Method for cryogenic separation of air, and air separation plant

Abstract

A method for cryogenic separation of air, in which an air separation plant having a rectification column arrangement which comprises a pressure column, a low-pressure column and a raw argon column is used. In the method, evaporation gas from a head gas condensation device associated with the raw argon column is partly or completely fed into the low-pressure column via a gas line. The gas line contains a first throttle valve which is adjusted by means of a control device so that argon is prevented from freezing out in the first head gas condensation arrangement. This creates, at least temporarily, a pressure drop of at least 50 mbar across the throttle valve. The present invention also relates to a corresponding air separation plant.

Description

[0001] The present invention relates to a method for the cryogenic separation of air and an air separation plant according to the respective preambles of the independent claims.BACKGROUND OF THE INVENTION

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

[0003] Air separation plants have rectification column arrangements which can be designed differently. In addition to rectification columns for obtaining nitrogen and / or oxygen in the liquid and / or gaseous state, that is to say rectification columns for nitrogen-oxygen separation which can be combined in particular in a known double column, rectification columns for obtaining other air components, in particular noble gases, or pure oxygen, can be provided.

[0004] The rectification columns of typical rectification column arrangements are operated at different pressure levels. Known double columns have a so-called pressure column (also referred to as a high-pressure column, medium-pressure column or lower column) and a so-called low-pressure column (upper column). The high-pressure column is typically operated at a pressure level of 4 to 7 bar, in particular about 5.3 bar; the low-pressure column on the other hand is operated at a pressure of typically 1 to 2 bar, in particular about 1.4 bar. In certain cases, even higher pressure levels may be used in these rectification columns. The pressures indicated here and below are absolute pressures at the top of the respective indicated rectification columns.

[0005] In order to extract argon, air separation plants with raw and pure argon columns can be used. An example is illustrated in Häring (see above) in FIG. 2.3A and described starting on page 26 in the section, “Rectification in the Low-pressure, Crude and Pure Argon Column,” and also starting on page 29 in the section, “Cryogenic Production of Pure Argon.” As explained there, argon accumulates in corresponding plants at a certain height in the low-pressure column. At this or at another favorable point, optionally also below the argon maximum, argon-enriched gas with an argon concentration of typically 5 to 15 mole percent can be drawn off from the low-pressure column and transferred into the raw argon column. A corresponding gas typically contains about 0.05 to 500 ppm of nitrogen and otherwise substantially oxygen. It should be expressly emphasized that the indicated values for the gas drawn off from the low-pressure column represent only typical sample values.

[0006] The raw argon column serves substantially to separate off the oxygen from the gas drawn off from the low-pressure column. The oxygen separated off in the raw argon column or a corresponding oxygen-rich fluid can be returned to the low-pressure column in liquid form. A gaseous fraction which remains in the raw argon column during the separation and contains substantially argon and nitrogen can be further separated in a pure argon column to obtain pure argon. The raw and, when appropriate, the pure argon column have top condensers which can be cooled in particular with a part of an oxygen-enriched, nitrogen-depleted liquid (so-called “enriched liquid) withdrawn from the pressure column, which partially evaporates during this cooling. This is also the case in the context of the present invention. The gas phase formed during partial evaporation and the corresponding remaining liquid are also fed into the low-pressure column at different feed points, the choice of which is explained below. In conventional methods, the pressure in the gas space of the top condenser is the same as at the point where the gas phase is fed into the low-pressure column. At this point, “equal pressure” is understood to mean a pressure range in which the two pressures do not differ by more than 25 mbar, preferably not more than 10 mbar.

[0007] The oxygen or the oxygen-rich fluid from the raw argon column is typically fed back from the pressure column into the low-pressure column several theoretical or practical plates below the feed points for the partially evaporated liquid used for cooling.

[0008] An object of the present invention is to provide means for improving the operation of an air separation plant with an argon recovery system having a raw argon column and a pure argon column.DISCLOSURE OF THE INVENTION

[0009] Against this background, the present invention proposes a method for the low-temperature separation of air and an air separation plant with the features of the respective independent patent claims. Each of the embodiments are the subject matter of the dependent claims and of the description below.

[0010] In the following, some terms used in describing the present invention and its advantages, as well as the underlying technical background, will first be explained in more detail.

[0011] The devices used in an air separation plant are described in the cited technical literature—for example, in Haring in Section 2.2.5.6, “Apparatus.” Unless the following definitions differ, reference is therefore explicitly made to the cited technical literature with respect to terminology used in the context of the present application.

[0012] In this case, a “condenser evaporator” refers to a heat exchanger in which a first, condensing fluid stream enters into indirect heat exchange with a second, evaporating fluid stream. Each condenser evaporator has a liquefaction chamber and an evaporation chamber. The liquefaction and evaporation chambers have liquefaction or evaporation passages. Condensation (liquefaction) of the first fluid stream is carried out in the liquefaction chamber, and evaporation of the second fluid stream in the evaporation chamber. The evaporation and liquefaction chambers are formed by groups of passages, which are in a heat-exchanging relationship with one another. Condenser evaporators are also referred to as “top condenser” and “bottom evaporator” according to their function, wherein a top condenser is a condenser evaporator in which head gas of a rectification column is condensed, and a bottom evaporator is a condenser evaporator in which bottom liquid of a rectification column is evaporated. However, the bottom liquid can also be evaporated in a top condenser—for example, as used in the context of the present invention.

