US20240393043A1

US20240393043A1 - Method for the low-temperature separation of air and air separation plant

Info

Publication number: US20240393043A1
Application number: US18/687,641
Authority: US
Inventors: Christian Kunz; Dimitri Golubev
Original assignee: Linde GmbH
Current assignee: Linde GmbH
Priority date: 2021-09-01
Filing date: 2022-08-24
Publication date: 2024-11-28
Also published as: TW202311682A; EP4396507A1; WO2023030679A1; CN117980677A; KR20240059619A

Abstract

A method for the low-temperature separation of air using an air separation plant which comprises a rectification column arrangement (10) having a pressure column, a low-pressure column and an argon column, wherein: the low-pressure column comprises a first and a second rectification region (A, B); the argon column comprises a first and a second rectification region (C, D, D1, D2); argon-enriched fluid is removed from the low-pressure column between the first and second rectification region (A, B) thereof and is fed into the first rectification region (C) of the argon column; and argon-depleted fluid is removed from the first rectification region (C) of the argon column (13 a, 13 b) and is fed into the low-pressure column between the first and second rectification region (A, B) thereof.

Description

The present invention relates to a method for the low-temperature separation of air and an air separation plant according to the respective preambles of the independent patent claims.

BACKGROUND OF THE INVENTION

The production of air products in the liquid or gaseous state by low-temperature separation of air in air separation plants is known and described, for example, in H.-W. Häring (editor), Industrial Gases Processing, Wiley-VCH, 2006, in particular Section 2.2.5, “Cryogenic Rectification.”
Air separation plants have rectification column arrangements which can be designed differently. In addition to rectification columns for obtaining nitrogen and/or oxygen in the liquid and/or gaseous state, that is to say rectification columns for nitrogen-oxygen separation which can be combined in particular in a known double column, rectification columns for obtaining other air components, in particular noble gases, or pure oxygen, can be provided.
The rectification columns of typical rectification column arrangements are operated at different pressure levels. Known double columns have a so-called pressure column (also referred to as a high-pressure column, medium-pressure column or lower column) and a so-called low-pressure column (upper column). The high-pressure column is typically operated at a pressure level of 4 to 7 bar, in particular about 5.3 bar; the low-pressure column on the other hand is operated at a pressure of typically 1 to 2 bar, in particular about 1.4 bar. In certain cases, and in particular also within the scope of embodiments of the present invention (see below), higher pressure levels can also be used in such rectification columns. The pressures indicated here and below are absolute pressures at the top of the respective indicated rectification columns.
Air separation plants can be designed differently depending on the air products to be delivered and their required aggregate and pressure states. For example, the so-called internal compression is known for providing gaseous pressure products. In this case, a cryogenic liquid is removed from the rectification column arrangement, subjected to a pressure increase in the liquid state, and converted into the gaseous or supercritical state by heating. For example, in this way, internally compressed gaseous oxygen, internally compressed gaseous nitrogen or internally compressed gaseous argon can be produced. The internal compression offers a range of advantages over an alternative, likewise possible external compression and is explained, for example, in Häring (see above), section 2.2.5.2, “Internal Compression.”
However, the internal compression is not in all cases advantageous or desired. Alternative plant configurations have therefore been proposed in particular for cases in which argon is to be supplied as well as compressed nitrogen at a pressure level of 9 to 14.5 bar. In general, in such alternative plant configurations, rectification columns for providing gaseous nitrogen can be used which already operate with the desired product pressure. For example, the pressure in a double column is accordingly increased so that a removal pressure from the pressure column corresponds to the required product pressure. This can also be the case within the scope of embodiments of the present invention. Therefore the removed nitrogen no longer has to be compressed. Rectification columns for argon production can also be used in this context.
The object of the present invention is to specify means which further improve the provision of air products, in particular according to the described requirements profile, and make them more efficient and simpler. In particular, the invention is to specify a solution by means of which, in addition to the specified air products, (ultra) high-purity oxygen can be obtained in the liquid or gaseous state.

