PROCESS AND PLANT FOR CRYOPHYTO-TEMPERATURE AIR SEPARATION

Description

[0001] The invention relates to a process for the low-temperature separation of air and a corresponding plant according to the preambles of the independent patent claims. State of the art

[0002] The production of air products in liquid or gaseous state by cryogenic separation of air in air separation plants is known and described, for example, in H.-W. Häring (ed.), Industrial Gases Processing, Wiley-VCH, 2006, especially Section 2.2.5, "Cryogenic Rectification".

[0003] Air separation plants have rectification column systems, which can traditionally be configured as two-column systems, particularly classic Linde double-column systems, but also as three- or multi-column systems. In addition to the rectification columns for the recovery of nitrogen and / or oxygen in the liquid and / or gaseous state, i.e., the rectification columns for nitrogen-oxygen separation, rectification columns can be provided for the recovery of other air components, particularly the noble gases krypton, xenon, and / or argon. The terms "rectification" and "distillation," as well as "column" and "column," or combinations thereof, are often used synonymously.

[0004] 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 (also referred to as the upper column). The high-pressure column is typically operated at a pressure level of 4 to 7 bar, in particular approximately 5.3 bar. The low-pressure column is typically operated at a pressure level of 1 to 2 bar, in particular approximately 1.4 bar. In certain cases, higher pressure levels can also be used in both rectification columns. The pressures stated here and below are absolute pressures at the top of the respective columns.

[0005] So-called SPECTRA processes are known from the prior art for providing compressed nitrogen as the main product. These are explained in more detail below. The present invention, in its embodiments, aims to improve such SPECTRA processes, primarily with regard to energy consumption and material yield. A particular focus of the object of the present invention is to provide a process and an air separation plant by means of which, in addition to larger quantities of high-purity, gaseous nitrogen at a significantly superatmospheric pressure level, another nitrogen product and / or argon can also be advantageously provided. Disclosure of the invention

[0006] Against this background, the present invention proposes a method for the cryogenic separation of air and a corresponding system having the features of the independent patent claims. A method for the cryogenic separation of air and a corresponding system according to the preambles of the respective independent claims are known from US 2009 / 120128 A1.

[0007] Preferred embodiments are the subject of the subclaims and the following description.

[0008] Before explaining the features and advantages of the present invention, some principles of the present invention are explained in more detail and terms used below are defined.

[0009] The devices used in an air separation plant are described in the cited technical literature, for example, in Häring (see above) in Section 2.2.5.6, "Apparatus." Unless the following definitions deviate from this definition, explicit reference is made to the cited technical literature for the terminology used in this application.

[0010] As used herein, liquids and gases may be rich or poor in one or more components, where "rich" may mean a content of at least 75%, 90%, 95%, 99%, 99.5%, 99.9%, or 99.99%, and "poor" may mean a content of at most 25%, 10%, 5%, 1%, 0.1%, or 0.01% on a molar, weight, or volume basis. The term "predominantly" may correspond to the definition of "rich." Liquids and gases may also be enriched or depleted in one or more components, where these terms refer to a content in a parent liquid or gas from which the liquid or gas was derived. The liquid or gas 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 concentration, and "depleted" if it contains at most 0.9 times, 0.5 times, 0.1 times, 0.01 times, or 0.001 times the concentration of a corresponding component, relative to the original liquid or gas. For example, if "oxygen," "nitrogen," or "argon" is mentioned here, this also includes a liquid or gas that is rich in oxygen or nitrogen, but does not necessarily have to consist exclusively of them.

[0011] This application uses the terms "pressure level" and "temperature level" to characterize pressures and temperatures. This 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 implement the inventive concept. However, such pressures and temperatures typically fluctuate within certain ranges, for example, within ± 1%, 5%, 10%, or 20% of a mean value. Corresponding pressure levels and temperature levels can lie in disjoint ranges or in ranges that overlap one another. In particular, pressure levels, for example, include unavoidable or expected pressure losses. The same applies to temperature levels. The pressure levels specified here in bar are absolute pressures.

[0012] When we talk about "expansion machines" here, we typically mean well-known turboexpanders. These expansion machines can also be coupled to compressors. These compressors can, in particular, be turbocompressors. A corresponding combination of turboexpander and turbocompressor is typically also referred to as a "turbine booster." In a turbine booster, the turboexpander and the turbocompressor are mechanically coupled, whereby the coupling can be at the same speed (for example, via a common shaft) or at different speeds (for example, via a suitable transmission gear). The term "compressor" is generally used here. A "cold compressor" refers to a compressor to which a fluid flow is fed at a temperature level significantly below 0 °C, in particular below -50, -75, or -100 °C and down to -150 or -200 °C.A corresponding fluid flow is cooled to a corresponding temperature level, in particular by means of a main heat exchanger (see below).

[0013] A "main air compressor" is characterized by the fact that it compresses all of the air supplied to the air separation plant and separated there. In contrast, in one or more optionally provided additional compressors, such as booster compressors, only a portion of this air previously compressed in the main air compressor is further compressed. Accordingly, the "main heat exchanger" of an air separation plant represents the heat exchanger in which at least the majority of the air supplied to the air separation plant and separated there is cooled. This occurs, at least in part, in countercurrent to material flows discharged from the air separation plant. Material flows or "products" "discharged" from an air separation plant, as used here, are fluids that no longer participate in the plant's internal circuits but are permanently removed from them.

[0014] A "heat exchanger" for use in the present invention can be designed in a manner conventional in the art. It serves for the indirect transfer of heat between at least two fluid streams, e.g., flowing countercurrently to one another, for example, a warm compressed air stream and one or more cold fluid streams, or a cryogenic liquid air product and one or more warm or warmer, but possibly also cryogenic fluid streams. A heat exchanger can be formed from a single or multiple heat exchanger sections connected in parallel and / or in series, e.g., from one or more plate heat exchanger blocks. This is, for example, a plate fin heat exchanger. Such a heat exchanger has "passages" designed as separate fluid channels with heat exchange surfaces, which are connected in parallel and separated by other passages to form "passage groups."The characteristic of a heat exchanger is that heat is exchanged between two mobile media at a time, namely at least one fluid flow to be cooled and at least one fluid flow to be heated.

[0015] A "condenser-evaporator" is 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 condensing chamber and an evaporating chamber. The condensing and evaporating chambers have condensation and evaporation passages, respectively. The condensation (liquefaction) of the first fluid stream takes place in the condensing chamber, and the evaporation of the second fluid stream takes place in the evaporating chamber. The evaporation and condensing chambers are formed by groups of passages that are in heat exchange relationship with each other.

[0016] The relative spatial terms "top," "bottom," "above," "below," "above," "below," "next to," "side by side," "vertical," "horizontal," etc., refer here to the spatial orientation of the rectification columns of an air separation plant during normal operation. An arrangement of two rectification columns or other components "one above the other" is understood here to mean that the upper end of the lower of the two apparatus sections is at a lower or equal geodetic height than the lower end of the upper of the two apparatus sections, and the projections of the two apparatus sections intersect in a horizontal plane. In particular, the two apparatus sections are arranged exactly one above the other, i.e., the axes of the two apparatus sections run on the same vertical line.However, the axes of the two apparatus parts do not have to be exactly perpendicular to each other, but can also be offset from each other, especially if one of the two apparatus parts, 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 cold box as another with a larger diameter.

[0017] The present invention comprises the low-temperature separation of air according to the so-called SPECTRA process, as described, inter alia, in EP 2 789 958 A1 and the other patent literature cited therein. In its simplest form, this is a single-column process. Such processes enable a high nitrogen yield. A reflux to what is, in the simplest case, a single rectification column is provided by condensing the overhead gas from this rectification column, or more precisely, a portion of this overhead gas, in a heat exchanger. Fluid withdrawn from the same rectification column is used for cooling in the heat exchanger. Additional overhead gas can be provided as a nitrogen-rich product of the process or plant.

[0018] Using a cold compressor, a portion of the fluid used to condense the thus-treated portion of the overhead gas is compressed and returned to the same rectification column. SPECTRA processes can achieve very favorable air ratios, i.e., a large amount of product per unit of air used. A corresponding process is explained in more detail below. The term "SPECTRA process" refers to the single-column process for nitrogen recovery described above or to a modified single-column process in which, as also explained below, an additional rectification column is used for oxygen recovery.

[0019] As with other cryogenic air separation processes, the SPECTRA process involves cooling compressed and pre-purified air to a temperature suitable for rectification. This allows it to be partially liquefied. The air is then fed into the rectification column mentioned above, where it is rectified under the typical pressure of a high-pressure column, as explained above, to obtain the aforementioned overhead gas, which is enriched in nitrogen compared to atmospheric air, and a liquid bottoms liquid, which is enriched in oxygen compared to atmospheric air.

[0020] In a SPECTRA process, the aforementioned rectification column is used in an air separation plant, in which a gaseous overhead product enriched in nitrogen compared to atmospheric air and a liquid bottom product enriched in oxygen compared to atmospheric air are formed. The terms "overhead product" and "overhead gas" on the one hand, and "bottom product" and "bottom liquid" on the other, are used synonymously here.

[0021] This rectification column, whose overhead gas is partially liquefied or partially liquefied in the manner described using expanded fluid from the same rectification column and then at least partially recycled to the same rectification column, is referred to here as the "first" rectification column. As mentioned, in known SPECTRA processes, this may also be the only rectification column. However, this is not the case within the scope of the present invention.

[0022] The fluid used to condense the thus-treated portion of the top gas from the first rectification column, which may in particular be a cryogenic liquid enriched in oxygen relative to atmospheric air, is withdrawn from the first rectification column in the form of one or more streams. At least a portion of the fluid is heated in the heat exchanger used to condense the thus-treated portion of the top gas from the first rectification column.

[0023] This or these material streams will be referred to below as the "first" material stream(s). The fluid can be passed through the heat exchanger in the form of only one first material stream or in the form of two or more separate first material streams. For example, one material stream can first be withdrawn from the rectification column and then split, or two separate first material streams, particularly with different oxygen contents, can be withdrawn separately from each other from the rectification column.

[0024] In the SPECTRA process, as already mentioned and expressed here again in other words, the fluid which is taken from the first rectification column in the form of the one or more first material streams and heated in the heat exchanger is compressed to a first part in one or more compressors and, after this compression, fed back into the first rectification column.

[0025] In a second part, the fluid which is withdrawn from the first rectification column in the form of the one or more first material streams and heated in the heat exchanger can be expanded in the SPECTRA process using one or more expansion machines and in particular discharged as a so-called residual gas mixture from the air separation plant.

[0026] The first and second portions of the fluid withdrawn from the rectification column in the form of one or more first streams, i.e., the compressed and expanded portions, can in turn be two first streams, as explained above, which have already been discharged separately from the first rectification column. However, they can also be portions of only one first stream withdrawn from the first rectification column. The first and second portions can also have been passed through the heat exchanger together and only then be divided into the first and second portions.

[0027] For the compression of the aforementioned first portion of the fluid, which is taken from the first rectification column in the form of the one or more first material streams and heated in the heat exchanger, one or more compressors can be used, which are coupled to one or more expansion machines. In the expansion machine(s), the aforementioned second portion of the fluid, which is taken from the first rectification column in the form of the one or more first material streams and heated in the heat exchanger, can be expanded, in particular. It is understood, however, that only portions of the first or second portion can be compressed or expanded in the correspondingly coupled units. An expansion machine not coupled to a corresponding compressor can, if present, be braked, in particular mechanically and / or regeneratively.Braking is also possible with a relaxation machine coupled to a compressor.

