Fuel gas supply system and method for supplying fuel gas to a high-pressure gas injection engine

Description

[0001] The invention relates to a fuel gas supply system. The invention further relates to a method for supplying a high-pressure gas-injected engine with fuel gas. State of the art

[0002] Natural gas is an increasingly important energy source. In commercial shipping, natural gas is increasingly being used as an alternative fuel to meet the shipping industry's new requirements regarding exhaust gas purity and greenhouse gas reduction. The natural gas used as fuel is typically stored on ships in liquid form as liquefied natural gas, or LNG for short, and in LNG tanks at approximately atmospheric pressure and a temperature of approximately -163°C. Due to the low boiling point of liquefied natural gas of approximately -162°C at atmospheric pressure, the heat acting on the LNG tanks from the outside continuously vaporizes the liquid gas, which accumulates at the top of the LNG tank as boil-off gas, or BOG for short, resulting in a pressure increase in the LNG tank.To counteract this pressure increase, it is known to install a BOG reliquefaction plant, which liquefies the evaporative gas and returns it to the LNG tank as liquid gas. Another option is to use the evaporative gas directly as marine propulsion fuel. For this purpose, natural gas is compressed to a high pressure, for example, in the range of 150 to 300 bara or 400 bara, to form high-pressure fuel gas and fed into a high-pressure gas injection engine. Such an engine is marketed, for example, by MAN-SE under the name ME-GI engine. Such an engine preferably forms the main propulsion system of a merchant vessel.

[0003] Document KR 10 2011 0030149 discloses a fuel gas supply system for supplying a high-pressure gas injection engine of a liquefied gas tanker with fuel gas. This system is capable of compressing natural gas stored in the LNG tank to such a high pressure that it can be fed to the high-pressure gas injection engine, and is capable of preventing an excessive pressure increase in the LNG tank by re-liquefying exhaust gas, if necessary, and then feeding it to the high-pressure gas injection engine and / or the LNG tank. The fuel gas supply system disclosed in document KR1020110030149 has the disadvantages of being relatively complex and expensive, using an external cooling circuit for re-liquefaction, and requiring considerable energy consumption for its operation.

[0004] Document KR 100 726 290 discloses a method for recycling excess evaporation gas by controlling the liquefaction, reliquefaction, or use of the evaporation gas. The method comprises the steps of liquefying the evaporation gas, selectively returning liquefied gas to a gas storage tank, or selectively supplying the liquefied gas to a liquefied gas vaporizer through first and second control valves. A specific amount of the liquefied gas is vaporized in the liquefied gas vaporizer so that it is suitable for supply as fuel by controlling the temperature, pressure, and flow. The method further comprises supplying the vaporized gas as fuel to a propulsion system and retrieving the liquefied evaporation gas or opening / closing the first, second, third, and fourth valves to combust a small amount of the evaporation gas.In this system, the specific heat capacity of injected subcooled LNG is used to reliquefy BOG. ​​However, it is a low-pressure system and is not suitable for supplying fuel gas to a high-pressure gas-injected engine. Description of the invention

[0005] The object of the invention is to create an economically advantageous fuel gas supply system. Furthermore, the object of the invention is to create an economically advantageous method for supplying a high-pressure gas-injected engine with fuel gas. This object is achieved by a fuel gas supply system having the features of claim 1. Dependent claims 2 to 10 relate to further advantageous embodiments. The object is further achieved by a method having the features of claim 11. Dependent claims 12 to 14 relate to further advantageous method steps.

[0006] The object is achieved in particular with a fuel gas supply system for supplying a high-pressure gas injection engine with gas stored in a liquefied gas tank, in particular an LNG tank, comprising a condenser, comprising a compressor which is fluidically connectable to the liquefied gas tank in order to supply exhaust evaporation gas from the liquefied gas tank, wherein the compressor is fluidically connected downstream via an inlet to an interior of the condenser in order to introduce the exhaust evaporation gas into the interior, and comprising a condensation nucleus generator, wherein the condensation nucleus generator is designed in such a way that it generates liquefied gas droplets which serve as condensation nuclei, wherein the condensation nucleus generator introduces the condensation nuclei into the interior in order to promote condensation of the introduced exhaust evaporation gas via the condensation nuclei, so that liquefied gas is formed therefrom,and wherein the liquefied gas formed in the condenser can be fed to the liquefied gas tank, wherein the system further comprises a high-pressure pump which is fluidly connectable to the liquefied gas tank in order to supply liquefied gas (F1) from the liquefied gas tank and to compress it into a high-pressure liquefied gas, wherein a high-pressure heat exchanger is arranged in the condenser, wherein a high-pressure evaporator is provided which is fluidly 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 liquefied gas into a high-pressure fuel gas, and the high-pressure fuel gas is fed to the high-pressure gas injection engine after the high-pressure evaporator, and wherein the condensation core generator is fluidly connected upstream to the high-pressure pump, wherein the liquefied gas formed in the condenser is additionally fed to the high-pressure pump,wherein the condensation nucleus generator is designed such that it generates liquid gas droplets from the high-pressure liquid gas, which serve as condensation nuclei.,

