Space division device

Abstract

The application discloses a kind of air separation devices, the air separation devices include sequentially pipeline connection of the flow direction of raw gas along compression system, precooling system, purification system, cold box system and pressure expansion system, cold box system includes first heat exchanger, first rectifying column, condensation evaporator and second rectifying column, first heat exchanger is located between the feed end of purification system and first rectifying column, the top of first rectifying column is connected with the bottom of condensation evaporator, the bottom of second rectifying column is communicated with the top of condensation evaporator, the top of second rectifying column is connected with first pipeline, first pipeline is sequentially communicated pressure expansion system and first heat exchanger, and is connected with purification system, the bottom of second rectifying column is connected with second pipeline, second pipeline passes through first heat exchanger, after the product of backflow rectification to first heat exchanger through first pipeline and second pipeline, raw material gas after cooling purification, improve the thermal efficiency of system, reduce energy consumption.

Description

Technical Field

[0001] This application relates to the field of oxygen-enriched combustion technology, and in particular to an air separation device. Background Technology

[0002] Oxygen-enriched combustion refers to an energy-saving combustion technology that uses combustion-supporting gases with an oxygen concentration higher than that of air. It is applied in fields such as glass kilns, pulverized coal boilers, and steel rolling furnaces. Oxygen-enriched combustion can accelerate fuel combustion rates, shorten production cycles, optimize flame stability, and reduce nitrogen oxide and dust emissions. Oxygen-enriched combustion, involving low-purity oxygen, can increase flame temperature by approximately 100°C, reduce smoke and dust emissions, decrease incomplete fuel combustion losses, and reduce energy consumption by approximately 10%–20%.

[0003] Currently, the method for preparing low-purity oxygen involves using an air separation unit to separate and purify the main components of air, such as oxygen, nitrogen, and argon. Cryogenic distillation is a commonly used air separation method. This method involves deeply cooling air to a liquid state and utilizing the differences in the boiling points of the components to gradually extract oxygen, nitrogen, and argon.

[0004] Currently, the commonly used process of pressurizing, revaporizing, and reheating low-purity liquid oxygen requires an air compressor in addition to a raw material air compressor to provide pressurized air that can efficiently exchange heat with the pressurized low-purity liquid oxygen in order to efficiently vaporize, reheat, and pressurize it. This increases the plant cost, subsequent operating cost, and management and maintenance cost. Utility Model Content

[0005] In view of the shortcomings of the prior art, the purpose of this application is to provide an air separation device that aims to reduce energy consumption in the process of separating air to produce low-purity oxygen.

[0006] To achieve the above objectives, this application adopts the following technical solution: This application discloses an air separation unit, which includes a compression system, a precooling system, a purification system, a cold box system, and a pressurization and expansion system connected sequentially along the flow direction of the feed gas. The compression system is used to compress and cool the feed gas, the precooling system is used to cool and wash the feed gas output from the compression system, the purification system is used to remove impurities from the feed gas, the cold box system is used to perform distillation separation on the feed gas, and the pressurization and expansion system is used to expand and refrigerate the gas output from the cold box system. The cold box system includes a first heat exchanger, a first distillation column, a condenser-evaporator, and a second distillation column. The first heat exchanger is located between the purification system and the feed end of the first distillation column. The top of the first distillation column is connected to the bottom of the condenser-evaporator via a pipeline, and the bottom of the second distillation column is connected to the top of the condenser-evaporator. The top outlet of the second distillation column is connected to a first pipeline, which is connected in sequence to the pressurization and expansion system and the first heat exchanger, and is also connected to the purification system. The bottom outlet of the second distillation column is connected to a second pipeline, which leads to the first heat exchanger. In some embodiments of this application, the pressurization and expansion system includes an expander and a pressurizer; The air separation unit includes a third pipeline, which is connected to the output end of the first heat exchanger along with the second pipeline. The third pipeline is connected to the booster compressor, and the first pipeline is connected to the expander.

