Method and system for cooling marine fuel

Abstract

The present invention relates to a method for cooling fuel for a ship. [Solution] A method comprising the steps of: taking a fuel flow BS from the liquid phase of fuel B contained in the fuel tank, a ship having at least one fuel tank 12 and one liquefied gas storage tank 14; guiding the fuel flow to a cooling unit; cooling the liquid fuel flow in the cooling unit 20, wherein the fuel flow in the cooling unit is cooled by a BOG flow that is released from the liquefied gas storage tank, reliquefied, and passes through the cooling unit; and returning the cooled fuel flow to the fuel tank.

Description

Technical Field

[0001] The present invention relates to a method for cooling marine fuel in a ship comprising at least one fuel tank and one liquefied gas storage tank. Further, the present invention relates to a system for cooling marine fuel in a ship comprising at least one fuel tank and one liquefied gas storage tank, said system comprising a fuel tank for storing fuel, at least one liquefied gas storage tank for storing liquefied gas, and a reliquefaction device for returning at least one BOG stream taken out from the storage tank back towards the storage tank after reliquefaction. The present invention also relates to a ship comprising such a system.

Background Art

[0002] In the prior art, such methods and systems are known and are used, for example, in relation to ships for transporting liquefied gas over long distances. Usually, liquefied gas is stored at extremely low temperatures, thus well below 0 °C, especially in low-pressure storage tanks.

Summary of the Invention

[0003] The storage tanks and the liquefied gas contained therein are usually heated during transportation. Even when the heat influx is restricted by appropriate insulation in the storage tanks, it is not possible to completely avoid the heat influx. Further, during storage of the liquefied gas and the fuel, a certain amount of the liquefied gas and the fuel evaporates due to the heat influx. In order to maintain the storage temperature and thus the storage pressure in the storage tanks filled with liquefied gas and the fuel tanks, both the liquefied gas and the fuel have to be cooled and the amount of evaporation, also known as boil-off gas or BOG, has to be removed from the storage tank or the fuel tank. The discharged BOG is compressed and condensed against a cooling medium in a pressurized state. By reliquefaction and return of the liquefied BOG, the cargo in the storage tank and the fuel in the fuel tank are cooled.

[0004] When the cargo and fuel for a ship's propulsion system are identical, the BOG (Burn-Off Gas) can be guided from the fuel tank along with the cargo through a common reliquefaction unit. For transport ships that use a different liquefied gas as fuel than the liquefied gas in the liquefied gas storage tank, cooling the fuel through a common reliquefaction unit for the liquefied gas from the storage tank involves at least a disproportionate amount of equipment and, if necessary, a workload. A reliquefaction unit, typically designed to cool cargo in liquefied gas storage tanks and capable of including multiple reliquefaction units operating in parallel, is consistently over-engineered for significantly small amounts of fuel. This results in frequent start-up and stop sequences of the recondensing units used to cool the fuel, or continuous, inefficient partial-load operation. Typically, this also reduces the number of reliquefaction units available for reliquefaction of cargo, meaning that the commercial efficiency of the reliquefaction unit is limited, for example, when the storage tank is loaded. When reliquefaction units are periodically switched between fuel tanks and liquefied gas storage tanks, time-consuming flushing and switching processes occur regularly, creating a potential risk of cross-contamination between fuel and cargo.

[0005] Therefore, the object of the present invention is to provide a method and system for cooling marine fuel that enables simple and efficient cooling of fuel existing as a liquefied gas different from the liquefied gas contained in a liquefied gas storage tank, compared to the prior art.

[0006] In a first embodiment, the present invention solves its underlying objective with a method for cooling marine fuel comprising the features of claim 1. In particular, the method includes the following steps: taking a fuel flow from the liquid phase of fuel absorbed into a fuel tank; guiding the fuel flow into a cooling unit; cooling the liquid fuel flow in the cooling unit, wherein the fuel flow is cooled in the cooling unit against a BOG flow supplied from a liquefied gas storage tank, reliquefied, and returned through the cooling unit; and returning the cooled fuel flow to the fuel tank.