[0007] The object is achieved in particular by a method for supplying a high-pressure gas injection engine with gas which is stored in a liquefied gas tank, in particular an LNG tank, partly as liquefied gas and partly as exhaust vapor gas, by feeding the exhaust vapor gas from the liquefied gas tank to a compressor and then introducing it into a condenser, wherein a stream of condensation nuclei in the form of liquefied gas droplets is generated from high-pressure liquefied gas in a condensation nucleus generator, which are fed to the introduced exhaust vapor gas in the condenser in order to promote condensation of the exhaust vapor gas into liquefied gas by the liquefied gas droplets, and by feeding the liquefied gas formed in the condenser to the liquefied gas tank, wherein the liquefied gas from the liquefied gas tank is fed to a high-pressure pump and compressed by the pump to form a high-pressure liquefied gas,wherein the high-pressure liquefied gas is then fed to a high-pressure heat exchanger arranged in a condenser and subsequently to a high-pressure evaporator, wherein the high-pressure liquefied gas is converted into a high-pressure fuel gas in the high-pressure evaporator, so that a high-pressure fuel gas is generated, which is fed to the high-pressure gas injection engine, and wherein the liquefied gas formed in the condenser is fed to the high-pressure pump and the flow of condensation nuclei in the form of liquefied gas droplets is generated from high-pressure liquefied gas.

[0008] The fuel gas supply system according to the invention uses a condenser for condensing exhaust vapor gases into liquefied gas. For this purpose, condensation nuclei are generated from liquefied gas using a condensation nucleus generator. These nuclei come into contact with exhaust vapor gas located in an interior of the condenser, so that the exhaust vapor gas adheres to the condensation nuclei and condenses into liquefied gas. The condensation nuclei are preferably generated using high-pressure liquefied gas, which is passed through a nozzle, in particular a spray nozzle, so that a plurality of liquid droplets are generated with the help of the nozzle, which serve as condensation nuclei.The fuel gas supply system according to the invention has the advantages that condensation takes place at a relatively low pressure, for LNG, for example, at a pressure in the range below 50 bara, preferably in a range from 20 to 30 bara, and particularly preferably in a range from 10 to 20 bara, and that a condensate or liquefied gas is produced at a relatively low temperature, for example with a temperature below -120°C, and preferably in the range from -120°C to -150°C. A pressure below 20 bara has the advantage that a two-stage compressor is sufficient to compress the exhaust vapor gas F2 in the compressor 9. For a pressure in the range between 40 and 50 bara, a three-stage compressor 9 is required. For cost reasons, a two-stage compressor 9 or compression of the exhaust vapor gas F2 in a range from 10 to 20 bara is particularly preferred.The relatively low pressure inside the condenser during condensation requires a lower specific enthalpy for the compression process of the exhaust gas upstream of the condenser, which takes place before the exhaust gas is fed to the condenser. This offers the advantage that a smaller and therefore more cost-effective compressor is sufficient for this compression process. If the condensate is subsequently fed to a high-pressure pump, the lower temperature of the condensate also leads to reduced evaporation in the high-pressure pump and therefore increases the mean time between maintenance of the high-pressure pump, also known as the MTBO, so that the fuel gas supply system according to the invention can be operated more cost-effectively and reliably.

[0009] A "high-pressure pump" within the meaning of the invention is understood in particular to be a pump that generates pressures of at least 80 bara, preferably 100 to 400 bara, typically 150 to 300 bara. It can be a positive-displacement pump, for example, a piston pump. A "low-pressure pump," on the other hand, is understood to be a pump, for example, a turbomachine, that generates pressures below 80 bara, typically 5 to 25 bara.

[0010] It is preferred that the liquefied gas tank be an LNG tank and the fuel gas be natural gas, especially methane. However, other fuel gases, especially ethylene, ethane, or ammonia, are also conceivable. In this case, the system and method would have to be operated under adapted pressure and temperature conditions. For example, if ammonia is used as the fuel, the high-pressure pump should generate a pressure of 300 to 400 bara. Such a liquefied gas could be introduced into the condensation section of a condenser as liquefied gas droplets, at a temperature of -10 to +10°C and a pressure of 5 to 10 bara. Are there other adaptations to the system that would be necessary for its functioning? Materials? Processes?

[0011] In a preferred embodiment, it is sufficient if only a small amount of liquefied gas is injected by means of the condensation nucleus generator compared to the mass flow of the gas stream to be condensed. In particular, it is sufficient if the mass flow of liquefied gas (F1) in the condensation nucleus generator is 1 to 5% of the mass flow of the gas to be condensed (F2).

[0012] The fuel gas supply system according to the invention thus has the advantage that the reliquefaction pressure and the reliquefaction temperature of the exhaust gas to be liquefied or the liquefied gas produced thereby are reduced.

