Air separation plant and process for separating air with split main heat exchanger

Abstract

This air separation plant and the respective process comprise a main heat exchanger (10) consisting of block(s) of a first or a second block type (11, 12), each block of a block type has the same internal structure concerning the two main passage groups (36, 40; 37, 41) for warming two main returns streams, the blocks of the first and second types both comprising one or more identical or similar passage groups for cooling feed air (15a, 15b) directed to the distillation system. the block(s) of the first type (11) comprising a passage group for guiding and warming pumped liquid oxygen (36, 37) and a passage group for impure gaseous nitrogen (31, 13) withdrawn from an intermediate point of the low-pressure column (18b), the block(s) of the second type (12) comprising a passage group for guiding and warming pumped liquid oxygen (36, 37) and a passage group for gaseous nitrogen (22, 23, 14) withdrawn from the top of the low-pressure column (18b), but no passage for impure gaseous nitrogen (31, 13) withdrawn from an intermediate point of the low-pressure column (18b).

Description

[0001] P40279-EP / P40279 PIF + P40325 PIF

[0002] 10.11.2025 - Imhof

[0003] 1

[0004] Description

[0005] Air Separation Plant and Process for Separating Air with Split Main Heat Exchanger

[0006] Split main heat exchangers are used in large air separation plants to realize a main heat exchanger, which cools feed air against cold return streams, in several blocks. Those blocks are plate-fin heat exchangers, in particular brazed aluminum plate-fin heat exchangers as described in CEP, December 2000, 39-49 or Chemical Engineering / August 1987, pp 131-135. A respective air separation plant is disclosed in DE 4204172 A1. This configuration is, however, applicable only for cases where the oxygen product is withdrawn from the distillation in gaseous form. Furthermore, the main heat exchanger shown in the configuration of DE 4204172 A1 is made up of just three blocks, one for each of the following streams from the low-pressure column: top nitrogen, impure nitrogen and oxygen, the impure nitrogen being withdrawn from an intermediate stage of the low-pressure column.

[0007] The invention seeks for a plant with internal compression of oxygen, meaning oxygen is withdrawn in liguid form from the distillation, pumped to a higher pressure and then vaporized and / or warmed in the main heat exchanger. The problem underlying the invention is to find a configuration allowing internal compression of oxygen and simultaneously minimizing piping effort for nitrogen products out of the low-pressure column.

[0008] Such problem is solved by the combination of the features of claim 1.

[0009] All blocks are used for the internally compressed oxygen, which optimizes the pressurized oxygen generation. As impure nitrogen and top nitrogen each go to the blocks of one type only, piping for those streams is minimized.

[0010] The blocks of each type can have identical internal structure. Alternatively, they have similar internal structure, meaning at least the three largest passage groups are identical in structure. If there are further, smaller passage groups, they may be different for the different blocks of a block type, so that those blocks are not completely identical, but similar. The blocks of different types are guite similar and normally differ just in a P40279-EP / P40279 PIF + P40325 PIF

[0011] 10.11.2025 - Imhof

[0012] 2 single passage group; in special embodiments, the blocks of the different types may be even identical. Both measures minimize engineering and manufacturing effort.

[0013] In practical applications to large air separation plants, the main heat exchanger may consist of six, eight, ten or even more blocks of similar or identical dimensions and capacity. In accordance with the ratio of impure nitrogen to top nitrogen, a number of main heat exchanger blocks are dedicated to impure and top nitrogen, i.e. they are of the first or second block type. To ensure a reasonable design, this ratio is chosen by the plant designer, if possible. Depending on product requirements, the similarity of the flow of impure and top nitrogen through each block may be more or less similar; consequently, the blocks of the two types are more or less similar or identical. Of course, flows - and thereby passage structures - may be varied to optimize power consumption of the plant. For a large air separation plant with ten main heat exchanger blocks, a ratio of 0.4 can be chosen. There are e.g., four blocks of the first type and six blocks of the second type.

[0014] In addition to the return streams mentioned in claim 1 , an additional nitrogen product stream may be directly withdrawn from the high-pressure column and distributed to all or a part of the blocks.

