TW202434845A - Method for separating air at low temperature and air separation equipment - Google Patents

Abstract

The invention relates to a method for cryogenic separation of air, in which an air separation plant (100-300) having a rectification column arrangement (10) which comprises a pressure column (11), a low-pressure column (12) and a raw argon column (13) is used. In the method, evaporation gas from a head gas condensation device (13.10) associated with the raw argon column (13) is partly or completely fed into the low-pressure column (12) via a gas line (13G). The gas line (13G) contains a first throttle valve (13V1) which is adjusted by means of a control device so that argon is prevented from freezing out in the first head gas condensation arrangement (13.10). This creates, at least temporarily, a pressure drop of at least 50 mbar across the throttle valve (13V1). The present invention also relates to a corresponding air separation plant (100-200).

Description

Method for separating air at low temperature and air separation equipment

The invention relates to a method for separating air at low temperatures and an air separation device as described in the preamble of the independent claim.

The production of liquid or gaseous air products by cryogenic separation of air in air separation plants is known in the art and is described, for example, in H.-W. Häring (Hrsg.), Industrial Gases Processing, Wiley-VCH, 2006, in particular in Section 2.2.5 "Cryogenic Rectification".

The air separation plant has a distillation column arrangement which can be of different designs. In addition to distillation columns for obtaining liquid and/or gaseous nitrogen and/or oxygen (i.e. in particular nitrogen-oxygen separation distillation columns which can be combined into the known double column), distillation columns can also be provided for obtaining other air components (in particular noble gases) or pure oxygen.

The rectification columns of a classic rectification column arrangement are operated at different pressure levels. The known double column has a so-called pressure column (also called high-pressure column, medium-pressure column or lower column) and a so-called low-pressure column (upper column). The high-pressure column is usually operated at a pressure level of 4 bar to 7 bar, in particular about 5.3 bar, the low-pressure column at a pressure level of usually 1 bar to 2 bar, in particular about 1.4 bar. In certain cases, higher pressure levels can also be used in such rectification columns. The pressures given here and below are the absolute pressures at the top of the relevant rectification column.

An air separation plant having a crude argon column and a purified argon column can be used to obtain argon. An example is shown in Figure 2.3A of Häring (supra) and is described in the section "Rectification in the Low-pressure, Crude and Pure Argon Column" from page 26 and in the section "Cryogenic Production of Pure Argon" from page 29. As described there, in corresponding plants, argon is enriched at a certain height in the low-pressure column. At this point or at another advantageous point, possibly below the argon maximum, an argon-enriched gas having an argon concentration of typically 5-15 mol % can be withdrawn from the low-pressure column and transferred to the crude argon column. The corresponding gas typically contains from about 0.05 ppm to 500 ppm of nitrogen, the remainder being essentially oxygen. It is expressly emphasized that the above values for gases extracted from a low-pressure column represent typical example values only.

The crude argon column is mainly used to separate oxygen from the gas extracted from the crude argon column. The oxygen separated in the crude argon column or the corresponding oxygen-rich fluid can be returned to the low-pressure column in liquid form. The gaseous distillate remaining in the crude argon column during the separation process, which essentially contains argon and nitrogen, can be further separated in the refined argon column to obtain pure argon. The crude argon column and the refined argon column have top condensers, which can be cooled in particular with a portion of the oxygen-enriched and nitrogen-depleted liquid (the so-called "enriched liquid") extracted from the pressure column, which liquid partially evaporates during this cooling process. This is also the case within the framework of the present invention. The gas phase formed during the partial evaporation and the corresponding residual liquid are fed to the low-pressure column at different feed points, the selection of which will be explained below. In the conventional method, the pressure in the top condenser gas chamber is the same as the pressure at the feed point where the gas phase is fed to the low-pressure column. "The same pressure" here means that the difference between the two pressures does not exceed 25 mbar, preferably does not exceed 10 mbar.

Oxygen or oxygen-rich fluid from the crude hydrogen column is returned from the pressure column to the lower pressure column usually at a point a number of theoretical or actual trays below the feed point of the partially evaporated liquid used in the cooling process.

The object of the present invention is to provide means for improving the operation of an air separation plant comprising an argon recovery system having a crude argon column and a refined argon column.

[to Answer 1]

In this context, the present invention proposes a method for separating air at low temperature and an air separation device having the characteristics of independent claims. The technical solutions are respectively the subject of the attached items and the following description.

Next, some terms and basic technical background used in describing the present invention and its advantages are described in detail.

The devices used in air separation equipment are described in the cited professional literature, for example in Häring in paragraph 2.2.5.6 "Apparatus". Taking into account the terminological conventions within the framework of this application, reference is expressly made to the cited professional literature whenever the following definitions do not differ.

"Condenser-evaporator" refers to a heat exchanger for indirect heat exchange between a first condensing fluid flow and a second evaporating fluid flow. Any condenser-evaporator has a liquefaction chamber and an evaporation chamber. The liquefaction chamber and the evaporation chamber have a liquefaction channel or an evaporation channel. The first fluid flow is condensed (liquefied) in the liquefaction chamber, and the second fluid flow is evaporated in the evaporation chamber. The evaporation chamber and the liquefaction chamber are composed of channels that have a heat exchange relationship with each other. The condenser-evaporator is also called a "top condenser" and a "bottom evaporator" according to its function, wherein the top condenser is a condenser-evaporator that condenses the top gas of the distillation tower, and the bottom evaporator is a condenser-evaporator that evaporates the bottom liquid of the distillation tower. Of course, the bottom liquid can also be evaporated in the top condenser (such as the top condenser used within the framework of the present invention).

