Method and device for liquefying gases

Abstract

A method for liquefying gases, in which the gas to be liquefied is brought into thermal contact with cryogenic, liquid, gaseous, or supercritical hydrogen in at least a first heat exchanger and thereby cooled, is characterized according to the invention in that, after passing through the first heat exchanger, the hydrogen is returned to a preheating exchanger arranged upstream of the first heat exchanger and there heats the hydrogen used for cooling to a temperature at which freezing of the gas to be liquefied in the first heat exchanger is prevented. Subsequently, the hydrogen is fed back to the first heat exchanger to be brought into thermal contact with the gas to be liquefied.

Description

[0001] The invention relates to a method for liquefying a gas, in which the gas is brought into thermal contact with a heat transfer medium in at least a first heat exchanger and thereby liquefied. The invention further relates to a corresponding device.

[0002] Gas liquefaction is used, for example, in cryogenic air separation processes to produce highly purified atmospheric gases such as nitrogen, oxygen, or argon. In this process, ambient air is drawn in, cleaned, and compressed to a pressure of, for example, 6 bar. The compressed air is then cooled to ambient temperature through thermal contact with a heat transfer medium, such as water, and subsequently to a temperature of -170 °C to -193 °C through thermal contact with the generated atmospheric gas components. Further cooling is achieved through expansion, causing the compressed air to partially liquefy before being separated into its main components, nitrogen and oxygen, in a separation column. Argon and, if desired, other noble gases are produced in a similar manner in subsequent process steps.For further storage or use, the gas components produced in gaseous form, especially nitrogen, can be liquefied by thermal contact with a heat transfer medium. The produced gas components are fed into a pipeline network or transported to their point of use in tank trucks.

[0003] An alternative method for separating air is, for example, the pressure swing adsorption (PSA) or VPSA process. However, the air gas component produced in pure form in this process, such as nitrogen or oxygen, is usually at ambient temperature and often has to be liquefied after its production, requiring considerable energy expenditure, for storage or transport purposes.

[0004] Liquid hydrogen (LH₂) is expected to play an increasingly important role in energy production in the future. It is produced, for example, in countries with a high potential for renewable energy sources such as solar or wind power, through electrolysis and transported to Europe in its cryogenically liquefied state. The boiling point of liquid hydrogen (at 1013 mbar) is -253°C; consequently, the cryogenic content of liquid hydrogen could be used, in particular, for the liquefaction of atmospheric gases. However, a problem arises because this temperature of hydrogen is also below the freezing point of most gases, meaning that when liquefying using the cryogenic properties of hydrogen, there is always a risk of ice formation in the process plants. While this could be counteracted, for example, with electric heating devices, this would drastically reduce the economic viability of the process.

[0005] It is also known to circulate a non-freezing heat transfer medium in an intermediate circuit, which facilitates the transfer of heat between two media at different temperatures. However, a disadvantage of this method is that the intermediate circuit leads to increased equipment costs and, due to the need for a pump or fan in the circuit, to additional energy costs, meaning that economic viability is not always guaranteed.

[0006] The object of the present invention is therefore to create an economical way to liquefy gases, in particular atmospheric gases, using cryogenically liquefied hydrogen.

[0007] This problem is solved by a method with the features of claim 1 and by a device with the features of claim 5. Advantageous embodiments of the invention are specified in the dependent claims.

[0008] A process of the type and purpose mentioned above is therefore characterized by the fact that cryogenically liquefied or cold gaseous or supercritical hydrogen is used as the heat transfer medium, which, as chilled hydrogen, passes through a preheating exchanger before passing through the first heat exchanger and, after passing through the first heat exchanger, is returned at least once in a partial stream to the preheating exchanger in order to heat the chilled hydrogen in the preheating exchanger to a temperature before it is fed to the first heat exchanger, which is chosen such that the gas to be liquefied is liquefied in the first heat exchanger but does not freeze.

