Method and apparatus for cryogenic separation of air
By designing a three-tower system and a condenser-evaporator, the problem of existing equipment being unable to efficiently produce high-purity nitrogen and impure oxygen has been solved, achieving efficient air separation and meeting the needs of semiconductor and display manufacturing.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- LINDE AG
- Filing Date
- 2021-03-05
- Publication Date
- 2026-07-24
AI Technical Summary
Existing air separation equipment is unable to efficiently provide relatively large amounts of high-purity nitrogen and a certain amount of impure oxygen, which cannot meet the needs of fields such as semiconductor manufacturing and display manufacturing.
A three-tower system is adopted, including a high-pressure tower, a low-pressure tower, and an additional third distillation tower. By adjusting the pressure levels of each tower and the design of the condenser and evaporator, the pressure of nitrogen products is increased, and impure oxygen is extracted in the third distillation tower. Efficient separation is achieved by using an expander and a condenser and evaporator.
It has achieved efficient air separation for the production of high-purity nitrogen and impure oxygen, improving production efficiency and meeting the needs of fields such as semiconductor and display manufacturing.
Smart Images
Figure CN115151771B_ABST
Abstract
Description
[0001] The present invention relates to a method and apparatus for cryogenic air separation according to the respective preamble of the independent claim. Background Technology
[0002] The preparation of liquid or gaseous air products by separating air at low temperatures in an air separation device is known and, for example, by H.-W., Wiley-VCH Publishing Company, 2006. The book "Industrial Gases Processing" specifically describes this in Chapter 2.2.5, "Cryogenic Rectification".
[0003] Air separation equipment includes distillation column systems, which can be designed as two-column systems, particularly double-column systems, but can also be designed as three-column or multi-column systems. In addition to distillation columns for extracting liquid and / or gaseous nitrogen and / or oxygen, i.e., distillation columns for nitrogen-oxygen separation, distillation columns for extracting other air components, particularly krypton, xenon, and / or argon, can also be provided.
[0004] This allows the distillation columns in the distillation column system to operate at different pressure levels. A known two-column system has a so-called high-pressure column (also referred to as a pressure column, intermediate-pressure column, or lower column) and a so-called low-pressure column (upper column). The high-pressure column typically operates at pressure levels of 4 bar to 7 bar, particularly about 5.3 bar. The low-pressure column typically operates at pressure levels of 1 bar to 2 bar, particularly about 1.4 bar. In some cases, even higher pressure levels may be used in both distillation columns. The pressures described here and below are absolute pressures at the top of the respective given column.
[0005] Different configurations of air separation equipment vary in their suitability for the desired product profile (i.e., the absolute and relative amounts of different liquid and gaseous air products that need to be produced from each other). For example, when a higher pressure level of gaseous nitrogen is required, the method described in, for example, EP 2 789 958A1 and its cited patent documents may be advantageous. This method can also be used in conjunction with a so-called pure oxygen tower and / or combined with a (vacuum) pressure swing adsorption function. Oxygen of varying purities can also be provided in this manner. However, in some cases, further optimization is required.
[0006] For certain purposes, air separation equipment or methods are required that, in addition to providing a relatively large amount of nitrogen of relatively high purity (approximately 80 ppb of oxygen or less), also provide a certain amount of impure oxygen byproducts. For example, semiconductor or display manufacturing may require the appropriate amount of nitrogen, while impure oxygen is required for glass production sites for corresponding displays. In particular, providing impure oxygen as an additional byproduct sometimes cannot achieve the desired efficiency with air separation equipment and methods known to date.
[0007] Therefore, there is a demand for methods and equipment for cryogenic air separation that can meet the above requirements in an advantageous manner. Summary of the Invention
[0008] To achieve this objective, the present invention provides a method and apparatus for cryogenic air separation having the corresponding features of the independent claims. Preferred embodiments are the subject of the respective independent claims and the following description.
[0009] The following will first provide a further explanation of some of the terminology used in describing the present invention and its advantages, as well as the basic technical background.
[0010] The apparatus used in air separation equipment is described in the cited technical documents, for example... See Section 2.2.5.6, “Apparatus”. Therefore, unless the definitions below deviate from this, the terminology used in the context of this application explicitly refers to the cited technical literature.
