EP3910274A1 - Method for the low-temperature decomposition of air and air separation plant - Google Patents

Abstract

The invention relates to a method for the low-temperature separation of air, in which an air separation plant (100-300) with a rectification column system (10) is used which has a high pressure column (11) and a low pressure column (12), the high pressure column (11) in addition to the low pressure column (12) is arranged. Gas from the high pressure column (11) is diverted using a first condenser evaporator (13) which is arranged in a compartment (15) at the top of the high pressure column (11), and using a second condenser evaporator (14) which is located in the bottom area of the low pressure column ( 12) is arranged, each condensed against bottom liquid from the low-pressure column (12). It is provided that at least the first condenser evaporator (13) is designed as a cascade evaporator, the bottom liquid from the low-pressure column (12) is fed to the first condenser evaporator (13) in an amount that exceeds an amount evaporated in the first condenser evaporator (13). A corresponding system (100-300) is also the subject of the invention.

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 claims.

Background of the invention

The production of air products in the liquid or gaseous state by the low-temperature decomposition of air in air separation plants is known and for example at H.-W. Häring (Ed.), Industrial Gases Processing, Wiley-VCH, 2006 , in particular Section 2.2.5, "Cryogenic Rectification".

Air separation plants of the classic type have rectification column systems which can be designed, for example, as two-column systems, in particular as double-column systems, but also as three- or multi-column systems. In addition to rectification columns for obtaining nitrogen and / or oxygen in the liquid and / or gaseous state, i.e. rectification columns for nitrogen-oxygen separation, rectification columns can be provided for obtaining further air components, in particular noble gases.

The rectification columns of the rectification column systems mentioned are operated at different pressure levels. Known double column systems have a so-called high pressure column (also referred to as a 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. This pressure level is referred to below as the "first pressure level". The low-pressure column, on the other hand, is operated at a pressure level of typically 1 to 2 bar. This pressure level is referred to below as the "second pressure level". In certain cases, higher pressure levels can also be used in the rectification columns. Specific pressure levels are given below. The pressure levels given here are absolute pressures at the top of the respective columns.

In an air separation plant which has a rectification column system with a high pressure column and a low pressure column, air is rectified in the high pressure column to obtain a bottom liquid which is enriched in oxygen compared to the air and to obtain a nitrogen-rich top gas at the first pressure level.

At least part of the bottom liquid of the high pressure column is, optionally after further use, for example as a coolant in top condensers of rectification columns set up for the recovery of argon, fed into the low pressure column, in which an oxygen-rich bottom liquid and a top gas are formed. At least part of the top gas of the high pressure column is condensed against the bottom liquid of the low pressure column, which partly evaporates, in a condenser evaporator, the so-called main condenser, which connects the high pressure column and the low pressure column in a heat-exchanging manner, and at least part of it is returned as reflux to the high pressure column.

The main condenser of an air separation plant can be designed in the form of a so-called cascade evaporator, as will be explained further below, and which offers operational advantages for certain reasons. The object of the present invention is to improve air separation using air separation plants with cascade evaporators.

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 claims. Refinements are the subject matter of the dependent claims and the following description.

In the following, some terms used in the description of the present invention and its advantages, as well as the underlying technical background, are explained in more detail.

The devices used in an air separation plant are described in the cited specialist literature, for example in Häring in Section 2.2.5.6, "Apparatus". Insofar as the following definitions do not deviate from this, express reference is therefore made to the technical literature cited for the language used in the context of the present application.

A “condenser evaporator” is a heat exchanger in which a first, condensing fluid stream enters into indirect heat exchange with a second, vaporizing fluid stream. For an intensive heat exchange, a plurality of passages is provided which are mutually and in groups in a heat exchange relationship and which are acted upon as liquefaction passages with the condensing fluid flow or as evaporation passages with the evaporating fluid flow. Regarding the condenser evaporators typically used in air separation plants, refer in particular to the subsections " Heat Exchangers and Condensers "on page 49 ff . and " Combined Evaporator / Condenser - Heat Transfer Units "on page 52 ff . referenced by Häring. They are typically brazed aluminum plate-fin heat exchangers (PFHE; designations according to the German and English edition of ISO 15547-2: 3005). Instead of the term “condenser evaporator”, the term “condenser” or “evaporator” is often used to simplify matters, depending on whether it is primarily the condensing or evaporating fluid that is being considered.