Specifically, the so-called main condenser which connects the high-pressure column and the low-pressure column of the air separation device in a heat exchange manner is designed as a condenser-evaporator. The main condenser or other condenser-evaporators can be designed as a single-layer or multi-layer bath evaporator, in particular a cascade evaporator (for example, as described in EP 1 287 302 B1), or as a falling film evaporator. The corresponding condenser-evaporator can be formed, for example, by a single heat exchanger block, or by a plurality of heat exchanger blocks arranged in a common pressure vessel.

In a forced-flow condenser-evaporator or a condenser-evaporator with forced guidance on the evaporation side (which can also be used in the present invention), the liquid flow passes through the evaporation chamber by its own pressure and partially evaporates there. (“Forced-flow evaporator” is sometimes also called “straight-through evaporator”.) This pressure is generated, for example, by a liquid column in the supply line to the evaporation chamber, which is formed due to the corresponding positioning of the liquid reservoir. In this case, the height of this liquid column corresponds at least to the pressure loss in the evaporation chamber. The gas or gas-liquid mixture (i.e. two-phase flow) emerging from the evaporation chamber is conveyed in a "straight-through" / "forced-flow" condenser-evaporator directly to the next process step or downstream device and, in particular, is not introduced into the liquid bath of the condenser-evaporator, where the remaining liquid fraction would otherwise be sucked in again, as is the case, for example, with conventional bath evaporators which operate on the basis of the known thermosyphon effect.

In the terminology used in this case, fluids (i.e., liquids and gases) may be enriched or depleted in one or more components, where "enriched" may represent at least 50%, 75%, 90%, 95%, 99%, 99.5%, 99.9% or 99.99% by mole, weight or volume, and "depleted" may represent up to 50%, 25%, 10%, 5%, 1%, 0.1% or 0.01% by mole, weight or volume. The term "mainly" may be equivalent to the definition of "enriched". A fluid may be enriched or depleted in one or more components, where these terms are related to the content in the initial fluid from which the fluid is formed. If the fluid contains at least 1.1, 1.5, 2, 5, 10, 100 or 1000 times the content of the corresponding component, it is called "enriched", and if the fluid contains at most 0.9, 0.5, 0.1, 0.01 or 0.001 times the content of the corresponding component, it is called "depleted". For example, if "oxygen" or "nitrogen" is mentioned, it also refers to a fluid rich in oxygen or nitrogen but not necessarily composed only of oxygen or nitrogen.

The present disclosure uses the terms "pressure range" and "temperature range" to represent pressure and temperature in order to indicate that the concept of the present invention does not require the use of precise pressure and temperature values to describe the corresponding pressure and temperature in the corresponding equipment. For example, different pressures exist at different locations in a pressure tower and a low-pressure tower, but these pressures fluctuate within a certain pressure range (also known as an operating pressure range). The corresponding pressure range and temperature range can be non-overlapping ranges or overlapping ranges.

Absolute and/or relative spatial specifications used hereinafter, such as "upper", "lower", "above", "below", "next to", and "side by side", refer in particular to the spatial orientation of the correspondingly named elements of the air separation plant (e.g. a rectification column, a subtower of a compound rectification column or a rectification zone of a rectification column) during normal operation. Two elements are arranged "stacked" in this context, meaning that the upper end of the lower of the two elements and the lower end of the upper of the two elements are at the same geodetic height or at a lower geodetic height and that the projections of the two elements on a horizontal plane overlap one another. In particular, the two elements can be arranged exactly stacked, i.e. the vertical center axes of the two elements lie on the same vertical straight line. Arranged "side by side" means in particular that the projections of the two elements on the horizontal plane do not overlap. When the refining tower is of composite design, terms such as "functionally below" or "functionally above" refer to the layout of the refining zone, while when the refining tower is of monolithic design, they refer to the layout of the sub-tower with the refining zone.

The air separation equipment designed according to the prior art has a crude argon tower (and a refined argon tower if necessary), wherein the top condenser of the crude argon tower is designed as a forced flow condenser evaporator in the above manner, but its operation stability is often unsatisfactory, especially under underload conditions (partial load operation), that is, the feed air fed into the equipment is less than the feed air volume during normal operation, for example, at least 5% less, preferably at least 10% less and/or at most 60% or 40% less. A reduction in air volume of 5% to 50% is usually referred to as underload. Advantages of the Invention

The present invention is different from the conventional operating method when using a forced flow condenser, according to which, in all operating modes, the first vaporized gas enters the low-pressure column with the smallest possible pressure loss, i.e., no pressure change measures are taken. This is fundamentally efficient.

In this case, the pressure in the evaporation chamber of the first top gas condenser is equal to the operating pressure of the low-pressure column plus the pipeline losses. This ensures stable operation of the equipment under normal conditions. In the context of the present invention, efforts to find the cause of unstable operation have revealed that in special operating conditions, such as partial load operation, the liquid argon can be insufficiently cooled, so that there is a risk that the condensation channels are blocked by frozen argon (triple point of argon: 83.8 K).

According to the present invention, the method for solving this problem is to guide the first vaporized gas through the first throttle valve between the first top gas condenser and the low-pressure tower. By partially closing the throttle valve, the pressure and temperature in the evaporation chamber can be increased under underload conditions, thereby effectively preventing the condenser evaporator from being blocked due to freezing. It is preferred to design the valve as an automatic valve; as an alternative, a manual valve can be used. In short, the operation of the first top gas condenser and the crude argon tower can be made particularly stable.

