System for efficiently preparing liquid nitrogen by using two-stage membrane separation technology

Abstract

The utility model discloses a system for efficiently preparing liquid nitrogen by using a two-stage membrane separation technology, and relates to the technical field of industrial purification and liquefied nitrogen. The membrane separation technology and the gas liquefaction technology are combined, so that nitrogen in air is purified, the residual pressure of medium-pressure gas is fully utilized to provide cold energy for high-concentration nitrogen liquefaction, and the residual potential energy of the high-concentration gas is utilized to improve the nitrogen generation efficiency. A compressor, a gas cooling module, a first-stage separator and a second-stage separator of the system are sequentially arranged in the flowing direction of air. A high-pressure outlet of the second-stage separator is communicated with a first hot end inlet of the first heat exchanger; a first outlet of the first heat exchanger is communicated with a hot end inlet of the second heat exchanger, a second hot end inlet is communicated with a side backpressure outlet of the first-stage separator, a second outlet is communicated with a cold end inlet of the second heat exchanger through an expansion machine, a third outlet is communicated with atmosphere, and the cold end inlet is communicated with a second outlet of the second heat exchanger; and a side backpressure outlet of the second-stage separator is communicated with the compressor.

Description

Technical Field

[0001] This application relates to the field of industrial purification and liquefied nitrogen technology, and in particular to a system for efficiently preparing liquid nitrogen using two-stage membrane separation technology. Background Technology

[0002] Currently, the most common methods for preparing liquid nitrogen are cryogenic air separation, molecular sieve air separation, and membrane air separation. Cryogenic air separation is a traditional method suitable for large-scale industrial nitrogen production. This method involves cooling air to a low temperature, liquefying the gas, and then separating nitrogen from the liquid air by fractional distillation, utilizing the difference in boiling points of different gases. The advantage of this method is that it can produce high-purity nitrogen, but it requires complex equipment, a large footprint, and high infrastructure costs. Molecular sieve air separation and membrane air separation utilize the selective adsorption of oxygen and nitrogen by molecular sieves and the selective permeability of special membranes to separate oxygen and nitrogen from the air, respectively. However, the extracted high-purity nitrogen still requires specialized refrigeration equipment for liquefaction to obtain high-purity liquid nitrogen products. Utility Model Content

[0003] The embodiments of this application provide a system for efficiently preparing liquid nitrogen using two-stage membrane separation technology. By combining membrane separation technology with gas liquefaction technology, the system not only purifies nitrogen from the air but also fully utilizes the residual pressure of the medium-pressure gas to provide cooling for the liquefaction of high-concentration nitrogen and utilizes the residual potential energy of the high-concentration gas to improve nitrogen production efficiency.

[0004] To achieve the above objectives, embodiments of this application provide a system for efficiently preparing liquid nitrogen using two-stage membrane separation technology, comprising a compressor, a gas cooling module, a membrane separation assembly, a first heat exchanger, a second heat exchanger, and an expander; the membrane separation assembly includes a first-stage separator and a second-stage separator; the compressor, gas cooling module, first-stage separator, and second-stage separator are arranged sequentially along the airflow direction; the high-pressure outlet of the second-stage separator is connected to the first hot-end inlet of the first heat exchanger; the first outlet of the first heat exchanger is connected to the hot-end inlet of the second heat exchanger; the side back pressure outlet of the first-stage separator is connected to the second hot-end inlet of the first heat exchanger; the second outlet of the first heat exchanger is connected to the cold-end inlet of the second heat exchanger via the expander; the second outlet of the second heat exchanger is connected to the cold-end inlet of the first heat exchanger; and the third outlet of the first heat exchanger is connected to the atmosphere; the side back pressure outlet of the second-stage separator is connected to the inlet of the compressor.

[0005] Furthermore, the membranes in both the first-stage separator and the second-stage separator are hollow fiber membranes; the oxygen permeation rate of the hollow fiber membrane is greater than the nitrogen permeation rate.

[0006] Furthermore, a regulating valve is also provided at the high-pressure outlet of the second-stage separator, and the regulating valve is connected to the first hot end inlet of the first heat exchanger and the high-pressure outlet of the second-stage separator through a tee.

[0007] Furthermore, a throttling valve is provided at the first outlet of the second heat exchanger.