[0028] For example, a compressor coupled to one of two expansion machines arranged in parallel can be used. If only one expansion machine is used, the compressor can be coupled to it. The wording used below purely for reasons of clarity, according to which "a" compressor is coupled to "an" expansion machine, does not exclude the use of multiple compressors and / or expansion machines in any mutual coupling. However, the compressor(s) described do not have to be driven, and in particular not exclusively, by the one or more expansion machines mentioned. Conversely, the compressor(s) do not have to absorb all of the work released during expansion.As will be illustrated below with an example, a supporting or exclusive drive can also be provided using an electric motor, or a brake can be interposed between the expansion machine(s) and the compressor(s).

[0029] The compressor(s) are one or more cold compressors, since the first portion of the fluid taken from the rectification column in the form of the one or more first material streams and heated in the heat exchanger is supplied to this or these compressors at a correspondingly low temperature level despite this heating and any subsequent further heating.

[0030] Instead of the described expansion of the second part of the fluid, which is taken from the rectification column in the form of the one or more first material streams and heated in the heat exchanger, and its described discharge from the air separation plant, a corresponding expansion can also be dispensed with and / or this second part can be fed, with or without expansion, into one or more further rectification columns, as will be explained further below.

[0031] In a more specific embodiment of a SPECTRA process, two first streams can be withdrawn from the first rectification column in the form of a liquid stream having a first oxygen content and a liquid stream having a second, higher oxygen content. The first stream having the first (lower) oxygen content can be withdrawn from the first rectification column from an intermediate tray or from a liquid retention device. The second stream having the second (higher) oxygen content can be formed, in particular, using at least a portion of the liquid bottom product of the first rectification column.

[0032] The first stream with the first (lower) oxygen content can, in particular, form the previously explained first portion of the fluid that is withdrawn from the first rectification column in the form of the one or more first streams and heated in the heat exchanger used to condense the thus-treated portion of the top gas from the first rectification column. The first stream with the first (lower) oxygen content can therefore form that first portion that is compressed after use in the one or more compressors and which is then fed back into the first rectification column.

[0033] The first stream with the second (higher) oxygen content, on the other hand, can in particular form the previously explained second portion of the fluid, which is withdrawn from the first rectification column in the form of the one or more first streams and heated in the heat exchanger used to condense the thus-treated portion of the top gas from the first rectification column. The first stream with the second (higher) oxygen content can thus form that second portion which, after use, is compressed in the one or more compressors and which is then fed back into the first rectification column.

[0034] In the aforementioned SPECTRA processes, so-called oxygen columns can also be used to obtain pure or ultrapure oxygen. These columns operate at the pressure level of typical low-pressure columns described above. Such an oxygen column is also referred to below as a "second" rectification column.

[0035] Further fluid from the first rectification column is fed into such a second rectification column. This further fluid contains oxygen, argon, and nitrogen and is withdrawn in liquid form from the first rectification column in the form of (at least) one further stream (hereinafter referred to as the "second" stream). In the embodiment just explained with two "first" streams with different oxygen contents, the second stream is withdrawn in particular above the first stream with the first (lower) oxygen content.

[0036] While the SPECTRA process was originally intended to provide gaseous nitrogen at the pressure level of the first rectification column, the use of an oxygen column of the type described in a corresponding process enables the additional production of pure oxygen. Advantages of the invention

[0037] The present invention is based on the finding that a process of the type described above can be particularly advantageously modified by constructing the oxygen column just described, i.e., a second rectification column used in a modified SPECTRA process, as part of a double column which, in addition to the second rectification column, comprises a third rectification column. This third column, as part of the double column, is arranged below the second rectification column and to which additional air is supplied. The present invention thus provides for air feed in a SPECTRA process not only into the first column, but also into the third column.

[0038] Overall, the present invention proposes, in the language of the patent claims, a process for the low-temperature separation of air, using an air separation plant with a first rectification column and a second rectification column. The first rectification column is operated at a first pressure level, and the second rectification column is operated at a second pressure level below the first pressure level.

[0039] Such first and second pressure levels are typical pressure levels, as they are also used in conventional air separation plants, in particular SPECTRA plants with oxygen recovery. The first pressure level can in particular be 7 to 12 bar, the second pressure level in particular 1.2 to 5 bar. The second pressure level can generally also be 1 to 4 bar. These are absolute pressures at the top of the respective rectification columns. The first rectification column and the second rectification column can in particular be arranged side by side and are typically not combined with one another in the form of a double column, whereby a "double column" is generally understood here to mean a separation apparatus formed from two rectification columns, which is designed as a structural unit in which the column shells of the two rectification columns are connected without any lines, i.e.are directly connected to one another, in particular welded. However, this direct connection alone does not necessarily create a fluidic connection.

[0040] The first rectification column and the second rectification column used in the present invention have already been described in detail with reference to the SPECTRA process. The second rectification column can, in particular, be an oxygen column.

[0041] Atmospheric air, which has been compressed and then cooled, is fed to the first rectification column. In particular, corresponding air can be fed to the first rectification column in the form of several material streams, which can be treated differently and, if necessary, passed through further apparatus beforehand. The air fed into the first rectification column can, in particular, be fed in the form of a liquefied partial stream and a non-liquefied partial stream. Further embodiments of the air feed, which can be used in particular within the scope of the present invention, are explained in more detail below. In contrast, no air is typically fed to the second rectification column; more generally, no material streams are typically fed to the second rectification column that have not already been taken from another rectification column or formed from such material streams.

[0042] As already explained in more detail above, fluid enriched in oxygen relative to atmospheric air is withdrawn from the first rectification column in the form of one or more first streams. As previously explained with regard to the more specific embodiment of a SPECTRA process, these can in particular be two first streams with different oxygen contents. Therefore, express reference is made to the more detailed explanations above.

[0043] Within the scope of the present invention, at least a portion of the fluid withdrawn from the first rectification column in the form of the one or more first streams is heated in a heat exchanger, and a portion thereof, i.e., the fluid heated in the heat exchanger (and previously withdrawn from the first rectification column in the form of the one or more first streams) (previously referred to as the "first portion"), is compressed within the scope of the present invention using a compressor and returned to the first rectification column. In particular, multiple compressors can also be used in this context, as mentioned. The return of the fluid to the first rectification column takes place, in particular, in the form of a feedback into a bottom region of the first rectification column.

[0044] The heat exchanger is used for cooling and condensing or partially condensing the overhead gas from the first rectification column, at least a portion of which is returned to the first rectification column as reflux. In this context, a first portion of the overhead gas from the first rectification column is (partially) condensed in the heat exchanger (and at least a portion of this is returned to the first rectification column as reflux). A second portion of the overhead gas is discharged from the process or plant as at least one nitrogen-rich air product.

[0045] This at least one air product, such as the overhead gas from the first rectification column from which it was formed, has a certain residual oxygen content, which can in particular be between 0.001 and 10 ppm. For example, corresponding overhead gas can be provided undiluted as a gaseous nitrogen product at the aforementioned first pressure level. This nitrogen product represents a main product of the proposed process. It can in particular be heated to ambient temperature in a main heat exchanger of the air separation plant and then provided at the first pressure level. However, a portion of the overhead gas can also be provided as a liquid nitrogen product of the process or plant, in particular after subcooling against a further portion, which is then in particular discarded.

[0046] As already explained, in the context of the present invention, in addition to the unliquefied overhead gas as the main product, oxygen, in particular high-purity oxygen, is also provided as an air product. In some embodiments, argon can also be provided as a product of the process.

[0047] A further portion of the fluid that was heated in the heat exchanger (and previously removed in the form of the one or more first streams from the first rectification column) (previously referred to as the "second portion") can be expanded in the manner explained within the scope of the present invention and, for example, discharged from the air separation plant. For further details, reference is expressly made to the above explanations in this context. In particular, one or more expansion machines used here can be coupled to the compressor(s) mentioned above. Reference is also made to the above explanations in this regard.

[0048] It should be understood that when reference is made here to a heat exchanger used for cooling or (partially) condensing the first portion of the overhead gas from the first rectification column, this heat exchanger differs from the main heat exchanger of the air separation plant and, in particular, is designed as a separate structural unit. The main heat exchanger of the air separation plant is characterized, as mentioned, in particular by the fact that it cools all or at least the majority of the air supplied to the air separation plant. This, however, is not the case in the heat exchanger in which the first portion of the overhead gas from the first rectification column is cooled or (partially) condensed, and through which the first material stream(s) are each at least partially conducted.

[0049] The process proposed according to the invention is, as mentioned, a SPECTRA process with additional oxygen production. In this process, additional fluid containing oxygen, nitrogen, and argon is withdrawn from the first rectification column. This additional fluid is used as a second stream or to form a second stream, which is transferred to the second rectification column. An oxygen-rich bottoms liquid is formed in the bottom of the second rectification column, and at least a portion of this is discharged in the form of a third stream from the second rectification column or the air separation plant as a whole. This oxygen-rich liquid has, in particular, a residual nitrogen content, as explained in more detail below.

[0050] The argon content of the further fluid withdrawn from the first rectification column and used as the second stream or to form the second stream, which is transferred to the second rectification column, is in particular 2 to 4 mol percent, and its oxygen content is in particular 10 to 30 mol percent. The argon content of this fluid depends in particular on the withdrawal height from the first rectification column, which is therefore selected appropriately. The withdrawal height of this fluid and thus of the second stream is typically, as mentioned, above the withdrawal height(s) of the fluid discharged in the form of the one or more first streams from the first rectification column. The separating trays located between corresponding withdrawal points in the first rectification column also block hydrocarbons in particular.Therefore, these extraction heights are advantageously selected also with regard to this aspect, so that the oxygen product obtained has the required purity with regard to hydrocarbons.

[0051] As explained in more detail below and already briefly mentioned above, a double-column system is used within the scope of the present invention, the upper part of which forms the second rectification column, and the lower part of which is referred to here as the "third" rectification column. In this case, the additional fluid withdrawn from the first rectification column can, for example, also be initially fed into this third rectification column. In this case, however, immediately below the feed point into the third rectification column, liquid is withdrawn from the third rectification column and fed into the second rectification column. The second stream or corresponding fluid is thus fed into the second rectification column "via a detour" via the third rectification column.However, such a case is also covered by the statement that fluid containing oxygen, nitrogen, and argon is withdrawn from the first rectification column and used "to form" the second stream. However, the second stream can also be a stream transferred directly to the second rectification column, i.e., without passing through another rectification column, in which case the stream from the first rectification column is used "as" the second stream in the terminology used here.

[0052] Any further fluid exchange between the first and second rectification columns is possible, in particular to balance the liquid balance. The invention is not limited by these measures.

[0053] According to the invention, as already mentioned, a third rectification column is used, with the second rectification column and the third rectification column being designed as parts of a double column, with the third rectification column being arranged below the second rectification column in the sense explained, and the third rectification column being fed with air. Regarding the term "double column," reference is made to the above explanations.

[0054] The third rectification column is operated, in particular, at a pressure level between the first and second pressure levels, i.e., between the operating pressure levels of the first and second rectification columns. This pressure level is, in particular, between 4 and 7 bar, in particular approximately 5.5 bar absolute pressure. Air is fed to the third rectification column that has previously been compressed and cooled and can be expanded, in particular by means of an additional expansion machine, to the pressure level at which the third rectification column is operated. The air fed to the third rectification column therefore comprises compressed and cooled air that is expanded using an expansion machine.

