Low-temperature rectification apparatus and rectification method

Abstract

The application discloses a low-temperature rectification device and rectification method, relates to the technical field of cryogenic air separation, and comprises a raw material air compressor, a precooling system, a purification system, an air booster and an air separation cold box which are sequentially connected. The precooling system is composed of two air cooling towers and water cooling towers which are arranged side by side. The air compressed by the raw material air compressor enters the air cooling tower, is cooled and cleaned by normal temperature water, is cooled by chilled water, and is then sent to the purification system. The purified air is connected with the air booster at the rear, and flows into the air separation cold box through different pipelines and expander sets. After being treated by the air separation cold box, medium-pressure or high-pressure oxygen, medium-pressure or high-pressure nitrogen, liquid oxygen, liquid nitrogen and liquid argon products are finally generated. The application can flexibly adjust the liquid yield by adding a low-pressure gas expander, can guarantee the switching of the rectification device between liquid production and no liquid production, and has the advantages of low energy consumption, high flexibility, good economy and the like.

Description

Technical Field

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

[0002] Cryogenic separation, also known as low-temperature distillation, is a gas liquefaction technology. It typically employs methods such as throttling expansion or adiabatic expansion to compress and cool the gas, then uses the differences in boiling points to separate the different gases. Its advantages include high product gas purity, but the energy consumption for compression and cooling is significant. This method is suitable for large-scale gas separation processes, such as air-to-oxygen production; currently, 80% of my country's oxygen production is accomplished using this method.

[0003] Air separation units are currently widely used in the steel, chemical, and new energy lithium battery industries. In addition to providing customers with oxygen, nitrogen, and argon products, air separation units also produce a large amount of liquid oxygen and liquid nitrogen as byproducts. Especially in economically developed regions, the demand for liquid products is increasing year by year. Liquid products have the advantages of convenient storage, convenient supply, guaranteed quality, and high transportation efficiency, and are increasingly being adopted by users, showing great market potential.

[0004] In traditional air separation processes, unrestricted expansion is ensured by using direct air expansion circulation or adding external circulation to meet large refrigeration capacity demands. However, because each expander can only meet 70%–110% of its load adjustment range, when the liquid market is sluggish and liquid product production is not required, the expanders cannot reduce their load, leading to a significant increase in energy consumption and high overall oxygen consumption per unit of air separation equipment. Therefore, those skilled in the art provide a cryogenic distillation apparatus and method to solve the problems mentioned in the background art. Summary of the Invention

[0005] The purpose of this invention is to provide a low-temperature distillation apparatus and distillation method. By adding a low-pressure gas expander, the distillation apparatus can be switched between producing liquid and not producing liquid during actual operation, ensuring that the overall energy consumption of the distillation apparatus is within an optimal range, thereby solving the above-mentioned shortcomings in the prior art.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] A low-temperature distillation apparatus includes a feed air compressor, a precooling system, a purification system, an air booster, and an air separation cold box connected in sequence. The precooling system consists of two side-by-side air-cooled towers and a water-cooled tower. Air compressed by the feed air compressor enters the air-cooled tower, is first cooled and cleaned with room temperature water, and then further cooled by chilled water before being sent to the purification system. The chilled water is obtained by circulating water being cooled by the absorption of moisture from dry nitrogen gas in the water-cooled tower, and then cooled by a chiller unit. The air precooled by the precooling system then enters the purification system, where impurities such as water and carbon dioxide are removed. The adsorber in the purification system consists of two adsors; when one is running, the other... The waste nitrogen gas from the cold box is regenerated by heating it through a regeneration heater. The purified air is connected to an air booster and flows into the air separation cold box through different pipes and expanders. After being processed by the air separation cold box, medium-pressure or high-pressure oxygen, medium-pressure or high-pressure nitrogen, liquid oxygen, liquid nitrogen, and liquid argon products are finally produced. The air separation cold box includes a main heat exchanger, expanders, an air separation tower, a crude argon tower, and a refined argon tower connected in sequence. The expanders consist of a medium-pressure gas expander, a high-pressure gas expander, a low-pressure gas expander, and a liquid expander. When no liquid products are being produced, only the low-pressure gas expander needs to be started. When a large amount of liquid products are being produced, all four expanders are started simultaneously.