[0009] The invention proposes using the coldness of hydrogen, which is present in cryogenically liquefied, gaseous, or supercritical form from a source, for example a storage tank or pipeline, at a temperature below the freezing point of the gas to be liquefied (hereinafter also referred to as "cold hydrogen"), in the first heat exchanger for the liquefaction of a gas, for example a gas produced in a cryogenic air separation process or a PSA process. For example, the gas to be liquefied is N₂, O₂, argon or another noble gas, carbon dioxide or a mixture of several of these gases, or air.

[0010] The temperature chosen so that the gas to be liquefied is liquefied in the first heat exchanger without freezing is a temperature value which, taking into account the thermal resistance of the first heat exchanger, is at least sufficient to ensure that the gas to be liquefied never falls below its freezing point within the first heat exchanger. The minimum temperature of the chilled hydrogen supplied to the first heat exchanger will generally be at or just below the freezing point of the gas to be liquefied, for example, by 0.1 K to 5 K; the maximum temperature will be sufficiently below the boiling point of the gas to be liquefied to guarantee its liquefaction in the first heat exchanger.

[0011] According to the invention, the hydrogen heated during heat exchange with the gas to be liquefied at a first heat exchanger surface in the first heat exchanger is used to heat the chilled hydrogen in the preheating exchanger to a temperature at which freezing of the gas to be liquefied is prevented. The hydrogen supplied from the first heat exchanger is either at least partially mixed with the chilled hydrogen, or an indirect heat transfer takes place in the preheating exchanger, whereby the hydrogen, cooled during the heating of the chilled hydrogen, can then be used again to cool the gas to be liquefied at at least a second heat exchanger surface in the first heat exchanger. The invention thus eliminates the need for an intermediate circuit or heating devices, resulting in high efficiency.

[0012] Depending on the respective thermodynamic conditions, it may prove useful or necessary to feed the hydrogen through the first heat exchanger and / or the preheating exchanger several times in succession in loops, with the hydrogen in each loop contributing to the cooling of the gas to be liquefied or to the heating of the chilled hydrogen at a separate heat exchanger surface.

[0013] Furthermore, within the scope of the invention, it is also possible to divide the function of the first heat exchanger between two devices connected in series. The gas to be liquefied is preferably guided in counterflow to the hydrogen, i.e., first through the heat exchanger located further downstream (in the direction of hydrogen flow), where it is brought to a temperature close to its boiling point by thermal contact with the hydrogen supplied from the front heat exchanger, and then through the front heat exchanger, where it is liquefied upon thermal contact with the hydrogen and brought to a predetermined temperature below its boiling point but above its freezing point; in the case of nitrogen, for example, to a temperature between 65 K and 75 K.

[0014] In a preferred embodiment of the invention, a partial stream of hydrogen is recycled to the preheating exchanger after passing through the first heat exchanger and mixed there with the chilled hydrogen. In this case, the "preheating exchanger" is therefore a mixer. By temperature-controlled regulation of the flow rate of the recycled partial stream, the temperature of the chilled hydrogen at the inlet to the first heat exchanger can be precisely adjusted. The hydrogen partial stream that is not recycled is used, for example, to precool the gas to be liquefied.

[0015] An alternative embodiment of the process according to the invention provides for at least a partial flow of hydrogen, after its initial passage through the first heat exchanger and the preheating exchanger, to be passed through the first heat exchanger at least once more, where it is again subjected to indirect heat exchange with the gas to be liquefied at a second and, if necessary, further heat exchanger surface. The advantage of this embodiment is, in particular, that no pump or similar device is required for the return of the hydrogen flow or partial flow.

[0016] After a second pass through the first heat exchanger, at least a portion of the hydrogen flow can then be routed through a second heat exchanger surface in the preheating exchanger and used there again to heat the chilled hydrogen. The cooled hydrogen can then be brought back into thermal contact with the gas to be liquefied at a third heat exchanger surface in the first heat exchanger. In this way, the hydrogen, or at least a portion of it, can traverse multiple loops, in each of which it is successively brought into thermal contact with the gas to be liquefied in the first heat exchanger and with the chilled hydrogen in the preheating exchanger at separate heat exchanger surfaces, before being returned to the first heat exchanger.It is particularly advantageous to be able to regulate the total flow rate of hydrogen and / or the flow rate of a partial flow recycled in a loop, in order, for example, to be able to precisely adjust the temperature of the chilled hydrogen supplied to the first heat exchanger.