[0015] Although the invention works with a main heat exchanger comprising exactly two blocks, the application of the invention to plants with a higher number of blocks is preferred, e.g. if the main heat exchanger comprises at least four blocks, two blocks of the first type and two blocks of the second type. The number of blocks can be higher, e.g. 8, 12, 16 or 20.

[0016] The plant of the invention is particularly suited for high air pressure (HAP) processes, where the total feed air is compressed not only to the intermediate pressure, the high- pressure column is operated at, but to a considerably higher pressure, e.g. at least 5 bars above the intermediate pressure. As the blocks of the main heat exchanger of the invention all comprise the same air passages, the system is well suited for a process with the same pressure in the total feed air. The invention is suited as well for MAC- BAC processes, the main air compressor (MAC) compressing the total feed air to an intermediate pressure, preferably the operating pressure of the high-pressure column P40279-EP / P40279 PIF + P40325 PIF

[0017] 10.11.2025 - Imhof

[0018] 3 plus line losses, and just a portion of the feed air being further compressed in a booster air compressor (BAC).

[0019] If the ratio of impure nitrogen and top nitrogen matches the block number, the system is at its optimum without additional measure. But the ratio between the impure nitrogen stream and the top nitrogen product stream doesn't necessarily fit with an optimum number of heat exchanger blocks (cores). For example, no equal flow / block distribution can be reached if e.g., eight (and not ten) cores are applied. The "flow maldistribution" would lead to increase in plant power consumption, so the optimum core number will be either not chosen or is burdened with a certain power penalty.

[0020] In a particular variant of the invention comprising the withdrawal of nitrogen product directly from the high-pressure column, this further problem is solved by sending such nitrogen product through all blocks, controlling the single flows through each block and thereby balancing the heat transfer between the blocks. Thereby, the optimum number of blocks can be chosen in terms of capacity and manufacturing. Still the heat transfer in the blocks can be simultaneously optimized ("balancing"). Such balancing is preferably used for the design operation in most cases and for variable operation in all cases.

[0021] The balancing of the heat exchanger blocks means that the heat capacities of "cold" streams (M x cp, whereas M is a total flow and cp an average heat capacity) in both heat exchanger types are equalized resulting in unchanged outlet conditions for all "warm" streams distributed between all blocks.

[0022] The plant may comprise one or two (or even more) turbines for work-expanding portions of the feed from an intermediate temperature of the main heat exchanger. In this case, the respective turbine air stream(s) are split to all blocks, cooled in respective passage groups in all blocks preferably to an intermediate temperature, then reunified and sent to the respective turbine.

[0023] For balancing, a nitrogen turbine, fed by gaseous nitrogen from the top or an intermediate position of the high-pressure column may be used for balancing. The three possible methods are described in claim 7. P40279-EP / P40279 PIF + P40325 PIF

[0024] 10.11.2025 - Imhof

[0025] 4

[0026] In addition or as an alternative to the above balancing by a pressurized nitrogen product from the high-pressure column, the balancing might be partially or completely made by "air balancing" using one or more air streams to the high-pressure column for the purpose described in claim 8.

[0027] Sometimes there is one or are more special additional return streams with particularly low amount of less than 5 mol-% of the total feed air amount during normal operation of the plant. In that case, it would be expensive to have a separate special return passage in all blocks of a block type. Consequently, just a part of the blocks of the respective type have one or more special return passages, the others do not. In that case, not all blocks of a particular block type are identical, but there are two similar groups. Such special return stream has, in practice, less than 5 mol-% of the total feed air stream, or even about 2 mol-%. It may be formed by internally compressed nitrogen, internally compressed argon, gaseous argon or gaseous oxygen.

[0028] In most air separation plants, a subcooler comprising one or more blocks is used for cooling liquid streams from the columns against cold gaseous streams from the low- pressure column as top nitrogen and impure nitrogen from the low-pressure column. In the invention, the subcooler may consist of a single block or two or more identical blocks in parallel, wherein both nitrogen streams go through all of blocks.

[0029] Alternatively there may be two subcooler block types similar to the two main heat exchanger block types for top nitrogen and impure nitrogen separately. In another variant, the subcooler blocks may be integrated into the main heat exchanger blocks.

