Low-pressure liquid nitrogen production device

Abstract

The invention discloses a low-pressure liquid nitrogen production device which comprises an air filtering and compressing system used for primarily purifying air and compressing air; the pre-cooling system is used for cooling the compressed air; the molecular sieve purification system is used for purifying air; the heat exchanger system is used for cooling the purified air to a saturation temperature; the rectification system comprises a rectification tower and a synergy tower, a lower tower of the rectification tower is connected with the heat exchanger system, the synergy tower is higher than the lower tower, a synergy tower condenser is arranged in the synergy tower, the input end of the synergy tower condenser is connected with the top of the lower tower, and the output end of the synergy tower condenser is communicated with a liquid nitrogen output position lower than the preset height of the synergy tower condenser through a liquid outlet pipe; and the nitrogen cooler is used for cooling nitrogen into liquid nitrogen, pressurizing to the pressure meeting the requirement and outputting. According to the low-pressure liquid nitrogen production device, as the condenser of the synergistic tower is higher than the liquid nitrogen output position, the potential difference of the static liquid column in the liquid outlet pipe can be utilized for pressurizing, so that the low-pressure liquid nitrogen production device is suitable for various low-pressure liquid nitrogen production working conditions, electric energy consumption is saved, and the production cost is low.

Description

Technical Field

[0001] The present invention relates to the technical field of low-pressure liquid nitrogen production, and more specifically, to a low-pressure liquid nitrogen production device. Background Art

[0002] In the existing low-pressure liquid nitrogen production device, when producing low-pressure liquid nitrogen (for example, 0.75MPa liquid nitrogen), the liquid nitrogen pressure generated after the air is distilled through the lower tower is about 0.42MPa. Usually, two methods of external compression and internal compression are used. The external compression method is: an additional liquid nitrogen pump is added outside the lower tower, which is used alone to pressurize the liquid nitrogen to 0.75MPa. This method is not suitable for working conditions with low liquid nitrogen output, that is, the scope of application is narrow, and it causes energy waste and high production cost. The internal compression method is: a liquid nitrogen pump is added in the lower tower, and a throttle valve is used for post-pump throttling. The liquid nitrogen output by this method is mixed with other gases, and it also causes energy waste and high production cost.

[0003] In summary, how to solve the problems of narrow application range, poor quality of produced liquid nitrogen and high production cost of existing low-pressure liquid nitrogen production devices is an urgent problem to be solved by technical personnel in this field. Summary of the invention

[0004] In view of this, the object of the present invention is to provide a low-pressure liquid nitrogen production device. Since the condenser of the efficiency tower is higher than the liquid nitrogen output position, the low-pressure liquid nitrogen production device can increase the pressure by utilizing the static liquid column potential difference in the liquid outlet pipe, and no additional liquid nitrogen pump or throttle valve is required for pressurization. Therefore, the low-pressure liquid nitrogen production device is suitable for a variety of low-pressure liquid nitrogen production conditions, saves electricity and energy consumption, and has low production costs.

[0005] In order to achieve the above object, the present invention provides the following technical solutions:

[0006] A low-pressure liquid nitrogen production device comprises an air filtration and compression system, a precooling system, a molecular sieve purification system and a heat exchanger system, and a distillation system which are connected in sequence;

[0007] The air filtration and compression system is used to preliminarily purify the air and compress the air;

[0008] The precooling system is used to cool the compressed air;

[0009] The molecular sieve purification system is used to purify the air;

[0010] The heat exchanger system is used to cool the purified air to the saturation temperature;

[0011] The distillation system includes a distillation tower and a synergist tower. The lower tower of the distillation tower is connected to the heat exchanger system, and is used for distilling the air after heat exchange to obtain oxygen-enriched liquid air, nitrogen and liquid nitrogen. The synergist tower is higher than the lower tower, and a synergist tower condenser is arranged inside the synergist tower. The input end of the synergist tower condenser is connected to the top of the lower tower, and the output end is connected to a liquid nitrogen output position at a preset height lower than the synergist tower condenser through a liquid outlet pipe, and is used for cooling the nitrogen into liquid nitrogen and pressurizing it to a required pressure before outputting it.

