A method for producing high-purity nitrogen with low energy consumption by oxygen-enriched expansion into a low-pressure column for rectification

Abstract

This application relates to the field of gas production technology, specifically disclosing a low-energy-consumption method for producing high-purity nitrogen through oxygen-enriched expansion followed by low-pressure column distillation. The method involves expanding oxygen-enriched gas evaporated in a high-pressure column condenser and then introducing it into a low-pressure column as feed gas. During the expansion process, the oxygen-enriched gas generates a large amount of cooling, reducing the need for external cooling input. Therefore, the pressure of the low-pressure column condenser only needs to be slightly higher than atmospheric pressure, significantly reducing the operating pressure of the low-pressure column. This increases the relative volatility of oxygen and nitrogen components, improving the nitrogen extraction rate. The expansion and cooling of the oxygen-enriched gas evaporated in the high-pressure column condenser reduces or eliminates the need for additional air expansion cooling, allowing more or all of the high-pressure air to enter the high-pressure column distillation, thereby increasing the oxygen content of the oxygen-enriched gas entering the low-pressure column distillation and improving the nitrogen extraction rate. The preparation method of this application has the advantages of high extraction rate and low energy consumption.

Description

Technical Field

[0001] This application relates to the field of gas production technology, and more specifically, it relates to a low-energy-consumption method for producing high-purity nitrogen through oxygen-enriched expansion into a low-pressure column for distillation. Background Technology

[0002] High-purity nitrogen is widely used in precision electronics, biomedicine, chemical industry, food preservation and other fields. With the rapid development of these industries, the demand for high-purity nitrogen has increased dramatically. Typically, the pressure of high-purity nitrogen is required to be 0.7-1.2 MPa and the purity of nitrogen is required to reach 99.9%-99.9999%.

[0003] Currently, the use of cryogenic distillation to separate and produce high-purity nitrogen from air is the mainstream technology in industry. However, existing technologies still face the following technical problems in producing high-purity nitrogen, especially high-pressure high-purity nitrogen: (1) the nitrogen extraction rate is relatively low, typically between 60% and 75%; (2) to ensure system cooling balance, the low-pressure tower operates at a relatively high pressure, affecting distillation efficiency; (3) the energy utilization of the expansion medium is insufficient, with some expansion gas being discharged only as regeneration gas, resulting in nitrogen loss; and (4) the product form is limited, making it difficult to simultaneously meet the market demand for both gaseous and liquid products. A balance between extraction rate, low energy consumption, and product diversification cannot be achieved. Summary of the Invention

[0004] In order to achieve high extraction rate and low energy consumption while meeting the requirement of high nitrogen pressure, this application provides a low-energy method for producing high-purity nitrogen by oxygen-enriched expansion into a low-pressure column for distillation.

[0005] In a first aspect, this application provides a low-energy-consumption method for producing high-purity nitrogen through oxygen-enriched expansion followed by distillation in a low-pressure column, employing the following technical solution: A low-energy-consumption method for producing high-purity nitrogen via oxygen-enriched expansion followed by low-pressure column distillation includes the following steps: The raw air is cooled by the main heat exchanger and then fed into the high-pressure tower for distillation to separate high-pressure nitrogen and oxygen-enriched liquid air. Oxygen-enriched liquid air is fed into the high-pressure tower condenser-evaporator for evaporation to obtain medium-pressure oxygen-enriched gas and residual oxygen-enriched liquid air; the medium-pressure oxygen-enriched gas is expanded to the pressure of the low-pressure tower through the first turbine expander and then fed into the low-pressure tower for rectification; the residual oxygen-enriched liquid air is throttled and depressurized and then fed into the low-pressure tower condenser-evaporator as a cold source. The high-pressure nitrogen obtained from the high-pressure tower is divided into two paths. The first path is output as a high-purity nitrogen product, and the second path is condensed into liquid nitrogen by the high-pressure tower condenser-evaporator and used as the reflux liquid of the high-pressure tower. After medium-pressure enriched oxygen is distilled in a low-pressure column, medium-pressure nitrogen and oxygen-enriched liquid are obtained. The medium-pressure nitrogen is condensed into liquid nitrogen in the condenser-evaporator of the low-pressure column. The liquid nitrogen is divided into three paths: the first path is output as liquid nitrogen product, the second path is pressurized by a liquid nitrogen pump and fed into the high-pressure column as reflux liquid, and the third path is used as reflux liquid for the low-pressure column. The oxygen-enriched liquid obtained from the low-pressure column distillation is cooled and throttled before being passed into the low-pressure column condenser-evaporator for evaporation to obtain oxygen-enriched gas. After reheating, the oxygen is output as the regeneration gas for the purifier.

