Method and apparatus for reliquefaction and recycling of boil-off gas into an LNG tank

Abstract

The invention relates to a method for re-liquefaction and recycling of boil-off gas (BOG) into a Liquefied Natural Gas (LNG) Tank, comprising the steps: compressing a BOG extracted from the head space of an LNG tank (3) to a pressure phigh; cooling the compressed gas to a temperature T1, preferably by means of water cooling: (50); expanding at least a part of the gas from step c) to a pressure pexpand; cooling the gas expanded in step d), preferably by means of a heat exchanger (20) in the reverse flow with cooling BOG (F2) from the head space of the LNG tank 3 to a temperature T4; recycling the gas from step e) into the LNG tank (3); wherein the pressure phigh has a value of at least 200 bar, preferably at least 250 bar, particularly preferably at least 300 bar, and wherein the pressure pexpand has a value of 80 to 180 bar, preferably 120 to 160 bar, particularly preferably 150 bar.

Description

[0001] Method and device for reliquefying and returning evaporation gas to an LNG tank

[0002] The invention relates to the technical field of reliquefaction of boil-off gas (BOG) from a liquefied natural gas (LNG) tank.

[0003] Recently, the consumption of liquefied gases such as liquefied natural gas (LNG) has increased significantly worldwide. Liquefied gas, which is produced by cooling natural gas to an extremely low temperature, has a small volume and is therefore well suited for storage and transportation. Furthermore, liquefied gases such as LNG are low in pollutants and therefore more compatible with regulations than, for example, heavy fuel oil.

[0004] LNG is a colorless and transparent liquid obtained by cooling natural gas, which consists primarily of methane, to approximately -163°C. However, because natural gas is liquefied at an extremely low temperature of -163°C under atmospheric pressure, LNG can easily evaporate if the temperature rises slightly. Therefore, in an LNG storage tank, LNG continuously evaporates naturally, generating boil-off gas (BOG).

[0005] The formation of BOG means a loss of stored LNG and thus reduces transport efficiency, for example, on an LNG tanker. If BOG accumulates in a storage tank, there is also a risk of pressure rising in the storage tank and tank damage.

[0006] To solve this problem, a method has been proposed that involves reliquefying BOG for recycling to an LNG storage tank, feeding BOG as an energy source to an internal combustion engine, such as a marine engine, and combinations thereof. For example, US2019 / 0351988 proposes feeding BOG from an LNG tank to a DFDE engine, an X-DF engine, or a ME-GI marine engine. At the same time, it is planned to use BOG as a refrigerant for reliquefying compressed BOG in a partial reliquefaction system (PRS). However, this system has the disadvantage that the availability of BOG as a refrigerant is limited, and therefore, when reliquefaction demand is high, sufficiently low temperatures cannot be achieved. As a result, only a small portion of the BOG can be effectively reliquefied.A significant portion of the compressed and cooled gas is fed back into the reliquefaction cycle in gaseous form, and the system proves to be inefficient.

[0007] It is therefore the object of the present invention to provide a process for the partial reliquefaction of BOG or a partial reliquefaction system (PRS) in which BOG is used directly as a coolant and in which a high efficiency is nevertheless achieved.

[0008] The object is achieved by a method having the features of claim 1, or a device having the features of claim 5.

[0009] In particular, the object is achieved by a method for reliquefying and returning boil-off gas (BOG) to a liquefied natural gas (LNG) tank, comprising the steps of: a) removing BOG (F2) from the headspace of an LNG tank; b) compressing the BOG to a pressure р high; c) cooling the compressed gas to a temperature T1, preferably by water cooling; d) expanding at least part of the gas from step c) to a pressure p expand ; e) cooling the gas expanded in step d), preferably by means of a heat exchanger in countercurrent with cooling BOG

[0010] (F2) from the headspace of the LNG tank to a temperature T4; f) returning the gas from step e) to the LNG tank; wherein the pressure р high at least 200 bar, preferably at least 250 bar, particularly preferably at least 300 bar, and wherein the pressure p expand 80 to 180 bar, preferably 120 to 160 bar, particularly preferably 150 bar.