[0017] In both of the aforementioned variants, a loop system can also be implemented in such a way that a partial flow of the hydrogen leaving the first heat exchanger is returned directly to the first heat exchanger for the purpose of cooling the gas to be liquefied, whereby its flow rate is regulated depending on a measured temperature, for example that of the chilled hydrogen supplied to the first heat exchanger.

[0018] For example, to liquefy nitrogen or oxygen present at ambient temperature (300K) with hydrogen present at a temperature of 25K to 35K, it proves advantageous that at least the largest part of the hydrogen supplied to the first heat exchanger is passed through the first heat exchanger and the preheating exchanger in at least three successive loops as described.

[0019] A further advantageous embodiment of the invention provides that, after passing through the first heat exchanger, the hydrogen passes through a second heat exchanger (precooler) to cool the gas to be liquefied to a temperature preferably above its boiling point. In this case, the gas to be liquefied enters the first heat exchanger at a lower temperature than its initial temperature, but still generally in a gaseous state.

[0020] The inventive method is preferably used in the liquefaction of a gas obtained in an air separation process, in particular in a cryogenic air separation process, such as the Linde process or in pressure swing adsorption (PSA or VPSA) processes.

[0021] The object of the invention is also solved by a device with the features of claim 5.

[0022] An inventive device for liquefying gases has a storage tank for cryogenically liquefied hydrogen, to which a chilled hydrogen supply line is connected, in which, if necessary,a conveying device may be installed, and is equipped with a first heat exchanger, which has a supply line for the gas to be liquefied, an outlet line for the liquefied gas, at least a first hydrogen supply line and at least a hydrogen outlet corresponding to the first hydrogen supply line and a first heat exchanger surface corresponding to these for thermal contact with the gas to be liquefied, as well as with a preheating exchanger, which has a cold hydrogen supply line, a cold hydrogen outlet and a first hydrogen supply line connected downstream to the first hydrogen outlet of the first heat exchanger for heating the hydrogen (cold hydrogen) supplied from the storage tank in the cold hydrogen supply line in the preheating exchanger.

[0023] "Corresponding" here means that the hydrogen supplied via the first hydrogen inlet completely passes through the first heat exchanger surface, is brought into indirect thermal contact with the gas to be liquefied, and is then completely discharged from the first heat exchanger via the first hydrogen outlet. If n (where n is a non-zero natural number) heat exchanger surfaces are present in the first heat exchanger, "corresponding" means that the hydrogen supplied via the nth hydrogen inlet completely passes through the nth heat exchanger surface, is brought into thermal contact with the gas to be liquefied, and is completely discharged from the first heat exchanger via the nth hydrogen outlet; the same principle applies analogously to the conditions in the preheating exchanger, provided it has one or more heat exchanger surfaces.

[0024] The device according to the invention thus provides for at least partial recirculation of the hydrogen heated in the first heat exchanger to the preheating exchanger for heating the cold hydrogen passed through it, with the aim of heating the cold hydrogen to a temperature before its supply to the first heat exchanger, which is selected such that the gas to be liquefied is liquefied in the first heat exchanger, but does not freeze.

[0025] Hydrogen is typically stored in a storage tank in a cryogenically liquefied state, meaning it has a temperature lower than the boiling point of most other gases. When the liquid hydrogen is pumped from the storage tank, it is subsequently in a liquid, gaseous, or supercritical state, but still at a temperature lower than the boiling point of the gas being liquefied. The hydrogen drawn from the storage tank and entering the preheating exchanger for the first time (referred to here as "cold hydrogen") is therefore in a cryogenically liquefied, cold gaseous, or cold supercritical state.The term "cold" gaseous or supercritical state refers here to gaseous or supercritical hydrogen that exists at a temperature above its boiling point at ambient pressure, but below the boiling point of the gas to be liquefied, for example, at a temperature between 25 K and 90 K. The hydrogen heats up by absorbing heat from the gas to be liquefied; if hydrogen is used below its critical pressure (13 bar), it evaporates; above its critical point, it heats up without a phase change. Liquid hydrogen is particularly preferred, as it is intended to be converted into the gaseous or supercritical state anyway for further transport, processing, or combustion; according to the invention, the energy required for this conversion is at least partially provided by the gas to be liquefied.