The term "throttle valve" herein refers to a "throttle device" in a general sense, including, for example, a "throttle baffle".

In at least one operating condition, the pressure drop achieved by the first throttling valve can be, for example, between 300 mbar and 50 mbar, preferably between 250 mbar and 80 mbar. Generally, this throttling of the first vaporized gas is carried out in an underload situation. Depending on the degree of underload, a lower or higher pressure drop and thus a lower or higher temperature is set. In an example, when the composition of the ???? contains approximately 57.4% nitrogen, 1.8% argon and 40.8% oxygen, the following values are obtained: [Table 1] Evaporator inlet pressure, bar 1.49 1.39 1.29 1.19 Boiling temperature, K 84.20 83.52 82.80 82.03 Equipment load, % (approx.) 100% 83% 64% 40%

In order to prevent argon from freezing, the first throttle valve is adjusted by the control device according to the invention so that the temperature of the first coolant liquid entering the first top gas condenser is higher than the triple point temperature of argon. This inlet temperature is preferably at least 0.1 K higher than the triple point of argon, in particular at least 0.25 K higher. The temperature difference is preferably between 0.1 K and 2.0 K, and preferably at most between 0.2 K and 1.0 K.

In principle, the replacement of the first throttle valve by a throttle valve (see also FIG. 1 ) is already known in the prior art, but only for systems with a bath evaporator at the top of the crude argon column. In the case of a bath evaporator, however, the throttle valve has a completely different function, namely controlling the gas flow at the column inlet. In the case of a forced-flow evaporator, this flow control is achieved by backflowing the liquid at the evaporator outlet (condensation side); in this case, a valve between the condenser and the low-pressure column would only cause an undesirable pressure loss and would not be necessary for flow control. The present invention still uses a throttling valve, which is fully open in many operating conditions, but can unexpectedly effectively improve the operating stability of the condenser evaporator in certain operating conditions. Of course, such throttling will also cause avoidable pressure loss, thereby reducing process energy efficiency; however, within the scope of the present invention, it is found that such throttling does not produce the expected disadvantages, but unexpectedly has an energy-saving effect.

The design and dimensions of the condenser are determined according to the design situation (normal operation). In the underload situation, the heat exchange surface of the condenser is relatively large. Therefore, the condenser must be "braked" in the underload situation to set the appropriate capacity. In plants with bath evaporators, this is achieved by increasing the evaporation pressure (conventional control of the evaporator). In plants with forced flow evaporators, since there is no valve between the evaporation chamber of the condenser and the low-pressure column, the capacity (load of the crude argon column) is controlled by backflowing liquid and covering part of the heat exchange surface. Under underload conditions, the working pressure in the low-pressure tower is significantly lower than the working pressure under design conditions; therefore, the pressure (or temperature) in the evaporation chamber of the forced-flow evaporator will also decrease, which may cause argon freezing. In order to cope with this situation, the pressure in the low-pressure tower must be artificially increased. However, this requires energy consumption. The method according to the present invention can avoid such energy loss.

The control device according to the invention can be of analog or digital design and can be integrated in particular in an operating control system. The control device ensures that the first throttle valve is partially closed in the corresponding operating conditions in order to set the required pressure difference without manual intervention. This measure is preferably integrated in an automatic load adjustment device, thereby ensuring stable operation of the system, for example when switching from normal load operation to underload operation.

In the present invention, a first portion of the oxygen-enriched liquid from the pressure column is used to form a first pressurized liquid stream, and the first pressurized liquid stream is expanded to obtain a first flash gas and leave a first low-pressure liquid.

The crude argon column is operated using a first top gas condensing device in which the top gas of the crude argon column is condensed with partial evaporation of a first refrigerant liquid, wherein the first low-pressure liquid or a portion thereof is used to provide the first refrigerant liquid. The first top gas device is also referred to hereinafter as the top condenser of the crude argon column.

In the method and the apparatus, a refining column may also be provided, and the refining column may be operated using a second top gas condensing device, in which the top gas of the refining column is condensed under partial evaporation of a second cooling liquid, wherein the second low-pressure liquid or a portion thereof is used to provide the second cooling liquid. The second top gas device is also referred to hereinafter as the top condenser of the refining column.

The first evaporated gas or a portion thereof formed in the process of partially evaporating the first cooling liquid and the first excess liquid or a portion thereof remaining in the process of partially evaporating the first cooling liquid are fed into the low-pressure tower.

The second evaporated gas or a part thereof formed in the process of partially evaporating the second cooling liquid and the second excess liquid or a part thereof remaining in the process of partially evaporating the second cooling liquid are fed to the low-pressure tower.

The term "evaporated gas" refers to the portion that evaporates in the top gas condenser or condenser-evaporator due to heat transfer from the top gas of the crude and refined columns. The liquid residue left is referred to herein as "excess liquid". In contrast to the term "evaporated gas", the term "flash gas" refers to the gas portion or vapor portion formed only by expansion.

In the present invention, the second throttling valve (13V2) is preferably used to control the liquid level on the evaporation side of the top gas condensing device (13.10), and the throttling valve can be used to throttle the first cooling liquid upstream of the top gas condensing device (13.10).