[0011] This process is based on the idea that the cooling liquid used to reliquefy the BOG in step e) is only available in limited quantities and / or should be used sparingly. In the case of a separate cooling circuit with a corresponding refrigerant, typically N2, cooling costs energy. If BOG from the LNG tank is used as the coolant instead, a low flow rate is desirable from a storage / transport efficiency perspective, particularly if an engine running on natural gas does not need to be operated simultaneously or if the engine only has a low fuel requirement (temporarily). In contrast, however, the cooling liquid for cooling the compressed gas to ambient temperature, especially water, is available in virtually unlimited quantities.

[0012] The inventors have recognized that it may therefore be useful to provide a gas with low heat for the cooling step e). This can be achieved by heating the gas to a comparatively high pressure p high is compressed and cooled at this high pressure by water cooling. If the gas is then at least partially isoenthalpically expanded in step d) before being subjected to cooling in step e), a higher proportion of gas can be reliquefied with the available cooling capacity than if reliquefaction were carried out without step d) or starting from a lower pressure (e.g., 150 bar).

[0013] A method is preferred for supplying a high-pressure gas injection engine with gas which is stored in an LNG tank partly as evaporation gas (BOG, F2), and for reliquefying and recycling BOG, comprising the steps according to claim 1, wherein in step d) at least a first part of the gas from step c) is supplied to the high-pressure gas injection engine via an outlet in the amount of the fuel required by a high-pressure gas injection engine, and at least a second part of the gas from step c) is pressurized to the pressure p expand is extended.

[0014] In this embodiment, the highly compressed gas at pressure р highIt can either be used to power a high-pressure gas-injection engine or reliquefied. Natural gas is the fuel of choice, particularly on a liquefied gas carrier, to keep air pollutant emissions to a relatively low level. The adjustable amount of fuel fed to the gas-injection engine or the PRS allows for flexible adjustment to climatic and meteorological conditions as well as the fuel requirements of the high-pressure gas-injection engine.

[0015] Furthermore, it is preferred if, in the method as described above, step b) is preceded by a step 0) and step 0) is the selection between - an operating mode i) compressing the BOG to a pressure p high comprising steps b) to d); and - an operating mode ii) compressing the BOG to a pressure Plow, comprising the steps b1) compressing the BOG to a pressure p lowfrom 100 to 199 bar, preferably 140 to 160 bar; and d1) expanding at least part of the gas from step c) to a pressure p expand , provided p low > p ex- pand ; where in the case of operating mode ii), steps b1) and d1) replace steps b) and d).

[0016] In such a process, it is possible to adjust the operating mode. It has been shown that at low reliquefaction rates, it can be efficient to simply switch to a lower pressure p low to compress (step b1), because the BOG provides sufficient cooling capacity to cool the gas stream to be liquefied to a sufficiently low temperature level. In contrast, compression to a high pressure at a high liquefaction rate proves to be more efficient, because the additional cooling due to the expansion of the gas to be liquefied from p high on p lowcontributes to a higher reliquefaction rate and thus to a more efficient overall system.

[0017] Particularly preferred is a method in which in step 0) in operating mode i) a target value p high in the range of 200 to 300 bar and / or in operating mode ii) a setpoint p low in the range of 100 to 199 bar. The continuously adjustable pressure between 100 and 300 bar allows for even greater flexibility in the reliquefaction cycle.