[0012] Preferably, the air filtration and compression system includes an air filter and a compressor, the air filter is provided with an air inlet connected to the external air, the air inlet end of the compressor is connected to the air outlet of the air filter, and the air outlet end is connected to the air inlet end of the precooling system.

[0013] Preferably, the precooling system includes an air cooling tower, the interior of the air cooling tower is divided from bottom to top into a normal temperature zone with normal temperature water and a cooling zone with cooling water, the normal temperature zone is connected to the air outlet of the air filtration and compression system, the normal temperature zone is connected to the cooling zone, and the cooling zone is connected to the air inlet of the molecular sieve purification system.

[0014] Preferably, the precooling system further comprises a water cooling tower and a normal temperature water source, the liquid outlet of the water cooling tower is connected to the cooling zone, and the normal temperature water source is connected to the normal temperature zone.

[0015] Preferably, the molecular sieve purification system comprises two molecular sieve adsorbers, and the heat exchanger system comprises a plate heat exchanger, an expander and a cooler;

[0016] Among them, the air inlet ends of the two molecular sieve adsorbers are connected to the air outlet ends of the precooling system through the first automatic switching valve group, and the air outlet ends of the two molecular sieve adsorbers are divided into two paths, one path is connected in sequence to the boost end of the expander, the cooler, the cold end of the plate heat exchanger, the expansion end of the expander and the upper tower of the distillation tower, and the other path is connected in sequence to the hot end of the plate heat exchanger and the lower tower of the distillation tower.

[0017] Preferably, the bottom of the lower tower of the distillation tower is connected to the middle of the upper tower of the distillation tower through a first reflux pipeline, and a subcooler is arranged on the reflux pipeline.

[0018] Preferably, the upper part of the upper tower of the distillation tower is connected to the cold end of the plate heat exchanger through a second reflux pipeline, and then a branch is separated, and the branch is connected to the gas outlet ends of the two molecular sieve adsorbers through a second automatic switching valve group.

[0019] Preferably, the branch line is provided with an electric heater located between the plate heat exchanger and the second automatic switching valve group.

[0020] Preferably, the upper part of the upper tower of the distillation tower is connected to the cold end of the plate heat exchanger through a second reflux pipeline and then another branch is separated, and the branch is connected to the liquid inlet end of the water cooling tower.

[0021] Preferably, the upper middle part of the upper tower of the distillation tower is connected to the efficiency-enhancing tower through an argon fraction pipeline, the efficiency-enhancing tower is used to distill the argon fraction to obtain crude liquid argon, and the bottom of the efficiency-enhancing tower is connected to the upper tower of the distillation tower through a third reflux pipeline, and the third loop pipeline is used to reflux the crude liquid argon into the upper tower of the distillation tower.

[0022] When the low-pressure liquid nitrogen production device provided by the present invention is used to produce low-pressure liquid nitrogen, the air is initially purified by the air filtration and compression system to remove dust and mechanical impurities, and the air can be controlled to be compressed to a certain pressure, such as 0.58MPa. At this time, the air temperature can be controlled not to exceed 105°C. The compressed air enters the precooling system to be cooled to a certain temperature, such as about 16°C. The cooled air enters the molecular sieve purification system for purification, which can remove moisture and carbon dioxide in the air. The purified air enters the heat exchanger system to be cooled to the saturation temperature, and then enters the lower tower of the distillation tower for distillation to obtain oxygen-enriched liquid air, nitrogen and liquid nitrogen (it should be noted that If the nitrogen in the lower tower is directly condensed and discharged through the cooler at this time, the pressure will be about 0.4MPa, which does not meet the requirements). The nitrogen rises and enters the booster tower cooler to condense into liquid nitrogen. Since the output end of the booster tower condenser (i.e., the liquid outlet position) is connected to the liquid nitrogen output position through the liquid outlet pipe, and the booster tower condenser is higher than the preset height of the liquid nitrogen output position, a static liquid column is formed from the liquid inlet to the liquid outlet of the liquid outlet pipe. According to the calculation formula of the static liquid column pressure ‌P (pressure) = ρ (fluid density) × g (gravitational acceleration) × h (fluid depth), if the liquid nitrogen output is about 0.75MPa, the booster tower condenser is about 40-50m higher than the liquid nitrogen output position.