[0011] A "condenser-evaporator" refers to a heat exchanger in which a first condensing fluid flow and a second evaporating fluid flow exchange heat indirectly. Each condenser-evaporator has a liquefaction chamber and an evaporation chamber. The liquefaction chamber and the evaporation chamber have liquefaction channels and evaporation channels. In the liquefaction chamber, the first fluid flow is condensed (liquefied), and in the evaporation chamber, the second fluid flow is evaporated. The evaporation chamber and the liquefaction chamber are formed by a group of channels that have mutual heat exchange relationships.
[0012] Specifically, the so-called main condenser, which connects the high-pressure and low-pressure towers of the air separation unit via heat exchange, is designed as a condenser-evaporator. Specifically, the main condenser can be designed as a single-layer or multi-layer submerged evaporator, particularly as a cascaded evaporator (e.g., as described in EP 1 287 302 B1), but it can also be designed as a falling film evaporator. The main condenser can consist of a single heat exchanger block or multiple heat exchanger blocks arranged in the same pressure vessel.
[0013] In a forced-flow condenser-evaporator (also used in the context of this invention), a liquid flow passes through an evaporation chamber under its own pressure and partially evaporates within the chamber. This pressure is generated, for example, by a liquid column in an inlet line leading to the evaporation chamber. The height of this liquid column corresponds to the pressure loss within the evaporation chamber. The gas or gas-liquid mixture discharged from the evaporation chamber can be directly passed to the next process step or downstream device in this type of forced-flow condenser-evaporator, and in particular, is not introduced into the liquid tank of the condenser-evaporator from which the liquid portion may be re-drawn.
[0014] An expansion turbine or expander, which can be connected via the same shaft to other expansion turbines or energy converters (e.g., hydraulic brakes, generators, or compressors), is adapted to expand a gaseous flow or a medium flow that is at least partially liquid. In this invention, in particular, the expansion turbine may be designed as a turbine expander. If the compressor is driven by one or more expansion turbines and does not have an externally fed energy source (e.g., from an electric motor), the term "turbine-driven" compressor or alternatively "booster" is used. The combination of a turbine-driven compressor and an expansion turbine is also referred to as a "booster turbine."
[0015] In air separation equipment, a multi-stage turbo compressor is used to compress the added air to be separated; this turbo compressor is referred to herein as the "main air compressor." The mechanical structure of the turbo compressor is generally a well-known technical field for those skilled in the art. In a turbo compressor, the medium to be compressed is compressed by means of turbine blades arranged on a turbine or impeller or directly on a shaft. Here, the turbo compressor forms a structural unit, although this structural unit may have multiple compression stages in a multi-stage turbo compressor. The compression stages here typically involve corresponding arrangements of turbine blades. All these compression stages may be driven by the same shaft. However, they can also be configured to be driven in groups by different shafts, wherein the shafts may also be connected to each other via a reduction gear.
[0016] Furthermore, the main air compressor is characterized in that all the air supplied to the distillation column system and used to prepare air products is compressed by the main air compressor; that is, all the added air is compressed. Correspondingly, a "secondary compressor" can also be provided, but in this secondary compressor, only a portion of the air compressed in the main air compressor is increased to a higher pressure. This compressor can also be designed as a turbo compressor. The same compressor or a compression stage of such a compressor can also be used as both the main air compressor and the secondary compressor. To achieve the purpose of compressing a portion of the air, other turbo compressors in the form of boosters are generally also provided in the air separation equipment; the compression range of these other turbo compressors is usually relatively smaller compared to the main air compressor or the secondary compressor.
[0017] In the language used herein, fluids and gases may be rich in or poor in one or more components, where “rich in” can mean a content of at least 50%, 75%, 90%, 95%, 99%, 99.5%, 99.9%, or 99.99% on a molar, weight, or volume basis, and “poor in” can mean a content of at most 50%, 25%, 10%, 5%, 1%, 0.1%, or 0.01%. The term “major” can be used to correspond to the definition of “rich in”. Furthermore, liquids and gases may be enriched in or depleted in one or more components, where these terms refer to the content in the initial liquid or gas, i.e., the liquid or gas from which it was extracted. A liquid or gas is considered "enriched" if it contains at least 1.1, 1.5, 2, 5, 10, 100, or 1,000 times the content of the corresponding component relative to the initial liquid or gas; and "depleted" if it contains at most 0.9, 0.5, 0.1, 0.01, or 0.001 times the content of the corresponding component. The term "oxygen" or "nitrogen" as used herein may also be understood as a liquid or gas rich in oxygen or nitrogen, but its composition is not limited to these definitions.
