Low-temperature air separation method and air separation apparatus

Abstract

The method and corresponding air separation apparatus for cryogenic air separation utilize a high-pressure column (101), a low-pressure column (102), a typical main condenser (103), and a crude argon column (107a / b / c) connected to the low-pressure column (102) at a first intermediate location, i.e., an argon transition point. Secondary top nitrogen (40) is extracted from the top of the low-pressure column (102) and used as recirculating nitrogen (41,42,44,47,48), which is introduced in gaseous form (48) into the high-pressure column (101) and / or into the main condenser (103) and / or into the bottom reboiler of the separation column (81,77). The air separation apparatus also includes a medium-pressure column (104), which operates at medium pressure and is fed by a first oxygen-enriched fraction (33,34) from the high-pressure column (101), which is introduced as feed into the medium-pressure column (104). A portion (38) of the argon transition fraction is introduced as a heating medium into the bottom evaporator (106) of the intermediate-pressure column (104). A first portion (362) of the third overhead nitrogen (361) in gaseous form from the intermediate-pressure column (104) is heated in the main heat exchanger (9) and eventually removed as gaseous nitrogen product (UHPGAN). A second portion (53) of the third overhead nitrogen (361) is liquefied in the top condenser (105) of the intermediate-pressure column (104) and used as reflux in the intermediate-pressure column (104). A second oxygen-enriched fraction is removed from the intermediate-pressure column (104) and introduced as a cooling medium (38) into the top condenser (105) of the intermediate-pressure column (104). At least a portion of the oxygen-enriched gas (36) produced in the top condenser (10) is introduced into the low-pressure column (102) at a second intermediate position at least 25 theoretical plates above the first intermediate position.

Description

[0001] This invention relates to methods and apparatus for cryogenic air separation devices according to the preamble of the independent patent claims.

[0002] This type of system is disclosed in Figure 3 of WO 2021204424 A1. It shows that nitrogen recirculation compensates for the reduction in distillation efficiency caused by the increased pressure in the column.

[0003] Although known methods are already relatively efficient for high-voltage systems, the purpose of this invention is to further save energy during system operation.

[0004] During the development of this invention, it was discovered that recycling was a relevant source of inefficiency. The solution of this invention is to add a specific third tower, according to the characterizing features of the independent patent claims, to perform an additional separation step between the high-pressure and low-pressure towers.

[0005] The medium-pressure column has certain specific characteristics, particularly that it is reboiled with a portion of the argon transition fraction, which is at least partially liquefied in the reboiler at the bottom of the medium-pressure column. This liquefied argon transition fraction is preferably returned to the low-pressure column. A certain amount of vapor generated in the reboiler at the bottom of the medium-pressure column is partially reliquefied in the condenser at the top of the medium-pressure column, thus generating a corresponding amount of additional vapor on the evaporation side. This additional vapor is introduced into the low-pressure column, but at a location much higher than where the return stream from the argon transition fraction to the reboiler at the bottom of the medium-pressure column is taken.

[0006] These measures have a significant impact on the amount of vapor rising in the low-pressure column above the argon transition and below the introduction from the top condenser of the medium-pressure column. Vapor is removed at the lower end of this section and reintroduced in a corresponding amount at the upper end. The amount of vapor rising in this section is relatively low, and the liquid-vapor ratio (L / V) is significantly higher than in the prior art by about 20%. In this invention, this L / V is significantly increased to between about 1.85 at the upper end of this section and 1.98 at the lower end, thereby bringing it closer to the equilibrium line and improving the separation efficiency in the low-pressure column.

[0007] Another important feature of the medium-pressure column of this invention is the extraction of nitrogen product from the top of the column. This configuration has proven to be more efficient than the conventional production method using reflux liquid from low-pressure columns.

[0008] In embodiments of the invention, 80% to 94%, for example 89%, of the gaseous nitrogen product is taken from the low-pressure tower, 20% to 6%, for example 11%, of the gaseous nitrogen product is taken from the third top nitrogen gas at the top of the medium-pressure tower, and no gaseous nitrogen product is taken from the high-pressure tower. Preferably, as long as it is not introduced into the top condenser of the medium-pressure tower, all the third top nitrogen gas forms gaseous nitrogen product, and there is no third portion.

