FUEL-GAS SUPPLY SYSTEM AND METHOD FOR SUPPLYING A HIGH-PRESSURE GAS INJECTION ENGINE WITH FUEL GAS

Abstract

Fuel gas supply system for supplying a high-pressure gas injection engine with gas stored in a liquefied gas tank, preferably an LNG tank, having a high-pressure pump to which liquefied gas is supplied. The system including a condenser with a high-pressure heat exchanger, a high-pressure vaporizer which is connected to the high-pressure pump via the high-pressure heat exchanger and is arranged downstream of the condenser. Gas fed to the high-pressure gas injection engine downstream of the high-pressure evaporator. A compressor to which boil-off gas is fed is connected downstream to the condenser via an inlet. A condensation core generator to which liquid gas is supplied from the high-pressure pump in such a manner that the condensation nuclei generated by the condensation nucleus generator promote condensation of the supplied boil-off gas. The liquid gas formed in the condenser is supplied to the high-pressure pump and/or to the liquid gas tank.

Claims

1-19. (canceled)

20. A fuel gas supply system for supplying a high-pressure gas injection engine with gas stored in a liquefied gas tank, comprising a liquefied gas tank and a high-pressure pump which can be connected in a fluid-conducting manner to the liquefied gas tank in order to supply liquefied gas from the liquefied gas tank and to compress it to a high-pressure liquefied gas, comprising a condenser in which a high-pressure heat exchanger is arranged, comprising a high-pressure evaporator which is fluid-conductively connected to the high-pressure pump via the high-pressure heat exchanger and is arranged downstream of the condenser, wherein the high-pressure evaporator converts the high-pressure liquid gas into a high-pressure fuel gas, and the high-pressure fuel gas is supplied to the high-pressure gas injection engine downstream of the high-pressure evaporator, comprising a compressor which is fluid-conductively connectable to the liquid gas tank to supply boil-off gas from the liquefied gas tank, the compressor being fluid-conductively connected downstream via an inlet to an inner space of the condenser to introduce the boil-off gas into the inner space, and comprising a condensation core generator fluid-conductively connected upstream to the high-pressure pump, wherein the condensation core generator is configured such in that it generates liquid gas droplets from the high-pressure liquid gas, which droplets serve as condensation nuclei, the condensation nucleus generator introducing the condensation nuclei into the inner space in order to promote condensation of the introduced boil-off gas via the condensation cores, so that liquefied gas is formed therefrom, and in that the liquefied gas formed in the condenser is fed to the high-pressure pump and/or to the liquefied gas tank.

21. The fuel gas supply system according to claim 20, wherein a second heat exchanger is arranged upstream of the compressor, which exchanges heat with the supplied boil-off gas, and wherein the condensation core generator is fluid-conductively connected upstream to the second heat exchanger and subsequently to the high-pressure pump in order for the second heat exchanger to exchange heat with the supplied high-pressure liquid gas.

22. The fuel gas supply system according to claim 20, wherein a second heat exchanger is arranged upstream of the compressor, which exchanges heat with the supplied boil-off gas, and wherein the compressor is fluid-conductively connected upstream in turn to the second heat exchanger in order for the second heat exchanger to exchange heat with the boil-off gas compressed by the compressor.

23. The fuel gas supply system according to claim 20, wherein the inlet of the boil-off gas is from above into the condenser, that the high-pressure heat exchanger extends in vertical direction inside the condenser, and wherein the high-pressure heat exchanger is arranged in such a way that the high-pressure liquid gas flows in the high-pressure heat exchanger from bottom to top.

24. The fuel gas supply system according to claim 20, wherein the condensation core generator has at least one high-pressure nozzle.

25. The fuel gas supply system according to claim 20, wherein the condensation core generator is arranged such that condensation cores generated by the condensation core generator are introduced into a condensation section in the inner space of the condenser in which the inner space has a condensation temperature.

26. The fuel gas supply system according to claim 25, wherein the condensation core generator is arranged in such a way that the condensation cores enter the inner space of the condenser, in the flow direction of the liquid gas, in a first half of the cooling line of the high-pressure heat exchanger.