[0026] An advantageous first embodiment of a device according to the invention provides that the first hydrogen supply line of the preheating exchanger opens into the cold hydrogen outlet of the preheating exchanger, and that a device for controlling the return of a partial flow of hydrogen to the hydrogen supply line of the preheating exchanger is provided at the first hydrogen outlet of the first heat exchanger. In this case, the "preheating exchanger" is thus a mixer in which the cold hydrogen flow is mixed with a partial flow of the hydrogen heated in the first heat exchanger. The temperature of the hydrogen discharged via the cold hydrogen outlet and subsequently supplied to the first heat exchanger results from the mixing ratio and the temperatures of the mixed hydrogen flows.In this particular configuration, it is also advantageous to provide a further heat exchanger or precooler (here called "second heat exchanger") downstream of the first heat exchanger (viewed in the direction of hydrogen flow), which precools the gas to be liquefied before it is fed to the first heat exchanger.

[0027] In another advantageous embodiment of a device according to the invention, the hydrogen passes through a plurality of heat exchanger surfaces, both in the first heat exchanger and in the preheating exchanger, and is brought into indirect thermal contact with the gas to be liquefied or with the chilled hydrogen; thus, no mixing takes place.If the preheating exchanger has – in addition to the cold hydrogen inlet and outlet – n (where n is a non-zero natural number) hydrogen inlets and n corresponding heat exchanger surfaces and hydrogen outlets, and the first heat exchanger has n+1 hydrogen inlets and n+1 corresponding heat exchanger surfaces and hydrogen outlets, then the cold hydrogen outlet of the preheating exchanger is connected to the first hydrogen inlet of the first heat exchanger, and the nth hydrogen outlet of the preheating exchanger is connected to the (n+1)th hydrogen inlet of the first heat exchanger, and the nth hydrogen outlet of the first heat exchanger is connected to the nth hydrogen inlet of the preheating exchanger. The (n+1)th hydrogen outlet of the first heat exchanger does not return to the preheating exchanger.

[0028] After exiting the first heat exchanger and / or the preheating exchanger at an nth hydrogen outlet (or at several of them), a partial flow of hydrogen can be extracted and discharged in this configuration. The division into the partial flows of recycled hydrogen and extracted hydrogen is preferably achieved by means of a control system based on measured parameters, such as the temperature of the chilled hydrogen upon entering the first heat exchanger.

[0029] A particularly advantageous further embodiment of the invention is characterized by a second heat exchanger, which – viewed in the direction of hydrogen flow – is arranged downstream of the first heat exchanger. This second heat exchanger has an inlet for the gas to be liquefied and an outlet for the gas to be liquefied, as well as a hydrogen inlet and a hydrogen outlet. The second heat exchanger serves in particular for pre-cooling the gas to be liquefied.

[0030] A third heat exchanger, if present, installed downstream of the first or first two heat exchangers, preferably serves to preheat the hydrogen leaving the upstream heat exchangers. The heat required for this can be taken, for example, from a process medium, such as a cooling water stream.

[0031] Preferably, the device according to the invention is equipped with a control unit by means of which at least a partial flow of a hydrogen stream passing through the first heat exchanger can be regulated. The regulation is carried out according to a predefined program and / or depending on a measured parameter, such as the temperature of the liquefied gas and / or the hydrogen at a point upstream or downstream of the first heat exchanger. Such a control unit can, in particular, regulate the flow of all hydrogen passed through the chilled hydrogen supply, or a partial flow that passes through one or more of the loops described above. The control, in particular, enables the full functionality of the device according to the invention even with fluctuating flow rates and / or temperatures of the gas to be liquefied.