[0007] In some embodiments of this application, the pressurization and expansion system includes a cooler located in the third pipeline and connected to the discharge end of the pressurizer.

[0008] In some embodiments of this application, the purification system includes a molecular sieve adsorber and an electric heater. The feed end of the molecular sieve adsorber is connected to the precooling system, the discharge end of the molecular sieve adsorber is connected to the first heat exchanger, and the discharge end of the molecular sieve adsorber is also connected to the first pipeline. The electric heater is located in the first pipeline and between the molecular sieve adsorber and the first heat exchanger.

[0009] In some embodiments of this application, the cold box system includes a second heat exchanger, which is located on the first pipeline between the top discharge end of the second distillation column and the pressurization and expansion system.

[0010] In some embodiments of this application, the cold box system includes a first reflux pipe connected between the discharge end of the condenser-evaporator and the second distillation column, and the first reflux pipe passes through the second heat exchanger.

[0011] In some embodiments of this application, the cold box system includes a second reflux pipe, which is connected between the bottom discharge end of the first distillation column and the second distillation column.

[0012] In some embodiments of this application, the discharge end of the condenser-evaporator is connected to a liquid nitrogen discharge pipeline and a liquid oxygen discharge pipeline.

[0013] In some embodiments of this application, the air separation unit further includes a filtration system connected to the feed end of the compression system for filtering impurities in the raw gas.

[0014] In some embodiments of this application, the precooling system includes an air-cooled tower and a water-cooled tower. The bottom of the air-cooled tower is connected to the discharge end pipe of the compression system, the top of the air-cooled tower is connected to the feed end pipe of the purification system, and the lower part of the water-cooled tower is connected to the upper part of the air-cooled tower. The precooling system also includes a circulating water pipeline, which is connected to the air-cooled tower and the water-cooled tower respectively.

[0015] Beneficial effects: The air separation unit provided in this application connects a first pipeline between the top of the second distillation column and the first heat exchanger. This first pipeline, via a pressurization and expansion system, allows nitrogen gas extracted from the top of the second distillation column to expand and cool, serving as a system cold source. The nitrogen then enters the first heat exchanger to cool the purified feed gas. A second pipeline connects the bottom outlet of the second distillation column to the first heat exchanger, allowing low-purity oxygen generated at the bottom of the second distillation column to enter the first heat exchanger and cool the purified feed gas. This improves the system's thermal efficiency and reduces energy consumption. Furthermore, this unit eliminates the need for a separate air pressurization device, reducing equipment costs and the space occupied by the unit. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the structure of an air separation device provided in one embodiment of this application.

[0017] Figure 2 This is a schematic diagram of the structure of an air separation device provided in another embodiment of this application.

[0018] Figure 3 This is a schematic diagram of the structure of an air separation device provided in another embodiment of this application.

[0019] Explanation of key component symbols: 1. Filtration system; 2. Compression system; 3. Precooling system; 31. Air-cooled tower; 32. Water-cooled tower; 33. Circulating water pipeline; 4. Purification system; 41. Molecular sieve adsorber; 42. Electric heater; 43. Silencer; 5. Cold box system; 51. First heat exchanger; 52. First distillation column; 53. Condenser-evaporator; 54. Second distillation column; 55. Second heat exchanger; 56. First reflux pipeline; 57. Second reflux pipeline; 58. Liquid nitrogen discharge pipeline; 59. Liquid oxygen discharge pipeline; 6. Supercharged expansion system; 61. Expander; 62. Supercharger; 63. Cooler; 7. First pipeline; 8. Second pipeline; 9. Third pipeline. Detailed Implementation

[0020] This application provides an air separation device. To make the purpose, technical solution, and effects of this application clearer and more explicit, the following detailed description is provided with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only for explaining this application and are not intended to limit this application.

[0021] In the description of this application, it should be understood that the terms "upper," "lower," "left," and "right," etc., indicating orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or a specific orientational structure and operation. Therefore, they should not be construed as limitations on this application. Furthermore, "first" and "second" are only for descriptive purposes and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this application, unless otherwise stated, "multiple" means two or more.