Bath evaporators and their variants are explained in more detail below; For the falling film evaporators that can also be used in air separation plants and their function, reference is made to the cited specialist literature.

Bath evaporators or bath condensers are devices that work on the basis of the thermosiphon effect. A bath evaporator has a heat exchanger block with evaporation passages which are open at the bottom and which are immersed in a liquid bath, in the case of an air separation plant of the type explained above, in the bottom liquid of the low-pressure column. The fluid to be condensed is applied to the liquefaction passages, in the case of an air separation plant of the type explained above with top gas from the high pressure column. During evaporation in the evaporation passages, a two-phase mixture is formed, which rises in the evaporation passages due to its lower density. After exiting the evaporation passages at the top of the bath evaporator, the liquid portion of the two-phase mixture flows back into the liquid bath, while the evaporated portion continues to rise in gaseous form.

The greater the immersion depth of the heat exchanger block in the liquid bath, the higher the mean hydrostatic pressure in the evaporation passages and the worse the liquid evaporates, since the boiling temperature of the liquid rises in accordance with the vapor pressure curve. As the main condenser in a rectification column system of an air separation plant, two or more bath evaporators arranged next to one another can therefore also be used, which are then connected in parallel on the evaporation and liquefaction sides.

The efficiency of a bath evaporator can, however, also be increased by dividing the heat exchanger block into several sections arranged one above the other. The advantage of such an arrangement is that the immersion depth in each of the sections is smaller than in the case of a single high heat exchanger block. In this way, the hydrostatic pressure in the evaporation passages is reduced and the liquid can evaporate more easily. Because the non-evaporated liquid flows from top to bottom into the liquid bath in each of the sections and is sucked in again from there, the sections are also referred to as circulation sections.

From the DE 199 39 294 a multi-storey bath condenser is known in which two heat exchanger blocks are arranged parallel to one another and in which there are liquid storage containers for the liquid to be evaporated between the heat exchanger blocks for each floor. The evaporation passages are subdivided in the vertical direction into several floors, each of which forms its own circulation section of the type described. The immersion depth is kept relatively small.

In a so-called cascade evaporator ("Kasko"), the floors on the evaporation side are connected in series, i.e. non-evaporated liquid from an upper floor does not flow directly from the upper floors into the lowest liquid bath, but cascades further to the floor below, which has a separate liquid bath . For example, in the EP 1 287 302 A1 disclosed cascade evaporators are provided at least two superimposed circulation sections, which are each fed with liquid from a separate liquid bath or liquid storage container. As a result of the vertical subdivision, the liquid level in the liquid storage containers of the respective circulation sections can be significantly reduced compared to the liquid level in a single, continuous condenser block. The liquid enters the evaporation passages via inlet openings located at the lower end of a circulation section, flows upwards, partially evaporates and leaves the evaporation passages at the upper end of the circulation section via suitable outlet openings. The liquid component in the two-phase mixture emerging from the passages flows back to the inlet openings of this circulation section and, depending on the liquid level in the liquid storage container of the circulation section, to the inlet openings of the circulation section below, in order to be knocked over there again via the evaporation passages.

In the case of a cascade evaporator, at least two of the circulation sections can be formed by a heat exchanger section of a common heat exchanger block. However, at least one of the circulation sections can also be formed by a separate heat exchanger block. On the liquefaction side, cascade evaporators can preferably also be connected in series, for example by means of liquefaction passages of a common heat exchanger block, which extend over all floors. Alternatively, the floors of a cascade evaporator can also be connected in parallel on the condensing side.

The rectification column system of an air separation plant of the type described is supplied with compressed and cooled feed air, which can be provided in different ways and in the form of one or more partial flows of the same or different physical state and at different pressure levels. The provision of the feed air can be provided in different ways within the scope of the present invention and the present invention is not restricted to a specific embodiment.