[0009] The crude argon column can be implemented in one or more sections (e.g., two or three sections). It can be accompanied by a classic pure argon column for nitrogen removal.

[0010] The pressure in the high-pressure tower is preferably between 9 and 14 bar. The separation tower, which may be heated by a portion of the recycled nitrogen, can be any corresponding tower in the system. In the example, the krypton-xenon enrichment tower and / or the pure oxygen tower can be heated separately.

[0011] In an embodiment of the invention, no portion of the liquid nitrogen fraction produced in the top condenser of the intermediate-pressure column is introduced into the low-pressure column. Therefore, a higher quantity of gaseous product nitrogen extracted from the intermediate-pressure column is available.

[0012] In embodiments of the invention, the first and second portions of the nitrogen gas at the top of the third column account for at least 95%, particularly at least 98% or 100%, of the nitrogen gas at the top of the third column. Therefore, the top product of the intermediate-pressure column is exclusively or almost exclusively used as reflux or gaseous product of the intermediate-pressure column. In some cases, for example, a small portion of the third portion may be taken as reflux or liquid product of another column.

[0013] In an embodiment of the invention, no portion of the nitrogen gas from the top of the first column of the high-pressure tower is directed to the main heat exchanger and subsequently removed as a product. Therefore, all nitrogen generated at the top of the high-pressure tower can be obtained as liquid reflux from the tower (particularly the low-pressure and high-pressure towers) to improve separation efficiency. In this case, a small amount can be removed as a liquid product.

[0014] Furthermore, refrigeration can be generated by a cryogenic expansion turbine fed with a waste oxygen stream mixed with a second stream from a low-pressure tower. The second stream can be, for example, part of a gaseous stream from a crude argon condenser or gas from the top condenser of a medium-pressure tower. The cryogenic expansion turbine is preferably a single cryogenic gas expansion turbine.

[0015] In particular, no part of the recirculated nitrogen is turbine expanded.

[0016] The top condenser of the crude argon column is preferably implemented as a forced flow evaporator (also known as a single-pass evaporator) on its evaporation side. It is typically arranged in a separate container on top of the crude argon column. This arrangement improves the transportability of the distillation box (an insulated cold box surrounding one, some, or all of the columns).

[0017] In conventional crude argon distillation, a portion or all of the first oxygen-enriched fraction from the high-pressure column is used directly as the cooling medium for the top condenser of the crude argon column. In contrast, in some embodiments of the invention, it is advantageous to use a different fraction as this cooling medium, i.e., to partially evaporate the remaining liquid from the top condenser of the medium-pressure column. This measure further improves the system, particularly by reducing the volume of the top condenser of the crude argon column. This type of cooling of the crude argon column, combined with the use of a forced-flow evaporator as the top condenser, offers specific advantages; however, this type of cooling can also be applied if a bath evaporator is used as the top condenser of the crude argon column.

[0018] Preferably, a portion or all of the first oxygen-enriched fraction is fed directly into the low-pressure column without being pre-fed into the evaporator. Such "direct introduction" may include a cooling step, such as in a subcooler, prior to introduction into the low-pressure column, or a heating step without evaporation, such as in the bottom evaporator of a pure argon column, but without an evaporation step.

[0019] Additionally or alternatively, the first oxygen-enriched fraction may be indirectly fed into the low-pressure column by introducing a portion or all of it into an evaporator, for example, into the top condenser of the crude argon column, and sending the evaporated portion and the remaining liquid portion to the low-pressure column.

[0020] In a preferred embodiment, the first portion of the nitrogen gas at the top of the third column is ultimately removed as a pressurized gaseous nitrogen product, i.e., at ultra-atmospheric pressure, particularly at least 1 bar, at least 2 bar, or at least 3 bar above atmospheric pressure.

[0021] The device of the present invention is described in independent claim 13. It may be supplemented by one or more features of the dependent method claims, which are written in the form of a device.

[0022] The invention and further details thereof are described below with reference to the accompanying drawings, which show:

[0023] Figure 1 According to a first embodiment of the method and apparatus of the present invention, and

[0024] Figure 2 Compare Figure 1 A simple second embodiment, but illustrating all the features of the invention.