[0030] From Augustin Rampp's patent EP 2503269 B1 it is known to suspend subcooler blocks on main heat exchanger blocks. Such technology may be applied in the invention by using one or more subcooler blocks which is / are suspended on a pair of main heat exchanger blocks via connection pipelines between the subcooler and the respective main heat exchanger blocks.

[0031] The invention and further details of the invention are described with reference to the drawings: P40279-EP / P40279 PIF + P40325 PIF

[0032] 10.11.2025 - Imhof

[0033] 5

[0034] Figure 1 is a schematic representation of a first embodiment of the invention applied to a HAP process,

[0035] Figure 2 is a schematic representation of a second embodiment of the invention applied to a MAC-BAC process,

[0036] Figures 3 to 6B show several variants of a second type of embodiment applied to a HAP process and

[0037] Figures 7 to 9 show several combinations of main heat exchangers and subcoolers applicable in all embodiments and variants of the invention.

[0038] In Figure 1 , a process of the HAP (high air pressure) type is shown, where the total feed air is compressed to a particular high pressure. Atmospheric air (AIR) 1 flows as feed air through a filter 2 to main air compressor (MAC 3). The MAC 3 comprises in reality two parallel compressors of equal capacity. Downstream aftercooler 4, the feed air 5 has a high air pressure of 16.8 bar. The pressurized feed air 5 is purified in a purification unit 6. After dividing some instrument air (Cust. Air) 8 from the purified feed air, the remaining feed air 9 is split onto the blocks of the main heat exchanger 10. Contrary to the simplified representation in the drawing, the main heat exchanger 10 of the embodiment does not contain just two blocks 11 , 12, but ten blocks in total. The two blocks shown in the drawing are representative for the two types of blocks used in this system, a first type of blocks 11 and a second type of blocks 12. The blocks 11 of the first type comprise a passage group for impure gaseous nitrogen 13 withdrawn from an intermediate point of the low-pressure column, but no passage for gaseous nitrogen 14 withdrawn from the top of the low-pressure column. The blocks 12 of the second type comprise a passage group for gaseous nitrogen withdrawn from the top of the low-pressure column 14, but no passage for impure gaseous nitrogen 13 withdrawn from an intermediate point of the low-pressure column. In the real embodiment, the main heat exchanger consists of four blocks 11 of the first type and six blocks 12 of the second type.

[0039] A first portion of the feed air under high air pressure flows through passage groups 15a, 15b, through the full length of the main heat exchanger 10 as the so-called throttle stream and is finally fed to the high-pressure column 17, being part of the distillation system further comprising a low-pressure column 18a / 18b and a main condenser 19 for realizing the heat exchange relationship between the two main columns. The invention does not need a split low-pressure column as shown here, it could likewise be realized by a single-part low-pressure column arranged on top of the high-pressure P40279-EP / P40279 PIF + P40325 PIF

[0040] 10.11.2025 - Imhof

[0041] 6 column or beneath the high-pressure column. All other parts of the distillation system as krypton-xenon concentration column 20, conventional argon rectification 21 or connection point 51 , 52, 53 for later adding a neon production are also optional.

[0042] Gaseous nitrogen withdrawn from the top of the low-pressure column (LPGAN 22, 23) is warmed in a subcooler 24 and then sent to the main heat exchanger blocks 12 of the second type via line(s) 14. The warmed LPGAN 26 may be withdrawn as product 27 or - at least temporarily - sent to the atmosphere (ATM) via line 28. A liquid nitrogen product 29 may also be withdrawn from the top of the low-pressure column 18b.

[0043] Alternatively or temporarily, liquid nitrogen 30 from a tank external to the air separation plant may be introduced here as a source for refrigeration.

[0044] Impure gaseous nitrogen 31 (sometimes called waste nitrogen) is withdrawn from an intermediate point of the low-pressure column 18b warmed in a subcooler 25 and then sent to the main heat exchanger blocks 11 of the first type via line(s) 13. The warmed impure nitrogen 32 may be used as regeneration gas in the purification unit 6.

[0045] In the system, pressurized gaseous nitrogen GOX IC1 is produced by internal compression. Liquid oxygen 33 is withdrawn either from the bottom of the low-pressure column 18a - or, as shown here, some trays above the bottom - pumped to a high product pressure of e.g. 40 bar in pump 34 and then split to all blocks 11 , 12 via lines 36, 37. After warming to ambient temperature, the oxygen streams are reunified and withdrawn as product stream 38.