Liquids and gases, as used herein, can be rich or poor in one or more components, with "rich" meaning a content of at least 50%, 75%, 90%, 95%, 99%, 99.5%, 99.9% or 99.99% and "poor" for a content of at most 50%, 25%, 10%, 5% , 1%, 0.1%, or 0.01% on a mole, weight, or volume basis. The term "predominantly" can match the definition of "rich". Liquids and gases can also be enriched or depleted in one or more components, these terms referring to a content in a starting liquid or a starting gas from which the liquid or gas under consideration was obtained. The liquid or gas is "enriched" if this or this is 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 this or this 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 liquid or the starting gas.

The present disclosure uses the terms "pressure level" and "temperature level" to characterize pressures and temperatures, which is intended to express that corresponding pressures and temperatures in a corresponding system do not have to be used in the form of exact pressure or temperature values to realize the inventive concept. However, such pressures and temperatures typically move in certain ranges, for example 1%, 5%, 10%, 20% or even 50% around a mean value. Corresponding pressure levels and temperature levels can be in disjoint areas or in areas that overlap one another. In particular, pressure levels include, for example, unavoidable or expected pressure losses. The same applies to temperature levels. As mentioned, the pressure data here are absolute pressures and, in the event that these relate to pressure levels in rectification columns, in each case to pressure levels which are present at the top of these rectification columns.

In general, a “rectification column” is understood here to be a separating apparatus in which a gas rising from bottom to top is sent towards a liquid trickling down from top to bottom. Gas and liquid, which can each be formed using one or more different material flows, are subjected to a mass transfer, supported by surface-enlarging structures or known dividing trays. In a lower one In the area of a rectification column ("bottom"), the composition of the liquid ("bottom liquid") that has changed due to the mass transfer collects, while the rising gas ("top gas") with a correspondingly changed composition in an upper area ("top"). In a rectification column as understood here, in contrast to a pure absorption column, either a condensation of at least part of the top gas, which is then at least partly returned in condensed form to the rectification column under consideration, and / or an evaporation of at least part of the bottom liquid, which is then also at least partially returned to the rectification column in vaporized form.

The relative spatial terms "above", "below", "above", "below", "above", "below", "next to", "next to one another", "vertical", "horizontal" etc. refer to the spatial alignment of the rectification columns of an air separation plant or other components in normal operation. An arrangement of two components "one above the other" is understood here to mean that the upper end of the lower of the two components is at a lower or the same geodetic height as the lower end of the upper of the two components and that the projections of the two components overlap in a horizontal plane but not in a vertical plane. In particular, the two components are arranged exactly one above the other, that is, the axes of the two components run on the same vertical straight line. The axes of the two components do not have to be exactly perpendicular, but can also be offset from one another, especially if one of the two components, for example a rectification column or a column part with a smaller diameter, is to have the same distance from the sheet metal jacket of a coldbox as another with a larger one Diameter. Correspondingly, an arrangement of two components “next to one another” is understood here to mean that the projections of the two components under consideration overlap in a vertical plane, but the lower or upper ends do not have to be exactly in a horizontal plane.

Advantages of the invention

The present invention is used in an air separation plant which has a high pressure column and a low pressure column. The high pressure column is operated at the first pressure level mentioned, which can in particular also be 5 to 6 bar, for example approx. 5.3 bar. The low-pressure column is operated at the mentioned second pressure level, which in particular can also be about 1.1 to 1.5 bar, for example about 1.2 bar. In the context of the invention, the low-pressure column is arranged next to the high-pressure column in the sense explained above. The rectification column system used in the context of the present invention is therefore not a classic double column system in which the high and low pressure columns are arranged one above the other and together form a double column. By arranging the high and low pressure columns next to each other, the total height of the air separation plant can be reduced and transport and construction can be simplified. For example, this improves assembly on a construction site, where, for example, too high a total height can be critical for the erection of the rectification columns due to the possibly unavailability of cranes.