[0007] Accordingly, in contrast to conventionally known techniques, the present invention proposes selectively extracting the fuel flow from the liquid phase of the fuel, introducing it into a cooling unit, cooling the BOG flow that is discharged from the liquefied gas storage tank, reliquefied, and returned through the cooling unit, and then returning the cooled fuel flow to the fuel tank. With the help of the method steps according to the present invention, a fuel cooling process that can be implemented simply and efficiently is shown. Furthermore, the cooling process is optimally adapted for fuel cooling. This allows the fuel in the fuel tank to be kept preferably at a consistently low temperature, which can counteract the generation of BOG in the fuel tank. In addition, this type of cooling avoids time-consuming switching of process steps in the system. Since reliquefaction in the reliquefaction unit is performed without switching to the fuel tank, all reliquefaction units can be used to reliquefy the BOG generated in the storage tank. Preferably constant fuel cooling can also suppress the harmful pressure rise caused by BOG generated in the fuel tank. In this case, the medium used as a refrigerant to cool the fuel is a medium that must be cooled periodically during storage anyway, and does not require any additional adjustments for the reliquefaction of the liquefied gas itself absorbed into the liquefied gas storage tank.

[0008] In a preferred further embodiment of this method, the liquid fuel flow in the cooling unit is cooled to more than 5K, preferably about 10K, under the storage conditions present in the fuel tank. By cooling the fuel flow by a temperature difference of at least 5K as defined herein, the fuel in the fuel tank is preferably kept at a consistently low level, which can more favorably counteract BOG formation in the fuel tank. Determining such a temperature difference between the temperature in the fuel tank and the cooled fuel flow just before it flows into the fuel tank is the use of a fuel that is sufficiently different from the cargo in the liquefied gas storage tank. Preferably, the steps of this method can be effectively used when the evaporation temperature of the cargo in the liquefied gas storage tank is lower than the boiling point of the fuel contained in the fuel tank. For example, this method can be used when ethane is stored as a liquefied gas in the liquefied gas storage tank and ammonia is used as fuel. Another possible combination is when ethylene is stored in the liquefied gas storage tank and ethane is used as fuel.

[0009] In a further embodiment of this method, when the cooled fuel flow is returned to the fuel tank, at least a portion of the cooled fuel flow is mixed with the liquid phase of the fuel in the fuel tank. Selectively adding the cooled fuel flow to the liquid phase of the fuel is a simple means of maintaining the temperature of the fuel in the fuel tank at a desired storage condition, such as the storage temperature. The amount of the cooler fuel flow mixed with the liquid phase of the fuel in the fuel tank is large and preferably adjustable, and is set to compensate for heat inflow from the environment surrounding the fuel tank.

[0010] In alternative or optional embodiments of this method, when the cooled fuel flow is returned to the fuel tank, at least a portion of the cooled fuel flow is sprayed onto the gaseous phase of the fuel in the fuel tank. By spraying a fuel flow that is significantly colder than the gaseous phase of the fuel in the fuel tank, the temperature in the gaseous phase of the fuel is preferably lowered, thereby preventing further BOG formation in the fuel tank. Preferably, with the help of the fuel flow sprayed onto the gaseous phase, at least partial liquefaction of the BOG in the gaseous phase of the fuel tank is possible. In addition to maintaining a constant temperature in the fuel tank, this suppresses further BOG formation and, consequently, an undesirable pressure increase in the fuel tank.

[0011] In one possible embodiment of this method, when extracting the fuel flow from the liquid phase, the fuel flow is extracted from the fuel tank by a fuel pump that supplies fuel and preferably transported toward a cooling unit by a cooling unit. The method for cooling fuel in a fuel tank as described herein is further optimized to the advantage of using a fuel pump primarily used for fuel supply to extract the fuel flow from the fuel tank and transport it toward a cooling unit. Instead of providing a separate transport system, existing components normally used to transport fuel toward the ship's propulsion system can be used to carry out the transport process. Preferably, the fuel pump for pumping fuel is designed to generate a flow rate higher than that required to transport fuel toward the ship's propulsion system. Preferably, the fuel flow directed toward the cooling unit is branched from a fuel line downstream of the fuel pump along the direction of fuel flow.

[0012] In a preferred embodiment of this method, in the step of cooling the liquid fuel flow within a cooling unit, the BOG flow transported by the cooling unit is defined as a sub-flow of the BOG flow branched off from the BOG flow that is reliquefied by the reliquefaction unit and returned to the storage tank. This means that only the proportion actually required for effective cooling of the fuel flow is branched off from the reliquefied BOG flow and supplied to the cooling unit. Preferably, the size of the sub-flow branched off from the entire reliquefied BOG flow can be adjusted to match the size of the fuel flow taken out of the fuel tank. This achieves optimal efficiency in cooling the fuel flow within the cooling unit. Typically, the residual BOG flow of the reliquefied fuel that is not used to cool the fuel flow, which is significantly larger than the sub-flow branched off towards the cooling unit, is directed towards at least one liquefied gas storage tank to cool the cargo.