[0022] In the description of this application, it should be noted that, unless otherwise expressly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection, an electrical connection, or a connection that allows communication between them; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication between two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this application according to the specific circumstances.

[0023] Figure 1 A schematic diagram of the structure of an air separation device provided in one embodiment of this application; Figure 2 A schematic diagram of the structure of an air separation device provided in another embodiment of this application; Figure 3 This is a schematic diagram of the structure of an air separation device provided in another embodiment of this application.

[0024] Please see Figures 1 to 3 This application provides an air separation unit. This air separation unit uses air as the feed gas to produce low-purity oxygen.

[0025] Specifically, the air separation unit includes a compression system 2, a precooling system 3, a purification system 4, a cold box system 5, and a pressurization and expansion system 6, which are connected sequentially along the flow direction of the feed gas. The compression system 2 is used to compress and cool the feed gas, the precooling system 3 is used to cool and wash the feed gas output from the compression system 2, the purification system 4 is used to remove impurities from the feed gas, the cold box system 5 is used to perform distillation separation on the feed gas, and the pressurization and expansion system 6 is used to expand and refrigerate the gas output from the cold box system 5.

[0026] The cold box system 5 includes a first heat exchanger 51, a first distillation column 52, a condenser-evaporator 53, and a second distillation column 54. The first heat exchanger 51 is located between the purification system 4 and the feed end of the first distillation column 52. The top of the first distillation column 52 is connected to the bottom of the condenser-evaporator 53 via a pipeline, and the bottom of the second distillation column 54 is connected to the top of the condenser-evaporator 53 via a pipeline. The upper discharge end of the first distillation column 52 is connected to the condenser-evaporator 53 via a pipeline, and the discharge end of the condenser-evaporator is connected to both the first distillation column 52 and the second distillation column 54 via a pipeline. Through the condenser-evaporator, heat exchange is achieved between the first distillation column 52 and the second distillation column 54, and two-stage distillation of the feed gas is realized, improving the separation effect of the feed gas and increasing the purity of the product. The low-purity oxygen product prepared by the above device has a concentration of 35%–95% and a pressure of 2.5–5 barA, which can be directly supplied to the kiln.

[0027] The top outlet of the second distillation column 54 is connected to a first pipeline 7, which sequentially connects to the pressurization and expansion system 6 and the first heat exchanger 51, and is also connected to the purification system 4. The bottom outlet of the second distillation column 54 is connected to a second pipeline 8, which leads to the first heat exchanger 51. Nitrogen gas collected from the top of the second distillation column 54 is returned to the pressurization and expansion system 6 via the first pipeline 7 for expansion and refrigeration. This allows the expanded and refrigerated nitrogen gas to serve as a cold source for the purified feed gas, reducing energy consumption during operation and improving system thermal efficiency. The bottom of the second distillation column 54 is connected to the first heat exchanger 51 via the second pipeline 8, allowing the low-purity oxygen output from the bottom of the second distillation column 54 to exchange heat with the purified feed gas, reheating the low-purity oxygen and further improving system thermal efficiency.

[0028] In some embodiments, the air separation unit further includes a filtration system 1 connected between the feed end of the compression system 2 and the air source. The filtration system 1 can filter dust and mechanical impurities in the raw material air, improving the purity of the raw material air entering the compression system 2.

[0029] The filtration system 1 can consist of multi-stage filtration components, including but not limited to pre-filters, medium-efficiency filters, and high-efficiency filters. The pre-filter primarily intercepts larger particles of dust and impurities in the air, extending the lifespan of subsequent filters. The medium-efficiency filter further filters smaller particles of pollutants, improving air cleanliness. The high-efficiency filter removes tiny particles and microorganisms from the air, ensuring that the feed gas entering the compression system 2 meets extremely high purity standards. In some embodiments, the filtration system 1 is also equipped with automatic filter cleaning and replacement functions to reduce the frequency of manual maintenance and improve the overall operating efficiency and stability of the air separation unit.

