A method and apparatus for preparing liquid oxygen

Abstract

This invention discloses a method for preparing liquid oxygen, comprising the following steps: S1, introducing nitrogen, liquid nitrogen, and oxygen into a heat exchanger for heat exchange; S2, liquefying the nitrogen in the heat exchanger, throttling it to a first pressure, mixing it with liquid nitrogen outside the heat exchanger, and then introducing it into the heat exchanger; S3, when the liquid nitrogen vaporizes in the heat exchanger and is reheated to a first temperature, it is extracted and sent to an expander, where it expands to a second pressure and is then introduced into the heat exchanger for heat exchange with oxygen and nitrogen; S4, the oxygen is liquefied, and the nitrogen is reheated and then recycled or safely discharged. Addressing the technical problem of unreasonable overall heat exchange temperature difference distribution in existing heat exchangers, this invention provides a liquid oxygen preparation method and apparatus that recovers cold energy through an expander, making the overall heat exchange temperature difference distribution of the heat exchanger more reasonable, thereby reducing energy consumption.

Description

Technical Field

[0001] This invention relates to the field of cryogenic air separation technology, specifically to a method and apparatus for preparing liquid oxygen. Background Technology

[0002] Liquid nitrogen and liquid oxygen have a wide range of industrial applications. For example, liquid nitrogen can be used as a deep refrigerant for rapid freezing and transportation of food and for research in low-temperature physics; liquid oxygen is a strong oxidant and has important applications in aerospace, submarines and the gas industry.

[0003] Currently, liquid nitrogen and liquid oxygen are obtained industrially from cryogenic air separation units, but the output is relatively small, only meeting the needs of small-scale users. The large quantities of liquid nitrogen and liquid oxygen required for industrial production and large-scale cryogenic experiments are generally obtained from liquefaction units independent of the air separation unit.

[0004] In particular, during the preparation of liquid oxygen, the existing heat exchangers have an unreasonable overall heat exchange temperature difference distribution, resulting in high energy consumption during preparation. Summary of the Invention

[0005] 1. The technical problem that the invention aims to solve

[0006] To address the technical problem of unreasonable overall heat exchange temperature difference distribution in existing heat exchangers, this invention provides a liquid oxygen preparation method and apparatus. It recovers cold energy through an expander, making the overall heat exchange temperature difference distribution of the heat exchanger more reasonable, thereby reducing energy consumption.

[0007] 2. Technical Solution

[0008] To solve the above problems, the technical solution provided by the present invention is as follows:

[0009] A method for preparing liquid oxygen includes the following steps: S1, nitrogen, liquid nitrogen, and oxygen are introduced and heat exchanged in a heat exchanger; S2, after the nitrogen in the heat exchanger is liquefied, it is throttled to a first pressure, mixed with liquid nitrogen outside the heat exchanger, and then introduced into the heat exchanger; S3, when the liquid nitrogen is vaporized in the heat exchanger and reheated to a first temperature, it is extracted and sent to an expander, expanded to a second pressure in the expander, and then introduced into the heat exchanger to exchange heat with oxygen and nitrogen; S4, after the oxygen is liquefied and the nitrogen is reheated, it is recycled or safely discharged.

[0010] Optionally, the first pressure is 0.2 to 0.35 MPaG.

[0011] Optionally, the first temperature is 125K to 133K.

[0012] Optionally, the second pressure is 0.015 MPaG to 0.03 MPaG.

[0013] A liquid oxygen preparation apparatus suitable for the above-described liquid oxygen preparation method includes a liquid oxygen cold box and a first heat exchanger disposed within the liquid oxygen cold box. It also includes a nitrogen heat exchange pipeline, an oxygen heat exchange pipeline, a first liquid nitrogen heat exchange pipeline, and a second nitrogen heat exchange pipeline flowing through the first heat exchanger. The outlet end of the nitrogen heat exchange pipeline is connected to the inlet end of the first liquid nitrogen heat exchange pipeline, and a throttling valve is provided at the outlet end of the nitrogen heat exchange pipeline. The outlet end of the nitrogen heat exchange pipeline is connected to the inlet end of the first liquid nitrogen heat exchange pipeline and is equipped with a first expander.