[0032] The method and apparatus according to the invention are particularly suitable for the liquefaction of gases that are produced in the course of a process for separating air, for example for gases that are to be liquefied in a process for cryogenic air separation, or gases that are to be liquefied following air separation by means of PSA or VPSA.

[0033] The hydrogen leaving the first and / or second heat exchanger and / or the hydrogen evaporating in the storage tank due to natural heat input can be used, in particular, for power generation, for example in a downstream fuel cell. The electricity generated in the power generation unit can be used, for example, in an air separation unit where the gas to be liquefied is produced, or to operate power-consuming components, such as a compressor used to compress the air.

[0034] Furthermore, the remaining cooling capacity of the hydrogen and / or the generated liquid nitrogen stream can also be used to cool another gas stream generated in an air separation unit, for example an oxygen stream.

[0035] An embodiment of the invention will be explained in more detail with reference to the drawing. The schematic views show: Fig. 1: A device according to the invention in a first embodiment. Fig. 2: A device according to the invention in a second embodiment.

[0036] The in Fig. 1The device 1 shown according to the invention comprises a first heat exchanger 2, a second heat exchanger 3, and a preheating exchanger 4. The second heat exchanger 3 has a supply line 5 for a gas to be liquefied, nitrogen in the exemplary embodiment, and an outlet line 6 for the gas to be liquefied. The outlet line 6 is connected to a supply line 7 for the gas to be liquefied of the first heat exchanger 2. Furthermore, the first heat exchanger 2 has an outlet line 8 for the liquefied gas.

[0037] A chilled hydrogen supply line 11, containing a pump 12 for conveying the hydrogen, leads from a storage tank 10, in which hydrogen is stored in a cryogenically liquefied state, to the preheating exchanger 4. The hydrogen supplied there exits the preheating exchanger 4 at a chilled hydrogen outlet 13. The chilled hydrogen outlet 13 is connected to a first hydrogen supply line 15a of the first heat exchanger 2. The hydrogen then passes through a first heat exchanger surface 16a in the first heat exchanger 2, where it comes into indirect thermal contact with the gas to be liquefied, which is supplied via the feed line 7, and exits the first heat exchanger 2 via a first hydrogen outlet 17a.

[0038] At a junction with a three-way valve 18, the hydrogen outlet 17a enters a hydrogen line 20. The hydrogen line 20 passes through a heat exchanger surface 21 of the second heat exchanger 3, where the hydrogen carried through the hydrogen line 20 is brought into indirect thermal contact with the gas to be liquefied, which is supplied via the feed line 5.

[0039] Downstream of the second heat exchanger 3, an optional third heat exchanger 22 can be arranged in the hydrogen line 20, which serves to utilize the residual cooling effect of the hydrogen. From there, the hydrogen line 20 leads to a consumer 23, which is not specified in detail here and could be, for example, a power generation facility, a gas line, or a facility for filling gaseous hydrogen.

[0040] Furthermore, a flow connection exists at the three-way valve 18, which returns a partial flow of hydrogen in a first loop 25 to the preheating exchanger 4. The hydrogen returned in the loop 25 flows into the preheating exchanger 4 via a first hydrogen supply line 26a, passes through a first heat exchanger surface 27a, where it comes into indirect thermal contact with the hydrogen supplied from the storage tank 10 via the cold hydrogen supply line 11, and leaves the second preheating exchanger 4 via a first hydrogen outlet 28a.

[0041] The first hydrogen outlet 28a is connected to a second hydrogen supply line 15b of the first heat exchanger 2. The hydrogen then passes through a second heat exchanger surface 16b in the first heat exchanger 2, where it comes into indirect thermal contact with the gas to be liquefied, which is supplied via the feed line 7, and exits the first heat exchanger 2 via a second hydrogen outlet 17b. This outlet is connected via a second loop 29 to a second hydrogen supply line 26b of the preheating exchanger 4. The hydrogen flows into the preheating exchanger 4 via this line, passes through a second heat exchanger surface 27b of the second heat exchanger 3, where it comes into indirect thermal contact with the hydrogen supplied from the storage tank 10 via the chilled hydrogen supply line 11, and exits the preheating exchanger 4 via a second hydrogen outlet 28b.