[0006] By adopting the above technical solution, the medium-pressure enriched oxygen used in this application originates from the oxygen-enriched liquid air in the high-pressure column reboiler. This oxygen-enriched liquid air has undergone preliminary distillation in the high-pressure column, and the nitrogen components have been significantly removed, resulting in a relatively high oxygen content. The medium-pressure enriched oxygen obtained after evaporation is essentially an "oxygen-enriched" gas, not the raw material air. When this enriched oxygen expands into the low-pressure column, due to its high oxygen content and low nitrogen content, it will not dilute the purity of the nitrogen at the top of the low-pressure column. Instead, it helps to form a steeper oxygen-nitrogen concentration gradient in the lower part of the low-pressure column, promoting nitrogen enrichment at the top of the column. At the same time, the enriched oxygen generates a large amount of cooling energy during the expansion process. This cooling energy is used to maintain the low-temperature distillation environment of the low-pressure column and to condense the nitrogen at the top of the column, thereby reducing the external cooling energy input requirement. In this way, this application not only increases the nitrogen extraction rate to 70-80% but also controls the energy consumption to 0.2-0.25 kWh / Nm³. 3 The N2 level is relatively low. Meanwhile, since the expanded oxygen-rich gas directly enters the low-pressure column bottom as the rising gas phase, no additional reboiler heating is required, further simplifying the system structure and reducing energy consumption.

[0007] Preferably, the medium-pressure oxygen-enriched gas is reheated to a predetermined temperature by the main heat exchanger before entering the first turbine expander, and then expanded to the pressure of the low-pressure tower.

[0008] By adopting the above technical solution, the expansion after reheating can ensure that the inlet medium of the expander is a pure gas phase, avoiding liquid damage to the gas film stability of the gas bearing turbine expander, preventing liquid slugging and bearing failure. At the same time, the increase in inlet temperature increases the temperature difference between the inlet and outlet of the expander, increases the cooling capacity per unit mass flow rate, and improves the cooling efficiency. The reheating process is completed in the main heat exchanger using the residual cooling of the nitrogen gas in the product, realizing the cascade utilization of cooling capacity without increasing energy consumption.

[0009] Preferably, the medium-pressure oxygen-enriched gas is not reheated and is directly introduced into the first turbine expander to expand to the pressure of the low-pressure tower, after which it is partially liquefied.

[0010] By adopting the above technical solution, medium-pressure oxygen-enriched gas expands directly at low temperature. When the expansion ratio is sufficiently large, the temperature drops below the saturation temperature after expansion, resulting in partial liquefaction. The liquid produced after expansion can be used as reflux liquid or a cooling source for the low-pressure tower, enhancing the mass and heat transfer effect within the tower. Partial liquefaction means that the feed air entering the high-pressure tower, required to maintain the cooling balance of the unit, changes from a partially liquefied state to a superheated state. The high-pressure vented gas at the bottom of the high-pressure tower becomes rising steam and participates in distillation, thus improving the nitrogen extraction rate. This solution is suitable for oil-bearing turbine expanders and applications requiring high liquid nitrogen production.

[0011] Preferably, the method further includes the following steps: extracting a portion of the raw material air from the middle of the main heat exchanger, expanding the raw material air through the second turbine expander, mixing it with the medium-pressure enriched oxygen expanded by the first turbine expander, and sending them together into the low-pressure column for distillation.

[0012] By adopting the above technical solution, adding a second expander can significantly increase the total cooling capacity of the system, meeting the cooling balance required for producing more liquid nitrogen products. The expanded feed air has an oxygen content of approximately 21%, which provides a large amount of cooling capacity and increases the feedstock for distillation after entering the low-pressure tower. Although the introduced oxygen component will cause a slight decrease in nitrogen extraction rate, it will still remain at a high level. The two expanders can be adjusted independently to achieve flexible distribution of cooling capacity and optimize system energy consumption.