As is conventional when using a forced flow evaporator, the first evaporation gas is preferably withdrawn from the top gas condenser together with the first excess liquid as a first two-phase stream without recirculating part of the excess liquid through the evaporator.

In a particularly advantageous technical solution of the present invention, one or more "forced flow" condenser-evaporators of the aforementioned type can be used in the first top gas condensation device. Please refer to the above description. Specifically, the first low-pressure liquid or a part of it as the first cooling liquid is forcibly guided through one or more condenser-evaporators (the one or more condenser-evaporators are designed as part of the first top gas condensation device), and partially evaporates in this process to form a first evaporated gas and a first excess liquid. "Forced guidance" here means feeding the evaporation chamber under pressure, for example by means of a pipeline.

During operation, in particular in normal operation (first operating mode), the throttle valve can be at least temporarily fully opened. However, in at least one underload situation (second operating mode), a pressure drop of at least 50 mbar occurs.

In the context of the present invention, in addition to the first evaporated gas, preferably also the first excess liquid is fed to the low-pressure column. In a first variant of the present invention, the gas and the liquid can be fed partly or completely together as a first two-phase flow to the low-pressure column, in particular in the first feed zone. In this case, the gas line is designed as a two-phase line, the first throttle valve is designed as a two-phase valve, and the two-phase flow or the part that flows into the low-pressure column is guided through the first throttle valve.

In a second variant, the first two-phase flow is introduced into a phase separator. In this case, the gas line between the phase separator and the low-pressure tower is designed as a pure gas line, and the first throttle valve is designed as a pure gas valve. The first excess liquid is guided between the top gas condenser and the first throttle valve through the phase separator, and in the phase separator, the first evaporated gas and the first excess liquid are separated from each other. Then, the first evaporated gas is introduced into the low-pressure tower separately from the first excess liquid. Here, the pressure in the evaporation chamber is not regulated by the valve in the first excess liquid line, but by the first valve in the pure gas line, which connects the phase separator to the low-pressure tower on the gas side.

The liquid level in the phase separator can be measured. Based on the measured value, the amount of first cooling liquid introduced into the first top gas condenser is preferably adjusted. The amount of liquid produced in the phase separator is preferably controlled.

The present invention can be applied in principle to all process loop topology structures with argon capture function, regardless of the refrigeration method or product compression method. Specifically, the process circuit topology with argon capture function includes: the so-called MAC/BAC process or HAP process described, for example, in EP 3 196 573 A1, paragraphs [0022] to [0025], the nitrogen cycle process described, for example, in EP 2 235 460 A2 or in H. Hausen and H. Linde, "Tieftemperaturtechnik: Erzeugung sehr tiefer Temperaturen, Gasverflüssigung und Zerlegung von Gasgemischen" (2nd edition, 1985, Springer, Heidelberg, section 4.5.2.2), and/or the nitrogen cycle process described in Hausen/Linde, section 4.5.1.6 or Häring (see above), section 2.2.5.2 "Internal Compression" is an air separation device with internal compression function.

The invention also proposes an air separation device, with respect to the features of which reference is expressly made to the corresponding independent claims. The air separation device is particularly used for implementing the method described above as a technical solution. Therefore, reference is expressly made to the above description of the method of the invention and its advantageous technical solutions.

The present invention will be described in detail below with reference to the attached drawings, which illustrate preferred technical solutions of the present invention.

FIG. 1 illustrates an air separation device of a non-inventive design in the present invention in the form of a process flow diagram, which is indicated as a whole at 90 .

Air separation equipment of the type shown is described elsewhere, for example (see above), Industrial Gases Processing, Wiley-VCH, 2006, in particular Section 2.2.5 "Cryogenic Rectification", in conjunction with Figure 2.3A. For detailed descriptions of the structure and operation, please refer to the relevant technical literature. Air separation equipment using the present invention can be designed in many ways. As mentioned above, the present invention is applicable in principle to all process circuit topologies with argon extraction function, regardless of the refrigeration method or product compression method.

The air separation device 90 illustrated as an example in FIG1 includes, but is not limited to, a main air compressor 1, a precooling device 2, a purification system 3, a booster compressor device 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 illustrated example, the rectification column system 10 includes a classic double-tower configuration consisting of a pressure column 11 and a low-pressure column 12, as well as a crude argon column 13 and a rectification column 14. The crude argon column 13 and the rectification column 14 have top gas condensing devices 13.10 and 14.10, which are referred to herein as "first" and "second" top gas condensing devices, and each includes a reflux condenser-evaporator or a bath condenser-evaporator.

In the air separation device 90, the main air compressor 1 draws in the feed air stream through an unnumbered filter and compresses it. The compressed feed air stream is sent to the pre-cooling device 2 which operates with cooling water. The pre-cooled feed air stream is purified in the purification system 3. In the purification system 3, which usually includes a pair of alternating adsorption vessels, most of the water and carbon dioxide are removed from the pre-cooled feed air stream.

Downstream of the purification system 3, the feed air flow is divided into several partial flows. The air of the feed air flow is cooled in the main heat exchanger 7 in a basically known manner. In the example illustrated here, two so-called turbine flows are formed in the corresponding turbines. The booster unit of the turbocharger 6 is designed as a so-called cold booster, i.e. it is fed with cooled air from the main heat exchanger 7. The air that has been completely cooled in the main heat exchanger 7 is expanded in the liquefied state through a throttle valve that is not individually numbered and is fed to the distillation column system as a so-called throttling flow.