[0042] The hydrogen outlet 28b is connected to a third hydrogen supply line 15c of the first heat exchanger 2. Within the first heat exchanger 2, the hydrogen passes through a third heat exchanger surface 16c, where it again comes into indirect thermal contact with the gas to be liquefied, which is supplied via the feed line 7. It then exits the first heat exchanger 2 via a third hydrogen outlet 17c, which leads into the hydrogen line 20. Upon thermal contact with the hydrogen at the heat exchanger surfaces 16a, 16b, and 16c, the gas supplied via the feed line 7 is liquefied and discharged via the outlet line 8.

[0043] Furthermore, the hydrogen from the hydrogen outlet 17c can subsequently be fed back into the preheating exchanger 4 and then into the first heat exchanger 2 in at least one further loop in the same manner as described above, although this is not shown here for the sake of clarity. The total number of loops 25, 29 traversed by the hydrogen in the heat exchangers 2, 4 results from the respective thermodynamic conditions. For example, to liquefy nitrogen at ambient temperature (300 K) and hydrogen that is stored in the storage tank at 20 K but has a temperature of, for example, 33 K after passing through pump 12, four loops 25, 29 are sufficient; that is, after passing through the first heat exchanger 2 for the first time, the hydrogen is passed through the preheating exchanger 4 and the first heat exchanger 2 four more times to liquefy the nitrogen.Depending on the properties of the gas to be liquefied, however, fewer or more loops may be used, for example only one or two, or up to ten loops or more.

[0044] By means of a control unit 30, which, for example, measures the temperature of the liquefied gas in the cold hydrogen outlet 13, a variable partial flow of hydrogen from the hydrogen outlet 17c is recirculated via loops 25 and 29 according to a predefined program to pass through the preheating exchanger 4 and the first heat exchanger 3. The non-recirculated partial flow is discharged via the hydrogen line 20 and, together with the hydrogen flowing in from the hydrogen outlet 17c, is used in the second heat exchanger 3 by thermal contact at the heat exchanger surface 21 to pre-cool the gas to be liquefied, which is supplied via the feed line 5.

[0045] Any residual cooling effect of the hydrogen can then be used in the third heat exchanger 22 to cool another medium, for example, cooling water. After passing through the third heat exchanger 22, the hydrogen is finally supplied to the consumer 23.

[0046] In the device 1, the gas to be liquefied is repeatedly brought into thermal contact with the hydrogen taken from the storage tank 10 in the heat exchangers 2 and 3, thereby cooling it to a temperature below its boiling point, i.e., liquefying it. The gas to be liquefied preferably passes through the first heat exchanger 2 in counterflow to the hydrogen (as shown here). In the preheating exchanger 4, the hydrogen taken from the storage tank 10 ("cold hydrogen") is heated by thermal contact with the hydrogen already heated in the first heat exchanger 2 to such an extent that no temperature is reached in the first heat exchanger 2 at which the gas to be liquefied would freeze. The heat exchangers 2, 3, and 4 are all designed as indirect heat exchangers, in which there is no direct contact between the gas to be liquefied and the hydrogen, or the hydrogen from the individual loops 25 and 29.

[0047] The in Fig. 2 The device 31 shown according to the invention has, similarly to the device 1, Fig. 1 The system comprises a first heat exchanger 32, a second heat exchanger 33, and a preheating exchanger 34, the latter being configured as a mixer in this embodiment. The second heat exchanger 33 has a supply line 35 for a gas to be liquefied, nitrogen in this embodiment, and an outlet line 36 for the gas to be liquefied. The outlet line 36 is connected to a supply line 37 for the gas to be liquefied in the first heat exchanger 32. Furthermore, the first heat exchanger 2 has an outlet line 38 for the liquefied gas.