[0055] In the process according to the invention, the second rectification column can be operated with a condenser-evaporator arranged in a bottom region of the second rectification column and heated using fluid withdrawn from and / or fed to the third rectification column. In this way, particularly energy-efficient processes can be realized.

[0056] In particular, the air which is optionally expanded by means of the expansion machine and with which the third rectification column is fed can be at least partially liquefied in the condenser evaporator which is arranged in the bottom region of the second rectification column and returned to the third rectification column as liquid reflux.

[0057] In the condenser-evaporator, which can be arranged in the bottom region of the second rectification column, overhead gas from the third rectification column can also be at least partially liquefied and returned to the second or third rectification column as reflux. In other words, a gaseous overhead product from the third rectification column can be used to heat a condenser-evaporator of the second rectification column, with the resulting liquid being partially used as reflux to the second rectification column and as reflux to the third rectification column. Such a configuration has the advantage of achieving a further increase in argon yield and overall energy range.

[0058] Within the scope of the present invention, bottoms liquid, in particular, can be formed in the third rectification column, which can be fed into the second rectification column. It can also be provided that a portion of this bottoms liquid is used to cool a top condenser of an additional argon column (i.e., a "fourth" column as explained below) and only then fed into the second rectification column. A further portion, however, can be transferred directly to the second rectification column, bypassing such a top condenser.

[0059] The third rectification column receives, in particular, as mentioned, air previously expanded in an expansion machine as the gaseous feed stream. In other words, the third rectification column can be fed, in particular, with the previously compressed and cooled air, which is expanded by means of an expansion machine. It is understood that this is additional air that is subjected to separation in the process or plant in addition to the air fed into the first rectification column.

[0060] Approximately in the middle of the third rectification column, more generally in a region between the bottom and the top, a further liquid stream can optionally be withdrawn from the third rectification column, which can be fed back into the first rectification column, in particular by means of a pump.

[0061] As mentioned, oxygen-rich fluid is formed in the bottom of the second rectification column. This can be withdrawn from the second rectification column. The withdrawal can take place partly in gaseous and partly in liquid form. This fluid typically has an oxygen content of more than 97 mol percent, in particular more than 99.0 mol percent. Further fluid can be withdrawn from the top of the second rectification column, which, in one embodiment of the invention, can be discharged from the air separation plant and discarded. This fluid is a nitrogen-oxygen mixture. In another embodiment of the present invention, however, the top gas of the second rectification column is formed as a further nitrogen-rich fluid and provided as a further nitrogen-rich air product.

[0062] The top gas of the second rectification column can be obtained with higher purity by removing a gaseous substream slightly below the top of the second rectification column. By removing this substream, a nitrogen product with typically only approximately 1 ppm, but a maximum of 100 ppm, of oxygen is produced at the top of the second rectification column, similar to the procedure in a conventional air separation plant.

[0063] This product can either be heated directly in the main heat exchanger to a temperature level at or close to ambient temperature, or partially heated and compressed in a warm compressor to a pressure level of, for example, approximately 1.7 to 2.5 bar, in particular approximately 2.2 bar. During the heating process, this product, or a partial stream thereof, can be removed from the skin heat exchanger at an intermediate temperature level, passed through a cold compressor, and fed back to the main heat exchanger for further heating. Compression in the warm compressor can follow this. The cold compressor can, in particular, be coupled to an expansion machine that expands compressed and partially cooled feed air, which is fed into the third rectification column. In this context, a nitrogen-rich liquid reflux to the second rectification column can, in particular, be used.

[0064] In a corresponding embodiment, the invention is characterized in particular in that nitrogen-rich overhead gas is formed at the top of the second rectification column, and in that at least a portion of the nitrogen-rich overhead gas is recovered as a further nitrogen-rich air product with a residual oxygen content that is above the residual oxygen content of the overhead gas of the first rectification column, but still significantly below the residual oxygen content of fluids that are withdrawn from the top of these oxygen columns in regular SPECTRA processes with oxygen columns. Within the scope of this embodiment of the present invention, this can also be made possible in particular by providing additional trays or trays compared to conventional oxygen columns.Packing areas are installed in the second rectification column, that another fluid is withdrawn below, and that a liquid, nitrogen-rich reflux is fed to the top of the second rectification column.

[0065] In the context of the present invention, the top gas of the first rectification column has a residual oxygen content of 0.1 ppb to 10 ppm, more particularly from 0.5 ppb to 1 ppm or up to 100 ppb. The residual oxygen content of the at least one nitrogen-rich air product provided in the context of the present invention, which is formed using this top gas, is therefore within this range. The top gas of the second rectification column has a higher residual oxygen content in the just-mentioned embodiment of the present invention. This residual oxygen content is in particular 10 ppb to 100 ppm, in particular 100 ppb or 500 ppb to 10 ppm. The residual oxygen content of the further nitrogen-rich air product provided in the context of the present invention using this top gas is therefore within this range. All figures in ppb or ppm refer to the molar fraction.

[0066] The residual oxygen content of the further nitrogen-rich air product obtained in the aforementioned embodiment of the invention, which is provided using the overhead gas of the second rectification column, can, as mentioned, be achieved in particular by equipping the second rectification column with additional trays or packing areas. Therefore, in this embodiment of the present invention, the second rectification column preferably has 50 to 120, for example 70 to 95, in particular 72 to 90, theoretical trays.

[0067] As also mentioned, the residual oxygen content of the further nitrogen-rich air product provided using the top gas of the second rectification column, achieved in the aforementioned embodiment of the invention, can in particular be achieved by using a nitrogen-rich liquid reflux to the second rectification column. The provision of a nitrogen-rich liquid stream and its delivery as reflux in an upper region of the second rectification column is therefore provided within the scope of a particularly preferred embodiment of the present invention. The reflux has a residual oxygen content that is in particular lower than the residual oxygen content of the top gas of the second rectification column.

[0068] The nitrogen-rich liquid stream used in this embodiment of the present invention to form the reflux to the second rectification column can be taken in particular from the first rectification column or a further rectification column.

[0069] Particularly for the supply of semiconductor plants (so-called fabs), in addition to gaseous, ultra-pure and, if possible, particle-free nitrogen and, if necessary, oxygen, the supply of comparatively small quantities of gaseous argon is increasingly required. For this purpose, liquid argon can either be delivered or vaporised on site, or gaseous argon can be produced on site. The delivery of liquid argon not only entails economic disadvantages (transport costs, refuelling losses, cold losses when vaporising against ambient air), but also places high demands on the reliability of the logistics chain. Therefore, for the aforementioned applications, there is increasing demand for plants for the low-temperature separation of air, which can deliver smaller quantities of gaseous argon in addition to larger quantities of gaseous, ultra-pure nitrogen. The nitrogen produced should typically only have a concentration of approx.1 ppb, maximum 1000 ppb, oxygen, be essentially particle-free, and be able to be delivered at a pressure level significantly above atmospheric.

[0070] Argon extraction is typically carried out using air separation plants with double-column systems and so-called crude and, in some cases, pure argon columns. An example is illustrated by Häring (see above) in Figure 2.3A and described starting on page 26 in the section "Rectification in the Low-pressure, Crude and Pure Argon Column" and starting on page 29 in the section "Cryogenic Production of Pure Argon." As explained there, argon accumulates in such plants at a certain height in the low-pressure column (the so-called argon maximum). At this or another favorable point, possibly even below the argon maximum (at the so-called argon transition), argon-enriched gas with an argon concentration of typically 5 to 15 mol percent can be withdrawn from the low-pressure column and transferred to the crude argon column. Such gas typically contains approximately 0.05 to 100 ppm nitrogen and otherwise essentially oxygen.It should be expressly emphasized that the values given for the gas withdrawn from the low-pressure column are only typical example values.

[0071] The crude argon column essentially serves to separate the oxygen from the gas withdrawn from the low-pressure column. The oxygen separated in the crude argon column, or a corresponding oxygen-rich fluid, can be returned to the low-pressure column in liquid form. The oxygen or oxygen-rich fluid is typically fed into the low-pressure column several theoretical or practical plates below the feed point for the oxygen-enriched and nitrogen-depleted, and possibly at least partially vaporized, liquid withdrawn from the high-pressure column. A gaseous fraction remaining in the crude argon column during the separation, which essentially contains argon and nitrogen, is further separated in the pure argon column to obtain pure argon.The crude and pure argon columns have overhead condensers that can be cooled, in particular, with a portion of the oxygen-enriched and nitrogen-depleted liquid withdrawn from the high-pressure column, which partially evaporates during this cooling process. Other fluids can also be used for cooling.

[0072] In principle, a pure argon column can be dispensed with in corresponding plants. In this case, the plant is typically designed and operated in such a way that the nitrogen content at the argon transition is below 1 ppm or below the required product purity. However, this is not a mandatory requirement. In this case, argon of the same quality as from a conventional pure argon column is withdrawn from the crude argon column or a comparable column, typically somewhat further below the fluid conventionally transferred to the pure argon column. The trays in the section between the crude argon condenser, i.e., the top condenser of the crude argon column, and a corresponding outlet for an argon product serve in particular as barrier trays for nitrogen.

[0073] Even if only comparatively small quantities of argon are demanded, a complete air separation plant with argon rectification (i.e. equipped with a conventional low-pressure column for oxygen production) must still be installed to produce the gaseous argon, as explained above. The amount of air to be processed in such an air separation plant is determined by gaseous argon or gaseous nitrogen, i.e. a large amount of the gaseous oxygen is produced as residual gas that is either unusable or difficult to use. Furthermore, it is not possible in conventional plants to produce nitrogen at a pressure level significantly above atmospheric while simultaneously producing large quantities. The nitrogen is produced here as a low-pressure product. Known plants that use a high-pressure column for nitrogen production are typically not well suited to argon production.

[0074] In a particularly preferred embodiment, the present invention proposes a method and an air separation plant by means of which, in addition to larger quantities of high-purity, gaseous nitrogen at a significantly superatmospheric pressure level, comparatively smaller quantities of argon can also be advantageously provided.

[0075] Within the scope of the present invention, according to this particularly preferred embodiment, fluid is withdrawn from the second rectification column to recover argon and used as a fourth stream or to form a fourth stream, this fluid having a higher argon content than the oxygen-rich bottom liquid formed in the bottom of the second rectification column. This fluid also has a lower oxygen content than the oxygen-rich bottom liquid formed in the bottom of the second rectification column. In particular, it can contain 45 to 60 mol percent oxygen, 40 to 55 mol percent argon, and less than 1 mol percent nitrogen.The fluid which is withdrawn from the second rectification column and used as the fourth material stream or to form the fourth material stream can be withdrawn at the level of the so-called argon maximum, as occurs in known low-pressure columns of air separation plants.

[0076] In this embodiment, a fourth rectification column is used into which the fourth stream is fed, wherein an argon-rich fluid is formed in the fourth rectification column which has a content of more than 95 mol percent argon and which can be used in particular directly or after further purification as an argon product.

[0077] A nitrogen content of less than 1 ppm in the fourth stream can be achieved, in particular, by conducting appropriate nitrogen removal above the argon transition in the second column using suitable additional trays. If the fluid withdrawn from the second rectification column and used to form the fourth stream has a correspondingly low nitrogen content, it can be provided as a product of the fourth rectification column, in particular without using a conventional pure argon column. If the nitrogen content is significantly higher, a pure argon column is typically used in addition to a corresponding fourth rectification column, which then corresponds to a conventional crude argon column.As an alternative to using a pure argon column, liquid argon can also be withdrawn slightly below the top of the fourth rectification column as the fluid conventionally transferred to the pure argon column, so that argon of the same quality as from a conventional pure argon column can be obtained.

