A low-temperature nitrogen production method and system based on PSA technology

Abstract

The application relates to the technical field of nitrogen production, in particular to a low-temperature nitrogen production method and system based on PSA technology. The method comprises the following steps: S1, obtaining high-pressure raw material gas by pressurizing, filtering and low-temperature treating air; S2, adsorbing and separating nitrogen from the bottom of an A adsorption tower by the high-pressure raw material gas, and discharging from the top of the A adsorption tower; B adsorption tower is subjected to pressure reduction and desorption treatment; S3, connecting the top of the A adsorption tower and the top of the B adsorption tower to perform upper pressure equalization; connecting the middle of the A adsorption tower and the bottom of the B adsorption tower to perform lower pressure equalization; S4, adsorbing and separating nitrogen from the bottom of the B adsorption tower by the high-pressure raw material gas, and discharging from the top of the B adsorption tower; and the A adsorption tower is subjected to pressure reduction and desorption treatment. The technical bottleneck of traditional single-path top equalization is broken, the tower top gas and the tower middle gas are transported in a partitioned manner and are not mixed with each other, the purity of the recovered nitrogen is improved, and the service life of the device is prolonged.

Description

Technical Field

[0001] This application relates to the field of nitrogen production technology, and in particular to a low-temperature nitrogen production method and system based on PSA technology. Background Technology

[0002] Pressure Swing Adsorption (PSA) utilizes the different diffusion rates of oxygen and nitrogen in the air within carbon molecular sieves. Oxygen molecules are adsorbed within the carbon molecular sieve, while nitrogen molecules are enriched in the gas phase, achieving air separation. Simultaneously, the oxygen adsorption capacity of the carbon molecular sieve increases with increasing ambient pressure and decreases with decreasing pressure. The process of separating air through a cycle of pressure adsorption and depressurization desorption is called PSA nitrogen production.

[0003] Traditional PSA nitrogen production uses an equal pressure equalization scheme, which connects the tops of the two towers through a single pipeline to recover the pressure energy in the adsorption tower and pre-pressurize the desorption tower to reduce subsequent compressed air consumption. However, because single-path equalization mixes the pure nitrogen at the top of the tower with the oxygen-enriched gas at the bottom, the purity of the recovered gas is low. Furthermore, during single-path equalization, the gas only flows into the desorption tower from the top, creating a reverse airflow impact at the bottom, which can easily lead to local loosening and flow deviation of the molecular sieve bed.

[0004] Therefore, there is a need to provide an improved technical solution that addresses the shortcomings of the existing technology. Summary of the Invention

[0005] The purpose of this application is to provide a low-temperature nitrogen production method and system based on PSA technology to solve or alleviate the problems existing in the prior art.

[0006] To achieve the above objectives, this application provides the following technical solution: A method for low-temperature nitrogen production based on PSA technology, comprising: Step S1: Pressurize, filter, and cryogenically treat the air to obtain high-pressure raw material gas; Step S2: The high-pressure raw material gas is adsorbed and separated into nitrogen at the bottom of adsorption tower A and discharged from the top of adsorption tower A; adsorption tower B is used for depressurization and desorption treatment; Step S3: Connect the top of adsorption tower A and the top of adsorption tower B to perform upper pressure equalization; connect the middle of adsorption tower A and the bottom of adsorption tower B to perform lower pressure equalization; Step S4: The high-pressure raw material gas is adsorbed and separated into nitrogen at the bottom of adsorption tower B and discharged from the top of adsorption tower B; adsorption tower A is depressurized and desorbed.