[0018] One aspect of the invention relates to a device for reliquefying and returning evaporative gas (BOG) to a liquefied natural gas (LNG) tank, comprising - a heat exchanger having a line for conducting cooling fluid, preferably BOG from an LNG tank, and a line for conducting compressed gas to be cooled; - a multi-stage compressor arrangement which is configured to pressurize BOG (F2) from the LNG tank to a pressure p high to compress; - a first cooler; - a return line; and - a first expansion unit arranged to compress gas from a pressure р high to a pressure p expandto expand; wherein the multi-stage compressor arrangement is connected upstream, optionally via the line of the heat exchanger for conducting cooling fluid, to a withdrawal line opening into the headspace of the LNG tank, and wherein the multi-stage compressor arrangement is connected downstream, carrying fluid to the first cooler, further downstream via the return line to the first expansion unit and even further downstream to the line of the heat exchanger for conducting compressed gas to be cooled, in order to return the compressed and cooled gas to the LNG tank; wherein the pressure p high at least 200 bar, preferably at least 250 bar, particularly preferably 300 bar; and wherein the pressure pexpand is 80 to 180 bar, preferably 120 to 160 bar, particularly preferably 150 bar.

[0019] This device solves the problem described above. For the cooling step in the indirect heat exchanger, a gas with a low heat content is provided. This is achieved by heating the gas to a comparatively high pressure p high is compressed and cooled at this high pressure by water cooling. If the gas is then at least partially isenthalpically expanded in step d) before being fed to the cooling stage in the heat exchanger, a higher proportion of gas can be reliquefied with the available cooling capacity than if the gas were cooled and reliquefied without prior expansion, ie starting from a gas compressed only to a lower pressure (e.g., 150 bar).

[0020] An advantage associated with the device is the efficiency gain at high flow rates of BOG, as described above at the process level. A further design advantage is that the pressure in the intermediate stage(s) before the last compression stage does not need to be controlled. If, for example, a branch line following an intermediate stage (for example at p low ) a portion of the gas were extracted and fed to the PRS, the pressure after this intermediate stage would typically have to be regulated with a pressure control valve (PCV). If, on the other hand, the entire produced BOG quantity were to be uniformly controlled to the pressure р highis compressed, a single PCV is sufficient, which reduces the cost of the device. Finally, thanks to the improved efficiency of the device, a smaller PRS and, thanks to the lower gas flow, a smaller multi-stage compressor arrangement are sufficient. This is surprisingly true even despite the fact that all compression stages must be designed to process the entire BOG flow. Smaller devices save valuable space, especially if the device is to be used on a ship, e.g., a tanker. Less energy is also required for efficient reliquefaction.

[0021] In a preferred embodiment, the device is part of a fuel gas supply system for supplying a high-pressure gas injection engine with gas stored in an LNG tank, additionally comprising - an outlet which is arranged in a fluid-conducting manner downstream of the multi-stage compressor arrangement and opens further downstream into a supply line for a high-pressure gas injection engine, wherein the compressed gas, insofar as the amount exceeds the fuel requirement of the high-pressure gas injection engine, can be fed to the return line.

[0022] The advantage of such a device as part of a fuel gas supply system is that the highly compressed gas at pressure р highcan be reliquefied or used to power a high-pressure gas-injection engine. The adjustability of the amount fed to the gas-injection engine or the PRS allows for flexible adjustment of climatic and meteorological conditions, as well as the fuel requirements of the high-pressure gas-injection engine (e.g., driving speed).

[0023] In one embodiment, the device further comprises - a second expansion unit which is configured to compress gas from a pressure p expand at a touch of a button knock- out-drum(typically 1-3 bar above the tank pressure), - a gas-liquid separator, which carries fluid and is connected downstream of the second expansion unit and is configured to feed a liquefied gas portion back into the LNG tank at a pressure of the knock-out drum and to feed a gaseous portion into the extraction line; wherein the second expansion unit and the gas-liquid separator are arranged, carrying fluid, between the line of the heat exchanger for conveying compressed gas to be cooled and the LNG tank. Due to the renewed expansion in the second expansion unit (e.g. expansion valve, expander), the gas undergoes further cooling through Joule-Thomsen expansion. The gaseous component separated by the gas-liquid separator can then be combined with the BOG taken from the storage tank and fed to the heat exchanger as a coolant. The liquid component is fed into the storage tank.Thanks to the described arrangement, a higher relative proportion of the BOG can be re-liquefied, preferably with the same amount of available coolant.