[0013] In particular, what is referred to as the main condenser, which connects a high-pressure column and a low-pressure column of an air separation plant in a heat-exchanging manner, is designed as a condenser evaporator. The main condenser or other condenser evaporator can be designed in particular as single-level or multi-level bath evaporators, in particular as a cascade evaporator (as described, for example, in EP 1 287 302 B1), but also as a falling-film evaporator. A corresponding condenser evaporator can be formed, for example, by a single heat exchanger block or by multiple heat exchanger blocks arranged in a common pressure vessel.

[0014] In a “forced-flow” condenser evaporator or a condenser evaporator with forced flow on the evaporation side, which can also be used in the context of the present invention, a liquid stream is pressed by means of its own pressure through the evaporation chamber and partly evaporated there. (“Forced-flow” evaporators are sometimes also referred to as “once-through evaporators.”) This pressure is generated, for example, by a liquid column in the supply line to the evaporation chamber, which liquid column results from the corresponding positioning of a liquid reservoir. In this case, the height of this liquid column at least corresponds to the pressure loss in the evaporation chamber. The gas or gas-liquid mixture leaving the evaporation chamber, i.e., a two-phase flow, is passed directly to the next method step or to a downstream device in a once-through / forced-flow condenser evaporator and, in particular, is not introduced into a liquid bath of the condenser evaporator, from which the remaining liquid proportion would be drawn in again, as is the case, for example, in a conventional bath evaporator operating on the basis of the known thermosiphon effect.

[0015] Fluids, i.e., liquids and gases, can, in the terminology used herein, be rich or low in one or more components, wherein “rich” can refer to a content of at least 50%, 75%, 90%, 95%, 99%, 99.5%, 99.9%, or 99.99%, and “low” can refer to a content of at most 50%, 25%, 10%, 5%, 1%, 0.1%, or 0.01% on a molar, weight, or volume basis. The term “predominantly” can correspond to the definition of “rich.” Fluids can further be enriched or depleted by one or more components, wherein these terms relate to a content in a starting fluid from which the fluid was obtained. The fluid is “enriched” if it contains at least 1.1 times, 1.5 times, 2 times, 5 times, 10 times, 100 times, or 1,000 times the content, and “depleted” if it contains at most 0.9 times, 0.5 times, 0.1 times, 0.01 times, or 0.001 times the content of a corresponding component, based upon the starting fluid. If, by way of example, reference is made here to “oxygen” or “nitrogen,” this is also understood to mean a fluid that is rich in oxygen or nitrogen, but need not necessarily consist exclusively thereof.

[0016] The present disclosure uses the terms “pressure range” and “temperature range” to characterize pressures and temperatures, which means that corresponding pressures and temperatures in a corresponding plant do not have to be used in the form of exact pressure or temperature values in order to realize the inventive concept. For example, there are different pressures at different positions within the pressure and low-pressure column, but they are within a certain pressure range, also referred to as the operating pressure range. Corresponding pressure ranges and temperature ranges can be disjoint ranges or ranges that overlap one another.

[0017] Absolute and / or relative spatial indications used below, such as in particular “over,”“under,”“above,”“below,”“next to,” and “next to one another,” refer in particular here to the spatial orientation of the correspondingly designated elements of an air separation plant, e.g., rectification columns, sub-columns of multi-part rectification columns, or rectification regions of rectification columns in normal operation. An arrangement of two elements “one above the other” is understood here in particular to mean that the upper end of the lower of the two elements is located at a lower or the same geodetic height as the lower end of the upper of the two elements, and the projections of the two elements overlap in a horizontal plane. In particular, the two elements can be arranged exactly one above the other, i.e., the vertical center axes of the two elements run on the same vertical straight line. An arrangement “next to one another” is to mean in particular that the projections of the two elements do not overlap in a horizontal plane. In the case of a rectification column designed in multiple parts, terms such as “functionally below” or “functionally above” refer to the arrangement of rectification regions or sub-columns that they would have if the rectification column were of a single-part design.

[0018] Air separation plants designed according to the prior art with a raw column (and optionally with a pure argon column), in which the top condenser of the raw argon column is designed as a force-flow condenser evaporator in the manner explained above, often have unsatisfactory operating stability, in particular in the underload case (partial load operation), i.e., when less feed air is introduced into the plant than in a normal operating case—for example, at least 5%, preferably at least 10%, less and / or at most 60% or 40% less. A reduction in the air volume of 5 to 50% is usually referred to as an underload case.Advantages of the Invention

[0019] The invention deviates from the usual operating method for forced-flow condensers, according to which, in all operating modes, the first evaporation gas is introduced into the low-pressure column with the lowest possible pressure loss, i.e., without pressure-changing measures. This is, fundamentally, efficient.

