Methods and apparatus for cryogenic air separation using a mixed-gas turbine

Abstract

The present invention discloses a method and apparatus for cryogenic air separation, wherein the separation tower system comprises a high-pressure tower (12), a low-pressure tower (13), and a crude argon tower (18). A mixed gas flow (73, 74) generated by mixing gaseous oxygen (72) and a gas flow (31, 71) from the evaporation space of the argon top condenser (21) expands by doing work in a mixed gas turbine (75).

Description

[0001] This invention relates to a method and corresponding equipment for separating air at low temperatures.

[0002] The cryogenic separation of air that produces gaseous and liquid products is generally known, for example, from the following literature: H.-W. Industrial Gases Treatment, Wiley-VCH, 2006, especially Section 2.2.5, “Cryogenic Distillation”.

[0003] Cryogenic air separation units traditionally comprise separation tower systems in the form of dual-tower systems, particularly the Linde dual-tower system. They can also be systems with three or more towers. In addition to these towers used for oxygen-nitrogen separation to produce nitrogen and / or oxygen in liquid and / or gaseous forms, the separation tower system may include additional towers for recovering other air components (especially rare gases) or for producing oxygen and / or nitrogen products of particularly high purity.

[0004] In this invention, a high-pressure tower and a low-pressure tower are used, with the low-pressure tower located at least partially above the high-pressure tower and the main condenser. The method of this invention is of the pressurized type, such that the high-pressure tower operates not at the conventional pressure of about 5.3 bar (4 to 7 bar), but at a higher pressure, for example, 8 to 14 bar, preferably 9 to 13 bar. The low-pressure tower operates not at the conventional pressure of about 1.3 bar (1.2 to 1.5 bar), but at a higher pressure, for example, 2 to 5 bar, preferably 2.5 to 4.5 bar. These pressures are absolute and measured at the top of the respective towers and are also used in this invention.

[0005] If the air separator produces pressurized gaseous products, they can be compressed in a gas compressor (“external compression”). Alternatively, an “internal compression” method can be used, which involves discharging a cryogenic liquid from the tower, pressurizing (e.g., pumping) it to the desired pressure, and converting the liquid into a gaseous state by heating it, for example, in the main heat exchanger.

[0006] The object of this invention is to find a further improved air separation method, particularly for the co-production of pressurized nitrogen and argon, and a relatively high liquid yield, for example, a liquid yield (LIN equivalent [Nm3 / h]: LIN [Nm3 / h] + 1.07 x LOX [Nm3 / h] + 0.9 x LAR [Nm3 / h]) divided by the amount of pressurized GAN product in the range of 0.00 to 0.06. (In this application, all these quantities are molar quantities, unless otherwise stated.)

[0007] This objective is achieved by the method and apparatus according to the present invention.

[0008] The fraction discharged from the high-pressure column and introduced into the low-pressure column is typically the bottom fraction of the high-pressure column. At least a portion of it can be introduced directly into the low-pressure column, ultimately passing through a subcooler, or indirectly by guiding the high-pressure column fraction into the evaporation space of the argon top condenser and separately introducing the gas and residual liquid from the evaporation space of the argon top condenser into the low-pressure column.

[0009] Gaseous oxygen is typically discharged from the lower part of the low-pressure column, such as from the very bottom of the column.

[0010] An expander can be any type, such as a turbine; therefore, it can be called a "mixed gas turbine".