[0024] It is preferred that the first cooler be a water cooler; preferably, water from the ship's cooling water system is used as the coolant, so that the compressed gas can be cooled to a temperature of 35 to 45°C. Water is plentiful, especially when the device is used on a ship. Cooling to the achievable temperature of 35 to 45°C from a gas with a particularly high pressure results in a lower enthalpy after the first cooling step compared to processes starting at lower pressures.

[0025] In a preferred embodiment, the multi-stage compressor arrangement has a first compression stage, wherein the first compression stage is configured to compress BOG (F2) from the LNG tank to a first pressure p1 between 6 and 18 bar, and wherein the first compression stage has at least one labyrinth-sealed piston compressor.

[0026] If the first compression stage comprises at least one labyrinth-sealed piston compressor, preferably exclusively labyrinth-sealed piston compressors, the first compression stage can be operated with little or no lubricant. This has the advantage that the quality of the compressed gas is not impaired by lubricant contamination. It also avoids the risk of the lubricant (typically oil) solidifying at the low temperatures of the BOG at low compression stages, which could promote wear on the machine components.

[0027] In a preferred embodiment, the multi-stage compressor arrangement of the device has a middle and a last compression stage, which are designed to reduce pre-compressed gas from a first pressure p1 to the pressure p high , preferably optionally on the pressure р high or the pressure p lowto compress, wherein the last compression stage has a bypass with a controllable valve to control the return flow and thus the delivery pressure after the last compression stage, wherein gas can be fed back via the bypass in such a way that the gas at the outlet reaches the specified target pressure value p high , prefers the specified target pressure value pressure р high or p low , has.

[0028] Such a device has the previously mentioned advantages of improving the efficiency of reliquefaction for high gas production rates and reducing the size of the device elements. If the multi-stage compressor arrangement can now be operated variably thanks to the bypass with controllable valve, or thus at the outlet gas having a variable pressure between p low and p highcan be provided, further advantages arise. The multi-stage compressor arrangement can be designed so that the side stream for recondensation at low recondensation rates is only reduced to p low compressed, which is more efficient for small recondensation rates. Furthermore, the life expectancy of the units can be improved if they are operated at only 50% of the nominal pressure for a significant portion of their operating time.

[0029] It is particularly preferred if the bypass is adjustable with a controllable valve so that any desired pressure between 100 and 300 bar can be set. This allows the user additional flexibility to accommodate climatic and meteorological conditions as well as the fuel requirements of the engine(s).

[0030] In one embodiment, the final compression stage comprises at least one piston-ring sealed piston compressor, preferably two piston-ring sealed piston compressors. Piston-ring sealed, preferably lubricated, piston compressors enable the gas to be compressed to a pressure in the range of r high .

[0031] The device as described above may further comprise a branch line which is arranged to conduct fluid downstream of the first compression stage and which opens further downstream into a supply line for a low-pressure gas injection engine and / or a gas combustion unit.

[0032] This allows an engine that operates at low pressure (p1), such as an X-DF engine, to be supplied with fuel that is extracted after the first compression stage. In this embodiment, it is particularly advantageous if the first compression stage is sealed with little or no lubricant, because in this way a high-quality fuel can be fed to the low-pressure gas injection engine and / or the gas combustion unit. The invention relates to the use of the device as described above on a ship, for example a natural gas tanker, in particular a ship that is powered by a high-pressure gas injection engine. When used on a ship, the aforementioned advantages, in particular the reduced size of the device, become particularly apparent due to the limited space available.

[0033] The invention is further explained with the aid of figures. The figures serve for illustration purposes and are not to be construed as limiting.

[0034] They show:

[0035] Figure 1 Schematic representation of a device according to the present invention;

[0036] Figure 2 Schematic Mollier diagram to illustrate a method according to the present invention.