[0046] As an optional product, pressurized nitrogen product 39, 40, 41 can be withdrawn from the high-pressure column 17 at its top or - as shown in Figure 1 - some theoretical or practical trays below. It is likewise split to all blocks 11, 12 via lines 40, 41 and reunified after being warmed from lines 48 / 49 to stream 42. A portion 43 may be used as seal gas. The bulk can be recovered as final pressurized gaseous nitrogen product (PGAN 44), optionally after being further compressed in a product compressor 45.

[0047] A further optional product of the system is liquid oxygen LOX 46. P40279-EP / P40279 PIF + P40325 PIF

[0048] 10.11.2025 - Imhof

[0049] 7

[0050] As an addition stream, an argon-enriched stream 80 withdrawn from the argon rectification section 21 may be optionally warmed in the main heat exchanger 11 , 12. It is then split to all blocks.

[0051] A portion 60a, 60b of the feed air is withdrawn from each block of the main heat exchanger at the same first intermediate temperature and unified to a partial air stream 61 , which is compressed in a turbine-booster 62. The boosted partial air stream 63 is split to the blocks again (lines 64a, 64b) and reintroduced into the main heat exchanger 10 at a second intermediate temperature, which is higher than the first intermediate temperature. The first partial stream is further cooled and withdrawn at a third intermediate temperature, which is lower than the first intermediate temperature. The further cooled first partial air stream 65a, 65b, 66 is introduced into a first turbine 67 to be work expanded. The work expanded first partial air stream 68 is fed via line 69 to the bottom of the high-pressure column 17 as gaseous feed.

[0052] At a fourth intermediate temperature, even lower than the third intermediate temperature, a second partial air stream 70a, 70b, 71 is withdrawn from the main heat exchanger 10 and sent to second turbine 72 to be work expanded.

[0053] The second turbine 72 is preferably realized as a single machine and as generatorturbine. Combination of the first turbine 67 and the booster 62 can be realized by two identical machines being connected in parallel.

[0054] The invention, however, can be applied to any single-turbine system and to any multiple-turbine system.

[0055] Figure 2 shows a different class of air separation process, a MAC / BAC system. In many other details, it is similar to the HAP process of Figure 1 .

[0056] In Figure 2, atmospheric air (AIR) 1 flows as feed air through a filter 2 to main air compressor (MAC 3). The MAC 3 comprises in reality two parallel compressors of equal capacity. Downstream aftercooler 4, the feed air 5 has a intermediate air pressure of 5.7 bar. The pressurized feed air 5 is purified in a purification unit 6. After dividing some instrument air (Cust. Air) 8 from the purified feed air, the remaining feed air 9 is split onto the blocks of the main heat exchanger. Contrary to the simplified representation in the drawing, the main heat exchanger 10 of the embodiment does not P40279-EP / P40279 PIF + P40325 PIF

[0057] 10.11.2025 - Imhof

[0058] 8 contain just two blocks 11 , 12, but ten blocks in total. The two blocks shown in the drawing are representative for the two types of blocks used in this system, a first type of blocks 11. The blocks 11 of the first type comprise a passage group for impure gaseous nitrogen 13 withdrawn from an intermediate point of the low-pressure column, but no passage for gaseous nitrogen 14 withdrawn from the top of the low-pressure column. The blocks 12 of the second type comprise a passage group for gaseous nitrogen withdrawn from the top of the low-pressure column 14, but no passage for impure gaseous nitrogen 13 withdrawn from an intermediate point of the low-pressure column. In the real embodiment, the main heat exchanger consists of four blocks 11 of the first type and six blocks 12 of the second type.

[0059] A first portion of the feed air under high air pressure flows through passage groups 15a, 15b, through the full length of the main heat exchanger 10 as the so-called throttle stream and is finally fed to the high-pressure column 17, being part of the distillation system further comprising a low-pressure column 18a / 18b and a main condenser 19 for realizing the heat exchange relationship between the two main columns. The invention does not need a split low-pressure column as shown here, it could likewise be realized by a single-part low-pressure column arranged on top of the high-pressure column or beneath the high-pressure column. All other part of the distillation system as krypton-xenon concentration column 20, conventional argon rectification 21 or connection point 51 , 52, 53 for later adding a neon production are also optional.