[0023] Therefore, the condenser of the efficiency-enhancing tower is placed higher than the liquid nitrogen output position in the present invention, and the static liquid column potential difference in the liquid outlet pipe can be used for pressurization without the need to additionally provide a liquid nitrogen pump or a throttle valve for pressurization. Thus, the present invention is suitable for a variety of low-pressure liquid nitrogen production conditions, saves electricity and energy consumption, and has low production costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying creative work.

[0025] Figure 1 This is a schematic structural diagram of a low-pressure liquid nitrogen production device provided by the present invention.

[0026] Reference numerals:

[0027] 1-air filter; 2-compressor; 3-air cooling tower; 3-a-normal temperature zone; 3-b-cooling zone; 4-water cooling tower; 5-normal temperature water source; 6-low temperature water pump; 7-normal temperature water pump; 8-molecular sieve adsorber; 9-first automatic switching valve group; 10-second automatic switching valve group; 11-electric heater; 12-plate heat exchanger; 13-expander; 13-a-boosting end; 13-b-expansion end; 14-cooler; 15-lower tower; 16-upper tower; 17-subcooler; 18-efficiency tower; 19-efficiency tower condenser; A-about 0.4MPa liquid nitrogen; B-about 0.75Mpa liquid nitrogen; C-liquid oxygen; D-product oxygen; E-product nitrogen. DETAILED DESCRIPTION

[0028] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0029] The core of the present invention is to provide a low-pressure liquid nitrogen production device. Since the condenser of the efficiency tower is higher than the liquid nitrogen output position, the low-pressure liquid nitrogen production device can increase the pressure by utilizing the static liquid column potential difference in the liquid outlet pipe, and no additional liquid nitrogen pump or throttle valve is required for increasing the pressure. Therefore, the low-pressure liquid nitrogen production device is suitable for a variety of low-pressure liquid nitrogen production conditions, saves electricity and energy consumption, and has low production costs.

[0030] Please refer to Figure 1 The present application provides a low-pressure liquid nitrogen production device, including an air filtration and compression system, a precooling system, a molecular sieve purification system and a heat exchanger system, and a distillation system connected in sequence.

[0031] The air filtration and compression system is used to initially purify and compress the air;

[0032] The pre-cooling system is used to cool the compressed air;

[0033] Molecular sieve purification systems are used to purify air;

[0034] A heat exchanger system is used to cool the purified air to saturation temperature;

[0035] The distillation system includes a distillation tower and a performance enhancing tower 18. The lower tower 15 of the distillation tower is connected to the heat exchanger system, which is used to obtain oxygen-enriched liquid air, nitrogen and liquid nitrogen from the air after distillation heat exchange. The performance enhancing tower 18 is higher than the lower tower 15, and a performance enhancing tower condenser 19 is arranged inside the performance enhancing tower 18. The input end of the performance enhancing tower condenser 19 is connected to the top of the lower tower 15, and the output end is connected to the liquid nitrogen output position at a certain height below the performance enhancing tower condenser 19 through a liquid outlet pipe, so as to cool the nitrogen into liquid nitrogen and pressurize it to a required pressure before outputting it.

[0036] It should be noted that the distillation tower is composed of an upper tower 16 and a lower tower 15, wherein the function of the lower tower 15 is to preliminarily distill the air to obtain oxygen-enriched liquid air with an oxygen content of 36-40%, 99.99% nitrogen, and 94.7% or more of distillate liquid nitrogen, and the function of the upper tower 16 is to distill the oxygen-enriched liquid air and distillate liquid nitrogen discharged from the lower tower 15, and finally obtain high-purity nitrogen at the top. The specific structure of the distillation tower can refer to the prior art, which is not the focus of protection of this application and will not be described in detail herein.

