EP3193114A1 - Method for obtaining an air product in an air breakdown assembly and air breakdown assembly - Google Patents

Abstract

A process for recovering an air product (GOX-IC) by means of an air separation plant (100) having a distillation column system (12, 38) and a tank system (70) having a first tank (71) and a second tank (72) is proposed a cryogenic liquid (41) is withdrawn from the distillation column system (12, 38), at least partially stored in the tank system (70), and thereafter used at least in part as the air product (GOX-IC), the cryogenic liquid (41) during a first period the first tank (71) and not the second tank (72) and during a second period of the second tank (72) and not the first tank (71) supplied and during the first period the second tank (72) and is not the first tank (71) and during the second period of the first tank (71) and not the second tank (71) is removed. It is envisaged that as the tank system (70) a tank system (70) with an additional third tank (73) is used, and that the cryogenic liquid (41) during the first period of the second tank (72) and during the second period is taken from the first tank (71) is transferred at least partially unheated in the third tank (73), wherein nd the air product is at least partially provided using the unheated in the third tank (73) transferred deep-cold liquid or a part thereof wherein the cryogenic liquid used to provide the air product (GOX-IC) is taken out of the third tank (73) in a liquid state, vaporized or transferred to the supercritical state and discharged from the air separation plant (100), and / or wherein the Supplying the air product (GOX-IC) used cryogenic liquid in liquid state taken from the third tank (73) and in the liquid state stored in a fourth tank (76). An air separation plant (100) is also the subject of the invention.

Description

The invention relates to a method for obtaining an air product in an air separation plant and to an air separation plant configured for carrying out such a method.

State of the art

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

For a range of industrial applications, pressurized oxygen is needed, for the production of which air separation plants with so-called internal compression can be used. Corresponding air separation plants are also described, for example, in Häring and with reference to the local FIG. 2 .3A explained. In such air separation plants, a cryogenic liquid, in particular liquid oxygen, is brought to liquid pressure in the cryogenic state, vaporized against a heat carrier, and finally released as a gaseous pressure product. The internal compression has, among other things, energy advantages compared to a subsequent compression of an already gaseous product.

At supercritical pressure, there is no phase transition in the true sense, instead, the cryogenic liquid is brought from the liquid state into a supercritical state. For this purpose, the term "pseudo-vaporization" or "liquefaction" is used. Against the deep-cold liquid brought from the liquid state to the supercritical state, the high-pressure heat carrier is liquefied (or possibly subjected to a "pseudo-liquefaction" when it is under supercritical pressure). The heat transfer medium is frequently formed by a part of the air supplied to the air separation plant.

The above explanations apply equally to other air products such as nitrogen or argon, which can also be obtained using the internal compression in gaseous or supercritical state and are previously present as cryogenic liquids.

To increase the pressure of air products in air separation plants, the so-called pressure build-up compression is known and, for example in the DE 676 616 C and the EP 0 464 630 A1 described. Such as in the US Pat. No. 6,295,840 B1 disclosed, an air product can also be stored by means of a partial flow of compressed feed air in a tank system and brought there to pressure.

There is a need for improved possibilities for producing corresponding air products in air separation plants, in particular in air separation plants with the illustrated tank systems.

Disclosure of the invention

Against this background, the present invention proposes a method for obtaining an air product in an air separation plant and an air separation plant equipped for carrying out such a method with the features of the independent patent claims. Preferred embodiments are subject of the dependent claims and the following description.

The present application uses the terms "pressure level" and "temperature level" to characterize pressures and temperatures, which is to express that pressures and temperatures in a given equipment need not be used in the form of exact pressure or temperature values to achieve this to realize innovative concept. However, such pressures and temperatures typically range in certain ranges that are, for example, ± 1%, 5%, 10%, 20% or even 50% about an average. Corresponding pressure levels and temperature levels can be in disjoint areas or in areas that overlap one another. In particular, for example, pressure levels include unavoidable pressure losses or expected pressure drops, for example due to cooling effects or Line losses, a. The same applies to temperature levels. The pressure levels indicated here in bar are absolute pressures.