[0007] A cryogenic nitrogen generation system includes: a pretreatment system, a nitrogen generation system, and a gas storage tank; After being processed by the pretreatment system, the air is fed into the nitrogen generation system, which then outputs nitrogen gas into the storage tank. The nitrogen generation system includes an inlet main valve, branch pipes, an outlet main valve, an A adsorption tower, a B adsorption tower, a first inlet valve, a second inlet valve, a first pressure reducing valve, a second pressure reducing valve, an upper pressure equalizing valve, a first lower pressure equalizing valve, a second lower pressure equalizing valve, a first exhaust valve, and a second exhaust valve. The bottoms of adsorption towers A and B are connected to branch pipes via the first and second inlet valves, respectively, and then to the main inlet valve; the tops of adsorption towers A and B are connected to the main outlet valve via the first and second exhaust valves, respectively; the middle sections of adsorption towers A and B are connected to branch pipes via the first and second lower pressure equalization valves, respectively; the bottoms of adsorption towers A and B are also connected to the atmosphere via the first and second pressure reducing valves, respectively; the tops of adsorption towers A and B are also interconnected via the upper pressure equalization valve. The other end of the intake manifold is connected to the pretreatment system; the other end of the exhaust manifold is connected to the air storage tank.

[0008] Preferably, the nitrogen generation system also includes a silencer; the bottoms of adsorption tower A and adsorption tower B are respectively connected to the silencer via a first pressure-reducing valve and a second pressure-reducing valve, and the other end of the silencer is connected to the atmosphere.

[0009] Preferably, gas rectifiers are installed at the bottom of adsorption tower A and adsorption tower B to homogenize the high-pressure raw material gas.

[0010] Preferably, the pretreatment system includes an air compressor, a filter, and a refrigerated air dryer connected in sequence.

[0011] Preferably, the filter includes a first filter and a second filter; The first filter is located between the air compressor and the air dryer, and the second filter is located between the air dryer and the nitrogen generation system.

[0012] Preferably, the pretreatment system further includes a first air buffer tank; the first air buffer tank is disposed between the air compressor and the first filter.

[0013] Preferably, the pretreatment system further includes a second air buffer tank; the second air buffer tank is disposed between the second filter and the nitrogen generation system.

[0014] Preferably, the top of the air storage tank, the first air buffer tank, and the second air buffer tank are all connected to an air vent valve, and the bottom of the air storage tank, the first air buffer tank, the second air buffer tank, the first filter, and the second filter are all connected to a drain valve.

[0015] Compared with the closest prior art, the technical solution of this application has the following beneficial effects: This application provides a core process for asymmetric stratified pressure equalization, employing an unequal pressure equalization method where the top of the adsorption tower is equal to the top of the desorption tower, and the middle of the adsorption tower is equal to the bottom of the desorption tower. This process overcomes the technical bottleneck of traditional single-path top equalization, separating and transporting the gas from the top and middle sections of the tower without mixing, thus improving the purity of nitrogen recovery. Simultaneously, the desorption tower can achieve rapid pre-pressurization by relying on the natural pressure gradient between the middle and bottom of the adsorption tower, significantly reducing the amount of compressed air required for subsequent replenishment, lowering energy consumption, and improving nitrogen purity. Furthermore, the dual-path gas exchange from the top and middle of the adsorption tower to the bottom of the desorption tower results in a more uniform airflow distribution within the desorption tower, which weakens the impact of local high-speed airflow on the molecular sieve and extends the service life of the device. Attached Figure Description

[0016] The accompanying drawings, which form part of this application, are used to provide a further understanding of this application. The illustrative embodiments and descriptions of this application are used to explain this application and do not constitute an undue limitation of this application. Wherein: Figure 1 This is an overall schematic diagram of a cryogenic nitrogen generation system provided according to some embodiments of this application; Figure 2 This is a schematic diagram of a nitrogen generation system provided according to some embodiments of this application.