[0013] Preferably, a sub-flow of the BOG flow, branched to cool the fuel flow, evaporates as it passes through the cooling unit, and the evaporated sub-flow is added to the BOG flow discharged from the storage tank and used for reliquefaction. In this configuration, where the liquid fuel flow is cooled within the cooling unit by a sub-flow of the BOG flow passing through the cooling unit, the cooling energy contained in the sub-flow is preferably fully utilized to cool the fuel flow transported from the fuel tank, particularly to overcome a desired temperature difference of more than 5K under the storage conditions present in the fuel tank. The sub-flow preferably evaporates completely within the cooling unit due to the "release of cooling energy" or "absorption of thermal energy" from the sub-flow of the reliquefied BOG flow, thereby easily returning to the already carried out reliquefaction process. The cooling energy introduced into the BOG flow by the reliquefaction process is efficiently used to cool the fuel in the fuel tank, in addition to cooling the liquefied gas storage tank. The evaporated sub-flow leaving the cooling unit is significantly smaller than the BOG flow discharged from the storage tank and can be easily handled by the reliquefaction equipment carrying out the reliquefaction. This further reduces the equipment load when implementing this method.

[0014] In one embodiment of this method, the evaporated partial flow of BOG after leaving the cooling unit is supplied to the reliquefaction process before the compression process performed during reliquefaction. In yet another embodiment, for example, in a combination using ethylene as the liquefied gas to be transported and propane as the fuel, the evaporated partial flow is preferably supplied between the first and second compression stages of the two-stage compression process performed during reliquefaction. Such solutions are used when the temperature difference between the fuel storage temperature and the evaporation temperature of the partial flow of the BOG at medium pressure is sufficiently large. For example, in the operation of the cooling unit, it may be specified that the cooling unit is flooded during the cooling process, so the evaporation temperature of the partial flow evaporated during the cooling of the fuel flow is determined by the suction pressure of the downstream reliquefaction. This ensures that the lowest possible temperature level is achieved within the process. Alternatively, superheating control in the cooling unit is also possible, and the magnitude of the partial flow of the reliquefaction BOG supplied to the cooling unit is adjusted by temperature and pressure values ​​recorded for the partial flow at the outlet of the cooling unit.

[0015] In another embodiment of this method, in the step of cooling the liquid fuel flow in a cooling unit, the BOG flow passing through the cooling unit is specified to be the entire BOG flow that is continuously reliquefied and returned to the storage tank. This makes it possible to further simplify the method. The entire reliquefied BOG flow continuously generated by the reliquefaction process is about 4 to 10 times larger than the fuel flow taken out of the fuel tank. If the entire BOG flow passes through the cooling unit, the cooling unit must be hydraulically large, but the entire reliquefied BOG flow is used to cool the fuel. The reliquefied BOG flow increases in temperature as it passes through the cooling unit, but includes at least a two-phase state. This two-phase BOG flow is directed towards at least one liquefied gas storage tank, without the intervention of any other process, and cools the cargo even if the cooling effect of the reliquefied BOG flow introduced into the liquefied gas storage tank is reduced. Preferably, according to the present invention, which cools a fuel different from the liquefied gas in the liquefied gas storage tank, the advantage is obtained that the utilization efficiency of the reliquefaction process carried out by the reliquefaction device is improved.

[0016] Further embodiments of this method include the following steps: controlling the fuel cooling process in a fuel tank by temporarily interrupting the cooling of the fuel flow supplied to a cooling unit when the demand for reliquefaction of BOG flow discharged from one or more storage tanks increases. In particular, during the process of loading liquefied gas into a liquefied gas storage tank, the demand for reliquefaction of the liquefied gas stored in the ship's storage tank may increase. The fuel cooling process in the fuel tank can be easily interrupted for a certain period of time and can be simply restarted without any switching process after the increased demand for reliquefaction of the stored liquefied gas has been met. To control the fuel cooling process, for example, a control device is used, which controls not only the fuel cooling process in the fuel tank but also the cooling of the liquefied gas in at least one liquefied gas storage tank by reliquefaction of BOG generated during liquefied gas storage. When controlling the fuel cooling process, not only is an on / off switching process controlled, but a number of process variables are recorded at each stage of the method according to the present invention. For example, the control unit is used to adjust the mass flow rate of a partial flow of fuel or reliquefied BOG flow, or to record the temperature and pressure at the inlet and outlet of the cooling unit.

[0017] In a second aspect, the present invention relates to a system for cooling marine fuel, particularly for carrying out a method according to any of the embodiments described above, the system comprising: a fuel tank for storing fuel; at least one liquefied gas storage tank for storing liquefied gas; and a reliquefaction device for at least one BOG flow taken out of the storage tank and returned towards the storage tank after reliquefaction.