[0048] A chilled hydrogen supply line 41, containing a pump 42 for conveying the hydrogen, leads from a storage tank 40, in which hydrogen is stored in a cryogenically liquefied state, to the mixer or preheating exchanger 34. The hydrogen supplied there exits the preheating exchanger 34 via a chilled hydrogen outlet 43. The chilled hydrogen outlet 43 is connected to a hydrogen supply line 45 of the first heat exchanger 32. The hydrogen then passes through a heat exchanger surface 46 in the first heat exchanger 32, where it comes into indirect thermal contact with the gas to be liquefied, which is supplied via the feed line 37, and exits the first heat exchanger 32 via a hydrogen outlet 47.At the heat exchanger surface 46, the gas to be liquefied is brought into thermal contact with the hydrogen supplied via the cold hydrogen outlet 43 and is thereby cooled to a temperature below its boiling point, i.e., liquefied. The gas to be liquefied passes through the heat exchangers 32, 33 preferably (as shown here) in countercurrent flow to the hydrogen.

[0049] At a branch point with a three-way valve 48, the hydrogen outlet 47 is connected to a hydrogen line 50. The hydrogen line 50 passes through a heat exchanger surface 51 of the second heat exchanger 33, where the hydrogen carried through the hydrogen line 50 comes into indirect thermal contact with the gas to be liquefied, which is supplied via the feed line 35. The hydrogen in the hydrogen line 50 is then supplied to a consumer 52, possibly after passing through a third heat exchanger (not shown here) used to cool another medium.

[0050] By means of a control unit 53, which, for example, measures the temperature of the liquefied gas in the chilled hydrogen outlet 43, a variable partial flow is drawn off from the hydrogen outlet 47 according to a predefined program and returned to the preheating exchanger 34 via a return line 54 by means of a pump 55. At a mixing point 56, the return line 54 opens into the chilled hydrogen supply line 41. By mixing the drawn-off partial flow into the chilled hydrogen supplied to the first heat exchanger 32 via the chilled hydrogen supply line 43, the chilled hydrogen is brought to a temperature at which no gas to be liquefied freezes at any point in the first heat exchanger.

[0051] Devices 1, 31 are particularly suitable for liquefying atmospheric gases, such as nitrogen, oxygen, or argon, using the cooling capacity of liquid hydrogen. The hydrogen, which evaporates and is heated upon thermal contact with the gas to be liquefied, is then fed into the consumer 26, 52 for its intended use. Reference symbol list

[0052] 1 device 29 Ribbon 2 First heat exchanger 30 control 3 Second heat exchanger 31 device 4 Preheater exchanger 32 First heat exchanger 5 Supply line 33 Second heat exchanger 6 Exit line 34 Preheater exchanger 7 Supply line 35 Supply line 8 Exit line 36 Exit line 9 - 37 Supply line 10 Storage tank 38 Exit line 11 Cold hydrogen supply line 39 - 12 pump 40 Storage tank 13 Cold hydrogen detoxification 41 Cold hydrogen supply line 14 - 42 pump 15a, b, c Hydrogen supply line 43 Cold hydrogen detoxification 16a, b, c Heat exchanger surface 44 - 17a, b, c Hydrogen detoxification 45 Hydrogen supply line 18 Three-way valve 46 Heat exchanger surface 19 - 47 Hydrogen detoxification 20 Hydrogen pipeline 48 Three-way valve 21 Heat exchanger surface 49 - 22 Third heat exchanger 50 Hydrogen pipeline 23 consumer 51 Heat exchanger surface 24 - 52 consumer 25 Ribbon 53 control 26a, b Hydrogen supply line 54 Return line 27a, b Heat exchanger surface 55 pump 28a, b Hydrogen detoxification 56 Mixing point

Claims

1. A method for liquefying a gas, in which gas is brought into thermal contact with a heat transfer medium in at least one first heat exchanger (2, 32) and is thereby liquefied, characterized by that cryogenically liquefied cold gaseous or supercritical hydrogen is used as the heat transfer medium, which passes through a preheat exchanger (4, 34) as cold hydrogen before passing through the first heat exchanger (2, 32) and which, after passing through the first heat exchanger (2, 32), is returned at least once in a partial flow to the preheat exchanger (4, 34) in order to heat the cold hydrogen in the preheat exchanger (4, 34) before it is fed to the first heat exchanger (2, 32) to a temperature which is selected such that the gas to be liquefied is liquefied in the first heat exchanger but does not freeze.