[0017] Explanation of reference numerals in the attached figures: 1. Air compressor; 2. First air buffer tank; 3. First filter; 4. Refrigerated air dryer; 5. Second filter; 6. Second air buffer tank; 7. Main inlet valve; 8. Main outlet valve; 9. First inlet valve; 10. Second inlet valve; 11. First outlet valve; 12. Second outlet valve; 13. Upper equalizing valve; 14. First lower equalizing valve; 15. Second lower equalizing valve; 16. First pressure reducing valve; 17. Second pressure reducing valve; 18. Silencer; 19. A adsorption tower; 20. B adsorption tower; 21. Air storage tank; 22. Exhaust valve; 23. Drain valve. Detailed Implementation

[0018] The present application will now be described in detail with reference to the accompanying drawings and embodiments. Various examples are provided by way of explanation and not by way of limitation. In fact, those skilled in the art will recognize that modifications and variations can be made to the present application without departing from the scope or spirit thereof. For example, a feature shown or described as part of one embodiment may be used in another embodiment to produce yet another embodiment. Therefore, it is desirable that the present application encompass such modifications and variations that fall within the scope of the appended claims and their equivalents.

[0019] In the following description, the terms "first / second / third" are used merely to distinguish similar objects and do not represent a specific order of objects. It is understood that "first / second / third" may be interchanged in a specific order or sequence where permitted, so that the embodiments of this application described herein can be implemented in an order other than that illustrated or described herein.

[0020] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs. The terminology used herein is for the purpose of describing embodiments of this disclosure only and is not intended to limit this disclosure.

[0021] In the description of this application, the terms "longitudinal," "lateral," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," and "bottom," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing this application and do not require that this application be constructed and operated in a specific orientation, and therefore should not be construed as limiting this application. The terms "connected," "linked," and "set up" used in this application should be interpreted broadly. For example, they can refer to fixed connections or detachable connections; direct connections or indirect connections through intermediate components; wired connections, radio connections, or wireless communication signal connections. Those skilled in the art can understand the specific meaning of the above terms according to the specific circumstances.

[0022] The following is in conjunction with the appendix Figure 1-2 This application provides a more detailed description of a low-temperature nitrogen generation method and system based on PSA technology.

[0023] A method for low-temperature nitrogen production based on PSA technology, comprising: Step S1: Pressurize, filter, and cryogenically treat the air to obtain high-pressure raw material gas; Step S2: The high-pressure raw material gas is adsorbed and separated into nitrogen at the bottom of adsorption tower A 19 and discharged from the top of adsorption tower A 19; adsorption tower B 20 depressurizes and desorbs the nitrogen. Step S3: Connect the top of adsorption tower A 19 and the top of adsorption tower B 20 to perform upper pressure equalization; connect the middle of adsorption tower A 19 and the bottom of adsorption tower B 20 to perform lower pressure equalization; Step S4: The high-pressure raw material gas is adsorbed and separated into nitrogen at the bottom of adsorption tower 20 B, and discharged from the top of adsorption tower 20 B; adsorption tower 19 depressurizes and desorbs the nitrogen.

[0024] The essence of pressure equalization is to recover nitrogen gas (the gas that was not adsorbed by the molecular sieve after adsorption) from the space inside the adsorption tower. However, the gas inside the adsorption tower is not uniformly mixed; rather, there are two natural gradients. This is the design basis for the inequality-based pressure equalization in this application. 1. Pressure gradient: At the end of adsorption, the entire column is under high pressure (0.7-0.8 MPa), but the pressure at the top is slightly higher than that at the bottom; at the end of desorption, the entire column is under normal pressure (0.1 MPa), and the pressure at the top is slightly lower than that at the bottom.