[0008] As a further description of the above technical solution: the low-pressure gas expander adopts either booster braking or fan braking.

[0009] As a further description of the above technical solution: the air separation tower consists of an upper tower, a main condenser-evaporator, and a lower tower from top to bottom. The crude argon tower is equipped with a crude argon condenser at the top and is connected to the upper tower at the bottom via a liquid oxygen circulation pump. The refined argon tower is equipped with a refined argon condenser at the top and a refined argon evaporator at the bottom.

[0010] A low-temperature distillation method, based on the aforementioned low-temperature distillation apparatus, specifically includes the following steps:

[0011] S01: After the air is compressed to a first pressure by the raw material air compressor, the compressed air is cooled to a range between 10 and 20°C by the pre-cooling system. The cooled air is then purified in the purification system to remove impurities such as water, carbon dioxide, and some hydrocarbons, resulting in clean air. The air cooled and purified at the first pressure is divided into at least three parts:

[0012] a. The first portion of air is cooled in the main heat exchanger and conveyed to the lower column of the air separation column, which operates at a first pressure;

[0013] b. The second part of the air is cooled in the main heat exchanger and then sent to a low-pressure gas expander to expand to the upper column of the air separation tower operating under the second pressure. The low-pressure gas expander can be a booster brake or a blower brake.

[0014] c. The third portion of air is pressurized to a second pressure in the air booster. This second-pressure airflow is divided into at least three parts: the first part of the medium-pressure airflow is cooled in the main heat exchanger, liquefied by heat exchange with the returning low-pressure liquid oxygen and medium-pressure liquid nitrogen, and then conveyed to the lower and upper columns of the air separation tower after passing through the medium-pressure liquid throttling valve; the second part of the medium-pressure airflow is compressed to a third pressure in the booster end of the medium-pressure gas expander, cooled, and then sent to the booster end of the high-pressure gas expander to be further compressed to a fourth pressure, cooled, and then sent to the main heat exchanger. After being cooled to the first temperature, most of the high-pressure air is sent to the high-pressure gas expander and expanded to the lower column of the air separation tower operating at the first pressure. The remaining high-pressure air continues to be cooled in the main heat exchanger. After exchanging heat with the refluxing high-pressure liquid oxygen and high-pressure liquid nitrogen, it is liquefied and then sent to the lower and upper columns of the air separation tower after passing through the high-pressure liquid expander or the high-pressure liquid throttle valve. The third part of the medium-pressure air is sent to the main heat exchanger for cooling. After being cooled to the second temperature, it is sent to the medium-pressure gas expander and expanded to the lower column of the air separation tower operating at the first pressure.

[0015] S02: Liquid oxygen product is extracted from the bottom of the upper tower of the air separation cold box, and after being pressurized to different pressure ranges by the liquid oxygen pump, it is sent to the main heat exchanger for matching and heat exchange with medium-pressure air at a certain pressure after being pressurized by the air booster or high-pressure air at a certain pressure after being expanded and pressurized. The reheated oxygen is sent to the pipeline network as oxygen product.

[0016] S03: Liquid nitrogen product is extracted from the top of the lower tower of the air separation cold box, pressurized to different pressure ranges by a liquid nitrogen pump, and then sent to the main heat exchanger for heat exchange with medium-pressure air at a certain pressure after being pressurized by an air booster or high-pressure air at a certain pressure after being expanded and pressurized. The reheated nitrogen is then sent to the pipeline network as nitrogen product.

[0017] As a further description of the above technical solution: the air booster in S01 can be composed of one or more boosters connected in parallel.

[0018] As a further description of the above technical solution: the main heat exchanger in S01 is any one of a low-pressure plate heat exchanger, a medium-high pressure plate heat exchanger, or an integral combined plate heat exchanger.