[0060] Gaseous nitrogen withdrawn from the top of the low-pressure column (LPGAN 22, 23) is warmed in a subcooler 24 and then sent to the main heat exchanger blocks 12 of the second type via line(s) 14. The warmed LPGAN 26 may be withdrawn as product 27 or - at least temporarily - sent to the atmosphere (ATM) via line 28. Liquid nitrogen product 29 may also be withdrawn from the top of the low-pressure column 18b. Alternatively or temporarily, liquid nitrogen 30 from a tank external to the air separation plant may be introduced here as a source for refrigeration.

[0061] Impure gaseous nitrogen 31 (sometimes called waste nitrogen) is withdrawn from an intermediate point of the low-pressure column 18b warmed in a subcooler 25 and then sent to the main heat exchanger blocks 11 of the first type via line(s) 13. The warmed impure nitrogen 32 may be used as regeneration gas in the purification unit 6. P40279-EP / P40279 PIF + P40325 PIF

[0062] 10.11.2025 - Imhof

[0063] 9

[0064] In the system, pressurized gaseous oxygen GOX IC1 is produced by internal compression. Liquid oxygen 33 is withdrawn either from the bottom of the low-pressure column 18a - or, as shown here, some trays above the bottom - pumped to a high product pressure of e.g. 40 bar in pump 34 and the split to all blocks 11, 12 via lines 36, 37. A portion 54 of the pumped oxygen 35 may be fed back to the low-pressure column 18a.

[0065] After warming to ambient temperature, the oxygen streams are reunified and withdrawn as product stream 38.

[0066] As an optional product, pressurized nitrogen product 39, 40, 41 can be withdrawn from the high-pressure column 17. It is likewise split to all blocks 11 , 12 via lines 40, 41 and reunified after being warmed from lines 48 / 49 to stream 42. A portion 43 may be used as seal gas. The bulk can be recovered as final pressurized gaseous nitrogen product (PGAN 44), optionally after being further compressed in a product compressor 45.

[0067] A further optional product of the system is liquid oxygen LOX 46.

[0068] As a further, but optional product, a nitrogen product is withdrawn from slightly below the top of the high-pressure column 17.

[0069] As an addition stream, an argon-enriched stream 47 withdrawn from argon rectification 80 may be optionally warmed in the main heat exchanger 11 , 12. It is then split to all blocks.

[0070] A portion 60a, 60b of the feed air is withdrawn from each block of the main heat exchanger at the same first intermediate temperature and unified to a partial air stream 61 , which is compressed in a turbine-booster 62. The boosted partial air stream 63 is split to the blocks again (lines 64a, 64b) and reintroduced into the main heat exchanger 10 at a second intermediate temperature, which is higher than the first intermediate temperature, the first partial stream is further cooled withdrawn at a third intermediate temperature, which is lower than the first intermediate temperature. The further cooled first partial air stream 65a, 65b, 66 is introduced into a first turbine 67 to be work expanded. The work expanded first partial air stream 68 is fed via line 69 to the bottom of the high-pressure column 17 as gaseous feed. P40279-EP / P40279 PIF + P40325 PIF

[0071] 10.11.2025 - Imhof

[0072] 10

[0073] At a fourth intermediate temperature, even lower than the third intermediate temperature, a second partial air stream 70a, 70b, 71 is withdrawn from the main heat exchanger 10 and sent to second turbine 72 to be work expanded.

[0074] The second turbine 72 is preferably realized as a single machine and as generatorturbine. Combination of the first turbine 67 and the booster 62 can be realized by two identical machines being connected in parallel.

[0075] In the embodiment of Figure 2, air balancing is used as described above.

[0076] The invention, however, can be applied to any single-turbine system and to any multiple-turbine system.