[0008] Furthermore, it also includes an air mixing device; the inlet of the air mixing device is connected to the air source and the side back pressure outlet of the second stage separator, and the outlet of the air mixing device is connected to the inlet of the compressor.

[0009] Furthermore, the compressor and the expander are connected coaxially via a motor.

[0010] Furthermore, the compressor is a closed-loop compressor.

[0011] Furthermore, the expander is a closed-loop turbine expander.

[0012] This application has the following advantages over the prior art:

[0013] 1. The system for efficiently preparing liquid nitrogen using two-stage membrane separation technology in this application uses two-stage membrane separators to form a membrane separation component, which can fully separate oxygen and nitrogen in the air to obtain high-purity nitrogen. The residual pressure of the gas on the back pressure side of the first-stage separator is expanded and utilized to provide the required cooling capacity for the preparation of liquid nitrogen. There is no need to recompress, cool and liquefy the product gas, thus reducing energy consumption.

[0014] 2. The system for efficiently preparing liquid nitrogen using two-stage membrane separation technology in this application utilizes a turbine expander to make use of the residual pressure of the gas. While providing cooling capacity, it can also recover expansion work, further achieving energy savings.

[0015] 3. In the embodiment of this application, the nitrogen-rich waste gas on the back pressure side of the second-stage separator of the system that utilizes two-stage membrane separation technology to efficiently prepare liquid nitrogen is mixed with air before entering the compressor, thereby increasing the nitrogen concentration of the gas entering the compressor and improving the preparation efficiency of high-purity liquid nitrogen products.

[0016] 4. The system process for efficiently preparing liquid nitrogen using the two-stage membrane separation technology in this application embodiment is simple and the equipment is small, making it suitable for small-scale high-purity liquid nitrogen extraction needs and easy to use and maintain. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0018] Figure 1 This is a schematic diagram of the system for efficiently preparing liquid nitrogen using a two-stage membrane separation technology, as described in an embodiment of this application. Detailed Implementation

[0019] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0020] In the description of this application, it should be understood that the terms "center", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They 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 be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this application.

[0021] In the description of this application, it should be noted that, unless otherwise expressly specified and limited, the terms "installation", "connection" and "joining" should be interpreted broadly, for example, they can refer to fixed connections, detachable connections, or integral connections; those skilled in the art can understand the specific meaning of the above terms in this application based on the specific circumstances.

[0022] The terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" can explicitly or implicitly include one or more of that feature. In the description of this application, unless otherwise stated, "a plurality of" means two or more.

[0023] Reference Figure 1 The embodiments of this application provide a system for efficiently preparing liquid nitrogen using two-stage membrane separation technology, including a membrane separation component S, an expander E, a compressor C, a gas cooling module D, a motor M, a first heat exchanger H1, a second heat exchanger H2, and a throttle valve F2.

[0024] The membrane separation assembly S includes a first-stage separator S1, a second-stage separator S2, and a regulating valve F1.

[0025] Both the first-stage separator S1 and the second-stage separator S2 are membrane separation devices using hollow fiber membranes as the material. For this type of hollow fiber membrane, the oxygen permeation rate is greater than the nitrogen permeation rate.

[0026] The first heat exchanger H1 includes a first hot-end inlet H101, a second hot-end inlet H102, a cold-end inlet H106, a first outlet H104, a second outlet H105, and a third outlet H103. Specifically, the first outlet H104 corresponds to the first hot-end inlet H101, the second outlet H105 corresponds to the second hot-end inlet H102, and the third outlet H103 corresponds to the cold-end inlet H106.

[0027] The second heat exchanger H2 includes a hot-end inlet H201, a cold-end inlet H204, a first outlet H203, and a second outlet H202. The first outlet H203 corresponds to the hot-end inlet H201, and the second outlet H202 corresponds to the cold-end inlet H204.

[0028] The inlet of the first-stage separator S1 is connected to the outlet of the compressor C via the gas cooling module D. The high-pressure outlet of the first-stage separator S1 is connected to the inlet of the second-stage separator S2. The high-pressure outlet of the second-stage separator S2 is connected to the regulating valve F1 and the first hot-end inlet H101 of the first heat exchanger via a three-way valve. High-purity nitrogen gas is obtained from the outlet of the regulating valve F1. The first outlet H104 of the first heat exchanger is connected to the hot-end inlet H201 of the second heat exchanger H2. The first outlet H203 of the second heat exchanger is connected to the inlet of the throttle valve F2. High-purity liquid nitrogen product is obtained from the outlet of the throttle valve F2.