[0030] Compression system 2 includes a multi-stage compressor and an interstage cooler. The raw gas is compressed by the multi-stage compressor and cooled by the interstage cooler before being delivered to precooling system 3.

[0031] Multistage compressors employ a step-by-step compression method, effectively increasing the pressure of the feed gas to meet the conditions required for subsequent processes. Interstage coolers are installed between the multistage compressors to cool the feed gas after the first stage of compression, lowering its temperature to prevent excessive heat from affecting compressor performance and feed gas quality. This also helps improve compression efficiency and reduce energy consumption. The feed gas, after being compressed by the multistage compressors and cooled by the interstage coolers, is delivered to the pre-cooling system 3 in a stable state and at a suitable temperature, preparing it for subsequent processes such as distillation.

[0032] The precooling system 3 includes an air-cooled tower 31 and a water-cooled tower 32. The bottom of the air-cooled tower 31 is connected to the outlet pipe of the compression system 2, the top of the air-cooled tower 31 is connected to the inlet pipe of the purification system 4, and the lower part of the water-cooled tower 32 is connected to the upper part of the air-cooled tower 31. Thus, cooling water entering the air-cooled tower 31 from the water-cooled tower 32 flows downwards from the top of the air-cooled tower 31, and the raw material gas passes through the air-cooled tower 31 from bottom to top for cooling and washing, and then exits from the top of the air-cooled tower 31 to enter the purification system 4.

[0033] The precooling system 3 also includes a circulating water pipeline 33, which is connected to a water source and to both the air-cooled tower 31 and the water-cooled tower 32. The circulating water pipeline 33 is connected to the top of the water-cooled tower 32, flows from top to bottom through the tower, and exits from the bottom of the tower to the top of the air-cooled tower 31. Connecting pipelines between the circulating water pipeline 33 and the air-cooled tower 31 and water-cooled tower 32 are positioned at different heights on the air-cooled tower 31 to fully utilize the cooling and washing effects of the circulating water and the cooling water in the water-cooled tower 32 on the raw gas.

[0034] Furthermore, a cooling water pump is installed on the connecting pipeline between the air-cooled tower 31 and the water-cooled tower 32. A cooling water pump is also installed on the circulating water pipeline 33. The installation of the cooling water pump ensures an effective supply of washing water and avoids the influence of pipeline installation height on the washing water supply.

[0035] The purification system 4 includes a molecular sieve adsorber 41 and an electric heater 42. The feed end of the molecular sieve adsorber 41 is connected to the precooling system 3, and the discharge end is connected to the first heat exchanger 51. The discharge end of the molecular sieve adsorber 41 is also connected to the first pipeline 7. The molecular sieve adsorber 41 can adsorb moisture, carbon dioxide, and trace amounts of hydrocarbons from the raw material gas. After impurities are removed by the molecular sieve adsorber 41, the raw material gas output from the air-cooled tower 31 enters the first heat exchanger 51 of the cold box system 5. The electric heater 42 is located in the first pipeline 7, between the molecular sieve adsorber 41 and the first heat exchanger 51.

[0036] Part of the nitrogen gas after passing through the first heat exchanger 51 is sent to the regeneration end of the molecular sieve adsorber 41; part of it is sent to the water cooling tower 32 to participate in the cooling process inside the water cooling tower 32 and help reduce the water temperature; the remaining part of the nitrogen gas is output to the low-pressure, low-purity nitrogen usage system.

[0037] The electric heater 42 is connected to the molecular sieve adsorber 41 via a pipeline. After the molecular sieve adsorber 41 completes its adsorption process, the electric heater 42 can regenerate the molecular sieve. During regeneration, the electric heater 42 heats the gas, and the heated gas passes in reverse through the molecular sieve adsorber 41, desorbing the moisture, carbon dioxide, and trace amounts of hydrocarbons adsorbed on the molecular sieve. This restores the molecular sieve's adsorption capacity, ensuring that the molecular sieve adsorber 41 can operate continuously and stably, providing high-quality purification for the raw gas entering the cold box system 5.