Advantages of the invention

The present invention proposes a method of recovering an air product by means of an air separation plant having a distillation column system and a tank system having a first tank and a second tank.

As part of the process according to the invention, a cryogenic liquid, for example pure oxygen or one of the other air products explained above, is removed from the distillation column system and stored at least partly in liquid form in the tank system. After removal from the tank system, the cryogenic liquid may be used as the air product. In the context of the present invention, a tank system with a first and a second tank is used, which are charged in alternating operation with the cryogenic liquid. In other words, the cryogenic liquid is supplied to the first tank and not to the second tank during a first period and to the second tank and not to the first tank during a second period. The alternate operation further includes taking the cryogenic liquid from the first tank rather than the first tank during the first time period and the first tank and not the second tank during the second time period. It may also be provided to use more than two tanks, which are subjected to a corresponding cycle. However, these always include a first and a second tank and a corresponding supply or withdrawal in a first or second period.

By using a corresponding tank system, it becomes possible to provide a product with a specified purity in an interior compression process because the process allows the use of non-continuous analytical methods. This is not possible in conventional internal compression processes in which the pressure is increased by means of pumps, since here the pump outflow is continuously fed directly to the heating. In the context of the method according to the invention, for example, after the first period in the first tank and after the second period the In the second tank stored deep cold liquid to be checked for their purity. If this purity meets a preset value, the cryogenic liquid is provided as the air product. If the purity does not correspond to the standard value, a corresponding cryogenic liquid can be discarded or, advantageously, returned to the distillation column system.

In such alternating operation, however, especially in the switching between the tanks, i. between the first period and the second period or the second period and the first period, or when the tank contents can not be provided as the air product due to, for example, insufficient purity, interruptions in the provision of the cryogenic liquid from the tank system ultimately occur precipitate in a discontinuous production of the air product. As a result, problems in the connected to a corresponding air separation plant consumers that are not adequately supplied, but also adverse effects in a possibly used for heating the cryogenic liquid device, such as the main heat exchanger of the air separation plant arise.

The present invention therefore proposes to use as the tank system a tank system with an additional third tank, wherein the cryogenic liquid, which is taken during the first period of the second tank and during the second period of the first tank, at least partially (and in particular at least temporarily) is transferred unheated in the third tank. It may therefore be provided in this context, only a part of the cryogenic liquid, which is taken during the first period of the second tank and during the second period of the first tank unheated transferred to the third tank and another part of the cryogenic liquid directly, as explained below, via a by-pass as an air product or to use in another form. The third tank serves as a template or buffer storage, which is filled with a suitable amount of cryogenic liquid, which is sufficient to bridge the previously explained periods.

A transfer to the third tank is "unheated" when the cryogenic liquid, which is taken during the first period of the second tank and during the second period of the first tank, at the removal temperature level of the second or first tank is transferred to the third tank. This is the case when the cryogenic liquid is not subjected to active temperature-increasing measures or heating. The cryogenic liquid is thus led in particular by no heat exchanger, heater, countercurrent, etc. for heating. However, as already explained above for the term "temperature level", this does not exclude that, due to unavoidable heat inputs, there is a certain, but not active, heating. The term "temperature level", takes this into account, so that the aforementioned removal temperature level can still be within the specified extent below a feed temperature level in the third tank. The unheated transfer to the third tank is therefore particularly to avoid evaporation losses.

According to the invention, therefore, the cryogenic liquid stored in the first and second tanks is no longer or not exclusively discharged therefrom and used as the air product. Rather, the air product is provided, at least in part, using the cryogenic liquid transferred unheatedly into the third tank, or a portion thereof. In the context of the present invention, however, it is also possible, as mentioned, to provide bypass lines which allow a discharge from the first or second tank, so that the air product is also partly stored using the cryogenic liquid stored there but not transferred to the third tank can be provided. In this way, for example, when the third tank is completely filled and sufficient purity is ensured, a direct removal from the first or the second tank can be done. It may further be provided that not all of the cryogenic liquid that has been unheatedly transferred to the third tank is used to provide the air product. Part of the cryogenic liquid transferred unheated into the third tank can be taken out of the third tank and used in a different way. It is also possible that, for example, the portion of the cryogenic liquid evaporated in the respective tanks is not used to provide the air product.