27. The fuel gas supply system according to claim 20, wherein a storage tank for intermediate storage of boil-off gas is arranged downstream of the liquefied gas tank.

28. The fuel gas supply system according to claim 20, wherein the high pressure pump comprises at least a first high pressure pump and a second high pressure pump, wherein the first high-pressure pump is fluid-conductively connected to the condensation core generator and fluid-conductively connected to the high-pressure evaporator via the high-pressure heat exchanger, and wherein the second high-pressure pump is fluid-conductively connected to the high-pressure evaporator, bypassing the high-pressure heat exchanger.

29. The fuel gas supply system according to claim 28, wherein the first high-pressure pump is fluid-conductively connected to the liquefied gas tank to supply liquefied gas, and the second high-pressure pump is fluid-conductively connected to an outlet of the condenser to supply liquefied gas accumulated in the condenser to the second high-pressure pump.

30. The fuel gas supply system according to claim 29, wherein the second high-pressure pump is both fluid-conductingly connected to the outlet of the condenser and fluid-conductingly connected to the liquefied gas tank, wherein valves are provided to control the portion of liquefied gas supplied from the condenser and the portion of liquefied gas supplied from the liquefied gas tank.

31. A method for supplying a high-pressure gas injection engine with gas which is stored in a liquefied gas tank, partly as liquefied gas and partly as evaporated gas, comprising the steps of feeding the liquefied gas from the liquefied gas tank to a high-pressure pump and compressing the liquefied gas by the latter to a high-pressure liquefied gas, then feeding the high-pressure liquid gas to a high-pressure heat exchanger arranged in a condenser and subsequently to a high-pressure evaporator, converting the high-pressure liquid gas in the high-pressure evaporator into a high-pressure fuel gas, so that a fuel gas under high pressure is produced which is fed to the high-pressure gas injection engine by feeding the boil-off gas from the liquefied gas tank to a compressor and then introducing it into the condenser, generating a stream of condensation nuclei in the form of liquefied gas droplets in a condensation nucleus generator from high-pressure liquefied gas, which nuclei are fed in the condenser to the introduced boil-off gas in order to promote condensation of the boil-off gas to liquefied gas by the liquefied gas droplets, and feeding the liquefied gas formed in the condenser to the high-pressure pump and/or to the liquefied gas tank.

32. The method according to claim 31, wherein the stream of condensation nuclei in the form of liquid gas droplets generated in the condensation nucleus generator, which is fed in the condenser to the introduced boil-off gas, has a mass flow rate of 1 to 5%, based on the mass flow rate of the gas to be condensed.

33. The method according to claim 31, wherein in the condenser the liquid gas is conveyed from the bottom to the top in the high-pressure heat exchanger, and wherein the boil-off gas is conveyed in the condenser in counterflow from the top to the bottom.

34. The method according to claim 31, wherein a condensation section is generated in the inner space of the condenser, within which the boil-off gas has a temperature which is below the boiling temperature of the liquid gas, and wherein condensation nuclei in the form of supercooled liquid gas droplets are sprayed into this condensation section.

35. The method according to claim 34, wherein a temperature of -140° C. to -80° C. and a pressure of 5 to 30 bara are present in the generated condensation section.

36. The method according to claim 31, wherein a side stream of high-pressure liquid gas is withdrawn from or downstream of the high-pressure pump, wherein this side stream is cooled in a heat exchanger, wherein boil-off gas discharged from the liquefied gas tank is simultaneously heated in the heat exchanger, wherein the boil-off gas is fed to the condenser downstream of the heat exchanger, and wherein the high-pressure liquefied gas is fed to the condensation core generator downstream of the heat exchanger.

37. The method according to claim 31, wherein the high-pressure liquid gas is compressed to a pressure in the range between 150 bara and 400 bara.

38. A merchant vessel comprising a fuel gas supply system according to claim 20.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0021] The drawings used to explain the embodiments show:

[0022] FIG. 1 schematically a first embodiment of a fuel gas supply system;

[0023] FIG. 2 schematically a second embodiment of a fuel gas supply system;

[0024] FIG. 3 schematically a third embodiment of a fuel gas supply system;

[0025] FIG. 4 schematically a fourth embodiment of a fuel gas supply system;

[0026] FIG. 5 schematically a fifth embodiment of a fuel gas supply system;

[0027] FIG. 6 schematically a condenser.