[0011] To enhance distillation in low-pressure columns, according to one embodiment of the invention, nitrogen recirculation can be used, directly or indirectly, to the separation column system, particularly to the high-pressure and / or low-pressure columns. The "recirculated gas" stream is a stream from the low-pressure column that is compressed in a nitrogen compressor and subsequently cooled but not liquefied in the main heat exchanger. Product gases from the low-pressure column may or may not be guided with the recirculated gas through heating in the main heat exchanger and compression in the nitrogen compressor. The cooled recirculated gas can be guided at least partially directly in gaseous form to the high-pressure column, for example, at the top or at the bottom 3 to 11 theoretical plates. An alternative is indirect introduction into the high-pressure and / or low-pressure columns, for example, by liquefying the recirculated gas in a condenser (e.g., the main condenser and / or another column reboiler) and then introducing at least a portion of the liquefied recirculated gas into the column (particularly the high-pressure and / or low-pressure column). In the first example, at least a portion of the cooled recirculated gas is introduced into the high-pressure column via the liquefaction space of the main condenser. In another example, at least a portion of the cooled recirculated gas is introduced into the low-pressure column via the liquefaction space of the bottom condenser of the pure oxygen column (preferably including subcooling the liquid in a separate passage in a subcooler and expanding the subcooled liquid in an expansion valve). For example, a first portion of the recirculated gas is guided into the high-pressure column via a first path (e.g., directly or via the main condenser), and a second portion of the recirculated gas is guided into the low-pressure column via a second path (e.g., through the bottom condenser of the pure oxygen column).

[0012] In the first variation, the cooled recirculated gas can be directly introduced into the high-pressure tower, for example, at its top. One embodiment of the invention describes a second variation in which the recirculated gas is introduced into a main condenser, liquefied therein, and then introduced as a liquid to the top of the high-pressure tower. These two variations can be combined by introducing a portion of the cold recirculated gas into the main condenser and another portion directly into the tower. The remaining portion of the recirculated gas can be used at different locations within the facility.

[0013] According to one embodiment of the present invention, pressurized pure argon product can be generated through internal compression. A portion of the total argon product can be produced in liquid form and stored in a tank.

[0014] According to one technical solution of the present invention, the crude argon column can be in the form of a split column. It has at least two parts. In principle, it can have three or more parts.

[0015] According to one embodiment of the present invention, the separation may further include a pure oxygen tower. The feed liquid to the pure oxygen tower comes from the bottom of the crude argon tower or from the middle point of the crude argon tower, for example, from several theoretical plates above the bottom.

[0016] This type of pure oxygen tower is preferably arranged below the first part of the crude argon tower and within a common container with the first part of the crude argon tower.

[0017] According to one embodiment of the invention, the pure oxygen tower preferably has a bottom reboiler, which can be heated by gaseous nitrogen from the high-pressure tower and / or by a portion of the cooled recirculated gas, which does not directly enter the high-pressure tower—see another embodiment of the invention. The recirculated gas is preferably at least partially liquefied in the bottom reboiler of the pure oxygen tower and then sent as reflux liquid to the high-pressure or low-pressure tower.

[0018] In operating modes where not all argon products are required, an argon-oxygen mixture can be discharged from the crude argon column via an intermediate gas outlet according to one embodiment of the invention. This feature reduces the load on the crude argon column. The argon-oxygen mixture is heated in the main heat exchanger to restore its energy.

[0019] This specific implementation applies to both single-section crude argon columns and split-flow crude argon columns. In the latter case, the intermediate gas outlet can be located in any section of the crude argon column. Preferably, it is located at an intermediate height in the second section.

[0020] In this invention, according to one technical solution of the invention, using a diversion low-pressure tower can be advantageous.

[0021] In a variation of the method, according to one embodiment of the invention, it is preferable that no recirculated gas is present, and the top gas of the high-pressure tower (12) is discharged as a pressurized gaseous nitrogen product (302). Alternatively or additionally, the top gas (64, 65) from the low-pressure towers (13, 113 / 213) is compressed in a nitrogen compressor and discharged as a pressurized gaseous nitrogen product, particularly by mixing it with the heated top gas from the high-pressure tower (12). The nitrogen compressor preferably does not compress other streams, particularly the recirculated gas.

[0022] The invention and further details thereof are described below with reference to embodiments shown in the accompanying drawings.

[0023] Figure 1 A first embodiment of the invention with a single-section low-pressure tower is shown.

[0024] Figure 2 A second embodiment with a diversion low-pressure tower is shown, and

[0025] Figure 3 A third embodiment is shown in which GAN products are partially discharged from the top of a high-pressure tower.