[0018] This application uses the terms "pressure level" and "temperature level" to characterize pressure and temperature, thereby indicating that corresponding pressure and temperature in the form of precise pressure or temperature values are not necessarily required in the corresponding equipment to achieve the concept of the invention. However, such pressure and temperature typically fluctuate within a certain range, for example, ±1%, 5%, or 10% of the average value. Here, the corresponding pressure level and temperature level may be within non-overlapping or overlapping ranges. In particular, for example, pressure level includes unavoidable or anticipated pressure loss. The corresponding content applies to temperature level. The pressure level here, in bar, refers to absolute pressure.
[0019] Features and advantages of the present invention
[0020] To meet the product requirements mentioned at the beginning, namely to provide a relatively large amount of nitrogen with high purity and increased pressure, while simultaneously providing a certain amount of impure oxygen products, the method described in EP 3 557 166 A1 can be used in principle. This method utilizes a so-called mixing tower and a pressurization loop for a high-pressure tower, wherein the dual-tower system operates at increased pressure.
[0021] Furthermore, a method for nitrogen extraction is known from EP 3 521 739 A1, in which the low-pressure column of the dual-tower system used has a top condenser (also known as the "dual-column, dual-condenser" or DCDC method). This method is configured to use a forced-flow condenser evaporator and a residual gas turbine to generate process cooling capacity.
[0022] The method known from EP 3 521 739 A1 is well-suited for pure gas production with nitrogen product pressures of approximately 8 to 8.5 bar (or also well-suited for significantly higher pressures, if post-product compression is taken into account). For slightly higher product pressures (e.g., 11 bar), the method has so far remained efficient only when a relatively large amount of liquid (e.g., liquid nitrogen, LIN) is produced in addition to gaseous nitrogen as the primary product. This is because the cooling capacity in the process is adjusted / changed by the pressure in the evaporation space of the condenser in the low-pressure column. If the required cooling capacity in the process is low (e.g., in pure gas production), the pressure in the evaporation space or the pressure gradient at the residual gas turbine is also low. However, the low evaporation pressure also results in low operating pressures in both distillation columns and relatively low (approximately 8 to 8.5 bar) nitrogen product pressures. If the required cooling capacity in the process is high (e.g., in liquid production), the pressure in the evaporation space or the pressure gradient at the residual gas turbine is also high. Thus, high evaporation pressures result in high operating pressures in both distillation columns and high nitrogen product pressures.
[0023] In principle, this invention is based on the understanding that methods of the type described above can be extended using additional columns to overcome the aforementioned problems. In the context of this invention, higher pressures can be used in the evaporation space of the top condenser of the low-pressure column, making it feasible to correspondingly increase the nitrogen product pressure (e.g., to the desired 11 bar) without increasing the liquid capacity of the equipment. According to this invention, only a portion of the residual gas from the evaporation space of the top condenser of the low-pressure column undergoes work expansion. Thus, the cooling capacity remains relatively low. Another portion of the residual gas "drives" the distillation process in an additional distillation column. Impure oxygen is extracted from the bottom of this additional distillation column, and subsequently, this impure oxygen is also extracted as an internally compressed stream. For the term "internal compression," refer to the technical literature mentioned at the beginning.
[0024] Compared with the known methods described above, the method provided according to the present invention has significantly higher efficiency.
[0025] In general, the present invention proposes a method for cryogenic air separation, wherein an air separation apparatus having a first distillation column and a second distillation column is used, wherein the first distillation column operates at a pressure level of 9 bar to 13.5 bar, particularly about 11.3 bar, and the second distillation column operates at a pressure level of 5.5 bar to 8.5 bar, particularly about 7.3 bar. Specifically, the above values are pressure values at the top of the respective distillation column. In particular, the first and second distillation columns can be combined according to a known dual-column configuration.
[0026] Cooled compressed air is supplied to the first distillation column, and the liquid from or formed therefrom is supplied to the second distillation column. This does not preclude the possibility of further feed streams to the first and second distillation columns, and represents only the minimum conditions for carrying out the invention.