According to the invention, it is further provided that the cryogenic liquid used to provide the air product is taken from the third tank in liquid state from the third tank, evaporated or transferred from the liquid to the supercritical state and discharged from the air separation plant, and / or that the cryogenic liquid used to provide the air product is taken out of the third tank in the liquid state and stored liquid in a fourth tank in a liquid state.

The fourth tank can be part of the tank system with the first to third tank, but it can also be provided separately, for example as part of another tank system. The fourth tank may be located within the air separation plant, for example within a cold box, or within a thermally insulating outer shell which also includes the first to third tanks. However, the fourth tank can also be arranged outside the air separation plant. In the context of the present invention, the air product may thus be a gaseous or supercritical air product and / or a liquid air product. Like the liquid air product, the gaseous air product can also be stored inside or outside the air separation plant, in particular in a corresponding gas tank.
Advantageously, the cryogenic liquid is removed from the distillation column system of the air separation plant at a pressure level on which a corresponding column of the distillation column system, in particular a pure oxygen column, hereinafter also referred to as "second separation column", is operated. The cryogenic liquid is supplied to the first tank and the second tank of the tank system at a pressure level referred to herein as a "first" pressure level. The first pressure level may correspond to the pressure level at which the cryogenic liquid was withdrawn from the distillation column system if no pressure-influencing devices such as pumps are arranged between the separation column and the first and second tanks, respectively. If, for example, a corresponding pump is used, the first pressure level can also be above the pressure level of the separation column. The cryogenic liquid is supplied to the third tank of the tank system at a second, higher pressure level (storage pressure), which can depend in particular on the pressure (product pressure) at which the air product is to be provided. The storage pressure is advantageously slightly above the product pressure, so that a discharge is possible without additional pumps or compressors. The second pressure level can be achieved, in particular, by carrying out a pressure build-up evaporation in the first and / or the second tank.

The present invention, through the use of the illustrated tank system and pressure increase, combines the advantages of a traditional internal compression process, namely the continuous production of the air product, with the advantages of improved analysis capability. Through this improved analysis option, a high purity of the air product can be guaranteed and documented at any time.

After removal of the cryogenic liquid from the third tank (or via said bypass lines from the first and the second tank) may, as mentioned, in particular vaporized or transferred from the liquid to the supercritical state, if a gaseous or in supercritical Condition existing air product to be produced. The evaporation or conversion to the supercritical state (hereinafter the term "evaporation" is used for the sake of simplicity in both cases) can be carried out within the air separation plant used, for example using its main heat exchanger. In cases where the air separation plant is not available, a backup system with a standby evaporator that does not draw heat of vaporization from the air separation plant can also be used. However, as already mentioned, the cryogenic liquid can also be discharged from the third tank (or via the bypass lines from the first and the second tank) in liquid form from the air separation plant, in liquid form, for example in a tank. transported to a consumer and used there in liquid or (after evaporation) gaseous state.

Advantageously, the first pressure level, ie the pressure level at which the cryogenic liquid is supplied to the first and the second tank, is approximately 1.3 to 4 bar. The second pressure level is, depending on the requirement, at 2 to 100 bar, but above the first pressure level. In the context of the present invention, a particularly flexible pressure increase in time can take place taking into account the pressure requirements of a consumer.

According to one embodiment of the invention, the cryogenic liquid may be brought to the first pressure level before being fed to the first tank and the second tank using a pump. The present invention combines the advantages of conventional in this embodiment Internal compression method using appropriate pumps, however, do not allow the implementation of discontinuous analysis methods due to the continuous pressure increase, with processes in which alternately different tanks are charged.