[0028] In principle, in the drawings the same parts are designated with the same reference numbers.

WAYS TO CARRY OUT THE INVENTION

[0029] FIG. 1 shows a fuel gas supply system 1 for supplying a high-pressure gas injection engine 2, preferably an ME-GI engine, with fuel gas, preferably methane. The fuel gas is stored in an LNG tank 3, partly in the form of liquid gas F1 and, due to the vaporization of the liquid gas F1 occurring in the LNG tank 3, partly in the form of boil-off gas F2. This boil-off gas F2 is also referred to as BOG or NBOG (Natural Boil-Off Gas). To supply the high-pressure gas injection engine 2 with fuel gas at a pressure in the range of, for example, 150 to 300 bara, the liquefied gas F1 located in the LNG tank 3 is fed via a low-pressure pump 4 and a low-pressure fluid line 16a to a high-pressure pump 5, which increases the pressure of the liquefied gas F1 to a high pressure of, for example, between 150 and 300 bara. This high-pressure liquid gas is then fed via a high-pressure fluid line 17a, a high-pressure heat exchanger 13 and a high-pressure fluid line 17b to a high-pressure evaporator 7, which evaporates the high-pressure liquid gas to a gaseous or supercritical high-pressure gas, this high-pressure gas, having a pressure of about 300 bara in the embodiment shown, being fed to the high-pressure gas injection engine 2. The illustrated fuel gas supply system 1 further comprises a condenser 6 having an inner space 6d, in which liquid gas F1 and boil-off gas F2 are present at least during operation of the fuel gas supply system. The boil-off gas F2 is supplied via a gas line 15a from the LNG-tank 3 to a compressor 9, which compresses the boil-off gas F2, whereby this compressed boil-off gas F2 is fed via a gas line 15c and via a subsequent inlet 15d into the inner space 6d of the condenser 6. The fuel gas supply system 1 also comprises a condensation core generator 10, to which high-pressure liquid gas is supplied by the high-pressure pump 5 via a side stream or via the high-pressure fluid line 18a. The condensation core generator 10 and the inlet 15d are arranged in the condenser 6 to cooperate in such a way that the liquid condensation cores 10a or liquid gas droplets generated by the condensation core generator 10 and sprayed into the inner space 6d, promote condensation of the supplied boil-off gas F2 in the condenser 6, so that boil-off gas F2 accumulates on the condensation core and condenses to liquid gas F1, and then accumulates in the lower region of the condenser 6. This liquid gas F1 accumulating in the condenser 6 is fed to the high-pressure pump 5 via an outlet 6e and a return line 21, or, as shown in FIG. 3, is optionally fed to the high-pressure pump 5 and/or the LNG tank 3. The high-pressure heat exchanger 13 is arranged in or inside the condenser 6, as shown in FIG. 1, in order to cool the content of the condenser 6, in particular the boil-off gas F2 located therein, by indirect heat exchange and also to condense it. The supercritical high-pressure liquid gas flowing through the heat exchanger 13 thus has the function of a heat sink. The compressor 9 is designed, for example, as a piston compressor, for example as a labyrinth piston compressor, and for example as a two-stage or three-stage piston compressor, wherein at least one of the piston compressors, preferably the first piston compressor arranged downstream of the LNG tank 3, is designed as a labyrinth piston compressor. However, the compressor or at least one compressor stage could also be designed as a turbo compressor or in another compressor technology.

[0030] Optionally, the fuel gas supply system 1 further comprises a low-pressure fluid line 16b and a valve 25a to supply at least a partial flow of the liquid gas F1 delivered by the low-pressure pump 4 to a low-pressure vaporizer 12, which vaporizes the liquid gas F1 to gaseous low-pressure gas, having a pressure in the range of, for example, 7 to 9 bara. This low-pressure gas is fed to a low-pressure consumer 11, for example a gas-powered generator or boiler.