[0018] The fuel cooling system according to the present invention solves the problems inherent in the method of the present invention by providing a fuel cooling unit that is fluidly connected to the fuel tank. Here, the cooling unit is connected to the fuel tank by an annular line for taking the fuel flow to be cooled from the fuel tank and returning the cooled fuel flow to the fuel tank, and further, the cooling unit has at least one fluid-transport connection to a portion of the fluid line connecting the reliquefaction unit to the storage tank, and the cooling unit is configured to exchange heat between the fuel flow and at least a portion of the reliquefied BOG flow passing through the cooling unit. The system configured in this way according to the present invention provides a simple configuration for easily cooling fuel in a fuel tank different from the liquefied gas absorbed in at least one liquefied gas storage tank without additional large equipment burden. Existing systems can avoid time-consuming switching and conversion processes. The cooling energy generated by reliquefaction is effectively transferred from at least a portion of the reliquefied BOG flow passing through the cooling unit to the fuel flow, preferably with the help of the cooling unit, and used to cool the fuel flow.

[0019] In a preferred embodiment of the present invention, the cooling unit comprises a heat exchanger for transferring cooling energy between a fuel flow and at least a portion of a reliquefied BOG flow. The use of a heat exchanger provides a simple means of transferring energy between a fuel flow to be cooled to a predetermined temperature and at least a portion of a BOG flow having the required cooling energy, without direct mass exchange. Thus, the use of a heat exchanger avoids cross-contamination of impurities contained in the fuel or liquefied gas. The heat exchanger can be configured as a shell-and-tube heat exchanger, thereby enabling simple heat transfer between fluid flows that do not directly contact each other.

[0020] In further embodiments of the present invention, it is specified that the cooling unit is coupled at its outlet to a section of line located upstream of the reliquefaction unit for at least a portion of the BOG flow, or that the cooling unit is fluid-conveyingly coupled at its outlet to at least one liquefied gas storage tank for the BOG flow, preferably still in a reliquefied state. Whether the outlet of the cooling unit is coupled to a section of line immediately preceding the reliquefaction unit or to the inlet of the liquefied gas storage tank depends in particular on the cooling unit used in the system, especially its hydraulic design. If the cooling unit installed in the system is configured to receive only a portion of the reliquefied BOG flow and evaporate this reliquefied portion, its outlet is coupled to a supply section of the reliquefaction unit intended for the reliquefaction of the BOG flow. In one embodiment, after leaving the cooling unit, the evaporated portion of the BOG is introduced into a section of the supply line located before the compression unit of the reliquefaction. In yet another embodiment, for example, in a combination using ethylene as the liquefied gas to be transported and propane as the fuel, a portion of the evaporated BOG flow is introduced into a section within the reliquefaction unit, preferably between the first and second compression stages of the compression unit. However, if a cooling unit, preferably configured as a heat exchanger, is intended to pass the entire reliquefied BOG flow through the cooling unit, its outlet is connected to the inlet of one or more liquefied gas storage tanks.

[0021] In a further embodiment of the system according to the present invention, an annular line branches off from a fuel line that provides fuel to the ship's propulsion system, and at least one fuel pump is located in the fuel line upstream of the branching point of the annular line. By providing a branching point of the annular line within the fuel line, and configuring the annular line to transport the fuel flow through a cooling unit and back to the fuel tank from there, a structurally simple means is realized for configuring two parallel flows in different directions with only a single transport device, a fuel pump, primarily for transporting fuel to the ship's propulsion system. The fuel pump has sufficient capacity to transport the required fuel supply and is suitable for transporting the fuel flow toward the cooling unit in addition to actually supplying fuel to the ship's propulsion system. Preferably, the fuel pump used to transport the fuel flow through the cooling unit is a main fuel pump. In one embodiment, if the main fuel pump is insufficient to simultaneously supply fuel to the ship's propulsion system and transport fuel toward the cooling unit for fuel cooling, a backup fuel pump may also be provided. A backup fuel pump, connected in parallel with the main fuel pump, can assist in pumping fuel toward the cooling unit via an actuator in the appropriate fluid line. This ensures a basic fuel supply toward the ship's propulsion system even if the main fuel pump fails.