2. Method according to claim 1, characterized in thatAt least a partial stream of the hydrogen, after passing through the first heat exchanger (32), is mixed in the preheat exchanger (34) with the cold hydrogen fed to the first heat exchanger. The method according to claim 1, characterized in that the hydrogen, after passing through the first heat exchanger (2) and the preheat exchanger (4) for the first time, is returned at least once again to the first heat exchanger (2) in at least a partial flow for the purpose of cooling the gas to be liquefied.

3. Method according to one of the preceding claims, characterized in that the hydrogen, after passing through the first heat exchanger (2, 32), passes through a second heat exchanger (2, 32) for pre-cooling the gas to be liquefied.

4. Method according to one of the preceding claims, characterized by the use for liquefying a gas produced during the separation of air. 5.A device for liquefying gases, comprising a storage tank (10, 40) for cryogenically liquefied hydrogen, comprising a cold hydrogen supply line (11, 41) fluidly connected to the storage tank (10, 40), comprising a first heat exchanger (2, 32) which has a supply line (7, 37) for the gas to be liquefied and an outlet line (8, 38) for the liquefied gas, as well as at least one first hydrogen supply line (15a, 45), a hydrogen outlet line (17a, 47) corresponding to the first hydrogen supply line (15a, 45) and a first heat exchanger surface (16a, 46) corresponding to these, and comprising a preheat exchanger (4, 34) which has a cold hydrogen supply line (11, 41) and a cold hydrogen outlet line (13, 43) as well as a first hydrogen outlet line (17a, 47) of the first heat exchanger (2, 32) has a hydrogen supply line (26a, 54) connected downstream thereto for heating the hydrogen supplied from the storage tank (10, 40) in the preheat exchanger (4, 34).

6. Device according to claim 5, characterized in that the hydrogen supply line (54) of the pre-heat exchanger opens into the cold hydrogen outlet (43) of the pre-heat exchanger (34) at a mixing point (56); a device (53) for regulating the return of at least a partial flow of the hydrogen into the hydrogen supply line (54) is provided at the first hydrogen outlet (47), and a pump (55) is arranged in the hydrogen supply line (54) of the pre-heat exchanger (34).

7. Device according to claim 5, characterized in that the preheat exchanger (4) - next to the cold hydrogen supply line (11) and the cold hydrogen outlet line (13) - n Hydrogen supply lines (26a, 26b) and n corresponding hydrogen outlets (28a, 28b) and heat exchanger surfaces (27a, 27b) and the first heat exchanger (2) n+1 Hydrogen supply lines (15a, 15b, 15c) and n+1corresponding heat exchanger surfaces (16a, 16b, 16c) has hydrogen outlets (17a, 17b, 17c), wherein the n -th hydrogen outlet (28a, 28b) of the preheat exchanger (4) to the ( n +1)-th hydrogen supply line (15b, 15c) of the first heat exchanger (2) is connected and the n -th hydrogen outlet (17a, 17b) of the first heat exchanger (2) to the n -th hydrogen supply line (26a, 26b) of the preheat exchanger (4), where n is a natural number other than zero.

8. Device according to one of claims 5 to 7, characterized bya second heat exchanger (3, 33) which - viewed in the direction of flow of the hydrogen - is arranged downstream of the first heat exchanger (2, 32), which second heat exchanger (3, 33) has an inlet (5, 35) for the gas to be liquefied and an outlet (6, 36) for the gas to be liquefied, a hydrogen inlet (20, 50) and a hydrogen outlet, and a heat exchanger surface (21, 51) for thermally contacting the gas to be liquefied, which is to be fed to the first heat exchanger (2, 32), with the hydrogen flowing out of the first heat exchanger (2, 32).

9. Device according to one of claims 5 to 8, characterized by a control device (30, 53) by means of which at least a partial flow of the through the first heat exchanger (2, 32) is controllable.

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