[0037] The synergist tower 18 is higher than the lower tower 15 of the distillation tower, so that the nitrogen obtained by the distillation of the lower tower 15 rises and enters the condenser in the synergist tower 18, and the nitrogen is condensed into liquid nitrogen by the synergist tower condenser 19. In addition, it is necessary to ensure that the synergist tower condenser 19 is higher than the liquid nitrogen output position (such as a collection device placed on the ground) by a certain height, so that the liquid outlet pipe connected between the output end of the synergist tower condenser 19 and the liquid nitrogen output position also has a certain height. Since the static liquid column pressure is the pressure generated by the weight of the liquid when it is stationary, as the height of the discharge port of the liquid outlet pipe decreases (that is, as the depth of the liquid outlet pipe extends downward increases), the liquid nitrogen pressure in the liquid outlet pipe increases, so as to achieve the purpose of increasing the liquid nitrogen pressure. It should be noted that the length of the infusion pipe required for the output of the low-pressure liquid nitrogen required for production can be obtained according to the calculation formula of the static liquid column pressure ‌P (pressure) = ρ (fluid density) × g (gravitational acceleration) × h (fluid depth), and then the height position of the synergist tower condenser 19 is set higher than the liquid nitrogen output position. For example, if Figure 1 As shown, if the nitrogen obtained by distillation in the lower tower 15 of the distillation tower is directly condensed into liquid nitrogen A at about 0.45MPa through the cooler 17, but the production requires liquid nitrogen B at about 0.75MPa, then the condenser 19 of the booster tower needs to be about 40-50m higher than the liquid nitrogen output position.

[0038] In summary, compared with the existing external compression and internal compression methods, the present invention adds a booster tower 18 with a certain height and a condenser therein, and utilizes the automatic rise of nitrogen into the booster tower condenser 19 to condense into liquid nitrogen, and then uses the static liquid column potential difference in the liquid outlet pipe to boost the pressure. There is no need to additionally set up a liquid nitrogen pump with high power consumption and large pump liquid volume. It is not only suitable for a variety of low-pressure liquid nitrogen production conditions, such as conditions with low or high liquid nitrogen production, to improve the scope of application, but also saves power consumption and reduces production costs.

[0039] Considering the specific implementation of the air filtration and compression system, based on the above embodiments, please refer to Figure 1 The air filtration and compression system includes an air filter 1 and a compressor 2. The air filter 1 is provided with an air inlet connected to the external air. The air inlet end of the compressor 2 is connected to the air outlet of the air filter 1, and the air outlet end is connected to the air inlet end of the precooling system.

[0040] Thus, the raw air is sucked in from the air inlet of the air filter 1, and dust and other mechanical impurities are removed by the air filter 1 to preliminarily purify the air. The filtered air enters the compressor 2, and the compressor 2 compresses the air to a certain pressure.

[0041] Considering the specific implementation of the precooling system, based on the above embodiment, please refer to Figure 1 The precooling system includes an air cooling tower 3. The interior of the air cooling tower 3 is divided from bottom to top into a normal temperature zone 3-a with normal temperature water and a cooling zone 3-b with cooling water. The normal temperature zone 3-a is connected to the air outlet of the air filtration and compression system, and the normal temperature zone 3-a is connected to the cooling zone 3-b. The cooling zone 3-b is connected to the air inlet of the molecular sieve purification system.

[0042] Specifically, the interior of the air cooling tower 3 is divided into a normal temperature zone 3-a and a cooling zone 3-b from bottom to top, and the normal temperature zone 3-a and the cooling zone 3-b are connected, wherein the normal temperature zone 3-a has normal temperature water, and the cooling zone 3-b has cooling water, the normal temperature zone 3-a is connected to the air outlet of the compressor 2, and the cooling zone 3-b is connected to the air inlet of the molecular sieve purification system. Thus, the compressed air first enters the normal temperature zone 3-a for preliminary cooling, and then rises to the cooling zone 3-b to be cooled to a specified temperature range. In this way, the air is cooled by combining normal temperature water and cooling water, which can save the consumption of cooling water and save costs, and in the process of air rising, the normal temperature water and cooling water also play a role in cleaning the air together to further remove impurities and other mechanical impurities in the air.

[0043] To further optimize the precooling system, based on the above examples, please refer to Figure 1 The precooling system also includes a water cooling tower 4 and a normal temperature water source 5. The liquid outlet of the water cooling tower 4 is connected to the cooling zone 3-b, and the normal temperature water source 5 is connected to the normal temperature zone 3-a.

