EP4065878A1

EP4065878A1 - System comprising at least two cryogenic vessels for providing a fluid

Info

Publication number: EP4065878A1
Application number: EP20780903.9A
Authority: EP
Inventors: Matthias Rebernik
Original assignee: Cryoshelter GmbH
Current assignee: Cryoshelter Biolng GmbH; Cryoshelter Lh2 GmbH
Priority date: 2019-11-29
Filing date: 2020-09-23
Publication date: 2022-10-05
Also published as: WO2021102489A1; US20230003344A1; CO2022008673A2; AU2020390422A1; CA3158688A1

Abstract

The invention relates to a system (1) for providing a fluid, comprising at least one first and one second cryogenic vessel (7, 8) for storing the fluid, wherein the system (1) comprises a first withdrawal line (11) which connects to the first cryogenic vessel (7) for withdrawing a first mass flow (M1) of fluid, and a second withdrawal line (12) which connects to the second cryogenic vessel (8) for withdrawing a second mass flow (M2) of fluid, wherein the system (1) comprises means (13) which are designed to form the two mass flows (M1, M2) to be differently sized, such that, in a first operating mode, a holding time of the two cryogenic vessels (7, 8) converges at the removal and/or, in a second operating mode, the holding time of the two cryogenic vessels (7, 8) decreases substantially at the same rate, if the holding times of the two cryogenic vessels (7, 8) are substantially equal.

Description

System with at least two cryogenic containers for providing a fluid

The invention relates to a system for providing a fluid, comprising at least a first and a second cryocontainer for storing the fluid, wherein the first cryocontainer has a container volume which is greater than a container volume of the second cryocontainer, and wherein the system furthermore has a first extraction line, which connects to the first cryocontainer for withdrawing a first mass flow of fluid, and comprises a second withdrawal line which connects to the second cryocontainer for withdrawing a second mass flow of fluid.

According to the prior art, liquefied gases can be stored in containers (“cryogenic containers”) in order to store them as fuel for an engine, for example. Liquefied gases are gases that are in a liquid state at boiling point, the boiling point of this fluid being pressure-dependent. If such a cryogenic liquid is filled into a cryocontainer, then, apart from thermal interactions with the cryocontainer itself, a pressure corresponding to the boiling temperature is established. If, for example, methane is used as fuel, this means that the methane must be at a sufficiently high temperature in order to achieve a sufficiently high tank pressure for engine operation after the fuel has been filled from the petrol station into the vehicle tank. If the pressure applied to the injection valves of the engine falls below the specified minimum, the engine cannot be operated.

During operation, when the fluid is removed from the container and fed to the motor, the fluid in the cryocontainer is therefore present at a working pressure which is between 6 and 8 bar, for example. When the system is switched off and removal is ended, the pressure in the cryocontainer rises again due to the flow of heat into the fluid. So that the pressure in the cryocontainer does not become too high and damage or accidents are prevented, the cryocontainer is equipped with a pressure relief valve which is triggered at a predetermined pressure. The time from the completion of the withdrawal at the working pressure to the reaching of the predetermined pressure of the pressure relief valve is referred to as "hold time" in specialist circles.

If the hold time is exceeded, the pressure relief valve is triggered and fluid is drained, so that a further increase in pressure is prevented. However, the draining of fluid is on the one hand an economic loss because fuel escapes unused, and on the other hand an environmental problem because the storage efficiency drops and methane is released into the environment is blown off. It is therefore desirable that the hold time of the cryocontainer is as long as possible in order to enable long shutdown times.

It is also known from the prior art to mount two cryocontainers on a motor vehicle, the fluid being used as fuel for the motor vehicle. The cryocontainers are usually mounted on the left and right on the support frame of the vehicle between axles of the vehicle.

Due to the different space available on both sides of the motor vehicle, it can be useful to use two cryocontainers with different container volumes, for example a shorter and a longer cryocontainer. A problem that arises here, however, is that cryogenic containers with different container volumes have different hold times. The "total" hold time of the system is thus calculated from the cryocontainer with the lower hold time.