[0025] 2. Concentration Gradient: As the gas passes through the molecular sieve bed from bottom to top, oxygen is gradually adsorbed. Therefore, the nitrogen purity increases progressively from the bottom to the top of the column. For example, at the top: the gas in the dead space has a purity completely consistent with the product gas (≥99.9%), which is the part with the highest recovery value; in the middle of the column: nitrogen-rich gas with a purity of 80%-95%; at the bottom of the column: the raw material gas that has just entered, with a purity of about 78% (close to air, with the lowest recovery value). This application provides a core process for asymmetric stratified pressure equalization, employing an unequal pressure equalization method where the top of the adsorption tower is equal to the top of the desorption tower, and the middle of the adsorption tower is equal to the bottom of the desorption tower. This process overcomes the technical bottleneck of traditional single-path top equalization, separating and transporting the gas from the top and middle sections of the tower without mixing, thus improving the purity of nitrogen recovery. Simultaneously, the desorption tower relies on the natural pressure gradient between the middle and bottom of the adsorption tower for rapid pre-pressurization, significantly reducing the amount of compressed air required for subsequent replenishment and lowering energy consumption. Furthermore, the dual-path gas exchange from the top and middle of the adsorption tower to the bottom of the desorption tower results in a more uniform airflow distribution within the desorption tower, weakening the impact of local high-speed airflow on the molecular sieve and extending the service life of the device.

[0026] A cryogenic nitrogen generation system based on PSA technology includes: a pretreatment system, a nitrogen generation system, and a gas storage tank 21; After being processed into high-pressure raw material gas by the pretreatment system, the air is input into the nitrogen generation system, and the nitrogen generation system outputs nitrogen gas to the storage tank 21. The nitrogen generation system includes an inlet main valve 7, an outlet main valve 8, branch pipes, an A adsorption tower 19, a B adsorption tower 20, a first inlet valve 9, a second inlet valve 10, a first pressure reducing valve 16, a second pressure reducing valve 17, an upper pressure equalizing valve 13, a first lower pressure equalizing valve 14, a second lower pressure equalizing valve 15, a first exhaust valve, and a second exhaust valve. The bottoms of adsorption towers A and B are connected to branch pipes via the first inlet valve 9 and the second inlet valve 10, respectively, and then to the main inlet valve 7. The tops of adsorption towers A and B are connected to the main outlet valve 8 via the first exhaust valve and the second exhaust valve, respectively. The middle sections of adsorption towers A and B are connected to branch pipes via the first lower equalizing valve 14 and the second lower equalizing valve 15, respectively. The bottoms of adsorption towers A and B are also connected to the atmosphere via the first pressure reducing valve 16 and the second pressure reducing valve 17, respectively. The tops of adsorption towers A and B are also interconnected via the upper equalizing valve 13. The other end of the intake manifold is connected to the pretreatment system; the other end of the exhaust manifold is connected to the air storage tank 21.

[0027] In a specific embodiment of this application, The valve on / off states in step S2 are as follows: the main inlet valve 7, the main outlet valve 8, the first inlet valve 9, the first exhaust valve, and the second pressure reducing valve 17 are connected, while the remaining valves are disconnected; the high-pressure raw material gas enters the bottom of adsorption tower A 19 sequentially through the main inlet valve 7 and the first inlet valve 9, and the nitrogen gas separated by adsorption is discharged from the top of adsorption tower A 19 sequentially through the first outlet valve 11 and the main outlet valve 8; the carbon molecular sieve saturated with adsorption in adsorption tower B 20 is depressurized and desorbed by the second pressure reducing valve 17 to complete regeneration; The valve on / off states in step S3 are as follows: the upper equalizing valve 13, the first lower equalizing valve 14, and the second inlet valve 10 are connected, and the remaining valves are disconnected; the gas in the top space of adsorption tower A 19 enters the top space of adsorption tower B 20 through the upper equalizing valve 13, and the gas in the middle space of adsorption tower A 19 enters the bottom space of adsorption tower B 20 through the first lower equalizing valve 14, the branch pipe, and the second inlet valve 10 in sequence, thus completing the equalization; The valve on / off states in step S4 are as follows: the main inlet valve 7, the main outlet valve 8, the second inlet valve 10, the second outlet valve 12, and the first pressure reducing valve 16 are connected, while the remaining valves are disconnected. High-pressure raw material gas enters the bottom of adsorption tower B 20 sequentially through the main inlet valve 7 and the second inlet valve 10. The adsorbed and separated nitrogen gas is discharged from the top of adsorption tower B 20 sequentially through the second outlet valve 12 and the main outlet valve 8. The carbon molecular sieve saturated with adsorption in adsorption tower A 19 undergoes pressure reduction and desorption treatment via the first pressure reducing valve 16, completing regeneration.