[0013] Preferably, the extraction rate of the high-purity nitrogen product is 70-80%.

[0014] By adopting the above technical solution, the oxygen-enriched expansion into the tower avoids the interference of oxygen components in the feed air on the distillation of the low-pressure tower; the operating pressure of the low-pressure tower is reduced, which is conducive to nitrogen enrichment; the cold energy generated by the expansion is precisely used for condensation and distillation, reducing cold energy loss and achieving a higher extraction rate, which means that more products are produced per unit of feed air, resulting in better economic efficiency.

[0015] Preferably, the unit energy consumption is 0.2-0.25 kWh / Nm³. 3 N2.

[0016] By adopting the above technical solutions, energy consumption is the core indicator for measuring the economic efficiency of nitrogen production. The energy consumption of existing technologies is approximately 0.25-0.3 kWh / Nm³. 3 N2, this application improves the extraction rate while keeping energy consumption at a similar or even better level.

[0017] Secondly, this application provides a high-purity nitrogen, employing the following technical solution: A high-purity nitrogen is prepared by a low-energy-consumption method of producing high-purity nitrogen by oxygen-enriched expansion into a low-pressure column for distillation.

[0018] By adopting the above technical solution and the method, the high-purity nitrogen produced inherits the advantages of high efficiency and low energy consumption of the process route. The oxygen-enriched expansion into the tower ensures excellent separation conditions in the low-pressure tower. The product nitrogen has high purity and stable pressure. At the same time, this method can flexibly produce both gaseous nitrogen and liquid nitrogen to meet the needs of different users. The nitrogen produced fully meets the requirements of precision electronics, biomedicine, chemical industry and other fields.

[0019] Preferably, the high-purity nitrogen has a pressure of 0.7-1.2 MPa and a purity of 99.9-99.9999%.

[0020] By adopting the above technical solution, the pressure and purity range covers the needs of most industrial application scenarios. The pressure of 0.7-1.2MPa can be directly used in processes such as electronic chip purging, chemical protective gas, and pharmaceutical production without secondary pressurization. The purity of 99.9%-99.9999% means that the oxygen content can be as low as below 1ppm, which meets the stringent requirements of high-precision manufacturing for impurity content. This application achieves stable production of this high-purity product through a dual-tower distillation coupling design of high-pressure tower and low-pressure tower, combined with precise reflux liquid control.

[0021] In summary, this application has the following beneficial effects: 1. Because this application uses oxygen-rich gas that has been evaporated in a high-pressure tower condenser and expanded before entering a low-pressure tower as raw material gas, it avoids the decrease in extraction rate caused by unrefined air directly entering the tower, and achieves a nitrogen extraction rate as high as 70-80%.

[0022] 2. In this application, oxygen-enriched gas is preferably reheated or directly expanded to the pressure of the low-pressure tower, which can be flexibly matched with different types of expanders and effectively reduce the operating pressure of the low-pressure tower, thereby further improving the nitrogen extraction rate.

[0023] 3. The method in this application optimizes the distribution of cooling capacity and the reflux liquid path, achieving energy consumption as low as 0.2-0.25 kWh / Nm³ while ensuring high-pressure nitrogen and high purity. 3 It can produce N2 and simultaneously produce gaseous and liquid nitrogen products, which has good economic benefits and market prospects. Attached Figure Description

[0024] Figure 1 This is a process flow diagram of Embodiment 1 of this application; Figure 2 This is a process flow diagram of Embodiment 2 of this application; Figure 3 This is a process flow diagram of Embodiment 3 of this application.

[0025] Explanation of reference numerals in the attached diagram: 1. High-pressure tower; 2. High-pressure tower condenser-evaporator; 3. First turbine expander; 4. Low-pressure tower; 5. Low-pressure tower condenser-evaporator; 6. Main heat exchanger; 7. Liquid nitrogen pump; 8. Subcooler; 9. Second turbine expander; 10. Throttling valve one; 11. Throttling valve two; 12. Throttling valve three. Detailed Implementation

[0026] The present application will be further described in detail below with reference to the accompanying drawings and embodiments. Example

[0027] Example 1 Adopting such Figure 1 The process flow shown is for producing high-purity nitrogen, and the specific steps are as follows: After purification and drying, 18200Nm 3 At a pressure of 0.88 MPa, the feed air is introduced into the main heat exchanger 6 and cooled to -166.6℃ before entering the bottom of the high-pressure tower 1. The operating pressure of the high-pressure tower 1 is 0.88 MPa. The feed air is distilled in the high-pressure tower 1 and separated into high-pressure nitrogen and oxygen-enriched liquid air.