[0031] FIG. 6 shows an embodiment of a condenser 6 in detail, as it could be used in the fuel gas supply system 1 according to FIG. 1. The boil-off gas F2 is introduced into the inner space 6d of the condenser 6 via the gas line 15c and the inlet 15d at the top. A side stream of the high-pressure liquid gas is injected into the inner space 6d of the condenser 6 via the high-pressure line 18a and the condensation core generator 10, forming a plurality of droplets 10a serving as condensation cores. A return line 21 opens into the bottom of the inner space of the condenser 6 to discharge the liquid gas F1 located in the lower portion of the inner space. The high-pressure heat exchanger 13 extends in the inner space 6d of the condenser 6 preferably in a vertical direction from bottom to top, the high-pressure liquid gas being supplied via the high-pressure fluid line 17a and discharged via the high-pressure fluid line 17b. Advantageously, the high-pressure heat exchanger 13 as shown in FIG. 4 extends for the most part, for example 9/10, within that part of the inner space 6d in which the boil-off gas F2 or a mixture of boil-off gas F2 and droplets of liquid gas F1 is located.

[0032] During operation, the condenser 6 can be operated, for example, with the following process parameters. The high-pressure liquid gas is fed to the high-pressure heat exchanger 13 at a pressure of 300 bara, and leaves it at essentially the same pressure. The boil-off gas F1 is introduced at a pressure of 17 bara and a temperature of +40° C. via the inlet 15d from above into the inner space 6d of the condenser 6. The boil-off gas F1 flowing downward inside the condenser 6 from the inlet 15d is cooled by the high-pressure heat exchanger 13 so that a condensation section 6a is formed between the surface 6b of the liquid gas F1 and a boundary region 6c, within which the boil-off gas F2 has a temperature which, taking into account the pressure present in the inner space 6d, is below the boiling temperature of liquid gas F1. The condensation nuclei in the form of liquid gas droplets 10a generated by the condensation nucleus generator 10 are preferably sprayed into the condensation section 6a so that the boil-off gas F2 located in this section condenses on these condensation nuclei and is subsequently fed via the surface 6b to the partial volume 6e of the condenser 6 containing the liquid gas F1. The liquid gas F1 has a pressure of 17 bara and a temperature of -120° C. in the partial volume 6e in the process example described here.

[0033] The method for operating the fuel gas supply system 1 is explained in detail on the basis of the following example. In contrast to a liquefied gas tanker, the stowage space of which consists largely of LNG tanks, a common merchant ship has a relatively small LNG tank, since the stowage space is available for goods to be transported. The high-pressure gas injection engine 2 of such a merchant ship has a gas demand of, for example, about 10 t / h during the voyage. In the LNG tank of the merchant ship, the boil-off rate (BOR), therefore the amount of liquid gas F1 evaporated to boil-off gas F2 is, for example, about 800 kg / h. On the one hand, the fuel gas supply system 1 has the task of supplying the high-pressure gas injection engine 2 with a sufficiently large quantity of high-pressure fuel gas, which varies depending on the load. In addition, the fuel gas supply system 1 has the task of monitoring the gas pressure in the LNG-15 tank and ensuring that the gas pressure does not exceed a predetermined value. In addition, the fuel gas supply system 1 has the task of ensuring that the excess boil-off gas located in the LNG tank is used in an economically as well as ecologically advantageous manner, and in particular is used to feed the high-pressure gas injection engine 2, and if necessary to feed a low-pressure consumer 11.

[0034] The liquefied gas F1 in the LNG tank 3, stored at about atmospheric pressure and a temperature of about -163° C., is conveyed to the high-pressure pump 5 by means of the low-pressure pump 4, and thereby compressed to a pressure of about 7 bara, at a temperature of -150° C. In order to supply the high-pressure gas injection engine 2 with sufficient high-pressure fuel gas, the liquid gas F1 is subsequently compressed in the high-pressure pump 5 to high-pressure liquid gas to a pressure of 300 bara, at a conveying temperature of -150° C., and then vaporized in the high-pressure vaporizer 7 to gaseous or supercritical high-pressure fuel gas. The high-pressure fuel gas thus produced is supplied to the high-pressure gas injection engine 2. The quantity of high-pressure fuel gas supplied can be controlled by appropriately controlling the conveying rate of the high-pressure pump 5 and, if necessary, the low-pressure pump 4.