[0026] exist Figure 1 In this implementation, atmospheric air (AIR) 1 flows through filter 2 to the main air compressor 3 and is compressed thereto to a pressure of approximately 11 to 12 bar. The compressed air stream is cooled in coolers 4 and 5 and sent to separator 6, from which liquid water (H2O) is discharged. The air from separator 6 is sent to purification unit 7, where water vapor, carbon dioxide, and other impurities are removed by adsorption. The purified air 8 is introduced into the main heat exchanger 9. The total feed air is completely cooled up to the cold end of the main heat exchanger 9 and then introduced into the high-pressure tower 12 of the twin towers, which also includes a low-pressure tower 13 and a main condenser 14.

[0027] Figure 1 The separation tower system of the proposed implementation consists of two towers 12 / 13, a pure oxygen tower 16, a methane removal tower 17, a single-section crude argon tower 18, and a pure argon tower 19. The pure oxygen tower has a bottom reboiler 20, the crude argon tower has a top condenser 21, and the pure argon tower has a top condenser 22 and a bottom reboiler 23. All these condensers and reboilers, as well as the main condenser 14, are condenser-evaporators, each with its own liquefaction space and evaporation space. The exception is the bottom reboiler 23 of the pure argon tower 19, which is heated by sensible heat.

[0028] The crude liquid oxygen 24 from the bottom of the high-pressure column 12 is cooled in the subcooler 25. A first portion 27 of the cooled crude liquid oxygen 26 is partially fed through the bottom reboiler 23 of the pure argon column and then introduced into the evaporation space of the top condenser 21 of the crude argon column 18. The remaining liquid 28 is sent to the low-pressure column 13. A first portion 30 of the evaporation section 29 is also sent to the low-pressure column. The second portion 31 is considered as the "stream with a higher nitrogen content" 31 according to the invention and will be described in detail later.

[0029] The second portion 32 of the cooled crude liquid oxygen 26 is introduced into the evaporation space of the top condenser of the pure argon column 19. The remaining liquid 33 is sent to the low-pressure column 13. The evaporation portion 34 mixes with the evaporation portion 29 from the evaporation space of the top condenser 21 of the crude argon column 18. It then enters the low-pressure column 13 or the "stream with higher nitrogen content" 31.

[0030] Most of the gaseous nitrogen 35 from the top of the high-pressure tower 12 is at least partially liquefied in the main condenser 14. The remaining portion 37 is at least partially liquefied in the bottom reboiler of the pure oxygen tower. The liquid nitrogen from the bottom reboiler of the pure oxygen tower is cooled in the subcooler 25. The cooled liquid nitrogen 39 is sent to the top of the low-pressure tower 13.

[0031] Liquid nitrogen 40 from the main condenser 14 is partially returned to the top of the high-pressure tower 12. Another portion 42 is cooled in the subcooler 25. The first portion of the cooled liquid nitrogen 43 is sent to the top of the low-pressure tower 13, while the second portion 45 is discharged as pure liquid nitrogen product (PLIN).

[0032] The gaseous argon-containing fraction, namely the argon transition fraction 46, from the low-pressure column 13 is introduced into the bottom of the methane removal column 17. Conversely, the bottom liquid 47 of the methane removal column 17 is reintroduced into the low-pressure column 13. This bottom liquid contains almost all the methane from fraction 46, ensuring that the top of the methane removal column 17 is methane-free. The top gas 48 of this column, along with the top gas 80 from the pure oxygen column 16, is sent to the bottom of the crude argon column 18.

[0033] The bottom liquid 78 of the crude argon column 18 is lifted by pump 79. A first portion 49, as methane-free reflux, enters the pure oxygen column 16. Ultra-high purity liquid oxygen 50 is discharged from the bottom of the pure oxygen column 16 and directed to storage tank 51. The liquid in the tank can be pressurized in the tank or by a pump (not shown) using a tank compressor. The high-pressure liquid oxygen can be heated in the main heat exchanger 9 and recovered as an internally compressed ultra-high purity gaseous oxygen product (GOXIC).