[0029] An air mixing device (not shown in the figure) is provided at the inlet of compressor C. The inlet of the air mixing device is connected to the air source and the side back pressure outlet of the second-stage separator S2, respectively. The outlet of the air mixing device is connected to the inlet of compressor C.

[0030] The side back pressure outlet of the first-stage separator S1 is connected to the second hot-end inlet H102 of the first heat exchanger. The second outlet H105 of the first heat exchanger is connected to the inlet of the expander E, the outlet of the expander E is connected to the cold-end inlet H204 of the second heat exchanger, the second outlet H202 of the second heat exchanger is connected to the cold-end inlet H106 of the first heat exchanger, and the third outlet H103 of the first heat exchanger is connected to a pipeline for air exhaust.

[0031] Expander E and compressor C are coaxially connected via motor M. The work recovered by expander E, along with that of motor M, powers compressor C. Compressor C is a closed-circuit compressor. Expander E is a closed-circuit turbine expander.

[0032] Thus, the ambient temperature high-pressure stream 3 discharged from the gas cooling module D passes through the first-stage separator S1, where it becomes a high-concentration nitrogen stream 4 at its high-pressure outlet, and a medium-pressure oxygen-enriched stream 9 on its back pressure side. The medium-pressure oxygen-enriched stream 9 enters the first heat exchanger H1 for pre-cooling, and then enters the expander E to expand using residual pressure to provide cooling for the system.

[0033] After passing through the second-stage separator S2, the high-concentration nitrogen stream 4 becomes the ultra-high-concentration nitrogen stream 5 required for the product at its high-pressure outlet, and a normal-pressure nitrogen-rich gas stream 14 with a concentration higher than that in the air is obtained on its back-pressure side. The ultra-high-concentration nitrogen stream 5 can be directly led out through regulating valve F1 to obtain the first high-purity nitrogen stream 15, thereby controlling the flow rate of the second high-purity nitrogen stream 16 entering the first heat exchanger H1. The normal-pressure nitrogen-rich gas stream 14 mixes with the air stream 1, increasing the nitrogen concentration in the air stream 1 to obtain the mixed gas stream 2, thereby improving the nitrogen production efficiency of the entire system.

[0034] The first heat exchanger H1 uses the cooling energy provided by the atmospheric pressure medium-low temperature gas stream 12 to precool the second high-purity nitrogen stream 16 and the medium-pressure oxygen-enriched stream 9, which are flowing out of the high-pressure outlet of the first-stage separator S1, into low-temperature gases.

[0035] The second heat exchanger H2 uses the cooling energy provided by the atmospheric pressure low-temperature gas stream 11 to liquefy the low-temperature high-concentration nitrogen stream 6 into a high-concentration liquid nitrogen stream 7.

[0036] The working principle of this application embodiment is as follows:

[0037] Air stream 1 (normal pressure air with a nitrogen concentration of 79%) is mixed with nitrogen-rich gas stream 14 with a nitrogen concentration of 85% at the back pressure on the side of the second-stage separator S2, and then becomes nitrogen-rich mixed gas stream 2 with a nitrogen concentration of 83%.

[0038] The nitrogen-rich mixed gas stream 2 is compressed by compressor C and cooled by gas cooling module D, becoming a room-temperature high-pressure stream 3 with a pressure of 0.8 MPa. After being separated by the first-stage separator S1, the room-temperature high-pressure stream 3 produces a high-concentration nitrogen stream 4 with a nitrogen concentration of 95% and a pressure of 0.7 MPa at its high-pressure outlet, and a medium-pressure oxygen-rich stream 9 with a pressure of approximately 0.3 MPa and an oxygen concentration of 26% on its back pressure side.

[0039] After passing through the second-stage separator S2, the high-concentration nitrogen stream 4 is obtained at its high-pressure outlet as an extremely high-concentration nitrogen stream 5 with a nitrogen concentration of 99.9% and a pressure of 0.64 MPa, and at its back pressure side as an atmospheric pressure nitrogen-rich gas stream 14 with a nitrogen concentration of 85%.