[0035] The boil-off gas F2 is withdrawn from the tank 3 at approximately atmospheric pressure and a temperature of about -162° C., and then compressed in a compressor 9 to a pressure of about 18 bara, with an outlet temperature of + 40° C. The boil-off gas F2 thus compressed is preferably introduced into the interior 6d of the condenser 6 at this pressure and temperature. The boil-off gas F2 compressed in this way is preferably introduced into the inner space 6d of the condenser 6 at this pressure and temperature.

[0036] As shown in FIG. 6, inside the condenser 6 the high-pressure liquid gas located in the high-pressure heat exchanger 13 flows upwardly at a pressure of 300 bara and a conveying temperature of -150° C., whereas the compressed boil-off gas F2 is introduced into the inner space 6d of the condenser 6 from above, and flows downwardly in the upper section of the condenser 6 along the high-pressure heat exchanger 13, and the compressed exhaust steam gas F2 thus flows in countercurrent with respect to the high-pressure liquid gas flowing inside the high-pressure heat exchanger 13, whereby the exhaust steam gas F2 is cooled, and preferably cooled to its condensation temperature. At a pressure of 17 bara, the boiling temperature of the boil-off gas F1 is about -110° C. In order to achieve complete reliquefaction of the exhaust steam gas F2 in the condenser 6, the high-pressure heat exchanger 13 or the high-pressure gas flowing therein must have sufficient potential to take over the enthalpy at temperatures below -110° C. Taking into account a necessary supersaturation for condensation at 17 bar, the actual condensation temperature will be about 5 to 10 K below the boiling temperature at 17 bar a, so that condensation takes place at about -120° C.

[0037] The -150° C. at which the supercritical high-pressure gas or the high-pressure liquid gas enters the high-pressure heat exchanger 13 on the high-pressure side is not directly available for heat transfer, since several temperature gradients must be taken into account for heat transfer through the supercritical high-pressure gas and the wall of the high-pressure heat exchanger 13. As a first approach, it is assumed that the wall temperature of the high pressure heat exchanger 13 on the side facing the boil-off gas F2 is -145° C. This allows enthalpy transfer from the boil-off gas F2 to the supercritical high-pressure gas or the high-pressure liquid gas in a temperature window of 25°K.

[0038] In order to increase the efficiency of reliquefaction of boil-off gas F2 to liquefied gas F1 in the condenser 6, a condensation nucleus generator 10 is used to generate liquefied gas droplets as condensation nuclei, which are fed into the interior 6d of the condenser 6. For this purpose, a portion of the liquid gas F1 compressed to high-pressure liquid gas by the high-pressure pump 5 is supplied to the condensation core generator 10 in a side stream 18a, the supplied high-pressure liquid gas having a pressure of 300 bara and a temperature of -150° C. The droplets 10a generated in the condensation core generator 10, for example with the aid of at least one nozzle, are introduced into a condensation section 6a of the condenser 6, in which the temperature of the boil-off gas F2 is already below its condensation temperature of -110° C. The liquid gas droplets 10a entering the condenser 6 are thus subcooled, since the condensation temperature of the boil-off gas F2 is 110° C. at 17 bara.

[0039] The supercooled liquid gas droplets 10a serve as condensation nuclei for the boil-off gas F2 to be condensed. That is, each supercooled liquid gas droplet 10a attracts gas molecules from the boil-off gas F2 to be condensed. Condensation of the boil-off gas F2 on the liquid gas droplets 10a is more effective than condensation on the outer wall of the high-pressure heat exchanger 13, for the following reasons: [0040] The liquid gas droplets are supercooled at -150° C., resulting in a higher potential for attracting gas molecules of the boil-off gas F2 due to the larger temperature difference. [0041] The specific surface area of a liquid gas droplet is larger than the comparable surface area of the outer wall of the high-pressure heat exchanger 13, since the area of a sphere is pi times larger than the area of a flat or curved surface.