An obvious solution would be to better insulate the cryocontainer with the smaller container volume, which typically has a shorter hold time, in order to reduce the heat flow into the fluid. As a result, cryogenic containers could be reached with a similar hold time. However, this solution is very inflexible since the cryocontainers have to be precisely matched to one another.

In systems with two cryogenic containers of the same size, the same mass flow is usually taken from both cryogenic containers. Here, too, however, due to external influences or incorrect adjustments of the system, there may be a different amount of fluid in the two cryogenic containers, so that the two containers have a different hold time. This in turn means that the "entire" hold time of the system is not optimal at all times.

It is therefore the object of the invention to create a system with at least two cryogenic containers for providing a fluid which overcomes the disadvantages mentioned.

This object is achieved by a system for providing a fluid, comprising at least a first and a second cryocontainer for storing the fluid, wherein the first cryocontainer has a container volume which is greater than a container volume of the second cryocontainer, and wherein the system furthermore has a first Withdrawal line, which connects to the first cryocontainer for withdrawing a first mass flow of fluid, and a second withdrawal line, which connects to the second cryocontainer for withdrawing a second mass flow of fluid, the system comprising means which for this purpose are designed to form the two mass flows of different sizes, so that in a first operating mode the hold time of the two cryocontainers converges during removal and / or in a second operating mode the hold time of the two cryocontainers decreases essentially at the same rate, if it essentially decreases are of the same size, the hold time being the period from the termination of the removal to the point in time at which the pressure in the cryocontainer reaches a predefined threshold value.

The solution according to the invention solves the problem mentioned at the outset in that the different hold times of the cryocontainers are compensated for by the different withdrawals of the fluid from the containers. With the solution according to the invention, it is thus possible to increase the hold time of the overall system from the two cryogenic containers without making structural changes to one of the two containers.

The first operating mode has the effect that the hold time of the two cryocontainers is brought closer, so that the total hold time of the overall system increases, which is given by the lower hold time of the two cryocontainers. The second operating mode has the effect that after the same hold time of the two cryocontainers has been reached for the first time, the hold time of the overall system decreases as little as possible when the fluid is removed again. It is also possible to equip the system with only the second operating mode, for example if the two cryocontainers are filled in such a way that they have the same hold time.

In the case of cryogenic containers with an equally large container volume, the solution according to the invention can be used in particular when the extraction lines have different line lengths or, more generally, different flow losses. In this case, the means or a control unit of the means can control the mass flows in such a way that the different flow losses are compensated for.

The first cryocontainer preferably has a container volume which is greater than a container volume of the second cryocontainer. In this embodiment, the solution according to the invention can be used with particular preference, because the hold time of the cryocontainers will generally be different and not only when the hold time of the two cryocontainers is different due to external circumstances. In this embodiment it is particularly preferred if, for example, the first operating mode is started immediately after the tank has been completely filled - and particularly preferably after the working pressure has been reached in the cryogenic containers - and the second operating mode is started after an equally long hold time has been reached. In the simplest case, the first operating mode could be implemented in that a rigid throttle is provided in the first extraction line so that the hold time of the two cryocontainers approaches when the fluid is withdrawn from both cryocontainers. However, it is preferred if the means comprise a control unit which is designed to regulate the first and / or the second mass flow. This allows dynamic control of the hold time as a function of the current hold time or the fill level of the cryocontainer.

In this embodiment it is advantageous if the control unit is designed to essentially only withdraw fluid from the first cryocontainer in the first operating mode until the hold time of the first cryocontainer essentially corresponds to the hold time of the second cryocontainer. In the simplest case, this can be achieved by an on / off valve in the first or second extraction line, which is controlled by the control unit.

Alternatively, a further improvement can be provided, namely in that the control unit is designed to remove essentially only such an amount of fluid from the second cryocontainer in the first operating mode that the hold time of the second cryocontainer remains constant, and the remaining fluid to be taken from the first cryocontainer. This enables the hold time of the second cryocontainer not to decrease while the majority of the fluid is being withdrawn from the first cryocontainer.