[0019] As a further description of the above technical solution: the second pressure in S01 is 2.0 to 3.0 MPaG, the third pressure is 3.0 to 4.0 MPaG, and the fourth pressure is 4.0 to 6.5 MPaG.

[0020] As a further description of the above technical solution: the first temperature in S01 is 193-163K, and the second temperature is 283-253K.

[0021] In the above technical solution, the low-temperature distillation apparatus and distillation method provided by the present invention have the following beneficial effects:

[0022] This invention allows for flexible adjustment of liquid production by adding a low-pressure gas expander. In actual operation, it ensures that the distillation unit can switch between producing liquid and not producing liquid. If no liquid product is produced, only the low-pressure expander can be operated to provide the cooling required for air separation. At this time, the air compressor and booster compressor will not deviate from their optimal efficiency points, ensuring that the overall energy consumption of the air separation unit remains within a good range. This invention has the advantages of low energy consumption, high flexibility, and good economy.

[0023] It should be understood that the foregoing general description and the following detailed description are exemplary and illustrative only, and are not intended to limit this disclosure.

[0024] This application provides an overview of various implementations or examples of the technology described in this disclosure, and is not a full disclosure of the entire scope or all features of the disclosed technology. Attached Figure Description

[0025] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in this invention. For those skilled in the art, other drawings can be obtained based on these drawings.

[0026] Figure 1 This is a schematic diagram of a low-temperature distillation apparatus provided in an embodiment of the present invention.

[0027] Explanation of reference numerals in the attached figures:

[0028] 1. Raw material air compressor; 2. Precooling system; 3. Purification system; 4. Air booster; 5. Air separation cold box; 6. Air separation tower; 7. Crude argon tower; 8. Refined argon tower; 9. Liquid oxygen circulating pump; 10. Main heat exchanger; 11. Medium-pressure gas expander; 12. High-pressure gas expander; 13. Low-pressure gas expander; 14. Medium-pressure liquid throttle valve; 15. Liquid expander; 16. High-pressure liquid throttle valve; 17. Liquid oxygen pump; 18. Liquid nitrogen pump; 19. Adsorber; 20. Silencer tower; 21. Regeneration heater. Detailed Implementation

[0029] To make the objectives, technical solutions, and advantages of the embodiments of this disclosure clearer, the technical solutions of the embodiments of this disclosure will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this disclosure. All other embodiments obtained by those skilled in the art based on the described embodiments of this disclosure without creative effort are within the scope of protection of this disclosure.

[0030] Unless otherwise defined, the technical or scientific terms used in this disclosure shall have the ordinary meaning understood by one of ordinary skill in the art to which this disclosure pertains. The terms "comprising" or "including," and similar terms used in this disclosure, mean that an element or object preceding the term encompasses the elements or objects listed following the term and their equivalents, without excluding other elements or objects. Terms such as "connected" or "linked" are not limited to physical or mechanical connections, but may also include electrical connections, whether direct or indirect. Terms such as "upper," "lower," "left," and "right" are used only to indicate relative positional relationships; these relative positional relationships may change accordingly when the absolute position of the described objects changes.

[0031] Please see Figure 1 This invention provides a technical solution: a low-temperature distillation apparatus, comprising a raw material air compressor 1, a precooling system 2, a purification system 3, an air booster 4, and an air separation cold box 5 connected in sequence. The precooling system 2 consists of two air-cooled towers and a water-cooled tower arranged side by side. Air compressed by the raw material air compressor 1 enters the air-cooled tower, is first cooled and cleaned with room temperature water, and then further cooled by chilled water before being sent to the purification system 3. The chilled water is obtained by circulating water being cooled by the absorption of moisture from dry nitrogen gas in the water-cooled tower, and then cooled by a chiller unit. The purification system 3 is equipped with a silencer tower 20. The air precooled by the precooling system 2 then enters the purification system 3, where water, carbon dioxide, and other impurities are removed. The adsorber 19 in the purification system 3 consists of two adsorbers 19. When one is running... The other unit regenerates the waste nitrogen from the cold box by heating it with a regeneration heater 21. The purified air is connected to the air booster 4 at the rear and flows into the air separation cold box 5 through different pipes and expanders. After being processed by the air separation cold box 5, medium-pressure or high-pressure oxygen, medium-pressure or high-pressure nitrogen, liquid oxygen, liquid nitrogen, and liquid argon products are finally produced. The air separation cold box 5 includes a main heat exchanger 10, an expander unit, an air separation tower 6, a crude argon tower 7, and a refined argon tower 8 connected in sequence. The expander unit consists of a medium-pressure gas expander 11, a high-pressure gas expander 12, a low-pressure gas expander 13, and a liquid expander 15, and is equipped with a liquid oxygen pump 17 and a liquid nitrogen pump 18. When no liquid products are being produced, only the low-pressure gas expander 13 needs to be started. When a large amount of liquid products are being produced, all four expanders are started simultaneously.

