System for producing and liquefying methane

Abstract

The invention relates to a system (10) for producing and liquefying methane, comprising a methane production apparatus (11) for producing methane from hydrogen and carbon dioxide, comprising a methane liquefaction apparatus (17) for liquefying the methane, wherein the methane produced by the methane production apparatus (11) is conductable via a first conduit (18) from the methane production apparatus (11) in the direction of the methane liquefaction apparatus (17), comprising a methane storage apparatus (19) for receiving the liquefied methane, wherein the methane liquefied by the methane liquefaction apparatus (17) is conductable via a second conduit (20) from the methane liquefaction apparatus (17) in the direction of the methane storage apparatus (19), comprising at least one flash tank (21a, 21b, 21c) disposed in the second conduit (19) in order to at least partly remove impurities from the liquefied methane, wherein the impurities are conductable out of the respective flash tank (21a, 21b, 21c) via a respective third conduit 5 (22a, 22b, 22c).

Description

[0001] System for the production and liquefaction of methane

[0002] The invention relates to a system for the production and liquefaction of methane.

[0003] Hydrogen plays a crucial role in the decarbonization of the energy sector. In particular, hydrogen can store and transport renewable energies. To transport hydrogen efficiently, for example by ship, it can be liquefied. However, the liquefaction and transport of liquefied hydrogen is very complex.

[0004] Alternatively, for storing and transporting hydrogen produced using renewable energy, it is possible to convert the hydrogen into methane using carbon dioxide and then liquefy the methane for transport. Liquefying methane and transporting liquid methane requires less effort than liquefying hydrogen and transporting liquefied hydrogen. The synthetically produced methane can also be transported in conventional natural gas pipelines and, if necessary, mixed with natural gas.

[0005] The quality of the methane produced from hydrogen and carbon dioxide plays a crucial role in its liquefaction. Methane derived from hydrogen and carbon, also known as Synthetic Natural Gas (SNG), can contain impurities such as hydrogen gas, carbon dioxide, water, and inert gases. Such impurities impair the methane liquefaction process. Therefore, a system for the production and liquefaction of methane is needed that can efficiently produce gaseous methane from hydrogen and carbon dioxide and then liquefy it, particularly while minimizing losses of hydrogen and methane gas.

[0006] Based on this, the present invention aims to create a novel system for the production and liquefaction of methane.

[0007] This problem is solved by a system for the production and liquefaction of methane according to claim 1.

[0008] The system according to the invention for the production and liquefaction of methane comprises a methane production device for the production of methane from hydrogen and carbon dioxide.

[0009] The system according to the invention for the production and liquefaction of methane further comprises a methane liquefaction device for liquefying the produced methane, wherein the methane produced by the methane production device can be conveyed via a first line from the methane production device towards the methane liquefaction device.

[0010] The system according to the invention for the production and liquefaction of methane further comprises a methane storage device for receiving the liquefied methane, wherein the methane liquefied by the methane liquefaction device can be conveyed from the methane liquefaction device towards the methane storage device via a second line. The system according to the invention for the production and liquefaction of methane further comprises at least one flash tank arranged in the second line in order to at least partially remove impurities from the liquefied methane, wherein the impurities can be discharged from the respective flash tank via a respective third line.

[0011] In the system according to the invention, the methanization of hydrogen and the liquefaction of the resulting methane are combined in one system. The liquefied methane is purified of impurities via at least one flash tank, which is arranged in a line running from the methane liquefaction device to the methane storage device, whereby the impurities can be selectively discharged from the respective flash tank.

[0012] Preferably, a first flash tank is arranged in the second line to at least partially remove hydrogen from the liquefied methane, wherein the hydrogen from the first flash tank can be returned to the methane generation device via a third line. When the system according to the invention includes the first flash tank, hydrogen gas can be selectively extracted from the liquefied methane. This methane gas does not escape into the environment but is instead returned to the methane generation device to produce methane from the hydrogen in the methane generation device. The first flash tank can also be referred to as a high-pressure flash tank.