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 withdrawn from the pressure column 11 and expanded in several portions into the evaporation chambers of the reflux or bath condenser evaporators in the top gas condensation devices 13.10 and 14.10. The gaseous component formed by the expansion and evaporation of the top gases of the crude and refined argon columns 13 and 14 in the opposite direction is sent to the low-pressure column 12, as is the unevaporated liquid therein.

The air separation apparatus 90 illustrated here is operated in a manner customary in the art, and reference is therefore made to the cited technical literature. The crude argon column 13 is fed by the low pressure column 11 in a conventional manner, and the refined argon column 14 is fed by the crude argon column 13 in a conventional manner.

FIG. 2 to FIG. 8 show air separation devices designed according to the present invention, which are marked as 100, 200 and 300 respectively.

In all cases, the oxygen-rich liquid withdrawn from the pressure column 11 is designated A. With a first part thereof, a first pressurized liquid stream B is formed, which is expanded in a valve not individually designated to obtain a first flash gas and leave a first low-pressure liquid. The first evaporated gas from the top gas condenser 13.10 is introduced into the low-pressure column 12 via a gas line 13G comprising a first throttling valve 13V1.

In the designs 100 and 200 shown in FIGS. 2 to 4 (for simplicity, the designs use the same symbols as before), the aforementioned "forced flow" condenser-evaporator 13.12 is used in the first top gas condensation device 13.10, and a separate phase separator 13.11 is arranged next to it. The first low-pressure liquid from the phase separator passes through the evaporation channel of the "forced flow" condenser-evaporator 13.12 under the pressure of the formed liquid column; the first flash gas can be extracted as shown in C. The essential difference between the designs 100 and 200 is that the turbocharger 6 does not exist in the design 200 of FIG. 3.

In all cases, a second portion of the oxygen-rich liquid from the pressure column 11 is used to form a second pressurized liquid stream D which is expanded to obtain a second flash gas, which is always designated E, leaving a second low-pressure liquid.

That is, the crude argon column 13 is always operated using the first top gas condenser 13.10, in which the top gas of the crude argon column 13 is condensed under partial evaporation of the first refrigerant, wherein the first low-pressure liquid or a part thereof is used to provide the first refrigerant,

The clarification column 14 is operated using a second top gas condenser 14.10 in which the top gas of the clarification column 14 is condensed with partial evaporation of a second cooling liquid, wherein the second cooling liquid is provided by the second low-pressure liquid or a portion thereof.

In the two designs 100, 200 shown in Figures 2 to 4, the first evaporated gas or a portion thereof formed in the partial evaporation process of the first refrigerant and the first excess liquid or a portion thereof remaining in the partial evaporation process of the first refrigerant are fed into the low-pressure tower 12, as shown in F and G.

Similarly, as shown in H and I, the second evaporated gas or a portion thereof formed in the process of partial evaporation of the second refrigerant liquid and the second excess liquid or a portion thereof remaining in the process of partial evaporation of the second refrigerant liquid are fed into the low-pressure tower 12.

The first vaporized gas F or the portion thereof fed to the low-pressure column 12 is always fed partly or entirely to the low-pressure column 12 in the first feed zone, particularly at a position common to the first excess liquid G.

The second evaporated gas H or its portion fed to the low-pressure column 12 is partially or completely fed to the low-pressure column 12 in the second feed zone. Similarly, the second excess liquid I or its portion fed to the low-pressure column 12 is partially or completely fed to the low-pressure column 12 in the second feed zone. The first flash gas C or a portion thereof is partially or completely fed to the low-pressure column 12 in the second feed zone and is separated from the first evaporated gas F.

The transfer stream from the crude hydrogen column 13 to the refined hydrogen column is additionally labeled T in FIG. 4 and also exists in other designs.

Figure 5 shows very schematically the upper ends of the columns 10, 13 and 14. The process is the same as Figure 2 or Figure 3, but instead of using a separate separator as a phase separator for the first pressurized liquid stream B, only the evaporation chamber of the second top gas condensation device 14.10 (pure argon top condenser) is used. The gas line 13G is designed here as a two-phase line and the first throttle valve 13V1 is designed as a two-phase valve.

To this end, the two pressurized liquid streams B and H are expanded together in the valve 601 downstream of the bottom evaporator 600 of the purifying column 14, and are introduced together through the pipeline 602 into the evaporation chamber of the second top gas condenser 14.10, which acts as a common phase separator. The first flash gas C is extracted together with the second evaporated gas E produced in the condenser evaporator 14.10 through the pipeline 603. The first cooling liquid K is extracted together with the second excess liquid I from the evaporation chamber of the second top gas condenser 14.10 through the pipeline 604, and is introduced separately into the evaporation chamber of the first top gas condenser (13.10) for partial evaporation. The first top gas condenser (13.10) is designed as a forced flow evaporator on the evaporation side. The remaining fluids entering and exiting the first top gas condensing device (13.10) are guided in the manner shown in Figures 2 and 3.

Compared with Figures 2 to 4, the manufacturing cost of the equipment is reduced and the footprint is reduced, so the number of boxes used for insulated cold boxes and the filling amount of insulation materials such as perlite are also reduced.