[0032] This invention addresses the issue of large fluctuations in the production of liquid products from air separation by rationally configuring expanders with different pressure levels. This distillation method can flexibly adjust the output of liquid oxygen and liquid nitrogen products according to market fluctuations. When a large amount of liquid product needs to be produced, three expanders can be started. When energy conservation and production restriction are required and liquid product is not needed, only one expander can be started to ensure the cooling capacity required for normal operation of the air separation unit. This method can simultaneously meet both no-liquid-production and large-volume liquid-production conditions. Moreover, under both conditions, the expanders and boosters operate at their optimal efficiency points, offering advantages such as low energy consumption, high flexibility, and good economy, thus solving the problem of high unit energy consumption under small-volume liquid conditions.

[0033] In another embodiment of the present invention, the low-pressure gas expander 13 adopts either booster braking or fan braking. When energy prices are high, configuring the liquid expander 15 can save the total energy consumption of the distillation unit.

[0034] In another embodiment of the present invention, the air separation tower 6 consists of an upper tower, a main condenser-evaporator, and a lower tower from top to bottom. The crude argon tower 7 is equipped with a crude argon condenser at the top and is connected to the upper tower at the bottom via a liquid oxygen circulation pump 9. The refined argon tower 8 is equipped with a refined argon condenser at the top and a refined argon evaporator at the bottom.

[0035] A low-temperature distillation method, based on the aforementioned low-temperature distillation apparatus, specifically includes the following steps:

[0036] S01: After the air is compressed to a first pressure by the raw material air compressor 1, it passes through the pre-cooling system 2 and the purification system 3. The air cooled and purified under this first pressure is divided into at least three parts:

[0037] a. The first portion of air is cooled in the main heat exchanger 10 and conveyed to the lower column of the air separation column 6, which operates at a first pressure.

[0038] b. The second part of the air is cooled in the main heat exchanger 10. After being cooled to a certain temperature, it is sent to the low-pressure gas expander 13 and expanded to the upper column of the air separation tower 6, which operates under the second pressure.

[0039] c. The third part of the air is pressurized to the second pressure in the air booster 4. This second-pressure airflow is divided into at least three parts: the first part of the medium-pressure airflow is cooled in the main heat exchanger 10, and after liquefying by heat exchange with the returning low-pressure liquid oxygen and medium-pressure liquid nitrogen, it is sent to the lower and upper towers of the air separation tower 6 after passing through the medium-pressure liquid throttle valve 14. The second part of the medium-pressure airflow is compressed to the third pressure in the booster end of the medium-pressure gas expander 11, cooled, and then sent to the booster end of the high-pressure gas expander 12 to be further compressed to the fourth pressure. After cooling, it is sent to the main heat exchanger 10 for further cooling. After being cooled to the first temperature, most of the air is sent to the high-pressure gas expander 12 and expanded to the lower tower of the air separation tower 6 operating at the first pressure. The remaining high-pressure air continues to be cooled in the main heat exchanger 10. After exchanging heat with the backflowing high-pressure liquid oxygen and high-pressure liquid nitrogen and liquefying, it is then sent to the lower and upper towers of the air separation tower 6 after passing through the high-pressure liquid expander 15 or the high-pressure liquid throttle valve 16. The third part of the medium-pressure air is sent to the main heat exchanger 10 for cooling. After being cooled to the second temperature, it is sent to the medium-pressure gas expander 11 and expanded to the lower tower of the air separation tower 6 operating at the first pressure.