[0013] Alternatively, or preferably in addition to the first flash tank, a second flash tank is arranged in the second line to at least partially remove inert gas from the liquefied methane, the inert gas being discharged from the second flash tank into the environment via a third line. In this context, the term "inert gas" refers to gases that have a lower liquefaction temperature than methane, excluding hydrogen gas. This primarily includes nitrogen gas.

[0014] Then, if the system according to the invention includes the second flash tank, a defined inert gas, such as nitrogen, can be extracted from the liquefied methane. The inert gas can be released into the environment. The second flash tank can also be referred to as a medium-pressure flash tank.

[0015] Alternatively, or preferably in addition to the first and / or second flash tank, a third flash tank is arranged in the second line to separate gaseous methane from the liquefied methane, wherein the gaseous methane from the third flash tank can be returned to the methane liquefaction device via a third line. When the system according to the invention includes the third flash tank, gaseous methane can be separated from the liquefied methane and returned to the methane liquefaction device to prevent methane from escaping into the environment. The third flash tank can also be referred to as a low-pressure flash tank.

[0016] The quality of the liquefied methane can be improved using the first, second, and / or third flash tanks. The hydrogen removed from the liquefied methane in the first flash tank is recirculated to the methane generation unit. This prevents the accumulation of hydrogen gas in the system and minimizes hydrogen losses. The inert gas, particularly nitrogen, removed from the liquefied methane in the second flash tank can be vented to the environment. This also prevents the accumulation of inert gas in the system. The gaseous methane removed from the liquefied methane in the third flash tank is recirculated towards the methane liquefaction unit. This minimizes methane losses.Preferably, the system for generating and liquefying methane comprises a first recuperation heat exchanger, through which, on the one hand, a partial flow of the methane to be liquefied is passed, cooled, and condensed, and, on the other hand, impurities removed from the liquefied methane can be conveyed in the respective flash tank. When the system according to the invention includes the first recuperation heat exchanger, the temperature of the liquefied methane can be reduced, particularly for the separation or removal of inert gases, thereby enabling more effective separation or removal of the inert gases from the liquid methane.

[0017] Alternatively, or preferably in addition to the first recuperation heat exchanger, the system for the production and liquefaction of methane has a second recuperation heat exchanger. This second heat exchanger allows, on the one hand, a partial flow of the methane to be liquefied, diverted upstream of the methane liquefaction device from the first line, to be routed through it. On the other hand, it allows flash gas and impurities removed from the liquefied methane in the respective flash tank to be routed through it. When the system according to the invention has the second recuperation heat exchanger, the partial flow routed through the second heat exchanger can be cooled particularly deeply in order to achieve especially high impurity removal rates.

[0018] Preferably, at least one purification device is arranged in the first line to separate water and / or carbon dioxide from the methane produced by the methane generation device, wherein the separated water and / or the separated carbon dioxide can be returned to the methane generation device via a line. This has the advantage that carbon dioxide and, if applicable, separated water separated from the gaseous methane do not escape into the environment, but are returned to the methane generation device. Preferred embodiments of the invention are described in the dependent claims and the following description. Exemplary embodiments of the invention are explained in more detail with reference to the drawing, without being limited thereto. The drawing shows:

[0019] Fig. 1 shows a first system according to the invention for the production and liquefaction of methane;

[0020] Fig. 2 shows a second system according to the invention for the production and liquefaction of methane;

[0021] Fig. 3 shows a third system according to the invention for the production and liquefaction of methane;

[0022] Fig. 4 is a diagram illustrating the functioning of the systems according to the invention for the production and liquefaction of methane.

[0023] The invention relates to a system 10 for the production and liquefaction of methane. The system 10 comprises a methane production device 11, which serves to produce methane CH₄ from hydrogen H₂ and carbon dioxide CO₂.

[0024] The hydrogen H2 can in particular be green hydrogen, which has been produced using renewable energy sources.

[0025] The hydrogen (H2) is supplied via line 12. The carbon dioxide (CO2) required for the production of methane (CH4) in the methane production device 11 is supplied via line 13. The carbon dioxide (CO2) may be contaminated, in particular with nitrogen (N2).

[0026] The hydrogen supplied via line 12 and the carbon dioxide supplied via line 13 are mixed upstream of the methane generation device 11 in a mixing unit 14. Downstream of the methane generation device 11, gaseous methane CH4 is present, which can be cooled via an optional heat exchanger 15 and compressed via an optional compressor 16.