FIG. 6 also schematically illustrates a further design based on FIG. 5 . However, the further design can also be applied to FIG. 2 to FIG. 4 , in which the first top gas condensing device (13.10) also has a forced flow evaporator. The gas line 13G is designed as a two-phase line here, and the first throttle valve 13V1 is designed as a two-phase valve. In FIG. 6 , the first throttle valve 13V1 is installed in the downcomer line 702 of the two-phase flow 701. The downcomer line is part of the gas line 13G. During normal operation, the first throttle valve 13V1 is usually fully open. Under special operating conditions, such as during partial load operation, according to the present invention, the two-phase flow can be throttled to increase the pressure and temperature in the first top gas condensing device (13.10). This effectively prevents argon freezing and enables particularly stable operation. In this case, the valve can be designed as pressure-controlled (an alternative is temperature-controlled). As shown in Figure 5, liquid 604 is divided into flows K and I; the corresponding proportions are set by valve FIC1.

Figure 6 also illustrates the corresponding control components. Their meanings are: FIC - Flow indication and control - Flow measurement and flow regulation LIC - Liquid level indication and control - Liquid level measurement and regulation PIC - Pressure indication and control - Pressure measurement and pressure regulation

The data lines between the measuring element and the control element are shown as dashed lines in FIG. 7 (as well as in FIG. 8 and FIG. 9 ).

The supply of the second excess liquid I to the low pressure column 12, i.e. the division of the liquid stream 604, is controlled by FIC1. FIC2 controls the supply of the condensate from the first top gas condenser (13.10) according to the feed rate of the crude argon column. The evaporation side pressure of the second top gas condenser (14.10) is controlled by PIC1. The amount of the first cooling liquid flowing into the first top gas condenser (13.10) is controlled by LIC1. LIC2 controls the total amount of cooling liquid by measuring the bottom material level in the pressure column.

The evaporator capacity is controlled by FIC2 in such a way that the liquid flows back into block 13.10 and covers a part of the condensation surface.

The liquid fraction in stream 701 is determined computationally and adjusted using FIC1 if necessary.

An alternative solution that helps achieve particularly stable operation is to use an additional phase separator 804 to separate the two-phase flow 701 into a first vaporized gas F and a first excess liquid G. This variant is shown in Figure 7. The gas pipeline 13G is designed as a pure gas pipeline here, extending from the phase separator 804 to the low-pressure column 12, and includes a throttle valve 13V1. According to the present invention, the first vaporized gas F separated in the phase separator 804 will flow into the low-pressure column 12 through this gas pipeline 13G and the first throttle valve 13V1.

The control system is also illustrated in Figure 7. The functions of PIC1 and LIC2 are the same as in Figure 7. The evaporation side pressure of the second top gas condenser (14.10) can be controlled by PIC2.

As an alternative, a TIC (temperature indication and control) controller can be used instead of PIC2 to control the temperature of the first refrigerant liquid when it enters the first top gas condenser (13.10). LIC3 controls the amount of the first refrigerant liquid flowing into the first top gas condenser (13.10) based on the measured value at the filling height in the phase separator 804. The amount of the second excess liquid I flowing to the low-pressure column is regulated by LIC4 based on the liquid level on the evaporation side of the pure argon condenser. In addition, controllers FIC3 and FIC4 are also provided in the pipelines for the second excess liquid G and crude argon, which is transported to the refined argon column 14. Controller FIC3 is particularly important here. This allows the liquid fraction in stream 701 to be controlled directly (rather than being determined computationally), and dry evaporation in the condenser can be avoided.

FIG8 illustrates in a simplified manner a special device design of the invention shown in FIG7. Here, the heat exchanger block of the first top gas condenser 13.10 is arranged inside the phase separator 804, in which the first evaporated gas and the first excess liquid are separated from each other. In this case, the first top gas condenser does not lose its characteristics as a forced flow evaporator. On the contrary, the liquid to be evaporated still flows into the evaporation channel in a forced guided manner through the pipes at LIC3 and the header on the heat exchanger block, instead of being sucked from the liquid bath of the separator 804, which is different from the case of a bath evaporator.

The special measures in Figures 6 to 8, especially the phase separator 804, can also be applied to the entire process flow shown in Figures 2 to 5. As shown in Figure 8, a separate phase separator can be set for the first pressurized liquid flow, or the phase separator can be integrated into the top gas condenser.

The above embodiments are all optimized for thermodynamic efficiency or maximum yield of argon product. However, in some cases, the decisive criterion is, for example, equipment cost or tower height or similar factors, rather than thermodynamic efficiency or maximum yield of argon product. In this case, it may be more advantageous to minimize the feed point of the low-pressure tower as shown in Figures 9 to 11. As far as the rest of the diagrams are concerned, Figures 9 to 11 are consistent with Figures 6 to 8.

For example, the pipeline I and valve FIC1 in FIG6 are abandoned in FIG9. Instead, the entire liquid stream 604 extracted from the evaporation chamber of the top condenser 14.10 of the refined hydrogen column 14 flows through the top condenser 13.10 of the crude hydrogen column 13. The control function here is the same as that in FIG6 except that the valve FIC1 for dividing the first pressurized liquid stream is omitted.

FIG. 10 is similarly different from FIG. 7 . The valve LIC4 and the corresponding pipeline are omitted. In addition, the vapor 901 from the separator 804 and the vapor 902 from the top condenser 14.10 of the refined hydrogen column 14 are combined and sent to the low-pressure column through a common pipeline 903, preferably at the same position as the liquid G from the separator 804. The entire liquid stream 604 extracted from the evaporation chamber of the top condenser 14.10 of the refined hydrogen column 14 flows through the top condenser 13.10 of the crude hydrogen column 13.

