and liquefy the raw gas to form mist nitrogen (it is not finished liquid nitrogen at this time); The power required by the compression end of the high-temperature expander 6 is provided by the energy released by the expansion of the cold gas at its expansion end, thereby reducing energy waste; Among them, the second pipeline 4 passing through the main heat exchanger 10 branches out a second pipeline branch 9, and the raw gas of the mist nitrogen is cooled in the main heat exchanger 10, and a part of it enters the expansion end of the low-temperature expander 8 through the second pipeline branch 9 to expand and cool, thereby increasing the liquid content in the mist nitrogen, so as to ensure the stability of the form of the mist nitrogen at this time, and also facilitate the subsequent heat exchange liquefaction; S3: The mist nitrogen in S2 enters the gas-liquid separator 15 through the second pipeline 4 for gas-liquid separation. The mist nitrogen stops flowing in the gas-liquid separator 15, and the light gaseous part rises and is separated. It passes through the main heat exchanger 10 through the reflux pipeline to provide cooling capacity, realizing cooling capacity recovery, and then flows back to the vent pipeline 1 to form a circulation loop; the heavy liquid part in the gas-liquid separator 15 forms suspended liquid nitrogen; S4: The suspended liquid nitrogen in S3 passes through the subcooler 11 along the second pipeline 4, and is liquefied by heat exchange with the other liquid nitrogen introduced in the subcooler 11 to generate finished liquid nitrogen that meets the needs of the user. The finished liquid nitrogen flows into a storage tank for storage, or is introduced into a liquid nitrogen backup system for use by the user; S5: The liquid nitrogen used for heat exchange with the suspended liquid nitrogen in the subcooler 11 to provide cooling capacity is provided by the liquid measuring cylinder 12, and the liquid measuring cylinder 12 transports the liquid nitrogen to the subcooler 11 through the liquid nitrogen discharge pipeline 13 at the bottom thereof; after passing through the subcooler 11, the liquid nitrogen in the liquid nitrogen discharge pipeline 13 is heated to generate nitrogen gas (the temperature is still very low); the finished liquid nitrogen generated in S4 is connected to the storage tank or the liquid nitrogen backup system, and another path is separated to communicate with the liquid measuring cylinder 12, so as to replenish the liquid nitrogen to the liquid measuring cylinder; A nitrogen mist discharge pipeline 14 is provided at the top of the liquid measuring cylinder 12. The nitrogen mist formed in the liquid measuring cylinder 12 is discharged through the nitrogen mist discharge pipeline 14 and passes through the main heat exchanger 10 along the nitrogen mist discharge pipeline 14 to provide cooling capacity in the main heat exchanger 10, and is heated to a suitable temperature to form finished nitrogen, which is then used by nitrogen users. The liquid nitrogen discharge pipeline 13 passes through the subcooler 11 and is connected to the mist nitrogen discharge pipeline 14 , and is heated up as the mist nitrogen discharge pipeline 14 passes through the main heat exchanger 10 to form finished nitrogen for use by nitrogen users.

[0033] Based on the recovery device and recovery method in the above-mentioned Examples 1 and 2, the nitrogen that needs to be vented from the distillation tower can be completely recovered for reuse, thereby reducing waste; the cooling capacity used in the entire recovery process is provided by the vented nitrogen to be recovered, and several circulation loops allow the nitrogen after providing cooling to flow back to the recovery system, thereby ensuring that the entire recovery device can continue to work uninterruptedly and ensuring the recovery efficiency and recovery effect.

[0034] The present invention is described above by way of example in conjunction with the accompanying drawings. It is obvious that the specific implementation of the present invention is not limited to the above-mentioned method. As long as various non-substantial improvements are made using the technical solution of the present invention, or the concept and technical solution of the present invention are directly applied to other occasions without improvement, they are all within the protection scope of the present invention.

Claims

1. A device for recovering and liquefying excess nitrogen discharged from a high-purity nitrogen device, characterized in that: The recovery liquefaction device includes a nitrogen compressor connected to a fractionation tower, an expander, a main heat exchanger, a gas-liquid separator, a subcooler and a liquid measuring cylinder; The discharge pipeline of the nitrogen compressor is divided into a first pipeline and a second pipeline, the first pipeline passes through the main heat exchanger and then connects to the expansion end inlet of the expander, and extends from the expansion end outlet and then passes through the main heat exchanger, and the first pipeline after passing through the main heat exchanger is connected to the vent pipeline between the fractionation tower and the nitrogen compressor; The second pipeline is connected to the compression end inlet of the expander, extends from the compression end outlet and passes through the main heat exchanger, the second pipeline after passing through the main heat exchanger is connected to the gas-liquid separator, and the second pipeline after passing through the gas-liquid separator passes through the subcooler, and the finished liquid nitrogen is prepared by the subcooler; the liquid nitrogen discharge pipeline at the bottom of the liquid measuring cylinder passes through the subcooler to provide cooling capacity, and the liquid nitrogen in the liquid measuring cylinder is supplemented by the liquid nitrogen prepared by the subcooler.