[0034] The second portion 52 of the bottom liquid 78 of the crude argon tower 18 is fed into the top of the methane removal tower 17.

[0035] The liquefaction space of the top condenser 21 of the crude argon tower 18 is a bath condenser. At its top, crude argon stream 58 is discharged from the crude argon tower 18 and introduced into the pure argon tower 19. Exhaust gas 60 is discharged from the top of the pure argon tower and released into the atmosphere (ATM). At the bottom, pure argon product 59 is recovered and sent to an internal compressor (line 62) with pump 61 for heating in the main heat exchanger 9. At the hot end (line 63) of the main heat exchanger 9, the internally compressed gaseous argon product (GARIC) is discharged in pressurized form.

[0036] The gaseous nitrogen fraction 64 from the top of the low-pressure column 13 is partially used as recirculation gas and is first preheated in the subcooler 25. The preheated gaseous nitrogen fraction 65 is sent to the cold end of the main heat exchanger 9 and fully heated therein. The heated gaseous nitrogen fraction 66 is compressed in the nitrogen compressor 67 to a product pressure preferably 8 bar to 15 bar, more preferably 9.5 bar to 12.5 bar. The compressor 67 has an aftercooler. The compressed nitrogen fraction 68 is separated into a product fraction 69, which is discharged as pressurized gaseous nitrogen product (PGAN) and recirculation gas 70. The pressurized recirculation gas is fully cooled again in the main heat exchanger 9. The cooled recirculation gas (89) is mixed with gaseous nitrogen 35 from the top of the high-pressure column 12, i.e., liquefied in the main condenser 14 or in the reboiler 20 at the bottom of the pure oxygen column. Thus, a portion of the recirculation gas (now liquid) enters the high-pressure column via line 41.

[0037] Pressurized gaseous oxygen is generated through internal compression. Liquid oxygen 84 from the bottom of the low-pressure tower 13 (or from the evaporation space of the main condenser 14) is pumped to the desired product pressure in pump 85, fully heated in the main heat exchanger 9, and finally recovered as an internally compressed product (GOXIC) via line 86.

[0038] The aforementioned "high nitrogen content stream" 31, originating at least partially from the evaporation space of the top condenser 21 of the crude argon tower 18, is heated in the subcooler 25. The heated stream 71 mixes with a gaseous oxygen stream 72 from the bottom of the low-pressure tower 13. The mixed gas 73 is partially heated to an intermediate temperature of 150 K to 230 K in the main heat exchanger 9 and expands by performing work in a mixed gas turbine 75 operating as a generator turbine. The expanded mixed gas 76 is reintroduced into the main heat exchanger 9 and fully heated. The heated low-pressure mixed gas 77 / 78 can be released to the atmosphere (ATM) or sent as regeneration gas to the purification unit 7.

[0039] exist Figure 1 In this embodiment, some of the gas rising in the crude argon tower 18 can be discharged via intermediate gas outlet 81 to reduce the amount of argon products 59 / 62 / 63 and thereby reduce energy consumption. The discharged gas 82 is fully heated in a separate channel of the main heat exchanger 9. The heated gas 83 can be mixed with the expanding mixed gas 77 and released into the atmosphere or used as regeneration gas in the purification unit 7.

[0040] Figure 2 Methods and Figure 1 The main difference lies in the split argon column and the split low-pressure column. The above discusses... Figure 1 The explanation for Figure 2 The corresponding steps and units are also valid. Figure 2 The reference numerals in the attached figures are taken from... Figure 1In order to identify the same or similar features and functions.

[0041] The crude argon column is divided into a first section 118 and a second section 218, with an argon top condenser 21 arranged on top of the second section 218. A gas fraction 190 from the top of the first section 118 is introduced into the bottom of the second section 218. At least a first portion 193 of the bottom liquid 191 of the second section 218 is introduced into the top of the first section 118.