[0014] Optionally, the outlet end of the oxygen heat exchange pipeline is connected to a liquid oxygen transfer pump and a liquid oxygen storage tank.

[0015] Optionally, it also includes a liquid nitrogen preparation device, wherein the inlet of the first liquid nitrogen heat exchange pipeline is connected to the liquid nitrogen preparation pipeline of the liquid nitrogen preparation device.

[0016] Optionally, the liquid oxygen cold box is connected to the liquid nitrogen preparation device using a skid-mounted structure.

[0017] 3. Beneficial effects

[0018] Compared with the prior art, the technical solution provided by this invention has the following advantages:

[0019] (1) Compared with the traditional oxygen liquefaction process, this liquid oxygen preparation method recovers cold energy through an expander, making the overall heat exchange temperature difference distribution of the heat exchanger more reasonable, thereby reducing energy consumption. The expansioner is added to provide more cold energy and reduce the consumption of liquid nitrogen, ultimately achieving the purpose of energy saving. The expanded nitrogen is still low-temperature cold energy, which needs to be sent to the heat exchanger to recover the cold energy and reduce the consumption of liquid nitrogen, so as to achieve the purpose of energy saving.

[0020] (2) Throttling the liquid nitrogen formed by liquefying the nitrogen in the heat exchanger to the first pressure is to make the vaporization temperature of liquid nitrogen lower than that of oxygen. Compared with directly throttling the liquid nitrogen from the liquid oxygen preparation device to the first pressure to exchange heat with oxygen, this liquid oxygen preparation method increases the liquefaction of medium-pressure nitrogen and changes the heat exchange curve. According to actual measurement, the logarithmic mean temperature difference (LMTD) of this method is only 2.8°C, while the logarithmic mean temperature difference (LMTD) of direct heat exchange between oxygen and liquid nitrogen is 11.4°C. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the structure of a liquid oxygen preparation device according to an embodiment of the present invention;

[0022] 1. Liquid oxygen cold box; 2. First heat exchanger; 3. Nitrogen heat exchange pipeline; 4. Oxygen heat exchange pipeline; 5. First liquid nitrogen heat exchange pipeline; 6. Second nitrogen heat exchange pipeline; 7. Liquid nitrogen preparation device; 8. First expander; 9. Liquid oxygen transfer pump; 10. Liquid oxygen storage tank; 11. Liquid nitrogen storage tank. Detailed Implementation

[0023] To further understand the content of this invention, please refer to the accompanying drawings. Figure 1 The present invention will be described in detail with reference to the embodiments.

[0024] Example 1

[0025] This embodiment of a liquid oxygen preparation method includes the following steps: S1, nitrogen, liquid nitrogen, and oxygen are introduced, the nitrogen pressure is approximately 3.0 MPaG, and the oxygen comes from an air separation pipeline with a pressure of approximately 0.02 MPaG. Heat exchange takes place in a heat exchanger, with the liquid nitrogen simultaneously exchanging heat with both nitrogen and oxygen; S2, after the nitrogen in the heat exchanger is liquefied, it is throttled to a first pressure, which is 0.2–0.35 MPaG, such as 0.2 MPaG, 0.25 MPaG, and 0.35 MPaG, preferably 0.3 MPaG. The liquid nitrogen throttled to the first pressure (formed after the nitrogen in the heat exchanger is liquefied) mixes with the liquid nitrogen outside the heat exchanger and is then introduced into the heat exchanger to simultaneously exchange heat with both nitrogen and oxygen; S3, when the liquid nitrogen vaporizes in the heat exchanger and is reheated to a first temperature, which is 125 K–133 K, For example, 125K, 130K, and 133K, preferably 133K, are used. After being expanded to the second pressure in the expander, the gas is introduced into the heat exchanger to exchange heat with oxygen. The second pressure is 0.015MPaG to 0.03MPaG, for example, 0.015MPaG, 0.02MPaG, and 0.03MPaG, preferably 0.02MPaG; S4, oxygen is liquefied, and nitrogen is reheated and recycled or safely discharged.