[0037] Figure 1 schematically shows a fuel gas supply system according to the present invention with a device for reliquefying and returning exhaust gas (BOG) to a liquefied natural gas (LNG) tank 3. The BOG (F2) accumulating in the headspace of LNG tank 3 is fed via extraction line 5 to a heat exchanger 20 to be used as a cooling fluid in indirect heat exchange, and then compressed by a multi-stage compressor arrangement 10 to a high pressure р highof typically approx. 300 bar.

[0038] In the embodiment shown, the multi-stage compressor arrangement 10 comprises a first compression stage with piston compressors 71 and 72 and associated coolers, a middle compression stage with piston compressor 73 and associated cooler, and a final compression stage with piston compressors 74 and 75 and associated coolers. The first compression stage 71, 72 is designed to compress the BOG to a pressure p1 of typically 7 bar. A portion of the thus compressed, preferably lubricant-free, BOG can be fed to the low-pressure gas injection engine 4 via branch line 6, if required. The first compression stage can be pressure-controlled by means of a bypass having a pressure control valve (not shown).

[0039] The multi-stage compressor arrangement 10 is connected downstream in a fluid-conducting manner to a first water cooler 50, whereby the compressed gas is cooled to typically 40°C. The outlet pressure of the highest compression stage, here consisting of piston compressors 75 and 74 and associated water coolers, is regulated via a bypass 19 with a pressure control valve 9. After exiting the first water cooler 50, the compressed BOG can either be fed as fuel to a high-pressure gas injection engine 2 via the outlet 7 or fed via the return line 8 to a first expansion unit 60, for example an expansion valve or an expander. Typically, excess BOG that exceeds the fuel requirement of the engine 2 is fed to the return line 8. The gas is compressed in the first expansion unit 60 to a pressure p ex- pandof approximately 150 bar. Due to the isenthalpic pressure reduction, the compressed natural gas undergoes further cooling and can thus be further cooled from approximately 20°C in indirect heat exchange with the BOG (F2) from the LNG tank 3 in heat exchanger 20.

[0040] The BOG compressed by the compressor assembly and cooled by water cooling 50, expansion 60, and heat exchange 20 is expanded again in a second expansion unit 30, now to a knock-out pressure of typically 1 bar, and finally separated into a liquid component and a gaseous component by a gas / liquid separator 40. The liquid component separated by the gas / liquid separator 40 is fed back into the LNG tank, and the gaseous component separated by the gas / liquid separator is combined with the BOG exiting the LNG tank in the extraction line 5 and then fed to the heat exchanger 20 to be used as a cooling fluid.

[0041] In the BOG reliquefaction system shown in Figure 1, the reliquefaction of natural gas is performed using BOG taken from the storage tank as the refrigerant, without requiring a separate cycle for reliquefaction of BOG. ​​It should be understood that the present invention is not limited thereto, and a separate refrigeration cycle may be established to ensure the reliquefaction of the entire BOG, if necessary. Such a separate cycle can ensure the reliquefaction of the BOG, but requires separate equipment or an additional energy source.

[0042] Figure 2 shows the compression and cooling circuit in a schematic Mollier diagram using dashed lines. The BOG is located in its initial state to the right of the dew point at an atmospheric pressure of 1 bar and approximately -160°C. When removed from the LNG tank a), particularly when used as a coolant in indirect heat exchange, the BOG warms up to ambient temperature or higher, approximately T1.

[0043] In step b) the compression to p follows high, for example, according to the compressor arrangement shown in Figure 1, using five piston compressors. These can be arranged as the first compression stage 101, the middle compression stage 102, and the last compression stage 103, each with subsequent water cooling to temperature T1. Overall, the natural gas can thus be compressed to a pressure of typically 300 bar. After the final cooling to T1 by water cooling in step c), at least a portion of the gas is isenthalpically expanded to a pressure p in step d). expandof typically 150 bar. Due to the Joule-Thomson effect, the temperature of the gas is reduced to T2, typically to approximately 20°C. In step e), the gas is further cooled to a temperature T4 of approximately -75°C. This occurs in the device shown in Figure 1 in the indirect heat exchanger 20 with cooling BOG from the headspace of the LNG tank. Step f) is the return of the gas to the LNG tank, which typically involves further isenthalpic expansion and the

[0044] Separation of liquid and gaseous parts in the gas / liquid separator.