In the context of the present invention, it was found that the function of the main condenser of an air separation plant in such a scenario is particularly advantageous through the combination of a cascade evaporator with a further condenser evaporator, which is also in the form of a cascade evaporator or in the form of another type of condenser evaporator such as a single-stage Bath evaporator can be designed, can be taken over. In the first case, a two-part cascade evaporator is provided, so to speak, in the second case a cascade evaporator with an additional condenser evaporator, which is not designed as a cascade evaporator, is provided. In the context of the present invention, the cascade evaporator is arranged in a compartment at the top of the high pressure column. This compartment can, in particular, be arranged in a common outer shell with the separating devices of the high pressure column or be permanently connected to the high pressure column. Also a provision of two different outer shells, which are connected to one another via an edge region, for example welded, or in which, for example, the outer shell of the Compartment is attached to an outer shell of the high pressure column is basically possible. A "fixed" connection is thus intended to denote a connection that takes place via structures that represent connection structures that go beyond pure lines.

As is known, the function of the main capacitor can also be distributed over two structural units in different compartments. For example, the DE 827 364 B proposed to provide a first condenser evaporator at the top of the high pressure column and a second condenser evaporator in the bottom of the low pressure column, which is arranged here next to the high pressure column. Both condenser evaporators are designed here as bath evaporators. In the first and the second condenser evaporator, part of the top gas of the high pressure column is condensed and part of the bottom liquid of the low pressure column is evaporated. Something similar is also provided in the DE 24 02 246 A1 proposed for the production of oxygen of medium purity.

The division of a cascade evaporator or the provision of a further condenser evaporator in the manner mentioned is technically not easily feasible compared to the division of a bath evaporator or the provision of separate bath evaporators. The fluid dynamic conditions in cascade evaporators differ fundamentally from those in pure bath evaporators. In the case of a single-stage bath evaporator, a significantly larger part of the liquid that has not evaporated in the evaporation passages flows into the liquid bath in which the bath evaporator is immersed. Since this only takes place once in a single-stage bath evaporator or on one stage, the loss of liquid is relatively low here, i.e. a comparatively small proportion of the liquid is carried away by the so-called entrainment into the gas phase. In this way, a bath evaporator can be divided up in a relatively simple manner, since the amounts of liquid in each of the parts formed can be easily adjusted.

In the case of a cascade evaporator, on the other hand, there is a loss of liquid in this way in each stage. The total amount of liquid required for a cascade evaporator is determined by the amount of liquid required in the second lowest stage of the cascade evaporator, since the liquid flowing down from top to bottom evaporates and closes in each of the stages above Part of it is also subjected to entrainment. In contrast, the bottom liquid bath is less critical because further liquid collects here, including some of the previously entrained liquid droplets. In other words, when operating a cascade evaporator, the entire chain of liquid baths must always be monitored in terms of control technology in order to avoid a shortage of liquid in one of the liquid baths (especially in the second from the bottom). A pure division of a cascade evaporator into two parts is therefore obviously associated with a significantly increased control and regulation effort, since this doubles the control effort.

At the same time, dividing a cascade evaporator into two parts is advantageous and desirable, since in this way the overall height of the system can be reduced or the advantageous functions of a condenser evaporator, as explained above, even in larger systems in which the buildability limits for cascade evaporators can be achieved. The division into two also has the advantage that the described problem of entrainment, as recognized according to the invention, is less critical here, since the amount of liquid that is passed over the cascade evaporator increases in relative terms.

The present invention solves this problem in that the bottom liquid from the low-pressure column is fed to the first condenser-evaporator in an amount which exceeds an amount which has evaporated therefrom in the first condenser-evaporator. The amount of bottom liquid from the low-pressure column that has not evaporated in the first condenser-evaporator can at least partially be returned to the low-pressure column and / or, for example, discharged from the air separation plant to provide an oxygen product. In other words, within the scope of the present invention, the first condenser evaporator, which is designed as a cascade evaporator, is supplied with the liquid to be evaporated in an excess amount that exceeds the liquid requirement in the first condenser evaporator. In this way, within the scope of the present invention, the control engineering effort for operating the first condenser evaporator, which is designed as a cascade evaporator, is significantly simplified, whereby the basic advantages of using a cascade evaporator are used and the division of the main condenser function improves, in particular, structural height and transportability.