[0042] FIGS. 2 and 3 show further embodiments of fuel gas supply systems 1 in which, in contrast to the embodiment according to FIG. 1, a heat exchanger 8 is arranged in the boil-off gas flow, after the boil-off gas F2 has left the LNG tank 3, which serves to further cool the high-pressure liquid gas after the high-pressure pump 5 and before it enters the condensation core generator 10. As a result, the boil-off gas F2 flowing in the fluid line 15a, 15b is heated in the heat exchanger 8. The heat exchanger 8 is preferably supplied by a side stream 18a of the high-pressure fluid gas, wherein the side stream 18a is taken from the high-pressure pump 5 or downstream of the high-pressure pump 5 from the high-pressure fluid line 17a, is supplied to the heat exchanger 8, and is subsequently preferably supplied to the condensation core generator 10. The heat exchanger 8 is preferably arranged upstream of the compressor 9, as shown in FIG. 2.

[0043] For the fuel gas supply system 1 according to the invention, it is important that the condensation of the boil-off gas F2 supplied to the condenser 6, as shown in FIG. 6, in the inner space 6d of the condenser 6 preferably takes place as energy-efficiently as possible. It is generally known to a person skilled in the art that the fuel gas supply system 1 shown in FIGS. 1 to 5 comprises a control device not shown, as well as a plurality of signal lines, for example for controlling the low-pressure pump 4, the high-pressure pump 5, the compressor 9, and the valves 25a to 25g, and comprises a plurality of signal lines as well as sensors, for example for detecting pressure and / or temperature at a wide variety of points at which the liquid gas F1 and boil-off gas F2, as well as high-pressure liquid gas and high-pressure fuel gas, flows through the fuel gas supply system 1. It is therefore easy for a person skilled in the art to understand, on the basis of the present disclosure, which control options and which parameter optimizations the fuel gas supply system 1 according to the invention offers in order to operate the fuel gas supply system 1 according to the invention advantageously, and in particular in order to ensure that the condensation in the condenser 6 proceeds advantageously, preferably energy-efficiently. Thus, for example, it can be derived in a simple manner from FIG. 1 that the condensation of the boil-off gas F2 in the condenser 6 is effected by means of the delivery rate of boil-off gas F2 delivered by the compressor 9, and if necessary also its temperature, and/or by means of the conveying rate of high-pressure liquid gas supplied by the side stream 18a, 18b to the condensation core generator 10, and in particular also its temperature, and/or by the size and quantity of condensation nuclei 10a produced by the condensation nucleus generator 10, and/or by the arrangement and orientation of the flow of liquid gas droplets 10a in the inner space 6d of the condenser 6 and/or by the arrangement and configuration of the high-pressure heat exchanger 13 in the inner space 6d of the condenser 6. Moreover, the temperature of the liquid droplets 10a sprayed into the inner space 6d, and/or the temperature difference of the introduced boil-off gas F2 and liquid droplets 10a can be influenced by the use and skillful arrangement and design of a heat exchanger 8 shown in FIGS. 2 to 5. Therefore, based on the idea of the invention disclosed herewith, it is possible for a person skilled in the art, on the basis of his expertise, to select process parameters in a simple manner in such a way that the fuel gas supply system can be operated in an economically advantageous manner, and in particular in an energy-efficient manner, and that in particular the condensation process taking place in the condenser 6 has a high condensation rate.

[0044] In a further embodiment, FIG. 3 shows a gas storage tank 14 which is connected to the gas lines 15a, 15c via controllable valves 25d, 25e. This gas storage tank 14 is used to hold boil-off gas F2, in particular during periods of time during which the high-pressure gas injection engine 2 does not require fuel, for example because the merchant ship is stationary. During such a period of time, no high-pressure liquid gas is supplied to the high-pressure gas injection engine 2, so that the high-pressure liquid gas in the heat exchanger 13 in the condenser 6 cannot serve as a heat sink, and therefore no cooling takes place in the condenser 6, so that condensation in the condenser 6 comes to a standstill. However, during the standstill of the merchant vessel, evaporated gas F2 still accumulates in the LNG tank 3, which must be discharged from the LNG tank 3 in order to prevent an impermissible pressure increase in the LNG tank 3. The gas storage tank 14 is particularly advantageous during such time periods because the boil-off gas F2 can be conveyed to the gas storage tank 14 via the compressor 9, can be temporarily stored therein, and can subsequently be removed from the gas storage tank 14 and liquefied in the condenser 6 during a voyage of the merchant vessel, or during the supply of high-pressure liquefied gas to the high-pressure gas injection engine 2.