[0045] Figure 2 shows the advantage that gas compression has on the pressure р high with subsequent cooling c) and relaxation d) results in: Compared to compression to only p expand followed by water cooling, an enthalpy difference 104 can be obtained in the form of a lower temperature T2 of the gas. If only p expandcompressed, the gas is at the same pressure p expand at a higher temperature T1 and the cooling capacity of the coolant available in the heat exchanger must be used to cool the warmer gas (dotted line). Since the coolant is not available in unlimited quantities in the case of BOG, the less compressed gas can often only be cooled to temperature T3 instead of T4 in the heat exchanger and the subsequently expanded gas is only reliquefied to a lesser extent, according to arrow 105. Not shown in Figure 2 is the operating mode ii) as described above, in which the BOG is cooled to a pressure p low compressed and in the case of p low > p expand on p expand This operating mode requires that the middle and last compression stages are set up to reduce pre-compressed gas from a first pressure p1 to a pressure p high of, for example, 300 bar or to a pressure plow of, for example, 150 bar. The pressure can be regulated, for example, by a bypass with a controllable valve arranged in the last compression stage 103. If the controllable valve is adjustable in such a way that any desired pressure between Piow and p high is adjustable, further pressures in the return line 8 of Figure 1 or in the diagram of Figure 2 parallel below the dashed line c) are conceivable.

Claims

Patent claims 1. A method for reliquefying and returning boil-off gas (BOG) to a liquefied natural gas (LNG) tank, comprising the steps of: a) withdrawing BOG (F2) from the headspace of an LNG tank (3); b) compressing the BOG to a pressure p high ; c) cooling the compressed gas to a temperature T1, preferably by water cooling (50); d) expanding at least a portion of the gas from step c) to a pressure p expand ; e) cooling the gas expanded in step d), preferably by means of a heat exchanger (20) in countercurrent with cooling BOG (F2) from the headspace of the LNG tank 3 to a temperature T4; f) returning the gas from step e) to the LNG tank (3); wherein the pressure р high at least 200 bar, preferably at least 250 bar, particularly preferably at least 300 bar, and wherein the pressure p expand 80 to 180 bar, preferably 120 to 160 bar, particularly preferably 150 bar.

2. Method for supplying a high-pressure gas injection engine (2) with gas which is stored in an LNG tank (3) partly as evaporation gas (BOG, F2), and for reliquefying and recycling BOG, comprising the steps according to claim 1, wherein in step d) at least a first part of the gas from step c) is supplied to the extent of the fuel requirement of a high-pressure gas injection engine (2) via an outlet (7) to the high pressure gas injection engine (2) and at least a second part of the gas from step c) is fed to the Pressure p expand 3. Method according to one of the preceding claims, wherein step b) is preceded by a step 0) and step 0) is the selection between - an operating mode i) compressing the BOG to a pressure p high comprising steps b) to d); and - an operating mode ii) compressing the BOG to a pressure p low, comprising the steps b1) compressing the BOG to a pressure p low from 100 to 199 bar, preferably 140 to 160 bar; and d1) expanding at least part of the gas from step c) to a pressure p expand ,provided p low > p expand ; wherein in the case of operating mode ii), steps b1) and d1) replace steps b) and d).

4. Method according to claim 3, wherein in step 0) in operating mode i) a target value p high in the range of 200 to 300 bar is selected and / or in operating mode ii) a setpoint value p low in the range of 100 to 199 bar.