[0020] This is because a pressure is then established in the evaporation chamber of the first head gas condensation arrangement which corresponds to the operating pressure of the low-pressure column plus line losses. This ensures stable operation of the system under normal conditions. In the effort to find the cause of the undesirably fluctuating operation, it has been found in the context of the invention that, in special operating situations, e.g., during partial load operation, the liquid argon can be undercooled to such an extent that there is a risk that the condensation passages will be blocked by freezing argon (triple point of argon: 83.8 K).

[0021] This problem is solved according to the invention in that the first evaporation gas is passed through a first throttle valve between the first head gas condensation arrangement and the low-pressure column. By partially closing the throttle valve, the pressure and thus the temperature in the evaporation chamber can be increased in the event of an underload, thereby effectively preventing the condenser evaporator from becoming blocked due to freezing. Preferably, the valve is designed as an automatic valve; alternatively, a manual valve can be used. Overall, this results in particularly stable operation of the first head gas condensation arrangement and the raw argon column.

[0022] The term “throttle valve” is used here in the general sense of “throttle device” and includes, for example, throttle flaps.

[0023] The pressure drop across the first throttle valve in at least one operating case can, for example, be between 300 and 50 mbar, preferably between 250 and 80 mbar. Generally, this throttling of the first evaporation gas is carried out in an underload case. Depending upon the extent of the underload, a lower or higher pressure drop and thus a lower or higher temperature is set. In a sample case, the following values result for a composition of the ???? of approximately 57.4% nitrogen, 1.8% argon, and 40.8% oxygen:TABLE 1Pressure at the evaporator inlet, bara1.491.391.291.19Boiling point, K84.2083.5282.8082.03Plant load, % (approx.)100%83%64%40%

[0024] In order to prevent the freezing of argon, the first throttle valve is adjusted by means of the control device according to the invention so that the temperature of the first cooling liquid upon entering the first head gas condensation arrangement is above the triple point temperature of argon. This entry temperature is preferably at least 0.1, in particular at least 0.25 K, above the triple point of argon. The temperature difference is preferably between 0.1 and 2.0 K, most preferably between 0.2 and 1.0 K.

[0025] In principle, a throttle valve at the location of the first throttle valve is known from the prior art (see also FIG. 1), but only in systems with a bath evaporator at the head of the raw argon column. In a bath evaporator, however, the valve has a completely different function, viz., a quantity control for the gas flow at the column inlet. In a forced-flow evaporator, however, this flow control is achieved by backing up the liquid at the evaporator outlet (on the condensation side); a valve between the condenser and the low-pressure column would only produce undesirable pressure loss and is unnecessary for quantity control there. In the context of the invention, a throttle valve is again used, which is completely open in many operating cases, but in certain operating cases, surprisingly, effectively improves the stability of the operation of the condenser evaporator. Of course, this throttling also causes an avoidable pressure loss and thus tends to reduce the energy efficiency of the process; however, it has been found in the context of the invention that the effect of this throttling does not result in the expected disadvantage, but rather, surprisingly, in a saving of energy.

[0026] The condenser is as a rule designed and dimensioned for the design case (normal operation). It offers a comparatively large heat exchange surface in underload cases. Therefore, it must be “braked” in underload cases in order to set the appropriate performance. In plants with bath evaporators, this works, for example, by increasing the evaporation pressure (usual control of an evaporator). In plants with forced-flow evaporators, however, the power (the load on the raw argon column) is regulated by backing up the liquid and covering part of the heat exchange surface, since there is no valve between the evaporation chamber of the condenser and the low-pressure column. The operating pressure in the NDS in underload cases is noticeably lower than in the design case; therefore, the pressure (or temperature) in the evaporation chamber of the forced-flow evaporator is also lower, and freezing of the argon can occur. To counteract this, the pressure in the low-pressure column must be artificially increased. This costs energy, however. This energy loss is prevented by the method according to the invention.

[0027] The control device according to the invention can be analog or digital and in particular can be integrated into an operational control system. It ensures, without human intervention, that the first throttle valve is partially closed in the corresponding operating cases in order to set the desired pressure difference. This measure is preferably integrated into an automatic load adjustment and thus ensures consistently stable operation of the system—for example, when transitioning from normal load operation to underload operation.

[0028] In the invention, using a first proportion of an oxygen-enriched liquid from the pressure column, a first liquid pressure flow is formed, which is expanded while a first flash gas is obtained and a first low-pressure liquid remains.

[0029] The raw argon column is operated using a first head gas condensation arrangement in which head gas of the raw argon column is subjected to condensation with partial evaporation of a first cooling fluid provided using the first low-pressure liquid or a part thereof. The first head gas arrangement is also referred to below as the top condenser of the raw argon column.

[0030] In the method and the plant, moreover, a pure argon column can be provided that is operated using a second head gas condensation arrangement in which head gas of the pure argon column is subjected to condensation, with partial vaporization of a second cooling fluid, which is provided using the second low-pressure liquid or a part thereof. The second head gas arrangement is also referred to below as, for short, the top condenser of the pure argon column.

[0031] A first evaporation gas formed during the partial evaporation of the first cooling fluid or a part thereof and a first excess liquid remaining after the partial evaporation of the first cooling fluid or a part thereof are fed into the low-pressure column.

[0032] A second evaporation gas formed during the partial evaporation of the second cooling fluid or a part thereof and a second excess liquid remaining after the partial evaporation of the second cooling fluid or a part thereof are fed into the low-pressure column.