[0078] In any case, the fourth rectification column is a rectification column that largely corresponds to the typical crude argon column of a conventional process for the cryogenic separation of air. If required, a pure argon column can be provided. However, given the low nitrogen contents discussed above, a pure argon column is typically not necessary. If the nitrogen content is higher than the aforementioned 1 ppm, the oxygen and argon contents can be correspondingly lower. Typically, the oxygen contents here are also between 45 and 60 mol percent and the argon content between 40 and 55 mol percent, but in this case, based on the non-nitrogen content of a corresponding fluid.

[0079] The fourth stream fed into the fourth rectification column may, in particular, also be a stream taken from another rectification column, which in turn is fed with fluid from the second rectification column. Reference is made to the explanations below. In this case, too, however, the fluid taken from the second rectification column is used to form the fourth stream, namely via the further rectification column.

[0080] By separating argon, impure oxygen (with 90 to 98% mol percent oxygen content), technical oxygen (with 98 to 99.8% mol percent oxygen content) and high-purity oxygen (with traces of argon or hydrocarbons in the ppb range) can be produced as additional products within the scope of a corresponding embodiment of the present invention, as will also be partly explained below.

[0081] In principle, within the scope of the present invention, an oxygen product can always be withdrawn from the second rectification column, even if, for example, a third rectification column is provided for oxygen production. For example, an oxygen-rich gas can be withdrawn from the second rectification column and (in contrast to admixture with other streams, such as, for example, in Figure 31 illustrated), are passed separately through the main heat exchanger and discharged from the plant as a product. This produces oxygen with a purity of 99% or better, which corresponds to the purity of so-called technical oxygen.

[0082] In the embodiment described, a bottom liquid is formed in the bottom of the fourth rectification column, which can be recycled, in particular, by means of a pump, to the second rectification column. A feed point into the second rectification column is located, in particular, at the same height or near the withdrawal point of the fluid used as the third stream or to form the third stream, where "near" is understood here to mean a feed position that differs by no more than 10 theoretical or practical plates. Since the two streams to and from the fourth rectification column are in equilibrium, the feed can also be made at the same height, i.e., in particular, to the same plate.

[0083] A particularly significant advantage of the embodiment of the present invention just explained is that by supplementing a SPECTRA process with additional argon recovery, up to 50% of the argon contained in the process air can be recovered as product without the need for complex conventional oxygen rectification. The problems explained above are therefore eliminated within the scope of the embodiment of the present invention just explained. Within the scope of the present invention, liquid argon can also be recovered, which can be subjected to a known internal compression process. Pure oxygen formed in the plant can also be subjected to an internal compression process, as is known from the specialist literature cited at the beginning.

[0084] According to a particularly preferred embodiment of the present invention, the second rectification column, as mentioned, is operated with a condenser-evaporator arranged in its bottom region. Material streams other than those mentioned can also be used to heat the condenser-evaporator. For example, within the scope of the present invention, a portion of the atmospheric air that has been previously compressed and cooled can be used for this purpose. Corresponding air can, for example, be present at the pressure level of the first rectification column or can be previously expanded by means of an expansion machine. In the former case, the air is typically cooled by means of a main condenser of the air separation plant to a temperature level close to its condensing temperature, i.e. a temperature level that is not more than 50 K, 25 K or 10 K above the condensing temperature.In the latter case, the air is only cooled to a temperature level before expansion, which is in particular below -50°C, but at least 50 K above the condensation temperature. In this case, expansion typically takes place to a pressure level below the first pressure level at which the first rectification column is operated, typically to approximately 4 to 6 bar absolute pressure. The air used to heat the condenser evaporator liquefies at least partially and can therefore be fed in a corresponding form into the first and / or third rectification column. Any pressure differences that may occur can be compensated by interposing a pump or by a purely hydrostatic-geodetic pressure increase.

[0085] However, one or more further material streams can also be used to heat the condenser-evaporator in the second rectification column. In particular, this can be the fluid containing oxygen, nitrogen and argon, which is withdrawn from the first rectification column as the second material stream or is used to form the second material stream and which is transferred to the second rectification column, or a part thereof. A corresponding second liquid material stream is withdrawn, for example, from the first rectification column, passed through the condenser-evaporator, subcooled in the process and then fed to the second rectification column, in particular below a head region, i.e. in particular below the nitrogen-rich reflux. This second material stream can thus be used as reflux to the second rectification column.The condenser evaporator can also be operated with top gas from the third rectification column, as mentioned.

[0086] Within the scope of the present invention, as mentioned, a nitrogen-rich reflux to the second rectification column can be formed using nitrogen-rich liquid from the first rectification column. In this case, a corresponding stream can be cooled, in particular, in the condenser-evaporator of the second rectification column; however, it is also possible to feed a corresponding stream uncooled into the second rectification column. In any case, this stream is advantageously withdrawn significantly above the second stream from the first rectification column. The withdrawal typically takes place in the range of 20 theoretical or practical plates below the top region of the first rectification column.

[0087] Within the scope of the present invention, overhead gas is withdrawn from the second rectification column and, in particular, discharged from the air separation plant, as already explained above in various embodiments. According to one embodiment of the present invention, at least a portion of this overhead gas is expanded by means of a further expansion machine, heated, and discharged from the air separation plant.

[0088] Within the scope of the present invention, the second rectification column can, as mentioned, be operated at the second pressure level, in particular at a pressure level of 1.1 to 1.6 bar absolute pressure, wherein previously compressed and cooled air is fed to the first rectification column, a partial stream of which is expanded by means of an expansion machine to the second pressure level at which the second rectification column is operated. After being expanded, this partial stream can be at least partially liquefied in the condenser-evaporator, which is arranged in the bottom region of the second rectification column, and fed into the first rectification column. Such a configuration has the advantage that both the argon yield and the total energy range are significantly improved.The expansion machine used for this expansion can be coupled to a compressor, which, in the previously explained embodiment of the invention, warm-compresses the additional air product formed using overhead gas from the second rectification column. In addition to or as an alternative to such a coupling, braking, for example, by means of a generator and / or an oil brake, can also be provided. However, in one embodiment of the present invention, additional fluid can also be expanded using a comparable additional expansion machine.

[0089] In general, within the scope of the present invention, the fourth rectification column, in the embodiments in which it is present, can be operated with a top condenser whose evaporation space is operated at a pressure level of less than 1.2 bar absolute pressure or 150 mbar gauge pressure and is cooled with fluid which is subsequently fed into the second rectification column or discharged from the air separation plant. This fluid can in particular be bottoms liquid from the first or, if present, the third rectification column, or a corresponding fluid can comprise part of this bottoms liquid(s). However, other fluids can also be used. Such an operating pressure level of the evaporation space of the top condenser can increase the argon yield within the scope of the invention.This can be made possible in particular by not using the corresponding fluid as regeneration gas in the air separation plant.

[0090] In particular, within the scope of the present invention or a corresponding embodiment, fluid obtained in the bottom of a rectification column, in particular the first or third rectification column, can be used in the top condenser in part as the fluid or as a part of the fluid by means of which the top condenser of the fourth rectification column is cooled. As mentioned, corresponding fluid can subsequently be discharged, in particular, from the air separation plant or advantageously used in another way.

[0091] Within the scope of a corresponding embodiment of the present invention, the overhead gas formed in the fourth rectification column can, in particular, have an argon content of more than 99.999 mol percent. In this embodiment, this overhead gas can be discharged from the air separation plant as an argon product without further rectification. As mentioned, correspondingly high argon contents result, in particular, when a fluid with a particularly low nitrogen content is withdrawn from the second rectification column and transferred to the fourth rectification column.

[0092] Alternatively, it is also possible to form a head gas in a corresponding configuration in the fourth rectification column with a lower argon content, for example, with an argon content of more than 95 and less than 99.999 mol percent. In this configuration, a further rectification column in the form of a known pure argon column can then be provided, in particular, in which this head gas can subsequently be rectified to obtain an argon product with a corresponding purity of more than 99.999 mol percent. For known crude and pure argon columns, reference is made to the specialist literature cited above.

[0093] As also mentioned, in corresponding embodiments, instead of top gas, an argon-rich fluid in liquid form can be withdrawn from the third rectification column below the top in the form of the fifth material stream.

[0094] In the context of the present invention, as mentioned several times, an amount of the argon product formed in the air separation plant can comprise 1% to 50% of a total amount of argon supplied to the air separation plant in the form of atmospheric air.

[0095] According to a variant of the process according to the invention, for the production of ultra-high purity oxygen having an oxygen content of, for example, 99.5 mol percent with a residual content of up to 1 ppb methane, 10 ppb argon and not more than 1 ppb of other air components, a fifth rectification column can be used in which a liquid having an oxygen content is formed which is above an oxygen content of the oxygen-rich bottom liquid which is formed in the bottom of the second rectification column.

[0096] This fifth rectification column can, in particular, be designed as a double column having an upper and a lower section separated from each other in a fluid-tight manner. In each case, a top gas and a bottom liquid are formed in the upper and lower sections of the double column. The upper section can be used as a barrier column against high boilers such as hydrocarbons and, functionally speaking, is a separate part of the fourth rectification column. The lower section, i.e., the fifth rectification column itself, is used as a stripping column for separating lighter boilers such as argon.

[0097] Overall, within the scope of the present invention, a liquid having an oxygen content which is above an oxygen content of the oxygen-rich bottom liquid formed in the bottom of the second rectification column can be formed in the fifth rectification column or its lower part, and the fifth rectification column can be used to form the third stream which is fed into the fourth rectification column using the fluid which is withdrawn from the second rectification column and has a higher argon content than the oxygen-rich bottom liquid of the second rectification column.

[0098] At least a portion of the fluid withdrawn from the second rectification column can be fed into the upper part of the fifth column just explained, which is designed as a double column, i.e. into the part functionally belonging to the second rectification column, and is used as the fourth material stream or to form the fourth material stream.

[0099] The upper and lower parts of the double column just explained may each be operated with a reflux provided using bottoms liquid of the fourth rectification column, if any, overhead gas of the upper and lower parts of the double column just explained may be fed to the fourth rectification column, and the liquid having the oxygen content which is above the oxygen content of the oxygen-rich bottoms liquid formed in the bottom of the second rectification column may be formed in the form of bottoms liquid of the lower part.

[0100] The invention may in particular comprise that the lower part of the double column, i.e. the fifth rectification column in the true sense, is heated by means of a condenser evaporator in which fluid from the fourth rectification column is cooled.

[0101] The present invention also extends to an air separation plant configured to carry out a process according to a previously explained embodiment of the present invention. For features and advantages of a corresponding air separation plant, reference is expressly made to the corresponding independent patent claim and the above explanations. In particular, such an air separation plant comprises means configured to carry out a process according to one of the explained embodiments.

[0102] In a particularly preferred embodiment of the air separation plant proposed according to the invention, it has a main heat exchanger arranged in a first prefabricated cold box, and the first rectification column with the heat exchanger used to cool its overhead gas is arranged in a second prefabricated cold box. The second and third rectification columns are arranged in a third prefabricated cold box in such an air separation plant.

[0103] Such an air separation plant may, in particular, comprise one or more further rectification columns, as previously explained with reference to the fourth and fifth rectification columns. The one further rectification column or at least one of the several further rectification columns may be arranged in the third prefabricated coldbox or in one or more further prefabricated coldboxes.