In other words, the present invention proposes a method for the cryogenic separation of air, in which an air separation plant is used with a rectification column system which has a high pressure column and a low pressure column, the high pressure column being arranged next to the low pressure column and gas from the high pressure column using a first condenser-evaporator, which is arranged in a compartment at the top of the high-pressure column, and a second condenser-evaporator, which is arranged in the bottom area of the low-pressure column, is each condensed against bottom liquid from the low-pressure column.

According to the invention, at least the first condenser evaporator is designed as a cascade evaporator, the bottom liquid from the low-pressure column is fed to the first condenser evaporator in an amount that exceeds an amount evaporated therefrom in the first condenser evaporator. Bottom liquid from the low-pressure column that has not evaporated in the first condenser-evaporator can, as mentioned, be at least partially returned to the low-pressure column and / or, for example, discharged from the air separation plant to provide an oxygen product. It goes without saying that when it is said that "non-evaporated bottom liquid from the low-pressure column is at least partially returned to the low-pressure column" or "discharged from the air separation plant", the entire, non-evaporated bottom liquid of this or only a part of this can be affected and that, if necessary, further liquid is also fed into the low-pressure column together with this bottom liquid.

In the context of the present invention, the unevaporated bottom liquid from the low pressure column, which is returned to the low pressure column in a corresponding embodiment, can be fed into the bottom area of the low pressure column above or below an upper end of the second condenser evaporator and above a liquid level of the bottom liquid in the low pressure column . The exact type of feed depends in particular on the type of second condenser evaporator used and the ratio of the quantities of liquid to be evaporated in the first and second condenser evaporators. Through the Feeding in above the upper end of the second condenser evaporator, in particular a larger amount of liquid can be circulated via the cascade evaporator, so that fewer problems arise with the aforementioned entrainment. However, there is a higher manufacturing cost. Conversely, the infeed below the upper end of the second condenser evaporator reduces the manufacturing outlay accordingly.

As also mentioned, this second condenser evaporator can, in embodiments of the present invention, be designed as a (further) cascade evaporator, as a single-stage bath evaporator or as a falling film evaporator. In all cases, the respective advantages of the corresponding evaporator types can be used. For bath evaporators, these consist in the fact that no device is required to collect the liquid and feed it directly to the evaporator, whereas a cascade evaporator has advantages due to the lower immersion depth, as described above.

In the context of the present invention, the first and second condenser-evaporators can be supplied with the gas to be liquefied from the high-pressure column and / or with the bottom liquid from the low-pressure column in series or in parallel. A parallel application can be particularly advantageous because it allows pressure losses and thus energy consumption to be minimized. A serial application can be advantageous because an enrichment of helium and / or neon can be used in this way.

In the context of the present invention, the bottom liquid not evaporated in the first condenser evaporator from the low pressure column and furthermore gas evaporated in the first condenser evaporator can be returned to the low pressure column in the form of one or more streams. For example, the non-evaporated bottom liquid and the evaporated gas can be returned in the form of a two-phase flow, but it can also be provided that separate lines are used for this purpose.

Instead of transferring vaporized gas into the low-pressure column, the gas can also be fed in the opposite direction. The evaporation chambers of the two condenser evaporators can also be at different pressures and thus Temperature level are operated. The pressure in the bottom of the low-pressure column results from the pressure loss in the low-pressure column plus the pressure loss in the exhaust air (e.g. for regeneration). In particular, when gaseous oxygen is generated, which is drawn off directly from the bottom of the low-pressure column, i.e. no internal compression takes place, the evaporation space of the first condenser-evaporator in the compartment at the top of the high-pressure column can be at a lower pressure level of, for example, 1.1 to 1.25 bar be operated as the evaporation chamber of the second condenser evaporator in the bottom of the low-pressure column, which can be, for example, 1.2 to 1.4 bar, whereby heating surface can be saved. In this case, liquid evaporated in the first condenser-evaporator cannot be fed into the low-pressure column but, conversely, gas into the evaporation space of the first condenser-evaporator via a line from the bottom of the low-pressure column.