[0028] Considering that the rapid discharge of high-pressure exhaust gas during the depressurization of the adsorption tower will generate noise of more than 100dB, the nitrogen generation system also includes a silencer 18; the bottom of adsorption tower A 19 and adsorption tower B 20 are also connected to the silencer 18 through the first pressure reducing valve 16 and the second pressure reducing valve 17, respectively, and the other end of the silencer 18 is connected to the atmosphere.

[0029] In a specific embodiment of this application, the silencer 18 can be an impedance composite silencer 18, which reduces the desorption exhaust noise from more than 100dB to less than 80dB, meeting the requirements of the "Design Specification for Noise Control of Industrial Enterprises" GB / T50087-2013 and improving the on-site working environment.

[0030] To ensure a balanced airflow distribution, improve nitrogen production rate, and buffer the impact of airflow on the carbon molecular sieve, gas rectifiers are installed at the bottom of adsorption tower A 19 and adsorption tower B 20 to homogenize the high-pressure raw material gas.

[0031] In a specific embodiment of this application, the gas rectifier adopts a lotus-shaped structure, is vertically installed directly above the air inlet of the lower end cap of the adsorption tower, 300mm from the bottom of the tower, and is fixed to the tower wall by three radial support ribs.

[0032] The pretreatment system includes an air compressor 1, a filter, and a refrigerated air dryer 4 connected in sequence, which sequentially perform air pressurization, impurity removal, cooling, and dehydration treatment.

[0033] The filters include a first filter 3 and a second filter 5; The first filter 3 is located between the air compressor 1 and the refrigerated air dryer 4, and the second filter 5 is located between the air dryer and the nitrogen generation system.

[0034] In a specific embodiment of this application, the first filter 3 is a Class C filter used to remove liquid and particulate impurities larger than 3μm from the compressed air; the second filter 5 is a multi-stage filter consisting of Class A, Class T and Class H filters connected in series, used to remove the ultrafine oil mist and solid particles remaining after the gas is cooled and dried, so as to achieve further purification treatment.

[0035] The pretreatment system also includes a first air buffer tank 2; the first air buffer tank 2 is located between the air compressor 1 and the first filter 3 to stabilize the compressed air pressure and initially separate liquid impurities.

[0036] In a specific embodiment of this application, the first air buffer tank 2 is a vertical pressure vessel, the outlet of the air compressor 1 is connected to the lower inlet of the first air buffer tank 2, and the upper outlet of the first air buffer tank 2 is connected to the inlet of the first filter 3.

[0037] The pretreatment system also includes a second air buffer tank 6; the second air buffer tank 6 is located between the second filter 5 and the nitrogen generation system to further stabilize the intake pressure and ensure the stability of the adsorption process.

[0038] In a specific embodiment of this application, the second air buffer tank 6 is a vertical pressure vessel, the outlet of the second filter 5 is connected to the lower inlet of the second air buffer tank 6, and the upper outlet of the second air buffer tank 6 is connected to the main air inlet valve 7 of the nitrogen generation system.

[0039] The top of the air storage tank 21, the first air buffer tank 2, and the second air buffer tank 6 are all connected to an air vent valve 22, and the bottom of the air storage tank 21, the first air buffer tank 2, the second air buffer tank 6, the first filter 3, and the second filter 5 are all connected to a drain valve 23.

[0040] In a specific embodiment of this application, the vent valve 22 is a solenoid valve that is linked with the PLC control cabinet. It automatically opens to purge residual air in the pipeline when the machine is turned on, and automatically jumps to release pressure when there is overpressure. The drain valve 23 is a ball valve. The first air buffer tank 2 and the first filter 3 are drained every 2 hours, the second air buffer tank 6 and the second filter 5 are drained every 4 hours, and the air storage tank 21 is drained every 8 hours.