[0038] Multiple molecular sieve adsorbers 41 can be set up, and multiple sets of molecular sieve adsorbers 41 can be set up in parallel to improve the purification efficiency of the purification device.

[0039] The molecular sieve adsorber 41 is also connected to a silencer 43. The silencer 43 is installed at the exhaust end of the molecular sieve adsorber 41 and reduces the noise generated during gas emission during the regeneration process. The silencer 43 employs a special sound-absorbing structure that effectively absorbs and weakens the sound wave energy generated by the gas flow, thereby controlling the noise within a reasonable range, reducing the impact on the surrounding environment, and ensuring the environmental friendliness of the entire air separation unit during operation.

[0040] The cold box system 5 also includes a second heat exchanger 55, which is located on the first pipeline 7 between the top discharge end of the second distillation column 54 and the pressurization and expansion system 6. The second heat exchanger 55 is used to heat the nitrogen gas taken from the top of the second distillation column 54 before it is delivered to the pressurization and expansion system 6.

[0041] In some embodiments, the second heat exchanger 55 employs a high-efficiency heat exchange element, capable of rapidly and uniformly heating nitrogen to the required temperature, ensuring a stable nitrogen temperature entering the pressurized expansion system 6, thereby guaranteeing the normal operation of the pressurized expansion system 6. It is understood that the second heat exchanger 55 has excellent sealing performance, effectively preventing nitrogen leakage and ensuring the safety and stability of the entire cold box system 5. The second heat exchanger 55 can adopt a compact structure, occupying a small area, facilitating installation and maintenance within the cold box system 5.

[0042] In some embodiments, the cold box system 5 includes a first reflux pipe 56, which connects the outlet end of the condenser-evaporator 53 to the second distillation column 54, and passes through a second heat exchanger 55. The outlet end of the condenser-evaporator 53 is connected to a liquid nitrogen outlet pipe 58. Nitrogen gas output from the top of the first distillation column 52 to the condenser-evaporator 53 exchanges heat with liquid oxygen at the bottom of the second distillation column 54 to form liquid nitrogen. A portion of the condensed liquid nitrogen flows back to the first distillation column 52 through the connecting pipe between the condenser-evaporator 53 and the first distillation column 52; another portion is subcooled and throttled by the second heat exchanger 55, then flows back to the top of the second distillation column 54 through the first reflux pipe 56; the remaining portion, as liquid nitrogen product, is led out of the cold box system 5 through the liquid nitrogen outlet pipe 58 and sent to the liquid nitrogen storage system.

[0043] The first reflux pipe 56 allows liquid nitrogen flowing from the outlet of the condenser-evaporator 53 to be appropriately conditioned by the second heat exchanger 55 before being returned as reflux liquid to the top of the second distillation column 54 for further distillation. This helps to further optimize the distillation process and improve separation efficiency and product quality. A control valve can be installed on the first reflux pipe 56 to facilitate precise adjustment of the liquid nitrogen reflux flow rate and velocity, meeting the operational requirements of the air separation unit under different conditions.

[0044] In some embodiments, the cold box system 5 includes a second reflux pipe 57, which connects the bottom outlet of the first distillation column 52 to the second distillation column 54. The second reflux pipe 57 is connected to the middle of the second distillation column 54 to reflux the oxygen-enriched liquid air from the bottom of the first distillation column 52 to the middle of the second distillation column 54 for distillation. After distillation in the second distillation column 54, low-purity oxygen is obtained at the bottom of the second distillation column 54.

[0045] A control valve can also be installed on the second reflux pipeline 57. This control valve can precisely control the reflux flow rate and reflux speed of the oxygen-enriched liquid air to adapt to the operating conditions of the air separation unit under different production stages and different product requirements, and ensure that the air separation unit can stably and efficiently produce low-purity oxygen products that meet the requirements.