DISCLOSURE OF THE INVENTION

Against this background, the present invention proposes a method for the low-temperature separation of air and an air separation plant with the features of the respective independent patent claims. Each of the embodiments are the subject matter of the dependent claims and of the description below.
In the following, some terms used in describing the present invention and its advantages, as well as the underlying technical background, will first be explained in more detail.
The devices used in an air separation plant are described in the cited technical literature, for example in Häring, Section 2.2.5.6, “Apparatus.” Unless the following definitions differ, reference is therefore explicitly made to the cited technical literature with respect to terminology used within the framework of the present application.
A “condenser evaporator” refers to a heat exchanger in which a first, condensing fluid stream enters into indirect heat exchange with a second, evaporating fluid stream. Each condenser evaporator has a liquefaction chamber and an evaporation chamber. The liquefaction and evaporation chambers have liquefaction or evaporation passages. Condensation (liquefaction) of the first fluid stream is carried out in the liquefaction chamber, and evaporation of the second fluid stream in the evaporation chamber. The evaporation and liquefaction chambers are formed by groups of passages, which are in a heat-exchanging relationship with one another. Condenser evaporators are also referred to as “top condenser” and “sump evaporator” according to their function, wherein a top condenser is a condenser evaporator in which head gas of a a rectification column is condensed, and a sump evaporator is a condenser evaporator in which sump liquid of a rectification column is evaporated. However, the sump liquid can also be evaporated in a top condenser, for example as used in the context of the present invention.
An “expansion turbine” or “expansion machine,” which can be coupled via a common shaft to further expansion turbines or energy converters such as oil brakes, generators or compressors, is configured for expanding a gaseous or at least partially liquid material stream. In particular, expansion turbines for use in the invention can be designed as turbo-expanders. In the present case, in particular a so-called residual gas turbine, which expands impure nitrogen from the rectification column arrangement to obtain cold, can be used.
Fluids, that is to say liquids and gases can, in the terminology used herein, be rich or low in one or more components, wherein “rich” can refer to a content of at least 50%, 75%, 90%, 95%, 99%, 99.5%, 99.9% or 99.99%, and “low” can refer to a content of at most 50%, 25%, 10%, 5%, 1%, 0.1% or 0.01% on a molar, weight or volume basis. The term “predominantly” can correspond to the definition of “rich.” Fluids can further be enriched or depleted by one or more components, wherein these terms relate to a content in a starting fluid from which the fluid was obtained. The fluid is “enriched” if it contains at least 1.1 times, 1.5 times, 2 times, 5 times, 10 times, 100 times or 1,000 times the content, and “depleted” if it contains at most 0.9 times, 0.5 times, 0.1 times, 0.01 times or 0.001 times the content of a corresponding component, based on the starting fluid. If, by way of example, reference is made here to “oxygen” or “nitrogen,” this is also understood to mean a fluid that is rich in oxygen or nitrogen but need not necessarily consist exclusively thereof.
The term “high-purity oxygen” (or “oxygen 6.0”) is to be understood here to mean liquid oxygen (HLOX) or gaseous oxygen (HGOX) with an oxygen content of at least 99.9999 mole percent. In other words, a maximum of 1 ppm impurities in total (mainly argon and methane) are present here. Accordingly, the term “ultra-high-purity oxygen” is to correspondingly refer to oxygen with an even higher oxygen content, in particular at least 99.99999 mole percent. If reference is made to the formation of high-purity oxygen, this can also comprise the formation of ultra-high-purity oxygen.
The present disclosure uses the terms “pressure range” and “temperature range” to characterize pressures and temperatures, which means that corresponding pressures and temperatures in a corresponding plant do not have to be used in the form of exact pressure or temperature values in order to realize the inventive concept. For example, there are different pressures at different positions within the pressure and low-pressure column, but they are within a certain pressure range, also referred to as the operating pressure range. Corresponding pressure ranges and temperature ranges can be disjoint ranges or ranges that overlap one another.
Absolute and/or relative spatial indications used below, such as in particular “over,” “under,” “above”, “below”, “next to” and “next to one another,” refer in particular here to the spatial orientation of the correspondingly designated elements of an air separation plant, for example rectification columns, sub-columns of multi-part rectification columns, or rectification regions of rectification columns in normal operation. An arrangement of two elements “one above the other” is understood here in particular to mean that the upper end of the lower of the two elements is located at a lower or the same geodetic height as the lower end of the upper of the two elements, and the projections of the two elements overlap in a horizontal plane. In particular, the two elements can be arranged exactly one above the other, that is to say the vertical center axes of the two elements run on the same vertical straight line. An arrangement “next to one another” is to mean in particular that the projections of the two elements do not overlap in a horizontal plane. In the case of a rectification column designed in multiple parts, terms such as “functionally below” or “functionally above” refer to the arrangement of rectification regions or sub-columns that they would have if the rectification column had a single-part design.
The term “rectification region” herein is to refer to any section within a rectification column or sub-column of a multi-part rectification column that is configured to carry out rectification and is designed for this purpose, in particular with corresponding material exchange structures such as separating plates or ordered or disordered packings. In particular, fluid outlets or feed-in points, for example side feed-in points, can be provided between rectification regions. Below a (functionally) lowermost rectification region is the “sump” of the rectification column; above the (functionally) upper rectification region is its “head.” A “nitrogen section” is the uppermost region of a low-pressure column, if provided, which is intended to be able to draw off (substantially) pure nitrogen at its head.
As set out in Häring (see above) with reference to FIG. 2.4A, although argon is contained in atmospheric air with a content of less than 1 mole percent, it exerts a strong influence on the concentration profile in the low-pressure column. The separation in the lowermost separating section of the low-pressure column, which typically comprises 30 to 40 theoretical or practical plates, can thus be regarded as a substantially binary separation between oxygen and argon. Such a rectification region is also referred to as the “oxygen section.” Only starting at the discharge point for the gas transferred into the crude argon column, the separation changes within a few theoretical or practical plates into a ternary separation of nitrogen, oxygen and argon.