In the last-mentioned embodiment it is further preferred if the system is designed to remove fluid from the second cryocontainer in the first operating mode only in a gaseous state. This has the effect that less mass has to be removed from the second cryocontainer in order to keep the hold time constant.

In all embodiments it is preferred if the control unit is designed to switch from the first to the second operating mode after the same hold time of the two cryocontainers has been reached for the first time. As a result, a system can be achieved which controls the hold time of the two cryocontainers as efficiently as possible.

It is further preferred if the control unit is designed to choose between removing the fluid in a liquid phase and / or removing the fluid in a gas phase when the fluid is removed from the first and / or the second cryocontainer. This can be provided for both the first and the second operating mode. In normal operation, the fluid is withdrawn in the liquid phase. However, should the pressure exceed the desired working pressure, fluid can be withdrawn in the gas phase become. This enables a so-called economizer function to be achieved, taking the hold time into account.

Furthermore, a third operating mode can preferably be provided, the system in the third operating mode being designed to develop a different working pressure in the two cryocontainers during operation and to remove fluid only from the first or only from the second cryocontainer. The smaller of the cryocontainers is preferably lowered to the lower working pressure and fluid is only taken from the larger cryocontainer when an expected required power of the system is above a threshold value and fluid is only taken from the smaller cryocontainer when the expected required power of the system is below the threshold. Furthermore, an expected route profile can preferably be used here in order to determine the required power. These measures can further increase the usable content of the cryocontainer, because by lowering the working pressure in one of the cryocontainers to a level at which the system can only support a low engine output, the hold time of this cryocontainer can be extended.

Furthermore, the system can be switched to a fourth operating state if the pressure in both cryogenic containers lies between a working pressure and the aforementioned threshold value, and in the fourth operating mode the system is designed to select the two mass flows in such a way that the pressure in both cryogenic containers is lowered to the working pressure and the hold time of the two cryocontainers converges during removal and / or increases at essentially the same rate. As a result, an operating mode can be achieved which is selected immediately after the system has been started, i.e. in the above-mentioned embodiments before the first or second operating mode. The fourth operating mode enables the pressure in the cryogenic container to be reduced to the working pressure, taking the hold time into account.

In the fourth operating mode, it is also preferred if fluid is only withdrawn from the cryocontainer in the gas phase, since this allows the working pressure to be reached as quickly as possible. However, it can also be provided that the fluid is withdrawn from one of the cryocontainers in the gas phase and from the other cryocontainer in the liquid phase, for example if this helps the hold time to converge more quickly.

On the one hand, the control unit could regulate the mass flows according to a prescribed scheme, for example control the said on / off valve after a predetermined time, whereby the first operating mode can be achieved. However, the control unit preferably comprises a computing unit which is designed to record the current hold time of the first and / or to calculate the second cryocontainer and to control the mass flows based on the calculated hold time. This can be done, for example, by measuring a current fill level and / or a current pressure in the cryocontainer in order to determine the current hold time therefrom. A calculated hold time has the advantage that the mass flows can be controlled more precisely and an improved hold time of the overall system can thereby also be achieved.

Furthermore, the control unit can be designed to determine the current hold time of the first and / or the second cryocontainer from precalculated values or from values measured during a reference measurement. For this purpose, for example, the removal rate of the fluid from the two cryocontainers can be measured during the removal or simply an operating time of the system can be used.

The system according to the invention can be implemented in a particularly simple manner in that the system comprises a first valve in the first extraction line and a second valve in the second extraction line, and the control unit is designed to control the valves in order to set the first and second mass flow rates. This enables a particularly simple construction of the system and, in particular, also enables existing systems to be retrofitted.

In the embodiments mentioned, it is preferred if the system comprises a measuring device which is designed to measure a current volume of the fluid and / or a current working pressure of the fluid in the first cryocontainer and / or in the second cryocontainer and to send it to the control unit. In this way, the hold time of the two cryocontainers can be determined particularly precisely.