[0027] If, as mentioned above and below, liquid from or "formed therefrom" is used in some way, then "formed therefrom" should be specifically understood as a liquid for which the liquid is used directly from the corresponding distillation column, and whose composition is altered by incomplete evaporation, but, where appropriate, by evaporating a portion of its components. Cooling, heating, pressurization, and expansion may also be provided.
[0028] In the context of this invention, the top gas of the first distillation column is condensed by means of a first condenser-evaporator (which in particular may represent a main condenser that connects the first and second distillation columns in a heat-exchange manner, and may be designed as a forced-flow condenser-evaporator) and the liquid from or formed therefrom of the second distillation column is evaporated (see above) to obtain a gas phase, referred herein as the first evaporation product, for illustrative purposes only. The latter liquid is specifically the bottom liquid from or formed from the corresponding bottom liquid of the second distillation column.
[0029] Conversely, the top gas of the second distillation column is condensed using a second condenser-evaporator (which can also be designed as a forced-flow condenser-evaporator), and further liquid from or formed therefrom from the second distillation column is evaporated to obtain a second evaporation product. Specifically, this further liquid can also be the bottom liquid from or formed from such bottom liquid of the second distillation column.
[0030] In the context of this invention, a first portion of the second evaporation product is expanded, heated, and removed from the method using an expander. This first portion, the so-called impure nitrogen, can be, for example, directly released into the atmosphere, or used beforehand for the regeneration of an air purification adsorber unit if needed. As described, this portion (and consequently the cooling capacity) is lower than in conventional methods.
[0031] In the context of this invention, the top gas from the first distillation column is discharged from the method as a pure nitrogen product. By operating the first distillation column at the aforementioned relatively high pressure level, the pure nitrogen product can be provided to consumers at a corresponding pressure level.
[0032] As already mentioned and repeated here in other words, a third distillation column is used in the context of this invention. This third distillation column operates at a pressure level of 1.1 bar to 2.5 bar, particularly about 1.4 bar, which is particularly present at the top of the third distillation column.
[0033] Furthermore, in the context of this invention, as described, further residual gas is used to drive distillation in the third distillation column. This is achieved by means of a third condenser-evaporator, in which a second portion of the second evaporation product is condensed, and the bottom liquid of the third distillation column or the liquid formed therefrom is evaporated to obtain the third evaporation product. At least a portion of the second portion of the second evaporation product condensed by means of the third condenser-evaporator is then fed to the third distillation column. Furthermore, unevaporated further liquid or the liquid formed therefrom from the second distillation column is supplied to the third distillation column, and the further bottom liquid or the liquid formed therefrom from the third distillation column is internally compressed and removed from the method as the impure oxygen product described above.
[0034] Specifically, the further bottom liquid of the third distillation column, i.e., the impure oxygen product, has an oxygen content of 85% to 99.8% (e.g., 90% to 99.8%), for example, 96.8%. Therefore, it is not necessarily the product commonly referred to as impure oxygen, with an oxygen content as high as 98%. Specifically, in the context of this invention, a nitrogen product with a residual oxygen content of 10 ppm or less, particularly 5 ppm or less, can be provided. The production amount of the impure oxygen product (i.e., the amount of product shipped out in each case) can be, for example, 5% to 10% of the pure nitrogen product, particularly about 8.7%. In the embodiments described below, this amount can also reach 25%. Liquid nitrogen can also be extracted, wherein the amount of liquid nitrogen product is, however, generally less than 1% of the amount of pure nitrogen product, particularly less than 0.5%, for example, about 0.1%. Further air products are generally not formed, or not formed in greater quantities than the air products described above.
[0035] In the context of this invention, the second condenser evaporator operates at an evaporation pressure level of 2 to 5 bar, particularly about 3.6 bar. This evaporation pressure level, as described, is associated within a certain range with the rectification pressure levels of the first and second distillation columns. In particular, in the context of this invention, a first portion of the second evaporation product is fed into an expander at the evaporation pressure level, by means of which the first portion of the second evaporation product is expanded, heated, and removed from the method.
[0036] In the context of a particularly preferred embodiment of the invention, the liquid from the bottom of the second distillation column is partially evaporated using a first condenser evaporator to obtain a first evaporation product and an unevaporated residue. A first portion of this unevaporated residue can be evaporated using a second condenser evaporator to obtain a second evaporation product. In this way, particularly, the composition can be altered by reducing (or enriching) low-boiling compounds in the first condenser evaporator. If complete evaporation is performed as in the second condenser evaporator, the composition will not change, as no corresponding reduction or enrichment occurs.