Advantages of the Invention

For the requirements profile mentioned at the beginning, that is to say the obtaining of gaseous compressed nitrogen at a pressure level of 9 to 14.5 bar and the provision of argon, a double column arrangement having a pressure column and a low-pressure column can be operated at an increased pressure level in a particularly advantageous manner, wherein nitrogen is simultaneously withdrawn at the head of the low-pressure column and a portion of this is heated, compressed, cooled again and fed into the double column arrangement, that is to say into the pressure column and/or into the low-pressure column, in the form of a recirculating stream.
The recirculating stream can optionally be passed (partially, or in parts, or completely) through the main condenser and/or through a sump evaporator of the pure oxygen column before it is fed into the pressure column and/or the low-pressure column. However, it is also possible to initially feed the recirculating stream completely into the pressure column and to further purify the nitrogen-rich fluid of the recirculating stream in the pressure column in this way. In this case, the head gas from the pressure column comprises further purified fluid from the recirculating stream. Of this, a portion of the head gas from the pressure column can be passed through the main condenser and/or through the sump evaporator of the pure oxygen column, and a further portion can be obtained as a nitrogen product. A certain portion of the recirculating stream that is fed into the pressure column, at least in part, can be removed from the pressure column, in other words above the feed-in point in the pressure column. The nitrogen-rich fluid contained in the recirculating stream can be further purified in this way and made available as a product. However, it is also possible in principle to use a part of the recirculating stream directly as a product, that is to say to dispense with feeding it into the pressure column.
In the context of such a method, the low-pressure column is in particular configured, by using a suitable nitrogen section in the upper region, to provide a corresponding nitrogen-rich head gas with the specifications explained below, which is used in the formation of the recirculating stream.
In the context of such a method, one or more additional rectification columns for argon production, for example a crude argon column and a pure argon column of known type are also used. Instead of a crude argon column and a pure argon column, a single column can also be provided for obtaining an argon product that partially combines the functions of the crude and pure argon columns with one another by having a further section provided for separating off nitrogen. If the following refers to an argon column, this can therefore be a crude argon column in particular, which is present next to a pure argon column, but also a correspondingly modified crude argon column, next to which no pure argon column is present.
In such a method, a pure oxygen column can also be used, which is configured to obtain high-purity or ultra-high-purity oxygen in the explained sense and which is fed with liquid from an intermediate point of the argon column, which is fed at the head of the pure oxygen column. The argon column can also be designed in two parts, wherein a functionally lower part of the argon column can be accommodated in a common column shell with the pure oxygen column up to the intermediate point mentioned, and the functionally upper part is arranged separately. A corresponding embodiment is explained below in connection with FIG. 1 . However, it is not essential that a corresponding pure oxygen column is designed accordingly. FIG. 2 shows, for example, a separate pure oxygen column that is not combined with parts of the argon column.
The rectification process in the pure oxygen column is driven by the evaporation of the sump liquid by means of a sump evaporator (reboiler). The heating medium for such sump evaporator can be the recirculating stream mentioned, which can be passed at least in part in parallel through the main condenser, which connects the pressure column and the low-pressure column in a heat-exchanging manner, and the sump evaporator. Upon a further purification of the recirculating stream in the pressure column, its head gas can also be used in a corresponding manner. Such a topology can have certain advantages compared to a design using compressed air, which is condensed accordingly.
Due to the requirements for high efficiency, the main condenser connecting the pressure column and the low-pressure column in a heat-exchanging manner is designed with a comparatively low mean temperature difference (about 1.0 K or slightly above), which also results in the low mean temperature difference in the sump evaporator of the pure oxygen column (about 1.0 K or slightly below, taking into account a certain pressure drop for the control valve in the partial stream of the recirculating stream or of the head gas from the pressure column to said sump evaporator).
In addition to the so-called design case, there is usually a plurality of other operating cases that are specified by the customer or driven by product development requirements. The operating cases with greatly reduced main product (compressed nitrogen) and in particular relatively high removal of the pure oxygen product and/or lower oxygen content in the feed stream into the pure oxygen column pose a challenge here, as the load ratio of both evaporators (the main condenser and the sump evaporator of the pure oxygen column, as illustrated in the table below using an example) changes significantly. The load of the main condenser in case 1 (design case) is about a factor of 10 greater than the load of the sump evaporator of the pure oxygen column. In contrast, the load of the main condenser in case 5 (operating case with greatly reduced compressed nitrogen product and process air streams) is only a factor of 5 greater than the load of the sump evaporator of the pure oxygen column.

TABLE 1

Case	Case	1	Case 5	Case 6

Load of main condenser [kW]	4,997	2,190	2,186
Load of sump evaporator of pure oxygen	532	428	568
column [kW]
Ratio	9.4	5.1	3.9

