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

Abstract

The invention 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] The present application relates to the technical field of industrial purification and liquefied nitrogen, and in particular to a system for efficiently preparing liquid nitrogen using a two-stage membrane separation technology. Background Art

[0002] At present, the most common methods for preparing liquid nitrogen are cryogenic air separation, molecular sieve air separation and membrane air separation. Among them, cryogenic air separation is a traditional method for nitrogen production, which is suitable for large-scale industrial nitrogen production. This method cools the air to a low temperature to liquefy the gas, and then uses the difference in boiling points of different gases to separate nitrogen from liquid air by fractional distillation. The advantage of this method is that it can produce high-purity nitrogen, but the equipment is complex, the floor space is large, and the infrastructure cost is high. The molecular sieve air separation method and the membrane air separation method use the selective adsorption of molecular sieves for oxygen and nitrogen and the selective permeability of special membranes for oxygen and nitrogen to separate oxygen and nitrogen in the air, respectively. However, the extracted high-purity nitrogen still needs special refrigeration equipment to liquefy in order to obtain high-purity liquid nitrogen products. Summary of the Invention

[0003] The embodiments of the present 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 fully utilizes the residual pressure of the medium-pressure gas to provide cooling capacity for liquefying high-concentration nitrogen, but also utilizes the residual potential energy of the high-concentration gas to improve nitrogen production efficiency while completing the purification of nitrogen from the air.

[0004] To achieve the above-mentioned objectives, an embodiment of the present application provides a system for efficiently preparing liquid nitrogen using a 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 comprises a first-stage separator and a second-stage separator; the compressor, the gas cooling module, the first-stage separator and the second-stage separator are arranged in sequence along the flow direction of air; a first regulating valve is provided between the first-stage separator and the second-stage separator; 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 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 the first-stage separator and the second-stage separator are both hollow fiber membranes; the oxygen permeation rate of the hollow fiber membrane is greater than the nitrogen permeation rate.

[0006] Furthermore, a second regulating valve is provided between the first-stage separator and the first heat exchanger.

[0007] Furthermore, a third regulating valve is provided at the high-pressure outlet of the second-stage separator, and the third 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.

[0008] Furthermore, a throttle valve is provided at the first outlet of the second heat exchanger.

[0009] 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 respectively, and the outlet of the air mixing device is connected to the inlet of the compressor.

[0010] Furthermore, the compressor and the expander are coaxially connected via a motor.

[0011] Furthermore, the compressor is a closed compressor.

[0012] Furthermore, the expander is a closed turbine expander.

[0013] Compared with the prior art, this application has the following beneficial effects:

[0014] 1. The system for efficiently preparing liquid nitrogen using dual-stage membrane separation technology in the embodiment of the present application uses a two-stage membrane separator to form a membrane separation assembly, which can fully separate oxygen and nitrogen in the air to obtain high-purity nitrogen. The system also expands and utilizes the residual pressure of the gas on the back-pressure side of the first-stage separator to provide the required cooling capacity for preparing liquid nitrogen. This eliminates the need to re-compress and cool the product gas for liquefaction, thereby reducing energy consumption.

[0015] 2. In the embodiment of the present application, the system for efficiently preparing liquid nitrogen using a two-stage membrane separation technology is provided with a regulating valve between the side back pressure outlet of the first-stage separator and the hot end inlet of the heat exchanger, so that the residual pressure and flow rate of the gas on the back pressure side of the first-stage separator can be adjusted, and the cooling capacity provided can also be adjusted.

[0016] 3. The system for efficiently preparing liquid nitrogen using double-stage membrane separation technology in the embodiment of the present application utilizes a turbine expander to utilize the excess pressure of the gas, thereby recovering expansion work while providing cooling capacity, further realizing energy savings.

[0017] 4. In the embodiment of the present application, the nitrogen-rich waste gas on the back-pressure side of the second-stage separator in the system for efficiently preparing liquid nitrogen using a two-stage membrane separation technology is mixed with air before entering the compressor, thereby increasing the nitrogen concentration of the gas entering the compressor and improving the efficiency of preparing high-purity liquid nitrogen products.

[0018] 5. The embodiment of the present application utilizes a two-stage membrane separation technology to efficiently prepare liquid nitrogen. The system process is simple and the equipment is small, which is suitable for small-scale high-purity liquid nitrogen extraction needs and is easy to use and maintain. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0020] Figure 1 This is a schematic diagram of the structure of a system for efficiently preparing liquid nitrogen using double-stage membrane separation technology in an embodiment of the present application. DETAILED DESCRIPTION

[0021] The following will be combined with the drawings in the embodiments of this application to clearly and completely describe the technical solutions in the embodiments of this application. Obviously, the embodiments described are only part of the embodiments of this application, not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0022] In the description of this application, it should be understood that the terms "center", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", etc., indicating the orientation or position relationship, are based on the orientation or position relationship shown in the accompanying drawings, and 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, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on this application.