In the conventional methods, which are carried out using tank systems with two tanks, there is a pressure build-up evaporation. In a pressure build-up evaporation due to the required for the pressure build-up portion of a corresponding cryogenic liquid product loss is inevitable. This product loss can be up to 10%. By using a pump, such product loss is reduced. The unavoidable flash losses in the tanks are at about 5% significantly lower than the losses due to the pressure build-up evaporation. Although a corresponding pump has an additional energy requirement, the higher product yield possibly outweighs this additional energy requirement.

The invention develops particular advantages in air separation plants that have very high purity requirements of the respective air product, such as oxygen. With such very high purity requirements, conventional fast (routine) analytical methods can approach the detection limit, and more sensitive analytical methods such as gas chromatography must be used. Corresponding more sensitive analysis methods, however, take much longer to determine the measured value than conventional methods, so that a discontinuous measurement must be carried out.

The inventive method also saves energy compared to methods in which an evaporation of a corresponding air product, such as oxygen, takes place only at the consumer. Overall, energy savings of about 1 kW per Nm ³ / h of oxygen can be achieved.

Of the advantages associated with the present invention in particular benefit smaller air separation plants, whose capacity is limited by the maximum transport dimensions. Improving the efficiency increases the yield accordingly.

Although the described increase in pressure of the cryogenic liquid by means of a pump can be advantageous in certain cases, the present invention can be used in principle and with particular advantage in corresponding tank systems with pure pressure build-up evaporation. In this way, can be completely dispensed with a pump, which allows a more cost-effective creation of a corresponding air separation plant. The absence of moving or driven parts in a pressure build-up evaporation allows a particularly energy-saving and low-maintenance operation. The evaporation losses which inevitably result in a pressure build-up evaporation do not fall into consideration, in particular, if a gaseous or supercritical air product is to be provided anyway. A combination of an increase in pressure by means of a pump and an additional pressure build-up evaporation is possible.

As already mentioned, the method according to the invention is particularly suitable for providing highly pure air products, because a discontinuous analysis before heating and delivery to the plant boundary is possible. In other words, within the scope of the present invention, a purity of the cryogenic liquid which is supplied to the first tank during the first period and to the second tank during the second period is advantageously determined. Conventional methods for purity testing, for example spectroscopic methods and / or gas chromatography, can be used for a corresponding analysis.

In the context of the present invention, the cryogenic liquid is advantageously transferred from the second tank and into the third tank during the first period and from the first tank during the second period and into the third tank during the second period if its purity corresponds to a preset value. The third tank is thus always filled with cryogenic liquid of defined purity and can be used at any time without additional analysis to provide the air product.

On the other hand, if the purity of the cryogenic liquid does not meet the standard value, it may advantageously be returned from the second tank during the first period and from the first tank to the distillation column system during the second period. In particular, in such a variant of the method, the present invention proves by the use of a third tank as particularly advantageous because a corresponding interruption can be compensated by removing the cryogenic liquid from the third tank. Advantageously, it is therefore provided that in the third tank an amount of the cryogenic liquid is kept, which is at least as large as a quantity of the cryogenic liquid which can be stored in the first tank and / or in the second tank, or at least as large is that the switching times, during which no liquid can be removed from the first two containers, bridged to allow a continuous withdrawal. In this way, deep cryogenic liquid can be continuously heated and released as an air product, even if the contents of a completely filled first or second tank must be returned or discarded due to a non-default purity in the distillation column system.

In particular, the present invention is used in air separation plants for the production of pure oxygen. In such an air separation plant, the distillation column system has a first separation column and a second separation column. Using the first separation column, a fluid stream enriched in a first oxygen content of oxygen is generated using which liquid pure oxygen is generated in the second separation column, which is withdrawn from the second separation column at least in part as the cryogenic liquid. The present invention allows continuous supply of high purity oxygen through the use of the third tank.