[0042] The low-pressure column is divided into a bottom section 113 and a top section 213. Unlike a single-section low-pressure column, these two sections are arranged side by side. A gaseous connecting stream 195 is taken from the top gas 194 of the bottom section and introduced into the bottom of the top section 213. A liquid connecting stream 196 is discharged from the bottom of the top section 213 and delivered to the top of the bottom section 213 via the bottom of the first section 118 of the crude argon column, line 197, pump 198, and line 199. Another portion of the top gas 194 in the bottom section 113 of the low-pressure column is considered as argon transition fraction 46 and is introduced into the bottom of the first section 118 of the crude argon column. The bottom liquid of the first section 118 (mixed with the bottom liquid 196 from the top section 213 of the low-pressure column) is delivered to the top of the bottom section 113 of the low-pressure column via line 197, pump 198, and line 199.

[0043] The lowermost section 117 of the first part 118 of the crude argon tower also serves as a methane removal tower. At an intermediate height directly above the lowermost section 117, the first part 118 is connected to the top of the pure oxygen tower 16 via a liquid line 149 and a gas line 180.

[0044] In this specific embodiment of the multi-tank system 200 according to US10209004 B2, ultra-high purity liquid oxygen 50 from the bottom of the pure oxygen tower 16 is pressurized and then fully heated (via line 201) in the main heat exchanger 9. The warm ultra-high purity oxygen 202 is recovered as a final product (UHPGOX). Liquid oxygen 84 from the bottom of the low-pressure tower 113 (or from the evaporation space of the main condenser 14) is subcooled in the subcooler 25 (not shown) and then discharged as liquid oxygen product (LOX).

[0045] Cooled recirculated gas 89 is fed into the liquefaction space of the main condenser 14 (along with some top nitrogen from the top nitrogen 35 of the high-pressure tower 12). The recirculated gas is liquefied there. A first portion 41 of the liquefied recirculated gas is fed into the top of the high-pressure tower 12; second portions 42 and 44 of the liquefied recirculated gas are fed into the top of the low-pressure tower 213.

[0046] Alternatively, the cooled recirculated gas 89 can be divided into a first portion for the main condenser and a second portion introduced into the liquefaction space of the bottom reboiler of the pure oxygen tower 16. In another alternative, the recirculated gas is fed entirely into the liquefaction space of the bottom reboiler of the pure oxygen tower 16, supplemented if necessary by some gaseous nitrogen 35 from the top of the high-pressure tower 12.

[0047] Figure 3 In many parts with Figure 2 Similar or identical, but different in two main aspects:

[0048] - Gaseous nitrogen originates from the top of the high-pressure tower and is discharged as pressurized gaseous nitrogen product (UHPGAN) via lines 300, 301 and 302.

[0049] - There is no recirculated gas. All top gaseous nitrogen 64 / 65 / 66 / 369 from low-pressure tower 213 is discharged downstream of nitrogen compressor 67 as pressurized gaseous nitrogen product (UHPGAN) by mixing it with nitrogen from high-pressure tower 12.

[0050] This invention can also be applied to systems that do not have a methane removal tower and / or a pure oxygen tower.