[0033] The term “evaporation gas” refers to the evaporated proportion formed by the heat transfer from the respective head gases of the raw and pure argon column in the head gas condensation arrangements or condenser evaporators. Any remaining liquid residue is referred to here as an “excess liquid.” In contrast to the term “evaporation gas,” the term “flash gas” is used to describe the gas or vapor proportion which is formed only by expansion.

[0034] Preferably, in the invention, the liquid level on the evaporation side of the head gas condensation arrangement (13.10) is regulated by a second throttle valve (13V2), by means of which the first cooling fluid upstream of the head gas condensation arrangement (13.10) can be throttled.

[0035] As is also common with forced-flow evaporators, the first evaporation gas is preferably withdrawn, together with the first excess liquid as a first two-phase flow, from the head gas condensation arrangement, without any part of the excess liquid being circulated via the evaporator.

[0036] In a particularly advantageous embodiment of the invention, one or more “forced-flow” condenser evaporators of the type described can be used in the first head gas condensation arrangement. Reference is made in this context to the explanations above. In particular, the first low-pressure liquid or a part thereof as the first cooling fluid is thus forced through one or more condenser evaporators, which is or are formed as part of the first head gas condensation arrangement, and is thereby subjected to partial evaporation to form the first evaporation gas and the first excess liquid. In this case, “forced through” is defined as feeding into the evaporation chamber under pressure—for example, by means of a pipeline.

[0037] The throttle valve can be fully open at least temporarily during operation, in particular during normal operation (first operating mode). However, in at least one underload case (second operating mode), the pressure drop of at least 50 mbar is generated.

[0038] In addition to the first evaporation gas, in the context of the invention the first excess liquid is preferably also fed into the low-pressure column. In a first variant of the invention, the gas and the liquid can be fed together as a first two-phase flow partially or completely into the low-pressure column, in particular in a first feed region. In this case, the gas line is designed as a two-phase line and the first throttle valve as a two-phase valve, and the two-phase flow, or the part that flows into the low-pressure column, is conducted through the first throttle valve.

[0039] In a second variant, the first two-phase flow is fed into a phase separator. In this case, the gas line between the phase separator and the low-pressure column is designed as a pure gas line and the first throttle valve as a pure gas valve. In addition, the first excess liquid can be passed between the head gas condensation arrangement and the throttle valve, and through a phase separator in which the first evaporation gas and the first excess liquid are separated from one another. The first evaporation gas is then fed into the low-pressure column separately from the first excess liquid. The pressure in the evaporation chamber is here not due to the valve in the line for the first excess liquid, but due to the first a valve in the pure gas line that connects the phase separator at the gas side to the low-pressure column.

[0040] The liquid level in the phase separator can be measured. Depending upon the measured value, the amount of first cooling fluid introduced into the first head gas condensation arrangement is preferably adjusted. Preferably, the amount of liquid in the phase separator is quantitatively controlled.

[0041] The invention can in principle be applied to all process circuit topologies with argon recovery, regardless of the type of refrigeration or the type of product compression. These comprise, in particular, what are known as MAC / BAC or HAP processes as described, for example, in paragraphs to

[0025] of EP 3 196 573 A1, methods with a nitrogen cycle as described in EP 2 235 460 A2 or in H. Hausen and H. Linde, “Tieftemperaturtechnik: Erzeugung sehr tief Temperaturen, Gasverflüssigung und Zerlegung von Gasgemischen [Low temperature technology: generation of very low temperatures, gas liquefaction and breakdown of gas mixtures],” 2nd ed., 1985, Springer-Verlag, Heidelberg, Section 4.5.2.2, and / or air separation plants with internal compression as described in Hausen / Linde, Section 4.5.1.6 or Häring (see above), Section 2.2.5.2, “Internal Compression.”

[0042] Regarding the features of the air separation plant likewise proposed according to the invention, reference is made expressly to the corresponding independent claim. This air separation plant is in particular configured to carry out a method as previously explained in embodiments. Reference is therefore expressly made to the above explanations regarding the method according to the invention and its advantageous embodiments.

[0043] The invention will be described in more detail below with reference to the accompanying drawings, which illustrate preferred embodiments of the present invention.DESCRIPTION OF THE FIGURES

[0044] FIG. 1 illustrates an air separation plant according to an embodiment not according to the invention, in a simplified representation.

[0045] FIGS. 2 to 11 illustrate air separation plants according to embodiments of the invention in a simplified representation.

[0046] In the figures, elements that correspond to one another structurally or functionally are denoted by identical reference signs and, for the sake of clarity, are not repeatedly explained. Explanations relating to units and unit components apply in the same way to corresponding methods and method steps.DETAILED DESCRIPTION OF THE DRAWINGS

[0047] In FIG. 1, an air separation plant according to a non-inventive embodiment of the present invention is illustrated in the form of a simplified process flow diagram and is denoted as a whole by 90.