In the context of the present invention it can be provided in particular that a first condensate is formed from the gas from the high pressure column in the first condenser evaporator, and that the first condensate is at least partially in the high pressure column or both in the high pressure column and in the low pressure column is fed in. In the second condenser-evaporator, a second condensate can be formed from the gas from the high pressure column, which is also at least partially fed into the high pressure column or both into the high pressure column and into the low pressure column. This variant of the present invention thus differs from known processes from the prior art in which two-part bath condensers are used in that reflux liquid for the high pressure column is also provided using the condenser evaporator arranged in the low pressure column.

The two condensates can also be combined completely or at least in part and distributed in adjustable proportions between the high-pressure and the low-pressure column. In this way, particularly favorable return flow conditions can be set. However, at least some of the condensates can also be fed separately into the high-pressure and low-pressure columns. At least one of the two condensates can also be fed into the high-pressure column and / or into the low-pressure column without a pump.

The gas from the high pressure column, which is condensed using the first condenser evaporator and the second condenser evaporator, can in the context of the present invention exclusively comprise top gas from the high pressure column, but also gas removed from the high pressure column via a side take-off and top gas from the high pressure column. The gas withdrawn from the high pressure column via the side take-off and the top gas from the high pressure column can each be condensed separately from one another in one of the two condenser evaporators. The two correspondingly formed condensates can be fed together or separately from one another at the same or at different positions into the high pressure column and / or into the low pressure column.

In particular, within the scope of the present invention, energy can be saved through a reduced pressure level of the high pressure column if, using the first condenser evaporator, the top gas of the high pressure column and, using the second condenser evaporator, the gas withdrawn from the high pressure column via the side take-off, for example with a nitrogen content of 92 to 97%, in particular approx. 95%, are condensed. The top gas of the high pressure column in particular has a nitrogen content of more than 99%. The pressure in the evaporation space of the first condenser evaporator is advantageously lower than in the bottom of the low-pressure column. The former is, for example, from 1.1 to 1.25 bar, the latter, for example, from 1.2 to 1.4 bar. The high pressure column can be operated at 4.7 to 5.1 bar, for example.

Regarding the features of the air separation plant also proposed according to the invention, express reference is made to the corresponding independent patent claim. The air separation plant is set up, in particular, to carry out a method as has been explained above in embodiments. Reference is therefore expressly made to the above explanations with regard to the method according to the invention and its advantageous configurations.

The invention is explained in more detail below with reference to the accompanying drawings, which illustrate the preferred embodiments of the present invention.

Figure description

the Figures 1 to 3 illustrate air separation plants in accordance with different aspects of the present invention.

In the figures, structurally or functionally corresponding elements are indicated with identical reference symbols and are not explained repeatedly for the sake of clarity. Explanations relating to systems and system components apply in the same way to the corresponding processes and process steps.

The components, which are simplified in the figures in a block diagram, can be designed in any conventional manner. This involves a compression unit 1, which in particular comprises a known main air compressor, an air cleaning unit 2, which in particular comprises a known adsorption system, and a main heat exchange unit 3, which in particular comprises a known main heat exchanger. By means of these units, which are shown unlinked to illustrate the general applicability, two symbolically shown feed air flows A and B are provided in the examples illustrated in the figures. The invention is not limited by the specific way in which the feed air flows are provided and their type, number, physical state, pressure, etc. are not restricted. Air products formed in the respective air separation plants are not illustrated or not illustrated in their entirety.

The air separation plants can have any further components. For exemplary configurations, express reference is made to the cited specialist literature, in particular the mentioned section 2.2.5, “Cryogenic Rectification”, in Häring and the figure 2.3A there.

The air separation plants each have, as common features, a rectification column system 10 which comprises a high pressure column 11 and a low pressure column 12. The high pressure column 11 and the low pressure column 12 can be operated at known pressure levels. The high pressure column 11 is arranged next to the low pressure column 12. In each rectification column system 10, gas from the high pressure column 11 is under Use of a first condenser-evaporator 13, which is arranged in a compartment 15 at the top of the high-pressure column 11, and a second condenser-evaporator 14, which is arranged in the bottom area of the low-pressure column 12, each condensed against bottom liquid from the low-pressure column 12, as explained below for the individual configurations .