[0027] The gaseous methane CH4 present downstream of the methane generation device 11 may contain impurities such as water H2O, carbon dioxide CO2, nitrogen N2, hydrogen H2 and the like.

[0028] The system 10 according to the invention for the production and liquefaction of methane further comprises a methane liquefaction device 17, which serves to liquefy the gaseous methane produced in the methane production device 11.

[0029] The gaseous methane to be liquefied can be conveyed from the methane generation device 11 towards the methane liquefaction device 17 via a first line 18, in which, in the embodiment shown in Fig. 1, the optional cooling device 15 and the optional compressor 16 are arranged.

[0030] The system 10 according to the invention for the production and liquefaction of methane further comprises a methane storage device 19. The methane storage device 19, which is in particular a tank, preferably a transport tank, for the liquefied methane, is connected to the methane liquefaction device 17 via a second line 20, wherein the methane liquefied in the methane liquefaction device 17 can be conveyed via the second line 20 from the methane liquefaction device 17 towards the methane storage device 19.

[0031] In the second line 20, which extends from the methane liquefaction device 17 towards the methane storage device 19, at least one flash tank 21a, 21b, 21c is arranged to at least partially purify the liquefied methane downstream of the methane liquefaction device 17 and upstream of the methane storage device 19 from impurities. The impurities, together with the flash gas, can be discharged from the respective flash tank 21a, 21b, 21c via a respective third line 22a, 22b, 22c.

[0032] In the embodiment of Fig. 1, three flash tanks 21 a, 21 b and 21 c are arranged in the second line 20, through which methane liquefied in the methane liquefaction device 17 can be conveyed towards the methane storage device 19.

[0033] A first flash tank 21a serves to remove primarily hydrogen gas as an impurity from the liquefied methane. In the first flash tank 21a, which is a high-pressure flash tank, the liquid methane is separated from the gaseous hydrogen via phase separation. The gaseous hydrogen is then returned via the third line 22a towards the methane generation device 11, specifically to line 12 upstream of the methane generation device 11. Along with the hydrogen gas, a small amount of inert gas, particularly gaseous nitrogen, and gaseous methane can also be returned via the third line 22a towards the methane generation device 11.

[0034] Hydrogen gas separated in the area of ​​the first flash tank 21 a can be used again for methane production in the area of ​​the methane generation device 11, so that this hydrogen gas separated from the liquid methane in the area of ​​the first flash tank 21 a and the gaseous methane carried away together with the hydrogen gas is not lost.

[0035] As previously stated, the first flash tank 21a is a high-pressure flash tank. The inlet pressure of the first flash tank 21a can be at the outlet pressure of the methane liquefaction device 17. In Fig. 1, a throttle valve 23a is arranged immediately upstream of the first flash tank 21a to reduce the pressure of the liquefied methane upstream of the first flash tank 21a, or in its inlet region, to a level slightly below the outlet pressure of the methane liquefaction device 17. This throttle valve 23a is optional.

[0036] The second flash tank 21b, which is used either as an alternative to or preferably in addition to the first flash tank 21a, serves primarily to remove inert gases, especially nitrogen (N2), from the liquefied methane. The inert gas separated in the area of ​​the second flash tank 21b can be discharged from the second flash tank 21b via the third line 22b, and in particular can be discharged towards the environment. In this context, the term "inert gas" is understood to mean gases that have a lower liquefaction temperature than methane, excluding hydrogen gas. This includes primarily nitrogen (N2).

[0037] Along with the inert gas, a small amount of gaseous methane can also escape into the environment via the third line 22b. The proportion of methane lost in this process can be reduced by further developing the system shown in Fig. 2, specifically by using a recuperation heat exchanger 35.

[0038] The second Flashtank 21 b prevents the accumulation of inert gases, especially nitrogen, in the system. Specifically, it prevents the nitrogen content in the liquefied methane from exceeding 1.5 mol%.