[0013] The fuel gas supply system according to the invention has the further advantage that the compression of the exhaust gas upstream of the condenser requires a reduced specific enthalpy, so that this compressor can be designed more cost-effectively and, in addition, reduced operating costs (OPEX, "Operational Expenditures") and, in particular, reduced energy costs are incurred for this compressor.

[0014] The fuel gas supply system according to the invention has the further advantage that the improved condensation requires a smaller condenser design, which reduces capital expenditure (CAPEX). The heat exchanger according to the invention is a heat exchanger based on indirect heat transfer, i.e., the fluid flows are separated by a heat-permeable wall. This allows for the realization of a high-pressure heat exchanger in which the coolant is supplied to the cooling section at a high pressure (e.g., 80 to 300 bara) and leaves it again at essentially the same pressure. Due to the improved condensation, a high-pressure heat exchanger with a smaller heat transfer surface is sufficient, so that a smaller high-pressure heat exchanger and thus a smaller condenser are required within the condenser.

[0015] The fuel gas supply system according to the invention has the further advantage that the performance of the high-pressure pump is improved by the reduced, lower temperature of the liquid gas condensed from the exhaust gas.

[0016] Preferably, a side stream of high-pressure liquefied gas is extracted from or downstream of the high-pressure pump. This side stream of high-pressure liquefied gas is advantageously cooled in a heat exchanger, with exhaust steam gas from the liquefied gas tank being fed to this heat exchanger. The condenser advantageously comprises a condensation nucleus generator or an injector system for droplet generation for condensing the exhaust steam gas, to which the subcooled high-pressure liquefied gas is fed in order to generate condensation nuclei or aerosol droplets and introduce them into the interior of the condenser or spray them within the interior of the condenser. The condensation nuclei serve to improve the condensation of the exhaust steam gas. The LNG is injected using special nozzles that ensure the correct droplet size so that these LNG droplets can serve as condensation nuclei.This utilizes a physical surface effect, a curvature effect, or interfacial effect, also known as the Gibbs-Thomson effect. The technical principles are known from the fields of nanotechnology and aerosol technology. It is preferred if the nozzle is a high-pressure nozzle, particularly preferably a high-pressure nozzle with a nozzle diameter in the range of 1 to 1000 µm, preferably 5 to 500 µm. Such a high-pressure nozzle is suitable for generating droplets in the relevant range, typically droplets with a diameter of 100 nm to 100 µm, preferably 500 nm to 50 µm.

[0017] In a preferred embodiment, the exhaust evaporation gas (F2) is introduced into the condenser from above, with the high-pressure heat exchanger extending vertically within the condenser and the high-pressure heat exchanger being arranged such that the high-pressure liquefied gas flows from bottom to top in the high-pressure heat exchanger. This supports the natural temperature gradient in the interior of the condenser. Preferably, the condensation nucleus generator is arranged such that condensation nuclei generated by the condensation nucleus generator are introduced into a condensation section in the interior of the condenser, in which the interior has a condensation temperature. For example, at a pressure of 17 bara, the boiling point of natural gas is approximately -110°C. To achieve complete re-liquefaction of the exhaust evaporation gas F2 in the condenser, the actual condensation temperature would have to be approximately -120°C.Preferably, the condensation nucleus generator is arranged such that the condensation nuclei enter the interior of the condenser in a first half in the flow direction of the liquid gas (F1), preferably a first third in the flow direction of the liquid gas (F1), of the cooling line of the high-pressure heat exchanger.

[0018] The invention is described in detail below using several embodiments. Short description of the drawings

[0019] The drawings used to explain the embodiments show: Fig. 1 schematically shows a first embodiment of a fuel gas supply system; Fig. 2 schematically shows a second embodiment of a fuel gas supply system; Fig. 3 schematically shows a third embodiment of a fuel gas supply system; Fig. 4 schematically shows a fourth embodiment of a fuel gas supply system; Fig. 5 schematically shows a fifth embodiment of a fuel gas supply system; Fig. 6 schematically shows a condenser.

[0020] In principle, identical parts in the drawings are provided with the same reference symbols. Ways to implement the invention

[0021] Fig. 1shows 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 liquefied gas F1 and, due to the evaporation of the liquefied gas F1 occurring in the LNG tank 3, partly in the form of evaporation gas F2. This evaporation 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 liquefied 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 liquefied gas into a gaseous or supercritical high-pressure gas. This high-pressure gas, having a pressure of approximately 300 bar in the illustrated embodiment, is fed to the high-pressure gas injection engine 2. The illustrated fuel gas supply system 1 also comprises a condenser 6 with an interior space 6d, in which, at least during operation of the fuel gas supply system, liquefied gas F1 and exhaust vapor gas F2 are located. The exhaust vapor gas F2 is fed via a gas line 15a from the LNG tank 3 to a compressor 9, which compresses the exhaust vapor gas F2. This compressed exhaust vapor gas F2 is introduced into the interior space 6d of the condenser 6 via a gas line 15c and a subsequent inlet 15d.The fuel gas supply system 1 also comprises a condensation nucleus generator 10, to which high-pressure liquefied gas is supplied from the high-pressure pump 5 via a side stream or via the high-pressure fluid line 18a. The condensation nucleus generator 10 and the inlet 15d are arranged in cooperation in the condenser 6 such that the liquid condensation nuclei 10a or liquefied gas droplets generated by the condensation nucleus generator 10 and sprayed into the interior 6d promote condensation of the supplied exhaust vapor gas F2 in the condenser 6, so that the exhaust vapor gas F2 deposits on the condensation nucleus and condenses to liquefied gas F1, which then collects in the lower region of the condenser 6.

