Method for cryogenic separation of air and air separation plant

Abstract

The invention relates to a method for the cryogenic separation of air using an air separation plant (100-300) having a main heat exchanger (4) and a subcooled countercurrent (18), and a rectification column system (10) comprising a high-pressure column (11), a low-pressure column (12) and an argon system (400). The argon system (400) comprises a crude argon column (13a, 13b) operating at a pressure higher than 1.8 bar. At least one liquid flow (e, n1) from the high-pressure column (11) is cooled relative to at least one gas flow (n2) from the low-pressure column (12) in a subcooling countercurrent (18). The liquid argon product (v) from the argon system (400) is introduced into the subcooled countercurrent (18) and cooled there before being released as a final product. The invention also relates to a corresponding air separation device.

Description

[0001] The invention relates to a method for the cryogenic separation of air and an air separation plant according to the respective preambles of the independent patent claims. Background Art

[0002] The production of liquid or gaseous air products by cryogenic separation of air in air separation plants is known, for example from H.-W. (Hrsg.), Industrial Gases Processing, Wiley-VCH, 2006, in particular Section 2.2.5, "Cryogenic Rectification". In the following, the names known from the technical literature are used for components and plant parts used in air separation plants.

[0003] On page 22 of the monograph Figure 2 .3a shows a conventional process with a Linde twin column and an argon system, comprising a crude argon column and a pure argon column with associated top cooling and bottom heating. Argon product is withdrawn as a liquid at the bottom of the pure argon column and enters a product tank. Argon systems typically operate at very low pressures; that is, liquid argon product can be introduced into the product tank without significant decompression, and the product tank typically operates at approximately atmospheric pressure.

[0004] The situation is different if the entire plant and the argon system are operated at high pressure, and if, for example, the pressure in the crude argon column is greater than 1.8 bar or greater than 2.0 bar. The liquid argon product must then be depressurized to the tank pressure before it is introduced into the tank. This generates flash gas, which is lost during product production. (Unless otherwise stated, all pressure data in this application are to be understood as absolute pressures. Unless otherwise stated, the column pressure refers to the pressure at the top of the column.)

[0005] Such a process with increased pressure in a double column and in an argon system is known from WO 2021204424 A2.

[0006] The flash gas is usually returned to the pure argon column or reliquefied in a separate reliquefaction heat exchanger near the tank by indirect heat exchange with liquid nitrogen. Although this means high costs, it is not a problem from an operating technology point of view.

[0007] It is an object of the present invention to design a process of the aforementioned type such that the generation of flash gas in the liquid argon product is as low as possible, a relatively low outlay on equipment is required and the solution is nevertheless problem-free in terms of operation.

[0008] Against this background, the present invention provides a method for cryogenically separating air and an air separation system having the features of the respective independent claims. Embodiments are the subject matter of the dependent claims and the following description.

[0009] According to the invention, the liquid argon product is cooled in a subcooler countercurrent device of the air separation plant, which is present in any case, before being withdrawn as the final product (in particular before being depressurized to low pressure). This cooling is often also referred to as subcooling; it means cooling to a temperature (significantly) below the dew point.

[0010] In retrospect, using an already existing heat exchanger seems obvious. However, to our knowledge, no one has yet used a classic subcooling countercurrent to subcool the argon product. And for good reason. Since a regular, very cold gas stream, such as from the top of a low-pressure column, is used, there's also the risk of argon freezing, which can't be reduced by regulation. Surprisingly, when using a subcooling countercurrent to cool the liquid argon product, no precautions against freezing are required under all operating conditions. In contrast, in the present invention, fully functional operation of the subcooling countercurrent ensures that the system never freezes the argon.

[0011] In the present invention, the pressure in the rectification column (in each case at the top) is preferably

[0012] High pressure column.......................9 bar to 14.5 bar

[0013] Low pressure column.................................2 bar to 5 bar

[0014] Argon system (crude argon column) ................1.8 bar to 4.8 bar

[0015] Argon system (pure argon column) ................1.8 bar to 4.8 bar

[0016] Any other distillation column can be used in the embodiment of the present invention, in particular a further distillation column for obtaining an oxygen product and / or a further distillation column for obtaining a crude krypton / xenon mixture and / or a further distillation column for obtaining a crude helium / neon mixture, wherein reference is likewise made to the cited technical literature with regard to the formation of the crude krypton / xenon or helium / neon mixtures. In the corresponding embodiment, the turbine recycle stream or a portion thereof can be used as the heating medium for the bottom evaporator of the corresponding column.