The significantly lower load of the main condenser in the case (2,190 KW) leads to a noticeably lower pressure at the head of the pressure column due to the excessively large heat transfer surface. This pressure is too low for the condensation process in the sump evaporator of the pure oxygen column due to the relatively high load (428 KW). In order to solve this problem under the prior art, the main condenser would have to be designed with a significantly larger mean temperature difference, in order to have sufficient clearance (differential pressure) for the control valve in the recirculating stream or its partial stream or head gas from the pressure column upstream of the sump evaporator of the pure oxygen column in all operating cases. However, such a solution would lead to an efficiency disadvantage in the design case. In particular, the present invention now creates a possibility for robustly controlling the operation of the sump evaporator of the pure oxygen column in similar operating cases without causing an efficiency disadvantage in the design case.
A substantial aspect of the invention consists in particular of a separation of the pressure chambers of the double column and the argon column by providing an additional valve and, in embodiments, by providing a sufficient height difference for returning liquid from the argon column to the low-pressure column. This is not necessary if, in other embodiments, the low-pressure column is divided above the oxygen section with a liquid return via a pump.
The additional valve can be fully (or almost fully) opened in the design case and partially closed in all cases with a greatly reduced load ratio between the two condensers mentioned, which results in a reduced operating pressure in the argon column and the pure oxygen column. The reduced volume stream into the argon column is irrelevant, since this is operated with a reduced material stream compared to the design case. The cases with a reduced load ratio between the main condenser and the sump evaporator of the pure oxygen column are underload cases, that is to say operating cases with a lower process air stream.
The proposed solution enables robust plant operation in cases with a greatly reduced main product (gaseous compressed nitrogen) and relatively high removal of the pure oxygen product, and/or lower oxygen content in the feed stream into the pure oxygen column without leading to an efficiency disadvantage in the design case. The introduction of the mentioned valve alone results in a sufficient differential pressure for the control valve in the heating medium stream upstream from the sump evaporator of the pure oxygen column.
As a whole, the present invention proposes a method for the low-temperature separation of air using an air separation plant which comprises a rectification column arrangement having a pressure column, a low-pressure column and an argon column, wherein the low-pressure column is designed in one or more parts and comprises a first and a second rectification region (in the case of a one-part design in a common column shell, otherwise distributed over a plurality of column shells), and the argon column is designed in one or more parts and comprises a first and a second rectification region (in the case of a one-part design in a common column jacket, otherwise distributed over a plurality of column jacket). The first rectification region of the low-pressure column and the argon column is in particular the (functionally) lowermost; the second rectification region is directly above it.
The pressure column and the low-pressure column are operated in particular in such a way that a sump liquid of the pressure column, which is fed with at least feed air, comprises a content of 28 to 38% oxygen along with argon and nitrogen, and a head gas from the pressure column comprises a content of 0.001 to 100 ppb, for example about 10 ppb oxygen, 0.1 to 100 ppm, for example about 30 ppm argon, and otherwise substantially nitrogen and possibly lighter components. Furthermore, the pressure column and the low-pressure column are operated in particular in such a way that the head gas from the low-pressure column has a content of 0.001 to 1000 ppb, for example about 10 ppb oxygen, and 0.1 to 300 ppm, for example about 35 ppm argon.
Between the first and second rectification regions of the low-pressure column, in particular at the known argon pocket, a first transfer fluid enriched in argon is removed from the low-pressure column and fed into the argon column in a first transfer quantity below the first rectification region of the argon column. In this respect, the operation of the argon column corresponds to known methods in which a corresponding argon column is fed with a corresponding fluid. Below the first rectification region of the argon column, a second transfer fluid depleted of argon is removed from the argon column and fed (returned) into the low-pressure column in a second transfer quantity between the first and second rectification region of the low-pressure column, as is also known in the field of argon production.
In particular, the first transfer fluid is enriched in argon with respect to a sump liquid of the low-pressure column along with respect to its head gas. In particular, it can have 20 to 6%, for example 18 to 11%, argon and the remainder predominantly oxygen. The removal is at a point between corresponding rectification regions which are known to the person skilled in the art.
According to the invention, it is now provided that the air separation plant is operated in a first operating mode and in a second operating mode, wherein a nitrogen product is discharged from the air separation plant in a larger product quantity in the first operating mode than in the second operating mode. The nitrogen product can be formed in the manner already indicated and explained below. In particular, the first operating mode represents the explained design case, whereas the second operating mode corresponds to a special operating mode or the non-design case with reduced nitrogen removal. In the second operating mode, as explained below, a pressure reduction is undertaken in the argon column, while a smaller or no pressure reduction is undertaken in the low-pressure column, and the pressure therein, in particular, is kept substantially constant. In particular, the pressure is reduced in the manner explained below.
The conversion in the argon column is typically adjusted by means of a gas flap at the outlet of the evaporation chamber of the top condenser of the argon column, a condenser evaporator. If, for example, a lower conversion quantity is required (for example, for the underload case), the flap is closed more, and the pressure in the evaporation chamber is increased as a result. Increasing the pressure leads to an increase in the evaporation temperature and (as a result) to a reduction in the driving temperature difference in the condenser evaporator. With a lower temperature difference, less argon can be condensed in the condenser evaporator, and the conversion decreases. However, after these measures have been initiated, the pressure in the argon column is still the same as in the low-pressure column. If a valve in the inlet to the argon column from the low-pressure column is now closed, the pressure in the argon column is reduced. The pressure reduction also leads to a reduction in the condensation temperature (and as a result, also the driving temperature difference in the condenser evaporator). This would lead to a further reduction of the conversion. Therefore, the conversion is “held” by a suitable control by adjusting the mentioned gas flap at the outlet of the evaporation chamber, that is to say, the flap is opened more again in this case, so that the evaporation pressure is reduced, and the conversion quantity remains unchanged. As a result, the argon column is operated under lowered pressure and with the same conversion (matching the underload case). Alternatively, the argon column can also be operated at a slightly reduced pressure in the first operating mode; its operating pressure is then further reduced in the second operating mode.
In other words, the adjustment of the pressure in the argon column in a first step comprises, in particular, increasing the pressure in an evaporation chamber of a top condenser of the argon column, while increasing the evaporation temperature in the evaporation chamber and reducing a driving temperature difference and the conversion in the argon column. In a second step, the adjustment of the pressure in the argon column comprises, in particular, closing or closing more tightly the valve mentioned in the supply line. In a third step, the adjustment of the pressure in the argon column comprises, in particular, a pressure reduction in the evaporation chamber of the top condenser of the argon column, while reducing the evaporation temperature in the evaporation chamber and increasing a driving temperature difference and the conversion in the argon column.
In the context of the invention, a pressure is adjusted in the argon column in a pressure range that, in the first operating mode, corresponds to a pressure range in which the low-pressure column is operated and that, in the second operating mode, is below the pressure range in which the low-pressure column is operated. Here, as mentioned, the mentioned valve which is in a line that is provided for feeding the first transfer quantity into the low-pressure column, can be closed only in the second operating mode, or more tightly in the second operating mode than in the first operating mode. Such valve ensures the pressure loss or the lower operating pressure in the argon column and possibly the pure oxygen column, while a conversion quantity in the argon column can be adjusted via a valve at the outlet from an evaporation chamber of the crude argon condenser (that is to say, the top condenser of the argon column), as is known and has just been explained. The conversion quantity in the argon column is significantly smaller in the second operating mode because the amount of feed air is significantly smaller. Advantages of the measures proposed according to the invention which arise in particular, but not exclusively, in connection with the use of a pure oxygen column, have already been explained above. A particular advantage is the more efficient distillation at lower pressure.