[0041] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A method for low-temperature nitrogen production based on PSA technology, characterized in that, include: Step S1: Pressurize, filter, and cryogenically treat the air to obtain high-pressure raw material gas; Step S2: The high-pressure raw material gas is adsorbed and separated into nitrogen at the bottom of adsorption tower A and discharged from the top of adsorption tower A; adsorption tower B is used for depressurization and desorption treatment; Step S3: Connect the top of adsorption tower A and the top of adsorption tower B to perform upper pressure equalization; connect the middle of adsorption tower A and the bottom of adsorption tower B to perform lower pressure equalization; Step S4: The high-pressure raw material gas is adsorbed and separated into nitrogen at the bottom of adsorption tower B and discharged from the top of adsorption tower B; adsorption tower A is depressurized and desorbed.

2. A cryogenic nitrogen generation system employing the cryogenic nitrogen generation method described in claim 1, characterized in that, include: Pretreatment system, nitrogen generation system, gas storage tank; After being processed into high-pressure raw material gas by the pretreatment system, the air is input into the nitrogen generation system, and the nitrogen generation system outputs nitrogen gas to the storage tank. The nitrogen generation system includes an inlet main valve, branch pipes, an outlet main valve, an A adsorption tower, a B adsorption tower, a first inlet valve, a second inlet valve, a first pressure reducing valve, a second pressure reducing valve, an upper pressure equalizing valve, a first lower pressure equalizing valve, a second lower pressure equalizing valve, a first exhaust valve, and a second exhaust valve. The bottoms of adsorption towers A and B are connected to branch pipes via the first and second inlet valves, respectively, and then to the main inlet valve; the tops of adsorption towers A and B are connected to the main outlet valve via the first and second exhaust valves, respectively; the middle sections of adsorption towers A and B are connected to branch pipes via the first and second lower pressure equalization valves, respectively; the bottoms of adsorption towers A and B are also connected to the atmosphere via the first and second pressure reducing valves, respectively; the tops of adsorption towers A and B are also interconnected via the upper pressure equalization valve. The other end of the intake manifold is connected to the pretreatment system; the other end of the exhaust manifold is connected to the air storage tank.

3. The cryogenic nitrogen generation system as described in claim 2, characterized in that, The nitrogen generation system also includes a silencer; the bottoms of adsorption tower A and adsorption tower B are connected to the silencer via a first pressure-reducing valve and a second pressure-reducing valve, respectively, and the other end of the silencer is connected to the atmosphere.

4. The cryogenic nitrogen generation system as described in claim 2, characterized in that, Both adsorption tower A and adsorption tower B are equipped with gas rectifiers at the bottom for homogenizing the high-pressure raw material gas.

5. The cryogenic nitrogen generation system as described in claim 2, characterized in that, The pretreatment system includes an air compressor, a filter, and a refrigerated air dryer connected in sequence.

6. The cryogenic nitrogen generation system as described in claim 5, characterized in that, The filter includes a first filter and a second filter; The first filter is located between the air compressor and the air dryer, and the second filter is located between the refrigerated air dryer and the nitrogen generation system.

7. The cryogenic nitrogen generation system as described in claim 6, characterized in that, The pretreatment system further includes a first air buffer tank; the first air buffer tank is disposed between the air compressor and the first filter.

8. The cryogenic nitrogen generation system as described in claim 7, characterized in that, The pretreatment system also includes a second air buffer tank; the second air buffer tank is disposed between the second filter and the nitrogen generation system.

9. The cryogenic nitrogen generation system as described in claim 8, characterized in that, The top of the air storage tank, the first air buffer tank, and the second air buffer tank are all connected to an air vent valve, and the bottom of the air storage tank, the first air buffer tank, the second air buffer tank, the first filter, and the second filter are all connected to a drain valve.

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