In some cases, the control functions are also different. Like LIC2 in Figure 7, LIC1 is responsible for level control in the bottom layer of the pressure column (not shown here). The level in the evaporation chamber of the top condenser 14.10 of the rectifier column 14 is controlled by valve 13V2 (LIC2) by adjusting the amount of liquid extraction. Valve FIC2 therefore indirectly controls the amount of gas at the column inlet by backflowing liquid (thereby covering part of the heat exchange surface). In this way, the refrigeration capacity of the top condenser 13.10 is increased (in the case of relatively low liquid level) or reduced (in the case of relatively high liquid level). The top gas condensed on the condensing side will increase or decrease accordingly; the corresponding amount of gas is sucked from the low-pressure tower through the argon transfer line (not fully shown in Figure 10, but fully shown in Figures 1 to 4). According to the present invention, the valve 13V1 is pressure-controlled (PIC2), so that the temperature of the top condenser 13.10 can be adjusted, and thus its capacity can be adjusted. The discharge volume of the separator 804 is adjusted by LIC3, thereby controlling the liquid level in the separator.

FIG11 shows a particularly preferred embodiment, which is very similar to FIG8 , in particular, the heat exchanger block of the top condenser 13.10 of the crude argon column 13 is installed in the separator 804. Otherwise, the entire liquid stream 604 extracted from the evaporation chamber of the top condenser 14.10 of the refined argon column 14 will still be introduced into the evaporation chamber of the top condenser 13.10 of the crude argon column 13. Also similar to FIG10 , the vapor 901 from the separator 804 and the vapor 902 from the top condenser 14.10 of the refined argon column 14 are combined and sent to the low-pressure column via a common pipeline 903, preferably at the same position as the liquid G from the separator 804.

Like LIC2 in FIG8 , LIC1 is responsible for the material level control of the bottom layer of the pressure tower (not shown here). The material level in the evaporation chamber of the top condenser 14.10 of the refined argon tower 14 is regulated by valve 13V2 (LIC2) by adjusting the amount of liquid extraction. The flow regulation method of the liquefaction side of the top condenser 13.10 of the crude argon tower 13 is shown in FIG10 . According to the present invention, valve 13V1 is pressure controlled (PIC2), so that the temperature of the top condenser 13.10 can be adjusted, and thus its capacity can be adjusted. The discharge amount of the separator 804 is adjusted by LIC3, thereby controlling the liquid level in the separator. The pressure in the evaporation chamber of the top condenser 14.10 is regulated by PC1.

1: Main air compressor 2: Precooling device 3: Purification system 4: Booster compressor device 5: First booster turbine 6: Second booster turbine 7: Main heat exchanger 8: Pump 9: Pump 10: Refining tower system 11: Pressure tower 12: Low-pressure tower 13: Crude argon tower 13.10: Top gas condensation device/top condenser 13.11: Phase separator 13.12: "Forced flow" condenser evaporator 13G: Gas pipeline 13V1: First throttle valve 13V2: Second throttle valve 14: Refining argon tower 14.10: Top gas condenser/top condenser 90: Air separation equipment 100: Air separation equipment 200: Air separation equipment 300: Air separation equipment 600: Bottom evaporator 601: Valve 602: Pipeline 603: Pipeline 604: Pipeline/liquid/liquid flow 701: Two-phase flow 702: Downstream pipeline 804: Phase separator 901: Steam 902: Steam 903: Pipeline A: Oxygen-enriched liquid B: First pressurized liquid flow C: First flash gas D: Second pressurized liquid flow E: Second flash gas F: First evaporating gas FIC1: valve FIC2: valve FIC3: controller FIC4: controller G: first excess liquid H: second evaporated gas I: second excess liquid/pipeline K: first cooling liquid LIC1: control component LIC2: control component LIC3: control component LIC4: valve PIC1: control component PIC2: control component T: transfer flow

[Figure 1] shows a simplified diagram of an air separation device that is not designed according to the present invention, wherein the air separation device has a bath evaporator. [Figures 2] to [Figure 11] show simplified diagrams of air separation devices that are designed according to the present invention.

In the drawings, components that are identical in structure or function are labeled with the same symbols, and are not described repeatedly for the sake of clarity. The descriptions related to the apparatus and apparatus components are also applicable to the corresponding methods and method steps.

1: Main air compressor

2: Pre-cooling device

3: Purification system

5: First turbocharger

6: Second turbocharger

7: Main heat exchanger

8: Pump

9: Pump

10: Distillation tower system

11: Pressure tower

12: Low-pressure tower

13: Crude Argon Tower

13.10: Top gas condenser/top condenser

13.12: "Forced flow" condenser evaporator

13G: Gas pipeline

13V1: First throttle valve

13V2: Second throttle valve

14: Refined Argon Tower

14.10: Top gas condenser/top condenser

100: Air separation equipment

A: Oxygen-enriched liquid

B: First pressurized liquid flow

D: Second pressurized liquid flow

E: Second flash gas

F: First evaporating gas

G: First excess liquid

I: Second excess liquid/pipeline

Claims (14)