In a particularly advantageous embodiment of the invention, the rectification column arrangement comprises a pure oxygen column in which a pressure is adjusted in a pressure range that, in the first operating mode, corresponds to the pressure range in which the low-pressure column is operated and that, in the second operating mode, is below the pressure range in which the low-pressure column is operated. Furthermore, the pure oxygen column is operated with a liquid as the return flow which is removed from the argon column between the first and second rectification regions of the argon column, and a head gas is removed from the pure oxygen column which is fed into the argon column between the first and second rectification regions of the argon column. As mentioned, the invention can offer particular advantages by adapting to load changes between the main condenser and the sump evaporator of the pure oxygen column.
In particular, the present invention can be advantageous when forming a recirculating stream, as described in principle above. Here, the pressure column and the low-pressure column are, as is generally customary, connected in a heat-exchanging manner by means of a main condenser, wherein a recirculating stream is formed using head gas from the low-pressure column, which is heated, compressed, cooled down again, passed partially or completely through the main condenser and/or partially or completely through a sump evaporator of the pure oxygen column, condensed there at least partially, and fed back into the rectification column arrangement, that is to say the pressure column and/or the low-pressure column. Compression occurs on the warm side of the main heat exchanger in particular. If head gas from the low-pressure column is used to form the recirculating stream and is not returned to the rectification column arrangement in the form of the recirculating stream, such head gas can be fed up to this point together with the remainder used to form the recirculating stream, and the nitrogen product can in this case be diverted from the recirculating stream upstream or downstream from the compression.
The recirculating stream can be partially or completely passed through the main condenser and/or partially or completely through a sump evaporator of the pure oxygen column, at least partially condensed there, and returned to the rectification column arrangement. However, it can also be possible to feed the recirculating stream, in particular completely, into the pressure column without previously passing it through the main condenser and/or the sump evaporator of the pure oxygen column. In the latter case, as mentioned, gas, in particular head gas, is removed from the pressure column above the feed-in point of the recirculating stream, which is further purified in this way with respect to the recirculating stream, and instead of the recirculating stream, this can itself now be passed partially or completely through the main condenser and/or partially or completely through the sump evaporator of the pure oxygen column where it is at least partially condensed, and returned to the rectification column arrangement.
In the context of the present invention, the nitrogen product can be provided using head gas from the pressure column, wherein the pressure column is fed with at least a portion of the recirculating stream for this purpose in the mentioned embodiment with additional purification of the recirculating stream. In this embodiment, the nitrogen-rich fluid of the recirculating stream is therefore further purified in the pressure column in order to obtain a correspondingly pure product. Alternatively, the nitrogen product can also be provided using head gas from the low-pressure column that is not fed into the pressure column in the form of the recirculating stream. In particular, the nitrogen product is diverted on the warm side of the main heat exchanger and in particular prior to or after a corresponding compression of a remainder of the head gas used to form the recirculating stream.
In a particularly advantageous embodiment of the invention, a product quantity of the nitrogen product that is discharged from the air separation plant in the second operating mode can be at least 2.5% less, at least 10% less or 10% to 60% less than in the first operating mode. In the second operating mode, a pressure in the argon column that is at least 50 mbar, at least 100 mbar and/or up to 700 mbar or up to 900 mbar lower than in the low-pressure column can be adjusted, while a pressure in the low-pressure column is kept substantially constant, that is to say, does not change by more than 100 mbar.
In a first group of embodiments of the present invention, the first rectification region and the second rectification region of the low-pressure column can be accommodated in a common column shell in which the second rectification region of the low-pressure column is arranged above the first rectification region of the low-pressure column. This first group of embodiments of the invention thus relates to an “undivided” low-pressure column. In the following, variants of this first group of embodiments of the invention are initially described.
In the first group of embodiments, the first and second rectification regions of the argon column can in particular be accommodated in separate column shells, wherein the column shell in which the first rectification region of the argon column is accommodated is arranged above a column shell of the pure oxygen column and is connected thereto or is designed integrally therewith. The first rectification region of the argon column and the pure oxygen column can therefore be arranged, fluidically separated, in a common outer structure.
In a second group of embodiments of the present invention, the first rectification region of the low-pressure column can be accommodated in a first column shell, the second rectification region of the low-pressure column can be accommodated in a second column shell, and the first and second column shells can be arranged next to one another.
In the second group of embodiments, the first column shell and a column shell that surrounds the pressure column are arranged in particular one above the other and in the form of a double column. Thus, the functionally lower part of the low-pressure column is placed on the pressure column.
In the second group of embodiments, the second rectification region of the argon column can be subdivided into a first subregion and a second subregion, wherein the first rectification region of the argon column is accommodated in a third column shell, the first subregion of the second rectification region of the argon column is accommodated above the first rectification region of the argon column in the third column shell, and the second subregion of the second rectification region of the argon column is accommodated in the fourth column shell. Such an embodiment is explained further, in particular with reference to FIG. 2 .
In the second group of embodiments, gas can be withdrawn from the first column shell above the first rectification region of the low-pressure column and fed into the second column shell in a first portion below the second rectification region of the low-pressure column and into the third column shell as the first transfer fluid in a second portion below the first rectification region of the argon column. Furthermore, liquid can be withdrawn from the third column shell below the first rectification region of the argon column and fed into the first column shell as the second transfer fluid above the first rectification region of the low-pressure column, and liquid can be withdrawn from the second column shell below the second rectification region of the low-pressure column and fed into the third column shell below the first rectification region of the argon column.
In the second group of embodiments, a lower end of the second column shell is arranged in particular geodesically above a feed-in position of the first transfer fluid into the third column shell, so that the first transfer fluid can be transferred into the third column shell purely by gravity, that is to say in particular without using a pump.
In the context of the present invention, the first pressure level is from 9 to 14.5 bar, for example about 11.8 bar, at the top of the first rectification column, and the second pressure level is 2 to 5 bar, for example about 3.8 bar, at the top of the second rectification column.
Regarding the features of the air separation plant likewise proposed according to the invention, reference is made expressly to the corresponding independent claim. This air separation plant is in particular configured to carry out a method as previously explained in embodiments. Reference is therefore expressly made to the above explanations regarding the method according to the invention and its advantageous embodiments.
The invention will be described in more detail below with reference to the accompanying drawings, which illustrate preferred embodiments of the present invention.