[0023] In the description of this application, it should be noted that, unless otherwise clearly specified and limited, the terms "install", "connect", and "connect" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection. For ordinary technicians in this field, they can understand the specific meanings of the above terms in this application according to specific circumstances.

[0024] The terms "first" and "second" are used for descriptive purposes only and should not be understood to indicate or imply relative importance or implicitly specify the number of the technical features indicated. Therefore, features qualified as "first" or "second" may explicitly or implicitly include one or more of such features. In the description of this application, unless otherwise specified, "plurality" means two or more.

[0025] Reference Figure 1An embodiment of the present application provides a system for efficiently preparing liquid nitrogen using a 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 F4.

[0026] The membrane separation assembly S includes a first-stage separator S1, a second-stage separator S2, a first regulating valve F1, a second regulating valve F2 and a third regulating valve F3.

[0027] Both the first-stage separator S1 and the second-stage separator S2 are membrane separation devices using hollow fiber membranes as materials. For such hollow fiber membranes, the permeation rate of oxygen is greater than the permeation rate of nitrogen.

[0028] The first heat exchanger H1 includes a first hot-end inlet H101 of the first heat exchanger, a second hot-end inlet H102 of the first heat exchanger, a cold-end inlet H106 of the first heat exchanger, a first outlet H104 of the first heat exchanger, a second outlet H105 of the first heat exchanger, and a third outlet H103 of the first heat exchanger. The first outlet H104 of the first heat exchanger corresponds to the first hot-end inlet H101 of the first heat exchanger, the second outlet H105 of the first heat exchanger corresponds to the second hot-end inlet H102 of the first heat exchanger, and the third outlet H103 of the first heat exchanger corresponds to the cold-end inlet H106 of the first heat exchanger.

[0029] 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.

[0030] The inlet of the first-stage separator S1 is connected to the outlet of compressor C through a 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, with a first regulating valve F1 positioned between them. The high-pressure outlet of the second-stage separator S2 is connected to a third regulating valve F3 and the first hot-end inlet H101 of the first heat exchanger, respectively. High-purity nitrogen is produced at the outlet of the third regulating valve F3. 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 a throttle valve F4, which produces high-purity liquid nitrogen.

[0031] An air mixing device (not shown) is provided at the inlet of the 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, and the outlet of the air mixing device is connected to the inlet of the compressor C.

[0032] The side backpressure outlet of the first-stage separator S1 is connected to the second hot-end inlet H102 of the first heat exchanger, with a second regulating valve F2 positioned between them. The second outlet H105 of the first heat exchanger is connected to the inlet of the expander E, which in turn 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. The third outlet H103 of the first heat exchanger is connected to the pipeline exhaust gas.

[0033] Expander E and compressor C are coaxially connected via motor M. The work recovered by expander E, together with motor M, powers compressor C. Compressor C is a closed-type compressor. Expander E is a closed-type turbine expander.

[0034] Thus, the ambient-temperature, high-pressure stream 3 discharged from the gas cooling module D passes through the first-stage separator S1, yielding a high-concentration nitrogen stream 4 at its high-pressure outlet and a medium-pressure, oxygen-enriched stream 9 at its back-pressure outlet. The medium-pressure, oxygen-enriched stream 9 enters the first heat exchanger H1 for precooling before entering the expander E, where it expands at residual pressure to provide cooling for the system. The first regulating valve F1 adjusts the pressure and flow of the high-concentration nitrogen stream 4. The second regulating valve F2 adjusts the pressure and flow of the medium-pressure, oxygen-enriched stream 9.

[0035] After passing through the second-stage separator S2, high-concentration nitrogen stream 4 produces the extremely high-concentration nitrogen stream 5 required for the product at its high-pressure outlet, and a normal-pressure nitrogen-enriched gas stream 14 with a nitrogen concentration higher than that in air at its back-pressure outlet. This extremely high-concentration nitrogen stream 5 can be directly channeled through a third regulating valve F3 to produce a first high-purity nitrogen stream 15, thereby controlling the flow rate of a second high-purity nitrogen stream 16 entering the first heat exchanger H1. The mixing of normal-pressure nitrogen-enriched gas stream 14 with air stream 1 increases the nitrogen concentration in air stream 1, producing a mixed gas stream 2, thereby improving the nitrogen production efficiency of the entire system.