[0039] The second flash tank 21b is a medium-pressure flash tank whose inlet pressure is lower than the inlet pressure of the first flash tank 21a, wherein, as shown in Fig. 1, a throttle valve 23b is arranged in line 20 downstream of the first flash tank 21a and upstream of the second flash tank 21b. In the region of the third flash tank 21c, gaseous methane can be separated from the liquefied methane, wherein the third flash tank 21c is a low-pressure flash tank whose inlet pressure is lower than the outlet pressure of the first flash tank 21a and also lower than the outlet pressure of the second flash tank 21b.

[0040] The third flash tank 21 c can be used alternatively or additionally to the first flash tank 21 a and / or the second flash tank 21b, wherein in Fig. 1 a further throttle valve 23c is arranged in the line 20 downstream of the second flash tank 21 b and upstream of the third flash tank 21c.

[0041] The gaseous methane, which is separated from the liquid methane in the area of ​​the third flash tank 21c, can be returned via the third line 22c towards the first line 18, specifically towards the methane liquefaction device 17, in order to further utilize the separated gaseous methane 22c and to liquefy it again in the area of ​​the methane liquefaction device 17.

[0042] In the embodiment shown in Fig. 1, the system 10 for generating and liquefying methane has a recuperation heat exchanger 24. A partial stream of the methane to be liquefied, branched off from the first line 18 via a branch line 25, can be liquefied via the recuperation heat exchanger 24. The partial stream of methane liquefied in the recuperation heat exchanger 24 is discharged from the recuperation heat exchanger 24 via a line 26 and, in the area of ​​a junction 27 with the second line 20, can be combined with the main stream of methane liquefied in the methane liquefaction device 17. The liquefied methane is then passed through the flash tanks 21a, 21b, 21c and purified of impurities in them. The recuperation heat exchanger 24 can be integrated into the methane liquefaction device 17. According to Fig.1. On the one hand, the partial flow of the methane to be liquefied, branched off from the first line 18 via the branch line 25, can be conveyed via the recuperation heat exchanger 24; on the other hand, the third lines 22a, 22b and 22c lead via the recuperation heat exchanger 24 in order to convey the impurities separated or separated from the liquefied methane in the area of ​​the respective flash tank 21a, 21b, 21c via the recuperation heat exchanger 24 and to recuperate the thermal energy of these diverted impurities in the recuperation heat exchanger 24 and to use it for the liquefaction of the partial flow of gaseous methane diverted via the branch line 25.

[0043] In the system 10 according to the invention shown in Fig. 1, gaseous methane CH4 is produced from gaseous hydrogen H2 and gaseous carbon dioxide CO2 in the area of ​​the methane production device 11. The methane production device 11 can be designed in various ways. All methods known from practice can be used, such as biological or catalytic processes, to obtain methane from hydrogen and carbon dioxide.

[0044] In the methane liquefaction unit 17, the gaseous methane produced from hydrogen and carbon dioxide in the methane generation unit 11 is liquefied. All refrigeration machines known from the prior art can be used for this purpose. The refrigeration machine used can operate a closed or an open refrigeration cycle. In an open refrigeration cycle, the methane itself can serve as the refrigerant.

[0045] In the embodiment shown in Fig. 1, the optional cooling device 15 and the optional compressor 16 are arranged in the second line 18, through which the gaseous methane can be guided from the methane generation device 11 towards the methane liquefaction device 17. Furthermore, a cleaning device 28 is arranged in the second line 18 upstream of the methane liquefaction device 17. This cleaning device serves to separate, in particular, carbon dioxide from the gaseous methane upstream of the methane liquefaction device 17. Thus, in the area of ​​the cleaning device 28, carbon dioxide and, if applicable, water can be separated from the gaseous methane, with the separated carbon dioxide and, if applicable, water being returned via a line 29 from the cleaning device 28 towards the methane generation device 11, namely upstream of the mixing device 14.The water can be separated from the carbon dioxide, which is returned via line 29 from the cleaning device 28 towards the methane generation device 11, using an optional cooler 30 and water separator 31.

[0046] In the area of ​​the cleaning device 28, the methane to be liquefied is therefore treated by removing water H2O and carbon dioxide CO2 in order to prevent water and carbon dioxide from precipitating as solid ice during the liquefaction of the methane at cryogenic temperatures.