[0044] Specifically, the liquid outlet of the water cooling tower 4 is connected to the cooling zone 3-b through a water cooling pipeline, a low temperature water pump 6 is arranged on the water cooling pipeline, and a normal temperature water source 5 is connected to the normal temperature zone 3-a through a normal temperature water pipeline, and a normal temperature water pump 7 is arranged on the normal temperature water pipeline. In this way, by turning on the low temperature water pump 6, cooling water can be supplied to the cooling zone 3-b to ensure that the cooling water in the cooling zone 3-b is sufficient. Similarly, by turning on the normal temperature water pump 7, normal temperature water can be supplied to the normal temperature zone 3-a to ensure that the normal temperature water in the normal temperature zone 3-a is sufficient, thereby ensuring that the air cooling tower 3 can continuously perform air cooling operations, which is conducive to improving the production efficiency of low-pressure liquid nitrogen.

[0045] Considering the specific implementation methods of the molecular sieve purification system and the heat exchanger system, based on the above embodiments, please refer to Figure 1 The molecular sieve purification system includes two molecular sieve adsorbers 8 , and the heat exchanger system includes a plate heat exchanger 12 , an expander 13 and a cooler 14 .

[0046] On the one hand, the air inlet ends of the two molecular sieve adsorbers 8 are connected to the air outlet end of the precooling system through the first automatic switching valve group 9.

[0047] Specifically, the function of the molecular sieve adsorber 8 is to remove various impurities in the air, including water and carbon dioxide, etc. The specific structure of the molecular sieve adsorber 8 can refer to the prior art. It is not the focus of protection of this application and will not be described in detail herein. The present invention adopts two molecular sieve adsorbers 8, and the cooling zone 3-b of the air cooling tower 3 is connected to one end of the drain pipeline. The other end of the drain pipeline is divided into two pipelines, which are respectively connected to the air inlet ends of the two molecular sieve adsorbers 8, and both pipelines are provided with a first automatic switching valve, which is used to control the air on and off between the cooling zone 3-b and the molecular sieve adsorber 8. In this way, the two molecular sieve adsorbers 8 are used to work alternately, thereby ensuring that the molecular sieve purification system can continuously perform air purification operations, which is beneficial to improving the production efficiency of low-pressure liquid nitrogen.

[0048] It should be noted that the expander 13 includes a boost end 13-a and an expansion end 13-b. The boost end 13-a is used to increase the gas pressure before the gas enters the expansion end 13-b of the expander 13 to be compressed, which helps to improve the efficiency and refrigeration effect of the expander 13. The expansion end 13-b is used to compress the gas to expand to a low pressure and reduce the gas temperature. The plate heat exchanger 12 includes a cold end and a hot end. The hot end is used to transfer the heat of the medium flowing into the hot end to the cold end, and the cold end is used to absorb the heat of the hot end to cool the medium at the hot end.

[0049] On the other hand, please refer to Figure 1The gas outlet ends of the two molecular sieve adsorbers 8 are divided into two paths, one path is connected in sequence to the boost end 13-a of the expander 13, the cooler 14, the hot end of the plate heat exchanger 12, the expansion end 13-b of the expander 13 and the upper tower 16 of the distillation tower, and the other path is connected in sequence to the cold end of the plate heat exchanger 12 and the lower tower 15 of the distillation tower.

[0050] Thus, the purified air is divided into two streams, one part flows into the boosting end 13-a of the expander 13 to be boosted to a certain pressure, the boosted air then flows into the cooler 14 to be cooled to a certain temperature, the cooled air flows into the cold end of the plate heat exchanger 12 to absorb the heat of the hot end, the heated air then flows into the expansion end 13-b of the expander 13 to be depressurized and cooled, and then flows into the upper tower 16 of the distillation tower to participate in distillation; the other part directly flows into the hot end of the plate heat exchanger 12 to be cooled to the saturation temperature, and the cooled air flows into the lower tower 15 of the distillation tower for distillation. In this way, the purified air is divided into two streams, one as the cold source of the plate heat exchanger 12, and the other as the air source to be flowed into the lower tower 15 for distillation, which not only makes full use of the purified air to avoid the additional setting of the cold end medium, but also makes the air after heat exchange at the cold end flow back to the upper tower 16 to participate in distillation, thereby greatly saving production costs.