[0017] Preferably, the liquid argon product is decompressed after cooling in the subcooler countercurrent (18) and before being released as the final product. This decompression is usually carried out in a throttle valve. In this case, the pressure is preferably reduced by at least 0.5 bar, in particular by 1.0 to 2.0 bar or even by at least 2.5 bar.

[0018] Preferably, the cooled and depressurized argon product is introduced into a liquid tank from which the final product is withdrawn.

[0019] In the present invention, the entire final product or the first portion thereof can be withdrawn from the liquid tank as a liquid final product. This withdrawal can be carried out continuously or intermittently.

[0020] Alternatively or additionally, the entire end product or a second portion thereof can be obtained as a gaseous end product by evaporation in the main heat exchanger. The end product can be obtained at low pressure or, for example, at high pressure by internal compression. At supercritical pressure, pseudo-evaporation occurs in the main heat exchanger, rather than evaporation in the strict sense, i.e., heating without a phase change.

[0021] It is also advantageous if the liquid argon product is fed to the subcooling countercurrent at an intermediate temperature and is taken off at the cold end. The corresponding temperature values ​​in the subcooling countercurrent are, for example:

[0022] Intermediate temperature................105K to 93K, preferably 102.7K to 94.2K

[0023] Cold end 94.5K to 84.3K, preferably 91.7K to 85.1K

[0024] Hot end 113.3K to 104.0K, preferably 111.3K to 104.0K

[0025] Liquid argon flows through the subcooler at a pressure of 1.8 bar to 4.8 bar, in particular 2.0 bar to 4.0 bar.

[0026] The gas stream introduced from the low-pressure column into the subcooling countercurrent device can be formed, in particular, by gaseous nitrogen from the top of the low-pressure column. The above values ​​apply in particular when the pressure of the gaseous nitrogen is from 2 bar to 5 bar, in particular from 2.2 bar to 4.2 bar. This is calculated at a minimum temperature difference of 0.5 K in the subcooler (between liquid argon and nitrogen).

[0027] The liquid argon in the subcooling countercurrent device is preferably guided in a cross-countercurrent manner with the gas flow coming from the low-pressure column. For this purpose, in addition to the countercurrent channel, the subcooling countercurrent device also comprises a crossover channel, which is particularly arranged directly at the cold end.

[0028] Preferably, the subcooler countercurrent is operated in such a way that the temperature of the liquid argon product at the outlet of the subcooler countercurrent is lower than the outlet temperature of the liquid stream from the higher pressure column, in particular even lower than the outlet temperature of all other liquid streams cooled in the subcooler countercurrent.

[0029] In this case, the temperature of the liquid argon product at the outlet of the subcooler countercurrent device may not be regulated. Since the temperature of the coldest stream in the subcooler countercurrent device (usually formed by gaseous nitrogen from the low pressure column) is higher than the triple point temperature of argon, the liquid argon cannot freeze.

[0030] The invention is explained in more detail below with reference to the accompanying drawings, which illustrate preferred embodiments of the invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figures 1 to 4 Air separation plants according to various embodiments of the invention are shown.

[0032] In the figures, structurally or functionally corresponding elements are shown with the same reference numerals and are not explained again for the sake of clarity. The explanations concerning the apparatus and apparatus components also apply to the corresponding methods and method steps.

[0033] exist Figure 1 An air separation system according to the embodiment of the invention is shown in FIG. 1 in the form of a simplified flow diagram and is generally designated by 100 .

[0034] In air separation plant 100, air is drawn in through filter 2 by means of a main air compressor 1 and compressed to a pressure level of, for example, approximately 12.5 bar. After cooling and water deposition in an adsorption station 3 of known construction, residual water and carbon dioxide are removed from the compressed air. The design of the relevant components can be found in the technical literature cited above.