[0047] The cleaning device 28 can, for example, be an absorption dryer that filters water and carbon dioxide from the gaseous methane to be liquefied. Such absorption dryers can have several tanks that are alternately loaded during filter operation and subsequently regenerated during regeneration operation. A partial stream of the gaseous methane can be used for the regeneration of the absorption material. After the filter material has been regenerated, the methane, loaded with water and carbon dioxide, is returned towards the methane generation device 11, namely upstream of the mixing device 14.

[0048] In the area of ​​flash tanks 21a, 21b, and 21c, the liquefied methane is purified by separating hydrogen gas, inert gas, and gaseous methane from the liquefied methane. This process converts the liquefied methane into an atmospheric storage state for storage in the methane storage device 19. The liquefied methane can also be stored in a pressure tank.

[0049] Upstream of the respective flash tank 21 a, 21 b, 21 c or in the inlet area thereof, a respective throttle valve 23a, 23b, 23c may be present, these throttle valves 23a, 23b and 23c also being referred to as flash valves, which serve to reduce the pressure level of the liquid methane and to transfer it into a corresponding two-phase region in order to remove the corresponding impurity from the liquid methane via a corresponding gas phase.

[0050] Then, when hydrogen gas is separated from the liquid methane in the area of ​​the first flash tank 21a, it is recycled and returned to the methane generation device 11. Gaseous methane separated in the area of ​​the third flash tank 21c is also recycled and returned to the methane liquefaction device 17. Inert gas separated from the liquid methane in the area of ​​the second flash tank 21b can be released into the environment.

[0051] The pressure levels in the flash tanks 21 a, 21 b, 21c are chosen such that the gas phase accumulating in the respective flash tank 21 a, 21 b, 21 c primarily contains the contaminant to be removed, i.e. hydrogen gas in the area of ​​the first flash tank 21 a, inert gas in the area of ​​the second flash tank 21 b and gaseous methane in the area of ​​the third flash tank 21 c.

[0052] It is also possible to omit the second flash tank 21b, particularly if the gaseous methane to be liquefied contains a small amount of intergases. In this case, the system would then have the first flash tank 21a and / or the third flash tank 21c. The volumetric or mass flow rate of the gas separated in the area of ​​the respective flash tanks 21a, 21b, and 21c is routed through the recuperation heat exchanger 24 to liquefy the thermal energy of the respective gas phase for cooling the partial flow of methane to be liquefied, which is diverted via the branch line 25. The recuperation heat exchanger 24, like the methane liquefaction device 17, thus serves to liquefy gaseous methane; specifically, the methane liquefaction device 17 liquefies the main flow, and the recuperation heat exchanger 24 liquefies a partial flow of gaseous methane.

[0053] Preferably, at least flash tank 21a and flash tank 21c are present to separate hydrogen gas and methane gas from the liquid methane, respectively, and to recycle and return them to a suitable location within the system. Flash tank 21b, which serves to separate inert gas, is particularly optional.

[0054] Depending on the pressure level in the respective flash tank 21a, 21b, 21c, optional compressors 32, 33 may be present in the respective third line 22a, 22b, 22c to return the separated impurities to the appropriate location in the system 10 at a suitable pressure level. Fig. 1 shows compressors 32, 33, namely compressor 32 in the third line 22a and compressor 33 in the third line 22c, each downstream of the recuperation heat exchanger 24.

[0055] Downstream of the third flash tank 21c, the liquid methane is transferred to the methane storage device 19. This transfer can be accomplished either by using the pre-pressure from the flash tank 21c or by employing a separate pump (not shown). In the illustrated embodiment, a further throttle valve 34 is connected between the third flash tank 21c and the methane storage device 19. Fig. 2 shows a further development of the system 10 of Fig. 1. To avoid unnecessary repetition, the same reference numerals are used for identical assemblies, and details that distinguish the system 10 of Fig. 2 from the system 10 of Fig. 1 are discussed below.