[0051] Please note that, please refer to Figure 1 The bottom of the lower tower 15 of the distillation tower is connected to the middle of the upper tower 16 of the distillation tower through the first reflux pipeline, and a subcooler 17 is arranged on the reflux pipeline. In this way, the oxygen-rich liquid air and liquid nitrogen obtained by the distillation of the lower tower 15 are throttled and depressurized by the subcooler 17 and then refluxed to the middle of the upper tower 16 as raw materials for further distillation. The distillation principle is the same as that of the lower tower 15. When the liquid flows down, it evaporates more after multiple evaporations, and more oxygen remains in the liquid phase. The oxygen concentration in the downstream liquid is continuously increased. Liquid oxygen C with high oxygen content can be obtained at the bottom of the upper tower 16, and the upper tower 16 can obtain high-purity product nitrogen E and part of the product oxygen D. Figure 1 shown.

[0052] In order to recover the polluted nitrogen gas (nitrogen gas containing 1% to 3% oxygen) from the upper tower 16 as the regeneration gas for the molecular sieve adsorber 8, based on the above embodiment, please refer to Figure 1 The upper part of the upper tower 16 of the distillation tower is connected to the cold end of the plate heat exchanger 12 through the second reflux pipeline, and then a branch is separated, and the branch is connected to the gas outlet ends of the two molecular sieve adsorbers 8 through the second automatic switching valve group 10.

[0053] It is understandable that the dirty nitrogen can be used as one of the regeneration gas sources for the molecular sieve adsorber 8. After the air separation system starts normally, the dirty nitrogen is used as a regeneration gas source, and the impurity gas adsorbed on the molecular sieve is released by heating and decompression, so that the molecular sieve can restore its adsorption capacity. Thus, the upper part of the upper tower 16 passes through the cold end of the plate heat exchanger 12 through the second reflux pipeline and then separates out a first branch, and the first branch then separates out two pipelines respectively connected to the gas outlet end of the molecular sieve adsorber 8, and a second automatic switching valve is set on both pipelines. In this way, the second automatic switching valve corresponding to one molecular sieve adsorber 8 is closed to perform purification operations, while the corresponding second automatic switching valve of the other molecular sieve adsorber 8 is opened, and the dirty nitrogen in the upper tower 16 is reheated after the cold end of the plate heat exchanger 12 and flows to the molecular sieve adsorber 8 as a regeneration gas source, thereby recycling the dirty nitrogen in the upper tower 16, which not only saves production costs, but also facilitates the efficient operation of the overall device.

[0054] For further optimization, please refer to Figure 1 The first branch is provided with an electric heater 11 between the plate heat exchanger 12 and the second automatic switching valve group 10. It should be noted that heating the contaminated nitrogen can not only remove moisture and other impurities in the contaminated nitrogen, ensure the purity of the regeneration gas source, and thus ensure the regeneration effect of the molecular sieve, but also help to improve the surface activity of the molecular sieve.

[0055] In order to recover the coldness of the contaminated nitrogen gas in the upper tower 16, based on the above embodiment, please refer to Figure 1 The upper part of the upper tower 16 of the distillation tower is connected to the cold end of the plate heat exchanger 12 through the second reflux pipeline, and then a second branch is separated, and the second branch is connected to the liquid inlet end of the water cooling tower 4. In this way, the dirty nitrogen in the upper tower 16 flows into the water cooling tower 4 after being reheated by the cold end of the plate heat exchanger 12, so as to recycle the cold capacity of the dirty nitrogen, which not only avoids the waste of the dirty nitrogen, but also uses the dirty nitrogen as the refrigerant source of the water cooling tower 4, saving cooling water, thereby saving production costs.

[0056] In order to recover the coldness of the crude argon gas in the upper tower 16, based on the above embodiment, please refer to Figure 1 The upper middle part of the upper tower 16 of the distillation tower is connected to the booster tower 18 through an argon fraction pipeline. The booster tower 18 is used to distill the argon fraction to obtain crude liquid argon. The bottom of the booster tower 18 is connected to the upper tower 16 of the distillation tower through a third reflux pipeline. The third loop pipeline is used to reflux the crude liquid argon into the upper tower 16 of the distillation tower.