[0025] Atmospheric air (AIR) flows through a filter and is compressed to approximately 11.9 bar in an intercooled four-stage main air compressor 2. (All pressure values ​​given here are absolute pressures.) After the heat of compression is removed in coolers 3a and 3b, liquid water is removed in separator 4, and the air is purified primarily from water vapor and carbon dioxide in purification unit 5 using two adsors. The purified air 6 is cooled to approximately its dew point in the main heat exchanger 9 and then sent to high-pressure tower 101 via line 8. (In this case, a small amount of air may be discharged via bypass 10.)

[0026] The first oxygen-enriched fractions 33 and 34 are drawn from the bottom of the high-pressure column 101, cooled in the subcooler 60, and a first portion 35 of the first oxygen-enriched fractions 33 and 34 is fed directly into the low-pressure column 102. A second portion 161 is introduced as feed into the medium-pressure column at the bottom or a higher section. The first overhead nitrogen 61 is drawn from the top of the high-pressure column 101 and introduced into the main condenser (103) for near-complete liquefaction. The resulting liquid nitrogen 62 is introduced as reflux into the high-pressure column. Below one or more He-Ne barrier trays 163, a portion 64 of the liquid nitrogen 62 is drawn, cooled in the subcooler 50, and introduced via lines 65 and 66 into the top of the low-pressure column 102.

[0027] Liquid oxygen 67 generated at the bottom of the low-pressure column is completely fed into the evaporation space of the main condenser 103 to generate rising vapor 68 for the low-pressure column 102. Gaseous waste oxygen fraction 69 is removed via line 69 to avoid enrichment in non-volatile components. Krypton-free liquid oxygen fraction 93 can be internally compressed by pump 94 and heated in the main heat exchanger 9 so that it can be removed as the internally compressed gaseous oxygen product GOCIC; a portion of liquid 93 can be recovered as liquid oxygen product (LOX). As shown, it can be used to drive the expansion turbine 92, optionally together with additional fractions 90, 91 mixed at mixing point 95. Secondary overhead nitrogen 40 is drawn from the top of the low-pressure column 102 and used as recirculating nitrogen 41, 42, 44, 47, 48. In the cycle, recirculating nitrogen 41 is heated in the subcooler 50 and then sent to the cold end of the main heat exchanger 9, where it is fully heated. In a two-stage nitrogen compressor 45, most or all of the heated nitrogen 44 is compressed to a pressure of approximately 11.0 bar to 12.0 bar. The heat of compression is ultimately removed in a cooler 46. A portion 70 of the gaseous nitrogen is taken out from the outlet of the compressor 45 as the final product UHPGAN. The remaining portion 47 is returned as recycle nitrogen to the main heat exchanger 9, where it is cooled to near the dew point but not actually liquefied. At least a portion of the cooled recycle nitrogen 48 is introduced in gaseous form into the main condenser 103. (Alternatively, it may be introduced to the top or below the high-pressure column 101.) At the argon transition (the first intermediate position of the low-pressure column (102)), the argon-rich fractions (36, 37) are taken out and introduced as rising vapor into the first section 107a of the crude argon column. In this embodiment, the crude argon column consists of a total of three sections 107a / b / c. The argon column operates in the usual manner and has a crude argon top condenser 108 at its top to produce reflux liquid. The crude argon top condenser 108 operates as a forced flow evaporator and is powered by a liquid 71 as the cooling medium, which originates from the evaporation space of the top condenser 105 of the intermediate-pressure column 104, as will be explained later. The evaporated cooling medium 72 and the remaining liquid 73 are sent to a low-pressure column. The remaining gas from the crude argon condenser 108 is sent via line 71 to a pure argon column 72, which operates in a conventional manner. 9. In this embodiment, the cooling medium 38 is only partially evaporated in the top condenser 105 of the intermediate-pressure column 104. The remaining liquid 74 is used as the cooling medium for the top condenser 108 of the crude argon column 107.