[0048] Air separation plants of the type shown are often described elsewhere, e.g., in (see above), Industrial Gases Processing, Wiley-VCH, 2006, in particular section 2.2.5, “Cryogenic Rectification,” and in conjunction with FIG. 2.3A. For detailed explanations regarding structure and operating principle, reference is therefore made to corresponding technical literature. An air separation plant for use of the present invention can be designed in a variety of ways. As mentioned, the present invention can in principle be applied to all process circuit topologies with argon recovery, regardless of the type of refrigeration or the type of product compression.

[0049] The air separation plant 90 shown by way of example in FIG. 1 has, among other things, a main air compressor 1, a pre-cooling device 2, a cleaning system 3, a secondary compressor assembly 4, a first booster turbine 5, a second booster turbine 6, a main heat exchanger 7, pumps 8 and 9, and a rectification column system 10. In the example shown, the rectification column system 10 comprises a classic double-column assembly made up of a pressure column 11 and a low-pressure column 12 and a raw argon column 13 and a pure argon column 14. The raw argon column 13 and the pure argon column 14 have head gas condensation arrangements 13.10 and 14.10, referred to here as “first” and “second” head gas condensation arrangements, each of which comprises a reflux or bath condenser evaporator.

[0050] In the air separation plant 90, a feed air flow is suctioned in and compressed by means of the main air compressor 1 via a filter (not labeled). The compressed feed air flow is supplied to the pre-cooling device 2 that is operated with cooling water. The pre-cooled feed air flow is cleaned in the cleaning system 3. In the cleaning system 3, which typically comprises a pair of adsorber vessels used in alternating operation, the pre-cooled feed air flow is largely freed of water and carbon dioxide.

[0051] Downstream of the cleaning system 3, the feed air flow is divided into subflows. The air of the feed air flow is cooled in the main heat exchanger 7 in a fundamentally known manner. In the example illustrated here, two so-called turbine flows are formed in the corresponding turbines. In this case, the booster unit of the turbine booster 6 is designed as what is known as a cold booster, i.e., it is fed with already cooled air from the main heat exchanger 7. Air which has been completely cooled in the main heat exchanger 7 is expanded in a liquefied state via throttle valves, which are not separately labeled, and fed into the rectification column system as what are known as throttle flows.

[0052] An oxygen-enriched liquid bottom fraction and a nitrogen-enriched gaseous top fraction are formed in the pressure column 11. The oxygen-enriched liquid bottom fraction is drawn off from the pressure column 11 and expanded in proportions into the evaporation chambers of the reflux or bath condenser evaporators in the head gas condensation arrangements 13.10 and 14.10. Gas proportions formed by the expansion and evaporation against the head gas of the raw or pure argon column 13, 14 are fed into the low-pressure column 12, as is the case here with unevaporated liquid.

[0053] The operation of the air separation plant 90 illustrated here is common knowledge in this technical field, such that reference is made to the technical literature cited. The raw argon column 13 is usually fed from the low-pressure column 11, while the pure argon column 14 is usually fed from the raw argon column 13.

[0054] FIGS. 2 to 8 show air separation plants according to embodiments of the invention and labeled with 100, 200, or 300.

[0055] In all cases, an oxygen-enriched liquid drawn off from the pressure column 11 is labeled with A. Using a first proportion thereof, a first liquid pressure flow B is formed, which is expanded while a first flash gas is obtained and a first low-pressure liquid remains in a valve not separately labeled. The first evaporation gas from the head gas condensation arrangement 13.10 is introduced into the low-pressure column 12 via a gas line 13G, which contains a first throttle valve 13V1.

[0056] In the embodiments 100 and 200 according to FIGS. 2 to 4, in which identical reference signs are used as before for the sake of simplicity, in the first head gas condensation arrangement 13.10, a previously described “forced-flow” condenser evaporator 13.12 is used, next to which a separate phase separator 13.11 is arranged. The first low-pressure liquid is forced out of this by the pressure of the forming liquid column through evaporation passages of the forced-flow condenser evaporator 13.12; the first flash gas can be drawn off as illustrated with C. The embodiments 100 and 200 differ from one another substantially in that the turbine booster 6 is not present in the embodiment 200 of FIG. 3.

[0057] In all cases, using a second proportion of the oxygen-enriched liquid from the pressure column 11, a second liquid pressure flow D is formed, which is expanded while a second flash gas is obtained and a second low-pressure liquid remains, wherein the second flash gas is labeled in each case with E.

[0058] The raw argon column 13 is thus operated here in each case using a first head gas condensation arrangement 13.10 in which head gas of the raw argon column 13 is subjected to condensation with partial evaporation of a first cooling fluid provided using the first low-pressure liquid or a part thereof.

[0059] The pure argon column 14 is operated using a second head gas condensation arrangement 14.10 in which head gas of the pure argon column 14 is subjected to condensation with partial evaporation of a second cooling fluid provided using the second low-pressure liquid or a part thereof.

[0060] A first evaporation gas formed during the partial evaporation of the first cooling fluid or a part thereof and a first excess liquid remaining after the partial evaporation of the first cooling fluid or a part thereof are fed into the low-pressure column 12 in both embodiments 100, 200 according to FIGS. 2 to 4, as illustrated by F and G.

[0061] Likewise, a second evaporation gas formed during the partial evaporation of the second cooling fluid or a part thereof and a second excess liquid remaining after the partial evaporation of the second cooling fluid or a part thereof are fed into the low-pressure column 12, as illustrated by H and I.