[0026] Compared to traditional oxygen liquefaction processes, this liquid oxygen preparation method recovers cold energy through an expander, resulting in a more rational overall heat exchange temperature difference distribution in the heat exchanger, thereby reducing energy consumption; the liquid nitrogen formed after liquefying nitrogen in the heat exchanger is throttled to the first pressure. The purpose is to ensure that the vaporization temperature of liquid nitrogen is lower than that of oxygen. If the liquid nitrogen from the liquid oxygen preparation unit is used directly without throttling to the first pressure, it will be impossible to liquefy the oxygen because the vaporization temperature of liquid nitrogen is approximately -179°C, which is higher than the liquefaction temperature of oxygen. Heat exchange between liquid nitrogen and oxygen requires a matching pressure. Compared to directly throttling the liquid nitrogen from the liquid oxygen preparation unit to the first pressure for heat exchange with oxygen, this liquid oxygen preparation method adds the liquefaction of medium-pressure nitrogen, changing the heat exchange curve. According to actual measurements, the logarithmic mean temperature difference (LMTD) of this method is only 2.8°C, while the logarithmic mean temperature difference (LMTD) of direct heat exchange between oxygen and liquid nitrogen is 11.4°C. The expansion unit is added to provide more cooling capacity, reduce liquid nitrogen consumption, and ultimately achieve energy saving. The expanded nitrogen is still low-temperature cooling capacity and needs to be sent to the heat exchanger to recover the cooling capacity, further reducing liquid nitrogen consumption and achieving energy saving.

[0027] Example 2

[0028] Combined with appendix Figure 1 A liquid oxygen preparation apparatus applicable to the liquid oxygen preparation method described in Embodiment 1 includes a liquid oxygen cold box 1 and a first heat exchanger 2 installed inside the liquid oxygen cold box 1. It also includes a nitrogen heat exchange pipeline 3, an oxygen heat exchange pipeline 4, a first liquid nitrogen heat exchange pipeline 5, and a second nitrogen heat exchange pipeline 6 flowing through the first heat exchanger 2. The first liquid nitrogen heat exchange pipeline 5 is located between the nitrogen heat exchange pipeline 3 and the oxygen heat exchange pipeline 4 to exchange heat with both simultaneously. The outlet end of the nitrogen heat exchange pipeline 3 is connected to the inlet end of the first liquid nitrogen heat exchange pipeline 5 via a pipeline. A throttling valve is installed at the outlet end, which throttles the liquid nitrogen flowing out of the outlet end of the nitrogen heat exchange pipeline 3 to 0.2~0.35MPaG. The outlet end of the first liquid nitrogen heat exchange pipeline 5 and the inlet end of the second nitrogen heat exchange pipeline 6 are connected through the first expander 8. The first expander 8 is to provide more cooling capacity, reduce the consumption of liquid nitrogen, and ultimately achieve the purpose of energy saving. However, the expanded nitrogen is still low-temperature cooling capacity and needs to be sent to the heat exchanger to recover the cooling capacity and reduce the consumption of liquid nitrogen in order to achieve the purpose of energy saving.

[0029] As an optional embodiment of the present invention, the outlet end of the oxygen heat exchange pipeline 4 is connected to a liquid oxygen transfer pump 9 and a liquid oxygen storage tank 10. The prepared liquid oxygen is pressurized by the liquid oxygen transfer pump 9 and then enters the liquid oxygen storage tank 10 for storage and use.