[0057] It should be noted that the argon fraction is a mixed gas containing oxygen, argon and nitrogen, wherein the argon content is about 8% to 12%, the nitrogen content is generally less than 0.06%, and the rest is oxygen. The argon fraction flows into the efficiency tower 18 through the argon fraction pipeline for further distillation to obtain crude liquid argon, which then flows back to the upper tower 16 through the third reflux pipeline. The crude liquid argon continues to be distilled in the upper tower 16 to the top of the tower to obtain crude argon gas, which is reheated through the cold end of the plate heat exchanger 12 through the second reflux pipeline and flows into the water cooling tower 4 to recycle the cold capacity of the crude argon gas, which not only avoids the waste of the argon fraction, but also uses the crude argon gas as the refrigerant source of the water cooling tower 4, further saving cooling water, thereby further saving production costs.

[0058] In summary, the low-pressure liquid nitrogen production device provided by the present invention can be used to produce low-pressure liquid nitrogen products. In a specific embodiment, the raw air is sucked in from the air inlet of the air filter 1, and the dust and other mechanical impurities are removed by the air filter 1. The purified air is compressed to about 0.58MPa by the compressor 2, and the outlet temperature is ≤105°C. The compressed air enters the air cooling tower 3 for cooling. The air temperature output by the air cooling tower 3 is about 16°C, and the air cooling tower 3 cleans the air at the same time. After the air exits the air cooling tower 3, it enters the molecular sieve adsorber 8 in working state. The molecular sieve adsorber 8 removes moisture and carbon dioxide in the air, and controls the carbon dioxide content in the air discharged by the molecular sieve adsorber 8 to be ≤1ppm. Part of the purified air flows into the boosting end 13-a of the expander 13 to be boosted to 0.8~0.9MPa, and the boosted air flows into the cooler 14 to be cooled to about 40°C, and then flows into the cold end of the plate heat exchanger 12 to absorb the heat of the hot end. The heated air flows into the expansion end 13-b of the expander 13 to be expanded to 0.13MPa, and then flows into the upper tower 16 of the distillation tower to participate in distillation; the other part directly flows into the hot end of the plate heat exchanger 12 to be cooled to the saturation temperature, and the cooled air flows into the lower tower 15 of the distillation tower for distillation. The lower tower 15 distills the air to obtain oxygen-enriched liquid air, nitrogen and fractional liquid nitrogen. It should be noted that if the nitrogen is discharged directly through the cooler 17, it will be condensed into liquid nitrogen A at about 0.4 MPa. The nitrogen in the lower tower 15 directly rises into the efficiency tower condenser 19 to condense into liquid nitrogen. The efficiency tower condenser 19 is about 40-50m higher than the liquid nitrogen output position. The liquid nitrogen flows to the liquid nitrogen output position through the liquid outlet pipe and is pressurized to about 0.75 MPa, so that the device produces the required liquid nitrogen B at about 0.75 MPa. Figure 1 shown.

[0059] In this specification, relational terms such as first and second are used merely to distinguish one entity from other entities, but do not necessarily require or imply any such actual relationship or order between these entities.

[0060] The various embodiments in this specification are described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the various embodiments can be referenced to each other.

[0061] The low-pressure liquid nitrogen production device provided by the present invention is introduced in detail above. Specific examples are used herein to illustrate the principles and implementation methods of the present invention. The description of the above embodiments is only used to help understand the method of the present invention and its core idea. It should be pointed out that for ordinary technicians in this technical field, without departing from the principle of the present invention, several improvements and modifications can be made to the present invention, and these improvements and modifications also fall within the scope of protection of the claims of the present invention.