[0104] A coldbox is an insulated metal container that surrounds the aforementioned device(s) and is filled with insulating material, such as perlite. Advantageously, the coldbox houses the one or more aforementioned devices, along with the equipment required for operation, such as heat exchangers and / or fittings. This means that only piping is required when constructing a corresponding system. This simplifies installation on site. Prefabrication includes, in particular, the construction of the coldbox outer shell and, if necessary, the installation of the aforementioned devices with the corresponding piping. Therefore, only one connection (piping) remains to be made on site.

[0105] The invention is explained in more detail below with reference to the accompanying drawings in which preferred embodiments of the present invention are illustrated. Short description of the drawings

[0106] The Figures 1 to 31 illustrate air separation plants and parts of air separation plants in whole or in part. Detailed description of the drawings

[0107] In the following figures, air separation plants of different embodiments of the present invention are illustrated and designated 100 to 3100. The components of corresponding plants are initially described with reference to the Figure 1 and the non-inventive air separation plant 100 illustrated therein is explained. In the air separation plants 200 to 3100 according to the Figures 2 to 31 Existing structurally or functionally corresponding elements are not explained repeatedly there.

[0108] In Figure 1 an air separation plant 100 not according to the invention is illustrated in the form of a schematic plant diagram.

[0109] A feed air stream a is supplied to the air separation plant 100 from a warm part of the air separation plant 100, which is schematically illustrated here at 110 and in particular comprises devices for purifying and compressing feed air. This feed air stream a is cooled in a main heat exchanger 1 of the air separation plant 100 and removed from the main heat exchanger 1 near its cold end. The warm part 110 of the air separation plant can be designed in a manner customary in the art. For an example that does not limit the present invention, reference is made to the explanations of Figure 2.3A in Häring (see above).

[0110] The feed air stream a is then divided into two substreams b and c, with substream b being fed directly into a first rectification column 11. Substream c, on the other hand, is passed through a condenser evaporator 121 of a second rectification column 12 and then, particularly after combining with other material streams as explained below, also fed into the first rectification column 11. Substreams b and c are each fed into the first rectification column 11 at a suitable height.

[0111] In the first rectification column 11, which is operated at a previously explained "first" pressure level, a nitrogen-enriched or substantially nitrogen-containing overhead gas and an oxygen-enriched bottom liquid are formed. Two streams d and e are withdrawn from the first rectification column 11, each comprising fluid that is enriched in oxygen compared to atmospheric air.

[0112] Stream d is first further cooled in main heat exchanger 1 and then passed through a heat exchanger 2, which, as explained below, is used to cool overhead gas from the first rectification column 11. Stream e is first treated in a similar manner to stream d, whereby a portion of stream e can be branched off as stream e1 before the remainder of stream e, which for the sake of simplicity is referred to as e, is fed to heat exchanger 2. Liquid nitrogen X can also be fed externally to stream e if required. In the example shown, stream e is taken from the bottom of the first rectification column 11, while stream d is taken from a position several theoretical or practical plates above the bottom of the first rectification column 11. Streams d and e are passed through heat exchanger 2 separately from one another.

[0113] The material stream e is then partially heated in the main heat exchanger 1 and expanded into two partial streams by means of an expansion machine 3 and, if necessary, a bypass valve (not specifically designated). These partial streams are then combined with each other and with other material streams, heated in the main heat exchanger 1, and discharged from the air separation plant in the form of a collective stream f or used in the warm section 110, for example, for the regeneration of absorbers.

[0114] Stream d, on the other hand, is compressed in a compressor 5 coupled to one of the expansion machines 3 shown here, possibly after branching off and venting a partial stream to atmosphere A, then cooled and, similar to stream c, returned to the first rectification column 11. As illustrated by the dashed stream d1, a bypass can also occur here. Compressor 5 is coupled to the expansion machine 3 and also has an oil brake not specifically designated here.

[0115] Overhead gas from the top of the first rectification column 11 is passed through the heat exchanger 2 in the form of a stream g and at least partially liquefied there. This partially liquefied overhead gas can be partially recycled to the first rectification column 11 in the form of a reflux stream and a further portion can be provided as liquid nitrogen product B. For this purpose, a portion can be subcooled in a subcooler 6 and discharged as correspondingly subcooled liquid nitrogen product B. A portion expanded in the subcooler 6 for cooling can be combined with the aforementioned stream e. A portion of the stream g can also be discharged as a so-called purge P. Further overhead gas can be heated in the form of a stream h in the main heat exchanger 1 and discharged as gaseous nitrogen product C or used as sealing gas D.The gaseous nitrogen product C represents a "nitrogen-rich air product" previously explained in relation to different embodiments of the invention.

[0116] In the Figure 1 In the example illustrated, a stream i is discharged in liquid form from the first rectification column 11, which stream is subcooled in the condenser evaporator 121 of the second rectification column and fed as reflux to the second rectification column 12. From a region near the top of the first rectification column 11, in any case significantly above the stream i, a further, correspondingly nitrogen-rich, stream i1 is withdrawn in liquid form and fed above the stream i, in particular at the top, as reflux to the second rectification column 12.

[0117] A liquid, oxygen-rich stream k can be withdrawn from the bottom of the second rectification column 12, which can be pressurized by means of an internal compression pump 7 or by pressure build-up evaporation and then heated in the main heat exchanger 1 and provided as internally compressed oxygen pressure product E. A portion of the stream k can also be provided as liquid oxygen product F. Further oxygen-rich liquid, but with a lower oxygen content, can be withdrawn analogously in the form of a stream k1 from the second rectification column 12, pressurized by means of a further internal compression pump 7a and provided as a further internally compressed oxygen pressure product E1. A portion can optionally also be recycled in the form of a stream k2. A portion can also be provided as liquid oxygen product F.In the example shown, a stream I is withdrawn from the top of the second rectification column 12, which stream can also be heated after combining with another stream and, in the example shown, released into the atmosphere A. Streams i and i1 are subcooled against stream I in a subcooler 9 before being fed into the second rectification column 12.

[0118] From a middle region of the second rectification column 12, in particular at the argon transition, a material stream m is withdrawn and fed into a lower region of a rectification column 14, which for reasons of consistency is referred to as the fourth rectification column 14 (in the non-inventive embodiment illustrated here, the third rectification column 13 used according to the invention is not present). From the bottom of the fourth rectification column 14, a further material stream n is withdrawn by means of a pump 8 and returned to the second rectification column 12. From the fourth rectification column 14, a material stream o is withdrawn in an upper region, passed through a top condenser 141 of the fourth rectification column 141, at least partially liquefied there, and returned as reflux to the fourth rectification column 14. A non-evaporated portion can be released into the atmosphere A.A liquid argon product G is withdrawn in liquid form below the top of the fourth rectification column 14 in the form of a stream p. A corresponding stream p can also be at least partially pressurized by means of a pump and heated in the main heat exchanger 1, so that an internally compressed argon product can be provided in this way.

[0119] The top condenser 141 of the fourth rectification column 14 is cooled with liquid, which can be fed to the top condenser 141 in the form of the aforementioned stream q. The stream q can be formed using at least a portion of the also aforementioned stream e1 and optionally the stream k2. Portions not used to form the stream q can be combined with the stream c in the form of a stream q1 and fed into the first rectification column 11. A stream r can be withdrawn from an evaporation space of the top condenser 141 of the fourth rectification column 14. After combining with the stream I, it can be heated in the main heat exchanger 1, preferably without backpressure or essentially without backpressure, as explained with regard to this stream I, and can be discharged from the plant. In this way, a low pressure can be established in the evaporation space of the top condenser 141.Optionally, a portion r1 of stream r can also be fed into the second rectification column 12. Liquid from the evaporation space of the top condenser 141 of the fourth rectification column 14 can, if required, be combined in the form of a stream s with the partial streams of stream e before their heating in the main heat exchanger 1.

[0120] As already mentioned, streams i and / or i1 can be subcooled against stream I in subcoolers designated 9. The same optionally applies to stream q relative to stream r. Several subcoolers 9 can also be combined in a common apparatus.

[0121] In Figure 2 another air separation plant not according to the invention is illustrated in the form of a schematic plant diagram and is designated overall by 200.

[0122] In contrast to the Figure 1In the illustrated air separation plant 100, a partial flow a1 of the feed air flow a is taken from the main heat exchanger 1 at an intermediate temperature level, expanded by means of an expansion machine 201, which is coupled to a generator, and otherwise like the material flow c according to Figure 1 used. If a corresponding expansion machine is available and used for the same or a comparable purpose, it is also designated 201 in the following figures. The features that differ from the air separation plant 100 can be provided individually or jointly and / or combined with any features described above and below.

[0123] In Figure 3 a further air separation plant not according to the invention is illustrated in the form of a schematic plant diagram and is designated overall by 300.

[0124] As illustrated here, a material flow a1 of the Figure 2 The corresponding material flow, after being expanded in the expansion machine 201, can also be fed back to the main heat exchanger 1, heated there, and released into the atmosphere A. For further details, reference is expressly made to the explanations of the preceding figures. The features that differ from those in the preceding figures can also be provided here individually or jointly and / or combined with any features described previously and subsequently.

[0125] In Figure 4 another air separation plant not according to the invention is illustrated in the form of a schematic plant diagram and is designated overall by 400.

[0126] In contrast to the air separation plants 100 to 300 illustrated in the preceding figures, no material stream corresponding to material stream i1 is used here. For further details, please refer expressly to the explanations of the preceding figures. The features that differ from those in the preceding figures can also be provided individually or jointly here and / or combined with any features described previously and below.

[0127] In Figure 5 an air separation plant according to an embodiment of the present invention is illustrated in the form of a schematic plant diagram and designated overall by 500.

[0128] The air separation unit 500 according to Figure 5differs from the previously explained embodiments in particular in that the second rectification column 12 is designed as part of a double column, which additionally has the already mentioned third rectification column 13. A portion of the feed air stream a, designated as above with a1 and treated accordingly, is fed into a lower region of this third rectification column 13.

[0129] A stream q2, which is otherwise reused in a manner comparable to stream q of the preceding figures and is therefore also designated q further downstream, is formed in the air separation plant 500 using bottoms liquid from the third rectification column 13, the substream e2, and optionally the stream k2. Top gas from the third rectification column 13 is at least partially liquefied in the form of a stream u in the condenser evaporator 121 and subsequently used in the form of a substream u1 as reflux to the third rectification column 13 and in the form of a substream u2 as reflux to the second rectification column 12.

[0130] Nitrogen-rich liquid is withdrawn in the form of a stream v via a side draw from the third rectification column 13 and conveyed into the first rectification column 11 by means of a pump 501.

[0131] For further details, please refer to the explanations of the preceding figures. The features that differ from those shown in the preceding figures may also be provided individually or jointly and / or combined with any features described previously or subsequently.

[0132] In Figure 6 Another air separation plant not according to the invention is illustrated in the form of a schematic plant diagram and is designated overall by 600. The illustration differs in Figure 6 and the following figures slightly different from those in the Figures 1 to 5 However, part of the function of the elements shown is identical or comparable in terms of technical function and is therefore indicated with identical reference symbols.

[0133] The air separation plant 600 is supplied with a feed air stream a, which is formed from atmospheric air L, from a warm part, which is also summarized here as 110. The warm part 110 includes, among other things, a filter 111 through which feed air L is sucked in, a main air compressor 112 with aftercoolers (not separately designated), a direct contact cooler operated with water W, and an absorber set 115. The feed air stream a is also cooled in a main heat exchanger 1 of the air separation plant 600 and removed from the main heat exchanger 1 near its cold end.