[0022] This liquid gas F1 accumulating in the condenser 6 is fed via an outlet 6e and a return line 21 to the high pressure pump 5, or, as in Figure 3shown, optionally fed to the high-pressure pump 5 and / or the LNG tank 3. The high-pressure heat exchanger 13 is, as shown in Figure 1 shown, arranged in or within the condenser 6 in order to cool the contents of the condenser 6, in particular the exhaust evaporation gas F2 located therein, by indirect heat exchange and also to condense it. The supercritical high-pressure liquefied gas flowing through the heat exchanger 13 thus functions as 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, with at least one of the piston compressors, preferably the first piston compressor arranged downstream of the LNG tank 3, being designed as a labyrinth piston compressor. However, the compressor or at least one compressor stage could also be designed as a turbocompressor or using another compressor technology.

[0023] Optionally, the fuel gas supply system 1 also comprises a low-pressure fluid line 16b and a valve 25a for supplying at least a partial flow of the liquefied gas F1 delivered by the low-pressure pump 4 to a low-pressure evaporator 12, which evaporates the liquefied gas F1 into gaseous low-pressure gas having a pressure in the range of, for example, 7 to 9 bara. This low-pressure gas is supplied to a low-pressure consumer 11, for example, a gas-powered generator or boiler.

[0024] Figure 6 shows an embodiment of a condenser 6 in detail, as it is used in the fuel gas supply system 1 according to Figure 1could be used. The exhaust gas F2 is introduced via the gas line 15c and the inlet 15d at the top into the interior 6d of the condenser 6. A side stream of the high-pressure liquefied gas is sprayed into the interior 6d of the condenser 6 via the high-pressure line 18a and the condensation nucleus generator 10, forming a plurality of droplets 10a serving as condensation nuclei. A return line 21 opens into the interior of the condenser 6 at the bottom to discharge the liquefied gas F1 located in the lower region of the interior. The high-pressure heat exchanger 13 extends in the interior 6d of the condenser 6, preferably in a vertical direction from bottom to top, with the high-pressure liquefied 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 extends as shown in Figure 4shown for the most part, for example 9 / 10, within that part of the interior space 6d in which the evaporation gas F2 or a mixture of evaporation gas F2 and droplets of liquid gas F1 is located.

[0025] The condenser 6 can be operated, for example, with the following process values. The high-pressure liquefied gas is fed to the high-pressure heat exchanger 13 at a pressure of 300 bara and leaves it again at essentially the same pressure. The exhaust evaporation gas F1 is introduced at a pressure of 17 bara and a temperature of +40°C via the inlet 15d from above into the interior 6d of the condenser 6. The exhaust evaporation gas F1 flowing downwards within the condenser 6 from the inlet 15d is cooled by the high-pressure heat exchanger 13, so that a condensation section 6a forms between the surface 6b of the liquefied gas F1 and a boundary region 6c, within which the exhaust evaporation gas F2 has a temperature which, taking into account the pressure present in the interior 6d, is below the evaporation temperature of the liquefied 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 exhaust gas F2 located in this section condenses on these condensation nuclei and is then fed via the surface 6b to the sub-volume 6e of the condenser 6 containing the liquid gas F1. In the process example described here, the liquid gas F1 has a pressure of 17 bar and a temperature of -120°C in the sub-volume 6e.

[0026] The method for operating the fuel gas supply system 1 is explained in detail using the following exemplary embodiment. In contrast to a liquefied gas tanker, whose storage space consists largely of LNG tanks, a conventional merchant ship has a relatively small LNG tank, since the storage space is available for goods to be transported. The high-pressure gas injection engine 2 of such a merchant ship has a gas requirement of, for example, approximately 10 t / h while en route. In the LNG tank of the merchant ship, the boil-off rate (BOR), hence the amount of liquefied gas F1 evaporated to exhaust gas F2, is, for example, approximately 800 kg / h. The fuel gas supply system 1 has the task, on the one hand, of supplying the high-pressure gas injection engine 2 with a load-dependent, yet sufficiently large, amount of high-pressure fuel gas.In addition, the fuel gas supply system 1 is responsible for monitoring the gas pressure in the LNG-15 tank and ensuring that the gas pressure does not exceed a specified value. Furthermore, the fuel gas supply system 1 is responsible for ensuring that the excess evaporation gas in the LNG tank is used in an economically and ecologically advantageous manner, and in particular, for feeding the high-pressure gas injection engine 2 and, if necessary, for feeding a low-pressure consumer 11.