[0040] S02: Liquid oxygen product is drawn from the bottom of the upper column of the air separation tower 6 in the air separation cold box 5, and after being pressurized to different pressure ranges by the liquid oxygen pump 17, it is sent to the main heat exchanger 10 for matching and heat exchange with medium-pressure air at a certain pressure after being pressurized by the air booster 4 or high-pressure air at a certain pressure after being expanded and pressurized. The reheated oxygen is sent to the pipeline network as oxygen product. The liquid oxygen pump 17 can be a single unit or multiple pumps of different numbers connected in parallel, which can produce oxygen products at different pressure ranges.

[0041] S03: Liquid nitrogen product is drawn from the top of the lower column of the air separation tower 6 in the air separation cold box 5, and after being pressurized to different pressure ranges by the liquid nitrogen pump 18, it is sent to the main heat exchanger 10 for matching heat exchange with medium-pressure air at a certain pressure after being pressurized by the air booster 4 or high-pressure air at a certain pressure after being expanded and pressurized. The reheated nitrogen is sent to the pipeline network as nitrogen product. The liquid nitrogen pump 18 can be a single unit or multiple pumps of different numbers connected in parallel, which can produce nitrogen products at different pressure ranges without the need for an additional nitrogen booster, thus improving the reliability of the distillation unit.

[0042] In another embodiment of the present invention, the air booster 4 in S01 may be composed of one or more boosters connected in parallel.

[0043] In another embodiment of the present invention, the main heat exchanger 10 in S01 is any one of a low-pressure plate heat exchanger, a medium-high pressure plate heat exchanger, or an integrally combined plate heat exchanger.

[0044] In another embodiment of the present invention, the second pressure in S01 is 2.0 to 3.0 MPaG, the third pressure is 3.0 to 4.0 MPaG, and the fourth pressure is 4.0 to 6.5 MPaG.

[0045] In another embodiment of the present invention, the first temperature in S01 is 193-163K and the second temperature is 283-253K.

[0046] See Table 1 below.

[0047] Table 1 Comparison of existing technologies and the air separation method of this invention.

[0048]

[0049]

[0050] Compared with existing technologies, the distillation method of this invention for air separation, taking a 60,000 cubic meter air separation unit as an example, can save 3.93 million yuan in operating costs annually if two months of low-load production restrictions are considered each year. The economic benefits are significant. As energy costs increase, this method will generate greater and greater economic and social value.

[0051] The foregoing has only described certain exemplary embodiments of the present invention by way of illustration. Undoubtedly, those skilled in the art can modify the described embodiments in various ways without departing from the spirit and scope of the present invention. Therefore, the foregoing drawings and descriptions are illustrative in nature and should not be construed as limiting the scope of protection of the claims of the present invention.