Furthermore, the container volumes can preferably be stored in a database that can be queried by the control unit. This can be advantageous, for example, if the hold time is calculated immediately. In some embodiments, however, it is not necessary to store the container volumes, for example if reference values of the hold time are available.

Advantageous and non-limiting embodiments of the invention are explained in more detail below with reference to the drawings.

FIG. 1 shows a motor vehicle on which the system according to the invention is mounted.

FIG. 2 shows a diagram in which the hold time is plotted in relation to a current container fill level of two different cryogenic containers. FIG. 1 shows a motor vehicle 1 with a support frame 2 and two axles 3, 4. A cryocontainer 7, 8 is mounted on each side 5, 6 of the support frame 2 between the axles 3, 4. The cryogenic containers 7, 8 each store fluid, for example liquefied natural gas, which is also known to those skilled in the art as LNG (“Liquid Natural Gas”). The fluid is present in the cryogenic containers 7, 8 both in liquid form and in the gaseous state. If the cryocontainers 7, 8 are used in connection with a motor vehicle 1, the stored fluid can serve, for example, as fuel for an engine of the motor vehicle 1. In other embodiments, however, the cryocontainers 7, 8 could also be provided in other areas of use.

In the present system 1, the first cryocontainer 7 has a container volume VI which is larger than a container volume V2 of the second cryocontainer 8. Such configurations can be useful, for example, if the two sides 5, 6 of the motor vehicle 1 have a different amount of installation space Available.

If the system 1 is in operation, the pressure in the cryogenic containers 7, 8 is between 6 and 8 bar, for example. This pressure can be regulated, for example, by withdrawing fluid or by a heat exchanger protruding into the respective cryocontainer. However, as soon as the system 1 is no longer in operation, i.e. is switched off, the pressure in the cryogenic containers 7, 8 increases steadily due to a constant introduction of heat into the cryogenic containers 7, 8.

In order to prevent excessive pressure in the cryogenic containers 7, 8 and thus a breakage thereof, both the first cryogenic container 7 and the second cryogenic container 8 each have a pressure relief valve 9, 10, which is directly or indirectly connected to the respective cryogenic container via a connecting line 7, 8 is connected. The pressure relief valves 9, 10 trigger at a predetermined pressure, which is 16 bar, for example, and in the process emit fluid in a gaseous state. Usually, the two pressure relief valves 9, 10 trigger at the same predetermined pressure, but it can also be provided that they can trigger at different pressures.

The time span from the completion of the removal to a point in time at which the pressure in the cryocontainer 7, 8 reaches a predefined threshold value is referred to as the so-called hold time. It goes without saying that the hold time of the two cryocontainers 7, 8 should be as high as possible, since discharged fluid represents an economic loss and an adverse effect on the environment.

The hold time of the respective cryogenic container 7, 8 is calculated, among other things, from the container volume VI, V2, since a larger container surface area simultaneously a larger one Heat input means. Furthermore, the hold time depends on the current volume of fluid in the cryocontainer 7, 8 and the pressure difference between the trigger pressure of the respective overpressure valve 9, 10 and the operating pressure that prevails in the respective cryocontainer 7, 8 at the time the withdrawal is completed. A predetermined ambient temperature of the cryogenic containers 7, 8 or a predetermined heat input into the cryogenic containers 7, 8 can be assumed for the calculation of the hold time. However, the ratio of the hold time of the two cryogenic containers 7, 8 depends only slightly on the ambient temperature.

FIG. 2 shows a diagram in which the current volume of fluid is plotted in relation to the total container volume on the horizontal axis and the hold time in days is plotted on the vertical axis. HT1 shows the curve of the hold time of a first cryogenic container 7 with a container volume VI of 5001. The curve of the hold time of a cryocontainer 8 with a container volume V2 of 3001 is shown with HT2. It can be seen that the first cryocontainer 7 with the larger container volume VI has a longer hold time than the second cryocontainer 8 with the smaller container volume V2 at the same fill level. In the example shown, a minimum hold time of four days was selected.