[0022] Preferably, the system according to the present invention includes a control device configured to control the cooling process of the fuel in the fuel tank, and when the demand for reliquefaction of the BOG flow discharged from the storage tank increases, the cooling of the fuel flow supplied to the cooling unit is temporarily interrupted. By providing the system with a control device, a simple means is realized for controlling the cooling process of the fuel in the fuel tank as needed, in parallel with the cooling of the liquefied gas stored in at least one liquefied gas storage tank. The control device includes a number of sensors appropriately positioned within the system. Furthermore, the control device is coupled to corresponding actuators within the system, at least for signal transmission, thereby enabling adjustment of specific control variables, such as the mass flow rate defining the fuel flow or the partial flow of the reliquefied BOG flow. This allows for effective adjustment of desired temperatures and pressures at the inlet and / or outlet of the cooling unit.

[0023] In yet another embodiment, the present invention relates to a vessel equipped with a system for cooling fuel stored in a fuel tank, wherein the system is configured according to any of the preferred embodiments described above. In a vessel equipped with a system configured in this manner, it is possible to cool the fuel in the fuel tank, which is formed as a liquefied gas different from the liquefied gas received in at least one liquefied gas storage tank, in a simple and, above all, efficient manner. The special configuration of the system prevents cross-contamination between the cargo in the liquefied gas storage tank and the fuel absorbed into the fuel tank, and both are subjected to appropriately separated cooling processes.

[0024] Preferred or further embodiments described with respect to the method according to the present invention are also preferred embodiments of the system and the vessel according to the present invention. Preferred or further embodiments described with respect to the system or vessel according to the present invention are also preferred embodiments of the method according to the present invention.

[0025] The present invention will be described in further detail below based on preferred embodiments with reference to the accompanying drawings. The drawings show the following.

Brief Description of the Drawings

[0026] [Figure 1] Schematic diagram of a ship equipped with a first embodiment of the system according to the present invention [Figure 2] Schematic diagram of a ship equipped with a second embodiment of the system according to the present invention [Figure 3] Schematic diagram of a method for cooling ship fuel according to the present invention

Mode for Carrying Out the Invention

[0027] FIG. 1 schematically shows a ship 80 and a system 10 for cooling the fuel B of the ship 80. The system 10 includes a fuel tank 12 for storing the fuel B, and at least one liquefied gas storage tank 14 for storing the liquefied gas F, here three liquefied gas storage tanks 14. In this example, the system 10 is configured to cool the fuel B contained in the fuel tank 12 and the liquefied gas F contained in the liquefied gas storage tank 14. This aims to achieve a substantially constant temperature in the fuel B in the fuel tank 12 and in the liquefied gas storage tank 14 that houses the cargo (liquefied gas F) transported by the ship 80.

[0028] The system 10 includes a cooling unit 20 fluidly connected to the fuel tank 12 for cooling the fuel B in the fuel tank 12. Also, the system 10 includes a reliquefaction device 40 fluidly coupled to the liquefied gas storage tank 14 for cooling the liquefied gas F in the liquefied gas storage tank 14.

[0029] The cooling unit 20 is fluid-transporting to the fuel tank 12 by an annular line 22 configured to take the fuel flow BS to be cooled from the fuel tank 12 and return the cooled fuel flow BSk to the fuel tank 12. The annular line 22 branches off from or forms part or a section of the fuel line 24 that provides fuel to the ship's propulsion system (not shown). The fuel line 24 has at least one fuel pump 28, 28' located before the annular line branching point 26, which transports fuel B toward the ship's propulsion system and also transports the fuel flow BS toward the cooling unit.

[0030] In one embodiment, a main fuel pump 28 and a backup fuel pump 28' are provided in the fuel line 24. The main fuel pump 28 is configured to both supply fuel and transport the fuel flow BS toward the cooling unit 20. The backup fuel pump 28' is required as a backup in the event of failure of the main fuel pump 28 or to compensate for peak load.

[0031] The cooling unit 20 has at least one fluid transport connection at its inlet 32 ​​to a portion of the fluid line connecting the reliquefaction unit 40 to the storage tank 14, particularly the return line 42. In this example, the cooling unit 20 is configured to transfer heat between the fuel flow BS and at least a portion of the reliquefaction BOG flow BG flow BGT passing through the cooling unit 20.

[0032] In this example, the cooling unit 20 includes a heat exchanger 30 for transferring cooling energy between a fuel flow BS introduced into the cooling unit 20 via an annular line 22 and at least a partial flow BGT branched off from the reliquefied BOG flow BG traveling from the reliquefied BOG unit 40 toward the liquefied gas storage tank 14. When the partial flow BGT of the BOG flow passes through the cooling unit 20, the partial flow is discharged from the outlet 34 of the cooling unit 20.