[0028] According to the invention, a third column for nitrogen-oxygen separation, namely a medium-pressure column 104, is used. The liquid at the bottom of this column is taken out as a second oxygen-enriched fraction and introduced as a cooling medium 38 into the evaporation space of the top condenser 105 of the medium-pressure column 104. In the top condenser 105, it is partially evaporated to produce oxygen-enriched gas 36. At least a portion of the oxygen-enriched gas 36 is introduced into the low-pressure column 102 at a second intermediate position, in this embodiment, approximately 35 theoretical plates above the first intermediate position. (Generally, the number of theoretical plates between the first and second intermediate positions is at least 25, preferably at least 30, or 25 to 50.) The evaporation space of the top condenser 105 again operates as a forced-flow evaporator. As previously described, the remaining liquid 71 is sent to a crude argon condenser 108.

[0029] The overhead gas generated in the intermediate-pressure column 104 is taken out as third overhead nitrogen 361, which is separated into exactly two parts. The first part 362 is heated in the main heat exchanger 9 and is eventually taken out as gaseous nitrogen product (UHPGAN) via line 70. Previously, the heated third overhead nitrogen 63 was introduced into the nitrogen compressor 45 between the two stages and mixed with the heated and partially compressed second overhead nitrogen 44. The second part 53 of the third overhead nitrogen 361 is introduced into the top condenser 105 of the intermediate-pressure column 104, where it is liquefied by indirect heat exchange with the evaporative cooling medium 38, thereby producing a liquid nitrogen stream 54, which is preferably completely introduced into the intermediate-pressure column 104 as reflux. Preferably, the complete third overhead nitrogen 361 is divided into the first part and the second part 362, and there is no third part.

[0030] This embodiment includes three additional towers, which are known in themselves and are not necessarily part of the present invention, but may be combined with the present invention.

[0031] 1. High-purity oxygen production

[0032] A portion of the liquid pumped from the second section 107b of the crude argon column to the first section 107a is introduced into the top of the pure oxygen column 77. In this embodiment, the pure oxygen column 77 is installed directly at the bottom of the first crude argon column 107; they may have a common external container and be separated by a tight horizontal plate. The bottom reboiler 78 is driven by the recirculating nitrogen section 48. In the tank system 79, for example, using two so-called operating tanks and a third tank acting as a buffer tank, the high-purity liquid oxygen product is pressurized to a desired product pressure of 11 to 12 bar. The tank system of this embodiment is implemented according to one of the corresponding patents EP 2989400 B1 or EP 3193114 B1. The pressurized liquid oxygen 80 evaporates and is fully heated in the main heat exchanger 9, and is then removed as the ultra-high purity gaseous oxygen product UHPGOX.

[0033] 2. Krypton-Xenon Production

[0034] Kr-Xe concentration tower 81 can also be added in the conventional manner. It produces liquid concentrate 82 (crude KrXe), which is collected in a tank for further purification steps.

[0035] 3. Helium-Neon Production

[0036] Similarly, He-Ne concentration tower 84 can be added in a conventional manner. It produces gaseous concentrate 83, which is collected in a cylinder for conveying to further purification steps.

[0037] Regarding compressor technology, the four stages of the main air compressor 2 and nitrogen compressor 45 can be integrated into a single machine by using the same drive unit on a common shaft or within a geared machine.

[0038] Figure 2 An embodiment of the present invention is shown, which is similar to Figure 1 However, it does not have the three additional columns mentioned above. The crude argon column is implemented in two sections, 107b and 107c. Figure 1 Another difference is the use of a bath evaporator instead of a forced flow evaporator. Alternatively or additionally, the top condenser of the medium-pressure tower can be replaced by a bath evaporator.

[0039] exist Figure 2 In, there is no such thing as Figure 1 The pipeline 35, which directly guides the xy% fractions of oxygen-enriched fractions 33 and 34 from the high-pressure tower 101 to the low-pressure tower 102, is as described in the example. Figure 2 In the process, oxygen-enriched fractions 33 and 34 are fed entirely indirectly to low-pressure tower 102 via pipelines 72, 73, 137, 138, and 139; otherwise, these pipelines would have the same characteristics as... Figure 1 The same function is described. Figure 2 In the process, the fully oxygen-enriched fractions 33 and 34 from the high-pressure tower 101 are fed into the medium-pressure tower 104 via pipeline 261.