[0046] In some embodiments, the second return pipe 57 is made of a material that is resistant to low temperature and high pressure to ensure long-term stable operation under low temperature and high pressure conditions, reduce the risk of pipe damage and leakage, and further improve the safety and reliability of the air separation unit.

[0047] In some embodiments, the bottom outlet of the condenser-evaporator 53 is connected to a liquid oxygen outlet pipe 59. Through the liquid oxygen outlet pipe 59, a portion of the liquid oxygen at the bottom of the condenser-evaporator 53 can be led out of the cold box system 5 and sent as a byproduct to the liquid oxygen storage system.

[0048] In some embodiments, a flow regulating valve is installed on the liquid oxygen discharge line 59. The flow regulating valve can precisely adjust the output flow rate of liquid oxygen according to actual production needs.

[0049] In some embodiments, a temperature sensor is installed on the liquid oxygen discharge line 59. The temperature sensor can monitor the temperature of the liquid oxygen in real time to ensure that the output liquid oxygen temperature meets the storage and usage requirements. The liquid oxygen storage system adopts a special insulation design, which can effectively reduce the evaporation loss of liquid oxygen and ensure the storage quality of liquid oxygen.

[0050] like Figure 1 and Figure 3 As shown, in some embodiments, the pressurization-expansion system 6 includes an expander 61 and a booster 62. The air separation unit includes a third pipeline 9, which is connected to the output end of the first heat exchanger 51 via the second pipeline 8. The third pipeline 9 is connected to the booster 62, and the first pipeline 7 is connected to the expander 61.

[0051] The booster compressor 62 is used to pressurize the low-purity oxygen passing through the first heat exchanger 51 to obtain high-pressure low-purity oxygen, which meets the pressure requirements of subsequent processes. The expander 61 is used to expand and cool the nitrogen gas after it has been heated by the second heat exchanger 55, providing the required cooling capacity for the air separation unit. Through the coordinated operation of the booster compressor 62 and the expander 61, the pressure and temperature parameters within the air separation unit can be effectively regulated, improving the operating efficiency and stability of the air separation unit.

[0052] In the above, by setting up a pressurization and expansion system 6, and by feeding the low-purity oxygen output from the bottom of the second distillation column 54 into the booster compressor 62 after passing through the first heat exchanger 51, the air separation unit can not only produce medium-pressure low-purity oxygen, but also obtain high-pressure low-purity oxygen.

[0053] In some embodiments, expander 61 is a turbine expander. Turbine expanders are compact, reliable, and highly efficient. During operation, the turbine expander can precisely control the expansion ratio, ensuring efficient cooling of nitrogen in expander 61 and providing continuous and suitable cooling capacity for the stable operation of the air separation unit. The booster compressor 62 can flexibly adjust the boosting rate of low-purity oxygen according to actual process requirements, ensuring that the pressure of high-pressure low-purity oxygen remains stable within a reasonable range, further improving the overall economic efficiency and stability of the air separation unit.

[0054] In some embodiments, the booster-expand system 6 includes a cooler 63. The cooler 63 is located in the third line 9, downstream of the booster-expander 61, and connected to the booster 62. The cooler 63 cools the low-purity oxygen exiting the booster 62, further reducing the temperature of the medium to meet the temperature requirements of subsequent processes.

[0055] This application also provides a method for preparing low-purity oxygen by air separation, which uses the above-mentioned air separation device and includes the following steps: S100. Filter the raw material gas. The raw material gas is introduced into the air filtration system 1 to remove dust and mechanical impurities.

[0056] S200: The raw material gas is compressed and cooled. The filtered raw material gas enters the compression system 2, where it is compressed and cooled by a multi-stage compressor and an interstage cooler.

[0057] S300, Remove impurities from the raw gas. The compressed and cooled raw gas enters the molecular sieve adsorber 41 to adsorb and remove impurities such as moisture and carbon dioxide, and then all of it enters the downstream cold box system 5. After the impurities are adsorbed, nitrogen gas heated by the electric heater 42 is introduced into the molecular sieve adsorber 41 for desorption.