[0028] Oxygen-enriched liquid air is throttled to 0.5 MPa via throttling valve 10 and then enters the high-pressure tower condenser-evaporator 2 for evaporation, yielding 7055 Nm³. 3 / h of medium-pressure oxygen-enriched water and 3577Nm 3 The remaining oxygen-enriched liquid air is returned to the main heat exchanger 6 at medium pressure. After being reheated to -158℃, it enters the first turbine expander 3 and expands to 0.24MPa at a temperature of -173.9℃. The expanded medium-pressure oxygen-enriched air enters the bottom of the low-pressure tower 4. The remaining oxygen-enriched liquid air is depressurized to 0.025MPa through the second throttling valve 11 and then enters the low-pressure tower condenser-evaporator 5 as a heat source.

[0029] The high-pressure nitrogen separated from high-pressure tower 1 is divided into two streams, the first stream being 10940 Nm. 3 The high-pressure nitrogen gas, at a rate of / h, is reheated by the main heat exchanger 6 and output as a high-purity nitrogen product. The high-purity nitrogen product has a pressure of 0.859MPa and an oxygen content of ≤3ppm; the second path is 7962Nm 3 High-pressure nitrogen gas at a rate of / h is condensed into liquid nitrogen by the high-pressure tower condenser-evaporator 2, and then pressurized by the liquid nitrogen pump 7 to obtain 3382 Nm³ of liquid nitrogen. 3 After being mixed at / h, it is used as the reflux liquid for high-pressure tower 1.

[0030] The expanded, medium-pressure enriched oxygen enters low-pressure column 4 for rectification and separation. The operating pressure in low-pressure column 4 is 0.238 MPa. 7642 Nm³ of oxygen is obtained at the top of low-pressure column 4. 3 / h of medium-pressure nitrogen, with an oxygen content ≤3ppm, is used to obtain oxygen-enriched liquid from the bottom of low-pressure tower 4. The medium-pressure nitrogen then enters the low-pressure tower condenser / evaporator 5 and is condensed into liquid nitrogen. The liquid nitrogen is divided into three streams, the first stream being 30Nm 3 Liquid nitrogen is output as a liquid nitrogen product at a rate of / h, with the second channel providing 3340Nm. 3 Liquid nitrogen at 0.23 MPa per hour enters liquid nitrogen pump 7 and is pressurized to 1.05 MPa. After mixing with the liquid nitrogen output from the high-pressure tower condenser evaporator 2, it is used as the reflux liquid of the high-pressure tower 1. The remaining liquid nitrogen in the third path is used as the reflux liquid at the top of the low-pressure tower 4.

[0031] The oxygen-enriched liquid obtained from the distillation of the low-pressure tower 4 is subcooled by the cooler 8, and then throttled to 0.025MPa by the throttling valve 12 before entering the low-pressure tower condenser-evaporator 5 to evaporate into oxygen-enriched gas. The oxygen-enriched gas is then reheated to 18°C ​​by the cooler 8 and the main heat exchanger 6 and output as the regeneration gas of the purifier.

[0032] The nitrogen extraction rate in this embodiment is 77.2%, and the unit energy consumption is 0.22 kWh / Nm³. 3 The high-purity nitrogen product has a purity of 99.999%, an oxygen content of ≤3ppm, and a pressure of 0.859MPa.

[0033] Example 2

[0034] Adopting such Figure 2 The process flow shown is for producing high-purity nitrogen. The difference between this process and Example 1 is that the medium-pressure enriched oxygen does not undergo reheating in the main heat exchanger 6. Instead, it directly enters the first turbine expander 3 from the outlet of the high-pressure tower condenser evaporator 2 and expands to 0.24 MPa. After expansion, it partially liquefies, and the gas-liquid two-phase enriched oxygen enters the bottom of the low-pressure tower 4. The remaining steps are the same as in Example 1.