[0036] The first heat exchanger H1 uses the cooling capacity provided by the atmospheric pressure medium and low temperature gas stream 12 to pre-cool the second high purity nitrogen stream 16 and the medium pressure oxygen-rich stream 9 flowing out of the high pressure outlet of the first stage separator S1 into low temperature gas.

[0037] The second heat exchanger H2 utilizes 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 .

[0038] The working principle of the embodiment of this application is as follows:

[0039] Air stream 1 (normal pressure air with a nitrogen concentration of 79%) is mixed with normal pressure nitrogen-rich gas stream 14 with a nitrogen concentration of 85% at the back pressure of the side of the second stage separator S2 to become nitrogen-rich mixed gas stream 2 with a nitrogen concentration of 83%.

[0040] The nitrogen-rich mixed gas stream 2 is compressed by compressor C and cooled by gas cooling module D to become a room-temperature, high-pressure stream 3 at a room-temperature pressure of 0.8 MPa. After separation by first-stage separator S1, this room-temperature, high-pressure stream 3 yields a high-concentration nitrogen stream 4 at a nitrogen concentration of 95% and a pressure of 0.7 MPa at its high-pressure outlet. On the back-pressure side, a medium-pressure, oxygen-rich stream 9 at a pressure of approximately 0.3 MPa and an oxygen concentration of 26% is obtained.

[0041] After the high-concentration nitrogen gas stream 4 passes through the second-stage separator S2, an extremely high-concentration nitrogen gas stream 5 with a nitrogen concentration of 99.9% and a pressure of 0.64 MPa is obtained at its high-pressure outlet, and a normal-pressure nitrogen-rich gas stream 14 with a normal-pressure nitrogen concentration of 85% is obtained at its back-pressure side.

[0042] Intermediate-pressure oxygen-rich stream 9 is pre-cooled by first heat exchanger H1 to become intermediate-pressure, intermediate-temperature gas stream 10 at -165°C. Intermediate-pressure, intermediate-temperature gas stream 10 then enters expander E, where it expands, reduces its pressure and temperature, and becomes atmospheric-pressure, low-temperature gas stream 11 at -186°C. Atmospheric-pressure, low-temperature gas stream 11 provides cooling through second heat exchanger H2, itself heating up to become atmospheric-pressure, intermediate-temperature gas stream 12 at -178°C.

[0043] The atmospheric pressure and low temperature gas stream 12 provides cooling energy through the first heat exchanger H1 and is converted into the atmospheric pressure and normal temperature gas stream 13 with a temperature of 26° C. Finally, the atmospheric pressure and normal temperature gas stream 13 is exhausted.

[0044] Close the third regulating valve F3, allowing the entire high-concentration nitrogen stream to pass through the first heat exchanger H1, where it is cooled to become low-temperature, high-concentration nitrogen stream 6 at -174°C and a pressure of 0.635 MPa. Low-temperature, high-concentration nitrogen stream 6 then passes through the second heat exchanger H2, where it is cooled to become high-concentration liquid nitrogen stream 7 at -184°C and a pressure of 0.63 MPa. Finally, high-concentration liquid nitrogen stream 7 is depressurized by throttle valve F4 to produce the desired high-concentration liquid nitrogen product 8. The work recovered by expander E, together with motor M, powers compressor C, completing the entire system process.

[0045] The above are only specific embodiments of the present application, but the scope of protection of the present application is not limited thereto. Any changes or replacements within the technical scope disclosed in this application should be included in the scope of protection of the present application. Therefore, the scope of protection of the present application should be based on the scope of protection 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 component, 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; a compressor, a gas cooling module, a first-stage separator and a second-stage separator are arranged in sequence along the flow direction of the air; a first regulating valve is provided between the first-stage separator and the second-stage separator; 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 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.

2. The system for efficiently preparing liquid nitrogen using double-stage membrane separation technology according to claim 1, characterized in that: The membranes in the first-stage separator and the second-stage separator are both 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 double-stage membrane separation technology according to claim 2, characterized in that: A second regulating valve is provided between the first-stage separator and the first heat exchanger.

4. The system for efficiently preparing liquid nitrogen using double-stage membrane separation technology according to claim 3, characterized in that: A third regulating valve is further provided at the high-pressure outlet of the second-stage separator, and the third 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.

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

6. The system for efficiently preparing liquid nitrogen using a double-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 respectively, and the outlet of the air mixing device is connected to the inlet of the compressor.

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

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

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

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