In order to remove fluid from the cryocontainers 7, 8 for operation, the system 1 comprises a first extraction line 11, which connects to the first cryocontainer 7 for removing a first mass flow Ml of fluid, and a second extraction line 12, which connects to the second cryocontainer 8 connects to the removal of a second mass flow M2 of fluid.

The system 1 according to the invention comprises means 13 which are designed to form the two mass flows Ml, M2 of different sizes. This is used with the aim of achieving as long as possible after the withdrawal has ended, at which time one of the two pressure relief valves 9, 10 is triggered. This is achieved when the hold time of the two cryocontainers 7, 8 is essentially the same during removal.

The means 13 can be designed, for example, as a control unit 14 which controls the mass flows Ml, M2. This can be achieved, for example, via valves 15, 16, which are each arranged in the extraction lines 11, 12 and are controlled by the control unit 14. In alternative embodiments, however, the means 13 can also only comprise a rigid throttle in one of the extraction lines 11, 12.

In order to determine how large the mass flows should be in the first or second operating mode, the control unit 14 can comprise a computing unit which is designed to process the to calculate the current hold time of the first and / or the second cryocontainer 7, 8. For this purpose, the system 1 can in particular comprise a measuring device which is designed to measure a current volume of the fluid and / or a current working pressure of the fluid in the first cryocontainer 7 and / or in the second cryocontainer 8 and to send it to the control unit 14. Other measured values could also be measured and sent to the control unit 14 in order to control the mass flows Ml, M2 even more efficiently.

Alternatively, the control unit 14 can also control the mass flows Ml, M2 without direct measurements on the fluid in the cryogenic containers 7, 8, for example by controlling the mass flows Ml, M2 according to a predetermined scheme, for example also as a function of the withdrawal time or a expected withdrawal volume of the fluid.

The system 1 can be operated in a first operating mode and / or in a second operating mode by means of the means 13, by means of which the mass flows Ml, M2 can be configured to be of different sizes. In the first operating mode, the mass flows Ml, M2 are set in such a way that the hold time of the two cryogenic containers 7, 8 converges. In the second operating mode, the mass flows Ml, M2 can be set in such a way that the hold time of the two cryogenic containers 7, 8 decreases essentially at the same rate if the hold time of the two cryogenic containers 7, 8 are essentially the same.

In principle, it could be provided that the system 1 is operated only in the first or only in the second operating mode. If the system 1 is operated, for example, only in the first operating mode and if the mass flows Ml, M2 are set to the same size after reaching the same hold time, the hold time will diverge again. In some cases, however, this divergence can be accepted, for example if a simplified control is to be achieved. The system 1 could also be switched back to the first operating mode if the divergence exceeds a threshold value.

If the system 1 is designed to be operated both in the first and in the second operating state, the system 1 is preferably operated first in the first operating state until the hold time of the two cryogenic containers 7, 8 is essentially the same. The system 2 is then operated in the second operating state, so that the hold time of the two cryocontainers 7, 8 decreases essentially at the same rate. Should it happen that the hold time of the two cryocontainers 7, 8 deviates again, for example due to external influences, it is possible to switch back to the first operating mode until the hold Time of the two cryogenic containers 7, 8 is again the same, in order to then switch back to the second operating mode.

As a rule, fluid is withdrawn in the first and / or in the second operating state in the liquid phase in order to achieve the highest possible performance. However, in the first and / or in the second operating state, fluid can also be withdrawn in the gas phase, as a result of which, for example, an economizer function can be achieved. For this purpose, when setting the mass flows M1, M2, the control unit 14 can also make a selection as to whether fluid is to be withdrawn in the gas phase or in the liquid phase in order to achieve a converging or constant hold time.

With regard to FIG. 2, this will now be explained using a practical example. If both cryocontainers 7, 8 are fully filled, fluid would initially only be removed from the 5001 cryocontainer 7 until it has a remaining hold time of 7.2 days, which corresponds to the hold time of the full 3001 cryocontainer 8. In general, however, just enough fluid, preferably in the gas phase, can be withdrawn from the small cryocontainer 8 in the first operating mode in order to keep the pressure therein constant, as a result of which a maximum hold time of this cryocontainer 8 is achieved.