Claims

1. A low-temperature distillation method, comprising a low-temperature distillation apparatus, characterized in that, The cryogenic distillation unit includes a raw material air compressor, a precooling system, a purification system, an air booster, and an air separation cold box connected in sequence. The precooling system consists of two air-cooled towers and a water-cooled tower arranged side by side. The air separation cold box includes a main heat exchanger, an expander unit, an air separation tower, a crude argon tower, and a refined argon tower connected in sequence. The expander unit consists of a medium-pressure gas expander, a high-pressure gas expander, a low-pressure gas expander, and a liquid expander. When no liquid products are being produced, only the low-pressure gas expander needs to be started. When a large amount of liquid products are being produced, all four expanders are started simultaneously. The method specifically includes the following steps: S01: After the air is compressed to the first pressure by the raw material air compressor, it enters the air-cooled tower, where it is first cooled and cleaned with room temperature water, and then further cooled by chilled water before being sent to the purification system to remove water and carbon dioxide impurities. The chilled water is obtained by circulating water being cooled by the hygroscopic absorption of dry nitrogen gas in a water-cooled tower, and then cooled by a chiller unit. The air cooled and purified under this first pressure is divided into at least three parts: a. The first portion of air is cooled in the main heat exchanger and conveyed to the lower column of the air separation column, which operates at a first pressure; b. The second part of the air is cooled in the main heat exchanger and then sent to a low-pressure gas expander to expand to the upper column of the air separation tower operating under the second pressure. c. The third portion of air is pressurized to a second pressure in the air booster. This second-pressure airflow is divided into at least three parts: the first part of the medium-pressure airflow is cooled in the main heat exchanger, liquefied by heat exchange with the returning low-pressure liquid oxygen and medium-pressure liquid nitrogen, and then conveyed to the lower and upper columns of the air separation tower after passing through the medium-pressure liquid throttling valve; the second part of the medium-pressure airflow is compressed to a third pressure in the booster end of the medium-pressure gas expander, cooled, and then sent to the booster end of the high-pressure gas expander to be further compressed to a fourth pressure, cooled, and then sent to the main heat exchanger. After being cooled to the first temperature, most of the high-pressure air is sent to the high-pressure gas expander and expanded to the lower column of the air separation tower operating at the first pressure. The remaining high-pressure air continues to be cooled in the main heat exchanger. After exchanging heat with the refluxing high-pressure liquid oxygen and high-pressure liquid nitrogen, it is liquefied and then sent to the lower and upper columns of the air separation tower after passing through the high-pressure liquid expander or the high-pressure liquid throttle valve. The third part of the medium-pressure air is sent to the main heat exchanger for cooling. After being cooled to the second temperature, it is sent to the medium-pressure gas expander and expanded to the lower column of the air separation tower operating at the first pressure. S02: Liquid oxygen product is extracted from the bottom of the upper tower of the air separation cold box, and after being pressurized to different pressure ranges by the liquid oxygen pump, it is sent to the main heat exchanger for matching and heat exchange with medium-pressure air at a certain pressure after being pressurized by the air booster or high-pressure air at a certain pressure after being expanded and pressurized. The reheated oxygen is sent to the pipeline network as oxygen product. S03: Liquid nitrogen product is extracted from the top of the lower tower of the air separation cold box, pressurized to different pressure ranges by a liquid nitrogen pump, and then sent to the main heat exchanger for heat exchange with medium-pressure air at a certain pressure after being pressurized by an air booster or high-pressure air at a certain pressure after being expanded and pressurized. The reheated nitrogen is then sent to the pipeline network as nitrogen product.

2. The low-temperature distillation method according to claim 1, characterized in that, The purification system (3) consists of two adsorbers (19). When one is running, the other is regenerated by the waste nitrogen gas from the cold box being heated by the regeneration heater (21).

3. The low-temperature distillation method according to claim 1, characterized in that, The low-pressure gas expander (13) adopts either booster braking or fan braking.

4. The low-temperature distillation method according to claim 1, characterized in that, The air separation tower (6) consists of an upper tower, a main condenser evaporator, and a lower tower from top to bottom. The crude argon tower (7) is equipped with a crude argon condenser at the top and is connected to the upper tower at the bottom via a liquid oxygen circulation pump (9). The fine argon tower (8) is equipped with a fine argon condenser at the top and a fine argon evaporator at the bottom.

5. The low-temperature distillation method according to claim 1, characterized in that, The air booster (4) in S01 is one unit or composed of multiple boosters connected in parallel.

6. The low-temperature distillation method according to claim 1, characterized in that, The main heat exchanger (10) in S01 is any one of a low-pressure plate heat exchanger, a medium-high pressure plate heat exchanger, or an integrated plate heat exchanger.

7. The low-temperature distillation method according to claim 1, characterized in that, The second pressure in S01 is 2.0 to 3.0 MPaG, the third pressure is 3.0 to 4.0 MPaG, and the fourth pressure is 4.0 to 6.5 MPaG.

8. The low-temperature distillation method according to claim 4, characterized in that, The first temperature in S01 is 193–163 K, and the second temperature is 283–253 K.

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