[0027] The liquefied gas F1 contained in the LNG tank 3, stored at approximately atmospheric pressure and a temperature of approximately -163°C, is pumped to the high-pressure pump 5 by the low-pressure pump 4, where it is compressed to a pressure of approximately 7 bara and a temperature of -150°C. To supply the high-pressure gas injection engine 2 with sufficient high-pressure fuel gas, the liquefied gas F1 is subsequently compressed in the high-pressure pump 5 to high-pressure liquefied gas at a pressure of 300 bara, at a delivery temperature of -150°C, and then evaporated in the high-pressure evaporator 7 to gaseous or supercritical high-pressure fuel gas. The high-pressure fuel gas thus produced is fed to the high-pressure gas injection engine 2. The quantity of high-pressure fuel gas supplied can be regulated by appropriately controlling the delivery rate of the high-pressure pump 5 and, if applicable, the low-pressure pump 4.

[0028] The exhaust gas F2 is taken from the tank 3 at approximately atmospheric pressure and a temperature of approximately -162°C and then compressed in a compressor 9 to a pressure of approximately 18 bara, with an outlet temperature of +40°C. The thus compressed exhaust gas F2 is preferably introduced into the interior space 6d of the condenser 6 at this pressure and temperature.

[0029] As in Figure 6As shown, within the condenser 6, the high-pressure liquefied gas located in the high-pressure heat exchanger 13 flows upwards at a pressure of 300 bara and a delivery temperature of -150°C, whereas the compressed evaporative gas F2 is introduced from above into the interior 6d of the condenser 6 and flows downwards in the upper section of the condenser 6 along the high-pressure heat exchanger 13. The compressed evaporative gas F2 thus flows in countercurrent to the high-pressure liquefied gas flowing within the high-pressure heat exchanger 13, as a result of which the evaporative gas F2 is cooled, and preferably cooled to its condensation temperature. At a pressure of 17 bara, the boiling point of the evaporative gas F1 is approximately -110°C. In order to achieve complete re-liquefaction of the evaporative gas F2 in the condenser 6, the high-pressure heat exchanger 13 orThe high-pressure gas flowing therein must have sufficient potential to absorb the enthalpy at temperatures below -110°C. Taking into account the necessary supersaturation for condensation at 17 bar, the actual condensation temperature will be approximately 5 to 10 K below the boiling temperature at 17 bar a, so that condensation takes place at approximately -120°C.

[0030] The -150°C at which the supercritical high-pressure gas or high-pressure liquefied gas enters the high-pressure heat exchanger 13 on the high-pressure side is not directly available for heat transfer, as multiple temperature gradients must be considered 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 exhaust gas F2 is -145°C. This enables enthalpy transfer from the exhaust gas F2 to the supercritical high-pressure gas or high-pressure liquefied gas within a temperature window of 25°K.

[0031] In order to increase the efficiency of the reliquefaction of exhaust vapor gas F2 into liquid gas F1 in the condenser 6, liquid gas droplets are generated as condensation nuclei with the aid of a condensation nucleus generator 10, which are injected into the interior 6d of the condenser 6. For this purpose, a portion of the liquid gas F1 compressed into high-pressure liquid gas by the high-pressure pump 5 is fed to the condensation nucleus generator 10 in a side stream 18a, wherein the supplied high-pressure liquid gas has a pressure of 300 bara and a temperature of -150°C. The droplets 10a generated in the condensation nucleus 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 exhaust vapor 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 exhaust gas F2 is 110°C at 17 bara.

[0032] The subcooled liquid gas droplets 10a serve as condensation nuclei for the exhaust gas F2 to be condensed. This means that each subcooled liquid gas droplet 10a attracts gas molecules from the exhaust gas F2 to be condensed. The condensation of the exhaust 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: The liquid gas droplets are subcooled at -150°C, which creates a higher potential for attraction of gas molecules of the exhaust gas F2 due to the larger temperature difference. 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.

[0033] The Figures 2 and 3 show further embodiments of fuel gas supply systems 1, in which, in contrast to the embodiment according to Figure 1, in the exhaust gas stream, after the exhaust gas F2 has exited the LNG tank 3, a heat exchanger 8 is arranged, which serves to further cool the high-pressure liquefied gas after the high-pressure pump 5 and before entering the condensation core generator 10. As a result, the exhaust 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 liquefied 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 fed to the heat exchanger 8, and subsequently preferably fed to the condensation core generator 10. The heat exchanger 8 is preferably as in Figure 2 shown, arranged upstream of the compressor 9.