[0062] The first evaporation gas F or the part thereof fed into the low-pressure column 12 is always partially or completely fed into the low-pressure column 12 in a first feed-in region, in particular at a common position with the first excess liquid G.

[0063] The second evaporation gas H or the part thereof fed into the low-pressure column 12, on the other hand, is partially or completely fed into the low-pressure column 12 in a second feed-in region. Likewise, the second excess liquid I or the part thereof fed into the low-pressure column 12 is partially or completely fed into the low-pressure column 12 in the second feed-in region. The first flash gas C or a part thereof is partially or completely, and separately from the first evaporation gas F, fed into the low-pressure column 12 in the second feed-in region.

[0064] A transfer flow from the raw argon column 13 to the pure argon column is additionally labeled with T in FIG. 4 and is also present in the other embodiments.

[0065] FIG. 5 shows the upper ends of columns 10, 13, and 14 very schematically. The process is the same as in FIG. 2 or FIG. 3, but a separate separator is not used as the phase separator of the first liquid pressure flow B; rather, simply the evaporation chamber of the second head gas condensation arrangement 14.10 (pure argon top condenser) is so used. The gas line 13G is designed here as a two-phase line, and the first throttle valve 13V1 as a two-phase valve.

[0066] For this purpose, the two liquid pressure flows B and H are expanded together downstream of the bottom evaporator 600 of the pure argon column 14 in valve 601 and fed together via line 602 into this evaporation chamber of the second head gas condensation arrangement 14.10, which acts as a common phase separator. The first flash gas C is drawn off via line 603, together with the second evaporation gas E produced in the condenser evaporator 14.10. The first cooling fluid K is drawn off from the evaporation chamber of the second head gas condensation arrangement 14.10 together with the second excess liquid I via line 604 and fed separately into the evaporation chamber of a first head gas condensation arrangement (13.10) for the purpose of partial evaporation. The first head gas condensation arrangement (13.10) is designed as a forced-flow evaporator on the evaporation side. The remaining fluids to and from the first head gas condensation arrangement (13.10) are conducted as shown in FIGS. 2 and 3.

[0067] Compared to FIGS. 2 to 4, this results in lower manufacturing costs for the plant and a smaller footprint, and therefore also smaller boxes for the insulating cold box and its filling with insulating material such as perlite.

[0068] FIG. 6 shows, also schematically, a further development based upon FIG. 5. However, the further development can also be applied to FIGS. 2 to 4, in which the first head gas condensation arrangement (13.10) also has a forced-flow evaporator. The gas line 13G is designed here as a two-phase line, and the first throttle valve 13V1 as a two-phase valve. In FIG. 6, the first throttle valve 13V1 is installed in the descending pipe 702 of the two-phase flow 701. The descending pipe is part of the gas line 13G. The first throttle valve 13V1 is usually fully open during normal operation. During special operating situations, e.g., during partial load operation, the two-phase flow can be throttled in accordance with the invention, to increase the pressure and thus the temperature in the first head gas condensation arrangement (13.10). This effectively prevents the argon from freezing and ensures particularly stable operation. The valve can be pressure-controlled (or, alternatively, temperature-controlled). The liquid 604 is divided into the flows K and I as shown in FIG. 5; the corresponding proportions are adjusted by the valve FIC1.

[0069] FIG. 6 also shows the corresponding control elements. The following meanings apply:

[0070] FIC—Flow Indication and Control

[0071] LIC—Liquid Indication and Control

[0072] PIC—Pressure Indication and Control

[0073] The data lines between the measuring and actuating elements are shown as dashed lines in FIG. 7 (and also in FIGS. 8 and 9).

[0074] FIC1 controls the supply of second excess liquid I into the low-pressure column 12, i.e., the division of the liquid flow 604. FIC2 controls the supply of condensate from the first head gas condensation arrangement (13.10) as a function of the feed quantity for the raw argon column. PIC1 controls the pressure on the evaporation side of the second head gas condensation arrangement (14.10). LIC1 controls the quantity of first cooling fluid flowing into the first head gas condensation arrangement (13.10). LIC2 controls the total quantity of coolant via the bottom level measurement in the pressure column.

[0075] FIC2 controls the evaporator capacity (by backing up the liquid into block 13.10 and covering part of the condensing surface).

[0076] The liquid proportion in flow 701 is determined by calculation and optionally adjusted by FIC1.

[0077] Alternatively, particularly stable operation can be achieved by using an additional phase separator 804 to separate the two-phase flow 701 into the first evaporation gas F and the first excess liquid G. This variant is shown in FIG. 7. The gas line 13G is designed here as a pure gas line, extends from the phase separator 804 to the low-pressure column 12, and contains the throttle valve 13V1. The first evaporation gas F separated in the phase separator 804 then flows according to the invention via this gas line 13G and through the first throttle valve 13V1 into the low-pressure column 12.

[0078] The control is also shown in FIG. 7. PIC1 and LIC2 have the same function as in FIG. 7. The pressure on the evaporation side of the second head gas condensation arrangement (14.10) can be controlled with PIC2.