[0045] The gas storage container 14 is advantageously filled with a highly porous solid (e.g. adsorbent or metal hydride) or a liquid solvent, which considerably increases the storage capacity of the gas storage container 14, compared to that of an empty container, at the same pressure and temperature. When the gas storage tank 14 is not in storage operation or is being emptied, the gas storage tank 14 is connected to the suction line 15b of the compressor 9 by opening the valve 25d and closing the valve 25e. When the gas storage tank 14 is in storage mode, it is connected to the discharge line 15c downstream of the compressor 9 by the valve 25e being open, and the valve 25d being closed. It may also prove advantageous to supply at least part of the boil-off gas F2 to a low-pressure consumer 11 via a fluid line 15e, preferably a controllable valve 25c and preferably also a controllable valve 25b being provided to control the flow of gas to the low-pressure consumer 11 and, if necessary, to control a division of the gas quantities between the condenser 6 and the low-pressure consumer 11.

[0046] It may also prove advantageous to feed the liquid gas F1 flowing out of the inner space 6d of the condenser 6 via the return line 21 controllably via a valve 25f of the high-pressure pump 5 and/or via a valve 25g to the LNG tank 3.

[0047] FIG. 4 shows a further embodiment of a fuel gas supply system 1, in which the boil-off gas F2 is fed to the heat exchanger 8 downstream of the tank 3, is then compressed in the compressor 9 to form compressed boil-off gas F2, this compressed boil-off gas F2 being fed in turn to the heat exchanger 8, so that the compressed boil-off gas F2 is strongly cooled in the heat exchanger 8, and, cooled in this way, is fed via the inlet 15d to the condenser 6. This compressed and strongly cooled exhaust steam gas F2 has the advantage that in the condenser 6 this exhaust steam gas F2 condenses better or more simply and thus more energy-efficiently.

[0048] FIG. 5 shows a further embodiment of a fuel gas supply system 1 which, in contrast to the embodiment shown in FIG. 3, has two separate high-pressure pumps 5, namely a first high-pressure pump 5a and a second high-pressure pump 5b, and two separate high-pressure fluid lines 17a, 17c connected thereto. In addition, the embodiment example according to FIG. 5, in contrast to the embodiment example according to FIG. 3, has no valve 25g in the return line 21, and thus no return to the tank 3. The embodiment according to FIG. 5 is preferably operated in such a way that liquid gas F1 from the tank 3 is supplied only to the first high-pressure pump 5a and is compressed in the first high-pressure pump 5a to form high-pressure liquid gas. This high-pressure liquid gas is fed to the high-pressure heat exchanger 13 and then to the high-pressure evaporator 7, as shown in FIG. 5. In an advantageous process, the liquid gas F1, essentially a condensate, located in the condenser 6 is fed to the second high-pressure pump 5b and compressed in the second high-pressure pump 5b into high-pressure liquid gas, which, bypassing the condenser 6, is fed into the high-pressure fluid line 17b and/or directly into the high-pressure evaporator 7. This arrangement or process has the advantage that the liquid gas F1 discharged from the tank 3 is not heated by condensate or liquid gas F1 generated in the condenser 6, and liquid gas F1 fed back into the low-pressure fluid line 16a. Therefore, this embodiment has the advantage that the condensation in the condenser 6 has a higher efficiency or efficiency factor. In another possible method, the second high-pressure pump 5b can either be supplied only with condensate or liquid gas F1 from the condenser 6 via the valve 25f, or can be supplied only with liquid gas F1 from the tank 3 via the valve 25g, or can comprise a mixture comprising a proportion of liquid gas F1 from the condenser 6 and a proportion of liquid gas F1 from the tank 3 by controlling both valves 25f, 25g accordingly. The mixing ratio of these two portions of liquid gas F1 can be varied, depending on the respective operating point of the fuel gas supply system 1, for example in order to optimize the efficiency of the fuel gas supply system 1, for example depending on the amount of high-pressure fuel gas requested by the high-pressure gas injection engine 2.