For example, a full cryocontainer 7 with 5001 holds approx. 160 kg of LNG. A 3001 cryocontainer 8, on the other hand, holds approx. 95 kg of LNG. In the first operating mode, the first 65 kg are only removed from the 5001 cryocontainer 7. During this time, just enough is removed from the 3001 cryocontainer 8 to keep the pressure constant.

If the journey is continued after the 65 kg of LNG removed, a switch is made to the second operating mode and the removal rates of the two cryocontainers 7, 8 are adjusted so that both cryocontainers 7, 8 have the same remaining hold time.

The hold time is subsequently shortened by one day when approx. 18.5 kg of LNG are removed from the 5001 cryocontainer 7 and approx. 16.7 kg of LNG are removed from the 3001 cryocontainer 8. Thus, while maintaining this withdrawal ratio, the 5001 cryocontainer 7 can be operated up to a residual amount of approx. 34 kg LNG (level 13%) and the 3001 cryocontainer 8 up to a residual amount of 42 kg (level 37%). The minimum hold time of four days is reached at these levels.

In total, this results in a usable LNG content of 160 kg - 34 kg = 126 kg for the 5001 cryocontainer 7. For the 3001 cryocontainer 8 this results in a usable LNG content of 95 kg - 42 kg = 53 kg. Overall, the system 1 thus has a usable LNG content of 126 kg + 53 kg = 179 kg. Without an adaptation of the mass flows Ml, M2, only twice 53 kg = 106 kg can be used for the remaining hold time of four days, because each additional mass removed reduces the hold time of the smaller cryocontainer 8 to below four days.

A further increase in the usable contents of the cryocontainer can be achieved if a third operating state is also provided. Here, the smaller cryocontainer 8 can be lowered to a lower pressure in order to achieve a hold time of four days again through the greater pressure interval thus created. This is possible if, towards the end of the planned journey, the motor is supplied with lower pressures in partial load operation from the smaller cryocontainer 8. To this end, it is necessary to remove either from one or the other cryocontainer 7, 8, since a simultaneous removal would lead to a pressure equalization between the cryocontainers 7, 8. In order to regulate from which cryocontainer 7, 8 fluid is withdrawn, a route profile can be used, which can be read, for example, from a map recorded in advance.

If, for example, the pressure of the 3001 cryocontainer is reduced from 8 bar to 6 bar in the third operating mode, the remaining mass for 4 days of hold time is reduced by 16 kg from 42 kg to 26 kg and the total usable mass increases from 179 kg to 195 kg .

The third operating mode can either be controlled by the aforementioned control unit 14 or by a separate control unit which can be connected to the aforementioned control unit 14. In particular, heat exchangers which protrude into the respective cryocontainer 7, 8 can be activated to adjust the pressure.

A fourth operating mode could also be provided, which is selected, for example, as the start mode when the pressure in one or in both cryogenic containers 7, 8 is above a desired working pressure. In the prior art, as much fluid as possible is withdrawn from both cryocontainers 7, 8 for this purpose, so that the working pressure is reached as quickly as possible. In the present fourth operating mode, the mass flows Ml, M2 can be designed to be of different sizes in this fourth operating mode, on the one hand to reach the working pressure quickly, but on the other hand also to achieve a converging or constant hold time. In the fourth operating mode, fluid is usually withdrawn in the gas phase. However, fluid could also be withdrawn in the liquid phase if this helps to achieve a converging or constant hold time.

In further embodiments, the cryocontainers 7, 8 can also have an equally large volume VI, V2. The setting of different mass flows Ml, M2 can then be advantageous if the fill level of the two cryocontainers is different, since this results in a different hold time of the two cryocontainers 7, 8. In embodiments with cryogenic containers 7, 8 of different sizes, no second operating mode is usually provided, ie the second operating mode is only provided in some embodiments if the cryogenic containers have container volumes VI, V2 of different sizes.