[0077] Figure 3 differs from Figure 1 in the valves 101, 102 in the warm PGAN lines 48, 49, which are not optional in this embodiment of the invention. Each block has such a valve. Whilst a valve in the line of a pressurized product line is generally not desirable, as it is always connected to pressure loss, in the invention, it turned out that those particular valves surprisingly improve the energy efficiency of the process. They allow balancing the load between the two types of blocks 10, 11 of the main heat exchanger. In a numerical example for a particular operating mode, the impure nitrogen stream 13 has a flow of 124,500 Nm3 / h and the top nitrogen 14 has a flow of 130,600 Nm3 / h (these numbers refer to the sums of flows through the blocks of the respective block type). As all other flows through the main heat exchanger 10, 11 are equal, there is an unbalancing of 6.100 Nm3 / h across the block types. Consequently, not all blocks cannot be operated at there energetic optimum.

[0078] According to the improved version of the invention as shown in Figure 2, the situation is balanced by a respective setting of the valves 101, 102, so that the flow through line 40 is 11 ,900 Nm3 / h and the flow through line 41 5,800 Nm3 / h, thereby balancing the difference in streams 13 and 14 (pressurized nitrogen balancing). Thereby, all blocks can be operated at there energetic optimum. Surprisingly the respective advantage is much higher than the loss by the throttling in valves 101 , 102. P40279-EP / P40279 PIF + P40325 PIF

[0079] 10.11.2025 - Imhof

[0080] 11

[0081] Additionally or alternatively to the air balancing of Figure 1 and the pressurized nitrogen balancing of Figure 3 further kinds of balancing may be used in the invention as shown in Figures 4 to 7.

[0082] Figure 4 shows a system with GOXIC balancing, i.e. the partial streams of the internally compressed oxygen 38 are controlled in valves 201 , 202 in order to balance the different block types.

[0083] In Figure 5, in addition to two liquid withdrawals, oxygen is taken out in gaseous form from the low-pressure column 18a (and / or likewise from the krypton-xenon concentration column 20). Such gaseous oxygen is used for balancing by valves 301 , 302. This system would work as well in a variant without withdrawal of gaseous nitrogen 40, 41 from the high-pressure column.

[0084] In the system of Figure 6A, a pressurized GAN stream 39, 40, 41 is used for balancing like in Figure 2. Contrary to Figure 3, such stream is not completely warmed in the main heat exchanger 10 but split inside the heat exchanger blocks 11 , 12 into two portions. A first portion is fully warmed and withdrawn as warm product 48, 49 from the plant; a second portion is withdrawn from the main heat exchanger 11 , 12 at the intermediate temperature and then work-expanded in a nitrogen turbine 610. The work- expanded nitrogen 611 is mixed with gaseous nitrogen 14 from the top of the low- pressure column and then fed to the block(s) of the second type only. The balancing works by varying the nitrogen turbine stream 39, which can be done by varying the performance of the main condenser 19: Condensing more top nitrogen in 19 reduces the gaseous nitrogen stream 39 used for balancing. An alternative could be to control the splitting 40 / 41 of the nitrogen stream 39 withdrawn from the high-pressure column.

[0085] In the system of Figure 6B, a pressurized GAN stream 39, 40, 41 is used for balancing like in Figure 2. Contrary to Figure 2, such stream is not fully warmed in the main heat exchanger 10 but withdrawn at an intermediate temperature and then work-expanded in a nitrogen turbine 610. A first portion (through valve 602) of the expanded nitrogen is combined with the top nitrogen 14 from the low-pressure column 18b and the mixed stream is introduced into the blocks (12) of the second type. A second portion 611 of the expanded nitrogen 611 is sent to the blocks 11 of the first type. Balancing is performed by valves 601 , 602. P40279-EP / P40279 PIF + P40325 PIF

[0086] 10.11.2025 - Imhof

[0087] 12

[0088] All previous drawing show a set of two subcoolers 24 and 25. They may be realized as shown there, i.e. exactly one subcooler block per block type, or differently. Further variations of the inventions concerning the subcooler construction are depicted in Figure 7 to 9.

[0089] In the very schematic drawing of Figure 7, eight main heat exchanger blocks 11 , 12 are shown. Each block type has a single subcooler 24, 25. Those subcoolers 24, 25 are suspended on all of the respective heat exchangers via a pipeline 621 per main heat exchanger block. The details of such suspending of a subcooler on two ore more main heat exchanger blocks is described in EP 2503269 B1 , which is incorporated here by reference insofar.