[0033] At the outlet 34 of the cooling unit 20, the partial flow BGT of the BOG flow, after transferring cooling energy to the fuel flow BS, exists in the gas phase as evaporated partial flow BGTv. The evaporated partial flow BGTv after passing through the cooling unit 20 is returned to the reliquefaction unit 40 and subjected to a second reliquefaction process. In this example shown in Figure 1, the outlet 34 of the cooling unit 20 is fluid-transportedly coupled to a section of the supply line 44 located upstream of the reliquefaction unit 40 and to a section within the reliquefaction unit 40, particularly to the suction side of the second compression stage 52, where a suction separator 46' is located upstream of the second compression stage 52. Whether the evaporated partial flow BGTv is introduced to the suction separator 46 located before the reliquefaction unit 40, or to the suction separator 46' and the suction side of the second compression stage 52, depends in particular on the combination of liquefied gas F and fuel B present in the system 10.

[0034] The supply line 44 extracts the gas that continuously evaporates during the storage of liquefied gas F, known as boil-off gas (BOG), from at least one storage tank 14 as a BOG flow and supplies it to the reliquefaction unit 40. The reliquefaction unit 40 is equipped with a suction separator 46 located within the supply line 44, which separates the water contained in the BOG flow BG. The BOG flow BG, from which the water has been removed, is then supplied to a compression unit 48, which includes a first compression stage 50 and a second compression stage 52. After passing through the compression unit 48, the compressed BOG flow BGv is transported through a condenser 54, a gas cooler 56, and another condenser 58, where it exists as a pure liquid phase downstream of the condenser 58 in the flow direction and is introduced into the liquefied gas tank 60.

[0035] The liquefied gas tank 60 is equipped with an outlet 62 for discharging the completely reliquefied BOG flow BGr towards the liquefied gas storage tank 14 via a return line 42. In this embodiment, a supply line 36 branches off from the return line 42 towards the heat exchanger 30 of the cooling unit 20 in order to supply a partial flow of the reliquefied BOG flow TBG through the cooling unit. The supply line 36 is connected to the inlet 32 ​​of the cooling unit 20.

[0036] System 10 also includes a control device 16 for controlling the cooling process of fuel B in the fuel tank 12. In particular, the control device 16 can also be used to control the cooling process of liquefied gas F in the liquefied gas storage tank 14. Especially when the cooling demand for the liquefied gas storage tank 14 increases, and consequently the reliquefaction of BOG flow BG released from one or more storage tanks 14 is required, the cooling of fuel B in the fuel tank 12, and consequently the cooling of fuel flow BS supplied to the cooling unit 20, can be interrupted for at least a certain period of time.

[0037] Figure 2 shows another embodiment of a vessel 80, comprising a system 10 configured according to the present invention for cooling fuel B stored in a fuel tank 12. For the basic configuration of this embodiment, refer to the embodiment of the vessel 80 shown in Figure 1. The vessel 80 shown in Figure 2 also comprises a system 10 comprising a fuel tank 12 for storing fuel B and, in this example, three liquefied gas storage tanks 14 for storing liquefied gas F. The system also includes a cooling unit 20 comprising a heat exchanger 30, which is fluid-conveyed to the fuel tank 12 via an annular line 22. The liquefied gas storage tanks 14 are connected to a reliquefied gas storage unit 40 via a supply line 44 to supply a BOG flow BG consisting of BOG generated in the liquefied gas storage tanks 14. The reliquefied gas storage unit 40 is fluid-conveyed downstream via a return line 42 to return the reliquefied BOG flow BGr generated in the reliquefied gas storage unit 40.

[0038] The embodiment shown in Figure 2 differs from the first embodiment in that the entire reliquefied BOG flow BGr directed toward the liquefied gas storage tank 14 is used as a refrigerant for the fuel flow BS passing through the cooling unit 20. Therefore, the heat exchanger 30 provided in the cooling unit 20 has a hydrodynamically different configuration from the embodiment shown in Figure 1 because the fluid flow rate to be passed through it is significantly larger.

[0039] Unlike the embodiment shown in Figure 1, the inlet 32 ​​and outlet 34 of the cooling unit 20 are directly fluid-transported to the return line 42 to the liquefied gas storage tank 14, rather than supplying a partial flow from the outlet 34 to the supply line 44 of the reliquefied gas storage unit. In contrast to the first embodiment shown in Figure 1 of the present invention, the reliquefied BOG flow BGr introduced into the liquefied gas storage tank 14 in the embodiment of Figure 2 has a smaller temperature difference with respect to the liquefied gas F in the storage tank 14 than the reliquefied BOG flow BGr introduced into the storage tank 14 in the embodiment of Figure 1.