[0034] For the fuel gas supply system 1 according to the invention, it is important that the Figure 6The condensation of the exhaust gas F2 supplied to the condenser 6 in the interior 6d of the condenser 6 preferably takes place in the most energy-efficient manner possible. It is generally known to a person skilled in the art that the Figures 1 to 5The fuel gas supply system 1 shown comprises a control device (not shown) and 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 a plurality of signal lines and sensors, for example for detecting pressure and / or temperature at various points of the liquefied gas F1 and exhaust gas F2 flowing through the fuel gas supply system 1, as well as of the high-pressure liquefied gas and the high-pressure fuel gas. Based on the present disclosure, it is therefore easy for a person skilled in the art to understand which control options and parameter optimizations the fuel gas supply system 1 according to the invention offers in order to advantageously operate the fuel gas supply system 1 according to the invention, and in particular to ensure that the condensation in the condenser 6 proceeds advantageously, preferably in an energy-efficient manner.For example, . Figure 1 It can be easily deduced that the condensation of the exhaust evaporation gas F2 in the condenser 6 can be influenced by the delivery rate of exhaust evaporation gas F2 delivered by the compressor 9, and possibly also its temperature, and / or by the delivery rate of high-pressure liquid gas supplied to the condensation nucleus generator 10 by the side stream 18a, 18b, and in particular also its temperature, and / or by the size and quantity of condensation nuclei 10a generated by the condensation nucleus generator 10, and / or the arrangement and orientation of the flow of the liquid gas droplets 10a in the interior 6d of the condenser 6 and / or the arrangement and design of the high-pressure heat exchanger 13 in the interior 6d of the condenser 6. In addition, by using and cleverly arranging and designing a Figures 2 to 5The temperature of the liquid droplets 10a sprayed into the interior 6d and / or the temperature difference between the introduced exhaust evaporation gas F2 and the liquid droplets 10a can be influenced by the heat exchanger 8 shown. Therefore, based on the inventive concept disclosed herein, a person skilled in the art can easily select process parameters based on their specialist knowledge in such a way that the fuel gas supply system is economically advantageous and, in particular, energy-efficient, and that, in particular, the condensation process taking place in the condenser 6 has a high condensation rate.

[0035] Figure 3shows, in a further embodiment, a gas storage tank 14 which is connected to the gas lines 15a, 15c via controllable valves 25d, 25e. This gas storage tank 14 serves to accommodate exhaust vapor gas F2, particularly during periods during which the high-pressure gas injection engine 2 does not require fuel, for example because the merchant vessel is stationary. During such a period, no high-pressure liquefied gas is supplied to the high-pressure gas injection engine 2, so that the high-pressure liquefied 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, while the merchant vessel is stationary, exhaust vapor gas F2 still accumulates in the LNG tank 3, which must be discharged from the LNG tank 3 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 exhaust evaporation gas F2 can be conveyed via the compressor 9 into the gas storage tank 14, can be temporarily stored there, and can then 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.

[0036] The gas storage vessel 14 is advantageously filled with a highly porous solid (e.g., an adsorbent or metal hydride) or a liquid solvent, which significantly increases the storage capacity of the gas storage vessel 14 compared to that of an empty vessel at the same pressure and temperature. When the gas storage vessel 14 is not in storage mode or is being emptied, the gas storage vessel 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 vessel 14 is in storage mode, it is connected to the pressure line 15c downstream of the compressor 9 by opening the valve 25e and closing the valve 25d.It may also prove advantageous to supply at least a portion of the exhaust evaporation gas F2 to a low-pressure consumer 11 via a fluid line 15e, wherein preferably a controllable valve 25c and preferably also a controllable valve 25b are provided in order to control the gas flow to the low-pressure consumer 11 and, if necessary, to control a distribution of the gas quantities between the condenser 6 and the low-pressure consumer 11.

[0037] It may also prove advantageous to supply the liquefied gas F1 flowing out of the interior 6d of the condenser 6 via the return line 21 to the high-pressure pump 5 via a valve 25f and / or to the LNG tank 3 via a valve 25g.

[0038] Figure 4shows a further embodiment of a fuel gas supply system 1, in which the exhaust evaporation gas F2 is fed to the heat exchanger 8 after the tank 3, is then compressed in the compressor 9 to form compressed exhaust evaporation gas F2, wherein this compressed exhaust evaporation gas F2 is in turn fed to the heat exchanger 8, so that the compressed exhaust evaporation gas F2 is significantly cooled in the heat exchanger 8, and thus cooled, is fed to the condenser 6 via the inlet 15d. This compressed and significantly cooled exhaust evaporation gas F2 has the advantage that this exhaust evaporation gas F2 condenses better or more easily in the condenser 6 and is therefore more energy-efficient.