[0134] The feed air stream a is divided as before into two partial streams b and c, with partial stream b being fed directly into the first rectification column, also designated here by 11. The second partial stream c is in turn passed through a condenser evaporator 121 of a second rectification column 12, also designated here by 12, but here is subsequently discharged from the air separation plant 600 as explained below. In contrast to the Figures 1 to 5 illustrated condenser evaporator 121 is in the condenser evaporator 121 according to Figure 6 the current flow is not shown crosswise,

[0135] In the first rectification column 11, which is also operated at the previously explained "first" pressure level, a nitrogen-enriched or essentially nitrogen-containing overhead gas and an oxygen-enriched bottom liquid are formed. Here, too, two streams d and e are withdrawn from the first rectification column 11, each of which comprises a fluid that is enriched in oxygen compared to atmospheric air.

[0136] Stream d is first further cooled in main heat exchanger 1 and then passed through a heat exchanger 2, which, as explained below, is used to cool overhead gas from the first rectification column 11. Stream e is initially treated in a similar manner to stream d, whereby stream e is first combined with stream c and then a further stream q3 is branched off from it. Only then is this stream, referred to as e for the sake of simplicity, further cooled in main heat exchanger 1 and fed to heat exchanger 2. Stream q3 will be referred to as q in the following for comparability with the previous figures and due to its corresponding use.

[0137] As before, liquid nitrogen X can be added to stream e if required. In the example shown, stream e is taken from the bottom of the first rectification column 11, while stream d is taken from a position several theoretical or practical plates above the bottom of the first rectification column 11. Streams d and e are passed separately through heat exchanger 2.

[0138] The material stream e is then partially heated in the main heat exchanger 1 and expanded into two partial streams by means of an expansion machine 3 and, if necessary, an expansion valve or via a bypass. These partial streams are then combined with each other and with other material streams, heated in the main heat exchanger 1, and discharged from the air separation plant in the form of a collective stream f or used in the warm section 110 of the air separation plant 600, for example, to regenerate the absorbers of the adsorber set 114.

[0139] Stream d, on the other hand, is compressed in a compressor 5 coupled to one of the expansion machines 3 shown here, possibly after branching off and venting a partial stream to atmosphere A, then cooled and returned to the first rectification column. As illustrated by the dashed stream d1, a bypass can also be provided here. Compressor 5 is coupled to the expansion machine 3 and also has an oil brake (not specifically designated here). Any other combinations are also possible.

[0140] Overhead gas from the top of the first rectification column 11 is passed through the heat exchanger 2 in the form of a material stream g and is at least partially liquefied there. This partially liquefied overhead gas can be partially returned to the first rectification column in the form of a reflux stream and a further portion can be made available as liquid nitrogen product B. For this purpose, a portion can be subcooled in a subcooler 6 and discharged as correspondingly subcooled liquid nitrogen product B. A portion expanded in the subcooler 6 for cooling can be combined with the aforementioned material stream e. A portion can also be discharged as so-called purge P. Further overhead gas can be heated in the form of a material stream h in the main heat exchanger 1 and discharged as gaseous nitrogen product C or used as sealing gas D.

[0141] Also in the Figure 6In the example illustrated, a material stream i is discharged in liquid form from the first rectification column 11, which stream is subcooled in the condenser evaporator 121 of the second rectification column 120 and can be fed as reflux to the second rectification column 12.

[0142] A liquid, oxygen-rich stream k can be withdrawn from the bottom of the second rectification column 12 and fed in liquid form into a tank system 101. A corresponding liquid, oxygen-rich stream, denoted here by k3, can be withdrawn from the tank system 101 or another tank and subsequently heated in the main heat exchanger 1 and provided as a gaseous oxygen product U. The second rectification column 12 can, in particular, be designed and operated such that it can provide an ultra-high-purity oxygen product U with the specifications explained above. This need not be the case with the second rectification columns 12 of the air separation plants 100 to 500.

[0143] Further oxygen-rich liquid can be withdrawn analogously in the form of a stream k1 from the second rectification column 12, pressurized by an internal compression pump 7a, and provided as internally compressed oxygen pressure product E1. In the example shown, a stream I is withdrawn from the top of the second rectification column 12, which is also used here to form the aforementioned stream f.

[0144] From a middle region of the second rectification column 12, in particular at the argon transition, a material stream m is withdrawn and fed into a lower region of a fourth rectification column, also designated 14 here. From the bottom of the fourth rectification column 14, a further material stream n is withdrawn as above by means of a pump 8 and returned to the second rectification column 12. From the top of the fourth rectification column 14, overhead gas rises into a condensation space of a top condenser 141, is at least partially liquefied there and returned as reflux to the fourth rectification column 14. A non-evaporated portion can be released into the atmosphere A. A material stream p is withdrawn in liquid form below the top of the fourth rectification column 14.The material flow p is pressurized by means of a pump 7b and then heated in the main heat exchanger 1, so that in this way an internally compressed argon product I can be provided.

[0145] The top condenser 141 of the fourth rectification column 14 is also cooled here with liquid, which can be fed to the top condenser 141 in the form of the aforementioned stream q3, which is denoted by q hereinafter. A stream r can be withdrawn from an evaporation space of the top condenser 141 of the fourth rectification column 14. This stream r can be heated, preferably without backpressure or essentially without backpressure, in the main heat exchanger 1 after combining with stream I and the stream s explained below, as explained with respect to this stream I, and can be discharged from the air separation plant. In this way, a low pressure can be established in the evaporation space of the top condenser 141.

[0146] Liquid from the evaporation space of the top condenser 141 of the fourth rectification column 14 is withdrawn here in the form of stream s.

[0147] In Figure 7an air separation plant according to a further embodiment of the present invention is illustrated in the form of a schematic plant diagram and designated overall by 700.

[0148] In contrast to the Figure 6 In the illustrated air separation plant 600, a partial flow of the feed air flow a, which, as first described in Figure 2 designated a1, is taken from the main heat exchanger 1 at an intermediate temperature level and expanded by means of an expansion machine designated 201 as above.

[0149] The remainder of the feed air stream a is at least partially fed into the first rectification column, wherein a cross connection a2 is provided between the partial stream a1 and the material stream a.

[0150] The Figure 7The air separation plant 700 illustrated is further characterized in that the second rectification column 12 is formed as part of a double column, which additionally has a third rectification column 13. The expanded portion of the feed air stream a, designated a1, is fed into a lower region of this third rectification column 13.

[0151] A material stream, which is otherwise reused in a manner comparable to the material stream q of the preceding figures and is therefore also designated q here, is formed in the air separation plant 700 using bottom liquid from the third rectification column 13. Top gas from the third rectification column 13 is at least partially liquefied in the form of a material stream u in the condenser evaporator 121 and subsequently used in the form of a partial stream u1 as reflux to the third rectification column 13 and in the form of a partial stream u2 as reflux to the second rectification column 12.

[0152] Nitrogen-rich liquid is withdrawn in the form of stream v via a side draw from the third rectification column 13 and conveyed into the first rectification column 11 by means of a pump, designated 501 as above. A further stream k4 is withdrawn in gaseous form from the second rectification column 12 and combined with streams I and r to form a stream designated here as f1. Like stream f, stream f1 is heated in the main heat exchanger 1 and used accordingly. In the example shown, streams q, i, and u2 are subcooled against stream I in a common subcooler 9.

[0153] For further details, please refer to the explanations of the above figures, in particular the Figures 5 and 6 , expressly referred to. The features differing from the preceding figures can also be implemented here individually or jointly.

[0154] In Figure 8 an air separation plant according to a further embodiment of the present invention is illustrated in the form of a schematic plant diagram and is designated overall by 800.

[0155] The air separation unit 800 according to Figure 8 differs from the previously shown and explained air separation plants 100 to 700 in particular in that a fifth rectification column 15 is used, which is set up as a rectification column for providing high-purity oxygen.

[0156] Furthermore, in the air separation plant 800, stream i is fed into the third rectification column 13, and in a region of this feed, stream w is withdrawn in liquid form and fed into the second rectification column 12. The feed of stream i into the second rectification column 12 thus takes place "via the detour" of the third rectification column 13. Furthermore, a portion of the bottom liquid from the third rectification column 13 is fed directly into the second rectification column 12 in the form of stream q4. This is equivalent to bypassing the top condenser 141 of the fourth rectification column 14, which is only fed with the remaining residue.

[0157] A stream m1 is withdrawn from the second rectification column 12 and fed into an upper section 15a of the fifth rectification column 15, which is separated from a lower section 15b by a barrier plate 15c. Liquid separating on the barrier plate 15c is returned to the second rectification column 12 in the form of a stream n1. The previously explained streams r and s are fed back into the second rectification column 12. The upper section 15a of the fifth rectification column 15 serves in particular to discharge argon, which is transferred predominantly to the fourth rectification column 14 via a stream m2. The material stream m2 also includes top gas from the lower part 15b of the fifth rectification column 15. Bottom liquid from the fourth rectification column 14 is fed in the form of a material stream m2 to the top of the upper and lower parts 15a, 15b of the fifth rectification column 15.

[0158] The fifth rectification column 15 is provided with a condenser-evaporator 151 which is operated with a nitrogen-rich gas which is taken from the third rectification column 13 in the form of a stream x, at least partially liquefied in the condenser-evaporator 151 and returned to the third rectification column 13.

[0159] In the example presented here, a stream k is also taken from the bottom of the second rectification column 12 and transferred to a tank system 101. However, this is subsequently internally compressed by means of a pump 7c. Furthermore, ultra-high-purity oxygen in the form of a stream k5 is taken from the fifth rectification column 5. This is transferred to a tank system 102, temporarily stored there, evaporated in the main heat exchanger 1, and provided as ultra-high-purity oxygen product U1. Intermediate storage of the argon product in a tank system 103 is also possible.

[0160] For further details, please refer to the explanations of the above figures, in particular the Figures 5 to 7 , expressly referred to. The features differing from the preceding figures can also be implemented here individually or jointly.

[0161] The Figures 9 to 28 illustrate a number of further variants of air separation plants according to embodiments of the invention and according to non-inventive configurations. Although different designations are used here for certain material streams and apparatus than in the preceding figures, these may also correspond to one another.

[0162] In Figure 9merely as a basis for the explanations of the following figures, an air separation plant not according to the invention with an oxygen column next to the first rectification column 11, i.e. a second rectification column 12, but without further rectification columns, is illustrated and designated overall by 900. The majority of the Figure 9 The components illustrated have already been explained several times. As in Figure 9 As illustrated, a further storage tank 104 can be used and the material flow I can be passed separately through the main heat exchanger 1.

[0163] In Figure 10 an air separation plant is illustrated and designated 1000, which is a variant of the air separation plant 900 according to Figure 9and in which a material stream k6 is withdrawn from the second rectification column 12 via an intermediate draw-off and, if necessary, after intermediate storage in a buffer tank 105 and internal compression in an internal compression pump 7d and heating in the main heat exchanger 1, is discharged as the corresponding oxygen product U2.

[0164] In Figure 11 a further air separation plant not according to the invention is illustrated and designated 1100, which is a further variant of the plants 900 and 1000 according to the Figures 9 and 10 The air separation plant 1100 comprises a fourth rectification column 14, from which the previously explained material stream p is withdrawn in liquid form. The corresponding argon can be temporarily stored in a buffer tank 103 and, after internal compression in an internal compression pump 7b and heating in the main heat exchanger 1, discharged as the corresponding argon product I.

[0165] As illustrated here with 1101, a cross connection between the material streams f and I can be provided on the cold side of the main heat exchanger 1. This cross connection can be activated in particular in the event of a failure of one or more rectification columns, in order to avoid having to shut down the air separation plant 1100 entirely.