[0040] The system 10 shown in Figure 2 also includes a control device 16 for controlling the cooling process of fuel B in the fuel tank 12 and the cooling process of liquefied gas F in the liquefied gas storage tank 14, as well as actuators and / or sensors located in the line.

[0041] Figure 3 shows one embodiment of a method 100 for cooling the fuel of a vessel 80, the vessel 80 comprising at least one fuel tank 12 for storing fuel B and a liquefied gas storage tank 14 for storing liquefied gas F.

[0042] The method 100 first includes, as a first step 102, the step of extracting a fuel flow BS from the liquid phase of fuel B contained in the fuel tank 12. The next step 104 relates to the step of guiding the liquid fuel flow BS to the cooling unit 20. In the following step 106, the liquid fuel flow BS is cooled in the cooling unit, and the fuel flow BS is cooled by a reliquefied BOG flow BGr supplied from a liquefied gas storage tank that passes through the cooling unit. The subsequent step 108 relates to the step of returning the cooled fuel flow BSk to the fuel tank 12.

[0043] In the cooling of the liquid fuel flow BS in step 106, according to sub-step 106a, the fuel flow BS in the cooling unit is cooled to over 15K, preferably over 30K, under the storage conditions present in the fuel tank 12, particularly the temperature of the fuel B contained in the fuel tank 12.

[0044] With regard to the recirculation of the cooled fuel flow BSK in step 108, according to step 108a, at least a portion of the cooled fuel flow BSK can be added to the liquid phase of fuel B in the fuel tank 12, or according to step 108b, a portion of the cooled fuel flow BSK can be sprayed into the gas phase of fuel B in the fuel tank.

[0045] In a preferred embodiment of the present method 100, in step 102, the fuel flow BS is taken out of the fuel tank 12 by fuel pumps 28, 28' that supply fuel to the ship's propulsion system, in which case the fuel pumps supply fuel to the ship's propulsion system and also transport it toward the cooling unit 20.

[0046] The cooling process 106 of the liquid fuel flow BS can be carried out by a partial flow of the reliquefied BOG flow TBG, which is branched off from the reliquefied BOG flow BG that is reliquefied and returned to the storage tank 12. When cooling the fuel flow, the branched partial flow of the reliquefied BOG flow TBG passing through the cooling unit 20 evaporates, while the fuel flow BS passing through the cooling unit 20 is further cooled. The evaporated partial flow is then added to the BOG flow BG that is released from the liquefied gas storage tank 14 and supplied for reliquefaction.

[0047] In another embodiment of the method 100, during the cooling process 106 of the liquid fuel flow BS, the entire amount of the reliquefied BOG flow BGr that is returned towards the liquefied gas storage tank 14 is passed through the cooling unit 20.

[0048] In this method 100, when the demand for reliquefaction of the BOG flow BG released from the liquefied gas storage tank 14 increases, the cooling process of the fuel B in the fuel tank 12 can be controlled to temporarily interrupt the cooling of the fuel flow BS supplied to the cooling unit 20. [Explanation of symbols]

[0049] 10 Systems 12 fuel tanks 14. Liquefied gas storage tanks 16 Control device 20 Cooling Units 22 Ring Line 24 Fuel line 26 Circular line connection section 28,28' Fuel pump 30 heat exchanger 32 Entrance 34 Exit 36 supply lines 40 Reliquefaction equipment 42 Return Line 44 supply lines 46 Suction Separator 48 Compression Units 50 First Compression Stage 52 Second Compression Stage 54 Condenser 56 Gas Cooler 58 Condenser 60 liquefied gas tanks 62 Exit 80 ships 100 ways 102 Removal process 104 Introduction process 106 Cooling process 108 Reversal process B Fuel F Liquefied gas BS fuel flow BSk Cooled fuel flow BG BOG style BGv compressed BOG stream BGr Reliquefied BOG flow BGT BOG flow partial flow

Claims

1. A method (100) for cooling fuel (B) of a vessel (80), wherein the vessel (80) comprises at least one fuel tank (12) and one liquefied gas storage tank (14), The process (102) involves extracting a fuel flow (BS) from the liquid phase of the fuel (B) contained in the fuel tank (12), The process (104) of guiding the fuel flow (BS) to the cooling unit (20), A step (106) of cooling the liquid fuel flow (BS) within the cooling unit (20), wherein the fuel flow (BS) within the cooling unit (20) is cooled by a BOG flow (BGr) that is released from the liquefied gas storage tank (14), reliquefied, and passes through the cooling unit (20), A method (100) comprising the step (108) of returning the cooled fuel flow (BSk) to the fuel tank (12).