[0037] In the embodiments described above, the second portion of the unevaporated residue is fed to the third distillation column. In any case, the unevaporated further liquid or liquid formed therefrom from the second distillation column supplied to the third distillation column, and the second portion or a portion thereof of the second evaporation product condensed by means of the third condenser evaporator, may each be fed to the third distillation column in the top region, wherein "top region" is understood as the region on which there is no further separation device.
[0038] In another embodiment, a liquid extracted from the second distillation column via a side outlet, and which thus has a lower oxygen content than the liquid at the bottom of the column, can be used as the unevaporated further liquid from the second distillation column or the liquid formed therefrom, supplied to the third distillation column. In this embodiment, the third distillation column may specifically have a first separation section and a second separation section arranged above the first separation section, wherein the unevaporated further liquid from the second distillation column, or the liquid formed therefrom, supplied to the third distillation column is delivered to the third distillation column above the second separation section, and wherein a second portion or a portion thereof of the second evaporation product delivered to the third distillation column, condensed by means of a third condenser evaporator, is delivered to the third distillation column between the first and second separation sections.
[0039] In one embodiment of the invention, the cooling compressed air supplied to the first distillation column may be entirely gaseous, cooled, or partially pre-liquefied compressed air, and the pressure level at which the compressed air is compressed is not the operating pressure level of the first distillation column.
[0040] In another embodiment, the cooled compressed air supplied to the first distillation column comprises gaseous, cooled compressed air compressed at a pressure level not at which the first distillation column operates, and also includes liquefied air compressed at a pressure level higher than the operating pressure level of the first distillation column. The liquefied air is liquefied after compression and expanded into the first distillation column. In this embodiment, a product amount up to 25% of the pure nitrogen product amount, as previously described, can also be prepared, for example, about 20% impure oxygen. Specifically, a separate air booster can be used to further compress the air to be liquefied.
[0041] In the method according to the invention, the third distillation column may have 15 to 25, particularly 20, theoretical separation plates. The first distillation column may have 50 to 70, particularly 60, theoretical separation plates, and the second distillation column may have 40 to 60, particularly 50, theoretical separation plates.
[0042] The features of the air separation device also proposed according to the invention should be explicitly referred to in the corresponding independent claims. This air separation device is particularly suited for performing the methods as previously described in the embodiments. Therefore, reference should be made explicitly to the foregoing description of the method according to the invention and its advantageous embodiments.
[0043] The invention will now be described in more detail with reference to the accompanying drawings, which illustrate preferred embodiments of the invention. Attached Figure Description
[0044] Figure 1 Figure 5 is a simplified schematic diagram of an air separation device according to an embodiment of the present invention.
[0045] In the accompanying drawings, identical or identical elements are given by the same reference numerals and will not be repeated for clarity. Equipment components may also represent corresponding method steps, thus the following description of the air separation equipment also refers to the corresponding methods. In the drawings, liquid flow is indicated by black (filled) flow arrows, while gaseous flow is indicated by white (unfilled) flow arrows. Detailed Implementation
[0046] Figure 1 An embodiment of the air separation device of the present invention is shown in the form of a process flow diagram, and is generally represented by 100.
[0047] In device 100, supplemental air or treatment air P is drawn in via filter 1 by main air compressor 2. After precooling the corresponding compressed air in a heat exchanger (not shown) and a direct contact cooler operating with water W, it is sent to adsorber station 3, where unwanted components such as water and carbon dioxide are removed. Subsequently, the air is fed into the main heat exchanger 4 of air separation device 100 in the form of supplemental air stream a, and is extracted from the main heat exchanger at the cold end. The supplemental air stream, further marked a, is delivered to the first distillation column (high-pressure column) 11 of distillation column system 10, which, in addition to the first distillation column 11, also has a second distillation column (low-pressure column) 12 and a third distillation column 13 forming a twin column with the first distillation column 11.
[0048] In the first distillation column 11, top gas and bottom liquid are formed, wherein the bottom liquid from the first distillation column 11 is guided entirely in the form of feed stream b through the subcooled countercurrent unit 5 and delivered to the second distillation column 12. In the second distillation column 12, top gas and bottom liquid are formed.