[0079] Alternatively, instead of PIC2, a TIC (Temperature Indication and Control) controller can be used to control the temperature of the first cooling fluid as it enters the first head gas condensation arrangement (13.10). LIC3 controls the quantity of first cooling fluid flowing into the first head gas condensation arrangement (13.10), but in this case as a function of the value of the fill level in the phase separator 804. The quantity of second excess liquid I flowing to the low-pressure column is adjusted by means of LIC4 as a function of the liquid level on the evaporation side of the pure argon condenser. There are also FIC3 and FIC4 controllers in the lines for the second excess liquid G and the raw argon, which is transferred to the pure argon column 14. The FIC3 controller is particularly important here. This means that the liquid proportion in the flow 701 can be controlled directly (and not determined by calculation), and dry evaporation in the condenser can be avoided.

[0080] FIG. 8 is a simplified illustration of a particular apparatus embodiment of the invention according to FIG. 7. Here, the heat exchanger block of the first head gas condensation arrangement 13.10 is arranged inside the phase separator 804, in which the first evaporation gas and the first excess liquid are separated from each other. The first head gas condensation arrangement does not lose its character as a forced-flow evaporator. Rather, the liquid to be evaporated continues to flow forcibly, and the line at LIC3 and the header on the heat exchanger block into the evaporation passages, and is not drawn in from the liquid bath of the separator 804, as would be the case with a bath evaporator.

[0081] The special measures of FIGS. 6 to 8, in particular the phase separator 804, can also be applied to the overall methods of FIGS. 2 to 5, both with a separate phase separator for the first liquid pressure flow and with one integrated into the head gas condensation arrangement, as shown in FIG. 8.

[0082] The previous exemplary embodiments are optimized for thermodynamic efficiency and the maximum yield of argon product. In some cases, however, the decisive criterion is not this, but rather, for example, the equipment costs or the height of the columns or the like. In this case, it may be more advantageous to minimize the feed points into the low-pressure column in the manner shown in FIGS. 9 to 11, which otherwise correspond to FIGS. 6 to 8.

[0083] In FIG. 9, for example, the line I according to FIG. 6 and the valve FIC1 are omitted. Instead, the entire liquid flow 604, which is taken from the evaporation chamber of the top condenser 14.10 of the pure argon column 14, flows through the top condenser 13.10 of the raw argon column 13. The control also works here as in FIG. 6, except that the valve FIC1 for dividing the first liquid pressure flow is omitted.

[0084] FIG. 10 differs from FIG. 7 in a similar way. The valve LIC4 and the corresponding line are omitted. In addition, the vapor 901 from the separator 804 and the vapor 902 from the top condenser 14.10 of the pure argon column 14 are combined and fed into the low-pressure column via a common line 903, preferably at the same point as the liquid G from the separator 804. The entire liquid flow 604, which is withdrawn from the evaporation chamber of the top condenser 14.10 of the pure argon column 14, flows through the top condenser 13.10 of the raw argon column 13.

[0085] The control also works differently in part. LIC1, like LIC2 in FIG. 7, is responsible for level control in the bottom of the pressure column (not shown here). The level in the evaporation chamber of the top condenser 14.10 of the pure argon column 14 is regulated by adjusting the amount of liquid withdrawn through valve 13V2 (LIC2). The FIC2 valve thus indirectly regulates the gas quantity at the column inlet by backing up the liquid (and thus covering part of the heat exchange surface). This gives the top condenser 13.10 a higher cooling capacity (at a relatively low liquid level) or a lower one (at a relatively high liquid level). Accordingly, more or less head gas is condensed on the liquefaction side; a corresponding amount of gas is suctioned in from the low-pressure column via the argon transition line (not fully shown in FIG. 10, but in FIGS. 1 to 4). According to the invention, the valve 13V1 is pressure-controlled (PIC2) and thus adjusts the temperature of the top condenser 13.10, and thus its power. LIC3 adjusts the liquid outflow from the separator 804 and thus regulates the liquid level in the separator.

[0086] A particularly preferred embodiment is shown in FIG. 11, which is very similar to FIG. 8; in particular, here the heat exchanger block of the top condenser 13.10 of the raw argon column 13 is incorporated into the separator 804. Otherwise, the entire liquid flow 604, which is taken from the evaporation chamber of the top condenser 14.10 of the pure argon column 14, is introduced into the evaporation chamber of the top condenser 13.10 of the raw argon column 13. Also, analogously to FIG. 10, the vapor 901 from the separator 804 and the vapor 902 from the top condenser 14.10 of the pure argon column 14 are combined and fed into the low-pressure column via the common line 903, preferably at the same point as the liquid G from the separator 804.

[0087] LIC1, like LIC2 in FIG. 8, is responsible for level control in the bottom of the pressure column (not shown here). The level in the evaporation chamber of the top condenser 14.10 of the pure argon column 14 is adjusted by adjusting the amount of liquid withdrawn through valve 13V2 (LIC2). The flow on the liquefaction side of the top condenser 13.10 of the raw argon column 13 is adjusted as shown in FIG. 10. According to the invention, the valve 13V1 is pressure-controlled (PIC2) and thus adjusts the temperature of the top condenser 13.10, and thus its power. LIC3 adjusts the liquid outflow from the separator 804 and thus regulates the liquid level in the separator. The pressure in the evaporation chamber of the top condenser 14.10 is adjusted via PC1.