2. The method according to claim 1, A method wherein the fuel flow (BS) in the cooling unit is cooled to a temperature more than 5K, preferably about 10K, lower than the storage conditions in the fuel tank (12).

3. A method according to claim 1 or claim 2, A method wherein at least a portion of the cooled fuel flow (BSk) is added to the liquid phase of the fuel (B) in the fuel tank (12).

4. A method according to any one of claims 1 to 3, A method wherein at least a portion of the cooled fuel flow (BSk) is sprayed into the gas phase of the fuel (B) in the fuel tank (12).

5. A method according to any one of claims 1 to 4, The fuel flow (BS) is taken out of the fuel tank (12) by a fuel pump (28, 28') that converts the fuel supply and transports it toward the cooling unit (20).

6. A method according to any one of claims 1 to 5, A method wherein the BOG flow (BG) passing through the cooling unit (20) is a partial flow (BGT) of the BOG flow that is branched off from the reliquefied BOG flow (BGr) that is returned towards the liquefied gas storage tank (14).

7. The method according to claim 6, A method comprising: a partial flow (BGT) of the reliquefied BOG flow (BGr), which is branched to cool the fuel flow (BS), evaporating as it passes through the cooling unit (20), and the evaporated partial flow being added to the BOG flow (BG) that is discharged from the liquefied gas storage tank (14) and supplied to the reliquefied system.

8. A method according to any one of claims 1 to 7, A method wherein the reliquefied BOG flow (BGr) passing through the cooling unit (20) is the entire amount of the reliquefied BOG flow (BGr) circulating toward the liquefied gas storage tank (14), particularly the entire continuous amount.

9. A method according to any one of claims 1 to 8, A method comprising the step of controlling the cooling process of the fuel (B) in the fuel tank (12) by temporarily interrupting the cooling of the fuel flow (BS) supplied to the cooling unit (20) when the demand for reliquefaction of the BOG flow (BG) discharged from the liquefied gas storage tank (14) increases.

10. A system (10) for cooling the fuel (B) of a ship, more particularly a system (10) for carrying out the method described in any one of claims 1 to 9, A fuel tank (12) for storing the aforementioned fuel (B), A liquefied gas storage tank (14) for storing liquefied gas (F), The system includes a reliquefaction device (40) for at least one BOG flow (BGr) that is withdrawn from the liquefied gas storage tank (14) and returned to the liquefied gas storage tank (14) after reliquefaction, A cooling unit (20) for the fuel (B) is provided, and the cooling unit (20) is connected to the fuel tank (12) in a manner that allows for fluid transport. The cooling unit (20) is connected to the fuel tank (12) by an annular line (22) for taking a fuel flow (BS) to be cooled from the fuel tank (12) and supplying the cooled fuel flow (BSk) to the fuel tank (12). The cooling unit (20) is provided with a portion of the fluid line (42) connecting the reliquefaction device (40) and the liquefied gas storage tank (14) and at least one fluid-transporting connection, The system (10) is configured such that the cooling unit (20) performs heat exchange between the fuel flow (BS) and a partial flow (BGT) which is at least a portion of the reliquefied BOG flow (BGr) flowing through the cooling unit (20).

11. The system (10) according to claim 10, The cooling unit (20) comprises a heat exchanger (30) for transferring cooling energy between the fuel flow (BS) and at least the partial flow (BGT) of the reliquefied BOG flow (BGr), in a system (10).

12. A system (10) according to claim 10 or claim 11, The cooling unit (20) is connected at its outlet (34) to a line section located upstream of the reliquefaction device (40) with respect to at least the partial flow (BGT) of the BOG flow. or The system (10) is configured such that the cooling unit (20) is connected at its outlet (34) to at least one liquefied gas storage tank (14) in a manner that allows for fluid transport of BOG flow (BGr).

13. A system (10) according to claim 10 or claim 11, The aforementioned annular line (22) branches off from the fuel line (24) that defines the fuel supply, The fuel line (24) is equipped with at least one fuel pump (28, 28') located before the annular line connection (26) for pumping fuel (B), in the system (10).

14. A system (10) according to any one of claims 10 to 13, The system includes a control device (16) configured to control the cooling process of the fuel (B) in the fuel tank (12), System (10) in which, when the demand for reliquefaction of BOG flow (BG) released from liquefied gas storage tank (14) increases, the cooling of fuel flow (BS) supplied to cooling unit (20) is temporarily interrupted.

15. A ship (80) equipped with a system (10) for cooling fuel (B) when storing fuel (B) in a fuel tank (12), A ship (80) wherein the system (10) is configured as the system (10) according to any one of claims 10 to 14.

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