Claims

Expectations:

1. System (1) for providing a fluid, comprising at least a first and a second cryocontainer (7, 8) for storing the fluid, the system (1) having a first extraction line (11) which is connected to the first cryocontainer (7) for removal of a first mass flow (Ml) of fluid, and comprises a second removal line (12) which connects to the second cryocontainer (8) for removal of a second mass flow (M2) of fluid, characterized in that the system (1) Means (13) which are designed to form the two mass flows (Ml, M2) of different sizes so that a hold time of the two cryocontainers (7, 8) converges during removal in a first operating mode and / or in a second operating mode the hold time of the two cryocontainers (7, 8) decreases essentially at the same rate when the hold time of the two cryocontainers (7, 8) are essentially the same, the hold time being the period of time from completion of the removal e is up to the point in time at which the pressure in the cryocontainer (7, 8) reaches a predefined threshold value.

2. System according to claim 1, wherein the first cryocontainer (7) has a container volume (VI) which is greater than a container volume (V2) of the second cryocontainer (8).

3. System according to claim 1, wherein the first cryocontainer (7) has a container volume (VI) which is the same size as a container volume (V2) of the second cryocontainer (8), the extraction lines (11, 12) having a different flow resistance .

4. System (1) according to one of claims 1 to 3, wherein the means (13) comprise a control unit (14) which is designed to regulate the first and / or the second mass flow (Ml, M2).

5. System (1) according to claim 4, wherein the control unit (14) is designed to only withdraw fluid from the first cryocontainer (7) in the first operating mode until the hold time of the first cryocontainer (7) is essentially the hold time of the second cryocontainer (8).

6. System (1) according to claim 4 or 5, wherein the control unit (14) is designed to in the first operating mode essentially only such an amount of fluid from the second It can be seen from the cryocontainer (8) that the hold time of the second cryocontainer (8) remains constant, and the remaining fluid can be removed from the first cryocontainer (7).

7. System (1) according to claim 6, wherein the system (1) is designed to remove fluid from the second cryocontainer (8) only in the gaseous state in the first operating mode.

8. System (1) according to one of claims 4 to 7, wherein the control unit (14) is designed to switch from the first to the second operating mode after the same hold time of the two cryogenic containers (7, 8) has been reached for the first time.

9. System (1) according to one of claims 4 to 8, wherein the control unit (14) is designed to, when the fluid is removed from the first and / or the second cryocontainer (7, 8) between a removal of the fluid in a To choose liquid phase and / or a withdrawal of the fluid in gas phase.

10. System (1) according to one of claims 4 to 9, wherein the system (1) can be placed in a third operating state, and wherein the system (1) is designed in the third operating mode to have a different working pressure in the two during operation Form cryocontainer (7, 8) and remove fluid only from the first or only from the second cryocontainer (7, 8).

11. System (1) according to one of claims 4 to 10, wherein the system (1) can be placed in a fourth operating state when the pressure in both cryogenic containers (7, 8) is between a working pressure and said threshold value, and wherein the System (1) is designed in the fourth operating mode to select the two mass flows (Ml, M2) in such a way that the pressure in both cryogenic containers (7, 8) is lowered to the working pressure and the hold time of the two cryogenic containers (7, 8) converges on extraction and / or increases at substantially the same rate.

12. System (1) according to claim 11, wherein fluid in the fourth operating mode is removed from the cryogenic containers (7, 8) only in the gas phase.

13. System (1) according to one of claims 4 to 12, wherein the control unit (14) comprises a computing unit which is designed to calculate the current hold time of the first and / or the second cryocontainer (7, 8).

14. System (1) according to one of claims 4 to 13, wherein the system (1) has a first valve (15) in the first extraction line (11) and a second valve (16) in the second Sampling line (12), and wherein the control unit (14) is designed to control the valves (15, 16) in order to set the first and the second mass flow (Ml, M2).

15. System (1) according to one of claims 4 to 14, wherein the system (1) comprises a measuring device which is designed to measure a current fill level of the fluid and / or a current working pressure of the fluid in the first cryocontainer (7) and / or to measure in the second cryocontainer (8) and to send it to the control unit (14).