[0035] The compressed air stream a formed accordingly is conducted from the hot end to the cold end via the main heat exchanger 4 and, in this case, is fed in essentially gaseous form into the pressure column 11 ("first distillation column") of the distillation column system 10. In the example shown, the distillation column system 10 comprises, in addition to the pressure column 11, a low-pressure column 12 ("second distillation column") and an argon system (400), which in turn comprises a two-part crude argon column 13 ("third distillation column") having two column sections 13a (upper) and 13b (lower), as well as a pure argon column 14. In addition, a distillation column 15 for obtaining a crude krypton / xenon mixture and a distillation column 16 for obtaining a crude helium / neon mixture are provided. The pressure column 11 is connected to the low-pressure column 12 in a heat exchange manner via a main condenser 11a, which can be in the form of a multi-stage bath evaporator, for example, and a bottom evaporator 15a is arranged in the bottom of the distillation column 15 for obtaining a crude krypton / xenon mixture. In the example shown, the distillation column system 10 is furthermore provided with a subcooling countercurrent device 18 .

[0036] A top gas forms at the top of the pressure column 11. In the example shown, a portion of this gas, as stream b, passes through the main condenser 11a, while another portion, as stream c, passes through the bottom evaporator 15a of the rectification column 15 to produce a crude krypton / xenon mixture. The condensate formed in the main condenser 11a is returned to the pressure column 11. The uncondensed portion is fed to the rectification column 16 to produce a crude helium / neon mixture. Further condensate formed in the bottom evaporator 15a of the rectification column 15, used to produce the crude krypton / xenon mixture, can be passed through a subcooling countercurrent device 18 as a liquid nitrogen stream m and fed into the low-pressure column 12 at the top of the column. Condensate b1 removed via the liquid withdrawal device at the top of the pressure column can be processed in this manner. Stream d, which has been cooled in the main heat exchanger 4, can be fed to the top gas of the pressure column 11. Its origin will be explained below.

[0037] A bottom liquid forms at the bottom of the pressure column 11 and is withdrawn from the bottom in the form of stream e. Stream e is first passed through a subcooling countercurrent device 18 and then used in a manner known per se to cool the top condensers (not designated separately) of the crude argon column 13 and the pure argon column 14. The evaporated and unevaporated fraction is fed to the low-pressure column 12 in the form of stream f or used to form stream k, which will be explained below.

[0038] A bottom liquid ("second bottom liquid") forms in low-pressure column 12 and is fed to the evaporation chamber of main condenser 11a. Gas is then fed from main condenser 11a to the bottom of low-pressure column 12. Liquid h is withdrawn from above the bottom of low-pressure column 12. A first portion of this liquid, in the form of stream h1, is pressurized in pump 5, heated in main heat exchanger 4, and discharged as internally compressed oxygen product. A second portion of liquid h is fed to rectification column 15 in the form of stream h2 to obtain a crude krypton / xenon mixture, a third portion of which is discharged from air separation plant 100 in the form of stream h3, specifically as a liquid product.

[0039] The gas is withdrawn above the bottom of the low-pressure column 12 in the form of stream i, combined with the streams k and o explained below to form a collection stream l containing, for example, about 90% oxygen, partially heated in the main heat exchanger 4, expanded in the generator turbine or the residual gas turbine 6, heated again in the main heat exchanger 4 and used, for example, as regeneration gas in the adsorption station 3.

[0040] A pressurized nitrogen gas stream is withdrawn from the top of the low-pressure column 12 in the form of stream n. It is present, for example, at a pressure level of approximately 3.5 bar and has an oxygen content of, for example, approximately 50 ppb. It is used to form the turbine recycle stream, which is first heated in the subcooling countercurrent 18 ("first heating"), then heated in the main heat exchanger 4 ("second heating"), compressed in the compressor 7, then compressed in the supercharger of the supercharger turbine assembly 9, cooled again in the main heat exchanger 4, and decompressed in the decompression turbine of the supercharger turbine assembly 9. The circuit is closed by feeding it into the subcooling countercurrent 18. The above-mentioned stream n is branched off downstream of the compressor 7 and cooled in the main heat exchanger 4. Further partial streams can be branched off upstream and downstream of the compressor 7 and used, for example, as pressurized nitrogen product, blow-off gas, and seal gas. Any combination is possible. A distillation recycle stream is partially routed together with the turbine recycle stream; however, the distillation recycle stream does not undergo a second compression and decompression, but is instead cooled in the main heat exchanger 4 and then used as described above.

[0041] Argon-rich gas is withdrawn from low-pressure column 12 in the form of stream o and fed to crude argon column 13. From crude argon column 13, bottom liquid is returned to low-pressure column 12 in the form of stream p via a pump (not separately designated).