[0035] The nitrogen extraction rate in this embodiment is 78.2%, and the unit energy consumption is 0.218 Wh / Nm³. 3 High-pressure nitrogen production: 11078 Nm³ 3 The nitrogen purity was 99.999%, the oxygen content was ≤3ppm, and the pressure was 0.858MPa. Due to the partial liquefaction after expansion, additional liquid phase reflux was provided for low-pressure tower 4, which slightly improved the extraction rate.

[0036] Example 3

[0037] Adopting such Figure 3 The process flow shown is for producing high-purity nitrogen. The difference from Example 1 is that a portion of the raw material air is extracted from the middle of the main heat exchanger 6. This portion of raw material air is then introduced into the second turbine expander 9 through a valve and expanded to 0.24 MPa. The expanded raw material air is then mixed with the medium-pressure enriched oxygen expanded by the first turbine expander 3 and sent together into the low-pressure tower 4 for distillation. The remaining steps are the same as in Example 1.

[0038] In this embodiment, the nitrogen extraction rate is 70.8%, and the unit energy consumption is 0.245 Wh / Nm³. 3 The product has a nitrogen purity of 99.999%, an oxygen content of ≤3ppm, and a pressure of 0.860MPa. Due to the introduction of undistilled raw material air, the extraction rate is slightly reduced, but the total cooling capacity of the system is increased. It is suitable for high-temperature environments or occasions with higher requirements for liquid nitrogen production. Comparative Example

[0039] Comparative Example 1 Comparative Example 1 uses the method of Example 1 in patent publication number CN106196887A to produce high-purity nitrogen: the raw air is divided into two streams, one of which expands and enters directly into a medium-pressure distillation column, and the other stream is pressurized and enters a high-pressure distillation column. The raw air volume is 18200 Nm³. 3 / h, pressure 0.88MPa.

[0040] The nitrogen extraction rate in this comparative example was 70.2%, and the unit energy consumption was 0.255 kWh / Nm³. 3 The product has a nitrogen purity of 99.999% and a pressure of 0.85 MPa.

[0041] Comparative Example 2 Comparative Example 2 uses the method described in the embodiment of the patent with authorization publication number CN212481841U to produce high-purity nitrogen: the oxygen-enriched gas evaporated in the low-pressure tower condenser is reheated and expanded to a pressure slightly higher than atmospheric pressure, which is used as the regeneration gas for the purifier. The feed air volume is 18200 Nm³. 3 / h, pressure 0.88MPa.

[0042] The nitrogen extraction rate in this comparative example was 70.5%, and the unit energy consumption was 0.25 kWh / Nm³. 3 The product has a nitrogen purity of 99.999% and a pressure of 0.86 MPa. Since the pressure of the low-pressure tower condenser evaporator needs to be maintained at 0.4-0.7 MPa, the low-pressure tower distillation pressure increases, resulting in a decrease in the extraction rate.

[0043] Comparative Example 3 Comparative Example 3 adopts a conventional dual-tower distillation process, namely, an oxygen-free expansion process into the low-pressure tower: the feed air is cooled by the main heat exchanger and then enters the high-pressure tower. The nitrogen at the top of the tower is used as a product, and part of it is condensed and refluxed; the oxygen-enriched liquid air in the bottom of the high-pressure tower enters the low-pressure tower for further distillation; the cooling capacity of the system is provided by the expander expanding the feed air.

[0044] The nitrogen extraction rate in this comparative example was 65.5%, and the unit energy consumption was 0.31 kWh / Nm³. 3 The product has a nitrogen purity of 99.999% and a pressure of 0.85 MPa. Performance testing

[0045] The nitrogen extraction rate, unit energy consumption, product purity (expressed as oxygen content), and product pressure of each embodiment and comparative example are shown in Table 1.