In particular, the invention can be used in connection with the so-called SPECTRA method of the applicant, as used for example in the US 2009/107177 A1 is described. However, the invention is not limited thereto. Such a method comprises, using the first separation column, further generating a fluid stream enriched in a second oxygen content of oxygen and a fluid stream enriched in a third oxygen content of oxygen. The fluid stream enriched in oxygen at the second oxygen content is advantageously taken from the first separation column below the fluid stream enriched in oxygen at the first oxygen content. He therefore has a higher oxygen content. The fluid stream enriched in the third oxygen content of oxygen is advantageously taken from the bottom of the first separation column. The two fluid streams are then in particular in one Head condenser of the first separation column and heated in a main heat exchanger to different temperatures, wherein the oxygen enriched to the second oxygen content, heated fluid stream is at least partially compressed in a compressor coupled with a relaxation machine, cooled and recycled to the first separation column. On the other hand, part of the fluid stream enriched in the third oxygen content of oxygen is used to drive the expansion machine. For further details of such a procedure, see the attached FIG. 1 directed. A corresponding method proves to be particularly advantageous in terms of energy.

Advantageously, a main heat exchanger of the air separation plant is used for heating the cryogenic liquid which is subsequently provided as the air product. Additionally or alternatively, however, a separate evaporator may also be used. A corresponding evaporator can also be used in particular if a capacity of the main heat exchanger of the air separation plant is insufficient and / or if additional amounts of air products are to be provided than it is able to provide a corresponding main heat exchanger (also temporary).

The present invention also extends to an air separation plant adapted to recover an air product. The air separation plant comprises a distillation column system and a tank system with a first tank and a second tank and has features as indicated in the corresponding device claim.
Advantageously, a corresponding air separation plant is set up for carrying out a method, as has been explained in detail above. Reference should therefore be made to the relevant features and advantages at this point.

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

Brief description of the drawings

• FIG. 1 shows an air separation plant according to an embodiment of the invention in the form of a schematic diagram of the system.
• FIG. 2 shows a tank system according to an embodiment of the invention in the form of a schematic diagram of the system.
• FIG. 3 shows a tank system according to an embodiment of the invention in the form of a schematic diagram of the system.

Detailed description of the drawings

In the following figures, corresponding elements are given identical reference numerals and will not be explained repeatedly for the sake of clarity. The FIGS. 2 and 3 each show tank systems, as in an air separation plant according to FIG. 1 or a deviating trained air separation plant may be involved. The integration of the tank system results from the also in FIG. 1 specified elements.

In FIG. 1 an air separation plant according to an embodiment of the present invention is shown schematically in the form of an installation diagram. The air separation plant is designated 100 in total.
Atmospheric air 1 (AIR) is sucked in via a filter 2 from an air compressor 3 and compressed there to an absolute pressure of 6 to 20 bar, preferably about 9 bar. After flowing through an aftercooler 4 and a water separator 5 for separating water (H 2 O), the compressed air 6 is cleaned in a cleaning device 7 which has a pair of containers filled with adsorption material, preferably molecular sieve. The purified air 8 is cooled in a main heat exchanger 9 to about dew point and partially liquefied. A first part 11 of the cooled air 10 is introduced via a throttle valve 51 into a first separation column 12, which is designed as a single column. The feed is preferably some practical or theoretical soils above the sump.

The operating pressure of the first separation column 12 is at the top 6 to 20 bar, preferably about 9 bar. Your top condenser 13 is cooled with a fluid stream 18 and a fluid stream 14. The fluid stream 18 is from an intermediate point some practical or theoretical plates above the air supply or at the same level as this, the fluid stream 14 withdrawn from the bottom of the first separation column 12. The fluid stream 18 has been referred to in the above discussion as a "second oxygen oxygenated fluid stream" and the fluid stream 14 is referred to as a "third oxygen oxygenated fluid stream."

As the main product of the first separation column 12, gaseous nitrogen 15, 16 is withdrawn at the top of the first separation column 12, heated in the main heat exchanger 9 to about ambient temperature and finally withdrawn via line 17 as gaseous pressure product (PGAN). Additional gaseous nitrogen is passed through the top condenser 13. A part 53 of the condensate 52 obtained in the top condenser 13 may be recovered as liquid nitrogen product (PLIN); the rest 54 is given up as reflux to the top of the separation column 12.