Claims

1. A method for cryogenic air separation using an air separation device, the air separation device having a high-pressure column (101) operating at a first pressure above 9 bar, a low-pressure column (102) operating at a second pressure below the first pressure, and a crude argon column (107a / b / c), the high-pressure column (101) and the low-pressure column (102) being thermally integrated by a main condenser (103) liquefying first-top nitrogen from the high-pressure column (101) to prevent evaporation of the bottom liquid from the low-pressure column (102), - The compressed air (6) is cooled in the main heat exchanger (9), - Cooling air (8) from the main heat exchanger (9) is introduced into the high-pressure tower (101). - Nitrogen gas (61) from the top of the first column is taken out from the high-pressure column and introduced into the main condenser (103) to produce liquid nitrogen. - The first oxygen-enriched fraction (33, 34) is taken out from the high-pressure column (101), and at least a portion (35, 72, 73, 137, 138, 139) of the first oxygen-enriched fraction (33, 34) is preferably fed directly or indirectly into the low-pressure column (102). - An argon-rich fraction (36) is taken from the first intermediate position of the low-pressure column (102), and at least a first portion (37) of the argon-rich fraction is introduced as rising vapor into the crude argon column (107a / b / c). - Nitrogen gas (40) from the top of the second column is taken out from the top of the low-pressure column (102) and used as recirculated nitrogen (41, 42, 44, 47, 48), which is heated, compressed (35), and cooled in the main heat exchanger (9) but not liquefied in the main heat exchanger (9). At least a portion of the cooled recirculated nitrogen (48) is introduced in gaseous form (48) into the high-pressure column (101) and / or into the main condenser (103) and / or into the bottom reboiler of the separation column (81, 77). Its features are, - The air separation device further includes a medium-pressure tower (104) that operates at a third pressure lower than the first pressure and higher than the second pressure. - At least a portion (161, 261) of the first oxygen-enriched fraction (33, 34) is introduced as feed into the medium-pressure tower (104). - The second portion (38) of the argon-rich distillate is introduced as a heating medium into the bottom evaporator (106) of the medium-pressure column (104). - Nitrogen gas (361) at the top of the third column is generated in the medium-pressure column (104). - A first portion (362) of the nitrogen gas (361) at the top of the third column is taken out in gaseous form from the intermediate-pressure column (104), heated in the main heat exchanger (9), and finally taken out as a gaseous nitrogen product (UHPGAN). - A second portion (53) of the nitrogen gas (361) at the top of the third column is introduced into the top condenser (105) of the intermediate-pressure column (104), where it is liquefied by indirect heat exchange with the evaporative cooling medium (38) to produce a liquid nitrogen stream (54), which is introduced into the intermediate-pressure column (104) as a reflux. - The second oxygen-enriched fraction is taken from the intermediate-pressure column (104) and introduced as a cooling medium (38) into the top condenser (105) of the intermediate-pressure column (104), where it evaporates at least partially to produce oxygen-enriched gas (36), at least a portion of which is introduced into the low-pressure column (102) at a second intermediate position at least 25 theoretical plates above the first intermediate position.

2. The method according to claim 1, wherein any portion of the liquid nitrogen fraction (54) produced in the top condenser (105) of the medium-pressure tower (104) is not introduced into the low-pressure tower (102).

3. The method according to any one of the preceding claims, wherein the first and second portions (53, 362) of the third column top nitrogen (50) account for at least 95%, particularly at least 98% or 100%, of the top gas of the medium-pressure column (104).

4. The method according to any one of the preceding claims, wherein no portion of the first top nitrogen from the high-pressure tower (101) is directed to the main heat exchanger (9), or less than 5%, particularly less than 2%, is directed to the main heat exchanger (9) and subsequently removed as a product.

5. The method according to any one of the preceding claims, wherein refrigeration is generated by a cryogenic expansion turbine, the cryogenic expansion turbine being fed at least by a gaseous oxygen-enriched fraction (69) from the low-pressure tower (102), the cryogenic expansion turbine preferably being a single cryogenic gas expansion turbine.

6. The method according to any one of the preceding claims, wherein any portion of the recirculated nitrogen is not turbine expanded.

7. The method according to any one of the preceding claims, wherein the top condenser (108) of the crude argon tower (107) is a forced flow evaporator on its evaporation side.

8. The method according to any one of the preceding claims, wherein a first portion (35) of the first oxygen-enriched fraction (33, 34) is directly fed into the low-pressure tower (102), while a second portion (161) of the first oxygen-enriched fraction (33, 34), preferably the remaining portion of the first oxygen-enriched fraction (33, 34), is introduced as feed into the medium-pressure tower (104).