Claims

1. A method for cryogenic separation of air in a separation tower system, the separation tower system comprising a high-pressure tower (12), a low-pressure tower (13), a main condenser (14), and a crude argon tower (18), the main condenser being a condenser-evaporator having liquefaction space and evaporation space, and the top of the high-pressure tower and the bottom of the low-pressure tower being in a heat exchange relationship, the crude argon tower having an argon top condenser (21), the argon top condenser being a condenser-evaporator having liquefaction space and evaporation space, the method comprising -Compression (3) Total feed airflow (1), - The compressed feed air (8) is cooled in the main heat exchanger (9). - Introduce at least a portion of the feed air into the high-pressure tower (12), - At least one fraction (24, 26) from the high-pressure column (12) is introduced directly or indirectly into the low-pressure column (13). - The argon transition fractions (46, 48) are introduced from the low-pressure column (13) into the crude argon column (18). - The liquid cooling fraction (27) from the high-pressure tower (12) is introduced into the evaporation space of the argon top condenser (21). - A gaseous oxygen stream (72) is discharged from the low-pressure tower (13). - The gaseous oxygen stream (72) is mixed with another gas stream having a higher nitrogen content than the gaseous oxygen stream to form a mixed gas stream (73). -The mixed gas flow is heated in the main heat exchanger (9) to form a heated mixed gas flow (74). - The heated mixed gas stream (74) is expanded by work in the expander (75) to form an expanded mixed gas stream (76), and -The expanding mixed gas stream (76) is fully heated in the main heat exchanger (9). Its features The aforementioned streams (29, 31, 71) with higher nitrogen content are discharged from the evaporation space of the argon top condenser (21).

2. The method according to claim 1, characterized in that... - The gaseous nitrogen fractions (64, 65) from the low-pressure tower (13) are used as recirculation gas. - The recirculated gas is heated in the main heat exchanger (9) to form heated recirculated gas (66). The heated recirculating gas (66) is compressed in a nitrogen compressor (67) to form compressed recirculating gas (70). The compressed recirculated gas (70) is cooled in the main heat exchanger (9) to form cooled recirculated gas (89), and is discharged from the main heat exchanger (9) in gaseous form. - Introduce at least a first portion of the cooled recirculated gas (89) into the separation tower system in gaseous or liquefied form.

3. The method according to claim 2, characterized in that, At least a portion of the cooled recirculated gas (89) is introduced (36, 40, 41) into the high-pressure tower (12) via the liquefaction space of the main condenser (14).

4. The method according to any one of claims 1 to 3, characterized in that... -The separation tower system also includes a pure argon tower (19), - The crude argon stream (58) is discharged from the crude argon tower (18) or the argon top condenser (21). - The crude argon stream (58) is introduced into the pure argon tower (19). - Liquid pure argon stream (59) is discharged from the pure argon tower (19), - The liquid pure argon stream (59) is pressurized (61) in a liquid state to form a pressurized pure argon stream (62). - The pressurized pure argon stream (62) is heated in the main heat exchanger (9), and - Finally, it was recovered as a pressurized argon product (63).

5. The method according to claim 1, characterized in that, The crude argon column is divided into a first section (118) and a second section (218), with the argon top condenser (21) arranged on top of the second section (218), whereby the gas fraction (190) from the top of the first section (118) is introduced into the bottom of the second section (218), and at least a first portion (193) of the bottom liquid (191) of the second section is introduced into the top of the first section (118).

6. The method according to claim 5, characterized in that... -The separation tower system also includes a pure oxygen tower (16), - The liquid fractions (49, 149) from the crude argon column (18, 118) are introduced into the top of the pure oxygen column (16), and - Liquid pure oxygen fraction (50) is discharged from the bottom of the pure oxygen tower (16).

7. The method according to claim 6, characterized in that, The pure oxygen tower (16) is arranged directly below the methane removal tower (17), with only a single bottom / top plate between them.

8. The method according to claim 6 or 7, characterized in that, The pure oxygen tower (16) has a bottom reboiler (20), which is a condenser-evaporator with a liquefaction space and an evaporation space.

9. The method according to claim 8, characterized in that, - The gaseous nitrogen fractions (64, 65) from the low-pressure tower (13) are used as recirculation gas. - The recirculated gas is heated in the main heat exchanger (9) to form heated recirculated gas (66). The heated recirculating gas (66) is compressed in a nitrogen compressor (67) to form compressed recirculating gas (70). The compressed recirculated gas (70) is cooled in the main heat exchanger (9) to form cooled recirculated gas (89), and is discharged from the main heat exchanger (9) in gaseous form. - Introducing at least a first portion of the cooled recirculated gas (89) into the separation tower system in gaseous or liquefied form, and The second portion (37) of the cooled recirculated gas (89) is introduced into the liquefaction space of the reboiler (20) at the bottom of the pure oxygen tower.