[0049] A portion of the top gas from the first distillation column 11 is condensed using the first condenser-evaporator 111 (the main condenser, which is designed here as a forced-flow condenser-evaporator). Another portion of the top gas is extracted as stream c, directed through the subcooled countercurrent unit 5 and the main heat exchanger 4, and discharged as pure nitrogen product C. The condensed portion of the top gas from the first distillation column 11 is returned to the first distillation column 11 as stream d.
[0050] In addition, a portion of the bottom liquid in the second distillation column 12 is evaporated using the first condenser evaporator 111. This evaporated portion rises in the second distillation column 12.
[0051] The top gas of the second distillation column 11 is condensed by the second condenser evaporator 121, wherein the top gas is fed into the second condenser evaporator 121 in the form of feed stream e. A portion of the condensed top gas is directed back to the second distillation column 12 and a portion is provided as liquid nitrogen product E. Other top gas from the second distillation column 12 can be extracted in the form of feed stream f, directed through the subcooled countercurrent unit 5 and the main heat exchanger 4, and provided as further pressurized nitrogen product F.
[0052] The liquid collected in the liquid holding device at the top of the second distillation column 12 can be guided in the form of a feed stream g through the subcooling countercurrent device 5 and back to the first distillation column 11 (“backflow”) by means of pump 6. At this time, a branch of the feed stream for forming liquid nitrogen product E can also be delivered, and the branch stream can be expanded to subcool the liquid nitrogen product E.
[0053] Further bottom liquid from the second distillation column 12 is evaporated by means of the second condenser evaporator 121. After the further bottom liquid is guided through the subcooled counterflow 5 beforehand, the further bottom liquid is fed into the second condenser evaporator 121 in the form of feed stream h.
[0054] With the aid of an expander 7 that can be connected to a simple brake or generator, a first portion of the further bottom liquid from the second distillation column 12, evaporated by the second condenser evaporator 121, is expanded in the form of a feed stream i, wherein the first portion is heated before and after expansion in the subcooled countercurrent unit 5 and the main heat exchanger 4, and is discharged from the method, i.e., discharged into the atmosphere A, and used as regeneration gas in the adsorber station 3 when needed.
[0055] A second portion of the bottom liquid from the second distillation column 12, which is further evaporated by the second condenser evaporator 121, is condensed in the form of a feed stream k using a third condenser evaporator 131, which is designed as the bottom evaporator of the third distillation column 13. Additionally, the bottom liquid of the third distillation column 13 is evaporated in the third condenser evaporator 131.
[0056] At least a portion of the second portion of the further liquid evaporated by the second condenser evaporator 121 from the second distillation column 12 is condensed by the third distillation evaporator 131 and fed to the third distillation column 13. Additionally, the unevaporated further liquid from the second distillation column 12 is supplied to the third distillation column 13 in the form of stream l. The bottom liquid of the third distillation column 13 is internally compressed by pump 8 in the form of stream m and discharged from the process as the internally compressed oxygen product M.
[0057] According to Figure 1 In the air separation unit 100, the unevaporated further liquid from the second distillation column 12, supplied in the form of a feed stream l to the third distillation column, is the bottom liquid of the second distillation column 12. Similarly, the unevaporated further liquid, which is a second portion or a portion of the further liquid from the second distillation column 12 that has been evaporated by the second condenser evaporator 121 and condensed by the third distillation evaporator 131, is also fed to the third distillation column 13 in the top region. An additional feeding of liquid nitrogen X is also shown.
[0058] According to Figure 2 In the air separation device 200 (the figure illustrates a further embodiment of the invention), the conveying is carried out in a different manner. The liquid from the feed stream n extracted from the second distillation column 12 via the side outlet is used here as further unevaporated liquid from the second distillation column 12 to be supplied to the third distillation column 13.
[0059] According to Figure 2In the air separation device 200, the third distillation column 13 has a first separation section 13a and a second separation section 13b arranged above the first separation section 13a, wherein the unevaporated further liquid (i.e., feed stream n) supplied to the third distillation column 13 from the second distillation column 12 is delivered to the third distillation column 13 above the second separation section 13b, and wherein a second portion or a portion thereof (i.e., feed stream k) of the further fluid from the second distillation column 12 that has been evaporated by the second condenser evaporator 121 and delivered to the third distillation column 13 is condensed by the third condenser evaporator 131 and delivered to the third distillation column 13 between the first separation section 13a and the second separation section 13b.