The fluid flow 14 is in the top condenser 13 under a pressure of 2 to 9 bar, preferably about 4 bar, evaporated and then flows in gaseous form via a line 19 to the cold end of the main heat exchanger 9. From this it is taken at an intermediate temperature in the form of the stream 20 and in a relaxation machine 21, which is designed in the example shown as a turboexpander, work-performing expanded to about 300 mbar above atmospheric pressure. The expansion machine 21 is mechanically coupled to a (cold) compressor 30 and a braking device 22, which is formed in the illustrated example by an oil brake. The expanded fluid stream 23 is heated in the main heat exchanger 9 to approximately ambient temperature. The warm fluid stream 24 is blown off into the atmosphere (ATM) as fluid flow 25 and / or used as regeneration gas 26, 27, optionally after heating in the heating device 28.

The fluid stream 18 is vaporized in the top condenser 13 under a pressure of 2 to 9 bar, preferably about 4 bar, and flows in gaseous form via a line 29 to the compressor 30, in which it is recompressed to approximately the operating pressure of the first separation column 12. The recompressed fluid stream 31 is cooled again in the main heat exchanger 9 to column temperature and finally fed via line 32 of the first separation column 12 at the bottom again. The explained treatment of the fluid streams 14 and 18 corresponds to the already mentioned, so-called SPECTRA method.

A fluid stream 36, previously referred to as a "first oxygen-enriched oxygen-rich fluid stream" that is substantially free of less volatile contaminants, is withdrawn from an intermediate location of the separation column 12 in the liquid state, leaving 5 to 25 theoretical or practical levels above the air supply is arranged. The fluid stream 36 is optionally subcooled in a sump evaporator 37 of a second separation column 38, which is designed as a pure oxygen column, and then fed via a line 39 and a throttle valve 40 to the top of the second separation column 38. The operating pressure of the second separation column 38 (at the top) is 1.3 to 4 bar, preferably about 2.5 bar.

The sump evaporator 37 of the second separation column 38 is also operated by means of a second part 42 of the cooled feed air 10. The feed air stream 42 is thereby at least partially, for example completely, condensed and flows via a line 43 to the first separation column 12, where it is introduced approximately at the level of feeding the remaining feed air 11 or into the column bottom.

From the bottom of the second separation column 38 pure oxygen is removed as cryogenic liquid 41, optionally brought by a pump 55 to an elevated pressure of 2 to 100 bar, preferably about 12 bar, and in a tank assembly 70, which in the following FIGS. 2 and 3 is fed. After an intermediate storage in the tank assembly 70, the cryogenic liquid is passed via a line 56 to the cold end of the main heat exchanger 9, evaporated there under the increased pressure and warmed to about ambient temperature and finally recovered via line 57 as a gaseous product (GOX-IC).

A top gas 58 of the second separation column 38 is admixed with the above-explained expanded second fluid stream 23 (see link A). If necessary, part of the feed air for pump prevention of the cold compressor 30 is led to its inlet via a bypass line 59 (so-called anti-surge control).

If necessary, the liquid separation plant 100 upstream of and / or downstream of the pump 55 liquid oxygen can be removed as a liquid fraction (in the drawing with LOX). In addition, an external liquid, such as liquid argon, liquid nitrogen or liquid oxygen, even from a liquid tank, in the main heat exchanger 9 are evaporated in indirect heat exchange with the feed air (not shown in the drawing).

In FIG. 2 is a tank system according to an embodiment of the invention, which in an air separation plant 100, as shown in FIG. 1 is illustrated, illustrated in the form of a schematic system diagram and designated overall by 70.

By means of the already referring to FIG. 1 explained pump 55, the cryogenic liquid of the fluid flow 41 is brought from a first pressure level to a second pressure level. The first pressure level may in particular correspond to a pressure level at which a second separation column 38 (pure oxygen column) of an air separation plant 100, as described in US Pat FIG. 1 is shown, can be operated. The second pressure level is for example 2 to 100 bar.