[0058] S400, the purified raw gas is introduced into the first heat exchanger 51 for cooling and heat exchange.

[0059] The purified feed gas is introduced into the first heat exchanger 51 and exchanges heat with the nitrogen gas flowing back into the second distillation column 54.

[0060] S500: The feed gas after passing through the first heat exchanger 51 enters the first distillation column 52 for distillation and separation, yielding nitrogen and oxygen-enriched liquid air. The nitrogen separated by the first distillation column 52 is output from the top of the first distillation column 52 to the condenser-evaporator 53, while the oxygen-enriched liquid air flows back to the second distillation column 54 through a pipe connected to the bottom of the first distillation column 52 for distillation and separation, yielding nitrogen and low-purity oxygen. The nitrogen separated by the second distillation column 54 is output from the top of the second distillation column 54 and enters the pressurized expansion system 6 for expansion and refrigeration. The expanded and refrigerated nitrogen enters the first heat exchanger 51, while the low-purity oxygen is introduced into the first heat exchanger 51 through a second pipe 8 connected to the bottom of the second distillation column 54, where it exchanges heat with the purified feed gas.

[0061] The nitrogen gas output from the top of the second distillation column 54, after undergoing expansion and refrigeration and participating in heat exchange in the first heat exchanger 51, can be partially allocated according to the overall energy balance requirements of the system. A portion of the nitrogen gas can be fed into the purification system 4 for backflushing and desorption of the molecular sieve adsorber 41; another portion can be fed into the water-cooling tower 32 to participate in the cooling process and help lower the water temperature; the remaining nitrogen gas can be output to the low-pressure, low-purity nitrogen application system to meet the needs of relevant industrial production for low-pressure, low-purity nitrogen. The low-purity oxygen obtained through distillation separation in the first distillation column 52 and the second distillation column 54 maintains a stable purity within a certain range, meeting the quality requirements of different industrial production processes for low-purity oxygen and providing a reliable material basis for subsequent production processes using low-purity oxygen as raw material.

[0062] After the nitrogen gas from the top of the second distillation column 54 is heated by heat exchange, it is introduced into the pressurized expansion system 6 for expansion and cooling. The nitrogen gas after expansion and cooling enters the first heat exchanger 51 for heat exchange.

[0063] The nitrogen gas collected from the top of the second distillation column 54 is heated by the second heat exchanger 55, and then enters the expander 61 for expansion and cooling to obtain low-temperature nitrogen gas, which meets the cooling requirements of the air separation unit.

[0064] The pressurized and expanded nitrogen gas then enters the first heat exchanger 51 to exchange heat with the raw material gas from the purification system 4, achieving efficient energy utilization and recovery. During this process, the nitrogen gas absorbs heat from the raw material gas, further increasing its own temperature and creating conditions for subsequent distribution and utilization. This not only ensures the energy balance and efficient circulation within the air separation unit but also effectively improves the overall system's operating efficiency and stability.

[0065] The low-purity oxygen output from the bottom of the second distillation column 54 (S520) is sent to the user's website as medium-pressure low-purity oxygen after heat exchange in the first heat exchanger 51, and another part enters the pressurization and expansion system 6 to obtain high-pressure low-purity oxygen.

[0066] The low-purity oxygen that enters the pressurization and expansion system 6 undergoes pressurization within the system, resulting in a significant increase in pressure and the production of high-pressure low-purity oxygen. This allows for the simultaneous production of medium-pressure and high-pressure low-purity oxygen within a single system.

[0067] S530, after the nitrogen gas entering the condenser-evaporator 53 is condensed, part of it flows back to the first distillation column 52, part of it flows back to the second distillation column 54, and part of it is led out of the cold box system 5 to the liquid nitrogen storage system.