DESCRIPTION OF THE FIGURES

FIGS. 1 and 2 illustrate air separation plants according to different embodiments of the present invention.

In the figures, elements that correspond to one another structurally or functionally are denoted by identical reference signs and, for the sake of clarity, are not repeatedly explained. Explanations relating to plants and plant components apply in the same way for corresponding methods and method steps.
In FIG. 1 , an air separation plant according to an embodiment of the present invention is illustrated in the form of a simplified process flow diagram and is denoted as a whole by 100.
In the air separation plant 100, air is sucked by means of a main air compressor 1 via a filter 2 and compressed to a pressure level of, for example, about 12.5 bar. After cooling and separation of water, the correspondingly compressed air is freed of residual water and carbon dioxide in an pre-cleaning unit 3, which can be designed in a manner known per se. For the design of the mentioned components, reference is made to the technical literature cited at the outset.
A correspondingly formed compressed air stream a is fed from the warm to the cold end through a main heat exchanger 4 and into a pressure column 11 of a rectification column arrangement 10. In addition to the pressure column 11, which comprises a column shell 11′, the rectification column arrangement 10 in the shown example comprises a low-pressure column 12 with a column shell 12′, a crude argon column divided into two and consisting of the column sections 13 a and 13 b with column shells 13 a′ and 13 b′ along with a pure oxygen column 14 with a column shell 14′ and a pure argon column 15. The pressure column 11 is connected in a heat-exchanging manner to the low-pressure column 12 via a main condenser 16, which can in particular be designed as a multi-level bath evaporator, and a sump evaporator 17 is arranged in the bottom of the pure oxygen column 14. In the example shown, a subcooling heat exchanger 18 is also associated with the rectification column system 10.
The low-pressure column 12 and the argon column 13 a, 13 b comprise rectification regions A to D, wherein first and second rectification regions A, B are provided in the low-pressure column 12, and first and second rectification regions C, D are also provided in the argon column. Between the first and second rectification regions A, B of the low-pressure column 12, a first transfer fluid enriched in argon is removed from the low-pressure column 12 in the form of a material stream t1 and fed into the argon column 13 a, 13 b in a first transfer quantity below the first rectification region C of the argon column 13 a, 13 b. Below the first rectification region C of the argon column 13 a, 13 b, a second transfer fluid depleted of argon is removed from the argon column 13 a, 13 b in the form of a material stream t2 and fed into the low-pressure column 12 in a second transfer quantity between the first and second rectification regions A, B of the low-pressure column 12.
The pure oxygen column 14 is operated with a liquid as the return flow, which is removed from the argon column 13 a, 13 b in the form of a material stream r between the first and second rectification regions C, D of the argon column 13 a, 13 b, and a head gas is removed from the pure oxygen column 14 in the form of a material stream g, which is fed into the argon column 13 a, 13 b between the first and second rectification regions C, D of the argon column 13 a, 13 b.
The pressure column 11 and the low-pressure column 12 are connected by means of the main condenser 16 in a heat-exchanging manner, wherein a recirculating stream c is formed using head gas from the low-pressure column 12, which is passed through the subcooling heat exchanger 18, heated in the main heat exchanger 4, compressed by means of a compressor 5, cooled again in the main heat exchanger 4, passed in part c1 through the main condenser 16 and in part c2 through the sump evaporator 17 of the pure oxygen column 14, at least partially condensed there, and fed back into the pressure column 11 and the low-pressure column 12. Portions of the head gas from the low-pressure column are diverted from the recirculating stream c and discharged in the form of a gas product stream c3 and a liquid product stream c4, wherein the latter can be subcooled by expanding a partial stream c5.
In contrast to the embodiment illustrated here, the recirculating stream c can also be fed back into the pressure column 11 without diverting the gas product stream c3 on the warm side of the main heat exchanger 4 after cooling in the main heat exchanger 4, in particular substantially completely, without first passing it through the main condenser 16 and/or the sump evaporator 17 of the pure oxygen column 14. In the latter case, as mentioned, gas, in particular head gas, is removed from the pressure column 11 above the feed-in point of the recirculating stream c, which is further purified in this way with respect to the recirculating stream c, and instead of the recirculating stream itself, this can now be passed partially or completely through the main condenser 16 and/or partially or completely through the sump evaporator 17 of the pure oxygen column 14, where it is at least partially condensed, and returned to the rectification column arrangement 10. In the latter case, the nitrogen product can be provided using head gas from the pressure column 11.
In the embodiment illustrated in FIG. 1 , the first rectification region A and the second rectification region B of the low-pressure column 12 are accommodated in the common column shell 12′ in which the second rectification region B of the low-pressure column 12 is arranged above the first rectification region A of the low-pressure column 12. Furthermore, the first rectification region C of the argon column 13 a, 13 b is accommodated in the column shell 13 a′, and the second rectification region D of the argon column 13 a, 13 b is accommodated in the separate column shell 13 b′. The column shell 13 a′, in which the first rectification region C of the argon column 13 a, 13 b is accommodated, is arranged above the column shell 14′ of the pure oxygen column 14 and is connected thereto or designed integrally therewith.
Further aspects of the operation of the air separation plant 100 according to FIG. 1 will now be explained, some of which are also realized in the air separation plant 200 according to FIG. 2 in the same or a similar way.
Sump liquid is removed from the pressure column in the form of a material stream s and, after passing through the subcooling heat exchanger 18 and partial use as a heating medium in a sump evaporator of the pure argon column 15, is fed into liquid baths of the top condensers of the argon column 13 a, 13 b and the pure argon column 15. The gas formed there and the corresponding flushing quantities are fed into the low-pressure column 12 in the form of material streams s1 to s3. Gas from above the first rectification region C of the argon column 13 a, 13 b and head gas from the pure oxygen column g is transferred to the corresponding part 13 b of the argon column 13 a, 13 b below the second rectification region D, as already mentioned in part. The sump liquid accrued here is returned by means of a pump 18 to the corresponding part 13 a of the argon column 13 a, 13 b above the first rectification region A and, as mentioned, to the pure oxygen column 14.
The argon column 13 a, 13 b, designed here as a crude argon column, and the pure argon column 15 are operated as is generally known from the field of argon production. Therefore, reference is made to the relevant technical literature. In particular, a pure argon stream p is removed from the pure argon column 15 in liquid form, which is internally compressed and discharged as a gaseous argon pressure product. A pure oxygen stream o is withdrawn in liquid form from the bottom of the pure oxygen column 14, which can be stored in a tank system (not shown), for example.
A gas stream t can be withdrawn from the low-pressure column 12 below the first rectification region A, subjected to any dilution gas stream v, heated in the main heat exchanger 8, expanded to an intermediate temperature by means of a residual gas turbine 8 braked by a generator G, for example, and released to the atmosphere or heated and used in the pre-cleaning unit 3. As illustrated in the form of the material stream o1, pure oxygen can be evaporated in the main heat exchanger and released as a corresponding pure oxygen product.
For further features of the air separation plant 100 illustrated in FIG. 1 , reference is again made to the relevant technical literature.
FIG. 2 illustrates a simplified representation of an air separation plant 200 according to a further embodiment of the invention.
In the air separation plant 200 according to FIG. 2 , the first rectification region A of the low- pressure column 12 a, 12 b is accommodated in a first column shell 12 a′, the second rectification region B of the low- pressure column 12 a, 12 b is accommodated in a second column shell 12 b′, and the first and second column shells 12 a′, 12 b′ are arranged next to one another. The first column shell 12 a′ and the column shell 11′ of the pressure column 11 are arranged one above the other and are designed in the form of a double column. The second rectification region D of the argon column 13 a, 13 b is subdivided into a first subregion D1 and a second subregion D2, wherein the first rectification region C of the argon column 13 a, 13 b is accommodated in a third column shell 13 a′, the first subregion D1 of the second rectification region D of the argon column 13 a, 13 b is accommodated above the first rectification region C of the argon column 13 a, 13 b in the third column shell 13 a′, and the second partial region D1 of the second rectification region D of the argon column 13 a, 13 b is accommodated in the fourth column shell 13 b′.
As illustrated in FIG. 2 , gas in the form of a material stream k above the first rectification region A of the low- pressure column 12 a, 12 b is withdrawn from the first column shell 12 a′, and a first portion in the form of a material stream k1 below the second rectification region B of the low- pressure column 12 a, 12 b is fed into the second column shell 12 b′, and a second portion in the form of a material stream k2 below the first rectification region C of the argon column 13 a, 13 b is fed into the third column shell 13 b′ as the first transfer fluid.
Liquid is withdrawn from the third column shell 13 b′ in the form of a material stream m below the first rectification region C of the argon column 13 a, 13 b and fed into the first column shell 12 a′ above the first rectification region A of the low- pressure column 12 a, 12 b as the second transfer fluid, and liquid is withdrawn from the second column shell 12 b′ in the form of a material stream n below the second rectification region B of the low- pressure column 12 a, 12 b and fed into the third column shell 13 a′ below the first rectification region C of the argon column 13 a, 13 b. A lower end of the second column shell 12 b′ is arranged geodesically above a feed-in position of the first transfer fluid into the third column shell 13 a′, so that the first transfer fluid is transferred into the third column shell 13 a′ purely by gravity.
The pure oxygen column 14 is operated with a liquid as the return flow, which is removed from the argon column 13 a, 13 b in the form of a material stream r between the first and second rectification regions C, D of the argon column 13 a, 13 b, and a head gas is removed from the pure oxygen column 14 in the form of a material stream g, which is fed into the argon column 13 a, 13 b between the first and second rectification regions C, D of the argon column 13 a, 13 b.
For further details regarding the design and mode of operation of the air separation plant 200 in accordance with FIG. 2 , reference is made to the explanations for FIG. 1 and the air separation plant 100 and to technical literature.
The air separation plant 100 according to FIG. 1 and the air separation plant 200 according to FIG. 2 are operated in a first operating mode and in a second operating mode, wherein a nitrogen product formed in the low-pressure column 12 after its compression in the compressor 5 is discharged from the air separation plant 100, 200 in the second operating mode in a smaller product quantity than in the first operating mode in the form of a material stream c3, and in the second operating mode, the first transfer quantity of the material stream t1 or k2, that is to say of the first transfer fluid, is adjusted to a lower value than in the first operating mode.