[0040] The medium-pressure oxygen-enriched gas stream 9 is pre-cooled by the first heat exchanger H1, becoming a medium-pressure, medium-temperature gas stream 10 at -165°C. The medium-pressure, medium-temperature gas stream 10 then enters the expander E, where it expands, depressurizes, and cools, becoming an atmospheric pressure, low-temperature gas stream 11 at -186°C. The atmospheric pressure, low-temperature gas stream 11 receives cooling energy through the second heat exchanger H2, and heats up to become an atmospheric pressure, medium-low temperature gas stream 12 at -178°C.

[0041] The atmospheric pressure low-temperature gas stream 12 is cooled by the first heat exchanger H1 and transformed into an atmospheric pressure and ambient temperature gas stream 13 with a temperature of 26°C. Finally, the atmospheric pressure and ambient temperature gas stream 13 is vented.

[0042] Close regulating valve F1, allowing the entire ultra-high concentration nitrogen stream to pass through the first heat exchanger H1, where it is cooled and transformed into a low-temperature, high-concentration nitrogen stream 6 at -174°C and 0.635 MPa. The low-temperature, high-concentration nitrogen stream 6 then passes through the second heat exchanger H2, where it is cooled and transformed into a high-concentration liquid nitrogen stream 7 at -184°C and 0.63 MPa. Finally, the high-concentration liquid nitrogen stream 7 is depressurized through throttling valve F3 to obtain the desired high-concentration liquid nitrogen product 8. The expander E recovers power, which, together with the motor M, powers the compressor C, completing the entire system process.

[0043] The above are merely specific embodiments of this application, but the scope of protection of this application is not limited thereto. Any changes or substitutions within the technical scope disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A system for efficiently preparing liquid nitrogen using a two-stage membrane separation technology, characterized in that, It includes a compressor, a gas cooling module, a membrane separation assembly, a first heat exchanger, a second heat exchanger, and an expander; The membrane separation assembly includes a first-stage separator and a second-stage separator; the compressor, gas cooling module, first-stage separator, and second-stage separator are arranged sequentially along the airflow direction; The high-pressure outlet of the second-stage separator is connected to the first hot-end inlet of the first heat exchanger; the first outlet of the first heat exchanger is connected to the hot-end inlet of the second heat exchanger. The side back pressure outlet of the first stage separator is connected to the second hot end inlet of the first heat exchanger. The second outlet of the first heat exchanger is connected to the cold end inlet of the second heat exchanger through an expander. The second outlet of the second heat exchanger is connected to the cold end inlet of the first heat exchanger. The third outlet of the first heat exchanger is connected to the atmosphere. The side back pressure outlet of the second-stage separator is connected to the compressor inlet.

2. The system for efficiently preparing liquid nitrogen using two-stage membrane separation technology according to claim 1, characterized in that, Both the first-stage separator and the second-stage separator use hollow fiber membranes; the oxygen permeation rate of the hollow fiber membrane is greater than the nitrogen permeation rate.

3. The system for efficiently preparing liquid nitrogen using a two-stage membrane separation technology according to claim 1, characterized in that, The high-pressure outlet of the second-stage separator is also equipped with a regulating valve, which is connected to the first hot end inlet of the first heat exchanger and the high-pressure outlet of the second-stage separator via a tee.

4. The system for efficiently preparing liquid nitrogen using two-stage membrane separation technology according to claim 1, characterized in that, A throttling valve is provided at the first outlet of the second heat exchanger.

5. The system for efficiently preparing liquid nitrogen using two-stage membrane separation technology according to claim 1, characterized in that, It also includes an air mixing device; the inlet of the air mixing device is connected to the air source and the side back pressure outlet of the second stage separator, and the outlet of the air mixing device is connected to the inlet of the compressor.

6. The system for efficiently preparing liquid nitrogen using a two-stage membrane separation technology according to claim 1, characterized in that, The compressor and expander are connected coaxially via a motor.

7. The system for efficiently preparing liquid nitrogen using two-stage membrane separation technology according to claim 1, characterized in that, The compressor is a closed-loop compressor.

8. The system for efficiently preparing liquid nitrogen using a two-stage membrane separation technology according to claim 1, characterized in that, The expander is a closed-type turbine expander.

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