[0060] According to Figure 1 and Figure 2 In the air separation devices 100 and 200, the cooled compressed air supplied to the first distillation column 11 is entirely gaseous, cooled or pre-liquefied compressed air, and the pressure level at which this compressed air is compressed in the main air compressor 2 is not the operating pressure level of the first distillation column 11.
[0061] According to Figure 3 In the air separation device 300 (illustrated in a further embodiment of the invention), the air delivery is carried out in a different manner. The cooled compressed air supplied to the first distillation column 11 includes the gaseous, cooled compressed air of feed stream a, which is compressed at a pressure level not at the operating pressure level of the first distillation column 11, but additionally includes liquefied air of feed stream o, which is compressed at a pressure level higher than the operating pressure level of the first distillation column 11 by means of a post-compressor 9, and after compression, the liquefied air is liquefied in the main heat exchanger 4 and expanded to the first distillation column 11.
[0062] According to Figure 4 In the air separation device 400 (which illustrates a further embodiment of the invention), unlike the previously shown air separation device, the liquid collected in the liquid holding device at the top of the second distillation column 12 is not guided back to the first distillation column 11. However, a diversion of the feed stream used to form the liquid nitrogen product E can still be delivered to the first distillation column 11 (not shown), causing the diversion to expand and thus supercool the liquid nitrogen product E.
[0063] Here, the feed stream c is heated without first guiding it through the subcooling counterflow unit 5. Therefore, the subcooling counterflow unit 5 typically does not have a corresponding channel. The channel for the liquid collected at the top of the second distillation column 12 and guided back to the first distillation column 11, as shown in the previously illustrated apparatus, is usually omitted, but both channels are... Figure 4 The middle part is still roughly shown.
Claims
1. A method for cryogenic air separation, wherein an air separation apparatus (100–400) having a first distillation column (11) and a second distillation column (12) is used, wherein - The first distillation column (11) operates at a pressure level of 9 bar to 13.5 bar, and the second distillation column (12) operates at a pressure level of 5.5 bar to 8.5 bar. - Cooled compressed air is supplied to the first distillation column (11), and liquid from or formed therefrom from the first distillation column (11) is supplied to the second distillation column (12). - The top gas of the first distillation column (11) is condensed by means of the first condenser evaporator (111), and the liquid from or formed therefrom from the second distillation column (12) is evaporated to obtain the first evaporation product. - The top gas of the second distillation column (12) is condensed by means of the second condenser evaporator (121), and further liquid from or formed therefrom from the second distillation column (12) is evaporated to obtain the second evaporation product. - The first portion of the second evaporation product is expanded using an expander (7), heated, and removed from the process. - The top gas from the first distillation column (11) is removed from the method as a pure nitrogen product. Its features are, - A third distillation column (13) is used, which operates at a pressure level of 1.1 bar to 2.5 bar. - A second portion of the second evaporation product is condensed using a third condenser evaporator (131), and the bottom liquid or liquid formed therefrom of the third distillation column (13) is evaporated to obtain the third evaporation product. - At least a portion of the second portion of the second evaporation product condensed by means of the third condenser evaporator (131) is fed to the third distillation column (13). - The unevaporated further liquid from the second distillation column (12), or the liquid formed therefrom, is supplied to the third distillation column (13), and - The further bottom liquid of the third distillation column (13) or the liquid formed therefrom is compressed internally and removed from the method as an impure oxygen product.
2. The method of claim 1, wherein the further bottom liquid of the third distillation column has an oxygen content of 85% to 99.8%.
3. The method according to claim 1 or 2, wherein at least the second condenser evaporator (121) is a forced flow condenser evaporator.
4. The method according to claim 1 or 2, wherein the second condenser evaporator (121) operates at an evaporation pressure level of 2 bar to 5 bar.
5. The method according to claim 4, wherein the first portion of the second evaporation product is fed into the expander (7) at the evaporation pressure level, and the first portion of the second evaporation product is expanded, heated and removed from the method by means of the expander (7).