In all cases, regardless of the non-specific graphic representation, at least the first condenser evaporator 13 is designed as a cascade evaporator, and the bottom liquid from the low-pressure column 12 is fed to the first condenser evaporator 13 in an amount that exceeds an amount evaporated in the first condenser evaporator 13 . Bottom liquid from the low-pressure column 12 that has not evaporated in the first condenser-evaporator 13 is returned to the low-pressure column 12.

A subcooling countercurrent 16, pumps 17 and 18 and a separating tank are illustrated as further components in the following figures. These elements are not present in all configurations.

In Figure 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 designated as a whole by 100.

As illustrated with reference to the air separation plant 100, only top gas of the high pressure column 11 is condensed in the first condenser evaporator 13 and in the second condenser evaporator 14. This is removed from the high pressure column 11 in the form of a stream C and passed through the first condenser evaporator 13 and the second condenser evaporator 14 in the form of substreams D and E. Condensate formed from substream D is here partially combined with condensate formed from substream E and conveyed by means of the pump 17 to form a collective flow F and returned to the high pressure column 11 as reflux. A substream G can also be passed through the subcooling countercurrent 16 and fed into the low-pressure column 12 in the manner illustrated. Since there is in particular no or only a very small nitrogen section 12a in the low-pressure column 12, this material flow G can be small or can be omitted. The high pressure column 11 is furthermore, gas is withdrawn via a side take-off in the form of a stream H, which in the example shown is likewise passed through the subcooling countercurrent 16 and fed into the low-pressure column 12.

Bottom liquid from the low-pressure column 12 can be discharged as a product in the form of a stream K. Further sump liquid is fed to the compartment 15 or to the first condenser evaporator 13 in the form of a material flow L by means of the pump 18. As mentioned, this is an amount which exceeds an amount evaporated in the first condenser evaporator 13. Bottom liquid from the low-pressure column 12 that has not evaporated in the first condenser-evaporator 13 is returned to the low-pressure column 12 in the form of a stream M. Correspondingly, vaporized gas is also returned to the low-pressure column 12 in the form of a stream N.

As not explained separately, impure nitrogen O, gaseous nitrogen P and liquid nitrogen Q can be discharged from the low-pressure column 12.

In Figure 2 an air separation plant according to a further embodiment of the present invention is illustrated in the form of a simplified process flow diagram and designated as a whole by 200.

In contrast to the in Figure 1 The air separation plant 100 illustrated here is not condensed in the second condenser evaporator 14 at the top of the high pressure column 11, i.e. the stream E, but gas from a side take-off of the high pressure column 11 in the form of a stream R. In this way, the pump 17 can be dispensed with. The top gas of the high-pressure column 11, which is also condensed in the first condenser-evaporator 13 here, is also denoted by D here. The condensed material flow R and further fluid, which is withdrawn from the high pressure column 11 in the form of a material flow S via a side take-off, is fed into the separating vessel 19. Gas from the separating vessel 19, which is not specifically designated, can be released into the atmosphere, whereas liquid from the separating vessel 19 in the form of a material flow T is passed through the subcooling countercurrent 16 and then fed into the low-pressure column 12.

In Figure 3 an air separation plant according to a further embodiment of the present invention is illustrated in the form of a simplified process flow diagram and designated as a whole by 300.

The air separation plant 300 is similar to that in FIG Figure 1 illustrated air separation plant 100, however, has the separation container 19. A portion of the stream D, denoted here by V, and the stream E are fed into these and are not fed into the high-pressure column 11 in the form of a stream U. Here, too, gas can be released into the atmosphere from the separator container 19, which is not specifically designated, whereas liquid from the separator container 19 in the form of a material flow W is passed through the subcooling countercurrent 16 and then fed into the low-pressure column 12.