5. Device for reliquefying and returning boil-off gas (BOG) to a liquefied natural gas (LNG) tank, comprising - a heat exchanger (20) comprising a line for passing cooling fluid, preferably BOG (F2) from an LNG tank (3), and a line for passing compressed gas to be cooled; - a multi-stage compressor arrangement (10) which is designed to pressurise BOG (F2) from the LNG tank (3) to a pressure p high to compact; - a first cooler (50); - a return line (8); and - a first expansion unit (60) arranged to supply compressed gas of a pressure р high to a pressure p expandto expand; wherein the multi-stage compressor arrangement is connected upstream, optionally via the line of the heat exchanger (20) for conducting cooling fluid, to a discharge line (5) opening into the head space of the LNG tank (3), and wherein the multi-stage compressor arrangement (10) is connected downstream, conducting fluid to the first cooler (50), further downstream via the return line (8) to the first expansion unit (60) and even further downstream to the line of the heat exchanger (20) for conducting compressed gas to be cooled, in order to return the compressed and cooled gas to the LNG tank (3); wherein the pressure р high at least 200 bar, preferably at least 250 bar, particularly preferably 300 bar; and wherein the pressure p expand80 to 180 bar, preferably 120 to 160 bar, particularly preferably 150 bar.

6. Device according to claim 5, wherein the device is part of a fuel gas supply system for supplying a high-pressure gas injection engine (2) with gas stored in an LNG tank, additionally comprising - an outlet (7) arranged in a fluid-conducting manner downstream of the multi-stage compressor arrangement (10), and further downstream into a supply line for a high-pressure gas injection engine (2), wherein the compressed gas, to the extent that the amount exceeds the fuel requirement of the high-pressure gas injection engine (2), can be fed to the return line (8).

7. Device according to one of claims 5 or 6, further comprising - a second expansion unit (30) which is arranged to supply compressed gas of a pressure p expand to expand to a pressure рknock-out-drum, - a gas-liquid separator (40) which is connected downstream of the second expansion unit (30) and is designed to knock-out at a pressure drumto feed a liquefied gas portion back into the LNG tank (3) and to feed a gaseous portion into the extraction line (5); wherein the second expansion unit (30) and the gas-liquid separator are arranged in a fluid-conducting manner between the line of the heat exchanger (20) for passing compressed gas to be cooled and the LNG tank (3).

8. Device according to one of claims 5 to 7, wherein the first cooler (50) is a water cooler, preferably using water at ambient temperature as a coolant, so that the compressed gas can be cooled to a temperature of 35 to 45°C.

9. Device according to one of claims 5 to 8, wherein the multi-stage compressor arrangement (10) has a first compression stage (71, 72), wherein the first compression stage is configured to to compress a first pressure p1 between 6 and 18 bar, and wherein the first compression stage comprises at least one labyrinth-sealed piston compressor.

10. Device according to one of claims 5 to 9, wherein the multi-stage compressor arrangement (10) comprises a middle (73) and a last compression stage (74, 75) which are designed to compress pre-compressed gas from a first pressure p1 to the pressure p high , preferably optionally to the pressure p high or the pressure p low , to compress, wherein the last compression stage (74, 75) has a bypass (19) with a controllable valve (9) in order to control the return flow and thus the delivery pressure after the last compression stage, wherein gas can be fed back via the bypass in such a way that the gas at the outlet (7) reaches the predetermined target pressure value p high , prefer the specified target pressure value pressure р high or p low, has.

11. Device according to claim 10, wherein the bypass (19) with controllable valve (9) is adjustable such that each target pressure between 100 and 300 bar can be set.

12. Device according to claim 10 or 11, wherein the last compression stage (74, 75) comprises at least one piston compressor sealed with a piston ring, preferably two piston compressors sealed with a piston ring.

13. Device according to one of claims 9 to 12, further comprising: - a branch line (6) which is arranged downstream of the first compression stage (71, 72) to conduct fluid and which further downstream leads into a supply line device for a low-pressure gas injection engine (4) and / or a gas combustion unit.

14. Use of a device according to one of claims 5 to 13 on a ship, in particular a ship driven by a high-pressure gas injection engine (2).

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