[0056] System 10 of Fig. 2 includes a further recuperation heat exchanger 35, which can be used additionally or alternatively to the recuperation heat exchanger 24. At least a partial flow of the liquid methane, which has been freed from hydrogen gas in the flash tank 21a, can be routed through this recuperation heat exchanger 35. Likewise, at least the partial flows of the impurities in the liquid methane, which are discharged via the third lines 22b, 22c, can be routed through this recuperation heat exchanger in order to further cool the liquid methane, which is conveyed from the flash tank 21a via a line 36 towards the recuperation heat exchanger 35. This allows the temperature level of the liquid methane supplied to the flash tank 21 b, which is conveyed from the recuperation heat exchanger 35 via a line 37 towards the second flash tank 21 b, to be reduced.This allows for cryogenic separation of inert gases in the area of ​​flash tank 21b. According to Fig. 2, a partial flow of the liquid methane, largely freed from hydrogen gas in the area of ​​flash tank 21a, can be directed via line 36 towards the recuperation heat exchanger 35, while a second partial flow can be directed via line 37 directly towards the third flash tank 21c, depending on the position of a valve 38 integrated into line 37.

[0057] In the embodiment shown in Fig. 2, cryogenic separation of inert gas is therefore possible in the second flash tank 21b. A partial flow of liquid methane is routed from flash tank 21a through the recuperation heat exchanger 35 and further cooled. This occurs in the recuperation heat exchanger 35 at the highest possible pressure. Subsequent expansion allows a state parameter to be reached in which the inert gas to be separated can be extracted from the liquid phase in a particularly high concentration. In the embodiment shown in Fig. 2, compared to Fig. 1, more inert gas can be separated using the recuperation heat exchanger 35 and the cryogenic separation of inert gas, thus reducing the proportion of methane lost.

[0058] Fig. 4 illustrates the difference between the embodiments shown in Figs. 1 and 2 with regard to the separation of inert gas in the area of ​​the second flash tank 21b. In Fig. 4, the ratio of inert gas IG to methane CH4 is plotted on the x-axis, with 0% inert gas and 100% CH4 on the far left and 100% inert gas and 0% CH4 on the far right. State I in Fig. 4 shows the mixture ratio of the liquid methane, which in Fig. 4 is exemplified as 30% inert gas and 70% CH4. If the separation of the inert gas takes place in flash tank 21b of Fig. 1, the liquid methane of state I is converted into a gas phase of state II and a liquid phase of state III. If the separation takes place at cryogenic temperatures in the flash tank 21 b of Fig. 2, the liquid methane of state I is converted into the gas phase of state IV and the liquid phase of state V.

[0059] Fig. 4 shows that during cryogenic separation of the inert gas, the resulting gas phase (state IV) has a higher concentration of inert gas ICH than the gas phase of state II, which formed during expansion in the flash tank 21 b of Fig. 1, so that inert gas separation is carried out with higher efficiency at cryogenic temperatures.

[0060] In the embodiment shown in Fig. 2, after inert gas separation in flash tank 21b, the liquid methane is transferred to flash tank 21c to separate gaseous methane. This gaseous methane is then stored in the methane storage device 19, preferably under atmospheric conditions. The gaseous methane separated in flash tank 21c is not lost but is returned to the methane liquefaction device 17 via the third line 22c.

[0061] The water discharged via the third line 22c in Fig. 2 is routed through both recuperation heat exchangers 35 and 24 in Fig. 2. Optionally, as shown in the dashed lines in Fig. 2, liquid methane can also be diverted between the two flash tanks 21b and 21c and routed through the recuperation heat exchanger 35 to further cool the partial flow of liquid methane diverted from flash tank 21a via line 36 to an even lower temperature, thus improving the inert gas separation in flash tank 21b.

[0062] Fig. 3 shows a modification of the embodiment of Fig. 2 with the two recuperation heat exchangers 24 and 35, thus again a further development of the embodiment of Fig. 1, whereby in Fig. 3, the same reference numerals are used for identical assemblies to avoid unnecessary repetition.