[0090] Figure 8, likewise schematic, shows a four-block embodiment having two blocks 11 , 12 respectively per block type. In this case, the subcoolers are integrated into a single subcooler block, which may be again suspended according to EP 2503269 B1 , e.g. via pipelines 13 and 14.

[0091] In another embodiment shown in Figure 9, the principle of integration of the subcooler into the main exchanger is used. Normally that means a single physical heat exchanger block preforming the functions of both, the main heat exchanger and the subcooler. In this cases that means that the number subcoolers 24, 25 is equal to the number of main heat exchanger blocks, i.e. eight.

Claims

P40279-EP / P40279 PIF + P40325 PIF10.11.2025 - Imhof13Patent Claims1. Air separation plant comprising- a source of compressed feed air (9),- a main heat exchanger (10) for cooling compressed feed air (9) and for warming return streams,- a distillation system comprising a high-pressure column (17) being in heat exchange relationship (19) with a low-pressure column (18a, 18b),- the main heat exchanger (10) comprising of at least or exactly four blocks,- each block being of a first or a second block type (11, 12),- the main heat exchanger comprising at least or exactly two blocks of the first block type (11) and at least or exactly two blocks of the second block type (12),- each block of a block type having the same internal structure concerning the two main passage groups (36, 40; 37, 41) for warming two main returns streams,- a block of the first block type (11) having an identical internal structure as or a similar but different internal structure than a block (12) of the second type,- the blocks of the first and second types both comprising one or more identical or similar passage groups for cooling feed air (15a, 15b) directed to the distillation system,- the blocks of the first and second types both comprising a passage group for guiding and warming pumped liquid oxygen (36, 37) for producing a high- pressure gaseous oxygen product (38),- the blocks of the first type comprising a passage group for impure gaseous nitrogen (31, 13) withdrawn from an intermediate point of the low-pressure column (18b), but no passage for gaseous nitrogen (22, 23, 14) withdrawn from the top of the low-pressure column (18b),- the blocks of the second type comprising a passage group for gaseous nitrogen(22, 23, 14) withdrawn from the top of the low-pressure column (18b), but no passage for impure gaseous nitrogen (31, 13) withdrawn from an intermediate point of the low-pressure column (18b).

2. Air separation plant according to claim 1 , wherein the high-pressure column (17) is configured to be operated under an intermediate pressure and the plant comprises a main air compressor (3) for compressing the feed air to a high pressure at least 5 bar above the intermediate pressure.P40279-EP / P40279 PIF + P40325 PIF10.11.2025 - Imhof143. Air separation plant according to claim 1 or 2, wherein each block of a block type has the same internal structure concerning the three main passage groups for warming three main return streams.

4. Air separation plant according to any of the proceeding claims, wherein- all blocks have a further passage group for warming a nitrogen product withdrawn from the high-pressure column,- each block of the main heat exchanger is connected with a pressurized nitrogen product line for recovering the warmed nitrogen product withdrawn from the high-pressure column and- each of the nitrogen product lines comprises a control valve (101 , 102) for controlling the flows of nitrogen product through the blocks of the first and second types.

5. Air separation plant according to any of the proceeding claims, comprising a first turbine (67, 72) for work-expanding a first turbine air stream (66, 71), the first turbine air stream being cooled in parallel in each of the blocks of the main heat exchanger.

6. Air separation plant according to claim 5, comprising a second turbine (72, 67) for work-expanding a second turbine air stream (71 , 66), the second turbine air stream being cooled in parallel in each of the blocks of the main heat exchanger.

7. Air separation plant according to any of the proceeding claims, comprising- a nitrogen turbine (610) for expanding at least a portion of a nitrogen stream withdrawn from the top or an intermediate section of the high-pressure column (17) and warmed in all blocks (11 , 12) of the main heat exchanger to an intermediate temperature and producing an expanded nitrogen stream and at least one of the following installations:- means for mixing the complete expanded nitrogen stream with the gaseous nitrogen (14) withdrawn from the top of the low-pressure column (18b) and for feeding the mixed stream to the blocks 12 of the second type of the main heat exchanger only,P40279-EP / P40279 PIF + P40325 PIF10.11.2025 - Imhof15- means (601 , 601) for controlled splitting of the expanded gaseous nitrogen to first and second portions, means for mixing the first portion of the expanded nitrogen with the gaseous nitrogen (14) withdrawn from the top of the low-pressure column (18b) and for feeding the mixed stream to the blocks 12 of the second type of the main heat exchanger only and means for mixing the second portion (611) of the expanded nitrogen with the impure gaseous nitrogen (13) withdrawn from an intermediate point of the low-pressure column (18b) to produce a further mixed stream and means for feeding the further mixed stream to the blocks 11 of the first type of the main heat exchanger only.