[0030] As an optional embodiment of the present invention, it also includes a liquid nitrogen preparation device 7. How the liquid nitrogen preparation device 7 prepares liquid nitrogen is prior art and will not be described in detail here. The first liquid nitrogen heat exchange pipeline 5 is connected to the liquid nitrogen preparation pipeline of the liquid nitrogen preparation device 7. A liquid nitrogen storage tank 11 is connected to the liquid nitrogen preparation pipeline. The liquid nitrogen prepared by the liquid nitrogen preparation device 7 can be directly used for the preparation of liquid oxygen, so that liquid nitrogen and liquid oxygen can be produced simultaneously. Moreover, the preparation amount of liquid nitrogen and liquid oxygen can be freely adjusted. For example, if more liquid nitrogen is used to prepare liquid oxygen, the liquid nitrogen preparation amount will decrease and the liquid oxygen preparation amount will increase. It has the advantages of high flexibility, good economy and low cost.

[0031] As an optional solution of the present invention, the liquid oxygen cold box 1 adopts a skid-mounted structure and is connected to the liquid nitrogen preparation device 7. It has a high degree of standardization and can be flexibly relocated or modified between different factories. For example, in a factory area with only the liquid nitrogen preparation device 7, setting up another set of liquid oxygen cold box 1 can realize the simultaneous production of liquid nitrogen and liquid oxygen, which can reduce the total investment cost and optimize resource allocation.

[0032] The present invention and its embodiments have been described above illustratively. This description is not restrictive, and the figures shown are only one embodiment of the present invention; the actual structure is not limited thereto. Therefore, if those skilled in the art are inspired by this description and design similar structures and embodiments without departing from the spirit of the present invention, such designs should fall within the protection scope of the present invention.

Claims

1. A method for preparing liquid oxygen, characterized in that: Includes the following steps, S1. Nitrogen, liquid nitrogen and oxygen are introduced and heat exchange takes place in the heat exchanger; S2. After the nitrogen in the heat exchanger is liquefied, it is throttled to the first pressure, mixed with liquid nitrogen outside the heat exchanger, and then introduced into the heat exchanger. S3. When liquid nitrogen is vaporized and reheated to the first temperature in the heat exchanger, it is extracted and sent to the expander. After expanding to the second pressure in the expander, it is introduced into the heat exchanger to exchange heat with oxygen and nitrogen. S4. Oxygen is liquefied, and nitrogen is reheated and recycled or safely discharged. It also includes a liquid oxygen preparation apparatus suitable for the above method, comprising a liquid oxygen cold box and a first heat exchanger disposed within the liquid oxygen cold box, and further comprising a nitrogen heat exchange pipeline, an oxygen heat exchange pipeline, a first liquid nitrogen heat exchange pipeline and a second nitrogen heat exchange pipeline flowing through the first heat exchanger, wherein the outlet end of the nitrogen heat exchange pipeline is connected to the inlet end of the first liquid nitrogen heat exchange pipeline, and a throttling valve is provided at the outlet end of the nitrogen heat exchange pipeline, and the outlet end of the nitrogen heat exchange pipeline is connected to the inlet end of the second liquid nitrogen heat exchange pipeline and is provided with a first expander.

2. The method for preparing liquid oxygen according to claim 1, characterized in that: The first pressure is 0.2~0.35 MPaG.

3. The method for preparing liquid oxygen according to claim 1, characterized in that: The first temperature is 125K~133K.

4. The method for preparing liquid oxygen according to claim 1, characterized in that: The second pressure is 0.015 MPaG to 0.03 MPaG.

5. The method for preparing liquid oxygen according to any one of claims 1, characterized in that: The outlet end of the oxygen heat exchange pipeline is connected to a liquid oxygen transfer pump and a liquid oxygen storage tank.

6. The liquid oxygen preparation method according to claim 1, characterized in that: It also includes a liquid nitrogen preparation device, wherein the inlet end of the first liquid nitrogen heat exchange pipeline is connected to the liquid nitrogen preparation pipeline of the liquid nitrogen preparation device.

7. The liquid oxygen preparation method according to claim 1, characterized in that: The liquid oxygen cold box is a skid-mounted structure connected to the liquid nitrogen preparation device.

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