The pressure-increased fluid flow 41 is supplied to a first tank 71 or a second tank 72. As explained in more detail, the tanks 71 and 72 are alternatively charged with the cryogenic liquid of the fluid flow 41, i.e., with each other. during a first period, the cryogenic liquid of the fluid stream 41 is supplied to the first tank 71 and not to the second tank 72 and to the second tank 72 and not the first tank 71 for a second period. For controlling correspondingly inserted valves 71a and 72a, a tank controller 80 may be provided, for example.

As also explained several times, deep-cold liquid is always withdrawn from the tank 71, 72, to which no cryogenic liquid of the fluid flow 41 is currently supplied. This is unheated transferred to a third tank 73. As already explained, it can also be provided, for example, when the third tank 73 is completely filled, as illustrated here by means of a line 74, to forward corresponding fluid directly and to supply it to a heating. The heating of the fluid can, as also mentioned, for example, in a main heat exchanger 9 of a corresponding air separation plant, for example, the air separation plant 100 according to FIG. 1 , and / or take place in an additional evaporator 90.

FIG. 3 illustrates a tank system according to another embodiment of the invention in the form of a schematic diagram of the system. Also the tank system of FIG. 3 is designated 70. The tank system 70, which in FIG. 3 is equipped with a pressure build-up evaporator 75. A pump 55 as in the tank system 70 according to FIG. 2 or in the air separation plant 100 according to FIG. 1 is optional here. In a pressure build-up evaporation, a corresponding pump 55 is regularly omitted and the cryogenic liquid of the stream 41 is fed to the tanks 71 and 72 at the distillation pressure in the pure oxygen column 38, which here corresponds to the "first pressure level". In the pressure build-up evaporator 75, a portion of the cryogenic liquid of the stream 41 removed in liquid form from the tanks 71 and 72 is vaporized. The vaporized and pressurized gas is supplied to a head space of the tanks 71 and 72, respectively. In this way, the pump 55 can be saved and it can only be a pressure build-up evaporation used.

As illustrated herein, the cryogenic liquid used to provide the liquid air product may be removed from the third tank 73 in the liquid state and vaporized in the main heat exchanger 9 and / or in the additional evaporator 90 or transferred from the liquid to the supercritical state and discharged from the air separation plant become. However, the cryogenic liquid used to provide the liquid air product can also be removed from the third tank 73 in the liquid state and stored in a fourth tank 76 until it is liquid. Details have already been explained. Further withdrawals upstream and / or downstream of the third tank 73 are possible.

Claims (14)