[0039] Figure 5 shows a further embodiment of a fuel gas supply system 1, which, in contrast to the one in Figure 3illustrated embodiment comprises two separate high-pressure pumps 5, namely a first high-pressure pump 5a and a second high-pressure pump 5b, as well as two separate high-pressure fluid lines 17a, 17c. In addition, the embodiment according to Figure 5 , in contrast to the embodiment according to Figure 3 , in the return line 21 there is no valve 25g, and thus no return to the tank 3. The embodiment according to Figure 5 is preferably operated in such a way that only the first high-pressure pump 5a is supplied with liquid gas F1 from the tank 3 and is compressed in the first high-pressure pump 5a to high-pressure liquid gas. This high-pressure liquid gas is, as in Figure 5shown, is fed to the high-pressure heat exchanger 13 and then to the high-pressure evaporator 7. In an advantageous method, the liquefied gas F1 located in the condenser 6, essentially a condensate, is fed to the second high-pressure pump 5b and compressed in the second high-pressure pump 5b to form high-pressure liquefied gas, which is fed into the high-pressure fluid line 17b and / or directly into the high-pressure evaporator 7, bypassing the condenser 6. This arrangement or method has the advantage that the liquefied gas F1 discharged from the tank 3 is not heated by the condensate or liquefied gas F1 generated in the condenser 6 and the liquefied gas F1 fed back into the low-pressure fluid line 16a. This embodiment therefore has the advantage that the condensation in the condenser 6 is more efficient.In a further possible method, the second high-pressure pump 5b can either be supplied with only condensate or liquid gas F1 from the condenser 6 via the valve 25f, or with only liquid gas F1 from the tank 3 via the valve 25g, or with a corresponding control of both valves 25f, 25g a mixture comprising a portion of liquid gas F1 from the condenser 6 and a portion of liquid gas F1 from the tank 3. The mixing ratio of these two portions of liquid gases 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 required by the high-pressure gas injection engine 2.

Claims

1. Fuel gas supply system (1) for supplying a high-pressure gas injection engine (2) with gas stored in a liquefied gas tank (3), in particular an LNG tank, comprising a condenser (6) comprising a compressor (9) which is fluid-conductively connectable to the liquid gas tank (3) to supply boil-off gas (F2) from the liquefied gas tank (3), the compressor (9) being fluid-conductively connected downstream via an inlet (15d) to an inner space (6d) of the condenser (6) to introduce the boil-off gas (F2) into the inner space (6d), and comprising a condensation nucleus generator (10), wherein the condensation nucleus generator (10) is configured such in that it generates liquid gas droplets (10a), which droplets serve as condensation nuclei, the condensation nucleus generator (10) introducing the condensation nuclei into the inner space (6d) in order to promote condensation of the introduced boil-off gas (F2) via the condensation nuclei, so that liquefied gas (F1) is formed therefrom, and wherein the liquefied gas (F1) formed in the condenser (6) may be fed to the liquefied gas tank (3), wherein the system furthermore comprises a high-pressure pump (5) which can be connected in a fluid-conducting manner to the liquefied gas tank (3) in order to supply liquefied gas (F1) from the liquefied gas tank (3) and to compress it to a high-pressure liquefied gas, wherein in the condenser (6) a high-pressure heat exchanger (13) is arranged, wherein a high-pressure evaporator (7) is provided which is fluid-conductively connected to the high-pressure pump (5) via the high-pressure heat exchanger (13) and is arranged downstream of the condenser (6), wherein the high-pressure evaporator (7) 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 (2) downstream of the high-pressure evaporator (7), and wherein the condensation nucleus generator (10) is fluid-conductively connected upstream to the high-pressure pump (5), wherein the liquefied gas (F1) formed in the condenser (6) is additionally fed to the high-pressure pump (5), wherein the condensation nucleus generator (10) is designed such that it generates liquid gas droplets (10a) from the high-pressure liquid gas, which serve as condensation nuclei.

2. Fuel gas supply system (1) according to claim 1, characterized in that a heat exchanger (8) is arranged upstream of the compressor (9), which exchanges heat with the supplied boil-off gas (F2), and in that the condensation nucleus generator (10) is fluid-conductively connected upstream to the heat exchanger (8) and subsequently to the high-pressure pump (5) in order for the heat exchanger (8) to exchange heat with the supplied high-pressure liquid gas.

3. Fuel gas supply system (1) according to claim 1, characterized in that a heat exchanger (8) is arranged upstream of the compressor (9), which exchanges heat with the supplied boil-off gas (F2), and in that the compressor (9) is fluid-conductively connected upstream in turn to the heat exchanger (8) in order for the heat exchanger (8) to exchange heat with the boil-off gas (F2) compressed by the compressor (9).

4. Fuel gas supply system (1) according to any one of the preceding claims, characterized in that the inlet (15d) of the boil-off gas (F2) is from above into the condenser (6), that the high-pressure heat exchanger (13) extends in vertical direction inside the condenser (6), and that the high-pressure heat exchanger (13) is arranged in such a way that the high-pressure liquid gas flows in high-pressure heat exchanger (13) from bottom to top.