Claims

1. A method for the low-temperature separation of air using an air separation plant which comprises a rectification column arrangement having a pressure column, a low-pressure column and an argon column, wherein:

the low-pressure column is designed in one or more parts and comprises a first and a second rectification region (A, B), and the argon column is designed in one or more parts and comprises a first and a second rectification region (C, D, D1, D2),

between the first and second rectification regions (A, B) of the low-pressure column, a first transfer fluid enriched in argon is removed from the low-pressure column and fed into the argon column in a first transfer quantity below the first rectification region (C) of the argon column,

below the first rectification region (C) of the argon column, a second transfer fluid depleted of argon is removed from the argon column and fed into the low-pressure column in a second transfer quantity between the first and second rectification regions (A, B) of the low-pressure column,

wherein

the air separation plant is operated in a first operating mode and in a second operating mode,

a nitrogen product is discharged from the air separation plant in the first operating mode in a larger product quantity than in the second operating mode,

a pressure is set in the argon column in a pressure range that in the first operating mode

corresponds to a pressure range in which the low-pressure column is operated, or

a pressure range that is at least 50 mbar, at least 100 mbar and/or up to 700 mbar or 900 mbar lower,

and which in the second operating mode is at least 50 mbar, at least 100 mbar and/or up to 700 mbar or 900 mbar below the pressure range of the argon column in the first operating mode,

and in that the rectification column arrangement comprises a pure oxygen column in which a pressure is adjusted in a pressure range that in the first operating mode

corresponds to the pressure range in which the low-pressure column is operated, or

and which in the second operating mode is at least 50 mbar, at least 100 mbar and/or up to 700 mbar or 900 mbar below the pressure range of the pure oxygen column in the first operating mode, wherein the pure oxygen column is operated with a liquid as the return flow, which is removed from the argon column between the first and second rectification regions (C, D) of the argon column, and wherein a head gas is removed from the pure oxygen column and fed into the argon column between the first and second rectification regions (C, D, D1, D2) of the argon column.