[0042] The operation of the crude argon column 13 and the pure argon column 14 essentially corresponds to the operation known from the prior art and will not be explained separately. A pure argon stream v is withdrawn from the pure argon column 14 as liquid argon product, which, according to the invention, is cooled in a subcooling countercurrent device 18. The cooled argon product stream w is introduced into a liquid tank T and stored there or temporarily stored. Basically, the liquid end product can be taken directly from the liquid tank T and, for example, filled into a tanker. Figure 1 In the example of FIG, the liquid argon product is withdrawn from the tank, evaporated and heated in the main heat exchanger 4, and finally obtained as a gaseous final product x, whose oxygen content is, for example, about 200 ppb. The pressure required for withdrawing the gaseous final product can be generated, for example, by pressure evaporation or by a pump.

[0043] The above-mentioned stream k is formed using gas taken from the top condenser of the crude argon column 13. The stream o comes from the top of the rectification column 15 for obtaining a crude krypton / xenon mixture which is withdrawn from the bottom of the rectification column 15 in the form of a stream not specified separately.

[0044] At the top of the low-pressure column 12, liquid is withdrawn, part of which is subcooled in the form of a stream x and provided as liquid nitrogen product, and another part y is fed to the evaporation chamber of the rectification column 16 to obtain a crude helium / neon mixture which is withdrawn therefrom in the form of a stream z.

[0045] exist Figure 2 , an air separation plant according to another embodiment of the present invention is shown in the form of a simplified flow diagram and is generally designated by 200 .

[0046] According to Figure 1 Compared with the air separation plant 100, Figure 2 The air separation plant 200 shown has an integrated crude argon column 13 and no separate vessel for the low-pressure column 12. It also includes a pure oxygen column 17. It is operated by a bottom evaporator 17a and has an upper region and a lower region separated by a dividing wall 17b. The upper region is fed with stream o, from which stream p is withdrawn. Functionally, it represents the "external oxygen section" of the low-pressure column. Bottom evaporator 17a operates with stream d. The resulting condensate u is processed into stream m. The upper and lower sections of pure oxygen column 17 operate with bottom liquid r from the crude argon column as reflux, and a portion of the overhead gas s from pure oxygen column 17 is fed into the crude argon column 13. Pure oxygen is withdrawn from pure oxygen column 17 in the form of stream t, for example, by pressure evaporation using a tank system T2, and discharged from the plant. This type of tank system is described, for example, in US Pat. No. 10,209,004 B2. Also shown here is a liquid argon tank system T3, into which the first part of the cooled liquid argon product w is introduced after being decompressed in valve E. The second part is brought to a high product pressure of, for example, 12 bar by an argon pump P and then similarly Figure 1 It is evaporated in the main heat exchanger 4 and heated to ambient temperature (internal compression). Hot and compressed argon product xx is obtained as gaseous final product. Optionally, the separation between tank T3 and internal compression (pump P) can be carried out upstream of the subcooler 18, for example in line v.

[0047] As an alternative to what is shown in the drawings, the liquid tank T3 can also be Figure 1Then take out the liquid for pump P from tank T.

[0048] exist Figure 3 In the form of a simplified flow diagram, an air separation plant according to another embodiment of the present invention is shown and generally designated by 300. It corresponds to Figure 2 .

[0049] According to Figure 2 Compared with the air separation equipment 200, Figure 3 The air separation plant 300 shown has a bypass around the subcooling counterflow device 18 , so that the substance flow n, after its decompression, can be fed back to the portion n1 and / or n2 upstream or downstream of the subcooling counterflow device 18 .

[0050] Treatment of liquid argon product v Figure 2 same.

[0051] Figure 4 Also roughly corresponds to Figure 2 However, this variant is not a twin-turbo system, but a single-turbo system, where the Figure 2 The hybrid gas turbine 6 known per se serves as the only internal cooling source. Figures 1 to 3 In the example shown in Figure 1, the mixed stream is formed by combining the multiple residual streams from the low-pressure column or krypton-xenon enrichment column 15 and the evaporation chamber of the top condenser of the crude argon column. (There is no krypton-xenon extraction, only two streams.) Figure 4 There is no second turbine in the 1000 MW turbine. External cooling (liquid assist) can be introduced via liquid nitrogen line 21, for example into the top of the low pressure column.