[0068] The nitrogen recirculated to the first distillation column 52 and the second distillation column 54 provides a stable cold source for the distillation process, ensuring a reasonable temperature distribution within the distillation columns and helping to improve the separation efficiency, thereby increasing the purity of products such as low-purity oxygen. The liquid nitrogen drawn to the liquid nitrogen storage system can serve as a backup cold source, to be used in case of emergencies or when additional cooling is required, enhancing the flexibility and reliability of the entire air separation unit.

[0069] It is understood that those skilled in the art can make equivalent substitutions or changes based on the technical solution and concept of this application, and all such substitutions or changes should fall within the protection scope of the appended claims.

Claims

1. An air separation unit, characterized in that, include: The system comprises a compression system, a precooling system, a purification system, a cold box system, and a pressurization and expansion system, which are connected sequentially along the flow direction of the raw gas. The compression system is used to compress and cool the raw gas. The precooling system is used to cool and wash the raw gas output from the compression system. The purification system is used to remove impurities from the raw gas. The cold box system is used to perform distillation and separation on the raw gas. The pressurization and expansion system is used to expand and refrigerate the gas output from the cold box system. The cold box system includes a first heat exchanger, a first distillation column, a condenser-evaporator, and a second distillation column. The first heat exchanger is located between the purification system and the feed end of the first distillation column. The top of the first distillation column is connected to the bottom of the condenser-evaporator via a pipeline, and the bottom of the second distillation column is connected to the top of the condenser-evaporator. The top outlet of the second distillation column is connected to a first pipeline, which is connected in sequence to the pressurization and expansion system and the first heat exchanger, and is also connected to the purification system. The bottom outlet of the second distillation column is connected to a second pipeline, which leads to the first heat exchanger.

2. The air separation unit according to claim 1, characterized in that, The pressurization and expansion system includes an expander and a pressurizer; The air separation unit includes a third pipeline, which is connected to the output end of the first heat exchanger along with the second pipeline. The third pipeline is connected to the booster compressor, and the first pipeline is connected to the expander.

3. The air separation unit according to claim 2, characterized in that, The pressurization and expansion system includes a cooler, which is located in the third pipeline and connected to the discharge end of the pressurizer.

4. The air separation unit according to claim 1, characterized in that, The purification system includes a molecular sieve adsorber and an electric heater. The feed end of the molecular sieve adsorber is connected to the precooling system, the discharge end of the molecular sieve adsorber is connected to the first heat exchanger, and the discharge end of the molecular sieve adsorber is also connected to the first pipeline. The electric heater is located in the first pipeline and between the molecular sieve adsorber and the first heat exchanger.

5. The air separation unit according to claim 1, characterized in that, The cold box system includes a second heat exchanger, which is located on the first pipeline between the top discharge end of the second distillation column and the pressurization and expansion system.

6. The air separation unit according to claim 5, characterized in that, The cold box system includes a first reflux pipe, which is connected between the discharge end of the condenser-evaporator and the second distillation column, and the first reflux pipe passes through the second heat exchanger.

7. The air separation unit according to claim 1, characterized in that, The cold box system includes a second reflux pipe, which is connected between the bottom discharge end of the first distillation column and the second distillation column.

8. The air separation unit according to claim 1, characterized in that, The discharge end of the condenser-evaporator is connected to a liquid nitrogen discharge pipeline and a liquid oxygen discharge pipeline, respectively.

9. The air separation unit according to claim 1, characterized in that, The air separation unit also includes a filtration system connected to the feed end of the compression system for filtering impurities in the raw gas.

10. The air separation unit according to claim 1, characterized in that, The precooling system includes an air-cooled tower and a water-cooled tower. The bottom of the air-cooled tower is connected to the discharge end pipe of the compression system, the top of the air-cooled tower is connected to the feed end pipe of the purification system, and the lower part of the water-cooled tower is connected to the upper part of the air-cooled tower. The precooling system also includes a circulating water pipeline, which is connected to the air-cooled tower and the water-cooled tower respectively.

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