[0063] In the embodiment shown in Fig. 3, the two recuperation heat exchangers 24 and 35 are also present, although in Fig. 3 the second recuperation heat exchanger 35 is connected differently or integrated into the system 10 differently. While in Fig. 2 the second line 20 leads from the methane liquefaction device 17 into the first flash tank 21a, in the area of ​​which hydrogen gas is separated from the liquid methane, and the recuperation heat exchanger 35 serves to cool the liquid methane which is conveyed from the first flash tank 21a via line 36 towards the recuperation heat exchanger 35 and via line 37 into the second flash tank 21b, in order to enable the separation of inert gas at cryogenic temperatures in the second flash tank 21b, in Fig.Figure 3 provides that the second line 20, originating from the methane liquefaction device 17, carries a partial flow towards the flash tank 21c and another partial flow towards the recuperation heat exchanger 35. The partial flow of methane liquefied in the methane liquefaction device 17, which passes through the recuperation heat exchanger 35, is cooled more extensively in the region of the recuperation heat exchanger 35, in order to enable cryogenic separation of hydrogen in flash tank 21a and cryogenic separation of inert gas in flash tank 21b. The second line 20 leads from the methane liquefaction device 17 to the third flash tank 21c. A branch line 39 serves to divert a partial flow of the liquefied methane and feed this partial flow towards the recuperation heat exchanger 35.Impurities that are separated from the liquid methane as a gas phase in the area of ​​the respective flash tank 21 a, 21 b and 21 c are conveyed via the lines 22a, 22b and 22c to the recuperation heat exchanger 35 for cooling the liquid methane.

[0064] In Fig. 3, in the main flow of liquid methane, vaporous methane is first separated in the area of ​​the flash tank 21 c and this gas phase is returned towards the first line 18 and thus to the methane liquefaction device 17, whereby in the partial flow routed via the branch line 39 and the recuperation heat exchanger 35, hydrogen separation takes place in the flash tank 21 a, followed by inert gas separation in the flash tank 21 b and subsequently methane flash gas separation in the flash tank 21 c.

[0065] In Fig. 3, the recuperation heat exchanger 35 can additionally be coupled to another cooling circuit via lines 41, 42.

[0066] In Fig. 3, boil-off gas can be withdrawn from the methane storage device 19 via a line 40 and returned via line 22c towards the methane liquefaction device 17. This can also be done in Figs. 1 and 2.

[0067] Another difference between the embodiment shown in Fig. 3 and the embodiment shown in Figs. 1 and 2 is that two cleaning devices 28a and 28b are arranged in the first line 18 downstream of the methane generation device 11 and upstream of the methane liquefaction device 17.

[0068] The cleaning device 28a serves to separate CO2, which is returned via the return line 29a towards the methane generation device 11. In the area of ​​the cleaning device 28b, water is separated from the gaseous methane, whereby the water separated in the area of ​​the cleaning device 28b can be returned via the return line 29b towards the compressor 16.

[0069] The use of the purification devices 28a, 28b according to Fig. 3 is particularly advantageous when the methane produced by the methane generation device 11 has a high carbon dioxide content. In this case, CO2 can be separated in the area of ​​the purification device 28a, which preferably uses an amine scrubbing process, while the gaseous methane is then dried in the area of ​​the purification device 28b, separating water. Adsorption devices that utilize the principle of temperature-change adsorption can be used for this purpose. The water returned via the return line 29b can then be reused in the amine scrubbing process.

[0070] Alternatively, the water from the drying process 28b can be returned directly to the amine washing process 28a via a pump.