A method for low-temperature separation of air using an air separation device (100, 200), the air separation device comprising a distillation tower device (10) having a pressure tower (11), a low-pressure tower (12) and a crude argon tower (13), wherein: - at least a portion of the oxygen-enriched liquid from the pressure tower (11) is directly or indirectly used to form a first pressurized liquid stream, and the first pressurized liquid stream is expanded to produce a first low-pressure liquid; - The crude argon tower (13) is operated using a first top gas condensing device (13.10), in which the top gas of the crude argon tower (13) is condensed by partially evaporating a first refrigerant, wherein the first low-pressure liquid or a portion thereof is used to provide the first refrigerant, - the first top gas condensing device (13.10) has a forced flow condenser evaporator, and - the first evaporated gas or a portion thereof formed during the partial evaporation of the first refrigerant is fed into the low-pressure tower (12) via a gas line (13G), characterized in that - the gas line (13G) comprises a first throttling valve (13V1), - The first throttle valve (13V1) is adjusted by a control device in order to avoid freezing of argon in the first top gas condensation device (13.10) and at the same time - a pressure drop of at least 50 mbar is generated at least temporarily via the throttle valve (13V1). A method as described in claim 1, wherein a second throttling valve (13V2) is used to control the liquid level on the evaporation side of the top gas condensing device (13.10), and the throttling valve can be used to throttle the first cooling liquid upstream of the top gas condensing device (13.10). A method as described in claim 1 or 2, wherein the first evaporated gas or a portion thereof is extracted from the first top gas condensation device (13.10) together with the first excess liquid or a portion thereof as a first two-phase flow, but the first excess liquid or a portion thereof is not returned to the one or more condenser-evaporators. A method as described in any one of claims 1 to 3, wherein the first two-phase flow is directed through the first throttling valve (13V1) between the first top gas condensation device (13.10) and the low-pressure tower (12). A method as claimed in any of the preceding claims, wherein the first throttle valve (13V1) is -       fully open in a first operating mode (normal operation), and -       is set to produce a pressure drop of at least 50 mbar across the throttle valve (13V1) in a second operating mode (underload condition). A method as described in any of the preceding claims, wherein the throttling valve (13V1) is adjusted so that the temperature of the first coolant when entering the first top gas condenser (13.10) is preferably at least 0.1 K higher than the triple point temperature of argon. A method as claimed in any of the preceding claims, wherein -       during the expansion of the first pressurized liquid stream, a first flash gas is formed in addition to the first low-pressure liquid, -       at least a portion of the oxygen-enriched liquid from the pressure column (11) is used to form a second pressurized liquid stream, the second pressurized liquid stream is expanded to produce a second flash gas and leave a second low-pressure liquid, -       the argon column (14) is operated using a second top gas condenser (14.10), in which the top gas of the argon column (14) is condensed with partial evaporation of a second cooling liquid, wherein the second low-pressure liquid or a portion thereof is used to provide the second cooling liquid, wherein -      Extracting a second evaporated gas from the second top gas condensing device (14.10), mixing the second evaporated gas with the first evaporated gas and introducing the mixture into the low-pressure tower, and -       extracting a second excess liquid from the second top gas condensing device (14.10), and using the second excess liquid to form the first cooling liquid for the first top gas condensing device (13.10). A method as described in claim 7, wherein the bottom liquid level of the pressure tower (11) is measured and the amount of the second cooling liquid introduced into the second top gas condensing device (14.10) is set (LIC1, LIC2) according to the measured value. A method as claimed in any one of claims 7 or 8, wherein the liquid level in the evaporation chamber of the second top gas condenser device (14.10) is measured and kept constant by adjusting (LIC2) the feed amount to the first condenser device (13.10). A method as described in any of the preceding claims, wherein the first evaporated gas or its portion and the first excess liquid or its portion are introduced into the low-pressure column as a two-phase flow through the gas line (13G) and the first throttling valve (13V1). A method as described in any one of claims 1 to 9, wherein the first two-phase flow is introduced into a phase separator (804) between the top gas condensing device (13.10) and the low-pressure tower (12), in which the first evaporated gas and the first excess liquid are separated from each other, wherein the separated evaporated gas passes through the throttling valve (13V1) between the phase separator and the low-pressure tower (12) under the guidance of the gas pipeline (13G). A method as described in claim 11, wherein the liquid level in the phase separator (804) is measured and maintained constant by the amount of first excess liquid introduced into the low-pressure column. A method as described in any of the preceding claims, wherein the top gas condensation device (13.10) has a heat exchanger block, which is arranged inside the phase separator (804), in which the first evaporated gas and the first excess liquid are separated from each other. An air separation device (100, 200) comprises a rectification tower device (10), the rectification tower device having a pressure tower (11), a low-pressure tower (12) and a crude argon tower (13), wherein the air separation device (100, 200) is designed to - directly or indirectly utilize a first portion of the oxygen-enriched liquid from the pressure tower (11) to form a first pressurized liquid stream, expand the first pressurized liquid stream to produce a first flash gas and leave a first low-pressure liquid, - The crude argon tower (13) is operated using a first top gas condensing device (13.10), and in the first top gas condensing device, the top gas of the crude argon tower (13) is condensed under the condition of partial evaporation of the first refrigerant, wherein the first low-pressure liquid or a part thereof is used to provide the first refrigerant, wherein the first top gas condensing device (13.10) has a forced flow condenser evaporator, and - the first evaporated gas or a part thereof formed in the partial evaporation of the first refrigerant is fed into the low-pressure tower (12), and is characterized in that - the gas pipeline (13G) includes a first throttling valve (13V1), and - The first throttle valve (13V1) is designed to be adjustable by means of a control device in order to avoid freezing of argon in the first top gas condensation device (13.10) while at the same time generating a pressure drop of at least 50 mbar via the throttle valve (13V1) at least temporarily.