[0166] As illustrated by 1102, in this embodiment, externally supplied liquid nitrogen and a liquid, nitrogen-rich stream i1 from the first rectification column can also be fed to the top of the second rectification column 12. The latter has a lower nitrogen content than the top gas of the second rectification column 12. An additional separation section in the second rectification column 12 is designated 1103.

[0167] A stream k7 is withdrawn from the second rectification column 12, combined with stream I, and discharged in the form of this stream, referred to as I for simplicity, or fed to the warm section 110. In this way, the overall yield of gaseous, internally compressed argon (stream p or product I) can be increased. Stream r is fed to stream I, whereas stream s is used to form stream f.

[0168] In Figure 12 a further air separation plant not according to the invention is illustrated and designated 1200, which in particular is a variant of the air separation plant 1100 according to Figure 11 The air separation plant 1200 has the further expansion machine 201. The partial stream a1 is expanded in this further expansion machine 201 and used as explained several times.

[0169] The remainder of stream a not expanded in the expansion machine 201 is treated in a manner comparable to the previously explained stream b and is therefore designated accordingly. Furthermore, a subcooler 9, already explained several times, is shown here. The second rectification column 12 is arranged, with its lowest point, more than 6 m above the lowest point of the first rectification column 11.

[0170] In Figure 13 an air separation plant is illustrated and designated 1300, which in particular is a variant of the air separation plant 1200 according to Figure 12 , but in contrast to this, represents an embodiment of the present invention.

[0171] The air separation plant 1200 has the third rectification column 13 and the fifth rectification column 15, which have already been explained Figure 8The explanations for air separation unit 800 according to Figure 8 is therefore also expressly referred to in Annex 900.

[0172] Deviating from the air separation plant 800 according to Figure 8 In particular, external liquid nitrogen X is fed into the second rectification column 12, and a partial stream of stream r is combined with stream I and stream k3. This is particularly the case because there is no need for complete reflux in the second rectification column 12, or rather, an optimum exists in this regard. As illustrated, stream i is subcooled here in the condenser evaporator 121 before being fed into the second rectification column 12.

[0173] In Figure 14 an air separation plant is illustrated and designated 1400, which in particular comprises a variant according to the invention of the air separation plant 1300 according to Figure 13The air separation unit 1400 is designed to provide an additional pressurized nitrogen product D1.

[0174] For this purpose, the top stream of the second rectification column 12 is obtained with a higher purity than the previous stream I. This is therefore designated I1 here. This is achieved by withdrawing an additional stream I2 from the second rectification column 12 below the top. Furthermore, the second rectification column is provided with an additional separation section 12a. The illustrated design also has a positive effect on argon yield and purity.

[0175] The air separation plant 1300 according to Figure 13The material streams combined with material stream I are now combined with material stream I2 to form a material stream, which for the sake of simplicity is again designated I. After being heated in the main heat exchanger 1, material stream I1 is partially compressed in an external compressor 1401. A further part enters the warm part 110. Further details can be found in the Figures 27 and 28 illustrated in more detail.

[0176] In Figure 15 an air separation plant is illustrated and designated overall by 1500, which in particular comprises a variant of the air separation plant 1400 according to the invention according to Figure 14 represents.

[0177] The air separation plant 1400 according to Figure 14 The bottoms liquid of the third rectification column 13, which is only used to form the material stream q, is partly used here to form a material stream q4 (see also air separation plant 800 according to Figure 8) is used, which is fed to the second rectification column 12. The second rectification column 12 and the feed point of stream i are adjusted accordingly.

[0178] In Figure 16 an air separation plant is illustrated and designated 1600, which is a particularly inventive variant of the air separation plant 1500 according to Figure 15 represents.

[0179] The material stream x formed in the previously explained plants 800 and 1300 to 1500 is not used here. Instead, a material stream x1 is branched off as a substream of the overhead gas withdrawn from the third rectification column 13 and, like the material stream x previously, is partially liquefied in the condenser evaporator 151 and returned as reflux to the third rectification column 13. A further portion is heated in the form of a material stream x2 and at least partially discharged as another nitrogen product D2 from the air separation plant 1600.

[0180] In Figure 17 An air separation plant is illustrated and designated 1700, which in particular represents a variant according to the invention of the plants according to the previous figures, in which a fifth rectification column 15 is used. However, this is present here in a modified form and, as before, is designated 15a.

[0181] The rectification column 15a corresponds to the upper part 15a of the fifth rectification column 15 of the previous figures. From its top, a stream m3 is transferred to the fourth rectification column 14 and fed into a region above the bottom, which functionally corresponds to the lower part 15b of the fifth rectification column 15 of the previous figures and is therefore designated here by 15b'. The liquid obtained here is pumped back to the rectification column 15a in the form of a stream n3 by means of a pump (not specifically designated). Due to the design according to Figure 17 In particular, freedom from non-ferrous metals in the oxygen product U can be achieved because, thanks to this arrangement, the fluid which is fed to the sub-column 15b' does not come into contact with a pump impeller which is usually made of bronze.

[0182] In Figures 18 and 19 Variants of systems are illustrated and designated 1800 and 1900, in which essentially the warm part 110 and the routing of material flows through the main heat exchanger 1 are modified. Only this warm part 110 and a section of the main heat exchanger 1 as well as material flows necessary for understanding this variant are shown in Figures 18 and 19 shown.

[0183] The air compressed, cooled and cleaned in the main air compressor 112 is Figure 18divided into partial streams a2 and a3, of which partial stream a2 is passed from the warm to the cold end through the main heat exchanger 1. The material stream a3, however, is further compressed by means of a compressor or a compressor stage 112a, which is coupled to the main air compressor 112, and then treated like the material stream a of the previous figures. In particular, a partial stream, designated here as before with a1, is expanded in the expansion machine 201 and then combined with the material stream a2. As in the variant according to Figure 19 As illustrated, an expansion machine 201 and the formation of the material flow a1 can also be dispensed with.

[0184] By using the Figures 18 and 19 The measures illustrated can reduce energy consumption because not all of the air needs to be brought to a high pressure, but only the portion of the material flow a3.

[0185] In Figure 20a variant of an air separation plant according to the invention is illustrated and designated 2000, which has similarities with the air separation plant 800 according to Figure 8 and other previously described plants, particularly with regard to the treatment of streams i and w. This allows the third rectification column 13 to be used to separate stream i, and a higher proportion of nitrogen product can be obtained. Reference is made to the above explanations, and only a few streams are individually identified here and below.

[0186] The design according to Figure 20 (and according to Figure 8 ) has the particular advantage that the condenser-evaporator 121 is simplified and a similarly simplified control system can be used. In particular, the material flow w can be controlled like a conventional Joule-Thomson flow.

[0187] In a variant of this invention, which is described in Figure 21shown and designated 2100, a material stream q5 is formed using bottoms liquid from the fourth rectification column 14, passed by means of a pump 7e through the modified heat exchanger 2, designated here by 2a, and cooled in the process and then returned to the third rectification column 13. This makes it possible, in particular, to improve the recovery of nitrogen in the third rectification column 13, thereby enabling higher expansions of all products.

[0188] In a further variant of the invention, which is Figure 22 and designated 2200, a material stream k5 formed by bottom liquid of the fifth rectification column 15 is treated accordingly and returned to the fifth rectification column 15.

[0189] In Figure 23An air separation plant according to a further embodiment of the invention is illustrated and designated 2300. This differs from the previously shown embodiments in particular by a condenser-evaporator 131 arranged in the bottom of the third rectification column 13. Functionally, this can be considered a division of the condenser-evaporator in the second rectification column 12, which is designated here by 121a. In this way, the recovery of nitrogen in the second rectification column 12 or the third rectification column 13 can be improved.

[0190] As shown here, fluid in the form of a stream i2 can be withdrawn from the second rectification column 2 via a side draw, passed through the condenser evaporator 141, at least partially liquefied, and fed into the third rectification column 13. At the same height, liquid can be withdrawn from the third rectification column 13 and returned to the second rectification column 12 by means of a pump 7r.

[0191] A variant not according to the invention shows Figure 24based on the plant designated 2400, which lacks the third rectification column 13 or in which its function is integrated into the first rectification column 11. Here, the material stream i2 is partially heated in the main heat exchanger 1, expanded in an expansion machine 201a, cooled again in the main heat exchanger 1, and a portion is passed through the condenser evaporator 121 of the second rectification column, at least partially liquefied in the process, and in turn fed in portions to the first and second rectification columns 11, 12. The expansion machine 201a is coupled, for example, to a generator.

[0192] In Figure 25An air separation plant according to the invention is illustrated in accordance with a further embodiment of the present invention and is designated overall by 2500. This differs from the previous plants, in which a material stream a1 is formed and expanded, by the further treatment of this material stream a1.

[0193] In the air separation plant 2500, the partial stream a1 is divided into partial streams a4 and a5, the proportions of which can each be adjusted via valves not specifically designated. Instead of partial stream e, as was previously the case, the partial stream a4 is expanded in the expansion machine 3 and, if applicable, the parallel expansion valve and is thus partially used to drive the compressor 5. The partial stream a5, like the entire partial stream a1 previously, is fed, for example, into the third rectification column 13. The material stream e is nevertheless formed and partially treated as before, but is not expanded by means of the expansion machine 3 and the expansion valve 4. It is fed into the third rectification column 13 below the material stream a5. The third rectification column 13 can be provided with an additional separation section 13a.

[0194] Through the Figure 25Using the measures illustrated, the rectification columns 11 to 15 can be thermally coupled. Residual gas from the first rectification column 11 can be used to recover argon, oxygen, and nitrogen. Stream e can be fed in whole or in part to the second rectification column 12. The remainder can be discharged via the expansion machine 3 as residual gas for use in the warm section 110.

[0195] In Figure 26An air separation plant according to a further embodiment of the present invention is illustrated and designated overall by mi5 2600. This represents, in particular, a variant of the air separation plant 2500. Here, too, the partial stream a1 is divided into partial streams a4 and a5, but here the material stream a4 is fed to the material stream I before it is heated and discharged or fed to the warm part 110. The partial stream a5 is fed into the second rectification column 12. The function of the expansion turbine 201 therefore corresponds to that of a Lachmann turbine. The illustrated measures allow the rectification columns 11 to 15 to be thermally coupled.

[0196] The partial flow d is formed and compressed as before, whereby a compressor used for this purpose, which is therefore denoted as 5a, is driven purely by a motor. The partial flow e is, as before, Figure 25explained, fed into the fourth rectification column 14.

[0197] In the Figures 27 and 28 In the partial representation of the air separation plants 2700 and 2800 according to embodiments of the invention, the first time Figure 14 material stream I1 mentioned above. Reference is expressly made to the explanations therein. As in Figure 28 As illustrated by the air separation plant 2800, the material flow I1 can first be partially heated in the main heat exchanger 1, compressed in a compressor 201b coupled to the expansion machine 201, then fed back to the main heat exchanger 1 at an intermediate temperature level, further heated, and then fed to the compressor 1401.

[0198] As in Figure 29 illustrated in partial representation, in an air separation plant 2900 according to an embodiment of the invention, the nitrogen of the material stream h can also be separated as before with respect to Figures 28 and29 illustrated, be compressed accordingly. The use of the compressor designated 1401' here is optional.

[0199] In Figure 30 an air separation plant 3000 according to a non-inventive embodiment is illustrated in the form of a schematic plant diagram.