Claims

1. A method for cryogenically separating air using an air separation apparatus (100-300), the air separation apparatus comprising a main heat exchanger (4) and a subcooling countercurrent device (18), and a distillation column system (10), the distillation column system comprising a high-pressure column (11), a low-pressure column (12) and an argon system (400), wherein: - the high-pressure column (11) is operated at a first pressure, - the low-pressure column (12) is operated at a second pressure lower than the first pressure, - the argon system (400) comprises a crude argon column (13a, 13b) operating at a third pressure higher than 1.8 bar, - Gaseous or partially liquefied compressed air is cooled in the main heat exchanger (4) and introduced into the high-pressure column (11), - withdrawing the bottom liquid (e) from the first distillation column (11) and introducing it directly or indirectly into the low-pressure column (12), - In the subcooling countercurrent device (18), - at least one liquid stream (e, n1) coming from the high-pressure column (11) is cooled in the subcooling countercurrent device (18), - at least one gas stream (n2) coming from the low-pressure column (12) is heated in the subcooling countercurrent device (18), - withdrawing argon-rich fluid (o) from the low-pressure column (12) and introducing it into the argon system (400), - withdrawing liquid argon product (v) from said argon system (400) and obtaining it as a final product, It is characterized in that - The liquid argon product (v) is introduced into the subcooler countercurrent vessel (18) and cooled there before being released as the final product.

2. The method according to claim 1, wherein The liquid argon product (w) is depressurized (22) after being cooled in the subcooler countercurrent vessel (18) and before being released as the final product.

3. The method according to claim 2, wherein: The cooled and depressurized argon product is introduced into liquid tank (T, T3).

4. The method according to claim 3, wherein: At least a first portion of the final product is withdrawn from the liquid tank as a liquid final product.

5. The method according to claim 3 or 4, wherein: At least a second portion of the final product is taken out of the liquid tank in liquid form, pressurized by a cryogenic pump (P), evaporated or pseudo-evaporated and heated in the main heat exchanger (4), and finally obtained as a gaseous final product.

6. A method according to any one of the preceding claims, wherein The liquid argon product (v) is supplied to the subcooling countercurrent vessel (18) at an intermediate temperature.

7. A method according to any one of the preceding claims, wherein The cooled argon product (w) is withdrawn from the subcooling countercurrent vessel (18) at the cold end.

8. A method according to any one of the preceding claims, wherein The liquid argon product (v) to be cooled passes in the subcooling countercurrent device (18) through a cross-channel which is arranged in particular directly at the cold end.

9. A method according to any one of the preceding claims, wherein The temperature of the liquid argon product (w) at the outlet of the subcooling countercurrent (18) is lower than the outlet temperature of the liquid stream (e) from the high-pressure column, in particular lower than the outlet temperature of all other liquid streams (e, n1) cooled in the subcooling countercurrent (18).

10. A method according to any one of the preceding claims, wherein The temperature of the liquid argon product (w) at the outlet of the subcooling countercurrent device (18) is not regulated.

11. An air separation plant (100-300) comprising a main heat exchanger (4) and a subcooling countercurrent device (18), and a distillation column system (10), the distillation column system comprising a high-pressure column (11), a second low-pressure column (12) and an argon system (400), wherein the air separation plant is configured such that the high-pressure column (11) is operated at a first pressure, - the low-pressure column (12) is operated at a second pressure lower than the first pressure, - the argon system (400) comprises a crude argon column (13a, 13b) operating at a third pressure higher than 1.8 bar, - Gaseous or partially liquefied compressed air is cooled in the main heat exchanger (4) and introduced into the high-pressure column (11), - withdrawing the bottom liquid (e) from the first distillation column (11) and introducing it directly or indirectly into the low-pressure column (12), - In the subcooling countercurrent device (18), - at least one liquid stream (e, n1) coming from the high-pressure column is cooled in the subcooling countercurrent device (18), - at least one gas stream (n2) coming from the low-pressure column is heated in the subcooling countercurrent device (18), - withdrawing argon-rich fluid (o) from the low-pressure column (12) and introducing it into the argon system (400), - withdrawing liquid argon product (v) from said argon system (400) and obtaining it as a final product, It is characterized in that - The air separation plant (100) is arranged to introduce the liquid argon product (v) into the subcooler countercurrent vessel (18) and cool it there before being released as a final product.

Images