2. The method according to claim 1, wherein a valve that is provided in a line for feeding the first transfer quantity into the argon column is closed in the second operation mode, or more tightly in the second operation mode than in the first operation mode.

3. The method according to claim 1, in which the pressure column and the low-pressure column are connected in a heat-exchanging manner by means of a main condenser, wherein a recirculating stream is formed using head gas from the low-pressure column, which is heated, compressed, cooled again, passed partially or completely through the main condenser and/or partially or completely through a sump evaporator of the pure oxygen column, condensed there at least partially, and fed back into the pressure column and/or the low-pressure column.

4. The method according to claim 1, wherein a product quantity of the nitrogen product that is discharged from the air separation plant in the second operation mode is at least 2.5% less, at least 10% less, or 10% to 60% less than in the first operation mode.

5. The method according to claim 1, wherein, between the first and the second operating mode, the pressure in the low-pressure column is changed by not more than 100 mbar.

6. The method according to claim 1, with which the first rectification region (A) and the second rectification region (B) of the low-pressure column are accommodated in a common column shell in which the second rectification region (B) of the low-pressure column is arranged above the first rectification region (A) of the low-pressure column.

7. The method according to claim 1, with which the first and second rectification regions (C, D) of the argon column are accommodated in separate column shells, and with which the column shell, in which the first rectification region (C) of the argon column is accommodated, is arranged in particular above a column shell of the pure oxygen column and is connected thereto or is designed integrally therewith.

8. The method according to claim 1, wherein the first rectification region (A) of the low-pressure column is accommodated in a first column shell, the second rectification region (B) of the low-pressure column is accommodated in a second column shell, and the first and second column shells are arranged next to one another.

9. The method according to claim 8, with which the first column shell and a column shell of the pressure column are arranged one above the other and are designed in the form of a double column.

10. The method according to claim 8, with which the second rectification region (D) of the argon column is subdivided into a first subregion (D1) and a second subregion (D2), wherein the first rectification region (C) of the argon column is accommodated in a third column shell, the first subregion (D1) of the second rectification region (D) of the argon column is accommodated above the first rectification region (C) of the argon column in the third column shell, and the second subregion (D1) of the second rectification region (D) of the argon column is accommodated in the fourth column shell.

11. The method according to claim 10, with which gas above the first rectification region (A) of the low-pressure column is withdrawn from the first column shell and fed into the second column shell in a first portion below the second rectification region (B) of the low-pressure column and into the third column shell as the first transfer fluid in a second portion below the first rectification region (C) of the argon column, with which liquid is withdrawn from the third column shell below the first rectification region (C) of the argon column and is fed into the first column shell as the second transfer fluid above the first rectification region (A) of the low-pressure column, and with which liquid is withdrawn from the second column shell below the second rectification region (B) of the low-pressure column and is fed into the third column shell below the first rectification region (C) of the argon column.

12. The method according to claim 11, with which a lower end of the second column shell lies geodesically above an inlet position of the first transfer fluid into the third column shell, the first transfer fluid is transferred purely into the third column shell.

13. The method according to claim 1, with which the pressure column is operated at a pressure in an operating pressure range of 9 to 14.5 bar, and with which the low-pressure column is operated at a pressure in an operating pressure range of 2 to 5 bar.

14. An air separation plant which comprises a rectification column arrangement having a pressure column, a low-pressure column and an argon column, wherein:

the low-pressure column is designed in one or more parts and comprises a first and a second rectification region (A, B), and the argon column is designed in one or more parts and comprises a first and a second rectification region (C, D, D1, D2), and

the air separation plant is configured such that

between the first and second rectification regions (A, B) of the low-pressure column, a first transfer fluid enriched in argon is to be removed from the low-pressure column and is to be fed into the argon column in a first transfer quantity below the first rectification region (C) of the argon column,

below the first rectification region (C) of the argon column, a second transfer fluid depleted of argon is to be removed from the argon column and is to be fed into the low-pressure column in a second transfer quantity between the first and second rectification regions (A, B) of the low-pressure column,

wherein

is configured for operation in a first operating mode and in a second operating mode, wherein:

the air separation plant is configured to discharge a nitrogen product from the air separation plant in the first operating mode in a larger product quantity than in the second operating mode, and

the air separation plant is configured to adjust a pressure in the argon column in a pressure range that, in the first operating mode,

and in that the rectification column arrangement comprises a pure oxygen column, wherein the air separation plant is configured to adjust a pressure in the pure oxygen column in a pressure range that, in the first operating mode,

and which in the second operating mode is at least 100 mbar and/or up to 700 mbar or 900 mbar below the pressure range of the pure oxygen column (14) in the first operating mode, wherein the air separation plant is configured for the pure oxygen column to be operated with a liquid as the return flow, which is removed from the argon column between the first and second rectification regions of the argon column, and wherein the pure oxygen column comprises means for removing a head gas that is fed into the argon column between the first and second rectification regions of the argon column.