Claims (15)

Process for the low-temperature separation of air, in which an air separation plant (100-300) with a rectification column system (10) is used which has a high pressure column (11) and a low pressure column (12), the high pressure column (11) being arranged next to the low pressure column (12) and wherein gas from the high pressure column (11) using a first condenser evaporator (13) which is arranged in a compartment (15) at the top of the high pressure column (11), and a second condenser evaporator (14) which is located in the bottom area of the low pressure column ( 12) is arranged, each condensed against bottom liquid from the low pressure column (12), characterized in that at least the first condenser evaporator (13) is designed as a cascade evaporator, that the first condenser evaporator (13) the bottom liquid from the low pressure column (12) in a Amount is supplied which exceeds an amount evaporated in the first condenser evaporator (13). Process according to Claim 1, in which at least part of the bottom liquid not evaporated in the first condenser-evaporator (13) is returned from the low-pressure column (12) to the low-pressure column (12). Method according to Claim 1 or 2, in which at least part of the bottom liquid which has not evaporated in the first condenser-evaporator (13) is discharged from the air separation plant (100-300). Method according to one of the preceding claims, in which the unevaporated bottom liquid from the low-pressure column (12), which is returned to the low-pressure column (12), above or below an upper end of the second condenser-evaporator (14) and above a liquid level of the bottom liquid in the Low-pressure column (12) is fed into the bottom region of the low-pressure column (12). Method according to one of the preceding claims, in which the second condenser evaporator (14) is designed as a cascade evaporator, as a single-stage bath evaporator or as a falling film evaporator. Method according to one of the preceding claims, in which the first condenser evaporator (13) and the second condenser evaporator (14) in series or in parallel with the gas to be liquefied from the high pressure column (11) and / or in series or in parallel with the bottom liquid from the low pressure column (12) ) can be applied. Method according to one of the preceding claims, in which the bottom liquid not evaporated in the first condenser evaporator (13) and furthermore gas evaporated in the first condenser evaporator is returned in the form of one or more material flows to the low-pressure column (12). Method according to one of the preceding claims, in which a first condensate is formed in the first condenser-evaporator (13) from the gas from the high-pressure column (11), and in which the first condensate is at least partly in the high-pressure column (11) or in the High pressure column (11) and is fed into the low pressure column (12). Process according to Claim 8, in which a second condensate is formed in the second condenser-evaporator (14) from the gas from the high-pressure column (11), and in which the second condensate is at least partially in the high-pressure column (11) or in the high-pressure column ( 11) and is fed into the low-pressure column (12). Process according to Claim 9, in which the first and / or the second condensate is distributed at least in part in adjustable proportions to the high-pressure column (11) and to the low-pressure column (12). Process according to one of Claims 9 or 10, in which the first and / or the second condensate is fed into the high-pressure column (11) and / or into the low-pressure column (12) without a pump. Method according to one of the preceding claims, in which the gas from the high-pressure column (11) which is produced using the first condenser-evaporator (13) and the second condenser-evaporator (14) is condensed, comprises gas withdrawn from the high pressure column (11) via a side take-off and top gas from the high pressure column (11). Process according to Claim 10, in which the gas withdrawn from the high pressure column (11) via the side take-off and the top gas from the high pressure column (11) are condensed separately from one another in one of the two condenser evaporators (13, 14). Method according to one of the preceding claims, in which the evaporation chamber of the first condenser evaporator (11) is operated at a lower pressure level than the evaporation chamber of the second condenser evaporator (12). Air separation plant (100-300) with a rectification column system (10) which has a high pressure column (11) and a low pressure column (12), the high pressure column (11) being arranged next to the low pressure column (12), a first condenser evaporator (13) in one Compartment (15) is provided at the top of the high-pressure column (11), a second condenser-evaporator (14) is provided in the bottom area of the low-pressure column (12), and the first condenser-evaporator (13) and the second condenser-evaporator (14) are set up to discharge gas the high pressure column (11) to condense against bottom liquid from the low pressure column (12), characterized in that at least the first condenser evaporator (13) is designed as a cascade evaporator, and that means are provided which are set up to the first condenser evaporator (13) the To feed bottom liquid from the low pressure column (12) in an amount that is one in the first condensa evaporator (13) exceeds the amount evaporated.

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