6. The method according to any one of claims 1 to 2 and 5, wherein the bottom liquid from the second distillation column (12) is partially evaporated by means of the first condenser evaporator (111) to obtain the first evaporation product and the unevaporated residue, and wherein a first portion of the unevaporated residue is evaporated by means of the second condenser evaporator (121) to obtain the second evaporation product.
7. The method of claim 6, wherein a second portion of the unevaporated residue is fed to the third distillation column (13).
8. The method according to claim 7, wherein, The unevaporated further liquid or the liquid formed therefrom from the second distillation column (12) supplied to the third distillation column (13), and the second portion or a portion thereof of the second evaporation product condensed by means of the third condenser evaporator (131) delivered to the third distillation column (13), are conveyed to the third distillation column (13) in the top region.
9. The method according to any one of claims 1 to 2, 5, 7 and 8, wherein the liquid extracted from the second distillation column (12) via a side outlet is used as further unevaporated liquid from the second distillation column (12) or liquid formed therefrom and supplied to the third distillation column (13).
10. The method of claim 9, wherein the third distillation column (13) has a first separation section (13a) and a second separation section (13b) disposed above the first separation section (13a), wherein the unevaporated further liquid or liquid formed therefrom from the second distillation column (12) supplied to the third distillation column (13) is delivered to the third distillation column (13) above the second separation section (13b), and wherein the second portion or a portion thereof of the second evaporation product delivered to the third distillation column (13) condensed by means of the third condenser evaporator (131) is delivered to the third distillation column (13) between the first separation section (13a) and the second separation section (13b).
11. The method according to any one of claims 1 to 2, 5, 7 to 8 and 10, wherein the cooled compressed air supplied to the first distillation column (11) is entirely gaseous, cooled or partially pre-liquefied compressed air, and the pressure level of the compressed air is not the operating pressure level of the first distillation column (11).
12. The method according to any one of claims 1 to 2, 5, 7 to 8 and 10, wherein the cooled compressed air comprises gaseous, cooled compressed air supplied to the first distillation column (11), the pressure level at which the compressed air is compressed is not the operating pressure level of the first distillation column (11), and wherein the cooled compressed air further comprises liquefied air supplied to the first distillation column (11), the pressure level at which the liquefied air is compressed is higher than the operating pressure level of the first distillation column (11), and the liquefied air is liquefied and expanded to the first distillation column (11) after compression.
13. The method according to any one of claims 1 to 2, 5, 7 to 8 and 10, wherein the third distillation column (13) has 10 to 45 theoretical separation plates.
14. An air separation device (100-400), said air separation device having a first distillation column (11) and a second distillation column (12), and said air separation device being adapted to: - The first distillation column (11) operates at a pressure level of 9 bar to 13.5 bar, and the second distillation column (12) operates at a pressure level of 5.5 bar to 8.5 bar. - Cooled compressed air is supplied to the first distillation column (11), and liquid from or formed therefrom from the first distillation column (11) is supplied to the second distillation column (12). - The top gas of the first distillation column (11) is condensed by means of the first condenser evaporator (111), and the liquid from or formed therefrom from the second distillation column (12) is evaporated to obtain the first evaporation product. - The top gas of the second distillation column (12) is condensed by means of the second condenser evaporator (121), and further liquid from or formed therefrom from the second distillation column (12) is evaporated to obtain the second evaporation product. - The first portion of the second evaporation product is expanded using an expander (7), heated, and removed from the process. - The top gas of the first distillation column (11) is discharged from the method as a pure nitrogen product. Its features are, - A third distillation column (13) is provided, which is adapted to operate at pressure levels from 1.1 bar to 2.5 bar. - A third condenser evaporator (131) is provided, the third condenser evaporator being adapted to condense a second portion of the second evaporation product and evaporate the liquid from the bottom of the third distillation column (13) or the liquid formed therefrom, to obtain the third evaporation product. - Provide an apparatus adapted to convey at least a portion of the second portion of the second evaporation product condensed by means of the third condenser evaporator (131) to the third distillation column (13). - Provide an apparatus adapted to supply unevaporated further liquid or liquid formed therefrom from the second distillation column (12) to the third distillation column (13), and - Provide an apparatus adapted to compress the further bottom liquid of the third distillation column (13) or the liquid formed therefrom and remove it from the method as an impure oxygen product.
15. The air separation device according to claim 14, wherein the air separation device is adapted to perform the method according to any one of claims 1 to 13.