Claims

1. A method for the cryogenic separation of air, in which an air separation plant having a rectification column arrangement which has a pressure column, a low-pressure column, and a raw argon column is used, wherein;with direct or indirect use of at least part of an oxygen-enriched liquid from the pressure column, a first liquid pressure flow is formed, which is expanded to produce a first low-pressure liquid;the raw argon column is operated using a first head gas condensation arrangement in which head gas of the raw argon column is subjected to condensation with partial evaporation of a first cooling fluid provided using the first low-pressure liquid or a part thereof;the first head gas condensation arrangement has a forced-flow condenser evaporator; anda first evaporation gas formed during the partial evaporation of the first cooling liquid or a part thereof is fed into the low-pressure column via a gas line, wherein:the gas line contains a first throttle valve;the first throttle valve is adjusted by means of a control device such that freezing of argon in the first head gas condensation arrangement is avoided, and in the process; anda pressure drop of at least 50 mbar is generated at least temporarily across the throttle valve.

2. The method according to claim 1, in which the liquid level on the evaporation side of the head gas condensation arrangement is regulated by a second throttle valve by which the first cooling liquid upstream of the head gas condensation arrangement can be throttled.

3. The method according to claim 1, in which the first evaporation gas or a part thereof together with the first excess liquid or a part thereof are withdrawn from the first head gas condensation arrangement as a first two-phase flow without returning the first excess liquid or a part thereof to the one or more condenser evaporators.

4. The method according to claim 1, in which the first two-phase flow is conducted between the first head gas condensation arrangement and the low-pressure column through the first throttle valve.

5. The method according to claim 1, in which the first throttle valve:is fully open in a first operating mode (normal operation); andin a second operating mode (underload case) is set so that a pressure drop across the throttle valve of at least 50 mbar is generated.

6. The method according to claim 1, in which the throttle valve is adjusted such that the temperature of the first cooling fluid is preferably at least 0.1 K above the triple point temperature of argon upon entering the first head gas condensation arrangement.

7. The method according to claim 1, in which:when the first liquid pressure flow is expanded, a first flash gas is formed in addition to the first low-pressure liquid;using at least a part of the oxygen-enriched liquid from the pressure column, a second liquid pressure flow is formed, which is expanded, with production of a second flash gas while a second low-pressure liquid remains;the pure argon column is operated using a second head gas condensation arrangement in which head gas of the pure argon column is subjected to condensation with partial evaporation of a second cooling fluid provided using the second low-pressure liquid or a part thereof;a second evaporation gas is withdrawn from the second head gas condensation arrangement and mixed with the first evaporation gas and introduced into the low-pressure column; anda second excess liquid is withdrawn from the second head gas condensation arrangement and used to form the first cooling liquid for the first head gas condensation arrangement.

8. The method according to claim 7, in which the liquid level in the bottom of the pressure column is measured, and the amount of first cooling fluid introduced into the second head gas condensation arrangement is adjusted as a function of the measured value.

9. The method according to claim 7, in which the liquid level in the evaporation chamber of the second head gas condensation arrangement is measured and kept constant by adjusting the feed quantity to the first condenser arrangement.

10. The method according to claim 1, in which the first evaporation gas or the part thereof, together with the first excess liquid or the part thereof, are fed into the low-pressure column together as a two-phase flow via the gas line and the first throttle valve.

11. The method according to claim 1, in which the first two-phase flow between the head gas condensation arrangement and the low-pressure column is conducted into a phase separator in which the first evaporation gas and the first excess liquid are separated from each other, wherein the separated evaporation gas is conducted between the phase separator and the low-pressure column via the gas line through the throttle valve.

12. The method according to claim 11, in which the liquid level in the phase separator is measured and, with the amount of first excess liquid introduced into the low-pressure column, kept constant.

13. The method according to claim 1, in which the head gas condensation arrangement has a heat exchanger block, and said heat exchanger block is arranged in the interior of the phase separator, in which the first evaporation gas and the first excess liquid are separated from each other.

14. An air separation plant with a rectification column arrangement having a pressure column, a low-pressure column, and a raw argon column, wherein the air separation plant is configured,with direct or indirect use of a first proportion of an oxygen-enriched liquid from the pressure column, to form a first liquid pressure flow and to expand said first liquid pressure flow with production of a first flash gas while a first low-pressure liquid remains;to operate the raw argon column using a first head gas condensation arrangement and subject this head gas of the raw argon column to condensation with partial evaporation of a first cooling fluid provided using the first low-pressure liquid or a part thereof, wherein the first head gas condensation arrangement has a forced-flow condenser evaporator; andto feed a first evaporation gas, or a part thereof, formed during the partial evaporation of the first cooling liquid into the low-pressure column, and wherein:the gas line contains a first throttle valve; andthe first throttle valve is designed to be adjusted by means of a control device in such a way that freezing of argon in the first head gas condensation arrangement is avoided, and in the process a pressure drop across the throttle valve of at least 50 mbar is at least temporarily generated.

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