5. Fuel gas supply system (1) according to one of the preceding claims, characterized in that the condensation nucleus generator (10) has at least one high-pressure nozzle, preferably a high-pressure nozzle with a nozzle diameter in the range from 1 to 1000 µm, particularly preferably 5 to 500 µm.

6. Fuel gas supply system (1) according to any one of the preceding claims, characterized in that the condensation nucleus generator (10) is arranged such that condensation nuclei (10a) generated by the condensation nucleus generator (10) are introduced into a condensation section (6a) in the inner space (6d) of the condenser (6) in which the inner space (6d) has a condensation temperature, wherein preferably the condensation nucleus generator (10) is arranged in such a way that the condensation nuclei enter the inner space (6d) of the condenser (6), in the flow direction of the liquid gas (F1), in a first half, preferably a first third of the cooling line of the high-pressure heat exchanger (13).

7. Fuel gas supply system (1) according to any one of the preceding claims, characterized in that a storage tank (14) for intermediate storage of boil-off gas (F2) is arranged downstream of the liquefied gas tank (3).

8. Fuel gas supply system (1) according to one of the preceding claims, characterized in that the high pressure pump (5) comprises at least a first high pressure pump (5a) and a second high pressure pump (5b), wherein the first high-pressure pump (5a) is fluid-conductively connected to the condensation nucleus generator (10) and fluid-conductively connected to the high-pressure evaporator (7) via the high-pressure heat exchanger (13), and wherein the second high-pressure pump (5b) is fluid-conductively connected to the high-pressure evaporator (7), bypassing the high-pressure heat exchanger (13).

9. The fuel gas supply system (1) according to claim 8, characterized in that the first high-pressure pump (5a) is fluid-conductively connected to the liquefied gas tank (3) to supply liquefied gas (F1), and that the second high-pressure pump (5b) is fluid-conductively connected to an outlet (6e) of the condenser (6) to supply liquefied gas (F1) accumulated in the condenser (6) to the second high-pressure pump (5b).

10. Fuel gas supply system (1) according to claim 9, characterized in that the second high-pressure pump (5b) is both fluid-conductingly connected to the outlet (6e) of the condenser (6) and fluid-conductingly connected to the liquefied gas tank (3), wherein valves (25f, 25g) are provided to control the portion of liquefied gas (F1) supplied from the condenser (6) and the portion of liquefied gas (F1) supplied from the liquefied gas tank (3).

11. Method for supplying a high-pressure gas injection engine (2) with gas which is stored in a liquefied gas tank (3), in particular an LNG tank, partly as liquefied gas (F1) and partly as evaporated gas (F2), by feeding the boil-off gas (F2) from the liquefied gas tank (3) to a compressor (9) and then introducing it into a condenser (6), wherein a stream of condensation nuclei in the form of liquefied gas droplets is generated in a condensation nucleus generator (10), which nuclei are fed in the condenser (6) to the introduced boil-off gas (F2) in order to promote condensation of the boil-off gas (F2) to liquefied gas (F1) by the liquefied gas droplets, and wherein the liquefied gas (F1) formed in the condenser (6) is fed to the liquefied gas tank (3), wherein the liquefied gas (F1) is fed from the liquefied gas tank (3) to a high-pressure pump (5) and is compressed by the latter to a high-pressure liquefied gas, wherein the high-pressure liquid gas is then fed to a high-pressure heat exchanger (13) arranged in a condenser (6) and subsequently to a high-pressure evaporator (7), wherein the high-pressure liquid gas is converted in the high-pressure evaporator (7) 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 (2), and wherein the liquefied gas (F1) formed in the condenser (6) is fed to the high-pressure pump (5), and the stream of condensation nuclei in form of liquid gas droplets is generated from the high-pressure liquid gas.

12. The method according to claim 11, wherein the stream of condensation nuclei in the form of liquid gas droplets generated in the condensation nucleus generator (10), which is fed in the condenser (6) to the introduced boil-off gas (F2), has a mass flow rate of 1 to 5%, based on the mass flow rate of the gas to be condensed.

13. Method according to any one of claims 11 to 12, characterized in that a condensation section (6a) is generated in the inner space (6d) of the condenser (6), within which the boil-off gas (F2) has a temperature which is below the boiling temperature of the liquid gas (F1), and in that condensation nuclei in the form of supercooled liquid gas droplets (10a) are sprayed into this condensation section (6a).

14. Method according to one of the claims 11 to 13, characterized in that a side stream of high-pressure liquid gas is withdrawn from or downstream of the high-pressure pump (5), in that this side stream is cooled in a heat exchanger (8), in that boil-off gas (F2) discharged from the liquefied gas tank (3) is simultaneously heated in the heat exchanger (8), in that the boil-off gas (F2) is fed to the condenser (6) downstream of the heat exchanger (8), and in that the high-pressure liquefied gas is fed to the condensation nucleus generator (10) downstream of the heat exchanger (8).

15. A merchant vessel comprising a fuel gas supply system 1 according to any one of claims 1 to 10.