[0046] Table 1. Process parameters and corresponding product parameters project Nitrogen extraction rate / % <![CDATA[Unit energy consumption / (kWh / Nm 3 )]]> Product purity / % Product pressure / MPa Example 1 72.5 0.22 ≤3ppm 0.859 Example 2 78.2 0.218 ≤3ppm 0.858 Example 3 70.8 0.245 ≤3ppm 0.86 Comparative Example 1 70.2 0.255 ≤3ppm 0.85 Comparative Example 2 70.5 0.25 ≤3ppm 0.85 Comparative Example 3 65.5 0.31 ≤3ppm 0.85 As can be seen from Table 1, Examples 1-3, and Comparative Examples 1-3, the high-purity nitrogen prepared in Examples 1-3 has a high nitrogen extraction rate and low unit energy consumption. The product purity and pressure both meet the high-purity nitrogen standards, with an oxygen content ≤3ppm and a pressure of 0.85-0.86MPa, demonstrating good technical performance. Examples 1-3 adopted a technology scheme of oxygen-enriched expansion into a low-pressure distillation column. The medium-pressure oxygen-enriched gas evaporated from the high-pressure column condenser is expanded and sent to the low-pressure column as feed gas. This oxygen-enriched gas originates from the oxygen-enriched liquid air in the high-pressure column bottom, with high oxygen content and low nitrogen content. After entering the low-pressure column, it does not dilute the nitrogen concentration at the top of the column, but instead forms a steeper oxygen-nitrogen concentration gradient, promoting nitrogen enrichment at the top of the column. At the same time, the expansion process generates a large amount of cooling, and the temperature can be reduced to -173.9℃, which is used to maintain the low-temperature distillation environment of the low-pressure column, thereby effectively improving the nitrogen extraction rate and reducing the unit energy consumption.

[0047] Compared to Example 1, Example 2 shows a slightly higher nitrogen extraction rate and slightly lower unit energy consumption. Example 2 employs a technique where medium-pressure enriched oxygen is directly expanded to the low-pressure tower pressure without reheating. After expansion, partial liquefaction occurs, and the gas-liquid two-phase enriched oxygen enters the bottom of the low-pressure tower. The liquid produced after expansion serves as additional liquid-phase reflux in the low-pressure tower, enhancing mass and heat transfer within the tower, thereby further improving the extraction rate and reducing energy consumption. This technique is suitable for oil-bearing turbine expanders and can achieve even better technical results within the limits of equipment capacity.

[0048] Compared to Example 1, Example 3 shows a decrease in nitrogen extraction rate and a slight increase in unit energy consumption. Example 3 adds a second turbine expander, which extracts a portion of the raw air from the middle of the main heat exchanger, expands it, mixes it with oxygen-enriched air, and then enters the low-pressure tower. Although the total cooling capacity of the system increases, the expanded raw air contains approximately 79% nitrogen and 21% oxygen. The oxygen component slightly dilutes the nitrogen concentration at the top of the low-pressure tower, leading to a decrease in extraction rate. Simultaneously, the additional expander increases the system's cooling input, but the product nitrogen quantity does not increase proportionally, thus resulting in a slight increase in unit energy consumption. This solution is suitable for high-temperature environments or applications requiring higher liquid nitrogen production, improving the system's cooling capacity while sacrificing a small amount of extraction rate.

[0049] Compared to Example 1, Comparative Example 1 had a lower nitrogen extraction rate and higher unit energy consumption. In Comparative Example 1, a stream of feed air was expanded and directly fed into a medium-pressure distillation column. This feed air had not been distilled in a high-pressure column and contained a large amount of oxygen. Upon entering the medium-pressure column, it diluted the nitrogen concentration inside the column, inhibiting nitrogen accumulation at the top of the column and resulting in a decrease in the extraction rate. To maintain product yield, it was necessary to increase the feed air throughput or increase the operating pressure, thereby increasing unit energy consumption.

[0050] Compared with Example 1, Comparative Example 2 has a lower nitrogen extraction rate and higher unit energy consumption. In Comparative Example 2, the oxygen-enriched gas evaporated in the low-pressure tower condenser is reheated and expanded to slightly above atmospheric pressure, which is then used as the regeneration gas output of the purifier. In this scheme, the pressure of the low-pressure condenser must be maintained at 0.4-0.7 MPa to generate sufficient cooling capacity, which leads to an increase in the distillation pressure of the low-pressure tower. This reduces the relative volatility of nitrogen and oxygen in the tower, making separation more difficult and thus lowering the nitrogen extraction rate. The higher operating pressure also increases the compression energy consumption of the system.

[0051] Compared with Example 1, Comparative Example 3 had the lowest nitrogen extraction rate and the highest unit energy consumption. Comparative Example 3 adopted a conventional dual-tower distillation process, in which the system cooling capacity was provided by the expansion of the feed air by the expander. The expanded feed air did not pass through the high-pressure tower distillation and was directly used for refrigeration and was usually vented or used as regeneration gas. The nitrogen resources in it were not recovered and utilized, resulting in a large nitrogen loss. At the same time, the operating pressure of the low-pressure tower in the conventional dual-tower process was high, and the separation efficiency was low, resulting in the lowest extraction rate and the highest energy consumption.