9. The method according to any one of the preceding claims, wherein the cooling medium (38) is only partially evaporated in the top condenser (105) of the intermediate pressure tower (104), and the remaining liquid (74) from the partial evaporation in the top condenser (105) of the intermediate pressure tower (104) is sent as the cooling medium to the top condenser (108) of the crude argon tower (107).

10. The method according to any one of the preceding claims, wherein a portion (35) or all of the first oxygen-enriched fraction (33, 34) is fed directly into the low-pressure tower (102) without being pre-fed into the evaporator.

11. The method according to any one of the preceding claims, wherein a portion or all (34) of the first oxygen-enriched fraction (33) is indirectly fed into the low-pressure column (102) by introducing a portion or all (34) of the first oxygen-enriched fraction (33) into the evaporator (108, 105) and feeding the evaporated portion (72, 137) and the remaining liquid portion (73) to the low-pressure column (102).

12. The method according to any one of the preceding claims, wherein the first portion of the nitrogen at the top of the third column is ultimately removed as a pressurized gaseous nitrogen product.

13. An air separation apparatus comprising a high-pressure column (101) configured to operate at a first pressure above 9 bar, a low-pressure column (102) configured to operate at a second pressure below the first pressure, and a crude argon column (107a / b / c), a main condenser (103) for liquefying first-top nitrogen from the high-pressure column (101) to prevent evaporation of the bottom liquid from the low-pressure column (102), and - Main heat exchanger (9) for cooling compressed air. - A device for introducing cooling air (8) from the main heat exchanger (9) into the high-pressure tower (101), -A device for removing first top nitrogen gas (61) from the high-pressure tower and introducing the first top nitrogen gas into the main condenser (103), -A device for removing a first oxygen-enriched fraction (33, 34) from the high-pressure tower (101) and feeding the first oxygen-enriched fraction directly or indirectly (35, 72, 73, 137, 138, 139) into the low-pressure tower (102). -A device for removing argon-rich fraction (36) from a first intermediate position of the low-pressure column (102), and a device for introducing at least a first portion (37) of the argon-rich fraction into the crude argon column (107a / b / c). - A device for extracting second top nitrogen (40) from the top of the low-pressure tower (102) and using the second top nitrogen as recirculating nitrogen (41, 42, 44, 47, 48), a heating channel in the main heat exchanger (9) for heating the recirculating nitrogen (41), a compressor (35) for compressing the heated recirculating nitrogen, a cooling channel in the main heat exchanger (9), and a device for introducing the cooled recirculating nitrogen (48) in gaseous form (48) into the high-pressure tower (101) and / or into the main condenser (103) and / or into the bottom reboiler of the separation tower (81) of the air separation device. Its features are, - A medium-pressure tower (104) operating at a third pressure lower than the first pressure and higher than the second pressure. - A means for introducing at least a portion (161, 261) of the first oxygen-enriched fraction (33, 34) as feed into the medium-pressure tower (104), -A device for introducing the second portion (38) of the argon-rich distillate as a heating medium into the bottom evaporator (106) of the medium-pressure column (104), -A device for removing nitrogen (361) from the top of the third column in the intermediate-pressure column (104), - An additional heating channel in the main heat exchanger (9) for heating the first portion (362) of the third column top nitrogen (361), and a device for removing the heated third column top nitrogen as the final gaseous nitrogen product (UHPGAN), - A device for introducing a second portion (53) of the nitrogen gas (361) from the top of the third column into the top condenser (105) of the intermediate-pressure column (104), and a device for introducing the liquid nitrogen stream generated in the top condenser (105) of the intermediate-pressure column (104) as a reflux into the intermediate-pressure column (104). - A means for removing a second oxygen-enriched fraction from the intermediate-pressure column (104) and introducing it as a cooling medium (38) into the top condenser (105) of the intermediate-pressure column (104), and a means for introducing at least a portion of the oxygen-enriched gas (36) generated in the top condenser (105) of the intermediate-pressure column (104) into the low-pressure column (102) at a second intermediate position at least 25, preferably at least 30 theoretical plates above the first intermediate position.

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