Claims

1. A low-pressure liquid nitrogen production device, characterized in that: It includes an air filtration and compression system, a precooling system, a molecular sieve purification system and a heat exchanger system, and a distillation system connected in sequence; The air filtration and compression system is used to preliminarily purify the air and compress the air; The precooling system is used to cool the compressed air; The molecular sieve purification system is used to purify the air; The heat exchanger system is used to cool the purified air to the saturation temperature; The distillation system comprises a distillation tower and a synergist tower (18), wherein the lower tower (15) of the distillation tower is connected to the heat exchanger system and is used for distilling the air after heat exchange to obtain oxygen-enriched liquid air, nitrogen and liquid nitrogen, wherein the synergist tower (18) is higher than the lower tower (15), and a synergist tower condenser (19) is provided inside the synergist tower (18), wherein the input end of the synergist tower condenser (19) is connected to the top of the lower tower (15), and the output end is connected to a liquid nitrogen output position at a preset height lower than the synergist tower condenser (19) through a liquid outlet pipe, and is used for cooling the nitrogen into liquid nitrogen and pressurizing it to a required pressure before outputting it.

2. The low-pressure liquid nitrogen production device according to claim 1, characterized in that: The air filtration and compression system comprises an air filter (1) and a compressor (2); the air filter (1) is provided with an air inlet connected to external air; the air inlet end of the compressor (2) is connected to the air outlet of the air filter (1), and the air outlet end is connected to the air inlet end of the precooling system.

3. The low-pressure liquid nitrogen production device according to claim 1, characterized in that: The precooling system comprises an air cooling tower (3), the interior of the air cooling tower (3) being divided into a normal temperature zone (3-a) having normal temperature water and a cooling zone (3-b) having cooling water from bottom to top, the normal temperature zone (3-a) being connected to an air outlet of the air filtration and compression system, the normal temperature zone (3-a) being in communication with the cooling zone (3-b), and the cooling zone (3-b) being connected to an air inlet of the molecular sieve purification system.

4. The low-pressure liquid nitrogen production device according to claim 3, characterized in that: The precooling system further comprises a water cooling tower (4) and a normal temperature water source (5), wherein the liquid outlet of the water cooling tower (4) is connected to the cooling zone (3-b), and the normal temperature water source (5) is connected to the normal temperature zone (3-a).

5. The low-pressure liquid nitrogen production device according to claim 4, characterized in that: The molecular sieve purification system comprises two molecular sieve adsorbers (8), and the heat exchanger system comprises a plate heat exchanger (12), an expander (13) and a cooler (14); The air inlet ends of the two molecular sieve adsorbers (8) are connected to the air outlet end of the precooling system via a first automatic switching valve group (9); the air outlet ends of the two molecular sieve adsorbers (8) are divided into two paths, one path is sequentially connected to the boost end (13-a) of the expander (13), the cooler (14), the cold end of the plate heat exchanger (12), the expansion end (13-b) of the expander (13) and the upper tower (16) of the distillation tower, and the other path is sequentially connected to the hot end of the plate heat exchanger (12) and the lower tower (15) of the distillation tower.

6. The low-pressure liquid nitrogen production device according to claim 5, characterized in that: The bottom of the lower tower (15) of the distillation tower is connected to the middle of the upper tower (16) of the distillation tower via a first reflux pipeline, and a subcooler (17) is provided on the reflux pipeline.

7. The low-pressure liquid nitrogen production device according to claim 6, characterized in that: The upper part of the upper tower (16) of the distillation tower is connected to the cold end of the plate heat exchanger (12) through a second reflux pipeline, and then a branch is separated. The branch is connected to the gas outlet ends of the two molecular sieve adsorbers (8) through a second automatic switching valve group (10).

8. The low-pressure liquid nitrogen production device according to claim 7, characterized in that: The branch line is provided with an electric heater (11) located between the plate heat exchanger (12) and the second automatic switching valve group (10).

9. The low-pressure liquid nitrogen production device according to claim 6, characterized in that: The upper part of the upper tower (16) of the distillation tower is connected to the cold end of the plate heat exchanger (12) through a second reflux pipeline, and then another branch is separated, and the branch is connected to the liquid inlet end of the water cooling tower (4).

10. The low-pressure liquid nitrogen production device according to claim 6, characterized in that: The upper middle part of the upper tower (16) of the distillation tower is connected to the booster tower (18) via an argon fraction pipeline, and the booster tower (18) is used to distill the argon fraction to obtain crude liquid argon. The bottom of the booster tower (18) is connected to the upper tower (16) of the distillation tower via a third reflux pipeline, and the third loop pipeline is used to reflux the crude liquid argon into the upper tower (16) of the distillation tower.

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