[0052] This specific embodiment is merely an explanation of this application and is not intended to limit it. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of this application.

Claims

1. A low-energy-consumption method for producing high-purity nitrogen through oxygen-enriched expansion followed by low-pressure column distillation, characterized in that: Includes the following steps: After the raw material air is cooled by the main heat exchanger (6), it is fed into the high-pressure tower (1) for distillation to separate high-pressure nitrogen and oxygen-enriched liquid air. Oxygen-enriched liquid air is fed into the high-pressure tower condenser-evaporator (2) for evaporation to obtain medium-pressure enriched oxygen and residual oxygen-enriched liquid air; the medium-pressure enriched oxygen is expanded to the pressure of the low-pressure tower (4) by the first turbine expander (3) and then fed into the low-pressure tower (4) for distillation; the residual oxygen-enriched liquid air is throttled and depressurized and fed into the low-pressure tower condenser-evaporator (5) as a cold source. The high-pressure nitrogen obtained from the high-pressure tower (1) is divided into two paths. The first path is output as a high-purity nitrogen product, and the second path is condensed into liquid nitrogen by the high-pressure tower condenser evaporator (2) and used as the reflux liquid of the high-pressure tower (1). After medium-pressure oxygen is distilled in a low-pressure tower (4), medium-pressure nitrogen and oxygen-enriched liquid are obtained. The medium-pressure nitrogen is condensed into liquid nitrogen in a low-pressure tower condenser evaporator (5). The liquid nitrogen is divided into three paths: the first path is output as liquid nitrogen product, the second path is pressurized by a liquid nitrogen pump (7) and then fed into a high-pressure tower (1) as reflux liquid, and the third path is used as reflux liquid in the low-pressure tower (4). The oxygen-enriched liquid obtained by distillation in the low-pressure tower (4) is cooled and throttled before being passed into the low-pressure tower condenser-evaporator (5) for evaporation to obtain oxygen-enriched gas. After reheating, the oxygen is output to obtain the regenerated gas of the purifier.

2. The method for producing high-purity nitrogen with low energy consumption through oxygen-enriched expansion followed by low-pressure column distillation according to claim 1, characterized in that: Before entering the first turbine expander (3), the medium-pressure oxygen-enriched gas is reheated to a predetermined temperature by the main heat exchanger (6) and then expanded to the pressure of the low-pressure tower (4).

3. The method for producing high-purity nitrogen with low energy consumption through oxygen-enriched expansion followed by low-pressure column distillation according to claim 1, characterized in that: The medium-pressure oxygen-enriched gas is directly introduced into the first turbine expander (3) without reheating and expanded to the pressure of the low-pressure tower (4), after which it partially liquefies.

4. The method for producing high-purity nitrogen with low energy consumption through oxygen-enriched expansion followed by low-pressure column distillation according to claim 1, characterized in that: It also includes the following steps: A portion of the raw material air is drawn from the middle of the main heat exchanger (6), and after the raw material air is expanded by the second turbine expander (9), it is mixed with the medium-pressure oxygen-enriched oxygen expanded by the first turbine expander (3) and sent together to the low-pressure tower (4) for distillation.

5. The method for producing high-purity nitrogen with low energy consumption through oxygen-enriched expansion followed by low-pressure column distillation according to claim 1, characterized in that: The extraction rate of the high-purity nitrogen product is 70-80%.

6. The method for producing high-purity nitrogen with low energy consumption through oxygen-enriched expansion followed by low-pressure column distillation according to claim 1, characterized in that: The unit energy consumption is 0.2-0.25 kWh / Nm³. 3 N2.

7. A high-purity nitrogen, characterized in that: The method for producing high-purity nitrogen with low energy consumption by oxygen-enriched expansion into a low-pressure column for distillation, as described in any one of claims 1-6, is as follows.

8. The high-purity nitrogen according to claim 7, characterized in that: The high-purity nitrogen has a pressure of 0.7-1.2 MPa and a purity of 99.9-99.9999%.

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