Process for obtaining an air product (GOX-IC) by means of an air separation plant (100) with a distillation column system (12, 38) and a tank system (70) having a first tank (71) and a second tank (72), in which the distillation column system ( 12, 38), a cryogenic liquid (41) is removed, stored at least in part in the tank system (70), and then at least partially used as the air product (GOX-IC), wherein the cryogenic liquid (41) during a first period the first tank (71) and not the second tank (72) and during a second period the second tank (72) and not the first tank (71) supplied and during the first period the second tank (72) and not the first tank (71) and during the second period is taken from the first tank (71) and not the second tank (71), characterized in that a tank system (70) with an additional third tank (73) is used as the tank system (70) , and that di e cryogenic liquid (41), which during the first period of the second tank (72) and during the second period, the first tank (71) is removed, at least partially unheated in the third tank (73) is transferred, and that the air product at least partially provided using the cryogenic liquid transferred to the third tank (73) or a portion thereof, wherein the cryogenic liquid used to provide the air product (GOX-IC) from the third tank (73) is in the liquid state from the third tank (73) is removed, vaporized or transferred from the liquid to the supercritical state and discharged from the air separation plant (100), and / or wherein the cryogenic liquid used to provide the air product (GOX-IC) from the third tank (73) in liquid state from the third tank (73) and stored in the liquid state in a fourth tank (76). The method of claim 1, wherein the cryogenic liquid (41) is supplied at a first pressure level to the first tank (71) and the second tank (72), and / or at which the cryogenic liquid (41) in the third tank (73 ) is stored at a second, higher pressure level. The method of claim 2, wherein the first pressure level is 1.3 to 7 bar and the second pressure level is 2 to 100 bar. A method as claimed in claim 2 or 3, wherein the cryogenic liquid (41), prior to being fed to the first tank (71) and the second tank (72), is in a liquid state from the first pressure level to the second level using a pump (55) Pressure level is brought. A method according to any one of the preceding claims, wherein the cryogenic liquid (41) in the first tank (71) and the second tank (72) is subjected to pressure build-up evaporation to the second pressure level. Method according to one of the preceding claims, in which a purity of the cryogenic liquid (41) which is supplied to the first tank (71) during the first period and to the second tank (72) during the second period, in the respective tank (71, 72) is determined. The method of claim 6, wherein the cryogenic liquid (41) only from the second tank (72) in the third tank (73) during the first period and from the first tank (71) into the third tank during the second period ( 73), if their purity corresponds to a standard value. The method of claim 7, wherein the cryogenic liquid (41) is returned from the second tank (72) during the first period and from the first tank (71) to the distillation column system (12, 38) during the second period if its purity does not match the default value. Method according to one of claims 1 to 8, wherein in the third tank (73) an amount of cryogenic liquid (41) is kept at least as large as an amount of the cryogenic liquid (41) in the first tank ( 71) and / or in the second tank (71) can be stored. The process of any one of the preceding claims, wherein the distillation column system (12, 38) comprises a first separation column (12) and a second separation column (38), wherein using the first separation column (12) generating oxygen enriched fluid stream (36) using a first oxygen content produced in the second separation column (38), which is withdrawn from the second separation column (38) at least in part as the cryogenic liquid (41). The method of claim 8 further comprising generating and heating to a different temperature using the first separation column (12) a second oxygen content oxygen enriched fluid stream (18) and a third oxygen enriched oxygen (14) fluid stream the heated to the second oxygen content of oxygen, heated fluid stream (14) at least partially compressed in a compressor with a relaxation machine (21) compressor (30), cooled and returned to the first separation column (12) and a portion of the third oxygen content oxygen-enriched, heated fluid stream (14) for driving the expansion machine (21) is used. Method according to one of the preceding claims, in which a main heat exchanger (9) of the air separation plant (100) and / or an evaporator (80) are used for heating the cryogenic liquid (41). An air separation plant (100) adapted to recover an air product (GOX-IC) comprising a distillation column system (12, 38) and a tank system (70) having a first tank (71) and a second tank (72), means adapted to remove from the distillation column system (12, 38) a cryogenic liquid (41), at least partly to store it in the tank system (70) and thereafter at least partly and to use it as the air product (GOX-IC), and with means arranged to supply the cryogenic liquid (41) to the first tank (71) and not to the second tank (72) during a first period and to the second tank (72) and not the first tank (71 ) and during the first period of time to remove the second tank (72) and not the first tank (71) and during the second period the first tank (71) and not the second tank (71), characterized in that the tank system ( 70) an additional a third tank (73), and in that means are provided which are arranged to supply the cryogenic liquid (41) which during the first period to the second tank (72) and during the second period of time is taken from the first tank (71), at least temporarily and at least partially unheated to transfer into the third tank (73) and the air product (GOX-IC) at least partially transferred unheated in the third tank (73) cryogenic liquid or a part thereof, wherein means are provided, which are adapted to remove the used for the provision of the air product (GOX-IC) cryogenic liquid from the third tank (73) in the liquid state from the third tank (73) to evaporate or transfer from the liquid to the supercritical state and to discharge it from the air separation plant (100), and / or which are adapted to supply the cryogenic liquid used to provide the air product (GOX-IC) from the third tank (73) to remove in the liquid state from the third tank (73) and to store liquid in a fourth tank (76). Air separation plant (100) according to claim 13, which is adapted to carry out a method according to one of claims 1 to 12.

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