10. The method according to any one of claims 1 to 3, 5 to 7 and 9, characterized in that, The argon-oxygen mixture (81) is discharged from the crude argon tower (18, 118) at least temporarily via the intermediate gas outlet, and the argon-oxygen mixture is heated in the main heat exchanger (9).

11. The method according to any one of claims 1 to 3, 5 to 7 and 9, characterized in that... -The low-pressure tower is divided into a bottom section (113) and a top section (213). - The gaseous connecting stream (194, 195) is discharged from the top of the bottom section (113). - The gaseous connecting flow (195) is introduced into the bottom of the top section (213). - Liquid connecting streams (196, 197, 199) are discharged from the bottom of the top section (213), and - The liquid connection flow is introduced into the top of the bottom section (113).

12. The method according to any one of claims 1 to 3, 5 to 7 and 9, characterized in that... - A portion (300) of the top gas of the high-pressure tower (12) is heated in the main heat exchanger (9) to form heated gas (301), and - The heated gas (301) is discharged as pressurized gaseous nitrogen product (302).

13. The method according to any one of claims 1 to 3, 5 to 7 and 9, characterized in that... - The top gas (64, 65) from the low-pressure tower (13, 113 / 213) is heated in the main heat exchanger (9) to form heated gas (66). The heated gas (66) is compressed in a nitrogen compressor (67) to form a compressed gas (369), and - The compressed gas (369) is discharged as pressurized gaseous nitrogen product (302).

14. The method according to any one of claims 2 to 3 and 9, characterized in that, The cooled recirculated gas (89) is introduced into the high-pressure tower (12) in gaseous form.

15. The method according to claim 2, characterized in that, At least a first portion of the cooled recirculated gas (89) is introduced into the high-pressure tower (12) and / or the low-pressure tower (13) in gaseous or liquefied form.

16. The method according to claim 13, characterized in that, The compressed gas (369) is discharged as a pressurized gaseous nitrogen product (302) by mixing the compressed gas (369) with the heated top gas from the high-pressure tower (12).

17. An apparatus for cryogenic air separation, the apparatus comprising a separation tower system including a high-pressure tower (12), a low-pressure tower (13), a main condenser (14), and a crude argon tower (18), the main condenser being a condenser-evaporator having liquefaction space and evaporation space, and configured to allow heat exchange between the top of the high-pressure tower and the bottom of the low-pressure tower, the crude argon tower having an argon top condenser (21), the argon top condenser being a condenser-evaporator having liquefaction space and evaporation space, and the apparatus further comprising... -The main air compressor (3) is used to compress the total feed airflow (1). -The main heat exchanger (9) is used to cool the compressed feed air (8). -A device (19) for introducing at least a portion of the feed air into the high-pressure tower (12), - An apparatus for directly or indirectly introducing at least one fraction (24, 26) from the high-pressure column (12) into the low-pressure column (13), - An argon transition line for introducing the argon transition fraction (46, 48) from the low-pressure column (13) to the crude argon column (18), - A means for introducing the liquid cooled fraction (27) from the high-pressure tower (12) into the evaporation space of the argon top condenser (21), -A device for discharging gaseous oxygen stream (72) from the low-pressure tower (13), - An apparatus for mixing the gaseous oxygen stream (72) with another gas stream having a higher nitrogen content than the gaseous oxygen stream to form a mixed gas stream (73), - A device for introducing the mixed gas flow into the main heat exchanger (9) for heating to form a heated mixed gas flow (74), - An expander (75) for expanding the heated gas mixture (74) to form an expanded gas mixture (76), and -A device for fully heating the expanded mixed gas stream (76) in the main heat exchanger (9), Its features The apparatus (29, 31, 71) for mixing the gaseous oxygen stream (72) with another gas stream having a higher nitrogen content is connected to the evaporation space of the argon top condenser (21).

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