[0200] The air separation unit 3000 according to Figure 30 has great similarities with the Figure 1 illustrated, also not according to the invention. Only differences are explained below.

[0201] Here, the partial stream c, after being passed through the condenser evaporator 121 of the second rectification column 12, is not combined with other streams before being fed into the first rectification column 11. Furthermore, no part of the stream e is combined here as in Figure 1or the air separation plant 100, the material flow e1 is branched off, so that the entire material flow e is fed to the heat exchanger 2. The expansion of the material flow e takes place here in the form of two partial flows in two expansion machines 3 and 4. The expansion machine 4 is coupled to a generator.

[0202] As illustrated here, stream j, designated differently here, is discharged from the second rectification column above stream i and, in particular, is fed to the top of the second rectification column 2. Stream I is withdrawn from the top of the second rectification column 12, which can be heated without combining with another stream and, in particular after compression in a compressor 3001, discharged as a further gaseous nitrogen product H from the air separation plant 100. The gaseous nitrogen product H represents the "further nitrogen-rich air product" previously explained in relation to various embodiments of the invention.

[0203] As indicated here in a highly simplified manner, in the air separation plant 3000, the main heat exchanger 1 can be arranged in a first prefabricated cold box 3010. The first rectification column 11 with the heat exchanger 2 used to cool its head gas can be arranged in a second prefabricated cold box 3020. The second rectification column can be arranged in a third prefabricated cold box 3030. These surround, unlike in the highly simplified representation of the Figure 1 , the respective elements mentioned completely.

[0204] In Figure 31 is a variant of the air separation plant 3000 according to Figure 31 which, however, represents an embodiment of the present invention and is designated overall by 3100. In contrast to the Figure 30In the illustrated plant 3000, a partial stream a1 of the feed air stream is provided; the repeatedly mentioned third rectification column 13 is also provided, and argon recovery is also provided in a fourth rectification column 14. Furthermore, a fifth rectification column 15 is provided in the air separation plant 3100. The designations "first," "second," "third," "fourth," and "fifth" rectification column are used consistently with the above statements, so that reference can be made to them.

[0205] The formation and treatment of material flows d, e, f, g, h, i, k and l is essentially carried out as already described for Annex 100 and 3000 in accordance with Figure 130, respectively, wherein in the system 3100 only one expansion machine 4 is illustrated instead of the expansion machines 3 and 4, and the material stream i is not fed directly into the second rectification column 12, but is first passed through the condenser evaporator 121 and a subcooling counterflow 202. Furthermore, the material stream k can be temporarily stored in a tank system 203 in the example illustrated here. The material stream I is also passed through the subcooling counterflow 202.

[0206] A material stream corresponding to the material stream j according to plant 100 is not formed here. Instead, a liquid reflux n to the second rectification column 12 is formed by withdrawing overhead gas from the fourth rectification column in the form of a material stream m and liquefying it in the condenser evaporator 121. A portion of the liquefied overhead gas is passed through the subcooling countercurrent 202 and used in the form of material stream n; a further, undesignated portion is returned as reflux to the first rectification column 11. Further liquid can be provided in the form of liquid nitrogen X. From the third rectification column 13, a material stream o is returned to the first rectification column 1 in plant 200 by means of a pump 204.

[0207] The fifth rectification column 15 also represents a double column, the function of which is explained above. The lower part 15b is operated with a condenser-evaporator 151, which is heated using a material stream p, which is withdrawn from the third rectification column 13 and then, i.e., downstream of the condenser-evaporator 151, returned to the third rectification column 13. Furthermore, ultra-high-purity oxygen in the form of a material stream q is withdrawn from the lower part 15b. This is transferred to a tank system 205, temporarily stored there, evaporated in the main heat exchanger 1, and provided as ultra-high-purity oxygen product U.

[0208] A stream r is withdrawn from the second rectification column 12 in the region of the argon transition or below and fed into the upper part 15a of the fifth rectification column 15, which is separated from the lower part 15a by a barrier plate 15c. Liquid separating on the barrier plate 15c is recycled below stream r into the second rectification column 12. Top gas from the upper part 15a and the lower part 15b of the fifth rectification column 15 is transferred via a stream s to the fourth rectification column 14. Bottom liquid from the fourth rectification column 14 is fed in the form of a stream t to the top of the lower part 15a and the upper part 15b of the fifth rectification column 15.

[0209] A top condenser 141 of the third rectification column 13 is cooled using bottoms liquid from the second rectification column 12 in the form of a stream u, which has previously been passed through the countercurrent subcooling 202. Liquid from an evaporation space of the top condenser 141 is recycled to the second rectification column 12 in the form of a stream v. Gas from an evaporation space of the top condenser 141 is withdrawn in the form of a stream w and partially expanded into the second rectification column 12 and partially used to form a residual gas stream x, which also comprises fluid withdrawn from the second and third rectification columns 12, 13.

[0210] Below the top, argon-rich liquid is withdrawn from the fourth rectification column 14 in the form of a stream x. This liquid can be stored in a tank system 206 before being subjected to internal compression by a pump 207, heated, and provided as argon product V. Uncondensed top gas from the fourth rectification column 14 can be released to the atmosphere A in the form of a stream y.

[0211] Also in the air separation plant 3100 according to Figure 31The main heat exchanger 1 can be arranged in a first prefabricated cold box 3110. The first rectification column 11 with the heat exchanger 2 used to cool its overhead gas can be arranged in a second prefabricated cold box 3120. The second rectification column 12 can be arranged together with the third rectification column 13 in a third prefabricated cold box 3130. In the example shown, the fifth rectification column 15 is also arranged in the third cold box 3130. In the example shown, the fourth rectification column 14 is arranged in a further prefabricated cold box 3140, in which, however, the fifth rectification column 15 can also be arranged, for example. The fourth rectification column 14 can also be arranged in the third cold box 3130. Any distribution is possible.

[0212] It should be emphasized again that, although measures according to individual embodiments of the invention are described in the above figures as part of corresponding systems, these can also be used individually or in other systems without departing from the scope of the present invention. For example, in all cases, motor and / or turbine operation of a compressor can be provided, and / or expansion machines can be braked by generators and / or by means of brakes and / or by coupling with a compressor.

[0213] Although certain air separation plants are described above as variants of other previously explained plants, it is understood that the measures or features proposed here can also be used in plants other than those described as the basis.

Claims

1. Method for low-temperature air separation, in which an air separation unit (100-3100) having a first rectification column (11) and a second rectification column (12) is used, - the first rectification column (11) being operated at a first pressure level and the second rectification column (12) being operated at a second pressure level below the first pressure level, - fluid which is oxygen-enriched compared to atmospheric air being drawn from the first rectification column (11) in the form of one or more first material flows, - at least one portion of the fluid drawn from the first rectification column (11) in the form of the one or more first material flows being heated in a heat exchanger (2), - a portion of the fluid heated in the heat exchanger (2) being compressed using a compressor (5) and returned to the first rectification column (11), - a first portion of the head gas of the first rectification column (11) being condensed in the heat exchanger (2) and a second portion being discharged from the air separation unit (100, 3100) in the form of at least one nitrogen-rich air product, - additional fluid containing oxygen, nitrogen and argon being drawn from the first rectification column (11) and used as a second material flow or to form a second material flow which is transferred to the second rectification column (12), and - an oxygen-rich sump liquid being formed in the sump of the second rectification column (12) and at least one portion thereof being discharged from the air separation unit (100, 200) in the form of a third material flow, characterized in that - a third rectification column (13) is used, the second rectification column (12) and the third rectification column (13) being designed as parts of a double column, the third rectification column (13) being arranged below the second rectification column (12), and the third rectification column (13) being supplied with air.

2. Method according to claim 1, in which the air supplied to the third rectification column (13) comprises compressed and cooled air which is expanded using an expansion machine (201).

3. Method according to claim 2, in which the second rectification column (12) is operated with a condenser evaporator (121) which is arranged in a sump region of the second rectification column (12) and which is heated using fluid which is drawn from and / or supplied to the third rectification column (13).

4. Method according to claim 3, in which the air supplied to the third rectification column (13) is at least partially liquefied in the condenser evaporator (121) which is arranged in the sump region of the second rectification column (12) and is returned to the third rectification column (13) as liquid reflux.

5. Method according to any of claims 3 or 4, in which a head gas is formed in the third rectification column (13), which head gas is at least partially liquefied in the condenser evaporator (121) which is arranged in the sump region of the second rectification column (12) and is returned as reflux to the second and / or third rectification column (12, 13).

6. Method according to any of claims 3 or 4, in which a sump liquid is formed in the third rectification column (13), which is supplied at least in part into the second rectification column (12).

7. Method according to any of the preceding claims, in which a nitrogen-rich head gas is formed in the second rectification column (12) and at least a portion thereof is discharged from the air separation unit (3000, 3100) as an additional nitrogen-rich air product, wherein a residual oxygen content of the head gas of the first rectification column (11) is 1 ppb to 10 ppm and a residual oxygen content of the head gas of the second rectification column (12) is 10 ppb to 100 ppm.

8. Method according to claim 7, in which the second rectification column (12) is equipped with 50 to 120 theoretical plates and / or a nitrogen-rich liquid material flow is provided and added as reflux in an upper region of the second rectification column (12)9. Method according to any of the preceding claims, in which - fluid which has a higher argon content than the oxygen-rich sump liquid of the second rectification column (12) is drawn from the second rectification column (12) and used as a fourth material flow or to form a fourth material flow, - a fourth rectification column (14) is used, into which the fourth material flow is fed, wherein an argon-rich fluid which has a content of more than 95 mol percent argon is formed in the fourth rectification column (14).

10. Method according to claim 9, in which a fifth rectification column (15) is used in which a liquid having an oxygen content is formed above an oxygen content of the oxygen-rich sump liquid formed in the sump of the second rectification column (12), and in which the fifth rectification column (15) is used to form the fourth material flow using the fluid which is drawn from the second rectification column (12) and has a higher argon content than the oxygen-rich sump liquid of the second rectification column (12).

11. Method according to either claim 9 or claim 10, in which a quantity of the argon product formed in the air separation unit (100-3100) comprises 1 to 85 percent of a total argon quantity supplied as a whole in the form of air to the air separation unit (100-3100).

12. Air separation unit (100-3100) having a first rectification column (11), a second rectification column (12), a heat exchanger (2), and a compressor (5), which is designed to - operate the first rectification column (11) at a first pressure level and the second rectification column (12) at a second pressure level below the first pressure level, - draw fluid which is oxygen-enriched compared to atmospheric air, from the first rectification column (11) in the form of one or more first material flows, - heat in the heat exchanger (2) at least one portion of the fluid drawn from the first rectification column (11) in the form of the one or more first material flows, - compress a portion of the fluid heated in the heat exchanger (2) using the compressor (5) and to return it to the first rectification column (11), - condense a first portion of the head gas of the first rectification column (11) in the heat exchanger (2) and to discharge a second portion of the head gas from the air separation unit (100, 3100) in the form of at least one nitrogen-rich air product, - draw additional fluid containing oxygen, nitrogen and argon from the first rectification column (11) and to use it as a second material flow or to form a second material flow which is transferred to the second rectification column (12), and - form an oxygen-rich sump liquid in the sump of the second rectification column (12) and to discharge at least one portion thereof in the form of a third material flow from the air separation unit (100, 200), characterized in that - a third rectification column is provided in the air separation unit (100-3100), the second rectification column (12) and the third rectification column (13) being designed as parts of a double column and the third rectification column (13) being arranged below the second rectification column (12), the air separation unit (100-3100) being designed to supply the third rectification column (13) with air.