8. Air separation plant according to any of the preceding claims,- each block comprising at least one air passage group for cooling feed air,- the warm ends of the air passage groups being connected to an air introduction line respectively,- the cold ends of the air passage groups being connected with a common feed air line (9) for introducing feed air into the high-pressure column (17) and- each of the air introduction lines comprising a control valve for controlling the flows of feed air through the air passages of the blocks of the first and second types.

9. Air separation plant according to any of the preceding claims, having a further special return passage designed for a return stream comprising less than 5 mol-% of the total feed air amount, such return passage being arranged either- in a portion of the blocks of a single block only, the other blocks of such block type having no such special return passage or- in all blocks of a single block type only.

10. Air separation plant according to any of the preceding claims comprising a subcooler,- the subcooler consisting of at least two subcooler blocks,- each subcooler block being of a first or a second subcooler block type (24, 25),- the subcooler comprising at least one subcooler block of the first subcooler block type (24) and at least one subcooler block of the second subcooler block type (25),- each subcooler block of a subcooler block type (24, 25) having the same internal structure,P40279-EP / P40279 PIF + P40325 PIF10.11.2025 - Imhof16- a subcooler block of the first subcooler block type (24) having an identical or a similar but different internal structure than a block of the second subcooler block type (25),- the blocks of the first type comprising a passage group (25) for impure gaseous nitrogen (31) withdrawn from an intermediate point of the low-pressure column (18b), but no passage for gaseous nitrogen (22, 23) withdrawn from the top of the low-pressure column (18b),- the subcooler blocks of the second type comprising a passage group for gaseous nitrogen withdrawn (22, 23) from the top of the low-pressure column (18b), but no passage for impure gaseous nitrogen (31) withdrawn from an intermediate point of the low-pressure column (18b).

11. Air separation plant according to any of the preceding claims comprising a subcooler block (24, 25) which is suspended on at least two main heat exchanger blocks via connection pipelines (621, 622; 13, 14) between the subcooler and the respective main heat exchanger blocks.

12. Process for separating air, wherein - a source of compressed feed air, wherein- feed air (9) is cooled in a main heat exchanger (10)-- return streams are warmed in the main heat exchanger (10),- the cooled feed air (16, 69) is introduced into a distillation system comprising a high-pressure column (17) being in heat exchange relationship (19) with a low- pressure column (18a, 18b),- the main heat exchanger (10) comprising at least four blocks,- each block being of a first or a second block type (11 , 12),- the main heat exchanger comprising at least two blocks of the first block type (11) and at least two blocks of the second block type (12),- each block of a block type having the same internal structure concerning the two main passage groups (36, 40; 37, 41) for warming two main returns streams,- a block of the first block type (11) having an identical internal structure as or a similar but different internal structure than a block (12) of the second type,- the blocks of the first and second types both comprising one or more identical or similar passage groups for cooling feed air (15a, 15b) directed to the distillation system,P40279-EP / P40279 PIF + P40325 PIF10.11.2025 - Imhof17- the blocks of the first and second types both comprising a passage group for guiding and warming pumped liquid oxygen (36, 37) for producing a high- pressure gaseous oxygen product (38),- the blocks of the first type comprising a passage group for impure gaseous nitrogen (31, 13) withdrawn from an intermediate point of the low-pressure column (18b), but no passage for gaseous nitrogen (22, 23, 14) withdrawn from the top of the low-pressure column (18b),- the blocks of the second type comprising a passage group for gaseous nitrogen(22, 23, 14) withdrawn from the top of the low-pressure column (18b), but no passage for impure gaseous nitrogen (31, 13) withdrawn from an intermediate point of the low-pressure column (18b).

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