[0071] Reference symbol list

[0072] 10 System for the production and liquefaction of methane

[0073] 11 Methane generation device

[0074] 12 Line

[0075] 13 Management

[0076] 14 Mixing device

[0077] 15 heat exchangers

[0078] 16 compressors

[0079] 17 Methane liquefaction device

[0080] 18 first line

[0081] 19 Methane storage device

[0082] 20 second line

[0083] 21a Flashtank

[0084] 21 b Flashtank

[0085] 21c Flashtank

[0086] 22a third line

[0087] 22b third line

[0088] 22c third line

[0089] 23a Throttle valve

[0090] 23b Throttle valve

[0091] 23c Throttle valve

[0092] 24 recuperation heat exchangers

[0093] 25 branch line

[0094] 26 Management

[0095] 27 Union office

[0096] 28 Cleaning device

[0097] 28a Cleaning device

[0098] 28b Cleaning device

[0099] 29 Management

[0100] 29a Line

[0101] 30 coolers

[0102] 31 Water separator 32 Compressor

[0103] 33 compressors

[0104] 34 Throttle valve

[0105] 35 Recuperation heat exchanger 36 Line

[0106] 37 Management

[0107] 38 valve

[0108] 39 Branch line

[0109] 40 Line 41 Line

[0110] 42 Management

Claims

Claims 1. System (10) for the production and liquefaction of methane, comprising a methane production device (11) for the production of methane from hydrogen and carbon dioxide, a methane liquefaction device (17) for the liquefaction of the methane, wherein the methane produced by the methane production device (11) is conveyable via a first line (18) from the methane production device (11) towards the methane liquefaction device (17), a methane storage device (19) for receiving the liquefied methane, wherein the methane liquefied by the methane liquefaction device (17) is conveyable via a second line (20) from the methane liquefaction device (17) towards the methane storage device (19), and at least one flash tank (21a, 21b, 21c) arranged in the second line (20) to at least partially remove impurities from the liquefied methane, wherein the impurities are removed by the respective Flashtank (21 a, 21 b,21 c) can be discharged via a respective third line (22a, 22b, 22c).

2. System (10) according to claim 1, characterized by a first or high-pressure flash tank (21a) arranged in the second line (20) to at least partially remove hydrogen from the liquefied methane, wherein the hydrogen can be returned from the first or high-pressure flash tank (21a) via a third line (22a) towards the methane generation device (11).

3. System (10) according to claim 1 or 2, characterized by a second or medium-pressure flash tank (21b) arranged in the second line (20) to at least partially remove inert gas from the liquefied methane, wherein the inert gas can be discharged from the second or medium-pressure flash tank (21b) into an environment via a third line (22b).

4. System (10) according to claim 3, characterized in that the second or medium-pressure flash tank (21 b) is arranged downstream of the first or high-pressure flash tank (21a) in the second line (20).

5. System (10) according to one of claims 1 to 4, characterized by a third or low-pressure flash tank (21c) arranged in the second line (20) to separate gaseous methane from liquefied methane, wherein the gaseous methane can be returned from the third or low-pressure flash tank (21c) via a third line (22c) towards the methane liquefaction device (17).

6. System (10) according to claim 5, characterized in that the third or low-pressure flash tank (21c) is arranged downstream of the first or high-pressure flash tank (21a) and / or the second or medium-pressure flash tank (21b) in the second line (20).

7. System (10) according to one of claims 1 to 6, characterized by a first recuperation heat exchanger (35) through which, on the one hand, a partial flow of the liquefied methane can be conveyed for cooling the liquefied methane and, on the other hand, impurities removed from the liquefied methane can be conveyed in the respective flash tank (21a, 21b, 21c).

8. System (10) according to claims 2 and 7, characterized in that the partial stream of liquefied methane starting from the first or high-pressure flash tank (21a) can be supplied via a line (36) to the first recuperation heat exchanger (35) in order to cool the partial stream of liquefied methane more.

9. System (10) according to claims 3 and 8, characterized in that the more strongly cooled partial flow of the liquefied methane from the first recuperation heat exchanger (35) can be supplied to the second or medium-pressure flash tank (21a) via a line (37).

10. System (10) according to one of claims 1 to 9, characterized by a second recuperation heat exchanger (24), through which, on the one hand, a partial flow of the methane to be liquefied, branched off upstream of the methane liquefaction device (17) from the first line (18), can be conveyed for the purpose of liquefying methane, and through which, on the other hand, impurities removed from the liquefied methane in the respective flash tank (21a, 21b, 21c) can be conveyed.

11. System (10) according to one of claims 1 to 10, characterized in that a throttle valve (23a, 23b, 23c) is arranged directly upstream of at least one flash tank (21a, 21b, 21c) or in the inlet area thereof, in order to release the liquefied methane directly upstream of the respective flash tank (21a, 21b, 21c) or in the inlet area thereof.

12. System (10) according to one of claims 1 to 11, characterized in that at least one purification device (28, 28a, 28b) is arranged in the first line (18) to separate water and / or carbon dioxide from the methane produced by the methane generation device (11), wherein the separated water and / or the separated carbon dioxide can be returned via a line (29, 29a) towards the methane generation device (11).

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