2. The device for recovering and liquefying excess nitrogen discharged from a high-purity nitrogen device according to claim 1, characterized in that: A mist nitrogen discharge pipeline extends out of the top of the liquid measuring cylinder, and the mist nitrogen discharge pipeline passes through the main heat exchanger and is connected to a finished nitrogen pipeline to provide finished nitrogen for users.

3. The device for recovering and liquefying excess nitrogen discharged from a high-purity nitrogen device according to claim 2, characterized in that: The liquid nitrogen discharge pipeline at the bottom of the liquid measuring cylinder passes through the supercooler and is connected to the mist nitrogen discharge pipeline at the top of the liquid measuring cylinder.

4. The device for recovering and liquefying excess nitrogen discharged from a high-purity nitrogen device according to claim 1, characterized in that: The expander includes a high-temperature expander and a low-temperature expander. The second discharge pipe is connected to the compression ends of the high-temperature expander and the low-temperature expander in sequence. Coolers are provided on the second pipeline behind the high-temperature expander and the low-temperature expander. The first pipeline passes through the main heat exchanger and is connected to the expansion end of the high-temperature expander.

5. The device for recovering and liquefying excess nitrogen discharged from a high-purity nitrogen device according to claim 4, characterized in that: A second pipeline branch is provided on the portion of the second pipeline passing through the main heat exchanger, and the second pipeline branch is connected to the expansion end of the low-temperature expander and then merged with the second pipeline.

6. A method for recovering and liquefying excess nitrogen discharged from a high-purity nitrogen device, characterized in that: The method comprises the following steps: S1: The excess nitrogen discharged from the fractionation tower of the high-purity nitrogen device is passed into the nitrogen compressor through a pipeline. The nitrogen pressurized by the nitrogen compressor is separated into two streams, namely the raw gas and the cold gas. The cold gas passes through the main heat exchanger and then enters the expander to expand and reduce its own temperature. The cooled cold gas passes through the main heat exchanger again to provide coldness, and then the cold gas flows back to the pipeline between the fractionation tower and the nitrogen compressor; S2: The raw gas in S1 is re-pressurized and passes through the main heat exchanger, where it is cooled and liquefied through heat exchange to form mist nitrogen; S3: The mist nitrogen in S2 is separated by a gas-liquid separation device, where the mist nitrogen stops flowing, the nitrogen still in gaseous state is separated, and the remaining forms suspended liquid nitrogen; S4: The suspended liquid nitrogen in S3 is liquefied after liquid nitrogen heat exchange to generate finished liquid nitrogen, which is stored in a storage tank or enters a liquid nitrogen backup system; S5: The liquid nitrogen used for heat exchange with suspended liquid nitrogen in S4 is heated to generate nitrogen gas. The liquid nitrogen used for heat exchange with suspended liquid nitrogen is provided by a stream separated from the finished liquid nitrogen.

7. The method for recovering and liquefying excess nitrogen discharged from a high-purity nitrogen device according to claim 6, characterized in that: The nitrogen gas generated in S5 flows through the main heat exchanger to be heated to a suitable temperature to form finished nitrogen gas, which is then used by users.

8. The method for recovering and liquefying excess nitrogen discharged from a high-purity nitrogen device according to claim 6, characterized in that: The pressurization of the raw gas in S2 is completed in two steps, namely primary pressurization and secondary pressurization, to ensure that the required pressure value is reached.

9. The method for recovering and liquefying excess nitrogen discharged from a high-purity nitrogen device according to claim 8, characterized in that: The driving force required for the first stage of pressurization is provided by the expansion and cooling process of the cold gas.

10. The method for recovering and liquefying excess nitrogen discharged from a high-purity nitrogen device according to claim 9, characterized in that: After the raw gas flows through the main heat exchanger, a single stream is separated to expand and cool down and provide driving force for the secondary pressurization.

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